Prothena Announces First Human Dosed in Phase 1 Study of PRX003 for the Treatment of Psoriasis and Other Inflammatory Diseases

DUBLIN, Ireland, June 9, 2015 (GLOBE NEWSWIRE) -- Prothena Corporation plc (Nasdaq:PRTA), a late-stage clinical biotechnology company focused on the discovery, development and commercialization of novel protein immunotherapy programs, today announced the successful first human dosing in a Phase 1 clinical trial of its proprietary protein immunotherapy, PRX003. PRX003 is a monoclonal antibody targeting melanoma cell adhesion molecule (MCAM) for the potential treatment of psoriasis and other inflammatory diseases.

"PRX003, our third program to advance into clinical development, further demonstrates our commitment to develop a robust pipeline of protein immunotherapies that have the potential to transform patients' lives," said Gene Kinney, PhD, Chief Scientific Officer and Head of Research and Development for Prothena. "MCAM allows disease-causing immune cells to migrate into the surrounding tissues to initiate and/or maintain a pathogenic process and we believe that blocking this process holds tremendous promise for the treatment of inflammatory diseases. We look forward to assessing the safety and tolerability of PRX003 in subjects through this Phase 1 single ascending dose study and also expect to initiate a multiple ascending dose study in patients with psoriasis in 2016."

The Phase 1 clinical trial is a randomized, double-blind, placebo-controlled, single ascending dose study designed to assess the safety, tolerability, pharmacokinetics and immunogenicity of PRX003. Prothena plans to enroll up to 40 subjects in the U.S.

About PRX003

PRX003 is a monoclonal antibody for the potential treatment of psoriasis and other inflammatory diseases. Within the immune system, Th-17 white blood cells initiate the body's response to infections, and are known to be a key participant in both normal inflammatory reactions and autoimmune diseases. MCAM is expressed on the surface of Th-17 cells, and allows certain cells traveling in the blood stream to leave the circulation and enter tissues, primarily to initiate or continue a disease process. PRX003 is designed to block MCAM and not allow the migration of these pathogenic cells into tissues. PRX003 may be useful for treating a variety of inflammatory diseases such as psoriasis, psoriatic arthritis, rheumatoid arthritis, multiple sclerosis, sarcoidosis, uveitis, vasculitis, and Behcet's disease. For more information about the ongoing Phase 1 clinical study of PRX003, please visit www.clinicaltrials.gov and search identifier NCT02458677.

About Prothena

Prothena Corporation plc is a late-stage clinical biotechnology company focused on the discovery, development and commercialization of novel protein immunotherapy programs for the potential treatment of diseases that involve amyloid or cell adhesion. The company is developing antibody-based product candidates that target a number of potential indications including AL amyloidosis (NEOD001), Parkinson's disease and other related synucleinopathies (PRX002), and psoriasis and other inflammatory diseases (PRX003).

For more information, please visit the company's web site at www.prothena.com.

Forward-looking Statements

This press release contains forward-looking statements. These statements relate to, among other things,the timing of initiating a multiple ascending dose study of PRX003; enrollment in the single ascending dose study of PRX003; and the potential clinical benefits of PRX003. These statements are based on estimates, projections and assumptions that may prove not to be accurate, and actual results could differ materially from those anticipated due to known and unknown risks, uncertainties and other factors, including but not limited to the risks, uncertainties and other factors described in the "Risk Factors" sections of our Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on March 13, 2015 and our subsequent Quarterly Reports on Form 10-Q filed with the SEC. Prothena undertakes no obligation to update publicly any forward-looking statements contained in this press release as a result of new information, future events or changes in Prothena's expectations.

CONTACT: Investors:  Tran Nguyen, CFO
         650-837-8535, IR@prothena.com
         
         Media:  Angela Bitting
         925-202-6211, angela.bitting@prothena.com