Examination for estrogenic activities of soyasaponin I and related compounds

The estrogenic activities, i.e., i) the binding ability to human estrogen receptors (hERs) α and β, ii) the effect on hER-dependent β-galactosidase induction, and iii) the effect on the estrogen-dependent growth of MCF-7 cells, of soybean saponin [soyasaponin I (1)] and related compounds [soyasapogenol B (3) and its monoglucuronide (2)] were investigated, since the amount of saponins in soybean is more than that of isoflavones which are known as phytoestrogen. The estrogenic activities of soybean saponins and related compounds were less than those of isoflavones. The binding and β-galactosidase-inducive behavior of compounds 1-3 was similar to that of tamoxifen which is known as an estrogen antagonist. However, their antagonistic activity was far less potent than that of tamoxifen. Contrary to the antagonistic activity, compounds 1-3 inhibited hER-dependent growth of MCF-7 cells. Especially, the sapogenol (3) showed anti-proliferative activity (IC ₅₀ < 1 μM) against MCF-7 cells.