Developing analytical ion exchange chromatography methods for antibody drug conjugates containing the hydrolysis-prone succinimide-thioether conjugation chemistry

Charge variants are one of the most important quality attributes for protein therapeutics, including antibody drug conjugates (ADCs). ADCs are conjugation products between monoclonal antibodies (mAbs) and highly potent payloads. After attaching a payload, the charge profile of a mAb can be modified due to the change in net charge or surface charge. In this study, we present a unique challenge of charge assay development that arises from a desirable engineering of ADCs that incorporates the hydrolysis-prone succinimide-thioether conjugation chemistry. This engineered hydrolysis at conjugation sites is usually not complete during conjugation process and continuously progressing during mild stress. This hydrolysis also creates a carboxylic functional group, which manifests as acidic peaks in the ADC charge profiles. As a result, ion exchange chromatograms become sensitive measurements of this hydrolysis, which often masks the charge profile change due to other important post-translational modifications. In this study, two approaches were explored to address this unique challenge: to remove the hydrolysis heterogeneity by incubating ADCs under high pH conditions to drive complete hydrolysis; and to analyze charge variants at the subunit level after IdeS digestion. Acceptable charge profiles and quantitative integration results were successfully obtained by both approaches.