Estrogenic activity of stilbene derivatives

We previously reported that trans-stilbene is metabolically activated to estrogenic compounds by a liver microsomal enzyme system. In this study, we demonstrated the structural requirement for estrogenic activity of various stilbene derivatives including proestrogens. High estrogenic activity in 4,4'-dihydroxystilbene, 4-amino-4'-hydroxystilbene, 4,4'-dihydroxy-alpha-methylstilbene, hexestrol, and diethylstilbestrol (DES), moderate activity in 4-hydroxystilbene, 4-aminostilbene, 4-hydroxyazobenzene, and 4-hydroxy-4'-nitrostilbene, low activity in 4-nitrostilbene, 4,4'-dihydroxydibenzyl, resveratrol, and 4-hydroxy-alpha-methylstyrene, and marginal activity in 4,4'-dimethoxystilbene and 4-hydroxymethylstilbene were observed in an estrogen reporter assay using the estrogen-responsive human breast cancer cell line MCF-7 and a binding assay with rat uterus estrogen receptor. In contrast, alpha-methylstilbene, 4,4'-dimethoxystilbene, 4-hydroxymethylstilbene, dibenzyl, tolan and azobenzene also exhibited estrogenic activities after incubation with liver microsomes of 3-methylcholanthrene- or phenobarbital-treated rats in the presence of NADPH. These results suggest that the structural requirements for the estrogenic activities of stilbene derivatives are a p-hydroxyl group in the A-phenyl ring, vinyl linkage, and a B-phenyl ring for the maximal activity, and hydrophobicity of the linkage for higher activity as observed in DES. p-Nitro and amino groups in the A-phenyl ring are also effective for the estrogenic activity.