As filed with the Securities and Exchange Commission on November 9, 2018April 19, 2022

RegistrationNo. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Acer Therapeutics Inc.

(Exact Name of Registrant as Specified in Its Charter)

One Gateway Center, Suite 351

300 Washington Street

Newton, MA 02458

(844)902-6100

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Chris Schelling

President and Chief Executive Officer

Acer Therapeutics Inc.

One Gateway Center, Suite 351

300 Washington Street

Newton, MA 02458

(844)902-6100

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective, as determined by market conditions and other factors.

(Approximate date of commencement of proposed sale to the public)

If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.  ☐

If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.  ☒

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

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

If this form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462 (e)462(e) under the Securities Act, check the following box.  ☐

If this form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, anon-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” inRule 12b-2 of the Exchange Act.

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

CALCULATION OF REGISTRATION FEE

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

SUBJECT TO COMPLETION, DATED NOVEMBER 9, 2018Subject To Completion, Dated April 19, 2022

PROSPECTUS

$100,000,000

ACER THERAPEUTICS INC.

Acer Therapeutics Inc.

Debt Securities

2,478,000 Shares of Common Stock

Preferred Stock

Depositary Shares

Warrants

Rights

We may,This prospectus relates to the offer and resale from time to time offer and sellby the securitiesselling stockholders, identified above in one or more offerings. The aggregate initial offering price of all securities sold under this prospectus, and any of their respective permitted assigns (each, a “Selling Stockholder” and collectively, the “Selling Stockholders”) of up to 2,478,000 shares of our common stock, $0.0001 par value per share (the “common stock”), issuable upon conversion of our 6.5% secured convertible notes due 2025.

We are not selling any shares covered by this prospectus and will not exceed $100,000,000.

This prospectus describesreceive any proceeds from the general termssale of these securities andshares of common stock by the general manner in which these securities will be offered. We will provide the specific terms of these securities in supplementsSelling Stockholders pursuant to this prospectus. The prospectus supplements will also describe

We are registering the manner in which these securities will be offeredoffer and may also add to, update or change information contained in this prospectus. You should read carefullysale of the shares covered by this prospectus to satisfy certain registration rights we have granted to the Selling Stockholders. The Selling Stockholders or their respective permitted assignees may offer all or part of the shares covered by this prospectus for resale from time to time through public or private transactions, at either prevailing market prices or at privately negotiated prices. The Selling Stockholders or their respective permitted assignees may sell shares through ordinary brokerage transactions or through any other means described in the section entitled “Plan of Distribution” herein. In connection with any sales of shares offered hereunder, the Selling Stockholders and any underwriters, agents, brokers or dealers participating in such sales may be deemed to be “underwriters” within the accompanying prospectus supplement before you invest.meaning of the Securities Act of 1933.

We may offer and sellwill pay certain expenses associated with the registration of the securities separately or together in any combination for sale directly to investors or through underwriters, dealers or agents. If any underwriters, dealers or agents are involvedcovered by this prospectus, as described in the salesection entitled “Plan of these securities we will set forth their names and describe their compensation in the applicable prospectus supplement.Distribution.”

Our common stock is listedtraded on the Nasdaq Capital Market under the symbol “ACER.” On November 8, 2018,April 14, 2022, the last reported sale price of our common stock on the Nasdaq Capital Market was $24.62$2.30 per share.

Investing in our securities involves risks. See the section entitled “Risk Factors” includedbeginning on page 9 in or incorporated by reference into the accompanyingthis prospectus supplement and in the documents we incorporate by reference in this prospectus. You should carefully consider these risk factors, as well as the information contained in this prospectus and in other documents that we incorporate by reference before you invest.

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

The date of this prospectus is                , 20182022.

TABLE OF CONTENTS

You should rely only on the information incorporated by reference or provided in this prospectus, any prospectus supplement, any applicable free writing prospectus and the registration statement. We have not authorized anyone else to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information in this prospectus, any prospectus supplement, any applicable free writing prospectus or the documents incorporated by reference, is accurate only as of the dates of those documents. Our business, financial condition, results of operations and prospects may have changed since those dates.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the U.S. Securities and Exchange Commission or SEC,(“SEC”) under the Securities Act of 1933, as amended (the “Securities Act”), using a “shelf” registration or continuous offering, process. Under this shelf registration process, weprospectus, the Selling Stockholders may, from time to time, offer and sell separately or together in any combination the securitiesshares of our common stock described in this prospectus in one or more offerings up to a maximum aggregate offering price of $100,000,000.

offerings. This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information aboutoffered by the terms of that offering and the offered securities.Selling Stockholders. Any prospectus supplement or information incorporated by reference in this prospectus or any prospectus supplement that is of a more recent date, may also add, update or change information contained in this prospectus. Any statement that we make in this prospectus will be modified or superseded by any inconsistent statement made by us in a prospectus supplement.

