Radiation Enhancing Effect of Gold Nanoparticles: an In Vitro Study and Monte Carlo Simulation

Abstract

PURPOSE: The aim of the present study is to evaluate the biocompatibility of gold nanoparicles (GNPs) in lung cancer cells and radiation enhancing effect in an in vitro situation and to compare with Monte Carlo simulation results. METHODS: GNPs with average diameter of 3.7 ± 0.5 nm were prepared and then modified with poly ethylene glycol (PEG) to improve stability. GNPs were first surface-modified with 3-mercaptopropionic acid (MPA) to form a self-assembled monolayer and subsequently conjugated with NH2-PEG-NH2 through amidation between the amine end groups on PEG and the carboxylic acid groups on the particles. The biocompatibility and intracellular fate of PEG-modified GNPs (AuNP@MPA-PEG) were then studied in lung cancer (NCI-H1299, NCI-H460) cells. After AuNP@MPA-PEG was synthesized, the cytotoxicity of AuNP@MPA-PEG nanoparticles in NCI-H1299 and NCI-H460 cells was examined in terms of the effect of AuNP exposure on cell proliferation by the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a yellow tetrazole) assay and clonogenic assay. Uptake study of GNPs using coupled plasma mass spectroscopy was conducted and fluorescein isothiocyanate (FITC) showed the intracellular fate of AuNP@MPA-PEG. Radiation enhancing effects on the clonogenic assay with or without GNPs were evaluated and compared with the result of Monte Carlo simulation. A number of nanoparticles were presumed to be uniformly distributed in 3D into a small volume, or tally. Nanoparticles' concentration, size, and distribution were considered to be the factors affecting dose enhancement to simulate the realistic geometry. DNA double helix breakage was counted using immunofluorescent detection of γH2AX to figure out the effect of GNPs on radiation induced DNA double helix breakage. RESULTS: AuNP@MPA-PEG was synthesized with an average diameter of 3.7 ± 0.5 nm. More than 85% viability in NCI-H460 cells and more than 80% viability in NCI-H1299 cells were observed at an AuNP concentration of up to 50 μM. AuNP@MPA-PEG penetrated into the nucleus of mammalian cells upon exposure for 24 hours under confocal microscopy and transmission electron microscopy (TEM). In NCI-H460 cells a combination of 50 μM GNPs and irradiation induced an inhibition of cancer cell growth of 20% (2 Gy) or 48% (4 Gy) (P<0.05). The inhibition of cancer cell growth was higher in NCI-H1299 cells comparing with NCI-H460 cells (P<0.05). In Monte Carlo simulation when 1.04x1012 GNPs (0.0057% of total volume of plate) are supposed to be in cell plate the dose enhancement factor (Absorbed radiation dose with GNP/absorbed radiation dose without GNP) was 1.01 but when 1.04×1014 GNPs are supposed in cell plate, the dose enhancement factor was increased to be 1.64. GNP showed a larger radiation enhancing effect in an in vitro situation than calculated photoelectric effect using Monte Carlo simulation. With 50 μM GNP prior to 2 Gy irradiation, increased radiation-induced γH2AX foci formation was found in both cell lines. Like the results of the clonogenic assay, the number of radiation-induced γH2AX foci in NCI-H1299 cells was more increased with GNPs comparing to the increased number of γH2AX foci in NCI-H460 cells. CONCLUSIONS: Surface modification of GNP can enhance the stability and improve the biocompatibility. GNPs demonstrated radiation enhancing effects and these enhancing effects were more significant in radioresistent cell lines.