ETOPOSIDE (VP-16) IS A POTENT INDUCER OF MICRONUCLEI IN MALE-RAT MEIOSIS - SPERMATID MICRONUCLEUS TEST AND DNA FLOW-CYTOMETRY AFTER ETOPOSIDE TREATMENT

The genotoxic and cytotoxic effects of etoposide (VP-16), a topoisomer ase II inhibitor, on male rat spermatogenic cells were studied by anal ysing induction of micronuclei during meiosis. Micronuclei (MN) were s cored in early spermatids after different time intervals corresponding to exposure of different stages of meiotic prophase. Etoposide had a strong effect on diplotene-diakinesis I cells harvested 1 day after ex posure, and a significant effect also on late pachytene cells harveste d 3 days after exposure. The effect at 18 days corresponding to exposu re of preleptotene stage of meiosis (S-phase) was weaker but also stat istically significant. Adriamycin was used as a positive control in th is study. The results indicate a different mechanism of action of etop oside compared with adriamycin and other chemicals studied previously with the spermatid micronucleus test. DNA flow cytometry was carried o ut to assess cytotoxic damage at the same time intervals (1, 3, and 18 days after treatment) at stages I and VII of the seminiferous epithel ial cycle allowing a study of cytotoxicity to different spermatogenic cell stages. Damage of differentiating spermatogonia was observed by a decrease in the cell numbers of the 2C peak 1 and 3 days after treatm ent and by a reduction of the number of 4C cells (primary spermatocyte s) 18 d after etoposide treatment. Adriamycin also killed differentiat ing spermatogonia. Since the cell population which showed a high induc tion of MN by etoposide was not reduced in number, the genotoxic effec t is remarkable. We conclude that etoposide is a potent inducer of gen otoxicity and patients treated with this agent during cancer chemother apy are at a risk of genetic damage. (C) 1994 Wiley-Liss, Inc.