Gamma-tocotrienol suppresses prostate cancer cell proliferation and invasion through multiple-signalling pathways

Gamma-tocotrienol treatment increased peroxiredoxin-4 expression in HepG2 liver cancer cell line

Background

To determine the antiproliferative effect of gamma-tocotrienol (GTT) treatment on differential protein expression in HepG2 cells.

Methods

HepG2 cells were treated with 70 μM GTT for 48 hours and differentially expressed protein spots were determined by two-dimensional electrophoresis (2DE), identified by MALDI-TOF mass spectrometer (MS) and validated by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

GTT treatment on HepG2 cells showed a total of five differentially expressed proteins when compared to their respective untreated cells where three proteins were down-regulated and two proteins were up-regulated. One of these upregulated proteins was identified as peroxiredoxin-4 (Prx4). Validation by qRT-PCR however showed decreased expression of Prx4 mRNA in HepG2 cells following GTT treatment.

Conclusions

GTT might directly influence the expression dynamics of peroxiredoxin-4 to control proliferation in liver cancer.

Y-tocotrienol inhibits angiogenesis-dependent growth of human hepatocellular carcinoma through abrogation of AKT/mTOR pathway in an orthotopic mouse model

Angiogenesis is one of the key hallmarks of cancer. In this study, we investigated whether γ-tocotrienol can abrogate angiogenesis-mediated tumor growth in hepatocellular carcinoma (HCC) and if so, through what molecular mechanisms. We observed that γ-tocotrienol inhibited vascular endothelial growth factor (VEGF)-induced migration, invasion, tube formation and viability of HUVECs in vitro. Moreover, γ-tocotrienol reduced the number of capillary sprouts from matrigel embedded rat thoracic aortic ring in a dose-dependent manner. Also, in chick chorioallantoic membrane assay, γ-tocotrienol significantly reduced the blood vessels formation. We further noticed that γ-tocotrienol blocked angiogenesis in an in vivo matrigel plug assay. Furthermore, γ-tocotrienol inhibited VEGF-induced autophosphorylation of VEGFR2 in HUVECs and also suppressed the constitutive activation of AKT/mammalian target of rapamycin (mTOR) signal transduction cascades in HUVECs as well as in HCC cells. Interestingly, γ-tocotrienol was also found to significantly reduce the tumor growth in an orthotopic HCC mouse model and inhibit tumor-induced angiogenesis in HCC patient xenografts through the suppression of various biomarkers of proliferation and angiogenesis. Taken together, our findings strongly suggest that γ-tocotrienol might be a promising anti-angiogenic drug with significant antitumor activity in HCC.

Cytotoxicity and apoptotic activities of alpha-, gamma- and delta-tocotrienol isomers on human cancer cells

Background

Tocotrienols, especially the gamma isomer was discovered to possess cytotoxic effects associated with the induction of apoptosis in numerous cancers. Individual tocotrienol isomers are believed to induce dissimilar apoptotic mechanisms in different cancer types. This study was aimed to compare the cytotoxic potency of alpha-, gamma- and delta-tocotrienols, and to explore their resultant apoptotic mechanisms in human lung adenocarcinoma A549 and glioblastoma U87MG cells which are scarcely researched.

Methods

The cytotoxic effects of alpha-, gamma- and delta-tocotrienols in both A549 and U87MG cancer cells were first determined at the cell viability and morphological aspects. DNA damage types were then identified by comet assay and flow cytometric study was carried out to support the incidence of apoptosis. The involvements of caspase-8, Bid, Bax and mitochondrial membrane permeability (MMP) in the execution of apoptosis were further expounded.

Results

All tocotrienols inhibited the growth of A549 and U87MG cancer cells in a concentration- and time-dependent manner. These treated cancer cells demonstrated some hallmarks of apoptotic morphologies, apoptosis was further confirmed by cell accumulation at the pre-G₁ stage. All tocotrienols induced only double strand DNA breaks (DSBs) and no single strand DNA breaks (SSBs) in both treated cancer cells. Activation of caspase-8 leading to increased levels of Bid and Bax as well as cytochrome c release attributed by the disruption of mitochondrial membrane permeability in both A549 and U87MG cells were evident.

Conclusions

This study has shown that delta-tocotrienol, in all experimental approaches, possessed a higher efficacy (shorter induction period) and effectiveness (higher induction rate) in the execution of apoptosis in both A549 and U87MG cancer cells as compared to alpha- and gamma-tocotrienols. Tocotrienols in particular the delta isomer can be an alternative chemotherapeutic agent for treating lung and brain cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/1472-6882-14-469) contains supplementary material, which is available to authorized users.

Antiproliferation and induction of caspase-8-dependent mitochondria-mediated apoptosis by β-tocotrienol in human lung and brain cancer cell lines

The pure vitamin isomer, β-tocotrienol has the least abundance among the other vitamin E isomers that are present in numerous plants. Hence, it is very scarcely studied for its bioactivity. In this study, the antiproliferative effects and primary apoptotic mechanisms of β-tocotrienol on human lung adenocarcinoma A549 and glioblastoma U87MG cells were investigated. It was evidenced that β-tocotrienol had inhibited the growth of both A549 (GI50=1.38±0.334μM) and U87MG (GI50=2.53±0.604μM) cells at rather low concentrations. Cancer cells incubated with β-tocotrienol were also found to exhibit hallmarks of apoptotic morphologies including membrane blebbing, chromatin condensation and formation of apoptotic bodies. The apoptotic properties of β-tocotrienol in both A549 and U87MG cells were the results of its capability to induce significant (P<0.05) double-strand DNA breaks (DSBs) without involving single-strand DNA breaks (SSBs). β-Tocotrienol is said to induce activation of caspase-8 in both A549 and U87MG cells guided by no activation when caspase-8 inhibitor, z-IETD-fmk was added. Besides, disruption on the mitochondrial membrane permeability of the cells in a concentration- and time-dependent manner had occurred. The induction of apoptosis by β-tocotrienol in A549 and U87MG cells was confirmed to involve both the death-receptor mediated and mitochondria-dependent apoptotic pathways. These findings could potentiate the palm oil derived β-tocotrienol to serve as a new anticancer agent for treating human lung and brain cancers.

Polysaccharopeptide enhanced the anti-cancer effect of gamma-tocotrienol through activation of AMPK

Background

Prostate cancer (PCa) frequently relapses after hormone ablation therapy. Unfortunately, once progressed to the castration resistant stage, the disease is regarded as incurable as prostate cancer cells are highly resistant to conventional chemotherapy.

