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

Recent advances in SN-38 drug delivery system

DNA topoisomerase I plays a key role in lubricatingthe wheels of DNA replication or RNA transcription through breaking and reconnecting DNA single-strand. It is widely known that camptothecin and its derivatives (CPTs) have inhibitory effects on topoisomerases I, and have obtained some clinical benefits in cancer treatment. The potent cytotoxicity makes 7-ethyl-10-hydroxycamptothecin (SN-38) become a brilliant star among these derivatives. However, some undesirable physical and chemical properties of this compound, including poor solubility and stability, seriously hinder its effective delivery to tumor sites. In recent years, strategies to alleviate these defects have aroused extensive research interest. By focusing on the loading mechanism, basic nanodrug delivery systems with SN-38 loaded, like nanoparticles, liposomes and micelles, are demonstrated here. Additionally, functionalized nanodrug delivery systems of SN-38 including prodrug and active targeted nanodrug delivery systems and delivery systems designed to overcome drug resistance are also reviewed. At last, challenges for future research in formulation development and clinical translation of SN-38 drug delivery system are discussed.

Succinate dehydrogenase complex subunit C: Role in cellular physiology and disease

Succinate dehydrogenase complex subunit C (SDHC) is a subunit of mitochondrial complex II (MCII), which is also known as succinate dehydrogenase (SDH) or succinate: ubiquinone oxidoreductase. Mitochondrial complex II is the smallest respiratory complex in the respiratory chain and contains four subunits. SDHC is a membrane-anchored subunit of SDH, which connects the tricarboxylic acid cycle and the electron transport chain. SDH regulates several physiological processes within cells, plays an important role in generating energy to maintain normal cell growth, and is involved in apoptosis. Currently, SDHC is generally recognized as a tumor-suppressor gene. SDHC mutations can cause oxidative damage in the body. It is closely related to the occurrence and development of cancer, neurodegenerative diseases, and aging-related diseases. Here, we review studies on the structure, biological function, related diseases of SDHC, and the mev-1 Animal Model of SDHC Mutation and its potential use as a therapeutic target of certain human diseases.

Nanocarrier-Based Delivery of SN22 as a Tocopheryl Oxamate Prodrug Achieves Rapid Tumor Regression and Extends Survival in High-Risk Neuroblastoma Models

Despite the use of intensive multimodality therapy, the majority of high-risk neuroblastoma (NB) patients do not survive. Without significant improvements in delivery strategies, anticancer agents used as a first-line treatment for high-risk tumors often fail to provide clinically meaningful results in the settings of disseminated, recurrent, or refractory disease. By enhancing pharmacological selectivity, favorably shifting biodistribution, strengthening tumor cell killing potency, and overcoming drug resistance, nanocarrier-mediated delivery of topoisomerase I inhibitors of the camptothecin family has the potential to dramatically improve treatment efficacy and minimize side effects. In this study, a structurally enhanced camptothecin analog, SN22, reversibly coupled with a redox-silent tocol derivative (tocopheryl oxamate) to allow its optimally stable encapsulation and controlled release from PEGylated sub-100 nm nanoparticles (NP), exhibited strong NB cell growth inhibitory activity, translating into rapid regression and durably suppressed regrowth of orthotopic, MYCN-amplified NB tumors. The robust antitumor effects and markedly extended survival achieved in preclinical models recapitulating different phases of high-risk disease (at diagnosis vs. at relapse with an acquired loss of p53 function after intensive multiagent chemotherapy) demonstrate remarkable potential of SN22 delivered in the form of a hydrolytically cleavable superhydrophobic prodrug encapsulated in biodegradable nanocarriers as an experimental strategy for treating refractory solid tumors in high-risk cancer patients.

