San Francisco-based biotechnology company Assembly Biosciences, Inc. (NASDAQ: ASMB) on Friday announced interim Phase 1b data for its long-acting herpes simplex virus (HSV) helicase-primase inhibitor ABI-5366.

The study evaluated two dosing cohorts in participants with recurrent genital herpes. Assembly Biosciences says that ABI-5366 was found to be well tolerated at both a 30 mg weekly dose following a 150 mg loading dose and at a 350 mg weekly dose. The pharmacokinetic profile supports both weekly and potentially monthly dosing.

In the 350 mg cohort, statistically significant reductions were observed compared to placebo, including a 94% decrease in HSV-2 shedding rate, a 98% decrease in high viral load shedding rate, and a 94% decrease in genital lesion rate.

Assembly Biosciences is also evaluating a monthly dosing regimen of ABI-5366 and conducting a Phase 1b study of ABI-1179, another HSV helicase-primase inhibitor contributed by Gilead Sciences, Inc. (NASDAQ: GILD). Interim data from both studies is expected later this fall, with Phase 2 studies of ABI-5366 planned for mid-2026.

Both ABI-5366 and ABI-1179 remain investigational candidates that have not been approved globally, and their safety and efficacy have not been established.