(R)-Equol ((+)-Equol) is an ERα and ERβ agonist with Kis of 27.4 and 15.4 nM, respectively.

ERα:27.4 nM (Ki), ERβ:15.4 nM (Ki)

(R)-Equol produced a dose-dependent inhibitory effect on the invasive ability of MDA-MB-231 cells, and this inhibitory effect was obvious at the highest test concentration (50 μM).Following 48-h exposure to (R)-Equol, invasion is reduced by 62% (p=0.009, versus untreated cells) with 50 μM (R)-Equol. Matrix metalloproteinase-2 (MMP-2) expression is significantly down-regulated following treatment with 50 μM (R)-Equol (p=0.035) [2].

In animals, (R)-Equol significantly reduces the number of palpable tumors over time compared to controls (P=0.002). The number of palpable tumors per rat in the (R)-Equol-fed group is significantly lower than in rats treated with S-(-)equol (P=0.008). (R)-Equol-fed animals exhibit 43% fewer tumors than the control group, with this difference being highly statistically significant (P=0.004). The number of tumors per tumor-bearing animal is significantly lower in (R)-Equol-fed animals compared to controls (3.3±0.4 versus 5.5±0.5, P=0.004). At necropsy, the mean (±SEM) tumor weight per animal for (R)-Equol-fed rats (5.3±1.1 mg) is significantly reduced (P=0.04) compared to controls (9.9±1.4 mg). Feeding the (R)-Equol diet also results in significantly increased tumor latency (P=0.003) [3].