The registration statement we filed with the SEC includes exhibits that provide more detail of the matters discussed in this prospectus. This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part. You should read this prospectus and the related exhibits filed with the SEC and any prospectus supplement, and any applicable free writing prospectus, together with additional information described under the headings “Where“Where You Can Find More Information” and “Incorporation“Incorporation by Reference” before making your investment decision.

You should rely only on the information incorporated by reference or provided in this prospectus, any prospectus supplement and the registration statement. Neither we nor the Selling Stockholders have authorized anyone else to provide you with different or additional information other than that contained in or incorporated by reference in this prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. Offers to sell, and solicitations of offers to buy, our common stock are being made only in jurisdictions where offers and sales are permitted. You should assume that the information in this prospectus and any prospectus supplement, or incorporated by reference, is accurate only as of the dates of those documents. Our business, financial condition, results of operations and prospects may have changed since those dates.

All references in this prospectus supplement to “Acer,” the “company,“Company,” “we,” “us” and “our” refer to Acer Therapeutics Inc. and its consolidated subsidiaries,, except where the context otherwise requires or as otherwise indicated.

“ACER THERAPEUTICS,” “EDSIVO” and the Acer logo are our trademarks. This prospectus and the documents incorporated by reference into this prospectus may also contain trademarks and trade names that are the property of their respective owners. We do not intend our use or display of other companies’ trade names, trademarks or service marks to imply relationships with, or endorsements or sponsorship of us by, these other companies.

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RISK FACTORS

Investing in our common stock involves a 505(b)(2) NDA.

We were originallyhigh degree of risk. You should consider the important factors set forth below and in the documents incorporated as Sportan United Industries, Inc. (“Sportan”)by reference in Texasthis prospectus, including the discussion under the section entitled “Risk Factors” in March 1991. In June 2004, PharmaFrontiers Corp. (“PharmaFrontiers”) was acquiredour Annual Report on Form 10-K for the fiscal year ended December 31, 2021 and subsequent Quarterly Reports on Form 10-Q, which are incorporated herein by Sportan in a transaction accounted for as a reverse acquisition. In October 2004, PharmaFrontiers acquiredreference, together with all of the outstandingother information contained in or incorporated by reference this prospectus, before deciding to invest in our common stock. Additional risks and uncertainties not presently known to us, or that we may view as immaterial, may also impair our business. If any of these risks or uncertainties actually occur, they could materially and adversely affect our business, financial condition, results of operations, cash flows or prospects, which could in turn materially and adversely affect the price of our common stock and you could lose all or part of Opexa Pharmaceuticals, Inc. (“Opexa Pharmaceuticals”). In June 2006, we changed our name to Opexa Therapeutics, Inc. and, in January 2007, we merged with our wholly owned subsidiary, Opexa Pharmaceuticals, with Opexa Therapeutics, Inc. being the surviving company. In September 2017, we merged with Acer Therapeutics Inc. and changed our name to Acer Therapeutics Inc. On May 15, 2018, we changed our state of incorporation from the State of Texasyour investment.

Risks Relating to the StateOffering

The number of Delawareshares being registered for sale is significant in relation to our trading volume.

All of the shares of common stock underlying the Secured Convertible Notes being registered for resale on behalf of the Selling Stockholders are “restricted securities” as that term is defined in Rule 144 under the Securities Act. We are registering the offer and sale of the shares covered by this prospectus to satisfy certain registration rights we have granted to the Selling Stockholders, and so that the shares may be offered for sale into the public market by the Selling Stockholders. If all such shares were sold into the market all at once or at about the same time, it could depress the market price of our stock during the period the registration statement remains effective and also could affect our ability to raise equity capital.

A substantial number of shares of our common stock may be issued pursuant to the terms of the Secured Convertible Notes, which could cause the price of our common stock to decline.

The Secured Convertible Notes are convertible into shares of our common stock immediately after issuance at a planconversion price of $2.50, for an aggregate of 2,400,000 shares, or approximately 16.8% of our common stock outstanding immediately prior to conversion of the original principal amount (without taking into account the limitations on the conversion of the Secured Convertible Notes as described elsewhere in this prospectus). Furthermore, the number of shares of common stock to be issued upon conversion of the Secured Convertible Notes may be substantially greater if accrued but unpaid interest on the Secured Convertible Notes is converted into shares of common stock at the same time as the principal is converted. We are unable to predict if and when the Holders will convert their Secured Convertible Notes, and whether or not any accrued but unpaid interest will also be converted. While accrued interest on the Secured Convertible Notes is payable in cash according to their terms, any accrued but unpaid interest is also convertible into shares of common stock at the same time as the Holder otherwise converts principal on the Secured Convertible Notes.

