Assembly Biosciences is advancing its herpes drug to Phase II trials after it showed 94% antiviral efficacy in a Phase Ib trial.
In the study (NCT06385327), ABI-5366, an investigational long-acting herpes simplex virus (HSV) helicase-primase inhibitor, reduced the rate of viral shedding by 94% compared to placebo in patients with recurrent genital herpes and positive for herpes simplex virus type 2 (HSV-2) – far higher than the 80%-85% goal set by Assembly Bio.
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High benefit was also seen in the secondary clinical endpoint of genital lesion rate, with a 94% reduction compared to placebo.
The rate of samples with high viral load, a potential surrogate for HSV-2 transmission and a secondary endpoint, was reduced by 98%.
The drug was also well tolerated, with a higher rate of adverse events (AEs) in the placebo (90.0%) group than in patients who received ABI-5366 (67.5%). Five patients discontinued treatment in the trial. However, just one was due to an adverse event (AE). The AE was not considered to be treatment-related. Three patients withdrew consent, and one withdrew due to the recurrence of genital herpes.
Assembly Bio’s chief medical officer Dr Anuj Gaggar said: “We 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.
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By GlobalData“These 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.”
The company is now planning its Phase II programme of the drug, which will likely launch in mid-2026.
While the PK profile supports the current once-weekly dosing, it also signals potential for once-monthly oral dosing regimens. As a result, the Phase Ib study will also evaluate once-monthly dosing, as well as once-weekly.
ABI-5366 is being investigated through a collaboration agreement between Assembly Bio and Gilead Sciences. The agreement grants Gilead the right to opt in to an exclusive licence for further development and commercialisation of ABI-5366 and another asset, ABI-1179, following completion of the Phase Ib studies. Phase Ib data for ABI-1179 is expected in Q3 2025.
Assembly Bio also announced last week that Gilead has purchased just under 2.3 million shares of the company.
Last year, GSK discontinued development of its HSV vaccine candidate GSK3943104 after a Phase I/II clinical trial failed to meet its primary efficacy goals. This opens the doors for both Moderna and BioNTech, who are each developing mRNA vaccines for HSV.
According to GlobalData, there are an estimated 52 million cases of HSV-2 in 2024 and an additional 13 million cases of combined HSV-1 and HSV-2 infections across 16 major markets (16MM: Australia, Brazil, Canada, China, France, Germany, India, Italy, Japan, Mexico, Russia, South Africa, South Korea, Spain, UK, and US).
Cases are set to rise, with HSV-2 and combined HSV-1 and 2 cases in the 16MM projected to reach 54 million and 14 million cases, respectively, by 2029.
GlobalData is the parent company of Clinical Trials Arena.
