This section highlights FDA-related milestones and regulatory updates for drugs developed by Assembly Biosciences (ASMB).
Over the past two years, Assembly Biosciences has reported clinical trial outcomes, regulatory submissions, approvals, and other FDA events for drugs and therapies such as
ABI-6250, ABI-5366, ABI-1179, and ABI-4334. For definitions of regulatory abbreviations such as NDA, BLA, or PDUFA, see the event status legend.
Select a button below to view the list of FDA events for that drug.
ABI-6250 FDA Regulatory Timeline and Events
ABI-6250 is a drug developed by Assembly Biosciences for the following indication: For Hepatitis Delta Virus.
This drug is under review by the U.S. Food and Drug Administration (FDA).
Below is a timeline of key regulatory milestones for this therapy.
- Drug:
- ABI-6250
- Announced Date:
- May 22, 2026
- Indication:
- For Hepatitis Delta Virus
Announcement
Assembly Biosciences, Inc announced plans to expand the clinical development of ABI-6250, its oral entry inhibitor candidate for chronic hepatitis delta virus (HDV) infection, into primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), broadening the program into cholestatic liver diseases.
AI Summary
Assembly Biosciences said it plans to expand development of ABI-6250, its oral entry inhibitor, beyond chronic hepatitis delta virus (HDV) into cholestatic liver diseases. The company is preparing a Phase 2 study in primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), with the trial expected to begin in the first quarter of 2027.
The new program builds on ABI-6250’s completed Phase 1a study and its ongoing work in HDV. Assembly Bio said the move broadens the drug’s potential use in serious liver conditions where treatment options are limited. ABI-6250 is still an investigational candidate, so its safety and effectiveness have not yet been proven.
Read Announcement- Drug:
- ABI-6250
- Announced Date:
- May 7, 2025
- Indication:
- For Hepatitis Delta Virus
Announcement
Assembly Biosciences, announced new preclinical and in vitro data for two therapeutic candidates featured in poster presentations, including one late-breaker, at the European Association for the Study of the Liver (EASL) Congress, taking place May 7-10, 2025, in Amsterdam, the Netherlands.Inc
AI Summary
Assembly Biosciences recently presented new preclinical and in vitro data at the European Association for the Study of the Liver (EASL) Congress in Amsterdam, May 7‑10, 2025. One late-breaker poster showcased ABI‑6250, an oral inhibitor for chronic hepatitis D virus (HDV) infection. The data demonstrate that ABI‑6250 effectively targets both HDV and hepatitis B virus (HBV) at low nanomolar levels in cell studies, with minimal effects on cell viability. The findings support its advancement into a Phase 1a clinical study, where total bile acids may serve as a biomarker for target engagement.
Another poster detailed in vitro studies on ABI‑4334, a next‑generation capsid assembly modulator aimed at reducing markers of chronic HBV infection. ABI‑4334 has shown promising results by sustainably reducing HBV nucleic acids and antigens in human hepatocytes. Both candidates continue to progress, offering potential new treatment options for viral hepatitis.
Read Announcement- Drug:
- ABI-6250
- Announced Date:
- February 26, 2025
- Indication:
- For Hepatitis Delta Virus
Announcement
Assembly Biosciences, Inc announced that the first participant has been dosed in the Phase 1a trial of ABI-6250, the company's orally bioavailable, small molecule hepatitis delta virus (HDV) entry inhibitor candidate.
AI Summary
Assembly Biosciences, Inc. recently announced that the first participant has been dosed in the Phase 1a trial of ABI-6250, its new orally bioavailable small molecule designed to block hepatitis delta virus (HDV) from entering liver cells. The trial will investigate both single and multiple ascending doses in healthy volunteers, with safety, tolerability, and pharmacokinetics being key objectives. Researchers will also measure changes in serum bile acids as a biomarker to see if ABI-6250 effectively targets the NTCP transporter, which HDV relies on to infect liver cells. Data from the study, expected in the third quarter of 2025, will help determine the best dosing approach for future research. This initial clinical step marks an important move toward developing the first potential oral treatment option for chronic HDV infection, a serious liver condition with limited therapies available.
