Aneuploidy induction by mitotic arrestants. Effects of diazepam on diploid Chinese hamster cells.

We used diazepam, a mild mitotic arrestant, as a model chemical to develop a cytogenetic assay protocol for aneuploid induction in a diploid Chinese hamster cell system. At 100 micrograms/ml, diazepam almost completely arrested mitosis at metaphase. However, mitotic block could be quickly reversed when diazepam was removed from the medium. When the duration of arrest was relatively short (2 h), anaphases in the recovering cell population were essentially normal; but when the arresting period was prolonged (7 h), anaphases in the recovering cell populations exhibited a high rate of multipolar spindles and lagging chromosomes. Filial cell populations (18-24 h after removal of the drug) showed a high frequency of aneuploid elements. Mitotic cells shaken off from monolayer cultures as starting cell populations for enumeration of aneuploidy proved to be superior to non-shaken-off cell populations.