Prothena Presents Phase 1 Study Results of PRX004 in Oral Presentation at AAN 2021

• Slowing of neuropathy progression for all 7 evaluable patients, evidenced by a +1.29 point mean change in NIS, was more favorable than expected progression of +9.2 points
• Improvement in neuropathy for 3 of these 7 evaluable patients demonstrated by a mean change in NIS of -3.33 points
• Improvement in cardiac function for all 7 evaluable patients demonstrated by a decrease in global longitudinal strain (GLS)
• Emerging Science Oral Presentation today at AAN 2021

DUBLIN, Ireland, April 18, 2021 (GLOBE NEWSWIRE) -- Prothena Corporation plc (NASDAQ:PRTA) today presented positive results from the Phase 1 study of PRX004 as part of the Emerging Science Session at the American Academy of Neurology (AAN) 2021 Virtual Annual Meeting. PRX004 showed favorable results as demonstrated by slowing of neuropathy progression for all 7 evaluable patients at 9 months, including improvement in neuropathy in 3 of the 7 patients, and improved cardiac systolic function for all 7 patients. In this Phase 1 study, PRX004 was found to be generally safe and well tolerated across all dose levels. The positive results were presented by Dr. Ole Suhr, Senior Professor, Department of Public Health and Clinical Medicine, Umeå University, gastroenterologist and internist who was a principal investigator in the study and were previously highlighted by Prothena on December 9, 2020.

For all of the evaluable patients, slowing of neuropathy progression was demonstrated by a mean change from baseline in Neuropathy Impairment Score (NIS) of +1.29 points at 9 months. This compares favorably to a calculated mean change in NIS of +9.2 points at 9 months in untreated and placebo-treated patients with hereditary ATTR peripheral neuropathy (hATTR-PN) based on analysis of published historical data. In addition, the change in NIS for each of these evaluable patients was more favorable than the published historical data. In this highly progressive disease, it was encouraging to see 3 of 7 patients demonstrate improvement in neuropathy with a mean change in NIS of –3.33 points at 9 months. These positive results were observed in patients with or without concomitant use of stabilizer therapy. PRX004 also demonstrated improvement in cardiac systolic function in each of the 7 evaluable patients, with a mean change in GLS of –1.21% at 9 months (centrally read). For the 3 patients who improved on NIS, GLS improvement was more pronounced, with a mean change of –1.51% at 9 months. Taken together, these positive clinical findings suggest PRX004’s depleter mechanism of action can result in benefits in both neuropathy and cardiac function.