SRP-9001 for treating patients with Duchenne muscular dystrophy

The investigational gene therapy SRP-9001 (delandistrogene moxeparvovec) had a biological and possibly clinically relevant effect in children with Duchenne muscular dystrophy (DMD). The safety profile and durable response provides proof-of-concept support for continued clinical trials to assess SRP-9001 in patients with DMD.

SRP-9001 is developed for targeted expression of a shortened functional micro-dystrophin protein in skeletal and cardiac muscle. It uses the adeno-associated virus serotype rh74 (rAAVrh74) vector to deliver the micro-dystrophin-encoding gene to skeletal and cardiac muscle tissue. Efficacy and safety are evaluated in a three-part, phase 1/2 trial (NCT03769116) in patients with DMD. Participants were 4 ambulatory boys between 4 and 8 years old at study initiation with a confirmed DMD mutation between exons 18–58. They received a single intravenous infusion of SRP-9001 at an intended dose of 2.0x10¹⁴ vg/kg. The latest long-term (3-year; mean age of patients 8.2 years) safety and functional data from this study were presented by Dr Jerry Mendell (Nationwide Children's Hospital, OH, USA) [1].

North Star Ambulatory Assessment (NSAA) showed long-term overall improvements from baseline that were maintained over 3 years, indicating a durable response (see Figure). NSAA scores improved by a mean of 7.5 points overall. Dr Mendell stressed the importance of these outcomes. “There is no question about this treatment's unequivocal efficacy.” One indication was the mean change from baseline in walking 100 metres, which improved by 10.3 seconds after 3 years. NSAA improvements were generally associated with improvement in ambulation over 3 years compared with decline generally expected in untreated natural history patients.

Figure: NSAA total scores over 3 years after SRP-9001 treatment [1]



 

 

 

 

 

 

 

 

 

 

No new safety signals were detected. Safety data were consistent with the wider SRP-9001 clinical trial program. Treatment-related safety events in this study mostly occurred in the first 90 days after infusion and all resolved. These results, said Dr Mendell, reinforce the overall long-term acceptable safety profile of SRP-9001.

1. Mendell JR, et al. A Phase 2 Clinical Trial Evaluating the Safety and Efficacy of SRP-9001 for Treating Patients with Duchenne Muscular Dystrophy. S23.002, AAN 2022, 02–07 April, Seattle, USA.

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Posted on 2 June, 2022