Acer Therapeutics (ACER) S-1/A IPO registration (amended)

As filed with the Securities and Exchange Commission on June 1, 2020

RegistrationNo. 333-238192

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 1

to

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

ACER THERAPEUTICS INC.

(Exact Name of Registrant as Specified in Its Charter)

Delaware	2834	32-0426967
(State or Other Jurisdiction of Incorporation or Organization)	(Primary Standard Industrial Classification Code Number)	(I.R.S. Employer Identification Number)

One Gateway Center

300 Washington Street, Suite 351

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, 300 Washington Street, Suite 351

Newton MA 02458

(844)902-6100

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

Copies to:

Mike Hird, Esq.

Patty M. DeGaetano, Esq.

Pillsbury Winthrop Shaw Pittman LLP

12255 El Camino Real, Suite 300

San Diego, CA 9130

(619)234-5000

Approximate date of commencement of proposed sale to the public:From time to time after this registration statement becomes effective, as determined by the selling stockholder.

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

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

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

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

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

Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Smaller reporting company	☒
		Emerging growth company	☐

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

CALCULATION OF REGISTRATION FEE

Title of Each Class of Securities to be Registered	Amount to be Registered(1)	Proposed Maximum Offering Price Per Share(2)	Proposed Maximum Aggregate Offering Price	Amount of Registration Fee(3)
Common Stock, $0.0001 par value	1,840,148	$2.23	$4,098,193.94	$531.95

(1) Represents 148,148 shares of common stock previously issued to the selling stockholder named herein and 1,692,000 shares of common stock that are issuable pursuant to a purchase agreement with the selling stockholder named herein. Pursuant to Rule 416(a) under the Securities Act of 1933, the registrant is also registering hereunder an indeterminate number of shares that may be issued and resold resulting from stock splits, stock dividends or similar transactions.

(2) Estimated pursuant to Rule 457(c) solely for the purpose of calculating the registration fee, based upon the average of the high and low prices for the registrant’s common stock as reported on the Nasdaq Capital Market on May 6, 2020.

(3) Previously paid.

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this 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 June 1, 2020

PROSPECTUS

1,840,148 Shares of Common Stock

ACER THERAPEUTICS INC.

This prospectus relates to the offer and sale of up to 1,840,148 shares of common stock, $0.0001 par value per share, of Acer Therapeutics Inc., a Delaware corporation, by Lincoln Park Capital Fund, LLC, or Lincoln Park or the selling stockholder.

The shares of common stock being offered by the selling stockholder may be issued pursuant to the purchase agreement dated April 30, 2020 that we entered into with Lincoln Park. See “The Lincoln Park Transaction” for a description of that agreement and “Selling Stockholder” for additional information regarding Lincoln Park. The prices at which Lincoln Park may sell the shares will be determined by the prevailing market price for the shares or in negotiated transactions.

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

The selling stockholder may sell the shares of common stock described in this prospectus in a number of different ways and at varying prices. See “Plan of Distribution” for more information about how the selling stockholder may sell the shares of common stock being registered pursuant to this prospectus. The selling stockholder is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act of 1933, as amended.

The selling stockholder will pay all brokerage fees and commissions and similar expenses. We will pay the expenses (except brokerage fees and commissions and similar expenses) incurred in registering the shares, including legal and accounting fees. See “Plan of Distribution.”

Our common stock is currently listed on the Nasdaq Capital Market under the symbol “ACER”. On May 29, 2020, the last reported sale price of our common stock on the Nasdaq Capital Market was $         per share.

Investing in our common stock involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” beginning on page 9 of this prospectus, and under similar headings in any amendments or supplements to this prospectus.

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

The date of this Prospectus is                , 2020.

TABLE OF CONTENTS

	Page
About this Prospectus		ii
Prospectus Summary		1
Risk Factors		9
Forward-Looking Statements		14
The Lincoln Park Transaction		15
Use of Proceeds		21
Dilution		22
Selling Stockholder		23
Market Price of our Common Stock and Related Stockholder Matters		25
Description of Capital Stock		25
Plan of Distribution		27
Experts		29
Legal Matters		29
Where You Can Find More Information		29
Incorporation by Reference		29
Disclosure of Commission Position on Indemnification for  Securities Act Liabilities		30

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ABOUT THIS PROSPECTUS

This prospectus forms part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, and that includes exhibits that provide more detail of the matters discussed in this prospectus. You should read this prospectus and the related exhibits filed with the SEC, together with the additional information described under the headings “Where You Can Find More Information” and “Incorporation by Reference” before making your investment decision.

You should rely only on the information provided in this prospectus or in a prospectus supplement or any free writing prospectuses or amendments thereto. Neither we, nor the selling stockholder, have authorized anyone else to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. You should assume that the information in this prospectus is accurate only as of the date hereof. Our business, financial condition, results of operations and prospects may have changed since that date.

Neither we, nor the selling stockholder, are offering to sell or seeking offers to purchase these securities in any jurisdiction where the offer or sale is not permitted. We have not done anything that would permit this offering or possession or distribution of this prospectus in any jurisdiction where action for that purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus must inform themselves about, and observe any restrictions relating to, the offering of the securities as to distribution of the prospectus outside of the United States.

Unless the context otherwise requires, references in this prospectus to “Acer,” “the Company,” “we,” “us” and “our” refer to Acer Therapeutics Inc. Our Acer logo and all product names are our common law trademarks. Solely for convenience, trademarks and tradenames referred to in this prospectus may appear without the^® or^™ symbols, but such references are not intended to indicate in any way that we will not assert, to the fullest extent under applicable law, our rights, or that the applicable owner will not assert its rights, to these trademarks and tradenames.

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PROSPECTUS SUMMARY

This summary contains basic information about us and this offering. Because it is a summary, it does not contain all of the information that you should consider before investing. Before you decide to invest in our common stock, you should read this entire prospectus carefully, including the section entitled “Risk Factors,” and any documents incorporated by reference.

Our Business

We are a pharmaceutical company focused on the acquisition, development, and commercialization of therapies for serious rare and life-threatening diseases with significant unmet medical needs. Our pipeline includes four clinical-stage candidates: emetine hydrochloride (“emetine”) for the treatment of patients withCOVID-19; EDSIVO^™ (celiprolol) for the treatment of vascular Ehlers-Danlos syndrome (“vEDS”) in patients with a confirmed type III collagen (COL3A1) mutation;ACER-001 (a taste-masked, immediate release formulation of sodium phenylbutyrate) for the treatment of various inborn errors of metabolism, including urea cycle disorders (“UCDs”) and Maple Syrup Urine Disease (“MSUD”); and osanetant for the treatment of induced vasomotor symptoms where hormone replacement therapy is likely contraindicated. Our product candidates are believed to present a comparativelyde-risked profile, having one or more of a favorable safety profile, clinicalproof-of-concept data, mechanistic differentiation, and/or accelerated paths for development through specific programs and procedures established by the United States (“U.S.”) Food and Drug Administration (“FDA”).

Our current product candidate pipeline is summarized in the chart below:

* Initiation of an emetine trial in the third quarter of 2020 is subject to submission and clearance of an investigational new drug application (“IND”) and our ability to generate sufficient capital resources to fund this program. Although our emetine development program has not yet entered the clinic for COVID-19 indication, the clinical trial planned assuming clearance of an IND is a Phase 2/3 trial. Due to the substantial amount of safety data that is already available with respect to emetine and our ongoing pre-IND discussions with the FDA, we do not believe that a Phase 1 trial in healthy volunteers will be required

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** Complete Response Letter received June 2019; Formal Dispute Resolution Request submitted to the FDA December 2019; response received March 2020 denying appeal of the Complete Response Letter but describing possible paths forward for Acer to explore that could provide the substantial evidence of effectiveness needed to support a potential resubmission of the EDSIVO^TM new drug application (“NDA”)

*** Pivotal bioavailability and bioequivalence (“BE”) trial

• A pivotal trial evaluating the BE ofACER-001 to BUPHENYL^®(sodium phenylbutyrate) was successfully completed in the first quarter of 2020

• An IND submission for emetine is anticipated in the third quarter of 2020

• Targeting initiation in the third quarter of 2020 of an adaptive Phase 2/3 trial in high-riskCOVID-19 patients not requiring hospitalization, subject to our ability to generate sufficient capital resources to fund this program

• An IND submission for osanetant is anticipated in the fourth quarter of 2020

• Initiation of a Phase 1/2 pharmacokinetics/pharmacodynamics/safety trial of osanetant is expected in the first quarter of 2021, subject to our ability to generate sufficient capital resources to fund this program

• NDA submission forACER-001 in UCDs is anticipated in early 2021, subject to our ability to generate sufficient capital resources to fund this program, and assuming successful completion of additional nonclinical work and12-month stability data

Product Candidates

Emetine forCOVID-19

On May 11, 2020, we announced that we have entered into a research collaboration agreement with the National Center for Advancing Translational Sciences (“NCATS”), one of the National Institutes of Health (“NIH”), to develop emetine hydrochloride as a potential treatment for patients withCOVID-19, the disease caused by infection with theSARS-CoV-2 virus. Emetine is an active pharmaceutical ingredient of syrup of ipecac, given orally to induce emesis, and has also been formulated as an injectable to treat thousands of individuals with amebiasis. Several independent in vitro studies have demonstrated nanomolar potency against both DNA andRNA-replicating viruses, including Zika virus, Ebola virus¹, Rabies Lyssavirus, human cytomegalovirus, human immunodeficiency virus 1, influenza A virus, Rift Valley fever virus, echovirus 1, human metapneumovirus, and herpes simplex virus type 2². Clinically, emetine has been used to treat approximately 700 patients (including pediatrics) with viral hepatitis³ and varicella-zoster virus⁴. Additionally, emetine is a potent inhibitor of multiple genetically-distinct Coronaviruses and demonstrated in vitro the strongest anti-coronavirus activity in one study that screened and identified approved compounds with broad-spectrum efficacy against the replication of four Coronaviruses⁵ and specifically againstSARS-CoV-2.⁶

Pursuant to the NCATS research collaboration agreement, Acer and NCATS are working together to speed the clinical development of emetine for the treatment of SARS-CoV-2 infection (the “Research Project”). Acer has defined a target product profile for the clinical development program and will share details with NCATS on aspects of its clinical development program to facilitate the urgent development of this therapy. NCATS has completed a literature review of clinical experience with emetine use, as well as artifacts including previous drug product labels and a drug master file, that it will share with Acer. NCATS also has access to a quantity of emetine physical material to support further nonclinical studies by Acer. Inventions made in the course of the Research Project will be owned by the party employing the inventor or inventors; inventions that are invented jointly by employees of both parties will be owned jointly. The research collaboration agreement has a one-year term, may be extended or terminated upon mutual agreement of the parties and may be terminated by either party with 30 days written notice.

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We intend to initially seek FDA approval to market emetine in the U.S. using a regulatory pathway established under section 505(b)(2) of the Federal Food, Drug and Cosmetic Act that allows applicants to rely at least in part on third party data for approval. We are working toward an IND submission inmid-2020 and targeting a clinical trial initiation in the third quarter of 2020, subject to additional capital. We intend to rely in part on the existing preclinical and clinical safety data for emetine, while supplementing with theCOVID-19 safety and efficacy data to be generated in a proposed adaptive design Phase 2/3 randomized, blinded, placebo-controlled multi-center trial to evaluate the safety and antiviral activity of emetine in high-risk symptomatic adult patients with confirmedCOVID-19 infection not requiring hospitalization, as well as chemistry, manufacturing and controls information. Based on the substantial amount of safety data that is already available with respect to emetine and our ongoing pre-IND discussions with the FDA, we do not believe that a Phase 1 trial in healthy volunteers will be required, and we believe that we may be able to proceed directly to a Phase 2/3 clinical trial in COVID-19 patients. Although emetine’s potential cardiotoxicity, in cumulative doses above 650 mg, has been cited as a reason for its restricted clinical use in most recent years, patients treated with a subcutaneous injection of emetine at a cumulative dose of 650 mg did not experience any notable toxicity⁷. As an antiviral and for COVID-19 patients, we expect to administer emetine as a subcutaneous injection at a cumulative dose of approximately 150 mg. If the Phase 2/3 trial is completed successfully, following IND submission and clearance, we anticipate submitting to the FDA the 505(b)(2) NDA for emetine for the treatment ofCOVID-19.

The potential initiation of the Phase 2/3 trial, its conduct and completion and NDA submission are subject to our ability to generate sufficient capital resources to fund this program. Emetine is an investigational drug forCOVID-19 and is not currently FDA approved for any indication.

