Estrogenic properties of naturally occurring prenylated isoflavones in U2OS human osteosarcoma cells: Structure-activity relationships

Eight isoflavones derivatives, with isoprenyl and/or 7-methoxy substitution, isolated from Erythrina poeppigiana (Fabaceae) have been investigated for their estrogenic properties in receptor subtype-specific reporter gene assays. First we focused on their estrogen receptor alpha and beta (ER alpha and ER beta) selectivity, second we addressed structure-activity relationships, using bone-derived human osteosarcoma cell line (U2OS cells) stably expressing ER alpha or transiently expressing ER beta. Our results show that a substitution at position 3' together with a 7-methoxy substitution on the genistein skeleton is associated with a statistically significant activation of the ER alpha- and ER beta-dependent reporter gene expression in U2OS cells starting from 0.1 nM. Particularly, the 7-methoxy-3'-isoprenyl (1) and the 7-methoxy-3'-(3-methyl-2-hydroxybuten-3-yl) (3) derivatives of genistein induces an ER alpha- and ER beta-coupled luciferase activity at a concentration ten times lower than that of genistein, for which a statistically significant effect was observable at 1 nM. On the other hand, isoprenyl substitution at position 6 of the A ring, compound 5, seems to have very little impact on the genistein ability to induce ER-coupled luciferase activity in U2OS cells, while a double prenylation at positions 8 and 3', compound 7, is associated with an almost complete loss of function on the reporter gene activation in U2OS-ER alpha, but in ER beta expressing system the effectiveness remains on a statistically significant level, demonstrating an "exclusive ER beta-selectivity" in U2OS human osteosarcoma cells, and therefore 7 can be considered as an isotype-selective ER ligand. Finally all the tested isoflavones derivatives appear to exhibit a slightly pronounced ER beta preference, depending upon the position and the nature of the substituent moiety on the isoflavone skeleton. The estrogen-like effect of these prenylated isoflavone derivatives could be inhibited by the pure ER antagonist ICI 182 780, indicating that these effects were primarily mediated through ERs. (C) 2010 Elsevier Ltd. All rights reserved.