EVALUATION OF A MODIFIED MICRONUCLEUS ASSAY

The relationship between ionizing radiation-induced cell killing and D NA damage measured by the micronucleus assay was determined in three e stablished cell lines (L929, HL-60, and Chang). Our data revealed a do se-dependent increase of cells bearing multiple micronuclei. Cells wit h the same number of micronuclei were counted separately up to 50 h af ter irradiation. The counts of these subsets showed a parallel increas e and decrease throughout the study. In order to transform the peak of the micronucleus frequency, occurring over only a brief time period i nto a less time dependent value, we calculated ratios between the diff erent subsets of micronucleated cells. These ratios converged to value s which were almost constant beyond 30 h after irradiation. The values showed correlations with cell survival (clonogenic assay) and radiati on dose which were comparable with the correlations with the peak of t he micronucleus frequency (maximum micronucleus yield) when utilizing the conventional evaluation of the micronucleus assay performed withou t cytochalasin B. This means that large-scale time kinetics and additi onal drugs like cytochalasin B can be avoided by changing the evaluati on procedure of the conventional micronucleus assay. The modified assa y described in this manuscript revealed apoptosis-induced limitations as recently detected for the maximum micronucleus yield assay.