Assembly Biosciences Reports Positive Interim Phase 1a Results from Clinical Trial Evaluating Long-Acting Helicase-Primase Inhibitor ABI-1179 in Development for

A half-life of approximately four days and high exposure across the dose range evaluated exceeded Assembly Bio’s targets for a once-weekly oral dosing profile. ABI-1179 was well-tolerated with a favorable safety profile observed. At all doses evaluated, including the lowest dose of 50 mg, ABI-1179 exceeded Assembly Bio’s target plasma concentrations for antiviral activity, a target established from pharmacokinetic (PK) modelling and projected to achieve increased efficacy compared to approved therapies.

With these data, Assembly Bio plans to move directly into the Phase 1b portion of the ABI-1179 study in participants with recurrent genital herpes. This Phase 1b study will be conducted concurrently with the ongoing Phase 1b evaluation of ABI-5366, Assembly Bio’s other long-acting helicase-primase inhibitor candidate that began dosing in Phase 1b in the fourth quarter of 2024. The studies are anticipated to be conducted at the same sites using equivalent eligibility criteria and outcome measures for both candidates. Assembly Bio plans to report interim data for both candidates together in fall 2025 given adjustments to enrollment timelines that will enable the studies to run concurrently.

Millions of people live with life-altering symptoms of recurrent genital herpes, and these symptoms are not well-managed by available treatments. Unfortunately, no new therapeutic innovation has been made in decades. In Phase 1a, ABI-1179 and ABI-5366 both exceeded our target pharmacokinetic profile for our long-acting helicase-primase inhibitor program, and we are pleased to advance these two promising candidates with the potential to improve treatment outcomes for individuals with recurrent genital herpes. We look forward to reporting Phase 1b interim data for both candidates this fall, which will inform critical next steps in our data-driven portfolio strategy for this important indication.

said Jason Okazaki, chief executive officer and president of Assembly Bio.

ABI-1179 was contributed by Gilead Sciences, Inc. (Gilead) under the collaboration between Assembly Bio and Gilead. ABI-1179 and ABI-5366 are investigational product candidates that have not been approved anywhere globally, and their safety and efficacy have not been established.

Study ABI-1179-101 – Phase 1a Interim Results

Study Overview

ABI-1179-101 is a randomized, blinded and placebo-controlled Phase 1a/b clinical study of ABI-1179. Part A (Phase 1a) is ongoing, evaluating the safety, tolerability and PK of ABI-1179 following single ascending dose administration in healthy participants. Dosing is complete for three cohorts in Part A, evaluating doses of 50 mg, 100 mg and 300 mg, with each cohort randomized 6:2 between ABI-1179 and placebo. The study protocol includes a food effect cohort, which has not yet been conducted.

Safety and PK data reported here reflect data available as of the cut-off date, which reflects a follow-up period ranging by cohort from five days to the full follow-up period of 11 days after dosing. The study remains blinded and the reported interim safety data include data from both active and placebo treatment groups collectively.

Results

Across the Part A (Phase 1a) cohorts evaluated to date, ABI-1179 had a mean half-life of approximately four days when dosed orally, supporting once-weekly oral dosing, the target profile for ABI-1179. ABI-1179 is projected to maintain the target plasma concentrations for antiviral activity established by PK modelling at a low oral weekly dose.

In these cohorts to date, ABI-1179 was well-tolerated with a favorable safety profile observed. Treatment-emergent adverse events (AEs) were all mild in intensity and all were considered not related to study treatment by the study investigators; there were no serious AEs in any dose cohort. One self-limited grade 2 alanine transaminase (ALT) elevation was observed in the cohort evaluating the highest dose of 300 mg. There were no treatment-related grade 3 or 4 laboratory abnormalities and no protocol-defined stopping criteria were met. There were no clinically significant ECG abnormalities or patterns of AEs or laboratory abnormalities noted.

Study ABI-1179-101 – Phase 1b Design

Assembly Bio has initiated preparatory activities for Part B (Phase 1b) in participants seropositive for HSV type 2 (HSV-2) with recurrent genital herpes, which will evaluate multiple ascending doses of ABI-1179. Part B of the study will evaluate weekly oral dose administration of ABI-1179 over a 29-day treatment interval in up to four cohorts. Participants in Part B will be randomized 20:5 between ABI-1179 and placebo in each cohort, with a pooled analysis of placebo recipients.

In addition to assessing safety, tolerability and PK, Part B will also evaluate antiviral activity by assessing changes in viral parameters including HSV-2 shedding rate and levels of virus obtained from genital swab samples. Effects on clinical parameters including lesion recurrence rate and lesion duration will also be measured.

Additional information about the Phase 1a/b trial is available at clinicaltrials.gov using the identifier NCT06698575. Assembly Bio expects to submit complete data from the trial for presentation at future scientific meetings.