REGULATION OF THE FORMATION OF THE MAJOR DIETHYLSTILBESTROL DNA ADDUCT AND SOME EVIDENCE OF ITS STRUCTURE

Diethylstilbestrol (DES) induces kidney tumors in hamsters, In previou s studies, DES has been shown by P-32-postlabeling analysis to bind co valently to DNA in vivo and in vitro and DES-DNA adduct formation has been suggested to play a key role in DES-induced carcinogenicity. In t his study, we have examined the influence of the dose of DES, age of a nimals and organ specificity on adduct formation in hamsters. In addit ion, we examined the characteristics of DES-DNA adduct formation in vi tro and the structure of the major adduct. DES-DNA adducts were detect ed in liver and kidney of hamsters treated with at least 20 mg/kg DES. Adduct concentrations were higher at higher doses or in older compare d to younger animals. The covalent binding of DES to DNA catalyzed by hamster liver microsomes required cumene hydroperoxide as cofactor, wh ereas with NADPH, adducts were barely detectable, presumably because t he reactive metabolic intermediate DES quinone was reduced to DES. The major DES-DNA adduct formed in vitro was purified by semipreparative and analytical high pressure liquid chromatography. It is concluded th at DES-DNA adducts are formed from DES quinone at very low rates in vi tro and occur at low levels in vivo, even when hamsters receive very l arge doses of DES. The dependence of DES-DNA adduct concentrations in vitro on organic hydroperoxide cofactors required for cytochrome P450- mediated DES quinone formation indicates that stilbene-DNA adduction m ay occur only under conditions of oxidative stress.