Sensitive LC-MS/MS Quantification of Unconjugated Maytansinoid DM4 and its Metabolite S-methyl-DM4 in Human Plasma

Aim: To report the development and validation of an LC-MS/MS method for the simultaneous determination of unconjugated payload DM4 and its metabolite S-methyl-DM4 in human plasma. Methodology: A workflow of protein precipitation followed by reduction and solid phase extraction was employed to remove antibody–maytansinoid conjugates from plasma matrix, release DM4 from endogenous conjugates, and generate a clean sample extract for analysis, respectively. Sodium adduct species of both analytes were selected for multiple reaction monitoring to meet the assay sensitivity requirement in liquid chromatography with tandem mass spectrometry. Conclusion: The method was fully validated for a dynamic range of 0.100–50.0 ng/ml for both analytes along with desired stability and acceptable incurred sample reanalysis.