Sarepta shares more than double on positive data for Duchenne muscular dystrophy drug eteplirsen

Shares in Sarepta Therapeutics rose as much as 123 percent Wednesday after the company announced that the experimental exon-skipping compound eteplirsen met the main goal of a Phase IIb trial in patients with Duchenne muscular dystrophy (DMD). "This was really beyond all expectations," remarked CEO Chris Garabedian, adding "this is the best controlled study with favourable outcomes that has ever been conducted" for DMD.

Study 4658-US-201 assigned 12 boys aged 7 to 13 years with the appropriate deletions of the dystrophin gene to receive intravenous infusions of one of two doses of eteplirsen or placebo once weekly for 24 weeks. In an extension trial, called Study 4658-US-202, the four patients given placebo were rolled over at 24 weeks to receive one of the two doses of eteplirsen. Results released in July showed that for the primary clinical outcome of the 6-minute walk test, patients given the higher dose of eteplirsen demonstrated a decline of 8.7 meters in distance walked from baseline, versus a decline of 78 meters for patients who received placebo followed by delayed-eteplirsen treatment. The company noted that this amounted to a statistically significant treatment benefit of 69.4 meters over 36 weeks.

Updated results released Wednesday demonstrated that after 48 weeks, patients who received the higher dose of Sarepta's drug had an increase of 21.0 meters in distance walked from baseline, while those given placebo followed by delayed-eteplirsen treatment had a decline of 68.4 meters. The company noted that this resulted in a significant treatment benefit of 89.4 meters over 48 weeks. Further results indicated that there was no significant difference between patients who received the lower dose of eteplirsen and those given placebo followed by delayed-eteplirsen treatment.

Sarepta also noted that for the study's primary efficacy endpoint, patients given eteplirsen for 48 weeks had a significant increase in dystrophin-positive fibres to 47 percent of normal. The company added that for those who received placebo followed by delayed-eteplirsen treatment, there was also a significant increase in dystrophin-positive fibres to 38.3 percent of normal. According to Sarepta, there were no treatment-related adverse events, no serious adverse events and no discontinuations in the trial.

Garabedian said that Sarepta plans to discuss the latest data with the FDA, probably in early 2013. In April, the company indicated that it believed the results were strong enough to advance the drug into Phase III testing, but Garabedian has since suggested that it may be feasible for the company to seek FDA approval based on the current results under the agency’s accelerated approval pathway.

GlaxoSmithKline and partner Prosensa are also developing an exon-skipping drug for DMD, with results from a large study expected later this year.

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