pH and reduction dual responsive cross-linked polyurethane micelles as an intracellular drug delivery system

Abstract

Nano-vehicles that exhibit enhanced stability in blood circulation while spontaneously releasing therapeutic cargos at pathological sites in response to specific biological triggers are of interest for on-demand drug delivery. In this work, disulfide cross-linked polyurethane micelles (CL-PUMs) that respond to pH change and an intracellular reducing agent were developed. The micelles were prepared by cross-linking of poly(ethylene glycol)–polyurethane multiblock copolymers containing tertiary amino and cyclic disulfide moieties via a thiol–disulfide exchange reaction. The CL-PUMs tended to swell or decompose under a weakly acidic environment or in the presence of an intracellular reducing agent, glutathione (GSH), likely owing to the protonation of the tertiary amino groups and cleavage of the disulfide cross-linking bonds. The doxorubicin (DOX)-loaded CL-PUMs suppressed the initial burst release at pH 7.4 without GSH, while they displayed a triggered drug release manner in response to an acidic environment and GSH. It was found that the intracellular DOX release of the DOX-loaded CL-PUMs in HepG2 cells was accelerated by an acidic environment or enhanced intracellular GSH concentration. Moreover, the time-dependent cytotoxicity against HepG2 and HeLa cells of the DOX-loaded CL-PUMs was confirmed by an MTT assay. Overall, due to the enhanced stability, selective swelling and decomposition properties in response to intracellular micro-environments, the pH- and reduction-sensitive polyurethane cross-linked nano-carriers can serve as a potential system for intracellular drug delivery.