References

1. Yang S, et al. Emetine inhibits Zika and Ebola virus infections through two molecular mechanisms: inhibiting viral replication and decreasing viral entry. Cell Discov (2018) 4:31. doi:10.1038/s41421-018-0034-1.

2. Andersen, P.I., et al. Novel Antiviral Activities of Obatoclax, Emetine, Niclosamide, Brequinar, and Homoharringtonine. Viruses 2019, 11, 964.

3. Del Puerto, et al. Pren. méd. argent., 55: 818, 1968.

4. Annamalai, et al. Emetine Hydrochloride in the Treatment of Herpes Zoster. 1968.

5. Shen L, et al. High-Throughput Screening and Identification of Potent Broad-Spectrum Inhibitors of Coronaviruses. J Virol. 2019 May 29;93(12).

6. Choy, et al. Remdesivir, lopinavir, emetine, and homoharringtonine inhibit SARS-CoV-2 replication in vitro. Antiviral Res. 2020 Jun; 178: 104786.

7. Mastrangelo, et al. Cancer 31:1170-1175.

EDSIVO^™ for Vascular Ehlers-Danlos Syndrome (vEDS)

Ehlers-Danlos Syndrome (“EDS”) is a group of hereditary disorders of connective tissue. vEDS is the most severe subtype where patients suffer from life threatening arterial dissections and ruptures, as well as intestinal and uterine ruptures. There is currently no approved treatment option for vEDS. The median age of death is 51 years.¹An Acer-commissioned patient-finder study phenotypically identified 4,169 vEDS patients in the U.S. from an analysis of a commercially available patient claims database with data of approximately 190 million unique patient lives. Based on that information, Acer estimates the prevalence of phenotypically-defined vEDS in the U.S. could be greater than 1 in 45,000. Currently, there are noFDA-approved therapies for vEDS.

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We are advancing EDSIVO^™, a new chemical entity (“NCE”), for the treatment of vEDS based on published results from a randomized controlled clinical trial of celiprolol.¹ The FDA granted a priority review of the EDSIVO^™ NDA and subsequently issued a Complete Response Letter (“CRL”) in June 2019. The CRL stated that it will be necessary to conduct an adequate and well-controlled trial to determine whether celiprolol reduces the risk of clinical events in patients with vEDS. In December 2019, we submitted a Formal Dispute Resolution Request (“FDRR”) to the FDA’s Office of New Drugs appealing the FDA’s decision as outlined in the CRL. In March 2020, we received a response to our FDRR from the Office of New Drugs (“OND”) of the FDA stating that it had denied our appeal of the CRL. In its Appeal Denied letter, the OND described possible paths forward for Acer to explore that could provide the substantial evidence of effectiveness needed to support a potential resubmission of the EDSIVO^™ NDA for the treatment of patients with vEDS with a confirmed COL3A1 mutation. The OND referred to the FDA Guidance document issued in December 2019², where substantial evidence of effectiveness can be provided by two or more adequate and well-controlled studies demonstrating efficacy, or a single positive adequate and well-controlled study plus confirmatory evidence. While neither resubmission nor the prospect of approval of the EDSIVO^™ NDA is assured, we are evaluating our possible next steps with the goal of resubmission of the EDSIVO^™ NDA. EDSIVO^™ received FDA Orphan Drug Designation for the treatment of vEDS in 2015.

References

1. Ong KT, et al. Effect of celiprolol on prevention of cardiovascular events in vascular Ehlers-Danlos syndrome: a prospective randomised, open, blinded-endpoints trial. Lancet. 2010;376(9751):1476-1484.

2. FDA guidance “Demonstrating Substantial Evidence of Effectiveness for Human Drug and Biological Products,” December 2019.

ACER-001 for Urea Cycle Disorders (UCDs)

UCDs are a group of disorders caused by genetic mutations that result in a deficiency in one of the six enzymes that catalyze the urea cycle, which can lead to an excess accumulation of ammonia in the bloodstream, a condition known as hyperammonemia. Acute hyperammonemia can cause lethargy, somnolence, coma, and multi-organ failure, while chronic hyperammonemia can lead to headaches, confusion, lethargy, failure to thrive, behavioral changes, and learning and cognitive deficits. Common symptoms of both acute and chronic hyperammonemia also include seizures and psychiatric symptoms. Current treatments consist of dietary management, as well as treatment with phenylbutyrate available as sodium phenylbutyrate (NaPB), which is marketed as BUPHENYL^®, and glycerol phenylbutyrate, which is marketed as RAVICTI^®.

ACER-001 is a taste-masked, immediate-release formulation of NaPB developed using a microencapsulation process. We believe that ifACER-001 is approved, its taste-masked properties will make it a compelling alternative to existing NaPB-based treatments, as the unpleasant taste associated with NaPB is cited as a major impediment to patient compliance with those treatments.¹ In February 2020, we reported the successful completion and final data from Part B of our pivotal trial evaluating the bioavailability and bioequivalence ofACER-001 to BUPHENYL^® (sodium phenylbutyrate). Consistent with observations from Part A of the trial, data from Part B showedACER-001 to be bioequivalent to BUPHENYL^®. We anticipate submitting to the FDA the 505(b)(2) NDA forACER-001 for the treatment of UCDs in early 2021, assuming successful completion of nonclinical work and12-month stability data. NDA submission is subject to our ability to generate sufficient capital resources to fund this program.

References

1. Shchelochkov OA, et al. Barriers to drug adherence in the treatment of urea cycle disorders: Assessment of patient, caregiver and provider perspectives.Mol Genet Metab. 2016;8:43-47.

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Osanetant for Induced Vasomotor Symptoms (iVMS)

Hot flashes, flushing, and night sweats are known as Vasomotor Symptoms (“VMS”), and most often occur in women who are entering/in menopause. While VMS associated with menopause can be often be treated with hormone replacement therapy (“HRT”), there are patients who experience VMS who are not in menopause and for whom HRT is contraindicated.¹ VMS that are induced by either chemical or surgical intervention are referred to as induced Vasomotor Symptoms (“iVMS”). For example, patients receiving tamoxifen treatment for breast cancer, men receiving leuprolide treatment for prostate cancer, and women who are BRCA-positive who elect to have bilateral salpingo-oophorectomy (“BSO”)^2,3, all exhibit severe iVMS and should not receive HRT to alleviate these symptoms because their cancer is sensitive to hormones which could cause disease recurrence.^1,4

Osanetant is a clinical-stage, selective,non-peptide tachykinin NK3 receptor antagonist. NK3R is the main receptor for neurokinin B (“NKB”), a tachykinin peptide primarily found in the arcuate nucleus (ARC) of the hypothalamus. In December 2018, we entered into an exclusive license agreement with Sanofi to acquire worldwide rights to osanetant. We believe that several disorders involving the hypothalamus-pituitary-gonadal axis could benefit from treatment with an NK3R antagonist. We plan to evaluate osanetant in various patient populations with iVMS, including for BRCA-positive breast cancer following BSO and following treatment for Hormone Receptor (+) breast cancer and prostate cancer where HRT is likely contraindicated. We intend to submit an IND in the fourth quarter of 2020 and initiate a Phase 1/2 trial in the first quarter of 2021, subject to additional capital, evaluating pharmacokinetics, pharmacodynamics and safety, and to identify an optimal dosing strategy.

References

1. L. Holmberg, O.E. Iversen, C.M. Rudenstam, et al. Increased risk of recurrence after hormone replacement therapy in breast cancer survivors, J. Natl. Cancer Inst. 100 (7) (2008) 475–482.

2. Kotsopoulos J, Huzarski T, Gronwald J, Moller P, Lynch HT, Neuhausen SL, et al. Hormone replacement therapy after menopause and risk of breast cancer in BRCA1 mutation carriers: a case-control study. Breast Cancer Research and Treatment 2016;155(2):365–73.

3. Guidozzi F. Hormone therapy after prophylactic risk reducing bilateral salpingo-oophorectomy in women who have BRCA gene mutation. Climacteric 2016;19(5): 419–22.

4. Chlebowski RT, Kuller LH, Prentice RL, et al. Breast cancer after use of estrogen plus progestin in postmenopausal women. N Engl J Med.2009;360(6):573-587.

Our Corporate Information

We are a Delaware corporation. Our principal executive offices are located at One Gateway Center, 300 Washington Street, Suite 351, Newton, Massachusetts 02458, and our telephone number is (844)902-6100. Our website address is www.acertx.com. The information found on our website, or that may be accessed by links on our website, is not part of this prospectus. We have included our website address solely as an inactive textual reference. Investors should not rely on any such information in deciding whether to purchase our common stock.

THE OFFERING

On April 30, 2020, we entered into a purchase agreement with Lincoln Park, which we refer to in this prospectus as the Purchase Agreement, pursuant to which Lincoln Park has agreed to purchase from us up to an aggregate of $15,000,000 of our common stock (subject to certain limitations) from time to time over the term of the Purchase Agreement. Also on April 30, 2020, we entered into a registration rights agreement with Lincoln Park, which we refer to in this prospectus as the Registration Rights Agreement, pursuant to which we have filed

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with the SEC the registration statement that includes this prospectus to register for resale under the Securities Act of 1933, as amended, or the Securities Act, the shares of common stock that may be issued to Lincoln Park under the Purchase Agreement. Pursuant to the terms of the Purchase Agreement, at the time we signed the Purchase Agreement and the Registration Rights Agreement, we issued 148,148 Commitment Shares to Lincoln Park as consideration for its commitment to purchase shares of our common stock under the Purchase Agreement. The 148,148 Commitment Shares are also covered by this prospectus.

We do not have the right to commence any sales of our common stock to Lincoln Park under the Purchase Agreement until certain conditions set forth in the Purchase Agreement have been satisfied, including that the SEC has declared effective the registration statement that includes this prospectus. Thereafter, from time to time, at our sole discretion, we may direct Lincoln Park to purchase shares of our common stock in amounts up to 50,000 shares on any single business day, which amounts may be increased to up to 100,000 shares, depending on the market price of our common stock at the time of sale and subject to a maximum commitment by Lincoln Park of $1,000,000 per single purchase, which we refer to in this prospectus as “Regular Purchases.” In addition, at our discretion, Lincoln Park has committed to purchase other “accelerated amounts” and/or “additional accelerated amounts” under certain circumstances. We will control the timing and amount of any sales of our common stock to Lincoln Park. The purchase price of the shares that may be sold to Lincoln Park in Regular Purchases under the Purchase Agreement will be based on the market price of our common stock preceding the time of sale as computed under the Purchase Agreement. The purchase price per share will be equitably adjusted for any reorganization, recapitalization,non-cash dividend, stock split, or other similar transaction occurring during the business days used to compute such price. We may at any time in our sole discretion terminate the Purchase Agreement without fee, penalty or cost upon one business day notice. There are no restrictions on future financings, rights of first refusal, participation rights, penalties or liquidated damages in the Purchase Agreement or Registration Rights Agreement, other than a prohibition on our entering into certain types of transactions that are defined in the Purchase Agreement as “Variable Rate Transactions.” Lincoln Park may not assign or transfer its rights and obligations under the Purchase Agreement.

As of April 29, 2020, there were 10,101,034 shares of our common stock outstanding, of which 5,523,010 shares were held bynon-affiliates. Although the Purchase Agreement provides that we may sell up to $15,000,000 of our common stock to Lincoln Park, only 1,840,148 shares of our common stock are being offered under this prospectus, which represents shares which have been or may be issued to Lincoln Park in the future under the Purchase Agreement, if and when we sell shares to Lincoln Park under the Purchase Agreement. Depending on the market prices of our common stock at the time we elect to issue and sell shares to Lincoln Park under the Purchase Agreement, we may need to register for resale under the Securities Act additional shares of our common stock in order to receive aggregate gross proceeds equal to the $15,000,000 total commitment available to us under the Purchase Agreement. If all of the 1,840,148 shares offered by Lincoln Park under this prospectus were issued and outstanding as of the date hereof (without taking into account the 19.99% shareholder approval limitation), such shares would represent approximately 15.4% of the total number of shares of our common stock outstanding and approximately 25.0% of the total number of outstanding shares held bynon-affiliates, in each case as of the date hereof. If we elect to issue and sell more than the 1,840,148 shares offered under this prospectus to Lincoln Park, which we have the right, but not the obligation, to do, we must first register for resale under the Securities Act any such additional shares, which could cause additional substantial dilution to our stockholders. The number of shares ultimately offered for resale by Lincoln Park is dependent upon the number of shares we sell to Lincoln Park under the Purchase Agreement.

