As filed with the Securities and Exchange Commission on August 2, 2017June 13, 2018

RegistrationNo. 333-217904333-[•]

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 2

to

FORMFORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Mateon Therapeutics, Inc.

(Exact name of registrant as specified in its charter)

701 Gateway Blvd., Suite 210

South San Francisco, California 94080

(650)635-7000

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

William D. Schwieterman, M.D.

Chief Executive Officer

Mateon Therapeutics, Inc.

701 Gateway Blvd., Suite 210

South San Francisco, California 94080

(650)635-7000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:public As soon as practicable: From time to time after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box:  ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, anon-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided to Section 7(a)(2)(B) of the Securities Act.  ☐

CALCULATION OF REGISTRATION FEE

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. WeThe selling securityholders may not sell these securities until the registration statement filed with the Securities and Exchange Commission is declared effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Mateon Therapeutics, Inc.

16,666,66614,875,000 Shares of Common Stock

Pre-fundedShares underlying Warrants to Purchase Shares of Common Stock

Common Warrants to Purchase 8,333,33316,362,500 Shares of Common Stock

We are offeringThe selling securityholders named in this prospectus may use this prospectus to offer and sell from time to time up to 16,666,66614,875,000 shares of our common stock, and common warrants to purchase an aggregate of 8,333,3337,437,500 shares of our common stock (andissuable upon the exercise of Series A Warrants, or the Series A Warrants, and 7,437,500 shares of our common stock issuable upon the exercise of Series B Warrants, or the Series B Warrants and, with the Series A Warrants, the Warrants, held by the selling securityholders. The shares of common stock and Warrants were issued to the selling securityholders in connection with a private placement per the terms of Subscriptions Agreements by and between the Company and the selling securityholders dated April 12, 2018 and April 30, 2018. For more information regarding this private placement see the section entitled “Prospectus Summary-Private Placement Transaction” in this prospectus. We are also registering for resale 1,487,500 shares of our common stock issuable upon the exercise of warrants issued to the placement agent in the private placement.

We are not selling any securities under this prospectus and will not receive any of the proceeds from the sale of securities by the selling securityholders.

Except for underwriting discounts, selling commissions and all legal fees and expenses of legal counsel for any selling securityholder, which may be paid by such selling securityholder, we have agreed to pay the expenses incurred in connection with the registration of the shares of common stock that are issuable from time to time upon exercisecovered by this prospectus.

The selling securityholders may sell the shares of common stock described in this prospectus in a number of different ways and at varying prices. We provide more information about how the common warrants). We are also offering to each purchaser whose purchase ofselling securityholders may sell their shares of common stock in the section entitled “Plan of Distribution” in this offering would otherwise result inprospectus.

The selling securityholders are “underwriters” within the purchaser, together with its affiliates and certain related parties, beneficially owning more than 4.99% of our outstanding common stock immediately following the consummation of this offering, the opportunity to purchase, if the purchaser so chooses,pre-funded warrants, in lieu of shares of common stock that would otherwise result in the purchaser’s beneficial ownership exceeding 4.99% of our outstanding common stock (or at the electionmeaning of the purchaser, 9.99%). Eachpre-funded warrant will be exercisable for one shareSecurities Act of our common stock. The purchase price of eachpre-funded warrant will equal the price per share at which the shares of common stock are being sold to the public in this offering, minus $0.01, and the exercise price of eachpre-funded warrant will be $0.01 per share. This offering also relates to the shares of common stock issuable upon exercise of anypre-funded warrants sold in this offering. Each share of common stock andpre-funded warrant is being sold together with a common warrant to purchase one half a share of our common stock, at an exercise price of $        per share. For eachpre-funded warrant we sell, the number of shares of common stock we are offering will be decreased on aone-for-one basis. The common warrants will be exercisable immediately and will expire five years from the date of issuance. The shares of common stock andpre-funded warrants, and the accompanying common warrants, can only be purchased together in this offering but will be issued separately and will be immediately separable upon issuance.1933, as amended.

Our common stock is traded on the OTCQX MarketplaceOTC Market under the symbol “MATN.” The last reported sale price of our common stock on the OTCQX MarketplaceOTC Market on July 31, 2017June 8, 2018 was $0.36$0.25 per share. The public offering price per share of common stock and anypre-funded warrant and accompanying common warrant will be determined between us and the placement agent based on market conditions at the time of pricing, and may be at a discount to the current market price. We do not intend to apply for listing of the warrants on any securities exchange or other nationally recognized trading system. There is no established public trading market for thepre-funded warrants or common warrants, and we do not expect a market to develop.

Investing in our securities involves risks. See “Risk Factors” beginning on page 78 of this prospectus for a discussion of factors you should consider before making an investment in our securities.

We have retained H.C. Wainwright & Co., LLC as our exclusive placement agent to use its reasonable best efforts to solicit offers to purchase the securities in this offering. The placement agent has no obligation to buy any of the securities from us or to arrange for the purchase or sale of any specific number or dollar amount of the securities. Because there is no minimum offering amount required as a condition to closing in this offering, the actual public offering amount, placement agent’s fees, and proceeds to us, if any, are not presently determinable and may be substantially less than the total maximum offering amounts set forth above.

We have agreed to pay the placement agent a total cash fee equal to 6.5% of the gross proceeds of this offering (which may be reduced under certain circumstances). In addition to the placement agent’s fees, we have agreed to pay the placement agent anon-accountable expense allowance of $25,000, to reimburse the placement agent for fees and expenses of its legal counsel in an amount up to $100,000 and to reimburse the placement agent for any escrow or settlement fees in an amount not to exceed $10,000. As additional compensation, we plan to issue the placement agent warrants to purchase a number of shares of common stock equal to 4% of the number of shares of common stock and pre-funded warrants placed in this offering to investors which percentage shall be reduced in certain circumstances. The exercise price for these warrants will be $        per share, which represents 125% of the purchase price. See “Plan of Distribution.”

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

We expect to deliver the securities to investors on or about                , 2017.

Rodman & Renshaw

a unit of H.C. Wainwright & Co.

The date of this prospectus is , 2017.June 13, 2018.

TABLE OF CONTENTS

i

About This Prospectus

You should rely only on information contained in this prospectus. We have not, and the placement agent has not authorized anyone to provide you with additional information or information different from that contained in this prospectus. We are not making an offer of these securities in any state or other jurisdiction where the offer is not permitted. The information in this prospectus may only be accurate as of the date on the front of this prospectus regardless of time of delivery of this prospectus or any sale of our securities.

No person is authorized in connection with this prospectus to give any information or to make any representations about us, our common stock or any matter discussed in this prospectus, other than the information and representations contained in this prospectus. If any other information or representation is given or made, such information or representation may not be relied upon as having been authorized by us. This prospectus does not constitute an offer to sell, or a solicitation of an offer to buy our common stock in any circumstance under which the offer or solicitation is unlawful. Neither the delivery of this prospectus nor any distribution of our common stock in accordance with this prospectus shall, under any circumstances, imply that there has been no change in our affairs since the date of this prospectus.

Neither we nor the placement agentWe have not done anything that would permit this offering or possession or distribution of this prospectus in any jurisdiction where action for that purpose is required, other than the United States. You are required to inform yourself about, and to observe any restrictions relating to, this offering and the distribution of this prospectus.

This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, or will be filed as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the heading “Where You Can Find Additional Information.”

As used in this prospectus, unless the context indicates or otherwise requires, “the Company,” “our Company,” “Mateon,” “we,” “us,” and “our” refer to Mateon Therapeutics, Inc., a Delaware corporation.

Registered Trademarks and Trademark Applications: “OXi4503” is the subject of a trademark registration in the United States. Other brands, names and trademarks contained in this prospectus are the property of their respective owners. Solely for convenience, the trademarks, service marks and trade names referred to in this prospectus may appear without the^® and^TM symbols, but such references are not intended to indicate, in any way, that the owner thereof will not assert, to the fullest extent under applicable law, such owner’s rights to these trademarks, service marks and trade names. This prospectus contains additional trade names, trademarks and service marks of other companies, which, to our knowledge, are the property of their respective owners.

We obtained industry and market data used throughout and incorporated by reference into this prospectus through our research, surveys and studies conducted by third parties and industry and general publications. We have not independently verified market and industry data from third-party sources.

ii

SUMMARY CONSOLIDATED FINANCIAL DATA

The following summary consolidated financial data should be read together with our audited consolidated financial statements and accompanying notes and “Management Discussion and Analysis ofSummary Consolidated Financial Condition and Results of Operations” appearing in our Annual Report on Form10-K for the year ended December 31, 2016, filed with the SEC on March 30, 2017 and our Quarterly Report on Form10-Q for the quarter ended June 30, 2017, filed with the SEC on August 2, 2017, each of which are incorporated by reference into this prospectus.Data

The pro forma balance sheet data gives effect to the sale of securities offered by this prospectussold in the Private Placement at an assumed aggregate offering amount of $6 million, based on an assumed offeringa sales price of $0.36$0.20 per share of common stock and associated warrantWarrants to purchase common stock soldissued to the selling securityholders in this offeringconnection with the Private Placement and after deducting estimated placement agent fees and offering expenses payable by us. Our historical results are not necessarily indicative of results to be expected for any future period. The summary financial data in this section are not intended to replace our consolidated financial statements and the related notes. The following selected consolidated financial data should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated financial statements included elsewhere in this prospectus.

Statement of Operations Data:

Balance Sheet Data:

A $0.05 increase or decrease in the assumed public offering price of $0.36 per share of common stock and associated warrant, the last reported sale price for our common stock as reported on the OTCQX Marketplace on July 31, 2017, would decrease or increase the number of shares of our common stock issued in this offering and issuable upon the exercise of pre-funded warrants issued in this offering by approximately 2.0 million shares or 2.7 million shares, respectively.

Similarly, a one million share increase or decrease in the number of shares offered by us, as set forth on the cover page of this prospectus, would increase or decrease the net proceeds to us by approximately $337,000, assuming the assumed combined public offering price of $0.36 per share and accompanying warrant remains the same, and after deducting estimated placement agent fees and expenses and estimated offering expenses payable by us.

RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully review and consider the following risk factors and in the sections entitled “Risk Factors” contained in our most recent annual report on Form10-K, which has been filed with the SEC and is incorporated by reference in this prospectus, as well as any updates thereto contained in subsequent filings with the SEC, and all other information contained in this prospectus and incorporated by reference into the prospectus before purchasing our securities. The risks and uncertainties described below are not the only ones facing our Company. Additional risks and uncertainties that we are unaware of, or that we currently deem immaterial, also may become important factors that affect us. If any of the following risks occur, our business, financial condition or results of operations could be materially and adversely affected. In that case, the trading price of our common stock could decline, and you may lose some or all of your investment.

Risks Related to Our Business

If we are unable to obtain additional funding, we may be forced to cease operations.

We needhave experienced net losses every year since inception and, as of March 31, 2018, had an accumulated deficit of approximately $293 million. We have no source of revenue and do not expect to raisereceive any product revenue in the near future. If we remain in business, we expect to incur additional funds to financeoperating losses over the next several years, principally as a result of our continuing development of our investigational drugs. As of March 31, 2018, we had approximately $0.2 million in cash and cash equivalents and current liabilities of approximately $1.5 million. Based on our planned operations and $2.4 million in net proceeds from the private placement completed in April 2018, Management expects to be able to support operations only into the fourth quarter of 2018. Prior to this time, we will need to secure additional funding or we may be forced to terminate or further curtail operations. Because we do not currently have a guaranteed source of capital that will sustain operations for at least the next twelve months, Management has determined that there is substantial doubt about our ability to continue the developmentas a going concern.

The principal source of our product candidates, andworking capital to date has been the proceeds from the sale of equity. If we are unable to access additional funds in the near term, whether through the sale of additional equity or another means, we may not be able to do so when necessary. Even if we are able to raise additional funds, the terms of any financingscontinue in business. We also may not be advantageous to us.

Our operations to date have consumed substantial amounts of cash. Negative cash flows from our operations are expected to continue over at least the next several years. Our cash utilization amount is highly dependent on the product development programs we choose to pursue, the progress of these product development programs, the results of our preclinical studies and clinical trials, the cost, timing and outcomes of regulatory decisions regarding potential approval for our product candidates, the terms and conditions of our contracts with service providers for these programs, and the rate of recruitment of patients in our human clinical trials. In addition, the continuation of our clinical trials, and quite possibly our entire business, will depend on results of upcoming analyses and our financial resources at the time.

In orderable to continue the development of our product candidates, we are pursuing forms of capital infusion including public or privateinvestigational drugs. Any additional equity financing, strategic partnerships or other arrangements with organizations that have capabilities, products and/or resources that are complementaryif available to or could further extend our own capabilities, products or resources. However, there can be no assurances that we will complete any financings, strategic alliances or collaborative development agreements, and the terms of such arrangementsus, may not be advantageous to us.

Basedavailable on our current operating plansfavorable terms and assuming operations as presently planned, we expect our existing cash, without taking into account any proceeds of this offering, to support our operations into approximately October 2017. We expect that our planned level of cash utilization will allow us to advance our ongoing programs, including completion of at least two more interim analyses of our Phase 2/3 FOCUS Study of CA4P in combination with bevacizumab and chemotherapy in platinum-resistant ovarian cancer; completion of the treatment in the fifth cohort of an open-label Phase 1b/2 clinical trial of OXi4503 in combination with cytarabine in patients with AML; supporting a Phase 2 trial of CA4P in relapsed ovarian cancer in combination with pazopanib, which is being sponsored by twoUK-based nonprofit organizations; and additional preclinical studies of CA4P in combination with immune oncology agents. Any significant further clinical development of CA4P, including the completion of the Phase 2/3 clinical trial of CA4P in ovarian cancer, and of OXi4503 would be contingent upon our ability to raise additional capital through public or private financings or from one or more new collaborative research or license agreements with a third-party, as to which we can give you no assurance.

Our ongoing capital requirements will depend on numerous factors, including the progress and results of preclinical testing and clinical trials of our product candidates under development; the costs of complying with the FDA and other regulatory agency requirements; the progress of our research and development programs; the time and costs expended and required to obtain any necessary or desired regulatory approvals; our ability to enter into licensing arrangements, including any unanticipated licensing arrangements that may be necessary to enable us to continue our development and clinical trial programs; the costs and expenses of filing, prosecuting and, if necessary, enforcing our patent claims, or defending against possible claims of infringement by third-party patent or other technology rights; the cost of commercialization activities and arrangements, if any, undertaken by us; and, if and when approved, the demand for our products, which demand depends in turn on circumstances and uncertainties that cannot be fully known, understood or quantified unless and until the time of approval, including the range of indications for which any product is granted approval.

Our ability to raise additional capital was significantly impaired following the delisting of our common stock from The NASDAQ Capital Market. If we are unable to raise additional funds when needed, we will not be able to continue development of our product candidates or we will be required to delay, scale back or eliminate some or all of our development programs or cease operations. We may seek to raise funds through public or private financing, strategic partnerships or other arrangements. Any additional equity or convertible debt financing maymost likely be dilutive to our current stockholders andstockholders. Any debt financing, if available, may involve restrictive covenants.covenants and also be dilutive to current stockholders. If we raiseobtain funds through collaborative or licensing arrangements, we may be required to relinquish on terms that are not favorable to us, rights to some of our technologies or product candidates on terms that we would otherwise seekare not favorable to develop or commercialize.us. Our failureability to raiseaccess capital when needed is not assured.

In their audit report with regard to our financial statements as of December 31, 2017, our independent registered public accountants expressed an opinion that substantial doubt exists as to whether we can continue as a going concern. Because we have limited cash resources, we believe that it will be necessary for us to either raise additional capital before the end of 2018 or to enter into a license or other agreement with a larger pharmaceutical company before the end of 2018. If we do not succeed in doing so, we may be required to suspend or cease our business, which would likely materially harm the value of our business, financial conditioncommon stock.

We will require additional capital funding, the receipt of which may impair the value of our common stock.

Our future capital requirements depend on many factors, including our research, development, sales and results of operations.marketing activities. We will need to raise additional capital through public or private equity or debt offerings or through arrangements with strategic partners or other sources in order to continue to develop our product candidates. There can be no assurance that additional capital will be available when needed or on terms satisfactory to us, if at all. To the extent we raise additional capital by issuing equity securities, our shareholders may experience substantial dilution and the new equity securities may have greater rights, preferences or privileges than our existing common stock.

Due in part to our limited financial resources, we may fail to select or capitalize on the most scientifically, clinically or commercially promising or profitable indications or therapeutic areas for our product candidates, and we may be unable to pursue and complete the clinical trials that we would like to pursue and complete.

We have limited financial and technical resources to determine the indications on which we should focus the development efforts for our product candidates. Due to our limited available financial resources, we have curtailed clinical development programs and activities that might otherwise have led to more rapid progress of our product candidates through the regulatory and development processes. Further, our current clinical trial in platinum-resistant ovarian cancer is designed to be larger than any other clinical trial that we have conducted previously. We currently do not have thelimited financial resources to complete thisour planned drug development work, which is limited to one additional cohort in our Study OX1222 of OXi4503 for relapsed/refractory AML and initiating a clinical trial andof CA4P in combination with an approved immuno-oncology agent. Due to our limited financial resources, we cannot assure you that we will be able to obtain sufficient financial resources to complete the trial. If we are forced to terminate the trial early, our chanceseither of obtaining positive results from the clinical trial are likely to be reduced, due to the lower statistical power of smaller clinical trials.these programs.

We may make incorrect determinations with regard to the indications and clinical trials on which to focus the available resources that we do have. Furthermore, we cannot assure you that we will be able to retain adequate staffing levels to run our operations and/or to accomplish all of the objectives that we otherwise would seek to accomplish. We currently are pursuing clinical trials in several indications, but we are required by our financial resources to engage only in limited clinical activities. The decisions to allocate our research, management and financial resources toward particular indications or therapeutic areas for our product candidates may not lead to the development of viable commercial products and may divert resources from better opportunities. Similarly, our decisions to delay or terminate drug development programs may also cause us to miss valuable opportunities. In addition, from time to time, we mayin-license or otherwise acquire product candidates to supplement our internal development activities. Those activities may use resources that otherwise would have been devoted to our internal programs, and with research and development programs there is no way to assure that the outcome of any trials or other activities will be positive, whether the program was internally generated orin-licensed.

If we are unable to obtain required regulatory approvals, we will be unable to market and sell our product candidates.

Our product candidates are subject to extensive governmental regulations relating to development, clinical trials, manufacturing, oversight of clinical investigators, recordkeeping and commercialization. Rigorous preclinical testing and clinical trials and an extensive regulatory review and approval process are required to be successfully completed in the United States, in the European Union and in many other foreign jurisdictions before a new drug can be sold. Satisfaction of these and other regulatory requirements is costly, time consuming, uncertain, and subject to unanticipated delays. The time required to obtain approval by the FDA or the European Medicines Agency, or EMA, is unpredictable and often takes many years following the commencement of clinical trials.

In connection with the clinical development of our product candidates, we face risks that:

Only a small percentage of product candidates for which clinical trials are initiated are the subject of NDAs and even fewer receive approval for commercialization. Furthermore, even if we do receive regulatory approval to market a product candidate, any such approval may be subject to limitations such as those on the indicated uses for which we may market the product.

If we or the third parties on which we rely for the conduct of our clinical trials and results do not perform our clinical trial activities in accordance with good clinical practices and related regulatory requirements, we may not be able to obtain regulatory approval for or commercialize our product candidates.

We currently use independent clinical investigators in all of our clinical trials and, in many cases, also utilize contract research organizations, or CROs, and other third-party service providers to conduct and/or oversee the clinical trials of our product candidates and expect to continue to do so for the foreseeable future. We rely heavily on these parties for successful execution of our clinical trials. Nonetheless, we are responsible for confirming that each of our clinical trials is conducted in accordance with the FDA’s requirements and our general investigational plan and protocol. Currently, we have clinical trial activities involving CA4P and OXi4503 being conducted by clinical investigators who are independent of us, but with whom we have agreements for them to provide the results of their clinical trials to us. In order for us to rely on data from these ongoing clinical trials in support of a New Drug Application, or NDA, for approval of any of our product candidates by the FDA or similar types of marketing applications that are required by other regulatory authorities, the independent investigators are required to comply with applicable good clinical practice requirements.

