Characterization of Ring-Opening Reaction of Succinimide Linkers in ADCs

A new class of highly potent biopharmaceutical drugs, antibody-drug conjugates (ADCs), has been proven to be clinically effective to treat oncologic diseases. ADCs contain 3 major components: the monoclonal antibody, cytotoxic drug, and chemical linker. THIOMAB™ drug conjugates and interchain-cysteine ADCs are common ADC platforms that apply thiol-maleimide chemistry via Michael addition to conjugate linker-drugs to cysteine residues. However, the resulting succinimide ring in the linker is susceptible to ring-opening reactions via hydrolysis, especially at high pH and elevated temperatures. Once the succinimide ring is opened, in vivo stability of the ADCs can be changed and the therapeutic activity will be altered. In this study, we investigated the impact of conjugation sites on succinimide ring opening for ADCs. A new methodology based on imaged capillary isoelectric focusing was developed to monitor the formation of succinimide ring-opened products. In addition, a reverse-phase high-performance liquid chromatography method was used to monitor site-specific ring-opening reactions. Our data confirmed that succinimide ring-opening rates in ADCs are conjugation-site dependent. With a good understanding of the conjugation site impact on final product's stability, it is potentially feasible to modify ring-opening rates in vitro to achieve desirable in vivo stability and biological activity.