A simple LC-MS/MS assay for the quantification of E6011, a novel anti-fractalkine monoclonal antibody, in cynomolgus monkey serum - comparison with ligand binding assay.

E6011 is a monoclonal antibody that is currently under development for the treatment of rheumatoid arthritis. While ligand binding assays (LBAs) are typically employed for the determination of therapeutic antibodies, ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) represents an alternative platform. E6011 in monkey serum was treated with ammonium sulfate to obtain pellets for subsequent processing. The pellets were subjected to denaturalization reduction, alkylation, and tryptic digestion. The resulting signature peptide of E6011, TLADGVPSR, was assayed. The pellet digestion assay was validated in accordance with the established bioanalytical guidelines. E6011 in monkey serum was quantifiable from 3 to 729 µg/mL, with a sample volume of 0.02 mL. The selectivity was confirmed in 12 individual monkey sera. The accuracy and precision were within ± 11.2 % and 15.0 %, respectively. The validated UPLC-MS/MS assay was employed in a pharmacokinetic study in monkeys. After the intravenous dose at 1 mg/kg, E6011 reached the maximum of 27.4 μg/mL, then declined with the half-life of 169 h. The serum E6011 concentrations determined by the UPLC-MS/MS were comparable to those obtained by the LBA with electrochemiluminescence detection. These findings suggest that the established simple UPLC-MS/MS assay is reproducible and can serve as an alternative assay platform.