Septerna Announces Positive Phase 1 Data for SEP-631, an Oral MRGPRX2 NAM for the Treatment of Mast Cell-Driven Diseases, and Outlines Initial Phase 2 Development Strategy

SEP-631 Demonstrated Robust, Dose-Dependent Inhibition of Icatibant-Induced Skin Wheal Formation, with Complete Inhibition Observed at Doses as Low as 10 mg Once-Daily 

Well-Tolerated Across All Doses Studied with an Adverse Event Profile Comparable to Placebo; Pharmacokinetic Profile Supports Once-Daily Oral Dosing

Phase 2 Development Planned to Begin with Chronic Spontaneous Urticaria in the Second Half of 2026

Excerpt from the Press Release:

SOUTH SAN FRANCISCO, Calif., March 01, 2026 (GLOBE NEWSWIRE) — Septerna, Inc. (Nasdaq: SEPN), a clinical-stage biotechnology company pioneering oral small molecule GPCR-targeted medicines, today announced positive results from its Phase 1 clinical trial evaluating SEP-631, a potent and selective oral negative allosteric modulator (NAM) of Mas-related G protein-coupled receptor X2 (MRGPRX2). Based on these results, Septerna plans to advance SEP-631 into Phase 2 development for chronic spontaneous urticaria (CSU) and continue evaluation of additional mast cell-driven indications.

“These data mark an important milestone for the SEP-631 program and more broadly for our Native Complex Platform^®, which enables new approaches to GPCR drug discovery by reconstituting functional GPCR complexes outside of cells,” said Jae Kim, M.D., chief medical officer of Septerna. “Importantly, the robust inhibition of icatibant-induced wheal formation observed is consistent with the differentiated insurmountable NAM mechanism we characterized preclinically and provides clinical proof-of-mechanism for the MRGPRX2 pathway. Overall, we believe the strength and consistency of these results position SEP-631 as a potentially differentiated oral treatment for patients living with mast cell-driven diseases. With a clear path into Phase 2 development in chronic spontaneous urticaria, we are focused on translating this early validation into meaningful outcomes for patients and exploring additional high-need indications where MRGPRX2 biology is implicated.”

Phase 1 Results
SEP-631 was evaluated in a randomized, double-blind, placebo-controlled Phase 1 trial in healthy volunteers, including single-ascending dose, multiple-ascending dose and food-effect cohorts. The study assessed safety, tolerability, pharmacokinetics (PK) and pharmacodynamic (PD) activity.

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