For purposes of this prospectus, we have registered 2,478,000 shares of common stock in the event that up to six months of accrued but unpaid interest is included in the conversion. The actual number of shares issued upon conversion of the Secured Convertible Notes may be more or less than this amount depending upon the outstanding principal balance and the amount of any accrued but unpaid interest at the time. We may need to register more shares if the accrued but unpaid interest at the time of conversion represents more than 78,000 shares of our common stock. The foregoing amount of shares being registered does not take into account the limitations on conversion of the Secured Convertible Notes described elsewhere in this prospectus.

Sales of substantial amounts of our common stock by the Selling Stockholders, or the perception that these sales could occur, could adversely affect the price of our common stock.

The sale by the Selling Stockholders of a significant number of shares of common stock could have a material adverse effect on the market price of our common stock. In addition, the perception in the public

markets that the Selling Stockholders may sell all or a portion of their shares as a result of the registration of such shares pursuant to the registration statement of which this prospectus is a part could also eliminatedin and of itself have a material adverse effect on the market price of our holding company structurecommon stock. We cannot predict the effect, if any, that market sales of those shares of common stock or the availability of those shares of common stock for sale will have on the market price of our common stock.

Our share price is very volatile, may not reflect the underlying value of our net assets or business prospects, and you may not be able to resell your shares at a profit or at all.

The market price of our common stock could be subject to significant fluctuations. The market prices for securities of pharmaceutical and biotechnology companies, and early-stage drug discovery and development companies like ours in particular, have historically been highly volatile and may continue to be highly volatile in the future. The following factors, in addition to other risk factors described in or incorporated by merging our wholly owned subsidiary Acer Therapeutics Inc. with and into the parent company, with the parent company being the surviving entity. Our principal executive offices are located at One Gateway Center, Suite 351, 300 Washington Street, Newton, Massachusetts 02458, and our telephone number is (844)902-6100. Our website address is www.acertx.com. We do not incorporate the information on, or accessible through, our websitereference into this prospectus, may have a significant impact on the market price of our common stock:

Broad market and industry factors, as well as economic and political factors, also may materially adversely affect the market price of our common stock. The short-, medium-, and long-term impacts of the COVID-19 pandemic on the U.S. and global economies generally, and on our business specifically, are difficult to predict.

Risks Related to the Secured Convertible Notes and Bridge Loan

The requirement that we repay in cash the outstanding principal balance and accrued interest on the Bridge Loan and the Secured Convertible Notes under certain circumstances, and the restrictive covenants contained in these debt instruments, could adversely affect our business plans, liquidity, financial condition and results of operations and may prevent us from taking actions that we would otherwise consider to be in our best interests.

The Secured Convertible Notes bear interest at an annual rate of 6.5%, with such interest payable quarterly; provided, however, that until the first to occur of ACER-001 Approval and the repayment in full of the Bridge Loan, interest will not considerbe payable in cash but will accrue and be payable in cash within three business days of ACER-001 Approval. Additionally, each of the Holders of the Secured Convertible Notes has the right, during the 30-day periods beginning 12 months, 18 months and 24 months after the Convertible Note Financing, to require us to redeem the Secured Convertible Note held by such Holder in cash at a redemption price equal to the outstanding principal amount plus any informationaccrued but unpaid interest. Any outstanding principal of the Secured Convertible Notes, together with all accrued and unpaid interest, will be due and payable on March 14, 2025, or upon a change of control of the Company if earlier. With respect to the Bridge Loan, we have the option to capitalize the accrued interest on the Bridge Loan until November 15, 2022. Commencing November 15, 2022, the principal amount of the Bridge Loan amortizes at a rate of $650,000 payable quarterly, with the final maturity being the earlier of (i) 12 business days after ACER-001 Approval if such occurs on or accessible through,before September 30, 2022 or (ii) March 4, 2024 if ACER-001 Approval does not occur on or before September 30, 2022. We must also pay an exit fee to SWK of between 1.3 to 1.5 times the outstanding principal amount of the Bridge Loan, depending upon certain conditions and timing. Funding from the Term Loan will be available to us to be borrowed only upon and following ACER-001 Approval and until December 31, 2022, and repayment terms do not commence until thereafter. We intend to use the proceeds from the Term Loan to refinance certain other indebtedness, including the Bridge Loan. However, if ACER-001 Approval does not occur prior to December 31, 2022, then the Term Loan will not be available to us, and we may not have sufficient available cash or be able to obtain financing at the time we are required to make payments under our websiteindebtedness. Our failure to repurchase Secured Convertible Notes at a time when the repurchase is required by the notes, or to pay any cash for principal reduction or accrued interest on the Secured Convertible Notes or the Bridge Loan would constitute a default under the relevant indebtedness.

