Cytotoxic and radiosensitizing effects of nano-C-60 on tumor cells in vitro

Abstract

There is growing evidence in recent years that the pristine fullerene may be endowed with strong pro-oxidant capacity to biological samples. In this investigation we tested the hypothesis that water-soluble fullerene-C-60 (nano-C-60) may interact with ionizing radiation enhancing its antiproliferative effects. The two tumor cell lines with different radiosensitivity B16 and SMMU-7721 were treated by a combination of pristine fullerene and Co-60 gamma irradiation. We measured cell survival rates, apoptotic characteristics, reactive oxygen species (ROS) production and alteration of cell diameter with or without gamma-irradiation. There was reduced survival with B16 and SMMU-7721 cells exposed to nano-C-60, with the inhibitory concentrations reducing the viability by 50% to 65 part per billion (ppb) and 150 ppb respectively. For cells exposed to nano-C-60 prior to gamma-irradiation, damage to cell membranes and increased numbers of apoptotic cells were detected by morphologic Hoechst-staining analysis and Annexin V/propidium iodide double-staining. In cells exposed to nano-C-60, there were increased levels of ROS, as measured by fluorescence detection under laser confocal microscopy. Preincubation with non-toxic pristine C-60 before gamma-ray caused enlargement of cells with increased diameter. The results show that nano-C-60 inhibits the growth of tumor cells at certain concentrations and increases the effects of Co-60 gamma-irradiation, possibly through the elevated production of cellular ROS and the membrane disruption. Data in this study indicates a possible consideration of using C-60 as a candidate of sensitization modifier in tumor radiation biology.