Integrated mass spectrometric workflows enabling next-generation conjugate therapeutics in cancer research

Antibody-drug conjugates (ADCs) and the broader class of Antibody-X Conjugates (AXCs)-including emerging Antibody-Oligonucleotide Conjugates (AOCs)-are rapidly advancing as therapeutic modalities in oncology and autoimmunity. Their expanding impact increases the need for robust bioanalytical strategies capable of quantifying total and conjugated antibodies, released payloads, and associated biotransformation pathways.LC-MS/MS has become an essential platform for addressing the analytical complexity of AXCs, supporting hybrid LBA-LC-MS workflows for total and conjugated antibodies, as well as direct measurement of free payloads and payload metabolites. Click-chemistry-enabled drug systems, designed for tumor-selective activation, present similar analytical challenges that require high sensitivity and specificity. The platform described here meets these demands through enhanced sensitivity, selectivity, and comprehensive biotransformation characterization.We developed an integrated LC-MS/MS workflow tailored for ADC, AXC, and AOC programs. Optimized controlled-reduction and selective-extraction methods enabled accurate quantification of diverse payload classes-including auristatins (MMAE/MMAF), topoisomerase-I inhibitors (DXd, SN-38, exatecan), and associated linker-drug species-while minimizing artificial payload release. These assays demonstrated high sensitivity, linearity, and matrix robustness across plasma, tumor, tissue, and cell-based systems, supporting reliable pharmacokinetic, stability, and biotransformation assessments.A complementary bioorthogonal click-chemistry workflow using azide-alkyne and TCO-tetrazine reactions was also established to selectively tag precursor and product species, enhancing MS detectability and enabling quantitative analysis of activation behavior.Together, these LC-MS/MS-based approaches provide a unified analytical solution for ADCs, AOCs, AXCs, and click-activated therapeutics. The platform supports comprehensive in vitro, ex vivo, and in vivo pharmacokinetic studies across plasma and tissue matrices, facilitating robust PK/PD correlation and exposure profiling for these emerging modalities.