MICRONUCLEI IN NEONATAL LYMPHOCYTES TREATED WITH THE TOPOISOMERASE-IIINHIBITORS AMSACRINE AND ETOPOSIDE

It has been suggested that the enzyme topoisomerase II may be importan t in chromosome segregation due to the role played by the enzyme in de catenating the intertwined DNA molecules that result from DNA replicat ion. Inhibition of the enzyme has been found by some workers to inhibi t chromatid separation in mammalian cells, while others have reported that the passage of cells through mitosis is unaffected. Inhibition of the enzyme with topoisomerase II inhibiting drugs also results in the formation of micronuclei as a consequence of DNA damage. We have used the micronucleus assay with CREST staining to investigate whether the micronuclei formed in neonatal lymphocytes after inhibition of topois omerase II are formed from whole chromosomes, implying non-disjunction , or acentric fragments. We found that treatment with both amsacrine a nd etoposide caused a dose-related increase in the number of CREST neg ative micronuclei, with only a very small increase in the number of CR EST positive micronuclei at high concentrations of the compounds. Alth ough we cannot conclude from our experiments that treatment with topoi somerase II inhibitors does not affect the segregation of neonatal lym phocytes, the production of CREST negative micronuclei suggests that s egregation abnormalities are less important than other mechanisms whic h may cause cytotoxicity from exposure to these compounds.