UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  ☒                              Filed by a Party other than the Registrant  ☐

Check the appropriate box:

Acer Therapeutics Inc.

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

ACER THERAPEUTICS INC.

ONE GATEWAY CENTER, SUITE 351

300 WASHINGTON STREET

NEWTON, MASSACHUSETTS 02458

October 14, 2020April 16, 2021

To Our Stockholders:

You are cordially invited to attend the Annual Meeting of Stockholders of Acer Therapeutics Inc. on Thursday, November 19, 2020Friday, May 21, 2021 at 10:11:00 a.m. Eastern Time. In light of the ongoing developments related to the COVID-19 pandemic and to protect the health of our employees, stockholders and the community, the Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast. You will be able to attend the Annual Meeting via the Internet at https://www.cstproxy.com/acertx/2020 by using the control number which appears on your proxy card and the instructions that accompany your proxy materials.2021.

It is important that your shares be represented and voted at the virtual meeting. Whether or not you plan to attend the Annual Meeting, please complete, sign, date, and promptly return the accompanying proxy in the enclosed envelope or use one ofvote by Internet or by following the instructions on your voting methods described in the attached materials.instruction form. Returning the proxy does NOT deprive you ofor voting by Internet or vote instruction form will ensure your right to attend the Annual Meeting. If you decide to attendrepresentation at the Annual Meeting and wish to change your proxy vote,regardless of whether you may do so automatically by voting electronically atattend the meeting.virtual Meeting. Please note, however, that if your shares are held of record by a broker, bank or other nominee and you wish to attend and vote at the meeting, you must obtain from the record holder a legal proxy issued in your name.

Thank you for your ongoing support and continued interest in Acer.

Sincerely yours,

Chris Schelling, President and Chief Executive Officer

ACER THERAPEUTICS INC.

ONE GATEWAY CENTER, SUITE 351 300 WASHINGTON STREET

NEWTON, MASSACHUSETTS 02458

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD NOVEMBER 19, 2020MAY 21, 2021

The Annual Meeting of stockholders of Acer Therapeutics Inc. (the “Company”) will be held on Thursday, November 19, 2020,Friday, May 21, 2021, at 10:11:00 a.m. Eastern Time. In light of the ongoing developments related to the COVID-19 pandemic and to protect the health of our employees, stockholders and the community, the Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast. You will be able to attend the Annual Meeting via the Internet at https://www.cstproxy.com/acertx/2020 by using the control number which appears on your proxy card and the instructions that accompany your proxy materials.2021. Stockholders are being asked to vote to:

These business items are described more fully in the Proxy Statement accompanying this Notice.

Only stockholders who owned common stock at the close of business on September 30, 2020April 1, 2021 can vote at this meeting or any adjournments or postponements that may take place. All stockholders are cordially invited to attend the virtual meeting. However, to assure your representation at the meeting, you are urged to mark, sign and return the enclosed proxy as promptly as possible in the postage-prepaid envelope for that purpose or use one of the voting methods described in the attached materials.vote by Internet or by vote instruction form. Your stock will be voted in accordance with the instructions you have given. Any stockholder attending the virtual meeting may vote electronically even if he or she has previously returned a proxy. Please note, however, that if your shares are held of record by a broker, bank or other nominee and you wish to attend and vote at the meeting, you must obtain from the record holder a legal proxy issued in your name.

By Order of the Board of Directors,

Chris Schelling, President and Chief Executive Officer

Dated: October 14, 2020April 16, 2021

The Board of Directors solicits the enclosed proxy. Your vote is important no matter how large or small your stockholdings. To assure your representation at the meeting, please complete, sign, date and promptly mail the enclosed proxy card in the postage-paid envelope provided or use one of the voting methods described in the attached materials.vote by Internet or by vote instruction form.

Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to be held on November 19, 2020:May 21, 2021: This Proxy Statement and our 20192020 Annual Report on Form 10-K are available at https://www.cstproxy.com/acertx/20202021

ACER THERAPEUTICS INC.

PROXY STATEMENT

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD NOVEMBER 19, 2020MAY 21, 2021

INFORMATION CONCERNING SOLICITATION AND VOTING

General

The enclosed proxy is solicited on behalf of our Board of Directors (“Board”) for use at the annual meeting of stockholders to be held on Thursday, November 19, 2020,Friday, May 21, 2021, at 10:11:00 a.m. Eastern Time (the “Annual Meeting”), or at any adjournment or postponement of the Annual Meeting, for the purposes set forth in this Proxy Statement and in the accompanying Notice of Annual Meeting of Stockholders. The Annual Meeting will be held virtually at https://www.cstproxy.com/acertx/2020.2021. There will be no physical location. The meeting will only be conducted via an audio webcast. We intend to mail this Proxy Statement and accompanying proxy card to stockholders on or about October 14, 2020.April 16, 2021.

The Board of Acer Therapeutics Inc. prepared this Proxy Statement for the purpose of soliciting proxies for our Annual Meeting of Stockholders. The terms “we,” “our,” the “Company” or “Acer,” refer to Acer Therapeutics Inc., a Delaware corporation. Acer was formerly known as “Opexa Therapeutics, Inc.” prior to the September 19, 2017 merger between Acer (then known as Opexa), Acer Therapeutics Inc., a Delaware corporation (referred to as “Private Acer”), and Opexa Merger Sub, Inc. (the “Merger”).

