Prosensa stock goes into free fall as drisapersen fails in Ph III study

UK pharma giant GlaxoSmithKline (LSE: GSK) and Netherlands-based partner Prosensa (RNA: Nasdaq: GS) announced on Friday that GSK's Phase III clinical study of drisapersen, an investigational antisense oligonucleotide, for the treatment of Duchenne muscular dystrophy (DMD) patients with an amenable mutation, did not meet the primary endpoint of a statistically significant improvement in the 6 Minute Walking Distance (6MWD) test compared to placebo.

The news caused Prosensa shares to plunge 74% to $6.34 in very heavy trading, while GSK edged 1% higher. Prosensa does have a couple of other drugs in clinical studies. However, both of these rely on exon-skipping, as does drisapersen. The absolute worst-case scenario would be that exon-skipping is found to just not work for DMD, commented Keith Speights, writing on the Motley Fool blog, adding. “If that's the case, Prosensa can throw in the towel. It's over.”

Dutch firm remains committed to overall program