Case builds for Biogen, Stoke's Dravet syndrome drug

Hopes have risen for a new treatment option for a rare and severe form of childhood epilepsy, Dravet syndrome, after Biogen and Stoke Therapeutics reported new data for their recently partnered candidate zorevunersen.

The results come from a study that was used to design the phase 3 EMPEROR trial of zorevunersen, an investigational antisense oligonucleotide (ASO) that targets the SCN1A gene mutation that is thought to be responsible for most cases of Dravet.

According to Biogen, the analyses reported at the European Paediatric Neurology Society (EPNS) congress reveal improvements in multiple cognition and behaviour measures after 68 weeks of treatment with the drug that suggest improvements over standard therapies for the disorder.

Dravet syndrome is a severe form of developmental and epileptic encephalopathy which 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.

"Natural history data shows the limitations of treating this disease with anti-seizure medicines," said Dr Andreas Brunklaus, consultant paediatric neurologist at the Royal Hospital for Children in Glasgow, and a zorevunersen study investigator.

"The zorevunersen data gives us early evidence that this new genetically-targeted approach could address the underlying cause of Dravet syndrome, resulting in additional seizure control and offering patients the opportunity to experience improvements in cognition and behaviour," he added.

The data is a boost for Biogen, coming less than five months after it licensed rights to the drug from Stoke for $165 million upfront and up to $385 million in development and commercial milestone payments. The deal also gives it rights to certain follow-up candidates with a similar mechanism of action.

Biogen has been trying to build up its R&D pipeline 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.

It has built up its pipeline 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, but an attempt to take over Sage Therapeutics ended in failure after the company opted to merge with Supernus.

The EMPEROR trial of zorevunersen is expected to start in the second quarter of this year, with results due in the latter half of 2027.