Proteostasis Announces Formation of Independent Steering Committee of Leading Experts to Advise on t

Program to Pursue Broad Label for PTI-428 as an Add-On Therapy to CFTR Modulator Based Treatment

BRIGHTON, Mass., May 8, 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 the formation of an independent Steering Committee to guide the Phase 3 global clinical development program for PTI-428. This Steering Committee of leading CF experts will advise on the design and implementation of the Phase 3 global clinical program for PTI-428, the Company's novel cystic fibrosis transmembrane conductance regulator (CFTR) amplifier. PTI-428 is in development as an add-on therapy to approved CFTR modulator products such as Orkambi® and Symdeko™, and as part of PTI's proprietary once-a-day triple combination regimen that includes the potentiator PTI-808 and the corrector PTI-801.

"We are thrilled to have recruited such a distinguished group of clinicians and researchers to our PTI-428 Phase 3 Program Steering Committee," said Meenu Chhabra, Proteostasis Therapeutics' President and Chief Executive Officer. "Chaired by Dr. Jennifer Taylor-Cousar, this committee will provide invaluable guidance to PTI's Phase 3 development strategy pursuing a broad indication for PTI-428 as an add-on to CFTR small molecule modulator based treatment. With the help of these leaders in the field of CF, we aim to demonstrate the potential of PTI-428 to improve the efficacy of current or future standard of care."

"Cystic fibrosis treatment has greatly advanced in recent years, but people with CF across the spectrum of known mutations are still in need of new or additional therapeutic options," said Jennifer Taylor-Cousar M.D., M.S.C.S., the Steering Committee Chair and Associate Professor of Medicine and Pediatrics at the National Jewish Health. "As the FDA recently underscored by granting Breakthrough Therapy Designation to this genotype agnostic investigational CFTR modulator, PTI-428 holds the potential of providing benefit to currently underserved segments of the population of people with CF, and potentially improving the efficacy of available disease modifying treatments. I look forward to working with my esteemed colleagues on this Steering Committee to design a Phase 3 program for PTI's amplifier that could potentially provide evidence of its ability to improve the quality of life for a significant portion of the CF community."

The members of the PTI-428 Phase 3 Steering Committee are:

Jennifer L. Taylor-Cousar, M.D., M.S.C.S., is the Chair of the PTI-428 Phase 3 Program Steering Committee and is an Associate Professor of Medicine and Pediatrics at National Jewish Health, where she is also the co-Director and CF Therapeutics Development Network Director for the Adult CF Program. Dr. Taylor-Cousar was the co-lead investigator for the pivotal study evaluating Symdeko in patients homozygous for F508del, and Dr. Taylor-Cousar is a lead investigator for the PTI-428 study in CF subjects on Symdeko therapy. Dr. Taylor-Cousar earned her B.A. in Human Biology at Stanford University and her M.D. at Duke University and is currently the co-chair of the Vertex Pharmaceuticals Triple Combination Steering Committee.
Mark A. De Rosch Ph.D., FRAPS is a veteran regulatory affairs professional with over 25 years of experience, currently serving at Nightstar Therapeutics as Senior Vice President of Regulatory Affairs and Quality Assurance. His prior experience includes serving in multiple key roles at Vertex Pharmaceuticals, Inc., where he led the regulatory strategy and submissions process for Kalydeco® for CF, leading to approvals in the U.S. and E.U. Dr. De Rosch earned his B.S. at the University of Wisconsin – Parkside and his Ph.D. in Inorganic Chemistry at the University of California, San Diego.
Scott H. Donaldson, M.D., is an Associate Director and Professor of Medicine at the University of North CarolinaClinical and Translational Research Center (CRTC). Dr. Donaldson's clinical and research interests are focused on adults with CF. He was lead author for the Phase 2 study evaluating Symdeko in patients with CF. Dr. Donaldson earned his B.S. in Biology and his M.D. at the University of Michigan.
Patrick Flume, M.D., is a Professor of Medicine and Pediatrics at the Medical University of South Carolina, serving as the Powers-Huggins Endowed Chair for CF. He is recognized as a leader by the national and international CF community, having served as founding co-chair of the CF Foundation (CFF) Pulmonary Practice Guidelines Committee and on multiple other committees for the CFF. Dr. Flume was a principal investigator for the EXTEND study assessing the safety and efficacy of long-term treatment with Symdeko. Dr. Flume earned his M.D. at the University of Texas School of Medicine at San Antonio.
Nicole Mayer Hamblett, Ph.D., is a Professor in the Department of Pediatrics in the Division of Pulmonary Medicine and an Adjunct Professor in the Department of Biostatistics at the University of Washington. Dr. Hamblett is currently the Co-Executive Director of the CFF's Therapeutics Development Network (TDN) Coordinating Center and oversees the design, implementation, and analysis of numerous multicenter CF clinical studies, including co-authorship of the PROGRESS study assessing the long-term efficacy and safety of Orkambi. Dr. Hamblett earned her Ph.D. in Biostatistics at the University of Washington.
Richard B. Moss, M.D., is former chief of the Pediatric Pulmonary and Allergy Divisions, and allergy-immunology and pulmonary fellowship training programs director, at Stanford University. Dr. Moss was Director of the CF Center at Stanford (1991-2009) and site principal investigator for the CFF's TDN (1999-2009), where he was also inaugural Chair of the Protocol Review Committee. Dr. Moss has reviewed and consulted for the NIH, CFF, national and international foundations, peer-review journals and biopharmaceutical companies. In addition, he is a co-author of the PROGRESS study assessing the long-term efficacy and safety of Orkambi. Dr. Moss earned his B.A. at Columbia University and his M.D. at SUNY Downstate.
Carsten Schwarz, M.D., is the Head of the Adult Cystic Fibrosis Centre Department of Pediatric Pneumology and Immunology at Charité – Universitätsmedizin Berlin. Dr. Schwarz's clinical and research interests include evaluation and treatment of infectious pathogens in patients with CF and he is currently a member of the European Cystic Fibrosis Conference Committee. Dr. Schwarz obtained his M.D. from the Humboldt University in Berlin, Germany.

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 increase the amount of newly synthesized CFTR protein and to act synergistically with other CFTR modulators, such as correctors and potentiators. PTI-428 has received Fast Track, Orphan Drug and Breakthrough Therapy designations by the FDA.

In April, the TDN, the drug development arm of the CFF, endorsed Proteostasis' study protocol to investigate PTI-428 in CF patients on background Symdeko (tezacaftor/ivacaftor) therapy. Proteostasis plans to initiate this Phase 2 study in the third quarter of 2018. In December, PTI announced the results of a 28-day Phase 2 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). PTI-428 is also in an ongoing study of the Company's proprietary once-a-day dosing triple combination regimen, which includes the potentiator PTI-808 and the corrector PTI-801. The triple combination study received TDN endorsement and is expected to have preliminary data in the second half of 2018.

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 Brighton, 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 our triple combination study, as well as the intended label for our Phase 3 program. 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 comments delay, change or do not permit trial commencement, or intended label, 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®, Kalydeco® and Symdeko™ are trademarks of Vertex Pharmaceuticals Incorporated.

CONTACTS:

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