Eteplirsen for the treatment of Duchenne muscular dystrophy

Abstract

Objective: In prior open‐label studies, eteplirsen, a phosphorodiamidate morpholino oligomer, enabled dystrophin production in Duchenne muscular dystrophy (DMD) with genetic mutations amenable to skipping exon 51. The present study used a double‐blind placebo‐controlled protocol to test eteplirsen's ability to induce dystrophin production and improve distance walked on the 6‐minute walk test (6MWT). Methods: DMD boys aged 7 to 13 years, with confirmed deletions correctable by skipping exon 51 and ability to walk 200 to 400 m on 6 MWT, were randomized to weekly intravenous infusions of 30 or 50 mg/kg/wk eteplirsen or placebo for 24 weeks (n = 4/group). Placebo patients switched to 30 or 50 mg/kg eteplirsen (n = 2/group) at week 25; treatment was open label thereafter. All patients had muscle biopsies at baseline and week 48. Efficacy included dystrophin‐positive fibers and distance walked on the 6MWT. Results: At week 24, the 30 mg/kg eteplirsen patients were biopsied, and percentage of dystrophin‐positive fibers was increased to 23% of normal; no increases were detected in placebo‐treated patients ( p ≤ 0.002). Even greater increases occurred at week 48 (52% and 43% in the 30 and 50 mg/kg cohorts, respectively), suggesting that dystrophin increases with longer treatment. Restoration of functional dystrophin was confirmed by detection of sarcoglycans and neuronal nitric oxide synthase at the sarcolemma. Ambulation‐evaluable eteplirsen‐treated patients experienced a 67.3 m benefit compared to placebo/delayed patients ( p ≤ 0.001). Interpretation: Eteplirsen restored dystrophin in the 30 and 50 mg/kg/wk cohorts, and in subsequently treated, placebo‐controlled subjects. Duration, more than dose, accounted for dystrophin production, also resulting in ambulation stability. No severe adverse events were encountered. Ann Neurol 2013;74:637–647