Evaluation of in vitro screening system for estrogenicity: Comparison of stably transfected human estrogen receptor-α transcriptional activation (OECD TG455) assay and estrogen receptor (ER) binding assay

The estrogenic activity of industrial chemicals, di(2-ethylhexyl) phthalate (DEHP), di(n-butyl) phthalate (DBP), benzylbutyl phthalate (BBP), diethyl phthalate (DEP), tetrabromobisphenol A (TBBPA), bisphenol A (BPA), and nonylphenol (NP), was compared using OECD test guideline 455(TG455), stably transfected transcriptional activation (STTA) and estrogen receptor (ER) binding assays. The estrogenic activity of BBP, BPA and NP were approximately 180,000-fold (PC₅₀, 4.32 × 10^-6 M), 5,000-fold (PC₅₀, 1.26 × 10^-7 M) and 120,000-fold (PC₅₀, 2.92 × 10^-6 M) less than 17β-estradiol (PC₅₀, 2.43 × 10^-11M), whereas DEHP, DBP and DEP did not show any estrogenicity activity in the STTA assay. Moreover, binding affinities to human ERα of BBP, BPA, and NP were approximately 200,000-fold (IC₅₀, 4.91 × 10^-4 M), 8000-fold (IC₅₀, 1.92 × 10^-5 M) and 1400-fold (IC₅₀, 3.34 × 10^-6 M) less than 17β-estradiol (IC₅₀, 2.45 × 10^-9 M) in competitive human ERα binding assay. The relative potencies of STTA assay were very similar to ER binding, E-screen, and Yeast screening assays. Therefore, our results suggested that OECD test guideline TG455 may be useful as a screening test for potential endocrine disruptors.