Septerna (NASDAQ: SEPN) begins Phase 1 SEP-631 trial in mast cell diseases

Rhea-AI Filing Summary

Septerna, Inc. furnished an update on its drug development pipeline, reporting that it has begun dosing the first participants in a Phase 1 clinical trial of SEP-631. The press release describes SEP-631 as an oral small molecule MRGPRX2 negative allosteric modulator being studied for the treatment of mast cell-driven diseases, marking an early clinical step for this program. The communication is provided under Regulation FD as furnished information, not filed, and is attached as Exhibit 99.1.

Insights

Biotech clinical development analyst

Septerna advances SEP-631 into first-in-human Phase 1 testing.

Septerna reports dosing of the first participants in a Phase 1 clinical trial of SEP-631, described as an oral small molecule MRGPRX2 negative allosteric modulator for mast cell-driven diseases. Moving a program into Phase 1 typically tests safety, tolerability, and basic pharmacokinetics in humans, representing an early but important step in clinical development.

The update is furnished under Regulation FD, with details contained in a press release attached as Exhibit 99.1. No financial metrics, timelines, or efficacy data are provided in the excerpt, so implications for revenue or profitability are not described. Subsequent clinical disclosures in future company communications or filings would be needed to understand outcomes from this trial.

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 21, 2025

Septerna, Inc.

(Exact name of Registrant as Specified in Its Charter)

Delaware		001-42382		84-3891440
(State or Other Jurisdiction of Incorporation)		(Commission File Number)		(IRS Employer Identification No.)

250 East Grand Avenue
South San Francisco, California		94080
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s Telephone Number, Including Area Code: (650) 338-3533

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, par value $0.001 per share		SEPN		The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 7.01. Regulation FD Disclosure.

On August 21, 2025, Septerna, Inc. issued a press release titled “Septerna Announces Dosing of the First Participants in Phase 1 Clinical Trial of SEP-631, an Oral Small Molecule MRGPRX2 Negative Allosteric Modulator for the Treatment of Mast Cell-Driven Diseases.” A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information in Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

99.1		Press Release issued by Septerna, Inc. on August 21, 2025, furnished herewith.
104		Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

						Septerna, Inc.
Date: August 21, 2025				By:		/s/ Jeffrey Finer, M.D., Ph.D.
						Jeffrey Finer, M.D., Ph.D. Chief Executive Officer

FAQ

What did Septerna (SEPN) disclose in this 8-K filing?

Septerna reported that it has begun dosing the first participants in a Phase 1 clinical trial of SEP-631 and furnished a related press release as Exhibit 99.1.

What is SEP-631 in Septerna (SEPN)'s pipeline?

SEP-631 is described as an oral small molecule MRGPRX2 negative allosteric modulator being developed for the treatment of mast cell-driven diseases.

What stage of development is SEP-631 according to Septerna (SEPN)?

The company reports that SEP-631 has entered a Phase 1 clinical trial, with first participants now being dosed.

Is the SEP-631 Phase 1 dosing information considered filed or furnished by Septerna (SEPN)?

The information about SEP-631 under Item 7.01, including Exhibit 99.1, is furnished, not deemed filed, and is not subject to Section 18 liabilities of the Exchange Act.

Which exhibit in Septerna (SEPN)'s 8-K contains the SEP-631 press release?

Exhibit 99.1 contains the press release titled “Septerna Announces Dosing of the First Participants in Phase 1 Clinical Trial of SEP-631.”

Who signed Septerna (SEPN)'s 8-K related to the SEP-631 trial?

The report was signed on behalf of Septerna, Inc. by Jeffrey Finer, M.D., Ph.D., the company’s Chief Executive Officer.