Under applicable rules of the Nasdaq Capital Market, in no event may we issue or sell to Lincoln Park under the Purchase Agreement more than 19.99% of the shares of our common stock outstanding immediately prior to the execution of the Purchase Agreement (which is 2,020,205 shares based on 10,101,034) shares outstanding immediately prior to the execution of the Purchase Agreement), which limitation we refer to as the Exchange Cap, unless (i) we obtain stockholder approval to issue shares of common stock in excess of the Exchange Cap or

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(ii) the average price of all applicable sales of our common stock to Lincoln Park under the Purchase Agreement equals or exceeds $2.135 per share (which represents the average closing price of our common stock for the five trading days ending on April 29, 2020, the trading day immediately preceding the date the Purchase Agreement was executed) plus an incremental amount, such that issuances and sales of our common stock to Lincoln Park under the Purchase Agreement would be exempt from the Exchange Cap limitation under applicable Nasdaq rules. In any event, the Purchase Agreement specifically provides that we may not issue or sell any shares of our common stock under the Purchase Agreement if such issuance or sale would breach any applicable Nasdaq rules.

The Purchase Agreement also prohibits us from directing Lincoln Park to purchase any shares of common stock if those shares, when aggregated with all other shares of our common stock then beneficially owned by Lincoln Park and its affiliates, would result in Lincoln Park and its affiliates having beneficial ownership, at any single point in time, of more than 9.99% of the then total outstanding shares of our common stock, as calculated pursuant to Section 13(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, and Rule13d-3 thereunder, which limitation we refer to as the Beneficial Ownership Cap.

Issuances of our common stock in this offering will not affect the rights or privileges of our existing stockholders, except that the economic and voting interests of each of our existing stockholders will be diluted as a result of any such issuance. Although the number of shares of common stock that our existing stockholders own will not decrease, the shares owned by our existing stockholders will represent a smaller percentage of our total outstanding shares after any such issuance to Lincoln Park.

There are substantial risks to our shareholders as a result of the sale and issuance of common stock to Lincoln Park under the Purchase Agreement. These risks include substantial dilution, significant declines in our stock price and our inability to draw sufficient funds when needed. See “Risk Factors.” Issuance of our common stock to Lincoln Park under the Purchase Agreement will not affect the rights or privileges of our existing stockholders, except that the economic and voting interests of our existing stockholders will be diluted as a result of any such issuance. Although the number of shares of common stock that our existing stockholders own will not decrease, the shares owned by our existing stockholders will represent a smaller percentage of our total outstanding shares after any such issuance to Lincoln Park.

Securities Offered

Common stock to be offered by the selling stockholder	•   148,148 Commitment Shares issued to Lincoln Park upon execution of the Purchase Agreement. We will not receive any cash proceeds from the issuance of these Commitment Shares. •   Up to 1,692,000 shares we may sell to Lincoln Park under the Purchase Agreement from time to time after the date of this prospectus.
Common stock outstanding prior to this offering	10,101,034 shares
Common stock to be outstanding after this offering	11,941,182 shares, assuming the sale of a total of 1,692,000 shares of our common stock to Lincoln Park and the 148,148 Commitment Shares issued to Lincoln Park. The actual number of shares issued will vary depending upon the actual sales prices under this offering.

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Use of proceeds	We will receive no proceeds from the sale of shares of common stock by Lincoln Park in this offering. We may receive up to $15,000,000 aggregate gross proceeds under the Purchase Agreement from any sales we make to Lincoln Park pursuant to the Purchase Agreement after the date of this prospectus. Any proceeds that we receive from sales to Lincoln Park under the Purchase Agreement will be used for working capital and general corporate purposes. See “Use of Proceeds.”
Risk factors	This investment involves a high degree of risk. See “Risk Factors” for a discussion of factors you should consider carefully before making an investment decision.
Nasdaq Capital Market Symbol	“ACER”

Unless otherwise noted, the number of shares of our common stock outstanding prior to and after this offering is based on 10,095,176 shares outstanding as of December 31, 2019, and excludes:

• 1,313,475 shares of common stock issuable upon exercise of outstanding stock options as of December 31, 2019 at a weighted-average exercise price of $12.28;

• 9,000 shares of common stock issuable upon settlement of outstanding restricted stock units as of December 31, 2019; and

• 162,004 shares of common stock reserved for future issuance under our 2018 Stock Incentive Plan as of December 31, 2019, plus any future increases in the number of shares of common stock reserved for issuance pursuant to evergreen provisions.

The above also excludes 403,807 additional shares of common stock which became available for future issuance pursuant to the evergreen provision under our 2018 Stock Incentive Plan as of January 1, 2020.

To the extent that additional shares are issued pursuant to the foregoing, investors purchasing our common stock in this offering will experience further dilution. In addition, we may offer other securities in other offerings due to market conditions or strategic considerations. To the extent we issue such securities, investors may experience further dilution.

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RISK FACTORS

Investing in our securities involves a high degree of risk. Before making an investment decision with respect to our securities, we urge you to carefully consider the risks described in the “Risk Factors” sections of our most recent Annual Report on Form10-K filed with the SEC and incorporated by reference into this prospectus. In addition, the following risk factors present material risks and uncertainties associated with this offering. The risks and uncertainties incorporated by reference into this prospectus or described below are not the only ones we face. Additional risks and uncertainties not presently known or which we consider immaterial as of the date hereof may also have an adverse effect on our business. If any of the matters discussed in the following risk factors were to occur, our business, financial condition, results of operations, cash flows or prospects could be materially adversely affected, the market price of our securities could decline and you could lose all or part of your investment in our securities.

Risks Related to the Offering

Substantial doubt exists as to our ability to continue as a going concern.

As of December 31, 2019, we had an accumulated deficit of $76.3 million, cash and cash equivalents of $12.1 million, and current liabilities of $2.8 million. Based on available resources, we believe that our cash and cash equivalents currently on hand are sufficient to fund our operations into the fourth quarter of 2020, excluding support for a planned emetine clinical trial and EDSIVO^TM development and precommercial activities. Thus, our current capital resources are not sufficient to fund our planned operations for the next 12 months from the date of the financial statements incorporated into this prospectus. Moreover, we have not established a source of revenue and we expect to continue to incur losses for the foreseeable future as we continue our development of, and seek marketing approvals for, our product candidates. These factors individually and collectively raise substantial doubt about our ability to continue as a going concern and therefore it may be more difficult for us to attract investors. Unless we are able to raise additional capital to finance our operations, our long-term business plan may not be accomplished, and we may be forced to cease, reduce, or delay operations. In their audit report in respect of our 2019 audited financial statements, our independent registered public accounting firm included in its report an explanatory paragraph indicating that the substantial doubt as to our ability to continue as a going concern is of fundamental importance to understanding our financial statements.

The sale or issuance of our common stock to Lincoln Park may cause dilution and the sale of the shares of common stock acquired by Lincoln Park, or the perception that such sales may occur, could cause the price of our common stock to fall.

On April 30, 2020, we entered into the Purchase Agreement with Lincoln Park, pursuant to which Lincoln Park has committed to purchase up to $15,000,000 of our common stock. Upon the execution of the Purchase Agreement, we issued 148,148 Commitment Shares to Lincoln Park as consideration for its commitment to purchase shares of our common stock under the Purchase Agreement. The remaining shares of our common stock that may be issued under the Purchase Agreement may be sold by us to Lincoln Park at our discretion from time to time over a36-month period commencing after the satisfaction of certain conditions set forth in the Purchase Agreement, including that the SEC has declared effective the registration statement that includes this prospectus. The purchase price for the shares that we may sell to Lincoln Park under the Purchase Agreement will fluctuate based on the price of our common stock. Depending on market liquidity at the time, sales of such shares may cause the trading price of our common stock to fall.

We generally have the right to control the timing and amount of any sales of our shares to Lincoln Park under the Purchase Agreement. Sales of our common stock, if any, to Lincoln Park under the Purchase Agreement will depend upon market conditions and other factors to be determined by us. We may ultimately decide to sell to Lincoln Park all, some or none of the shares of our common stock that may be available for us to

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sell pursuant to the Purchase Agreement. If and when we do sell shares to Lincoln Park, after Lincoln Park has acquired the shares, Lincoln Park may resell all, some or none of those shares at any time or from time to time in its discretion. Therefore, sales to Lincoln Park by us could result in substantial dilution to the interests of other holders of our common stock. Additionally, the sale of a substantial number of shares of our common stock to Lincoln Park, or the anticipation of such sales, could make it more difficult for us to sell equity or equity-related securities in the future at a time and at a price that we might otherwise wish to effect sales.

We may not have access to the full amount available under the Purchase Agreement with Lincoln Park.

Pursuant to the Purchase Agreement with Lincoln Park, Lincoln Park has committed to purchase up to $15,000,000 of our common stock from time to time over a36-month period. The number of shares we may sell to Lincoln Park on any single business day in a Regular Purchase is 50,000, but that amount may be increased to up to 100,000 shares of our common stock, depending on the market price of our common stock at the time of sale and subject to a maximum limit of $1,000,000 per Regular Purchase. Depending on the prevailing market price of our common stock, we may not be able to sell shares to Lincoln Park for the maximum $15,000,000 over the term of the Purchase Agreement. In addition, under the rules of the Nasdaq Capital Market, in no event may we issue more than 19.99% of our shares outstanding under the Purchase Agreement unless we obtain stockholder approval or an exception pursuant to the rules of the Nasdaq Capital Market is obtained to issue more than 19.99%. This limitation will not apply in certain limited circumstances as set out in the Purchase Agreement. We are not required or permitted to issue any shares of common stock under the Purchase Agreement if such issuance would breach our obligations under the rules or regulations of the Nasdaq Capital Market. In addition, Lincoln Park will not be required to purchase any shares of our common stock if such sale would result in Lincoln Park’s beneficial ownership exceeding 9.99% of the then outstanding shares of our common stock. Our inability to access a portion or the full amount available under the Purchase Agreement, in the absence of any other financing sources, could have a material adverse effect on our business.

The extent we rely on Lincoln Park as a source of funding will depend on a number of factors including, the prevailing market price of our common stock and the extent to which we are able to secure working capital from other sources. If obtaining sufficient funding from Lincoln Park were to prove unavailable or prohibitively dilutive, we will need to secure another source of funding in order to satisfy our working capital needs. Even if we were to receive all $15,000,000 in gross proceeds under the Purchase Agreement with Lincoln Park, we may still need additional capital to fully implement our business, operating and development plans. Assuming a purchase price of $2.40 (which represents the closing price of our common stock on April 30, 2020), the purchase by Lincoln Park of the entire 1,692,000 purchase shares registered hereunder would result in gross proceeds to us of only $4,060,800. Should the financing we require to sustain our working capital needs be unavailable or prohibitively expensive when we require it, the consequences could be a material adverse effect on our business, operating results, financial condition and prospects.

Our share price is volatile, 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 this section, may have a significant impact on the market price of our common stock:

• announcements of significant changes in our business or operations;

• the development status of any of our drug candidates, including clinical study results and determinations by regulatory authorities with respect thereto, including but not limited to any continued development of EDSIVO^TM that we may or may not decide to pursue in light of the FDA’s March 2020 denial of our appeal of the June 2019 Complete Response Letter;

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• the initiation, termination or reduction in the scope of any collaboration arrangements or any disputes or developments regarding such collaborations;

• our capital and our inability to obtain additional funding;

• announcements of technological innovations, new commercial products or other material events by our competitors or by us;

• disputes or other developments concerning our proprietary rights;

• changes in, or failure to meet, securities analysts’ or investors’ expectations of our financial performance;

• additions or departures of key personnel;

• discussions of our business, products, financial performance, prospects or stock price by the financial and scientific press and online investor communities;

• public concern as to, and legislative action with respect to, the pricing and availability of prescription drugs or the safety of drugs and drug delivery techniques;

• regulatory developments in the U.S. and in foreign countries; or

• dilutive effects of sales of shares of common stock by us or our stockholders, and sales of common stock acquired upon exercise or conversion by the holders of options.

Broad market and industry factors, as well as economic and political factors, also may materially adversely affect the market price of our common stock.

We will require additional financing to obtain marketing approval of our product candidates and, if approved, to commercialize our product candidates, and a failure to obtain this necessary capital when needed on acceptable terms, or at all, could force us to delay, limit, reduce or terminate our product development, other operations or commercialization efforts.

