As filed with the Securities and Exchange Commission on March 27, 2017May 19, 2023.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington,
WASHINGTON, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

TRACON PHARMACEUTICALS, INC.

Pharmaceuticals, Inc.
(Exact name of registrant as specified in its charter)

8910 University Center Lane,

4350 La Jolla Village Drive, Suite 700800

San Diego, California 92122

(858) 550-0780

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Charles P. Theuer, M.D., Ph.D.

President and Chief Executive Officer

TRACON Pharmaceuticals, Inc.

8910 University Center Lane,4350 La Jolla Village Drive, Suite 700800

San Diego, California 92122

(858) 550-0780

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:As soon as practicable after the effective date of this registration statement.

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, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

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

If this Form is a 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, a non-accelerated filer, or 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” in Rule 12b-2 of the Exchange Act.

CALCULATION OF REGISTRATION FEEIf 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. ☐

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 whichthat 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 Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

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

PROSPECTUS SUBJECT TO COMPLETION, DATED MARCH 27, 2017MAY 19, 2023

3,231,515 Shares

Common Stock

5,000,000 Shares

This prospectus relates to the saleoffer and resale, from time to time, of up to 3,231,5155,000,000 shares of our common stock, par value $0.001 per share, by AspireLincoln Park Capital Fund, LLC. Aspire Capital is also referredLLC, which we refer to in this prospectus as Lincoln Park or the selling stockholder. The prices atshares of common stock to which the selling stockholderthis prospectus relates includes up to 4,400,784 shares that we may sell to Lincoln Park, from time to time after the date of this prospectus, in our sole discretion, pursuant to a purchase agreement between us and Lincoln Park dated May 8, 2023, which we refer to as the Purchase Agreement, and 599,216 shares will be determined bywe issued to Lincoln Park on May 8, 2023, in consideration for its commitment to purchase shares of our common stock at our direction under the prevailing market price for the shares or in negotiated transactions. Purchase Agreement.

We are not selling any securities under this prospectus and we will not receive any proceeds from the sale of the shares by the selling stockholder.Lincoln Park. However, we may receive aggregate gross proceeds of up to $21.0$26.0 million from the saleour sales of our common stock to Lincoln Park under the selling stockholder, pursuantPurchase Agreement, from time to a common stock purchase agreement entered into withtime in our discretion after the selling stockholder on March 14, 2017, once the registration statement,date of which this prospectus is a part, is declared effective.and after satisfaction of other conditions in the Purchase Agreement.

The selling stockholderLincoln Park is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act of 1933, as amended.amended, or the Securities Act.

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” on page for more information about how the selling stockholder may sell or otherwise dispose of the shares of common stock included in this prospectus. We will pay the expenses incurred by us in registering under the Securities Act the offer and resale of registering thesethe shares of common stock to which this prospectus relates, including legal and accounting fees, but all selling and other expenses incurred by the selling stockholder will be paid by the selling stockholder.

Our common stock is listed on The NASDAQ GlobalNasdaq Capital Market under the ticker symbol “TCON.” On March 24, 2017,May 18, 2023, the last reported saleclosing price per share offor our common stock, as reported on The Nasdaq Capital Market, was $4.10$0.63 per share.

You should read this prospectus and any prospectus supplement, together with additional information described under the headings “Incorporation“Incorporation of Certain Information by Reference”Reference” and “Where“Where You Can Find More Information,” carefully before you invest in any of our securities.

We are an “emerging growth company” as defined by the Jumpstart Our Business Startups Act of 2012 and, as such, we have elected to comply with certain reduced public company reporting requirements for this prospectus and future filings. Please see “Prospectus Summary – Implications of Being an Emerging Growth Company.”

Investing in our securitiescommon stock involves a high degree of risk. SeeYou should carefully review the risks and uncertainties described under the heading “Risk Factors” on page 97 of this prospectus.prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus, including those filed after the date hereof.

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 , 20172023

TABLE OF CONTENTS

i

We incorporate by reference important information into this prospectus. You may obtain the information incorporated by reference without charge by following the instructions under “Where“Where You Can Find More Information.Information.” You should carefully read this prospectus, as well as additional information described under “Incorporation“Incorporation of Certain Information by Reference,” before deciding to invest in our common stock.

Neither we nor the selling stockholder have authorized anyone to provide you with additional information or information different from that contained in this prospectus filed with the Securities and Exchange Commission.Commission, or the SEC. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. The selling stockholder is offering to sell, and seeking offers to buy, our common stock only in jurisdictions where offers and sales are permitted. The information contained in this prospectus is accurate only as of the date of this prospectus, regardless of the time of delivery of this prospectus or any sale of shares of our common stock. Our business, financial condition, results of operations and prospects may have changed since that date.

For investors outside the United States: NeitherStates, neither we nor the selling stockholder have 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 shares of common stock and the distribution of this prospectus outside the United States.

ii

RISK FACTORS

Investing in our common stock involves a high degree of risk. You should consider carefully the following risks and uncertainties as well as the risks and uncertainties described in the section entitled “Risk Factors” contained in our Annual Report on Form 10-K for the year ended December 31, 2016,2022, as filed with the Securities and Exchange Commission, or SEC on March 1, 2017,8, 2023, as well as in our subsequent Quarterly and Annual Reports filed with the SEC, which descriptions are incorporated in this prospectus by reference in their entirety, as well as in any prospectus supplement hereto. These risks and uncertainties are not the only risks and uncertainties we face. Additional risks and uncertainties not currently known to us, or that we currently view as immaterial, may also impair our business. If any of the risks or uncertainties described in our SEC filings or any additional risks and uncertainties actually occur, our business, financial condition, results of operations and cash flow could be materially and adversely affected. In that case, the trading price of our common stock could decline and you might lose all or part of your investment. You should carefully consider the following information about risks, together with the other information contained in this prospectus, before making an investment in our common stock.

We will needIt is not possible to raise substantial additional capital inpredict the future to fund our operations andactual number of shares of common stock we may be unablesell to raise such funds when needed and on acceptable terms.Lincoln Park under the Purchase Agreement, or the actual gross proceeds resulting from those sales.

We will need to raise substantial additional capital in the future to fund our operations. The extent to whichOn May 8, 2023, we utilizeentered into the Purchase Agreement with Aspire Capital as a source of funding will depend on a number of factors, including the prevailing market priceLincoln Park, pursuant to which Lincoln Park has committed to purchase up to $26.0 million of our common stock in a committed equity financing, including the volume$1.0 million Initial Purchase, subject to certain limitations and conditions set forth in the Purchase Agreement. The shares of trading in 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 an approximately 36-month period commencing on the Commencement Date.

We generally have the right to control the timing and amount of any sales of our shares of common stock to Lincoln Park under the extentPurchase Agreement. Sales of our common stock, if any, to whichLincoln 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 sell to Lincoln Park pursuant to the Purchase Agreement.

Because the purchase price per share to be paid by Lincoln Park for the shares of common stock that we are ablemay elect to secure funds from other sources. Thesell to Lincoln Park under the Purchase Agreement, if any, will fluctuate based on the market prices of our common stock at the time we elect to sell shares to Lincoln Park pursuant to the Purchase Agreement, if any, it is not possible for us to predict, as of the date of this prospectus and prior to any such sales, the number of shares of common stock that we will sell to Lincoln Park under the Purchase Agreement, the purchase price per share that Lincoln Park will pay for shares purchased from us under the Purchase Agreement, or the aggregate gross proceeds that we will receive from those purchases by Lincoln Park under the Purchase Agreement.

Moreover, although the Purchase Agreement provides that we may sell up to Aspire Capitalan aggregate of $26.0 million of our common stock to Lincoln Park, only 5,000,000 shares of common stock are being registered under the Purchase Agreement on any given day and duringSecurities Act for resale by Lincoln Park under the termregistration statement of which this prospectus forms a part, consisting of (i) the Purchase Agreement is limited. See “The Aspire Capital Transaction”599,216 Commitment Shares that we issued to Lincoln Park as consideration for additional information. Additionally, we and Aspire Capital may not effect any sales ofits commitment to purchase shares of our common stock under the Purchase Agreement during the continuance of an event of default or on any trading day that the closing sale priceand (ii) up to 4,400,784 shares of our common stock isthat we may elect to sell to Lincoln Park, in our sole discretion, from time to time from and after the Commencement Date under the Purchase Agreement.

If after the Commencement Date we elect to sell to the selling stockholder all of the 4,400,784 shares of common stock being registered for resale by Lincoln Park under this prospectus that are available for sale by us to the selling stockholder under the Purchase Agreement, depending on the market prices of our common stock at the time of such sales, the actual gross proceeds from the sale of all such shares of common stock by us to Lincoln Park may be substantially less than $0.50 per share. Even if we are ablethe $26.0 million total purchase commitment available to accessus under the full $21.0Purchase Agreement, which could materially adversely affect our liquidity.