The FDA and corresponding foreign regulatory authorities require us and our clinical investigators to comply with regulations and standards, commonly referred to as good clinical practices, or GCPs, for conducting and recording and reporting the results of clinical trials to assure that data and reported results are credible and accurate and that the trial participants are adequately protected. Our reliance on third parties that we do not control does not relieve us of these responsibilities and requirements. Third parties may not

complete activities on schedule or may not conduct our clinical trials in accordance with regulatory requirements or the respective trial plans and protocols. The failure of these third parties to carry out their obligations could delay or prevent the development, approval and commercialization of our product candidates or result in enforcement action against us.

We have taken and continue to take steps to strengthen our procedures and practices, , but we cannot assure you that the FDA will be satisfied with our procedures or that the FDA will not issue warning letters or take other enforcement action against us in the future. The steps we take to strengthen our procedures and conduct future clinical trials necessary for approval will be time-consuming and expensive.

We may encounter difficulties in expanding our operations successfully if and when we evolve from a company that is primarily involved in clinical development to a company that is also involved in commercialization.

As we advance our product candidates through later stages of clinical trials, we will need to expand our development, regulatory, manufacturing, marketing and sales capabilities or contract with third parties to provide these capabilities for us. As our operations expand, we expect that we will need to manage additional relationships with such third parties, as well as additional collaborators, distributors, marketers and suppliers.

Maintaining third party relationships for these purposes will impose significant added responsibilities on members of our management and other personnel. We must be able to manage our development efforts effectively, manage our participation in the clinical trials in which our product candidates are involved effectively, and improve our managerial, development, operational and finance systems, all of which may impose a strain on our administrative and operational infrastructure.

If, following any approval of our product candidates, we enter into arrangements with third parties to perform sales, marketing or distribution services, any product revenues that we receive, or the profitability of these product revenues to us, are likely to be lower than if we were to market and sell any products that we develop ourselves. In addition, we may not be successful in entering into arrangements with third parties to sell and market our products or in doing so on terms that are favorable to us. We likely will have little control over such third parties, and any of them may fail to devote the necessary resources and attention to sell and market our products effectively. If we do not establish sales and marketing capabilities successfully, either on our own or in collaboration with third parties, we will not be successful in commercializing our products.

If we were to submit an NDA for our drug candidates in the United States or a marketing application in the EU, we would need to undertake commercial scale manufacturing activities at significant expense to us in order to proceed with the application for approval for commercialization. We or our external vendors may encounter technical difficulties that preclude us from successfully manufacturing the required registration and validation batches of active pharmaceutical ingredient, or API, and/or drug product and we may be unable to recover any financial losses associated with the manufacturing activities. Further, our research or product development efforts may not be successfully completed, any compounds currently under development by us may not be successfully developed into drugs, any potential products may not receive regulatory approval on a timely basis, if at all, and competitors may develop and bring to market products or technologies that render our potential products obsolete. If any of these problems occur, our business would be materially and adversely affected.

We have no manufacturing capacity and have relied on, and expect to continue to rely on, third-party manufacturers to produce our product candidates.

We do not own or operate manufacturing facilities for the production of clinical or commercial quantities of our product candidates or any of the compounds that we are testing in our preclinical programs, and we lack the resources and the capabilities to do so. As a result, we currently rely, and we expect to rely for the foreseeable future, on third-party manufacturers to supply our product candidates. Reliance on third-party manufacturers entails risks to which we would not be subject if we manufactured our product candidates or products ourselves, including:

If we do not maintain our developed important manufacturing relationships, we may fail to find replacement manufacturers or develop our own manufacturing capabilities, which could delay or impair our ability to obtain regulatory approval for our products and substantially increase our costs or deplete profit margins, if any. If we do find replacement manufacturers, we may not be able to enter into agreements with them on terms and conditions favorable to us, and there could be a substantial delay before new facilities could be qualified and registered with the FDA, EMA and other foreign regulatory authorities.

The FDA, EMA and other foreign regulatory authorities require manufacturers to register manufacturing facilities. The FDA and corresponding foreign regulators also inspect these facilities to confirm compliance with current good manufacturing practices, or cGMPs. Contract manufacturers may face manufacturing or quality control problems causing drug substance production and shipment delays or a situation where the contractor may not be able to maintain compliance with the applicable cGMP requirements. Any failure to comply with cGMP requirements or other FDA, EMA and comparable foreign regulatory requirements could adversely affect our clinical research activities and our ability to develop our product candidates and market our products after approval.

Our current and anticipated future dependence upon others for the manufacture of our product candidates may adversely affect our ability to develop our product candidates, our ability to commercialize any products that receive regulatory approval and our potential future profit margins on these products.

Our product candidates have not completed clinical trials, and may never demonstrate sufficient safety and efficacy in order to do so.

Our product candidates are in the clinical stage of development. In order to achieve profitable operations, we alone or in collaboration with others, must successfully develop, manufacture, introduce and market our products. The time frame necessary to achieve market success for any individual product is long and uncertain. The products currently under development by us may require significant additional research and development and additional preclinical and clinical testing prior to application for commercial use. A number of companies in the biotechnology and pharmaceutical industries have suffered significant setbacks in clinical trials, even after showing promising results in early or later-stage studies or clinical trials. Although we have obtained some favorable results to date in preclinical studies and clinical trials of certain of our potential products, such results may not be indicative of results that will ultimately be obtained in or throughout such clinical trials, and clinical trials may not show any of our products to be safe or capable of producing a desired result. Additionally, we may encounter problems in our clinical trials that may cause us to delay, suspend or terminate those clinical trials.

Adverse events observed to date and associated with CA4P and OXi4503 have generally been found to be manageable for drugs treating the indications for which we are developing our product candidates. However, we will be required to continue to test and evaluate the safety of our product candidates in additional clinical trials, and to demonstrate their safety to the satisfaction of appropriate regulatory agencies, as a condition to receipt of any regulatory approvals. In clinical trials to date, transient hypertension believed to be associated with CA4P and OXi4503 has been effectively managed throughpre-treatment with anti-hypertensive medication. We cannot assure you, however, that we will be able to make the necessary demonstrations of safety to allow us to receive regulatory approval for our product candidates in any indication.

We only have a limited number of employees to manage and operate our business.

As of JuneMarch 30, 2017,2018, we had a total of 14two full-time employees. Our limited financial resources require us to manage and operate our business in a highly efficient manner. We cannot assure you that we will be able to retain adequate staffing levels to run our operations and/or to accomplish all of the objectives that we otherwise would seek to accomplish.

We have a history of losses, and we anticipate that we will continue to incur losses in the future; our auditors have included in their audit report an explanatory paragraph as to substantial doubt as to our ability to continue as a going concern.

We have experienced net losses every year since our inception and, as of June 30,December 31, 2017, had an accumulated deficit of over $286approximately $292 million. Our auditors have included in their audit report a “going concern” explanatory paragraph as to substantial doubt as to our ability to continue as a going concern that assumes the realization of our assets and the satisfaction of our liabilities and commitments in the normal course of business. We anticipate continuing to incur substantial additional losses over at least the next several years due to, among other factors, our continuing clinical trials and development activities with respect to our VDA drug candidates, technologies, and anticipated research and development activities and the general and administrative expenses associated with those activities. We have not yet commercialized any product candidates. Our ability to attain profitability will depend upon our ability to develop and commercialize products that are effective and commercially viable, to obtain regulatory approval for the manufacture and sale of our products and to license or otherwise market our products successfully. We may never achieve profitability.

We depend on our executive officers and principal consultants and the loss of their services could materially harm our business.

We believe that our success depends, and will likely continue to depend, upon our ability to retain the services of our current executive officers, particularly our Chief Executive Officer and Chief Financial Officer, our principal consultants and others. Our executive officers have been working at 50% salaries since early October 2017, which increases the risk that we may not be able to

retain their services. The loss of the services of any of these individuals could have a material adverse effect on our business. In addition to these key service providers, we have established relationships with universities, hospitals and research institutions, which have historically provided, and continue to provide, us with access to research laboratories, clinical trials, facilities and patients. Additionally, we believe that we may, at any time and from time to time, materially depend on the services of consultants and other unaffiliated third parties. We cannot assure you that consultants and other unaffiliated third parties will provide the level of service to us that we require in order to achieve our business objectives.

Our industry is highly competitive, and our product candidates may become obsolete.

We are engaged in a rapidly evolving field. Competition from other pharmaceutical companies, biotechnology companies and research and academic institutions is intense and likely to increase. Many of those companies and institutions have substantially greater financial, technical and human resources than we do. Many of those companies and institutions also have substantially greater experience in developing products, conducting clinical trials, obtaining regulatory approval and in manufacturing and marketing pharmaceutical products. Our competitors may succeed in obtaining regulatory approval for their products more rapidly than we do. Competitors have developed or are in the process of developing technologies that are, or in the future may be, the basis for competitive products. We are aware of at least four other companies that currently have a clinical-stage VDA for use in an oncology indication. Some of these competitive products may have an entirely different approach or means of accomplishing the desired therapeutic effect than products being developed by us. Our competitors may succeed in developing products that are more effective and/or cost competitive than those we are developing, or that would render our product candidates less competitive or even obsolete. In addition, one or more of our competitors may achieve product commercialization or patent protection earlier than we do, which could materially adversely affect us.

We depend extensively on the patents and proprietary technology we license from others, and we must maintain these licenses in order to preserve our business.

We have licensed in rights to CA4P, OXi4503 and other programs from third parties. If our license agreements terminate or expire, we may lose the licensed rights to our product candidates, including CA4P and OXi4503, and we may not be able to continue to develop them or, if they are approved, we may not be able to market or commercialize them.

We depend on license agreements with third-parties for certain intellectual property rights relating to our product candidates, including patent rights. Currently, we have licensed in certain patent rights from Arizona State University, or ASU, and the Bristol-Myers Squibb Company for CA4P and OXi4503 and from Baylor University for other programs. In general, our license agreements require us to make payments and satisfy performance obligations in order to keep these agreements in effect and retain our rights under them. These payment obligations can include upfront fees, maintenance fees, milestones, royalties, patent prosecution expenses, and other fees. These performance obligations typically include diligence obligations. If we fail to pay, be diligent or otherwise perform as required under our license agreements, we could lose the rights under the patents and other intellectual property rights covered by the agreements. While we are not currently aware of any dispute with any licensors under our material agreements with them, if disputes arise under any of ourin-licenses, including ourin-licenses from ASU, the Bristol-Myers Squibb Company and Baylor University, we could lose our rights under these agreements. Any such dispute may not be resolvable on favorable terms, or at all. Whether or not any disputes of this kind are favorably resolved, our management’s time and attention and our other resources could be consumed by the need to attend to and seek to resolve these disputes and our business could be harmed by the emergence of such a dispute.

If we lose our rights under these agreements, we may not be able to conduct any further activities with the product candidate or program that the license covered. If this were to happen, we might not be able to develop our product candidates further, or following regulatory approval, if any, we might be prohibited from marketing or commercializing them. In particular, patents previously licensed to us, such as the patents we previously licensed from Angiogene, might after termination be used to stop us from conducting activities in the patents’ respective fields.

We depend on patents and proprietary technology in the course of our business, and we must protect those assets in order to preserve our business.

Although we expect to seek patent protection for any compounds we discover and/or for any specific use we discover for new or previously known compounds, any or all of them may not be subject to effective patent protection. Further, the development of regimens for the administration of pharmaceuticals, which generally involve specifications for the frequency, timing and amount of dosages, has been, and we believe, may continue to be, important to our effort, although those processes, as such, may not be patentable. In addition, the issued patents may be declared invalid or our competitors may find ways to avoid the claims in the patents.

Our success will depend, in part, on our ability to obtain patents, protect our trade secrets and operate without infringing on the proprietary rights of others. We are the exclusive licensee, sole assignee orco-assignee on a number of granted United States patents, pending United States patent applications, and granted patents and/or pending applications in several other major markets, including the European Union, Canada and Japan. The patent position of pharmaceutical and biotechnology firms like us is generally highly uncertain and involves complex legal and factual questions, resulting in both an apparent inconsistency regarding the breadth of claims allowed in United States patents and general uncertainty as to their legal interpretation and enforceability. Accordingly, patent applications assigned or exclusively licensed to us may not result in patents being issued, any issued patents assigned or exclusively licensed to us may not provide us with competitive protection or may be challenged by others, and the current or future granted patents of others may have an adverse effect on our ability to do business and achieve profitability. Moreover, because some of the basic research relating to one or more of our patent applications and/or patents were performed at various universities and/or funded by grants, one or more of these universities, employees of such universities and/or grantors could assert that they have certain rights in such research and any resulting products. Further, others may independently develop similar products, may duplicate our products, or may design around our patent rights. In addition, as a result of the assertion of rights by a third-party or otherwise, we may be required to obtain licenses to patents or other proprietary rights of others in or outside of the United States. Any licenses required under any such patents or proprietary rights may not be made available on terms acceptable to us, if at all. If we do not obtain such licenses, we could encounter delays in product market introductions while our attempts to design around such patents or could find that the

development, manufacture or sale of products requiring such licenses is foreclosed. In addition, we could incur substantial costs in defending ourselves in suits brought against us or in connection with patents to which we hold licenses or in bringing suit to protect our own patents against infringement.

We require employees and the institutions that perform our preclinical and clinical trials to enter into confidentiality agreements with us. Those agreements provide that all confidential information developed or made known to a party to any such agreement during the course of the relationship with us be kept confidential and not be disclosed to third-parties, except in specific circumstances. Any such agreement may not provide meaningful protection for our trade secrets or other confidential information in the event of unauthorized use or disclosure of such information.

The use of our products may result in product liability exposure, and it is uncertain whether our insurance coverage will be sufficient to cover all claims.

The use of our product candidates in clinical trials may expose us to liability claims in the event such product candidates cause death, injury or disease, or result in adverse effects. We may be exposed to liability claims even if our product did not cause death, injury or diseases, but is merely presumed or alleged to have caused any of these. If our product candidates are ever commercially approved, the commercial use of these products may also expose us to similar liability claims. Any of these claims could be made by health care institutions, contract laboratories, patients or others using such products. Although we have obtained liability insurance coverage for our ongoing clinical trials, this coverage may not be in amounts sufficient to protect us from any product liability claims or product recalls which could have a material adverse effect on our financial condition and prospects. Further, adverse product and similar liability claims could negatively impact our ability to obtain or maintain regulatory approvals for our technology and product candidates under development.

If clinical trials or regulatory approval processes for our product candidates are prolonged, delayed or suspended, we may be unable toout-license or commercialize our product candidates on a timely basis, which would require us to incur additional costs and delay or prevent our receipt of any proceeds from potential license agreements or product sales.

We cannot predict whether we will encounter problems with any of our completed, ongoing or planned clinical trials that will cause us or any regulatory authority to delay or suspend those clinical trials or delay or invalidate the analysis of data derived from them. A number of events, including any of the following, could delay the completion of our other ongoing and planned clinical trials and negatively impact our ability to obtain regulatory approval for, and to market and sell, a particular product candidate:

Commercialization or licensure of our product candidates may be delayed or prevented by the imposition of additional conditions on our clinical trials by the FDA, EMA or another foreign regulatory authority or the requirement of additional supportive clinical trials by the FDA, EMA or another foreign regulatory authority. In addition, clinical trials require sufficient patient enrollment, which is a function of many factors, including the size of the patient population, the nature of the trial protocol, the proximity of patients to clinical sites, the availability of effective treatments for the relevant disease, the conduct of other clinical trials that compete for the same patients as our clinical trials, and the eligibility criteria for our clinical trials. Our failure to enroll patients in our clinical trials could delay the completion of the clinical trial beyond our expectations, or it could prevent us from being able to complete the clinical trial. In addition, the FDA and EMA could require us to conduct clinical trials with a larger number of subjects than we have projected for any of our product candidates. We may not be able to enroll a sufficient number of patients in a timely or cost-effective manner. Furthermore, enrolled patients may drop out of our clinical trials, which could impair the validity or statistical significance of the clinical trials.

We do not know whether our clinical trials will begin as planned, will need to be restructured, or will be completed on schedule, if at all. Delays in our clinical trials will result in increased development costs for our product candidates, and our financial resources may be insufficient to fund any incremental costs. In addition, if our clinical trials are delayed, our competitors may be able to bring products to market before we do and the commercial viability of our product candidates could be limited.

We have been granted orphan drug status for certain of our product candidates and may seek orphan drug status for additional indications for those product candidates or for additional product candidates. We may be unsuccessful in maintaining orphan drug exclusivity for our product candidates and may be unsuccessful in our efforts to seek orphan drug status and orphan drug exclusivity.

Regulatory authorities in some jurisdictions, including the United States and the European Union, may designate drugs for relatively small patient populations as orphan drugs. Under the Orphan Drug Act, the FDA may designate a product as an orphan drug if it is a drug intended to treat a rare disease or condition, which is generally defined as a disease with a patient population of fewer than 200,000 individuals in the United States. Our lead product candidate, OXi4503, has been awarded orphan drug status by the FDA and the European Commission for the treatment of acute myelogenous leukemia. Our other product candidate, CA4P, has been awarded orphan drug status by the FDA for the treatment of anaplastic, medullary, Stage IV papillary and Stage IV follicular thyroid cancers, ovarian cancer, neuroendocrine tumors and glioma. Our product candidate, OXi4503, has been awarded orphan drug status by the FDA for the treatment of acute myelogenous leukemia. CA4P has also been awarded orphan drug status by the European Commission in the European Union for the treatment of anaplastic thyroid cancer, ovarian cancer and neuroendocrine tumors. OXi4503 has been awarded orphan drug status by the European Commission in the European Union for the treatment of acute myelogenous leukemia.

Generally, if a product with an orphan drug designation subsequently receives the first marketing approval for the indication for which it has such designation, the product is entitled to a period of marketing exclusivity, which precludes the EMA or the FDA from approving another marketing application for the same drug for the same indication during the period of exclusivity. The applicable period is seven years in the United States and ten years in the European Union. The European exclusivity period can be reduced to six years if a drug no longer meets the criteria for orphan drug designation or if the drug is sufficiently profitable so that market exclusivity is no longer justified. Orphan drug exclusivity may be lost if the FDA or the EMA determines that the request for designation was materially defective, if the manufacturer is unable to assure sufficient quantity of the drug to meet the needs of patients with the rare disease or condition.

Even if we obtain orphan drug exclusivity for a product candidate or additional product candidates, that exclusivity may not effectively protect the product candidate from competition because different drugs can be approved for the same condition. Even after an orphan drug is approved, the FDA can subsequently approve a different drug for the same condition if the FDA concludes that the later drug is clinically superior in that it is shown to be safer, more effective or makes a major contribution to patient care.

Our product candidates will remain subject to ongoing regulatory review even if they receive marketing approval, and if we fail to comply with continuing regulations, we could lose these approvals and the sale of any approved commercial products could be suspended.

Even if we receive regulatory approval to market a particular product candidate, the manufacturing, labeling, packaging, adverse event reporting, storage, advertising, promotion, and record keeping related to the product will remain subject to extensive regulatory requirements. If we fail to comply with the regulatory requirements of the FDA, EMA and other applicable domestic and foreign regulatory authorities or previously unknown problems with any approved product, manufacturer, or manufacturing process are discovered, we could be subject to administrative or judicially imposed sanctions, including:

If physicians and patients do not accept our future products or if the market for indications for which any product candidate is approved is smaller than expected, we may be unable to generate significant revenue, if any.