Since our inception, substantially all of our resources have been dedicated to the clinical development of our product candidates. As of December 31, 2019, we had an accumulated deficit of $76.3 million, cash and cash equivalents of $12.1 million and current liabilities of $2.8 million. As discussed above, based on available resources, we believe that our cash and cash equivalents currently on hand are sufficient to fund our anticipated operating and capital requirements into the fourth quarter of 2020, excluding support for a planned emetine clinical trial and EDSIVO^TM development and precommercial activities. Thus, our current capital resources are not sufficient to fund our planned operations for the next 12 months from the date of the financial statements incorporated by reference into this prospectus.

We will need to raise additional capital in order to finance the completion of clinical development and regulatory preparedness of our product candidates, preparations for a commercial launch of our product candidates, if approved, and development of any other current or future product candidates we may choose to further develop. These expenditures will include costs associated with research and development, conducting preclinical studies and clinical trials, obtaining marketing approvals, and manufacturing and supply as well as marketing and selling any products approved for sale. In addition, other unanticipated costs may arise. Because the outcome of any drug development process is highly uncertain, we cannot reasonably estimate the actual amounts necessary to successfully complete the development and commercialization of our current product candidates, if approved, or future product candidates, if any.

Our operating plan may change as a result of factors currently unknown to us, and we may need to seek additional funds sooner than planned, through public or private equity or debt financings or other sources, such as strategic collaborations. Such financing may result in dilution to stockholders, imposition of debt covenants and

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repayment obligations, or other restrictions that may adversely affect our business. In addition, we may seek additional capital due to favorable market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans.

Our future capital requirements depend on many factors, including:

• the scope, progress, results, and costs of researching and developing our current product candidates and future product candidates, if any, including conducting preclinical and clinical trials;

• the cost of seeking regulatory and marketing approvals and reimbursement for our product candidates and future product candidates, if any;

• the cost of commercialization activities if our current product candidates and future product candidates, if any, are approved for sale, including marketing, sales and distribution costs, and preparedness of our corporate infrastructure;

• the cost of manufacturing current product candidates and future product candidates, if any, that we obtain approval for and successfully commercialize;

• our ability to establish and maintain strategic collaborations, licensing or other arrangements and the financial terms of such agreements;

• the number and characteristics of any additional product candidates we may develop or acquire;

• any product liability or other lawsuits related to our product candidates or commenced against us;

• the expenses needed to attract and retain skilled personnel;

• the costs associated with being a public company;

• the costs involved in preparing, filing, prosecuting, maintaining, defending and enforcing our intellectual property rights, including litigation costs and the outcome of such litigation; and

• the timing, receipt and amount of sales of, or royalties on, future approved products, if any.

Additional funds may not be available when we need them, on terms that are acceptable to us, or at all. If adequate funds are not available to us on a timely basis, we may be required to:

• delay, limit, reduce or terminate preclinical studies, clinical trials or other development activities for our current product candidates or future product candidates, if any;

• delay, limit, reduce or terminate our research and development activities; or

• delay, limit, reduce or terminate our establishment of sales and marketing capabilities or other activities that may be necessary to commercialize future approved products, if any.

Future sales of our common stock could cause dilution, and the sale of such common stock, or the perception that such sales may occur, could cause the price of our stock to decline.

Sales of additional shares of our common stock, as well as securities convertible into or exercisable for common stock, could result in substantial dilution to our stockholders and cause the market price of our common stock to decline. An aggregate of 10,095,176 shares of common stock were outstanding as of December 31, 2019. As of such date, another 1,322,475 shares of common stock were issuable upon exercise of outstanding options and the settlement of outstanding restricted stock units. A substantial majority of the outstanding shares of our common stock, as well as a substantial majority of the shares of common stock issuable upon exercise of outstanding options, are freely tradable without restriction or further registration under the Securities Act.

We may sell additional shares of common stock, as well as securities convertible into or exercisable for common stock, in subsequent public or private offerings. We may also issue additional shares of common stock,

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as well as securities convertible into or exercisable for common stock, to finance future acquisitions. We will need to raise additional capital in order to initiate or complete additional development activities for all of our product candidates, or to pursue additional disease indications for our product candidates, and this may require us to issue a substantial amount of securities (including common stock as well as securities convertible into or exercisable for common stock). There can be no assurance that our capital raising efforts will be able to attract the capital needed to execute on our business plan and sustain our operations. Moreover, we cannot predict the size of future issuances of our common stock, as well as securities convertible into or exercisable for common stock, or the effect, if any, that future issuances and sales of our securities will have on the market price of our common stock. Sales of substantial amounts of our common stock, as well as securities convertible into or exercisable for common stock, including shares issued in connection with an acquisition or securing funds to complete any clinical trial plans, or the perception that such sales could occur, may result in substantial dilution and may adversely affect prevailing market prices for our common stock.

Our management will have broad discretion over the use of the net proceeds from our sale of shares of common stock to Lincoln Park, you may not agree with how we use the proceeds and the proceeds may not be invested successfully.

Our management will have broad discretion as to the use of the net proceeds from our sale of shares of common stock to Lincoln Park, and we could use them for purposes other than those contemplated at the time of commencement of this offering. Accordingly, you will be relying on the judgment of our management with regard to the use of those net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. It is possible that, pending their use, we may invest those net proceeds in a way that does not yield a favorable, or any, return for us. The failure of our management to use such funds effectively could have a material adverse effect on our business, financial condition, operating results and cash flows.

We are a defendant in securities litigation, which may be costly and time-consuming to defend.

Following periods of market volatility in the price of a company’s securities or the reporting of unfavorable news, security holders have often instituted class action litigation. This risk is especially relevant for us because pharmaceutical companies like ours have experienced significant stock price volatility in recent years. Moreover, we were named in a putative securities class action complaint and a stockholders’ derivative suit as a result of the decline in our stock price following the June 25, 2019 announcement that we had received a Complete Response Letter from the FDA regarding our NDA for EDSIVO^™. See Item 3 – Legal Proceedings in our Annual Report on Form10-K for the fiscal year ended December 31, 2019 which is incorporated by reference into this prospectus for additional information. Regardless of the outcome, we could incur substantial legal costs and our management’s attention could be diverted from the operation of our business, causing our business to suffer.

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FORWARD-LOOKING STATEMENTS

This 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 of 1933, as amended, 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 “expects,” “believes,” “hopes,” “anticipates,” “estimates,” “may,” “could,” “intends,” “exploring,” “evaluating,” “progressing,” “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 emetine, EDSIVO^™ (celiprolol),ACER-001, and osanetant, constitute forward-looking statements. Such forward-looking statements are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated. These risks and uncertainties include, but are not limited to, those risks discussed in “Risk Factors,” as well as, without limitation, risks associated with:

• the strategies, prospects, plans, expectations and objectives of management for future operations, including the anticipated timing of regulatory submissions or actions;

• public health crises, pandemics and epidemics, such as the novel strain of coronavirus(COVID-19), and their effects on our preclinical and planned clinical activities;

• our ability to raise additional capital to continue our development programs;

• market conditions;

• the progress, scope or duration of the development of product candidates or programs;

• the benefits that may be derived from product candidates or the commercial or market opportunity in any target indication;

• our ability to protect our intellectual property rights;

• our anticipated operations, financial position, costs or expenses;

• statements regarding future economic conditions or performance;

• statements concerning proposed new products, services or developments;

• statements of belief and any statement of assumptions underlying any of the foregoing;

• our ability to sell shares of common stock to Lincoln Park pursuant to the terms of the Purchase Agreement and our ability to register and maintain the registration of the shares issued and issuable thereunder; and

• our anticipated use of the net proceeds from the potential sale of shares of our common stock to Lincoln Park.

These forward-looking statements speak only as of the date made. We assume no obligation or undertaking to update any forward-looking statements to reflect any changes in 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 the reports we file with the Securities and Exchange Commission (“SEC”).

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THE LINCOLN PARK TRANSACTION

General

On April 30, 2020, we entered into the Purchase Agreement and the Registration Rights Agreement with Lincoln Park. Pursuant to the terms of the Purchase Agreement, Lincoln Park has agreed to purchase from us up to $15,000,000 of our common stock (subject to certain limitations) from time to time during the term of the Purchase Agreement. Pursuant to the terms of the Registration Rights Agreement, we have filed with the SEC the registration statement that includes this prospectus to register for resale under the Securities Act the shares that may be issued to Lincoln Park under the Purchase Agreement. Pursuant to the terms of the Purchase Agreement, we previously issued 148,148 Commitment Shares to Lincoln Park as consideration for its commitment to purchase shares of our common stock under the Purchase Agreement. The 148,148 Commitment Shares are also covered by this prospectus

We do not have the right to commence any sales to Lincoln Park under the Purchase Agreement until certain conditions set forth in the Purchase Agreement have been satisfied, including the registration statement that includes this prospectus being declared effective by the SEC. Thereafter, from time to time, at our sole discretion, we may direct Lincoln Park to purchase shares of our common stock in amounts up to 50,000 shares on any single business day in a Regular Purchase, which maximum amount may be increased to up to 100,000 shares, depending on the market price of our common stock at the time of sale and subject to a maximum commitment by Lincoln Park of $1,000,000 per single Regular Purchase. In addition, at our discretion, Lincoln Park has committed to purchase other “accelerated amounts” and/or “additional accelerated amounts” under certain circumstances. The purchase price per share sold in Regular Purchases will be based on the market price of our common stock immediately preceding the time of sale as computed under the Purchase Agreement. Lincoln Park may not assign or transfer its rights and obligations under the Purchase Agreement.

As of April 29, 2020, there were 10,101,034 shares of our common stock outstanding, of which 5,523,010 shares were held bynon-affiliates. Although the Purchase Agreement provides that we may sell up to $15,000,000 of our common stock to Lincoln Park, only 1,840,148 shares of our common stock are being offered under this prospectus, which represents shares which have been or may be issued to Lincoln Park in the future under the Purchase Agreement, if and when we sell shares to Lincoln Park under the Purchase Agreement. Depending on the market prices of our common stock at the time we elect to issue and sell shares to Lincoln Park under the Purchase Agreement, we may need to register for resale under the Securities Act additional shares of our common stock in order to receive aggregate gross proceeds equal to the $15,000,000 total commitment available to us under the Purchase Agreement. If all of the 1,840,148 shares offered by Lincoln Park under this prospectus were issued and outstanding as of the date hereof (without taking into account the 19.99% shareholder approval limitation), such shares would represent approximately 15.4% of the total number of shares of our common stock outstanding and approximately 25.0% of the total number of outstanding shares held bynon-affiliates, in each case as of the date hereof. If we elect to issue and sell more than the 1,840,148 shares offered under this prospectus to Lincoln Park, which we have the right, but not the obligation, to do, we must first register for resale under the Securities Act any such additional shares, which could cause additional substantial dilution to our stockholders. The number of shares ultimately offered for resale by Lincoln Park is dependent upon the number of shares we sell to Lincoln Park under the Purchase Agreement.

Under applicable rules of the Nasdaq Capital Market, in no event may we issue or sell to Lincoln Park under the Purchase Agreement shares of our common stock in excess of the Exchange Cap (which is 2,020,205 shares, or 19.99% of the 10,101,034 shares of our common stock outstanding immediately prior to the execution of the Purchase Agreement), unless (i) we obtain stockholder approval to issue shares of common stock in excess of the Exchange Cap or (ii) the average price of all applicable sales of our common stock to Lincoln Park under the Purchase Agreement equals or exceeds $2.135 (which represents the average closing price of our common stock for the five trading days ending on April 29, 2020, the trading day immediately preceding the date the Purchase Agreement was executed) plus an incremental amount, such that issuances and sales of our common stock to

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Lincoln Park under the Purchase Agreement would be exempt from the Exchange Cap limitation under applicable Nasdaq rules. In any event, the Purchase Agreement specifically provides that we may not issue or sell any shares of our common stock under the Purchase Agreement if such issuance or sale would breach any applicable Nasdaq rules.

The Purchase Agreement also prohibits us from directing Lincoln Park to purchase any shares of common stock if those shares, when aggregated with all other shares of our common stock then beneficially owned by Lincoln Park and its affiliates, would result in Lincoln Park and its affiliates having beneficial ownership, at any single point in time, of more than 9.99% of the then total outstanding shares of our common stock, as calculated pursuant to Section 13(d) of the Exchange Act, and Rule13d-3 thereunder, which limitation we refer to as the Beneficial Ownership Cap.

