Tocotrienols, a subgroup within the vitamin E family of compounds, display potent antiproliferative and apoptotic activity against neoplastic mammary epithelial cells at treatment doses that have little or no effect on normal cell growth and function. Recent studies have shown that treatment with a growth inhibitory, but non-cytotoxic dose (4 microM) of gamma-tocotrienol inhibits phosphatidylinositol-3-kinase-dependent kinase (Pl3K)/Pl3K-dependent kinase 1 (PDK-1)/mitogenic signaling over a 2-3 day period following treatment exposure, and these effects were not found to be associated with an increased in either phosphatase and tensin homologue deleted from chromosome 10 (PTEN) or protein phosphatase type 2A (PP2A) phosphatase activity. In addition, this treatment caused a large decrease in NFKB transcriptional activity, apparently by suppressing I kappa B-kinase (IKK)-alpha/beta activation, an enzyme associated with inducing NFKB activation. Since Akt and NFkappaB are intimately involved in mammary tumor cell proliferation and survival, these findings strongly suggest that the antiproliferative effects of gamma-tocotrienol result, at least in part, from a reduction in Akt and NFkappa B activity. In contrast, treatment with 20 microM gamma-tocotrienol (cytotoxic dose) resulted in caspase-8 and -3 activation and apoptosis. It was also shown that this same treatment caused a rapid and large decrease in Pl3K/PDK/Akt signaling within 2-4h following treatment exposure, and a corresponding decrease in intracellular levels of FLIP, an antiapoptotic protein that inhibits caspase-8 activation. In summary, both the antiproliferative and apoptotic effects of gamma-tocotrienol appear to be mediated by a reduction in the Pl3K/PDK-1 /Akt signaling, an important pathway associated with cell proliferation and survival in neoplastic mammary epithelial cells.

Tocotrienols, a subgroup within the vitamin E family of compounds, have been shown to display potent anticancer activity and inhibit preneoplastic and neoplastic mammary epithelial cell proliferation at treatment doses that have little or no effect on normal cell growth and function. However, the specific intracellular mechanisms mediating the antiproliferative effects of tocotrienols are presently unknown. Because Akt and nuclear factor kappaB (NFkappaB) are intimately involved in mammary tumor cell proliferation and survival, studies were conducted to determine the effects of gamma-tocotrienol on Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells in vitro. Treatment with 0-8 microM gamma-tocotrienol for 0-3 days caused a dose-responsive inhibition in +SA cell growth and mitotic activity, as determined by MTT colorimetric assay and proliferating cell nuclear antigen immunocytochemical staining, respectively. Studies also showed that treatment with 4 microM gamma-tocotrienol, a dose that inhibited +SA cell growth by more than 50% compared with that of untreated control cells, decreased intracellular levels of activated phosphotidylinositol 3-kinase-dependent kinase (PI3K)-dependent kinase 1 (phospho-PDK-1) and Akt, and reduced phospho-Akt kinase activity. Furthermore, these effects were not found to be associated with an increase in either phosphatase and tensin homologue deleted from chromosome 10 (PTEN) or protein phosphatase type 2A phosphatase activity. In addition, gamma-tocotrienol treatment was shown to decrease NFkappaB transcriptional activity, apparently by suppressing the activation of IkappaB-kinase-alpha/beta, an enzyme associated with inducing NFkappaB activation. In summary, these findings demonstrate that the antiproliferative effects of gamma-tocotrienol result, at least in part, from a reduction in Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells.

