PTC's muscular dystrophy drug fails another key test with approval on the line

PTC Therapeutics' ($PTCT) in-development treatment for Duchenne muscular dystrophy (DMD) failed on its main goal in a Phase III trial. But, poring over subpopulation data, the company still believes it can make its case to global regulators.

The drug, ataluren, missed its primary endpoint of significantly improving patients' performance on a 6-minute walk test compared with placebo, the company said, helping DMD sufferers go only 15 meters farther on average. However, among the 99 volunteers who could only walk between 300 and 400 meters in 6 minutes at baseline, those in the ataluren group made it 47 meters farther than patients taking placebo, a statistically significant benefit, according to PTC.

PTC's management believes the data, added to results from an earlier Phase IIb trial that also failed, will be enough to support regulatory approval. The company is on track to file ataluren with the FDA by year's end, PTC said, and it now plans to submit its Phase III results to the European Medicines Agency, which granted the drug a conditional approval last year.

Investors seemed open to the possibility of success. The company's share price fell as much as 20% after hours on Thursday but gradually climbed back to settle about level with the day's close.

Ataluren's Phase III results among patients in the 300- to 400-meter baseline group match up with a similar benefit in the earlier Phase IIb data, PTC said, and are "consistent with the evolving understanding" of the 6-minute walk test. The company stressed that it had prespecified that group of patients before the trial started, an important distinction for regulators, who tend to look unfavorably upon poststudy data mining.

Whether the FDA and EMA are willing to accept a pair of failed studies as evidence of efficacy remains to be seen. DMD is a rare, debilitating disease with no approved treatments, affecting fewer than one in 4,000 boys. And PTC's drug is for an even smaller patient population, targeting the roughly 13% of DMD sufferers whose disease is caused by a certain genetic mutation. The combination of unmet need and small population could be enough to convince regulators to clear ataluren for a subgroup of patients.

Meanwhile, rivals Sarepta Therapeutics ($SRPT) and BioMarin Pharmaceuticals ($BMRN) are moving forward with more advanced therapies that treat larger numbers of DMD patients. BioMarin, thanks to its $680 million acquisition of Prosensa Therapeutics, is in the lead and slated to appear before a panel of FDA advisers in November to discuss its DMD treatment. Sarepta is tentatively scheduled to face the same committee in January. The FDA commonly hands down a final decision on a drug within a few months of such meetings.

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