Higher G2 sensitivity to the induction of chromosomal damage in the CHO mutant EM9 than in its parental line AA8 by camptothecin, an inhibitor of DNA topoisomerase I.

The induction of chromosomal alterations by camptothecin (CPT), an inhibitor of DNA topoisomerase I, in the G2 stage was studied in a CHO mutant cell line EM9, which has an elevated baseline frequency of SCEs, and in its parental cell line AA8. EM9 cells were found to be more sensitive to CPT than the parental cell line. It is proposed that the effect of camptothecin in this phase of the cell cycle is caused by a 'residual' DNA synthesis which is higher in EM9 than in AA8 cells.