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)all boxes that apply):

ACER THERAPEUTICS INC.

ONE GATEWAY CENTER, SUITE 351356

300 WASHINGTON STREET

NEWTON, MASSACHUSETTS 02458

OctoberApril 14, 20202023

To Our Stockholders:

You are cordially invited to attend the Annual Meeting of Stockholders of Acer Therapeutics Inc. on Thursday, NovemberFriday, May 19, 20202023 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, theThe Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast.webcast to provide a safe and convenient experience for our stockholders. 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.2023.

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,

/s/ Chris Schelling

Chris Schelling

Founder, President and Chief Executive Officer

ACER THERAPEUTICS INC.

ONE GATEWAY CENTER, SUITE 351 356

300 WASHINGTON STREET

NEWTON, MASSACHUSETTS 02458

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD NOVEMBERMAY 19, 20202023

The Annual Meeting of stockholders of Acer Therapeutics Inc. (the “Company”) will be held on Thursday, NovemberFriday, May 19, 2020,2023, 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, theThe Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast.webcast to provide a safe and convenient experience for our stockholders. 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.2023. 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 SeptemberMarch 30, 20202023 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,

/s/ Chris Schelling

Chris Schelling

Founder, President and Chief Executive Officer

Dated: OctoberApril 14, 20202023

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 NovemberMay 19, 2020:2023: This Proxy Statement and our 20192022 Annual Report on Form 10-K are available at https://www.cstproxy.com/acertx/20202023

ACER THERAPEUTICS INC.

PROXY STATEMENT

ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD NOVEMBERMAY 19, 20202023

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, NovemberFriday, May 19, 2020,2023, 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/2020.2023. 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 OctoberApril 14, 2020.2023.

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, 20192022 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 351,356, 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 18, 2023. 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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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

The Annual Meeting will be a completely virtual meeting of stockholders conducted via live audio webcast to provide a safe and convenient experience for our stockholders. 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, March 30, 2023, 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/2023 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.

Submission of Questions at the Virtual Annual Meeting

An online portal will be available to our stockholders at https://www.cstproxy.com/acertx/2023 for the Annual Meeting. By accessing this portal, stockholders will be able to submit questions in advance or at the

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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 2023 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 356, 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 SeptemberMarch 30, 2020 (the “Record Date”)2023 will be entitled to notice of and to vote at the virtual Annual Meeting. As of the Record Date,record date, there were 11,912,73123,421,534 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 entitled to vote present in person or represented and presentby proxy 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.

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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Brokers, banks and nominees do not have discretionary voting authority on certain non-routine matters and accordingly may not vote on such matters absent instructions from the beneficial holder. Discretionary items are proposals considered “routine” under the rules of the New York Stock Exchange (also applicable to Nasdaq-listed companies), such as the ratification of the appointment of our independent auditors.registered public accounting firm. Non-routine items for which brokers, banks and nominees do not have discretionary voting power include the election of directors.

If you hold your shares in street name or through a broker, bank or other nominee, it is important that you direct your broker how to vote your shares.

Vote Required

Proposal 1. Directors are elected by a plurality of the affirmative votes cast by those shares of common stock present, or represented by proxy, and entitled to vote at the virtual Annual Meeting. This means the five nominees for director receiving the highest number of affirmative votes will be elected. Proxies marked “Withhold Authority” will not affect the election of a candidate who receives a plurality of votes. The election of directors is a matter on which a broker, bank or other nominee is generally not empowered to vote using discretion, and therefore, broker non-votes may exist but will have no effect on the outcome of the election of nominees for director. Stockholders may not cumulate votes in the election of directors. We urge you to provide any necessary voting instructions to your broker, bank or nominee if you hold your shares in street name in order for your vote to be considered for this proposal.

Proposal 2. Approval of Proposal 2 (i.e., the ratification of the appointment of the independent auditors)registered public accounting firm) requires the affirmative vote of a majority of the shares of stock entitled to vote present in person or represented by proxy at the Annual Meeting. This means that a majority of the shares represented at the Annual Meeting must be voted “for” the proposal for it to be approved. Abstentions will have the same effect as a vote “against” this proposal. Proposal 2 is a matter on which a broker, bank or other nominee is generally empowered to vote, and therefore, broker non-votes are not expected to exist with respect to this proposal. Abstentions will not affect the outcome.

Attendance at the Virtual 2020 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.

The live audio webcast of the 2020 Annual Meeting will begin promptly at 10:00 a.m. Eastern Time. Online access to the audio webcast will open approximately 15 minutes prior to the start of the 2020 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.

