INHIBITORS OF TOPOISOMERASE-II DELAY PROGRESS THROUGH MITOSIS AND INDUCE A DOUBLING OF THE DNA CONTENT IN CHO CELLS

The effect of inhibition of topoisomerase II on chromosome segregation in CHO cells has been studied using cytogenetical techniques and measurements of nuclear DNA content. Cells were accumulated in metaphase, and their passages into the subsequent stages of mitosis, and into interphase, were examined. Of the compounds tested, five (Amsacrine, Etoposide, Hoechst 33342, Mitoxantrone, and nalidixic acid) greatly reduce the rate at which the chromosomes pass from metaphase through anaphase to the subsequent interphase and induce a high proportion of nuclei which contain a 4C amount of DNA. In several cases, the reformation of membranes around chromosomes can be seen although the chromosomes remain in a condition similar to metaphase, with the chromatids linked at the centromeres. Two other inhibitors of topoisomerase II, Hoechst 33258 and Merbarone, failed to delay cells in metaphase and did not induce tetraploidy. This failure may well be due to an inability of the compounds to penetrate the cells sufficiently quickly, or at a high enough concentration. Overall, the results are consistent with the hypothesis that topoisomerase II is essential for the segregation of chromosomes in mammals and other eukaryotes. (C) 1995 Academic Press, Inc.