Background Bioanalytically validated methods are needed for reliable measurement of B cell maturation antigen (BCMA) in clinical samples. BCMA contributes to multiple myeloma (MM) pathophysiology and is targeted by various novel immunotherapies. Soluble BCMA (sBCMA) is a promising novel biomarker for disease monitoring and prediction. To address the need for sBCMA measurement, we developed a mass spectrometry-based assays for the quantitation of total sBCMA in plasma.
Methods Immunoaffinity enrichment of sBCMA from human plasma was performed on a Agilent AssayMap Bravo platform using streptavidin cartridges. Recovered sBCMA protein was digested to peptides using trypsin, spiked with a fixed level of stable isotope labeled (SIL) peptide standard, and analyzed by multiple-reaction-monitoring (MRM) mass spectrometry. The MRM assay targeted a BCMA-specific endogenous peptide used as a surrogate measure of the protein, as well as the corresponding spiked SIL peptide at known concentration. An 8-point external calibration curve was prepared by spiking varying amounts of recombinant BCMA and fixed amounts of SIL peptides in surrogate matrix. Endogenous sBCMA levels were determined by back-calculating against the curve. To assess the performance of the method, ≥ 2 precision and accuracy runs were performed. To assess the impact of ligand or drug binding on the developed assay, performance of the assay was tested using plasma spiked at a range of concentrations with rhAPRIL, rhBAFF or simulated mAb drug.
Results The developed assay allowed the quantitation of sBCMA from 1 to 1000 ng/mL. The precision and accuracy at different QC levels was within 20% CV and 20% bias. The presence of binding proteins (rhAPRIL, rhBAFF, simulated mAb) did not interfere with the measurement of sBCMA indicating that the assay measures total sBCMA.
Conclusions We have developed an assay for the absolute quantitation of total sBCMA in human plasma. The assay can be analytically validated and deployed for clinical studies with a ~ 3-day turnaround time.
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