Assembly Biosciences' ABI-5366 Demonstrates Significant Reductions in HSV-2 Shedding and Genital Lesions

Assembly Biosciences reported positive interim results from its Phase 1b clinical trial of ABI-5366, a long-acting helicase-primase inhibitor for recurrent genital herpes. The study showed a 94% reduction in HSV-2 shedding and genital lesion rates, as well as a 98% reduction in high viral load shedding rate. ABI-5366 had a favorable safety profile and supports both weekly and monthly dosing regimens. Assembly plans to initiate Phase 2 studies by mid-2026. Gilead Sciences retains the option to acquire the program post-Phase 1b studies.

Assembly Biosciences, Inc. (Nasdaq: ASMB) has announced positive interim results from its Phase 1b clinical trial of ABI-5366, an investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitor. The trial, which evaluates ABI-5366 in participants seropositive for HSV type 2 (HSV-2) with recurrent genital herpes, demonstrated highly potent antiviral activity.

The study observed a 94% reduction in HSV-2 shedding rate and a 98% reduction in high viral load shedding rate, both statistically significant, in the cohort evaluating a 350 mg weekly oral dose compared to placebo over a 29-day evaluation period [1]. Additionally, a 94% reduction in genital lesion rate was observed with the 350 mg weekly dose, also statistically significant.

ABI-5366 was well-tolerated at oral doses up to 350 mg weekly, with a favorable safety and tolerability profile. The observed pharmacokinetic (PK) profile supports once-weekly and potentially once-monthly oral dosing regimens. The company expects to move directly into Phase 2 clinical study preparation in parallel with the completion of this Phase 1b study.

Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio, commented, "We are thrilled to see these interim data for ABI-5366 far exceeding the targets we had set in this study for antiviral activity and clinical outcomes in participants with recurrent genital herpes. These results underscore our conviction in the potential for ABI-5366 to reduce outbreaks and improve quality of life for those affected by the severe impacts of recurrent genital herpes."

Assembly Bio plans to initiate Phase 2 studies by mid-2026. Under the collaboration agreement with Gilead Sciences, Inc. (Gilead), Gilead has the right to opt in to an exclusive license for further development and commercialization of the helicase-primase inhibitor program after reviewing the option data package to be delivered by Assembly Bio following completion of the Phase 1b studies.

References:
[1] https://investor.assemblybio.com/news-releases/news-release-details/assembly-biosciences-reports-positive-interim-results-phase-1b