Biogen and Stoke Therapeutics Enter Dravet Syndrome Collaboration

Rare Daily Staff

Biogen has entered into a collaboration with Stoke Therapeutics to develop and commercialize Stoke’s experimental therapy, zorevunersen, a potential first-in-class disease-modifying medicine that is being developed for the treatment of the rare genetic epilepsy Dravet syndrome.

The agreement, which includes a $165 million upfront payment to Stoke, would give Biogen rights to zorevunersen in all territories outside the United States, Canada, and Mexico.

Dravet syndrome is a severe developmental and epileptic encephalopathy characterized by severe, recurrent seizures as well as significant cognitive and behavioral impairments. Most cases of Dravet are caused by mutations in one copy of the SCN1A gene, leading to insufficient levels of NaV1.1 protein in neuronal cells in the brain. More than 90 percent of patients continue to experience seizures despite treatment with the best available anti-seizure medicines.

Complications of the disease often contribute to a poor quality of life for patients and their caregivers. Developmental and cognitive impairments often include intellectual disability, developmental delays, movement and balance issues, language and speech disturbances, growth defects, sleep abnormalities, disruptions of the autonomic nervous system and mood disorders.

Zorevunersen is an experimental antisense oligonucleotide that targets the SCN1A gene, the underlying cause of most cases of Dravet syndrome. Stoke recently announced plans to initiate a global phase 3 registrational study of zorevunersen. The study is expected to begin in the second quarter of 2025, with a pivotal data readout expected in the second half of 2027, which is anticipated to support global regulatory filings.

The U.S. Food and Drug Administration awarded zorevunersen Breakthrough Therapy designation based on preliminary clinical evidence indicating that the drug may substantially improve over available therapy on clinically-significant endpoints. Data from Phase 1/2a and open-label extension studies of zorevunersen showed that patients treated with zorevunersen experienced substantial and durable reductions in convulsive seizure frequency and improvements in multiple measures of cognition and behavior. Zorevunersen has been generally well tolerated across the studies.

Under the terms of the deal, Stoke will continue to lead global development and retains exclusive development and commercialization rights for zorevunersen in the United States, Canada, and Mexico. The parties will share external clinical development costs for zorevunersen (30 percent Biogen; 70 percent Stoke). In addition to the upfront payment, Stoke may receive up to $385 million in development and commercial milestone payments. Stoke will also be eligible to receive tiered royalties ranging from low double digits to high teens on potential net sales in the Biogen territory.

Stoke has also granted Biogen an option to license rights outside of the United States, Canada, and Mexico to certain future follow-on ASO products targeting SCN1A, in exchange for separate milestone, cost sharing, and royalty considerations.

“With Biogen’s deep experience in neurology and track record of success in commercializing high-value disease-modifying medicines for rare genetic diseases globally, we aim to lead the treatment of Dravet syndrome into a new era by delivering zorevunersen to all patients who could benefit,” said Edward Kaye, CEO of Stoke Therapeutics. “Additionally, this collaboration provides cash flows, that when combined with Stoke’s financial position, support the company through to mid-2028.”