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Tocotrienols and tocopherols represent the 2 subgroups within the vitamin E family of compounds, but tocotrienols display significantly greater apoptotic activity against a variety of cancer cell types. However, the exact mechanism mediating tocotrienol-induced apoptosis is not understood. Studies were conducted to determine the effects of tocotrienols on mitochondrial-stress-mediated apoptotic signaling in neoplastic +SA mammary epithelial cells grown in vitro. Exposure for 24 h to 0-20 micromol/L gamma-tocotrienol resulted in a dose-responsive increase in +SA cells undergoing apoptosis, as determined by flow cytometric analysis of Annexin V staining. However, tocotrienol-induced apoptosis was not associated with a disruption or loss of mitochondrial membrane potential, or the release of mitochondrial cytochrome c into the cytoplasm, as determined by JC-1 flow cytometric staining and ELISA assay, respectively. Interestingly, apoptotic +SA cells showed a paradoxical decrease in mitochondrial levels of pro-apoptotic proteins Bid, Bax, and Bad, and a corresponding increase in mitochondrial levels of anti-apoptotic proteins, Bcl-2 and Bcl-xL, suggesting that mitochondrial membrane stability and integrity might actually be enhanced for a limited period of time following acute tocotrienol exposure. In summary, these findings clearly demonstrate that tocotrienol-induced apoptosis occurs independently of mitochondrial stress apoptotic signaling in neoplastic +SA mammary epithelial cells.

Tocopherols and tocotrienol represent the two subgroups within the vitamin E family of compounds, but only tocotrienols display potent anticancer activity at doses that have little or no effect on normal cell growth or function. Tocotrienols are potent antioxidants, but antitumor activity is independent of antioxidant activity. The exact reason why tocotrienols are more potent than tocopherols is not completely understood, but at least part of the reason is because of greater cellular accumulation. Furthermore, dose-response studies show that growth inhibitory doses of tocotrienolsare 5-6 times lower than their corresponding lethal doses, suggesting that the antiproliferative and cytotoxic effects of tocotrienols are mediated through different mechanisms. Recent studies showed that tocotrienol-induced programmed cell death (apoptosis) results from the activation of specific intracellular cysteine proteases (caspases) associated with death receptor activation and signal transduction. Furthermore, combined treatment with specific caspase inhibitors blocked the cytotoxic effects of tocotrienols in malignant mammary epithelial cells. In contrast, tocotrienolinhibition of cell proliferation appears to involve the suppression of multiple hormone- and growth factor-receptor mitogenic signaling pathways. Although additional studies are required to clarify the intracellular mechanisms mediating the anticancer effects of tocotrienols, experimental evidence strongly suggests that dietary supplementation of tocotrienols may provide significant health benefits in lowering the risk of breast cancer in women.

Vitamin E is a term that describes a group of compounds with similar yet unique chemical structures and biological activities. One interesting property possessed by certain vitamin E compounds-namely, delta-tocotrienol, RRR-alpha-tocopheryl succinate [vitamin E succinate (VES), a hydrolyzable ester-linked succinic acid analogue of RRR-alpha-tocopherol], and a novel vitamin E analogue referred to as alpha-TEA (alpha-tocopherol ether linked acetic acid analogue, which is a stable nonhydrolyzable analogue of RRR-alpha-tocopherol)-is their ability to induce cancer cells but not normal cells to undergo a form of cell death called apoptosis. In contrast, the parent compound, RRR-alpha-tocopherol, also referred to as natural or authentic vitamin E and known for its antioxidant properties, does not induce cancer-cell apoptosis. Efforts to understand how select vitamin E forms can induce cancer cells to undergo apoptosis have identified several nonantioxidant biological functions, including restoration of pro-death transforming growth factor-beta and Fas signaling pathways. Recent studies with alpha-TEA show it to be a potent inducer of apoptosis in a wide variety of epithelial cancer cell types, including breast, prostate, lung, colon, ovarian, cervical, and endometrial in cell culture, and to be effective in significantly reducing tumor burden and metastasis in a syngeneic mouse mammary tumor model, as well as xenografts of human breast cancer cells. Studies also show that alpha-TEA, in combination with the cyclooxygenase-2 inhibitor celecoxib and the chemotherapeutic drug 9-nitro-camptothecin decreases breast cancer animal model tumor burden and inhibits metastasis significantly better than do single-agent treatments.

