Used in the development of antibody-drug conjugates (ADCs) as a linker that connects cytotoxic drugs to monoclonal antibodies. Its design enables controlled release of the drug inside target cells through enzymatic cleavage by cathepsin B, which is overexpressed in tumor environments. The PAB (para-aminobenzyl) group acts as a spacer that enhances cleavage efficiency, while the Boc-protected amine provides stability during conjugation and circulation. This linker system improves the therapeutic index of ADCs by minimizing premature drug release and increasing specificity toward cancer cells. Commonly paired with potent cytotoxins like monomethyl auristatin E (MMAE) or F (MMAF) for targeted cancer therapy.