7

If it becomes necessary for us to issue and sell to Lincoln Park shares of common stock in excess of the Exchange Cap under the Purchase Agreement in order to receive aggregate gross proceeds equal to $26.0 million under the Purchase Agreement, then for so long as the Exchange Cap continues to apply to issuances and sales of common stock under the Purchase Agreement, we will still need additional capitalmust first obtain stockholder approval to fully implement our business, operatingissue shares of common stock in excess of the Exchange Cap in accordance with applicable Nasdaq listing rules. Furthermore, if we elect to issue and development plans.

The salesell to Lincoln Park more than the 4,400,784 shares of our common stock that we may elect to Aspire Capital may cause substantial dilutionissue and sell to our existing stockholders andLincoln Park under the sale ofPurchase Agreement that are being registered for resale by Lincoln Park hereunder, which we have the shares of common stock acquiredright, but not the obligation, to do, we must first file with the SEC one or more additional registration statements to register under the Securities Act for resale by Aspire Capital could cause the priceLincoln Park such additional shares of our common stock we wish to decline.

We are registering for sale the Commitment Shares and Initial Purchase Shares that we have issued and 2,813,567 additional shares that we may sell to Aspire Capital from time to time under the Purchase Agreement, which the SEC must declare effective, in each case before we may elect to sell any additional shares of our common stock to Lincoln Park under the Purchase Agreement. It is anticipatedAny issuance and sale by us under the Purchase Agreement of a substantial amount of shares of common stock in addition to the 4,400,784 shares of common stock that shareswe may elect to issue and sell to Lincoln Park under the Purchase Agreement that are being registered in this offering will be sold over a period of upfor resale by Lincoln Park hereunder could cause additional substantial dilution to approximately 30 months from the date of this prospectus.our stockholders. The number of shares of our common stock ultimately offered for sale by Aspire Capital under this prospectusLincoln Park is dependent upon the number of shares of common stock, if any, we elect toultimately sell to Aspire CapitalLincoln Park under the Purchase Agreement. Depending on a variety of factors, including market liquidity of our common stock,Agreement, and the sale of sharescommon stock under the Purchase Agreement may cause the trading price of our common stock to decline.

Aspire CapitalInvestors who buy shares at different times will likely pay different prices, and the sale of the shares of common stock acquired by Lincoln Park could cause the price of our common stock to decline.

Pursuant to the Purchase Agreement, we will have discretion, subject to market demand, to vary the timing, prices, and numbers of shares sold to Lincoln Park. If and when we do elect to sell shares of our common stock to Lincoln Park pursuant to the Purchase Agreement, after Lincoln Park has acquired such shares, Lincoln Park may ultimately purchaseresell all, some or none of such shares at any time or from time to time in its discretion and at different prices. As a result, investors who purchase shares from Lincoln Park in this offering at different times will likely pay different prices for those shares, and so may experience different levels of dilution and in some cases substantial dilution and different outcomes in their investment results. Investors may experience a decline in the $21.0 millionvalue of common stock that, together with the Commitment Shares and Initial Purchase Shares, is the subjectshares they purchase from Lincoln Park in this offering as a result of this prospectus. Aspire Capital may sell all, some or none of our shares that it holds or comes to hold under the Purchase Agreement. Salesfuture sales made by us to Aspire Capital ofLincoln Park at prices lower than the prices such investors paid for their shares pursuant toin this offering. Further, the Purchase Agreement may result in dilution to the interests of other holders of our common stock. The sale of a substantial number of shares of our common stock by Aspire Capital in this offering,Lincoln Park, or anticipation of such sales, could cause the trading price of our common stock to decline or 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 desire.

Our ability to issue and sell the full $26.0 million of shares of our common stock to Lincoln Park pursuant to the Purchase Agreement is constrained due to relatively few authorized shares available for future issuance.

Our ability to raise additional equity capital pursuant to the Purchase Agreement is currently constrained. On May 18, 2023, the closing price for our common stock, as reported on The Nasdaq Capital Market, was $0.63 per share. As a result of such closing price, we have relatively few authorized shares of common stock that are not issued and outstanding or reserved for future issuance. If we are unable to utilize the full potential of the Purchase Agreement on a timely basis, we may be required to curtail or terminate some or all of our business plans, which could adversely affect our financial performance, growth and ability to continue our operations.

8

Our management will have broad discretion over the use of the net proceeds, if any, 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 used effectively.

This prospectus relates to shares of our common stock that may be offered and sold from time to time by Lincoln Park. We will not receive any proceeds upon the sale of shares by Lincoln Park. However, we may receive gross proceeds of up to $26.0 million from the sale of shares under the Purchase Agreement to Lincoln Park, including pursuant to the Initial Purchase. The anticipated use of net proceeds from the sale of our common stock to Lincoln Park under the Purchase Agreement represents our intentions based upon our current plans and business conditions. Because we have not designated the amount of net proceeds from the sale of shares under the Purchase Agreement to be used for any particular purpose, 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. 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. Further, our management may use the net proceeds for corporate purposes that may not improve our financial condition or market value. 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 may not have access to the full amount available under the Purchase Agreement with Lincoln Park. We may require additional financing to sustain our operations, without which we may not be able to continue operations, and the terms of subsequent financings may adversely impact our stockholders.

We may direct Lincoln Park to purchase up to $26.0 million worth of shares of our common stock, less the $1.0 million Initial Purchase, if any, in a Regular Purchase from time to time under the Purchase Agreement over a 36-month period generally in amounts up to 125,000 shares of our common stock, which may be increased to up to 175,000 shares of our common stock depending on the closing sale price of our common stock at the time of sale, provided that Lincoln Park’s maximum purchase obligation under any single Regular Purchase shall not exceed $1.0 million. Moreover, under certain circumstances as set forth in the Purchase Agreement, we may, in our sole discretion, also direct Lincoln Park to purchase additional shares of common stock in “accelerated purchases,” and “additional accelerated purchases” as set forth in the Purchase Agreement.

Depending on the prevailing market price of our common stock, we may not be able to sell shares to Lincoln Park for the maximum $26.0 million over the term of the Purchase Agreement. We will need to seek stockholder approval before issuing more than the Exchange Cap limit of 4,809,486 shares of common stock under the Purchase Agreement, unless the average price per share of common stock for all shares of common stock sold by us to Lincoln Park under the Purchase Agreement equals or exceeds $0.8225 per share (representing the lower of the official closing price of the common stock on Nasdaq on the trading day immediately preceding the date of the Purchase Agreement and the average official closing price of the common stock on Nasdaq for the five consecutive trading days ending on the trading day immediately preceding the date of the Purchase Agreement, as adjusted under applicable Nasdaq rules to take into account the issuance of Commitment Shares to Lincoln Park for non-cash consideration), such that the Exchange Cap limitation would no longer apply to issuances and sales of common stock by us to Lincoln Park under the Purchase Agreement under applicable Nasdaq listing rules. 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 of our common stock exceeding the Beneficial Ownership Cap of 9.99% of the 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.

9

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. Assuming a purchase price of $0.63 per share (which represents the closing price of our common stock on May 18, 2023), the purchase by Lincoln Park of the entire 4,400,784 shares of common stock issuable under the Purchase Agreement being registered for resale by Lincoln Park hereunder would result in gross proceeds to us of only $2.8 million. 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 sell all $26.0 million of shares of our common stock to Lincoln Park under the Purchase Agreement, we may still need additional capital to finance our future production plans and working capital needs, and we may have to raise funds through the issuance of equity or debt securities.

Depending on the type and the terms of any financing we pursue, stockholders’ rights and the value of their investment in our common stock could be reduced. A financing could involve one or more types of securities including common stock, convertible debt or warrants to acquire common stock. These securities could be issued at or below the then prevailing market price for our common stock. In addition, if we issue secured debt securities, the holders of the debt would have a claim to our assets that would be prior to the rights of stockholders until the debt is paid. Interest on these debt securities would increase costs and negatively impact operating results. If the issuance of new securities results in diminished rights to holders of our common stock, the market price of our common stock could be negatively impacted.

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.

10

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, and the documents incorporated by reference herein, and any prospectus supplement in connection with this offering contain forward-looking statements thatwithin the meaning of the safe harbor provisions for the U.S. Private Securities Litigation Reform Act of 1955. Such forward-looking statements reflect our management’s beliefs and views with respect to future events and are subject to substantial risks and uncertainties. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties withinand other factors that may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of historical fact, contained in this prospectus and the documents incorporated by reference herein, including statements regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management, are forward-looking statements. Forward-looking statements can be identified by the use of forward-looking words such as “believes,” “expects,” “may,” “will,” “plans,” “intends,” “estimates,” “could,” “should,” “would,” “continue,” “seeks,” “aims,” “projects,” “predicts,” “pro forma,” “anticipates,” “potential” or other similar words (including their use in the negative), or by discussions of future matters such as the development of product candidates or products, technology enhancements, possible changes in legislation, and other statements thatmay include, but are not historical.