Deleterious effects of combination of lead and β-amyloid peptides in inducing apoptosis and altering cell cycle in human neuroblastoma cells

Lead (Pb) is a toxic pollutant known to cause several abnormalities related to the brain, including cognitive dysfunction, and it is ubiquitous in nature. β-amyloid peptides (AP) are crucially involved in Alzheimer’s disease (AD). It has been reported that there is a connection between lead and amyloid peptides in exerting similar kinds of altered functions in the brain and long-term exposure to lead leads ultimately to increased beta amyloid formation in the brain, lethal to human brain cells. There is still a lack of information on the mechanism by which Pb affects AP formation, exerting combined toxicity in AD patients. To fill the gap, we have systematically analyzed the toxicity individually and in combination of Pb and AP in human brain cells. We found that the combination of Pb and AP exerted a higher toxicity than individual exposures in human neuroblastoma cells. The lower inhibitory concentration values were determined by both time and concentration dependent manner on using MTT assay. The data resulted in the development of enhanced toxicity on exposure to Pb with both the combinations of AP(1-40) or (25-35) and with all combinations in human brain cells compared to individual exposures to Pb (1-40) or AP(25-35). The severe apoptotic effect and alteration in cell cycle by arresting at the S-phase evidenced the increased toxicity of combinational exposure to Pb and AP on human neuroblastoma cells. Furthermore, the quantitative determination of LDH and caspase-3 activity indicated the induction of severe toxicity. We conclude that both are synergistically associated with effects such as arresting the cell cycle and triggering apoptosis during the progression of Alzheimer’s disease.

Water-Soluble Vitamin E-Tocopheryl Phosphate

The hydrophobicity of vitamin E poses transport and metabolic challenges to regulate its bioavailability and to prevent its accumulation in lipid-rich tissues such as adipose tissue, brain, and liver. Water-soluble precursors of vitamin E (α-tocopherol, αT), such as its esters with acetate (αTA), succinate (αTS), or phosphate (αTP), have increased solubility in water and stability against reaction with free radicals, but they are rapidly converted during their uptake into the lipid-soluble vitamin E. Therefore, the bioavailability of these precursors as intact molecules is low; nevertheless, at least for αTS and αTP, the recent research has revealed unique regulatory effects on signal transduction and gene expression and the modulation of cellular events ranging from proliferation, survival/apoptosis, lipid uptake and metabolism, phagocytosis, long term potentiation, cell migration, telomere maintenance, and angiogenesis. Moreover, water-soluble derivatives of vitamin E including some based on αTP are increasingly used as components of nanocarriers for enhanced and targeted delivery of drugs and other molecules (vitamins, including αT and αTP itself, vitamin D3, carnosine, caffeine, docosahexaenoic acid (DHA), insulin) and cofactors such as coenzyme Q10. In this review, the chemical characteristics, transport, metabolic pathways, and molecular mechanisms of action of αTP in cells and tissues are summarized and put into perspective with its possible role in the prevention of a number of diseases.

α-Tocopherol succinate enhances pterostilbene anti-tumor activity in human breast cancer cells in vivo and in vitro

Vitamin E (Vit. E) is considered an essential dietary nutrient for humans and animals. An enormous body of evidence indicates the biological and protective effects of Vit. E consumption. Tocopherol-associated protein (TAP) is a major tocopherol-binding protein affecting Vit. E stimulation and downstream signaling transduction. However, how Vit. E utilizes TAP as an anti-cancer mechanism remains unclear. Microarray analysis of signature gene profiles in breast cancer cells treated with α-tocopheryl succinate (α-TOS, a Vit. E isoform) resulted in cell cycle arrest and anti-cancer activity in breast cancer cells. Pterostilbene (PS), a natural dietary antioxidant found in blueberries, in combination with α-TOS synergistically maximized breast cancer cell growth inhibition by disrupting signal transduction, transcription factors and cell cycle proteins. In a xenograft mouse model, PS treatment with Vit. E inhibited breast tumor growth and cell invasion, which were evaluated using our recently developed circulating tumor cell (CTC) detection assay. Because dietary Vit. E and PS supplementation contributed to preventative and therapeutic effects in vitro and in vivo, this combination may benefit breast cancer therapy in the clinic.

