Comparison of quaternary ammonium-based linkers for antibody–drug conjugates based on camptothecin derivatives

Antibody–drug conjugates (ADCs) with camptothecin derivatives as payloads have been a hot topic of interest and research since the launch of DS-8201a. As an important component of ADCs, the adequate stability of the linker during circulation and its rapid release at the target site are crucial for the efficient efficacy of ADCs. Although traditional quaternary ammonium ADCs based on dipeptide linkers were highly stable and could be released by specific enzymes, their poor in vitro anti-tumor activity had limited their further exploration. We applied a methylsulfonylethylamine-modified MAC self-elimination system to a valine-alanine linker and constructed a quaternary ammonium ADC (HER2-11) that combines both stability and cleavability. The optimization of the linker effectively improved the in vitro cellular activity of conventional quaternary ammonium ADCs, but the complex intracellular cleavage mechanism of HER2-11 resulted in a weaker anti-tumor activity compared to HER2-GGFG-DXd, which provides great reference value for the continued research of this type of linker in the future.