Availability of Annual Report on Form 10-K

Accompanying this Proxy Statement is our Annual Report on Form 10-K for the fiscal year ended December 31, 20192020 as filed with the Securities and Exchange Commission (the “SEC”). We make available, free of charge through our website (www.acertx.com), our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), as soon as reasonably practicable after such documents are electronically filed with or furnished to the SEC. These reports can be found under “SEC Filings” through the “Investor Relations” section of our website. We will provide to any stockholder without charge, upon the written request of that stockholder, a copy of our Annual Report on Form 10-K (without exhibits), including financial statements and financial statement schedules. Such requests should be addressed to Investor Relations, Acer Therapeutics Inc., One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458.

Voting

Before the meeting, you may vote your shares if they are registered directly in your name with our transfer agent, Continental Stock Transfer & Trust Company, by (i) completing, signing, dating and returning the enclosed proxy card by mail in the postage paid envelope provided so that it is received before the polls close at the Annual Meeting, or (ii) using the Internet to vote your proxy 24 hours a day, 7 days a week.week, so that your electronic vote is received by 11:59 p.m., Eastern Time, on May 20, 2021. If you would like to vote electronically haveand are a stockholder of record, you may do so by using the control number which appears on your proxy card in hand when youto log on and follow the instructions included with your proxy card. You are encouraged to vote electronically by Internet. If you vote by Internet, you do not need to return your proxy card. Please follow the directions on your proxy card carefully. Stockholders are encouraged to vote and submit proxies in advance of the Annual Meeting by Internet or mail as early as possible to avoid COVID-19 related processing delays.

If your shares are held in a brokerage account in the name of a broker, bank broker or other nominee (this is called “street name”), then you are the beneficial owner of the shares and these proxy materials are being forwarded to

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you by that organization. The organization holding your account is considered the stockholder of record for purposes of voting at the Annual Meeting. You have the right to direct your broker, bank or brokernominee on how to vote the shares in your account, and you may also be able to vote by telephone or via the Internet depending on the voting procedures used by your broker.broker, bank or nominee. You may receive a separate voting instruction form with this Proxy Statement, orand you may need to contact your broker, bank or other nominee to determine whether you will be able to vote electronically using the telephone or Internet. If you hold shares as a beneficial owner, please follow the voting instructions provided by your bank, broker or other nominee for any deadline to return your vote instruction form.

You will be able to attend the virtual Annual Meeting via the Internet at https://www.cstproxy.com/acertx/2020 by using the control number which appears on your proxy card and the instructions that accompany your proxy materials. Whether or not you plan to attend the meeting, however, we encourage you to vote your shares by proxy before the meeting. You may vote your shares at the meeting if you attend online, even if you previously submitted a proxy card or voted by Internet. Please note that if your shares are held in “street name” and you wish to vote at the meeting, you will not be permitted to do so unless you first obtain a legal proxy issued in your name from the broker, bank or nominee that holds your shares.

Attendance and Voting at the Virtual Annual Meeting

After careful consideration, in light of the ongoing developments related to the COVID-19 pandemic and to protect the health of our employees, stockholders and the community, the Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast. In addition, we believe that the virtual meeting format will expand stockholder access and participation. You will not be able to attend the Annual Meeting in person.

You are entitled to attend the virtual Annual Meeting, vote your shares electronically at the meeting and submit questions only if you were a stockholder of record as of the record date for the Annual Meeting, April 1, 2021, or if you hold a valid legal proxy for the Annual Meeting. The live audio webcast of the Annual Meeting will begin promptly at 11:00 a.m. Eastern Time. Stockholders participating in the virtual meeting will be in listen-only mode and will not be able to speak during the webcast. Online access to the audio webcast will open approximately 15 minutes prior to the start of the Annual Meeting to allow time for our stockholders to log in and test their device audio system. We encourage our stockholders to access the meeting in advance of the designated start time.

Registered Stockholders

If your shares are registered in your name with our transfer agent, Continental Stock Transfer & Trust, and you wish to attend the virtual Annual Meeting or vote at the Annual Meeting, go to https://www.cstproxy.com/acertx/2021 and enter the control number included on your proxy card, and click on the “Click here to preregister for the online meeting” link at the top of the page. Prior to the start of the meeting, you will need to log back into the meeting site using your control number. Pre-registration is recommended but is not required in order to attend.

Beneficial Owner: Shares Registered in the Name of a Broker, Bank or Other Nominee

Beneficial stockholders who wish to attend the online-only virtual Annual Meeting or vote at the Annual Meeting must obtain a legal proxy by contacting their account representative at the broker, bank or other nominee that holds their shares, and then e-mail a copy (a legible photograph is sufficient) of their legal proxy to our transfer agent, Continental Stock Transfer & Trust, proxy@continentalstock.com. Beneficial stockholders who e-mail a valid legal proxy will be issued a meeting control number that will allow them to register to attend and participate in the online-only meeting. After contacting Continental, a beneficial holder will receive an e-mail prior to the meeting with a link and instructions for entering the virtual meeting. Beneficial stockholders should contact Continental at least five business days prior to the meeting date.

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Submission of Questions at the Virtual Annual Meeting

An online portal will be available to our stockholders at https://www.cstproxy.com/acertx/2021 for the Annual Meeting. By accessing this portal, stockholders will be able to submit questions in advance or at the Annual Meeting. To demonstrate proof of stock ownership, you will need to log on to the portal by entering the control number included on your proxy card or the meeting control number provided by Continental to submit questions. We intend to answer questions submitted during the meeting that are pertinent to the Company and the items being brought before stockholder vote at the 2021 Annual Meeting, as time permits.

Technical Assistance Provided Before and During the Virtual Annual Meeting

Beginning 15 minutes prior to the start of and during the virtual Annual Meeting, we will have a support team ready to assist stockholders with any technical difficulties they may have accessing or hearing the virtual meeting. If you encounter any difficulties accessing the virtual meeting during the check-in or meeting time, you should call our support team at (917) 262-2373.

