Assembly Biosciences presented topline Phase 1a data on ABI-6250 at EASL 2026 (poster WED-579, Dr. Edward Gane, University of Auckland) — a first-in-class oral hepatitis D virus (HDV) entry inhibitor. The Phase 1a study evaluated safety, pharmacokinetics, and pharmacodynamic activity in healthy participants; the data supports advancing directly into a Phase 2 study by year-end. ABI-6250 is the only oral entry inhibitor in development for chronic HDV. The mechanistic context matters: Gilead's Hepcludex (bulevirtide) — a 47-amino-acid injectable lipopeptide NTCP entry inhibitor — just won FDA accelerated approval May 22 as the first US HDV treatment. ABI-6250 targets the same entry-inhibition step but as an oral small molecule rather than an injectable peptide, positioning it as a potential next-generation convenience competitor in the small but newly-validated HDV market. Assembly also announced May 22 an expansion of ABI-6250 development into cholestatic liver diseases. The peptide-vs-small-molecule dynamic in HDV mirrors the same competition that played out in GLP-1 (injectable semaglutide vs oral orforglipron).
The FDA granted accelerated approval on May 22, 2026 to Gilead Sciences' Hepcludex (bulevirtide-gmod) 8.5 mg, the first and only approved US treatment for adults living with chronic hepatitis delta virus (HDV) infection. Bulevirtide — formerly known as Myrcludex B — is a 47-amino acid, N-terminally myristoylated lipopeptide derived from the pre-S1 domain of the HBV large envelope protein. The molecule binds to the sodium taurocholate cotransporting polypeptide (NTCP) — the entry receptor that HDV and HBV both use to enter hepatocytes — and blocks viral entry as a first-in-class entry inhibitor. The Phase 3 MYR301 trial documented a statistically significant combined virologic and biochemical response at week 48 versus delayed-treatment control, supporting the accelerated-approval threshold. Continued approval depends on confirmatory trial verification of clinical benefit. Bulevirtide has been EU-approved under conditional marketing authorization since 2020. Gilead shares closed Friday at $134.36, up roughly 3%.
Bulevirtide's mechanism reveals why an entry inhibitor succeeded where small-molecule antivirals didn't. HDV is an obligate parasite of HBV — the delta virus uses the HBV envelope to assemble its virions and the HBV-derived large surface protein to enter hepatocytes via the sodium taurocholate cotransporting polypeptide (NTCP) receptor on hepatocyte cell membranes. Existing HBV antiviral nucleoside/nucleotide analogs (entecavir, tenofovir) suppress HBV replication but don't clear circulating HBsAg or interrupt the HDV entry cycle. Bulevirtide's 47-amino acid sequence — derived from the HBV pre-S1 domain — binds NTCP competitively and blocks both HDV and HBV entry. Real-world EU experience since 2020 shows roughly 50-60% of HDV patients achieve undetectable HDV RNA after 96 weeks of treatment, with a favorable safety profile dominated by injection-site reactions. The US approval expands access for an estimated 75,000-100,000 US patients with chronic HDV, most of whom were previously treated empirically with off-label interferon alfa with poor tolerability.