Polymer-Functionalized Graphene Oxide for Effective Gene and Drug Delivery

Abstract

Nanomaterials give us interesting physicochemical and biological properties for biomedical application owing to their nano size, large surface area and unique ability to interact with the biological system. In particular, graphene oxide (GO) has been considered “the future promising material” as it features their unique mechanical, electronic, and optical properties and has been exploited in novel electronic, store energy and other fields. The GO is now expanding its region from electronic and chemical application to biomedical areas such as biomolecule sensing and drug/gene delivery. Therefore, in Chapter I, we describe synthesis, properties and biological application of GO, and discuss the recent studies on the toxicity of GO to provide some perspective on the possible risks to their future development in materials and biomedical fields. In Chapter II, we describe the development of GO-based efficient gene delivery carrier through installation of polyethylenimine (PEI), a cationic polymer, which has been widely used as a non-viral gene delivery vector. It was revealed that hybrid gene carrier fabricated by conjugation of low molecular weight (LMW) branched PEI (BPEI) to GO increased the virtual molecular weight of BPEI, and consequently improved the DNA binding and condensation, and transfection efficiency. Furthermore this hybrid material facilitated bioimaging due to its tunable and intrinsic optical properties. Considering the extremely high transfection efficiency comparable to high molecular weight (HMW) BPEI, high cell viability, and its application as a bioimaging agent BPEI-GO hybrid material could be extended to drug delivery and photo thermal therapy. In Chapter III, we mention about development of photothermally controlled gene/drug delivery carrier by conjugating low molecular weight BPEI and reduced graphene oxide (rGO) via hydrophilic polyethylene glycol (PEG) spacer. The PEG-BPEI-rGO nanocomposite can form stable nano-sized complex with plasmid DNA (pDNA) as confirmed by physicochemical studies. In vitro gene transfection study, PEG-BPEI-rGO shows higher gene transfection efficiency without observable cytotoxicity compared to unmodified controls in PC-3 and NIH/3T3 cells. In addition, Moreover, PEG-BPEI-rGO nanocomposite demonstrates enhanced gene transfection efficiency upon NIR irradiation which is attributed to accelerated endosomal escape of polyplexes augmented by locally induced heat. Moreover, Meanwhile, PEG-BPEI-rGO also plays a role as a nanotemplate for photothermally triggered cytosolic drug delivery by inducing endosomal disruption and subsequent drug release. PEG-BPEI-rGO has ability to load more amount of Doxorubicin (DOX) than unreduced PEG-BPEI-GO via π-π and hydrophobic interactions, showing high water stability. Loaded DOX could be efficiently released by glutathione (GSH) and photothermal effect of irradiated near IR (NIR) in vials as well as in cells. Importantly, PEG-BPEI-rGO/DOX complex was found to escape from endosome after cellular uptake by photothermally induced endosomal disruption and proton sponge effect, followed by GSH-induced DOX release into cytosol. Finally, it was concluded that more cancer cell death efficacy was observed in PEG-BPEI-rGO/DOX complex-treated cells with NIR irradiation rather than without. This study demonstrated the development of the potential of PEG-BPEI-rGO nanocarrier as to photothermally triggered cytosolic gene/drug delivery via endosomal disruption. Even though GO has attracted huge interest in the area of biomedical application due to its unique physicochemical properties, the issue of its long-term toxicity in the body remains unclear. In Chapter IV, we describe the rationally designed GO nanotemplate (ssFGO) with PEG and BPEI via disulfide linkage to control the biological delivery and elimination in the body sequentially. Polymer-shielded GO was uptaken selectively as drawing a distinction between target cells and macrophages, and bioreducible ssFGO filled the role of the designed function that performs in reducible cellular environment. In the blood circulation, the shielding effect of PEG in ssFGO reduced their non-specific uptake by macrophages which induce unwanted elimination, thus improving their accumulation into target cells. After cellular uptake, the ssFGO easily escaped from endosome by photothermally induced endosome disruption, followed by fast gene dissociation and de-PEGylation under intracellular reducible environment, thereby showing much higher gene transfection efficiency with low toxicity than FGO and control BPEIs. Moreover, after exocytosis, de-PEGylated ssFGO easily entrapped in macrophage, followed by enzymatic degradation. The degradation process was monitored by photoluminescence enhancement from degraded GO fragments. These results highlight new directions in the design of biodegradable and multifunctional GO based nanomedicine. Our precisely designed ssFGO suggests a new strategy in a certainly biodegradable manner which facilitates elimination in the body, thus may overcome current impediments to use of GO derivatives in delivery system.