Used in the synthesis of antibody-drug conjugates (ADCs), this linker system enables targeted delivery of cytotoxic agents to cancer cells. The Val-Cit dipeptide acts as a protease-cleavable linker, stable in circulation but degraded inside tumor cells by cathepsin B. The PABC (para-aminobenzyloxycarbonyl) spacer facilitates efficient release of the active drug upon cleavage. The azide group allows for bioorthogonal conjugation via click chemistry, typically to alkyne-bearing antibodies or other targeting moieties. PEG1 enhances solubility and provides a short, flexible spacer that improves conjugation efficiency and stability. This construct is commonly employed in ADC development to improve pharmacokinetics, reduce off-target toxicity, and increase therapeutic efficacy.