EVALUATION OF A RECOMBINANT YEAST-CELL ESTROGEN SCREENING ASSAY

A wide range of chemicals with diverse structures derived from plant a nd environmental origins are reported to have hormonal activity. The p otential for appreciable exposure of humans to such substances prompts the need to develop sensitive screening methods to quantitate and eva luate the risk to the public. Yeast cells transformed with plasmids en coding the human estrogen receptor and an estrogen responsive promoter linked to a reporter gene were evaluated for screening compounds for estrogenic activity. Relative sensitivity to estrogens was evaluated b y reference to 17 beta-estradiol (E-2) calibration curves derived usin g the recombinant yeast cells, MCF-7 human breast cancer cells, and a prepubertal mouse uterotrophic bioassay. The recombinant yeast cell bi oassay (RCBA) was approximately two and five orders of magnitude more sensitive to E-2 than MCF-7 cells and the uterotrophic assay, respecti vely. The estrogenic potency of 53 chemicals, including steroid hormon es, synthetic estrogens, environmental pollutants, and phytoestrogens, was measured using the RCBA. Potency values produced with the RCBA re lative to E-2 (100) included estrone (9.6), diethylstilbestrol (74.3), tamoxifen (0.0047), alpha-zearalanol (1.3), equol (0.085), rt-nonylph enol (0.005), and butylbenzyl phthalate (0.0004), which were similar t o literature values but generally higher than those produced by the ut erotrophic assay. Exquisite sensitivity, absence of test compound biot ransformation, ease of use, and the possibility bf measuring antiestro genic activity are important attributes that argue for the suitability of the RCBA in screening for potential xenoestrogens to evaluate risk to humans, wildlife, and the environment.