The Study On Killing Human Gastrointestinal Cancer Cells By Photocatalytic Oxidation

Gastric cancer and colon carcinoma are severely harmed to people's health in our country. At present, there are mainly therapies such as surgical, radiological and chemotherapeutic treatments, etc, but the surgical treatment is limited to local treatment and radiological and chemotherapeutic treatments generate greater side effect in the body. It is imminent to seek an effective way which generates minor toxicity and side effect to human body.TiO₂ photocatalytic oxidation killing cancer cells is an exploring therapy for cancer. Up till now, such research on TiO₂ photocatalytic killing gastric cancer and colon carcinoma has not yet been reported. Its principle is as follows. Upon excitation by UV light whose wavelength is less than 390nm, the photon energy generates electron-hole pairs on the TiO₂ surface. Under the action of electric field in space charge layer, electrons, apart from holes, transfer to the surface of TiO₂ particles. When the photogenerated holes react with water attached on TiO₂ and when the photogenerated electrons react with oxygen in water, the reactive oxygen species(ROS) such as OH·, H₂O₂, HO₂· are produced.These ROS will react with biomolecules, which results in the damage of organism structure through a series of peroxidative chain reaction and killing cancer cells. It has advantages such as safety, little noxious and side effect, minor wound, basically no damage to normal tissues, no other external energy except ultraviolet light that can not be substituted by conventional therapies. Therefore, it is promising to become an effective therapy for gastric cancer and colon carcinoma that generate minor toxicity and side effect to human body. It is of theoretical significance and practical value to explore T1O2 photocatalytic oxidation killing gastric cancer and colon carcinoma.In the previous studies of TiO2 photocatalytic oxidation killing cancer cells, trypan blue exclusion test and colony forming test were mostly adopted to detect the survival rate. The cells in trypan blue exclusion test have to be accurately counted in short time or some-viable cells can be stained, which will interfere detection. In colony forming test, cultivating cells needed longer time, involved in many procedures and this method easily caused errors.In this paper, a flow cytometer was used to detect the cells between one thousand and five thousand per second, and this instrument can separate the cells when their difference is 0.2u.m. Fluorescent staining assay has been successfully adopted to examine the killing effect of immobilized TiO2 photocatalytic oxidation. These approaches can overcome above-mentioned shortcomings and raise the rate and degree of accuracy.The results of XRD and SEM showed that the crystalline form of TiO2prepared by coating technique is anatase; the TiO2 thin film displayed uniform nano-cluster structure; the average particle size of TiO2 in nano-cluster is 22.7 nm. A series of experiments including TiO2 alone, UV light exposure alone and TiO2 + UV light irradiation were conducted for human gastric cancers treatment. The results indicated that human gastric cancers could be killed by TiO2 photocatalytic oxidation. 70% of the cells were killed when the irradiation intensity was 1.06mW/cm2, with 0.98u.g/cm2 coated TiO2 and 40min irradiation time.The surface fractal dimensions of photocatalysts were calculated by box dimension model. The results showed that the fractal dimensions of catalysts range from 2.52 to 2.57 and surface area is relatively large. In our experimental conditions, the larger fractal dimension of nano-cluster is beneficial to killing effect of human gastric cancer cells. When the amount of TiO2 was 0.98(ig/cm2, the fractal dimension is the largest (2.57) and 70% of cells were killed after 40min of UV light irradiation.In order to investigate the mechanism of killing human gastric cancers by TiO2 photocatalytic oxidation, the effect of photoexcited nanometer TiO2 on human gastric cancer cells cycle was determined by flow cytometer. The results showed that photoexcited nanometer TiO2 could inhibit the synthesis of DNA in human gastric cancer cells, affect their proliferation and differentiation process as well as stop the differentiation of human gastric cancers G2 stage.To simulate photokilling cancer cells by TiO2 suspension in clinicalcondition, TiO2 colloid solution was prepared by sol-gel method in this paper. Using this slurry photocatalyst, we conducted photocatalytic killing human colon carcinoma cells. The influence of concentration of TiO2 colloid solution, the light intensity, irradiation time on photokilling effect and the temperature variations of RPMI1640-TiO2 caused by UV irradiation were inspected. The results showed that the higher concentration of TiO2 colloid is beneficial to killing effect of human colon carcinoma cells when concentration of TiO2 colloid changes in range from 200u g/mL to 1029u g/mL. With the 1029u g/mL of TiO2, 44% of the cells were killed after lOmin of UV light irradiation, and after 30min irradiation, 80% of the cells were killed. Although a higher concentration (C>1029ug/mL) of TiO2 could achieve a higher reaction rate, the sedimentation, the difficulties in separation and measurement would be considered. So the effect of a higher TiO2 concentration on Ls-174-t cell activity was not investigated. The concentration of TiO2 was set on <1029]ig/mL; when the light intensity was changed in the range of 0.72³.7mW/cm2, survival ratio decreased as light intensity increased. While light intensity was above 3.7mW/cm2, survival rate had no obvious variations as light intensity increased. The temperature increase of RPMI 1640-TiO2 is lower than 41°C, from the results we concluded that human colon carcinoma cells were killed by a photo effect, but a thermal effect.According to experimental results, the mechanism of killing human colon carcinoma cells by TiO2 photocatalytic oxidation was speculated in two steps: (1)the reactive oxygen species (ROS) such as OH*, H2O2, HO2? were produced on TiO2 colloid particle surface by photoexcited TiO2 colloid. These ROS had first contact with intact cells, and then the initial oxidative damage took place on the cell membranes, which became somewhat permeable after attacked by ROS. (2) Photocatalytic action made the cell membranes permeable, directly attack intracellular components, eventually leading the cell to death.In a word, the study of killing human gastric cancers and human colon carcinoma cells by TiO2 photocatalytic oxidation was first conducted in this paper and the results demonstrated that malignant tumors were effectively killed. The results provided reliable experimental evidence for applying TiO2 photocatalytic oxidation to clinical cancer treatment.