Onconetix, Inc.

S-11 ea0293708-s1_onconetix.htm REGISTRATION STATEMENT

As filed with the Securities and Exchange Commission on June 8, 2026

Registration No. 333-

UNITED STATES

**SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

Onconetix, Inc.

(Exact Name of Registrant as Specified in its Charter)

**201 E. Fifth Street, Suite 1900

Telephone: (513) 620-4101

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

**David A. White

Chief Executive Officer

**201 E. Fifth Street, Suite 1900

Telephone: (513) 620-4101

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

with copies to:

**Barry I. Grossman, Esq.

Jessica Yuan, Esq.

Ellenoff Grossman & Schole LLP

1345 Avenue of the Americas

New York, NY 10105

Phone: (212) 370-1300

Fax: (212) 370-7889

**Approximate date of commencement of proposed sale to the public:**From time to time after this registration statement becomes effective.

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, 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.

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

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, 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 named in this prospectus 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 we are not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permitted.

100,000,000 shares of Common Stock

This prospectus relates to the offer and sale from time to time by Keystone Capital Partners, LLC (“Keystone” or the “Selling Stockholder”) of up to 100,000,000 shares of common stock of Onconetix, Inc. (“we,” “us,” “our,” the “Company,” or “Onconetix”), par value $0.00001 per share (the “Common Stock”), that have been or may be issued by us to Keystone pursuant to that certain Common Stock ELOC Purchase Agreement, dated as of October 2, 2024, by and between us and Keystone (the “ELOC Purchase Agreement”), establishing an equity line of credit (“ELOC”). Such shares of our Common Stock include up to 100,000,000 shares of Common Stock (assuming the shares to be issued are sold at an assumed price of 0.1375 per share) that we may elect, in our sole discretion, to issue and sell to Keystone, from time to time from and after the commencement date under the ELOC Purchase Agreement, and subject to applicable stock exchange rules.

The actual number of shares of our Common Stock issuable will vary depending on the then-current market price of shares of our Common Stock sold to the Selling Stockholder under the ELOC Purchase Agreement, but will not exceed the number set forth in the preceding sentences unless we file an additional registration statement under the Securities Act of 1933, as amended (the “Securities Act”), with the U.S. Securities and Exchange Commission (SEC), See “The Keystone Equity Financing” for a description of the ELOC Purchase Agreement and “Selling Stockholder” for additional information regarding Keystone.

We are registering the shares on behalf of the Selling Stockholder, to be offered and sold by it from time to time. We are not selling any securities under this prospectus, and will not receive any proceeds from the sale of Common Stock by the Selling Stockholder pursuant to this prospectus. We may receive up to $25 million in aggregate gross proceeds from Keystone under the ELOC Purchase Agreement in connection with sales of the shares of our Common Stock pursuant to the ELOC Purchase Agreement at varying purchase prices after the date of this prospectus. However, the actual proceeds from Keystone may be less than this amount depending on the number of shares of our Common Stock sold and the price at which the shares of our Common Stock are sold. Through June 5, 2026, we have sold approximately 2.6 million split-adjusted shares under the ELOC Purchase Agreement for aggregate proceeds of approximately $11.3 million. The purchase price per share that Keystone will pay for shares of Common Stock purchased from us under the ELOC Purchase Agreement will fluctuate based on the market price of our shares at the time we elect to sell shares to Keystone and, further, to the extent that the Company sells shares of Common Stock under the ELOC Purchase Agreement, substantial amounts of shares could be issued and resold, which would cause dilution and may impact the Company’s stock price.

Our Common Stock is listed on The Nasdaq Capital Market under the symbol “ONCO.” The last reported sale price of our Common Stock on The Nasdaq Capital Market on June 5, 2026 was $1.03 per share. We recommend that you obtain current market quotations for our Common Stock prior to making an investment decision.

The Selling Stockholder is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act. The Selling Stockholder may offer all or part of the shares for resale from time to time through public or private transactions, at either prevailing market prices or at privately negotiated prices. Our registration of the shares of Common Stock covered by this prospectus does not mean that the Selling Stockholder will offer or sell any of the shares. With regard only to the shares the Selling Stockholder sells for its own behalf, the Selling Stockholder may be deemed an “underwriter” within the meaning of the Securities Act of 1933, as amended (the “Securities Act”). The Company has paid all of the registration expenses incurred in connection with the registration of the shares. We will not pay any of the selling commissions, brokerage fees and related expenses.

We will pay the expenses incurred in registering the shares, including legal and accounting fees. See “Plan of Distribution” on page 41 of this prospectus.

Investing in our Common Stock involves certain risks. See “Risk Factors” on page 10 of this prospectus, included in any accompanying prospectus supplement and in the documents incorporated by reference in this prospectus for a discussion of the factors you should carefully consider before deciding to purchase these securities.

We may amend or supplement this prospectus from time to time by filing amendments or supplements as required. We urge you to read the entire prospectus, any amendments or supplements, any free writing prospectuses, and any documents incorporated by reference carefully before you make your investment decision.

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 , 2026

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