In a strategic move to expand its rare disease portfolio, Biogen has secured ex-U.S. rights to zorevunersen, a promising experimental treatment for Dravet syndrome, through a deal with Stoke Therapeutics valued at $165 million upfront.
The agreement, announced on February 18, 2025, grants Biogen exclusive commercialization rights outside the United States, Canada, and Mexico. The partnership includes potential additional payments of up to $385 million tied to development and commercial milestones, along with a cost-sharing arrangement where Biogen will cover 70% of external development expenses.
Zorevunersen, currently preparing to enter Phase 3 clinical trials this year, represents a novel approach to treating Dravet syndrome, with results anticipated in 2027. The drug, classified as an antisense oligonucleotide, works by targeting specific RNA sequences to enhance the expression of sodium channel proteins associated with the rare epileptic condition.
The acquisition aligns with Biogen’s efforts to counteract declining revenues from its established products, including Spinraza and its multiple sclerosis treatments. Under CEO Christopher Viehbacher’s leadership since late 2022, the company has actively pursued strategic acquisitions, including the $7.3 billion purchase of Reata
Pharmaceuticals and a $1.2 billion deal for HI-Bio.
Stifel analyst Paul Matteis views the transaction favorably, noting the natural fit with Biogen’s existing rare neurological disease franchise, which includes Spinraza and Skyclarys. The relatively modest upfront payment could prove advantageous if zorevunersen achieves commercial success, though challenges remain.
Physician feedback indicates high efficacy expectations for the drug, with a TD Cowen survey of 25 epilepsy specialists revealing that 60% consider zorevunersen more promising than current Dravet syndrome treatments. However, potential hurdles include its intravenous administration in a market dominated by oral medications and pricing considerations in non-U.S. markets.
Recent clinical data has bolstered confidence in zorevunersen’s potential. Last spring, Stoke reported significant improvements in convulsive seizure frequency reduction compared to placebo in a small trial using high doses of the drug. The company has subsequently reached agreements with regulatory authorities in the United States, Europe, and Japan regarding the design of its upcoming Phase 3 study.
The targeted patient population for zorevunersen is substantial, with Biogen estimating up to 38,000 people affected by Dravet syndrome across the U.S., U.K., Japan, and several European nations. The condition represents a significant unmet medical need in the rare disease space.
The agreement also includes provisions for Biogen to potentially license rights to related products that employ similar mechanisms of action as zorevunersen. While the deal’s immediate impact on Biogen’s market position may be limited, analysts view it as a strategic addition to the company’s rare disease portfolio.
Despite the announcement, Biogen’s stock remained largely stable during Tuesday morning trading, suggesting investors are taking a measured approach to the long-term potential of this development program. The transaction reflects the ongoing industry trend of larger pharmaceutical companies leveraging partnerships and acquisitions to access innovative therapies, particularly in the rare disease space where unmet medical needs persist.
The success of this collaboration will ultimately depend on
zorevunersen’s performance in late-stage clinical trials and its ability to demonstrate meaningful benefits for patients with Dravet syndrome, a challenging condition that has historically been difficult to treat effectively with existing therapies.