Biogen Shares Rise After Alzheimer's Drug Diranersen Shows Promise in Mid-Stage Trial

Biogen Inc. (NASDAQ: BIIB) shares rose Tuesday after the company presented positive data from a mid-stage trial of its investigational Alzheimer’s treatment, diranersen. The company reported that the drug slowed cognitive decline and reduced key protein biomarkers, prompting it to plan for a late-stage Phase 3 study.

Key Trial Results

Data from the Phase 2 CELIA study, presented at the Alzheimer’s Association International Conference, showed the drug had a clinical benefit across all doses at 18 months. According to Biogen, the 60 mg dose demonstrated the strongest response, slowing clinical decline by 42% on the ADAS-Cog13 cognitive scale and 50% on the MMSE cognitive endpoint.

On a separate measure, the Clinical Dementia Rating-Sum of Boxes (CDR-SB), the 60 mg dose showed a 26% slowing of decline. However, the company noted that the study did not meet its primary endpoint of demonstrating a dose-dependent response on the CDR-SB scale at 18 months.

Biogen also highlighted that diranersen is the first tau-directed therapy to show reductions in both total tau protein in cerebrospinal fluid (mean reductions of 50-65%) and brain tau pathology as measured by PET scans. The buildup of tau is a key hallmark of Alzheimer's disease.

Market Reaction and Path Forward

Ad

Following the announcement, Biogen's stock climbed 2% in Tuesday trading. The company confirmed it plans to advance diranersen into a Phase 3 development program based on the overall results.

Diranersen is an antisense oligonucleotide (ASO) therapy that works by targeting the MAPT mRNA to lower the production of the tau protein. The U.S. Food and Drug Administration (FDA) granted the drug Fast Track designation for the treatment of Alzheimer's disease in 2025.

Study Details and Safety

The CELIA study enrolled 416 participants with early-stage Alzheimer's disease. Biogen stated that the treatment was generally well tolerated, with most adverse events categorized as mild or moderate in severity. The most frequently reported adverse events were procedural pain, post-lumbar puncture syndrome, and confusional state.

More than 90% of the participants who completed the 18-month placebo-controlled period elected to continue into an extension study, indicating a high level of patient retention.