A mid-stage study for ABI-5366 will begin mid next year, while Assembly continues to assess the Phase II potential of ABI-1179.
Two of Assembly Biosciences’ investigational long-acting therapies showed strong antiviral activity in Phase I studies in recurrent genital herpes, opening the company’s path to mid-stage development.
Analysts at Guggenheim Partners, in a Monday note to investors, called the California biotech’s data “striking,” adding that the readout “strongly reinforces the greater efficacy potential of [Assembly’s] more potent, next-gen oral helicase-primase inhibitors.”
On Monday, Assembly released interim results from two Phase I studies of its oral herpes drug candidates, the weekly ABI-1179 and the monthly ABI-5366. Both trials were randomized and placebo-controlled, and enrolled patients positive for herpes simplex virus 2 (HSV-2) infection with recurrent genital herpes.
In its study, a 50-mg dose of ABI-1179 lowered viral shedding by 98% versus placebo over a 29-day observation period, which exceeds Assembly’s previous target of 80% to 85% shedding reduction, according to the company’s announcement. ABI-1179 also lowered genital lesion rates by 91% compared to placebo.
Meanwhile, the trial for ABI-5366 showed that drug cut viral shedding by 76% over 29 days, accompanied by an 88% decrease in confirmed genital lesions. The number of samples with high viral load, a potential surrogate indicator for HSV-2 transmission, was 81% lower in those on Assembly’s drug compared to placebo.
In a follow-up note on Monday evening, sent after a call with Assembly management, Guggenheim analysts reiterated that in ABI-1179 and ABI-5366, the biotech “has two strong candidates with both differentiated efficacy and more favorable dosing vs. standard of care.” The former, in particular, could unlock a “potential blockbuster novel weekly treatment opportunity” for the company.
Moving forward, Assembly plans to push both assets into mid-stage development. ABI-5366 is expected to start Phase II trials by mid-2026, according to a Mizuho Securities note on Monday, while the company continues to assess the Phase II potential of ABI-1179.
ABI-5366 and ABII-1179 work by targeting a key viral enzyme complex involved in HSV-2 replication. Disrupting this crucial viral function, Assembly claims on its website, can lead to “superior efficacy” than the current nucleoside analogs used for herpes treatment.
ABI-1179 came to Assembly from Gilead under an October 2023 partnership, according to the biotech’s Monday release. The pharma at the time fronted $100 million to collaborate with the biotech on its infectious disease assets, giving Gilead the ability to gain exclusive rights over Assembly’s pipeline programs.