Even if any of our product candidates obtain regulatory approval, they may not gain market acceptance among physicians, patients, and third-party payers. Physicians may decide not to prescribe our drugs for a variety of reasons including:

If any of our product candidates is approved, but fails to achieve market acceptance, we may not be able to generate significant revenue and our business would suffer.

The uncertainty associated with pharmaceutical reimbursement and related matters may adversely affect our business.

Market acceptance and sales of any one or more of our product candidates that we develop will depend on reimbursement policies and may be affected by future healthcare reform measures in the United States and in foreign jurisdictions. Government authorities and third-party payers, such as private health insurers and health maintenance organizations, decide which drugs they will cover and establish payment levels. We cannot be certain that reimbursement will be available for any product candidates that we develop. Also, we cannot be certain that reimbursement policies will not reduce the demand for, or the price paid for, our products. If reimbursement is not available or is available on a limited basis, we may not be able to successfully commercialize any product candidates that we develop.

In the United States, the Medicare Prescription Drug, Improvement, and Modernization Act of 2003, also called the Medicare Modernization Act, or MMA, changed the way Medicare covers and pays for pharmaceutical products. The legislation established Medicare Part D, which expanded Medicare coverage for outpatient prescription drug purchases by the elderly but provided authority for limiting the number of drugs that will be covered in any therapeutic class. The MMA also introduced a new reimbursement methodology based on average sales prices for physician-administered drugs.

The United States and several foreign jurisdictions are considering, or have already enacted, a number of legislative and regulatory proposals to change the healthcare system in ways that could affect our ability to sell our products profitably. Among policy makers and payers in the United States and elsewhere, there is significant interest in promoting changes in healthcare systems with the stated goals of containing healthcare costs, improving quality and/or expanding access to healthcare. In the United States, the pharmaceutical industry has been a particular focus of these efforts and has been significantly affected by major legislative initiatives. We expect to experience pricing pressures in connection with the sale of any products that we develop due to the trend toward managed healthcare, the increasing influence of health maintenance organizations and additional legislative proposals.

In March 2010, the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Affordability Reconciliation Act, or collectively, ACA, became law in the U.S. The goal of ACA is to reduce the cost of health care and substantially change the way h health care is financed by both government and private insurers. While we cannot predict what impact on federal reimbursement policies this legislation will have in general or on our business specifically, the ACA may result in downward pressure on pharmaceutical reimbursement, which could negatively affect market acceptance of, and the price we may charge for, any products we develop that receive regulatory approval. We also cannot predict the impact of ACA on us as many of the ACA reforms require the promulgation of detailed regulations implementing the statutory provisions, which have not yet been fully implemented.

More recently, the current U.S. presidential administration has made statements suggesting plans to seek repeal of all or portions of the ACA, and the U.S. Congress is considering such repeal or partial repeal and replacement. There is uncertainty regarding the impact that the President’s administration may have on matters currently governed by the ACA, if any, and any regulatory or legislative changes will likely take time to unfold. These changes could have an impact on coverage and reimbursement for healthcare items and services covered by plans that were authorized by the ACA. However, we cannot predict the ultimate content, timing or effect of any healthcare reform legislation or the impact of potential legislation on us. Any reduction in reimbursement from Medicare or other government programs may result in a similar reduction in payments from private payors. The implementation of cost containment measures or other healthcare reforms may prevent us from being able to generate revenue, attain profitability, or commercialize our products.

Unfavorable global economic conditions could adversely affect our business, financial condition or results of operations.

Our operations and the financial results of our operations could be adversely affected by general conditions in the global economy and in the global financial markets. Global financial concerns have caused, and may continue to cause, extreme volatility and disruptions in the capital and credit markets. A severe or prolonged economic downturn could result in a variety of risks to our business, including our ability to raise additional capital when needed on acceptable terms, if at all. We cannot currently anticipate all of the ways in which the current economic climate and financial market conditions could adversely impact our business.

Our business and operations could suffer in the event of system failures.

Despite the implementation of security measures, our internal computer systems and those of our third-party CROs and other contractors and consultants are vulnerable to damage from computer viruses, unauthorized access, natural disasters, terrorism, war and telecommunication and electrical failures. Furthermore, we have little or no control over the security measures and computer systems of our third-party CROs and other contractors and consultants. While we have not experienced any material system failure, accident, or security breach to date, if such an event were to occur and cause interruptions in our operations, it could result in a material disruption of our programs. For example, the loss of clinical trial data for our product candidates could result in delays in our marketing approval efforts and significantly increase our costs to recover or reproduce the data. To the extent that any disruption or security breach results in a loss of or damage to our data or applications or other data or applications relating to our technology or product candidates, or inappropriate disclosure of confidential or proprietary information, we could incur liabilities and the further development of our product candidates could be delayed.

Our employees, principal investigators, CROs and consultants may engage in misconduct or other improper activities, includingnon-compliance with regulatory standards and requirements and insider trading.

We are exposed to the risk that our employees, principal investigators, CROs and consultants may engage in fraudulent conduct or other illegal activity. Misconduct by these parties could include intentional, reckless and/or negligent conduct or disclosure of unauthorized activities to us that violate the regulations of the FDA and other regulatory authorities, including those laws requiring the reporting of true, complete and accurate information to such authorities; healthcare fraud and abuse laws and regulations in the United States and abroad; or laws that require the reporting of financial information or data accurately. In particular, sales, marketing and business arrangements in the healthcare industry are subject to extensive laws and regulations intended to prevent fraud, misconduct, kickbacks, self-dealing and other abusive practices. Activities subject to these laws also involve the improper use of information obtained in the course of clinical trials or creating fraudulent data in our preclinical studies or clinical trials, which could result in regulatory sanctions and cause serious harm to our reputation.

We have a code of conduct applicable to all of our employees, but it is not always possible to identify and deter misconduct by employees and other third parties, and the precautions we take to detect and prevent this activity may not be effective in controlling unknown or unmanaged risks or losses or in protecting us from governmental investigations or other actions or lawsuits stemming from a failure to comply with these laws or regulations. Additionally, we are subject to the risk that a person could allege such fraud or other misconduct, even if none occurred. If any such actions are instituted against us, and we are not successful in defending ourselves or asserting our rights, those actions could have a significant impact on our business, including the imposition of civil, criminal and administrative penalties, damages, monetary fines, possible exclusion from participation in Medicare, Medicaid and other federal healthcare programs, contractual damages, reputational harm, diminished profits and future earnings, and curtailment of our operations, any of which could adversely affect our ability to operate our business and our results of operations.

We, or the third parties upon whom we depend, may be adversely affected by earthquakes or other natural disasters and our business continuity and disaster recovery plans may not adequately protect us from a serious disaster.

Earthquakes or other natural disasters could severely disrupt our operations and have a material adverse effect on our business, results of operations, financial condition and prospects. If a natural disaster, power outage or other event occurred that prevented us from using all or a significant portion of our headquarters, that damaged critical infrastructure, such as the manufacturing facilities of our third-party contract manufacturers, or that otherwise disrupted operations, it may be difficult or, in certain cases, impossible for us to continue our business for a substantial period of time. The disaster recovery and business continuity plans we have in place may prove inadequate in the event of a serious disaster or similar event. We may incur substantial expenses as a result of the limited nature of our disaster recovery and business continuity plans, which could have a material adverse effect on our business.

Risks Related To Our Common Stock

The price of our common stock is volatile, and is likely to continue to fluctuate due to reasons beyond our control; a limited public trading market may cause volatility in the price of our common stock. Quotation of shares of our common stock on an OTC market does not assure that holders of our common stock will have access to a consistent and liquid trading market.

The market price of our common stock has been, and likely will continue to be, highly volatile. Factors, including our financial results or our competitors’ financial results, clinical trial and research development announcements and government regulatory action affecting our potential products in both the United States and foreign countries, have had, and may continue to have, a significant effect on our results of operations and on the market price of our common stock. We cannot assure you that an investment in our common stock will not fluctuate significantly. One or more of these factors could significantly harm our business and cause a decline in the price of our common stock in the public market. Substantially all of the shares of our common stock issuable upon exercise of outstanding options and warrants have been registered or are likely to be registered for resale or are available for sale pursuant to Rule 144 under the Securities Act, and may be sold from time to time. As of April 30, 2018, there was an aggregate of 28,814,694 shares of common stock underlying currently outstanding warrants and options. Such sales, as well as future sales of our common stock by existing stockholders, or the perception that sales may occur at any time, could adversely affect the market price of our common stock.

Our common stock is currently quoted on the OTCQX Marketplace.OTCQB Market. The quotation of our common stock on the OTCQX MarketplaceOTCQB Market does not assure that a meaningful, consistent and liquid trading market currently exists, and in recent years such market has experienced extreme price and volume fluctuations that have particularly affected the market prices of many smaller companies like us. Our common stock is subject to this volatility. Sales of substantial amounts of common stock, or the perception that such sales might occur, could adversely affect prevailing market prices of our common stock and our stock price may decline substantially in a short time and our stockholders could suffer losses or be unable to liquidate their holdings.

We may not be able to achieve secondary trading of our stock in certain states because our common stock is no longer nationally traded, which could subject our stockholders to significant restrictions and costs.

Our common stock is not currently eligible for trading on the NASDAQ Capital Market or on a national securities exchange. Therefore, our common stock is subject to the securities laws“Penny Stock” Rules of the various statesSEC and jurisdictions of the United States in addition to federal securities law. While we may register our common stock or qualify for exemptions for our common stock in one of more states, if we fail to do so the investors in those states where we have not taken such steps may not be allowed to purchase our stock or those who presently hold our stock may not be able to resell their shares without substantial effort and expense. These restrictions and potential costs could be significant burdens on our stockholders.

If at any time our common stock is subject to the Securities and Exchange Commission’s “penny stock” rules, broker-dealers may experience difficulty in completing customer transactions and trading activitymarket in our securities is limited, which makes transactions in our stock cumbersome and may be adversely affected.reduce the value of an investment in our stock.

If at any timeAs of December 31, 2017, we havehad net tangible assets of $2,000,000 or less and our common stock hashad a market price per share of less than $5.00,$5.00. The Private Placement did not increase our net tangible assets to an amount above $2,000,000. As a result, transactions in our common stock will beare subject to the SEC’s “penny stock” rules. The designation of our common stock as a “penny stock” would limitlikely limits the liquidity of our common stock. Prices for penny stocks are often not available to buyers and sellers and the market may be very limited. Penny stocks are among the riskiest equity investments. Broker-dealers who sell penny stocks must provide purchasers of these stocks with a standardized risk-disclosure document prepared by the SEC. The document provides information about penny stocks and the nature and level of risks involved in investing in the penny stock market. A broker must also provide purchasers with bid and offer quotations and information regarding broker and salesperson compensation and make a written determination that the penny stock is a suitable investment for the purchaser and obtain the purchaser’s written agreement to the purchase. Many brokers choose not to participate in penny stock transactions. Because of the penny stock rules, there may be less trading activity in penny stocks. IfBecause shares of our common stock becomeare currently subject to these penny stock rules, your ability to trade or dispose of shares of our common stock may be adversely effected.affected.

We may not be able to achieve secondary trading of our stock in certain states because our common stock is no longer nationally traded, which could subject our stockholders to significant restrictions and costs.

Our common stock is not currently eligible for trading on the Nasdaq Capital Market or on a national securities exchange. Therefore, our common stock is subject to the securities laws of the various states and jurisdictions of the United States in addition to federal securities law. While we may register our common stock or qualify for exemptions for our common stock in one of more states, if we fail to do so the investors in those states where we have not taken such steps may not be allowed to purchase our stock or those who presently hold our stock may not be able to resell their shares without substantial effort and expense. These restrictions and potential costs could be significant burdens on our stockholders.

If we fail to maintain an effective system of internal controls over financial reporting, we may not be able to accurately report our financial results. As a result, current and potential stockholders could lose confidence in our financial reporting, which could harm our business and the trading price of our stock.

Effective internal controls over financial reporting are necessary for us to provide reliable financial reports. If we cannot maintain effective controls and reliable financial reports, our business and operating results could be harmed. For example, during the third quarter of 2013, our management determined that we had a material weakness related to the operation of our controls over financial reporting associated with a complexnon-routine financing transaction in the second quarter of 2013. We conducted an evaluation of the effectiveness of our internal control over financial reporting as of December 31, 20162017 based on the criteria established in Internal Control —- Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 Framework). Based on that evaluation, our management concluded that our internal control over financial reporting was effective as of December 31, 2016.2017. We continue to work on maintaining effective internal controls over financial reporting; however, there can be no assurance that another material weakness will not occur in the future. Any failure to implement and maintain controls over our financial reporting or difficulties encountered in the implementation of improvements in our controls, could cause us to fail to meet our reporting obligations. Any failure to maintain our internal controls over financial reporting or to address identified weaknesses in the future, if they were to occur, could also cause investors to lose confidence in our reported financial information, which could have a negative impact on the trading price of our stock.

Issuance of additional equity securities may adversely affect the market price of our common stock.

We are currently authorized to issue up to 70,000,000 shares of our common stock and 15,000,000 shares of preferred stock. As of JuneApril 30, 2017,2018, we had approximately 26,545,00041,419,934 shares of common stock issued and outstanding, and we had no shares of preferred stock outstanding. As of June 30, 2017,In addition, we also had approximately 9,626,00024,528,240 warrants and 5,941,0004,286,454 options outstanding. We are seeking stockholder approval for an increase in the number of authorized shares of common stock at our next annual meeting.

To the extent that additional shares of common stock are issued or options and warrants are exercised, holders of our common stock will experience dilution. In addition, in the event of any future issuances of equity securities or securities convertible into or exchangeable for common stock, holders of our common stock may experience dilution.

Moreover, ourOur board of directors is authorized to issue preferred stock without any action on the part of our stockholders. Our board of directors also has the power, without stockholder approval, to set the terms of any such preferred stock that may be issued, including voting rights, conversion rights, dividend rights, preferences over our common stock with respect to dividends or if we liquidate, dissolve or wind up our business and other terms. If we issue preferred stock in the future that has preference over our common stock with respect to the payment of dividends or upon our liquidation, dissolution or winding up, or if we issue preferred stock with voting rights that dilute the voting power of our common stock, the market price of our common stock could decrease. Any provision permitting the conversion of any such preferred stock into our common stock could result in significant dilution to the holders of our common stock.

We also consider from time to time various strategic alternatives that could involve issuances of additional common stock, including but not limited to acquisitions and business combinations, but do not currently have any definitive plans to enter into any of these transactions.

We have no plans to pay dividends on our common stock, and you may not receive funds without selling your common stock.

We have not declared or paid any cash dividends on our common stock, nor do we expect to pay any cash dividends on our common stock for the foreseeable future. We currently intend to retain any future earnings, if any, to finance our operations and growth and, potentially, for future stock repurchases and, therefore, we have no plans to pay cash dividends on our common stock. Any future determination to pay cash dividends on our common stock will be at the discretion of our board of directors and will be dependent on our earnings, financial condition, operating results, capital requirements, any contractual restrictions, and other factors that our board of directors deems relevant.

Accordingly, you may have to sell some or all of your common stock in order to generate cash from your investment in Mateon Therapeutics, Inc. You may not receive a gain on your investment when you sell our common stock and may lose the entire amount of your investment.

Risks Related To This Offering

We have broad discretion in the use of the proceeds of this offering and may apply the proceeds in ways with which you do not agree.

Substantially all of our net proceeds from this offering will be used, as determined by management in its sole discretion,Our ability to continue work toward development and regulatory approval of our product candidates, and for working capital and other general corporate purposes. Our management will have broad discretion over the use and investment of the net proceeds of this offering. The failure of our management to apply these funds effectively could harm our business. You will not have the opportunity, as part of your investment decision, to assess whether our proceeds are being used appropriately. Pending application of our proceeds, theya going concern may be placed in investments that do not produce income or that lose value.

There is no public market for the warrants to purchase common stock in this offering.

There is no established trading market for the warrants being offered in this offering, and we do not expect a market to develop. In addition, we do not intend to apply for listing of the warrants on any securities exchange. Without an active market, the liquidity of the warrants will be limited.

You may incur substantial dilution as a result of this offering and future equity issuances.

Baseddependent on our capitalization asstockholders passing a proposal to increase the aggregate number of June 30, 2017, purchasers of our securities in this offering will incur immediate dilution. See “Dilution” at p. 21 for a more detailed discussion of the dilution you will incur in this offering.

In addition to this offering, subject to market conditions and other factors, it is likely that we will pursue additional financings in the future, as we continue to build our business. In future years, we will likely need to raise significant additional capital to finance our operations and to fund the development and regulatory approval of our product candidates. Accordingly, we may conduct substantial future offerings of equity or debt securities. The exercise of outstanding options and warrants and future equity issuances, including future public offerings or future private placements of equity securities, will result in dilution to investors. In addition, the market price of our common stock could fall as a result of resales of any of these shares of common stock dueauthorized.

A total of 4,763,545 shares of common stock were available for future issuance as of April 30, 2018, prior to an increasedthe consideration of 7,437,500 shares required for the exercise of the Series B Warrants. With the current small pool of authorized and unissued shares of common stock, our management believes that it is at a higher risk of being unable to raise additional capital if our stockholders do not approve the authorization of additional shares of common stock. If we are unable to raise additional capital, we may be forced to scale back some or all of our programs, and we may not be able to continue in business.

If the proposal to increase the aggregate number of shares available for sale in the market.

The warrants mayof common stock is not have any value.

The warrants are exercisable at an exercise price of $             for afive-year term. In the eventapproved by our stockholders, it is possible that our financing alternatives may be limited by the lack of sufficient unissued and unreserved authorized shares of common stock, price does not exceedand stockholder value may be harmed by this limitation. In addition, our success depends in part on our continued ability to attract, retain and motivate highly qualified management and clinical and scientific personnel, and if the exercise priceproposal to increase the aggregate number of the warrants during the period when the warrants are exercisable, the warrants may not have any value.

Holders of our warrants will have no rights as a common stockholder until they exercise their warrants.

Until you receive shares of our common stock as a resultis not approved by our stockholders, the lack of exercising your warrants, you will have no rights with respectsufficient unissued and unreserved authorized shares of common stock to our common stock. Upon exercising your warrants, you will be entitled to exercise the rights of a common stockholder only as to matters for which the record date occurs after the exercise date.

Sales of our securities in this offering are limited to institutional investors; we have not applied to register the securities to be issued in this offering for sales to retail investors in any states.