Read Announcement
ABI-5366 FDA Regulatory Timeline and Events
ABI-5366 is a drug developed by Assembly Biosciences for the following indication: For recurrent genital herpes.
This drug is under review by the U.S. Food and Drug Administration (FDA).
Below is a timeline of key regulatory milestones for this therapy.
- Drug:
- ABI-5366
- Announced Date:
- April 9, 2026
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc announced Phase 1b clinical data for ABI-5366 and ABI-1179, herpes simplex virus (HSV) helicase-primase inhibitor candidates, will be featured in multiple presentations, including one late-breaker, at the 2026 Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) taking place April 17-21, 2026, in Munich, Germany.
AI Summary
Assembly Biosciences announced that Phase 1b clinical data for two herpes simplex virus (HSV) helicase-primase inhibitor candidates, ABI-5366 and ABI-1179, will be featured in multiple presentations at the 2026 Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), April 17–21, in Munich, Germany.
Additional Phase 1b data for ABI-5366, including results from a monthly dosing cohort, was selected for an oral presentation. Phase 1b data for ABI-1179 was accepted as a late-breaker poster presentation. Assembly plans to make the posters available on its website under “Events & Presentations” in the Investors section and “Publications” in the Pipeline section.
Both ABI-5366 and ABI-1179 are investigational product candidates that are not approved anywhere, and their safety and effectiveness have not been established. They are exclusively licensed to Gilead Sciences, which has sole responsibility for further clinical development and commercialization.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- October 10, 2025
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc announced that interim Phase 1b clinical data for its long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate ABI-5366 are featured in a late-breaking oral presentation during the 38th Congress of the International Union Against Sexually Transmitted Infections (IUSTI)- Europe, taking place October 9-11, 2025, in Athens, Greece.
AI Summary
Assembly Biosciences, Inc. announced that interim Phase 1b clinical data for its long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate ABI-5366 are being presented in a late-breaking oral session at the 38th Congress of the International Union Against Sexually Transmitted Infections (IUSTI)-Europe, held October 9–11, 2025, in Athens, Greece.
The presentation reports results from two cohorts of participants with recurrent genital herpes. In cohort one, subjects received a 150 mg loading dose followed by weekly 30 mg doses; cohort two received weekly 350 mg doses. ABI-5366 was well tolerated at both levels. In the 350 mg cohort, there were statistically significant reductions versus placebo: 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. Pharmacokinetics support weekly and potential monthly dosing.
Assembly Bio plans to share interim data on a monthly ABI-5366 regimen and weekly dosing of its second candidate, ABI-1179, later this fall, and expects to start Phase 2 studies of ABI-5366 in mid-2026.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- August 8, 2025
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc announced positive interim antiviral activity, clinical outcomes, safety and pharmacokinetic (PK) results from a Phase 1b study evaluating ABI-5366, an investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitor, in participants seropositive for HSV type 2 (HSV-2) with recurrent genital herpes.
AI Summary
Assembly Biosciences, Inc. reported positive interim results from a Phase 1b study of ABI-5366, an investigational long-acting helicase-primase inhibitor, in adults with recurrent genital herpes (HSV-2). The study evaluated weekly oral dosing over a 29-day period in participants seropositive for HSV-2.
In the cohort receiving a 350 mg weekly dose, ABI-5366 reduced HSV-2 shedding rate by 94% (p < 0.01), high viral load shedding by 98% (p < 0.05), and genital lesion rate by 94% (p < 0.01) versus placebo. This interim analysis included 50 participants, with 40 on ABI-5366 and 10 on placebo.
Safety and tolerability were favorable, with mostly mild to moderate adverse events similar to placebo. Pharmacokinetic data support once-weekly dosing and indicate the potential for a once-monthly oral regimen.
Based on these findings, Assembly Biosciences plans to move directly into Phase 2 study preparations, targeting initiation by mid-2026, while completing the ongoing monthly-dose cohort in the current Phase 1b trial.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- July 26, 2025
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc announced Phase 1a clinical and preclinical data for its herpes simplex virus (HSV) helicase-primase inhibitor candidates ABI-5366 and ABI-1179 are featured in multiple poster presentations, including one late-breaker, during the STI & HIV 2025 World Congress, taking place July 26-30, 2025, in Montreal, Canada, as well as in oral and poster presentations at the 49th Annual International Herpesvirus Workshop, taking place July 26-30, 2025, in Berlin, Germany.
