Biogen bags rights to epilepsy drug from Stoke in $550m deal

Biogen has bolstered its pipeline by licensing ex-US rights to a drug for Dravet syndrome – a rare form of epilepsy – from Stoke Therapeutics in a deal that included an upfront payment of $165 million.

The company now has rights to the potential first-in-class drug – called zorevunersen – outside the US, Canada, and Mexico, where Bedford, Massachusetts-based Stoke has retained exclusive ownership. It has also agreed to split external clinical development costs, with Biogen picking up 30% of the tab for those expenses.

Zorevunersen is an investigational antisense oligonucleotide (ASO) that targets the SCN1A gene, which Biogen says is the underlying cause of most cases of Dravet syndrome, and is on the brink of starting a phase 3 registration trial (EMPEROR) that could support filings in the US, Europe, and Japan.

Dravet syndrome is a severe form of developmental and epileptic encephalopathy that begins in infancy and causes prolonged seizures that do not respond well to current anticonvulsant drugs, as well as behavioural and developmental delays. Patients with the disorder face a 15% to 20% mortality rate due to sudden unexpected death in epilepsy (SUDEP) and need constant supportive care.

It is estimated that up to 38,000 people are living with Dravet syndrome in the US, UK, the four largest EU markets, and Japan.

Along with the $165 million upfront fee, Biogen has committed up to $385 million in development and commercial milestone payments for the zorevunersen programme under the terms of the deal, which also gives it rights to certain follow-up candidates with a similar mechanism of action.

The EMPEROR trial is expected to start in the second quarter of this year with results due in the latter half of 2027, shoring up a near-term pipeline for Biogen as it faces increased competition for its biggest-selling products like Spinraza (nusinersen) for spinal muscular atrophy (SMA) and its multiple sclerosis (MS) range, as well as slow growth for new Alzheimer's disease therapy Leqembi (lecanemab), partnered with Eisai.

"This collaboration broadens our late-stage pipeline with the addition of a phase 3-ready disease modifying investigational medicine and allows us to leverage our rare disease product commercialisation expertise and global footprint," commented Biogen's head of development Priya Singhal.

The company has been actively expanding its portfolio through a string of acquisitions, notably a $7.3 billion takeover of rare disease drug developer Reata in 2023 that added Friedreich's ataxia (FA) therapy Skyclarys (omaveloxolone) and $1.15 billion purchase of immunology specialist Hi-Bio and its anti-CD38 antibody felzartamab last year.

It is hoping to add Sage Therapeutics to that tally, offering around $442 million for its longstanding partner on antidepressant therapy Zurzuvae (zuranolone) and other R&D programmes, although Sage has rejected its advances and sued to block any such deal.