Novel dual VES phospholipid self-assembled liposomes with an extremely high drug loading efficiency

Vitamin E succinate (VES), a unique selective anti-cancer drug, has attracted much attention for its ability to induce apoptosis in various cancer cells. Importantly, it has been reported that VES is largely non-toxic to normal cells. However, poor aqueous solubility and bioavailability extensively restricted its clinical utility. In this report, dual VES phospholipid conjugate (di-VES-GPC) prodrug based liposomes were prepared in order to develop an efficient delivery system for VES. Di-VES-GPC was first synthesized by conjugating VES with l-α-glycerophosphorylcholine (GPC) using N,N'-dicyclohexylcarbodiimide (DCC) as a coupling agent. The di-VES-GPC prodrug was able to self-assemble into liposomes by reverse-phase evaporation method. The structure of the liposomes was characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and cryo-TEM. The results showed that di-VES-GPC assembled liposomes were spherical with an average diameter approximately 183nm. Cryo-TEM data confirmed the formation of multilamellar liposomes with the bilayer thickness about 5nm by the assembly of the conjugate without any excipient. The VES drug loading highly reaches up to 82.8wt% in the liposomes after a simple calculation. Furthermore, the in vitro release behavior of di-VES-GPC liposomes was evaluated in different media. It was found that the liposomes could release free VES at a weakly acidic microenvironment but exhibited good stability under a simulated biological condition. The cellular uptake and intracellular drug release tests demonstrated that di-VES-GPC liposomes could be internalized effectively and converted into parent drug VES in cancer cells. Furthermore, in vitro antitumor activities of the di-VES-GPC liposomes were evaluated by MTT assay and flow cytometry. It was revealed that the liposomes presented comparable cytotoxicities to free VES. Taken together, the di-VES-GPC liposomes might provide an excellent formulation of VES which have potential in the treatment of cancers.

VCPA, a novel synthetic derivative of α-tocopheryl succinate, sensitizes human gastric cancer to doxorubicin-induced apoptosis via ROS-dependent mitochondrial dysfunction

Gastric carcinoma is a common malignant disease worldwide and has a dismal prognosis. Doxorubicin (DOX), one of the most widely used chemotherapeutic agents, has limited use because of its side effects and the development of tumor-cell resistance. Combinations of doxorubicin and non-cross-resistant agents have been required for adjuvant chemotherapy of gastric cancer. Here, we report that VCPA, a novel synthetic derivative of α-Tocopheryl Succinate, induced apoptosis via production of reactive oxygen species (ROS). When used in combination with doxorubicin, lower doses of VCPA sensitized human gastric cancer cells to DOX-induced apoptosis. The DOX/VCPA combination treatment caused an imbalance in the ratio of Bcl-2 to Bax and induced a lethal mitochondrial dysfunction. MAPKs were also activated in response to the DOX/VCPA treatment but played a protective role in DOX-induced cell death. In vivo studies further confirmed the sensitizing effect of VCPA. Combining DOX with VCPA markedly inhibited tumor growth in a tumor xenograft model of human gastric cancer. Taken together, our study revealed that VCPA, through increased ROS production, could synergize with DOX and circumvent DOX resistance in human gastric cancer cells.

α-Tocopheryl Succinate Affects Malignant Cell Viability, Proliferation, and Differentiation

The widespread occurrence of malignant tumors motivates great attention to finding and investigating effective new antitumor preparations. Such preparations include compounds of the vitamin E family. Among them, α-tocopheryl succinate (vitamin E succinate (VES)) has the most pronounced antitumor properties. In this review, various targets and mechanisms of the antitumor effect of vitamin E succinate are characterized. It has been shown that VES has multiple intracellular targets and effects, and as a result VES is able to induce apoptosis in tumor cells, inhibit their proliferation, induce differentiation, prevent metastasizing, and inhibit angiogenesis. However, VES has minimal effects on normal cells and tissues. Due to the variety of targets and selectivity of action, VES is a promising agent against malignant neoplasms. More detailed studies in this area can contribute to development of effective and safe chemotherapeutic preparations.

Pheochromocytoma: Gasping for Air

There has been increasing evidence that pseudohypoxia--a phenomenon that we refer to as "gasping for air"--along with mitochondrial enzyme dysregulation play a crucial role in tumorigenesis, particularly in several hereditary pheochromocytomas (PHEOs) and paragangliomas (PGLs). Alterations in key tricarboxylic acids (TCA) cycle enzymes (SDH, FH, MDH2) have been shown to induce pseudohypoxia via activation of the hypoxia-inducible transcription factor (HIF) signaling pathway that is involved in tumorigenesis, invasiveness, and metastatic spread, including an association with resistance to various cancer therapies and worse prognosis. This review outlines the ongoing story of the pathogenesis of hereditary PHEOs/PGLs, showing the unique and most updated evidence of TCA cycle dysregulation that is tightly linked to hypoxia signaling.

