Target organ-specific covalent DNA damage preceding diethylstilbestrol-induced carcinogenesis.

The synthetic estrogen diethylstilbestrol (DES), a known human carcinogen, induces renal carcinoma in male Syrian hamsters within 6 months after s.c. implantation. Tumor formation could be evoked by its hormonal properties or by a reactive genotoxic metabolite binding to DNA, but previous attempts to detect adducts have failed. In the present study, kidney DNA of male Syrian hamsters, treated with s.c. DES implants to induce renal carcinoma, was analyzed for the presence of DES-induced adducts using 32P-postlabeling assay. Covalently-modified DNA nucleotides were detected in the kidneys after chronic DES treatment, but not in kidneys of untreated hamsters, or in liver or tumor tissue of DES-treated animals. This report demonstrates for the first time the ability of an estrogen to give rise to covalent DNA modification in vivo specifically in the target organ of carcinogenesis. DES-induced covalent DNA adducts are taken as evidence for tumor initiation by DES via damage to cellular macromolecules, in addition to tumor-promotional effects described previously.