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

April 12, 201916, 2021

To Our Stockholders:

You are cordially invited to attend the Annual Meeting of Stockholders of Acer Therapeutics Inc. on Friday, May 17, 201921, 2021 at 10:11:00 a.m. Eastern Time. The meeting will be held atIn light of the Company’s headquarters, One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458.

Information aboutongoing developments related to the COVID-19 pandemic and to protect the health of our employees, stockholders and the community, the Annual Meeting including matters on whichwill be a completely virtual meeting of stockholders conducted via live audio webcast. You will act, may be found inable to attend the Notice of Annual Meeting and Proxy Statement accompanying this letter.via the Internet at https://www.cstproxy.com/acertx/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 in person 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 in person 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 MAY 17, 201921, 2021

The Annual Meeting of stockholders of Acer Therapeutics Inc. (the “Company”) will be held on Friday, May 17, 2019,21, 2021, at 10:11:00 a.m. Eastern Time,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 the Company’s headquarters, One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458.https://www.cstproxy.com/acertx/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 March 29, 2019April 1, 2021 can vote at this meeting or any adjournments or postponements that may take place. All stockholders are cordially invited to attend the meeting in person.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 in personelectronically 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 in person 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: April 12, 201916, 2021

ACER THERAPEUTICS INC.

PROXY STATEMENT

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD MAY 17, 201921, 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 Friday, May 17, 2019,21, 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 the company’s headquarters, One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458.https://www.cstproxy.com/acertx/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 April 12, 2019.16, 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 Form10-K

Accompanying this Proxy Statement is our Annual Report on Form10-K for the fiscal year ended December 31, 20182020 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 Form10-K, quarterly reports on Form10-Q, current reports on Form8-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 Form10-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

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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. If 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 person. Attendancefor virtual attendance at the Annual Meeting alone will not by itself, revoke ayour proxy.

Quorum, Abstentions and BrokerNon-Votes

Only stockholders of record at the close of business on March 29, 2019 (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 10,087,36314,310,244 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 in persononline 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 in person or by proxyand 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 “brokernon-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

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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 sevenfive members, each with a term expiring at the Annual Meeting. Two current directors, i.e., Hubert Birner, Ph.D., MBA, and Luc Marengere, Ph.D., have indicated an intention not to stand for reelection to the Board of Directors. The Nominating and Corporate Governance Committee of the Board has recommended, and the Board has nominated, the other 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 2020 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 are:and their ages as of April 15, 2021 are as follows:

Biographical information for our directors nominated for reelectiondirector 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 President andthe Chief Executive Officer of Travere Therapeutics, Inc. (formerly known as Retrophin, Inc.), a Nasdaq-listed, fully integrated 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 2013,2020, 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 focused on the development and commercialization of novel therapeutics for patients with kidney disease.company. From May 2012 to May 2013, heMr. Amello served as Executive Vice President, Chief Financial Officer and Treasurer of ZIOPHARM Oncology, Inc., a Nasdaq-listed biopharmaceutical company focused on the discovery and development of new cancer therapies.company. From April 2000 to June 2011, Mr. Amellohe held various positions at Genzyme Corporation, a

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then Nasdaq-listed biotechnology company, focused on development of therapeutics for multiple diseases and disorders, most recently as Senior Vice President, Corporate Controller, and Chief Accounting Officer. Earlier in his career, Mr. Amello spent 10 years

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

Directors Not Continuing in Office

Current directors who are not standing for reelection to the Board of Directors at the Annual Meeting are:

Biographical information for our current directors who are not standing for reelection to the Board of Directors at the Annual Meeting is set forth below. The decisions of these current directors not to stand for reelection were not due to any disagreement with the Company on any matter.

Hubert Birner, Ph.D., MBA has served as a director since the completion of the Merger in September 2017. From April 2017 until the Merger, Dr. Birner served as a member of Private Acer’s Board of Directors. Since 2000, he has served in a variety of roles for TVM Capital, an independent affiliation of international private equity and venture capital firms, where he currently serves as the Managing Partner of TVM Capital and TVM Life Science Management. Dr. Birner currently serves as the Chairman of the Boards of Directors of Argos Therapeutics, Inc., a Nasdaq-listed immuno-oncology company, and NOXXON Pharma N.V., a EuroNext Growth Paris-listed biopharmaceutical company, and as a member of the Board of Directors of Proteon Therapeutics, Inc., a Nasdaq-listed biopharmaceutical company, as well as a number of privately held life science companies. Prior to his tenure at TVM Capital, Dr. Birner held roles at Zeneca Group PLC and McKinsey & Company. He served as the Vice Chairman of Evotec AG, a Frankfurt Stock Exchange-listed company focused on the discovery and development of small molecule drugs, from 2005 to 2013, and as a director of Probiodrug AG, a Euronext Amsterdam-listed biopharmaceutical company, from 2014 to 2015. Dr. Birner earned a Ph.D. in biochemistry from Ludwig-Maximilian University of Munich and an MBA from Harvard Business School.

