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Ginseng consists of over twenty different ginsenosides and ginseng polysaccharides. We hypothesized that ginseng′s recognized ability to inhibit cancer cell proliferation may be due to the net effect of its major bioactive constituents. First we determined the anti-cancer role of ginseng′s major constituents by testing the effects of a ginsenoside or ginseng polysaccharide extract, alone or in combination, on MCF-7 cell proliferation in vitro. We next examined the effects of ginsenoside combinations on MCF-7 proliferation and determined cellular mechanisms of action. Powdered root of Panax quinquefolium (American ginseng; Sigma-Aldrich, St. Louis, MO) was subjected to 48 hr of methanol extraction (ginsenoside fraction), followed by hot water extraction (polysaccharide fraction) and purity was verified. We determined that ginseng root contains approximately 15% ginsenosides and 10% total ginseng polysaccharides by weight. After 6 days of treatment, MCF-7 cell proliferation was inhibited by either the ginsenoside fraction (IC50=0.18 μg/μl) or the polysaccharide fraction (0.12 μg/μl), in a more potent manner than a crude ginseng extract that contains both ginsenosides and polysaccharides (0.6 μg/μl), suggesting an antagonism between the two fractions at the cellular level. When MCF-7 cells were then co-treated with the ginseng polysaccharide fraction + ginsenoside Rb1, the major ginsenoside found in ginsenoside fraction. efficacy of the polysaccharide fraction was reduced (IC50= 0.28 vs 0.13 μg/μl), indicating that Rb1 may be responsible, in part, for the antagonism between the ginsenoside and polysaccharide fractions. Several ginsenosides have been identified that exhibit anti-cancer activity, including ginsenosides Rc, Rg3 and Rh2. When MCF-7 cells were treated with an IC50 dose of Rc (50μM), co-treatment with another major ginsenoside, Rg1 (25μM), completely prevented the ability of Rc to inhibit cell proliferation. However, Rb1, Rg3 and Rh2 enhanced the efficacy of Rc on MCF-7 cells. In fact, combining three anti-cancer ginsenosides in sub-therapeutic concentrations [Rc(10μM):Rg3(10μM):Rh2 (20μM)] produced a synergistic inhibition of MCF-7 cell proliferation. Mechanistic studies revealed that this ginsenoside ′cocktail′ potently inhibited pRb and arrested cell cycle progression at the G1/S phase, while producing a >4-fold increase in the pro-apoptotic Bax/Bcl-2 ratio when compared to ginsenoside alone. Together, these data show that interactions exist between ginsenosides and ginseng polysaccharides that can contribute to or attenuate ginseng′s anti-cancer activity, and may be responsible for the ′net′ effect of ginseng on breast cancer cells. Finding ginseng components that work together to prevent breast cancer progression has potential therapeutic value in breast cancer treatment. (funded by grant # CA121074)

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA