Estrogenic activity of estradiol and its metabolites in the ER-CALUX assay with human T47D breast cells

A number of metabolites of 17β-estradiol were tested for their estrogenic activity using the ER-CALUX assay based on the increased expression of luciferase in exposed T47D breast cancer cells. E 2 β and estrone showed similar potencies in the test, whereas E 2 α was 100 times less active. Incubation of cells with estrone (0.35 μM) resulted in the formation of E 2 β, whereas the reverse reaction was observed for E 2 β. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17-hydroxy benzoate ester of E 2 β was 3 times less active than the parent compound. The 17-hydroxy palmitate and oleate esters of E 2 β, were respectively 25 and 200 times less active than the parent compound. The 2-hydroxy metabolites of E 2 β and estrone showed a 5,000 to 10,000 fold lower activity. The 4-hydroxy metabolites were more potent than the 2-hydroxy metabolites, showing only a 20-200 times lower activity. The 2- and 4-methoxyesters of estrone were 700 times less active. It is concluded that the estrogenic potency of metabolites formed in cattle after treatment with E 2 β, like estrone, E 2 α and especially the esters of E 2 β, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.