Assembly Biosciences Reports Positive Interim Results from Phase 1b Clinical Study of Long-Acting Helicase-Primase Inhibitor Candidate ABI-5366 Showing Reductions in Viral Shedding Rate and Genital Lesion Rate in Recurrent Genital Herpes
Assembly Biosciences (NASDAQ:ASMB) reported positive interim results from its Phase 1b study of ABI-5366, a long-acting helicase-primase inhibitor for recurrent genital herpes. The 350mg weekly oral dose demonstrated remarkable efficacy with a 94% reduction in HSV-2 shedding rate and genital lesion rate compared to placebo over a 29-day period.
Key highlights include a 98% reduction in high viral load shedding rate and favorable safety profile. The pharmacokinetic profile supports potential for both weekly and monthly dosing regimens. Assembly Bio plans to advance directly to Phase 2 clinical studies, expected to initiate in mid-2026.
Under their collaboration agreement, Gilead Sciences maintains the right to opt in for exclusive licensing following completion of Phase 1b studies.
Assembly Biosciences (NASDAQ:ASMB) ha riportato risultati positivi intermedi dal suo studio di Fase 1b su ABI-5366, un inibitore a lunga durata della elicasi-primasi per l'herpes genitale ricorrente. La dose orale settimanale di 350 mg ha mostrato un'efficacia notevole con una riduzione del 94% del tasso di eliminazione di HSV-2 e delle lesioni genitali rispetto al placebo in un periodo di 29 giorni.
I punti salienti includono una riduzione del 98% nel tasso di eliminazione a carica virale elevata e un profilo di sicurezza favorevole. Il profilo farmacocinetico supporta la possibilit脿 di regimi posologici sia settimanali che mensili. Assembly Bio prevede di passare direttamente alla Fase 2 degli studi clinici, il cui avvio 猫 previsto per met脿 2026.
Secondo l'accordo di collaborazione, Gilead Sciences mantiene il diritto di optare per una licenza esclusiva al completamento degli studi di Fase 1b.
Assembly Biosciences (NASDAQ:ASMB) inform贸 resultados interinos positivos de su estudio de Fase 1b con ABI-5366, un inhibidor de helicasa-primasa de acci贸n prolongada para el herpes genital recurrente. La dosis oral semanal de 350 mg demostr贸 una eficacia notable con una reducci贸n del 94% en la tasa de eliminaci贸n del HSV-2 y en la tasa de lesiones genitales en comparaci贸n con el placebo durante un per铆odo de 29 d铆as.
Los aspectos clave incluyen una reducci贸n del 98% en la tasa de eliminaci贸n con alta carga viral y un perfil de seguridad favorable. El perfil farmacocin茅tico respalda la posibilidad de reg铆menes de dosificaci贸n tanto semanales como mensuales. Assembly Bio planea avanzar directamente a los estudios cl铆nicos de Fase 2, que se espera inicien a mediados de 2026.
Seg煤n su acuerdo de colaboraci贸n, Gilead Sciences mantiene el derecho de optar por una licencia exclusiva tras la finalizaci贸n de los estudios de Fase 1b.
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Assembly Biosciences (NASDAQ:ASMB) a annonc茅 des r茅sultats interm茅diaires positifs de son 茅tude de Phase 1b sur ABI-5366, un inhibiteur h茅licase-primase 脿 action prolong茅e pour l'herp猫s g茅nital r茅current. La dose orale hebdomadaire de 350 mg a d茅montr茅 une efficacit茅 remarquable avec une r茅duction de 94 % du taux de diss茅mination du HSV-2 et du taux de l茅sions g茅nitales par rapport au placebo sur une p茅riode de 29 jours.
Les points cl茅s incluent une r茅duction de 98 % du taux de diss茅mination 脿 forte charge virale et un profil de s茅curit茅 favorable. Le profil pharmacocin茅tique soutient la possibilit茅 de sch茅mas posologiques hebdomadaires et mensuels. Assembly Bio pr茅voit de passer directement aux 茅tudes cliniques de Phase 2, dont le lancement est attendu pour mi-2026.
Dans le cadre de leur accord de collaboration, Gilead Sciences conserve le droit d'opter pour une licence exclusive apr猫s la fin des 茅tudes de Phase 1b.
Assembly Biosciences (NASDAQ:ASMB) berichtete positive Zwischenergebnisse aus seiner Phase-1b-Studie zu ABI-5366, einem langwirksamen Helikase-Primase-Inhibitor f眉r rezidivierenden Genitalherpes. Die w枚chentliche orale Dosis von 350 mg zeigte eine bemerkenswerte Wirksamkeit mit einer 94%igen Reduktion der HSV-2-Ausscheidungsrate und der genitalen L盲sionsrate im Vergleich zu Placebo 眉ber einen Zeitraum von 29 Tagen.
