Insight on photosensitivity of bispecific antibody-drug conjugates: ROS-mediated degradation and payload conjugation-induced structure alterations

Bispecific Antibody-Drug Conjugates (BsADCs) represent a promising class of targeted therapeutics, combining the bispecific targeting with the potency of cytotoxic payloads. However, their inherent structural complexity poses unique stability and photosensitivity challenges in development, manufacturing, and storage. In this study, we assessed the stability of three BsADCs under different light sources. Fluorescent lamp consistently induced BsADCs photodegradation, implicating its ultraviolet component as a key driver. Subsequent research results on the mechanism of photodegradation indicated that the fluorescent lamp-induced instability in BsADCs is primarily driven by the generation of reactive oxygen species from the payload upon photoexcitation, which subsequently induces photodegradation of the BsADCs. Notably, BsADCs exhibited significantly higher oxidation at conventional methionine residues of the Fc region than unconjugated parental bispecific antibodies (BsAbs). Integrated with the results from the carboxyl group footprinting and thermal stress study, suggested the structural differences between BsADCs and parental BsAbs. Our findings highlight that payload-mediated photoreactivity and structural alterations upon conjugation are critical factors contributing to the photodegradation of BsADCs compared with parental BsAbs. These insights underscore the importance of rigorous photostability assessment and appropriate light protection strategies throughout BsADCs development, manufacturing, and storage.