Nanoparticle-mediated delivery of a rapidly activatable prodrug of SN-38 for neuroblastoma therapy

Nanomedicine-based strategies have the potential to improve therapeutic performance of a wide range of anticancer agents. However, the successful implementation of nanoparticulate delivery systems requires the development of adequately sized nanocarriers delivering their therapeutic cargo to the target in a protected, pharmacologically active form. The present studies focused on a novel nanocarrier-based formulation strategy for SN-38, a topoisomerase I inhibitor with proven anticancer potential, whose clinical application is compromised by toxicity, poor stability and incompatibility with conventional delivery vehicles. SN-38 encapsulated in biodegradable sub-100 nm sized nanoparticles (NP) in the form of its rapidly activatable prodrug derivative with tocopherol succinate potently inhibited the growth of neuroblastoma cells in a dose- and exposure time-dependent manner, exhibiting a delayed response pattern distinct from that of free SN-38. In a xenograft model of neuroblastoma, prodrug-loaded NP caused rapid regression of established large tumors, significantly delayed tumor regrowth after treatment cessation and markedly extended animal survival. The NP formulation strategy enabled by a reversible chemical modification of the drug molecule offers a viable means for SN-38 delivery achieving sustained intratumoral drug levels and contributing to the potency and extended duration of antitumor activity, both prerequisites for effective treatment of neuroblastoma and other cancers.

Mitochondrial substrates in cancer: drivers or passengers?

The majority of cancers demonstrate various tumor-specific metabolic aberrations, such as increased glycolysis even under aerobic conditions (Warburg effect), whereas mitochondrial metabolic activity and their contribution to cellular energy production are restrained. One of the most important mechanisms for this metabolic switch is the alteration in the abundance, utilization, and localization of various mitochondrial substrates. Numerous lines of evidence connect disturbances in mitochondrial metabolic pathways with tumorigenesis and provide an intriguing rationale for utilizing mitochondria as targets for anti-cancer therapy.

Alteration of α-tocopherol-associated protein (TAP) expression in human breast epithelial cells during breast cancer development

Breast cancer is the most common malignancy among women and has an age-specific incidence profile. Over the last decade, many studies have demonstrated the anticancer activity of α-tocopherol, the main and most active form of natural vitamin E. α-Tocopherol-associated protein (TAP) was found to be one of the major α-tocopherol binding proteins in human serum and in liver, brain, and prostate tissues. In this study, we found that reduced TAP expression was significantly correlated with Her2/neu receptor expression, breast cancer stage and nodal stage in paired normal and cancerous breast tissue samples from 93 patients using real-time PCR analysis. A cell viability assay showed that α-tocopheryl succinate (α-TOS), a synthetic derivative of α-tocopherol, enhanced the cells' sensitivity to doxorubicin and resulted in a reduction in cell viability in breast cancers. Taken together, these data suggest that the use of vitamin E or its analogue as a dietary supplement may be beneficial for the treatment of cancer.

Inhibitors of succinate: quinone reductase/Complex II regulate production of mitochondrial reactive oxygen species and protect normal cells from ischemic damage but induce specific cancer cell death

Succinate:quinone reductase (SQR) of Complex II occupies a unique central point in the mitochondrial respiratory system as a major source of electrons driving reactive oxygen species (ROS) production. It is an ideal pharmaceutical target for modulating ROS levels in normal cells to prevent oxidative stress-induced damage or alternatively,increase ROS in cancer cells, inducing cell death.The value of drugs like diazoxide to prevent ROS production,protecting normal cells, whereas vitamin E analogues promote ROS in cancer cells to kill them is highlighted. As pharmaceuticals these agents may prevent degenerative disease and their modes of action are presently being fully explored. The evidence that SDH/Complex II is tightly coupled to the NADH/NAD+ ratio in all cells,impacted by the available supplies of Krebs cycle intermediates as essential NAD-linked substrates, and the NAD+-dependent regulation of SDH/Complex II are reviewed, as are links to the NAD+-dependent dehydrogenases, Complex I and the E3 dihiydrolipoamide dehydrogenase to produce ROS. This review collates and discusses diverse sources of information relating to ROS production in different biological systems, focussing on evidence for SQR as the main source of ROS production in mitochondria, particularly its relevance to protection from oxidative stress and to the mitochondrial-targeted anti cancer drugs (mitocans) as novel cancer therapies [corrected].