Wichtige Highlights umfassen eine 98%ige Reduktion der Ausscheidungsrate bei hoher Viruslast und ein g眉nstiges Sicherheitsprofil. Das pharmakokinetische Profil unterst眉tzt sowohl w枚chentliche als auch monatliche Dosierungsregime. Assembly Bio plant, direkt in Phase-2-Studien 眉berzugehen, die Mitte 2026 beginnen sollen.
Im Rahmen ihrer Kooperationsvereinbarung beh盲lt sich Gilead Sciences das Recht vor, nach Abschluss der Phase-1b-Studien eine exklusive Lizenzierung zu w盲hlen.
- 94% reduction in HSV-2 shedding rate, exceeding target of 80-85%
- 94% reduction in genital lesion rate with 350mg weekly dose
- 98% reduction in high viral load shedding rate, potentially reducing transmission risk
- Favorable safety and tolerability profile observed
- Pharmacokinetic profile supports potential for once-monthly oral dosing
- Five participants discontinued treatment during the study
- Higher proportion of treatment-emergent adverse events in treatment group (90%) vs placebo
- One grade 3 adverse event reported leading to study discontinuation
Insights
Assembly Bio's ABI-5366 shows remarkable 94% reduction in HSV-2 viral shedding and lesions, exceeding efficacy targets with favorable safety profile.
Assembly Biosciences' interim Phase 1b results for ABI-5366 represent a potentially significant breakthrough in genital herpes treatment. The data demonstrate remarkable antiviral activity with a
What makes these results particularly compelling is the combination of strong efficacy with a favorable safety and tolerability profile. The pharmacokinetic data continues to support a convenient weekly dosing regimen and even suggests potential for monthly oral dosing, which would represent a substantial improvement over current daily suppressive therapies for recurrent genital herpes.
The robust clinical profile observed in this small sample (20 participants receiving ABI-5366 at the effective dose versus 5 placebo recipients) has accelerated development plans, with management indicating they'll move directly to Phase 2 preparations while completing the remaining cohort evaluating monthly dosing. The company expects to initiate Phase 2 studies by mid-2026.
Importantly, these results also strengthen Assembly Bio's position with collaboration partner Gilead Sciences, which holds opt-in rights following completion of Phase 1b studies. A parallel Phase 1b study of another candidate, ABI-1179 (contributed by Gilead), is ongoing with data expected this fall alongside results from the monthly dosing cohort for ABI-5366.
For context, recurrent genital herpes represents a significant unmet medical need affecting millions worldwide. A long-acting oral therapy with this efficacy profile could substantially improve disease management and quality of life for affected individuals while potentially reducing transmission risk.
The interim Phase 1b results for ABI-5366 represent potentially transformative antiviral efficacy in the treatment of recurrent genital herpes. Most striking is the
The mechanism of action as a helicase-primase inhibitor targets a critical component of viral replication. Helicase-primase enzymes are essential for unwinding viral DNA during replication, and inhibiting this process effectively blocks viral multiplication. Previous helicase-primase inhibitors have shown promise but faced development challenges, making these robust results particularly noteworthy.
The observed
The shortened duration of both viral shedding (1.8 days vs 5.8 days for placebo) and genital lesions (1.8 days vs 6.3 days) further demonstrates ABI-5366's potent activity against HSV-2. Most significantly, no viral shedding above the transmission-relevant threshold occurred without lesions in the
The pharmacokinetic profile supporting weekly or monthly dosing represents a substantial improvement over nucleoside analogs like acyclovir, which require multiple daily doses for suppressive therapy due to short half-lives. This extended activity profile, combined with the significant reductions in viral parameters, positions ABI-5366 as potentially the most effective HSV therapy evaluated in clinical trials to date.
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鈥� Favorable safety and tolerability profile observed in the first two cohorts evaluating weekly oral doses of ABI-5366 鈥�
SOUTH SAN FRANCISCO, Calif., Aug. 08, 2025 (GLOBE NEWSWIRE) -- Assembly Biosciences, Inc. (Nasdaq: ASMB), a biotechnology company developing innovative therapeutics targeting serious viral diseases, today 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.