We have not applied to register our securities to be issued in this offering for offers and sales to retail customers. Each state has its own securities laws, often called “blue sky” laws, which limit sales of securities to a state’s residents unless the securities are registered in that state or qualify for an exemption from registration and govern the reporting requirements for broker-dealers and stock brokers doing business directly or indirectly in the state. Before a security is sold in a state, there must be a registration in place to cover the transaction, or it must be exempt from registration. In connection with this offering, we will rely on exemptions provided for sales to institutional investors under the state Blue Sky laws. The definition of an “institutional investor” varies from state to state but generally includes financial institutions, broker-dealers, banks, insurance companies and other qualified entities. We expect that resales of the securities purchased in this offering will be exempt from state registration requirements pursuant to one or more exemptions. Specifically, under the National Securities Markets Improvement Act of 1996, states are pre-empted from regulating transactions in certain categories of securities that are designated as “covered securities.” The securities issued in this offering will be considered “covered securities” in connection with secondary market transactions by persons other than the issuer of the securities, an underwriter or a dealer because we file periodic and annual reports under the Exchange Act. Therefore, so long as we file periodic and annual reports, resales of the securities to be issued in this offering are exempt from state registration requirements. Each state retains jurisdiction to investigate and bring enforcement actions with respect to fraud or deceit, or unlawful conduct by a broker or dealer, in connection with the sale of securities. If we were to cease being eligible for this exemption, itprovide future equity incentive opportunities could have a material adverse effect on youradversely impact our ability to sell the securities purchased in this offering. For a complete discussion of the Blue Sky laws and registrations affecting this offering, please see the section titled “Plan of Distribution — State Blue Sky Information”.achieve our goals.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act, that involve substantial risks and uncertainties. We generally identify forward-looking statements by terminology such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “would,” “intend,” “target,” “aim,” “project,” “believe,” “estimate,” “predict,” “potential,” “seek,” “indicate,” or “continue” or the negative of these terms or other similar words, although not all forward-looking statements contain these words. Forward-looking statements include, but are not limited to, statements regarding our or our management’s expectations, hopes, beliefs, intentions or strategies regarding the future, such as our estimates regarding anticipated operating losses, future performance, future revenues and projected expenses; our liquidity and our expectations regarding our needs for and ability to raise additional capital; our ability to continue as a going concern; our ability to select and capitalize on commercially desirable product opportunities as a result of limited financial resources; our ability to manage our expenses effectively and raise the funds needed to continue our business; our ability to retain the services of our current executive officers, directors and principal consultants; the competitive nature of our industry and the possibility that our products or product candidates may become obsolete; our ability to obtain and maintain regulatory approval of our existing products and any future products we may develop; the clinical development of and the process of commercializing CA4P, which is also known as combretastatinA4-phosphate, fosbretabulin or fosbretabulin tromethamine; the efficacy of the combination of CA4P with bevacizumab; the clinical development of and the process of commercializing OXi4503; the combination of OXi4503 with cytarabine; the initiation, timing, progress and results of our preclinical and clinical trials, research and development programs; regulatory and legislative developments in the United States and foreign countries; the timing, costs and other limitations involved in obtaining regulatory approval for any product; the further preclinical or clinical development and commercialization of our product candidates; our ability to obtain and maintain orphan drug exclusivity for some of our product candidates; the potential benefits of our product candidates over other therapies; our ability to enter into and maintain any collaboration with respect to product candidates; our ability to continue to develop or commercialize our products or product candidates in the event any license agreements in place with third parties expire or are terminated; the performance and conduct of third parties, including our third-party manufacturers and third party service providers used in our clinical trials; our ability to obtain and maintain intellectual property protection for our products and operate our business without infringing upon the intellectual property rights of others; the potential liability exposure related to our products and our insurance coverage for such exposure; the successful development of our sales and marketing capabilities; the size and growth of the potential markets for our products and our ability to serve those markets; the rate and degree of market acceptance of any future products; the volatility of the price of our common stock; the ability to achieve secondary trading of our stock in certain states; the dilutive effects of potential future equity issuances; our expectation that no dividends will be declared on our common stock in the foreseeable future; our ability to maintain an effective system of internal controls; the payment and reimbursement methods used by private or governmental third-party payers; our ability to retain adequate staffing levels; unfavorable global economic conditions; a failure of our internal computer systems or those of our contractors and consultants; potential misconduct or other improper activities by our employees, contractors or consultants; the ability of our business continuity and disaster recovery plans to protect us in the event of a natural disaster; and other factors discussed elsewhere in this prospectus or any document incorporated by reference herein or therein.

The forward-looking statements contained in this Prospectusprospectus are based on our current expectations and beliefs concerning future developments and their potential effects on us. There can be no assurance that future developments affecting us will be those that we have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond our control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. These risks and uncertainties include, but are not limited to, those factors described in the section titled “Risk Factors.” Should one or more of these risks or uncertainties materialize, or should any of our assumptions prove incorrect, actual results may vary from those projected in these forward-looking statements. We undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable securities laws. The section captioned “Risk Factors as well as other sections in this prospectus or incorporated by reference into this prospectus, discuss some of the factors that could contribute to these differences.

The forward-looking statements made in this prospectus relate only to events as of the date on which the statements are made. We undertake no obligation to update any forward-looking statement to reflect events or circumstances after the date on which the statement is made or to reflect the occurrence of unanticipated events.

USE OF PROCEEDS

We estimate that weEach of the selling securityholders will receive up to approximately $5.4 million inall of the net proceeds from the sale of our securities in this offering, based on an assumed offering price of $0.36 per share of common stock and associated warrant and assumingby that securityholder. We will not receive any of the net proceeds from the sale of 16,666,666such common stock. The selling securityholders will pay any underwriting discounts and commissions and expenses incurred by the selling securityholders for brokerage, accounting, tax or legal services or any other expenses incurred by the selling securityholders in offering or selling their common stock. We will bear all other costs, fees and expenses incurred in effecting the registration of the shares of common stock or pre-funded warrants incovered by this offering, and after deducting estimated placement agent fees and estimated offering expenses payableprospectus.

Assuming that all Warrants held by us. This estimate excludes the proceeds, if any, from the exercise of common warrants in this offering.

We intend to use the netselling securityholders are exercised for cash, we would receive proceeds of this offering for working capital, research and development activities and general corporate purposes, including continuing our research and development efforts for our investigational drugs CA4P and OXi4503. The primary programs and activities toapproximately $6.2 million, which we intend to devote the net proceeds of this offering are:

Our management will have broad discretion in the application of the net proceeds, and investors will be relying on the judgment of our management regarding the application of the proceeds of this offering.

Pending specific utilization of the net proceeds described above, we intend to invest the net proceeds in United States government securities and other short term, investment grade, interest bearing securities.

A $0.05 increase or decrease in the assumed public offering price of $0.36 per share of common stock and associated warrant, the last reported sale price for our common stock as reported on the OTCQX Marketplace on July 31, 2017, would decrease or increase the number of shares of our common stock issued in this offering and issuableto the selling securityholders upon the exercise of warrants issued in this offering by approximately 2.0 million shares or 2.7 million shares, respectively.the Warrants.

Similarly, a one million share increase or decrease inWe have agreed to bear the number of shares offered by us, as set forth on the cover page of this prospectus, would increase or decrease the net proceeds to us by approximately $337,000, assuming the assumed combined public offering price of $0.36 per share and accompanying warrant remains the same, and after deducting estimated placement agent fees and expenses and estimated offering expenses payable by us.

CAPITALIZATION

The following table describes our capitalization and cash and cash equivalents as of June 30, 2017 on an actual basis and on an adjusted basis to reflect our assumed sale of shares of our common stock in this offering at an assumed offering price of $0.36 per share of common stock and associated warrant, assuming all pre-funded warrants are exercised, and after deducting the estimated placement agent fees and estimated offering expenses payable by us.

You should read this capitalization table together with the financial statements and related notes that are incorporated by reference into this prospectus, as well as “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and the other financial information contained in our Annual Report on Form10-K for the year ended December 31, 2016 and our Quarterly Report on Form10-Q for the quarter ended June 30, 2017 and incorporated by reference into this prospectus.

Capitalization

The preceding table excludes 8,333,333 shares of common stock issuable upon the exercise of common warrants to be sold in this offering; 666,667 shares of common stock issuable upon the exercise of warrants to be issued to the placement agent in connection with this offering; 9,625,797 sharesthe registration of the common stock issuable uponbeing offered by the exercise of warrants outstanding as of June 30, 2017, at a weighted average exercise price of $2.56 per share; 5,941,434 shares of common stock issuable upon the exercise of options outstanding as of June 30, 2017, at a weighted average exercise price of $1.01 per share; 541,847 shares of common stock available for future issuanceselling securityholders under the 2015 Plan; and 242,500 shares of common stock available for future issuance under the 2017 Plan.

DILUTION

Our tangible book value at June 30, 2017 was approximately $5,104,000, or $0.19 per share. After giving effect to the sale of 16,666,666 shares of common stock in this offering at an assumed offering price of $0.36 per share of common stock and associated warrant,prospectus, which was the last reported sale price for our common stock on July 31, 2017, after deducting thewe have estimated placement agent’s fees and estimated expenses of this offering, our as adjusted net tangible book value would have been approximately $10,539,000, or $0.24 per share of common stock. Assuming the completion of this offering, this represents an immediate increase in as adjusted net tangible book value of $0.05 per share to our existing stockholders and an immediate dilution in the as adjusted net tangible book value of $0.12 per share to anyone who purchases our common stock in this offering. The following table illustrates this calculation on a per share basis:

The preceding table excludes 8,333,333 shares of common stock issuable upon the exercise of common warrants to be sold in this offering; 666,667 shares of common stock issuable upon the exercise of warrants to be issued to the placement agent in connection with this offering; 9,625,797 shares of common stock issuable upon the exercise of warrants outstanding as of June 30, 2017, at a weighted average exercise price of $2.56 per share; 5,941,434 shares of common stock issuable upon the exercise of options outstanding as of June 30, 2017, at a weighted average exercise price of $1.01 per share; 541,847 shares of common stock available for future issuance under the 2015 Plan; and 242,500 shares of common stock available for future issuance under the 2017 Plan.less than $0.1 million.

PRICE RANGE OF OUR COMMON STOCK

Effective DecemberJune 8, 2016, shares of our2018, the Company’s common stock began trading on the OTCQB Marketplace, operated by OTC Markets, under the symbol “MATN”. From December 8, 2016 to June 8, 2018, the Company’s common stock was traded on OTCQX Marketplace, operated by OTC Markets, under the symbol “MATN”. From June 20, 2016 to December 8, 2016, the Company’s common stock was traded on The NASDAQNasdaq Capital Market under the symbol “MATN”. Prior to June 20, 2016, the Company’s common stock was traded on The NASDAQNasdaq Capital Market under the symbol “OXGN”. The following table sets forth, for the periods indicated, the high and low sales prices or bid prices, as applicable, of our common stock, rounded to the nearest cent, on the OTCQX MarketplaceOTC Market and on The NASDAQNasdaq Capital Market, as applicable, as reported by each of the markets, for each quarterly period during the two most recent fiscal years. With respect toyears and the periods in which shares of our common stock were traded on the OTCQX Marketplace, the prices set forth below represent inter-dealer quotations, without adjustment for retailmark-up, mark-down or commission, and may not represent the prices of actual transactions.subsequent interim periods.

As of July 21, 2017,June 8, 2018, there were approximately 4178 stockholders of record of ourthe 41,419,934 outstanding shares of the Company’s common stock.

Because many of our shares of common stock are held by brokers and other institutions on behalf of stockholders, we are unable to estimate the total number of stockholders represented by these record holders.

DIVIDEND POLICY

We currently intend to retain any future earnings to finance the growth and development of our business. Therefore, we do not anticipate declaring or paying any cash dividends in the foreseeable future. Any future determination as to the declaration and payment of dividends, if any, will be at the discretion of our Board of Directors and will depend on then existing conditions, including our financial condition, operating results, contractual restrictions, capital requirements, business prospects and other factors our Board of Directors may deem relevant.

PENNY STOCK

Our stock is considered a penny stock. The SEC has adopted rules that regulate broker-dealer practices in transactions in penny stocks. Penny stocks are generally equity securities with a market price of less than $5.00, other than securities registered on certain national securities exchanges or quoted on the Nasdaq system, provided that current price and volume information with respect to transactions in such securities is provided by the exchange or system. The penny stock rules require a broker-dealer, prior to a transaction in a penny stock, to deliver a standardized risk disclosure document prepared by the SEC, that: (a) contains a description of the nature and level of risk in the market for penny stocks in both public offerings and secondary trading; (b) contains a description of the broker’s or dealer’s duties to the customer and of the rights and remedies available to the customer with respect to a violation of such duties or other requirements of the securities laws; (c) contains a brief, clear, narrative description of a dealer market, including bid and ask prices for penny stocks and the significance of the spread between the bid and ask price; (d) contains a toll-free telephone number for inquiries on disciplinary actions; (e) defines significant terms in the disclosure document or in the conduct of trading in penny stocks; and (f) contains such other information and is in such form, including language, type size and format, as the SEC shall require by rule or regulation.

The broker-dealer also must provide, prior to effecting any transaction in a penny stock, the customer with: (a) bid and offer quotations for the penny stock; (b) the compensation of the broker-dealer and its salesperson in the transaction; (c) the number of shares to which such bid and ask prices apply, or other comparable information relating to the depth and liquidity of the market for such stock; and (d) a monthly account statement showing the market value of each penny stock held in the customer’s account. In addition, the penny stock rules require that prior to a transaction in a penny stock not otherwise exempt from those rules, the broker-dealer must make a special written determination that the penny stock is a suitable investment for the purchaser and receive the purchaser’s written acknowledgment of the receipt of a risk disclosure statement, a written agreement as to transactions involving penny stocks, and a signed and dated copy of a written suitability statement.

These disclosure requirements may have the effect of reducing the trading activity for our common stock. Therefore, stockholders may have difficulty selling our securities.

MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Our management’s discussion and analysis of financial condition and results of operations contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These statements involve known and unknown risks and uncertainties that may cause our actual results or outcomes to be materially different from those anticipated and discussed herein. Important factors that we believe may cause such differences are discussed in the “Risk Factors” section of this prospectus and in other documents filed by us with the SEC. In assessing forward-looking statements contained herein, readers are urged to read carefully all Risk Factors and cautionary statements contained in this prospectus. Further, we operate in an industry sector where securities prices are volatile and may be influenced by regulatory and other factors beyond our control.

Overview

We are a clinical-stage biopharmaceutical company developing drugs for the treatment of orphan oncology indications, with our most advanced program evaluating our investigational drug OXi4503 in relapsed/refractory acute myeloid leukemia, or AML. In this clinical trial we have most recently observed that two of four patients in the fifth dose cohort of an ascending-dose study experienced complete remissions of their disease after just one cycle of treatment with 9.76 mg/m2 of OXi4503. Earlier in the clinical trial, at lower doses of our drug, we observed three patients with complete remissions following two cycles of treatment and two patients with partial remissions. Following fifth dose cohort, we paused enrollment in the study due to our lack of available cash to complete further testing. More recently, following the closing of approximately $2.4 million in net proceeds from a financing transaction, we instructed the clinical sites to begin screening new patients for the sixth dose cohort, and we expect that additional patients will enter the clinical trial within a few months.

We are also developing CA4P as an immuno-oncology agent. Recent preclinical data has shown treatment with the combination of CA4P and ananti-CTLA-4 antibody nearly doubles the amount of tumor necrosis (mean = 63.9%) compared to treatment with ananti-CTLA-4 antibody alone (32.8%), CA4P alone (37.3%) or vehicle control (25.8%) in a preclinicalCT-26 mouse colon cancer model. Results from this most recent analysis preclinically confirmed our earlier findings which showed that treatment with CA4P and an approved immuno-oncology agent resulted in increased overall median numbers of tumor infiltrating white blood cells, T cells and CD8+ T lymphocytes. The data also showed that the distribution of the beneficial CD8+T lymphocyte cells was observed throughout the tumor - in both the tumor rim and tumor core. Based on these data, and the existing clinical safety database of CA4P, we are planning to initiate a clinical trial of CA4P in combination with an immuno-oncology agent in the near future.

Important and Recent Developments

During 2017, our resources were primarily focused on three programs: 1) conducting a phase 1b clinical trial of OXi4503 in relapsed/refractory acute myeloid leukemia, 2) conducting preclinical studies of CA4P in combination with immuno-oncology agents and 3) conducting a phase 2 clinical trial of CA4P in platinum-resistant ovarian cancer.

On September 26, 2017, due to the lack of a clear efficacy signal in a planned interim analysis of our phase 2 platinum-resistant ovarian cancer study, we terminated the study and announced the termination of future development of CA4P in ovarian cancer. Thereafter, effective October 2, 2017, we terminated the employment of over half of our workforce and reduced the salaries of our executive officers by 50%, with reinstatement to previous compensation levels contingent on a change in control of the Company or the Company raising additional funding of at least $4 million. To date the Company has not achieved the specified level of additional funding to reinstate the salaries.

On April 12, 2018, we closed on net proceeds of approximately $2.4 million from a private placement transaction, or the Private Placement. In the Private Placement, we sold 58.5 units at a purchase price of $50,000 per unit. Each unit contained 250,000 shares of our common stock and Warrants to purchase up to 250,000 shares of our common stock. The purchase price of the common stock was $0.20 per share and Warrants are exercisable at $0.40 per share. The exercise price of the Warrants will only be payable in cash, with no cashless exercise provisions. The Private Placement terminated April 30, 2018. The registration statement of which this prospectus forms a part has been filed to register the shares of common stock that were issued and the shares of common stock that are issuable upon exercise of the warrants.

Critical Accounting Policies and Significant Judgments and Estimates

The preparation of financial statements in accordance with U.S. generally accepted accounting principles requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as the reported revenues and expenses during the reporting periods. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable under the circumstances at the time we make such estimates. Actual results and outcomes may differ materially from our estimates, judgments and assumptions. We periodically review our estimates in light of changes in circumstances, facts and experience. The effects of material revisions in estimates are reflected in the financial statements prospectively from the date of the change in estimate. Our significant accounting policies are more fully described in Note 1 to our financial statements for the year ended December 31, 2017.

We define our critical accounting policies as those accounting principles that require us to make subjective estimates and judgments about matters that are uncertain and are likely to have a material impact on our financial condition and results of operations, as well as the specific manner in which we apply those principles. We believe the critical accounting policies used in the preparation of our financial statements that require significant estimates and judgments are the following:

Research and development expenses

Research and development expenses consist of costs we incur for the development of our investigational drugs and, to a lesser extent, for preclinical research activities. Research and development costs are expensed as incurred. Research and development expenses include clinical trial costs, salaries and benefits of employees, including associated stock-based compensation, payments to clinical investigators, drug manufacturing costs, laboratory supplies and facility costs. Clinical trial costs are a significant component of our research and development expenses, and these can be difficult to accurately estimate. Included in clinical trial costs are fees paid to other entities that conduct certain research and development activities on our behalf, such as clinical research organizations, or CROs. We estimate clinical trial expenses based on the services performed pursuant to contracts with research institutions such as CROs and the actual clinical investigators. These estimates are based on actual time and expenses incurred by the CRO and the clinical investigators. Also included in clinical trial expenses are costs based on the level of patient enrollment into the clinical trial and the actual services performed under the related clinical trial agreement. Changes in clinical trial assumptions, such as the length of time estimated to enroll all patients, rate of screening failures, patientdrop-out rates, number and nature of adverse event reports and the total number of patients enrolled can impact the average and expected cost per patient and the overall cost of the clinical trial. Based on patient enrollment reports and services provided, we may periodically adjust estimates for the clinical trial costs. If we do not identify costs that we have begun to incur or if we underestimate or overestimate the level of services performed, the length of time for these services or the costs of these services, our actual expenses could differ from our estimates.

Share-based compensation

We record the estimated fair value of all share-based payments issued to employees and other service providers. Our share-based payments consist primarily of stock options. The valuation of stock options is an inherently subjective process, since market values are not available for any stock options in our equity securities. Market values are also not available on long-term,non-transferable stock options in other equity securities. With no market values on options to trade in our common stock and no comparable market values on any long-termnon-transferable stock options, the process of valuing our stock options is even more uncertain and subjective. Accordingly, we use a Black-Scholes option pricing model to derive an estimated fair value of the stock options which we issue. The Black-Scholes option pricing model requires certain input assumptions, including the expected term of the options and the expected volatility of our common stock. Changes in these assumptions could have a material impact on the estimated fair value that we record for share-based payments that we issue. We determine the term of the options based on the simplified method, which averages the vesting period and the contractual life of the stock option. We determine the expected volatility based on the historical volatility of our common stock over a period commensurate with the option’s expected term. The Black-Scholes option pricing model also requires assumptions for risk-free interest rates and the expected dividend yield of our common stock, but we feel that these values are more objective and note that changes in these values do not have a significant impact on the estimated value of the options when compared to the volatility and term assumptions.

We are also required to estimate the level of award forfeitures expected to occur and record compensation expense only for those awards that are ultimately expected to vest. Accordingly, we perform a historical analysis of option awards that are forfeited prior to vesting, and record total stock option expense that reflects this estimated forfeiture rate.

