From prodrug to pro-prodrug:hypoxia-sensitive antibody–drug conjugates

Dear Editor,Antibody‒drug conjugates(ADCs),famous as biological targeting prodrugs,are gradually revolutionizing clinical cancer therapy.However,less than 1%of the dosed ADCs accumulate in the tumors.1 Therefore,the nonspecific release of the highly toxic payload(MMAE et al.,10−12–10−10 M)is a real threat,which could induce severe off-target toxicity.2 This danger necessitates strict requirements for the design of the linker.To date,the mainstream enzyme cleavable linkers,includingβ-glucuronidase cleavable linkers,sulfatase-cleavable linkers,and the most popular cathepsin cleavable linkers(valine-citrulline linker),all face this nonspecific release problem,3 because their cleaving enzymes are widely distributed with no significant difference in their quantities between tumor tissues and normal tissues.