Chemical Site-Specific Conjugation Platform to Improve the Pharmacokinetics and Therapeutic Index of Antibody–Drug Conjugates

To overcome a lack of selectivity during the chemical modification of native non-engineered antibodies, we have developed a technology platform termed "AJICAP" for the site-specific chemical conjugation of antibodies through the use of a class of IgG Fc-affinity reagents. To date, a limited number of antibody-drug conjugates (ADCs) have been synthesized via this approach, and no toxicological study was reported. Herein, we describe the compatibility and robustness of AJICAP technology, which enabled the synthesis of a wide variety of ADCs. A stability assessment of a thiol-modified antibody synthesized by AJICAP technology indicated no appreciable increase in aggregation or decomposition upon prolonged storage, indicating that the unexpectedly stable thiol intermediate has a great potential intermediate for payload or linker screening or large-scale manufacturing. Payload conjugation with this stable thiol intermediate generated several AJICAP-ADCs. In vivo xenograft studies indicated that the AJICAP-ADCs displayed significant tumor inhibition comparable to benchmark ADC Kadcyla. Furthermore, a rat pharmacokinetic analysis and toxicology study indicated an increase in the maximum tolerated dose, demonstrating an expansion of the AJICAP-ADC therapeutic index, compared with stochastic conjugation technology. This is the first report of the therapeutic index estimation of site-specific ADCs produced by utilizing Fc affinity reagent conjugation. The described site-specific conjugation technology is a powerful platform to enable next-generation ADCs through reduced heterogeneity and enhanced therapeutic index.