Myotonic dystrophy drug SRP-1003 trial advances to higher doses
Phase 1/2 study in DM1 continues enrolling, dosing patients
A Phase 1/2 clinical trial testing SRP-1003, a treatment for myotonic dystrophy type 1 (DM1), is progressing as planned and continues to enroll patients at higher doses.
The Phase 1/2 study (NCT06138743) is expected to enroll 78 adults, ages 18 to 65, who have a genetically confirmed diagnosis of DM1. To be eligible, prospective participants must be able to walk 10 meters (about 33 feet) independently, and patients who are able to conceive children must agree to use effective contraception during the study and for a few months after. Additionally, DM1 symptoms must have first appeared after age 12.
Enrollment is continuing at sites in Australia, New Zealand, Thailand, and Taiwan.
The trial is testing various doses of SRP-1003, with the main goal of evaluating safety. According to a press release from Sarepta Therapeutics, the first two study groups, testing doses of 1.5 and 3 mg/kg, respectively, have finished, and a third cohort testing a dose of 4.5 mg/kg is fully enrolled and ongoing. The trial’s safety monitoring committee has recommended that the study continue as planned to test further higher doses.
Testing higher doses
Arrowhead Pharmaceuticals, which is sponsoring the clinical trial, has almost completed enrollment in a fourth cohort, which will test SRP-1003 at a dose of 6 mg/kg, according to a company press release. The company said it aims to start enrollment for a fifth group testing a 12 mg/kg dose in early 2026.
Sarepta acquired the rights to SRP-1003 (previously known as ARO-DM1) from Arrowhead, the therapy’s original developer, in a deal that closed earlier this year. Per that agreement, the trial advancing to this point means Sarepta will pay $200 million to Arrowhead. This follows a $100 million payment a few months ago when the study hit an early enrollment target.
DMI is caused by mutations in the DMPK gene. When genes are read to make proteins, the genetic code is copied into a temporary molecule called messenger RNA (mRNA), which is then used as a template for protein production. DM1-causing mutations lead to the production of an abnormally long DMPK mRNA, which forms toxic clumps in muscle cells.
SRP-1003 is a small piece of RNA engineered to stick to the mutant DMPK mRNA and trigger its destruction. The therapy is given by infusion into the bloodstream.
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