Abstract
Hypoxic fraction of tumor is resistant to the X-ray radiation for cancer therapy. To overcome this point we designed hypoxic cell radiosensitizers, novel 2-nitoroimidazole acetamide (2NIA) derivatives, and tested their effects on irradiation of X-ray and also carbon-ion beam to non-small-cell lung cancer (NSCLC) cells. Carbon ion radiation therapy has attracted attention as a novel effective modality for cancer therapy.
Human lung carcinoma cell line A549 was used through the experiments. 2NIA derivatives (TX-2141 and TX-2244) and their parental sensitizer TX-1877 were used as hypoxic cell radiosensitizers. The radiosensitizers had been dissolved in medium before 2hours experiments were started. Hypoxic condition was made by Anero pack. For the X-irradiation, cell culture dishes were irradiated with 4-MV X-ray (100 cGy/min) using a linear accelerator at Osaka University. For the carbon-ion beams irradiation, cells were irradiated with 290MeV/nucleon carbon-ion beams at the National Institute of Radiological Sciences in Japan. Cell survival curves were obtained by means of a standard colony formation assay. The cells were fixed with 10% formalin and stained with crystal violet. Colonies with over 50 cells were scored as survival fractions. Capability of tumor invasion was obtained by Boyden chamber assay. The number of cells that had migrated to the lower side of the filter was scored at *200 magnification in four independent fields. In vitro, the radiosensitizers had been dissolved in medium before 1 hour experiments were started. In vivo, in order to estimate tumor growth, four-week-old female BALB/c nude mice were inoculated with 1 * 106 A549 cells into the flank. TX-2244 had been injected before 30 min X-irradiation were started.
As the results of colony formation assay, oxygen enhancement ratio (OER) of hypoxic cells exposed to X-rays without the sensitizer was 2.78 based on 10% survival dose (D10). In the case of carbon-ion beams, OER was 1.07. For the X-irradiation, enhancement ratios (ER= (control D10) / (sensitizer D10)) in the presence of TX-2141 and TX-2244 were 1.32 and 1.50, respectively. On the other hand, for carbon-ion beams, ERs of them were no significant. As the results of Boyden chamber assay, we observed that invasion of A549 cells including 2NIA derivatives was decreased both X-ray and carbon-ion beams irradiation. In vivo, tumor growth was significantly suppressed by TX-2244.
These results suggested that TX-2244 was not only useful as the hypoxic cell radiosensitizer, but also effective for inhibition of tumor invasion of NSCLC cells.