Purchase of Shares Under the Purchase Agreement

Under the Purchase Agreement, we may from time to time, at our discretion, direct Lincoln Park to purchase on any single business day up to 50,000 shares of our common stock in a Regular Purchase, provided, however, that (i) the Regular Purchase may be increased to up to 75,000 shares, provided that the closing sale price of our common stock is not below $1.50 per share on the applicable purchase date (subject to adjustment for any reorganization, recapitalization,non-cash dividend, stock split, reverse stock split or other similar transaction as provided in the Purchase Agreement), and (ii) the Regular Purchase may be increased to up to 100,000 shares, provided that the closing sale price of our common stock is not below $2.00 per share on the applicable purchase date (subject to adjustment for any reorganization, recapitalization,non-cash dividend, stock split, reverse stock split or other similar transaction as provided in the Purchase Agreement) (such share amount limitations, the “Regular Purchase Share Limit”). In each case, Lincoln Park’s maximum commitment in any single Regular Purchase may not exceed $1,000,000. The Regular Purchase Share Limit is subject to proportionate adjustment in the event of a reorganization, recapitalization,non-cash dividend, stock split or other similar transaction; provided, that if after giving effect to such full proportionate adjustment, the adjusted Regular Purchase Share Limit would preclude us from requiring Lincoln Park to purchase common stock at an aggregate purchase price equal to or greater than $100,000 in any single Regular Purchase, then the Regular Purchase Share Limit will not be fully adjusted, but rather the Regular Purchase Share Limit for such Regular Purchase shall be adjusted as specified in the Purchase Agreement, such that, after giving effect to such adjustment, the Regular Purchase Share Limit will be equal to (or as close as can be derived from such adjustment without exceeding) $100,000.

The purchase price per share for each such Regular Purchase will be equal to the lower of:

• the lowest sale price for our common stock on the purchase date of such shares; or

• the arithmetic average of the three lowest closing sale prices for our common stock during the 10 consecutive business days ending on the business day immediately preceding the purchase date of such shares.

In addition to Regular Purchases described above, we may also direct Lincoln Park, on any business day on which we have properly submitted a Regular Purchase notice directing Lincoln Park to purchase the maximum number of shares of our common stock that we are then permitted to include in a single Regular Purchase notice and the closing sale price of our common stock on such business day is not below $0.50 per share (subject to adjustment for any reorganization, recapitalization,non-cash dividend, stock split, reverse stock split or other similar transaction as provided in the Purchase Agreement), to purchase an additional amount of our common stock, which we refer to as an Accelerated Purchase, not to exceed the lesser of:

• 30% of the aggregate shares of our common stock traded during all or, if certain trading volume or market price thresholds specified in the Purchase Agreement are crossed on the applicable Accelerated Purchase date, which is defined as the next business day following the purchase date for the corresponding Regular Purchase, the portion of the normal trading hours on the applicable Accelerated

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Purchase date prior to such time that any one of such thresholds is crossed, which period of time on the applicable Accelerated Purchase date we refer to as the Accelerated Purchase Measurement Period; and

• 3 times the number of purchase shares purchased pursuant to the corresponding Regular Purchase.

The purchase price per share for each such Accelerated Purchase will be equal to the lower of:

• 97% of the volume weighted average price of our common stock during the applicable Accelerated Purchase Measurement Period on the applicable Accelerated Purchase date; and

• the closing sale price of our common stock on the applicable Accelerated Purchase date.

We may also direct Lincoln Park, not later than 1:00 p.m., Eastern time, on a business day on which an Accelerated Purchase has been completed and all of the shares to be purchased thereunder (and under the corresponding Regular Purchase) have been properly delivered to Lincoln Park in accordance with the Purchase Agreement prior to such time on such business day, and provided that the closing price of our common stock on the business day immediately preceding such business day is not less than $0.50 per share (subject to adjustment for any reorganization, recapitalization,non-cash dividend, stock split, reverse stock split or other similar transaction as provided in the Purchase Agreement), to purchase an additional amount of our common stock, which we refer to as an Additional Accelerated Purchase, of up to the lesser of:

• 30% of the aggregate shares of our common stock traded during a certain portion of the normal trading hours on such Accelerated Purchase date as determined in accordance with the Purchase Agreement, which period of time we refer to as the Additional Accelerated Purchase Measurement Period; and

• 3 times the number of purchase shares purchased pursuant to the Regular Purchase corresponding to the Accelerated Purchase that was completed on such Accelerated Purchase date on which an Additional Accelerated Purchase notice was properly received.

We may, in our sole discretion, submit multiple Additional Accelerated Purchase notices to Lincoln Park prior to 1:00 p.m., Eastern time, on a single Accelerated Purchase date, provided that all prior Accelerated Purchases and Additional Accelerated Purchases (including those that have occurred earlier on the same day) have been completed and all of the shares to be purchased thereunder (and under the corresponding Regular Purchase) have been properly delivered to Lincoln Park in accordance with the Purchase Agreement.

The purchase price per share for each such Additional Accelerated Purchase will be equal to the lower of:

• 97% of the volume weighted average price of our common stock during the applicable Additional Accelerated Purchase Measurement Period on the applicable Additional Accelerated Purchase date; and

• the closing sale price of our common stock on the applicable Additional Accelerated Purchase date.

In the case of Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases, the purchase price per share will be equitably adjusted for any reorganization, recapitalization,non-cash dividend, stock split, reverse stock split or other similar transaction occurring during the business days used to compute the purchase price.

Other than as described above, there are no trading volume requirements or restrictions under the Purchase Agreement, and we will control the timing and amount of any sales of our common stock to Lincoln Park.

Minimum Share Price

Under the Purchase Agreement, we and Lincoln Park may not effect any sales of shares of our common stock under the Purchase Agreement on any purchase date that the closing sale price of our common stock is less than the floor price of $0.25 per share of common stock, subject to adjustment as provided in the Purchase Agreement.

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Events of Default

Events of default under the Purchase Agreement include the following:

• the effectiveness of the registration statement of which this prospectus forms a part lapses for any reason (including, without limitation, the issuance of a stop order), or any required prospectus supplement and accompanying prospectus are unavailable for the resale by Lincoln Park of our common stock offered hereby, and such lapse or unavailability continues for a period of 10 consecutive business days or for more than an aggregate of 30 business days in any365-day period;

• suspension by our principal market of our common stock from trading for a period of one business day;

• thede-listing of our common stock from the Nasdaq Capital Market, our principal market, provided our common stock is not immediately thereafter trading on the New York Stock Exchange, the Nasdaq Global Market, the Nasdaq Global Select Market, the NYSE American, NYSE Arca, or OTC Markets (or nationally recognized successor thereto);

• if at any time the Exchange Cap is reached unless and until stockholder approval is obtained, to the extent applicable;

• the failure of our transfer agent to issue to Lincoln Park shares of our common stock within three business days after the applicable date on which Lincoln Park is entitled to receive such shares;

• any breach of the representations or warranties or covenants contained in the Purchase Agreement or Registration Rights Agreement that has or would reasonably be expected to have a material adverse effect on us and, in the case of a breach of a covenant that is reasonably curable, that is not cured within five business days;

• any voluntary or involuntary participation or threatened participation in insolvency or bankruptcy proceedings by or against us; or

• if at any time we are not eligible to transfer our common stock electronically.

Lincoln Park does not have the right to terminate the Purchase Agreement upon any of the events of default set forth above, although the Purchase Agreement would automatically terminate in the event of any voluntary or involuntary participation or threatened participation in insolvency or bankruptcy proceedings by or against us. During an event of default, all of which are outside of Lincoln Park’s control, we may not direct Lincoln Park to purchase any shares of our common stock under the Purchase Agreement.

Our Termination Rights

We have the unconditional right, at any time, for any reason and without any payment or liability to us, to give notice to Lincoln Park to terminate the Purchase Agreement.

No Short-Selling or Hedging by Lincoln Park

Lincoln Park has agreed that neither it nor any of its affiliates shall engage in any direct or indirect short-selling or hedging of our common stock during any time prior to the termination of the Purchase Agreement.

Prohibitions on Variable Rate Transactions

There are no restrictions on future financings, rights of first refusal, participation rights, penalties or liquidated damages in the Purchase Agreement or Registration Rights Agreement other than a prohibition on entering into a “Variable Rate Transaction,” as defined in the Purchase Agreement.

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Effect of Performance of the Purchase Agreement on Our Stockholders

All shares registered in this offering that have been or may be issued or sold by us to Lincoln Park under the Purchase Agreement are expected to be freely tradable. It is anticipated that shares registered in this offering will be sold over a period of up to36-months commencing on the date that the registration statement including this prospectus becomes effective. The sale by Lincoln Park of a significant amount of shares registered in this offering at any given time could cause the market price of our common stock to decline and to be highly volatile. Sales of our common stock to Lincoln Park, if any, will depend upon market conditions and other factors to be determined by us. We may ultimately decide to sell to Lincoln Park all, some or none of the additional shares of our common stock that may be available for us to sell pursuant to the Purchase Agreement. If and when we do sell shares to Lincoln Park, after Lincoln Park has acquired the shares, Lincoln Park may resell all, some or none of those shares at any time or from time to time in its discretion. Therefore, sales to Lincoln Park by us under the Purchase Agreement may result in substantial dilution to the interests of other holders of our common stock. In addition, if we sell a substantial number of shares to Lincoln Park under the Purchase Agreement, or if investors expect that we will do so, the actual sales of shares or the mere existence of our arrangement with Lincoln Park may make it more difficult for us to sell equity or equity-related securities in the future at a time and at a price that we might otherwise wish to effect such sales. However, we have the right to control the timing and amount of any additional sales of our shares to Lincoln Park and the Purchase Agreement may be terminated by us at any time at our discretion without any cost to us.

Pursuant to the terms of the Purchase Agreement, we have the right, but not the obligation, to direct Lincoln Park to purchase up to $15,000,000 of our common stock (exclusive of the 148,148 Commitment Shares issued to Lincoln Park on the date of the Purchase Agreement). Depending on the price per share at which we sell our common stock to Lincoln Park pursuant to the Purchase Agreement, we may need to sell to Lincoln Park under the Purchase Agreement more shares of our common stock than are offered under this prospectus in order to receive aggregate gross proceeds equal to the $15,000,000 total commitment available to us under the Purchase Agreement. If we choose to do so, we must first register for resale under the Securities Act such additional shares of our common stock, which could cause additional substantial dilution to our stockholders. The number of shares ultimately offered for resale by Lincoln Park under this prospectus is dependent upon the number of shares we direct Lincoln Park to purchase under the Purchase Agreement.

The Purchase Agreement prohibits us from issuing or selling to Lincoln Park under the Purchase Agreement (i) shares of our common stock in excess of the Exchange Cap, unless and until we obtain stockholder approval to issue shares in excess of the Exchange Cap or the average price of all applicable sales of our common stock to Lincoln Park under the Purchase Agreement equals or exceeds $2.135 (which represents the average closing price of our common stock for the five trading days ending on April 29, 2020) plus an incremental amount, such that the transactions contemplated by the Purchase Agreement are exempt from the Exchange Cap limitation under applicable Nasdaq rules, and (ii) any shares of our common stock if those shares, when aggregated with all other shares of our common stock then beneficially owned by Lincoln Park and its affiliates, would exceed the Beneficial Ownership Cap.

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The following table sets forth the amount of gross proceeds we would receive from Lincoln Park from our sale of shares to Lincoln Park under the Purchase Agreement at varying purchase prices:

Assumed Average Purchase Price Per Share	Number of Registered Shares to be Issued if Full Purchase(1)	Percentage of Outstanding Shares After Giving Effect to the Issuance to Lincoln Park (2)	Gross Proceeds from the Sale of Shares to Lincoln Park Under the Purchase Agreement
$1.00	1,692,000	14.2%	$1,692,000
$2.00	1,692,000	14.2%	$3,384,000
$2.40(3)	1,692,000	14.2%	$4,060,800
$3.00	1,692,000	14.2%	$5,076,000
$4.00	1,692,000	14.2%	$6,768,000

(1) Although the Purchase Agreement provides that we may sell up to $15,000,000 of our common stock to Lincoln Park, we are only registering 1,840,148 shares under this prospectus which represents: (i) 148,148 Commitment Shares that we already issued to Lincoln Park as commitment fee for making the commitment under the Purchase Agreement; and (ii) an additional 1,692,000 shares which may be issued to Lincoln Park in the future under the Purchase Agreement, if and when we sell shares to Lincoln Park under the Purchase Agreement, and which may or may not cover all the shares we ultimately sell to Lincoln Park under the Purchase Agreement, depending on the purchase price per share. As a result, we have included in this column only those shares that we are registering in this offering. If we seek to issue shares of our common stock, including shares from other transactions that may be aggregated with the transactions contemplated by the Purchase Agreement under the applicable rules of the Nasdaq Capital Market, in excess of 2,020,205 shares, or 19.99% of the total common stock outstanding immediately prior to the execution of the Purchase Agreement, we may be required to seek stockholder approval in order to be in compliance with the rules of the Nasdaq Capital Market.

