Comparison of Analytical Methods for Antibody–Drug Conjugates Produced by Chemical Site-Specific Conjugation: First-Generation AJICAP

Antibody–drug conjugates (ADCs) have become a major class of oncology biopharmaceuticals. Traditional ADCs have a stochastic distribution of cytotoxic drugs attached at several different sites on the antibody. The heterogeneous nature of stochastic ADCs results in a complex compositional analysis. To improve on traditional ADC technology, we have developed a chemical conjugation platform termed “AJICAP” for the site-specific modification of native antibodies using a class of IgG Fc affinity reagents. Here we report further investigation focusing on several analyses of a first-generation AJICAP-ADC (Angew. Chem., Int. Ed. 2019, 58, 5592–5597). For drug–antibody ratio (DAR) determination, we examined and compared six different analytical methods. To the best of our knowledge, this is the first report of a comparison of analytical techniques to measure the DAR for ADCs produced by a site-specific technology such as AJICAP. Furthermore, a rapid analytical process for confirmation of the site selectivity of AJICAP conjugation was established by SEC–Q-TOF-MS. The analytical strategy reported here can be applied to the DAR determination of site-specific ADCs.