RESULTS OF OPERATIONS

Three months ended March 31, 2018 and 2017

Research and Development expenses

Research and development expenses decreased markedly for the three months ended March 31, 2018 compared to the same period in 2017 due to our significant reduction of nearly all operating activities in 2018 while we sought to obtain additional capital to continue operations. The table below summarizes the most significant components of our research and development expenses for the periods indicated and provides the amount and percentage change in these components (in thousands):

		Three months ended March 31,								Change
		2018				2017				Amount				%
Clinical studies		$	50			$	1,260			$	(1,210	)			-96	%
Employee compensation and related			54				964				(910	)			-94	%
Employee stock-based compensation			69				105				(36	)			-34	%
Consulting and professional services			33				197				(164	)			-83	%
Drug manufacturing			15				242				(227	)			-94	%
Other			4				80				(76	)			-95	%
Total research and development		$	225			$	2,848			$	(2,623	)			-92	%

All research and development activities declined substantially for the three months ended March 31, 2018 compared to the three months ended March 31, 2017. For the three months ended March 31, 2018, we conducted no new research and development activities and nearly all operating activities of the company were suspended while management sought additional capital to continue operations. During the three months ended March 31, 2018, clinical study activity was limited to maintaining the active status of Study OX1222, which is evaluating OXi4503 in relapsed/refractory acute myeloid leukemia and myelodysplastic syndromes, and accordingly clinical study expenses declined 96% compared to the 2017 period. Employee compensation declined 94% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 because the employment status of all research and development employees was terminated in early January 2018. For the same reason, employee stock-based compensation declined 36% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017, although stock-based compensation declined by a smaller percentage than employee compensation because we continued vesting certain stock options for former employees that continued to provide services to us. Consulting and professional services expenses declined by 83% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017, with expenses in the 2018 period limited to regulatory activity and maintaining the active status of Study OX1222. For the three months ended March 31, 2018, drug manufacturing expenses consisted of external storage fees for previously manufactured batches of our investigational drugs. Drug manufacturing expenses accordingly declined 94% compared to the three months ended March 31, 2017, when additional work on drug stability and manufacturing processes occurred.

Other expenses include facility related expenses which are generally allocated between research and development and general and administrative expenses based on employee headcount. With virtually no research and development headcount for the three months ended March 31, 2018, there was minimal allocation of expenses for the period, accounting for the decline of 95%.

Following our April 2018 Private Placement, we have resumed enrollment of patients into our study of OXi4503 in acute myeloid leukemia. We are also in the process of planning and initiating a study of CA4P in immuno-oncology, evaluating CA4P in combination with Opdivo^® (nivolumab, marketed by Bristol-Myers Squibb), in patients with advanced metastatic melanoma who have previously failed Opdivo and consequently have a poor prognosis. As a result, we expect research and development expenses to increase in subsequent quarters in 2018 as compared to the first three months of 2018, subject to our continuing ability to secure sufficient funding to continue with drug development activities.

General and administrative expenses

General and administrative expenses decreased by 49% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 primarily due to our significant reduction of nearly all operating activities in 2018 while we sought to obtain additional capital to continue operations. The table below summarizes the most significant components of our general and administrative expenses for the periods indicated and the amount and percentage change in these components (in thousands):

		Three months ended March 31,								Change
		2018				2017				Amount				%
Employee compensation and related		$	205			$	527			$	(322	)			-61	%
Employee stock-based compensation			116				135				(19	)			-14	%
Consulting and professional services			132				371				(239	)			-64	%
Other			118				89				29				33	%
Total general and administrative		$	571			$	1,122			$	(551	)			-49	%

Employee compensation and related expenses decreased by 61% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 due to our reduction in headcount to only two employees, our Chief Executive and Chief Financial Officers, who each had agreed to receive half of their regular salary. Employee stock-based compensation decreased by 14% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 due to lower headcount in the 2018 period. The percentage decline in stock-based compensation for the 2018 period was lower than the percentage decline for employee compensation due to the continued vesting of options, which was not affected by the salary reduction noted above. Consulting and professional services expenses decreased by 64% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 due to our minimization of all expenses with a focus on continuing in business and seeking new sources of capital.

Other expenses, which include facility related expenses such as rent, insurance expenses and taxes that are not based on income, are allocated between research and development and general and administrative expenses based on the headcount in each department. As with all other expenses, we reduced these expenses to only what was necessary to continue limited operations and seek funding, and the aggregate of other expenses decreased by approximately 28% for the three months ended March 31, 2018 compared to the three months ended March 31, 2017. However, because there were no research and development employees for the three months ended March 31, 2018, the resulting allocation of nearly all of these expenses into general and administrative expenses caused an increase of 33% of the amount reported in general and administrative expenses for the three months ended March 31, 2018 compared to the three months ended March 31, 2017.

We expect general and administrative expenses to increase for the remainder of 2018 compared to the first three months of 2018 in order to support our resumption of clinical trial activity and to pursue additional business development and investor relations activities, subject to our continuing ability to secure sufficient funding to continue planned operations.

Years ended December 31, 2017 and 2016

Research and Development expenses

The table below summarizes the most significant components of our research and development expenses for the periods indicated and provides the amount and percentage change in these components (in thousands):

Research and development expenses increased in 2017 compared to 2016 due to our clinical studies.

We incurred significantly higher expenses for clinical studies in 2017 compared to 2016, primarily due to higher costs for our FOCUS study of CA4P in platinum-resistant ovarian cancer prior to the study’s termination in late September 2017. When we terminated the FOCUS study we had enrolled a total of approximately 90 patients, compared to approximately 20 at the end of 2016. Direct costs for the FOCUS study were approximately $4.4 million in 2017 compared to $1.9 million in 2016, an increase of $2.5 million. In addition to our FOCUS study, we incurred clinical study expenses for the OX1222 study, which is ouron-going trial of

OXi4503 in acute myeloid leukemia. Expenses for the AML clinical trial were comparable in 2017 and 2016, at approximately $1.3 million each year. Besides the above-noted clinical trials in ovarian cancer and AML, which comprised the majority of our research and development efforts, in 2017 we also incurred higher expenses investigating CA4P as an immuno-oncology agent, which approximately offsets a decrease in clinical expenses incurred investigating CA4P in neuroendocrine tumors.

Employee compensation and related expenses declined in 2017 compared to 2016 primarily due to our termination of the majority of employees immediately after we terminated the FOCUS study. These lower employee compensation costs were partially offset by severance expenses.

Employee stock-based compensation was lower in 2017 than 2016 due to a lower average number of employees in 2017 as a result of the 2017 employee terminations. The percentage decline in stock-based compensation was lower than it was for employee compensation due to the grant levels of the specific employees who were terminated in 2017 and certain options which continued to vest for a former employee under a consulting agreement.

Consulting and professional services decreased in 2017 compared to 2016 due to cutbacks across virtually all areas, except for additional expenses incurred in the first two quarters of 2017 associated with recruiting patients into our FOCUS clinical trial.

Drug manufacturing expenses decreased in 2017 compared to 2016 due to higher expenses incurred in 2016 for supplying and labeling investigational drug for the FOCUS study.

Other expenses include facility related expenses and were generally comparable between the 2017 and 2016 periods, with changes not significant.

Our future research and development expenses will be dependent upon our ability to secure sufficient funding to continue drug development activities. We expect to prioritize obtaining additional clinical data for our OX1222 Study of OXi4503 in relapsed/refractory acute myeloid leukemia and obtaining initial data combining CA4P with an approved immuno-oncology agent.

General and administrative expenses

The table below summarizes the most significant components of our general and administrative expenses for the periods indicated and the amount and percentage change in these components (in thousands):

General and administrative expenses decreased in 2017 due tocut-backs in our operations.

Employee compensation and related expenses decreased in 2017 compared to 2016 due to reduced average headcount in 2017 and the lack of any 2017 incentive bonus expense as a result of the Company’s very low level of cash at the end of 2017.

The increase in stock-based compensation in 2017 compared to 2016 was due to additional emphasis on equity compensation over cash compensation in 2017 due to the Company’s generally low cash levels throughout the year.

Consulting and professional services decreased in 2017 compared to 2016 due to reduced expenses across nearly all external general and administrative services used, other than business development, and higherone-time market research costs incurred at the beginning of 2016.

Other expenses, which include facility related expenses and insurance expenses, decreased in 2017 compared to 2016 due to lower costs across most areas, none of which were individually significant.

Our future general and administrative expenses will be dependent upon our ability to secure sufficient funding to continue operations.

LIQUIDITY AND CAPITAL RESOURCES

We measure liquidity by the cash and other capital we have available to fund our operations, which are primarily focused on the development of our drug candidates. To date, we have financed our operations principally through proceeds received from the sale of equity. We have experienced net losses in each year since our inception, and negative cash flows from operations in nearly every year. As of March 31, 2018, we had an accumulated deficit of approximately $293 million, including a net loss of approximately $0.8 million for the three months ended March 31, 2018 and $13.8 million for the year ended December 31, 2017. As of March 31, 2018, we held cash and cash equivalents of only $0.2 million, which, together with net proceeds of approximately $2.4 million received in the Private Placement, we expect to be sufficient to fund our planned operating activities into the fourth quarter of 2018. If we are unable to secure additional funding prior to this time, we may be required to scale back or conclude our development activities altogether.

We will require additional capital before we can complete the development of OXi4503 and CA4P. Additional funding may not be available to us on acceptable terms, or at all. If we are unable to access additional funds in the near term we may not be able to continue the development of our product candidates and we could be required to terminate operations altogether. Any additional equity financing, if available, may not be available on favorable terms and would be dilutive to our current stockholders. Debt financing, if available, may involve restrictive covenants and could also be dilutive to our current stockholders. If we are able to access funds through collaborative or licensing arrangements, we may be required to relinquish rights to some of our technologies or product candidates that we would otherwise seek to develop or commercialize on our own, on terms that are not favorable to us. Our ability to access capital when needed is not assured and, if access is not achieved on a timely basis, will materially harm our business, financial condition and results of operations.

QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Our cash, cash equivalents and short-term investments are maintained in U.S. dollar accounts. We have adopted a policy for the cash, cash equivalents and investments that we hold, the primary objective of which is to preserve principal, while also maintaining liquidity to meet our operating needs and maximize yields to the extent possible. Although our investments are subject to credit risk, we follow procedures to limit the amount of credit exposure in any single issue, issuer or type of investment. Our investments are also subject to interest rate risk and would be likely to decrease in value if market interest rates increase. However, due to the generally conservative nature of our investments and relatively short duration, we believe that interest rate risk is mitigated. Although we may from time to time manufacture drugs and conduct trials and studies outside of the United States, we believe our exposure to foreign currency risk to be immaterial.

FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

See our Financial Statements and Schedules and any supplementary financial information filed as part of this Registration Statement.

BUSINESS

Our Business

Overview

We are a clinical stage biopharmaceutical company developing small molecule injectable drugs for the treatment of cancer. Our goal is to advance our product candidates into late stage pivotal clinical trials and either sell marketing rights to a larger pharmaceutical company or seek FDA approval ourselves.

We have two primary programs we are seeking to advance:

Both of these programs have potential to generate additional new data before the end of 2018.

CA4P as an Immuno-oncology Agent

Over the last several years, there have been significant advances in cancer immunotherapy, which makes use of the immune system to treat cancer. Immuno-oncology agents stimulate the body’s immune system to fight cancer cells, resulting in tumor cell death and tumor regressions in patients who otherwise would not have responded to therapy. Despite these advances, currentFDA-approved immuno-oncology agents have significant limitations when used alone to treat cancer, since relatively few patients achieve a durable clinical response following treatment. CA4P has the potential to increase the efficacy of these immuno-oncology agents – it has been shown in animal models of several different tumors to improve immune responses that lead to tumor cell death, resulting in increased tumor regressions compared to immune-oncology agents alone.

CA4P causes rapid and widespread tumor cell necrosis. This tumor-specific necrosis stimulates the immune system against the tumor. Animal models also show that CA4P significantly enhances the presence and activity of cancer-fightingT-cells within tumors, resulting in increased tumor cell death and tumor regressions. Given these data, we believe CA4P may result in more and/or better clinical responses in certain cancers when combined with immuno-oncology agents, including in patients who either have not experienced a response to therapy, or in patients who have initially responded but subsequently progressed after treatment with immuno-oncology agents alone.

The next step in the process of establishing CA4P as a safe and effective immuno-oncology agent will be to initiate a clinical study in a disease in which immuno-oncology agents are used as standard therapy. This clinical study will evaluate CA4P in combination with currently approved immuno-oncology agents in patients with advanced cancer who have previously failed treatment. We believe that the existing human safety database for CA4P, which includes over 500 patients, will help expedite the development timeline for advanced cancer.

Our initial immuno-oncology preclinical studies were completed in 2016. One of these studies combined CA4P with an anti-CTLA4 antibody, an approved and well-known immuno-oncology agent, in anEMT-6 mammary tumor model. This study showed that 7 out of 8 mice receiving a combination of CA4P and an anti-CTLA4 antibody experienced complete remission of their tumors, compared to only 1 of 8 in the CA4P monotherapy arm and 2 of 8 in the anti-CTLA4 antibody monotherapy arm.

Three of fourfollow-up preclinical studies confirmed that CA4P combined with immuno-oncology agents could delay tumor growth. Thesefollow-up studies were conducted in a CT26 colon cancer model, a larger tumorEMT-6 mammary cancer model, and a C3H mammary cancer model. Studies in aCT-26 colon cancer animal model using CA4P combined with anti-CTLA4 antibodies demonstrated a 77% reduction in tumor size compared to immune - oncology agents alone, and an 89% reduction in tumor size compared to control. This large tumor model also showed a survival benefit for the animals receiving combination therapy, with all animals in the combination surviving at the end of the study, compared to none on control and only half the animals receiving immuno-oncology agents alone. Initial data in an MC38 colon cancer model showed that when CA4P is combined with ananti-PD1 antibody there was a 53% reduction in tumor volume at the end of the study, compared with a 16% reduction for CA4P alone and a 15% reduction for theanti-PD1 antibody alone.

Additional analyses of changes induced within tumors following combination therapy have shown that CA4P increases tumor-fighting white blood cell counts,T-cells and cytotoxicT-cells compared to immuno-oncology agents alone. Tumor necrosis with the combination of CA4P and immuno-oncology agents is nearly double the necrosis with only immuno-oncology agents (63.9% compared to 32.8%, control = 25.8%).

The overall data from all these studies provides evidence that CA4P may enhance the activity of immuno-oncology agents for the treatment of cancer, including anti-CTLA4 antibodies and antiPD-1 antibodies. We believe CA4P offers the following potential benefits when used in combination with immuno-oncology agents:

OXi4503 for Acute Myeloid Leukemia

Acute myeloid leukemia, or AML, is a cancer of the myeloid blood cells, with approximately 21,000 new cases each year in the U.S. and approximately 10,500 deaths. AML is characterized by the rapid growth of abnormal white blood cells that pollute bone marrow and interfere with the production of normal blood cells. OXi4503 has been granted orphan drug designation in both the U.S. and the European Union for the treatment of AML, and has received Fast Track designation from the FDA for the treatment of AML.

Patients with relapsed/refractory AML are most commonly treated with chemotherapy, and generally have a poor prognosis, with aone-year survival of only 29% after their first relapse. Over the past 20 years, no new therapies have consistently improved patient outcomes in this indication when compared to chemotherapy.

Our most clinically advanced compound, OXi4503, is in development as a potential new treatment for relapsed/refractory AML. We have initiated Study OX1222, a clinical trial using escalating doses of OXi4503 in combination with cytarabine to treat relapsed/ refractory AML. In the most recently completed dose cohort of OX1222, the fifth dose tested in the study, two of four patients experienced complete remissions of their disease after just one cycle of treatment with 9.76 mg/m2 of OXi4503. In earlier, lower dose cohorts, there were three patients with complete remissions, which occurred following two cycles of treatment, and two additional patients with meaningful AML blast count reductions. With the lower doses of OXi4503 tested in OX1222, AML blast count reductions were generally observed after the first cycle of treatment, and the complete remissions were observed after two cycles of treatment. We believe that the remissions seen after just one cycle of treatment at the highest dose of OXi4503 tested to date, coupled with other partial response data, is a sign of a dose response. The next patients evaluated will be given 12.2 mg/m2 of OXi4503, a 25% increase compared to the most recently completed fifth cohort of the study. OXi4503 has been demonstrated in preclinical studies to work in AML by disrupting tumor blood vessels in the bone marrow, forcing otherwise-dormant leukemic stem cells, which are attached to these tumor blood vessels, into circulation in the blood stream as well as into the active cell cycle, where they become vulnerable to chemotherapy. OXi4503 has also been demonstrated to be cytotoxic itself and kill leukemic cells directly after it has been metabolized by enzymes located within leukemic cells.

In preclinical studies, OXi4503 has been shown to enhance the efficacy of cytarabine, idarubucin, azacitidine, and decitabine, which are each commonly-used chemotherapeutic agents for the treatment of many cancers, including AML. In early clinical studies, OXi4503 has shown complete responses in high risk patients both as a monotherapy and in combination with cytarabine. We believe OXi4503 offers the following potential benefits:

Our Strategy and Development Plan

Subject to securing sufficient funding to continue our operations, our primary objective is to advance our investigational drugs for multiple orphan oncology indications. We are currently focused on two core programs – CA4P as an immuno-oncology agent and OXi4503 for the treatment of AML. In our AML program, our aim is to obtain clinical data with a dose of OXi4503 higher than the five doses tested to date. In our immuno-oncology program, our aim is to obtain our first clinical data of CA4P in combination with immuno-oncology agents. The key elements of our strategy currently include:

Investigator Sponsored Study in Neuroendocrine Tumors

Approximately 14,000 patients in the U.S. are diagnosed with neuroendocrine tumors, or NETs, each year. Since patients with NETs can have prolonged survival rates of over 5 years, it is estimated that the overall prevalence is much higher, approximating 100,000 patients in the U.S. These tumors can produce increased amounts of vasoactive substances including hormones, many of which are biologically active and can result in debilitating symptoms including flushing, diarrhea, weight loss and, less frequently, bronchoconstriction and heart failure. It is our belief, based on the available preclinical data, that by reducing blood flow to these tumors using CA4P, we may be able to reduce the production of tumor-derived substances, including the biologically active hormones.

We have completed a phase 2 monotherapy clinical trial of CA4P in 18 patients with gastrointestinal or pancreatic NETs and elevated biomarkers. One patient (6%) experienced significant symptomatic improvement as measured by ECOG Status and had a partial response per investigator-assessed RECIST criteria, and an additional 7 patients (39%) had stable disease. In addition, a majority of patients (53%) experienced an improvement in patient-reported quality of life. A statistically significant mean change in biomarkers from baseline, the primary endpoint of the study, was not achieved due to the small sample size along with a high intra- and inter-patient variability observed in the biomarkers. A total of 7 patients were enrolled in afollow-up trial, of which 5 patients (71%) had stable disease, including one that continued for 14 months. The partial response and stable disease analyses, as well as other measures from the trial, suggest that CA4P monotherapy has activity in this indication. Based on the evidence of efficacy observed in this trial, plus an understanding of the benefits of vascular-targeted combination therapy, a lead investigator in this trial is sponsoring and funding a 20 patient study in NETs using CA4P in combination with everolimus (AFINITOR^®, marketed by Novartis), an anti-angiogenic agent which is already approved and commonly used in this indication.

CA4P has been granted orphan drug designation for the treatment of neuroendocrine tumors in both the U.S. and the European Union.

Glioblastoma Multiforme

We are interested in exploring recurrent glioblastoma multiforme, or GBM, as an additional indication for CA4P because:

CA4P has been granted orphan drug designation for the treatment of glioma in the United States. If funds become available for us to initiate and complete a clinical trial in GBM, we expect that we would pursue a trial. However, we currently do not plan to initiate a GBM clinical trial in the near term in order to conserve current resources.