In addition, the Secured Convertible Notes and the Bridge Loan and Term Loan contain certain restrictive covenants. These obligations and covenants could have important consequences on our business. In particular, they could:

The debt service requirements of the Secured Convertible Notes and the Bridge Loan could intensify these risks. Our ability to make scheduled payments of interest, principal or to repurchase or refinance our indebtedness depends on our future performance, which is subject to economic, financial, competitive and other factors beyond our control. We may not receive the ACER-001 Approval timely, or at all, which is a condition precedent in order to borrow under the Marathon Credit Agreement. Our business may not generate cash flow

from operations in the future sufficient to service our debt and make necessary capital expenditures. If we are unable to generate such cash flow, and if the Term Loan does not become available to us to be borrowed, we may be required to adopt one or more alternatives, such as partselling assets, restructuring debt or obtaining additional equity capital on terms that may be onerous or highly dilutive. No assurances can be given that we will be successful in making the required payments under our indebtedness, or in refinancing our obligations on favorable terms, or at all. Should we determine to refinance, it could be further dilutive to our stockholders. Our ability to refinance our indebtedness will depend on the capital markets and our financial condition at such time. We may not be able to engage in any of this prospectus.these activities or engage in these activities on desirable terms, which could result in a default on our debt obligations.

If we are unable to make the required cash payments or refinance our indebtedness, there could be a default under the Secured Convertible Notes and/or the Bridge Loan. In such event, or if a default otherwise occurs, including as a result of our failure to comply with the restrictive covenants contained therein, the interest rate on the outstanding principal balance of the Secured Convertible Notes will increase from 6.5% to 11.5% from and after any occurrence and during the continuance of an event of default, pursuant to the Secured Convertible Note Purchase Agreement.

The terms of the Secured Convertible Notes and Bridge Loan require us to meet certain operating and financial covenants and place restrictions on our operating and financial flexibility.

The Secured Convertible Notes and Bridge Loan, by which we borrowed $6.0 million and $6.5 million, respectively, are secured by a first priority lien on all of our assets (including our intellectual property). Upon repayment of the Bridge Loan, we are required to pay an exit fee so that SWK receives an aggregate amount (inclusive of all principal, interest and origination and other fees paid to SWK under the SWK Credit Agreement) equal to (a) 1.3 times the outstanding principal amount of the Bridge Loan if ACER-001 Approval or such payment occurs on or prior to September 30, 2022, or (b) 1.5 times the outstanding principal amount of the Bridge Loan if each of ACER-001 Approval and such payment does not occur until after September 30, 2022. Our Bridge Loan bears interest at an annual rate equal to three-month London Interbank Offered Rates (LIBOR) (or such other rate as may be agreed between SWK and us following the date on which three-month LIBOR is no longer available), subject to a 1.0% LIBOR floor, plus a margin of 11.0%, and is therefore sensitive to changes in interest rates. If three-month LIBOR can no longer be determined or if the applicable governmental authority ceases to supervise or sanction such rates, then we will endeavor to agree with SWK on an alternate rate of interest that gives due consideration to the then prevailing market convention for determining interest for comparable loans in the United States. We cannot predict what the impact of any such alternative rate would be to our interest expense. However, the discontinuation, reform, or replacement of LIBOR or any other benchmark rates may result in fluctuating interest rates that may have a negative impact on our interest expense and cash flows. Furthermore, we cannot predict or quantify the time, effort and cost required to transition to the use of new benchmark rates, including with respect to negotiating and implementing any necessary changes to the Bridge Loan, and implementing changes to our systems and processes.

The Secured Convertible Notes and SWK Credit Agreement restrict our ability to incur new indebtedness, sell assets, and to pursue certain mergers, acquisitions, amalgamations or consolidations, other than permitted indebtedness or permitted acquisitions, that we may believe to be in our best interest. In addition, the SWK Credit Agreement and the Term Loan contain financial covenants that require us to maintain a minimum cash balance level. If we default under the SWK Credit Agreement, the lenders will be able to declare all obligations immediately due and payable, including certain fees and other obligations. The lenders could declare an event of default upon the occurrence of any event that they interpret as a material adverse change or material adverse effect, as defined in the SWK Credit Agreement. Any declaration by the lenders of an event of default could significantly harm our business and prospects and could cause the price of our common stock to decline.

FORWARD-LOOKING STATEMENTS

When used in thisThis prospectus and the documents incorporated herein by reference contain forward-looking statements which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. Statements other than statements of historical fact constitute “forward-looking statements.” The words such as “believe,“expects,” “believes,” “hopes,” “anticipates,” “estimates,” “may,” “will,“could,” “estimate,“intends,” “continue,“exploring,” “anticipate,“evaluating,” “intend,“progressing,” “expect”“proceeding” and similar expressions are intended to identify forward-looking statements.