Method

We recently reported that the two natural compounds polysaccharopeptide (PSP) and Gamma-tocotrienols (γ-T3) possessed potent anti-cancer activities through targeting of CSCs. In the present study, using both prostate cancer cell line and xenograft models, we seek to investigate the therapeutic potential of combining γ-T3 and PSP in the treatment of prostate cancer.

Result

We showed that in the presence of PSP, γ-T3 treatment induce a drastic activation of AMP-activated protein kinase (AMPK). This was accompanied with inactivation of acetyl-CoA carboxylase (ACC), as evidenced by the increased phosphorylation levels at Ser 79. In addition, PSP treatment also sensitized cancer cells toward γ-T3-induced cytotoxicity. Furthermore, we demonstrated for the first time that combination of PSP and γ-T3 treaments significantly reduced the growth of prostate tumor in vivo.

Conclusion

Our results indicate that PSP and γ-T3 treaments may have synergistic anti-cancer effect in vitro and in vivo, which warrants further investigation as a potential combination therapy for the treatment of cancer.

Tissue distribution of emulsified γ-tocotrienol and its long-term biological effects after subcutaneous administration

Background

γ-tocotrienol (GT3), an analogue of vitamin E, has gained increasing scientific interest recently as it provides significant health benefits. It has been shown that emulsified GT3, after subcutaneous administration, has long-term biological effects. However, whether the effects are due to the increase of GT3 level in the early phase following administration or the persistent functions after accumulation in tissues is unknown. This study was conducted to determine the levels of GT3 in different tissues by high performance liquid chromatography (HPLC) with a fluorescence detector after a single-dose of GT3 with polyethylene glycol (PEG-400) emulsion via subcutaneous injection. Previous studies have explored that GT3 has favorable effects on bone and can inhibit osteoclast formation. To confirm the persistent biological activity of accumulated GT3 in tissues, receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) gene expressions, which have an important role in regulating osteoclast formation, were also evaluated in bone tissue on day 1, 3, 7 and 14 after a signal subcutaneous injection of GT3.

Methods

C57BL/6 female mice were administrated GT3 (100 mg/kg body weight) with PEG-400 emulsion by subcutaneous injection. GT3 levels in different tissues were determined by HPLC with a fluorescence detector. Gene expressions were measured by real-time PCR.

Results

GT3 predominantly accumulated in adipose and heart tissue, and was maintained at a relatively stable level in bone tissues after a single-dose administration. Accumulated GT3 in bone tissues significantly inhibited the increase in RANKL expression and the decrease in OPG expression induced by db-cAMP.

Conclusions

We investigated the tissue distribution of GT3 with PEG emulsion by subcutaneous administration, which has never been reported so far. Our results suggest that GT3 with PEG emulsion accumulated in tissues is able to carry out a long-term biological effect and has therapeutic value for treating and preventing osteoporosis.

The ID proteins: master regulators of cancer stem cells and tumour aggressiveness

Inhibitor of DNA binding (ID) proteins are transcriptional regulators that control the timing of cell fate determination and differentiation in stem and progenitor cells during normal development and adult life. ID genes are frequently deregulated in many types of human neoplasms, and they endow cancer cells with biological features that are hijacked from normal stem cells. The ability of ID proteins to function as central 'hubs' for the coordination of multiple cancer hallmarks has established these transcriptional regulators as therapeutic targets and biomarkers in specific types of human tumours.

Vitamin E δ-tocotrienol prolongs survival in the LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) transgenic mouse model of pancreatic cancer

Previous work has shown that vitamin E δ-tocotrienol (VEDT) prolongs survival and delays progression of pancreatic cancer in the LSL-Kras(G12D)(/+);Pdx-1-Cre mouse model of pancreatic cancer. However, the effect of VEDT alone or in combination with gemcitabine in the more aggressive LSL-Kras(G12D)(/+);LSL-Trp53(R172H)(/+);Pdx-1-Cre (KPC) mouse model is unknown. Here, we studied the effects of VEDT and the combination of VEDT and gemcitabine in the KPC mice. KPC mice were randomized into four groups: (i) vehicle [olive oil, 1.0 mL/kg per os twice a day and PBS 1.0 mL/kg intrapertoneally (i.p.) twice a week], (ii) gemcitabine (100 mg/kg i.p. twice a week), (iii) VEDT (200 mg/kg per os twice a day), and (iv) gemcitabine + VEDT. Mice received treatment until they displayed symptoms of impending death from pancreatic cancer, at which point animals were euthanized. At 16 weeks, survival was 10% in the vehicle group, 30% in the gemcitabine group, 70% in the VEDT group (P < 0.01), and 90% in the VEDT combined with gemcitabine group (P < 0.05). VEDT alone and combined with gemcitabine resulted in reversal of epithelial-to-mesenchymal transition in tumors. Biomarkers of apoptosis (plasma CK18), PARP1 cleavage, and Bax expression were more greatly induced in tumors subjected to combined treatment versus individual treatment. Combined treatment induced cell-cycle inhibitors (p27(Kip1) and p21(Cip1)) and inhibited VEGF, vascularity (CD31), and oncogenic signaling (pAKT, pMEK, and pERK) greater than individual drugs. No significant differences in body weight gain between drug treatment and control mice were observed. These results strongly support further investigation of VEDT alone and in combination with gemcitabine for pancreatic cancer prevention and treatment.

Prostate cancer chemoprevention in men of African descent: current state of the art and opportunities for future research

Prostate cancer is the most frequently diagnosed malignancy in men. However, African American/Black men are 60 % more likely to be diagnosed with and 2.4 times more likely to die from prostate cancer, compared to Non-Hispanic White men. Despite the increased burden of this malignancy, no evidence-based recommendation regarding prostate cancer screening exists for the high-risk population. Moreover, in addition to screening and detection, African American men may constitute a prime population for chemoprevention. Early detection and chemoprevention may thus represent an integral part of prostate cancer control in this population. Importantly, recent research has elucidated biological differences in the prostate tumors of African American compared to European American men. The latter may enable a more favorable response in African American men to specific chemopreventive agents that target relevant signal transduction pathways. Based on this evolving evidence, the aims of this review are threefold. First, we aim to summarize the biological differences that were reported in the prostate tumors of African American and European American men. Second, we will review the single- and multi-target chemopreventive agents placing specific emphasis on the pathways implicated in prostate carcinogenesis. And lastly, we will discuss the most promising nutraceutical chemopreventive compounds. Our review underscores the promise of chemoprevention in prostate cancer control, as well as provides justification for further investment in this filed to ultimately reduce prostate cancer morbidity and mortality in this high-risk population of African American men.

