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Drisapersen And Eteplirsen: Two Exon-Skipping Orphan Drug Competitors

April 13, 2013

Duchenne Muscular Dystrophy (DMD) has attracted a lot of interest from investors due to impressive positive results from Sarepta Therapeutics’ orphan drug Eteplirsen and their competitor, GlaxoSmithKline (GSK)/Prosensa’s orphan drug Drisapersen. Both drugs are designed to skip over the defective exon 51 in DMD patients and to produce functional dystrophin. The Orphan Druganaut Blog published in February 2013 a post on the business developments for these two rival DMD drugs. Here is a review of recent business developments since that Blog Post.

Exon-skipping is a genetic intervention that alters dystrophin expression in the skeletal muscle. The DMD gene is the largest known human gene that consists of a coding sequence of 79 exons. Exon-skipping excludes particular exons from the dystrophin to bypass mutations. This type of treatment can be applied to approximately 72% of DMD patients (Per Review of Phase II and Phase III clinical trials for Duchenne Muscular Dystrophy. Scully M, Pandya S, Moxley R. Expert Opinion on Orphan Drugs. Jan 2013; 1(1): 33-46).


An Abstract containing Phase IIb study results of a 53-participant, 48-week trial, of GSK/Prosena’s orphan drug Drisapersen with a placebo, is presented on April 11, 2013, at a RNA & Oligonucleotide Therapeutics Conference at Cold Spring Harbor Labs, New York.  Originally, no data from this Phase IIb Drisapersen study was to be announced until the third quarter 2013, when an ongoing Phase III study was expected to be completed. GSK reports in an Abstract, posted on the CureDuchenne website, that “the primary objective was achieved–the continuous treatment arm showed a clinically meaningful and statistically significant difference from placebo on 6MWD [6-minute walk distance] at week 24. At week 48, both treatment arms showed a clinically meaningful difference from placebo on 6MWD (supported by improvement in other secondary endpoints). Drisapersen may represent an important treatment option for boys with DMD having mutations correctable by exon 51 skipping.”

A second presentation is expected at the Muscular Dystrophy Association’s (MDA) Scientific Conference to be held April 21-24, 2013, in Washington, D.C.

Per a article, “another positive brought about by the Drisapersen Phase III trial is its potential impact on RNA-based therapeutics as a whole … Muscular dystrophy seems to be one of the first indications that RNA will thrive in …”.


Sarepta Therapeutics gives an update on April 5, 2013, on data from Study 202 (Phase IIb open-label extension study) for orphan drug Eteplirsen, for DMD for patients with genotype amenable to skipping of exon 51. The results of this clinical trial shows that at 74 weeks, there is a continuing stabilization of walking ability in patients treated with Eteplirsen on the 6-minute walk test (6MWT). At 74-weeks, patients taking Eteplirsen are able to perform the 6MWT with a “statistically significant treatment benefit of 65.2 meters when compared to the placebo/delayed-treatment cohort …. demonstrated less than a 5% decline from baseline in walking ability.”

Mr. Chris Garabedian, President and CEO of Sarepta Therapeutics, states that,”These data are particularly compelling when viewed in the context of published natural history studies, which showed substantial declines on the 6-minute walk test over this timeframe in a smilar ambulatory DMD population. These results continue to support the potential of Eteplirsen to be a major advance in the treatment of DMD…”. Sarepta Therapeutics is currently conducting an open label extension phase to this Phase IIb clinical trial.

Sarepta Therapeutics announces April 11, 2013, that the company enters an exclusive, worldwide licensing agreement with the University of Western Australia (UWA), for intellectual property rights to support development of exon-skipping drug candidates for the treatment of DMD. The agreement grants Sarepta Therapeutics “rights ot UWA’s extensive patient portfolio in DMD and enables the company to build out its exon-skipping pipeline with new candidates based on proprietary Phosphorodiamidate Morpholino Oligomer (PMO) technology to address the majority of patients with the disorder worldwide.” This expands an agreement between the two parties that is signed in 2008, which supports the development of several exon-skipping drugs including Eteplirsen.

Investors are waiting for the company to announce its FDA filing plans. That announcement is expected before the end of April.

At the 15th Annual TIDES (Oligonucleotide & Peptide Therapeutics From Research through Commercialization) Meeting, May 12 – 15, 2013, Jayant Aphale, Senior Vice President, Technical Operations at Sarepta Therapeutics, will give a presentation on Eteplirsen. The presentation is titled, “Eteplirsen: One Small Step for Sarepta, One Giant Leap for DMD Treatment”, scheduled at 4:30 – 5:00 PM, May 13, 2013, as part of a Session titled, “Üpdates on Commercialization of Therapeutic Candidates”. The description from the meeting brochure reads :

“Recent Phase II clinical data indicates Eteplirsen assists in significant slowdown of the fatal disease, Duchenne Muscular Dystrophy (DMD) in young boys as evident by significant increase in Dystrophin levels and the 6MWT results. Currently there is no therapy available for treating DMD. The journey of Eteplirsen, Sarepta’s lead candidate for the treatment of DMD, is discussed from a technology platform perspective.”

Please Note: “Swimmers at the 2007 Kingdom Games in Den Haag” by Knurftendans (Own work) [Public domain] | Wikimedia Commons.

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