To attend the 2020 Annual Meeting, stockholders will need to log-in to 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.

Submission of Questions at the Virtual 2020 Annual Meeting

An online portal will be available to our stockholders at https://www.cstproxy.com/acertxt/2020 at the 2020 Annual Meeting. By accessing this portal, stockholders will be able to submit questions and vote at the 2020 Annual Meeting. Stockholders may also submit questions and vote on the day of, or during, the 2020 Annual Meeting at https://www.cstproxy.com/acertx/2020. To demonstrate proof of stock ownership, you will need to enter the control number on your proxy card to submit questions and vote at our 2020 Annual Meeting. 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 2020 Annual Meeting, as time permits. Questions and answers will be grouped by topic and substantially similar questions will be answered only once.

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For a proposal by a stockholder not seekingor a director nomination to havebe properly brought before the proposal included in the proxy statement but seeking to have the proposal considered at our next annual meeting, pursuant to our bylaws, such stockholder must provide written notice of such proposal or director nomination so that it is received by our Secretary at our principal executive 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, stockholdersThe stockholder’s notice must set forth, as to each proposed matter, the information required by our bylaws. For director nominations, information required by our bylaws to be in the notice include the name and contact information for the candidate and the person making the nomination and other information about the nominee and the person making the nomination that must be disclosed in proxy solicitations under Section 14 of the Securities Exchange Act of 1934 and the related rules and regulations under that Section.

Stockholders must comply in all respects with the rules and regulations of the SEC then in effect and the requirements of our bylaws. In addition, stockholders who intend to solicit proxies in support of director nominees other than the Company’s nominees must also provide notice that sets forth the information required by Rule 14a-19 of the Exchange Act, no later than March 20, 2024.

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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 Meeting2024 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 14, 2023 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. (“Opexa”) (Nasdaq: OPXA), a biotechnology company, and private Acer. From October 2015 until the Merger,merger, Mr. Aselage served as the Chairman of Privateprivate Acer’s Board of Directors. Most recently, he was the Chief Executive Officer of Travere Therapeutics, Inc. (“Travere Therapeutics”) (formerly known as Retrophin, Inc.) (Nasdaq: TVTX), a Nasdaq-listed, biopharmaceutical company, from November 2014 until his retirement in January 2019, and remains a member of its Boardboard of Directors sincedirectors from October 2012.2012 to May 2022. From May 2014 to November 2014, Mr. Aselage served as the Chief Operations Officer and interim Chief Executive Officer of Retrophin.Travere Therapeutics. Prior to joining Retrophin,Travere Therapeutics, he held a variety of roles at BioMarin Pharmaceutical Inc. (“BioMarin”) (Nasdaq: BMRN), 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. (“Cell Therapeutics”) (Nasdaq: CTIC), Sangstata company that focuses on development, acquisition, and commercialization of drugs for the treatment of cancer, SangStat Medical Corporation, a biotechnology company, Advanced Tissue Sciences, Inc., a leading tissue engineering company, and Genentech, Inc., a biotechnology company. 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 Boardboard of Directorsdirectors at BioCryst Pharmaceuticals, Inc. (Nasdaq: BCRX), a pharmaceutical company, since January 2019, and at Acuitas Therapeutics, Inc., a biotechnology company. 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 and private Acer. Since September 2020,2022, Mr. Amello has served as Chief Financial Officer of Candel Therapeutics, Inc. (Nasdaq: CADL), a biopharmaceutical company. From September 2020 to September 2022, Mr. Amello served as Chief

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Financial Officer of Saniona AB, a rare disease biopharmaceutical company listed on Nasdaq Stockholm Small Cap.company. From September 2013 to August 2020, he served as Senior Vice President, Chief Financial Officer and Treasurer of Akebia Therapeutics, Inc. (Nasdaq: AKBA), 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 then Nasdaq-listed biotechnology company, most recently, from December 2008 to June 2011, as Senior Vice President, Corporate Controller, and

