Tocopherols and tocotrienols represent the two subgroups in the vitamin E family of compounds. However, only tocotrienols display potent antiproliferative and apoptotic activity on mammary cancer cells using treatment doses that have no effect on normal mammary epithelial cell growth or viability. Determining the mechanism(s) mediating the anticancer effects of tocotrienols would provide essential information necessary for understanding the potential health benefits of these compounds in reducing the risk of breast cancer in women. Several signaling pathways have been identified that may be involved in mediating the inhibitory effects of tocotrienols.
The specific aims of this proposal are: 1) to determine the role of vehicle fatty acid composition in modulating tocotrienol absorption and tissue distribution in vivo. Although the in vitro anticancer activity of tocotrienols are firmly established, and dietary intake of palm oil, the richest natural source of tocotrienols, inhibits carcinogen-induced mammary tumorigenesis, while palm oil diets stripped of tocotrienols have no protective effect, dietary supplementation of isolated tocotrienols has produced conflicting results in vivo. Since fat-soluble vitamins (tocotrienols) must be first emulsified by bile before absorption in the gut, and bile excretion is dependent upon the fatty acid composition in the diet, consumption of isolated tocotrienols alone is not sufficient to stimulate adequate bile excretion and is associated with the poor absorption of tocotrienols. It is believed that optimizing tocotrienol absorption and tissue distribution will enhance anticancer potency in vivo. 2) To determine the intracellular signaling mechanism(s) mediating the antiproliferative effects of tocotrienols in preneoplastic and neoplastic mammary epithelial cells in vitro. The antiproliferative effects of tocotrienols are associated with decreased signaling in multiple mitogenic pathways. However, the exact site(s) of action where tocotrienols act to inhibitory mitogenic signaling has not been determined; 3) To determine the intracellular signaling mechanism(s) mediating tocotrienol-induced caspase-8 activation and apoptosis in preneoplastic, neoplastic and malignant mammary epithelial cells in vitro. Although caspase-8 activation is associated with death receptor signaling, the exact receptor/ligand signaling mechanism(s) mediating tocotrienol-induced caspase-8 activation has not been determined.
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