Superoxide is responsible for apoptosis in rat vascular smooth muscle cells induced by alpha-tocopheryl hemisuccinate

Vitamin E succinate mediated apoptosis by juxtaposing endoplasmic reticulum and mitochondria

Vitamin E succinate (VES) is an esterified form of natural α-tocopherol, has turned out to be novel anticancer agent. However, its anticancer mechanisms have not been illustrated. Previously, we reported VES mediated Ca2+ release from the endoplasmic reticulum (ER) causes mitochondrial Ca2+ overload, leading to mitochondrial depolarization and apoptosis. Here, we elucidated the mechanism of VES-induced Ca2+ transfer from ER to mitochondria by investigating the role of VES in ER-mitochondria contact formation. Transmission electron microscopic observation confirms VES mediated ER-mitochondria contact while fluorescence microscopic analysis revealed that VES increased mitochondria-associated ER membrane (MAM) formation. Pre-treatment with the inositol 1,4,5-triphosphate receptor (IP3R) antagonist 2-aminoethyl diphenylborinate (2-APB) decreased VES-induced MAM formation, suggesting the involvement of VES-induced Ca2+ efflux from ER in MAM formation. The ER IP3R receptor is known to interact with voltage-dependent anion channels (VDAC) via the chaperone glucose-regulated protein 75 kDa (GRP75) to bring ER and mitochondria nearby. Although we revealed that VES treatment does not affect GRP75 protein level, it increases GRP75 localization in the MAM. In addition, the inhibition of Ca2+ release from ER by 2-APB decreases GRP75 localization in the MAM, suggesting the possibility of Ca2+-induced conformational change of GRP75 that promotes formation of the IP3R-GRP75-VDAC complex and thereby encourages MAM formation. This study identifies the mechanism of VES-induced enhanced Ca2+ transfer from ER to mitochondria, which causes mitochondrial Ca2+ overload leading to apoptosis.

Only one carbon difference determines the pro-apoptotic activity of α-tocopheryl esters

α-Tocopheryl succinate (TS), a redox-silent succinyl ester of natural α-Tocopherol, has emerged as a novel anti-cancer agent. However, the underlying mechanism is unclear. We found that the terminal dicarboxylic moiety of tocopheryl esters contributes to apoptosis induction and thus cytotoxicity. To further examine this relationship, we compared the pro-apoptotic activity of TS, which has four carbon atoms in the terminal dicarboxylic moiety, to that of a newly synthesized, tocopheryl glutarate (Tglu), which has five. Cytotoxicity assays in vitro confirmed that TS stimulated apoptosis, while Tglu was non-cytotoxic. In investigating biological mechanisms leading to these opposing effects, we found that TS caused an elevation of intracellular superoxide, but Tglu did not. TS increased intracellular Ca²⁺ in cultured cells, suggesting induction of endoplasmic reticulum (ER) stress; however, Tglu did not affect Ca²⁺ homeostasis. 1,4,5-trisphosphate (IP₃ ) receptor antagonist 2-Aminoethyl diphenylborinate (2-APB) decreased TS-induced intracellular Ca²⁺ , restored mitochondrial activity and cell viability in TS-treated cells, establishing the ER-mitochondria relationship in apoptosis induction. Moreover, real-time PCR, immunostaining and Western blotting assays revealed that TS downregulated glucose-regulated protein 78 (GRP78), which maintains ER homeostasis and promotes cell survival. Conversely, Tglu upregulates GRP78. Taken together, our results suggest a model in which TS-mediated superoxide production and GRP78 inhibition induce ER stress, which elevates intracellular Ca²⁺ and depolarizes mitochondria, leading to apoptosis. Because Tglu does not affect superoxide generation and increases GRP78 expression, it inhibits ER stress and is thereby non-cytotoxic. Our research provides insight into the structure-activity relationship of tocopheryl esters regarding the induction of apoptosis.

Development of a novel tocopheryl ester for suppression of lipid accumulation without cytotoxicity by optimization of dicarboxylic ester moiety

Tocopheryl succinate (Tsuc) is a succinic acid ester of the well-known antioxidant α-tocopherol (T). Tsuc exhibits various biological activities, including tumor growth suppression via activation of cell signaling and prevention of lipid accumulation in mouse adipocyte 3T3-L1 cells. The latter findings suggest that Tsuc may be a drug candidate for the treatment of obesity. However, Tsuc was found to induce apoptosis of normal cells (in addition to cancer cells), demonstrating the need to reduce the cytotoxicity of Tsuc without losing the suppression effect on lipid accumulation. Based on our previous findings, we focused on the ester structure of Tsuc for controlling cytotoxicity. Herein, we examined the cytotoxicity and lipid accumulation suppression effect of various T ester derivatives. We found that the terminal carboxylic group is necessary for suppression of lipid accumulation. We synthesized tocopheryl glutarate (Tglu) and tocopheryl adipate (Tadi) by elongation of carbon atoms 1 and 2 of the dicarboxylic moiety, respectively. Tglu and Tadi did not show any cytotoxicity, and both esters suppressed lipid accumulation, although their suppression activities were weaker than that of Tsuc. Tadi showed a more potent lipid accumulation inhibitory effect than Tglu. Although Tadi inhibited lipogenesis and promoted lipolysis, lipolysis was induced at lower concentrations than inhibition of lipogenesis, suggesting that Tadi mainly affects lipolysis. Taken together, we succeeded in the reduction of cytotoxicity, without loss of the suppression effect on lipid accumulation, by elongation of the dicarboxylic moiety of Tsuc. Tadi may be a promising candidate as an anti-obesity drug.

