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Assembly Biosciences Reports Positive Interim Results from Phase 1b Clinical Studies of Long-Acting Helicase-Primase Inhibitor Candidates

Assembly Biosciences, Inc. (ASMB) | December 8, 2025

By Ethan Davis

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Assembly Biosciences announced positive interim results from two Phase 1b studies of its investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitors in participants seropositive for HSV type 2 with recurrent genital herpes.

ABI-1179 showed a 98% reduction in HSV-2 shedding rate and a 91% reduction in virologically confirmed genital lesion rate in the weekly oral dose cohort.

ABI-5366 demonstrated a 76% reduction in HSV-2 shedding rate and an 88% reduction in virologically confirmed genital lesion rate in the monthly oral dose cohort.

High Efficacy

ABI-1179 achieved a >99% reduction in high viral load shedding rate and outperformed expectations for antiviral efficacy.

Clinical Outcomes

ABI-5366 showed significant improvements in clinical outcomes, supporting potential for monthly oral dosing regimens.

Phase 2 Plans

The company plans to initiate longer-duration Phase 2 studies for ABI-5366 and evaluate advancing ABI-1179 to Phase 2 clinical evaluation.

  • ABI-1179 demonstrated 98% reduction in HSV-2 shedding rate and >99% reduction in high viral load shedding rate with well-tolerated weekly oral dosing.
  • ABI-5366 showed a 76% reduction in HSV-2 shedding rate and an 81% reduction in high viral load shedding rate with monthly oral dosing, supporting the optimization for potential monthly regimens.

With promising results from the Phase 1b studies, Assembly Biosciences is poised to advance its innovative therapeutics targeting serious viral diseases into Phase 2 evaluations, signaling potential for significant clinical impact in the future.