Evidence for cyclophosphamide-induced gene conversion and mutation in mouse germ cells.

Cyclophosphamide (CP) is a widely used antineoplastic drug. It tests positive in several genotoxicity assays, including those with endpoints such as chromosomal aberrations in mammalian cells, mitotic recombination in Drosophila melanogaster, and dominant lethal mutations in rodents. We have explored the effects of CP on genome stability of mouse (Mus domesticus) spermatogenic cells, using a recombination-based transgenic assay called MUSCATEER. In this system, intrachromosomal gene conversion events between two mutually defective lacZ genes generates beta-galactosidase activity in spermatids. The frequency of gene conversion events is determined by scoring spermatids stained with the lacZ substrate, X-gal. A dose-dependent induction of lacZ-positive spermatids was observed following single intraperitoneal CP exposures of 10, 100, and 200 mg/kg. At 200 mg/kg, there was a 25-fold increase over baseline. Treatment of a control transgenic line containing only a frame-shifted lacZ transgene provided an indication that CP also induced reversion mutations. The timing of the response indicated that the induction of recombination and/or mutation occurred primarily in meiotic stage cells. These results demonstrate potent germline mutagenicity of CP, and validate the utility and sensitivity of genetic recombination as a rapid indicator of genotoxicity in whole animals.