Proteostasis Therapeutics Snags Breakthrough Designation

Investors in Cambridge, Mass.-based Proteostasis Therapeutics are smiling this morning after the U.S. Food and Drug Administration granted the company’s investigational cystic fibrosis add-on therapy the Breakthrough Therapy Designation.

Shares of company stock skyrocketed more than 50 percent in after-hours trading Monday following the announcement. The FDA awarded the designation to PTI-428, the company’s cystic fibrosis transmembrane conductance regulator (CFTR) amplifier. The FDA made the decision based on data from a Phase II trial that pairs PTI-428 with Vertex’s Orkambi. Meenu Chhabra, president and chief executive officer of Proteostasis, said the FDA designation reflects the strength of the results from the Phase II study.

The Proteostasis drug PTI-428 was combined with Orkambi as a background therapy for the treatment of cystic fibrosis in homozygous patients for the F508del mutation. The 28-day Phase II study results showed that the addition of 50 mg of PTI-428 for 28 consecutive days led to mean absolute improvements in breath measurements in one second. The study showed those patients who received PTI-428 had 5.2 percent improvements in percent predicted forced expiratory volume in 1 second at 14 days. Those improvements continued through 28 days, the company said in December when it first announced the data.

In addition to the improvements in breathing, the Phase II data also showed a positive increase in nasal mucosal CFTR protein in those patients who received the Proteostasis drug. The magnitude of change compared to baseline was consistent with the changes in CFTR protein levels observed in the in vitro human bronchial cell model, the company said. Those patients who received placebo did not show any such improvements, according to Proteostasis.

"PTI-428 can potentially be added to current and future standards of care, offering the potential for improvement in pulmonary function for patients with cystic fibrosis. We look forward to working closely with the FDA as we advance our clinical programs for PTI-428, including as part of our proprietary triple combination with PTI-801 and PTI-808, our third generation corrector and potentiator, respectively," Chhabra said in a statement late Monday.

Investors continue to remain happy with the company this morning. Shares have continued to climb and are up 64 percent as of 9:49 a.m. Shares of Proteostasis are trading at $6.82.

The FDA designation will expedite the development and review of PTI-428 if it goes before the regulatory agency for approval.

In February 2015 Proteostasis unveiled a new class of agents, CFTR Amplifiers, for the treatment of cystic fibrosis. CFTR amplifiers represent a new drug class able to enhance the effect of known cystic fibrosis transmembrane conductance regulator (CFTR) modulating agents, such as potentiators and correctors. The amplifiers are effective across CFTR mutation classes and form the basis for Proteostasis' strategy to develop a broad acting combination therapy able to serve CF patients with most mutations, the company said.

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