Tocotrienols promote apoptosis in human breast cancer cells by inducing poly(ADP-ribose) polymerase cleavage and inhibiting nuclear factor kappa-B activity

OBJECTIVES

Tocotrienols and tocopherols are members of the vitamin E family, with similar structures; however, only tocotrienols have been reported to achieve potent anti-cancer effects. The study described here has evaluated anti-cancer activity of vitamin E to elucidate mechanisms of cell death, using human breast cancer cells.

MATERIALS AND METHODS

Anti-cancer activity of a tocotrienol-rich fraction (TRF) and a tocotrienol-enriched fraction (TEF) isolated from palm oil, as well as pure vitamin E analogues (α-tocopherol, α-, δ- and γ-tocotrienols) were studied using highly aggressive triple negative MDA-MB-231 cells and oestrogen-dependent MCF-7 cells, both of human breast cancer cell lines. Cell population growth was evaluated using a Coulter particle counter. Cell death mechanism, poly(ADP-ribose) polymerase cleavage and levels of NF-κB were determined using commercial ELISA kits.

RESULTS

Tocotrienols exerted potent anti-proliferative effects on both types of cell by inducing apoptosis, the underlying mechanism of cell death being ascertained using respective IC50 concentrations of all test compounds. There was marked induction of apoptosis in both cell lines by tocotrienols compared to treatment with Paclitaxel, which was used as positive control. This activity was found to be associated with cleavage of poly(ADP-ribose) polymerase (a DNA repair protein), demonstrating involvement of the apoptotic cell death signalling pathway. Tocotrienols also inhibited expression of nuclear factor kappa-B (NF-κB), which in turn can increase sensitivity of cancer cells to apoptosis.

CONCLUSION

Tocotrienols induced anti-proliferative and apoptotic effects in association with DNA fragmentation, poly(ADP-ribose) polymerase cleavage and NF-κB inhibition in the two human breast cancer cell lines.

Effect of annatto-tocotrienols supplementation on the development of mammary tumors in HER-2/neu transgenic mice

Tocotrienols (T3), the lesser known isomers of vitamin E, have been reported to possess anticancer activity both in in vitro and in vivo experimental models of rodents transplanted with parental tumors or treated with carcinogens. We investigated the effects of dietary supplementation with annatto-T3 (90% δ-T3 and 10% γ-T3) on the spontaneous development of mammary tumors in HER-2/neu transgenic mice. Underlying mechanisms of the antitumor effect were evaluated by studying apoptosis, senescent-like growth arrest, immune modulation, oxidative effect and the expression of HER-2/neu in tumoral mammary glands of transgenic mice and in vitro in human and mice tumor cell lines. Annatto-T3 supplementation delayed the development of mammary tumors, reducing the number and size of mammary tumor masses and those of lung metastases. In annatto-T3-supplemented mice, both apoptosis and senescent-like growth arrest of tumor cells were increased in mammary glands while no immune modulation was observed. In vitro, a dose-dependent inhibition of cell growth, increased apoptosis and senescent-like growth arrest and a time-dependent accumulation of reactive oxygen species were observed in tumor cells treated with annatto-T3 or purified δ-T3. Annatto-T3 reduced both HER-2/neu mRNA and p185(HER-2/neu) protein in tumors and in tumor cell lines. The results show that the antitumor effect of annatto-T3 supplementation in HER-2/neu transgenic mice is mainly related to the direct induction of oxidative stress, senescent-like growth arrest and apoptosis of tumor cells rather than to an immune modulation.

A key regulator of cholesterol homoeostasis, SREBP-2, can be targeted in prostate cancer cells with natural products

There is growing evidence showing that prostate cancer cells have perturbed cholesterol homoeostasis, accumulating cholesterol to promote cell growth. Consequently, cholesterol-lowering drugs such as statins are being evaluated in prostate cancer treatment. Furthermore, natural products such as betulin (from birch tree bark) and tocotrienol (a minor form of vitamin E) have been shown to lower cholesterol levels. Using these drugs and oxysterols, we have determined which aspects of cholesterol homoeostasis should be targeted in prostate cancer, e.g. cellular cholesterol levels are increased by the transcription factor SREBP-2 (sterol-regulatory-element-binding protein isoform 2), whereas LXR (liver X receptor) promotes cholesterol efflux. Whereas betulin exerted non-specific effects on cell viability, tocotrienols produced a strong direct correlation between SREBP-2 activity and cell viability. Mechanistically, tocotrienols lowered SREBP-2 activity by degrading mature SREBP-2 independently of the proteasome. In contrast, no correlation was seen between LXR activity and cell viability, implying that SREBP-2 is a better target than LXR for prostate cancer treatment. Lastly, androgen-dependent and -independent LNCaP cells were both sensitive to tocotrienols. Overall, this suggests that tocotrienols and other drugs targeting the SREBP-2 pathway are a potential therapeutic option for prostate cancer.

δ- and γ-tocotrienols induce classical ultrastructural apoptotic changes in human T lymphoblastic leukemic cells

Tocotrienols are isomers of the vitamin E family, which have been reported to exert cytotoxic effects in various cancer cells. Although there have been some reports on the effects of tocotrienols in leukemic cells, ultrastructural evidence of tocotrienol-induced apoptotic cell death in leukemic cells is lacking. The present study investigated the effects of three isomers of tocotrienols (alpha, delta, and gamma) on a human T lymphoblastic leukemic cell line (CEM-SS). Cell viability assays showed that all three isomers had cytotoxic effects (p < 0.05) on CEM-SS cells with delta-tocotrienol being the most potent. Transmission electron microscopy showed that the cytotoxic effects by delta- and gamma-tocotrienols were through the induction of an apoptotic pathway as demonstrated by the classical ultrastructural apoptotic changes characterized by peripheral nuclear chromatin condensation and nuclear fragmentation. These findings were confirmed biochemically by the demonstration of phosphatidylserine externalization via flow cytometry analysis. This is the first study showing classical ultrastructural apoptotic changes induced by delta- and gamma-tocotrienols in human T lymphoblastic leukemic cells.

