Used in antibody-drug conjugates (ADCs) for targeted cancer therapy. Acts as a linker-payload system that connects monoclonal antibodies to cytotoxic agents. The dipeptide Val-Cit is cleaved by cathepsin B in lysosomes of cancer cells, releasing the potent microtubule-disrupting agent MMAF. The PAB (para-aminobenzyl) group serves as a self-immolative spacer, enabling efficient drug release after enzymatic cleavage. This design enhances tumor-specific delivery, minimizing systemic toxicity and improving therapeutic index in oncology applications.