The forward-looking statements in this prospectus include, among other things,limited to, statements about:

We may not actually achieve the plans, intentions or expectations disclosed in our11

In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “could,” “would,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “projects,” “predicts,” “potential” and similar expressions intended to identify forward-looking statements. We operate in a very competitiveThese statements reflect our current views with respect to future events, are based on assumptions and rapidly changing environment. It is not possible for our managementare subject to predict all risks nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make, and accordinglyuncertainties. Given these uncertainties, you should not place undue reliance on ourthese forward-looking statements. We have included important factorsdiscuss in greater detail, and incorporate by reference into this prospectus in their entirety, many of these risks under the headings “Risk Factors” of this prospectus and in our Annual Report on Form 10-K for the year ended December 31, 2022, which is incorporated herein by reference, as may be updated or superseded by the risks and uncertainties described under similar headings in the cautionary statements included in this prospectus, particularly inother documents that are filed after the “Risk Factors” section in this prospectusdate hereof and

the documents incorporated by reference herein, that we believe could cause actual results or events to differ materially from theinto this prospectus. Also, these forward-looking statements that we make. Our forward-looking statements do not reflectrepresent our estimates and assumptions only as of the potential impactdate of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.the document containing the applicable statement.

You should read this prospectus, the documents we have filed with the SEC that are incorporated by reference herein and the documentsany free writing prospectus that we have filed as exhibits to the registration statement of whichauthorized for use in connection with this prospectus is a partoffering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in this prospectus and the foregoing documents incorporated by reference herein by these cautionary statements. Except as

Unless required by law, we undertake no obligation to publicly update or revise any forward-looking statements whether as a result ofto reflect new information or future events or otherwise.

THE ASPIRE CAPITAL TRANSACTION

General12

USE OF PROCEEDS

On March 14, 2017, we entered into the Purchase Agreement, which provides that, upon the terms and subjectThis prospectus relates to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $21.0 million of our shares of common stock overthat may be offered and sold from time to time by Lincoln Park. We are not selling any securities under this prospectus and we will not receive any proceeds from the termsale of shares by Lincoln Park. We will pay the Purchase Agreement. In consideration for entering into the Purchase Agreement, concurrently with the execution of the Purchase Agreement, we issued to Aspire Capital the 195,726 Commitment Shares. Upon execution of the Purchase Agreement, we also sold to Aspire Capital the 222,222 Initial Purchase Shares for proceeds of $1.0 million. Concurrently with entering into the Purchase Agreement, we also entered into the Registration Rights Agreement,expenses incurred by us in which we agreed to file one or more registration statements as permissible and necessary to registerregistering under the Securities Act the offer and resale of the shares of common stock to which this prospectus relates, including legal and accounting fees, but all selling and other expenses incurred by the selling stockholder will be paid by the selling stockholder.

However, we may receive up to $26.0 million in aggregate gross proceeds under the Purchase Agreement from any sales of common stock we make to Lincoln Park pursuant to the Purchase Agreement after the date of this prospectus, including pursuant to the Initial Purchase. Any proceeds we receive from our sale of shares of common stock to Lincoln Park under the Purchase Agreement will be used for working capital and general corporate purposes, including research and development expenses and general and administrative expenses.

We have not determined the amount of net proceeds to be used specifically for such purposes, and the anticipated use of net proceeds from the sale of our common stock to Lincoln Park under the Purchase Agreement represents our intentions based upon our current plans and business conditions. As a result, management will retain broad discretion over the allocation of any proceeds from the sale of any shares of our common stock that have been and may be issued to Aspire Capital under the Purchase Agreement.

AsThe allocation of March 14, 2017, there were 16,165,659the net proceeds we receive from our sale of shares of common stock to Lincoln Park under the Purchase Agreement, if any, represents our estimates based upon our current plans and assumptions regarding industry and general economic conditions, our future expenditures.

The amounts and timing of our actual expenditures may vary significantly and will depend on numerous factors, including market conditions, cash generated or used by our operations, business developments and opportunities that may arise and related rate of growth. We may find it necessary or advisable to use portions of the proceeds we receive from our sale of shares of common stock to Lincoln Park under the Purchase Agreement for other purposes.

DIVIDEND POLICY

We have never declared or paid any dividends on our common stock. We currently intend to retain all available funds and any future earnings, if any, to fund the development and expansion of our business and we do not anticipate paying any cash dividends in the foreseeable future. Any future determination related to our dividend policy will be made at the discretion of our board of directors and will depend upon, among other factors, our results of operations, financial condition, capital requirements, contractual restrictions, business prospects and other factors our board of directors may deem relevant.

13

DILUTION

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

The price that Lincoln Park will receive for our common stock when resold pursuant to this prospectus will depend upon the timing of sales and will fluctuate based on the trading price of our common stock.

We calculate net tangible book value (deficit) per share by dividing our net tangible book value (deficit), which is tangible assets less total liabilities, by the number of outstanding excludingshares of our common stock. Dilution represents the 3,231,515difference between the portion of the amount per share paid by purchasers of shares offered that have been issuedin this offering and the as adjusted net tangible book value (deficit) per share of our common stock immediately after giving effect to this offering. As of March 31, 2023, we had a net tangible book value (deficit) of $(11.1 million), or may be issuable$(0.46) per share of common stock.

After giving effect to Aspire Capital(i) the sale of 4,400,784 shares of common stock to Lincoln Park for which we will receive cash proceeds pursuant to the Purchase Agreement. If allAgreement at an assumed price of such 3,231,515 shares$0.63 per share, the closing price of our common stock offered hereby were issuedon Nasdaq on May 18, 2023 and outstanding(ii) deducting estimated offering expenses of approximately $120,350 payable by us, and without giving effect to the Exchange Cap or Beneficial Ownership Cap under the Purchase Agreement, our as adjusted net tangible book value (deficit) as of the date hereof, such sharesMarch 31, 2023, would represent 19.9%have been approximately $(8.4 million), or $(0.30) per share. This represents an immediate increase in net tangible book value (deficit) of the total common stock outstanding. $0.16 per share to existing stockholders and an immediate dilution of $0.93 per share to new investors.

The following table illustrates this dilution on a per share basis:

The number of shares of our common stock ultimately offered for sale by Aspire Capitaloutstanding referenced above is dependentbased on 24,027,891 shares of common stock outstanding as of March 31, 2023, and excludes the following as of March 31, 2023:

Unless otherwise indicated, all information contained in this prospectus assumes or gives effect to no exercise of the outstanding options or warrants described above.

14

THE LINCOLN PARK TRANSACTION

General

On May 8, 2023, we entered into the Purchase Agreement including the Commitment Shares, may in no case exceed 3,231,515 shareswith Lincoln Park, pursuant to which Lincoln Park has agreed to purchase from us up to an aggregate of $26.0 million of our common stock (which is equal(subject to 19.99% ofcertain limitations) from time to time over the common stock outstanding on the dateterm of the Purchase Agreement) unless (i) shareholder approval is obtained to issue more, in which case this 3,231,515 share limitation will not apply, or (ii) shareholder approval has not been obtained and at any time the 3,231,515 share limitation is reached and at all times thereafter the average price paid for all shares issued under the Purchase Agreement (including the Commitment Shares) is equal to or greater than $4.15, referred to as the Minimum Price, a price equal to the closing sale price of our common stockAgreement.

Also on the business day prior to the date of the Purchase Agreement; provided that at no one point in time shall Aspire Capital (together with its affiliates) beneficially own more than 19.99% of our common stock.

Pursuant to the Purchase Agreement andMay 8, 2023, we entered into the Registration Rights Agreement, we are registering 3,231,515 shares of our common stock under the Securities Act, which includes the Commitment Shares and Initial Purchase Shares that have already been issuedpursuant to Aspire Capital and 2,813,567 shares of common stock which we may issue to Aspire Capital after this registration statement is declared effective underfiled with the Securities Act. All 3,231,515 shares of common stock are being offered pursuant to this prospectus. Under the Purchase Agreement, we have the right but not the obligation to issue more than the 3,231,515 shares of common stock included in this prospectus to Aspire Capital under some circumstances. If we elect to sell more than the 3,231,515 shares of common stock offered hereby, we must first register under the Securities Act the sale by Aspire Capital of any such additional shares.

After the Securities and Exchange Commission has declared effectiveSEC the registration statement of which this prospectus isforms a part to register under the Securities Act for resale by Lincoln Park up to 5,000,000 shares of common stock, consisting of (i) the 599,216 Commitment Shares that we previously issued to Lincoln Park on May 8, 2023 as consideration for its commitment to purchase shares of our common stock at our direction from time to time after the Commencement Date under the Purchase Agreement and (ii) up to 4,400,784 shares of our common stock that we may elect to sell to Lincoln Park, in our sole discretion, from time to time from and after the Commencement Date under the Purchase Agreement, including the Initial Purchase Shares.

