Proteostasis Receives Endorsement from the Cystic Fibrosis Foundation's Therapeutic Development Network for the Study of the Company's Amplifier, PTI-428, in CF Subjects on Background Symdeko™ Therapy

CAMBRIDGE, Mass., April 17, 2018 /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) and other diseases caused by dysfunctional protein processing, announced today that the Company's study protocol to investigate PTI-428 in CF patients on background Symdeko™ (tezacaftor/ivacaftor) therapy has received endorsement from the Therapeutics Development Network (TDN), the drug development arm of the Cystic Fibrosis Foundation (CFF).  The Phase 2 study is designed to investigate the safety, tolerability and pharmacokinetics (PK) of multiple doses of PTI-428 in a 28-day dosing study.

This will be the Company's next Phase 2 study of PTI-428, a first in class cystic fibrosis transmembrane conductance regulator (CFTR) amplifier, in CF patients. In December, PTI announced the results of a 28-day study in CF subjects on background Orkambi® therapy, in which PTI-428 demonstrated mean absolute improvements in ppFEV₁ of 5.2 percentage points from baseline compared to placebo (p<0.05).

"In in vitro studies of PTI-428, our amplifier complements marketed agents such as ivacaftor, lumacaftor and tezacaftor. This Phase 2 study is the next stepping stone within the broader development path for PTI-428 as an add-on to current CFTR modulator therapies as well as future options which could have Symdeko components as their backbone." said Meenu Chhabra, Proteostasis Therapeutics' President and Chief Executive Officer.

"We believe PTI-428 holds the promise of improving treatment efficacy for currently underserved segments of the CF population, as well as for those who have experienced a decline in lung function over time while on Orkambi. We are grateful and humbled to receive TDN endorsement for this latest study of PTI-428 and we plan to start dosing CF patients in the third quarter of this year. We aim to share initial results in early 2019. This study will allow us to broaden the planned pivotal trial next year that includes subjects on either Orkambi or Symdeko background therapy." concluded Ms. Chhabra.

TDN's support of the PTI-428 study in CF patients on background Symdeko therapy is the third PTI study protocol to receive TDN endorsement, adding to the existing endorsements of PTI-801 and the Company's proprietary triple combination study of PTI-428, PTI-801 and PTI-808.

Dr. Jennifer Taylor-Cousar from National Jewish Health in Denver and a lead investigator for the PTI-428 study in CF subjects on Symdeko therapy said, "As genotype agnostic CFTR modulators with a novel mechanism of action, amplifiers have the potential to provide benefit across various mutation classes and across complementary background therapies, including correctors and potentiators."

In the U.S., upon the protocol endorsement, the TDN provides access to 89 accredited care centers with demonstrated expertise in clinical research, and supports study participant recruitment and execution of studies.  Since its founding in 1998, the TDN has conducted more than 130 clinical studies for CF, including studies of CFTR modulators.

About PTI-428

PTI-428 is a first in class investigational CFTR amplifier for the treatment of CF in patients who are homozygous for the F508del mutation. PTI-428 is designed to act by increasing the amount of newly synthesized CFTR protein and act synergistically with other CFTR modulators, such as correctors and potentiators. PTI-428 is in development as an add-on therapy to approved CFTR modulator products such as Orkambi and Symdeko, as well as part of PTI's proprietary triple combination regimen that includes PTI-808, a potentiator, and PTI-801, a corrector. PTI-428 has received Fast Track, Orphan Drug and Breakthrough Therapy designations by 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 Cambridge, MA, the Proteostasis Therapeutics team focuses on identifying therapies that restore protein function. In addition to its multiple programs in cystic fibrosis, Proteostasis Therapeutics has formed a collaboration with Astellas Pharma, Inc. to research and identify therapies targeting the Unfolded Protein Response (UPR) pathway.

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 expected timing of the initiation of, patient enrollment in, data from, and the completion of, our clinical studies and cohorts for PTI-428 and the expected benefits of TDN endorsement.  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 FDA protocol comments delay or do not permit trial commencement, or the FDA 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, 2017 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.

Orkambi® and Symdeko™ are trademarks of Vertex Pharmaceuticals Incorporated.

CONTACTS:

Investors:
David Pitts
Argot Partners
212.600.1902
david@argotpartners.com

Media:
David Rosen
Argot Partners
212.600.1902
david.rosen@argotpartners.com

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SOURCE Proteostasis Therapeutics, Inc.