858 Therapeutics Announces FDA Fast Track Designation for PARG Inhibitor ETX-19477 for the Treatment of Patients with BRCA-Mutated, Platinum-Resistant Ovarian Cancer

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SAN DIEGO--(BUSINESS WIRE)--Jan 8, 2026--

858 Therapeutics, a clinical-stage biotechnology company, today announced that the U.S. Food and Drug Administration (FDA) has granted Fast Track designation to ETX-19477, the company’s internally discovered PARG inhibitor. The designation has been granted for the treatment of adult patients with BRCA-mutated, platinum-resistant, high-grade serous ovarian cancer (HGSOC).

“Patients with platinum-resistant ovarian cancer have a poor prognosis, and treatment options remain extremely limited, highlighting a substantial unmet need for new therapies,” said Jeffrey Stafford, Ph.D., CEO of 858 Therapeutics. “We are pleased that the FDA has granted Fast Track designation to ETX-19477 and we are committed to working closely with the FDA to accelerate its development. This designation was based on preclinical data and emerging clinical data from our ongoing Phase 1/2 trial of ETX-19477, including anti-tumor activity at tolerable doses.”

FDA Fast Track status is designed to facilitate the development and expedite the review of new therapies that are intended to treat serious conditions with unmet medical need. Under the Fast Track designation, the ETX-19477 development program will have access to more frequent interactions with the FDA and may be eligible for accelerated approval and/or priority review if certain criteria are met.

ETX-19477 is being evaluated in an ongoing Phase 1/2, open-label, multicenter study in patients with advanced solid tumors, designed to assess safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity. The trial is currently enrolling patients in Phase 1 backfill cohorts at multiple dose levels and enriching for select solid tumors harboring BRCA mutations, including HGSOC.

About ETX-19477

Poly(ADP-ribose) glycohydrolase (PARG) is an enzyme that catalyzes the removal of poly-ADP-ribose (PAR) chains from proteins during the DNA damage response. PARG inhibition leads to selective cell death in tumors with underlying replication fork defects, including BRCAm tumors, through a mechanism distinct from PARP inhibition. ETX-19477 is an oral, potent, and selective PARG inhibitor that shows robust preclinical activity in mouse models of ovarian, breast, and gastric cancers. 858 Therapeutics is evaluating ETX-19477 in a Phase 1/2 study in patients with advanced solid tumors at multiple sites in the U.S. For more information on the Phase 1/2 study, please visit: https://clinicaltrials.gov/study/NCT06395519.

About 858 Therapeutics

858 Therapeutics is a biotechnology and drug discovery company developing a portfolio of small molecule therapeutics directed against novel oncology and immunology targets. Its lead programs focus on important nodes in cancer biology, including DNA damage repair, innate immunity, and RNA epigenetics. 858 is headquartered in the biotech hub of San Diego, CA. For more information, please visit www.8five8tx.com.

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CONTACT: Media ContactsFor 858 Therapeutics:

Sanjay Trehan

[email protected]

KEYWORD: CALIFORNIA UNITED STATES NORTH AMERICA CANADA

INDUSTRY KEYWORD: WOMEN FDA CLINICAL TRIALS BIOTECHNOLOGY HEALTH CONSUMER PHARMACEUTICAL GENERAL HEALTH ONCOLOGY

SOURCE: 858 Therapeutics

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PUB: 01/08/2026 08:00 AM/DISC: 01/08/2026 08:00 AM

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