Simultaneous quantification of total antibody and antibody-conjugated drug for XMT-1522 in human plasma using immunocapture-liquid chromatography/mass spectrometry.

XMT-1522, an antibody-drug conjugate (ADC) currently in Phase I clinical development, represents the first Dolaflexin®-based, cleavable ADC with a high drug-antibody ratio (DAR). In this work, a novel immunocapture LC-MS/MS method was successfully developed for the simultaneous quantification of both total antibody and cleavable antibody-conjugated drug auristatin F-hydroxypropylamide (AF-HPA) in human plasma. This method utilized microwave-assisted enzymatic digestion for the total antibody and chemical release of the drug from ADC on a 96-well based immunocapture sample preparation platform. The total antibody and the conjugated drug AF-HPA were separated and subsequently quantified concurrently by LC-MS/MS. The linear range of the standard curve for total antibody was from 50 to 5000 ng/mL and for AF-HPA was from 3.3 to 330 ng/mL. The linearities showed R2 ≥ 0.993 for total antibody and R2 ≥ 0.996 for AF-HPA, respectively. The intra- and inter-day precision and accuracy were well within 15%. The validated method, with the characteristics of high efficiency, great selectivity, free of carryover, short LC-MS/MS time (˜3.5 min) and low sample volume (20 µl), was successfully applied for analyzing Phase 1 cancer patient samples.