For the powered antiviral endpoint, HSV-2 shedding rate, highly potent antiviral activity was observed with a
ABI-5366 was observed to be well-tolerated at oral doses up to 350 mg weekly in participants seropositive for HSV-2 with recurrent genital herpes. The observed PK profile continues to support once-weekly dosing and the potential for once-monthly oral dosing regimens. With these data, Assembly Bio expects to move directly into Phase 2 clinical study preparation in parallel with completion of this Phase 1b study, which includes an ongoing cohort evaluating a monthly oral dosing regimen. The in-life portions of chronic toxicology studies of ABI-5366 are now complete and these studies are expected to support longer-term dosing in Phase 2.
鈥淲e are thrilled to see these interim data for ABI-5366 far exceeding the targets we had set in this study for antiviral activity and clinical outcomes in participants with recurrent genital herpes,鈥� said Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio. 鈥淭hese results underscore our conviction in the potential for ABI-5366 to reduce outbreaks and improve quality of life for those affected by the severe impacts of recurrent genital herpes. We will now work quickly to move ABI-5366 into longer-duration Phase 2 clinical studies, which we expect to initiate in mid-2026, and look forward to its continued progress.鈥�
A Phase 1b study of ABI-1179, another long-acting HSV helicase-primase inhibitor candidate, is being conducted concurrently. Assembly Bio expects to share interim data from this study of ABI-1179 and the ongoing cohort of the ABI-5366 Phase 1b study evaluating a monthly dosing regimen in the fall of this year.
Under the collaboration agreement between Assembly Bio and Gilead Sciences, Inc. (Gilead), Gilead has the right to opt in to an exclusive license for further development and commercialization of the helicase-primase inhibitor program after reviewing the option data package to be delivered by Assembly Bio following completion of the Phase 1b studies.
ABI-1179 was contributed by Gilead under the collaboration between Assembly Bio and Gilead. ABI-5366 and ABI-1179 are investigational product candidates that have not been approved anywhere globally, and their safety and efficacy have not been established.
Study ABI-5366-101 鈥� Interim Phase 1b Results
Interim Results
The Phase 1b interim analysis reported here includes data from cohort B1, evaluating a loading dose of 150听mg and weekly doses of 30 mg (the 150/30 mg cohort), and cohort B2, evaluating a loading dose and weekly doses of 350 mg (the 350 mg cohort), through the data cutoff date of July 29, 2025.
A total of 50 participants have been enrolled in the 150/30 mg and 350 mg cohorts; 40 assigned to ABI-5366 (20 participants in each cohort) and 10 assigned to placebo (five in each cohort). 45 participants from these cohorts have completed the 29-day evaluation period while five discontinued treatment; one due to an adverse event (described below), three withdrew consent and one withdrew for recurrence of genital herpes.
Antiviral activity and clinical outcomes by treatment arm are summarized below.
| Antiviral Activity and Clinical Outcomes | PBO | 150/30 mg QW | 350 mg QW |
| HSV-2 Shedding Ratea | |||
| High Viral Load Shedding Rateb | |||
| Genital Lesion Ratec | |||
| Mean (SD) Duration of Viral Shedding; days | 5.8 (4.1) | 3.6 (2.7) | 1.8 (0.8) |
| Mean (SD) Duration of Genital Lesions; days | 6.3 (4.3) | 5.7 (4.3) | 1.8 (1.0) |
| PBO=placebo; QW=once weekly; SD=standard deviation; High viral load = >104 HSV DNA copies/mL. All outcomes measured over evaluation period. a HSV-2 shedding rate calculated as the number of positive HSV-2 anogenital swabs divided by the total number of swabs collected. b High viral load shedding rate calculated as the number of positive HSV-2 anogenital swabs with HSV-2 >104 copies/mL divided by the total number of swabs collected. c Genital lesion rate calculated as the number of days with genital lesions present divided by the total number of days assessed. | |||
| 听 | |||
Statistically significant reductions were observed in the viral shedding rate, high viral load shedding rate and genital lesion rate for the 350 mg cohort compared to placebo as summarized below.听
| % Rate Reductions ABI-5366 350 mg QW vs PBO QW | Rate Reduction | p-valuea听听 |
| % Reduction in HSV-2 Shedding Rate | p<0.01 | |
| % Reduction in High Viral Load Shedding Rate | p<0.05 | |
| % Reduction in Genital Lesion Rate | p<0.01 | |
| PBO=placebo; QW=once weekly; High viral load = >104 HSV DNA copies/mL a Statistical analysis conducted using Poisson regression models and the corresponding p-values estimated accordingly. | ||
| 听 | ||
No viral shedding of >104 HSV DNA copies/mL, a potential surrogate for HSV-2 transmission, was observed in the absence of lesions for the 350 mg cohort.
