OBJECTIVETo study the therapeutic effect of photocatalytic nano-TiO₂ on nasopharyngeal carcinoma xenograft in nude mice and underlying mechanism.

METHODSNude mice bearing human nasopharyngeal carcinoma xenograft were randomly divided into six groups: nano-TiO₂ + UV irradiation (with gradient concentration of nano-TiO₂); nano-TiO₂ alone and UV irradiation alone and blank control. The nano-TiO₂ suspension was injected into xenografts, and 24 h after UV light with the wave length of 330 - 400 nm, all the xenografts were removed and sectioned for HE staining. Ultrastructure and apoptosis of tumor cells in the xenografts were observed by transmission electron microscope (TEM). The expression of Caspase-3 was examined immunohistochemical staining and the apoptosis was detected with TUNEL.

RESULTSPathological analysis showed significant inflammatory responses (grade II and III) with local necrosis occurred in tumor tissues after nano-TiO₂ photodynamic therapy, but not in the negative control and blank control. TEM showed the nano-TiO₂ particles entered into the cytoplasm and the nucleus of tumor cells and many tumor cells had morphological changes for apoptosis. Significant positive expression of Caspase-3 and TUNEL-positive cells were found in the the xenografts with the treatments of nano-TiO₂ + UV irradiation compared to control (P < 0.01), which were enhanced with the increases in nano-TiO₂ concentration (P < 0.01).

CONCLUSIONPhotocatalytic nano-TiO₂ can inhibit the growth of nasopharyngeal carcinoma xenograft in nude mice by inducing Caspase-3 expression and apoptosis in the tumor cells.