PTC Therapeutics Announces Additional Results from Phase 2 Study
 of PTC124 in Duchenne Muscular Dystrophy

Data Presented at the World Muscle Society International Congress

SOUTH PLAINFIELD, NJ – October 18, 2007 - PTC Therapeutics, Inc. (PTC), a biopharmaceutical company focused on the discovery, development, and commercialization of small-molecule drugs targeting post-transcriptional control mechanisms, today announced additional data from a Phase 2 clinical trial of PTC124 in patients with Duchenne muscular dystrophy (DMD) due to a nonsense mutation.  The results, which include data from all three cohorts of the study, show that administration of PTC124 is associated with qualitative increases in muscle dystrophin expression and with reductions in serum creatine kinase values.  These data were presented today at the World Muscle Society (WMS) International Congress in Taormina, Italy.

Patients with DMD are boys and young men who lack dystrophin, a protein that is critical to the structural stability of muscle fibers.  This Phase 2 multi-site, open-label, dose-ranging clinical trial enrolled 38 boys with loss of dystrophin due to a nonsense mutation in the dystrophin gene.  Participants also had substantially elevated serum creatine kinase levels due to the disease, and symptoms associated with DMD.  Boys enrolled in the trial received 28 days of PTC124 treatment at one of three dose levels, with the primary endpoint of the trial being an increase in dystrophin expression in muscle.  Pre- and post-treatment muscle biopsies and blood analyses to assess muscle-derived creatine kinase were available from all 38 patients.  

An in vitro analysis demonstrated PTC124-induced dystrophin expression in cultured muscle cells from all 35 (100%) of the boys with samples evaluable in this analysis.  The in vivo data indicated that, across all three dose levels of PTC124, 18/38 (47%) of patients demonstrated visible improvement in the staining for dystrophin from muscle biopsies.  Response did not appear to be dependent on type of nonsense mutation.

Blood levels of muscle-derived creatine kinase were also measured as assessments of muscle integrity.  Statistically significant reductions in the concentrations of muscle-derived creatine kinase were observed during PTC124 treatment.  In addition, several parents and teachers reported that boys participating in the study had improvements in terms of greater activity level and increased endurance during the study duration.  

“We are very encouraged by these results, which show improvements in critical biomarkers of DMD,” said presenter and study investigator, Carsten Bönnemann, M.D., Assistant Professor Neurology and Pediatrics, Children's Hospital of Philadelphia and University of Pennsylvania School of Medicine and Co-Director of the Neuromuscular Program, Children's Hospital of Philadelphia.  “The combined in vitro and in vivo evidence of enhanced dystrophin expression and reduced muscle fragility offer signals of pharmacological activity that we hope to translate into potential clinical benefit for patients with DMD.”

“Coupled with the emerging safety profile of PTC124, these data provide the impetus for moving forward rapidly to initiate longer-term studies for boys with DMD,” said Langdon Miller, M.D., Chief Medical Officer of PTC.  “We are actively working with our clinical investigators and the regulatory agencies to finalize plans for additional clinical trials and we look forward to commencing these studies in the coming months.”

Stuart W. Peltz, Ph.D., President and Chief Executive Officer of PTC Therapeutics added, “These results, combined with the data presented earlier this month at the Child Neurology Society meeting and North American Cystic Fibrosis Conference, further support our belief that PTC124 represents a paradigm shift in the treatment of genetic disorders.  Our future plans for PTC124 include the initiation of longer-term studies in DMD and cystic fibrosis (CF) as well as additional proof of concept studies in other indications.  We hope that PTC124 will one day offer an improved treatment option for patients with nonsense-mediated DMD, CF, and a broad range of genetic disorders.”

About Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle disorder that causes the loss of both muscle function and independence.  DMD is perhaps the most prevalent of the muscular dystrophies and is the most common lethal genetic disorder diagnosed during childhood today.  Each year, approximately 20,000 children worldwide are born with DMD (one of every 3,500 male children).  More information regarding DMD is available through the Muscular Dystrophy Association (www.mdausa.org) and the Parent Project Muscular Dystrophy (www.parentprojectmd.org).

About PTC124

PTC124 is an orally delivered investigational new drug in Phase 2 clinical development for the treatment of genetic disorders due to nonsense mutations.  Nonsense mutations are single-point alterations in the genetic code that prematurely halt the translation process, producing a shortened, non-functional protein.  PTC124 has restored production of full-length, functional proteins in preclinical genetic disease models harboring nonsense mutations.  In Phase 1 clinical trials, PTC124 was generally well tolerated, achieved target plasma concentrations that have been associated with activity in preclinical models and did not induce ribosomal read through of normal stop codons.  PTC is currently conducting Phase 2 clinical trials of PTC124 in nonsense-mutation-mediated cystic fibrosis (CF) and Duchenne muscular dystrophy (DMD).

It is estimated that 10% of the cases of CF and 13% of the cases of DMD are due to nonsense mutations.  PTC believes that PTC124 is potentially applicable to a broad range of other genetic disorders in which a nonsense mutation is the cause of the disease.  The FDA has granted PTC124 Fast-Track designations and Orphan Drug designations for the treatment of CF and DMD due to nonsense mutations.  PTC124 has also been granted orphan drug status for the treatment of CF and DMD by the European Commission.  PTC124’s development is supported by grants from the Muscular Dystrophy Association (MDA), Cystic Fibrosis Foundation Therapeutics, Inc. (CFFT), Parent Project Muscular Dystrophy (PPMD), FDA’s Office of Orphan Products Development (OOPD) and by General Clinical Research Center grants from the National Center for Research Resources (NCRR).

About PTC Therapeutics, Inc.

PTC is a biopharmaceutical company focused on the discovery, development and commercialization of orally administered, proprietary, small-molecule drugs that target post-transcriptional control processes.  Post-transcriptional control processes regulate the rate and timing of protein production and are of central importance to proper cellular function.  PTC’s internally-discovered pipeline addresses multiple therapeutic areas, including genetic disorders, oncology and infectious diseases.  In addition, PTC has developed proprietary technologies and extensive knowledge of post-transcriptional control processes that it applies in its drug discovery and development activities, including the Gene Expression Modulation by Small-molecules (GEMS) technology platform, which has been the basis for collaborations with leading pharmaceutical and biotechnology companies such as Pfizer, Celgene, CV Therapeutics and Schering-Plough.

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