Analogs of vitamin E epitomized by alpha-tocopheryl succinate for pancreatic cancer treatment: in vitro results induce caution for in vivo applications

OBJECTIVES

alpha-Tocopheryl succinate (alpha-TOS) is thought to be toxic only for cancer cells. We ascertained in vitro alpha-TOS effects on pancreatic cancer (PC) and normal cell growth and verified whether the combination of nontoxic alpha-TOS and 5-fluorouracil (5-FU) doses causes cancer cell death and whether alpha-TOS effects are mediated by the proapoptotic proteins Bax/Bak and/or SMAD4/DPC4 status.

METHODS

Five PC cell lines, myoblasts, normal monocytes, wild-type (WT) and Bax/Bak double knockout mouse embryonic fibroblast (MEF) cells, and permanently SMAD4/DPC4-transfected PSN1 cells were cultured in 1% and 10% fetal calf serums (FCSs), without or with alpha-TOS (5-500 micromol/L). Nontoxic 5-FU (0.0001 mmol/L) and alpha-TOS alone or in combination were also evaluated.

RESULTS

Only PSN1 PC cell line, which had SMAD4/DPC4 homozygous deletion, was sensitive to nontoxic alpha-TOS doses (5 micromol/L in 1% FCS and 50 micromol/L in 10% FCS). A 20-micromol/L alpha-TOS inhibited MEF-WT, not MEF-double knockout growth. Only PSN1 cells were sensitive to nontoxic 5-FU and alpha-TOS combination. SMAD4/DPC4 transfection restored PSN1 resistance to the effects of combined 5-FU and alpha-TOS effects.

CONCLUSIONS

Only a minority of PC cells are sensitive to the antiproliferative effects of alpha-TOS, any sensitivity appearing to be correlated with SMAD4/DPC4 homozygous deletion and Bax/Bak expression.

Alpha-tocopheryl succinate potentiates the paclitaxel-induced apoptosis through enforced caspase 8 activation in human H460 lung cancer cells

Paclitaxel is one of the chemotherapeutic drugs widely used for the treatment of nonsmall cell lung cancer (NSCLC) patients. Here, we tested the ability of alpha-tocopheryl succinate (TOS), another promising anticancer agent, to enhance the paclitaxel response in NSCLC cells. We found that sub-apoptotic doses of TOS greatly enhanced paclitaxel-induced growth suppression and apoptosis in the human H460 NSCLC cell lines. Our data revealed that this was accounted for primarily by an augmented cleavage of poly(ADP-ribose) polymerase (PARP) and enhanced activation of caspase-8. Pretreatment with z-VAD-FMK (a pan-caspase inhibitor) or z-IETD-FMK (a caspase-8 inhibitor) blocked TOS/paclitaxel cotreatment-induced PARP cleavage and apoptosis, suggesting that TOS potentiates the paclitaxel-induced apoptosis through enforced caspase 8 activation in H460 cells. Furthermore, the growth suppression effect of TOS/paclitaxel combination on human H460, A549 and H358 NSCLC cell lines were synergistic. Our observations indicate that combination of paclitaxel and TOS may offer a novel therapeutic strategy for improving paclitaxel drug efficacy in NSCLC patient therapy as well as for potentially lowering the toxic side effects of paclitaxel through reduced drug dosage.

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.

Vitamin E analogues as mitochondria-targeting compounds: from the bench to the bedside?

Despite considerable effort focusing on designing and finding efficient anti-cancer drugs over the last decade, little progress has been achieved, in particular in case of highly recalcitrant malignancies. Also, since there is a trend suggesting that deaths from cancers may be more frequent than from cardiovascular diseases, it is important to look for novel efficient and selective therapeutic approaches to gradually start winning the battle with cancer. Redox-silent vitamin E analogues, epitomised by alpha-tocopheryl succinate, give some hope in the quest for drugs with such properties. Thus far, these agents have been successfully tested in experimental animals with different types of cancer, showing high efficacy against malignancies including HER2-positive breast carcinomas or malignant mesotheliomas. Further research will provide additional, necessary data to launch clinical trials, possibly in near future, translating into development of innovative anti-cancer drugs acting by targeting mitochondria selectively in cancer cells.

