Prothena Announces Phase 3 VITAL Clinical Trial Results Published in Blood Showing Survival Benefit in Patients with Mayo Stage IV AL Amyloidosis Treated with Birtamimab

Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today announced the publication of the Phase 3 VITAL clinical trial in Blood, a journal of the American Society of Hematology (ASH). The published data demonstrate that in a post hoc analysis of patients with Mayo Stage IV AL amyloidosis, a statistically significant survival benefit of 74 percent was observed for those treated with birtamimab plus standard of care (SOC) versus 49 percent in patients on placebo plus SOC at 9 months (HR 0.413, p=0.021). All participants in the clinical trial received concomitant bortezomib-containing chemotherapy regimens as part of SOC.

“For the first time, we have these important data published in a prestigious, peer-reviewed journal which show that treatment with birtamimab led to a survival benefit in patients with Mayo Stage IV AL amyloidosis and affirms its potential as a safe, well-tolerated and effective therapy,” said Morie Gertz, MD, Hematologist, Chair emeritus Internal Medicine, Mayo Clinic. “AL amyloidosis is a rare and life-threatening disease in which patients have no treatment options despite the high fatality rate. We look forward to learning more about the survival benefit of birtamimab in patients with Mayo Stage IV AL amyloidosis from the confirmatory Phase 3 AFFIRM-AL clinical trial.”

The article, entitled “Birtamimab plus standard of care in light chain amyloidosis: the phase 3 randomized placebo-controlled VITAL clinical trial”, also includes new data showing that there was no observed difference in hematologic response rates between the control arm and the treatment arms which suggests the survival benefit of birtamimab was not due to improved hematologic response, which is consistent with birtamimab’s depleter mechanism of action.

For two secondary endpoints, birtamimab demonstrated statistically significant improvements over placebo in a post hoc assessment of patients with Mayo Stage IV AL amyloidosis. The secondary endpoints were quality of life (assessed with the Short Form-36 version 2 physical component score, SF-36v2 PCS) and cardiac function (assessed with the 6-minute walk test). Patients treated with birtamimab showed a slower decline in quality of life with a mean decrease of 0.75 in the SF-36v2 PCS at 9 months compared to a mean decrease of 5.40 in the SF-36v2 PCS for patients on placebo at 9 months (a mean difference of 4.65 favoring birtamimab; p=0.046). Patients treated with birtamimab after 9 months demonstrated an increase in mean distance of 15.22 meters in the 6-minute walk test, compared to a decrease in mean distance of 21.15 meters for patients on placebo (a mean difference of 36.37 meters favoring birtamimab; p=0.022).