Mutation Research, 243 (1990) 309-312 309 Elsevier MUTLET 0331 Mutagenic activity of metabolites contained in the plasma of Sprague-Dawley rats treated with cyclophosphamide Deborah Arnsdorff-Roubicekand Hamilton J. Targa Dept. Biologia, Inst. Bioci~neias, Universidade de S6o Paulo, 05499 Silo Paulo, SP ( Brasil) (Accepted 23 November1989) Keywords." Metabolicactivation; Sister-chromatid exchange;Cyclophosphamide Summary In the present study we have tried to add some new results to those data previously obtained by Natarajan et al. (1983) and Darroudi and Natarajan (1985), where they have used in vivo metabolization and cytogenetic testing for in vitro analysis of xenobiotic compounds. Sprague-Dawley rats were treated in- traperitoneally with 2.5, 5.0, 10.0 and 20.0 mg/kg b.w. of cyclophosphamide in order to obtain plasma con- taining active metabolites of the drug. The mutagenic activity was assessed by estimating the frequencies of sister-chromatid exchanges (SCE) in human and rat lymphocytes. No influence of animal age was observed on the metabolism of cyclophosphamide, which could be detected by SCE analysis. The increase in SCE fre- quencies in both human and rat lymphocytes was dependent on the doses applied. SCE frequencies are highly variable among individuals, showing statistically significant differences. The same effect, but to a lesser ex- tent, was also found in rats. Rat lymphocytes can be assumed to be good biological material for chemical mutagenesis, as the animals can be maintained at almost constant experimental conditions. However, rat lymphocytes do not grow well in in vitro cultures. These data contribute to the preview proposal that combin- ing metabolism in vivo and chromosome SCE analysis in vitro can be regarded as an important and very sen- sitive system to detect the mutagenic activity of low-dose exposure to chemical compounds requiring metabolic activation. Mammalian cytogenetics has been widely used for the evaluation of mutagenic and clastogenic properties of chemical substances. Genetic changes are usually analyzed as chromosome aberrations, aneuploidy, sister-chromatid exchanges (SCE) and Correspondence: Dr. D. Arnsdorff-Roubicek, Dept. Biologia, Inst. Bioci~ncias,Universidadede S~o Paulo, CP 11461,05499 SgtoPaulo, SP (Brasil). point mutations. Some chemicals, such as cyclophosphamide (CP), a cytostatic drug used in some cancer therapies, are not mutagenic per se, but require metabolic activation. Drug activation in in vitro treatments is generally obtained by addi- tion to the cultures of a rat $9 liver homogenate, together with some cofactors. However, such $9 mix does not perform a complete activation/detox- ification process similar to that occurring in vivo. The addition, in in vitro tests, of body fluids, such 0165-7992/90/$ 03.50 © 1990Elsevier SciencePublishers B.V. (BiomedicalDivision)