Quantification of serum daratumumab in multiple myeloma patients by LC-MS/MS, comparison with ELISA.

Daratumumab is a fully human immunoglobulin G1 monoclonal antibody employed for treating relapsed/refractory multiple myeloma and light-chain amyloidosis. Quantifying monoclonal antibodies in serum presents challenges due to interference from biological matrices. This research aimed to develop and verify an liquid chromatography tandem-mass spectrometry (LC-MS/MS) approach for quantifying serum daratumumab, employing immunoglobulin G purification without alkylation, and to assess its applicability in patients with multiple myeloma receiving intravenous daratumumab. The chromatographic peaks of the daratumumab-derived peptides and internal standard were well-delineated from the serum digests, with an overall run time of 14 min. The calibration curves for serum daratumumab were linear across over 1-1000 μg/mL. The inter- and intra-day accuracy varied between 92.4 % and 108.4 %, with a coefficient-of-variation below 10 %. In patients receiving intravenous daratumumab, serum concentrations ranged from 181.8 to 975.3 µg/mL. Bland-Altman analysis revealed no significant bias, and Passing-Bablok regression demonstrated a good agreement between the LC-MS/MS method and enzyme-linked immunosorbent assay.