We do not have the right to commence any sales of common stock to Lincoln Park under the Purchase Agreement until all of the conditions set forth in the Purchase Agreement have been satisfied on the Commencement Date, including that the registration statement of which this prospectus forms a part is declared effective by the SEC and a final prospectus relating thereto is filed with the SEC. On the Commencement Date, at our discretion, we intend to issue and sell the Initial Purchase Shares, under the terms and subject to the conditions of the Purchase Agreement, to Lincoln Park. From and after the Commencement Date, on any tradingbusiness day that we select as the purchase date therefor on which the closing sale price of our common stock is not less than $0.50 per share,below the Floor Price, we have the right, inmay, from time to time and at our sole discretion for a period of up to present Aspire Capital with a Purchase Notice, directing Aspire Capital (as principal)36-months after the Commencement Date, by written notice delivered by us to Lincoln Park, direct Lincoln Park to purchase up to 75,000125,000 shares of common stock (subject to adjustment as set forth in the Purchase Agreement) in a Regular Purchase, at a purchase price per share that will be determined and fixed in accordance with the Purchase Agreement at the time we deliver such written notice to Lincoln Park on the purchase date for such Regular Purchase. The maximum share limit for a Regular Purchase shall be increased to higher share threshold amounts in the Purchase Agreement, up to a maximum share limit of 175,000 shares of common stock (subject to adjustment as set forth in the Purchase Agreement), with the applicable maximum share limit determined by whether the closing price for our common stock on the applicable purchase date exceeds certain price thresholds set forth in the Purchase Agreement. In any case, however, Lincoln Park’s maximum purchase commitment in any single Regular Purchase may not exceed $1.0 million. The purchase price per share of common stock sold in each such Regular Purchase, if any, will be based on market prices of the common stock over a specified period immediately preceding the time of sale as computed under the Purchase Agreement.

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 per share of common stock sold in each such accelerated purchase and additional accelerated purchase, if any, will be based on market prices of the common stock on the applicable purchase dates for such accelerated purchases and additional accelerated purchases as computed under the Purchase Agreement.

Under the applicable Nasdaq listing rules, in no event may we issue to Lincoln Park under the Purchase Agreement more than the Exchange Cap limit of 4,809,486 shares of our common stock, which number of shares is equal to 19.99% of the shares of common stock outstanding immediately prior to the execution of the Purchase Agreement, unless (i) we first obtain stockholder approval to issue shares of common stock in excess of the Exchange Cap in accordance with applicable Nasdaq listing rules, or (ii) at the time we have issued shares of common stock equal to the Exchange Cap and at all times thereafter, the average price per businessshare of common stock for all shares of common stock sold by us to Lincoln Park under the Purchase Agreement equals or exceeds $0.8225 per share (representing the lower of the official closing price of the common stock on Nasdaq on the trading day upimmediately preceding the date of the Purchase Agreement and the average official closing price of the common stock on Nasdaq for the five consecutive trading days ending on the trading day immediately preceding the date of the Purchase Agreement, as adjusted under applicable Nasdaq rules to $21.0 milliontake into account the issuance of Commitment Shares to Lincoln Park for non-cash consideration), such that the Exchange Cap limitation would no longer apply to issuances and sales of common stock by us to Lincoln Park under the Purchase Agreement under applicable Nasdaq listing rules.

15

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 common stock then beneficially owned by Lincoln Park (as calculated pursuant to Section 13(d) of the Exchange Act and Rule 13d-3 thereunder), would result in Lincoln Park beneficially owning more than the Beneficial Ownership Cap of 9.99% of the outstanding shares of common stock.

We will control the timing and amount of any sales of common stock to Lincoln Park pursuant to the Purchase Agreement. Lincoln Park has no right to require us to sell any shares of common stock to Lincoln Park under the Purchase Agreement, but Lincoln Park is obligated to make purchases of common stock as we direct, upon the terms and subject to the satisfaction of the conditions set forth in the Purchase Agreement. Neither we nor Lincoln Park may assign or transfer our respective rights and obligations under the Purchase Agreement; provided, however, that any transaction, whether by merger, reorganization, restructuring or consolidation, financing or otherwise, whereby we remain the surviving entity immediately after such transaction shall not be deemed an assignment by us. No provision of the Purchase Agreement or the Registration Rights Agreement may be modified or waived by us or Lincoln Park.

Actual sales of shares of common stock by us to Lincoln Park under the Purchase Agreement will depend on a variety of factors to be determined by us from time to time, including, among others, market conditions, the trading price of the common stock and determinations by us as to the appropriate sources of funding for us and our operations.

As consideration for Lincoln Park’s commitment to purchase shares of common stock from us at our direction from time to time from and after the Commencement Date pursuant to the Purchase Agreement, promptly following our execution of the Purchase Agreement and the Registration Rights Agreement, we issued 599,216 Commitment Shares to Lincoln Park on May 8, 2023. All 599,216 Commitment Shares that we issued to Lincoln Park are included in the 5,000,000 shares of common stock being registered under the Securities Act for resale by Lincoln Park under the registration statement of which this prospectus forms a part.

As of May 16, 2023, there were 24,746,044 shares of common stock outstanding (which includes the 599,216 Commitment Shares we issued to Lincoln Park on May 8, 2023 in consideration of Lincoln Park’s obligation to purchase shares of our common stock at our direction under the Purchase Agreement). Although the Purchase Agreement provides that we may, in our discretion, from time to time after the aggregate overdate of this prospectus and during the term of the Purchase Agreement, at a Purchase Price calculated by referencedirect Lincoln Park to the prevailing market price of our common stock over the preceding 10-business day period (as more specifically described below); however, no sale pursuant to a Purchase Notice may exceed $500,000 per trading day.

In addition, on any date on which we submit a Purchase Notice to Aspire Capital for 75,000 Purchase Shares, we also have the right, in our sole discretion, to present Aspire Capital with a VWAP Purchase Notice

directing Aspire Capital to purchase an amount of stock equal to up to 30% of the aggregate shares of our common stock tradedfrom us in one or more purchases under the Purchase Agreement, for a maximum aggregate purchase price of up to $26.0 million, only 5,000,000 shares of common stock (599,216 of which represent the Commitment Shares that have been issued by us to Lincoln Park on May 8, 2023, for which we will receive no cash proceeds) are being registered for resale under the NASDAQ Global Market on the next trading day, subjectregistration statement of which this prospectus forms a part. If, in addition to the VWAP599,216 Commitment Shares that are currently outstanding, all of the additional 4,400,784 shares of common stock offered for resale by Lincoln Park under this prospectus (without taking into account the 19.99% Exchange Cap limitation applicable to issuances and sales of common stock under the Purchase Share Volume MaximumAgreement) were issued and outstanding as of May 16, 2023, such shares would represent approximately 17.15% of the VWAP Minimum Price Threshold. The VWAP Purchase Price is calculated by reference to the prevailing market pricetotal number of shares of our common stock (as more specifically described below).outstanding as of May 16, 2023.

The Purchase Agreement provides that we and Aspire Capital shall not effect any salesPurchases of Shares of our Common Stock under the Purchase Agreement

The Initial Purchase

On the Commencement Date upon our request, Lincoln Park will purchase the Initial Purchase Shares at the Initial Purchase Price, which equals the lesser of (i) the closing sale price of the common stock on the business day immediately preceding the Commencement Date and (ii) the average of the closing sales prices of the common stock for the 10 consecutive business days ending on the business day immediately preceding the Commencement Date.

16

Regular Purchases

On the first business day following the Commencement Date, on any business day that we select as the purchase date wheretherefor on which the closing sale price of our common stock is less thannot below the Floor Price. TherePrice (and provided all shares of common stock subject to all prior Regular Purchases that we have effected under the Purchase Agreement, if any, have been received by Lincoln Park before we deliver notice to Lincoln Park for such Regular Purchase in accordance with the Purchase Agreement), we may, by written notice delivered by us to Lincoln Park, direct Lincoln Park to purchase up to 125,000 shares of common stock on such purchase date in a Regular Purchase, provided, however, that the maximum number of shares we may sell to Lincoln Park in a Regular Purchase may be increased to:

In any case, however, Lincoln Park’s maximum purchase commitment in any single Regular Purchase may not exceed $1.0 million.