Chromatographic analyses of tocopherols and tocotrienols in palm oil

Analyses of tocols (tocopherols and tocotrienols) in palm oil have been extensively reported in the past. However, due to the scarcity of individual tocotrienol standards, calibrations have mostly been carried out using only α-tocopherol as standard. Moreover, even if the individual tocotrienols are being used, their reliability is often questioned, because tocotrienols are highly susceptible to oxidation and deterioration. This paper reports on the study of the deterioration rate of individual tocotrienol standards upon storage as well as different calibration methods for the tocols in palm oil.

First evidence that γ-tocotrienol inhibits the growth of human gastric cancer and chemosensitizes it to capecitabine in a xenograft mouse model through the modulation of NF-κB pathway

PURPOSE

Because of poor prognosis and development of resistance against chemotherapeutic drugs, the existing treatment modalities for gastric cancer are ineffective. Hence, novel agents that are safe and effective are urgently needed. Whether γ-tocotrienol can sensitize gastric cancer to capecitabine in vitro and in a xenograft mouse model was investigated.

EXPERIMENTAL DESIGN

The effect of γ-tocotrienol on proliferation of gastric cancer cell lines was examined by mitochondrial dye uptake assay, apoptosis by esterase staining, NF-κB activation by DNA-binding assay, and gene expression by Western blotting. The effect of γ-tocotrienol on the growth and chemosensitization was also examined in subcutaneously implanted tumors in nude mice.

RESULTS

γ-Tocotrienol inhibited the proliferation of various gastric cancer cell lines, potentiated the apoptotic effects of capecitabine, inhibited the constitutive activation of NF-κB, and suppressed the NF-κB-regulated expression of COX-2, cyclin D1, Bcl-2, CXCR4, VEGF, and matrix metalloproteinase-9 (MMP-9). In a xenograft model of human gastric cancer in nude mice, we found that administration of γ-tocotrienol alone (1 mg/kg body weight, intraperitoneally 3 times/wk) significantly suppressed the growth of the tumor and this effect was further enhanced by capecitabine. Both the markers of proliferation index Ki-67 and for microvessel density CD31 were downregulated in tumor tissue by the combination of capecitabine and γ-tocotrienol. As compared with vehicle control, γ-tocotrienol also suppressed the NF-κB activation and the expression of cyclin D1, COX-2, intercellular adhesion molecule-1 (ICAM-1), MMP-9, survivin, Bcl-xL, and XIAP.

CONCLUSIONS

Overall our results show that γ-tocotrienol can potentiate the effects of capecitabine through suppression of NF-κB-regulated markers of proliferation, invasion, angiogenesis, and metastasis.

γ-Tocotrienol does not substantially protect DS neurons from hydrogen peroxide-induced oxidative injury

Background

Down syndrome (DS) neurons are more susceptible to oxidative stress and previous studies have shown that vitamin E was able to reduce oxidative stress and improve DS neurons' viability. Therefore, this study was done to investigate the protective role of γ-tocotrienol (γT3) in DS neurons from hydrogen peroxide (H₂O₂) -induced oxidative stress. The pro-apoptosis tendency of γT3 was compared to α-tocopherol (αT) in non-stress condition as well.

Methods

Primary culture of DS and euploid neurons were divided into six groups of treatment: control, H₂O₂, γT3 pre-treatment with H₂O₂, γT3 only, αT pre-treatment with H₂O₂ and αT only. The treatments were assessed by MTS assay and apoptosis assay by single-stranded DNA (ssDNA) apoptosis ELISA assay, Hoechst and Neu-N immunofluorescence staining. The cellular uptake of γT3 and αT was determined by HPLC while protein expressions were determined by Western blot. Comparison between groups was made by the Student's t test, one-way ANOVA and Bonferroni adjustment as well as two-way ANOVA for multiple comparisons.

Results

One day incubation of γT3 was able to reduced apoptosis of DS neurons by 10%, however γT3 was cytotoxic at longer incubation period (14 days) and at concentrations ≥ 100 μM. Pre-treatment of αT and γT3 only attenuate apoptosis and increase cell viability in H₂O₂-treated DS and euploid neurons by 10% in which the effects were minimal to maintain most of the DS cells' morphology. γT3 act as a free radical scavenger by reducing ROS generated by H₂O₂. In untreated controls, DS neurons showed lower Bcl-2/Bax ratio and p53 expression compared to normal neurons, while cPKC and PKC-δ expressions were higher in DS neurons. On the other hand, pre-treatment of γT3 in H₂O₂-treated DS neurons have reduced Bcl-2/Bax ratio, which was not shown in euploid neurons. This suggests that pre-treatment of γT3 did not promote DS cell survival. Meanwhile γT3 and αT treatments without H₂O₂ as well as pre-treatment of γT3 and αT induced changes in cPKC and PKC-δ expression in DS neurons suggesting interaction of γT3 and αT with PKC activity.

Conclusion

Our study suggests that γT3 pre-treatment are not sufficient to protect DS neurons from H₂O₂-induced oxidative assault, instead induced the apoptosis process.

Tocotrienol as a potential anticancer agent

Vitamin E is composed of two structurally similar compounds: tocopherols (TPs) and tocotrienols (T3). Despite being overshadowed by TP over the past few decades, T3 is now considered to be a promising anticancer agent due to its potent effects against a wide range of cancers. A growing body of evidence suggests that in addition to its antioxidative and pro-apoptotic functions, T3 possesses a number of anticancer properties that make it superior to TP. These include the inhibition of epithelial-to-mesenchymal transitions, the suppression of vascular endothelial growth factor tumor angiogenic pathway and the induction of antitumor immunity. More recently, T3, but not TP, has been shown to have chemosensitization and anti-cancer stem cell effects, further demonstrating the potential of T3 as an effective anticancer therapeutic agent. With most of the previous clinical studies on TP producing disappointing results, research has now focused on testing T3 as the next generation vitamin E for chemoprevention and cancer treatment. This review will summarize recent developments in the understanding of the anticancer effects of T3. We will also discuss current progress in clinical trials involving T3 as an adjuvant to conventional cancer therapy.

