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

A number of metabolites of 17 beta -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)beta and estrone showed similar potencies in the test, whereas E(2)alpha was 100 times less active. Incubation of cells with estrone (0.35 muM) resulted in the formation of E(2)beta, whereas the reverse reaction was observed for E(2)beta. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17-hydroxy benzoate ester of E(2)beta was 3 times less active than the parent compound. The 17-hydroxy palmitate and oleate esters of E(2)beta, were respectively 25 and 200 times less active than the parent compound. The 2-hydroxy metabolites of E(2)beta 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)beta, like estrone, E(2)alpha and especially the esters of E(2)beta, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.