Quantitative comparisons of in vitro assays for estrogenic activities

Substances that may act as estrogens show a broad chemical structural diver sity To thoroughly address the question of possible adverse estrogenic effe cts, reliable methods are needed to detect and identify the chemicals of th ese diverse structural classes. We compared three assays-in vitro estrogen receptor competitive binding assays (ER binding assays), yeast-based report er gene assays (yeast assays), and the MCF-7 cell proliferation assay (E-SC REEN assay)-to determine their quantitative agreement in identifying struct urally diverse estrogens. We examined assay performance for relative sensit ivity, detection of active/inactive chemicals, and estrogen/antiestrogen ac tivities. In this examination, we combined individual data sets in a specif ic, quantitative data mining exercise. Data sets for at least 29 chemicals from five laboratories were analyzed pair-wise by X-Y plots. The ER binding assay was a good predictor for the other two assay results when the anties trogens were excluded (r(2) is 0.78 for the yeast assays and 0.85 for the E -SCREEN assays). Additionally, the examination strongly suggests that biolo gic information that is not apparent From any of the individual assays can be discovered by quantitative pair-wise comparisons among assays. Antiestro gens are identified as outliers in the ER binding/yeast assay, while comple te antagonists are identified in the ER binding and E-SCREEN assays. Furthe rmore, the presence of outliers may be explained by different mechanisms th at induce an endocrine response, different impurities in different batches of chemicals, different species sensitivity, or limitations of the assay te chniques. Although these assays involve different level of biologic complex ity, the major conclusion is that they generally provided consistent inform ation in quantitatively determining estrogenic activity for the five data s ets examined. The results should provide guidance for expanded data mining examinations and the selection of appropriate assays to screen estrogenic e ndocrine disrupters.