Table 1.

Binding affinities and transcriptional activities for ERs and ERβ selectivity of compound C-1.

RBAa (%)			Transcriptional activity EC50 c (nM)
hERα	hERβ	β/αb	hERα	hERβ	Rel. β/αd
3.5 ± 1.5	32.1 ± 5.3	9.3	1,820 ± 433	0.91 ± 0.24	256

Binding affinities for ERs were determined by a fluorescence polarization displacement assay, and are expressed as RBA values compared to the affinity of E2. Transcription activities were determined by a cell-based ERs assay. pGL4.27-(ERE)3-Luc and expression vector containing ERα or ERβ were transfected into HEK293T cells. Luciferase activity was measured and the transcriptional activity of each compound was normalized by the hypothetical maximal response of E2 (=100). ^aRBA values were calculated by IC₅₀[E2]/IC₅₀[C-1] × 100 (RBA of E2 = 100), shown as mean ± SD of three independent experiments, performed in duplicate. ^bβ/α values = ERβ-RBA/ERα-RBA (ERβ selectivity of binding affinity). ^cEC₅₀ values are shown as mean ± SD of three or four independent experiments, performed in duplicate. ^dRel.β/α values = {ERβ-EC₅₀[E2]/ERβ-EC₅₀[C-1]}/{ERα-EC₅₀[E2]/ERα-EC₅₀[C-1]} (ERβ selectivity of agonistic activity). Detailed information can be found in ref. 27. Abbreviations: EC50, half maximal (50%) effective concentration; hER, human estrogen receptor; RBA, relative binding activity.