Biomarker Exposure-Response Analysis in Mild-To-Moderate Alzheimer’s Disease Trials of Bapineuzumab

Background: Bapineuzumab, an anti-amyloid monoclonal antibody, was evaluated as a candidate for immunotherapy in mild-to-moderate Alzheimer's disease (AD) patients. Objective: To assess the treatment effect of bapineuzumab therapy on disease-relevant biomarkers in patients with mild-to-moderate AD, using exposure-response modeling. Methods: Biomarker data from two Phase III studies were combined to model the impact of bapineuzumab exposure on week-71 change from baseline in brain amyloid burden by 11C-labeled Pittsburgh compound B (PiB) PET imaging (global cortical average of the Standardized Uptake Value ratio values), cerebrospinal fluid (CSF) phosphorylated (p)-tau concentrations, and brain volumetrics (brain boundary shift integral) by magnetic resonance imaging. Bapineuzumab or placebo was administered as a 1-hour intravenous infusion every 13 weeks for 78 weeks. Pharmacokinetic/pharmacodynamic modeling helped determine the most appropriate exposure-response model and estimate the impact of disease-relevant covariates (baseline biomarker value, APOE*E4 allele copy number, and baseline disease status as measured by Mini-Mental State Examination score) on the three biomarkers. Results: Linear exposure-response relationships with negative and significant slope terms were observed for PiB PET and CSF p-tau concentration. Baseline biomarker value and APOE*E4 carrier status were significant covariates for both biomarkers. No exposure-response relationship on brain boundary shift integral was detected. Conclusions: Bapineuzumab treatment induced exposure-dependent reductions in brain amyloid burden. Effects on CSF p-tau concentrations were significant only in APOE*E4 carriers. No apparent influence of bapineuzumab exposure on brain volume could be demonstrated.