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Duchenne Muscular Dystrophy Exon-Skipping Orphan Drugs And 2013 Business Developments

February 12, 2013

Sarepta Therapeutics and GlaxoSmithKline/Prosensa are developing exon-51 skipping orphan drugs for Duchenne Muscular Dystrophy (DMD). Sarepta Therapeutics’ Eteplirsen and GSK/Prosensa’s Drisapersen are the exon-51 skipping drugs for DMD.

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).

What follows are the 2013 business developments for Prosensa and Sarepta Therapeutics.


Prosensa, a Dutch pharmaceutical company, announces on January 29, 2013, that it has achieved Orphan Drug Designation (ODD) in the EU and the United States for all of its compounds for the treatment of Duchenne Muscular Dystrophy (DMD).

Prosensa currently has 6 exon-skipping compounds in development for treating DMD. The European Medicines Agency (EMA) assigns orphan drug status to Prosensa’s two preclinical compounds PRO052 and PRO055. The FDA grants ODD to Prosensa’s 4 preclinical compounds PrO045, PRO052, PRO053, and PRO055 on January 23, 2013. Prosensa’s 2 other Exon-specific compounds, PRO044 and PRO051 (Drisapersen), receive ODD prior to 2013.

According to a GlaxoSmithKline (GSK) update posted on the Parent Project Muscular Dystrophy (PPMD) website :

–          The last patient has been recruited for the Drisapersen US Phase II clinical study

–         The purpose of this exploratory study is to “assess safety, efficacy, and pharmacokinetics 2 doses of Drisapersen in the treatment of ambulant boys with DMD …… an exon 51 skip (up to 13% of all boys with DMD) …. Study is expected to complete in November 2013, with study results available in early 2014 ….”

Drisapersen is being developed in collaboration with GSK, in a fully enrolled, late stage Phase III clinical trial of 186 patients, in 47 trial sites in 20 countries.

Henri Termeer, former Genzyme CEO and Chairman who retired in 2011 after almost 30 years, joins Prosensa as a strategic adviser “providing advice for the biotech’s corporate strategy and growth plans’’. Mr. Termeer built Genzyme into a leader in rare diseases and orphan drugs.


The Internet has been buzzing the last few days on the topic of what the next steps will be for Sarepta Therapeutics. Much of the debate has been on the topic of whether Sarepta Therapeutics will file for FDA accelerated approval of Eteplirsen.  Accelerated approval allows for early approval of drugs to treat serious diseases and that also fill an “unmet medical need based on a surrogate endpoint.” If Eteplirsen receives accelerated approval, Sarepta Therapeutics can start to market the drug earlier than normal. The company must prove to the FDA that Etepelirsen clinical data shows that the drug is safe and effective.

Sarepta Therapeutics is dealing mostly with skipping exon 51. Approximately 1,950 U.S. DMD patients are affected by exon 51. Estimates are that the market can be worth $600 million – $1 billion/year. Approximately 2,600 patients in Europe can be treated with Eteplirsen.  Sarepta Therapeutics has identified “4 other exons that represents a potential market nearly twice the size of the population affected by exon 51”.

Plans are to have a Pre-Investigational New Drug Application (NDA) with the FDA in the 2nd half of 2013 for these other exons. Per Sarepta Therapeutics’ website,  about 85% of all DMD patients can potentially be treated with exon-skipping drugs.

A recent article, states that Sarepta Therapeutics is very unlikely to convince the FDA to give Eteplirsen accelerated approval. The FDA will probably ask the company to do a new, larger pivotal study prior to submitting for a FDA review of the drug. The article analyzes and reviews the clinical data to support this assertion.

Upcoming Catalysts

1) Two important upcoming meetings with the FDA during the 1st Quarter 2013 :

–  End-of-Phase II clinical meeting

–  End-of-Phase II Chemistry, Manufacturing, & Controls (CMC)

2) 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 titled, “Eteplirsen: One Small Step for Sarepta, One Giant Leap for DMD Treatment” 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.”

3) 74-week Eteplirsen clinical trial data should be available in 1st half of 2013 (J.P. Morgan Healthcare Conference).

Copyright © 2012-2013, Orphan Druganaut Blog. All rights reserved.

  1. Mary Almeida Ribeiro permalink

    Tenho um sobrinho com DMD, ele tem 15 anos, não anda mais, mas se encontra bem. A mutação dele ocorreu no exon 50, gostaria de saber se ele vai ser beneficiado com este medicamento.

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