UPDATE 2-GSK, Prosensa muscular dystrophy drug misses study goal
* Drug fails to help patients walk better in Phase III study
* Prosensa shares slump 75 percent in pre-market
(Adds Prosensa share slump, more details)
LONDON, Sept 20 (Reuters) - An experimental drug for Duchenne muscular dystrophy from GlaxoSmithKline and Prosensa failed to meet its goal in a late-stage clinical trial, sending shares in Prosensa tumbling 75 percent in pre-market trade.
The drug, drisapersen, did not show a statistically significant improvement in the distance that patients could walk in six minutes compared to placebo in the Phase III test, the companies said on Friday.
The setback also unnerved investors in Sarepta Therapeutics , which is developing a rival treatment for the rare muscle-wasting disorder, and its shares fell 8 percent in pre-market Nasdaq dealings.
GSK and Dutch-based Prosensa had previously been seen as ahead of the pack in making a drug for the untreatable condition, although data released on GSK's website last month had already indicated a substantial number of patients treated with drisapersen might not be getting a meaningful drug effect.
The news is a fresh late-stage pipeline blow for GSK - Britain's biggest drugmaker - which reported on Sept. 5 that an experimental cancer vaccine failed to help melanoma patients.
Up until now, 2013 has been a strong year for GSK research, with new drug approvals in HIV, cancer and respiratory disease. But finding a treatment for Duchenne muscular dystrophy (DMD), like developing a therapeutic cancer vaccine, was always a difficult prospect.
GSK and its partner Prosensa now plan to study the clinical trial results in detail to see if drisapersen has a future.
"We appreciate that these results will be disappointing for boys with DMD and their families," said Carlo Russo, head of rare diseases research at GSK.
"We are committed to evaluating the outcome of this study in the context of the overall development programme with experts in the field, and we expect such evaluation to help inform our next steps for drisapersen. It is our hope that progress will be made in an effort to help boys with DMD."
GSK has an exclusive worldwide licence to develop and commercialise drisapersen and other experimental DMD drugs from Prosensa. The Dutch firm is eligible for up to 428 million pounds ($687 million) in milestone payments from GSK and percentage royalties in the low teens on any future sales.
($1 = 0.6226 British pounds)
(Editing by Elaine Hardcastle)