Research Spotlight: Delivery of the vitamin E compound tocotrienol to cancer cells

Tocotrienol, a member of the vitamin E family of compounds, is currently receiving increased attention owing to its highly promising anticancer effects. However, its potential in cancer therapy is limited by its poor bioavailability and its inability to specifically reach tumors at therapeutic concentrations after intravenous administration. In order to address these problems, various delivery strategies have been proposed, such as the inclusion of tocotrienol in γ-cyclodextrins, prodrugs and emulsions, and entrapment in lipid nanoparticles and vesicles. Among these approaches, we have demonstrated that the entrapment of tocotrienol within vesicles bearing transferrin, whose receptors are overexpressed on numerous cancer cells, significantly improved the uptake by cancer cells overexpressing transferrin receptors. Consequently, the intravenous administration of tocotrienol entrapped in transferrin-bearing vesicles led to tumor regression and even complete tumor suppression in some cases in a murine tumor model, as well as improvement of animal survival. Transferrin-bearing vesicles are therefore highly promising for the delivery of tocotrienol to cancer cells in vitro and in vivo, and should be further investigated to optimize the anticancer therapeutic effect of tocotrienol.

γ-Tocotrienol is a novel inhibitor of constitutive and inducible STAT3 signalling pathway in human hepatocellular carcinoma: potential role as an antiproliferative, pro-apoptotic and chemosensitizing agent

BACKGROUND AND PURPOSE

Activation of signal transducer and activator of transcription 3 (STAT3) play a critical role in the survival, proliferation, angiogenesis and chemoresistance of tumour cells. Thus, agents that suppress STAT3 phosphorylation have potential as cancer therapies. In the present study, we investigated whether the apoptotic, antiproliferative and chemosensitizing effects of γ-tocotrienol are associated with its ability to suppress STAT3 activation in hepatocellular carcinoma (HCC).

EXPERIMENTAL APPROACH

The effect of γ-tocotrienol on STAT3 activation, associated protein kinases and phosphatase, STAT3-regulated gene products, cellular proliferation and apoptosis in HCC cells was investigated.

KEY RESULTS

γ-Tocotrienol inhibited both the constitutive and inducible activation of STAT3 with minimum effect on STAT5. γ-Tocotrienol also inhibited the activation of Src, JAK1 and JAK2 implicated in STAT3 activation. Pervanadate reversed the γ-tocotrienol-induced down-regulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that γ-tocotrienol induced the expression of the tyrosine phosphatase SHP-1 and deletion of the SHP-1 gene by small interfering RNA abolished the ability of γ-tocotrienol to inhibit STAT3 activation. γ-Tocotrienol also down-regulated the expression of STAT3-regulated gene products, including cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and vascular endothelial growth factor. Finally, γ-tocotrienol inhibited proliferation, induced apoptosis and significantly potentiated the apoptotic effects of chemotherapeutic drugs (paclitaxel and doxorubicin) used for the treatment of HCC.

CONCLUSIONS AND IMPLICATIONS

Overall, these results suggest that γ-tocotrienol is a novel blocker of the STAT3 activation pathway, with a potential role in future therapies for HCC and other cancers.

MAP Kinases and Prostate Cancer

The three major mitogen-activated protein kinases (MAPKs) p38, JNK, and ERK are signal transducers involved in a broad range of cell functions including survival, apoptosis, and cell differentiation. Whereas JNK and p38 have been generally linked to cell death and tumor suppression, ERK plays a prominent role in cell survival and tumor promotion, in response to a broad range of stimuli such as cytokines, growth factors, ultraviolet radiation, hypoxia, or pharmacological compounds. However, there is a growing body of evidence supporting that JNK and p38 also contribute to the development of a number of malignances. In this paper we focus on the involvement of the MAPK pathways in prostate cancer, including the less-known ERK5 pathway, as pro- or antitumor mediators, through their effects on apoptosis, survival, metastatic potential, and androgen-independent growth.

γ-Tocotrienol inhibits HGF-dependent mitogenesis and Met activation in highly malignant mammary tumour cells

OBJECTIVES

  Aberrant Met signalling is associated with aggressive cancer cell phenotypes. γ-tocotrienol displays potent anti-cancer activity that is associated with suppression of HER/ErbB receptor signalling. Experiments were conducted to investigate the effects of γ-tocotrienol treatment on HGF-dependent +SA mammary tumour cell proliferation, upon Met activation.

MATERIALS AND METHODS

  The +SA cells were maintained in serum-free defined media containing 10 ng/ml HGF as the mitogen. Cell viability was determined using the MTT assay, western blot analysis was used to measure protein expression, and Met expression and activation were determined using immunofluorescent staining.

RESULTS AND CONCLUSIONS

  Treatment with γ-tocotrienol or Met inhibitor, SU11274, significantly inhibited HGF-dependent +SA cell replication in a dose-responsive manner. Treatment with 4 μmγ-tocotrienol reduced both total Met levels and HGF-induced Met autophosphorylation. In contrast, similar treatment with 5.5 μm SU11274 inhibited HGF-induced Met autophosphorylation, but had no effect on total Met levels. Combined treatment with subeffective doses of γ-tocotrienol (2 μm) and SU11274 (3 μm) resulted in significant inhibition of +SA cell expansion compared to treatment with individual agents alone. These findings show, for the first time, the inhibitory effects of γ-tocotrienol on Met expression and activation, and strongly suggest that γ-tocotrienol treatment may provide significant health benefits in prevention and/or treatment of breast cancer, in women with deregulated HGF/Met signalling.

Novel tocotrienol-entrapping vesicles can eradicate solid tumors after intravenous administration

The therapeutic potential of tocotrienol, a vitamin E extract with anti-cancer properties, is hampered by its failure to specifically reach tumors after intravenous administration. In this work, we demonstrated that novel transferrin-bearing, tocopheryl-based multilamellar vesicles entrapping tocotrienol significantly improved tocotrienol uptake by cancer cells overexpressing transferrin receptors. This led to a dramatically improved therapeutic efficacy in vitro, ranging from 17-fold to 72-fold improvement depending on the cell lines, compared to the free drug. In vivo, the intravenous administration of this novel tocotrienol formulation led to complete tumor eradication for 40% of B16-F10 murine melanoma tumors and 20% of A431 human epidermoid carcinoma tumors. Animal survival was improved by more than 20 days compared to controls, for the two tumor models tested. These therapeutic effects, together with the lack of toxicity, potentially make transferrin-bearing vesicles entrapping tocotrienol a highly promising therapeutic system as part as an anti-cancer therapeutic strategy.

Tocotrienol rich fraction supplementation improved lipid profile and oxidative status in healthy older adults: A randomized controlled study

Background

Vitamin E supplements containing tocotrienols are now being recommended for optimum health but its effects are scarcely known. The objective was to determine the effects of Tocotrienol Rich Fraction (TRF) supplementation on lipid profile and oxidative status in healthy older individuals at a dose of 160 mg/day for 6 months.

