Used in antibody-drug conjugates (ADCs) as a cleavable linker to connect cytotoxic drugs to monoclonal antibodies. The Val-Cit-PABA segment is a substrate for cathepsin B, an enzyme overexpressed in tumor cells, enabling targeted drug release inside cancer cells. Mal-PEG2 provides a maleimide group for stable conjugation to thiol groups on antibodies and introduces hydrophilic spacing to improve solubility and reduce aggregation. This linker system enhances the therapeutic index of ADCs by promoting selective drug activation in tumors while minimizing systemic toxicity.