PTC Therapeutics Announces Additional Positive Interim Phase 2 Results of PTC124 in Duchenne Muscular Dystrophy

Data Presented at 59^th American Academy of Neurology Annual Meeting

BOSTON, MA and SOUTH PLAINFIELD, NJ – May 4, 2007 - PTC Therapeutics, Inc. (PTC), a biopharmaceutical company focused on the discovery and development of small-molecule drugs targeting post-transcriptional control processes, today announced positive interim data from a Phase 2 clinical trial of PTC124 in patients with Duchenne muscular dystrophy (DMD) due to a nonsense mutation. The results from the first two cohorts of the three-cohort study show that treatment with PTC124 was associated with increases in muscle dystrophin expression and reductions in serum creatine kinase values in at least 50 percent of evaluable patients. These data were presented today at the 59^th American Academy of Neurology (AAN) Annual Meeting.

Patients with DMD 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 is evaluating muscle dystrophin expression in patients with nonsense-mutation-mediated DMD.  Blood levels of muscle-derived creatine kinase are being measured as assessments of muscle integrity.  PTC124 safety, compliance, and pharmacokinetics are also being evaluated. 

“These data provide clinical evidence that PTC124 treatment may address the underlying cause of DMD,” said Dr. Richard Finkel, Director of the Neuromuscular Program, Children’s Hospital of Philadelphia, PA, who presented these results today at AAN as one of the trial’s lead investigators. “Development of PTC124 offers the potential for a new therapeutic option for patients with DMD due to a nonsense mutation.”

Langdon Miller, M.D., Chief Medical Officer of PTC, added, “We are very pleased with these additional pharmacologic proof-of-concept data from our short-term Phase 2 clinical trial of PTC124 in patients with DMD.  Based on the growing body of Phase 2 clinical data, we plan to initiate longer-term clinical trials to evaluate the clinical benefit of PTC124 in patients with DMD.” 

The Phase 2 clinical trial is being conducted at three sites in the United States: Children's Hospital of Philadelphia, Philadelphia, Pennsylvania; Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; and the University of Utah, Salt Lake City, Utah. In the study, patients have received 28 days of PTC124 treatment at one of three dose levels.  All clinical trial participants are boys with a nonsense mutation in the dystrophin gene, substantially elevated serum creatine kinase levels, and symptoms associated with DMD.  The analysis presented today includes data from 26 patients with DMD who received PTC124 at the low-dose and medium-dose levels.  Completion of accrual and analysis of data from a higher dose level are ongoing.

The primary endpoint of the trial has been the proportion of patients having an increase in dystrophin expression in muscle during 28 days of treatment with PTC124.  Pre- and post-treatment muscle biopsies were available from all 26 patients for analysis. In vitro treatment of patient muscle cells with PTC124 showed evidence of a dose-dependent increase in dystrophin expression in all of the evaluable patients. Preliminary review of the data indicate that, at both dose levels evaluated in this analysis, approximately half of the patients demonstrated visible improvement in the staining for muscle dystrophin in vivo. Overall, four of the six, or 67 percent, of patients treated at the lower dose level and 10 of the 20, or 50 percent, of patients treated at the medium dose level demonstrated an increase in the expression of dystrophin post-treatment. Response did not appear to be dependent on type of nonsense mutation. 

Additionally, statistically significant reductions in the concentrations of muscle-derived creatine kinase levels in the blood were observed during PTC124 treatment. Several parents and teachers reported that boys participating in the study had improvements in terms of greater activity level and increased endurance during treatment.  Individual subjects at both dose levels demonstrated some improvements in upper and lower muscle strength however in the overall analysis the magnitude of change was not statistically significant.

PTC124 was well tolerated among the 26 patients included in the study.  Adverse events were infrequent, mild to moderate in severity, and did not result in therapy interruptions or discontinuations.  There were no safety concerns based on physical examinations, vital sign measurements, electrocardiograms or laboratory parameters. Compliance with PTC124 treatment was excellent at both dose levels. 

Stuart W. Peltz, Ph.D., President and Chief Executive Officer of PTC Therapeutics, stated, “In addition to the clinical proof-of-concept data we disclosed late last year, these new insights provide us with further evidence supporting the potential of PTC124 in genetic disorders due to a nonsense mutation.  The findings in the DMD trials are consistent with the results observed in Phase 2 clinical trials of PTC124 in patients with cystic fibrosis and with preclinical results in the DMD mouse model that were recently published in Nature.  We are eager to extend testing of this concept into other nonsense-mediated 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 Committee for Orphan Medicinal Products (COMP) of the European Medicines Agency (EMEA). 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 and development 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, CV Therapeutics and Schering-Plough.

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