Exo-Cleavable Linkers: Enhanced Stability and Therapeutic Efficacy in Antibody–Drug Conjugates

Antibody–drug conjugates (ADCs) combine cytotoxic payloads with monoclonal antibodies through chemical linkers. Finding linkers that both enhance circulatory stability and enable effective tumor payload release remains a challenge. The conventional valine-citrulline (Val-Cit) linker is associated with several inherent drawbacks, including hydrophobicity-induced aggregation, a limited drug–antibody ratio (DAR), and premature payload release. This study introduces an exolinker approach, repositioning the cleavable peptide linker at the exo position of the p-aminobenzylcarbamate moiety, as an advancement over conventional linear linkers. This design, which incorporates hydrophilic glutamic acid, addresses the limitations of the Val-Cit platform and improves the ADC in vivo profiles. In vitro and in vivo evaluations showed that exolinker ADCs reduced premature payload release, increased drug-to-antibody ratios, and avoided significant aggregation, even with hydrophobic payloads. Furthermore, the payload remained stably attached to the ADC even in the presence of enzymes like carboxylesterases and human neutrophil elastase, indicating the potential for a favorable safety profile.