Estrogens induce cancer in laboratory animals and are increasingly found to be associated with appearance of certain cancers in humans. In studies of the mechanism of estrogen-induced kidney carcinogenesis in Syrian hamsters, covalent diethylstilbestrol (DES)-DNA adducts have been identified in vivo by 32P-postlabeling analysis, and diethylstilbestrol-4',4""""""""-quinone was the reactive metabolic intermediate. Steroid estrogens are oxidized to catechol metabolites and further to catechol quinones which also bind to DNA in vitro. The occurrence of these adducts in vivo and their carcinogenic potential will be investigated by correlating metabolic catechol estrogen formation and DNA adduct levels with expression of oncogenes. Because short-term treatment results in an approximately 15% kidney growth and long-term treatment in the development of tumors of sufficient size to permit analyses, these measurements will be carried out in hamsters treated with DES or estradiol for 1 week or 7-8 months. Genes to be investigated include (1.) c-erb-B-1, c-src, c-fes, c-abl, and the transferrin receptor as representatives of genes coding for growth factors, receptors, and membrane tyrosine kinases; (2.) c-H-, N- and Ki-ras as representatives of genes for G-like proteins found overexpressed in human or animal kidney tumors; (3.) c-mos and c-raf from the serine protein kinase family; (4.) c-erb-A, c-fos, c-jun, c-myc, and c-myb as representatives of the nuclear protein group. Our initial objective will be to identify types of oncogenes that are expressed during estrogen- induced kidney hypertrophy or tumor development. Studies to be carried out thereafter will address the mechanism of activation. Steroid estrogens with reduced or completely eliminated potential for catechol estrogen and thus catechol quinone formation will also be tested. It is expected that these modified steroids will possess high estrogenic potential yet no carcinogenic activity. It is further expected that the decrease in tumor incidence will be correlated with DNA adduct levels induced by the modified estrogens. These experiments will permit us to distinguish between activation/overexpression of oncogenes by estrogen-DNA adducts and that induced by normal estrogen receptor mediated events. The experiments also will determine whether formation of estrogen-DNA adducts in vivo is required for estrogen carcinogenesis.
