GSK dumps a failed muscular dystrophy drug back in Prosensa's lap

GlaxoSmithKline ($GSK) has shut the door on its hopes in Duchenne muscular dystrophy (DMD), handing back rare-disease drug drisapersen to Prosensa ($RNA), its former partner.

The once-promising drisapersen works by inducing exon skipping, basically convincing the body to ignore the faulty dystrophin proteins that cause DMD. That promise came tumbling down in September, however, when the drug failed to beat out placebo in improving walking distance in patients with the muscle-destroying disease, sending Prosensa's shares into a 70% tailspin.

Now, as GSK washes its hands of the breakthrough-designated drug, the Netherlands-headquartered Prosensa is planning to go it alone on a salvage project, heading back to the drawing board with a handful of candidates.

"Prosensa is now in a favorable strategic position to advance the DMD portfolio, which includes drisapersen and five additional compounds, three of which are currently in clinical development," CEO Hans Schikan said. "We will continue to work closely with patient groups, investigators, academia and regulators to ensure that we do everything we can to bring treatments to boys affected by DMD."

Prosensa wasn't the only victim of drisapersen's fall from grace. After the drug's Phase III failure, competitor Sarepta ($SRPT) got word that the FDA would not consider an early approval for eteplirsen, its rival exon-skipper. Sarepta said Prosensa's slip raised "considerable doubt" about the dystrophin biomarker, generating rumors that the agency was unconvinced of the method's efficacy and shaving about 60% off of the company's share price.

Prosensa dipped another 7% on the news of GSK's exit from their 5-year partnership, hovering at around $5.20 in premarket trading Monday.

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