•

Successful development of a novel tocopheryl ester as an anti-obesity drug candidate.

•

Reduction of cytotoxicity by elongation of dicarboxylic moiety of tocopheryl esters.

•

A novel tocopheryl ester mainly induces lipolysis of accumulated lipids.

Tocopheryl Phosphate Inhibits Rheumatoid Arthritis-Related Gene Expression In Vitro and Ameliorates Arthritic Symptoms in Mice

Anti-rheumatoid arthritis (RA) effects of α-tocopherol (α-T) have been shown in human patients in a double-blind trial. However, the effects of α-T and its derivatives on fibroblast-like synoviocytes (FLS) during the pathogenesis of RA remain unclear. In the present study, we compared the expression levels of genes related to RA progression in FLS treated with α-T, succinic ester of α-T (TS), and phosphate ester of α-T (TP), as determined via RT-PCR. The mRNA levels of interleukin (IL)-6, tumor necrosis factor-α (TNF-α), matrix metalloproteinase (MMP)-3, and MMP-13 were reduced by treatment with TP without cytotoxicity, while α-T and TS did not show such effects. Furthermore, intraperitoneal injection of TP ameliorated the edema of the foot and joint and improved the arthritis score in laminarin-induced RA model mice. Therefore, TP exerted anti-RA effects through by inhibiting RA-related gene expression.

The causes of cancer revisited: "mitochondrial malignancy" and ROS-induced oncogenic transformation - why mitochondria are targets for cancer therapy

The role of oncoproteins and tumor suppressor proteins in promoting the malignant transformation of mammalian cells by affecting properties such as proliferative signalling, cell cycle regulation and altered adhesion is well established. Chemicals, viruses and radiation are also generally accepted as agents that commonly induce mutations in the genes encoding these cancer-causing proteins, thereby giving rise to cancer. However, more recent evidence indicates the importance of two additional key factors imposed on proliferating cells that are involved in transformation to malignancy and these are hypoxia and/or stressful conditions of nutrient deprivation (e.g. lack of glucose). These two additional triggers can initiate and promote the process of malignant transformation when a low percentage of cells overcome and escape cellular senescence. It is becoming apparent that hypoxia causes the progressive elevation in mitochondrial ROS production (chronic ROS) which over time leads to stabilization of cells via increased HIF-2alpha expression, enabling cells to survive with sustained levels of elevated ROS. In cells under hypoxia and/or low glucose, DNA mismatch repair processes are repressed by HIF-2alpha and they continually accumulate mitochondrial ROS-induced oxidative DNA damage and increasing numbers of mutations driving the malignant transformation process. Recent evidence also indicates that the resulting mutated cancer-causing proteins feedback to amplify the process by directly affecting mitochondrial function in combinatorial ways that intersect to play a major role in promoting a vicious spiral of malignant cell transformation. Consequently, many malignant processes involve periods of increased mitochondrial ROS production when a few cells survive the more common process of oxidative damage induced cell senescence and death. The few cells escaping elimination emerge with oncogenic mutations and survive to become immortalized tumors. This review focuses on evidence highlighting the role of mitochondria as drivers of elevated ROS production during malignant transformation and hence, their potential as targets for cancer therapy. The review is organized into five main sections concerning different aspects of "mitochondrial malignancy". The first concerns the functions of mitochondrial ROS and its importance as a pacesetter for cell growth versus senescence and death. The second considers the available evidence that cellular stress in the form of hypoxic and/or hypoglycaemic conditions represent two of the major triggering events for cancer and how oncoproteins reinforce this process by altering gene expression to bring about a common set of changes in mitochondrial function and activity in cancer cells. The third section presents evidence that oncoproteins and tumor suppressor proteins physically localize to the mitochondria in cancer cells where they directly regulate malignant mitochondrial programs, including apoptosis. The fourth section covers common mutational changes in the mitochondrial genome as they relate to malignancy and the relationship to the other three areas. The last section concerns the relevance of these findings, their importance and significance for novel targeted approaches to anti-cancer therapy and selective triggering in cancer cells of the mitochondrial apoptotic pathway.

Autoschizis of T-cells is induced by the nutritional supplement, Cr(III)picolinate

In recent times, Cr(III)(picolinate)(3) [Cr(III)(pic)(3)] a nutritional supplement, is gaining attention because of its clastogenic and mutagenic properties. Earlier studies of ours indicated that Cr(III)(pic)(3) is cytotoxic to lymphocytes with ROS and mitochondrial events playing a role in bringing about apoptosis. Now, we report that, autoschizis is induced in lymphocytes in a concentration and time dependent manner which is confirmed through TEM and SEM. Lymphocytes treated with concentrations of 100microM of Cr(III)(pic)(3) exhibit features such as cytoplasmic bleb, self excision of cytoplasm, cytoplasmic leakage and membrane bound bodies formed from the excised pieces apart from apoptosis and necrosis. Though autoschizis has been described in tumor cell lines treated with menadione and ascorbate, occurrence of this cell death in normal T-lymphocytes is reported here. The cellular events that accompany autoschizis are found to be increase in intracellular Reactive Oxygen Species (ROS) and cytoplasmic lactate dehydrogenase, loss of mitochondrial membrane potential (MMP) and depletion of ATP. Further, autoschizis is effected through increases in DNase I and DNase II activity with a concomitant decrease in caspase-3 activity which leads to a random cleavage of the DNA as demonstrated by a smear like pattern after electrophoresis on agarose gel.