Methods

Sixty-two subjects were recruited from two age groups: 35-49 years (n = 31) and above 50 years (n = 31), and randomly assigned to receive either TRF or placebo capsules for six months. Blood samples were obtained at 0, 3^rd and 6^th months.

Results

HDL-cholesterol in the TRF-supplemented group was elevated after 6 months (p < 0.01). Protein carbonyl contents were markedly decreased (p < 0.001), whereas AGE levels were lowered in the > 50 year-old group (p < 0.05). Plasma levels of total vitamin E particularly tocopherols were significantly increased in the TRF-supplemented group after 3 months (p < 0.01). Plasma total tocotrienols were only increased in the > 50 year-old group after receiving 6 months of TRF supplementation. Changes in enzyme activities were only observed in the > 50 year-old group. SOD activity was decreased after 3 (p < 0.05) and 6 (p < 0.05) months of TRF supplementation whereas CAT activity was decreased after 3 (p < 0.01) and 6 (p < 0.05) months in the placebo group. GPx activity was increased at 6 months for both treatment and placebo groups (p < 0.05).

Conclusion

The observed improvement of plasma cholesterol, AGE and antioxidant vitamin levels as well as the reduced protein damage may indicate a restoration of redox balance after TRF supplementation, particularly in individuals over 50 years of age.

The tissue-specific stem cell as a target for chemoprevention

While cancer treatment modalities are gradually improving due to increased knowledge about tumor heterogeneity and the cancer stem cell hypothesis, there remains a disconnect between tumor detection and mortality rates. The increasing knowledge of stem cell biology and its contribution to cancer progression illuminates the potential for chemopreventative regimens that effectively target the tissue-specific stem cell. Several signaling pathways have emerged that are critical for regulating stem cell self-renewal and multilineage differentiation over a range of tissue types, including Wnt, Hedgehog, and Notch signaling. Dysregulation of these genes can lead to cancer, which supports the cancer stem cell hypothesis. Several known chemopreventative agents have recently been shown to impact these and other pathways in the stem cell population, suggesting that their efficacies may be attributed in part to maintaining homeostasis of tissue-specific stem cells. Further understanding of the mechanisms of action of chemopreventative agents and of stem cell biology will generate better chemoprevention regimens that can be recommended especially to those in high-risk populations.

Metabolism of tocotrienols in animals and synergistic inhibitory actions of tocotrienols with atorvastatin in cancer cells

Tocotrienols (T3s), members of the vitamin E family, exhibit potent anti-cancer, anti-oxidative, anti-inflammatory, and some other biological activities. To better understand the bioavailability and metabolism of T3s, T3s and their metabolites were identified in urine and fecal samples from mice on diet supplemented with mixed T3s using HPLC/electrochemical detection and liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS). Whereas the short-chain metabolites carboxyethyl hydroxychromans (CEHCs) and carboxymethylbutyl hydroxychromans (CMBHCs) were the major metabolites of T3s, several new metabolites with double bonds were also identified. Similar to tocopherols, the majority of T3 metabolites were excreted as sulfate/glucuronide conjugates in mouse urine. The distribution of γ- and δ-T3 and γ-T3 metabolites were also determined in different organs as well as in urine and fecal samples from mice on diets supplemented with corresponding T3s. The synergistic anti-cancer actions of γ-T3 and atorvastatin (ATST) were studied in HT29 and HCT116 colon cancer cell lines. The combination greatly potentiated the ability of each individual agent to inhibit cancer cell growth and to induce cell cycle arrest and apoptosis. The triple combination of γ-T3, ATST, and celecoxib exhibited synergistic actions when compared with any double combination plus the third agent. Mechanistic studies revealed that the synergistic actions of γ-T3 and ATST could be attributed to their mediation of 3-hydroxy-3-methyl-glutaryl-CoA reductase, and the subsequent inhibition of protein geranylgeranylation. It remains to be determined whether such a synergy occurs in vivo.

Gamma-tocotrienol induces apoptosis and autophagy in prostate cancer cells by increasing intracellular dihydrosphingosine and dihydroceramide

Although cell-based studies have shown that γ-tocotrienol (γTE) exhibits stronger anticancer activities than other forms of vitamin E including γ-tocopherol (γT), the molecular bases underlying γTE-exerted effects remains to be elucidated. Here we showed that γTE treatment promoted apoptosis, necrosis and autophagy in human prostate PC-3 and LNCaP cancer cells. In search of potential mechanisms of γTE-provoked effects, we found that γTE treatment led to marked increase of intracellular dihydroceramide and dihydrosphingosine, the sphingolipid intermediates in de novo sphingolipid synthesis pathway but had no effects on ceramide or sphingosine. The elevation of these sphingolipids by γTE preceded or coincided with biochemical and morphological signs of cell death and was much more pronounced than that induced by γT, which accompanied with much higher cellular uptake of γTE than γT. The importance of sphingolipid accumulation in γTE-caused fatality was underscored by the observation that dihydrosphingosine and dihydroceramide potently reduced the viability of both prostate cell lines and LNCaP cells, respectively. In addition, myriosin, a specific inhibitor of de novo sphingolipid synthesis, counteracted γTE-induced cell death. In agreement with these cell-based studies, γTE inhibited LNCaP xenograft growth by 53% (p < 0.05), compared to 33% (p = 0.07) by γT, in nude mice. These findings provide a molecular basis of γTE-stimulated cancer cell death and support the notion that elevation of intracellular dihydroceramide and dihydrosphingosine is likely a novel anticancer mechanism.

Why tocotrienols work better: insights into the in vitro anti-cancer mechanism of vitamin E

The selective constraint of liver uptake and the sustained metabolism of tocotrienols (T3) demonstrate the need for a prompt detoxification of this class of lipophilic vitamers, and thus the potential for cytotoxic effects in hepatic and extra-hepatic tissues. Hypomethylated (γ and δ) forms of T3 show the highest in vitro and in vivo metabolism and are also the most potent natural xenobiotics of the entire vitamin E family of compounds. These stimulate a stress response with the induction of detoxification and antioxidant genes. Depending on the intensity of this response, these genes may confer cell protection or alternatively they stimulate a senescence-like phenotype with cell cycle inhibition or even mitochondrial toxicity and apoptosis. In cancer cells, the uptake rate and thus the cell content of these vitamers is again higher for the hypomethylated forms, and it is the critical factor that drives the dichotomy between protection and toxicity responses to different T3 forms and doses. These aspects suggest the potential for marked biological activity of hypomethylated "highly metabolized" T3 that may result in cytoprotection and cancer prevention or even chemotherapeutic effects. Cytotoxicity and metabolism of hypomethylated T3 have been extensively investigated in vitro using different cell model systems that will be discussed in this review paper as regard molecular mechanisms and possible relevance in cancer therapy.

