Abstract
INTRODUCTION: Semorinemab, an anti-tau monoclonal antibody, was assessed in two Phase II trials for Alzheimer's disease (AD). Plasma and cerebrospinal fluid (CSF) biomarkers provided insights into the drug's potential mechanism of action. METHODS: Qualified assays were used to measure biomarkers of tau, amyloidosis, glial activity, neuroinflammation, synaptic function, and neurodegeneration from participant samples in Tauriel (NCT03289143) and Lauriet (NCT03828747) Phase II trials. RESULTS: Plasma phosphorylated Tau 181 (pTau181) and CSF chitinase-3-like protein 1 (YKL-40) increased following semorinemab treatment in both studies. In Lauriet, increasing plasma glial fibrillary protein (GFAP) concentrations stabilized with semorinemab, while this was not observed in Tauriel. Other AD pathophysiology biomarkers showed no consistent response to semorinemab. DISCUSSION: Increases in CSF YKL-40 suggest that semorinemab may stimulate microglia activation in the presence of AD-associated Tau pathology, but not in healthy controls. Stabilization of plasma GFAP in Lauriet indicates a possible impact on reactive gliosis in mild-to-moderate AD. TRIAL REGISTRATION: Tauriel ClinicalTrials.gov Identifier: NCT03289143. Lauriet ClinicalTrials.gov Identifier: NCT03828747. Phase 1 ClinicalTrials.gov Identifier: NCT02820896. HIGHLIGHTS: AD pathophysiology biomarkers were measured to assess the mechanism of action. Semorinemab increased CSF YKL-40 in participants with AD but not in healthy controls. Semorinemab possibly stabilized plasma GFAP in the Lauriet trial. Semorinemab treatment may activate microglia and moderate reactive gliosis.