Revocability of Proxies

Any proxy given pursuant to this solicitation may be revoked by the person giving ita stockholder of record at any time before its use by delivering to the Secretary of Acer, at the address of our executive offices noted above,One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458, written notice of revocation or a duly executed proxy bearing a later date or by attending the virtual Annual Meeting and voting electronically. AttendanceIf you are a “street name” holder, your broker, bank or other nominee can provide instructions explaining how you may change or revoke your voting instructions. Logging in for virtual attendance at the virtual Annual Meeting alone will not by itself, revoke ayour proxy.

Quorum, Abstentions and Broker Non-Votes

Only stockholders of record at the close of business on September 30, 2020 (the “Record Date”)April 1, 2021 will be entitled to notice of and to vote at the virtual Annual Meeting. As of the Record Date,record date, there were 11,912,73114,310,244 shares of common stock outstanding and entitled to vote. Each holder of record of shares of common stock on the Record Daterecord date will be entitled to one vote for each share held on all matters to be voted upon at the Annual Meeting. Shares of common stock may not be voted cumulatively.

Proxies properly executed, duly returned to us and not revoked will be voted in accordance with the specifications made. Where no specifications are given, such proxies will be voted:

It is not expected that any matters other than those referred to in this Proxy Statement will be brought before the Annual Meeting. If, however, any matter not described in this Proxy Statement is properly presented for action at the Annual Meeting, the person named as proxy in the enclosed form of proxy will have discretionary authority to vote according to his or her own discretion.

The required quorum for the transaction of business at the virtual Annual Meeting is a majority of the issued and outstanding shares of our common stock entitled to vote at the Annual Meeting, whether present online or represented by proxy. Our bylaws provide that unless otherwise provided by law or by our Certificate of Incorporation, all matters other than the election of directors shall be decided by the affirmative vote of a majority of the shares of stock represented and present at the Annual Meeting. Shares of common stock represented by a properly signed and returned proxy will be treated as present at the virtual Annual Meeting for purposes of determining a quorum, regardless of whether the proxy is marked as casting a vote or abstaining.

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The term “broker non-vote” refers to shares held by a brokerage firm, bank or other nominee (for the benefit of its client) that are represented at the meeting, but with respect to which such broker or nominee is not instructed to vote on a particular proposal and does not have discretionary authority to vote on that proposal.

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offices not less than 90 days nor more than 120 days prior to the anniversary of the date of the proxy statement for the prior year’s annual meeting; provided, however, that in the event that no annual meeting was held in the previous year or the date of the annual meeting is more than 30 days before or after the first anniversary of the preceding year’s annual meeting, notice by the stockholder must be received by the Secretary of the corporation not later than the close of business on the later of the 90th day prior to such annual meeting and the 10th day following the day on which public announcement of the date of such meeting is first made by means of a press release reported by the Dow Jones News Service, Associated Press or a comparable national news service or in a document publicly filed by us with the SEC. In addition, stockholders must comply in all respects with the rules and regulations of the SEC then in effect and the requirements of our bylaws.

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PROPOSAL 1

ELECTION OF DIRECTORS

The Board of Directors currently consists of five members, each with a term expiring at the Annual Meeting. The Nominating and Corporate Governance Committee of the Board has recommended, and the Board has nominated, the five incumbent directors for election at the Annual Meeting. TheUnless otherwise directed, the shares represented by the enclosed proxy will be voted for the election as directors of the five nominees named below to serve until the 2021 Annual Meeting2022 annual meeting or until their successors have been duly elected and qualified. All of the nominees have indicated to us that they will be available to serve as directors. If any of the nominees becomesbecome unavailable for any reason or if a vacancy should occur before the election (which events are not anticipated), the shares represented by the enclosed proxy may be voted for such other person or persons recommended by the Board as may be determined by the holders of the proxy. There are no family relationships among our executive officers and directors.

Director Nominees

Individuals nominated for election at the Annual Meeting and their ages as of September 30, 2020 are:April 15, 2021 are as follows:

Biographical information for our director nominees is set forth below:

Stephen J. Aselage has served as Chairman of the Board since the completion of the Merger in September 2017.2017 merger of Opexa Therapeutics Inc. and private Acer Therapeutics Inc. From October 2015 until the Merger,merger, Mr. Aselage served as the Chairman of Privateprivate Acer’s Board of Directors.Board. Most recently, he was the Chief Executive Officer of Travere Therapeutics, Inc. (formerly known as Retrophin, Inc.), a Nasdaq-listed, biopharmaceutical company, from November 2014 until his retirement in January 2019, and remains a member of its Board of Directors since October 2012. From May 2014 to November 2014, Mr. Aselage served as the Chief Operations Officer and interim Chief Executive Officer of Retrophin.Travere Therapeutics, Inc. Prior to joining Retrophin,Travere Therapeutics, Inc., he held a variety of roles at BioMarin Pharmaceutical Inc., a Nasdaq-listed biotechnology company, as Executive Vice President and Chief Business Officer from December 2009 to September 2012 and Senior Vice President of Global Commercial Development from July 2005 to December 2009. He has also held leadership roles at Cell Therapeutics, Inc., Sangstat Medical Corporation, Advanced Tissue Sciences, Inc. and Genentech, Inc. Mr. Aselage earned a B.S. in biology from the University of Notre Dame. Mr. Aselage currently serves on the Advisory Council for the Department of Science at the University of Notre Dame and also serves on the Board of Directors at BioCryst Pharmaceuticals, Inc. We believe that Mr. Aselage is qualified to serve on our Board of Directors due to his extensive experience in the pharmaceuticals and biotechnology industry, which will enable him to contribute important insights to our Board of Directors on strategic leadership and drug commercialization matters.

