In the past decade,nanoparticle-based drug delivery systems,such as gold nanoparticles,mesoporous silica nanoparticles(MSNs)and upconversion nanoparticles,have been extensively investigated for the treatment of cancer,aiming at improved therapeutic efficacy and reduced toxic side effect.However,the degradation of these nanoparticles is quite slow due to their stable network structures.As a result,the accumulation of these nanoparticles in liver,spleen and other tissues would cause inflammation and cell necrosis which limits their further clinical application.Hence it is of great significance and highly desirable to fabricate the degradable drug delivery systems to achieve cancer therapy.