Prothena Announces Major Layoffs Following Phase 3 Amyloidosis Drug Failure

Prothena Corporation, an Irish biotech company, has announced a significant restructuring following the failure of its phase 3 amyloidosis drug trial. The company will lay off 63% of its workforce as it navigates the fallout from abandoning birtamimab, its once-promising monoclonal antibody treatment for Mayo Stage IV AL amyloidosis.

Restructuring and Financial Outlook

The substantial reduction in Prothena's organizational size comes after the company entered 2025 with 163 employees. Despite the projected net loss of up to $248 million for 2025, Prothena expects to end the year with $298 million in cash reserves. This financial cushion includes an estimated $36 million in compensation expenses and up to $110 million in operating expenses associated with the discontinued birtamimab program.

CEO Gene Kinney, Ph.D., expressed gratitude to the affected employees, stating, "We have incredible Prothenians who are among the industry's most talented professionals and have dedicated their careers to advancing new treatments for patients."

Pipeline Updates and Partnerships

While the failure of birtamimab represents a significant setback, Prothena maintains a diverse pipeline with several ongoing collaborations:

• Initial phase 1 data for PRX012, Prothena's most advanced wholly owned asset for Alzheimer's disease, is expected in August.
• Roche has announced plans to advance prasinezumab, a Prothena-partnered monoclonal antibody, into phase 3 trials for early-stage Parkinson's disease. This decision comes despite the treatment's failure in a mid-stage study last year.
• The company continues to work with partners Bristol Myers Squibb and Novo Nordisk on other pipeline assets.

Historical Context and Future Prospects

This is not the first time Prothena has faced setbacks with birtamimab. The company previously encountered a phase 2 failure in 2018, which also resulted in layoffs. However, Prothena resurrected the program in 2021 based on a post hoc analysis of early phase 3 data that suggested improved all-cause mortality in high-risk patients.

As Prothena refocuses its efforts on its remaining pipeline and partnerships, the company faces the challenge of rebuilding investor confidence and advancing its other promising candidates through clinical development.