These forward-looking statements do not constitute guarantees of future performance. Investors are cautioned that statements which are not strictly historical statements, including, without limitation, statements regarding current or future financial payments, costs, returns, royalties, performance and position, plans and objectives for future operations, plans and objectives for product development, plans and objectives for present and future clinical trials and results of such trials, plans and objectives for regulatory approval, litigation, intellectual property, product development, manufacturing plans and performance, management’s initiatives and strategies, and the development of our product candidates, including ACER-001, EDSIVO^™ (celiprolol), ACER-801 (osanetant) and ACER-2820 (emetine), constitute forward-looking statements. Such forward-looking statements are subject to known and unknowna number of risks and uncertainties that could cause actual results to differ materially from those projectedanticipated. These risks and uncertainties include, but are not limited to, those risks discussed in the section entitled “Risk Factors” and in our SEC filings which are incorporated by reference, as well as, without limitation, risks associated with:

These forward-looking statements speak only as of the date of this prospectus.made. These statements reflect our current views with respect to future events and are based on assumptions and subject to risks and uncertainties. Given these risks and uncertainties, you should not place undue reliance on these forward-looking statements. We will discuss many of these risks and uncertainties in greater detail in any prospectus supplement under the heading “Risk Factors.” Additional cautionary statements or discussions of risks and uncertainties that could affect our results or the achievement of the expectations described in forward-looking statements may also be contained in the documents we incorporate by reference into this prospectus.

These forward-looking statements speak only as of the date of this prospectus. We expressly disclaim anyassume no obligation or undertaking to release publicly any updates or revisions toupdate any forward-looking statements contained herein to reflect any changechanges in our expectations with regard thereto or any change in events, conditions or circumstances on which any such statement is based. You should, however, review additional disclosures we make in our Annual Report onForm 10-K, Quarterly Reports onForm 10-Q, and Current Reports onForm 8-K filedthe reports we file with the SEC.

USE OF PROCEEDS

UnlessAll of the shares of common stock covered by this prospectus will be sold by the Selling Stockholders. We will not receive any proceeds from the resale of the shares of common stock under this prospectus by the Selling Stockholders. We cannot advise you as to whether or not the Selling Stockholders will convert their Secured Convertible Notes or will otherwise receive any of the shares of common stock upon conversion, and to the extent they do, whether or when they will in fact sell any or all of such shares.

PRIVATE PLACEMENT OF SECURED CONVERTIBLE NOTES

On March 4, 2022, we state otherwiseentered into the Secured Convertible Note Purchase Agreement with the Holders pursuant to which we issued and sold to the Holders the Secured Convertible Notes in an aggregate amount of $6.0 million, in a transaction exempt from registration under Section 4(a)(2) of the applicable prospectus supplement,Securities Act, and Rule 506 of Regulation D promulgated thereunder. The Convertible Note Financing closed and funded on March 14, 2022. On March 4, 2022, we also entered into the SWK Credit Agreement and the Marathon Credit Agreement, and the Bridge Loan closed and funded on March 14, 2022.

We intend to use the net proceeds from the sale of the securities offeredConvertible Note Financing (i) to pay fees, costs and expenses related to (a) the Secured Convertible Note Purchase Agreement, (b) the SWK Credit Agreement, which provides for the Bridge Loan consisting of a senior secured term loan facility in an aggregate amount of $6.5 million in a single borrowing, (c) the Marathon Credit Agreement, which provides for the Term Loan consisting of a senior secured term loan facility in an aggregate amount of up to $42.5 million in a single borrowing, which will be available to be borrowed only following ACER-001 Approval by this prospectusthe FDA and until December 31, 2022 (i.e., if ACER-001 Approval does not occur on or before December 31, 2022, then the Term Loan will not be available), and (ii) for other working capital and general corporate purposes. General corporate purposes may include additions

The Secured Convertible Notes bear interest at an annual rate of 6.5%, with such interest payable quarterly; provided, however, that until the first to working capital, financingoccur of capital expenditures,ACER-001 Approval and the repayment or redemption of existing indebtedness, repurchases of stock and future acquisitions and strategic investment opportunities. Unless we state otherwise in the applicable prospectus supplement, pending the application of net proceeds, we expect to invest the net proceeds in short- and intermediate-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or guaranteed obligationsfull of the U.S. government.Bridge Loan, interest will not be payable in cash, but will accrue and be payable in cash within three business days of ACER-001 Approval. If an event of default occurs under the Secured Convertible Notes, including as a result of our failure to comply with the restrictive or financial covenants contained therein, the interest rate on the outstanding balance of the Secured Convertible Notes will increase from 6.5% to 11.5% from and after any occurrence and during the continuance of an event of default pursuant to the Secured Convertible Note Purchase Agreement.

