Sarepta Advances SRP-1003 siRNA Therapy for Myotonic Dystrophy Type 1 with Positive Safety Review
Key Insights
Sarepta Therapeutics has completed the first two cohorts of its Phase 1/2 multiple ascending dose study for SRP-1003 (search), an investigational siRNA treatment for myotonic dystrophy type 1 (search).
Following a positive drug safety committee review, the study is advancing to higher dose cohorts, with cohort 4 currently dosing patients at 6 mg/kg and cohort 5 planned for early 2026.
The achievement of pre-specified patient enrollment targets triggered a $200 million milestone payment to collaboration partner Arrowhead Pharmaceuticals within 60 days.
Sarepta Therapeutics has reported significant progress in its Phase 1/2 clinical study of SRP-1003 (search), an investigational small interfering RNA (siRNA) therapeutic for type 1 myotonic dystrophy (DM1 (search)), with the completion of initial dose cohorts and advancement to higher dosing levels following positive safety reviews.
Clinical Trial Progress
The multiple ascending dose (MAD) study has successfully completed cohorts 1 (1.5 mg/kg) and 2 (3 mg/kg), with cohort 3 (4.5 mg/kg) fully enrolled and ongoing. Following a positive, pre-specified drug safety committee review, the study has been cleared to advance with additional drug escalating cohorts.
Patients are currently being dosed in cohort 4 at 6 mg/kg, with plans to initiate dosing in the final cohort, cohort 5 (12 mg/kg), in early 2026. The progression through these dose levels represents a systematic approach to establishing the optimal therapeutic dose for this investigational treatment.
Financial Milestone Achievement
The achievement of pre-specified patient enrollment targets has triggered a significant financial milestone, with Sarepta set to make a $200 million milestone payment to Arrowhead Pharmaceuticals within 60 days. This payment reflects the successful progression of the collaboration between the two companies in developing SRP-1003 (search), formerly known as ARO-DM1.
Broader siRNA Platform Strategy
SRP-1003 (search) is part of Sarepta's next-generation siRNA platform, which focuses on chronically administered therapies for neurodegenerative and pulmonary diseases. The platform includes investigational treatments for multiple conditions including facioscapulohumeral muscular dystrophy (search) (FSHD (search)), spinocerebellar ataxia type 2 (search) (SCA2 (search)), idiopathic pulmonary fibrosis (search) (IPF (search)), and Huntington's disease (search) (HD (search)).
The company is also pursuing preclinical programs for spinocerebellar ataxia types 1 and 3 (SCA1 and SCA3) and maintains an exclusive collaboration with Arrowhead Pharmaceuticals to develop therapies for skeletal muscle diseases, with plans to pursue up to six discovery targets in muscle or central nervous system disorders.
Company Position
Louise Rodino-Klapac, Ph.D., president of research & development and technical operations at Sarepta, emphasized the company's leadership position in genetic medicine for neuromuscular conditions. The advancement of SRP-1003 (search) represents part of Sarepta's broader mission to engineer precision genetic medicine for rare diseases.
The successful progression of this study adds to Sarepta's portfolio of genetic therapies, which includes established treatments for Duchenne muscular dystrophy (search) and an expanding pipeline across muscle, central nervous system, and cardiac diseases.