Could This DMD Treatment Become a Blockbuster Drug?

Duchenne muscular dystrophy, or DMD, is a muscle-wasting disease caused by a genetic mutation in the dystrophin gene -- the largest gene on the X chromosome -- which affects one in every 2,400 male births. Muscle weakness in DMD patients generally spreads from the legs to the pelvis, eventually reaching the arms, neck, and other areas, confining most patients to a wheelchair by age 12 and resulting in a maximum lifespan of around 25 years.

To date, there is no effective treatment for DMD, but there could be soon, thanks to three biotech companies: Sarepta Therapeutics (SRPT 6.09%), Prosensa Holding NV (NASDAQ: RNA), and GlaxoSmithKline (GSK -0.92%). However, Sarepta recently took the lead after Prosensa, which is partnered with GlaxoSmithKline, reported disappointing clinical trial data for its DMD treatment. Could Sarepta's treatment finally be the game-changing, blockbuster drug that DMD patients have been waiting for?

Sarepta gains the upper hand
Prosensa and GlaxoSmithKline's co-developed DMD treatment, drisapersen, is intended to increase the production of dystrophin, a protein that facilitates muscle growth that is absent in DMD patients. GSK and Prosensa recently released the eagerly anticipated results from drisapersen's phase 2 trials that concluded a year ago, but the results were fairly disappointing.

Drisapersen was shown to produce dystrophin in 72% of patients on a continuous dose, and in 59% of those who had intermittent doses of the drug. By comparison, Sarepta's competing drug, eteplirsen, showed a 100% success rate in increasing the dystrophin production rate in all dosed patients. Both drisapersen and eteplirsen are genetic treatments that work at the RNA level to modify dystrophin production.

Glaxo had previously administered a six-minute walk test (how far a patient can walk in six minutes) to patients dosed with drisapersen, which was found to increase the boys' average walking distance by 117 feet. Sarepta also beat Glaxo in that test as well, reporting an average walking distance increase of 152 feet with eteplirsen. However, investors should note that Glaxo's testing group is significantly larger, with 53 boys, compared to the 12 tested in Sarepta's studies.

Prosensa shareholders didn't take the news too well, since drisapersen is the company's most promising drug, and shares plunged 8% on Aug. 16. Glaxo was largely unaffected, but shares of Sarepta climbed 3%. Sarepta intends to file an FDA approval for eteplirsen early next year, but doubts have been raised regarding its ambitious plans to receive an accelerated approval.

Either treatment is forecast to generate more than $1 billion in annual revenues if approved. Prosensa and Glaxo intend to release the full results of its Phase III trial later this year for drisapersen, and Sarepta is expected to start a Phase III trial for eteplirsen next year.

A newcomer carves out a new niche
Although Sarepta, Prosensa, and Glaxo are currently the biggest names in DMD treatments now, that hasn't discouraged smaller competitors from exploring their own treatments. One notable newcomer is PTC Therapeutics (PTCT -0.79%), which only went public two months ago. PTC recently initiated a phase 3 clinical trial of ataluren, a treatment for patients with nonsense mutation DMD.

Nonsense mutation DMD is a subset of DMD. Usually, the inability to produce dystrophin is caused by a variety of mutations that cause deletions, duplications or single point mutations that disrupt the coding reading frame of the dystrophin gene. Of these single point mutations, 10% to 15% are categorized as "nonsense mutations" that are caused by an alteration of a single base in the DNA, which ends the translation of a gene into a protein. Nonsense mutation DMD cases are not treatable by the exon-skipping technology employed by treatments from Sarepta and Prosensa.

PTC's trial is intended to be much larger than either Glaxo or Sarepta's groups, with 220 patients at 50 global investigational sites. The company intends to test the safety of varying doses of the drug and use the six-minute walk test to determine efficacy. The trial will be double-blind and placebo-controlled.

A Foolish final thought
Even though these new DMD treatments sound promising, Sarepta, Prosensa, and PTC all fall under the textbook classification of speculative biotechs. These three companies don't have any approved treatments on the market and, therefore, no real source of earnings growth. Glaxo is the only established company in the field, but the success or failure of its DMD treatment won't have a huge impact on its top line growth.

All three companies have promising pipelines, with additional treatments for DMD, influenza, Huntington's disease, and cystic fibrosis in the works, but these treatments are all in the very early stages. For now, what matters most for these three companies is bringing a successful DMD treatment to the market. If one of them is successful, it will not only save children's lives, but also reward the true believers and backers of these companies.