New approaches to pharmacotherapy of tumors of the nervous system during childhood and adolescence

Tumors of the nervous system are among the most common and most chemoresistant neoplasms of childhood and adolescence. Malignant tumors of the brain collectively account for 21% of all cancers and 24% of all cancer-related deaths in this age group. Neuroblastoma, a peripheral nervous system tumor, is the most common extracranial solid tumor of childhood, and 65% of children with this tumor have only a 10 or 15% chance of living 5 years beyond the time of initial diagnosis. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the role of and current challenges to pharmacotherapy of malignant tumors of the nervous system during childhood and adolescence and discusses novel approaches aimed at overcoming these challenges.

Vitamin E and cancer: An insight into the anticancer activities of vitamin E isomers and analogs

Current observations in the literature suggest that vitamin E may be a suitable candidate for the adjuvant treatment of cancer. Even though historically most research focused on alpha-tocopherol, more recent evidence suggests that the other isomers of vitamin E (beta-, gamma- and delta-tocopherols and alpha-, beta-, gamma- and delta-tocotrienols) differ in their proapoptotic potencies. The main focus of this communication is the current understanding of the molecular mechanisms regulated by vitamin E isomers and their analogs during the induction of apoptosis. This review highlights that the mitochondria are the major target for the induction of apoptosis by vitamin E isomers and analogs and that the various signaling pathways regulated by these agents are likely to contribute towards maximizing the intrinsic pathway of apoptosis triggered initially by the mitochondria. Overall, the presentation of recent studies from the literature in this communication allows the drawing of the following important conclusions: (i) no direct link exists between the antioxidant activity of each isomer/derivative and proapoptotic potency, (ii) tocotrienols are more effective proapoptotic agents than tocopherols, (iii) synthetic modifications of the naturally occurring compounds may improve their apoptotic potency and (iv) vitamin E isomers and derivatives regulate caspase-independent pathways of apoptosis. The latter combined with the evidence presented in this review regarding the additive or synergistic anticarcinogenic effects obtained when vitamin E analogs are used in combination with other cancer chemotherapeutic agents, supports further research to design the most promising vitamin E derivatives and clinically test them in adjuvant chemotherapeutic treatments.

Supplementation with a synthetic polyphenol limits oxidative stress and enhances neuronal cell viability in response to hypoxia-re-oxygenation injury

Oxidative stress is associated with the pathology of acute and chronic neurodegenerative disease. Cultured human neuronal cells exposed to experimental hypoxia-re-oxygenation (H/R) injury responded with an increased production of reactive oxygen species (ROS) and a significant decrease in intracellular ATP. Expression of genes encoding for hypoxia-inducible factor 1-alpha (HIF1-alpha), inducible haemoxygenase-1 (HO-1), glucose transporter-1 (Glut-1), the oxygen-sensor neuroglobin (Nb) and Cu,Zn-superoxide dismutase (SOD1), catalase (CAT) and glutathione peroxidase-1 (Gpx-1) increased significantly in response to the insult. Enhanced expression of HO-1, SOD1 and CAT correlated with an increase in the corresponding protein activity. Despite the cellular response to bolster antioxidant capacity, apoptosis and necrosis increased following H/R injury. In contrast, ROS accumulation, the endogenous gene response and cell death was limited in neuronal cells pre-incubated with 50 or 100, but not 10 microM of the phenolic antioxidant 3,3',5,5'-tetra-t-butyl-biphenyl-4,4'-diol (BP) prior to H/R injury. These data indicate that the early endogenous gene response to H/R injury is unable to inhibit neuronal dysfunction and that increasing cellular antioxidant capacity with a synthetic polyphenol (>10 microM) is potentially neuro-protective.

