Used in the synthesis of antibody-drug conjugates (ADCs), this compound acts as a linker that connects cytotoxic drugs to monoclonal antibodies. The structure includes a protease-cleavable peptide (Val-Cit) and a self-immolative spacer (PAB), which allows for targeted drug release inside cancer cells. Upon internalization of the ADC into tumor cells, lysosomal enzymes cleave the peptide bond, triggering the release of the active drug. The PNP group serves as a model payload or can be replaced with potent cytotoxins like auristatins or maytansinoids. This system improves the therapeutic index of chemotherapy by minimizing off-target effects and enhancing tumor-specific drug delivery. Commonly used in research and development of next-generation ADCs for cancer therapy.