The
flavonoid family of phytochemicals, particularly those derived from soy, has received attention regarding their hormonal activity and their effects on
human health and
disease. The types and amounts of these compounds in soy and other plants are controlled by both constitutive expression and stress-induced
biosynthesis. The
health benefits of soy may therefore be dependent upon the amounts of the various hormonally active phytochemicals present. We have identified increased
biosynthesis of the
isoflavonoid phytoalexin compounds, Glyceollins I, II and III, in soy plants grown under stressed conditions (elicited soy), which exhibit marked anti-
estrogenic effects on ER function. Here we demonstrate that specific glyceollins, isolated from elicited soy, displayed anti-estrogenic activity, suppressing basal and
estrogen stimulated
colony formation of ER-positive
estrogen dependent
breast cancer cells and inhibiting ER-dependent
gene expression of
progesterone receptor (PgR) and stromal derived factor-1 (SDF1 / CXCL12). Examining the effects of
glyceollin on
in vivo tumor formation / growth we demonstrate the ability of glyceollins to significantly suppress basal and
estrogen-stimulated
tumor growth of ER-positive MCF-7 breast and BG-1
ovarian carcinoma cells in ovariectomized female nude mice. We further demonstrate that the effects of glyceollins on suppression of
tumor growth correlate with inhibition of estrogen stimulated PgR expression. In contrast to the uterotropic activity of
tamoxifen the glyceollins displayed no uterine
agonist activity. The
Glyceollin (I-III) compounds may represent an important component of the health effects of soy as well as represent novel anti-estrogens useful in the prevention or treatment of breast and
ovarian carcinoma.