Alpha-tocopheryl succinate induces rapid and reversible phosphatidylserine externalization in histiocytic lymphoma through the caspase-independent pathway

Phosphatidylserine (PS) externalization is a key feature of apoptotic cell death and plays an important role in clearance of apoptotic cells by phagocytes. PS externalization during apoptosis is generally an irreversible event mediated by caspase activation and is accompanied by other apoptotic events. We report here that an apoptosis inducer alpha-tocopheryl succinate (TOS) can induce PS externalization that is independent of apoptosis and reversible in the absence of fetal bovine serum (FBS) in histiocytic lymphoma U937 cells. In the presence of FBS, TOS induced PS externalization via a caspase-dependent mechanism accompanied by mitochondrial depolarization, cell shrinkage, increase of caspase-3 activity, and chromatin condensation. In contrast, in the absence of FBS, TOS induced the rapid PS externalization which was not accompanied by other apoptotic events. The PS externalization was reversible by removing TOS and was not involved in Ca(2+)-dependent scramblase activation and thiol oxidation of aminophospholipid translocase. A similar PS externalization was also induced by cholesteryl hemisuccinate (CS), the other succinate ester. These results suggested that the mechanism of TOS- and CS-induced PS externalization in the absence of FBS was different from it occurring during typical apoptosis.

Cancer chemoprevention: a radical perspective

Cancer chemopreventive agents block the transformation of normal cells and/or suppress the promotion of premalignant cells to malignant cells. Certain agents may achieve these objectives by modulating xenobiotic biotransformation, protecting cellular elements from oxidative damage, or promoting a more differentiated phenotype in target cells. Conversely, various cancer chemopreventive agents can encourage apoptosis in premalignant and malignant cells in vivo and/or in vitro, which is conceivably another anticancer mechanism. Furthermore, it is evident that many of these apoptogenic agents function as prooxidants in vitro. The constitutive intracellular redox environment dictates a cell's response to an agent that alters this environment. Thus, it is highly probable that normal cells, through adaption, could acquire resistance to transformation via exposure to a chemopreventive agent that promotes oxidative stress or disrupts the normal redox tone of these cells. In contrast, transformed cells, which typically endure an oxidizing intracellular environment, would ultimately succumb to apoptosis due to an uncontrollable production of reactive oxygen species caused by the same agent. Here, we provide evidence to support the hypothesis that reactive oxygen species and cellular redox tone are exploitable targets in cancer chemoprevention via the stimulation of cytoprotection in normal cells and/or the induction of apoptosis in transformed cells.

ATRA promotes alpha tocopherol succinate-induced apoptosis in freshly isolated leukemic cells from chronic myeloid leukemic patients

We investigated the in vitro efficacy of all-trans retinoic acid (ATRA) and alpha-tocopherol succinate (alpha-TS) alone and in combination on the induction of cell death in freshly isolated leukemic cells obtained from chronic myeloid leukemia (CML) patients. In vitro cytotoxicity and induction of lipid peroxidation by ATRA (10 microM) and alpha-TS (25 or 50 microM) were evaluated in primary leukemic cells by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and malondialdehyde formation respectively. Treatment of leukemic cells with alpha-TS alone or in combination with ATRA significantly (P < 0.05) decreased the cell viability in a concentration and time dependent manner as compared to peripheral blood mononuclear cells obtained from normal healthy controls. Lipid peroxidation was enhanced by 98% (P < 0.05) on combined treatment of cells with ATRA (10 microM) and alpha-TS (50 microM). ATRA alone did not enhance the externalization of phosphatidyl serine as studied by annexin-V binding using fluorescence activated cell sorter analysis, whereas in combination with alpha-TS it increased to 400% at 12 h. The treatment of leukemic cells to combination of ATRA with alpha-TS significantly decreased (P < 0.05) mitochondrial membrane potential and enhanced lysosomal destabilization. The combination of these drugs also increased mitochondrial and cytosolic reactive oxygen species (ROS) production, nitric oxide levels, and caspase-3 activity significantly and caused DNA fragmentation at 24 h in a concentration dependent manner in the leukemic cells. Our data suggest that ATRA in combination with alpha-TS efficiently induces apoptosis in leukemic cells, which may be a useful therapeutic modality in CML patients.

Vitamin E analogues as a novel group of mitocans: anti-cancer agents that act by targeting mitochondria

Mitochondria have recently emerged as new and promising targets for cancer prevention and therapy. One of the reasons for this is that mitochondria are instrumental to many types of cell death and often lie downstream from the initial actions of anti-cancer drugs. Unlike the tumour suppressor gene encoding p53 that is notoriously prone to inactivating mutations but whose function is essential for induction of apoptosis by DNA-targeting agents (such as doxorubicin or 5-fluorouracil), mitochondria present targets that are not so compromised by genetic mutation and whose targeting overcomes problems with mutations of upstream targets such as p53. We have recently proposed a novel class of anti-cancer agents, mitocans that exert their anti-cancer activity by destabilising mitochondria, promoting the selective induction of apoptotic death in tumour cells. In this communication, we review recent findings on mitocans and propose a common basis for their mode of action in inducing apoptosis of cancer cells. We use as an example the analogues of vitamin E that are proving to be cancer cell-specific and may soon be developed into efficient anti-cancer drugs.

