Effects of Dosage, Phénobarbital,and 2-Diethylaminoethyl-2,2-diphen\ balenate on the Binding of Cyclophosphamide and/or Its Metabolites to the DNA, RN A, and Protein of the Embryo and Liver in Pregnant Mice1

The effect of dosage and pretreatment with phénobarbital or 2-diethylaminoethyl-2,2-diphenylvalerate on the binding of labeled cyclophosphamide and/or its metabolites to macromolecular constituents of the embryo and maternal liver in pregnant mice was studied under conditions nearly identical to those of previous studies of cyclophosphamide teratogenicity. Cyclophosphamide and/or its metabolites were firmly bound, presumably covalently, to the DNA, RNA, and protein of the embryo and liver in pregnant mice. The proportion of drug bound to the DNA, RNA, and protein fractions was roughly related to the proportion of the three cellular constituents in embryonic and adult tissue, thus suggesting an indiscriminate attack by the drug and/or its metabolites on cellular constituents. The extent of binding to embryo and liver DNA was increased about 4-fold following a doubling of the dose, from 10 to 20 mg/kg, in nonpretreated pregnant mice, whereas the binding to RNA (except for liver) and protein was doubled. Pretreatment of pregnant mice with phénobarbital decreased the binding to embryo DNA and to liver RNA and increased the binding to liver protein produced by cyclophos phamide, 20 mg/kg, but no effect was observed on the binding to RNA or protein of the embryo or to liver DNA. Pretreatment with 2-diethylaminoethyl-2,2-diphenylvalerate decreased the binding to DNA and protein of liver produced by cyclophosphamide, 20 mg/kg, but no effect was observed on the binding to macromolecules of the embryo. The extent of binding to RNA or protein of the embryo showed no correlation with cyclophosphamide teratogenic responses, whereas the binding to DNA of the embryo showed a positive correlation with overall frequencies of malformations pro duced by cyclophosphamide. These findings are consistent with the hypothesis that cyclophosphamide and/or its metabo lites exert their teratogenic effects via the alkylation of embryo DNA.