Vascular Disrupting Agents: Background

According to Cancer Research UK, anon-profit cancer research organization in the United Kingdom, nearly 90% of all cancers are dependent upon a continually evolving vascular supply for their growth and survival. Vascular-targeted therapies, such as CA4P and OXi4503, are designed to interfere with a tumor’s vascular supply.

As illustrated in the table below, there are differences between our vascular targeted therapies and anti-angiogenic drugs which act via different mechanisms to produce complementary biological and anti-vascular effects.

		Anti-Angiogenic Drugs		CA4P		OXi4503
Plasma Half-life		MABs remain in circulation for days or weeks TKI half-lives vary, average range is4-12 hours		Approximately 4 hours		Approximately 2 hours OXi4503 metabolite half-life is approximately 20 hours
Side Effects		Chronic hypertension with long-term use; Acute-impairment in wound healing; Hemorrhage, hemoptysis, gastrointestinal perforation, proteinuria, nephrotic syndrome, thromboembolic events, etc.		Transient blood pressure increases; Tumor pain, nausea, hematological adverse events; Overlapping with anti-angiogenics: no cumulative toxicities observed		Transient acute blood pressure increases; Tumor pain, nausea, vomiting, headache, fatigue; Effects on hematopoiesis and white blood cell counts; In AML – similar to solid tumors with more pronounced effects on coagulation and hematopoiesis

We believe our drug candidates act on tumor blood vessels via two complementary mechanisms, tubulin depolymerization and disengagement of the junctional proteinVE-cadherin, which cause a change in the shape of tumor vascular endothelial cells, tumor vessel occlusion, and the subsequent blockage of blood-flow to the tumor, which deprives the tumor of oxygen and nutrients essential for survival.

In vitro studies have demonstrated that our drug candidates act in a reversible fashion on tubulin inside newly-formed and growing endothelial cells, such as the vascular endothelial cells comprising tumor vasculature. By binding to the tubulin, our candidates are able to alter the structural framework that normally maintains the cells’ flat shape. When this occurs, the shape of the cells changes from flat to round, resulting in physical blockage of the blood vessels. The resulting shutdown in blood-flow then deprives tumor cells of the oxygen and nutrients necessary for maintenance and growth and also prevents tumor cells from being able to excrete toxic metabolic waste products. The consequence of the tumor blood vessel blockage is extensive necrosis (cell death) within the tumor.

Preclinical research, published in the November 2005 issue of the Journal of Clinical Investigation, showed that our drug candidates also disrupt the molecular engagement ofVE-cadherin, a junctional protein important for endothelial cell survival and function. The authors of the research article conclude that this effect only occurs in endothelial cells which lack contact with smooth muscle cells, a known feature of abnormal vasculature associated with tumors and other disease processes. The disengagement ofVE-cadherin leads to endothelial cell detachment, which in turn, can cause permanent physical blockage of vessels.

Clinical study results and additional preclinical studies indicate that our investigational drugs exert their anti-vascular effects rapidly, within hours of administration, and the half-life of the active form of our drugs in humans is approximatelytwo-four hours. In part because the half-life is relatively short, the effects on tubulin are reversible. However, the pharmacodynamic effect lasts for weeks, so our agents are typically administered no more frequently than once per week. The side-effects are typically transient in nature, limited to the few hours following administration when the active form is in the body in significant concentrations.

Side-effects associated with our investigational drugs are generally transient and manageable. The most frequent side-effects include acute blood pressure increases, infusion-related side effects such as nausea, vomiting, headache and fatigue, and tumor pain, which is consistent with the drug’smechanism-of-action. The acute blood pressure increases are often manageable by controlling underlying hypertension or treating with short-acting anti-hypertensives prior to infusion. The incidence of serious cardiovascular side-effects such as angina and myocardial ischemia observed across all studies to date (including early studies in which hypertension management and prevention was not employed) was less than 3%, a frequency comparable to that reported with approved anti-angiogenic agents such as bevacizumab, sunitinib and sorafenib.

Collaborative Research and Development Arrangements

We have entered into a technology license from Arizona State University, or ASU, for rights to combretastatins, which includes CA4P and OXi4503. The ASU license is an exclusive, world-wide, royalty-bearing license for the commercial development, use and sale of products or services covered by certain patent rights to particular combretastatins. Combretastatins were originally isolated from the bark of the South African Bush Willow tree by researchers from Arizona State University but are now created by synthetic means and have tubulin-dependent anti-vascular and anti-proliferative properties. Under the ASU license, we have the right to grant sublicenses. ASU is entitled to single-digit royalty payments under the license agreement during the term of the patents licensed from

ASU. We bear the costs of preparing, filing, prosecuting and maintaining all patent applications under the ASU license. Under the license agreement, we have agreed to diligently proceed with the development, manufacture and sale of products using the licensed technology. ASU has the first responsibility of enforcing patents under the license agreement. License payments made to ASU to date have amounted to $2,700,000, with no further license payments due on the combretastatins we are developing. The agreement remains in force until the expiration of the last to expire patent subject to the ASU license. Either party may terminate the ASU license agreement upon material default or bankruptcy of the other party. In addition, we may terminate the agreement if we determine that filing for regulatory approval is not warranted or economically feasible or upon two months’ written notice.

We also have an exclusive, world-wide, royalty-bearing license from Bristol-Myers Squibb, or BMS, for commercial development, use and sale of products or services covered by certain patent rights to particular combretastatins, including among others, CA4P. Under the BMS license, we have the right to grant sublicenses, and BMS is entitled to low single-digit royalty payments for all commercial sales plus any remuneration we receive for sale of CA4P under named patient or compassionate use programs. All licensing fees and milestone payments under the BMS license, in the aggregate amount of $1,080,000, have been paid. We bear the costs of preparing, filing, prosecuting and maintaining all patent applications under the BMS license and have a right, but not a duty, of enforcing patents covered by the license. Either party may terminate the BMS license upon material default of the other party. The term of the BMS license ends upon the expiration of the licensed patents. The latest United States patent licensed under the BMS license is scheduled to expire in December 2021, excluding a patent term extension available under the Hatch-Waxman Act.

Company Background

We were originally incorporated in 1988 in New York as OXiGENE, Inc., reincorporating in Delaware in 1992. In 2016, we changed our name to Mateon Therapeutics, Inc. Our principal corporate office is in the United States at 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080 (telephone: (650)635-7000, fax: (650)635-7001). Our Internet address iswww.mateon.com. Our annual reports on Form10-K, quarterly reports on Form10-Q, current reports on Form8-K, and all amendments to those reports, are available to you free of charge through the “Investors & News” section of our web site as soon as reasonably practicable after such materials have been electronically filed with, or furnished to, the Securities and Exchange Commission. Information contained on, or that can be accessed through, our web site is not and shall not be deemed to be a part of this Registration Statement on FormS-1.

PROPERTIES

Mateon’s corporate headquarters is located in South San Francisco, California where we lease 5,275 square feet of general office space. The lease for this space, as amended, expires on June 30, 2019. We believe that these facilities will meet our needs for the foreseeable future.

LEGAL PROCEEDINGS

None.

MANAGEMENT

Directors and Executive Officers

The following table sets forth certain information about our directors and executive officers as of July 21, 2017.May 31, 2018.

David J. Chaplin, Ph.D.Dr. Chaplin has been a member of our Board of Directors since January 2013. Dr. Chaplin also served as ofour Chief Scientific Officer sincefrom May 2015.2015 through January 2018, when he retired from his position as Chief Scientific Officer. Prior to serving as our Chief Scientific Officer, Dr. Chaplin served as ourwas President and Chief Executive Officer from May 2014 until May 2015, and Dr. Chaplin previously served as our Head of Research and Development from July 2000 until August 2011. From May 2014 to December 2016, Dr. Chaplin provided consulting services to Mateon through Aston Biopharma Ltd., aUK-based entity which is controlled by Dr. Chaplin. From 1999 to 2000, Dr. Chaplin served as Vice President of Oncology at Aventis Pharma in Paris, where he was in charge of drug development from preclinical through phase 1 trials. Prior to the merger of Rhone Poulenc Rorer, (“RPR”)or RPR, with Hoechst Marion Roussell, Dr. Chaplin was Senior Director of Oncology at RPR from 1998 to 1999. From 1992 to 1998, Dr. Chaplin headed up the Cancer Research Campaign’s, (“CRC”)or CRC, Tumor Microcirculation Group, based at the Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, London. During this time, he was also a member of the CRC Phase I/II clinical trials committee. Dr. Chaplin also served as Section Head of Cancer Biology at Xenova in the U.K. from 1990 to 1992, and held a senior staff appointment at the British Columbia Cancer Research Centre from 1982 to 1990. Dr. Chaplin has a B.Sc. in chemistry from the University of Essex, a M.Sc. in pharmacology from the University of Southampton, and completed his Ph.D. in tumor biology at the University of London. Since January 2012, Dr. Chaplin has been a director of Smart Matrix Ltd, a privately held company based in the UK, which develops treatments for wound healing. Since July 2012, Dr. Chaplin has also been a director of PHusis Therapeutics, Inc., a privately held biopharmaceutical company. Since July 2013, Dr. Chaplin has been a Director of Aston Biopharma, a privateUK-based company that provides Scientific Consulting Services. Dr. Chaplin was also appointed as a director of Fast Biopharma in June 2016. Fast Biopharma is a private company based in the UK and is involved in the generation of antibody-based therapeutics.

Simon C. Pedder, Ph.D. Dr. Pedder has been a member of our Board of Directors since March 2016. Dr. Pedder currently serves as the Vice President of Corporate Strategy and Business Development of Athenix, Inc., a private global specialty oncology pharmaceutical company. From April 2014 through June 2015, Dr. Pedder served as the President and Chief Executive Officer of Cellectar Biosciences, Inc., a biopharmaceutical company developing compounds for the treatment, diagnosis and imaging of cancer, and served as Cellectar’s Acting Chief Executive Officer from October 2013 until April 2014. Dr. Pedder also served as a member of the board of directors of Cellectar from October 2013 until June 2015. From May 2004 through July 2012, Dr. Pedder served as President, Chief Executive Officer and as a director of Chelsea Therapeutics, Inc., a public development stage biopharmaceutical company. Dr. Pedder has a Bachelor of Environmental Studies from the University of Waterloo, a Master of Science in Toxicology from Concordia University and a Ph.D. in Pharmacology from the Medical College at the University of Saskatchewan College of Medicine. Dr. Pedder currently serves on the board of directors of Cerecor, Inc., Eboo Pharmaceuticals, Inc., a private development-stage pharmaceutical company, Ballantyne Therapeutics, Inc., a private pharmaceutical development company, and Atlantic Research Group, a private contract research organization. Dr. Pedder also served as a member of the board of directors of Cellectar from October 2013 until June 2015.

Donald R. ReynoldsMr. Reynolds has been a member of our Board of Directors since October 2016. Mr. Reynolds is a practicing attorney and partner at the law firm of Wyrick Robbins Yates & Ponton LLP with experience in the areas of capital markets, securities law, mergers & acquisitions, venture capital and general corporate law. Mr. Reynolds also currently teaches Securities Regulation at Campbell University’s law school and guest lectures on corporate governance at the University of North Carolina Chapel Hill’s Kenan-Flagler Business School. Since Mr. Reynolds’s elevation to partner at the law firm of Wyrick Robbins Yates & Ponton LLP in 1996, he has participated in a variety of the firm’s internal committees, including the firm’s Executive Committee, Strategic Planning Committee, Nominating Committee and Compensation Committee. Mr. Reynolds received his B.A. from Whitman College and his J.D. from New York University School of Law. He is currently licensed to practice law in California and North Carolina. Mr. Reynolds currently serves as a member of the board of directors of Atlantic Research Group, Inc., a private clinical research organization, and as Chair of the board of directors of USA Taekwondo, thenon-profit national governing body for the sport.

Bobby W. Sandage, Jr., Ph.DPh.D.. Dr. Sandage has been a member of our Board of Directors since October 2016. Dr. Sandage currently serves as the president and chief executive officer of Euclises Pharmaceuticals, Inc., a private drug discovery and development company advancingcyclooxygenase-2(COX-2) inhibitors for cancer therapy. Since August of 2016, he has served as a general partner of Cultivation Capital, a venture capital firm specializing in investments in private technology and life sciences companies. Dr. Sandage is currently a member of the board of directors of Immunophotonics, Inc., a private cancer vaccine development company, EDIS Solutions, LLC, a private healthcare information technology company, and Euclises Pharmaceuticals, Inc.

William D. Schwieterman, M.D.Since May 2015, Dr. Schwieterman has served as President and Chief Executive Officer of Mateon. Dr. Schwieterman has also been an independent consultant to biotech and pharmaceutical companies, including to Mateon, specializing in clinical development since July 2002. Dr. Schwieterman is a board-certified internist and a rheumatologist. Dr. Schwieterman was previously a part-time employee of Perceptive Advisors, LLC, a hedge fund based in New York, NY. From 2009 to 2014, Dr. Schwieterman was the Chief Medical Officer of Chelsea Therapeutics, Inc., a publicly traded biopharmaceutical development company, where he led the Chelsea Therapeutics clinical development team toward the approval of droxidopa for the treatment of symptoms of Parkinson’s disease and other neurogenerative diseases. Dr. Schwieterman was formerly Chief of the Medicine Branch and Chief of the Immunology and Infectious Disease Branch in the Division of Clinical Trials at the Food and Drug Administration (the “FDA”). In these capacities and others, Dr. Schwieterman spent 10 years at the FDA in the Center for Biologics overseeing a wide range of clinical development plans for a large number of different types of molecules. Dr. Schwieterman holds a B.S. and M.D. from the University of Cincinnati. Dr. Schwieterman does not currently serve, and has not served in the past five years, as a member of the board of directors of another reporting company or of any registered investment company.

Matthew M. LoarMr. Loar was appointed as our Chief Financial Officer in July 2015. Mr. Loar was previously Chief Financial Officer of KineMed, Inc., a privately held biotechnology company, from January 2014 to July 2015. From January 2010 to January 2014, Mr. Loar was an independent financial consultant to companies in the biopharmaceutical industry. While consulting, he also served as acting Chief Executive Officer and Chief Financial Officer of Neurobiological Technologies, Inc. (NTI), a publicly traded pharmaceutical company, beginning in February 2010 and currently continuing, and as Chief Financial Officer of Virolab, Inc., a biotechnology company, from May 2011 to August 2012. Previously, he was Chief Financial Officer of NTI from April 2008 to December 2009. Earlier in his career, Mr. Loar was Chief Financial Officer of Osteologix, Inc., a publicly traded pharmaceutical company, from 2006 to 2008, and of Genelabs Technologies, Inc., a publicly traded biopharmaceutical and diagnostics company, from 1995 to 2006. Mr. Loar currently serves on the board of directors of NTI. Mr. Loar received a B.A. in Legal Studies from the University of California, Berkeley and is a Certified Public Accountant (inactive) in California.

MANAGEMENT AND CORPORATE GOVERNANCE

The Board of Directors

Our Board of Directors currently consists of five members: Dr. David J. Chaplin, Dr. Simon C. Pedder, Mr. Donald R. Reynolds, Dr. Bobby W. Sandage, Jr. and Dr. William D. Schwieterman. Under ourBy-laws, the number of members of our Board of Directors is fixed from time to time by the Board of Directors, and directors serve in office until the next annual meeting of stockholders and until their successors have been elected and qualified.

Committees of the Board and Independence

Audit Committee.The Audit Committee consists of Dr. Sandage (Chairman), Dr. Pedder and Mr. Reynolds. Our Audit Committee has the authority to retain and terminate the services of our independent registered public accounting firm, reviews our annual financial statements, considers matters relating to accounting policy and internal controls, and reviews the scope of our annual audits. The Board has determined that Dr. Sandage is an “audit committee financial expert,” as the SEC has defined that term in Item 407 of RegulationS-K. The Board of Directors has adopted a charter for the Audit Committee, which is reviewed and reassessed annually by the Audit Committee. A copy of the Audit Committee’s written charter is publicly available on our website at www.mateon.com. All members of our Audit Committee qualify as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

Compensation Committee. The Compensation Committee consists of Dr. Pedder (Chairperson), Mr. Reynolds and Dr. Sandage. The Compensation Committee’s roles and responsibilities include making recommendations to the Board of Directors regarding the compensation philosophy and compensation guidelines for our executives, the role and performance of our executive officers, and appropriate compensation levels for our CEO, which are determined without the CEO present, and other executives based on a comparative review of compensation practices of similarly situated businesses. The Compensation Committee also makes recommendations to the Board regarding the design and implementation of our compensation plans and the establishment of criteria and the approval of performance results relative to our incentive plans. Our Compensation Committee also administers our 2015 Plan and the Mateon Therapeutics, Inc. 2017 Equity Incentive Plan, or the 2017 Plan. Each member of the Compensation Committee qualifies as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies, and qualifies as a“Non-Employee Director” within the meaning of Rule16b-3 under the Exchange Act.

The Compensation Committee reviews and assesses the three main components of each named executive officer’s compensation: base salary, incentive compensation, and equity compensation. Adjustments to base salary are generally only made when there has been a change in the scope of the responsibilities of the named executive officer or when, based on a review of the base salary component of executive officers in companies of a similar size and stage of development, the Compensation Committee members believe that an adjustment is warranted in order to remain competitive. The executive management of the Company determines and agrees with the Compensation Committee on its corporate goals and objectives for the ensuing year. At the end of each year, the attainment of each objective is assessed and incentive awards may be made to each executive based on his or her contribution to achieving the objectives. Awards are made based on either provisions of an executive’s employment agreement, or an assessment of each executive’s equity compensation position relative to the Company’s other executives.

The Compensation Committee also typically reviews our director compensation on at least an annual basis.

The Compensation Committee has the authority to directly retain the services of independent consultants and other experts to assist in fulfilling its responsibilities, although did not retain the services of any independent consultants in 2017.

A copy of the Compensation Committee’s written charter is publicly available on our website atwww.mateon.com.

Nominating and Governance Committee.During 2017, the Nominating and Governance Committee held one meeting. The Nominating and Governance Committee consists of Mr. Reynolds (Chairman), Dr. Pedder and Dr. Sandage. The Nominating and Governance Committee’s role and responsibilities include making recommendations to the full Board as to the size and composition of the Board and making recommendations as to particular nominees to the Board. All members of the Nominating and Governance Committee qualify as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

If a stockholder wishes to nominate a candidate to be considered for election as a director at the 2019 annual meeting of stockholders using the procedures set forth in theBy-laws, it must follow the procedures described below under “Stockholder Proposals and Nominations for Director” at the end of this proxy statement.

In addition, the Nominating and Governance Committee may consider candidates recommended by stockholders, as well as from other sources, such as current directors or officers, third-party search firms or other appropriate sources. For all potential candidates, the Nominating and Governance Committee may consider all factors it deems relevant, such as a candidate’s personal integrity and sound judgment, business and professional skills and experience, independence, knowledge of the biotechnology industry, possible conflicts of interest, diversity, the extent to which the candidate would fill a present need on the Board, and concern for the long-term interests of the stockholders. In general, persons recommended by stockholders will be considered on the same basis as candidates from other sources. If a stockholder wishes simply to propose a candidate for consideration as a nominee by the Nominating and Governance Committee, it should submit any pertinent information regarding the candidate to the Chairman of the Nominating and Governance Committee by mail at 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080. The Nominating and Governance Committee considers issues of diversity among its members in identifying and considering nominees for director, and strives where appropriate to achieve a diverse balance of backgrounds, perspectives, experience, age, gender, ethnicity and country of citizenship of the Board and its committees.

A copy of the Nominating and Governance Committee’s written charter is publicly available on our website at www.mateon.com.

EXECUTIVE COMPENSATION

Summary Compensation Table

The following table shows the total compensation paid or accrued during 2017 and 2016 to (1) our President and Chief Executive Officer, (2) our Chief Financial Officer and (3) our Chief Scientific Officer, the latter two of which are our next most highly compensated executive officers earning more than $100,000 in 2017.