Mitocans as anti-cancer agents targeting mitochondria: lessons from studies with vitamin E analogues, inhibitors of complex II

Recently mitochondria in cancer cells have emerged as the Achilles heel for tumour destruction. Anti-cancer agents specifically targeting cancer cell mitochondria are referred to as 'mitocans'. These compounds act by destabilising these organelles, unleashing their apoptogenic potential, resulting in the efficient death of malignant cells and suppression of tumour growth. Importantly, at least some mitocans are selective for cancer cells, and these are represented by the group of redox-silent vitamin E analogues, epitomised by alpha-tocopheryl succinate (alpha-TOS). This compound has proven itself in pre-clinical models to be an efficient anti-cancer agent, targeting complex II of the respiratory chain to displace ubiquinone binding. We propose that disrupting the electron flow of mitochondrial complex II results in generation of superoxide, triggering mitochondrial destabilisation and initiation of apoptotic pathways. Moreover, alpha-TOS is selective for cancer cells with their reduced anti-oxidant defenses and lower esterase activity than the normal (non-malignant) counterparts. In this mini-review we discuss the emerging significance of mitocans, as exemplified by alpha-TOS.

Vitamin E analogs, a novel group of "mitocans," as anticancer agents: the importance of being redox-silent

The search for a selective and efficient anticancer agent for treating all neoplastic disease has yet to deliver a universally suitable compound(s). The majority of established anticancer drugs either are nonselective or lose their efficacy because of the constant mutational changes of malignant cells. Until recently, a largely neglected target for potential anticancer agents was the mitochondrion, showing a considerable promise for future clinical applications. Vitamin E (VE) analogs, epitomized by alpha-tocopheryl succinate, belong to the group of "mitocans" (mitochondrially targeted anticancer drugs). They are selective for malignant cells, cause destabilization of their mitochondria, and suppress cancer in preclinical models. This review focuses on our current understanding of VE analogs in the context of their proapoptotic/anticancer efficacy and suggests that their effect on mitochondria may be amplified by modulation of alternative pathways operating in parallel. We show here that the analogs of VE that cause apoptosis (which translates into their anticancer efficacy) generally do not possess antioxidant (redox) activity and are prototypical of the mitocan group of anticancer compounds. Therefore, by analogy to Oscar Wilde's play The Importance of Being Earnest, we use the motto in the title "the importance of being redox-silent" to emphasize an essentially novel paradigm for cancer therapy, in which redox-silence is a prerequisite property for most of the anticancer activities described in this communication.

Vitamin E Analogues and Immune Response in Cancer Treatment

Chemotherapeutic drugs induce both proliferation arrest and apoptosis; however, some cancer cells escape drug toxicity and become resistant. The suppression of the immune system by chemotherapeutic agents and radiation promotes the development and propagation of various malignancies via "mimicry-induced" autoimmunity, and maintain a cytokine milieu that favors proliferation by inhibiting apoptosis. A novel, efficient approach is based on a synergistic effect of different anticancer agents with different modes of action. Recently, a redox-silent analogue of vitamin E, alpha-tocopheryl succinate (alpha-TOS), has come into focus due to its anticancer properties. alpha-TOS behaves in a very different way than its redox-active counterpart, alpha-tocopherol, since it promotes cell death. It exerts pleiotrophic responses in malignant cells leading to cell cycle arrest, differentiation, and apoptosis. Apart from its role in killing cancer cells via apoptosis, alpha-TOS affects expression of genes involved in cell proliferation and cell death in a "subapoptotic" manner. For example, it modulates the cell cycle machinery, resulting in cell cycle arrest. The ability of alpha-TOS to induce a prolonged S phase contributes to sensitization of cancer cells to drugs destabilizing DNA during replication. A cooperative antitumor effect was observed also when alpha-TOS was combined with immunological agents. alpha-TOS and TRAIL synergize to kill cancer cells either by upregulating TRAIL death receptors or by amplifying the mitochondrial apoptotic pathway without being toxic to normal cells. alpha-TOS and TRAIL in combination with dendritic cells induce INF-gamma production by CD4+ and CD8+ T lymphocytes, resulting in a significant tumor growth inhibition or in complete tumor regression. These findings are indicative of a novel strategy for cancer treatment that involves enhanced immune system surveillance.