Luc Marengere, Ph.D.has served as a director since the completion of the Merger in September 2017. From April 2016 until the Merger, Dr. Marengere served as a member of Private Acer’s Board of Directors. He serves as Managing Partner of TVM Life Science Venture VII, L.P., a venture capital fund, which he joined in March 2012. From October 2001 to March 2012, Dr. Marengere was a Managing General Partner with VG Partners, a merchant bank. He serves on the Boards of Directors of a number of privately held life science companies. From January 2015 to March 2017, Dr. Marengere served on the Board of Directors of CoLucid Pharmaceuticals, Inc., a Nasdaq-listed biopharmaceutical company. He has also held roles at CDP Capital – Technology Ventures and MDS Capital Corp. Dr. Marengere earned a Ph.D. from the University of Toronto, an M.S. in endocrinology from Queen’s University and a B.S. in biochemistry from the University of Ottawa.

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 20182020 annual meeting. During the year ended December 31, 2018,2020, the Board held fiveseven 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 Drs. Birner and Marengere, 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

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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), Dr. Marengere 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

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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.

Board Leadership Structure

The Board does not have a policy on whether the same person should serve as both the chief executive officer and chairman of the Board or, if the roles are separate, whether the chairman should be selected from thenon-employee directors or should be an employee. The Board believes that it should have the flexibility to make these determinations at any given point in time in the way that it believes best to provide appropriate leadership for the Company at that time. The Board believes that its current leadership structure, with Mr. Aselage serving as anon-employee Chairman of the Board and Mr. Schelling serving as Chief Executive Officer, is in the best interest of stockholders at this time. The current structure ensures a greater role for the independent directors in the oversight of the Company and active participation of the independent directors in setting agendas and establishing priorities and procedures for the work of the Board.

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Additional Committee Chair Cash Compensation:

Additional Committee Member 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 alsopre-approves all audit services, engagement fees and terms, and all permittednon-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 20182020 and has met and held discussions with management and Wolf & Company, P.C.,BDO USA, LLP, the Company’s independent auditors for fiscal 2018.2020. Management represented to the Audit Committee that the Company’s consolidated financial statements for fiscal 20182020 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 Wolf & Company, P.C.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).

Wolf & Company, P.C.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 Wolf & Company, P.C.BDO USA, LLP the accounting firm’s independence.

Based upon the Audit Committee’s discussion with management and Wolf & Company, P.C.,BDO USA, LLP, and the Audit Committee’s review of the representation of management and the report of Wolf & Company, P.C.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 Form10-K for the fiscal year ended December 31, 20182020 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

APPROVAL OFNON-BINDING ADVISORY VOTE ON EXECUTIVE COMPENSATION

TheDodd-Frank Wall Street Reform and Consumer Protection Act of 2010, or theDodd-Frank Act, requires that we provide our stockholders with the opportunity to vote to approve, on a nonbinding, advisory basis, the compensation of our named executive officers as disclosed in this Proxy Statement in accordance with the compensation disclosure rules of the SEC.

As described under the heading “Executive Compensation and Other Information – Executive Officer Compensation,” our executive compensation programs are designed to attract, motivate and retain our named executive officers, who are critical to our success. Under these programs, our named executive officers are rewarded for the achievement of annual,long-term and strategic goals and corporate objectives, and the creation of increased stockholder value. The Compensation Committee, which is comprised of independent directors, continually reviews the compensation programs for our named executive officers to ensure they achieve the desired goals of aligning our executive compensation structure with our stockholders’ interests and current market practices.

We are asking our stockholders to indicate their support for our named executive officer compensation as described in this Proxy Statement. This proposal, commonly known as a“say-on-pay” proposal, gives our stockholders the opportunity to express their views on our named executive officers’ compensation for the year ended December 31, 2018. This vote is advisory, which means that the vote on executive compensation is not binding on us, our Board of Directors or the Compensation Committee of the Board of Directors. This vote is not intended to address any specific item of compensation, but rather the vote relates to the compensation of our named executive officers as a whole, as described in this Proxy Statement in accordance with the compensation disclosure rules of the SEC. Accordingly, we will ask our stockholders to vote for the following resolution at the Annual Meeting:

“RESOLVED, that the Company’s stockholders approve, on anon-binding advisory basis, the compensation of the named executive officers, as disclosed in the Company’s Proxy Statement for the 2019 Annual Meeting of Stockholders pursuant to the compensation disclosure rules of the Securities and Exchange Commission, including the Summary Compensation Table and the other related tables and disclosure.”

THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” APPROVAL, ON ANON-BINDING ADVISORY BASIS, OF THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS.

