Recent Chemical Approaches for Site-Specific Conjugation of Native Antibodies: Technologies toward Next-Generation Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs), which consist of three components, antibody, linker, and payload, can function as "magic bullets". These conjugates offer the ability to target drug delivery to specific cells, based on cell-specific recognition and the binding of an antigen by a monoclonal antibody (mAb). In particular, by delivering a cytotoxic payload to cancer cells, ADCs are expected to provide a breakthrough in oncology treatments by providing a way to increase efficacy and decrease toxicity, in comparison with traditional chemotherapeutic treatments. The development of ADC therapeutics has dramatically progressed in the past decade and two ADCs have been approved and used as anticancer drugs in the clinic. However, several critical issues regarding the performance of ADCs are still being discussed and investigated. Indeed, in the past few years, several groups have reported that, changing the number and position of the drug payloads in the ADCs, affects the pharmacokinetics, drug release rates, and biological activity. The use of conventional heterogeneous conjugation methods for ADC preparation results in the drug/antibody ratio and connecting position of the payload having stochastic distributions. Therefore, it is important to investigate how these potential problems can be circumvented through site-specific conjugation. Herein, various site-specific chemical conjugation strategies with native mAbs that are currently used for the production of ADCs, including residue-selective labeling for generating ADCs, disulfide rebridging, and affinity-peptide-mediated site-specific chemical conjugation technologies, are reviewed and described.