Alpha-tocopheryl succinate induces apoptosis by targeting ubiquinone-binding sites in mitochondrial respiratory complex II

Alpha-tocopheryl succinate (alpha-TOS) is a selective inducer of apoptosis in cancer cells, which involves the accumulation of reactive oxygen species (ROS). The molecular target of alpha-TOS has not been identified. Here, we show that alpha-TOS inhibits succinate dehydrogenase (SDH) activity of complex II (CII) by interacting with the proximal and distal ubiquinone (UbQ)-binding site (Q(P) and Q(D), respectively). This is based on biochemical analyses and molecular modelling, revealing similar or stronger interaction energy of alpha-TOS compared to that of UbQ for the Q(P) and Q(D) sites, respectively. CybL-mutant cells with dysfunctional CII failed to accumulate ROS and underwent apoptosis in the presence of alpha-TOS. Similar resistance was observed when CybL was knocked down with siRNA. Reconstitution of functional CII rendered CybL-mutant cells susceptible to alpha-TOS. We propose that alpha-TOS displaces UbQ in CII causing electrons generated by SDH to recombine with molecular oxygen to yield ROS. Our data highlight CII, a known tumour suppressor, as a novel target for cancer therapy.

Vitamin E analogues inhibit angiogenesis by selective induction of apoptosis in proliferating endothelial cells: the role of oxidative stress

"Mitocans" from the vitamin E group of selective anticancer drugs, alpha-tocopheryl succinate (alpha-TOS) and its ether analogue alpha-TEA, triggered apoptosis in proliferating but not arrested endothelial cells. Angiogenic endothelial cells exposed to the vitamin E analogues, unlike their arrested counterparts, readily accumulated reactive oxygen species (ROS) by interfering with the mitochondrial redox chain and activating the intrinsic apoptotic pathway. The vitamin E analogues inhibited angiogenesis in vitro as assessed using the "wound-healing" and "tube-forming" models. Endothelial cells deficient in mitochondrial DNA (mtDNA) were resistant to the vitamin E analogues, both in ROS accumulation and apoptosis induction, maintaining their angiogenic potential. alpha-TOS inhibited angiogenesis in a mouse cancer model, as documented by ultrasound imaging. We conclude that vitamin E analogues selectively kill angiogenic endothelial cells, suppressing tumor growth, which has intriguing clinical implications.

Vitamin E: An overview of major research directions

During the last 90 years since the discovery of vitamin E, research has focused on different properties of this molecule, the focus often depending on the specific techniques and scientific knowledge present at each time. Originally discovered as a dietary factor essential for reproduction in rats, vitamin E has revealed in the meantime many more important molecular properties, such as the scavenging of reactive oxygen and nitrogen species with consequent prevention of oxidative damage associated with many diseases, or the modulation of signal transduction and gene expression in antioxidant and non-antioxidant manners. Research over the last 30 years has also resolved the biosynthesis and occurrence of vitamin E in plants, the proteins involved in the cellular uptake, tissue distribution and metabolism, and defined a congenital recessive neurological disease, ataxia with vitamin E deficiency (AVED), characterized by impaired enrichment of alpha-tocopherol in plasma as a result of mutations in the liver alpha-tocopherol transfer gene. This review is giving a brief introduction about vitamin E by following the major research directions since its discovery with a historical perspective.

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.

Ouabain activates signaling pathways associated with cell death in human neuroblastoma

Cardiotonic steroids (CTS) like ouabain are not only specific inhibitors of the sodium pump (Na(+),K(+)-ATPase), they also can influence various cytosolic signaling events in a hormone-like manner. In the neuroblastoma cell line SH-SY5Y ouabain triggers multiple signaling pathways. Within 30 min of incubation with 1 or 10 microM ouabain, SH-SY5Y cells generate reactive oxygen species to a level approximately 50% above control and show a modest but significant elevation in cytosolic [Ca(2+)] of about 25%. After 6 h of exposure, ouabain stimulates a series of anti-apoptotic actions in SH-SY5Y cells, including concentration-dependent phosphorylation of Erk1/2, Akt, and Bad. Nevertheless, at the same time this CTS also induces a series of events that inhibit retinoic acid-induced neuritogenesis and promote cell death. Both of these latter phenomena are possibly associated with the observed ouabain-induced reduction in the abundance of the anti-apoptotic proteins Bcl-XL and Bcl-2. In addition, ouabain treatment results in cytochrome c release into the cytosol and induces activation of caspase 3, events that point towards the stimulation of apoptotic pathways that are probably enhanced by the stimulation of p53 phosphorylation at Ser15 also observed in this study. These pathways may eventually lead to cell death: treatment with 10 nM ouabain results in a 20% decrease in cell number after 4 days of incubation and treatment with 1 microM ouabain decreases cells number by about 75%. The results obtained here emphasize the importance of further research in order to elucidate the various signalling cascades triggered by ouabain and possibly other CTS that are used in the treatment of heart failure and to identify their primary receptor(s).

