Assembly Biosciences, Inc. recently announced Phase 1b clinical data for its next-generation investigational capsid assembly modulator (CAM) ABI-4334 featured in a late-breaking poster presentation at the American Association for the Study of Liver Diseases (AASLD), The Liver Meeting. The conference is taking place November 7-11, 2025, in Washington, D.C.

“We are pleased to highlight positive data from our Phase 1b study for ABI-4334 with the scientific community,” said Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio. “These data demonstrate the very high potency we set out to achieve for ABI-4334 and support its potential to maximize antiviral activity as a component of multi-drug combination regimens targeting cures for chronic hepatitis B infection.”

The late-breaking poster presentation titled “Safety, pharmacokinetics and antiviral activity of the next-generation hepatitis B capsid assembly modulator ABI-4334 in patients with HBeAg-negative chronic hepatitis B infection not suppressed on nucleoside analogues: results from a randomized, blinded, Phase 1b study” highlights data in individuals with chronic hepatitis B infection treated with ABI-4334. This poster is the first scientific presentation of the complete Phase 1b data announced earlier this year by Assembly Bio.

Two cohorts of predominantly HBeAg-negative subjects were enrolled, evaluating 150 mg and 400 mg oral doses of ABI-4334 given once-daily over 28 days. ABI-4334 was well tolerated at both doses evaluated. Multi-log declines in hepatitis B virus (HBV) DNA and pregenomic RNA (pgRNA) were observed for both doses, consistent with the increased in vitro potency of ABI-4334 compared to first-generation CAMs. These declines in HBV DNA and pgRNA are supportive of full engagement of the first CAM mechanism of action, suppression of viral replication. Exposures multiple folds above levels anticipated to be required for inhibition of cccDNA formation, the second CAM mechanism of action, were also observed at both dose levels. As expected in predominantly HBeAg-negative patients with a short dosing interval, reductions in HBsAg were not observed.

The poster presentation is available on the “Events & Presentations” page in the “Investors” section and on the “Publications” page in the “Pipeline” section of Assembly Bio’s website at www.assemblybio.com.

Under the collaboration agreement between Assembly Bio and Gilead Sciences, Inc. (Gilead), Gilead has the right to opt in to an exclusive license for further development and commercialization of ABI-4334 after reviewing an option data package following completion of this Phase 1b study.

ABI-4334 is an investigational product candidate that has not been approved anywhere globally, and its safety and efficacy have not been established.

Assembly Biosciences is a biotechnology company dedicated to the development of innovative small-molecule therapeutics designed to change the path of serious viral diseases and improve the lives of patients worldwide. Led by an accomplished team of leaders in virologic drug development, Assembly Bio is committed to improving outcomes for patients struggling with the serious, chronic impacts of herpesvirus, hepatitis B virus (HBV) and hepatitis delta virus (HDV) infections. For more information, visit assemblybio.com.