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Proteostasis Therapeutics Initiates Dosing in Global Phase 2 Study in Cystic Fibrosis

BOSTON, July 25, 2019 /PRNewswire/ -- Proteostasis Therapeutics, Inc. (NASDAQ: PTI), a clinical stage biopharmaceutical company dedicated to the discovery and development of groundbreaking therapies to treat cystic fibrosis (CF), today announced that the first patient has been dosed in the Company's 28-day, Phase 2 study evaluating its proprietary cystic fibrosis transmembrane conductance regulator (CFTR) modulator combinations in F508del homozygous and heterozygous CF subjects.

Initiation of the 28-day Phase 2 study follows the positive results of the 14-day Phase 1 clinical studies of PTI's proprietary doublet (PTI-808 and PTI-801) and triplet (PTI-808, PTI-801 and PTI-428) combinations. The previous studies demonstrated a favorable safety and tolerability profile for the combinations, as well as statistically significant improvement in percent predicted FEV1 (ppFEV1) and sweat chloride concentration that was superior to the current CFTR modulator standard of care for F508del homozygous patients. The ongoing Phase 2 trial will explore efficacy over a longer duration and in additional genotypes including subjects heterozygous for the F508del mutation with PTI's doublet and triplet combinations. Dose selection (600 mg of PTI-801 and 300 mg or PTI-808, with or without 10 mg PTI-428) was based on the totality of dose range finding data from approximately 250 CF subjects studied thus far.    

"Despite the inclusion of CF subjects colonized with bacteria associated with a more rapid decline in lung function, our doublet and triplet studies have delivered a compelling signal of ppFEV1 improvement," said Geoffrey Gilmartin, M.D., M.M.Sc., Chief Medical Officer of Proteostasis. "By focusing on European centers, our next stage in development will target the recruitment of patients comparable to those used in other CFTR modulator combination studies which, together with optimal dose levels and longer treatment duration, could potentially further enhance the magnitude of pulmonary benefit."

Proteostasis' Phase 2, global, multicenter, randomized, placebo-controlled study is expected to enroll up to 30 F508del homozygous patients and up to 30 F508del heterozygous patients. Study endpoints include safety, changes in sweat chloride concentration and changes in ppFEV1. Data from the study are expected in the first quarter of 2020.  

About PTI-428, PTI-801, PTI-808

PTI-428 is an investigational CFTR amplifier in development for the treatment of CF in patients with at least one F508del mutation in the CFTR gene, as part of PTI's proprietary triple combination regimen that includes PTI-808, a novel potentiator, and PTI-801, a third-generation CFTR corrector. PTI-801 has Fast Track Designation from the U.S. Food and Drug Administration (FDA).  In May 2019, PTI-428 received Orphan Drug Designation (ODD) from the European Commission (EC).  In addition to ODD from the EC, PTI-428 has ODD, Breakthrough Therapy Designation and Fast Track Designation from the FDA. 

About Proteostasis Therapeutics, Inc.

Proteostasis Therapeutics, Inc. is a clinical stage biopharmaceutical company developing small molecule therapeutics to treat cystic fibrosis and other diseases caused by dysfunctional protein processing. Headquartered in Boston, MA, the Proteostasis Therapeutics team focuses on identifying therapies that restore protein function. For more information, visit

Safe Harbor

To the extent that statements in this release are not historical facts, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.  Words such as "aim," "may," "will," "expect," "anticipate," "estimate," "intend," and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements.  Examples of forward-looking statements made in this release include, without limitation, statements regarding the potential of our proprietary combination therapies for the treatment of CF, the potential benefit to patients of our proprietary combination therapies, expected timing of patient enrollment in, data from, the completion of, our clinical studies and cohorts for our clinical programs, including our planned Phase 2 program and initiation of a pivotal study.  Forward-looking statements made in this release involve substantial risks and uncertainties that could cause actual results to differ materially from those expressed or implied by the forward-looking statements, and we, therefore cannot assure you that our plans, intentions, expectations or strategies will be attained or achieved.  Such risks and uncertainties include, without limitation, the possibility final or future results from our drug candidate trials (including, without limitation, longer duration studies) do not achieve positive results or are materially and negatively different from or not indicative of the preliminary results reported by the Company (noting that these results are based on a small number of patients and small data set), uncertainties inherent in the execution and completion of clinical trials (including, without limitation, the possibility that FDA or other regulatory agency comments delay, change or do not permit trial commencement, or intended label, or the FDA or other regulatory agency requires us to run cohorts sequentially or conduct additional cohorts or pre-clinical or clinical studies), in the enrollment of CF patients in our clinical trials in a competitive clinical environment, in the timing of availability of trial data, in the results of the clinical trials, in possible adverse events from our trials, in the actions of regulatory agencies, in the endorsement, if any, by therapeutic development arms of CF patient advocacy groups (and the maintenance thereof), and those set forth in our Annual Report on Form 10-K for the year ended December 31, 2018, our Quarterly Report on Form 10-Q for the quarter ended March 31, 2019 and our other SEC filings.  We assume no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.


David Pitts / Claudia Styslinger
Argot Partners
212.600.1902 /

David Rosen
Argot Partners

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SOURCE Proteostasis Therapeutics, Inc.

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