Augmentation of the inhibitory effect of blue light on the growth of B16 melanoma cells by riboflavin.

We have demonstrated that blue light has anticancer effects in cultured cancer cells and tumor-bearing animals. Based on our experimental findings, in addition to cytostatic activity that suppresses the proliferation of B16 melanoma cells, blue light may exert cytocidal activity through interaction with vitamin(s) contained in the culture medium. The present study was undertaken to identify the specific vitamins with which blue light interacts and to investigate the factors responsible for its cytocidal activity. B16 melanoma cells were incubated in media supplemented with various vitamins and exposed to blue light for 10 min. Cell necrosis was observed only in media containing riboflavin (0.4 mg/l). The effects of other components of visible light on riboflavin were also studied. Riboflavin-containing media were exposed to light of each of the three primary colors (red, green and blue) and the effects on the colony-forming capacity of B16 melanoma cells were evaluated. Cell necrosis was induced only in media exposed to blue light. The effects of riboflavin increased in a concentration-dependent manner in the range from 0.3 to 1.0 mg/l in blue-light-exposed media and were antagonized by the presence of catalase (200 U/ml). These findings suggest that cell necrosis is probably induced by active oxygen species such as hydrogen peroxide formed by the reaction of riboflavin with blue light.

Blue light inhibits the growth of skin tumors in the v-Ha-ras transgenic mouse.

12-O-Tetradecanoylphorbol-13-acetate (TPA) was applied to the back skin of v-Ha-ras (TG-AC) female transgenic mice at a dose of 2.5 microg/200 microl twice a week for 9 weeks. The back skin was then exposed to blue light (wavelength, 470 nm; irradiance, 5.7 mW/cm2) for 1 h daily for 9 weeks. The mice to which TPA was applied developed skin tumors at 6 weeks after the start of application. The tumor incidence rates at 6, 7, 8 and 9 weeks after the start of application were 70%, 80%, 100% and 100%, respectively, and the numbers of tumors 1 mm or more in diameter were 1, 5, 10 and 19, respectively. In the mice that were exposed to blue light after TPA application, the tumor incidence rates were 10%, 40%, 60% and 80%, respectively, and the numbers of tumors 1 mm or more in diameter were 0, 2, 5 and 9, respectively. Histopathological examination of the skin revealed that TPA application induced diffuse hyperplasia, exaggerated keratinization, and papillomas in all 10 mice. A localized form of epidermal hyperplasia was also observed in 4 mice. The incidence rate of papillomas in the mice that were exposed to blue light after TPA application was lower and the degree of exaggerated keratinization was greater. Exaggerated keratinization was considered to represent a regressive change following exposure. These findings suggest that exposure to blue light may be a promising new approach in the treatment of skin tumors.

Inhibition of lung metastasis of B16 melanoma cells exposed to blue light in mice.

The effects of blue light on B16 melanoma cells and on the metastasis of these cells to the lungs were investigated in mice. The exposure of B16 melanoma cells to blue light in two 20-min sessions resulted in marked suppression of cell growth measured at 7 days after exposure. When these cells were harvested, re-inoculated into medium and incubated for a further 7 days, their growth activity returned to almost the same level as that of cultured cells from the non-exposure control group. The melanoma cells harvested after 7 days of incubation were injected intravenously into mice. In the non-exposure group, black nodules developed on the lung surface and the nodules increased in size over time. In the blue-light-exposure group, the development of such black nodules on the lung surface was delayed, and the nodules were smaller. Histopathological examination revealed that blue light suppressed the growth of metastatic tumor cells, and no increase in the number of melanin-containing cells or atypical cells was induced in the metastatic lesions. These results suggest that blue light suppresses the metastasis of B16 melanoma cells.

Effects of blue-light-exposure on growth of extracorporeally circulated leukemic cells in rats with leukemia induced by 1-ethyl-1-nitrosourea.

To explore the possibility of using blue light for extracorporeal circulation therapy in patients with leukemia, the effects of blue light on cell growth in vitro and in extracorporeally circulated blood of rats with leukemia were evaluated. When HL60 cells circulated extracorporeally using a peristaltic pump were exposed to blue light for 5 h, the growth of the cells was found to be markedly suppressed. Then, the blood of rats with erythroblastic leukemia, induced by the administration of tap water containing l-ethyl-l-nitrosourea (ENU) for 9-16 weeks, was circulated extracorporeally and exposed to blue light for 3 h. Lymphocytes were separated from the peripheral blood immediately after the end of blue-light-exposure and incubated for 7 days. The growth of leukemic cells was found to be significantly suppressed following exposure to blue light, whereas the growth of normal lymphocytes was unaffected. These findings suggest that cancer cells may be more sensitive to blue light than normal cells.

Inhibition by long-term fermented miso of induction of gastric tumors by N-methyl-N'-nitro-N-nitrosoguanidine in CD (SD) rats.

The present study was designed to investigate the effects of fermented miso in the diet on the induction of gastric tumors by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in male CD (SD) rats. A total of 120 animals, 6 weeks of age, were divided into 6 groups and given MNNG (100 ppm) in the drinking water for 16 weeks. Starting 1 week before the carcinogen treatment the rats were fed a normal control MF solid diet, or the same diet containing 10% long-term fermented, medium- or short-term fermented miso, or 1% NaCl until the end of the MNNG exposure period. They were then maintained on the MF control diet and normal tap water until the autopsy time point at 52 weeks. The long-term fermented miso significantly reduced the size of the gastric tumors as compared with the other groups. The present results thus indicate that dietary supplementation with long-term fermented miso could act as a chemopreventive agent for gastric carcinogenesis.