DMD: Prosensa, GSK Expand Exon-Skipping Program

Dutch biotechnology company Prosensa and multinational pharmaceutical company GlaxoSmithKline are moving ahead with plans to test drugs targeting several exons in the dystrophin gene

Article Highlights:
  • Prosensa has expanded its portfolio of potential treatments for Duchenne muscular dystrophy (DMD) based on skipping specific exons (sections) of the dystrophin gene; some of its exon-skipping program is being carried out in partnership with GlaxoSmithKline (GSK).
  • Compounds targeting exons 51 (drisapersen) and 44 (PRO044) are in clinical trials for DMD.
  • Compounds targeting exons 52 and 55 will be moved to clinical trials as soon as possible.
  • Compounds targeting exons 45 and 53 have received orphan drug designation from the European Commission and are expected to enter clinical development within the next six months.
by Margaret Wahl on October 29, 2012 - 5:00am

Update (Feb. 1, 2013): Dutch biopharmaceutical company Prosensa announced Jan. 29 that it has received orphan drug status in the United States and the European Union for compounds in development for the treatment of Duchenne muscular dystrophy.

Orphan drug status provides financial incentives for companies to develop drugs for rare diseases; the status does not affect regulatory approval of these new drugs. The European Medicines Agency assigned orphan drug status to Prosensa's compounds PRO052 and PRO055, and the U.S. Food and Drug Administration granted orphan drug status to PRO045, PRO052, PRO053 and PRO055.

Update (Jan. 10, 2013): The phase 2 trial of drisapersen for boys with Duchenne dystrophy who are able to walk is no longer recruiting new participants, according to a Jan. 10 communication from GlaxoSmithKline. GSK says the study is expected to be completed in November 2013, with results available in early 2014.

Compounds targeting exon 52 and exon 55 of the dystrophin gene as a way to treat some forms of Duchenne muscular dystrophy (DMD) will be moved into clinical trials as soon as possible, says Dutch biotechnology company Prosensa. The experimental compounds are known as PRO052 and PRO055.

Exons are sections of a gene. In DMD, the goal of the experimental treatment strategy known as exon skipping is to cause muscle fibers to leave out ("skip") flawed genetic instructions in the dystrophin gene and piece together instructions that can lead to production of a functional dystrophin protein. Dystrophin is the muscle protein that's missing in people with DMD.

The company also says it has received orphan drug designation from the European Commission to develop compounds targeting dystrophin exon 45 (PRO045) and exon 53 (PRO053). This type of designation gives companies financial incentives to spur development of treatments for rare disorders. These two compounds are expected to enter clinical development within the next six months.

Prosensa announced both developments in an Oct. 23, 2012, press release.

PRO051, PRO044 already in clinical trials

The company has developed two additional exon-skipping compounds that are already in clinical trials for DMD.

One, known as drisapersen (formerly known as PRO051/GSK2402968), targets dystrophin in exon 51 and is now in phase 3 clinical trials under the auspices of pharmaceutical company GlaxoSmithKline (GSK).

A phase 2 trial of drisapersen is open to recruitment at centers throughout the United States for boys with DMD who are at least 5 years old, able to walk, and have dystrophin mutations amenable to treatment by skipping exon 51. See Clinical Study to Assess Two Doses of GSK2402968 in Subjects with Duchenne Muscular Dystrophy (DMD114876); or enter NCT01462292 in the search box at You also can contact the U.S. GSK Clinical Trials Call Center at (877) 379-3718 or send an email to Refer to study number NCT01462292 in your communication.

A phase 3 trial of drisapersen is ongoing at 45 centers outside the United States but is no longer recruiting participants. See Clinical Study to Assess the Efficacy and Safety of GSK2402968 in Subjects with Duchenne Muscular Dystrophy (DMD114044); or enter NCT01254019 in the search box at

Prosensa's PRO044, targeting exon 44 of the dystrophin gene, is being tested in a clinical trial in Europe that is no longer open to new participants. See Phase I/II Study of PRO044 in Duchenne Muscular Dystrophy; or enter NCT01037309 in the search box at

Partnership with GSK

In 2009, Prosensa entered into a strategic alliance with GSK for part of its DMD exon-skipping program.

According to the Oct. 23 press release, Prosensa recently received a "milestone payment" of 10 million British pounds (about $16 million) from GSK for development of exon-skipping compounds for DMD. Milestone payments are made based on achievement of previously determined steps in the drug development process.

The press release also notes that Prosensa and GSK have initiated a global natural history study of DMD aimed at generating additional data to help with drug development.

About Clinical Trials

About Clinical Trials

A clinical trial is a test, in humans, of an experimental treatment. Although it's possible that benefit may be derived from participating in a clinical trial, it's also possible that no benefit, or even harm, may occur.

MDA has no ability to influence who is chosen to participate in a clinical trial.

To learn more, see Learn About Clinical Studies and Being a Co-Adventurer, which is about neuromuscular disease clinical trials. To see a continuously updated database of clinical trials, go to

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