Protagenic Therapeutics Inc美股招股说明书(2025-10-24版)

$1,750,000Common Stock In accordance with the terms of the Common Stock Sales Agreement, dated as of July 2, 2021, as amended on January 9, 2025, or thesales agreement, that we entered into with B. Riley Securities, Inc. (the “Sales Agent”), we may offer and sell shares of our commonstock having an aggregate offering price of up to $1,750,000 from time to time through or to the Sales Agent acting as our agent orprincipal. Our common stock currently trades on the Nasdaq Capital Market, where it is listed under the symbol “PTIX.” On October 23, 2025,the last reported sale price of our common stock was $2.99 per share. As of October 24, 2025, the aggregate market value of our outstanding common stock held by non-affiliates, or public float, wasapproximately $7,911,378, based on 1,927,898 shares of outstanding Common Stock held by non-affiliates as of the date of thisProspectus, at a price of $4.51 per share, which was the last reported sale price of our common stock on the Nasdaq Capital Market onAugust 25, 2025. We have sold $850,715 of securities pursuant to General Instruction I.B.6 of Form S-3 during the 12-month periodthat ends on and includes the date of this prospectus supplement. In no event will we sell shares pursuant to this prospectus supplementwith a value of more than one-third of the aggregate market value of our common stock held by non-affiliates in any 12-month period,so long as the aggregate market value of our common stock held by non-affiliates is less than $75,000,000. Sales of our common stock, if any, under this prospectus may be made in sales deemed to be “at the market offerings” as defined inRule 415 promulgated under the Securities Act of 1933, as amended, or the Securities Act. The Sales Agent is not required to sell anyspecific number or dollar amount of securities, but will act as a sales agent using commercially reasonable efforts consistent with itsnormal trading and sales practices, on mutually agreed terms between the Sales Agent and us. There is no arrangement for funds to bereceived in any escrow, trust or similar arrangement. The compensation to the Sales Agent for sales of common stock sold pursuant to the sales agreement will be an amount equal to 3.0%of the gross proceeds of any shares of common stock sold under the sales agreement. In connection with the sale of the common stockon our behalf, the Sales Agent will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation ofthe Sales Agent will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification andcontribution to the Sales Agent with respect to certain liabilities, including liabilities under the Securities Act or the SecuritiesExchange Act of 1934, as amended, or the Exchange Act. Investing in our common stock involves a high degree of risk. See “Risk Factors” beginning on page S-3 of this prospectussupplement and page 4 of the accompanying prospectus, as well as the sections captioned “Risk Factor Summary” and “Item1A-Risk Factors” in our most recently filed annual report on Form 10-K or quarterly report on Form 10-Q which isincorporated by reference into this prospectus supplement, for certain risks you should consider. You should read all of theinformation set forth in this prospectus supplement, as well as the documents incorporated by reference herein, carefullybefore you make your investment decision. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of thesesecurities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. B. Riley Securities The date of this prospectus is October 24, 2025. TABLE OF CONTENTS PageABOUT THIS PROSPECTUSS-iiPROSPECTUS SUMMARYS-1RISK FACTORSS-3SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTSS-iiiUSE OF PROCEEDSS-4DILUTIONS-5PLAN OF DISTRIBUTIONS-6LEGAL MATTERSS-7EXPERTSS-7WHERE YOU CAN FIND MORE INFORMATIONS-7INFORMATION INCORPORATED BY REFERENCES-7 PAGEABOUT THIS PROSPECTUS1PROSPECTUS SUMMARY2RISK FACTORS4SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS5USE OF PROCEEDS7DESCRIPTION OF CAPITAL STOCK8DESCRIPTION OF DEPOSITARY SHARES9DESCRIPTION OF DEBT SECURITIES12DESCRIPTION OF WARRANTS19PLAN OF DISTRIBUTION22LEGAL MATTERS24EXPERTS24LIMITATION ON LIABILITY AND DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION FORSECURITIES ACT LIABILITIES24WHERE YOU CAN FIND MORE INFORMATION24INFORMATION INCORPORATED BY REFERENCE25 We are offering to sell, and are seeking offers to buy, the securities only in jurisdictions where such offers and sales arepermitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the securitiesin certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectussupplement and the accompanying prospectus must inform themselves about and obse