Intracellular microenvironment responsive PEGylated polypeptide nanogels with ionizable cores for efficient doxorubicin loading and triggered release

Abstract

Two kinds of reduction and pH responsive disulfide-cross-linked poly(ethylene glycol)-polypeptide copolymers were prepared through one-step ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG NCA) or ε-benzyloxycarbonyl-L-lysine N-carboxyanhydride (ZLL NCA) and L-cystine N-carboxyanhydride (LC NCA) with amino group terminated monomethoxy poly(ethylene glycol) (mPEG-NH₂) as macroinitiator. Then, the copolymers were deprotected and dispersed in phosphate buffered saline, yielding PEG-polypeptide nanogels. Doxorubicin (DOX), a model anticancer drug, was effectively loaded into nanogels via electrostatic and hydrophobic interactions. The DOX release from all DOX-loaded nanogels was accelerated in intracellular reductive and acidic conditions, which controlled by Fickian diffusion and nanogels swelling. The enhanced intracellular DOX release was observed in glutathione monoester (GSH-OEt) pretreated HeLa cells. DOX-loaded nanogels showed higher cellular proliferation inhibition towards GSH-OEt pretreated HeLa and HepG2 cells than to unpretreated or buthionine sulfoximine (BSO) pretreated cells. Hemolysis tests indicated that nanogels were hemocompatible, and the presence of nanogels could reduce the hemolysis ratio (HR) of DOX significantly. These features suggest that the nanogels can efficiently load and deliver DOX into tumor cells and enhance the inhibition of cellular proliferation in vitro, providing a favorable platform to construct an efficient drug delivery system for cancer therapy.