Biogen has refueled its R&D engine, paying Stoke Therapeutics $165 million upfront for ex-U.S. rights to a phase 3-ready molecule that could become the first disease-modifying treatment for Dravet syndrome.
The deal, which features up to $385 million in milestones, gives Biogen exclusive rights to commercialize Stoke’s zorevunersen outside of the U.S., Canada and Mexico. Biogen 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 will continue to lead global development and plans to start a phase 3 study in the second quarter. If everything goes to plan, the biotech will report pivotal data in the second half of 2027 and clear a path to global regulatory filings.
Zorevunersen is advancing into phase 3 on the strength of evidence that the molecule triggers sustained reductions in the frequency of convulsive seizures. As well as showing reductions in seizures across two years of treatment, Stoke has tracked improvements in cognition and behavior within nine months that support the potential for disease modification.
The potential for disease modification sets zorevunersen apart from the competition. Existing treatments for Dravet include Jazz Pharmaceuticals’ Epidiolex and UCB’s Fintepla, but none of the approved products address the underlying genetic cause of the syndrome. Similarly, most current investigational candidates only target the symptoms.
One exception is ETX101, a gene therapy in clinical development at Encoded Therapeutics. ETX101 and zorevunersen represent different approaches to the same target, SCN1A. More than 85% of people with Dravet syndrome have an SCN1A mutation. Stoke is aiming to help those patients by using an antisense oligonucleotide to target RNA regulation. ETX101 delivers a regulatory gene to boost SCN1A expression.
Biogen gained familiarity with RNA-targeted therapies through its work with Ionis Pharmaceuticals. The Big Biotech identified Dravet as a potential target for Ionis’ antisense technology back in 2018, but, in the end, its expansion into the indication came through Stoke.
For Stoke, the deal answers the question of how it will fund the move into phase 3. Tommy Leggett, Stoke’s chief financial officer, discussed the options at the J.P. Morgan Healthcare Conference last month. “There's a significant amount of strategic interest around our asset, and so we're going to continue to explore potential relationships where we look at ex-U.S. potential [business development],” Leggett said.