IDENTIFICATION OF ENVIRONMENTAL CHEMICALS WITH ESTROGENIC ACTIVITY USING A COMBINATION OF IN-VITRO ASSAYS

Environmental chemicals that function as estrogens have been suggested to be associated with an increase in disease and dysfuncions in anima ls and humans. To characterize chemicals that may act as estrogens in humans, we have compared three in vitro assays which measure aspects o f human estrogen receptor (hER)-mediated estrogenicity. Chemicals were first tested for estrogen-associated transcriptional activity in the yeast estrogen screen (YES). This was created by expressing hER and tw o estrogen response elements linked to the lacZ gene in yeast. Second, chemicals that were tested in YES were then assayed for direct intera ction with hER in a competition binding assay. Third, chemicals were t ested in the estrogen-responsive MCF-7 human breast cancer cell line t ransiently transfected with a plasmid containing two estrogen response elements linked to the luciferase gene. Together, these assays have i dentified two metabolites of DDT, o,p'-DDD and p,p'-DDD, that have est rogenic activity. Interestingly, previous studies had reported that th e DDD metabolites were nonestrogenic in whole animal models. Alachlor, the most frequently used herbicide in the United States, cis-nonachlo r, and trans-nonachlor displayed weak estrogenic activity in the combi ned assays. The antifungal agent benomyl had no estrogenic activity. W e propose that a combination of in vitro assays can be used in conjunc tion with whole animal models for a more complete characterization of chemicals with estrogenic activity.