The purchase price per share of common stock sold in each such Regular Purchase, if any, will be equal to the lower of:

Accelerated Purchases

In addition to Regular Purchases described above, on any purchase date for a Regular Purchase 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 provided all shares of common stock subject to all prior Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases that we have effected under the Purchase Agreement prior to such purchase date, if any, have been received by Lincoln Park before we deliver notice to Lincoln Park for such Accelerated Purchase in accordance with the Purchase Agreement), we may, by written notice delivered by us to Lincoln Park simultaneously with such Regular Purchase notice for such corresponding Regular Purchase, direct Lincoln Park to purchase an additional amount of our common stock, which we refer to as an Accelerated Purchase, on the next business day following such purchase date for such corresponding Regular Purchase, which we refer to as the Accelerated Purchase Date, not to exceed the lesser of:

The purchase price per share for the shares of common stock subject to an Accelerated Purchase will be equal to 97% of the lower of:

17

Additional Accelerated Purchases

We may also direct Lincoln Park, by written notice delivered to Lincoln Park prior to 1:00 p.m., Eastern time, on the same Accelerated Purchase Date on which an Accelerated Purchase Measurement Period for an Accelerated Purchase has ended prior to such time (and provided all shares of common stock subject to all prior Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases that we have effected under the Purchase Agreement, including those prior Accelerated Purchases and Additional Accelerated Purchases effected on the same Accelerated Purchase Date as the applicable Additional Accelerated Purchase, if any, have been received by Lincoln Park in accordance with the Purchase Agreement before we deliver notice to Lincoln Park for such Additional Accelerated Purchase), to purchase an additional amount of our common stock on such same Accelerated Purchase Date, which we refer to as an Additional Accelerated Purchase, of up to the lesser of:

The purchase price per share for the shares subject to an Additional Accelerated Purchase will be equal to 97% of the lower of:

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, again provided all shares of common stock subject to all prior Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases, including those prior Accelerated Purchases and Additional Accelerated Purchases effected on the same Accelerated Purchase Date as the applicable Additional Accelerated Purchase have been properly delivered to Lincoln Park in accordance with the Purchase Agreement prior to such time.

In the case of the Initial Purchase, Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases, the purchase prices per share of common stock to be sold therein 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 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 Aspire Capital. AspireLincoln Park.

Events of Default

“Events of Default” under the Purchase Agreement include, among others, the following:

18

Lincoln Park does not have the right to requireterminate the Purchase Agreement upon the occurrence of any salesof the Events of Default set forth above, all of which are outside of Lincoln Park’s control, although the Purchase Agreement would automatically terminate without any action of us or Lincoln Park in the event of any voluntary or involuntary bankruptcy proceedings by or against us butthat are not discharged within 90 days. So long as an Events of Default has occurred and is obligatedcontinuing, or if any event which, after notice and/or lapse of time, would reasonably be expected to make purchases frombecome an Event of Default has occurred and is continuing, 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, as we directto terminate the Purchase Agreement upon one business day’s prior written notice to Lincoln Park. In the event of any voluntary or involuntary bankruptcy proceedings by or against us that are not discharged within 90 days, the Purchase Agreement would automatically terminate without any action of us or Lincoln Park. No termination of the Purchase Agreement will be effective during the pendency of any Regular Purchase, Accelerated Purchase or Additional Accelerated Purchase that has not then fully settled in accordance with the Purchase Agreement.

No Short-Selling or Hedging by Lincoln Park

Lincoln Park has represented to us that at no time prior to the time of execution of 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 under 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 agreed that during the term of the Purchase Agreement, it, its agents, representatives or affiliates will not enter into or effect, directly or indirectly, any of the foregoing transactions.

Prohibitions on Variable Rate Transactions

There are no limitations on use of proceeds, financial or business covenants, restrictions on future financings, rights of first refusal, participation rights, penalties or liquidated damages in the Purchase Agreement.

Aspire Capital may not assign its rightsAgreement or obligations underRegistration Rights Agreement, except we are prohibited, subject to certain exceptions, until the Purchase Agreement. The Purchase Agreement may be terminated by us at any time, at our discretion, without any penaltylater of May 8, 2026 or cost to us.

Purchase of Shares under the Purchase Agreement

Under the Purchase Agreement, on any trading day selected by us on which the closing sale price of our common stock exceeds $0.50 per share, we may direct Aspire Capital to purchase up to 75,000 shares of our common stock per trading day. The Purchase Price of such shares is equal to the lesser of:

In addition, onCommencement Date, irrespective of any date on which we submit a Purchase Notice to Aspire Capital for the purchase of up to 75,000 shares, we also have the right to direct Aspire Capital to purchase an amount of stock equal to up to 30% of the aggregate shares of the our common stock traded on the NASDAQ Global Market on the next trading day, subject to the VWAP Purchase Share Volume Maximum and the VWAP Minimum Price Threshold, which is equal to the greater of (a) 80% of the closing price of the Company’s common stock on the business day immediately preceding the VWAP Purchase Date or (b) such higher price as set forth by the Company in the VWAP Purchase Notice. The VWAP Purchase Price of such shares is the lower of:

The Purchase Price will be adjusted for any reorganization, recapitalization, non-cash dividend, stock split, or other similar transaction occurring during the trading day(s) used to compute the Purchase Price. We may deliver multiple Purchase Notices and VWAP Purchase Notices to Aspire Capital from time to time during the termearlier termination of the Purchase Agreement, so long asfrom effecting or entering into any agreement to effect an “equity line of credit” or other substantially similar equity line of credit offering with another third party in which we may offer, issue or sell, and the most recentpurchaser is irrevocably bound to purchase, has been completed.

Minimum Share Price

Under the Purchase Agreement, we and Aspire Capital may not effect any sales of shares of our common stock under the Purchase Agreement on any trading day that the closing sale price of ouror equities convertible or exercisable into common stock is less than $0.50 per share.at a future determined price.

Events of Default19

Generally, Aspire Capital may terminate the Purchase Agreement upon the occurrence of any of the following, among other, events of default:

Our Termination Rights

The Purchase Agreement may be terminated by us at any time, at our discretion, without any penalty or cost to us.

No Short-Selling or Hedging by Aspire Capital

Aspire Capital has agreed that neither it nor any of its agents, representatives and 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.

Effect of Performance of the Purchase Agreement on Our Stockholders

TheAll shares of our common stock being registered for resale hereunder which may be issued or sold by us to Lincoln Park under the Purchase Agreement does not limit the ability of Aspire Capitalare expected to sell any or all of the 3,231,515 shares registered in this offering.be freely tradable. It is anticipated that shares registered in this offering will be sold from time to time over a period of up to

approximately 30 months from 36-months commencing on the date that the registration statement of which this prospectus. The sale by Aspire Capital ofprospectus forms a significant amountpart becomes effective.

Pursuant to the Purchase Agreement, we will have discretion, subject to market demand, to vary the timing, prices, and numbers of shares registered in this offering at any given time could cause the market pricesold to Lincoln Park. Sales of our common stock, if any, to decline and/orLincoln Park under the Purchase Agreement will depend upon market conditions and other factors to be highly volatile. Aspire Capitaldetermined by us. We may ultimately purchasedecide to sell to Lincoln Park all, some or none of the 2,813,567shares of our common stock that may be available for us to sell to Lincoln Park pursuant to the Purchase Agreement. Because the purchase price per share to be paid by Lincoln Park for the shares of common stock that we may elect to sell to Lincoln Park under the Purchase Agreement, if any, will fluctuate based on the market prices of our common stock at the time we elect to sell shares to Lincoln Park pursuant to the Purchase Agreement, if any, it is not yet issued but registered inpossible for us to predict, as of the date of this offering. After itprospectus and prior to any such sales, the number of shares of common stock that we will sell to Lincoln Park under the Purchase Agreement, the purchase price per share that Lincoln Park will pay for shares purchased from us under the Purchase Agreement, or the aggregate gross proceeds that we will receive from those purchases by Lincoln Park under the Purchase Agreement.

If and when we do elect to sell shares of our common stock to Lincoln Park pursuant to the Purchase Agreement, after Lincoln Park has acquired such shares, itLincoln Park may sellresell all, some or none of such shares. Therefore,shares at any time or from time to time in its discretion and at different prices. As a result, investors who purchase shares from Lincoln Park in this offering at different times will likely pay different prices for those shares, and so may experience different levels of dilution and in some cases substantial dilution and different outcomes in their investment results. Investors may experience a decline in the value of the shares they purchase from Lincoln Park in this offering as a result of future sales to Aspire Capitalmade by us pursuant to Lincoln Park at prices lower than the prices such investors paid for their shares in this offering.

Moreover, although the Purchase Agreement alsoprovides that we may, result in substantial dilutionour discretion, from time to time after the date of this prospectus and during the term of the Purchase Agreement, direct Lincoln Park to purchase shares of our common stock from us in one or more purchases under the Purchase Agreement, for a maximum aggregate purchase price of up to $26.0 million, only 5,000,000 shares of common stock (599,216 of which represent the Commitment Shares that have been issued by us to Lincoln Park on May 8, 2023, for which we will receive no cash proceeds) are being registered for resale under the registration statement of which this prospectus forms a part.Therefore, only 4,400,784 of such shares of common stockrepresent shares that we may issue and sell to Lincoln Park for cash consideration in purchases under the Purchase Agreement from time to time, at our sole discretion, during the 36-month period commencing on the Commencement Date. If after the Commencement Date we elect to sell to the interestsselling stockholder all of other holdersthe 4,400,784 shares of common stock being registered for resale under this prospectus that are available for sale by us to the selling stockholder in purchases under the Purchase Agreement, depending on the market prices of our common stock. However, we havestock at the righttime of such sales, the actual gross proceeds from the sale of all such shares may be substantially less than the $26.0 million total purchase commitment available to control the timing and amount of any sales of our shares to Aspire Capital andus under the Purchase Agreement, may be terminated bywhich could materially adversely affect our liquidity.

