Prothena is laying off almost two-thirds of its workforce as the Irish biotech navigates the fallout from giving up on its failed amyloidosis drug.
In May, the company announced the failure of the monoclonal antibody birtamimab to improve mortality in a phase 3 trial of patients with Mayo stage IV AL amyloidosis. At the time, Prothena warned this clinical setback meant that as well as canning birtamimab for good, the biotech would require a “substantial reduction in organizational size.”
The details of that reorganization have now become clear and involve laying off 63% of Prothena’s workforce, the company explained in a post-market release June 18. The biotech entered 2025 with 163 employees.
“We have incredible Prothenians who are among the industry’s most talented professionals and have dedicated their careers to advancing new treatments for patients,” CEO Gene Kinney, Ph.D., said in the release. “I want to express my sincere gratitude to each Prothenian being affected by today’s announcement and thank them for their passion toward our mission to treat diseases caused by protein dysregulation.”
The updated strategy means Prothena now expects to end the year with $298 million still in the bank despite an estimated net loss of up to $248 million for 2025. This loss will likely include about $36 million in compensation expenses and up to $110 million in operating expenses associated with birtamimab, the company explained.
Prothena has other readouts coming up, but its most advanced assets after birtamimab are partnered with Bristol Myers Squibb, Novo Nordisk and Roche. Initial phase 1 data on PRX012, Prothena’s most advanced wholly owned asset, in Alzheimer’s disease are due in August.
In potential good news for Prothena, Roche announced earlier this week that it will advance Prothena-partnered prasinezumab into phase 3 trials for early-stage Parkinson’s disease, despite the monoclonal antibody’s failure in a midstage study last year.
Prothena had previously stuck with its amyloidosis drug birtamimab in the face of its own phase 2 failure back in 2018, which resulted in a separate wave of layoffs. The biotech resurrected the program in 2021 in response to a post hoc analysis of some early phase 3 data that linked birtamimab to significant improvement in all-cause mortality in a subset of high-risk patients. Unfortunately for Prothena, that show of faith wasn’t enough to ensure birtamimab’s survival after last month’s clinical miss.