Sarepta's stumble puts Prosensa in front for DMD therapy

Sarepta confirmed yesterday it will file its Duchenne muscular dystrophy (DMD) drug eteplirsen in mid-2015 in the US, several months later than hoped.

The delay - caused by FDA concerns over the quality of the data supporting eteplirsen - means rival DMD therapy developer Prosensa is now in pole position to bring its candidate drisapersen to market.

Both drugs are exon-skipping therapies designed to restore the function of a protein called dystrophin that is impaired in DMD, a disease which afflicts boys and is characterised by severe muscle-wasting that generally leads to death before the age of 30.

The US regulator has expressed concern about the clinical endpoints used in Sarepta's trial, which included just 12 patients, as well as they methodology used to measure the effects of the drug on dystrophin.

In contrast, Prosensa has data from studies involving more than 300 DMD patients and "has followed clear FDA guidelines," according to analysts Frank Gregori and Mick Cooper at Edison. With drisapersen already filed in the US under a 'rolling submission' due to complete before the end of the year, they suggest it could be on the market in the third quarter of 2015.

Both eteplirsen and drisapersen suitable for a subgroup of around 13% of DMD patients amenable to exon-skipping therapy, who number an estimated 4,000 across the US and Europe with some 200 new cases every year.

The FDA's requests for new data on Sarepta's drug "have paved the way for Prosensa to be the first targeted exon-skipping therapy for DMD," write the analysts in a research note.

Sarepta said in its third-quarter results statement yesterday that a confirmatory study of eteplirsen in ambulatory DMD patients, as well as a study in advanced/non-ambulatory patients, will begin dosing this month. Meanwhile, the company is "quickly moving forward with additional studies across our DMD programme," according to chief executive Chris Garabedian.

GlobalData analyst Nikhilesh Sanyal predicted however that Sarepta will "rebound strongly" from the setback, suggesting the company received a positive response to its data " showing eteplirsen's efficacy correlation with restored expression of the dystrophin protein" at the recent World Muscle Society meeting in Berlin.

"The company also plans to collaborate with academic institutions to collect additional natural history and magnetic resonance imaging data on DMD progression during 2015," according to Sanyal, who said a meeting with the FDA later this year "will allow the company to confirm the adequacy of its planned data collection and re-join the race."

Prosensa has already attempted to strengthen its future marketing position by filing blocking patents on the use of exon-51-skipping therapies to treat DMD in the EU, noted Sanyal.

"We believe that Sarepta may respond by establishing itself firmly in the US market for generating significant revenues from eteplirsen upon approval," he said.