Synthesis of an acid-labile polymeric prodrug DOX-acetal-PEG-acetal-DOX with high drug loading content for pH-triggered intracellular drug release

In this study, three PEGylated doxorubicin (DOX) prodrugs with acid-labile acetal and carbamate linkages have been prepared via the combination of Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of alkyne and azide (CuAAC) “click” reaction and ammonolysis reaction. The chemical structures of the prodrugs and the drug contents were characterized by 1H NMR, FT-IR and HPLC analyses. To avoid some side effects caused by the acidic degradation products from conventional hydrophobic polymers, DOX was directly linked to the PEG chain. These prodrugs could self-assemble into micelles in aqueous solution with DOX as the core and PEG chains as the corona. The dissociation of prodrug micelles was confirmed by monitoring the size change as a function of time through DLS analysis. Compared with free DOX, the pH-triggered DOX release of prodrugs exhibited a well-controlled and faster release behavior at pH 5.0 than at pH 7.4. In vitro cytotoxicity tests against HeLa cells by MTT assay demonstrated that these prodrugs displayed the desirable antitumor activity. The intracellular drug release was observed by a live cell imaging system at different DOX dosages. This work provides a strategy for the preparation of a new type of pH-cleavable and water-soluble antitumor prodrug for cancer chemotherapy.