[Measurement of oxygen concentration in tumor cells by fluorescent probe (nitrocompound)]

The hypoxic cell fraction in tumors is considered to be responsible for radioresistance. Estimating the population of the hypoxic cell fraction in tumor could develop the effective means to predict radiosensitivity. In this study, nitroacridine (fluorescent dye) was tested to estimate hypoxic status in single cells and in spheroids. The oxygen concentration in the medium was measured by oxygen electrodes utilizing polarography method, mean while that in cells was calculated from the fluorescence intensity of the dye. The fluorescent spectra from cells showed the same pattern in spite of the changed oxygen concentration in medium, on the other hand its intensity was dependent upon the oxygen concentration. Using a fixed nitroacridine concentration and a fixed staining time, oxygen concentration of cells could be determined within range from 0.1 to 1.0% values. These values are almost the same as the oxygen concentration of the radioresistant tumor cells. Thus, the fluorescent method we used in this study is considered to be useful to estimate radioresistance of tumor. However, fluorescent intensity would alter when used different cell lines, because of different cellular activity of nitroreductase.