AI Summary
Assembly Biosciences, Inc. announced that Phase 1a clinical and preclinical data for its long-acting herpes simplex virus helicase-primase inhibitors ABI-5366 and ABI-1179 will be showcased in multiple poster presentations at the STI & HIV 2025 World Congress (July 26–30, Montreal) and in oral and poster sessions at the 49th Annual International Herpesvirus Workshop (July 26–30, Berlin).
At the STI & HIV meeting, two posters detail safety and pharmacokinetic profiles of both candidates in healthy volunteers, supporting their advancement to Phase 1b. A late-breaker poster on ABI-1179 unveils its first clinical data, including no clinically significant food effect and unblinded safety results. Additional posters review preclinical studies of ABI-5366 and a retrospective analysis of U.S. genital herpes prevalence and treatment patterns.
At the Herpesvirus Workshop, one poster and one oral presentation describe preclinical profiles and interim safety/PK findings for both inhibitors. Assembly Bio expects interim proof-of-concept Phase 1b data in participants with recurrent genital herpes in fall 2025.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- April 9, 2025
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc. announced data from its herpes simplex virus (HSV) program featured in three poster presentations at the 2025 Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) taking place in Vienna, Austria, on April 11-15, 2025.
AI Summary
Assembly Biosciences, Inc. has presented promising data from its herpes simplex virus (HSV) program at the 2025 ESCMID Congress in Vienna, Austria, held from April 11-15, 2025. The company showcased three poster presentations detailing their novel long-acting helicase-primase inhibitor candidate, ABI-5366, designed for the treatment of recurrent genital herpes. Clinical and preclinical studies indicate that ABI-5366 is well tolerated at oral doses up to 350 mg, with a half-life of about 20 days, supporting a dosing schedule that could be once weekly or once monthly. One poster highlighted the safety and pharmacokinetics from a Phase 1a trial in healthy participants, while another detailed preclinical efficacy against both HSV-1 and HSV-2. A third poster provided insights into genital herpes prevalence and treatment patterns in the U.S., emphasizing the need for innovative therapies in this underserved area.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- March 20, 2025
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc provides recent highlights.
AI Summary
Assembly Biosciences recently shared updates on its antiviral pipeline, highlighting promising developments with four candidate therapies in clinical studies. Notably, the company expects to report interim Phase 1b proof-of-concept efficacy and safety data in fall 2025 for ABI-5366 and ABI-1179, two long-acting helicase-primase inhibitors aimed at treating recurrent genital herpes. Early Phase 1a data for ABI-1179 showed that it was well-tolerated, with measurements supporting the potential for once-weekly dosing. In addition to these candidates, Assembly Biosciences is advancing studies for treatments targeting hepatitis delta virus (HDV), hepatitis B virus (HBV), and transplant-associated herpesviruses. The company underscored the rapid progress achieved in 2024 and is optimistic that this momentum will continue through 2025, driven by a strong research and development effort and strategic collaboration with Gilead Sciences.
Read Announcement- Drug:
- ABI-5366
- Announced Date:
- September 23, 2024
- Indication:
- For recurrent genital herpes.
Announcement
Assembly Biosciences, Inc. announced positive interim pharmacokinetic (PK) and safety results from healthy participants in the Phase 1a portion of its ongoing Phase 1a/b study evaluating ABI-5366, an investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate for recurrent genital herpes.
AI Summary
Assembly Biosciences, Inc. announced positive interim results from the Phase 1a part of its study evaluating ABI-5366, a new long-acting HSV helicase-primase inhibitor aimed at treating recurrent genital herpes. In this early trial, healthy participants received single doses of ABI-5366, and the drug was well-tolerated with a favorable safety profile observed for up to 70 days. The data also showed that ABI-5366 has an oral half-life of approximately 20 days, supporting a dosing schedule of once-weekly or once-monthly. These promising results met the company's objectives for the Phase 1a study and have paved the way for the next phase.