Each of the Holders has the right, during the 30-day periods beginning 12 months, 18 months and 24 months after the Convertible Note Financing, to require us to redeem the Secured Convertible Note held by such Holder at a redemption price of the outstanding principal amount plus any accrued but unpaid interest. Any outstanding principal, together with all accrued and unpaid interest, will be payable on March 14, 2025, or upon a change of control of Acer if earlier. Each of the Holders also has the right at any time to convert all or any portion of the outstanding principal amount plus any accrued but unpaid interest under the Secured Convertible Note held by such Holder into shares of our common stock at a conversion price of $2.50, subject to certain limitations on conversion as further described below.

Pursuant to the terms of the Secured Convertible Notes and applicable rules of the Nasdaq Capital Market, in no event may a Holder convert any portion of their Secured Convertible Note (i) to the extent that the aggregate number of shares of common stock issued upon conversion, together with any other common stock issuable pursuant to any other security that is deemed integrated under the rules of the Nasdaq Capital Market, would be in excess of 19.99% of the number of shares of our common stock outstanding immediately prior to the issuance of the Secured Convertible Notes (which is 2,860,618 shares, or 19.99% of the 14,310,244 shares of our common stock immediately prior to issuance of the Secured Convertible Notes), or (ii) if the Holder, together

DESCRIPTION OF DEBT SECURITIESwith the Holder’s affiliates and associates, would beneficially own or control in excess of 19.99% of the number of shares or of the total voting power of our common stock outstanding immediately after giving effect to such issuance, unless and until we obtain stockholder approval in either case to issue shares of common stock in excess of such limits. If and only when the foregoing ownership limitations would prevent the Holders from converting their Secured Convertible Note, we are required to seek stockholder approval at our next annual meeting to solicit the affirmative vote of stockholders to approve the issuance of shares of common stock underlying the Secured Convertible Notes without regard to the foregoing ownership limitations.

Additionally, the Holders may not convert any portion of their Secured Convertible Notes to the extent that a Holder, together with its affiliates and any persons acting as a group, would beneficially own in excess of 4.99% of our outstanding common stock. A Holder may provide written notice to us at any time to increase or decrease that 4.99% limit, provided that any such change will not be effective until the 61^st day after such notice is delivered to us.

For so long as Marathon and its affiliates beneficially own at least 4.99% of our common stock, Marathon is entitled to designate one non-voting board observer, who must hold in confidence and trust and act in a fiduciary manner with respect to all information provided to that individual.

The following is a summaryconversion price of the general termsSecured Convertible Notes is adjustable upon the occurrence of stock splits and dividends, reverse stock splits and share combinations, and in the event of a capital reorganization, reclassification of our capital stock, consolidation or merger, or the sale of all or substantially all of our assets.

Each Holder has certain rights with respect to the registration for resale of the debt securities.shares of common stock issuable upon conversion of the Secured Convertible Note held by such Holder. We willare required to file a prospectus supplement thatregistration statement covering the resale of the shares underlying the Secured Convertible Notes within 45 days after the March 14, 2022 closing of the Convertible Note Financing and must use commercially reasonable efforts to cause the SEC to declare the registration statement effective within 90 days after such date.

Pursuant to the Secured Convertible Note Purchase Agreement, the Secured Convertible Notes are secured by a lien on collateral representing substantially all of our assets, although such security interest is subordinated to our obligations under the SWK Credit Agreement and may contain additional terms when we issue debt securities. also be subordinated to our obligations under the Marathon Credit Agreement (once the conditions precedent in order to borrow under such agreement have been met).

The terms presented here, together with the terms inabove disclosure contains only a related prospectus supplement, together with any pricing supplement or term sheet, will be abrief description of the material terms ofis qualified in its entirety by reference to the debt securities.

We may issue, from timeexhibits to time, debt securities, in one or more series. These debt securities that we may issue include senior debt securities, senior subordinated debt securities, subordinated debt securities, convertible debt securities and exchangeable debt securities. The debt securities we offer will be issued under an indenture between us andour Current Report on Form 8-K filed with the trustee named in the indenture. The following is a summary of the material provisions of the form of indenture filed as an exhibitSEC on March 7, 2022, which has been incorporated by reference to the registration statement of which this prospectus is a part. All capitalized terms have the meanings specified in the indentures. For each series of debt securities, the applicable prospectus supplement for the series may changeSee “Where You Can Find More Information” and supplement the summary below.

As used in this section only, “we,” “us” and “our” refer to Acer Therapeutics Inc. excluding any subsidiaries, unless expressly stated or the context otherwise requires.