Although all stock options in the table vest over a four year period, pursuant to rules of the SEC the value in the table represents full value at the grant date only and the values do not take into account subsequent increases or decreases in actual value to the recipient. See the Narrative Disclosure below for information regarding the number of shares granted to each of the named executive officers. See Note 6 to our Financial Statements included in our Annual Report on Form10-K for the year ended December 31, 2017 for additional information regarding the assumptions used to determine the fair value of each of the option awards in this table. See also our discussion of stock-based compensation under “Management’s Discussion and Analysis of Financial Condition and Results of Operations — Critical Accounting Policies and Significant Judgments and Estimates” in the FormS-1.

Narrative Disclosure to Summary Compensation Table

Dr. William D. Schwieterman. On May 15, 2015, we entered into an employment agreement with Dr. Schwieterman for his service as President and Chief Executive Officer, which was subsequently amended on July 31, 2015. Pursuant to the terms of this agreement, Dr. Schwieterman is entitled to receive an annual base salary of $410,000. In addition, he is eligible for an annual bonus of up to fifty percent of his then-current annual base salary, based on the Board of Directors’ assessment of his performance and the Company’s performance. For calendar year 2016, the Board of Directors determined that Dr. Schwieterman’s annual bonus would be at 50% of the targeted level, and for calendar year 2017, the Board of Directors determined that he would not receive an annual bonus due to the financial condition of the Company.

Dr. Schwieterman’s employment agreement also provides for the Company to pay the costs of furnished housing in San Francisco, California and the cost of one economy class roundtrip airplane ticket between San Francisco, California and Mobile, Alabama per month.

On October 2, 2017, the Company and Dr. Schwieterman agreed to a 50% reduction in his base annual salary (to $205,000), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Dr. Schwieterman continues to receive the reduced salary as of the date of the filing of this proxy statement.

Dr. Schwieterman may terminate his employment upon written notice to us. We may terminate his employment without prior written notice for cause, or without cause on sixty days’ prior written notice. If his employment is terminated by us for cause, by reason of his death or disability or by Dr. Schwieterman without good reason, we will pay him the amount of our accrued obligations as of the date of such termination. If his employment is terminated by us other than for cause or by Dr. Schwieterman with good reason, we will pay him the accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of health insurance premiums pursuant to the Consolidated Omnibus Budget Reconciliation Act of 1985, or COBRA, subject to the conditions outlined in the agreement.

If his employment is terminated by us other than for cause or by Dr. Schwieterman with good reason in the one year following the effective date of a change in control of the Company, we will pay him our accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of COBRA premiums on the same conditions described above. In addition, all of his unvested equity awards outstanding on the date of termination shall vest and be immediately exercisable. Dr. Schwieterman has also agreed not to directly or indirectly solicit for employment, during his employment and for a twelve month period following termination of his employment, any person who is (or has been in the past year) a Company officer, executive or key employee.

All payments made and benefits available to Dr. Schwieterman in connection with his employment agreement will comply with Internal Revenue Code Section 409A in accordance with the terms of his employment agreement.

On March 21, 2016, the Company granted Dr. Schwieterman options to purchase 500,000 shares of our common stock with an exercise price of $0.7277 per share, which vest over a four year period. On January 12, 2017, the Company granted Dr. Schwieterman options to purchase 550,000 shares of our common stock with an exercise price of $0.375 per share, which vest over a four year period.

Matthew M. Loar. On July 20, 2015, we entered into an employment agreement with Mr. Loar for his service as our Chief Financial Officer. Pursuant to the terms of this agreement, Mr. Loar is entitled to receive an annual base salary of $325,000. In addition, he is eligible for an annual bonus of up to thirty-five percent of his then-current annual base salary, based on the Board of Directors’ assessment of his performance and the Company’s performance. For calendar year 2016, the Board of Directors determined that Mr. Loar’s annual bonus would be at 50% of the targeted level, and for calendar year 2017, the Board of Directors determined that he would not receive an annual bonus due to the financial condition of the Company.

On October 2, 2017, the Company and Mr. Loar agreed to a 50% reduction in his base annual salary (to $162,500), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Mr. Loar continues to receive the reduced salary as of the date of the filing of this proxy statement.

Mr. Loar may terminate his employment agreement upon written notice to us. We may terminate the employment agreement without prior written notice for cause, or without cause on sixty days’ prior written notice. If his employment is terminated by us for cause, by reason of his death or disability or by Mr. Loar without good reason, we will pay him the amount of our accrued obligations, as of the date of such termination. If his employment is terminated by us other than for cause or by Mr. Loar with good reason, we will pay him the accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of health insurance premiums pursuant to COBRA, subject to the conditions outlined in the agreement.

If his employment is terminated by us other than for cause or by Mr. Loar with good reason in the one year following the effective date of a change in control of the Company, we will pay him our accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of COBRA premiums on the same conditions described above. In addition, all of his unvested equity awards outstanding on the date of termination shall vest and be immediately exercisable. Mr. Loar has also agreed not to directly or indirectly solicit for employment, during his employment and for a twelve month period following termination of his employment, any person who is (or has been in the past year) a Company officer, executive or key employee.

All payments made and benefits available to Mr. Loar in connection with his employment agreement will comply with Internal Revenue Code Section 409A in accordance with the terms of his employment agreement.

On March 21, 2016, the Company granted Mr. Loar options to purchase 262,500 shares of our common stock with an exercise price per share of $0.7277 per share, which vest over a four year period. On January 12, 2017, the Company granted Mr. Loar options to purchase 350,000 shares of our common stock with an exercise price of $0.375 per share, which vest over a four year period.

Dr. David J. Chaplin.On May 12, 2015 we entered into an amended and restated employment agreement with Dr. Chaplin for his services as our Chief Scientific Officer. Pursuant to the terms of his employment agreement, Dr. Chaplin is entitled to receive an annual base salary of $220,000. In addition, he is eligible to be awarded an annual bonus of up to thirty-five percent of his then-current annual base salary, based on the Board of Directors’ assessment of his performance and the Company’s performance. For calendar year 2016, the Board of Directors determined that Dr. Chaplin’s annual bonus would be at 50% of the targeted level, and for calendar year 2017, the Board of Directors determined that he would not receive an annual bonus due to the financial condition of the Company.

On October 2, 2017, the Company and Dr. Chaplin agreed to a 50% reduction in his base annual salary (to $110,000), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Dr. Chaplin continued to receive the reduced salary through his retirement from employment with the Company on January 11, 2018.

On March 21, 2016, we granted Dr. Chaplin options to purchase 262,500 shares of our common stock with an exercise price per share of $0.7277 per share which were scheduled to vest over a four year period. On January 12, 2017, the Company granted Dr. Chaplin options to purchase 262,500 shares of our common stock with an exercise price of $0.375 per share, which were scheduled to vest over a four year period. The unvested portion of these options terminated following Dr. Chaplin’s retirement.

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following tables set forth certain information with respect to the beneficial ownership of our common stock as of July 21, 2017,April 30, 2018 for (a) each of our named executive officers named in the Summary Compensation Table, (b) each of our directors, (c) all of our current directors and executive officers as a group, and (d) each stockholder known by us to own beneficially more than 5% of our common stock. Beneficial ownership is determined in accordance with the rules of the Securities and Exchange CommissionSEC and includes voting or investment power with respect to the securities. We deem shares of common stock that may be acquired by an individual or group within 60 days of July 21, 2017April 30, 2018 pursuant to the exercise of options or warrants to be outstanding for the purpose of computing the percentage ownership of such individual or group, but such shares are not deemed to be outstanding for the purpose of computing the percentage ownership of any other person shown in the tables. Except as indicated in footnotes to these tables, we believe that the stockholders named in these tables have sole voting and investment power with respect to all shares of common stock shown to be beneficially owned by them based on information provided to us by these stockholders. Ownership determinations are based on 26,544,93441,419,934 shares of common stock outstanding on July 21, 2017.April 30, 2018. Unless otherwise indicated, the address of each stockholder is c/o Mateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco, CA 94080.

The determination that there were no other persons, entities or groups known to us to beneficially own more than 5% of our outstanding common stock as of April 30, 2018, was based on a review of all statements filed with respect to us since the beginning of the past fiscal year with the Securities and Exchange CommissionSEC pursuant to Section 13(d) or 13(g) of the Exchange Act.

CERTAIN RELATIONSHIPS AND RELATED PERSON TRANSACTIONS

Our Audit Committee reviews and approves in advance all related person transactions.

Our Board of Directors has reviewed the materiality of any relationship that each of our directors has with the Company, either directly or indirectly. Based upon this review, our Board has determined that each of the nominees except for Dr. Chaplin and Dr. Schwieterman qualify as “independent directors” as defined under the rules of The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

Dr. Chaplin is a resident of the United Kingdom, and during 2016 the services he performed for Mateon while in the United Kingdom were conducted through Aston Biopharma LTD, an entity which Dr. Chaplin controlled, while the payment for services Dr. Chaplin performed for Mateon while he was in the United States were made directly to Dr. Chaplin. We paid Aston Biopharma LTD approximately $105,750 as compensation for services Dr. Chaplin performed while he was in the United Kingdom during 2016, and his compensation for services as an employee was reduced by this amount. Aston Biopharma LTD and Mateon terminated the consultancy agreement effective as of January 1, 2017 and all payments for Dr. Chaplin’s services were thereafter made directly to Dr. Chaplin. The compensation Dr. Chaplin has received from the Company is further described under “Executive Compensation”, and includes compensation received under the consultancy agreement with Aston Biopharma LTD.

On April 12, 2018, we closed the Private Placement in which we received net proceeds of approximately $2.4 million. Dr. Schwieterman purchased 2.5 Units and Mr. Loar and Mr. Reynolds each purchased one Unit in the Private Placement. The purchases of Dr. Schwieterman, Mr. Loar and Mr. Reynolds were reviewed in advance by disinterested directors on the Audit Committee. See the section entitled “Prospectus Summary-Private Placement Transaction” of this Prospectus for additional information regarding the Private Placement.

DESCRIPTION OF CAPITAL STOCK

The following description of our securities is intended as a summary only and is qualified in its entirety by reference to our amended and restated certificate of incorporation and amended and restatedby-laws, which are filed as exhibits to the registration statement of which the prospectus forms a part, and to the applicable provisions of the Delaware General Corporation Law. We refer in this section to our amended and restated certificate of incorporation as our certificate of incorporation, and we refer to our amended and restatedby-laws as ourby-laws.

Our authorized capital stock consists of 70,000,000 shares of common stock, $0.01 par value per share, and 15,000,000 shares of preferred stock, par value $0.01 per share, in one or more series. As of July 21, 2017,April 30, 2018, we had outstanding 26,544,93441,419,934 shares of our common stock. At that date, we also had an aggregate of 5,670,2884,286,454 shares of common stock reserved for issuance upon exercise of outstanding stock options granted under our stock incentive plans, an aggregate of 9,625,79717,090,740 shares of common stock reserved for issuance upon the exercise of outstanding warrants to purchase common stock 609,191(excluding 7,437,500 shares to be reserved for the Series B warrants), 1,678,389 shares of common stock available for issuance under the 2015 Equity Incentive Plan and 446,302760,938 shares of common stock available for issuance under the 2017 Equity Incentive Plan. At our annual meeting of stockholders expected to be held on June 20, 2018, our stockholders will be presented with proposals to approve a certificate amendment to our certificate of incorporation to increase the authorized number of shares of common stock from 70,000,000 shares to 150,000,000 shares and to approve an amended and restated 2015 Equity Incentive Plan which includes an increase in the number of available for the grant of awards under the 2015 Equity Incentive Plan from 4,725,781 shares to 7,250,000 shares.

Common Stock

Each holder of record of our common stock is entitled to one vote for each outstanding share of our common stock owned by that stockholder on every matter properly submitted to the stockholders for their vote. Holders of common stock are entitled to any dividend declared by our board of directors out of funds legally available for that purpose. Holders of common stock are entitled to receive, on a pro rata basis, all our remaining assets available for distribution to stockholders in the event of our liquidation, dissolution or winding up. Holders of common stock do not have any preemptive right to become subscribers or purchasers of additional shares of any class of our capital stock.

Preferred Stock

Our board of directors may, without further action by our stockholders, from time to time, direct the issuance of shares of preferred stock in series and may, at the time of issuance, determine the rights, preferences and limitations of each series, including voting rights, dividend rights and redemption and liquidation preferences. Satisfaction of any dividend preferences of outstanding shares of preferred stock would reduce the amount of funds available for the payment of dividends on shares of our common stock. Holders of shares of preferred stock may be entitled to receive a preference payment in the event of any liquidation, dissolution orwinding-up of our company before any payment is made to the holders of shares of our common stock. In some circumstances, the issuance of shares of preferred stock may render more difficult or tend to discourage a merger, tender offer or proxy contest, the assumption of control by a holder of a large block of our securities or the removal of incumbent management. Upon the affirmative vote of our board of directors, without stockholder approval, we may issue shares of preferred stock with conversion rights which could adversely affect the holders of shares of our common stock.

Certain Effects of Authorized but Unissued Stock

We have shares of common stock and preferred stock available for future issuance without stockholder approval. We may issue these additional shares for a variety of corporate purposes, including future public offerings to raise additional capital or facilitate corporate acquisitions or for payment as a dividend on our capital stock. The existence of unissued and unreserved common stock and preferred stock may enable our Board of Directors to issue shares to persons friendly to current management or to issue preferred stock with terms that could render more difficult or discourage a third-party attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise, thereby protecting the continuity of our management. In addition, if we issue preferred stock, the issuance could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation.

Delaware Law and Certificate of Incorporation andBy-laws Provisions

The provisions of Delaware law and of our restated certificate of incorporation, as amended, and amended and restatedby-laws discussed below could discourage or make it more difficult to accomplish a proxy contest or other change in our management or the acquisition of control by a holder of a substantial amount of our voting stock. It is possible that these provisions could make it more difficult to accomplish, or could deter, transactions that stockholders may otherwise consider to be in their best interests or the best interests of Mateon.

Delaware Statutory Business Combinations Provision.

In general, Section 203 of the Delaware General Corporation Law prohibits a publicly-held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a period of three years after the date of the transaction in which the person became an interested stockholder, unless the business combination is, or the transaction in which the person became an interested stockholder was, approved in a prescribed manner or another prescribed exception applies. For purposes of this Section 203, a “business combination” is defined broadly to include a merger, asset sale or other transaction resulting in a financial benefit to the interested stockholder, and, subject to certain exceptions, an “interested stockholder” is a person who, together with his or her affiliates and associates, owns (or within the prior three years, did own) 15% or more of the corporation’s voting stock.

Special Meetings of Stockholders.

Special meetings of the stockholders may be called by the chairman of our board of directors, the president, or the entire board of directors pursuant to a resolution adopted by a majority of directors present at a meeting at which a quorum is present. The president or secretary shall also call special meetings upon the written request of not less than 10% in interest of the stockholders entitled to vote at the meeting.

Liability Limitations and Indemnification

The Delaware General Corporation Law authorizes corporations to limit or eliminate, subject to certain conditions, the personal liability of directors to corporations and their stockholders for monetary damages for breach of their fiduciary duties. Our restated certificate of incorporation limits the liability of our directors to the fullest extent permitted by Delaware law.

We have obtained director and officer liability insurance to cover liabilities our directors and officers may occur in connection with their services to us, including matters arising under the Securities Act. Our restated certificate of incorporation and restatedby-laws also provide that we will indemnify any of our directors and officers who, by reason of the fact that he or she is one of our officers or directors, is involved in a legal proceeding of any nature. We will repay certain expenses incurred by a director or officer in connection with any civil or criminal action or proceeding, specifically including actions by us or in our name (derivative suits). These indemnifiable expenses include, to the maximum extent permitted by law, attorney’s fees, judgments, civil or criminal fines, settlement amounts and other expenses customarily incurred in connection with legal proceedings. A director or officer will not receive indemnification if he or she is found not to have acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interest. In addition, we have entered into agreements to indemnify our directors and officers. These agreements, among other things, will indemnify and advance expenses to our directors and officers for certain expenses, including attorney’s fees, judgments, fines and settlement amounts incurred by any such person in any action or proceeding, including any action by us arising out of such person’s services as our director or officer, or any other company or enterprise to which the person provides services at our request. Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers or persons controlling the registrant pursuant to the foregoing provisions, the registrant has been informed that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is therefore unenforceable.

Current Trading Symbol

Our common stock is quoted for trading on the OTCQX MarketplaceOTC Market under the symbol “MATN.”

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company, LLC.

DESCRIPTION OF SECURITIES WE ARE OFFERINGSELLING SECURITYHOLDERS

We are offering (i) 16,666,666 shares of our common stock orpre-funded warrants and (ii) common warrants to purchase up to an aggregate of 8,333,333 shares of our common stock. Each share of common stock orpre-funded warrant is being sold together with a common warrant to purchase one half a share of common stock. The shares of common stock orpre-funded warrants and accompanying common warrants will be issued separately. We are also registeringtable below lists the shares of common stock issuable from time to time upon exercisenames of thepre-funded warrants selling securityholders and common warrants offered hereby.

Common Stock

The material terms and provisions of our common stock and each other class of our securities which qualifies or limits our common stock are described underinformation regarding the caption “Description of Capital Stock” in this prospectus.

Pre-Funded Warrants

The following summary of certain terms and provisions ofpre-funded warrants that are being offered hereby is not complete and is subject to, and qualified in its entirety by, the provisions of thepre-funded warrant, the form of which is filed as an exhibit to the registration statement of which this prospectus forms a part. Prospective investors should carefully review the terms and provisions of the form ofpre-funded warrant for a complete description of the terms and conditions of thepre-funded warrants.

Duration and Exercise Price. Eachpre-funded warrant offered hereby will have an initial exercise price per share equal to $0.01. Thepre-funded warrants will be immediately exercisable and may be exercised at any time until thepre-funded warrants are exercised in full. The exercise price and number of shares of common stock issuable upon exercise is subject to appropriate adjustment in the event of stock dividends, stock splits, reorganizations or similar events affecting our common stock and the exercise price. Thepre-funded warrants will be issued separately from the accompanying common warrants, and may be transferred separately immediately thereafter.

Exercisability. Thepre-funded warrants will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full for the number of shares of our common stock purchased upon such exercise (except in the case of a cashless exercise as discussed below). A holder (together with its affiliates) may not exercise any portion of thepre-funded warrant to the extent that the holder would own more than 4.99% of the outstanding common stock immediately after exercise, except that upon at least 61 days’ prior notice from the holder to us, the holder may increase the amount of ownership of outstanding stock after exercising the holder’spre-funded warrants up to 9.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of thepre-funded warrants. Purchasers ofpre-funded warrants in this offering may also elect prior to the issuance of thepre-funded warrants to have the initial exercise limitation set at 9.99% of our outstanding common stock. No fractional shares of common stock will be issued in connection with the exercise of apre-funded warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

Cashless Exercise. If, at the time a holder exercises itspre-funded warrants, a registration statement registering the issuance of the shares of common stock underlying thepre-funded warrants under the Securities Act is not then effective or available and an exemption from registration under the Securities Act is not available for the issuance of such shares, then in lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may elect instead to receive upon such exercise (either in whole or in part) the net number of shares of common stock determined according to a formula set forth in thepre-funded warrants.

Transferability. Subject to applicable laws, apre-funded warrant may be transferred at the option of the holder upon surrender of thepre-funded warrant to us together with the appropriate instruments of transfer.

Trading Market. There is no trading market available for thepre-funded warrants on any securities exchange or nationally recognized trading system.

Right as a Stockholder. Except as otherwise provided in thepre-funded warrants or by virtue of such holder’sbeneficial ownership of shares of our common stock by the holdersselling securityholders. The second and third columns list the number and percentage of thepre-funded warrants do not have the rights or privilegesshares of holders of our common stock including any voting rights, until they exercise theirpre-funded warrants.

