Background: Graphene Oxide (GO) has shown great potential in biomedical applications for cancer therapeutics. The biosafety and stability issues of GO in biological media have been addressed by functionalization with polyethylene glycol (PEG). Methods: In this work, carboxylated, nanosized GO (nCGO) was evaluated as a potential carrier of paclitaxel (PCT). The effect of PEG characteristics on particle size and surface charge, colloidal stability, drug, and release, and the hemolytic potential of nCGO, was investigated. Optimum PEG-nCGO/PCT formulations based on the above properties were evaluated for their anticancer activity (cytotoxicity and apoptosis induction) in the A549 lung cancer cell line. Results: An increase in the length of linear PEG chains and the use of branched (4-arm) instead of linear PEG resulted in a decrease in hydrodynamic diameter and an increase in ζ potential of the pegylated nCGO particles. Pegylated nCGO exhibited high colloidal stability in phosphate-buffered saline and in cell culture media and low hemolytic effect, even at a relatively high concentration of 1 mg/mL. The molecular weight of PEG and branching adversely affected PCT loading. An increased rate of PCT release at an acidic pH of 6.0 compared to the physiological pH of 7.4 was observed with all types of pegylated nCGO/PCT. Pegylated nCGO exhibited lower cytotoxicity and apoptotic activity than non-pegylated nCGO. Cellular uptake of pegylated nCGO increased with incubation time with cells leading to increased cytotoxicity of PEG-nCGO/PCT with incubation time, which became higher than that of free PCT at 24 and 48 h of incubation. Conclusions: The increased biocompatibility of the pegylated nCGO and the enhanced anticancer activity of PEG-nCGO/PCT compared to free PCT are desirable properties with regard to the potential clinical application of PEG-nCGO/PCT as an anticancer nanomedicine.

The functionalization of GO nanomaterials with polyethylene glycol (PEG) polymers has been the most common method to ameliorate stability in physiological media and increase biocompatibility. In this work, carboxylated GO (CGO) was functionalized with PEG polymers of different molecular weight (MW) and structure and loaded with the anticancer drug paclitaxel (PCT). An increase in the MW of linear PEG from 2 to 20 kDA decreased the size and tended to increase the ζ-potential of the pegylated CGO nanoparticles (nCGO-PEG) and a branched (4 arm) PEG(10 kDa) provided nanoparticles with significantly lower size and higher ζ-potential compared to a linear PEG(10 kDa). All nCGO-PEG nanoparticle types exhibited good colloidal stability on storage and in PBS and cell culture medium with the exception of the nCGO-PEG functionalized with the relatively low MW PEG of 2 kDa. PCT loading efficiency fell when the MW of PEG was increased or a branched PEG was used. Pegylation decreased significantly the hemolytic potential of nCGO-PEG nanoparticles. Increased PCT release rate was observed at acidic pH 6.0 compared to physiological pH 7.4 for all PCT/nCGO-PEG formulations. Higher cytotoxicity and apoptotic activity of the nanocarrier-entrapped PCT compared to free PCT against the lung adenocarcinoma A549 cell line at longer incubation times was found as at these longer incubation times a high cellular uptake of the PCT/nCGO-PEG nanoparticles were observed. The results justify further investigation of the potential of PCT/nCGO-PEG as antitumor nanomedicine.