General Terms of the Indenture

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities for any series of debt securities up to the principal amount that we may authorize. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us. For each series of debt securities, any restrictive covenants for those debt securities will be described in the applicable prospectus supplement for those debt securities.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may, for United States federal income tax purposes, be treated as if they were issued with “original issue discount,” or OID, because of interest payment and other characteristics. Special United States federal income tax considerations applicable to debt securities issued with original issue discount will be described in more detail in any applicable prospectus supplement.

You should refer to the prospectus supplement relating to a particular series of debt securities for a description of the following terms of the debt securities offered“Incorporation by that prospectus supplement and by this prospectus:

The indenture imposes limitations on suits brought by holders of debt securities against us. Except for actions for payment of overdue principal or interest, no holder of debt securities of any series may institute any action against us under the indenture unless:SELLING STOCKHOLDERS

We will be required to file annually with the trustee a certificate, signed by one of our officers, stating whether or not the officer knows of any default by us in the performance, observance or fulfillment of any condition or covenant of the indenture.

Discharge, Defeasance and Covenant Defeasance

We can discharge or decrease our obligations under the indenture as stated below.

We may discharge obligations to holders of any series of debt securities that have not already been delivered to the trusteeSelling Stockholders for cancellation and that have either become due and payable or are by their terms to become due and payable, or are scheduled for redemption, within one year. We may effect a discharge by irrevocably depositing with the trustee cash or government obligations, as trust funds, in an amount certified to be enough to pay when due, whether at maturity, upon redemption or otherwise, the principal of, and any premium and interest on, the debt securities and any mandatory sinking fund payments.

Unless otherwise provided in the applicable prospectus supplement, we may also discharge any and all of our obligations to holders of any series of debt securities at any time, whichown accounts. When we refer to as defeasance. We may also be released from the obligations imposed bySelling Stockholders” in this prospectus, we mean the persons listed in the table below, and the pledgees, donees, transferees, assignees, successors and other who later come to hold any covenants of any outstanding series of debt securities and provisions of the indenture, and we may omit to comply with those covenants without creating an event of default under the trust declaration, which we refer to as covenant defeasance. We may effect defeasance and covenant defeasance only if, among other things:

In the case of a defeasance by us, the opinion we deliver must be based on a ruling of the Internal Revenue Service issued, or a change in U.S. federal income tax law occurring,common stock issuable thereunder after the date of this prospectus.

We are filing the indenture, since suchregistration statement of which this prospectus forms a result would not occur under the U.S. federal income tax laws in effect on that date.

Although we may discharge or decrease our obligations under the indenture as described in the two preceding paragraphs, we may not avoid, among other things, our duty to register the transfer or exchange of any series of debt securities, to replace any temporary, mutilated, destroyed, lost or stolen series of debt securities or to maintain an office or agency in respect of any series of debt securities.

Generally, a “business combination” includes a merger, asset or stock sale, or other transaction resulting in a financial benefit to the “interested stockholder” and an “interested stockholder” is a person who, together with affiliates and associates, owns or, within three years prior to the determination of interested stockholder status, did own 15% or more of a corporation’s outstanding voting stock. We expect the existence of this provision to have an anti-takeover effect with respect to transactions our board of directors does not approve in advance. We also anticipate that Section 203 may discourage business combinations or other attempts that might result in a premium over the market price for the shares of common stock held by our stockholders. The provisions of DGCL, our certificate of incorporation and our bylaws could have the effect of discouraging others from attempting hostile takeovers and, as a consequence, they may also inhibit temporary fluctuations in the market price of our common stock that often result from actual or rumored hostile takeover attempts. These provisions may also have the effect of preventing changes in our management. It is possible that these provisions could make it more difficult to accomplish transactions that stockholders may otherwise deem to be in their best interests.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Continental Stock Transfer and Trust Company. The transfer agent’s address is 1 State Street, 30th Floor, New York, New York 10004-1561.

PLAN OF DISTRIBUTION

WeThe Selling Stockholders may, from time to time, sell, transfer or otherwise dispose of any or all of their shares of common stock or interests in shares of common stock on any stock exchange, market or trading facility on which the securities offered by this prospectusshares are traded or in private transactions. These dispositions may be at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices.

The Selling Stockholders may use any one or more underwriters or dealers for public offering and sale by them or to investors directly or through agents. The accompanying prospectus supplement will set forth the terms of the offering and the methodfollowing methods when disposing of distribution and will identify any firms acting as underwriters, dealersshares or agents in connection with the offering, including:interests therein:

Only those underwriters identified in such prospectus supplement are deemed to be underwriters in connection with the securities offered in the prospectus supplement.