Jason Amello has served as a director since the completion of the Merger in September 2017.2017 merger of Opexa Therapeutics Inc. and private Acer Therapeutics Inc. Since September 2020, Mr. Amello has served as Chief Financial Officer of Saniona AB, a rare disease biopharmaceutical company listed on Nasdaq Stockholm Small Cap. From September 2013 to August 2020, he served as Senior Vice President, Chief Financial Officer and Treasurer of Akebia Therapeutics, Inc., a Nasdaq-listed biopharmaceutical company. From May 2012 to May 2013, Mr. Amello served as Executive Vice President, Chief Financial Officer and Treasurer of ZIOPHARM Oncology, Inc., a Nasdaq-listed biopharmaceutical company. From April 2000 to June 2011, he held various positions at Genzyme Corporation, a

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then Nasdaq-listed biotechnology company, most recently as Senior Vice President, Corporate Controller, and

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THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE ELECTION OF EACH THE ABOVE NOMINEES

Board and Committee Meetings

Members of the Board are encouraged to attend the Annual Meeting; however, we do not have a policy regarding director attendance at annual meetings. No directors attended the 20192020 annual meeting. During the year ended December 31, 2019,2020, the Board held seven meetings, and each director attended at least 75% of the total number of meetings held by the Board and all committees on which such director served during the period he or she was a director.

Director Independence

The Board has determined that Ms. Griffin and Messrs. Amello, Aselage and Dunn are each an independent director within the meaning of Nasdaq listing standards, which directors constitute a majority of the Board. The Board has determined that each member of the Board’s Audit, Compensation and Nominating and Corporate Governance Committees is independent (or similarly designated) based on the Board’s application of the standards of Nasdaq and the rules and regulations promulgated by the SEC or the Internal Revenue Service, as appropriate for such committee membership.

Committees of the Board of Directors

We currently have a standing Audit Committee, Compensation Committee, and Nominating and Corporate Governance Committee. The Board has adopted written charters for each of the committees, and copies of the charters are available on our website at www.acertx.com. Please note that the information contained on our website is not incorporated by reference in, or considered to be a part of, this proxy statement.

The current members of these committees are as follows:

C = Chair

Audit Committee

The Audit Committee of the Board currently consists of Ms. Griffin (chair), and Messrs. Amello and Dunn, each of whom is an independent, non-employee director. The Audit Committee selects, on behalf of our Board, an independent public accounting firm to audit our financial statements, discusses with the independent auditors their independence, reviews and discusses the audited financial statements with the independent auditors and management, recommends to our Board whether the audited financials should be included in our annual reports to be filed with the SEC, and oversees management’s identification, evaluation, and mitigation of major risks to the Company. The Audit Committee operates pursuant to a written charter. During the last fiscal year, the Audit Committee held fourfive meetings.

All of the members of the Audit Committee are non-employee directors who: (1) met the criteria for independence as required by Nasdaq listing standards and as set forth in Rule 10A-3(b)(1) under the Exchange Act;Exchange; (2) did not participate in preparation of our financial statements during the past three years; and (3) are able

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qualifies as an “audit committee financial expert” as defined in SEC rules and regulations and also possesses the financial sophistication and requisite experience as required under Nasdaq listing standards.

Compensation Committee

The Compensation Committee of the Board currently consists of Mr. Aselage (chair) and Ms. Griffin, each of whom is an independent director. The Compensation Committee reviews and approves (1) the annual salaries and other compensation of our executive officers and (2) individual stock and stock option grants. The Compensation Committee also provides assistance and recommendations with respect to our compensation policies and practices, and assists with the administration of our compensation plans. In evaluating executive officer compensation, the Compensation Committee considers recommendations from the Chief Executive Officer with respect to compensation of the other executive officers. From time to time and as it determines necessary or desirable, the Compensation Committee may retain the services of an independent compensation consultant to advise on compensation-related matters relating to the executive officers and independent directors. During the last fiscal year, the Compensation Committee held one meeting. In addition, the Compensation Committeedid not have a formal meeting and instead engaged in discussions, without formally meeting, to build consensus on various matters, with formal action thereafter taken by the Board.

The Board has established a Special Equity Grant Committee, the members of which are our President and Chief Executive Officer, Chris Schelling, our Chief Operating Officer and Chief Financial Officer, Harry S. Palmin, and our Chief Legal Officer, Donald R. Joseph. The Special Equity Grant Committee has been delegated the authority to make first-time option grants under our 2018 Stock Incentive Plan to employees (including new employees), other than to any member of our Board or to an officer at or above the level of vice president (whether or not designated as a “Section 16 officer”), within a specified range and subject to an overall cap as established by our Board.

Nominating and Corporate Governance Committee

The Nominating and Corporate Governance Committee of the Board currently consists of Messrs. Dunn (chair) and Aselage, each of whom was determined by the Board to be an independent director. The Nominating and Corporate Governance Committee assists our Board in fulfilling its responsibilities by: identifying and approving individuals qualified to serve as members of our Board, selecting director nominees for our annual meetings of stockholders, evaluating the performance of our Board, and developing and recommending to our Board corporate governance guidelines and oversight procedures with respect to corporate governance and ethical conduct. In identifying and evaluating candidates, the committee takes into consideration the criteria approved by the Board and such other factors as it deems appropriate. We do not have a formal diversity policy, and the committee considers a broad range of factors in evaluating prospective director nominees. These factors may include judgment, skill, diversity, experience with businesses and other organizations of comparable size, the interplay of the candidate’s experience with the experience of other Board members, and the extent to which the candidate would be a desirable addition to the Board and any committees of the Board. The Committee will consider properly submitted stockholder nominations for candidates for the Board. Following verification of the stockholder status of persons proposing candidates, recommendations will be aggregated and considered by the Committee. If any materials are provided by a stockholder in connection with the nomination of a director candidate, such materials will be forwarded to the Committee. During the last fiscal year, the Nominating and Corporate Governance Committee held one meeting. In addition, the Nominating and Corporate Governance Committee engaged in discussions without formally meeting, to build consensus on various matters, with formal action thereafter taken by the Board.

