Assembly Bio exercises U.S. profit-share option with Gilead for herpes program

Assembly Biosciences, Inc. (Nasdaq: ASMB) announced it has exercised its option to share 40% of U.S. development costs and profits for its herpes simplex virus (HSV) helicase-primase inhibitor (HPI) program under its collaboration agreement with Gilead Sciences, Inc.

The program targets recurrent genital herpes and includes two investigational compounds, GS-1179 and GS-5366. Gilead retains sole responsibility for clinical development and commercialization of the program.

Under the collaboration terms, Assembly Bio is eligible to receive up to $280 million in regulatory and commercial milestones, plus tiered royalties on net sales outside the U.S. ranging from the high single digits to low teens. If either party exercises opt-out or conversion rights from the U.S. profit-share arrangement, Assembly Bio could instead receive up to $330 million in milestones and similar tiered royalties on net sales.

GS-1179 is expected to advance into a Phase 2 clinical trial in recurrent genital herpes patients by the end of 2026, with potential evaluation in combination with HIV pre-exposure prophylaxis.

Assembly Bio said its cash runway remains projected into 2029, which includes a $75 million collaboration extension fee from Gilead payable in the fourth quarter of 2026, following the third anniversary of the collaboration agreement.

"Exercising this option underscores our confidence in the HSV HPI program and the meaningful opportunity it represents for Assembly Bio," said Jason Okazaki, chief executive officer and president of Assembly Bio.

The decision to exercise the option followed Assembly Bio's receipt and review of Gilead's complete development plan and budget for the program, according to a company press release.

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