Mc-MMAD [6-maleimidocaproyl-monomethyl auristatin D] is a potent cytotoxic payload-linker conjugate used primarily in the development of antibody-drug conjugates (ADCs) for targeted cancer therapy. The maleimide group allows thiol-selective conjugation to antibodies, delivering the monomethyl auristatin D (MMAD) warhead, which binds tubulin and inhibits microtubule polymerization, leading to cell cycle arrest and apoptosis. It is a key reagent in medicinal chemistry and oncology research, confined to laboratory and preclinical studies due to its high potency and toxicity.