Risk Oversight

A fundamental part of risk management is not only understanding the risks a company faces and what steps management is taking to manage those risks, but also understanding what level of risk is appropriate for each company. Our Board is actively involved in oversight of risks that could affect Acer. The full Board has retained

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the responsibility for general oversight of risks, but the Audit Committee primarily oversees those risks that may directly or indirectly impact our financial statements. The Board’s role in the risk oversight process includes receiving reports from members of management and the Audit Committee on areas of material risk to Acer, including operational, financial, legal and regulatory, and strategic risks which enable it to better understand our risk identification, management and mitigation strategies.

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Additional Committee Chair Cash Compensation:

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AUDIT COMMITTEE REPORT

The Audit Committee of the Board of Directors currently consists of Ms. Griffin and Messrs. Amello and Dunn, all of whom are independent, non-employee directors.

The Audit Committee operates under a written charter adopted by the Board, which is evaluated annually. The Audit Committee selects, evaluates and, where deemed appropriate, replaces the Company’s independent auditors. The Audit Committee also pre-approves all audit services, engagement fees and terms, and all permitted non-audit engagements, except for certain de minimis amounts.

Management is responsible for the Company’s internal controls and the financial reporting process. The Company’s independent auditors are responsible for performing an independent audit of Acer’s consolidated financial statements in accordance with auditing standards generally accepted in the United States of America and issuing a report on Acer’s consolidated financial statements. The Audit Committee’s responsibility is to monitor and oversee these processes.

In this context, the Audit Committee has reviewed the Company’s audited financial statements for fiscal 20192020 and has met and held discussions with management and BDO USA, LLP, the Company’s independent auditors for fiscal 2019.2020. Management represented to the Audit Committee that the Company’s consolidated financial statements for fiscal 20192020 were prepared in accordance with accounting principles generally accepted in the United States of America, and the Audit Committee discussed the consolidated financial statements with the independent auditors. The Audit Committee also discussed with BDO USA, LLP the matters required to be discussed by Auditing Standard No. 16, Communications with Audit Committees, as adopted byapplicable standards of the Public Company Accounting Oversight Board (PCAOB).

BDO USA, LLP also provided to the Audit Committee the written disclosures and the letter required by applicable requirements of the PCAOB regarding the independent auditors’ communications with the Audit Committee concerning independence, and the Audit Committee discussed with BDO USA, LLP the accounting firm’s independence.

Based upon the Audit Committee’s discussion with management and BDO USA, LLP, and the Audit Committee’s review of the representation of management and the report of BDO USA, LLP to the Audit Committee, the Audit Committee recommended to the Board of Directors that the audited consolidated financial statements be included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 20192020 filed with the SEC.

Submitted by the Audit Committee of the

Board of Directors of Acer Therapeutics Inc.:

Michelle Griffin, Chair

Jason Amello

John M. Dunn

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PROPOSAL 2

RATIFICATION OF INDEPENDENT AUDITORS

The Audit Committee has selected BDO USA, LLP (“BDO”) as an independent registered public accounting firm to audit our financial statements for the year ending December 31, 2020,2021, and our Board has directed that management submit the selection of our independent registered public accounting firm for ratification by our stockholders at the Annual Meeting. BDO has served as our independent registered public accounting firm since March 7, 2019 and audited our financial statements for the fiscal year ended December 31, 2019. Previously, Wolf & Company, P.C. (“Wolf”) audited our financial statements for the fiscal years ended December 31, 20172019 and 2018. Wolf also served as the independent registered public accounting firm to Private Acer prior to the Merger.2020.

A representative of BDO is expected to be present at the Annual Meeting, will have an opportunity to make a statement if the representative desires but is not expected to do so, and is expected to be available to respond to appropriate questions.

Neither our bylaws nor other governing documents or law require stockholder ratification of the selection of BDO as our independent registered public accounting firm. However, we are submitting the selection of BDO to the stockholders for ratification as a matter of good corporate practice. If our stockholders fail to ratify the selection, our Audit Committee will reconsider whether or not to retain that firm. Even if the selection is ratified, our Audit Committee in its discretion may direct the appointment of different independent auditors at any time during the year if they determine that such a change would be in the best interests of the Company and our stockholders.

AuditPrincipal Accountant Fees and Services

The following table presents (i) the aggregate fees billed to us for the fiscal year ended December 31, 2019 by BDO, who has served as our independent registered public accounting firm since March 7, 2019 and who audited our financial statements for the fiscal yearyears ended December 31, 2019 and (ii) the aggregate fees billed to us for the fiscal year ended December 31, 20182020 by Wolf, who served as our independent registered public accounting firm prior to the selection of BDO and who audited our financial statements for the fiscal year ended December 31, 2018.BDO.

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services. Pre-approval is generally provided for up to one year and any pre-approval is detailed as to the particular service or category of services and is generally subject to a specific budget. The independent auditors and management are required to periodically report to the Board regarding the extent of services provided by the independent auditors in accordance with this pre-approval, and the fees for the services performed to date. The Board may also pre-approve particular services on a case-by-case basis. TheWhile the Audit CommitteeCommittee’s practice is to pre-approvedpre-approve 100% of any audit-related services, tax services, or other services provided by our independent auditors, there were no such services rendered during the last two fiscal years.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE RATIFICATION OF

THE SELECTION OF BDO USA, LLP AS OUR INDEPENDENT AUDITORS.