Tocotrienols fight cancer by targeting multiple cell signaling pathways

Cancer cells are distinguished by several distinct characteristics, such as self-sufficiency in growth signal, resistance to growth inhibition, limitless replicative potential, evasion of apoptosis, sustained angiogenesis, and tissue invasion and metastasis. Tumor cells acquire these properties due to the dysregulation of multiple genes and associated cell signaling pathways, most of which are linked to inflammation. For that reason, rationally designed drugs that target a single gene product are unlikely to be of use in preventing or treating cancer. Moreover, targeted drugs can cause serious and even life-threatening side effects. Therefore, there is an urgent need for safe and effective promiscuous (multitargeted) drugs. "Mother Nature" produces numerous such compounds that regulate multiple cell signaling pathways, are cost effective, exhibit low toxicity, and are readily available. One among these is tocotrienol, a member of the vitamin E family, which has exhibited anticancer properties. This review summarizes data from in vitro and in vivo studies of the effects of tocotrienol on nuclear factor-κB, signal transducer and activator of transcription (STAT) 3, death receptors, apoptosis, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), hypoxia-inducible factor (HIF) 1, growth factor receptor kinases, and angiogenic pathways.

A paraptosis-like cell death induced by δ-tocotrienol in human colon carcinoma SW620 cells is associated with the suppression of the Wnt signaling pathway

Tocotrienol is considered a beneficial effect agent on inhibition of tumor development. In this study, we focused on the effects of δ-tocotrienol and its possible mechanism on induction of death in human colon cancer SW620 cells. δ-Tocotrienol inhibited proliferation of SW620 cell in a dose-dependent manner. Our findings showed that δ-tocotrienol effectively induced paraptosis-like death in SW620 cells, correlated with the vacuolation that may be from welling and fusion of mitochondria and/or the endoplasmic reticulum (ER) as well as caspase-3 nonactivated. However, there were no changes in apoptosis based on flow cytometry analysis. Of being noted, δ-tocotrienol reduced the expression of β-catenin and wnt-1 proteins by about 50% at the highest dose (20μmol/L). δ-Tocotrienol also decreased cyclin D1, c-jun and MMP-7 protein levels in SW620 cells. Altogether, these data indicate that δ-tocotrienol induces paraptosis-like cell death, which is associated with the suppression of the Wnt signaling pathway. Thus, our findings may provide a novel application in treatment of human colon carcinoma.

Gamma-tocotrienol induced apoptosis is associated with unfolded protein response in human breast cancer cells

Gamma-tocotrienol (γ-T3) is a member of the vitamin E family. Tocotrienols (T3s) are powerful antioxidants and possess anticancer, neuroprotective and cholesterol-lowering properties. Tocotrienols inhibit the growth of various cancer cell lines without affecting normal cells. Less is known about the exact mechanisms of action of T3s on cell death and other growth inhibitory pathways. In the present study, we demonstrate that γ-T3 induces apoptosis in MDA-MB 231 and MCF-7 breast cancer cells as evident by PARP cleavage and caspase-7 activation. Gene expression analysis of MCF-7 cells treated with γ-T3 revealed alterations in the expression of multiple genes involved in cell growth and proliferation, cell death, cell cycle, cellular development, cellular movement and gene expression. Further analysis of differentially modulated genes using Ingenuity Pathway Analysis software suggested modulation of canonical signal transduction or metabolic pathways such as NRF-2-mediated oxidative stress response, TGF-β signaling and endoplasmic reticulum (ER) stress response. Analysis of ER-stress-related proteins in MCF-7 and MDA-MB 231 cells treated with γ-T3 demonstrated activation of PERK and pIRE1α pathway to induce ER stress. Activating transcription factor 3 (ATF3) was identified as the most up-regulated gene (16.8-fold) in response to γ-T3. Activating transcription factor 3 knockdown using siRNA suggested an essential role of ATF3 in γ-T3-induced apoptosis. In summary, we demonstrate that γ-T3 modulates ER stress signaling and have identified ATF3 as a molecular target for γ-T3 in breast cancer cells.

Unleashing the untold and misunderstood observations on vitamin E

Paradoxically, meta-analysis of human randomized controlled trials revealed that natural but not synthetic α-tocopherol supplementation significantly increases all-cause mortality at 95% confidence interval. The root cause was that natural α-tocopherol supplementation significantly depressed bioavailability of other forms of vitamin E that have better chemo-prevention capability. Meta-analysis outcome demonstrated flaws in the understanding of vitamin E. Reinterpretation of reported data provides plausible explanations to several important observations. While α-tocopherol is almost exclusively secreted in chylomicrons, enterocytes secrete tocotrienols in both chylomicrons and small high-density lipoproteins. Vitamin E secreted in chylomicrons is discriminately repacked by α-tocopherol transfer protein into nascent very low-density lipoproteins in the liver. Circulating very low-density lipoproteins undergo delipidation to form intermediate-density lipoproteins and low-density lipoproteins. Uptake of vitamin E in intermediate-density lipoproteins and low-density lipoproteins takes place at various tissues via low-density lipoproteins receptor-mediated endocytosis. Small high-density lipoproteins can deliver tocotrienols upon maturation to peripheral tissues independent of α-tocopherol transfer protein action, and uptake of vitamin E takes place at selective tissues by scavenger receptor-mediated direct vitamin E uptake. Dual absorption pathways for tocotrienols are consistent with human and animal studies. α-Tocopherol depresses the bioavailability of α-tocotrienol and has antagonistic effect on tocotrienols in chemo-prevention against degenerative diseases. Therefore, it is an undesirable component for chemo-prevention. Future research directions should be focused on tocotrienols, preferably free from α-tocopherol, for optimum chemo-prevention and benefits to mankind.