The distribution of the securitiesSelling Stockholders may, be effected from time to time, pledge or grant a security interest in onesome or more transactions at a fixed priceall of the shares of common stock owned by them and, if they default in the performance of their secured obligations, the pledgees or prices, whichsecured parties may be changed, or at prices determined asoffer and sell the applicable prospectus supplement specifies. The securities may be sold through anat-the-market offering, a rights offering, forward contracts or similar arrangements. In addition, we may enter into derivative transactions with third parties, or sell securities not covered byshares of common stock, from time to time, under this prospectus, or under an amendment to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus andunder Rule 424(b)(3) or other applicable provision of the applicable prospectus supplement, includingSecurities Act amending the list of selling stockholders to include the pledgee, transferee or other successors in short sale transactions. If so,interest as selling stockholders under this prospectus. The Selling Stockholders also may transfer the third party may use securities pledged by usshares of common stock in other circumstances, in which case the transferees, pledgees or borrowed from us or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from usother successors in settlement of those derivatives to close out any related open borrowings of stock. The third party in such sale transactionsinterest will be an underwriter and, if not identified inthe selling beneficial owners for purposes of this prospectus, will be named in the applicable prospectus supplement (or a post-effective amendment). In addition, we may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus and an applicable prospectus supplement. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.prospectus.

In connection with the sale of our common stock or interests therein, the securities, underwriters, dealersSelling Stockholders may enter into hedging transactions with broker-dealers or agentsother financial institutions, which may be deemed to have received compensation from usin turn engage in short sales of the common stock in the formcourse of underwritinghedging the positions they assume. The Selling Stockholders may also sell shares of our common stock short and deliver these securities to close out their short positions, or loan or pledge the common stock to broker-dealers that in turn may sell these securities. The Selling Stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities which require the delivery to such broker-dealer or other financial institution of shares offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The aggregate proceeds to the Selling Stockholders from the sale of the common stock offered by them will be the purchase price of the common stock less discounts or commissions, if any. Each of the Selling Stockholders reserves the right to accept and, together with their agents from time to time, to reject, in whole or in part, any proposed purchase of common stock to be made directly or through agents. We will not receive any of the proceeds from this offering.

The Selling Stockholders also may receive commissions from securities purchasers for whomresell all or a portion of the shares in open market transactions in reliance upon Rule 144 under the Securities Act, provided that they may act as agent. Underwriters may sellmeet the securitiescriteria and conform to the requirements of that rule.

The Selling Stockholders and any underwriters, broker-dealers or through dealers, and the dealers may receive compensationagents that participate in the formsale of the common stock or interests therein may be “underwriters” within the meaning of Section 2(11) of the Securities Act. Any discounts, commissions, concessions or commissions from the underwriters or commissions from the purchasers for whom they may act as agent.

We will provide in the applicable prospectus supplement information regarding any underwriting discounts or other compensation that we pay to underwriters or agents in connection with the securities offering, and any discounts, concessions or commissions that underwriters allow to dealers. Underwriters, dealers and agents participating in the securities distribution may be deemed to be underwriters, and any discounts, commissions or concessions they receive and any profit they realizeearn on theany resale of the securitiesshares may be deemed to be underwriting discounts and commissions under the Securities Act. Selling Stockholders will be subject to the prospectus delivery requirements of the Securities Act, unless an exemption therefrom is available.

To the extent required, the shares of 1933. Underwritersour common stock to be sold, the names of the Selling Stockholders, the respective purchase prices and public offering prices, the names of any agents, dealer or underwriter, any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

In order to comply with the securities laws of some states, if applicable, the common stock may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the common stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

There can be no assurance that any Selling Stockholder will sell any or all of the shares of common stock registered pursuant to the shelf registration statement, of which this prospectus forms a part.

We have advised the Selling Stockholders that the anti-manipulation rules of Regulation M under the Exchange Act may apply to sales of shares in the market and to the activities of the Selling Stockholders and their controlling persons, dealers and agentsaffiliates. In addition, to the extent applicable we will make copies of this prospectus (as it may be entitled,supplemented or amended from time to time) available to the Selling Stockholders for the purpose of satisfying any prospectus delivery requirements of the Securities Act. The Selling Stockholders may indemnify any broker-dealer that participates in transactions involving the sale of the shares against certain liabilities, including liabilities arising under agreements entered into with us,the Securities Act.

We have agreed to indemnificationindemnify the Selling Stockholders against and contribution toward specific civil liabilities, including some liabilities under the Securities Act. SomeAct and in accordance with the Secured Convertible Note Purchase Agreement, relating thereto and to the registration of the underwriters, dealers or agents who participateshares offered by this prospectus. We may be indemnified by the Selling Stockholders against liabilities, including some liabilities under the Securities Act and in accordance with the securities distribution may engage in other transactions with,Secured Convertible Note Purchase Agreement, relating thereto and perform other services for, us or our subsidiaries into the ordinary courseregistration of business.