C2-Alkyl-substituted 1,1-bis(4-hydroxyphenyl)-2-phenylethenes were synthesized and assayed for estrogen receptor binding in a competition experiment with radiolabeled estradiol ([3H]-E2) using calf uterine cytosol. The relative binding affinity decreased with the length of the side chain R = H (3a: 35.2%) > Me (3b: 32.1%) > Et (3c: 6.20%) approximately CH2CF3 (3d: 5.95%) > n-Pr (3e: 2.09%) > Bu (3f: 0.62%). Agonistic and antagonistic effects were evaluated in the luciferase assay with MCF-7-2a cells stably transfected with the plasmid ERE(wtc)luc. All compounds showed high antiestrogenic activity without significant agonistic potency. The comparison of the IC(50) values for the inhibition of E2 (1 nM) documented the dependence of the antagonistic effects on the kind of the side chain: 3a (IC50 = 150 nM), 3b (IC50 = 30 nM), and 3f (IC50 = 500 nM) were weak antagonists, while 3c (IC50 = 15 nM), 3d (IC50 = 9 nM), and 3e (IC50 = 50 nM) were full antiestrogens and antagonized the effect of E2 completely. The most active compound 3d possessed the same antagonistic potency as 4-hydroxytamoxifen (4OHT: IC50= 7 nM) without bearing a basic side chain. 3d as well as all other 1,1-bis(4-hydroxyphenyl)-2-phenylalkenes were not able to influence the proliferation of hormone dependent MCF-7 cells despite the antagonistic mode of action. In this assay tamoxifen (TAM) and 4OHT reduced the cell growth concentration dependent up to T/C(corr) = 15% and 25%, respectively.

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C2-Alkyl substituted derivatives of the 1,1,2-tris(4-hydroxyphenyl)ethene 3a (alkyl = Me (3b), Et (3c), Prop (3d), But (3e)) were synthesized by reaction of 1,2-bis(4-methoxyphenyl)ethanone with the appropriate alkyl halide, followed by a Grignard reaction with 4-methoxyphenylmagnesium bromide, dehydration with phosphoric acid or hydrobromic acid, and ether cleavage with BBr(3). The compounds were tested for estrogen receptor (ER) binding affinity in a competition experiment with radio labeled estradiol ([(3)H]-E2) and for gene activation on the ER-positive MCF-7-2a cell line. All compounds showed high receptor binding affinity (RBA-value: 3b (52.1%) > 3a (45.5%) > 3c (29.6%) > 3d (4.03%) > 3e (0.95%)). The tests on hormone dependent MCF-7-2a breast cancer cells, stably transfected with the plasmid ERE(wtc)luc, revealed that all 1,1,2-tris(4-hydroxyphenyl)ethenes antagonized the effect of 1 nM estradiol (E2). The compounds 3b (IC(50) = 15 nM) and 3c (IC(50) = 10 nM) were equal in their effects to 4-hydroxytamoxifen (4OHT) (IC(50) = 7 nM). Agonistic effects were low. Only 3a and 3b activated the luciferase expression (relative activation at 1 microM: 3a 60%; 3b 35%). Despite their highly antagonistic potency, the 1,1,2-tris(4-hydroxyphenyl)ethenes showed only low cytotoxic properties on the hormone sensitive MCF-7 cell line.

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