PTC Therapeutics Announces Data from Additional Clinical Studies of PTC124 in Cystic Fibrosis Confirming Activity

- Data Presented at the 31st European Cystic Fibrosis Conference -

SOUTH PLAINFIELD, N.J. and PRAGUE, Czech Republic, June 12, 2008 /PRNewswire/ -- PTC Therapeutics, Inc. (PTC) today announced promising new data from two studies of PTC124 in cystic fibrosis (CF). Results from an Israeli Phase 2a extension study evaluating three months of oral PTC124 treatment in adult patients with nonsense-mutation-mediated CF demonstrated statistically significant improvements in the function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein and a statistically significant mean [28%] decrease in the frequency of cough, one of the most prominent and burdensome CF-related symptoms. Results from the Hadassah University Hospital in Israel were presented today by Michael Wilschanski, M.D., Director, Pediatric Gastroenterology, and by Eitan Kerem, M.D., principal investigator and head of the Department of Pediatrics and Cystic Fibrosis Center. Separately, results from a European study evaluating 14-day courses of PTC124 in pediatric patients with nonsense-mutation-mediated CF confirmed the CFTR activity observed in previous short-term studies in adult patients. Data from the European study were presented today by Isabelle Sermet-Gaudelus, M.D., Ph.D., principal investigator at l'Hopital Necker-Enfants Malade.

Patients with CF lack adequate levels of the CFTR protein, a chloride channel that maintains proper hydration of epithelial surfaces in the lung, pancreas, and liver. Patients with nonsense-mutation-mediated CF generally have a severe form of CF because virtually no CFTR protein is produced. Previous studies of PTC124 adult patients with CF evaluated nasal transepithelial potential difference (TEPD) as a surrogate for the presence and activity of the CFTR protein. Across the short- and long-term clinical trials at high and low doses of PTC124, TEPD assessments showed statistically significant improvements of mean CFTR-dependent chloride secretion in the airways.

The Phase 2a extension study in Israel assessed 3 months of oral PTC124 therapy at two different dose levels in 19 adult men and women with nonsense- mutation-mediated CF who had participated in a prior short-term PTC124 Phase 2a study. More than 90% of the patients had chronic CF-related lung infection and also had CF-induced pancreatic insufficiency. Results from the study showed that treatment with PTC124 resulted in statistically significant (p< 0.001) improvements in CFTR function as measured by TEPD in both dose groups. The proportion of patients showing improvement in TEPD chloride secretion increased over time in the extension study. Trends towards improvements in mean FEV1 and FVC values were observed. Baseline data showed that CF patients cough a remarkable 643 times per day on average, with a range of 324 to 1,569 coughs per day. In comparison, healthy individuals generally cough fewer than 16 times per day, according to the European Respiratory Journal (Hsu 1994). Patients receiving PTC124 experienced a mean [28%] decrease in cough frequency by the end of three months of therapy (p< 0.01). PTC124 was generally well tolerated, resulting in excellent mean compliance with the treatment regimen ( >90%).

"Three months of treatment with PTC124 in nonsense-mutation-mediated CF patients was associated with time-dependent improvements in nasal TEPD chloride conductance, pulmonary function and cough -- important markers suggesting the potential for benefit in patients with CF," stated Dr. Wilschanski. "PTC124 increases CFTR-mediated chloride secretion in patients with a variety of nonsense mutation types, which suggests a broad spectrum of activity across one of the major subpopulations in CF."

Dr. Kerem added, "The impact on cough that we observed in this study by objective measurement is particularly notable given that cough is one of the major symptomatic manifestations of the underlying disease process in CF. The reduction in cough achieved with PTC124 in this three-month study suggests secondary clinical effects of drug activity. Based on these findings, we believe that objective measurement of cough may offer a meaningful new way to evaluate drug efficacy in future CF clinical trials."

In a separate Phase 2a study in Europe, data are currently available from 21 children who received two 14-day treatment courses of oral PTC124 therapy at two different dose levels. Patients ranged in age from six to 18 years. All had nonsense-mutation-mediated disease, pathological lung infection, and pancreatic insufficiency. Statistically significant (p< 0.05) increases in the proportion of epithelial cells showing surface staining with the CFTR protein were observed. In addition, statistically significant (p< 0.05) improvements in CFTR-mediated chloride conductance as measured by TEPD were evident. PTC124 was generally well tolerated in pediatric patients and mean compliance with treatment was excellent ( >95%).

"We are encouraged to see the activity of PTC124 observed in adults reproduced in a pediatric population in France and Belgium," commented Dr. Sermet-Gaudelus. "PTC124 causes the missing protein to be made, to be located in the right place in the cell, and to have functional effect. Combined with the generally well-tolerated profile of PTC124, we believe these data support inclusion of pediatric patients in future clinical trials."

"We are gratified by these results from our Israeli, French, and Belgian investigators, which demonstrated the activity of PTC124 in patients across a variety of age ranges, geographies, and nonsense mutation types," stated Langdon Miller, M.D., Chief Medical Officer of PTC. "These data offer the basis for initiating a randomized, controlled Phase 2b study later this year to evaluate the clinical benefit of PTC124 in adults and children with nonsense-mutation-mediated CF."

About Cystic Fibrosis

Cystic fibrosis (CF) is among the most common life-threatening genetic disorders worldwide. According to the Cystic Fibrosis Foundation, CF affects approximately 30,000 adults and children in the United States and, according to the European Cystic Fibrosis Foundation, it affects a similar number of patients in Europe. There is a commercially available genetic test to determine if a patient's CF is caused by a nonsense mutation, and it is estimated that nonsense mutations are the cause of CF in approximately 10% of patients in the United States. There is currently no available therapy to correct defective CFTR production and function. Instead, available treatments for CF are designed to alleviate the symptoms of the disease. These treatments include chest physical therapy to clear the thick mucus from the lungs, antibiotics to treat lung infections and a mucus-thinning drug designed to reduce the number of lung infections and improve lung function. In addition, the majority of cystic fibrosis patients take pancreatic enzyme supplements to assist with food absorption in digestion. There is a significant unmet medical need for treatments that address the underlying cause of CF. More information regarding CF is available through the Cystic Fibrosis Foundation (www.cff.org).

About PTC124

PTC124 is an orally delivered investigational new drug for the treatment of genetic disorders due to nonsense mutations. Nonsense mutations are single-point alterations in the genetic code that prematurely stop the translation process, preventing production of a functional protein. In Phase 2a clinical trials in nonsense-mutation-mediated cystic fibrosis (CF) and in nonsense-mutation-mediated Duchenne muscular dystrophy (DMD), PTC124 has demonstrated the ability to produce functional protein across a variety of nonsense mutation types. Across all clinical studies to date, PTC124 has been generally well tolerated and has achieved target plasma concentrations that have been associated with activity in preclinical models. PTC124 is currently in Phase 2b development with the goal of demonstrating that increasing functional protein levels in patients with nonsense-mediated genetic disorders may provide clinical benefits.

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. For more information, visit the company's website, www.ptcbio.com.

CONTACT: Investors and Media, Jane Baj of PTC Therapeutics, Inc.,+1-908-912-9167, ; or Sheryl Seapy of Pure Communications,+1-949-608-0841, , for PTC Therapeutics,Inc.; or Patients, Patients' Families, and Patient Organizations, DianeGoetz of PTC Therapeutics, Inc., +1-908-912-9256, jbaj@ptcbio.com sheryl@purecommunicationsinc.com patientinfo@ptcbio.com

Web site: http://www.ptcbio.com/

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Posted: June 2008

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