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EXECUTIVE OFFICERS

Our executive officers are elected by the BoardThe names of Directors and serve at the discretion of the Board. Ourour executive officers and their ages as of September 30, 2020April 15, 2021 are as follows:

Biographical information for our executive officers other than Mr. Schelling is set forth below:

Chris Schelling. Refer to “Director Nominees” section above for Mr. Schelling’s biographical information.

Jefferson E. Davis was appointed as our Chief Business Officer in February 2021. He previously served as our head of corporate development from July 2020 to January 2021 and as Acting Chief Business Officer of private Acer and then public Acer from December 2013 to October 2018. He served as Vice President of Corporate Development for Censa Pharmaceuticals Inc. from November 2019 until its acquisition by PTC Therapeutics Inc. in May 2020, and as a consultant from May 2015 to November 2019. Mr. Davis was employed by Extera Partners from April 2011 to July 2020, having served as a Partner from October 2014. In addition, he held senior business and corporate development roles at Genzyme, Archemix, ImmunoGen, GenVec, and Eli Lilly during the period of 1996 to 2011. Mr. Davis earned a B.S. in biochemistry from North Carolina State University and an M.B.A. from Duke University.

Donald R. Joseph has served as our Chief Legal Officer and Secretary since April 2018. He previously served as an advisor and consultant to biopharmaceutical and global health organizations. He has over twenty years of biopharmaceutical industry experience, including senior management positions in global health non-profit organizations. Mr. Joseph served as Chief Legal Officer and Board Secretary of Humanigen (previously known as KaloBios Pharmaceuticals, Inc.), a publicly listed company, from June 2013 to November 2015. Prior to Humanigen, he was Chief Executive Officer of BIO Ventures for Global Health, or BVGH, from February to November 2012 and Chief Operating Officer from April 2010 to January 2012. He is a former Chairman and Secretary and former member of the BVGH Board of Directors. He previously served as General Counsel, Corporate Secretary, and in other senior management roles at publicly held biopharmaceutical companies, including Abgenix and Renovis. Mr. Joseph has served since August 2017 as lead independent director of Achieve Life Sciences, a publicly traded pharmaceutical company. Before entering the life sciences industry, Mr. Joseph practiced business law for a number of years in major firms, including as an international partner at Baker & McKenzie. He received his J.D. degree from the University of Texas School of Law, with honors.

John R.M. Klopp has served as our Chief Technical Officer since September 2019. He previously served as our Vice President, Manufacturing from January 2018 to September 2019. Prior to joining Acer, Mr. Klopp served as Senior Director, Manufacturing Management for Ultragenyx Pharmaceutical Inc., a biopharmaceutical company, where he worked from March 2013 to January 2018. Mr. Klopp holds a B.S. degree in chemistry from Pennsylvania State University and an M.S. in chemistry from the University of California, Berkeley.

Harry S. Palmin has served as our Chief Financial Officer since the completion of the Merger in September 2017 merger of Opexa Therapeutics, Inc. and private Acer Therapeutics Inc., and was appointed to the additional position of Chief Operating Officer in September 2018. From December 2013 to February 2016, Mr. Palmin served as the President, Chief Executive Officer and a director of Privateprivate Acer, and from February 2016 to September 2017 he served as Privateprivate Acer’s acting Chief Financial Officer. Prior to joining Privateprivate Acer, he served in a variety of

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roles at Novelos Therapeutics, Inc., a pharmaceutical company, including as President and director from 1998 to October 2013, Chief Executive Officer from January 2005 to October 2013 and acting Chief Financial Officer from 1998 to September 2005. He has also held roles at Lehman Brothers and Morgan Stanley. Mr. Palmin earned a B.A. in economics from Brandeis University and an M.A. in international economics and finance from the Brandeis University International Business School.

Matthew T. Seibt has served as our Chief Commercial Officer since September 2019. He previously served as our acting Chief Commercial Officer from March 2019 to September 2019 and as our Vice President, Market Access and Reimbursement from April 2018 to March 2019. Prior to joining Acer, Mr. Seibt served as Director, Account Management, Market Access, and Reimbursement at Biogen Inc., a biotechnology company, from December 2014 to April 2018. Mr. Seibt holds a B.A. in Economics and Government from the University of Texas.

1416

EXECUTIVE COMPENSATION AND OTHER INFORMATION

Executive Officer Compensation

The following table sets forth certain information concerning compensation earned by or paid to certain persons who we refer to as our “Named Executive Officers” for services provided for the fiscal years ended December 31, 20192020 and 2018.2019.

2020 Summary Compensation Table

Narrative Disclosure to Summary Compensation Table

Our Board of Directors reviews compensation annually for all of the executive officers. Compensation awarded to Named Executive Officers in 20192020 and 20182019 generally consisted of base salary, discretionary cash bonuses and equity awards for options to purchase shares of our common stock or restricted stock units.stock. In setting executive compensation, our Board retained the services of Radford (which is a part of Aon Hewitt, a business unit of Aon plc) as an independent compensation consultant and considered compensation for comparable positions in the market, the historical compensation levels of the executives, individual performance as compared to its expectations and objectives, the desire to motivate employees to achieve short- and long-term results that are in the best interests

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and non-employee directors. In reviewing the reports prepared by Radford, for Private Acer, our Compensation Committee considered the independence of Radford pursuant to SEC rules and the corporate governance rules of the Nasdaq Capital Market and concluded that no conflict of interest exists that would prevent Radford from independently advising the Compensation Committee.

