– Late-breaker poster highlights preclinical profile of ABI-6250, currently in Phase 1a with data anticipated in Q3 2025 –

– Second poster describes in vitro studies of effects on viral infection markers by ABI-4334, currently in Phase 1b with data anticipated in the first half of 2025 –

 Assembly Biosciences, Inc. (NASDAQ:ASMB), a biotechnology company developing innovative therapeutics targeting serious viral diseases, today announced new preclinical and in vitro data for two therapeutic candidates featured in poster presentations, including one late-breaker, at the European Association for the Study of the Liver (EASL) Congress, taking place May 7-10, 2025, in Amsterdam, the Netherlands.

"These two EASL poster presentations provide additional characterization of our therapeutic candidates in clinical development for viral hepatitis," said Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio. "Our late-breaker poster highlights ABI-6250's preclinical profile and potential as a once-daily oral therapy for chronic HDV infection, a severe form of viral hepatitis with limited treatment options available. Additionally, in vitro data presented for ABI-4334 provide further insights into the potential for next-generation capsid assembly modulators to impact markers of chronic HBV infection. We look forward to sharing data from ongoing clinical studies for both candidates later this year."

ABI-6250: An oral viral entry inhibitor candidate for hepatitis D virus (HDV) infection

The late-breaker poster presentation titled "Preclinical profiling of ABI-6250, a first-in-class oral therapeutic candidate for chronic hepatitis D" highlights preclinical data supporting the advancement of ABI-6250 into an ongoing Phase 1a clinical study.

Results demonstrate that in cell culture, ABI-6250 specifically inhibits both HDV and hepatitis B virus (HBV) at low nanomolar levels and shows selectivity versus a panel of other viruses. ABI-6250 showed minimal effects on cell viability in vitro across multiple cell types, and also selectively inhibited the sodium taurocholate cotransporting polypeptide (NTCP) bile acid transporter compared to a broad range of other transporters in vitro. In vivo, treatment with ABI-6250 elevated total bile acids at doses that did not increase biomarkers for inhibition of other transporters, indicating selective NTCP target engagement. These results support ABI-6250 as an inhibitor of NTCP and describe total bile acids as a biomarker for target engagement that Assembly Bio plans to evaluate in the ongoing Phase 1a study.

Chronic HDV infection (cHDV) is considered the most serious form of viral hepatitis, and can result in liver cirrhosis, liver cancer, decompensated liver disease or death. ABI-6250 acts to prevent the entry of HDV into cells by blocking access to the NTCP bile acid transporter, a clinically validated target for HDV infection. Currently, one therapy, a peptide inhibitor of NTCP requiring daily injections, is approved for cHDV in the European Union with no therapies approved in the United States.

ABI-4334: A next-generation highly potent capsid assembly modulator (CAM) for HBV

The poster presentation titled "Sustained inhibition of HBV replication and HBsAg levels after long-term treatment with CAM ABI-4334 in human hepatocytes" describes in vitro studies of ABI-4334 evaluating multiple viral biomarkers of HBV infection. These results showed durable reduction in HBV nucleic acids and antigens in human hepatocytes following a one-month course of treatment with ABI-4334.

HBV is a leading global cause of chronic liver disease and liver transplants. The WHO estimates 254 million people worldwide are chronically infected with HBV with an estimated 1.1 million deaths in 2022. The current standard of care for chronic HBV (cHBV) infection, nucleos(t)ide analog reverse transcriptase inhibitors (NrtIs), require lifelong administration and reduce, but do not eliminate, the virus and result in very low cure rates. No new mechanisms of action have been approved for the treatment of cHBV infection in over 25 years.

Assembly Bio intends to make the posters available on the "Events & Presentations" page in the "Investors" section and on the "Publications" page in the "Pipeline" section of its website at www.assemblybio.com.

ABI-6250 and ABI-4334 are investigational product candidates that have not been approved anywhere globally, and their safety and efficacy have not been