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services.Pre-approval is generally provided for up to one year and anypre-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 thispre-approval, and the fees for the services performed to date. The Board may alsopre-approve particular services on acase-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

OurThe names of our executive officers are elected by the Board of Directors and serve at the discretion of the Board. Our executive officerstheir ages as of March 29, 2019April 15, 2021 are as follows:

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

William T. Andrews, M.D., FACPChris Schelling. Refer to “Director Nominees” section above for Mr. Schelling’s biographical information.

Jefferson E. Davis haswas appointed as our Chief Business Officer in February 2021. He previously served as our Chief Medical Officer since October 2017. Prior to joining the Company, Dr. Andrews provided strategic consulting services to rare disease companieshead of corporate development from April 2016 to September 2017. Prior to that, he served Aegerion Pharmaceuticals, Inc., a biopharmaceutical company, as Senior Vice President, Business Development, from May 2014July 2020 to January 2016,2021 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 Medical Affairs,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 20122011 to MayJuly 2020, having served as a Partner from October 2014. He has alsoIn addition, he held senior business and corporate development roles at Santhera Pharmaceuticals, Sepracor, Inc.Genzyme, Archemix, ImmunoGen, GenVec, and ClinQuest, Inc. PriorEli Lilly during the period of 1996 to joining the biopharmaceutical industry over 15 years ago, Dr. Andrews practiced medicine for seven years full-time and 11 years part-time2011. Mr. Davis earned a B.S. in the Boston area as a board-certified internistbiochemistry from North Carolina State University and an attending physician at Brigham and Women’s Hospital and was on the clinical faculty at Harvard Medical School. Dr. Andrews earned a B.A. in biologyM.B.A. from Harvard University and a Ph.D. from Yale University School of Medicine.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 healthnon-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 currentformer 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 currently serveshas 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 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 aan 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.

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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, 2020 and 2019.

20182020 Summary Compensation Table

Narrative Disclosure to Summary Compensation Table

Our Board of Directors reviews compensation annually for all of ourthe executive officers. Compensation awarded to Named Executive Officers in 20182020 and 20172019 generally consisted of base salary, discretionary cash bonuses and equity awards for options to purchase shares of our common stock. In setting executive compensation, our Board of Directors 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 of our stockholders, and a long-term commitment to our company. We do not target a specific competitive position or a specific mix of compensation among elements of compensation. Prior to the September 2017 Merger, Private

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andnon-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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20182020 Outstanding Equity Awards at FiscalYear-End

The following table presents information regarding outstanding equity awards atas of December 31, 20182020 for each of the Named Executive Officers.

Certain Relationships and Related Party Transactions

Transactions with Related Persons

Since January 1, 2018,2020, we have engaged in nothe following reportable transactions with our directors, executive officers, beneficial holders of more than 5% of our voting securities, and affiliates or their immediate family members.members:

On July 24, 2020, we entered into a securities purchase agreement for the sale and issuance of an aggregate of 244,998 shares of our common stock, for an aggregate purchase price of $857,493, in a private placement transaction at a price per share of $3.50, which represented a 5.7% premium to the $3.31 closing price of the common stock on that day. The shares were purchased by the following directors, executive officers and employees:

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, 2018,2020, 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

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

Beneficial Ownership

The following table sets forth, as of March 29, 2019,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 March 29, 2019,April 1, 2021, there were 10,087,36314,310,244 shares of common stock issued and outstanding.

Beneficial ownership has been determined in accordance with Rule13d-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.

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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

April 12, 201916, 2021

Newton, Massachusetts

WHETHER OR NOT YOU PLAN TO ATTEND THE ANNUALVIRTUAL 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 ANNUALVIRTUAL MEETING AND WISH TO CHANGE YOUR PROXY VOTE, YOU MAY DO SO AUTOMATICALLY BY VOTING IN PERSONELECTRONICALLY 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 IN PERSON 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)

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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 Internetelectronic 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 May 16, 2019.20, 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 the control number from your proxy card to vote electronically at the meeting. To attend: https://www.cstproxy.com/acertx/2021
				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 May 17, 2019:21, 2021:

Our 2021 Proxy Statement and 20182020 Annual Report on Form10-K are available

available at: at https://www.cstproxy.com/acertx/20192021

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

PROXY

THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

ACER THERAPEUTICS INC.

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON FRIDAY, MAY 17, 201921, 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 May 21, 2021 at 11:00 a.m. Eastern Time, via the Company’s headquarters, One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458.Internet at https://www.cstproxy.com/acertx/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 PROPOSALSPROPOSAL 2, AND 4, EVERY THREE YEARS ON PROPOSAL 3, 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 APPEARINGVOTING ELECTRONICALLY AT THE ANNUAL MEETING AND VOTING IN PERSON.MEETING.

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