46P Gold nanoparticles as radiosensitizers for human colon carcinoma cells

The development of radiosensitizers is a promising way to increase the efficacy of radiotherapy. Gold nanoparticles (GNPs) attracts attention due to their biocompatibility, low toxicity, versatility of synthesis, and parameter settings. Newly synthesized GNPs (26±2 nm) were tested against HCT116 human colon carcinoma and its isogenic HCT116p53KO variant with non-functional p53. Intracellular accumulation was determined by atomic absorption spectroscopy. Cytotoxicity of GNPs alone and in combination with photon radiation was measured by MTT and colony formation assays. Irradiation of cells was performed on the experimental X-ray machine RUST-M1 (Diagnostics-M, Russia), 200 keV, 1-6 Gy single dose. GNPs readily entered the cells; maximum accumulation was achieved by 10 h. GNPs do not enter cells when active uptake stopped by cold (+4oC). At concentrations that did not alter the transparency of the GNP sols (up to 100 μg/ml) no significant cytotoxicity was observed for 72 h of cell exposure. Irradiation of HCT116 and HCT116p53KO cells led to an arrest in the G2/M phase of the cell cycle followed by the increase of DNA fragmentation and cell death. GNPs increased the number of HCT116 cells arrested in the G2/M phase by 10%. The most significant (4-fold) decrease in the number of colonies (by day 14 post-irradiation) was observed after 1 Gy in the presence of 10 μg/ml GNPs. In HCT116p53KO cells, GNPs increased the G2/M block only by 4% for all tested doses. The antioxidant N-acetyl-L-cysteine (NAC, 5 mM) attenuated GNP-mediated increase of the number of cells in G2/M suggesting that radiosensitization by GNPs is related to the oxygen burst. This initial effect of NAC on cell cycle distribution was not associated with survival/proliferation of single cells because the number of colonies after irradiation in the presence of GNPs and NAC was smaller compared to irradiation alone. The combination of GNPs and NACs treatment can be used simultaneously for the radiosensitization of tumor cells and the protection of normal tissues surrounding the tumor.