A New Reason to be Bullish About Sarepta Therapeutics

NEW YORK (TheStreet) --I've written about Sarepta Therapeutics (SRPT) twice over the past month, with good reason. Despite a modest $327 million market capitalization, recent clinical data suggest that the company's lead drug candidate eteplirsen may be an effective treatment for Duchenne muscular dystrophy (DMD) -- a progressive disease that leaves patients wheelchair bound by their teens and dead shortly thereafter.

My first article highlighted risks that I thought my colleague Adam Feuerstein missed in his bullish coverage. My second addressed comments I received from institutional investors who own Sarepta. They thought I was overly critical of eteplirsen even though I had declared Sarepta to be "a reasonable long position for biotech investors with a healthy appetite for risk."

Last week, I learned an important tidbit that I don't think is widely known by the investment community: Sarepta's Phase IIb study of eteplirsen remained effectively blinded for far longer than 24 weeks.

That's important and potentially very good news for Sarepta. Before I explain why, let's recap the eteplirsen study to date:

Eteplirsen induces the body to "skip" a mismatched section of the exon (a sequence of nucleic acids) that codes for dystrophin, a protein critical to muscle repair that is dysfunctional in patients with DMD. By skipping exon 51, the drug enables the creation of a semi-functional dystrophin protein.

After 36 weeks, Sarepta reported that four eteplirsen recipients in the company's phase IIb study walked 69.4 meters further in six minutes (6MWT) than four patients treated with 24 weeks of placebo and 12 weeks of drug. These results reached statistical significance and far exceeded Wall Street expectations, which had dimmed following an essentially equivocal 6MWT assessment at 24 weeks.

If these data hold at 48 weeks and patient dystrophin levels correlate with clinical response, Sarepta will have meaningfully de-risked the program and the stock could easily double. Investigators will present the 48-week data on Oct. 13 at the World Muscle Society conference in Australia, although the company could issue a press release with top-line results any day.

One of my chief complaints with the phase IIb data was that the control group might not accurately reflect the natural progression of DMD. The medical literature shows a highly variable clinical course for DMD, even among patients more than seven years old (experts agree that patients progress more rapidly after age seven.) Given Sarepta's small study size, aberrant control group results could meaningfully skew the drug-placebo differential.

Importantly, patients in Sarepta's control arm were "rolled over" to receive drug after 24 weeks. Most investors assumed the study blind had been broken at that point, meaning that everyone -- from investigators and patients to the physical therapists who administered the 6MWT -- was informed of patients' treatment assignments. I worried about the possible demotivating effect that unblinding might have on subsequent 6MWT scores for those patients previously on placebo.

Late last week, I had a lengthy conference call with Christopher Garabedian, Sarepta's amiable CEO. Our detailed discussion about the phase IIb study and the unblinding process made it clear that the patients, parents, and physical therapists likely didn't know treatment assignments until at least 32 weeks -- and perhaps as long as 36 weeks.

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