Assembly Biosciences announced positive interim antiviral activity, clinical outcomes, safety, and pharmacokinetic results from a Phase 1b study evaluating ABI-5366, a long-acting herpes simplex virus (HSV) helicase-primase inhibitor. The 350 mg weekly oral dose cohort demonstrated a statistically significant 94% reduction in HSV-2 shedding rate compared to placebo over a 29-day evaluation period, exceeding the company's target of 80-85%.
The study also showed a statistically significant 94% reduction in genital lesion rate and a 98% reduction in high viral load shedding rate compared to placebo with the 350 mg weekly dose. ABI-5366 was well-tolerated at oral doses up to 350 mg weekly, and its pharmacokinetic profile continues to support once-weekly and potentially once-monthly oral dosing regimens.
With these strong results, Assembly Bio expects to move directly into Phase 2 clinical study preparation, with initiation anticipated in mid-2026. The in-life portions of chronic toxicology studies for ABI-5366 are complete, supporting longer-term dosing in Phase 2. Interim data from the ABI-1179 Phase 1b study and the ongoing monthly dosing cohort of ABI-5366 are expected in fall 2025.
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