Proteostasis Therapeutics Stumbles Despite Positive Early Stage Data

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Proteostasis Therapeutics Inc. (NASDAQ: PTI) saw its shares slide early on Thursday after the company reported that it had positive data from its early stage trial in cystic fibrosis (CF). These results come from the firm’s ongoing Phase 1 dosing study of PTI-801 in CF patients on background Orkambi (lumacaftor/ivacaftor) therapy.

Ultimately, Proteostasis believes these results support the goal of studying PTI-801 as part of its proprietary double and triple combination therapy regimens.

The company issued its results as follows:

Safety and PK results were as expected. At higher doses, PTI-801 demonstrated a statistically significant improvement in sweat chloride (SC) and body mass index (BMI) in the 14-day treatment period. Overcoming the typical acute drop in FEV1 associated with lumacaftor exposure, an improvement in percent predicted forced expiratory volume (ppFEV1) was observed across all dose cohorts, although the change was not statistically significant. Two thirds of subjects in all PTI-801 cohorts were above ppFEV1 baseline by the end of the treatment period and approached baseline by the end of the 7-day follow up period. In hyperglycemic CFRD subjects, PTI-801 led to a statistically significant normalization of glucose levels at the three dose levels analyzed.

PTI-801 was generally well tolerated. The majority of adverse events were mild or moderate. The most common adverse events were pulmonary exacerbations (10%), regardless of treatment group. There was one discontinuation due to an adverse event in the PTI-801 100 mg treatment group (constipation) prior to the first dose of the study drug.

Manu Jain, M.D., lead investigator of the study and Professor of Medicine, Pulmonary and Critical Care, at Northwestern Medicine, commented:

Sweat chloride is the first diagnostic test to identify CF patients and the reduction of mean SC concentration levels to 55 mmol, levels below the CF disease diagnostic criteria, after only two weeks of treatment, is very encouraging and I believe a clear sign of a pharmacological effect of PTI-801. This is the first time the addition of a novel CFTR corrector in Orkambi treated CF subjects has improved sweat chloride values to Kalydeco-like levels.

Shares of Proteostasis traded down almost 35% Thursday morning to $3.20. The consensus analyst price target is $15.25, and a 52-week range of $1.41 to $8.61.