(2) The denominator is based on 10,101,034 shares outstanding as of April 29, 2020, adjusted to include (i) the 148,148 Commitment Shares issued to Lincoln Park upon execution of the Purchase Agreement and (ii) the number of shares set forth in the adjacent column which we would have sold to Lincoln Park, assuming the purchase price in the first column. The numerator is based on the number of shares issuable under the Purchase Agreement at the corresponding assumed purchase price set forth in the first column.

(3) The closing sale price of our common stock on April 30, 2020.

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USE OF PROCEEDS

This prospectus relates to shares of our common stock that may be offered and sold from time to time by Lincoln Park. We will receive no proceeds from the sale of shares of common stock by Lincoln Park in this offering. We may receive up to $15,000,000 aggregate gross proceeds under the Purchase Agreement from any sales we make to Lincoln Park pursuant to the Purchase Agreement. We estimate that the net proceeds to us from the sale of our common stock to Lincoln Park pursuant to the Purchase Agreement will be up to $14,869,468 over an approximately36-month period, assuming that we sell the full amount of our common stock that we have the right, but not the obligation, to sell to Lincoln Park under the Purchase Agreement, and after estimated fees and expenses. See “Plan of Distribution” elsewhere in this prospectus for more information.

We expect to use any proceeds that we receive under the Purchase Agreement for working capital and general corporate purposes. It is possible that no shares will be issued under the Purchase Agreement. We may also use a portion of the net proceeds to acquire or invest in complementary businesses, technologies, product candidates or other intellectual property, although we have no present commitments or agreements to do so.

The amounts and timing of these expenditures will depend on a number of factors, such as the timing and progress of our research and development efforts, regulatory actions affecting our product candidates and our business, technological advances and the competitive environment for our product candidates. As of the date of this prospectus, we cannot specify with certainty all of the particular uses for any net proceeds we receive. Accordingly, we will retain broad discretion over the use of these proceeds. Pending use of the net proceeds as described above, 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 obligations of the U.S. government.

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DILUTION

The sale of our common stock to Lincoln Park pursuant to the Purchase Agreement will have a dilutive impact on our stockholders. In addition, the lower our stock price is at the time we exercise our right to sell shares to Lincoln Park, the more shares of our common stock we will have to issue to Lincoln Park pursuant to the Purchase Agreement and our existing stockholders would experience greater dilution.

Our net tangible book value as of December 31, 2019 was $10,604,449, or $1.05 per share, based on 10,095,176 shares of our common stock outstanding as of that date. After giving effect to the sale of 1,692,000 shares of our common stock to Lincoln Park pursuant to the Purchase Agreement at an assumed sale price of $2.40 per share of our common stock (which represents the closing price of our common stock on April 30, 2020), and after the issuance of 148,148 shares of common stock to Lincoln Park as Commitment Shares and after deducting estimated offering expenses payable by us, ouras-adjusted net tangible book value as of December 31, 2019 would have been approximately $14.5 million, or $1.22 per share. This represents an immediate increase in net tangible book value of $0.17 per share to existing stockholders and an immediate dilution of $1.18 per share to investors in this offering.

The number of shares of common stock to be outstanding immediately after this offering is based on 10,095,176 shares outstanding as of December 31, 2019 and excludes:

• 1,313,475 shares of common stock issuable upon exercise of stock options outstanding as of December 31, 2019 under our equity incentive plans, with a weighted-average exercise price of $12.28 per share;

• 9,000 shares of common stock issuable upon vesting of restricted stock units under our equity incentive plans; and

• 162,004 shares of common stock reserved for future issuance under our 2018 Stock Incentive Plan, plus any future increases in the number of shares of common stock reserved for issuance pursuant to evergreen provisions.

The above also excludes 403,807 additional shares of common stock which became available for future issuance pursuant to the evergreen provisions under our 2018 Stock Incentive Plan as of January 1, 2020.

To the extent that additional shares are issued pursuant to the foregoing, investors purchasing our common stock in this offering will experience further dilution. In addition, we may offer other securities in other offerings due to market conditions or strategic considerations. To the extent we issue such securities, investors may experience further dilution.

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SELLING STOCKHOLDER

This prospectus relates to the possible resale by the selling stockholder, Lincoln Park, of shares of common stock that may be issued to Lincoln Park pursuant to the Purchase Agreement. We are filing the registration statement of which this prospectus forms a part pursuant to the provisions of the Registration Rights Agreement, which we entered into with Lincoln Park on April 30, 2020, concurrently with our execution of the Purchase Agreement, in which we agreed to provide certain registration rights with respect to sales by Lincoln Park of the shares of our common stock that may be issued to Lincoln Park under the Purchase Agreement.

Lincoln Park, as the selling stockholder, may, from time to time, offer and sell pursuant to this prospectus any or all of the shares that we may sell to Lincoln Park under the Purchase Agreement. The selling stockholder may sell some, all or none of its shares. We do not know how long the selling stockholder will hold the shares before selling them, and we currently have no agreements, arrangements or understandings with the selling stockholder regarding the sale of any of the shares.

The following table presents information regarding the selling stockholder and the shares of our common stock that it may offer and sell from time to time under this prospectus. The table is prepared based on information supplied to us by the selling stockholder, and reflects its holdings as of April 30, 2020. Neither Lincoln Park nor any of its affiliates has held a position or office, or had any other material relationship, with us or any of our predecessors or affiliates. Beneficial ownership is determined in accordance with Section 13(d) of the Exchange Act and Rule13d-3 thereunder.

Selling Stockholder	Shares Beneficially Owned Before this Offering			Percentage of Outstanding Shares Beneficially Owned Before this Offering			Shares to be Sold in this Offering Assuming the Company issues the Maximum Number of Shares Under the Purchase Agreement			Percentage of Outstanding Shares Beneficially Owned After this Offering
Lincoln Park Capital Fund, LLC (1)		148,148	(2)		1.47	% (3)		1,840,148	(4)		*

* Represents less than 1% of the outstanding shares and/or assumes all shares of common stock registered hereunder have been resold by Lincoln Park.

(1) Josh Scheinfeld and Jonathan Cope, the Managing Members of Lincoln Park Capital, LLC, are deemed to be beneficial owners of all of the shares of common stock owned by Lincoln Park Capital Fund, LLC. Messrs. Cope and Scheinfeld have shared voting and investment power over the shares being offered under the prospectus filed with the SEC in connection with the transactions contemplated under the Purchase Agreement. Lincoln Park Capital, LLC is not a licensed broker dealer or an affiliate of a licensed broker dealer.

(2) Represents 148,148 Commitment Shares issues to Lincoln Park upon our execution of the Purchase Agreement as a fee for its commitment to purchase shares of our common stock under the Purchase Agreement, all of which are covered by the registration statement that includes this prospectus.

(3) Based on 10,101,034 outstanding shares of our common stock as of April 29, 2020, which excludes the 148,148 Commitment Shares we have already issued to Lincoln Park pursuant to the Purchase Agreement.

(4) Although the Purchase Agreement provides that we may sell up to $15,000,000 of our common stock to Lincoln Park, only 1,840,148 shares of our common stock are being offered under this prospectus which represents: (i) 148,148 Commitment Shares issued to Lincoln Park upon our execution of the Purchase Agreement as a fee for its commitment to purchase shares of our common stock under the Purchase Agreement; and (ii) an aggregate of 1,692,000 shares that may be sold by us to Lincoln Park at our discretion from time to time over a36-month period commencing after the satisfaction of certain conditions set forth in the Purchase Agreement, including that the SEC has declared effective the registration statement that includes this prospectus. Depending on the price per share at which we sell our common stock to Lincoln Park pursuant to the Purchase Agreement, we may need to sell to Lincoln Park under the Purchase

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Agreement more shares of our common stock than are offered under this prospectus in order to receive aggregate gross proceeds equal to the $15,000,000 total commitment available to us under the Purchase Agreement. If we choose to do so, we must first register for resale under the Securities Act such additional shares. The number of shares ultimately offered for resale by Lincoln Park is dependent upon the number of shares we sell to Lincoln Park under the Purchase Agreement.

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MARKET PRICE OF OUR COMMON STOCK AND RELATED STOCKHOLDER MATTERS

Market Information

Our common stock is traded on the Nasdaq Capital Market under the symbol “ACER.”

Holders

As of April 30, 2020, there were approximately 90 registered holders of our common stock. This number does not include stockholders for whom shares were held in “nominee” or “street name.”

Dividend Policy

We have never declared or paid any cash dividends on our common stock and we do not intend to pay cash dividends in the foreseeable future. We currently expect to retain any future earnings to fund the operation and expansion of our business.

DESCRIPTION OF CAPITAL STOCK

The following is a summary of the rights of our common and preferred stock and some of the provisions of our certificate of incorporation and bylaws and of the Delaware General Corporation Law, or DGCL.

Our authorized capital stock consists of 150,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of undesignated preferred stock, $0.0001 par value per share. As of April 29, 2020, there were 10,101,034 shares of our common stock outstanding and no shares of our preferred stock outstanding.

Common Stock

Each holder of common stock is entitled to one vote for each share of common stock held on all matters submitted to a vote of stockholders. We have not provided for cumulative voting for the election of directors in our certificate of incorporation. This means that the holders of a majority of the shares voted can elect all of the directors then standing for election. Subject to preferences that may apply to shares of preferred stock outstanding at the time, the holders of outstanding shares of our common stock are entitled to receive dividends out of assets legally available at the times and in the amounts that our board of directors may determine from time to time. Upon our liquidation, dissolution orwinding-up, the holders of common stock are entitled to share ratably in all assets remaining after payment of all liabilities and the liquidation preferences of any outstanding preferred stock. Holders of common stock have no preemptive or conversion rights or other subscription rights. There are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are fully paid and nonassessable.

Anti-Takeover Effects of Delaware Law and Our Certificate of Incorporation and Bylaws

Certain provisions of Delaware law, our certificate of incorporation and our bylaws could have the effect of delaying, deferring or discouraging another party from acquiring control of us.

Certificate of Incorporation and Bylaws. Our certificate of incorporation and bylaws include provisions that:

• authorize the board of directors to issue, without stockholder approval, up to 10,000,000 shares of preferred stock with such designations, powers, preferences and other rights and qualifications, limitations or restrictions as our board of directors may authorize, which preferred stock could decrease the amount of earnings and assets available for distribution to holders of our common stock or adversely affect the rights and powers, including voting rights, of the holders of our common stock;

• establish advance notice requirements for stockholder nominations of directors and for stockholder proposals that can be acted on at stockholder meetings;

• limit who may call stockholder meetings;

• require that any action to be taken by our stockholders be effected at a duly called annual or special meeting and not by written consent;

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• provide that vacancies on our board of directors may be filled only by a majority of directors then in office, even if less than a quorum;

• require a super-majority of votes to amend certain provisions of our charter as well as to amend our bylaws generally;

• authorize us to indemnify officers and directors against losses that they may incur in investigations and legal proceedings resulting from their services to us, which may include services in connection with takeover defense measures; and

• establish the Court of Chancery of the State of Delaware as the sole and exclusive forum for certain derivative actions or proceeding brought on our behalf, any action asserting a claim of breach of fiduciary duty, any action asserting a claim against us arising pursuant to the DGCL, or any action asserting a claim governed by the internal affairs doctrine. Section 27 of the Exchange Act creates exclusive federal jurisdiction over all suits brought to enforce any duty or liability created by the Exchange Act or the rules and regulations thereunder. As a result, the exclusive forum provision will not apply to suits brought to enforce any duty or liability created by the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction. Section 22 of the Securities Act creates concurrent jurisdiction for federal and state courts over all suits brought to enforce any duty or liability created by the Securities Act or the rules and regulations thereunder. As a result, the exclusive forum provision will not apply to suits brought to enforce any duty or liability created by the Securities Act or any other claim for which the federal and state courts have concurrent jurisdiction.

