Development of a new cancer therapy using photoexcited semiconductor particles

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Photo-excited Ti02 semiconductor particles can drive various chemical reactions due to their strong oxidizing and reducing ability. To investigate the possible use of this effect for cancer treatment, the anti-tumor activity of photo-excited Ti02 particles were studied in vitro and in vivo. Human cancer cells, like T-24 human bladder cancer cells and HeLa cells, cultured in vitro were completely killed in the presence of Ti02 with photo-irradiation by a 500 W Hg lamp. In cotrast, very little cell death was observed by Ti02 treatment without photo-irradiation. Photoexcited Ti02 particles also suppressed growth of human cancer cells implanted in nude mice significantly, compared with those receiving Ti02 alone or photo-irradiation alone. The cell death caused by photo-excited Ti02 particles was significantly protected in the presence of L-tryptophan and catalase. These molecules are quenchers of hydroxyl radicals(OH^.) and scavengers of hydrogen peroxide (H_2O_2), respectively, suggesting that the cells were killed by the OH^. and H_2O_2 produced from photo-excited Ti02 particles. On the basis of these experimental observation, it can concluded that the cell killing effect of Ti02 under UV light irradiation could be adopted as one of anti-cancer modality.