Immunocapture-LC-MS/MS Method for Quantification of the Anti-Alzheimer’s Monoclonal Antibody Donanemab in Human and Mice Serum

Monoclonal antibodies hold significant promise for the treatment of Alzheimer's disease (AD), and donanemab is the latest therapeutic human IgG1 antibody approved for clinical use. The development and pharmacokinetic evaluation of antibody drugs necessitate accurate quantification. Currently, immunoassays are mainly used by clinical trials to measure those antibody drugs for AD. However, immunoassays often face limitations such as cross-reactivity, insufficient specificity, and poor interlaboratory comparability. Therefore, we developed a robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method incorporating immunoaffinity enrichment for serum donanemab. This LC-MS/MS method can effectively distinguish donanemab from endogenous immunoglobulins in serum and have sufficient sensitivity. This developed LC-MS/MS method involved: (1) immunoaffinity capture and enrichment of serum donanemab and its internal standard using protein G-conjugated magnetic beads; (2) tryptic digestion of the purified antibodies; and (3) targeted quantification of unique signature peptides via LC-MS/MS for quantification. In conclusion, this method demonstrated acceptable performance, including a lower limit of quantification of 0.1 μg/mL, satisfactory precision (total CV < 8%), high accuracy (95-100% recovery), and a wide linear range (0.2-200 μg/mL), and is the first reported LC-MS/MS method for donanemab offering an alternative for therapeutic antibody monitoring of monoclonal antibody drugs.