Delaware anti-takeover statute. We are subject to the provisions of Section 203 of the DGCL regulating corporate takeovers. In general, Section 203 prohibits a publicly-held Delaware corporation from engaging, under certain circumstances, in a business combination with an interested stockholder for a period of three years following the date the person became an interested stockholder unless:

• prior to the date of the transaction, the board of directors of the corporation approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder; or

• upon completion of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the voting stock outstanding, but not the outstanding voting stock owned by the interested stockholder, (1) shares owned by persons who are directors and also officers and (2) shares owned by employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

• at or subsequent to the date of the transaction, the business combination is approved by the board of directors of the corporation and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least66-2/3% of the outstanding voting stock which is not owned by the interested stockholder.

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.

Transfer Agent and Registrar

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

Listing

Our common stock is listed on The Nasdaq Stock Market under the symbol “ACER.”

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PLAN OF DISTRIBUTION

The common stock offered by this prospectus is being offered by the selling stockholder, Lincoln Park. The common stock may be sold or distributed from time to time by the selling stockholder directly to one or more purchasers or through brokers, dealers, or underwriters who may act solely as agents at market prices prevailing at the time of sale, at prices related to the prevailing market prices, at negotiated prices, or at fixed prices, which may be changed. The sale of the common stock offered by this prospectus could be effected in one or more of the following methods:

• ordinary brokers’ transactions;

• transactions involving cross or block trades;

• through brokers, dealers, or underwriters who may act solely as agents

• “at the market” into an existing market for the common stock;

• in other ways not involving market makers or established business markets, including direct sales to purchasers or sales effected through agents;

• in privately negotiated transactions; or

• any combination of the foregoing.

In order to comply with the securities laws of certain states, if applicable, the shares may be sold only through registered or licensed brokers or dealers. In addition, in certain states, the shares may not be sold unless they have been registered or qualified for sale in the state or an exemption from the state’s registration or qualification requirement is available and complied with.

Lincoln Park is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act.

Lincoln Park has informed us that it intends to use an unaffiliated broker-dealer to effectuate all sales, if any, of the common stock that it may purchase from us pursuant to the Purchase Agreement. Such sales will be made at prices and at terms then prevailing or at prices related to the then current market price. Each such unaffiliated broker-dealer will be an underwriter within the meaning of Section 2(a)(11) of the Securities Act. Lincoln Park has informed us that each such broker-dealer will receive commissions from Lincoln Park that will not exceed customary brokerage commissions.

Brokers, dealers, underwriters or agents participating in the distribution of the shares may receive compensation in the form of commissions, discounts, or concessions from the selling stockholder and/or purchasers for whom the broker-dealers may act as agent. The compensation paid to any such particular broker-dealer may be less than or in excess of customary commissions. Neither we nor Lincoln Park can presently estimate the amount of compensation that any agent will receive.

We know of no existing arrangements between Lincoln Park or any other stockholder, broker, dealer, underwriter or agent relating to the sale or distribution of the shares offered by this prospectus.

We may from time to time file with the SEC one or more supplements to this prospectus or amendments to the registration statement of which this prospectus forms a part to amend, supplement or update information contained in this prospectus, including, if and when required under the Securities Act, to disclose certain information relating to a particular sale of shares offered by this prospectus by the selling stockholder, including the names of any brokers, dealers, underwriters or agents participating in the distribution of such shares by the selling stockholder, any compensation paid by Lincoln Park to any such brokers, dealers, underwriters or agents, and any other required information.

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We will pay the expenses incident to the registration, offering, and sale of the shares to Lincoln Park. We have agreed to indemnify Lincoln Park and certain other persons against certain liabilities in connection with the offering of shares of common stock offered hereby, including liabilities arising under the Securities Act or, if such indemnity is unavailable, to contribute amounts required to be paid in respect of such liabilities. Lincoln Park has agreed to indemnify us against liabilities under the Securities Act that may arise from certain written information furnished to us by Lincoln Park specifically for use in this prospectus or, if such indemnity is unavailable, to contribute amounts required to be paid in respect of such liabilities.

Lincoln Park has represented to us that at no time prior to the Purchase Agreement has Lincoln Park or its agents, representatives or affiliates engaged in or effected, in any manner whatsoever, directly or indirectly, any short sale (as such term is defined in Rule 200 of Regulation SHO of the Exchange Act) of our common stock or any hedging transaction, which establishes a net short position with respect to our common stock. Lincoln Park has agreed that during the term of the Purchase Agreement, it and its agents, representatives or affiliates will not enter into or effect, directly or indirectly, any of the foregoing transactions.

We have advised Lincoln Park that it is required to comply with Regulation M promulgated under the Exchange Act. With certain exceptions, Regulation M precludes the selling stockholder, any affiliated purchasers, and any broker-dealer or other person who participates in the distribution from bidding for or purchasing, or attempting to induce any person to bid for or purchase any security which is the subject of the distribution until the entire distribution is complete. Regulation M also prohibits any bids or purchases made in order to stabilize the price of a security in connection with the distribution of that security. All of the foregoing may affect the marketability of the securities offered by this prospectus.

This offering will terminate on the earlier of (i) termination of the Purchase Agreement or (ii) the date that all shares offered by this prospectus have been sold by Lincoln Park.

Our common stock is listed on the Nasdaq Capital Market under the symbol “ACER.”

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EXPERTS

The consolidated financial statements as of and for the year ended December 31, 2019 incorporated by reference in this prospectus have been so incorporated in reliance on the report of BDO USA, LLP, an independent registered public accounting firm (the report on the consolidated financial statements contains an explanatory paragraph regarding the Company’s ability to continue as a going concern), incorporated herein by reference, given on the authority of said firm as experts in auditing and accounting.

The consolidated financial statements as of and for the year ended December 31, 2018 incorporated by reference from our Annual Report onForm 10-K for the year ended December 31, 2019 have been audited by Wolf & Company, P.C., an independent registered public accounting firm, as stated in their report, which is incorporated by reference and has been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

LEGAL MATTERS

The validity of any securities offered by this prospectus will be passed upon for us by Pillsbury Winthrop Shaw Pittman LLP, San Diego, California.

WHERE YOU CAN FIND MORE INFORMATION

We have filed a registration statement on FormS-1 with the SEC under the Securities Act. This prospectus is part of the registration statement but the registration statement includes additional information and exhibits. We file annual, quarterly and current reports, proxy statements and other information with the SEC. The SEC also maintains a web site that contains reports, proxy and information statements and other information regarding companies, such as ours, that file documents electronically with the SEC. The website address is www.sec.gov. The information on the SEC’s website is not part of this prospectus, and any references to this website or any other website are inactive textual references only.

INCORPORATION BY REFERENCE

The SEC permits us to “incorporate by reference” the information contained in documents we have filed with the SEC, which means that we can disclose important information to you by referring you to those documents rather than by including them in this prospectus. Information that is incorporated by reference is considered to be part of this prospectus and you should read it with the same care that you read this prospectus. We have filed with the SEC, and incorporate by reference in this prospectus:

• our Annual Report onForm10-K for the year ended December 31, 2019;

• our Quarterly Report onForm 10-Q filed with the SEC on May 14, 2020;

• our Current Reports on Form8-K filed with the SEC onJanuary 2, 2020,February 24, 2020,March  18, 2020,April 30, 2020 andMay  11, 2020 (each to the extent filed and not furnished); and

• the description of our common stock contained inexhibit 4.1 to our Annual Report on Form10-K for the fiscal year ended December 31, 2019, filed with the SEC on March 18, 2020, including any amendment or report filed with the SEC for the purpose of updating such description.

We are not, however, incorporating, in each case, any documents or information that we are deemed to furnish and not file in accordance with SEC rules.

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Any statement contained in any document incorporated by reference herein will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or any additional prospectus supplements modifies or supersedes such statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

All reports and other documents we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the termination of this offering, including all such documents we may file with the SEC after the date of the initial registration statement and prior to the effectiveness of the registration statement, but excluding any information furnished to, rather than filed with, the SEC, will also be incorporated by reference into this prospectus and deemed to be part of this prospectus from the date of the filing of such reports and documents.

We will provide without charge to each person, including any beneficial owner, to whom this prospectus is delivered, upon written or oral request, a copy of any or all documents that are incorporated by reference into this prospectus, but not delivered with the prospectus, other than exhibits to such documents unless such exhibits are specifically incorporated by reference into the documents that this prospectus incorporates. You should direct oral or written requests by one of the following methods. Attention: Investor Relations, Acer Therapeutics Inc., One Gateway Center, 300 Washington Street, Suite 351, Newton, Massachusetts 02458. Our telephone number is (844)902-6100, and our investor email address is investors@acertx.com. Our website address is www.acertx.com. The information found on our website, or that may be accessed by links on our website, is not part of this prospectus. We have included our website address solely as an inactive textual reference. Investors should not rely on any such information in deciding whether to purchase our common stock.

DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION FOR SECURITIES ACT LIABILITIES

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to our directors, officers, and controlling persons, we have been informed that in the opinion of the SEC this indemnification is against public policy as expressed in the Securities Act and is therefore unenforceable.

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1,840,148 Shares of Common Stock

ACER THERAPEUTICS INC.

PROSPECTUS

                    , 2020

PART II

Information Not Required in Prospectus

Item 13. Other Expenses of Issuance and Distribution.

The following is a statement of estimated expenses in connection with the offering described in this registration statement. All expenses incurred with respect to the registration of the common stock will be borne by us. All amounts are estimates except the SEC registration fee.

	Amount to be Paid*
SEC Registration Fee	$	532
Printing Expenses*		15,000
Legal Fees and Expenses*		75,000
Accounting Fees and Expenses*		25,000
Miscellaneous Expenses*		15,000
	$	130,532

* Estimated solely for the purpose of this Item. Actual expenses may vary.

Item 14. Indemnification of Directors and Officers.

Section 102 of the Delaware General Corporation Law (the “DGCL”) allows a corporation to eliminate the personal liability of directors of a corporation to the corporation or its stockholders for monetary damages for breach of fiduciary duty as a director, except where the director breached the duty of loyalty, failed to act in good faith, engaged in intentional misconduct or knowingly violated a law, authorized the payment of a dividend or approved a stock repurchase in violation of the DGCL or obtained an improper personal benefit.

Section 145 of the DGCL provides, among other things, that we may indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding—other than an action by or in our right—by reason of the fact that the person is or was our director, officer, agent or employee, or is or was serving at our request as a director, officer, agent or employee of another corporation, partnership, joint venture, trust or other enterprise against expenses, including attorneys’ fees, judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with such action, suit or proceeding. The power to indemnify applies (a) if such person is successful on the merits or otherwise in defense of any action, suit or proceeding, or (b) if such person acting in good faith and in a manner he or she reasonably believed to be in the best interest, or not opposed to the best interest, of us, and with respect to any criminal action or proceeding had no reasonable cause to believe his or her conduct was unlawful. The power to indemnify applies to actions brought by or in our right as well but only to the extent of defense expenses, including attorneys’ fees but excluding amounts paid in settlement, actually and reasonably incurred and not to any satisfaction of judgment or settlement of the claim itself, and with the further limitation that in such actions no indemnification shall be made in the event of any adjudication of liability to us, unless the court believes that in light of all the circumstances indemnification should apply.

Section 174 of the DGCL provides, among other things, that a director, who willfully or negligently approves of an unlawful payment of dividends or an unlawful stock purchase or redemption, may be held liable for such actions. A director who was either absent when the unlawful actions were approved or dissented at the time, may avoid liability by causing his or her dissent to such actions to be entered in the books containing minutes of the meetings of the board of directors at the time such action occurred or immediately after such absent director receives notice of the unlawful acts.

Our certificate of incorporation and bylaws, filed as Exhibits 3.3 and 3.4 to our Current Report onForm 8-K filed on May 15, 2018, provide that we shall indemnify our directors, officers, employees and other agents to the fullest extent not prohibited by the DGCL or any other applicable law. In addition, we have entered into

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agreements to indemnify our directors and officers and expect to continue to enter into agreements to indemnify all of our directors and officers. These agreements require us, among other things, to indemnify our directors and officers against certain liabilities which may arise by reason of their status or service as directors or officers to the fullest extent not prohibited by law. These indemnification provisions and the indemnification agreements may be sufficiently broad to permit indemnification of our officers and directors for liabilities, including reimbursement of expenses incurred, arising under the Securities Act of 1933.

We maintain insurance policies under which our directors and executive officers are insured, within the limits and subject to the limitations of those policies, against certain expenses in connection with the defense of, and certain liabilities that might be imposed as a result of, actions, suits or proceedings to which they are parties by reason of being or having been directors or officers. The coverage provided by these policies may apply whether or not we would have the power to indemnify such person against such liability under the provisions of the General Corporation Law of the State of Delaware.