Vitamin E analogues as anticancer agents: lessons from studies with alpha-tocopheryl succinate

The new millennium has witnessed considerable decrease in a number of previously fatal pathologies, largely due to the advancement in molecular medicine and modern approaches to treatment. In spite of this success, neoplastic disease remains a serious problem due to several reasons. These include an exceedingly high variability of cancer cells even within the same type of tumour. Cancer cells, albeit of clonal origin, mutate so that they escape established treatments, resulting in the fatal outcome of current therapies. Moreover, there are types of cancer, such as mesotheliomas, that cannot be treated at present. A novel group of clinically interesting anticancer drugs has been a recent focus in the literature that hold substantial promise as selective anticancer drugs. These compounds, epitomised by alpha-tocopheryl succinate, comprise redox-silent analogues of vitamin E that have been shown to suppress several types of cancer in animal models, including breast, colon and lung cancer as well as mesotheliomas and melanomas, while being nontoxic to normal cells and tissues. It is now proven that the strong anticancer effect of vitamin E analogues stems from their propensity to induce selective apoptosis in malignant cells. The results point to the novel group of vitamin E analogues as promising agents applicable to different types of tumours.

Molecular mechanism of 'mitocan'-induced apoptosis in cancer cells epitomizes the multiple roles of reactive oxygen species and Bcl-2 family proteins

Mitochondria have emerged recently as effective targets for novel anti-cancer drugs referred to as 'mitocans'. We propose that the molecular mechanism of induction of apoptosis by mitocans, as exemplified by the drug alpha-tocopheryl succinate, involves generation of reactive oxygen species (ROS). ROS then mediate the formation of disufide bridges between cytosolic Bax monomers, resulting in the formation of mitochondrial outer membrane channels. ROS also cause oxidation of cardiolipin, triggering the release of cytochrome c and its translocation via the activated Bax channels. This model may provide a general mechanism for the action of inducers of apoptosis and anticancer drugs, mitocans, targeting mitochondria via ROS production.

Tocopherol-associated protein-1 accelerates apoptosis induced by α-tocopheryl succinate in mesothelioma cells

Alpha-tocopheryl succinate (alpha-TOS), a redox-silent analogue of vitamin E, induces apoptosis in multiple cell lines in a selective manner, by activating the intrinsic pathway. Since it is a highly hydrophobic compound, it may require a carrier protein for its trafficking to intracellular targets like mitochondria. We studied the role of the ubiquitous tocopherol-associated protein-1 (TAP1 or sec14-like 2) in apoptosis induction by alpha-TOS in malignant mesothelioma (MM) cells. Over-expression of TAP1 in MM cells sensitised them to apoptosis by low doses of alpha-TOS which were sub-apoptotic for the parental cells. Apoptosis induced in TAP1-over-expressing cells was mitochondria- and caspase-dependent, as suggested by dissipation of mitochondrial trans-membrane potential and inhibition by zVAD-fmk, respectively. Binding assays showed affinity of alpha-TOS for TAP1. Finally, TAP1 over-expressing cells accumulated alpha-TOS at higher levels compared to their normal counterparts. We suggest that TAP1 may act as an intracellular shuttle for alpha-TOS, promoting apoptosis initiated by this vitamin E analogue, as shown here for MM cells.

α-Tocopheryl succinate selectively induces apoptosis in neuroblastoma cells: potential therapy of malignancies of the nervous system?

Vitamin E (VE) analogues, epitomized by alpha-tocopheryl succinate (alpha-TOS), are potent inducers of apoptosis and anti-cancer agents. Here, we tested their effect on the highly malignant N-type neuroblastoma (Nb) cells and their differentiated, neurone-like counterparts. Nb cells were highly susceptible to several VE analogues, while differentiated Nb cells were relatively resistant to alpha-TOS. The importance of caspase-9 rather than caspase-8, as judged by specific siRNAs studies, together with the loss of the inner mitochondrial potential, suggests that alpha-TOS triggers apoptosis in Nb cells via the mitochondrial pathway. Cultured Nb cells were sensitized to alpha-TOS by pre-treatment with Bcl-2, Bcl-xL or Mcl-1 siRNAs, while the malignant cell line was more resistant to the vitamin E analogue when Bax was knocked down. In contrast, overexpression of Bcl-2 in Nb cells rendered them more resistant to alpha-TOS-induced apoptosis. The resistance of differentiated Nb cells to alpha-TOS-mediated apoptosis occurred via two modes: first, by up-regulation of the anti-apoptotic Bcl-2 family proteins and second, by accumulation of decreased levels of reactive oxygen species when challenged with alpha-TOS. We conclude that alpha-TOS is highly selective in killing malignant brain cancer cells while relatively inert toward differentiated neuronal cells, and that vitamin E analogues may be novel therapeutics for the treatment of tumours such as neuroblastomas.

Mitochondria: A novel target for the chemoprevention of cancer

The mitochondria have emerged as a novel target for anticancer chemotherapy. This tenet is based on the observations that several conventional and experimental chemotherapeutic agents promote the permeabilization of mitochondrial membranes in cancerous cells to initiate the release of apoptogenic mitochondrial proteins. This ability to engage mitochondrial-mediated apoptosis directly using chemotherapy may be responsible for overcoming aberrant apoptosis regulatory mechanisms commonly encountered in cancerous cells. Interestingly, several putative cancer chemopreventive agents also possess the ability to trigger apoptosis in transformed, premalignant, or malignant cells in vitro via mitochondrial membrane permeabilization. This process may occur through the regulation of Bcl-2 family members, or by the induction of the mitochondrial permeability transition. Thus, by exploiting endogenous mitochondrial-mediated apoptosis-inducing mechanisms, certain chemopreventive agents may be able to block the progression of premalignant cells to malignant cells or the dissemination of malignant cells to distant organ sites as means of modulating carcinogenesis in vivo. This review will examine cancer chemoprevention with respect to apoptosis, carcinogenesis, and the proapoptotic activity of various chemopreventive agents observed in vitro. In doing so, I will construct a paradigm supporting the notion that the mitochondria are a novel target for the chemoprevention of cancer.

