Analytical Tools to Support Antibody Drug Conjugate Process Development: Troubleshooting Unexpected Conjugation Events

Antibody drug conjugates (ADCs) are an innovative and rapidly evolving class of biopharmaceuticals that harness the specificity of monoclonal antibody with the cell killing potency of a cytotoxic payload agent to selectively deliver chemotherapy to cancer cells. The synthesis of ADCs is intricate, requiring precise control of multiple process parameters such as conjugation method, stoichiometry, pH, temperature, and reaction time. Consistency in the conjugation process is essential to achieve a consistent drug-to-antibody ratio (DAR), which significantly impacts the therapeutic efficacy and safety profile of the ADC. Throughout the synthesis, side-products can arise from incomplete reactions, over-conjugation, aggregation, or other unwanted modifications to the antibody or payload. These side-products represent critical quality attributes (CQAs) because they could affect the stability, efficacy, or safety of the final drug product, underscoring the importance of monitoring and controlling them during process development. In this presentation, we will characterize a typical ADC synthesis process using techniques such as liquid chromatography-mass spectrometry (LC-MS), capillary electrophoresis, and other spectroscopic methods are used to characterize the molecular composition, purity, DAR distribution, and to identify side-products. Comprehensive characterization of these reaction mixtures not only provides crucial insights into the mechanism of ADC synthesis and side-product formation but also informs process optimization and risk mitigation strategies.