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

Abstract

A number of metabolites of 17b-estradiol were tested for their estrogenic activity using the ER-CA-LUX assay based on the increased expression of luciferase in exposed T47D breast cancer cells. E 2 b and estrone showed similar potencies in the test, whereas E 2 a was 100 times less active. Incubation of cells with estrone (0.35 mM) resulted in the formation of E 2 b, whereas the reverse reaction was observed for E 2 b. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17-hydroxy benzoate ester of E 2 b was 3 times less active than the parent compound. The 17-hydroxy palmitate and oleate esters of E 2 b, were respectively 25 and 200 times less active than the parent compound. The 2-hydroxy metabolites of E 2 b 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 b, like estrone, E 2 a and especially the esters of E 2 b, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.Key words: Estrogenicity; ER-CALUX; catecholestrogens; estradiol; estradiol-esters. L. A. P. Hoogenboom, RIKILT, Bornsesteeg 45, 6708PD Wageningen, The Netherlands, e-mail: L.A.P. Hoogenboom/rikilt.wag-ur.nl The use of 17b-estradiol for growth-promoting purposes in cattle may result in the increased formation of residues of not only the parent compound but also its metabolites. In order to investigate the potential risk for the consumer, it is essential to obtain information on the identity, levels and biological properties of these compounds. In cattle the major metabolites of E 2 b are estrone, the 17a-congener and their glucuronide conjugates (1-3). Previous studies showed increased levels of the parent compound, and the two major bovine metabolites,

Oestrogens, Xenoestrogens and Hormone-Dependent Cancers

“…Our observations were consistent with the results of [15], who demonstrated that 4-OH-E2 is more oestrogenic than 2-OH-E2. In [16] it was indicated that certain oestradiol metabolites, i.e., 4-OH-E2 and 16-OH-E2, are able to mimic the effects of 17β-oestradiol on proliferation and markers of tumour metastasis.…”

Screening of synthetic and plant-derived compounds for (anti)estrogenic and (anti)androgenic activities

“…Differences in metabolism were often responsible for the differences found between different cell lines and between cell lines and yeast-based bioassays [36,46,47]. Estrone for instance showed a REP of 0.2 in a proliferation test based on human breast cancer cells (Escreen) and the yeast estrogen bioassay, but was equally potent to E2 in a transcription activation assay based on human T47-D breast cancer cells [16,21,46]. In the ER-CALUX test with the T47-D breast cancer cells, the 17β-hydroxysteroid dehydrogenase 3 enzyme was responsible for the conversion of estrone into E2 and vice versa [46].…”

Steroid sulfatase inhibitors

“…[154][155][156][157][158] The prime motivation for studying these compounds was to search for potent STS inhibitors lacking the estrogenic effect displayed by EMATE based on the knowledge that 2-methoxyestradiol, an endogenous mammalian metabolite of estradiol, and 2-methoxyestrone are substantially less estrogenic than estrone and estradiol. 159,160 Indeed, the 2-methoxy analog 17a is a potent inhibitor of STS and shows tumor regression but no estrogenic effect in vivo. 65,154 With regard to STS inhibitory potency, 2-methoxy EMATE was approximately 7.5 times less active than EMATE as assessed in placental microsomes.…”