In biomedical applications, polyethylene glycol (PEG) functionalization has been a major approach to modify nanocarriers such as nano-graphene oxide for particular biological requirements. However, incorporation of a PEG shell poses a significant diffusion barrier that adversely affects the release of the loaded drugs. This study addresses this critical issue by employing a redox-responsive PEG detachment mechanism. A PEGylated nano-graphene oxide (NGO-SS-mPEG) with redox-responsive detachable PEG shell is developed that can rapidly release an encapsulated payload at tumor-relevant glutathione (GSH) levels. The PEG shell grafted onto NGO sheets gives the nanocomposite high physiological solubility and stability in circulation. It can selectively detach from NGO upon intracellular GSH stimulation. The surface-engineered structures are shown to accelerate the release of doxorubicin hydrochloride (DXR) from NGO-SS-mPEG 1.55 times faster than in the absence of GSH. Confocal microscopy shows clear evidence of NGO-SS-mPEG endocytosis in HeLa cells, mainly accumulated in cytoplasm. Furthermore, upon internalization of DXR-loaded NGO with a disulfide-linked PEG shell into HeLa cells, DXR is effectively released in the presence of an elevated GSH reducing environment, as observed in confocal microscopy and flow cytometric experiments. Importantly, inhibition of cell proliferation is directly correlated with increased intracellular GSH concentrations due to rapid DXR release.

The synthesis and biological efficacy of novel nanomicelles that rapidly disassemble and release their encapsulated payload intracellularly under tumor-relevant glutathione (GSH) levels are reported. The unique design includes a PEG-sheddable shell and poly(ε-benzyloxycarbonyl-l-lysine) core with a redox-sensitive disulfide linkage.

A dual stimulus-responsive mPEG-SS-PLL(15)-glutaraldehyde star (mPEG-SS-PLL(15)-star) catiomer is developed and biologically evaluated. The catiomer system combines redox-sensitive removal of an external PEG shell with acid-induced escape from the endosomal compartment. The design rationale for PEG shell removal is to augment intracellular uptake of mPEG-SS-PLL(15)-star/DNA complexes in the presence of tumor-relevant glutathione (GSH) concentration, while the acid-induced dissociation is to accelerate the release of genetic payload following successful internalization into targeted cells. Size alterations of complexes in the presence of 10 mM GSH suggest stimulus-induced shedding of external PEG layers under redox conditions that intracellularly present in the tumor microenvironment. Dynamic laser light scattering experiments under endosomal pH conditions show rapid destabilization of mPEG-SS-PLL(15)-star/DNA complexes that is followed by facilitating efficient release of encapsulated DNA, as demonstrated by agarose gel electrophoresis. Biological efficacy assessment using pEGFP-C1 plasmid DNA encoding green fluorescence protein and pGL-3 plasmid DNA encoding luciferase as reporter genes indicate comparable transfection efficiency of 293T cells of the catiomer with a conventional polyethyleneimine (bPEI-25k)-based gene delivery system. These experimental results show that mPEG-SS-PLL(15)-star represents a promising design for future nonviral gene delivery applications with high DNA binding ability, low cytotoxicity, and high transfection efficiency.

A novel amphiphilic camptothecin prodrug that spontaneously arranges into nanomicelles which preferentially release the cytotoxic drug under tumor-relevant reductive conditions is designed.