Molecular cytogenetic analysis in mouse sperm of chemically induced aneuploidy: studies with topoisomerase II inhibitors.

The ability of two topoisomerase II (topo II) inhibitors, etoposide (VP-16) and merbarone (MER), to induce meiotic delay and aneuploidy in mouse spermatocytes was investigated. The progression from meiotic divisions to epididymal sperm was determined by injecting male mice with 5-bromo-2'-deoxyuridine (BrdU) and treating the animals 13 days later with the test chemicals. At 20-24 days after treatment, BrdU-containing sperm were identified with a FITC-labelled anti-BrdU antibody and green fluorescent sperm were scored with a laser scanning cytometer (LSC). It was found that VP-16 (50mg/kg) treatment induced a meiotic delay of about 24h. A significant reduction of BrdU-labelled sperm was observed at 22 days compared to the controls (VP-16 group: 14.20%; controls: 41.10%, P<0.001). At 23 and 24 days, there were no significant differences between the VP-16 and the control groups. MER (80 mg/kg) treatment did not cause meiotic delay. To determine the frequencies of hyperhaploid and diploid sperm, male mice were treated with 12.5, 25 and 50mg/kg VP-16 or 15, 30 and 60 mg/kg MER. Sperm were sampled from the Caudae epididymes 24 days after VP-16 treatment or 22 days after MER treatment. Significant increases above the concurrent controls in the frequencies of total hyperhaploid sperm were found after treatment with 25, 50mg/kg VP-16 (0.074 and 0.122% versus 0.052%) and after treatment with 60 mg/kg MER (0.098% versus 0.044%). Furthermore, significant increases in the frequencies of diploid sperm were found after treatment of mice with all three doses of VP-16 (0.024, 0.032 and 0.056% versus 0.004 and 0.00%, respectively) and with 30 and 60 mg/kg MER (0.022 and 0.05% versus 0.004 and 0.002%, respectively). All dose responses could be expressed by linear equations. The results indicate that cancer patients may stand transient risk for siring chromosomally abnormal offspring after chemotherapy with these topo II inhibitors.