plastochromanol-8 and sesamin

γ-Tocotrienol and sesamin are phytochemicals that display potent anticancer activity. Since sesamin inhibits the metabolic degradation of tocotrienols, studies were conducted to determine if combined treatment with sesamin potentiates the antiproliferative effects of γ-tocotrienol on neoplastic mouse (+SA) and human (MCF-7 and MDA-MB-231) mammary cancer cells. Results showed that treatment with γ-tocotrienol or sesamin alone induced a significant dose-responsive growth inhibition, whereas combination treatment with these agents synergistically inhibited the growth of +SA, MCF-7 and MDA-MB-231 mammary cancer cells, while similar treatment doses were found to have little or no effect on normal (mouse CL-S1 and human MCF-10A) mammary epithelial cell growth or viability. However, sesamin synergistic enhancement of γ-tocotrienol-induced anticancer effects was not found to be mediated from a reduction in γ-tocotrienol metabolism. Rather, combined treatment with subeffective doses of γ-tocotrienol and sesamin was found to induce G1 cell cycle arrest, and a corresponding decrease in cyclin D1, CDK2, CDK4, CDK6, phospho-Rb, and E2F1 levels, and increase in p27 and p16 levels. Additional studies showed that the antiproliferative effect of combination treatment did not initiate apoptosis or result in a decrease in mammary cancer cell viability. Taken together, these findings indicate that the synergistic antiproliferative action of combined γ-tocotrienol and sesamin treatment in mouse and human mammary cancer cells is cytostatic, not cytotoxic, and results from G1 cell cycle arrest.

Topics: Animals; Antineoplastic Agents; Breast Neoplasms; Cell Line, Tumor; Chromans; Cyclin-Dependent Kinase Inhibitor Proteins; Cyclins; Dioxoles; Drug Synergism; Drug Therapy, Combination; E2F1 Transcription Factor; Female; Gene Expression Regulation, Neoplastic; Humans; Lignans; Mice; Molecular Structure; Retinoblastoma Protein; Vitamin E

Epidemiological studies have highlighted the ability of phytochemicals to reduce the risk of breast cancer by attenuating specific intracellular signaling pathways that regulate cell proliferation and survival. γ-Tocotrienol is a natural form of vitamin E that displays potent anticancer activity at doses that have no discernible toxicity toward normal cells. Sesamin is an abundant phytochemical found in sesame seed oil that also shows antiproliferative and antiangiogenic activity against human breast cancer cells. In this study, the combined treatment of subeffective doses of γ-tocotrienol and sesamin caused a synergistic inhibition of murine +SA mammary epithelial cell growth, as determined by the MTT assay and immunofluorescent Ki-67 staining. Western blot studies revealed that combined low-dose treatment of γ-tocotrienol and sesamin caused a marked reduction in EGF-induced ErbB3 and ErbB4 receptors phosphorylation (activation) and a relatively large decrease in intracellular levels of total and/or phosphorylated c-Raf, MEK1/2, ERK1/2, PI3K, PDK1, Akt, p-NFκB, Jak1, Jak2, and Stat1, as compared to cells treated with only one compound or in the vehicle-treated control group. These findings demonstrate that the synergistic growth inhibitory effects of γ-tocotrienol and sesamin treatment are associated with suppression of EGF-dependent mitogenic signaling in mammary tumor cells and suggest that dietary supplementation with these phytochemicals may provide some benefits in the prevention and/or treatment of breast cancer.

Topics: Animals; Antineoplastic Agents, Phytogenic; Breast Neoplasms; Cell Count; Cell Line, Tumor; Cell Survival; Chromans; Dioxoles; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Drug Synergism; Female; Lignans; MAP Kinase Signaling System; Mice; Mice, Inbred BALB C; Microscopy, Confocal; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-raf; Receptor, ErbB-3; STAT1 Transcription Factor; Vitamin E