α-Tocopheryl Succinate Inhibits Malignant Mesothelioma byDisrupting the Fibroblast Growth Factor Autocrine Loop

We have studied the potential effect against human malignant mesotheliomas (MM) of alpha-tocopheryl succinate (alpha-TOS), a redox-silent vitamin E analog with strong pro-apoptotic and anti-cancer activity. alpha-TOS at sub-apoptotic levels inhibited proliferation of MM cell lines, while being nontoxic to nonmalignant mesothelial cells. Because MM cells are typified by a highly metastatic phenotype, we investigated the effect of alpha-TOS on genes playing a major role in MM progression. Of these, alpha-TOS down regulated fibroblast growth factor (FGF)-1 and, in particular, FGF-2 on the transcriptional level in MM cells, and this was not observed in their nonmalignant counterparts. FGF-2 short interfering RNA suppressed proliferation of MM cells. Down-regulation of FGF-2 was likely because of inhibition of the egr-1 transcription activity that was decreased in MM cells via oxidative stress induced by alpha-TOS, as evidenced by EPR spectroscopy, whereas nonmalignant cells did not show this response. Treatment of MM cells with egr-1 short interfering RNA suppressed proliferation, which was overridden by exogenously added recombinant FGF-1 and, in particular, FGF-2. An analog of coenzyme Q targeted to mitochondria and superoxide dismutase overrode inhibition of MM cell proliferation by alpha-TOS as well as alpha-TOS-induced inhibition of egr-1-dependent transactivation. Finally, alpha-TOS significantly suppressed experimental MM in immunocompromised mice. Our data suggest that alpha-TOS suppresses MM cell proliferation by disrupting the FGF-FGF receptor autocrine signaling loop by generating oxidative stress and point to the agent as a selective drug against thus far fatal mesotheliomas.

Antioxidant effect of bovine serum albumin on membrane lipid peroxidation induced by iron chelate and superoxide

Albumin is supposed to be the major antioxidant circulating in blood. This study examined the prevention of membrane lipid peroxidation by bovine serum albumin (BSA). Lipid peroxidation was induced by the exposing of enzymatically generated superoxide radicals to egg yolk phosphatidylcholine liposomes incorporating lipids with different charges in the presence of chelated iron catalysts. We used three kinds of Fe3+-chelates, which initiated reactions that were dependent on membrane charge: Fe3+-EDTA and Fe3+-EGTA catalyzed peroxidation in positively and negatively charged liposomes, respectively, and Fe3+-NTA, a renal carcinogen, catalyzed the reaction in liposomes of either charge. Fe3+-chelates initiated more lipid peroxidation in liposomes with increased zeta potentials, followed by an increase of their availability for the initiation of the reaction at the membrane surface. BSA inhibits lipid peroxidation by preventing the interaction of iron chelate with membranes, followed by a decrease of its availability in a charge-dependent manner depending on the iron-chelate concentration: one is accompanied and the other is unaccompanied by a change in the membrane charge. The inhibitory effect of BSA in the former at high concentrations of iron chelate would be attributed to its electrostatic binding with oppositely charged membranes. The inhibitory effect in the latter at low concentrations of iron chelate would be caused by BSA binding with iron chelates and keeping them away from membrane surface where lipid peroxidation is initiated. Although these results warrant further in vivo investigation, it was concluded that BSA inhibits membrane lipid peroxidation by decreasing the availability of iron for the initiation of membrane lipid peroxidation, in addition to trapping active oxygens and free radicals.

Vitamin E analogs trigger apoptosis in HER2/erbB2-overexpressing breast cancer cells by signaling via the mitochondrial pathway

Alpha-tocopheryl succinate (alpha-TOS) is a redox-silent vitamin E (VE) analog with high pro-apoptotic and anti-neoplastic activity. Here we investigated whether alpha-TOS and several novel VE analogs kill breast cancer cells over-expressing the anti-apoptotic receptor protein HER2/erbB2. The agents induced apoptosis at comparable levels in both erbB2-low and -high cells. Generation of reactive oxygen species (ROS) preceded mitochondrial destabilization and execution of apoptosis, as evidenced by the anti-apoptotic effects of exogenous superoxide dismutase and mitochondrially targeted coenzyme Q. Dissipation of DeltaPsi(m) was followed by cytochrome c and Smac/Diablo re-localization and caspase-dependent cleavage of death substrate. A resistance to apoptosis for the corresponding rho(0) counterparts confirmed a critical dependency for mitochondria during the induction of apoptosis in breast cancer cells mediated by VE analogs and linked apoptosis to generation of radicals as judged by the delayed accumulation of ROS in the cybrid cell types. We conclude that alpha-TOS causes efficient apoptosis in breast cancer cells independent of their erbB2 status. Since erbB2 is frequently over-expressed in breast cancers and renders the neoplastic disease resistant to established treatment, our findings are of clinical interest.