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Chris Schelling has served as a director and as our President and Chief Executive Officer since the completion of the Merger in September 2017.2017 merger of Opexa and private Acer. Mr. Schelling founded Privateprivate Acer Therapeutics Inc. in December 2013 and served as a director from that time until the Merger.2017 merger. From December 2013 to February 2016, he served as Privateprivate Acer’s Chief Operating Officer, and from February 2016 until the Merger,merger, he served as Privateprivate Acer’s President and Chief Executive Officer. Prior to founding Privateprivate Acer, he served as Executive Director of Strategic Marketing at BioMarin Pharmaceutical Inc., a Nasdaq-listed biotechnology company, from May 2006 to October 2012. Mr. Schelling also founded Censa Pharmaceuticals Inc. (“Censa”), a biopharmaceutical company, in 2015 and currently servesserved as a director.director until the acquisition by PTC Therapeutics Inc., a biopharmaceutical company, in May 2020. He has also served as a director at Cascade Prodrug, Inc., a developer of chemotherapy technology, since June 2017. He has also held roles at Abgenix, Inc. (“Abgenix”), a biopharmaceutical company, Cell Therapeutics, Inc., Stanford Research Institute Consulting, a non-profit research institute, and Organon.Organon & Co. (NYSE: OGN), a pharmaceutical company. Mr. Schelling earned a B.A. degrees in biology and history from Carroll College. We believe that Mr. Schelling’s role in the founding of Acer, his experience as Acer’s Chief Executive Officer and his experience in the biotechnology industry qualify him to serve on our Board of Directors.Board.

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THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE ELECTION OF EACH OF THE DIRECTOR NOMINEES SET FORTH 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 20192022 annual meeting. During the year ended December 31, 2019,2022, the Board held sevennine 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.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 (chair) and Dunn and Ms. Griffin, 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 auditorsregistered public accounting firm their independence, reviews and discusses the audited financial statements with the independent auditorsregistered public accounting firm 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 foursix 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; (2) did not participate in preparation of our financial statements during the past three years; and (3) are able

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to read and understand fundamental financial statements, including a balance sheet, income statement, and cash flow statement. The Board of Directors has determined that Ms. Griffin and Messrs. Amello and Dunn each, individually, 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. AselageMs. Griffin (chair) and Ms. Griffin,Mr. Aselage, 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 Committee 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 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 committeeNominating and Corporate Governance 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 committeeNominating and Corporate Governance 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 Nominating and Corporate Governance 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 Nominating and Corporate Governance 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 Nominating and Corporate Governance 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.

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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 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, cybersecurity, legal and regulatory, and strategic risks which enable it to better understand our risk identification, management and mitigation strategies.

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Board Diversity Matrix

The following matrix discloses the gender and demographic backgrounds of our Board as self-identified by its members in accordance with Nasdaq Listing Rule 5606.

2022 Director Compensation

The following table presents summary information regarding compensation of the non-employee members of our Board of Directors who served during any part of the fiscal year ended December 31, 2019.2022.

Standard Compensation Arrangements

Independent directors receive compensation for their service on our Board of Directors that consists of cash compensation and equity awards as described below. A director who is also our employee does not receive any additional compensation for services as a member of our Board. We reimburse our directors for travel and lodging expenses in connection with their attendance at Board and committee meetings. Our annualstandard compensation arrangements consist of the following:

Board Member Cash Compensation:

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Additional Committee Chair Cash Compensation:

9

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.registered public accounting firm. 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 auditorsregistered public accounting firm 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 20192022 and has met and held discussions with management and BDO USA, LLP, the Company’s independent auditorsregistered public accounting firm for fiscal 2019.2022. Management represented to the Audit Committee that the Company’s consolidated financial statements for fiscal 20192022 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.registered public accounting firm. 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). and the SEC.

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’registered public accounting firm’s 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, 20192022 filed with the SEC.

Submitted by the Audit Committee of the

Board of Directors of Acer Therapeutics Inc.:

Michelle Griffin, Chair

Jason Amello, Chair

John M. Dunn

Michelle Griffin

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PROPOSAL 2

RATIFICATION OF INDEPENDENT AUDITORSREGISTERED PUBLIC ACCOUNTING FIRM

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, 2020,2023, 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, 2020, 2021, and 2018. Wolf also served as the independent registered public accounting firm to Private Acer prior to the Merger.2022.

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 auditorsregistered public accounting firm 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 yearyears ended December 31, 20192022 and 2021 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 year ended December 31, 2019, and (ii) the aggregate fees billed to us for the fiscal year ended December 31, 2018 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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Policy on Audit Committee Pre-Approval and Permissible Non-Audit Services of Independent AuditorsRegistered Public Accounting Firm

The Board’s policy is to pre-approve all audit and permissible non-audit services provided by the independent auditors.registered public accounting firm. These services may include audit services, audit-related services, tax services and other 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 auditorsregistered public accounting firm and management are required to periodically report to the Board regarding the extent of services provided by the independent auditorsregistered public accounting firm 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 Committee pre-approvedCommittee’s practice is to pre-approve 100% of any audit-related services, tax services, or other services provided by our independent auditorsregistered public accounting firm, 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.REGISTERED PUBLIC ACCOUNTING FIRM