On February 22, 2018, we entered into an employment agreement with each of Messrs. Schelling and Palmin, and on April 20, 2018, we entered into an employment agreement with Mr. Joseph. The terms and conditions of such employment agreements are described below and are identical for each executive officer, other than in respect of each individual’s title, duties, salary and target bonus percentage as set forth below.

Pursuant to each individual’s employment agreement, each executive is compensated at an annual base rate and is eligible to receive an annual discretionary cash bonus of up to a target bonus percentage of his base salary (i.e., currently 55% for Mr. Schelling and 40% for each of the other executive officers) per 12-month period, based upon the achievement of corporate objectives established from time to time by our Board, and subject to review and adjustment from time to time as determined by the Board. In addition, each executive receives our standard benefits and insurance coverage as generally provided to our employees. Each executive’s employment is at-will and he serves as an executive officer at the discretion of our Board.

In the event the executive’s employment is terminated by us without Cause (as defined in the agreement) or due to a Constructive Termination (as defined in the agreement), in each instance during the period commencing one month prior to a Change in Control (as defined in the agreement) and terminating 12 months after such Change in Control, the executive will be entitled to (i) a payment, less applicable taxes and withholdings, equal to his then-current base salary for a period of 12 months plus (ii) 1x times his annual discretionary target bonus calculated for such period. In the event the executive’s employment is terminated by us without Cause or due to a Constructive Termination occurring outside of a Change in Control Period (as defined in the agreement), the executive will be entitled to a payment, less applicable taxes and withholdings, equal to his then-current base salary for a period of 12 months. The executive would receive any such payment in the form of a lump sum 60 days following such termination of employment. In addition, whether in the context of a Change in Control or otherwise, (x) if the executive elects to continue his health insurance coverage under COBRA, then we will reimburse the executive for the same portion of the executive’s monthly premium over such 12-month period as we are then paying for health insurance coverage for active employees, and (y) to the extent not otherwise addressed by any equity-based compensation arrangements, the executive will be entitled to 12 months of credited vesting beyond the employment termination date for any outstanding equity-based awards. The severance benefits are subject to the executive having been continuously employed through the termination event as well as executing and delivering a general release and waiver of claims in favor of us. The timing of any payments to the executive under the employment agreement are subject to applicable requirements of Section 409A of the Internal Revenue Code of 1986 and the related Treasury Regulations and may be delayed or reformed to comply with such provisions. In the event any payment or benefit the executive might be entitled to receive would constitute a “parachute payment” under Section 280G of the Internal Revenue Code, such payment or benefit will be reduced so as not to trigger excise tax under Section 4999 of such Code.

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2020 Outstanding Equity Awards at Fiscal Year-End

The following table presents information regarding outstanding equity awards atas of December 31, 20192020 for each of the Named Executive Officers.

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The shares of common stock issued in the private placement constitute “restricted securities” under the federal securities laws and are subject to a minimum six-month holding period. The private placement closed on July 29, 2020.

Securities Authorized for Issuance Under Equity Compensation Plans

The following table sets forth information, as of December 31, 2019,2020, with respect to our compensation plans under which common stock is authorized for issuance. These plans consist of our 2018 Stock Incentive Plan, 2013 Stock Incentive Plan, and 2010 Stock Incentive Plan. We believe that the exercise price for all of the options granted under these plans reflect at least 100% of fair market value on the dates of grant for the options at issue.

Equity Compensation Plan Information

1720

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

Beneficial Ownership

The following table sets forth, as of September 30, 2020,April 1, 2021, the number and percentage of outstanding shares of our common stock beneficially owned by: (a) each person who is known by us to be the beneficial owner of more than 5% of our outstanding shares of common stock; (b) each of our directors and nominees; (c) the Named Executive Officers; and (d) all current directors and executive officers as a group. As of September 30, 2020,April 1, 2021, there were 11,912,73114,310,244 shares of common stock issued and outstanding.

Beneficial ownership has been determined in accordance with Rule 13d-3 under the Exchange Act. Under this rule, certain shares may be deemed to be beneficially owned by more than one person (if, for example, persons share the power to vote or the power to dispose of the shares). In addition, shares are deemed to be beneficially owned by a person if the person has the right to acquire shares (for example, upon exercise of an option or warrant) within 60 days of the date as of which the information is provided. In computing the percentage ownership of any person, the number of shares is deemed to include the number of shares beneficially owned by such person by reason of such acquisition rights. As a result, the percentage of outstanding shares of any person as shown in the following table does not necessarily reflect the person’s actual voting power at any particular date.

To our knowledge, except as indicated in the footnotes to this table and pursuant to applicable community property laws, the persons named in the table have sole voting and investment power with respect to all shares of common stock shown as beneficially owned by them.

Beneficial Ownership Table

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A number of brokers with account holders who are our stockholders may be “householding” our proxy materials. If householding is in effect, a single proxy statement will be delivered to multiple stockholders sharing an address unless contrary instructions have been received from the affected stockholders. Once you have received notice from your broker that they will be “householding” communications to your address, “householding” will continue until you are notified otherwise or until you revoke your consent. If, at any time, you no longer wish to participate in “householding” and would prefer to receive a separate copy of the proxy statement and annual report, please notify your broker. Stockholders who currently receive multiple copies of the proxy statement and/or annual report at their address and would like to request “householding” of their communications should contact their broker. We will deliver a separate set of proxy materials promptly upon written or oral request from a stockholder. Please direct any such requests to Investor Relations, Acer Therapeutics Inc., One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458, or call Investor Relations at (844) 902-6100.

