Dravet syndrome drug moves forward after Phase 3 enrollment

Enrollment has been completed in a Phase 3 clinical study of zorevunersen, an experimental treatment for Dravet syndrome being developed by Stoke Therapeutics, keeping the company on track to begin a rolling New Drug Application (NDA) submission with the U.S. Food and Drug Administration (FDA) in early 2027.

Building on earlier Phase 1/2 clinical data, EMPEROR (NCT06872125) is testing the efficacy of zorevunersen compared with a sham comparator in 162 children and adolescents with Dravet syndrome, ages 2 to younger than 18, who continue to have seizures despite treatment. The main goal is to measure percent change from baseline in major motor seizure frequency at week 28.

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Phase 3 study reaches enrollment goal

“With five years of clinical data for zorevunersen and strong awareness among patients, families and investigators, we completed enrollment in just 10 months and are on track for a Phase 3 data readout in the third quarter of 2027,” Ian F. Smith, Stoke’s CEO and director, said in a company press release.

A rolling NDA submission allows a company to submit sections of its application as they are completed, rather than waiting until all sections are complete. Stoke expects to have the entire application filed by the second half of 2027 and is preparing to deliver zorevunersen “to all patients in the U.S. who may benefit following a potential FDA approval and U.S. launch by early 2028,” Smith said.

Dravet syndrome is most often caused by mutations in the SCN1A gene, which contains instructions to make part of the sodium channel NaV1.1. These mutations can lead to insufficient levels of functional NaV1.1 protein in brain nerve cells, disrupting normal brain signaling and triggering seizures and other symptoms, such as slow development and problems with behavior, beginning in early childhood.

Developed in collaboration with Biogen, zorevunersen is an antisense oligonucleotide, a short strand of genetic material designed to help the healthy copy of the SCN1A gene produce more of the NaV1.1 protein. This is expected to help regulate when nerve cells fire, with the goal of reducing seizure frequency and improving neurodevelopment, cognition, and behavior.

Earlier studies showed seizure reductions

Data from two Phase 1/2 clinical studies — MONARCH (NCT04442295) and ADMIRAL (ISRCTN99651026) — and their open-label extensions — SWALLOWTAIL (NCT04740476) and LONGWING (ISRCTN12811235) — showed that patients treated with zorevunersen experienced fewer seizures and had improvements in measures of cognition and behavior.

In the EMPEROR study, patients are randomly assigned to receive zorevunersen or a sham comparator for a 52-week treatment period after an eight-week baseline period. Zorevunersen is delivered into the fluid around the spinal cord via a spinal tap. After they complete this clinical study, eligible patients will be offered ongoing treatment with zorevunersen as part of an open-label period of the study.

Of the 162 patients in the U.S., U.K., and Japan, about 50 have already completed 28 weeks of treatment, the point at which researchers measure the primary endpoint. So far, no patients have stopped treatment. An additional cohort of about 30 patients is being enrolled in Germany, France, Spain, and Italy, and site activation is underway in China. Data from these additional patients in Europe and China are not planned for inclusion in the U.S. NDA submission.

“We are deeply gratified to have played a role in designing and delivering clinical studies to create potential new medicines, from early natural history studies of Dravet syndrome through to the successful enrollment of this first-of-its-kind Phase 3 study,” said Mary Anne Meskis, CEO of the Dravet Syndrome Foundation, which funds and helps accelerate research on Dravet syndrome.

“This progress reflects our shared commitment to improving outcomes for patients, and we look forward to continuing to advance zorevunersen with the goal of building a very different future for people living with Dravet syndrome and their families,” Meskis said.