Japanese pharmaceutical company Eisai Co., Ltd. (TYO: 4523) on Monday reported new findings showing that its investigational anti-MTBR antibody etalanetug (E2814) reduced levels of plasma eMTBR-tau243, a biomarker linked to tau tangle pathology in Alzheimer's disease.

The blood biomarker assay measuring eMTBR-tau243 was developed as a potential alternative to cerebrospinal fluid (CSF) and Positron Emission Tomography (PET) testing, and the analysis compared plasma and CSF tau changes in participants with dominantly inherited Alzheimer's disease enrolled in the Phase Ib/II Study 103.

Etalanetug was found to reduce CSF eMTBR-tau243 by 62% at three months and 89% at nine months, while plasma eMTBR-tau243 levels fell by 78% at three months and by more than 90% at nine months.

Plasma phosphorylated tau species and t-tau increased after etalanetug administration in both Dominantly Inherited Alzheimer's Disease (DIAD) patients and healthy adults. Plasma eMTBR-tau243 was largely absent in healthy adults and detected only in DIAD patients, with levels reduced following treatment.

Etalanetug also reduced multiple CSF phosphorylated tau species and t-tau in DIAD patients, including p-tau205, a late-stage tau pathology marker.

Etalanetug is designed to inhibit propagation of tau seeds in the brain and is being developed as a potential disease-modifying therapy for tauopathies, including sporadic Alzheimer's disease. It is currently being evaluated in the Tau NexGen Phase II/III DIAD trial under DIAN-TU and in the Phase II Study 202, both assessing etalanetug added to lecanemab. The therapy received Fast Track designation from the US Food and Drug Administration in September 2025.