Cytotoxic and radiosensitizing effects of nano-C60 on tumor cells in vitro

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 watersoluble fullerene-C60 (nano-C60) 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 60Co c irradiation. We measured cell survival rates, apoptotic characteristics, reactive oxygen species (ROS) production and alteration of cell diameter with or without c-irradiation. There was reduced survival with B16 and SMMU-7721 cells exposed to nano- C60, with the inhibitory concentrations reducing the viability by 50% to 65 part per billion (ppb) and 150 ppb respectively. For cells exposed to nano-C60 prior to c-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-C60, there were increased levels of ROS, as measured by fluorescence detection under laser confocal microscopy. Preincubation with nontoxic pristine C60 before c-ray caused enlargement of cells with increased diameter. The results show that nano-C60 inhibits the growth of tumor cells at certain concentrations and increases the effects of 60Co c-irradiation, possibly through the elevated production of cellular ROS and the membrane disruption. Data in this study indicates a possible consideration of using C60 as a candidate of sensitization modifier in tumor radiation biology.