Assembly Biosciences Doses First Participant in Phase 1a/b Clinical Trial of Herpes Simplex Virus Helicase-Primase Inhibitor Candidate ABI-5366

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Assembly Biosciences has initiated a Phase 1a/b clinical trial for ABI-5366, a new helicase-primase inhibitor targeting herpes simplex virus (HSV). The Phase 1a trial involves single ascending doses in healthy participants, with interim data expected by Q3 2024. Phase 1b will start by the end of the year with multiple ascending weekly doses in patients with recurrent genital herpes, with interim data expected in the first half of 2025. ABI-5366 has shown strong potential in preclinical studies, potentially offering a long-acting treatment for HSV-1 and HSV-2. Existing treatments are and not fully effective, highlighting the need for new therapeutic options in this area.

  • First participant dosed in Phase 1a/b trial of ABI-5366.
  • Phase 1a trial interim data expected Q3 2024.
  • Phase 1b trial interim data expected 1H 2025.
  • ABI-5366 shows nanomolar potency against HSV-1 and HSV-2.
  • Potential for long-acting administration based on preclinical pharmacokinetic data.
  • Existing treatments are , emphasizing the need for new therapeutic options.
  • Interim data for Phase 1a only available by Q3 2024, indicating a long wait.
  • Interim data for Phase 1b not expected until 1H 2025, prolonging uncertainty.
  • Current treatments are only partially effective, implying a challenging market landscape.

Assembly Biosciences' initiation of the Phase 1a/b clinical trial for their HSV helicase-primase inhibitor, ABI-5366, marks a significant step in addressing the unmet medical need for recurrent genital herpes. The current landscape of herpes treatments often involves daily administration, which only partially controls the infection and reduces transmission risk. If ABI-5366 can deliver on its promise of a long-acting, once-weekly oral dosing, it would represent a major improvement in patient compliance and quality of life.

The specificity of ABI-5366 towards both HSV-1 and HSV-2, coupled with its nanomolar potency demonstrated in vitro, underlines its potential efficacy. However, the transition from preclinical to clinical phases is critical. The Phase 1a portion will provide valuable pharmacokinetic data from healthy participants, helping to establish the optimal dosage for efficacy while minimizing side effects. If successful, the Phase 1b portion will then evaluate clinical outcomes in patients, which will be the real test of the drug's effectiveness.

The market potential for ABI-5366 is substantial, given the prevalence of recurrent genital herpes and the current limitations of existing treatments. The lack of new therapeutic options in this space for over 25 years indicates a significant market opportunity for a novel drug that can provide more effective and convenient treatment. The estimated four million affected individuals in the U.S. and EU alone represent a sizable target market.

Investors should note that the interim data expected in Q3 2024 for the Phase 1a study and in 1H 2025 for the Phase 1b study, will be key milestones. Positive interim results could drive increased investor confidence and potentially lead to strategic partnerships or funding opportunities to support further development and commercialization efforts.

From a financial perspective, Assembly Biosciences’ advancement in the clinical trial phase with ABI-5366 could positively impact their valuation, especially if interim results are promising. Clinical trials are expensive, but success in early-phase trials often leads to increased investor interest and potential upswings in stock price. The company's ability to move from preclinical to clinical phases is a testament to their strong R&D capabilities and could attract further investments.

However, investors should remain cautious as clinical trials are inherently risky and the failure rate in early-phase trials is significant. It’s essential to monitor the Phase 1a outcomes closely to gauge the drug’s potential pharmacokinetic profile and its ability to meet the target concentrations for antiviral efficacy. The financial impact will largely depend on these results and subsequent Phase 1b data.

– Phase 1a study portion of single ascending dosing in healthy participants will inform the development of ABI-5366 with interim data expected in Q3 2024 –

– Phase 1b study portion of multiple ascending weekly doses in participants with recurrent genital herpes on track to initiate by end of year with interim data expected in 1H 2025 –

SOUTH SAN FRANCISCO, Calif., June 10, 2024 (GLOBE NEWSWIRE) -- Assembly Biosciences, Inc. (Nasdaq: ASMB), a biotechnology company developing innovative therapeutics targeting serious viral diseases, today announced that the first participant has been dosed in the Phase 1a/b trial of its long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate ABI-5366.

ABI-5366, which is being developed for recurrent genital herpes, has demonstrated nanomolar potency against both HSV type 1 (HSV-1) and HSV type 2 (HSV-2) in vitro and its pharmacokinetic (PK) profile in preclinical studies strongly supports the potential for long-acting administration. Recurrent genital herpes caused by HSV-1 and HSV-2 is common after an initial symptomatic infection and affects an estimated four million individuals in the United States and European Union. Existing treatments are limited and only partially effective in controlling the infection or reducing transmission risk despite daily, chronic administration. In studies of individuals with highly recurrent genital herpes (six or more recurrences a year), only 34% remained recurrence free for a year while on current suppressive therapies.

