Table 1.

Effects of BS in published reports using reporter gene assays.

Study	Assay details	Effect of BS	Positive control	Effect of positive control	Activity of BS vs. E2
Miller et al., [12]	YES assay	Submaximal induction, ca. 15 % efficacy vs. E2 at 5 × 10−5 M	E2	EC50 2 × 10−10 M	BS 600′000-fold weaker than E2; E2 EC50 36-fold higher than in human cell assays
Kunz et al. [4,5]	YES assay with estrogen α receptor	Submaximal induction, ca. 12 % efficacy vs. E2 at 10−3 M; EC50 rel. to this efficacy 1.66 × 10-4 M	E2	EC50 2.6 × 10−10 M	BS reported to be 860′000-fold weaker than E2 based on EC50
Charles and Darbre [1]	Estrogen-response-element (ERE) upstream of CAT gene in MCF7 cells containing endogenous ER	Submaximal induction, ca. 60 % efficacy vs. E2 at 2 × 10−4 M EC50 rel. to 60% efficacy 10−4 M; no effect at 5 × 10-5 M	E2	Only tested at 10−8 M, i.e. 2000-fold > EC50 of E2	No direct comparison to E2 possible
Tox21 [14]	BG1 ER-luc cell assay (luciferase gene under control of ERα receptor)	6 separate tests on 2 separate samples: sample 259418 inconclusive agonist in 3 experiments with 31 % efficacy; sample 256928 active agonist in 3 experiments with 36 % efficacy	E2	100 % efficacy at minimal test conc. of 1.18 × 10−9 M, i.e. 200-fold > EC50 of E2	No direct comparison to E2 possible
Tox21 [14]	ER-α -BLA HEK293 cell-based assay with β-lactamase gene under control of ERα receptor	2 × 9 separate tests on 2 separate samples: All 18 experiments concluded that BS is inactive (average efficacy < 3%)	E2	100 % efficacy at minimal test conc. of 9.8 × 10−10 M, i.e. 200-fold > EC50 of E2	BS not active
Present study	T47D-KBluc cell-based assay with luciferase gene under control of ER receptor	3 independent experiments in triplicate each; maximal efficacy 47 %; extrapolated EC50 of 7.1 × 10−5 M	E2	EC50 3.3 × 10−12 M	BS partial agonist; potency 21′000′000- fold below E2