Structural characteristic of terminal dicarboxylic moiety required for apoptogenic activity of alpha-tocopheryl esters

alpha-Tocopheryl succinate (TS) is known to induce apoptosis in various cells and has attracted attention as a chemotherapeutic agent. Recently, we reported the structural significance of the terminal dicarboxylic moiety for the action of TS [J. Nutr. Sci. Vitaminol. 49 (2003) 310-314]. In this study, to determine details of the relationship between the structure and the function of the terminal ester moiety of alpha-tocopherol (alpha-T), we synthesized four novel esters, alpha-tocopheryl oxalate (TO), alpha-tocopheryl malonate (TM), alpha-tocopheryl pimelate (TP) and alpha-tocopheryl succinate ethyl ester (TSE), and compared their apoptogenic activities with those of TS, alpha-T, gamma-tocopherol (gamma-T) and two commercially available alpha-T derivatives, alpha-tocopheryl nicotinate (TN) and alpha-tocopheryl acetate (TA), in vascular smooth muscle cells and a mouse breast cancer cell line C127I. TO and TM in addition to TS, but not the others, induced apoptosis in both cells. Particularly, TO was the most potent of all alpha-T derivatives used. The addition of exogenous superoxide dismutase (SOD) significantly prevented the apoptosis induced by TM as well as that by TS as reported previously, but did not affect TO-induced apoptosis. These results suggest that O(2)(-) generated exogenously participates in TM-induced apoptosis but not in TO-induced apoptosis. The difference in their apoptotic effects is attributed to structural properties of the terminal dicarboxylic moiety, which has an inflexible plane conformation in TO, while it is highly flexible in TM and TS.

Vitamin E succinate and cancer treatment: a vitamin E prototype for selective antitumour activity

Great hope has been given to micronutrients as anticancer agents, since they present natural compounds with beneficial effects for normal cells and tissues. One of these is vitamin E (VE), an antioxidant and an essential component of biological membranes and circulating lipoproteins. In spite of a number of epidemiological and intervention studies, little or no correlation between VE intake and incidence of cancer has been found. Recent reports have identified a redox-silent analogue of VE, α-tocopheryl succinate (α-TOS), as a potent anticancer agent with a unique structure and pharmacokinetics in vivo. α-TOS is highly selective for malignant cells, inducing them into apoptotic death largely via the mitochondrial route. The molecule of α-TOS may be modified so that analogues with higher activity are generated. Finally, α-TOS and similar agents are metabolised to VE, thereby yielding a compound with a secondary beneficial activity. Thus, α-TOS epitomises a group of novel compounds that hold substantial promise as future anticancer drugs. The reasons for this optimistic notion are discussed in the following paragraphs.

Role of reactive oxygen species in the induction of apoptosis by ?-tocopheryl succinate

Alpha-tocopheryl succinate (TOS), a vitamin E analog, is a promising anticancer agent due to its abilities to inhibit proliferation and to induce apoptosis in a variety of human malignant cell lines, while being relatively less active toward normal cells. However, the molecular mechanisms underlying the apoptotic effects of TOS are not precisely understood. Reports that TOS can generate reactive oxygen species (ROS) prompted us to investigate the role of ROS in TOS-induced apoptosis in cancer cells. We found that the human lung cancer A549 and H460 cell lines were much more sensitive to TOS-induced apoptosis than the human glioblastoma T98G and U87MG cell lines. Our data suggested that the differential TOS sensitivity was not caused by differences in the uptake and retention of TOS between TOS-sensitive and -resistant cancer cells. The differential ability of cancer cells to generate ROS in response to TOS appears to be an important factor in determining the susceptibility of cells to TOS-induced apoptosis. Our results further suggest that TOS-induced generation of ROS is involved in caspase-independent apoptosis. Taken together, our findings suggest an important role of ROS generation in TOS-induced, caspase-independent apoptosis of cancer cells.

Temporary membrane distortion of vascular smooth muscle cells is responsible for their apoptosis induced by platelet-activating factor-like oxidized phospholipids and their degradation product, lysophosphatidylcholine

To obtain information about the mechanism of apoptosis induced by oxidized low density lipoproteins (oxLDL) in atherosclerotic plaques, we examined the effects of lysophosphatidylcholine (LPC) and platelet-activating factor (PAF)-like lipids (PAF-LL), which can be derived from oxLDL, on rat vascular smooth muscle cells (VSMC). All the lipids with different structures examined induced apoptosis of VSMC, so we studied the mechanism of induction of apoptosis by LPC. LPC-induced apoptosis was inhibited by alpha-tocopherol (alpha-T) and cholesterol (Chol), but not by other antioxidants such as palmitoyl ascorbic acid and PAF receptor antagonist. The cells temporarily became spherical and highly permeable before induction of apoptosis, and their change in shape was prevented by alpha-T and Chol. From these results, we suggest that the apoptosis induced by oxLDL-derived phospholipids in VSMC is caused by temporary membrane distortion, not through specific receptors.

