Site-Specific Stability Evaluation of Antibody–Drug Conjugate in Serum Using a Validated Liquid Chromatography–Mass Spectrometry Method

Antibody-drug conjugate (ADC) consists of engineered antibodies and cytotoxic drugs linked via a chemical linker, and the stability of ADC plays a crucial role in ensuring its safety and efficacy. The stability of ADC is closely related to the conjugation site; however, no method has been developed to assess the stability of different conjugation sites due to the low response of conjugated peptides. In this study, an integrated strategy was developed and validated to assess the stability of different conjugation sites on ADC in serum. Initial identification of the conjugated peptides of the model drug ado-trastuzumab emtansine (T-DM1) was achieved by the proteomic method. Subsequently, a semiquantitative method for conjugated peptides was established in liquid chromatography-hybrid linear ion trap triple quadrupole mass spectrometry (LC-QTRAP-MS/MS) based on the qualitative information. The pretreatment method of the serum sample was optimized to reduce matrix interference. The method was then validated and applied to evaluate the stability of the conjugation sites on T-DM1. The results highlighted differences in stability among the different conjugation sites on T-DM1. This is the first study to assess the stability of different conjugation sites on the ADC in serum, which will be helpful for the design and screening of ADCs in the early stages of development.