Tocotrienols, the vitamin E of the 21st century: its potential against cancer and other chronic diseases

Initially discovered in 1938 as a "fertility factor," vitamin E now refers to eight different isoforms that belong to two categories, four saturated analogues (α, β, γ, and δ) called tocopherols and four unsaturated analogues referred to as tocotrienols. While the tocopherols have been investigated extensively, little is known about the tocotrienols. Very limited studies suggest that both the molecular and therapeutic targets of the tocotrienols are distinct from those of the tocopherols. For instance, suppression of inflammatory transcription factor NF-κB, which is closely linked to tumorigenesis and inhibition of HMG-CoA reductase, mammalian DNA polymerases and certain protein tyrosine kinases, is unique to the tocotrienols. This review examines in detail the molecular targets of the tocotrienols and their roles in cancer, bone resorption, diabetes, and cardiovascular and neurological diseases at both preclinical and clinical levels. As disappointment with the therapeutic value of the tocopherols grows, the potential of these novel vitamin E analogues awaits further investigation.

Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

Vitamin E succinate induced apoptosis and enhanced chemosensitivity to paclitaxel in human bladder cancer cells in vitro and in vivo

There have been several studies on the antitumor activities of vitamin E succinate (alpha-TOS) as complementary and alternative medicine. In the present study, we investigated the cytotoxic effect of alpha-TOS and the enhancement of chemosensitivity to paclitaxel by alpha-TOS in bladder cancer. KU-19-19 and 5637 bladder cancer cell lines were cultured in alpha-TOS and/or paclitaxel in vitro. Cell viability, flow cytometric analysis, and nuclear factor-kappa B (NF-kappaB) activity were analyzed. For in vivo therapeutic experiments, pre-established KU-19-19 tumors were treated with alpha-TOS and/or paclitaxel. In KU-19-19 and 5637 cells, the combination treatment resulted in a significantly higher level of growth inhibition, and apoptosis was significantly induced by the combination treatment. NF-kappaB was activated by paclitaxel; however, the activation of NF-kappaB was inhibited by alpha-TOS. Also, the combination treatment significantly inhibited tumor growth in mice. In the immunostaining of the tumors, apoptosis was induced and proliferation was inhibited by the combination treatment. Combination treatment of alpha-TOS and paclitaxel showed promising anticancer effects in terms of inhibiting bladder cancer cell growth and viability in vitro and in vivo. One of the potential mechanisms by which the combination therapy has synergistic cytotoxic effects against bladder cancer may be that alpha-TOS inhibits NF-kappaB induced by chemotherapeutic agents.

Present trends in vitamin E research

Nearly after one century of research and thousands of publications, the physiological function(s) of vitamin E remain unclear. Available evidence suggests a role in cell homeostasis that occurs through the modulation of specific signaling pathways and genes involved in proliferative, metabolic, inflammatory, and antioxidant pathways. Vitamin E presence in the human body is under close metabolic control so that only alpha-tocopherol and, to a lower extent, gamma-tocopherol are retained and delivered to tissues. Other vitamin E forms that are not retained in the body in significant amounts, exhibit responses in vitro that are different form those of alpha-tocopherol and may include tumor cell specific toxicity and apoptosis. These responses provide a therapeutic potential for these minor forms, either as such or metabolically modified, to produce bioactive metabolites. These cellular effects go beyond the properties of lipophilic antioxidant attributed to alpha-tocopherol particularly investigated for its alleged protective role in atherosclerosis or other oxidative stress conditions. Understanding signaling and gene expression effects of vitamin E could help assign a physiological role to this vitamin, which will be discussed in this review. Besides vitamin E signaling, attention will be given to tocotrienols as one of the emerging topics in vitamin E research and a critical re-examination of the most recent clinical trials will be provided together with the potential use of vitamin E in disease prevention and therapy.

Id1, inhibitor of differentiation, is a key protein mediating anti-tumor responses of gamma-tocotrienol in breast cancer cells

Gamma-tocotrienol has demonstrated anti-proliferative effect on breast cancer (BCa) cells, but mechanisms involved are largely unknown. This study aimed at deciphering the molecular pathways responsible for its activity. Our results showed that treatment of BCa cells with gamma-tocotrienol resulted in induction of apoptosis as evidenced by activation of pro-caspases, accumulation of sub-G1 cells and DNA fragmentations. Examination of the pro-survival genes revealed that the gamma-tocotrienol-induced cell death was associated with suppression of Id1 and NF-kappaB through modulation of their upstream regulators (Src, Smad1/5/8, Fak and LOX). Meanwhile, gamma-tocotrienol treatment also resulted in the induction of JNK signaling pathway and inhibition of JNK activity by specific inhibitor partially blocked the effect of gamma-tocotrienol. Furthermore, synergistic effect was observed when cells were co-treated with gamma-tocotrienol and Docetaxel. Interestingly, in cells that treated with gamma-tocotrienol, alpha-tocopherol or beta-aminoproprionitrile were found to partially restore Id1 expression. Meanwhile, this restoration of Id1 was found to protect the cells from gamma-tocotrienol induced apoptosis. Consistent outcome was observed in cells ectopically transfected with the Id-1 gene. Our results suggested that the anti-proliferative and chemosensitization effect of gamma-tocotrienol on BCa cells may be mediated through downregulation of Id1 protein.

Simultaneous induction of non-neoplastic and neoplastic lesions with highly proliferative hepatocytes following dietary exposure of rats to tocotrienol for 2 years

It was recently shown that 1-year chronic exposure of rats to tocotrienol (TT) induced highly proliferative liver lesions, nodular hepatocellular hyperplasia (NHH), and independently increased the number of glutathione S-transferase placental form (GST-P)-positive hepatocytes. Focusing attention on the pathological intrinsic property of NHH, a 104-week carcinogenicity study was performed in male and female Wistar Hannover rats given TT at concentrations of 0, 0.4 or 2% in the diet. The high-dose level was adjusted to 1% in both sexes from week 51 because the survival rate of the high-dose males dropped to 42% by week 50. At necropsy, multiple cyst-like nodules were observed, as in the chronic study, but were further enlarged in size, which consequently formed a protuberant surface with a partly pedunculated shape in the liver at the high dose in both sexes. Unlike the chronic study, NHH was not always accompanied by spongiosis, and instead angiectasis was prominent in some nodules. However, several findings in the affected hepatocytes such as minimal atypia, no GST-P immunoreactivity and heterogeneous proliferation, implied that NHH did not harbor neoplastic characteristics from increased exposure despite sustained high cell proliferation. On the other hand, in the high-dose females, the incidence of hepatocellular adenomas was significantly higher than in the control. There was no TT treatment-related tumor induction in any other organs besides the liver. Thus, the overall data clearly suggested that NHH is successively enlarged by further long-term exposure to TT, but does not become neoplastic. In contrast, TT induces low levels of hepatocellular adenomas in female rats.