Screening for Phase 1b has now begun in participants with recurrent genital herpes, where the drug will be tested at multiple doses under both weekly and monthly oral regimens. The company expects further interim results in the first half of 2025.
Read Announcement
ABI-1179 FDA Regulatory Timeline and Events
ABI-1179 is a drug developed by Assembly Biosciences for the following indication: For Recurrent Genital Herpes.
This drug is under review by the U.S. Food and Drug Administration (FDA).
Below is a timeline of key regulatory milestones for this therapy.
- Drug:
- ABI-1179
- Announced Date:
- December 8, 2025
- Indication:
- For Recurrent Genital Herpes
Announcement
Assembly Biosciences, Inc 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 (HSV-2) with recurrent genital herpes.
AI Summary
Assembly Biosciences reported positive interim Phase 1b results for two long-acting HSV helicase‑primase inhibitors in people seropositive for HSV‑2 with recurrent genital herpes. The announcement includes the first Phase 1b data for ABI‑1179 (weekly oral dosing) and new monthly dosing data for ABI‑5366, following earlier weekly results.
In the ABI‑1179 50 mg once‑weekly cohort, investigators saw a 98% reduction in HSV‑2 shedding versus placebo, a >99% reduction in high‑viral‑load swabs, and a 91% reduction in virologically confirmed genital lesions over 29 days. ABI‑1179 was well tolerated up to 50 mg weekly and its pharmacokinetics support once‑weekly dosing.
For ABI‑5366, a simulated monthly regimen produced a 76% drop in shedding, an 81% reduction in high‑viral‑load swabs, and an 88% reduction in virologically confirmed lesions. ABI‑5366 was also well tolerated, with PK supporting once‑weekly and potentially once‑monthly dosing. The company plans further development and Phase 2 activities.Read Announcement
- Drug:
- ABI-1179
- Announced Date:
- June 30, 2025
- Indication:
- For Recurrent Genital Herpes
Announcement
Assembly Biosciences, Inc. announced that the first participant has been dosed in the Phase 1b portion of the Phase 1a/b study of its long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate ABI-1179.
AI Summary
Assembly Biosciences, Inc. announced that the first participant has been dosed in the Phase 1b portion of its combined Phase 1a/b study for ABI-1179, a long-acting HSV helicase-primase inhibitor. The study will assess the candidate’s safety and antiviral activity through weekly oral doses over a 29-day period in individuals with recurrent genital herpes. Researchers will monitor both clinical outcomes, such as lesion frequency and duration, and viral parameters like HSV-2 shedding rate and DNA levels. Positive preliminary results from Phase 1a, including a pharmacokinetic profile that supports once-weekly dosing, have allowed the company to expand the trial. With the IND clearance, the study can now progress to additional sites in the United States. Data from these studies, alongside those for ABI-5366, are expected this fall 2025, promising new insights into managing recurrent genital herpes.
Read Announcement- Drug:
- ABI-1179
- Announced Date:
- February 20, 2025
- Indication:
- For Recurrent Genital Herpes
Announcement
Assembly Biosciences, Inc announced positive interim Phase 1a results in healthy participants from its ongoing Phase 1a/b study of ABI-1179, an investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitor candidate for recurrent genital herpes.
AI Summary
Assembly Biosciences announced promising interim Phase 1a results from its ongoing study of ABI-1179, a long-acting herpes simplex virus helicase-primase inhibitor designed for the treatment of recurrent genital herpes. In the study, ABI-1179 was well-tolerated in healthy participants and showed a half-life of around four days. The high drug exposure observed across all evaluated doses supports the potential for a once-weekly oral dosing regimen at a low dose. Moreover, even at the lowest dose of 50 mg, ABI-1179 exceeded the target plasma concentrations needed for antiviral activity as predicted by pharmacokinetic modeling. Based on these favorable results, the company will now move ABI-1179 directly into the Phase 1b portion of the study, which will include participants with recurrent genital herpes. The Phase 1b trial will run concurrently with studies of ABI-5366, with interim data anticipated in fall 2025.
Read Announcement
ABI-4334 FDA Regulatory Timeline and Events
ABI-4334 is a drug developed by Assembly Biosciences for the following indication: in Chronic Hepatitis B.
