Used in antibody-drug conjugates (ADCs) as a linker to connect cytotoxic drugs to monoclonal antibodies. The PEG8 spacer enhances solubility and flexibility, improving conjugation efficiency and stability in circulation. The val-gly dipeptide acts as a cleavable site by lysosomal enzymes, enabling targeted drug release inside cancer cells. The PAB (para-aminobenzyl alcohol) group serves as a self-immolative spacer, facilitating efficient release of the active drug after enzymatic cleavage. Mal-amido functionality allows site-specific conjugation to thiol groups on antibodies, ensuring controlled drug-to-antibody ratio and improved pharmacokinetics.