Common Warrants

The following summary of certain terms and provisions of common warrants that are being offered hereby is not complete and is subject to, and qualified in its entiretybeneficially owned by the provisionsselling securityholders as of the common warrants, the form of which is filed as an exhibit to the registration statement of which this prospectus forms a part. Prospective investors should carefully review the terms and provisions of the form of common warrant for a complete description of the terms and conditions of the common warrants.

Duration and Exercise Price. Each common warrant offered hereby will have an initial exercise price per share equal to $    .April 30, 2018. The common warrants will be immediately exercisable and will expire onfourth column lists the fifth anniversary of the original issuance date. The exercise price and number of shares of common stock issuable upon exercise is subject to appropriate adjustment in the event of stock dividends, stock splits, reorganizations or similar events affecting our common stock and the exercise price. The common warrants

will be issued separately from the common stock, andthat may be transferred separately immediately thereafter. A common warrant to purchase one half a share of our common stock will be issued for every one share of common stock orpre-funded warrant purchased inresold under this offering.

Exercisability.prospectus. The common warrants will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full forfifth and sixth columns list the number of shares of our common stock purchased upon such exercise (except in the case of a cashless exercise as discussed below). A holder (together with its affiliates) may not exercise any portion of the common warrant to the extent that the holder would own more than 4.99% of the outstanding common stock immediately after exercise, except that upon at least 61 days’ prior notice from the holder to us, the holder may increase the amount of ownership of outstanding stock after exercising the holder’s common warrants up to 9.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as suchand percentage ownership is determined in accordance with the terms of the common warrants. No fractional shares of common stock will be issued in connection with the exercise of a common warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

Cashless Exercise. If, at the time a holder exercises its common warrants, a registration statement registering the issuance of the shares of common stock underlying the common warrants under the Securities Act is not then effective or available and an exemption from registration under the Securities Act is not available for the issuance of such shares, then in lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may elect instead to receive upon such exercise (either in whole or in part) the net number of shares of common stock determined according to a formula set forth in the common warrants.

Transferability. Subject to applicable laws, a common warrant may be transferred at the option of the holder upon surrender of the common warrant to us together with the appropriate instruments of transfer.

Exchange Listing. We do not intend to list the common warrants on any securities exchange or nationally recognized trading system.

Right as a Stockholder. Except as otherwise provided in the common warrants or by virtue of such holder’s ownership of shares of our common stock, the holders of the common warrants do not have the rights or privileges of holders of our common stock, including any voting rights, until they exercise their common warrants.

PLAN OF DISTRIBUTION

Pursuant to an engagement agreement, we have engaged H.C. Wainwright & Co., LLC, or the Placement Agent, to act as our exclusive placement agent in connection with this offering of our securities pursuant to this prospectus on a reasonable best efforts basis. The terms of this offering were determined by us and the Placement Agent based on market conditions at the time of pricing. The engagement agreement does not give rise to any commitmentowned by the Placement Agent to purchase any of our securities, and the Placement Agent will have no authority to bind us by virtue of the engagement agreement. The Placement Agent may engagesub-agents or selected dealers to assist with the offering.

Only certain institutional investors purchasing the securities offered hereby will execute a securities purchase agreement with us, providing such investors with certain representations, warranties and covenants from us, which representations, warranties and covenants will not be available to other investors who will not execute a securities purchase agreement in connection with the purchase of the securities offered pursuant to this prospectus. Therefore, those investors shall rely solely on this prospectus in connection with the purchase of securities in the offering.

The Placement Agent is not purchasing or selling any of the securities offered by us under this prospectus, nor is it required to arrange the purchase or sale of any specific number or dollar amount of securities. The Placement Agent has agreed to use reasonable best efforts to arrange for the sale of the securities. There is no required minimum number of securities that must be sold as a condition to completion of this offering. Further, the Placement Agent does not guarantee that it will be able to raise new capital in any prospective offering.

The securities purchase agreement we entered with the investors provides that the obligations of the investors of the securities are subject to certain conditions precedent. We will deliver the securities being issued to the investors upon receipt of investor funds for the purchase of the securities offered pursuant to this prospectus. We expect to deliver the securities being offered pursuant to this prospectus on or about                , 2017.

The Placement Agent may be deemed to be an underwriter within the meaning of Section 2(a)(11) of the Securities Act, and any commissions received by the Placement Agent and any profit realized onsecurityholders after the resale of the shares of common stock soldregistered under this prospectus. Except as noted in the footnotes to the table below, the selling securityholders have not had any material relationship with us within the past three years.

Beneficial ownership is determined in accordance with the rules of the SEC, and includes voting and investment power with respect to our common stock. Shares of common stock subject to convertible debentures, warrants or options that are currently convertible or exercisable or convertible or exercisable within 60 days after April 30, 2018 are deemed to be beneficially owned by the Placement Agent while actingperson holding those securities for the purpose of computing the percentage ownership of that person but are not treated as outstanding for the purpose of computing the percentage ownership of any other stockholder.

Barry W. Blank Trust			2,467,060	(9)			5.8	%			1,892,500				574,560				1.3	%
Robert Settembre			1,000,000	(6)			2.4	%			1,000,000				—				—
Elise M. Lewis			500,000	(4)			1.2	%			500,000				—				—
Joy Singleton			500,000	(4)			1.2	%			500,000				—				—
Daniel Coller			500,000	(4)			1.2	%			500,000				—				—
Isaac Blake legal owner via Non Trust Custodial IRA with American Estate & Trust			1,025,000	(6)			2.4	%			1,000,000				25,000				*
Chad Michael Colvin legal owner via Non Trust Custodial IRA with American Estate & Trust			1,010,000	(6)			2.4	%			1,000,000				10,000				*
Paul K. Stanton via Non Trust Custodial IRA with American Estate & Trust			500,000	(4)			1.2	%			500,000				—				—
Bradford C. Nelson via Non Trust Custodial IRA with American Estate & Trust			1,000,000	(6)			2.4	%			1,000,000				—				—
Lester M. Foote Sr Revocable Trust			270,000	(8)			*				250,000				20,000				*
Donald R. Miles via Non Trust Custodial IRA with American Estate & Trust			2,000,000	(7)			4.7	%			2,000,000				—				—
Shelly R. Gerard via Non Trust Custodial IRA with American Estate & Trust			2,000,000	(7)			4.7	%			2,000,000				—				—
Carl Michael Farmis via Non Trust Custodial IRA with American Estate & Trust			500,000	(4)			1.2	%			500,000				—				—
Jon Baugh			500,000	(4)			1.2	%			500,000				—				—
Michael Cranmer			500,000	(4)			1.2	%			500,000				—				—
Harold and Myrna Gittler			500,000	(4)			1.2	%			500,000				—				—
Danielle Hughes			371,875	(10)			*				371,875				—				—
Divine Holdings, LLC			223,125	(11)			*				223,125				—				—

(6)	Includes 500,000 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

(7)	Includes 1,000,000 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

(8)	Includes 125,000 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

(9)	Includes 1,392,500 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

(10)	Includes 371,875 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

(11)	Includes 223,125 shares the selling securityholder has the right to acquire upon the exercise of the Warrants.

PLAN OF DISTRIBUTION

Each selling securityholder and any of their pledgees, assignees andsuccessors-in-interest may, from time to time, sell any or all of their securities covered hereby on the OTC Market or any other market or trading facility on which the securities are traded or in private transactions. These sales may be at fixed or negotiated prices. A selling securityholder may use any one or more of the following methods when selling securities:

The selling securityholders may also sell securities under Rule 144 under the Securities Act, if available, rather than under this prospectus.

Broker-dealers engaged by the selling securityholders may arrange for other brokers-dealers to participate in sales. Broker-dealers may receive commissions or discounts from the selling securityholders (or, if any broker-dealer acts as agent for the purchaser of securities, from the purchaser) in amounts to be negotiated, but, except as set forth in a supplement to this prospectus, in the case of an agency transaction not in excess of a customary brokerage commission in compliance with FINRA Rule 2440; and in the case of a principal transaction a markup or markdown in compliance with FINRAIM-2440.

In connection with the sale of the securities or interests therein, the selling securityholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the securities in the course of hedging the positions they assume. The selling securityholders may also sell securities short and deliver these securities to close out their short positions, or loan or pledge the securities to broker-dealers that in turn may sell these securities. The selling securityholders may also enter into option or other transactions with broker-dealers or other financial institutions or create one or more derivative securities which require the delivery to such broker-dealer or other financial institution of securities offered by this prospectus, which securities such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The selling securityholders and any broker-dealers or agents that are involved in selling the securities may be deemed to be “underwriters” within the meaning of the Securities Act in connection with such sales. In such event, any commissions received by such broker-dealers or agents and any profit on the resale of the securities purchased by them may be deemed to be underwriting discountscommissions or commissionsdiscounts under the Securities Act. As an underwriter,Each selling securityholder has informed us that it does not have any written or oral agreement or understanding, directly or indirectly, with any person to distribute the Placement Agent would besecurities.

We are required to comply withpay certain fees and expenses incurred by us incident to the registration of the securities. We have agreed to indemnify the selling securityholders against certain losses, claims, damages and liabilities, including liabilities under the Securities Act.

Because selling securityholders may be deemed to be “underwriters” within the meaning of the Securities Act, they will be subject to the prospectus delivery requirements of the Securities Act and the Exchange Act, including without limitation, Rule 415(a)(4)172 thereunder. In addition, any securities covered by this prospectus which qualify for sale pursuant to Rule 144 under the Securities Act may be sold under Rule 144 rather than under this prospectus. The selling securityholders have advised us that there is no underwriter or coordinating broker acting in connection with the proposed sale of the resale securities by the selling securityholders.

We agreed to keep this prospectus effective until the earlier of (i) the date on which the securities may be resold by the selling securityholders without registration and without the requirement to be in compliance with Rule10b-5 144(c)(1) and Regulation Motherwise without restriction or limitation pursuant to Rule 144 or (ii) all of the securities have been sold pursuant to this prospectus or Rule 144 under the Securities Act or any other rule of similar effect. The resale securities will be sold only through registered or licensed brokers or dealers if required under applicable state securities laws. In addition, in certain states, the resale securities may not be sold unless they have been registered or qualified for sale in the applicable state or an exemption from the registration or qualification requirement is available and is complied with.

Under applicable rules and regulations under the Exchange Act. TheseAct, any person engaged in the distribution of the resale securities may not simultaneously engage in market-making activities with respect to the common stock for the applicable restricted period, as defined in Regulation M, prior to the commencement of the distribution. In addition, the selling securityholders will be subject to applicable provisions of the Exchange Act and the rules and regulations thereunder, including Regulation M, which may limit the timing of purchases and sales of shares of the common stock by the Placement Agent acting as principal. Under these rules and regulations, the Placement Agent:

Commissions and Expenses

We have agreed to pay the Placement Agent a total cash fee equal to 6.5% of the gross proceeds of this offering (which may be reduced under certain circumstances). We will also pay the Placement Agent a reimbursement fornon-accountable expenses of $25,000 and a reimbursement for the Placement Agent’s legal fees and expenses in the amount of up to $100,000. This fee will be distributed among the Placement Agent and any selected-dealers that it has retained to act on their behalf in connection with this offering. We estimate the total offering expenses of this offering that will be payable by us, excluding the placement agent fees and expenses, will be approximately $175,000.

Placement Agent Warrants

In addition, we have agreed to issue to the Placement Agent warrants to purchase up to 666,667 shares of common stock (which represents 4.0% of the aggregate number of shares of common stock andpre-funded warrants sold in this offering, including the number of shares underlying thepre-funded warrants being offered hereby) at an exercise price of $        per share (representing 125% of the public offering price for the shares of common stock and related warrant to be sold in this offering), exercisable for 5 years from the date of the effectiveness of this offering. The placement agent warrants will have substantially the same terms as the warrants being sold to the investors in this offering. Pursuant to FINRA Rule 5110(g), the placement agent warrants and any shares of common stock issued upon exercise of the placement agent warrants shall not be sold, transferred, assigned, pledged, or hypothecated, or be the subject of any hedging, short sale, derivative, put or call transaction that would result in the effective economic disposition of the securities by any person for a period of 180 days immediately following the date of effectiveness or commencement of sales of this offering, except the transfer of any security: (i) by operation of law or by reason of our reorganization; (ii) to any FINRA member firm participating in the offering and the officers or partners thereof, if all securities so transferred remain subject to thelock-up restriction set forth above for the remainder of the time period; (iii) if the aggregate amount of our securities held by the Placement Agent or related persons do not exceed 1% of the securities being offered; (iv) that is beneficially owned on apro-rata basis by all equity owners of an investment fund, provided that no participating member manages or otherwise directs investments by the fund and the participating members in the aggregate do not own more than 10% of the equity in the fund; or (v) the exercise or conversion of any security, if all securities remain subject to thelock-up restriction set forth above for the remainder of the time period.

Right of First Refusal

We have also agreed to give the Placement Agent, subject to the completion of this offering, certain rights of first refusal for a period of six months with respect to any further capital raising transactions undertaken by us and a tail fee equal to the cash and warrant compensation in this offering, if any investor who was contacted by the Placement Agent provides us with further capital during suchsix-month period following the expiration or termination of our engagement with the Placement Agent.

Lock-up Agreements

Our executive officers and directors have agreed, subject to certain exceptions, not to offer, sell, agree to sell, directly or indirectly, or otherwise dispose of shares of common stock or warrantsselling securityholders or any other securities convertible into or exchangeable for sharesperson. We will make copies of common stock except forthis prospectus available to the shares of common stock offered in this offering without the prior written consentselling securityholders and have informed them of the representative forneed to deliver a period of 90 days after the consummationcopy of this offering. The Company has agreed, subjectprospectus to certain exceptions, not to issue (or to agree to issue) additional shares of its common stockeach purchaser at or certain securities convertible or exercisable into shares of its common stock for a period of 90 days after the consummation of this offering.

Indemnification

We have agreed to indemnify the Placement Agent and specified other persons against certain liabilities relating to or arising out of the Placement Agent’s activities under the placement agency agreement and to contribute to payments that the Placement Agent may be required to make in respect of such liabilities.

Determination of offering price

The offering price of the securities we are offering was negotiated between us and the investors, in consultation with the Placement Agent based on the trading of our shares of common stock prior to the offering, among other things. Other factors considered in determining the offering price of the shares of common stock we are offering include the history and prospects of the company, the stage of development of our business, our business plans for the future and the extent to which they have been implemented, an assessment of our management, general conditions of the securities markets at the time of the offering and such other factors as were deemed relevant.

Listing

Our common stock is traded on the OTCQX Marketplace under the symbol “MATN.”

Other Relationships

From time to time, the Placement Agent has provided, and may provide in the future, various advisory, investment and commercial banking and other services to us in the ordinary course of business, for which they have received and may continue to receive customary fees and commissions. However, except as disclosed in this prospectus, we have no present arrangementssale (including by compliance with the Placement Agent for any further services.

State Blue Sky Information

We have not applied to register the securities to be issued in this offering for offers and sales to retail customers. In connection with this offering, we will rely on exemptions from registration for sales of securities in this offering solely to institutional investors pursuant to an exemption provided for sales to these investors under the state Blue Sky laws. The definition of an “institutional investor” varies from state to state but generally includes financial institutions, broker-dealers, banks, insurance companies and other qualified entities.

The National Securities Markets Improvement Act of 1996, which is a federal statute, pre-empts the states from regulating transactions in certain securities, which are referred to as “covered securities.” The resale of shares of common stock issued or issuable upon the exercise of warrants issuable in this offering by persons other than underwriters or dealers is exempt from state registration requirements under the National Securities Markets Improvement Act because we are required to file periodic and annual reportsRule 172 under the Securities Exchange Act of 1934. However, states are permitted to require notice filings and collect fees with regard to these transactions and a state may suspend the offer and sale of securities within such state if any such required filing is not made or fee is not paid. As of the date of this prospectus, Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Utah, Virginia, Washington, West Virginia, Wisconsin and Wyoming either do not presently require any notice filings or fee payments or have not yet issued rules or regulations indicating whether notice filings or fee payments will be required. The District of Columbia, Illinois, Maryland, Montana, New Hampshire, North Dakota, Oregon, Puerto Rico, Rhode Island, Tennessee, Texas and Vermont currently permit the resale of the securities, if we have registered the common stock in the state or the proper notice filings and fees have been submitted. As of the date of this prospectus, we have not determined in which, if any, of these states we will submit the required notice filings or pay the required fee. Additionally, if any of the states that has not yet adopted a statute relating to the National Securities Markets Improvement Act adopts such a statute in the future requiring a filing or fee or if any state amends its existing statutes with respect to its requirements, we would need to comply with those new requirements in order for our common stock to continue to be eligible for resale in those jurisdictions pursuant to the exemption provided by the National Securities Markets Improvement Act.

Aside from the exemption from registration provided by the National Securities Markets Improvement Act, the shares of common stock issued in this offering or issuable upon warrants issued in this offering may be eligible for sale on a secondary market basis in various states based on the availability of other applicable exemptions from state registration requirements, in certain instances subject to waiting periods, notice filings or fee payments.

Selling Restrictions outside the United States

This prospectus does not constitute an offer to sell to, or a solicitation of an offer to buy from, anyone in any country or jurisdiction (i) in which such an offer or solicitation is not authorized, (ii) in which any person making such offer or solicitation is not qualified to do so or (iii) in which any such offer or solicitation would otherwise be unlawful. No action has been taken that would, or is intended to, permit a public offer of the securities or possession or distribution of this prospectus or any other offering or publicity material relating to the securities in any country or jurisdiction (other than the United States) where any such action for that purpose is required. Accordingly, the Placement Agent has undertaken that it will not, directly or indirectly, offer or sell any shares of common stock or have in its possession, distribute or publish any prospectus, form of application, advertisement or other document or information in any country or jurisdiction except under circumstances that will, to the best of its knowledge and belief, result in compliance with any applicable laws and regulations and all offers and sales of securities by it will be made on the same terms.

Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968, and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus may be distributed only to, and is directed only at, investors listed in the first addendum, or the Addendum, to the Israeli Securities Law, consisting primarily of joint investment in trust funds; provident funds; insurance companies; banks; portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange Ltd., underwriters, each purchasing for their own account; venture capital funds; entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors. Qualified investors shall be required to submit written confirmation that they fall within the scope of the Addendum.Act).

LEGAL MATTERS

The validity of the securities offered by this prospectus will be passed upon by Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., Boston, Massachusetts. Ellenoff Grossman & Schole LLP will pass upon certain legal matters for the placement agent.

EXPERTS

OUM & CO. LLP, independent registered public accounting firm, has audited our financial statements included in our Annual Report on Form10-K for the year ended December 31, 2016,2017, as set forth in their report (which contains an explanatory paragraph describing conditions that raise substantial doubt about the Company’s ability to continue as a going concern as described in Note 2 to the financial statements), which is incorporated by referenceincluded in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by referenceincluded in reliance on OUM & CO. LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on FormS-1 under the Securities Act with respect to the common stock. This prospectus does not contain all of the information included in the registration statement. For further information pertaining to us and our common stock and the common stock underlying the warrants,Warrants, you should refer to the registration statement and the exhibits and schedules filed with the registration statement. Whenever we make reference in this prospectus to any of our contracts, agreements or other documents, the references are not necessarily complete, and you should refer to the exhibits attached to the registration statement for copies of the actual contract, agreement or other document.

We are subject to the informational requirements of the Securities Exchange Act and file annual, quarterly and current reports, proxy statements and other information with the SEC. You can read our SEC filings, including the registration statement, over the Internet at the SEC’s website at www.sec.gov. You may also read and copy any document we file with the SEC at its Public Reference Room at 100 F Street, N.E., Washington, D.C., 20549. You may also obtain copies of the documents at prescribed rates by writing to the Public Reference Room of the SEC at 100 F Street, N.E., Washington, D.C., 20549. Please call the SEC at1-800-SEC-0330 for further information on the operation of the public reference facility.