Vitamin E is important not only for its cellular antioxidant and lipid-lowering properties, but also as an antiproliferating agent. It has also been shown to contribute to immunoregulation, antibody production, and resistance to implanted tumors. It has recently been shown that tocotrienols are the components of vitamin E responsible for growth inhibition in human breast cancer cells in vitro as well as in vivo through estrogen-independent mechanisms. Although tocotrienols act on cell proliferation in a dose-dependent manner and can induce programmed cell death, no specific gene regulation has yet been identified. In order to investigate the molecular basis of the effect of a tocotrienol-rich fraction (TRF) from palm oil, we performed a cDNA array analysis of cancer-related gene expression in estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-231) human breast cancer cells. The human breast cancer cells were incubated with or without 8 mug/mL of tocotrienols for 72 h. RNA was subsequently extracted and subjected to reverse transcription before being hybridized onto cancer arrays. Tocotrienol supplementation modulated significantly 46 out of 1200 genes in MDA-MB-231 cells. In MCF-7 cells, tocotrienol administration was associated with a lower number of affected genes. Interestingly, only three were affected in a similar fashion in both cell lines: c-myc binding protein MM-1, 23-kDa highly basic protein, and interferon-inducible protein 9-27 (IFITM-1). These proteins are most likely involved in the cell cycle and can exert inhibitory effects on cell growth and differentiation of the tumor cell lines. These data suggest that tocotrienols are able to affect cell homeostasis, possibly independent of their antioxidant activity.

Vitamin E derivative, RRR-alpha-tocopheryl succinate (vitamin E succinate, VES), is a potent pro-apoptotic agent, inducing apoptosis by restoring both transforming growth factor-beta (TGF-beta) and Fas (CD95) apoptotic signaling pathways that contribute to the activation of c-Jun N-terminal kinase (JNK)-mediated apoptosis. Objectives of these studies were to characterize signaling events involved in the pro-apoptotic actions of a naturally occurring form of vitamin E, delta-tocotrienol, and a novel vitamin E analog, alpha-tocopherol ether acetic acid analog [alpha-TEA; 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)chroman-6-yloxyacetic acid]. Like VES, alpha-TEA and delta-tocotrienol induced estrogen-nonresponsive MDA-MB-435 and estrogen-responsive MCF-7 human breast cancer cells to undergo high levels of apoptosis in a concentration- and time-dependent fashion. Like VES, the two compounds induced either no or lower levels of apoptosis in normal human mammary epithelial cells and immortalized but nontumorigenic human MCF-10A cells. The pro-apoptotic mechanisms triggered by the structurally distinct alpha-TEA and delta-tocotrienol were identical to those previously reported for VES, that is, alpha-TEA- and delta-tocotrienol-induced apoptosis involved up-regulation of TGF-beta receptor II expression and TGF-beta-, Fas- and JNK-signaling pathways. These data provide a better understanding of the anticancer actions of a dietary form of vitamin E (delta-tocotrienol) and a novel nonhydrolyzable vitamin E analog (alpha-TEA).

Tocotrienols, a subclass in the vitamin E family of compounds, have been shown to induce apoptosis by activating caspase-8 and caspase-3 in neoplastic mammary epithelial cells. Since caspase-8 activation is associated with death receptor apoptotic signaling, studies were conducted to determine the exact death receptor/ligand involved in tocotrienol-induced apoptosis. Highly malignant +SA mouse mammary epithelial cells were grown in culture and maintained in serum-free media. Treatment with 20 microM gamma-tocotrienol decreased+SA cell viability by inducing apoptosis, as determined by positive terminal dUTP nick end labeling (TUNEL) immunocytochemical staining. Western blot analysis showed that gamma-tocotrienol treatment increased the levels of cleaved (active) caspase-8 and caspase-3. Combined treatment with caspase inhibitors completely blocked tocotrienol-induced apoptosis. Additional studies showed that treatment with 100 ng/ml tumor necrosis factor-alpha (TNF-alpha), 100 ng/ml FasL, 100 ng/ml TNF-related apoptosis-inducing ligand (TRAIL), or 1 microg/ml apoptosis-inducing Fas antibody failed to induce death in +SA cells, indicating that this mammary tumor cell line is resistant to death receptor-induced apoptosis. Furthermore, treatment with 20 microM gamma-tocotrienol had no effect on total, membrane, or cytosolic levels of Fas, Fas ligand (FasL), or Fas-associated via death domain (FADD) and did not induce translocation of Fas, FasL, or FADD from the cytosolic to the membrane fraction, providing additional evidence that tocotrienol-induced caspase-8 activation is not associated with death receptor apoptotic signaling. Other studies showed that treatment with 20 microM gamma-tocotrienol induced a large decrease in the relative intracellular levels of phospho-phosphatidylinositol 3-kinase (PI3K)-dependent kinase 1 (phospho-PDK-1 active), phospho-Akt (active), and phospho-glycogen synthase kinase3, as well as decreasing intracellular levels of FLICE-inhibitory protein (FLIP), an antiapoptotic protein that inhibits caspase-8 activation, in these cells. Since stimulation of the PI3K/PDK/Akt mitogenic pathway is associated with increased FLIP expression, enhanced cellular proliferation, and survival, these results indicate that tocotrienol-induced caspase-8 activation and apoptosis in malignant +SA mammary epithelial cells is associated with a suppression in PI3K/PDK-1/Akt mitogenic signaling and subsequent reduction in intracellular FLIP levels.

