Cyclophosphamide: Interstrain differences in the production of mutagenic metabolites by S9‐fractions from liver and kidney in different mutagenicity test systems in vitro and in the teratogenic response in vivo between CBA and C 57 BL mice

The formation of mutagenic compounds from cyclophosphamide (CPA) by S9-fractions from liver (S9L) or kidney (S9K) of pregnant CBA and C 57 BL mice was investigated, using point mutations in Salmonella typhimurium (TA 1535) and the induction of sister chromatid exchanges (SCE) in human peripheral lymphocytes (HPL) or Chinese hamster ovary (CHO) cells as end points. In addition, the teratological response of CBA and C 57 BL mice to CPA on day 11 of pregnancy was analysed in vivo. The results are as follows: (1) S9L from CBA mice was more effective than S9L from C 57 BL mice in metabolizing CPA to products inducing mutations in Salmonella and SCEs in HPL and CHO cells. (2) S9L was more effective than S9K from both strains of mice. (3) In vivo pretreatment of mice with a single dose of CPA (20 mg/kg) reduced the in vitro metabolizing capacity of S9L and S9K significantly and led to the disappearance of the interstrain difference. (4) The embryolethal and teratogenic effects of CPA were stronger in C 57 BL than in CBA mice; the types of teratological effects were partially different in the two strains.