This drug is under review by the U.S. Food and Drug Administration (FDA).
Below is a timeline of key regulatory milestones for this therapy.
- Drug:
- ABI-4334
- Announced Date:
- November 7, 2025
- Indication:
- in Chronic Hepatitis B
Announcement
Assembly Biosciences, Inc. announced Phase 1b clinical data for its next-generation investigational capsid assembly modulator (CAM) ABI-4334 featured in a late-breaking poster presentation at the American Association for the Study of Liver Diseases (AASLD), The Liver Meeting®.
AI Summary
Assembly Biosciences, Inc. recently shared Phase 1b clinical results for its new capsid assembly modulator, ABI-4334, at the American Association for the Study of Liver Diseases (AASLD) meeting. The late-breaking poster highlighted that ABI-4334 was well tolerated in chronic hepatitis B patients who had not reached viral suppression on existing treatments.
The study tested two daily oral doses—150 mg and 400 mg—over 28 days. Both doses showed multi‐log reductions in hepatitis B virus (HBV) DNA and pregenomic RNA (pgRNA), confirming strong antiviral activity. Blood levels of ABI-4334 also exceeded those needed to block another key step in the virus life cycle.
No significant safety concerns emerged, and the drug’s high potency supports its potential use in multi‐drug regimens aimed at curing chronic hepatitis B. These findings mark the first complete Phase 1b data for ABI-4334.
Under an agreement with Gilead Sciences, Gilead may opt in to develop and commercialize ABI-4334 after reviewing the full data package following this study’s completion.
Read Announcement- Drug:
- ABI-4334
- Announced Date:
- June 25, 2025
- Indication:
- in Chronic Hepatitis B
Announcement
Assembly Biosciences, Inc announced positive topline efficacy, safety and pharmacokinetic (PK) results from a Phase 1b study evaluating ABI-4334, an investigational next-generation capsid assembly modulator (CAM), in participants with chronic hepatitis B virus (HBV) infection.
AI Summary
Assembly Biosciences, Inc. has announced positive topline results from a Phase 1b study of ABI‑4334, an investigational next‑generation capsid assembly modulator (CAM) for chronic hepatitis B virus infection. The study evaluated once‑daily oral doses, where both the 150 mg and 400 mg cohorts showed significant antiviral activity. The 150 mg dose achieved saturated inhibition of viral replication, resulting in a meaningful decline in HBV DNA levels, while the 400 mg dose reached exposure levels several times higher than the target, potentially maximizing the inhibition of cccDNA formation. Safety data revealed that ABI‑4334 was well‑tolerated, and the pharmacokinetic profile supports once‑daily dosing. These positive results provide a strong foundation for further development and will inform upcoming discussions with their partner, Gilead Sciences, regarding the future of ABI‑4334 in treating chronic HBV infection.
Read Announcement- Drug:
- ABI-4334
- Announced Date:
- June 18, 2024
- Indication:
- For the Treatment of Chronic Hepatitis B Virus Infection
Announcement
Assembly Biosciences, Inc. announced that the first participant has been dosed in the Phase 1b trial of ABI-4334, a next-generation capsid assembly modulator (CAM) candidate in development for the treatment of chronic hepatitis B virus (HBV) infection.
AI Summary
Assembly Biosciences, Inc. has begun dosing participants in its Phase 1b trial for ABI-4334, a next-generation capsid assembly modulator (CAM) designed to treat chronic hepatitis B virus (HBV) infection. This innovative treatment may work by both inhibiting HBV DNA replication and preventing the formation of new cccDNA, which helps the virus persist in the body. Previous Phase 1a studies in healthy volunteers indicated that once-daily oral dosing of ABI-4334 was safe and showed promising pharmacokinetic properties, with projected antiviral activity that significantly exceeds the required efficacy levels. The Phase 1b trial aims to evaluate the safety, pharmacokinetics, and antiviral effects of the drug in individuals with chronic HBV over a 28-day treatment period. The study will include dose escalation in multiple cohorts, which could help determine the optimal dosing strategy for future clinical trials.
Read Announcement
