USE OF THE MICRONUCLEUS ASSAY FOR THE SELECTIVE DETECTION OF RADIOSENSITIVITY IN BUDR-UNINCORPORATED CELLS AFTER PULSE-LABELING OF EXPONENTIALLY GROWING TUMOR-CELLS

To determine the radiosensitivity of non-S-phase tumour cells in vitro, survival curves of SCC VII tumour cells were obtained after a short block with hydroxyurea. Dose-response curves of micronucleus (MN) frequency appearing in non-S-phase cells were also determined by excluding S-phase cells with immunofluorescence staining to 5-bromo-2'deoxyuridine (BUdR). Both the dose-response curves of MN frequency and survival curves were analysed by a linear-quadratic model (surviving fraction = exp (-alpha;D - βD2), MN frequency = aD + bD2 + c). A good correlation between the αbeta; and a/b ratios was observed. In both BUdR-unincorporated and asynchronous cell cultures, the regression lines between the surviving fraction and micronucleus frequency were statistically identical. Therefore, it was shown that cell survival curves, which cannot be obtained directly by the routine colony-formation technique, can be calculated using the micronucleus frequency and the regression line in asynchronous cell cultures. Therefore, it should be possible to detect the response to irradiation of quiescent cells in tumours using the immunofluorescence staining to BUdR and the MN frequency assay. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.