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It has recently been shown that tocotrienols are the components of vitamin E responsible for inhibiting the growth of human breast cancer cells in vitro, through an estrogen-independent mechanism. Although tocotrienols act on cell proliferation in a dose-dependent manner and can induce programmed cell death, no specific gene regulation has yet been identified. To investigate the molecular basis of the effect of tocotrienols, we injected MCF-7 breast cancer cells into athymic nude mice. Mice were fed orally with 1 mg/d of tocotrienol-rich fraction (TRF) for 20 wk. At end of the 20 wk, there was a significant delay in the onset, incidence, and size of the tumors in nude mice supplemented with TRF compared with the controls. At autopsy, the tumor tissue was excised and analyzed for gene expression by means of a cDNA array technique. Thirty out of 1176 genes were significantly affected. Ten genes were downregulated and 20 genes up-regulated with respect to untreated animals, and some genes in particular were involved in regulating the immune system and its function. The expression of the interferon-inducible transmembrane protein-1 gene was significantly up-regulated in tumors excised from TRF-treated animals compared with control mice. Within the group of genes related to the immune system, we also found that the CD59 glycoprotein precursor gene was up-regulated. Among the functional class of intracellular transducers/effectors/modulators, the c-myc gene was significantly down-regulated in tumors by TRF treatment. Our observations indicate that TRF supplementation significantly and specifically affects MCF-7 cell response after tumor formation in vivo and therefore the host immune function. The observed effect on gene expression is possibly exerted independently from the antioxidant activity typical of this family of molecules.

Tocotrienols, which are Vitamin E isoforms, are known to inhibit the growth of human breast cancer cells due partly to apoptosis. However, the characterization of tocotrienol-induced apoptosis is incomplete, particularly what happens during the initiation phase that precedes execution of the cells. The objective of this study was to clarify the apoptotic effects of tocotrienols, with especial emphasis in determining if the mitochondria-mediated death pathway is activated when human breast cancer cells are incubated with a specific tocotrienol isomer. During incubation with gamma-tocotrienol, MDA-MB-231 human breast cancer cells showed membrane blebbing, and apoptotic bodies were present. Upon 4′,6-diamidino-2-phenylindole staining of the cells, chromatin condensation and fragmentation were observed. Additionally, the annexin V-binding assay detected the translocation of membrane phospholipid during earlier analysis of the cells. Taken together, these results further establish that gamma-tocotrienol can induce apoptosis in human breast cancer cells. To help elucidate how gamma-tocotrienol induced the apoptosis, some important parameters related to the mitochondria-mediated death pathway were examined next. In gamma-tocotrienol-treated cells, the mitochondria were disrupted. Collapse of the mitochondrial membrane potential was detected, and cytochrome c was released later from mitochondria. However, expression of Bax and Bcl-2 (mRNA and protein) did not change. Furthermore, poly-(ADP-ribose)-polymerase cleavage was not detected, suggesting that caspases were not involved in the gamma-tocotrienol-induced apoptosis. These results imply that cytochrome c is not the critical protein released from mitochondria that triggers gamma-tocotrienol-induced apoptosis in MDA-MB-231 cells.