A myriad of drug delivery systems such as liposomes,micelles,polymers and inorganic nanoparticles(NPs)have been developed for cancer therapy(1-3).Very few of them,however,have the amenability of integrating multiple functionalities such as specific delivery,controllable release and good biocompatibility and biodegradability in a single system to improve therapeutic efficacy.Therapeutic platforms based on small molecular prodrug have demonstrated unique advantages in cancer diagnosis and treatment due to their precise structural control and high sensitivity,which thereby effectively avoid inadequate treatment or overtreatment in chemotherapy(4-5).