Potentiation of anti-cancer effect by intravenous administration of vesiculated alpha-tocopheryl hemisuccinate on mouse melanoma in vivo

We examined the effect of alpha-tocopheryl hemisuccinate (TS) on the growth of mouse melanoma cells B16-F1 inoculated on the back of hairless mice by two administration procedures of TS, i.p. administration of TS dissolved with dimethyl sulfoxide (TS i.p.) and i.v. administration of TS vesicles (TS-vesicle i.v.). TS i.p. significantly prevented the tumor growth of only half the mice in the group. However, TS-vesicle i.v. almost completely inhibited the tumor growth of all mice. Furthermore, the mean survival of the TS-vesicle i.v. group was 1.4-fold those of the control and TS i.p. groups.

High cytotoxicity of alpha-tocopheryl hemisuccinate to cancer cells is due to failure of their antioxidative defense systems

Alpha-tocopheryl hemisuccinate (TS) has been reported to induce apoptosis in various cells, and to show higher toxicity to cancer cells than to normal cells. In this study, although TS induced apoptosis in both a mouse breast normal cell line NMuMG and a mouse breast cancer cell line C127I, the latter were more susceptible to TS. TS-induced apoptosis in C127I was inhibited by superoxide dismutase, alpha-tocopherol and butylated hydroxyanisol. From these results, superoxide (O(2)(-)) itself and reactive oxygen species derived from O(2)(-) and/or free radicals are assumed to be associated with TS toxicity, and the high toxicity of TS to cancer cells is suggested to be due to failure of their antioxidative defense systems.

Roles of Fas signaling pathway in vitamin E succinate-induced apoptosis in human gastric cancer SGC-7901 cells

AIM

To investigate the roles of Fas signaling pathway in vitamin E succinate-induced apoptosis in human gastric cancer SGC-7901 cells.

METHODS

Human gastric cancer SGC-7901 cells were treated with VES at 5, 10, 20 mg x L(-1), succinic acid and vitamin E as vehicle control and condition media only as untreated (UT) control. Apoptotic morphology was observed by DAPI staining. Western blot analysis was applied to measure the expression of Fas, FADD and caspase-8 proteins. After the cells were transiently transfected with Fas and FADD antisense oligonucleotides, respectively, caspase-8 activity was determined by flurometric method.

RESULTS

The morphologically apoptotic changes were observed after VES treatment by DAPI staining. 23.7 % and 89.6 % apoptosis occurred after 24 h and 48 h of 20 mg x L(-1) VES treatment, respectively. The protein levels of Fas, FADD and caspase-8 were evidently increased in a dose-dependent manner after 24 h of VES treatment. The blockage of Fas by transfection with Fas antisense oligonucleotides obviously inhibited the expression of FADD protein. After SGC-7901 cells were transfected with Fas and FADD antisense oligonucleotides, caspase-8 activity was obviously decreased (P<0.01), whereas Fas blocked more than FADD.

CONCLUSION

VES-induced apoptosis in human gastric cancer SGC-7901 cells involves Fas signaling pathway including the interaction of Fas, FADD and caspase-8.

The effects of vitamin E succinate on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells

AIM

To investigate the effects of vitamin E succinate (VES) on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells.

METHODS

After SGC-7901 cells were treated with VES at different doses (5,10,20 mg x L(-1)) at different time, reverse transcription-PCR technique was used to detect the level of c-jun mRNA; Western Blot was applied to measure the expression of c-jun protein.

RESULTS

After the cells were treated with VES at 20 mg x L(-1) for 3 h, the expression rapidly reached its maximum that was 3.5 times of UT control (P<0.01). The level of c-jun mRNA was also increased following treatment of VES for 6 h. However,the expression after treatment of VES at 5 mg x L(-1) for 24 h was 1.6 times compared with UT control (P<0.01). Western blot analysis showed that the level of c-jun protein was obviously elevated in VES-treated SGC-7901 cells at 20 mg x L(-1) for 3 h. The expression of c-jun protein was gradually increased after treatment of VES at 20 mg x L(-1) for 3, 6, 12 and 24 h, respectively, with an evident time-effect relationship.

CONCLUSION

The levels of c-jun mRNA and protein in VES-treated SGC-7901 cells were increased in a dose- and time-dependent manner; the expression of c-jun was prolonged by VES, indicating that c-jun is involved in VES-induced apoptosis in SGC-7901 cells.

Enhancement by alpha-tocopheryl hemisuccinate of nitric oxide production induced by lypopolysaccharide and interferon-gamma through the upregulation of protein kinase C in rat vascular smooth muscle cells

The effect of alpha-tocopheryl hemisuccinate (TS) on lipopolysaccharide (LPS)/interferon-gamma (IFN)-induced nitric oxide production in rat vascular smooth muscle cells (VSMC) was examined. The LPS/IFN-induced NO production was enhanced by TS but not by the other alpha-tocopherol (alpha-T) derivatives alpha-tocopheryl acetate (TA) and alpha-tocopheryl nicotinate (TN), or alpha-T itself. alpha-T, TA and TN inhibited the enhancement by TS of LPS/IFN-induced NO production. The enhancing effect of TS was observed in the presence of LPS, but not IFN, suggesting that TS participates in the LPS-stimulated signal pathway leading to NO production. Protein kinase C (PKC) inhibitors, but not protein kinase A inhibitors, inhibited the enhancing effect of TS on LPS/IFN-induced NO production. Furthermore, TS enhanced the amount of PKCalpha in VSMC. From these results, we concluded that the enhancing effect of LPS/IFN-induced NO production was caused by upregulation of PKC in VSMC.