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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 14, 2023 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 from November 2019 until its acquisition by PTC Therapeutics Inc. (Nasdaq: PTCT), a pharmaceutical company, in May 2020, and as a consultant from May 2015 to November 2019. Mr. Davis was employed by Extera Partners, an advisory and new venture creation firm in the life science industry, 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 Corporation, a biotechnology company, from January 2006 to May 2011, Archemix, a biotechnology company, from December 2003 to January 2006, ImmunoGen, Inc., (Nasdaq: IMGN), a biotechnology company, from October 2001 to December 2003, GenVec, Inc., a biotechnology company, from March 1998 to November 2001, and Eli Lilly and Company (NYSE: LLY), a pharmaceutical company, from March 1996 to February 1998. Mr. Davis earned a B.S. in biochemistry from North Carolina State University and an M.B.A. from Duke University.

Tanya Hayden was appointed as our Chief Operating Officer in June 2022. She previously served as our Vice President of Program and Strategic Alliance Management from June 2021 to June 2022. Prior to joining the Company, Ms. Hayden served as the Director of Operational Excellence at Lonza Group Ltd., a biotechnology research company, from April 2018 to June 2021, and as Director, Value Chain Management from November 2018 to May 2021. Prior to that, she served most recently as Vice President of Manufacturing at Bend Research Inc. – Capsugel, a pharmaceutical manufacturing company, from January 2014 to April 2018. Ms. Hayden received a B.S. degree in Chemistry from Gonzaga 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, Inc. (“Humanigen”) (Nasdaq: HGEN) (previously known as KaloBios Pharmaceuticals, Inc.), a publicly listedbiopharmaceutical company, from June 2013 to November 2015. Prior to Humanigen, he was Chief Executive Officer of BIO Ventures for Global Health or BVGH,(“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 from January 2005 to March 2006 and Renovis.Renovis, Inc., a biopharmaceutical company, from May 2006 to December 2006. Mr. Joseph has served since August 2017 as lead independent director of Achieve Life Sciences, Inc. (Nasdaq: ACHV), a publicly traded pharmaceutical

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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. (Nasdaq: RARE), 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 and private Acer and was appointed to the additional position of Chief Operating Officer infrom September 2018.2018 to June 2022. 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 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 Bernie Paulhas served was appointed as our Chief CommercialPeople Officer since September 2019.in January 2022. He previously served as our acting Chief Commercial OfficerVice President, Human Resources from MarchMay 2019 to September 2019 and as our Vice President, Market Access and Reimbursement from April 2018 to March 2019.January 2021. Prior to joining Acer, Mr. SeibtPaul served as Director, Account Management, Market Access,an advisor and Reimbursementconsultant to various corporations from December 2017 to May 2019. Mr. Paul served as Vice President of Human Resources at BiogenClarisonic, Inc., a skin care device production company, (acquired by L’Oréal Inc.) from June 2011 to December 2017. Earlier in his career, he served as Vice President Human Resources at Trubion Pharmaceuticals, Inc., a biopharmaceutical company, (acquired by Emergent BioSolutions Inc. (NYSE: EBS)) from May 2006 to March 2011 and as Vice President of Human Resources at Corixa Corporation, a biotechnology company, (acquired by GSK plc (NYSE: GSK)) from March 1995 to February 2006. Mr. Paul earned a B.S. in Education from Montana State University at Billings and an M.S. in Education from the State University of New York at Buffalo.

Adrian Quartel was appointed as our Chief Medical Officer in February 2022. He previously oversaw all scientific and medical functions as Chief Medical Officer at Adamas Pharmaceuticals, Inc., a biotechnology company, from December 2014September 2020 to April 2018. Mr. Seibt holdsFebruary 2022. From June 2017 to September 2020, he served as the Group Vice President, Global Medical Affairs at BioMarin. Prior to BioMarin, Dr. Quartel held senior medical leadership roles where he was responsible for clinical development, pharmacovigilance, and medical affairs at Astellas Pharma Inc. from January 2004 to September 2006, at Chiltern, a B.A.specialist contract research organization, from September 2006 to July 2007, and at ICON plc (Nasdaq: ICLR), a clinical research organization, from August 2001 to January 2004. Earlier in Economicshis career, Dr. Quartel worked as a clinical research fellow at UCLA Cedar Sinai and Governmentas a resident in cardio-thoracic surgery at Erasmus University Medical Center. Dr. Quartel received an M.D. from Erasmus University Medical School, Rotterdam, in the Netherlands, and a post graduate specialization in pharmaceutical medicine from the UniversityFaculty of Texas.Pharmaceutical Medicine in London. He is board certified by the General Medical Council (GMC) in pharmaceutical medicine in the United Kingdom.

