Functional 2-methylene-1,3-dioxepane terpolymer: a versatile platform to construct biodegradable polymeric prodrugs for intracellular drug delivery†
Functional 2-methylene-1,3-dioxepane (MDO) terpolymers were explored here as a versatile platform to construct biodegradable pH sensitive polymeric prodrugs for intracellular drug delivery. A series of MDO-based biodegradable functional polyester P(MDO-co-PEGMA-co-PDSMA) with different compositions were synthesized by terpolymerization of MDO, poly(ethylene glycol) methyl ether methacrylate (PEGMA) and pyridyldisulfide ethylmethacrylate (PDSMA) via a simple one-pot radical ring-opening copolymerization. Mal-DOX, which contains a pH-sensitive hydrazone bond between doxorubicin (DOX) and the maleimide group, was covalently conjugated in one pot to free thiol groups of PDSMA units via thiol–ene click chemistry in the presence of tri(2-carboxyethyl)phosphine (TCEP). The DOX-conjugated P(MDO-co-PEGMA-co-PDSMA) can self-assemble into prodrug micelles. The diameter and morphology of the polymeric prodrug micelles were measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Because of the existence of the pH-sensitive hydrazone bonds, in vitro drug release results showed that the release of DOX was much faster at pH 5.5 than that at pH 7.4. Flow cytometry and fluorescence microscopy demonstrated that the prodrug micelles could be efficiently internalized by cancer cells. In vitro cytotoxicity showed that the DOX-conjugated prodrug micelles can strongly inhibit the proliferation of cancer cells remarkably. Importantly, this work provides a versatile strategy for the fabrication of biodegradable polymeric prodrug nanocarriers.