Biogen Secures Ex-U.S. Rights to Stoke's Promising Dravet Syndrome Treatment

In a significant move to bolster its late-stage pipeline, Biogen has entered into a licensing agreement with Stoke Therapeutics for the ex-U.S. rights to zorevunersen, a phase 3-ready molecule with the potential to become the first disease-modifying treatment for Dravet syndrome. The deal, announced on February 18, 2025, involves an upfront payment of $165 million from Biogen to Stoke, with the possibility of up to $385 million in additional milestone payments.

Deal Structure and Development Plans

Under the terms of the agreement, Biogen will gain exclusive rights to commercialize zorevunersen outside of the United States, Canada, and Mexico. The pharmaceutical giant will cover 30% of external clinical development costs and pay tiered royalties ranging from low double digits to high teens on net sales in its territories.

Stoke Therapeutics will retain leadership of the global development program, with plans to initiate a phase 3 study in the second quarter of this year. The company anticipates reporting pivotal data in the second half of 2027, potentially paving the way for global regulatory filings.

Zorevunersen's Potential and Competitive Landscape

Zorevunersen has shown promise in early clinical trials, demonstrating sustained reductions in the frequency of convulsive seizures over two years of treatment. Moreover, improvements in cognition and behavior have been observed within nine months, supporting the molecule's potential for disease modification.

This potential sets zorevunersen apart from existing treatments for Dravet syndrome, such as Jazz Pharmaceuticals' Epidiolex and UCB's Fintepla, which primarily address symptoms rather than the underlying genetic cause. Zorevunersen targets SCN1A, a gene mutated in over 85% of people with Dravet syndrome, using an antisense oligonucleotide to regulate RNA.

The only other potential disease-modifying treatment in clinical development for Dravet syndrome is ETX101, a gene therapy being developed by Encoded Therapeutics. While both zorevunersen and ETX101 target SCN1A, they employ different approaches, with ETX101 delivering a regulatory gene to boost SCN1A expression.

Strategic Implications for Biogen and Stoke

For Biogen, this deal represents a significant addition to its R&D pipeline and builds upon the company's experience with RNA-targeted therapies, developed through its collaboration with Ionis Pharmaceuticals. The acquisition of zorevunersen aligns with Biogen's previously identified interest in Dravet syndrome as a potential target for antisense technology.

From Stoke Therapeutics' perspective, the agreement provides crucial funding for the advancement of zorevunersen into phase 3 trials. Tommy Leggett, Stoke's chief financial officer, had previously indicated at the J.P. Morgan Healthcare Conference that the company was exploring potential ex-U.S. business development relationships to support the molecule's progression.

As both companies move forward with this collaboration, the pharmaceutical industry will be watching closely to see if zorevunersen can fulfill its promise as a groundbreaking treatment for Dravet syndrome, potentially offering hope to patients and families affected by this rare and severe form of epilepsy.