Across the 150/30 mg and 350 mg cohorts, ABI-5366 demonstrated a PK profile that continues to be supportive of once-weekly and potentially once-monthly dosing. ABI-5366 was observed to be well-tolerated at oral doses up to 350 mg weekly in the study population of participants seropositive for HSV-2 with recurrent genital herpes.
As the study is ongoing, individual treatment assignments remain blinded. Overall, the proportion of participants reporting treatment-emergent adverse events (TEAEs) was similar between ABI-5366 (
The proportion of participants reporting treatment-emergent laboratory abnormalities was higher in placebo (
Study Overview
ABI-5366-101 is a randomized, blinded, placebo-controlled Phase 1a/b clinical study of ABI-5366. Positive interim data has been previously reported for Part A (Phase 1a), evaluating the safety, tolerability and PK of ABI-5366 following single dose administration in healthy participants. Part B (Phase 1b), in participants seropositive for HSV-2 with recurrent genital herpes, is evaluating weekly and monthly oral dose regimens over a 29-day dosing period in up to four cohorts randomized 20:5 between ABI-5366 and placebo with a pooled placebo analysis. Dosing is ongoing for cohort B3, evaluating a monthly dosing regimen of ABI-5366.
In addition to assessing safety, tolerability and PK, Part B also evaluates antiviral activity by measuring changes in viral parameters including shedding rate, quantification of HSV-2 DNA levels obtained from anogenital swab samples, and clinical parameters including genital lesion rate and duration. Due to the long half-life of ABI-5366, the safety follow-up period for participants extends for 98 days after dosing, with safety data available as of the data cutoff date through at least Day 56 for all participants from these cohorts that completed the evaluation period. The trial results will support dose selection for future clinical studies.
The ABI-5366 Phase 1b study uses pooled data from placebo recipients across cohorts as a control. As additional placebo recipients are enrolled in later cohorts, the sample size for the pooled placebos will change, which is expected to result in adjustments to both the observed effect sizes compared to placebo and the tests of statistical significance for those observed effects.
Additional information about the Phase 1a/b trial is available at using the identifier NCT06385327. Assembly Bio expects to submit data from the trial for presentation at future scientific meetings.
About Recurrent Genital Herpes
Genital herpes is a chronic viral infection caused by HSV that can result in painful genital lesions, serious psychological and social impacts, and an increased risk of acquiring human immunodeficiency virus (HIV). Epidemiologic studies estimate over four million people in the United States and France, Germany, Italy, Spain and the United Kingdom experience recurrent genital herpes, with most people with initial symptomatic genital HSV-2 infection having three or more recurrences per year. While genital herpes can be caused by either HSV type 1 (HSV-1) or HSV-2, recurrences are more likely to be experienced by individuals infected by HSV-2. The current standard of care for recurrent genital herpes is nucleoside analogs given intermittently for recurrences or as daily chronic suppressive therapy; however, these are only partially effective in preventing recurrences and in reducing transmission of the virus. No new drugs have been approved in the United States or Europe to treat genital herpes for more than 25 years.
About Helicase-Primase Inhibition
HSV helicase-primase inhibitors target the viral helicase-primase complex, an essential viral enzyme complex that is conserved across both HSV-1 and HSV-2 and has no host equivalent. Inhibition of the helicase-primase complex is a clinically validated mechanism that has shown the potential for superior efficacy to the current standard of care, nucleoside analogs, in short-duration clinical studies in participants with recurrent genital herpes.
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 assemblybio.com.
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鈥檚 ability to maintain financial resources and secure additional funding necessary to continue its research activities, clinical studies, other business operations and continue as a going concern; Assembly Bio鈥檚 ability to realize the potential benefits of its collaboration with Gilead, including all financial aspects of the collaboration and equity investments; Assembly Bio鈥檚 ability to initiate and complete clinical studies involving its therapeutic product candidates, including studies contemplated by Assembly Bio鈥檚 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鈥檚 product candidates; clinical and nonclinical data may not differentiate Assembly Bio鈥檚 product candidates from other companies鈥� candidates; potential effects of changes in government regulation, including as a result of the change in U.S. administration in 2025; 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鈥檚 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鈥檚 risks and uncertainties are more fully detailed under the heading 鈥淩isk Factors鈥� in Assembly Bio鈥檚 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.
Contacts
Investor and Corporate:
Shannon Ryan
SVP, Investor Relations, Corporate Affairs and Alliance Management
(415) 738-2992
Media:
Sam Brown Healthcare Communications
Alyssa Kuciunas
(331) 481-3751
FAQ
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