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

It has been suggested that the enzyme topoisomerase II may be important in chromosome segregation due to the role played by the enzyme in decatenating the intertwined DNA molecules that result from DNA replication. Inhibition of the enzyme has been found by some workers to inhibit 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 topoisomerase II are formed from whole chromosomes, implying non-disjunction, or acentric fragments. We found that treatment with both amsacrine and etoposide caused a dose-related increase in the number of CREST negative micronuclei, with only a very small increase in the number of CREST positive micronuclei at high concentrations of the compounds. Although we cannot conclude from our experiments that treatment with topoisomerase II inhibitors does not affect the segregation of neonatal lymphocytes, the production of CREST negative micronuclei suggests that segregation abnormalities are less important than other mechanisms which may cause cytotoxicity from exposure to these compounds.