20

If it becomes necessary for us at any time at our discretion without any penalty or cost to us.

Percentageissue and sell to Lincoln Park shares of Outstanding Shares after Giving Effectcommon stock in excess of the Exchange Cap under the Purchase Agreement in order to receive aggregate gross proceeds equal to $26.0 million under the Purchased Shares IssuedPurchase Agreement, then for so long as the Exchange Cap continues to Aspire Capital

In connection with entering intoapply to issuances and sales of common stock under the Purchase Agreement, we authorized the salemust first obtain stockholder approval to Aspire Capital of up to $21.0 million of ourissue shares of common stock. However,stock in excess of the Exchange Cap in accordance with applicable Nasdaq listing rules. Furthermore, if we estimateelect to issue and sell to Lincoln Park more than the 4,400,784 shares of our common stock that we willmay elect to issue and sell no more than 3,231,515 shares to Aspire CapitalLincoln Park under the Purchase Agreement (including the Commitment Shares and Initial Purchase Shares), all ofthat are being registered for resale by Lincoln Park hereunder, which are included in this offering. Subject to any required approval by our board of directors, we have the right, but not the obligation, to issuedo, we must first file with the SEC one or more thanadditional registration statements to register under the 3,231,515Securities Act for resale by Lincoln Park such additional shares included in this prospectusof our common stock we wish to Aspire Capitalsell from time to time under the Purchase Agreement, under some circumstances. Inwhich the eventSEC must declare effective, in each case before we may elect to issue more than 3,231,515sell any additional shares of our common stock to Lincoln Park under the Purchase Agreement. Any issuance and sale by us under the Purchase Agreement we will be required to fileof a new registration statement and have it declared effective by the SEC. The number of shares ultimately offered for sale by Aspire Capital in this offering is dependent upon the number of shares purchased by Aspire Capital under the Purchase Agreement. The following table sets forth the number and percentage of outstanding shares to be held by Aspire Capital after giving effect to the salesubstantial amount of shares of common stock soldin addition to Aspire Capital at varying purchase prices:

USE OF PROCEEDS

This prospectus relates to shares of our common stock that we may be offeredelect to issue and sold from timesell to time by Aspire Capital. We will not receive any proceeds upon the sale of shares by Aspire Capital. However, we have received proceeds of $1.0 million, and may receive additional proceeds of up to $20.0 million, for an aggregate of $21.0 million gross proceeds, from the sale of sharesLincoln Park under the Purchase Agreement that are being registered for resale by Lincoln Park hereunder could cause additional substantial dilution to Aspire Capital. The proceeds will be used for the advancement of our research and development activities, working capital and general corporate purposes. This anticipated use of net proceeds from the sale of our common stock to Aspire Capital under the Purchase Agreement represents our intentions based upon our current plans and business conditions.

SELLING STOCKHOLDERstockholders.

The selling stockholder may from time to time offer and sell any or all of the shares of our common stock set forth below pursuant to this prospectus. When we refer to the “selling stockholder” in this prospectus, we mean the entity listed in the table below, and its respective pledgees, donees, permitted transferees, assignees, successors and others who later come to hold any of the selling stockholder’s interests in shares of our common stock other than through a public sale.

The following table sets forth, as of the date of this prospectus, the name of the selling stockholder for whom we are registering shares for sale to the public, the number of shares of common stock beneficially ownedultimately resold by the selling stockholder prior toLincoln Park through this offering,prospectus is dependent upon the total number of shares of common stock, if any, we elect to issue and sell to Lincoln Park under the Purchase Agreement from and after Commencement and during the term of the Purchase Agreement. Issuances 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 selling stockholder may offer pursuant to this prospectuseconomic 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 our common stock that our existing stockholders own will not decrease, the selling stockholder will beneficially own after this offering. Except as noted below, the selling stockholder does not have, or within the past three years has not had, any material relationship with us or anyshares of our predecessors or affiliatescommon stock owned by our existing stockholders will represent a smaller percentage of our total outstanding shares of our common stock after any such issuance of shares of our common stock to Lincoln Park under the Purchase Agreement.

The following table sets forth the amount of gross proceeds we would receive from Lincoln Park from our sale of up to 4,400,784 shares of our common stock (which excludes the 599,216 Commitment Shares that we issued to Lincoln Park on May 8, 2023, for which we will receive no cash proceeds) that we are registering hereby that we may issue and sell to Lincoln Park in the selling stockholder is not or was not affiliated with registered broker-dealers.future under the Purchase Agreement at varying purchase prices from and after the Commencement Date:

Based

(1) Although the Purchase Agreement provides that we may sell up to $26.0 million of our common stock to Lincoln Park, we are only registering 5,000,000 shares of our common stock for resale under the registration statement of which this prospectus forms a part, including the 599,216 Commitment Shares that we issued to Lincoln Park on May 8, 2023 in consideration of Lincoln Park’s commitment to purchase shares of our common stock at our direction under the Purchase Agreement, for which we will receive no cash proceeds. Therefore, only 4,400,784 of such shares represent shares that we may issue and sell to Lincoln Park for cash consideration in purchases under the Purchase Agreement from time to time (including pursuant to the Initial Purchase), at our sole discretion, during the 36-month period commencing on the information providedCommencement Date, which may or may not cover all the shares of our common stock we ultimately sell to usLincoln Park under the Purchase Agreement, if any, depending on the purchase price per share. We have included in this column only the 4,400,784 shares that we may issue and sell to Lincoln Park for cash

21

consideration in purchases under the Purchase Agreement that are being registered for resale in the offering made by this prospectus (excluding the 599,216 Commitment Shares), giving effect to the Exchange Cap but without regard for the Beneficial Ownership Cap.

(2) The denominator is based on 24,746,044 shares of our common stock outstanding as of May 16, 2023 (which includes the 599,216 Commitment Shares we issued to Lincoln Park on May 8, 2023, promptly following our execution of the Purchase Agreement), adjusted to include the number of shares of our common stock set forth in the adjacent column. The numerator is based on the number of shares of our common stock set forth in the adjacent column.

(3) The closing sale price per share of our common stock on May 18, 2023.

22

SELLING STOCKHOLDER

This prospectus relates to the possible resale by the selling stockholder, assumingLincoln Park, of up to 5,000,000 shares of our common stock, consisting of: (i) 599,216 Commitment Shares that we issued to Lincoln Park as consideration for its commitment to purchase shares of our common stock under the selling stockholder sells allPurchase Agreement and (ii) up to 4,400,784 shares of common stock that we have reserved for issuance and sale to Lincoln Park under the Purchase Agreement from time to time from and after the Commencement Date, if and when we determine to sell shares of our common stock to Lincoln Park under 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 May 8, 2023 concurrently with our execution of the Purchase Agreement, in which we agreed to provide certain registration rights with respect to resales by Lincoln Park of the shares of our common stock beneficially owned by it that have been registered by us and doesor may be issued to Lincoln Park under the Purchase Agreement. The selling stockholder may sell some, all or none of the shares of common stock included in this prospectus. We do not acquire any additional shares during the offering,know how long the selling stockholder will not own any shares, as reflected in the column entitled “Beneficial Ownership After This Offering.” We cannot advise you as to whether the selling stockholder will in fact sell any or all of such shares of common stock. In addition, the selling stockholder may have sold, transferred or otherwise disposed of, or may sell, transfer or otherwise dispose of, at any time and from time to time,hold the shares of our common stock before selling them, and we currently have no agreements, arrangements or understandings with the selling stockholder regarding the sale of any of the shares of common stock. See “Plan of Distribution.”

The table below sets forth, to our knowledge, information concerning the beneficial ownership of shares of our common stock by the selling stockholder as of May 16, 2023. The percentages of shares owned before and after the offering are based on 24,746,044 shares of common stock outstanding as of May 16, 2023, which includes the 599,216 Commitment Shares that we issued to Lincoln Park on May 8, 2023 following our execution of the Purchase Agreement on May 8, 2023. The information in transactions exemptthe table below with respect to the selling stockholder has been obtained from the selling stockholder.

Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to shares. The inclusion of any shares in this table does not constitute an admission of beneficial ownership for the person named below.

(1) Josh Scheinfeld and Jonathan Cope, the Managing Members of Lincoln Park Capital, LLC, the manager of Lincoln Park Capital Fund, 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 this prospectus filed with the SEC in connection with the transactions contemplated under the Purchase Agreement. Neither Lincoln Park Capital, LLC nor Lincoln Park Capital Fund, LLC is a licensed broker dealer or an affiliate of a licensed broker dealer.