“We are pleased to advance ABI-5366 into clinical development for recurrent genital herpes, a disease which significantly impacts the lives of millions of people, and where no new therapeutic options have been approved in over 25 years," said Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio. “Importantly, since the HSV helicase-primase is a clinically validated viral target, the PK data from healthy participants in the Phase 1a part of this study will enable us to assess the ability of ABI-5366 to achieve the target concentrations we have established for antiviral efficacy and to support a once-weekly oral dosing profile. These data will also inform our dose selection for the multiple ascending dose Phase 1b part of the study, where we will evaluate viral and clinical outcomes in individuals with recurrent genital herpes.”

About ABI-5366-101

ABI-5366-101 is a randomized, blinded and placebo-controlled Phase 1a/b clinical study of ABI-5366. Dosing has initiated for Part A in healthy participants, which will evaluate the safety, tolerability and PK of ABI-5366 following single ascending dose administration. Participants in Part A will be randomized 6:2 between ABI-5366 and placebo in up to five cohorts at different doses.

Assembly Bio plans to move directly into Part B in participants seropositive for HSV-2 with recurrent genital herpes, which will evaluate ABI-5366 in multiple ascending dose administration and is expected to initiate by the end of the year. Part B will evaluate a weekly oral dose of ABI-5366 for a 29-day dosing period. Participants in Part B will be randomized 20:5 between ABI-5366 and placebo in four cohorts, exploring four dose levels with a pooled placebo analysis.  

In addition to assessing safety, tolerability and PK, Part B will also evaluate antiviral efficacy by measuring changes in viral parameters including viral shedding rate and HSV-2 DNA levels obtained from swab samples, and clinical parameters including lesion recurrence rate and lesion duration. The trial results will support dose selection for a future Phase 2 trial.

Additional information about the Phase 1a/b trial is available at using the identifier NCT06385327. Data from preclinical research supporting clinical advancement for ABI-5366 will be presented in a poster presentation at the 48th Annual International Herpesvirus Workshop, taking place in Portland, Ore., July 13-17, 2024.

ABI-5366 is an investigational product candidate that has not been approved anywhere globally, and its safety and efficacy have not been established.

About Assembly Biosciences
Assembly Biosciences is a biotechnology company dedicated to the development of innovative small-molecule therapeutics designed to change the path of serious viral diseases and improve the lives of patients worldwide. Led by an accomplished team of leaders in virologic drug development, Assembly Bio is committed to improving outcomes for patients struggling with the serious, chronic impacts of herpesvirus, hepatitis B virus (HBV) and hepatitis delta virus (HDV) infections. For more information, visit

Forward-Looking Statements
The information in this press release contains forward-looking statements that are subject to certain risks and uncertainties that could cause actual results to materially differ. These risks and uncertainties include: Assembly Bio’s ability to realize the potential benefits of its collaboration with Gilead Sciences, Inc., including all financial aspects of the collaboration and equity investments; Assembly Bio’s ability to initiate and complete clinical studies involving its therapeutic product candidates, including studies contemplated by Assembly Bio’s collaboration with Gilead, in the currently anticipated timeframes or at all; safety and efficacy data from clinical or nonclinical studies may not warrant further development of Assembly Bio’s product candidates; clinical and nonclinical data presented at conferences may not differentiate Assembly Bio’s product candidates from other companies’ candidates; results of nonclinical studies may not be representative of disease behavior in a clinical setting and may not be predictive of the outcomes of clinical studies; and other risks identified from time to time in Assembly Bio’s reports filed with the U.S. Securities and Exchange Commission (the SEC). You are urged to consider statements that include the words may, will, would, could, should, might, believes, hopes, estimates, projects, potential, expects, plans, anticipates, intends, continues, forecast, designed, goal or the negative of those words or other comparable words to be uncertain and forward-looking. Assembly Bio intends such forward-looking statements to be covered by the safe harbor provisions contained in Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. More information about Assembly Bio’s risks and uncertainties are more fully detailed under the heading “Risk Factors” in Assembly Bio’s filings with the SEC, including its most recent Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K. Except as required by law, Assembly Bio assumes no obligation to update publicly any forward-looking statements, whether as a result of new information, future events or otherwise.


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What is ABI-5366?

ABI-5366 is a helicase-primase inhibitor developed by Assembly Biosciences for the treatment of recurrent genital herpes.

When will the interim data for the Phase 1a trial of ABI-5366 be available?

Interim data for the Phase 1a trial of ABI-5366 is expected in Q3 2024.

What does the Phase 1b trial for ABI-5366 involve?

The Phase 1b trial will involve multiple ascending weekly doses in participants with recurrent genital herpes, with interim data expected in the first half of 2025.

What is the potential benefit of ABI-5366?

ABI-5366 has shown strong potential in preclinical studies for long-acting treatment of HSV-1 and HSV-2.

Why is there a need for new treatments like ABI-5366?

Existing treatments for recurrent genital herpes are and not fully effective, indicating the need for new therapeutic options.

Assembly Biosciences, Inc.


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