Multiplexed Quantitative Analysis of Antibody–Drug Conjugates with Labile CBI-Dimer Payloads In Vivo Using Immunoaffinity LC-MS/MS

Quantitative analysis of antibody–drug conjugates (ADCs) involves cleavage of ADCs into smaller analytes representing different components and subsequent measurements from multiple assays for a more comprehensive pharmacokinetic (PK) assessment. Multiple PK analytes including the drug remaining conjugated to the antibody (or antibody-conjugated drug, acDrug) and total antibody can be accessed simultaneously using a multiplex assay by proteolytic digestion of an ADC, if the sites of conjugation are homogeneous for an ADC and the linker drug is stable to proteases. Herein, a multiplexed immunoaffinity liquid chromatography-mass spectrometry (LC-MS)/MS PK assay is described involving immunoaffinity enrichment, enzymatic conversion of prodrug, trypsin digestion, and LC-MS/MS as applied to next-generation ADCs constructed from linker drugs bearing dimeric cyclopropabenzindole (CBI) payloads (duocarmycin analogues). The cytotoxic payload is chemically labile, requiring extensive optimization in sample preparation steps to stabilize the drug without ex vivo modification and to convert the prodrug into a single active form of the drug. The qualification data for this assay format showed that this approach provides robust acDrug and total antibody data and can be extended to ADCs with different monoclonal antibody frameworks and linker chemistries. Applications of this multiplexed assay to support preclinical studies are presented.