(2) Represents the 599,216 Commitment Shares that we issued to Lincoln Park on May 8, 2023 as consideration for its commitment to purchase our common stock at our direction under the Purchase Agreement. In accordance with Rule 13d-3(d) under the Exchange Act, we have excluded from the number of shares of our common stock beneficially owned prior to the offering all of the 4,400,784 shares of our common stock that we may issue and sell to Lincoln Park pursuant to the Purchase Agreement from and after the Commencement Date that are being registered for resale under the registration requirementsstatement of which this prospectus forms a part, because the issuance and sale of such shares to Lincoln Park under the Purchase Agreement is solely at our discretion and is subject to certain conditions, the satisfaction of all of which are outside of Lincoln Park’s control, including the registration statement of which this prospectus forms a part becoming and remaining effective under the Securities Act. Furthermore, under the terms of the Purchase Agreement, issuances and sales of shares of our common stock to Lincoln Park under the Purchase Agreement are subject to certain limitations on the amounts we may sell to Lincoln Park at any time, including the Exchange Cap and the Beneficial Ownership Cap. See the description under the heading “The Lincoln Park Transaction“ for more information about the Purchase Agreement.

23

(3) Although the Purchase Agreement provides that we may sell up to $26.0 million of our common stock to Lincoln Park, we are only registering 5,000,000 shares of our common stock for resale under this prospectus, including the 599,216 Commitment Shares that we issued to Lincoln Park on May 8, 2023 as consideration for its commitment to purchase our common stock at our direction under the Purchase Agreement, for which we will receive no cash proceeds. Therefore, only 4,400,784 of such shares represent shares that we may issue and sell to Lincoln Park for cash consideration in purchases under the Purchase Agreement from time to time, at our sole discretion, during the 36-month period commencing on the Commencement Date. 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 full $26.0 million available to us under the Purchase Agreement, including pursuant to the Initial Purchase. If we choose to do so, we must first register for resale under the Securities Act aftersuch additional shares. The number of shares ultimately offered for resale by Lincoln Park is dependent upon the date onnumber of shares we sell to Lincoln Park under the Purchase Agreement.

(4) Assumes the sale of all shares of our common stock registered for resale by the selling stockholder pursuant to the registration statement of which it providedthis prospectus forms a part, although the information set forth in the table below.selling stockholder is under no obligation known to us to sell any shares of common stock at any particular time.

24

PLAN OF DISTRIBUTION

Mr. Komissopoulos may be deemed to be a beneficial owner of common stock held by Aspire Fund. Each of Aspire Partners, SGM, Red Cedar, Chrisko, Mr. Martin, Mr. Brown, and Mr. Komissopoulos disclaims beneficial ownership of the common stock held by Aspire Fund.

(3)

As of the date hereof, 417,948The shares of our common stock have been acquired by Aspire Capital under the Purchase Agreement, consisting of the 195,726 Commitment Shares we issued to Aspire Capital as a commitment fee and the 222,222 Initial Purchase Shares sold to Aspire Capital. We may elect in our sole discretion to sell to Aspire Capital up to an additional 2,813,567 shares under the Purchase Agreement but Aspire Capital does not presently beneficially own those shares as determined in accordance with the rules of the SEC.

PLAN OF DISTRIBUTION

The common stock offered by this prospectus isare being offered by Aspire Capital, the selling stockholder.stockholder, Lincoln Park. The common stockshares 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 theour common stock offered by this prospectus maycould be effected in one or more of the following methods:

In order to comply with the securities laws of certain states, if applicable, the shares of our common stock offered by this prospectus may be sold only through registered or licensed brokers or dealers. In addition, in certain states, the shares of our common stock offered by this prospectus 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.

The selling stockholder may also sell sharesLincoln 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 our common stock under Rule 144 promulgated underthat it has acquired and may in the future acquire 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, if available, rather than under this prospectus. In addition, the selling stockholder may transfer the shares of common stock by other meansAct. Lincoln Park has informed us that each such broker-dealer will receive commissions from Lincoln Park that will not described in this prospectus.exceed customary brokerage commissions.

Brokers, dealers, underwriters or agents participating in the distribution of the shares as agentsof our common stock offered by this prospectus may receive compensation in the form of commissions, discounts, or concessions from the selling stockholder and/or purchasers, of the common stock for whom the broker-dealers may act as agent. Aspire Capital has informed us that eachagent, of shares of our common stock sold by Lincoln Park through this prospectus. The compensation paid to any such particular broker-dealer will receive commissions from Aspire Capital which will not exceedby any such purchasers of shares of our common stock sold by Lincoln Park may be less than or in excess of customary brokerage commissions.

Aspire Capital is an “underwriter” within the meaning of the Securities Act.

Neither we nor Aspire CapitalLincoln Park can presently estimate the amount of compensation that any agent will receive. receive from any purchasers of shares of our common stock sold by Lincoln Park.

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

We may from time to time file with the timeSEC 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 offersale of shares is made, aof our common stock offered by this prospectus supplement, if required, will be distributed that will set forthby the selling stockholder, including the names of any agents,brokers, dealers, underwriters or dealers andagents participating in the distribution of such shares of our common stock by the selling stockholder, any compensation from the selling stockholder,paid by Lincoln Park to any such brokers, dealers, underwriters or agents, and any other required information.

We will pay all of the expenses incident to the registration offering,under the Securities Act of the offer and sale of the shares of our common stock included in this prospectus by Aspire Capital toLincoln Park. We estimate total expenses for the public other than commissions or discounts of underwriters, broker-dealers, or agents. offering will be approximately $120,353.

25

We have agreed to indemnify Aspire CapitalLincoln Park and certain other persons against certain liabilities in connection with the offering of shares of our common stock offered hereby,by this prospectus, 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. Aspire CapitalLincoln Park has agreed to indemnify us against liabilities under the Securities Act that may arise from certain written information furnished to us by Aspire CapitalLincoln 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.

Aspire Capital andLincoln Park has represented to us that at no time prior to the Purchase Agreement has Lincoln Park or its agents, representatives or affiliates have agreed not to engageengaged in or effected, in any directmanner whatsoever, directly or indirectindirectly, any short selling or hedgingsale (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 agreed that during the term of the Purchase Agreement.Agreement, it, its agents, representatives or affiliates will not enter into or effect, directly or indirectly, any of the foregoing transactions.

We have advised Aspire CapitalLincoln Park that while it is engaged in a distribution of the shares included in this prospectus it is required to comply with Regulation M promulgated under the Securities Exchange Act of 1934, as amended.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 sharessecurities offered herebyby this prospectus.

We may suspend the sale of shares by Aspire Capital pursuant to this prospectus for certain periods of time for certain reasons, including if the prospectus is required to be supplemented or amended to include additional material information.

This offering will terminate on the date that all shares of our common stock offered by this prospectus have been sold by Aspire Capital.

26

LEGAL MATTERS

The validity of the securitiescommon stock offered hereby is being passed upon for us by Cooley LLP, San Diego, CA.California.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2016,2022, as set forth in their report (which contains an explanatory paragraph describing conditions that raise substantial doubt about the Company’s ability to continue as a going concern as described in Note 1 to the consolidated financial statements), which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our consolidated financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-1 under the Securities Act, with respect to the securitiescommon stock being offered by this prospectus. This prospectus does not contain all of the information in the registration statement and its exhibits. For further information with respect to us and the securities offered by this prospectus, we refer you to the registration statement and its exhibits. Statements contained in this prospectus as to the contents of any contract or any other document referred to are not necessarily complete, and in each instance, we refer you to the copy of the contract or other document filed as an exhibit to the registration statement. Each of these statements is qualified in all respects by this reference.

We are subject to the information and periodic reporting requirements of the Exchange Act, and we file periodicannual, quarterly and current reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC, including us. The address of the SEC website is www.sec.gov. You can read our SEC filings, including the registration statement, over the Internet at the SEC’s website at www.sec.gov. You may also read and copy any document we file with the SEC at its public reference facilities at 100 F Street NE, Washington, D.C. 20549. You may also obtain copies of these documents at prescribed rates by writing to the Public Reference Section of the SEC at 100 F Street NE, Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference facilities.such address. You may also request a copy of these filings, at no cost, by writing us at 8910 University Center Lane,4350 La Jolla Village Drive, Suite 700,800, San Diego, CACalifornia 92122 or telephoning us at (858) 550-0780.

We also maintain a website atwww.traconpharma.com, at which you may access these materials free of charge after they are electronically filed with, or furnished to, the SEC. The information contained in, or that can be accessed through, our website is not incorporated by reference in, and is not part of, this prospectus.

27

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The SEC file number for the documents incorporated by reference in this prospectus is 001-36818. The information incorporated by reference is considered to be part of this prospectus.