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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” or “NEOs” for services provided for the fiscal years ended December 31, 20192022 and 2018.2021.

2022 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 20192022 and 20182021 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 previously 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

15

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.

2022 Outstanding Equity Awards at Fiscal Year-End

The following table presents information regarding outstanding equity awards at December 31, 20192022 for each of the Named Executive Officers.

20

16

Equity Compensation Plan Information

Pay Versus Performance Table

The following table shows the total compensation for our Named Executive Officers for the past two fiscal years as set forth in the Summary Compensation Table, the “compensation actually paid” to our Chief Executive Officer (Chris Schelling), and on an average basis, our other Named Executive Officers (in each case, as determined under SEC rules), our total stockholder return (“TSR”) and our net income.

1722

The valuation assumptions and processes used to recalculate fair values did not materially differ from those disclosed at the time of grant.

(d) “Compensation actually paid” does not necessarily represent cash and/or equity value transferred to the applicable Named Executive Officer without restriction, but rather is a value calculated under applicable SEC rules.

Narrative Disclosure to Pay Versus Performance Table

The charts below show the relationship of “compensation actually paid” to (i) the Company’s TSR; and (ii) the Company’s net income. The following graphs illustrate the alignment between compensation actually paid to our Named Executive Officers and the Company’s performance. Specifically, a large portion of the Named Executive Officers’ compensation is reliant on TSR and as such the Chief Executive Officer and other Named Executive Officers’ “compensation actually paid” each year was aligned with our TSR performance and increased when our TSR performance increased but declined when our TSR performance declined.

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24

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

Beneficial Ownership

The following table sets forth, as of SeptemberMarch 30, 2020,2023, 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) theour Named Executive Officers; and (d) all current directors and executive officers as a group. As of SeptemberMarch 30, 2020,2023 there were 11,912,73123,421,534 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

25

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Delinquent Section 16(a) Reports

Section 16(a) of the Exchange Act requires our directors and executive officers, and persons who beneficially own more than 10% of a registered class of our equity securities, to file with the SEC initial reports of ownership and reports of changes in ownership. These reporting persons are required by SEC regulations to furnish us with copies of all such reports they file. To our knowledge, based solely on our review of the copies of such reports furnished to us and written representations from certain insiders that no other reports were required, we believe that all of the reporting persons complied with all applicable Section 16(a) filing requirements applicable to them with respect to transactions during the fiscal year ended December 31, 20192022 except oneas follows: Mr. Paul filed a Form 4 reporting the grant ofon January 21, 2022 with respect to an employee stock option for each of the following executive officersacquisition that was due on September 20, 2019 and wasrequired to be filed on September 23, 2019: Harry S. Palmin, William T. Andrews, Donald R. Joseph, and Matthew T. Seibt; and one Form 4 that was due on September 20, 2019 and filed on September 25, 2019 for John M. Klopp.by January 19, 2022.

HOUSEHOLDING

The SEC has adopted rules that permit companies and intermediaries (e.g., brokers) to satisfy the delivery requirements for proxy statements and annual reports with respect to two or more stockholders sharing the same address by delivering a single proxy statement addressed to those stockholders. This process, which is commonly referred to as “householding,” potentially means extra convenience for stockholders and cost savings for companies.

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 351,356, 300 Washington Street, Newton, Massachusetts 02458, or call Investor Relations at (844) 902-6100.

2027

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,

/s/ Chris Schelling

Chris Schelling

Founder, President and Chief Executive Officer

OctoberApril 14, 20202023

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)

2128

YOUR VOTE IS IMPORTANT. PLEASE VOTE TODAY.

Vote by Internet – QUICK ««« EASY

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

ACER THERAPEUTICS INC.				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 NovemberMay 18, 2020.2023.
							ACER THERAPEUTICS INC.
				INTERNET/MOBILE —
		INTERNET – https://www.cstproxyvote.com
						Use the Internet to vote your proxy. Have your proxy card available when you access the above website. 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/20202023
PLEASE DO NOT RETURN THE PROXY CARD IF YOU ARE VOTING BY INTERNET.						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 NovemberMay 19, 2020:2023:

Our 20202023 Proxy Statement and 20192022 Annual Report on

Form 10-K are

available at

https://www.cstproxy.com/acertx/20202023

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, NOVEMBERFRIDAY, MAY 19, 20202023

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 NovemberMay 19, 20202023 at 10:11:00 a.m. Eastern Time, via the Internet at https://www.cstproxy.com/acertx/2020.2023. 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 THEALL 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)