Eisai Co., Ltd. has announced promising findings for its investigational anti-MTBR antibody, etalanetug, which demonstrated a reduction in plasma eMTBR-tau243, a key biomarker associated with Alzheimer's disease (AD) tau tangle pathology. The results were shared at the Alzheimer’s Association International Conference 2026.
Etalanetug targets the microtubule-binding region of tau protein, potentially preventing the progression of tau pathology in the brain. Tau tangles are a hallmark of Alzheimer's and are linked to memory loss and cognitive decline. The investigational drug reduced plasma eMTBR-tau243 by 78% at three months and over 90% at nine months, closely mirroring changes observed in cerebrospinal fluid (CSF).
The study also noted increases in plasma phosphorylated tau species and t-tau levels after etalanetug administration, attributed to the stabilization of non-CNS tau species in peripheral tissues. Plasma eMTBR-tau243 was largely absent in healthy adults, suggesting its specificity to disease-related tau pathology.
Etalanetug's impact on tau pathology in the brain was further evidenced by reductions in multiple CSF phosphorylated tau species, including p-tau205, a marker of late-stage tau pathology. This marks the first report of an anti-tau therapy reducing CSF p-tau205 in patients with dominantly inherited Alzheimer’s disease (DIAD).
The development of plasma eMTBR-tau243 as a less invasive biomarker could play a significant role in future clinical developments. Etalanetug is currently being evaluated in ongoing clinical studies, including the Tau NexGen Phase II/III trial in DIAD and a Phase II global trial in early sporadic AD, both in combination with lecanemab.
In September 2025, etalanetug received Fast Track designation from the U.S. Food and Drug Administration, underscoring its potential as a disease-modifying therapy for tauopathies.
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