See Note 6 to the consolidated financial statements included in our Annual Report on Form10-K for the fiscal year ended December 31, 2019 filed on March 18, 2020 and incorporated by reference into this prospectus for a description of pending securities litigation to which we are a party and where we may be required or permitted to indemnify certain of our directors and officers.

Item 15. Recent Sales of Unregistered Securities.

On April 30, 2020, we completed a private placement to Lincoln Park Capital Fund, LLC pursuant to which we have the right to sell to Lincoln Park up to $15,000,000 in shares of common stock, subject to certain limitations, from time to time over the36-month period commencing on the date that a registration statement covering the resale of the shares is declared effective by the SEC. We issued 148,148 Commitment Shares to Lincoln Park as consideration for its commitment to purchase our shares under the Purchase Agreement. In the Purchase Agreement, Lincoln Park represented to the Company, among other things, that it was an “accredited investor” (as such term is defined in Rule 501(a) of Regulation D under the Securities Act of 1933, or the Securities Act). The securities were sold by the Company under the Purchase Agreement in reliance upon an exemption from the registration requirements under the Securities Act afforded by Section 4(a)(2) of the Securities Act.

Item 16. Exhibits and Financial Statement Schedules.

(a) Exhibits

The exhibits to the registration statement are listed in the Exhibit Index to this registration statement and are incorporated herein by reference.

(b) Financial statement schedules

All schedules have been omitted because either they are not required, are not applicable or the information is otherwise set forth in the financial statements and related notes thereto.

Item 17. Undertakings.

The undersigned registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate,

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represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Securities and Exchange Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided,however, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) above do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Securities and Exchange Commission by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(A) Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(B) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5) or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.Provided,however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(5) That, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

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(6) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

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EXHIBIT INDEX

Exhibit No.	Description
2.1#	Agreement and Plan of Merger and Reorganization, dated as of June  30, 2017, by and among Acer Therapeutics Inc. (formerly Opexa Therapeutics, Inc.), Opexa Merger Sub, Inc. and Acer Therapeutics Inc. (incorporated by reference to Exhibit 2.1 to the Company’s Current Report on Form8-K filed on July 3, 2017).
3.1	Certificate of Incorporation, as filed with the Delaware Secretary of State on May  15, 2018 (incorporated by reference to Exhibit 3.3 to the Company’s Current Report on Form8-K filed on May 15, 2018).
3.2	Bylaws, effective May 15, 2018 (incorporated by reference to Exhibit 3.4 to the Company’s Current Report on Form8-K filed on May 15, 2018).
3.3	Certificate of Ownership and Merger, as filed with the Delaware Secretary of State on May  15, 2018 (incorporated by reference to Exhibit 3.5 to the Company’s Current Report on Form8-K filed on May 15, 2018).
4.1	Description of the Company’s capital stock registered pursuant to Section  12 of the Securities Exchange Act of 1934 (incorporated by reference to Exhibit 4.1 to the Company’s Annual Report on Form10-K filed on March 18, 2020).
4.2	Specimen common stock certificate (incorporated by reference to Exhibit 4.1 to the Company’s Current Report on Form8-K filed on May 15, 2018).
5.1&	Opinion of Pillsbury Winthrop Shaw Pittman LLP
10.1+^	Acer Therapeutics Inc. Amended and Restated 2010 Stock Incentive Plan (incorporated by reference to Appendix A to the Company’s Definitive Proxy Statement on Schedule 14A filed on April 11, 2016).
10.2+^	Amendment No.  1 to the Acer Therapeutics Inc. Amended and Restated 2010 Stock Incentive Plan (incorporated by reference to Exhibit 10.35 to the Company’s Registration Statement on FormS-4, as amended, (FileNo. 333-219358) filed on July 19, 2017).
10.3+^	Form of award agreement for awards made under the Acer Therapeutics Inc. Amended and Restated 2010 Stock Incentive Plan (incorporated by reference to Exhibit 10.1 to the Company’s Quarterly Report on Form10-Q filed August 14, 2014).
10.4+^	Form of restricted stock agreement for awards made under the Acer Therapeutics Inc. Amended and Restated 2010 Stock Incentive Plan (incorporated by reference to Exhibit 10.3 to the Company’s Quarterly Report on Form10-Q filed on May 12, 2015).
10.5+	Acer Therapeutics Inc. 2013 Stock Incentive Plan, as amended (incorporated by reference to Exhibit 10.3 to the Company’s Current Report on Form8-K filed on September 20, 2017).
10.6+	Acer Therapeutics Inc. 2018 Stock Incentive Plan (incorporated by reference to Appendix G to the Company’s Definitive Proxy Statement on Schedule 14A filed on April 9, 2018).
10.7+	Form of Notice of Stock Option Grant and Stock Option Agreement for option awards to be made under the 2018 Stock Incentive Plan (incorporated by reference to Exhibit 10.3 to the Company’s Current Report on Form8-K filed on May 15, 2018).
10.8+	Form of Notice of Restricted Stock Unit Award and Restricted Stock Unit Agreement for awards under the 2018 Stock Incentive Plan (incorporated by reference to Exhibit 10.8 to the Company’s Annual Report on Form10-K for the year ended December 31, 2019).

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Exhibit No.	Description
10.9◆	Agreement of Access and Use of Clinical Trial Data, dated as of August  3, 2016, by and between Acer Therapeutics Inc. and L’Assistance Publique—Hôpitaux de Paris (incorporated by reference to Exhibit 10.16 to the Company’s Registration Statement on FormS-4, as amended (FileNo. 333-219358), filed on July 19, 2017).
10.10◆	License Agreement for Development and Exploitation, dated as of September  19, 2018, by and between Acer Therapeutics Inc. and Assistance Publique – Hôpitaux de Paris (incorporated by reference to Exhibit 10.1 to the Company’s Quarterly Report on Form10-Q filed on November 9, 2018).
10.11◆	Exclusive License Agreement, dated as of April  4, 2014, by and between Acer Therapeutics Inc. and Baylor College of Medicine (incorporated by reference to Exhibit 10.17 to the Company’s Registration Statement on FormS-4, as amended (FileNo. 333-219358), filed on July 19, 2017).
10.12	First Amendment to License Agreement dated April  28, 2014 by and between Baylor College of Medicine and Acer Therapeutics Inc. (incorporated by reference to Exhibit 10.18 to the Company’s Registration Statement on FormS-4, as amended (FileNo. 333-219358), filed on July 19, 2017).
10.13	Second Amendment to License Agreement, dated March  17, 2015, by and between Acer Therapeutics Inc. and Baylor College of Medicine (incorporated by reference to Exhibit 10.19 to the Company’s Registration Statement on FormS-4, as amended (FileNo. 333-219358), filed on July 19, 2017).
10.14	Third Amendment to License Agreement, dated September  8, 2016, by and between Acer Therapeutics Inc. and Baylor College of Medicine (incorporated by reference to Exhibit 10.20 to the Company’s Registration Statement on FormS-4, as amended (FileNo. 333-219358), filed on July 19, 2017).
10.15	Exclusive License Agreement, dated as of December  21, 2018, by and between Acer Therapeutics Inc. and Sanofi (incorporated by reference to Exhibit 99.1 to the Company to the Company’s Current Report on Form8-K filed on January 2, 2019.)
10.16+	Employment Agreement, dated February  22, 2018, by and between Acer Therapeutics Inc. and Chris Schelling (incorporated by reference to Exhibit 10.1 to the Company’s Current Report on Form8-K filed on February 27, 2018).
10.17+	Employment Agreement, dated February  22, 2018, by and between Acer Therapeutics Inc. and William Andrews (incorporated by reference to Exhibit 10.2 to the Company’s Current Report on Form8-K filed on February 27, 2018).
10.18+	Employment Agreement, dated February  22, 2018, by and between Acer Therapeutics Inc. and Harry Palmin (incorporated by reference to Exhibit 10.3 to the Company’s Current Report on Form8-K filed on February 27, 2018).
10.19+	Employment Agreement, dated April  20, 2018, by and between Acer Therapeutics Inc. and Donald Joseph (incorporated by reference to Exhibit 10.4 to the Company’s Quarterly Report on Form10-Q filed on May 14, 2018).
10.20+	Employment Agreement, dated September  18, 2019, by and between Acer Therapeutics Inc. and John Klopp (incorporated by reference to Exhibit 10.1 to the Company’s Quarterly Report on Form10-Q filed on November 13, 2019).
10.21+	Employment Agreement, dated September  18, 2019, by and between Acer Therapeutics Inc. and Matthew T. Seibt (incorporated by reference to Exhibit 10.2 to the Company’s Quarterly Report on Form10-Q filed on November 13, 2019).

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Exhibit No.	Description
10.22	Lease Agreement, dated March  6, 2018, by and between Acer Therapeutics Inc. and Commonwealth Development LLC, as trustee of the Gateway Realty Trust (incorporated by reference to Exhibit 10.5 to the Company’s Quarterly Report on Form10-Q filed on May 14, 2018).
10.23	Lease Agreement, dated March  5, 2019, by and between Acer Therapeutics Inc. and Commonwealth Development LLC, as trustee of the Gateway Realty Trust (incorporated by reference to Exhibit 10.1 to the Company’s Quarterly Report on Form10-Q filed on August 13, 2019).
10.24	Triple Net Lease, dated April  1, 2018, by and between Acer Therapeutics Inc. and Eastern Western Corp. (incorporated by reference to Exhibit 10.6 to the Company’s Quarterly Report on Form10-Q filed on May 14, 2018).
10.25+	Form of Indemnification Agreement between the Company and its directors and officers (incorporated by reference to Appendix F to the Company’s Definitive Proxy Statement on Schedule 14A filed on April 9, 2018).
10.26	Sales Agreement, dated November  9, 2018 by and between Acer Therapeutics Inc. and Roth Capital Partners, LLC (incorporated by reference to Exhibit 10.1 to the Company’s Current Report on Form8-K filed on November 9, 2018).
10.27	Amended and Restated Sales Agreement, dated March  18, 2020 by and among Acer Therapeutics Inc., Roth Capital Partners, LLC, and JonesTrading Institutional Services LLC (incorporated by reference to Exhibit 10.27 to the Company’s Annual Report on Form10-K filed on March 18, 2020).
10.28	Purchase Agreement, dated April  30, 2020, by and between Acer Therapeutics Inc. and Lincoln Park Capital Fund, LLC (incorporated by reference to Exhibit 10.1 to the Company’s Current Report on Form8-K filed on April 30, 2020).
10.29	Registration Rights Agreement, dated April  30, 2020, by and between Acer Therapeutics Inc. and Lincoln Park Capital Fund LLC (incorporated by reference to Exhibit 10.2 to the Company’s Current Report on Form8-K filed on April 30, 2020).
10.30*	Research Collaboration Agreement, dated March 26, 2020, by and between Acer Therapeutics Inc. and the National Center for Advancing Translational Sciences.
23.1*	Consent of Independent Registered Public Accounting Firm BDO USA, LLP.
23.2*	Consent of Independent Registered Public Accounting Firm Wolf & Company, P.C.
23.3&	Consent of Pillsbury Winthrop Shaw Pittman LLP (included in Exhibit 5.1).
24.1&	Power of Attorney (see the signature page hereof).

* Filed herewith.

& Previously filed.

+ Management contract or compensatory plan or arrangement.

# The schedules and exhibits to this exhibit have been omitted pursuant to Item 601(b)(2) of RegulationS-K. A copy of any omitted schedule and/or exhibit will be furnished to the SEC upon request.

◆ Confidential treatment was granted with respect to certain portions of this exhibit. Omitted portions have been filed separately with the Securities and Exchange Commission.

^ The name of this plan has been amended to reflect the current name of the Company.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Newton, State of Massachusetts, on June 1, 2020.

ACER THERAPEUTICS INC.
By:	/s/ Chris Schelling
	Chris Schelling
	President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Name	Title	Date
/s/ Chris Schelling Chris Schelling	President, Chief Executive Officer and Director (Principal Executive Officer)	June 1, 2020
/s/ Harry S. Palmin Harry S. Palmin	Chief Operating Officer and Chief Financial Officer (Principal Financial and Accounting Officer)	June 1, 2020
/s/ * Jason Amello	Director	June 1, 2020
/s/ * Steven J. Aselage	Chairman of the Board	June 1, 2020
/s/ * John M. Dunn	Director	June 1, 2020
/s/ * Michelle Griffin	Director	June 1, 2020

*By:	/s/ Chris Schelling
	Chris Schelling
	Attorney-in-fact

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