Prosensa’s RNA based therapeutic PRO051 shows favourable results in the first systemic study in patients with Duchenne muscular dystrophy

Leiden, The Netherlands, September 14, 2009 – Prosensa, the Dutch based biopharmaceutical company focusing on RNA modulating therapeutics announces positive results from its phase I/IIa clinical study on its lead product candidate: the systemic delivery of PRO051 in patients with Duchenne muscular dystrophy (DMD) was well tolerated and induced novel expression of dystrophin. The data of the clinical study were presented at the 14th Annual International Congress of the World Muscle Society (WMS) in Geneva, Switzerland by Dr Nathalie M. Goemans, MD, from the Department of Pediatric Neurology, University of Leuven, Belgium.

The completed phase I/IIa open label study evaluated the systemic delivery of PRO051 in twelve DMD patients receiving weekly subcutaneous injections over a period of five weeks. Four dosing cohorts were applied (0.5 mg/kg, 2 mg/kg, 4 mg/kg, 6 mg/kg), comprising three patients each. The effect of PRO051 was assessed at the RNA level, to demonstrate specific exon 51 skipping, and at the protein level, to demonstrate novel dystrophin expression.

Muscle biopsies were taken before and two weeks after the last administration for patients in cohort 1, and at two and seven weeks after the last administration for all other patients. Adverse events were recorded and safety assessments (laboratory analysis and ECG) performed at regular intervals. All patients in this study entered a long term extended treatment phase.

Subcutaneous administration of PRO051 resulted in specific exon 51 skipping in cohorts 2, 3 and 4, and induced dystrophin expression in a dose related manner in all cohorts. The treatment was well tolerated by all patients and none discontinued their participation in the study. A review of the safety data revealed no clinically significant changes in laboratory values and ECGs. Antibodies against dystrophin were not detected in any of the patients.

The study was performed in close collaboration with the Universities of Leuven, Belgium and Gothenburg, Sweden. Dr. Goemans commented: “The data from this first Phase I/IIa study evaluating the systemic delivery of PRO051 are very promising. The subcutaneous administration was straightforward and well tolerated.”

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