2023

OTHER BUSINESS

The Board knows of no other business to come before the Annual Meeting. However, if any other matters are properly brought before the Annual Meeting, the person named in the accompanying form of proxy or his or theirher substitutes will vote in their discretion on those matters.

By Order of the Board of Directors

Chris Schelling

President and Chief Executive Officer

October 14, 2020April 16, 2021

Newton, Massachusetts

WHETHER OR NOT YOU PLAN TO ATTEND THE VIRTUAL MEETING, PLEASE COMPLETE, SIGN, DATE, AND PROMPTLY RETURN THE ACCOMPANYING PROXY IN THE ENCLOSED ENVELOPE OR USE ONE OFVOTE BY INTERNET OR BY FOLLOWING THE VOTING METHODS DESCRIBED IN THE ATTACHED MATERIALS.INSTRUCTIONS ON YOUR VOTE INSTRUCTION FORM. YOU MAY REVOKE YOUR PROXY AT ANY TIME PRIOR TO THE ANNUAL MEETING. IF YOU DECIDE TO ATTEND THE VIRTUAL MEETING AND WISH TO CHANGE YOUR PROXY VOTE, YOU MAY DO SO AUTOMATICALLY BY VOTING ELECTRONICALLY AT THE MEETING.MEETING IF YOU ARE A STOCKHOLDER OF RECORD. IF YOUR SHARES ARE HELD OF RECORD BY A BROKER, BANK OR OTHER NOMINEE AND YOU WISH TO ATTEND AND VOTE AT THE MEETING, YOU MUST OBTAIN FROM THE RECORD HOLDER A LEGAL PROXY ISSUED IN YOUR NAME.

THANK YOU FOR YOUR ATTENTION TO THIS MATTER. YOUR PROMPT RESPONSE WILL GREATLY FACILITATE ARRANGEMENTS FOR THE ANNUAL MEETING.

If you need additional copies of this Proxy Statement or the enclosed proxy card, or if you have other questions about the proposals or how to vote your shares, you may contact our proxy solicitor:

ADVANTAGE PROXY

(877) 870-8565 (toll free)

2124

YOUR VOTE IS IMPORTANT. PLEASE VOTE TODAY.

Vote by Internet – QUICK ««« EASY

IMMEDIATE – 24 Hours a Day, 7 Days a Week or by Mail

		As a stockholder of Acer Therapeutics Inc., you have the option of voting your shares electronically through the Internet, eliminating the need to return the proxy card. Your electronic vote authorizes the named proxies to vote your shares in the same manner as if you marked, signed, dated and returned your proxy card. Votes submitted electronically over the Internet must be received by 11:59 p.m., Eastern Time, on November 18, 2020.May 20, 2021.
ACER THERAPEUTICS INC.
				INTERNET/MOBILE —
				https://www.cstproxyvote.com
				Use the Internet to vote your proxy. Have your proxy card available when you access the above website.website and enter your control number. Follow the prompts to vote your shares.
				Vote at the Meeting — If you plan to attend the virtual online Annual Meeting, you will need yourthe control number from your proxy card to vote electronically at the meeting. To attend: https://www.cstproxy.com/acertx/20202021
				MAIL – Mark, sign and date your proxy card and return it in the postage-paid envelope provided.

Important Notice Regarding the Availability of Proxy Materials

for the Annual

Meeting of Stockholders to be held on November 19, 2020:May 21, 2021:

Our 20202021 Proxy Statement and 20192020 Annual Report on Form 10-K are available

available at https://www.cstproxy.com/acertx/20202021

p FOLD HERE •● DO NOT SEPARATE •● INSERT IN ENVELOPE PROVIDED p

PROXY

THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

ACER THERAPEUTICS INC.

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON THURSDAY, NOVEMBER 19, 2020FRIDAY, MAY 21, 2021

The undersigned stockholder of Acer Therapeutics Inc. (the “Company”) hereby acknowledges receipt of the Notice of Annual Meeting of Stockholders and appoints each of Harry S. Palmin and Donald R. Joseph, each with full power of substitution, as proxy to vote as specified in this Proxy all the shares of common stock of the Company ofheld by the undersigned at the Annual Meeting of Stockholders of the Company to be held on November 19, 2020May 21, 2021 at 10:11:00 a.m. Eastern Time, via the Internet at https://www.cstproxy.com/acertx/2020.2021. Each such proxy or substitute shall have and may exercise all of the powers of said proxy hereunder. The undersigned stockholder hereby revokes any proxy or proxies heretofore executed for such matters.

THIS PROXY, WHEN PROPERLY EXECUTED, WILL BE VOTED IN THE MANNER AS DIRECTED HEREIN BY THE UNDERSIGNED STOCKHOLDER. IF NO DIRECTION IS MADE, THIS PROXY WILL BE VOTED FOR THE ELECTION OF THE NOMINEES IN PROPOSAL 1 AND FOR PROPOSAL 2, AND IN THE DISCRETION OF THE PROXIES AS TO ANY OTHER MATTERS THAT MAY PROPERLY COME BEFORE THE MEETING, INCLUDING ANY ADJOURNMENT OR POSTPONEMENT OF THE MEETING. THE UNDERSIGNED STOCKHOLDER MAY REVOKE THIS PROXY AT ANY TIME BEFORE IT IS VOTED BY DELIVERING TO THE SECRETARY OF THE COMPANY EITHER A WRITTEN REVOCATION OF THE PROXY OR A DULY EXECUTED PROXY BEARING A LATER DATE, OR BY VOTING ELECTRONICALLY AT THE ANNUAL MEETING.

(Continued, and to be marked, dated and signed, on the other side)