We incorporate by reference into this prospectus and the registration statement of which this prospectus formforms a part the information or documents listed below that we have filed with the SEC, and any future filings we will make with the SEC under Sections 13(a), 13(c), 14, or 15(d) of the Exchange Act after the date of the initial filing of the registration statement of which this prospectus isforms a part and prior to effectiveness of such registration statement, and until the termination of the offering of the shares covered by this prospectus (other than information furnished under Item 2.02 or Item 7.01 of any current reports on Form 8-K):

Any statement contained in this prospectus or in a document incorporated or deemed to be incorporated by reference into this prospectus 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 other subsequently filed document that is deemed to be incorporated by reference into this prospectus modifies or supersedes the statement. Any statements so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

We will furnishprovide to each person, including any beneficial owners, to whom this prospectus is delivered without charge, to you, onupon written or oral request, a copy of any or all of the documents that are incorporated by reference ininto this prospectus but not delivered with this prospectus, including exhibits to thesewhich are specifically incorporated by reference into such documents. You should direct any requests for documents to TRACON Pharmaceuticals, Inc. 8910 University Center4350 La Jolla Village Drive, Suite 700800, San Diego, CACalifornia 92122; telephone: (858) 550-0780.

You also may access these filings on our website at www.traconpharma.com. We do not incorporate the information on our website into this prospectus or any supplement to this prospectus and you should not consider any information on, or that can be accessed through, our website as part of this prospectus or any supplement to this prospectus (other than those filings with the SEC that we specifically incorporate by reference into this prospectus).

DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION FOR SECURITIES ACT LIABILITY

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to our directors, officers andor persons controlling persons, we havethe registrant pursuant to the foregoing provisions, the registrant has been advisedinformed that in the opinion of the SEC thissuch indemnification is against public policy as expressed in the Securities Act and is therefore unenforceable.

28

5,000,000 Shares

3,231,515 Shares

Common Stock

PROSPECTUS

                    , 2017

, 2023

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 13. Other Expenses of Issuance and Distribution

The following table sets forth the expenses to be incurred in connection with the offering described in this registration statement, all of which will be paid by the registrant. All amounts are estimates except the Securities and Exchange Commission, or SEC, registration fee.

Item 14. Indemnification of Directors and Officers

We are incorporated under the laws of the State of Delaware. Section 145 of the Delaware General Corporation Law, or DGCL, provides that a Delaware corporation may indemnify any persons who were, are, or are threatened to be made, parties to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative (other than an action by or in the right of such corporation), by reason of the fact that such person is or was an officer, director, employee or agent of such corporation, or is or was serving at the request of such corporation as an officer, director, employee or agent of another corporation or enterprise. The indemnity may include expenses (including attorneys’ fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by such person in connection with such action, suit or proceeding, provided that such person acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the corporation’s best interests and, with respect to any criminal action or proceeding, had no reasonable cause to believe that his or her conduct was illegal. A Delaware corporation may indemnify any persons who were, are, or are threatened to be made, a party to any threatened, pending or completed action or suit by or in the right of the corporation by reason of the fact that such person is or was a director, officer, employee or agent of such corporation, or is or was serving at the request of such corporation as a director, officer, employee or agent of another corporation or enterprise. The indemnity may include expenses (including attorneys’ fees) actually and reasonably incurred by such person in connection with the defense or settlement of such action or suit provided such person acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the corporation’s best interests except that no indemnification is permitted without judicial approval if the officer or director is adjudged to be liable to the corporation. Where an officer or director is successful on the merits or otherwise in the defense of any action referred to above, the corporation must indemnify him or her against the expenses (including attorneys’ fees) actually and reasonably incurred.

Our amended and restated certificate of incorporation, as amended, and amended and restated bylaws provide for the indemnification of our directors and officers to the fullest extent permitted under the Delaware General Corporation Law.DGCL.

Section 102(b)(7) of the Delaware General Corporation LawDGCL permits a corporation to provide in its certificate of incorporation that a director or officer of the corporation shall not be personally liable to the corporation or its stockholders for monetary damages for breach of fiduciary duties as a director or officer, except for liability for any:

II-1

Our amended and restated certificate of incorporation, as amended, includes such a provision.provision with respect to our directors. Expenses incurred by any officer or director in defending any such action, suit or proceeding in advance of its final disposition will be paid by us upon delivery to us of an undertaking, by or on behalf of such director or officer, to repay all amounts so advanced if it shall ultimately be determined that such director or officer is not entitled to be indemnified by us.

Section 174 of the Delaware General Corporation LawDGCL 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.

As permitted by the Delaware General Corporation Law,DGCL, we have entered, into, and continue to enter, into separate indemnity agreements with each of our directors and executive officers that require us to indemnify such persons against any and all costs and expenses (including attorneys’, witness or other professional fees) actually and reasonably incurred by such persons in connection with any action, suit or proceeding (including derivative actions), whether actual or threatened, to which any such person may be made a party by reason of the fact that such person is or was a director or officer or is or was acting or serving as an officer, director, employee or agent of ours or any of our affiliated enterprises. Under these agreements, we are not required to provide indemnification for certain matters, including:

The indemnification agreements also set forth certain procedures that will apply in the event of a claim for indemnification thereunder.

There is at present no pending litigation or proceeding involving any of our directors or executive officers as to which indemnification is required or permitted, and we are not currently aware of any threatened litigation or proceeding that may result in a claim for indemnification.

II-2

We have an insurance policy in place that covers our officers and directors with respect to certain liabilities, including liabilities arising under the Securities Act or otherwise.

Any underwriting agreement that we may enter into may provide that the underwriters are obligated, under some circumstances, to indemnify our directors, officers and controlling persons against specified liabilities, including liabilities under the Securities Act.

Item 15. Recent Sales of Unregistered Securities

Set

The following list sets forth below is information regarding shares of common stock and preferred stockall unregistered securities issued and options granted, by us since January 1, 2014 that were not registered under2020 through the Securities Act of 1933, as amended (the Securities Act). Also included is the consideration, if any, received by us for such shares and options and information relating to the sectiondate of the Securities Act, or rule of the Securities and Exchange Commission, under which exemption from registration was claimed.

(a) Issuances of Securities

On March 14, 2017, we entered into the Common Stock Purchase Agreement with Aspire Capital Fund, LLC, or Aspire Capital. Pursuant to the termsprospectus that is a part of this registration statement:

II-2

The offers, sales and issuances of the securities described in this section (a) of Item 15 were deemed to be exempt from registration under the Securities Act in reliance on Section 4(a)(2) of the Securities Act and

II-3

and/or Rule 506 promulgated under Regulation D promulgated thereunder as transactions by an issuer not involving a public offering. The recipients of securities in each of these transactions represented to us that they acquired the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were affixed to the securities issued in these transactions. Each of the recipients of securities in these transactions was an accredited investor within the meaning of Rule 501 of Regulation D under the Securities Act and had adequate access, through employment, business or other relationships, to information about the Company.our company. No underwriters were involved in these transactions.

(b) Stock Option and Restricted Stock GrantsII-3

Since January 1, 2014, we have granted stock options to purchase an aggregate of 1,921,64 shares of our common stock, with exercise prices ranging from $0.70 to $17.38 per share, of which 209,895 stock options have been forfeited and 130,209 stock options have been exercised as of March 14, 2017. Since January 1, 2014, we have granted 306,780 restricted stock units, of which zero have been forfeited and 64,878 have been released as of March 14, 2017.

The securities described in this section (b) of Item 15 were deemed to be exempt from registration under the Securities Act in reliance on Rule 701 in that the transactions were under compensatory benefit plans and contracts relating to compensation as provided under Rule 701. The recipients of such securities were the Registrant’s employees, directors or bona fide consultants and received the securities under the Company’s 2011 Equity Incentive Plan. Appropriate legends were affixed to the securities issued in these transactions. Each of the recipients of securities in these transactions had adequate access, through employment, business or other relationships, to information about the Company.

Item 16. Exhibits and Financial Statement Schedules

(a) Exhibits

II-4

II-5

II-6

(b) Financial Statement Schedules

No financial statement schedules are provided because the information called for is not required or is shown either in the financial statements or related notes, which are incorporated herein by reference.

Item 17. Undertakings

II-4

II-7

II-8

Insofar as indemnification for liabilities arising under the Securities Act may be permitted for our directors, officers and controlling persons of the Registrant pursuant to our Amended and Restated Certificate of Incorporation or Amended and Restated Bylaws, or otherwise, the registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act 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 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 the registrant is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

II-5II-9

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this registration statementRegistration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California on March 27, 2017.May 19, 2023.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Charles P. Theuer, M.D., Ph.D. and Patricia L. Bitar,Scott B. Brown, CPA, and each and either of them, his or her true and lawful attorney-in-factattorneys-in-fact and agent,agents, each with full power of substitution and resubstitution, for him or her and in his or her name, place, and stead, in any and all capacities, to (i) act on, sign and file with the Securities and Exchange Commission any and all amendments (including post-effective amendments) to this registration statement together with all schedules and exhibits thereto and any subsequent registration statement filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended, together with all schedules and exhibits thereto, (ii) act on, sign and file such certificates, instruments, agreements and other documents as may be necessary or appropriate in connection therewith, (iii) act on and file any supplement to any prospectus included in this registration statement or any such amendment or any subsequent registration statement filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended, and (iv) take any and all actions which may be necessary or appropriate to be done, as fully for all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorney-in-factattorneys-in-fact and agent,agents, or histheir or herhis substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

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

Exhibit Index