Prilenia Achieves Last Patient Last Visit in Phase 3 PROOF-HD Clinical Study for Huntington's Disease

Prilenia Therapeutics B.V., a clinical stage biotechnology company focused on the urgent mission to develop novel therapeutics to slow the progression of neurodegenerative diseases and neurodevelopmental disorders, today announced that the last participant in PROOF-HD, a global Phase 3 study in Huntington's disease (HD), has completed the last planned visit of the blinded treatment period, marking the completion of the main study. Almost all patients (98 percent) that were eligible elected to continue in the ongoing open-label extension of PROOF-HD. Topline results of the PROOF-HD study are expected in early Q2 2023.

The PROOF-HD study has been conducted with the Huntington Study Group (HSG), a world leader in clinical research for HD and valued collaborator for Prilenia.

"There is an urgent need for treatments that can alter the course of HD and bring hope to individuals and families impacted by the disease," said Dr. Michael R. Hayden, CEO and Founder of Prilenia. "Our team is working diligently to bring topline results to the community as quickly as possible. We thank the Huntington Study Group and their partners, study investigators, and most importantly study participants and their families for their contribution to this important research."

PROOF-HD is a Phase 3, randomized, double-blind, placebo-controlled study evaluating the safety and efficacy of pridopidine (45 mg twice daily for 65 to 78 weeks), an oral, highly selective and potent investigational sigma-1 receptor (S1R) agonist, in individuals with HD. The aim of the study is to evaluate pridopidine's ability to preserve the functional ability of individuals living with HD, with a primary endpoint of a change from baseline in the Unified Huntington Disease Rating Scale-Total Functional Capacity (UHDRS-TFC) score at 65 weeks. The trial enrolled 499 individuals and was conducted in the U.S., Canada, Austria, Czech Republic, France, Germany, Italy, the Netherlands, Poland, Spain and the United Kingdom. The study was completed on time and as planned.

About Pridopidine

Pridopidine (45 mg twice daily) is an oral, highly selective and potent investigational S1R agonist that has exhibited a safety and tolerability profile similar to placebo in clinical studies to date. The S1R protein is highly expressed in the brain and spinal cord where it regulates several key processes that are commonly impaired in various neurodegenerative diseases. Activation of the S1R by pridopidine stimulates multiple cellular pathways, including autophagy, axonal transport, mitochondrial energy production, and calcium homeostasis which are essential to neuronal function and survival and may lead to neuroprotective effects.

Prilenia holds Orphan Drug designation for pridopidine in HD and ALS in the U.S. and EU. In addition, pridopidine has received Fast Track designation by the U.S. Food and Drug Administration (FDA) for the treatment of HD.

About Prilenia

Prilenia is a clinical stage biotechnology company founded in 2018 focused on the urgent mission to develop novel therapeutics to slow the progression of neurodegenerative diseases and neurodevelopmental disorders.

Prilenia is backed by a group of well-respected investors including: Forbion, Morningside, Sands Capital, SV Health Investors, Sectoral Asset Management, Talisman, Amplitude Ventures and the ALS Investment Fund. The Company is based in Naarden, the Netherlands, Herzliya, Israel and Waltham, Massachusetts in the U.S.

For more information visit www.prilenia.com and follow us on LinkedIn and Twitter.

About Huntington Study Group / HSG Clinical Research, Inc.

Founded in 1993 in Rochester, NY, the Huntington Study Group (HSG) is a not-for-profit organization composed of the world's first and largest collaborative network of over 800 experts in Huntington's disease at more than 130 HSG credentialed research sites worldwide. HSG Clinical Research, Inc., a wholly owned subsidiary of the HSG, is a full-service clinical research organization that specializes in conducting HD trials. The HSG also offers educational services for healthcare professionals and care providers on treating patients with HD. For more information, visit www.huntingtonstudygroup.org.

^©2023 Prilenia Therapeutics B.V.

For a copy of this release, visit Prilenia's website at www.prilenia.com.