A peptide conjugate of vitamin E succinate targets breast cancer cells with high ErbB2 expression

Overexpression of erbB2 is associated with resistance to apoptosis. We explored whether high level of erbB2 expression by cancer cells allows their targeting using an erbB2-binding peptide (LTVSPWY) attached to the proapoptotic alpha-tocopheryl succinate (alpha-TOS). Treating erbB2-low or erbB2-high cells with alpha-TOS induced similar levels of apoptosis, whereas alpha-TOS-LTVSPWY induced greater levels of apoptosis in erbB2-high cells. alpha-TOS rapidly accumulated in erbB2-high cells exposed to alpha-TOS-LTVSPWY. The extent of apoptosis induced in erbB2-high cells by alpha-TOS-LTVSPWY was suppressed by erbB2 RNA interference as well as by inhibition of either endocytotic or lysosomal function. alpha-TOS-LTVSPWY reduced erbB2-high breast carcinomas in FVB/N c-neu transgenic mice. We conclude that a conjugate of a peptide targeting alpha-TOS to erbB2-overexpressing cancer cells induces rapid apoptosis and efficiently suppresses erbB2-positive breast tumors.

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 and cancer

Perhaps not surprisingly, vitamin E which has been touted to be potentially beneficial for a variety of disorders, including cancer, heart disease, and even Alzheimer's disorder, based on its function as an antioxidant has failed to withstand the scrutiny of recent, double-blinded, placebo-controlled clinical trials, including failure to provide science-based support for vitamin E as a potent anticancer agent. Although less studied, vitamin E forms other than RRR-alpha-tocopherol or synthetic all-rac-alpha-tocopherol show promise as anticancer agents in preclinical studies. This chapter will (1) review basic information about natural and synthetic vitamin E compounds as well as vitamin E analogues, (2) summarize the current status of human intervention trials, (3) review data from preclinical cell culture and animal model studies of vitamin E compounds and novel vitamin E-based analogues in regards to future potential for cancer treatment, and (4) summarize some of the insights that have been gained into the anticancer mechanisms of action of vitamin E-based compounds which are providing interesting insights into their potent proapoptotic effects, which include restoration of apoptotic signaling pathways and blockage of prosurvival signaling events.

Alpha-tocopheryl succinate (α-TOS) influences cell vitality and enzyme activity in Ehrlich ascites carcinoma cells

Background: One of the most important strategies in research and development of new anticancer agents is the tumor-specific induction of apoptosis. The effects of semisynthetic derivative of vitamin E, (?-TOS, D-?-tocopheryl succinate), appear to be largely restricted to malignant cells. Methods: We investigated the in vivo effects of intraperitoneally administered ?-TOS on vitality of Ehrlich ascites carcinoma cells (EAC) in mice, as well as the influence of ?-TOS on specific activity of enzymes involved in antioxidative mechanisms in EAC cells. Results: According to our results, the intraperitoneal application of ?-TOS induces the decrease of the EAC vitality, and the statistically significant alteration of the glutathione-dependent enzyme activity in EAC cells. Conclusion: We may conclude that ?-TOS is an important micronutrient, with significant impact on vitality and metabolism of malignant cells.

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.

Role of thioredoxin-1 in apoptosis induction by alpha-tocopheryl succinate and TNF-related apoptosis-inducing ligand in mesothelioma cells

Malignant mesothelioma (MM) is a fatal type of cancer. We studied the role of the redox-active protein thioredoxin-1 (Trx-1) in apoptosis induced in MM cells and their non-malignant counterparts (Met-5A) by alpha-tocopheryl succinate (alpha-TOS) and TNF-related apoptosis-inducing ligand (TRAIL). MM cells were susceptible to alpha-TOS and less to TRAIL, while Met-5A cells were susceptible to TRAIL and resistant to alpha-TOS. MM cells expressed very low level of the Trx-1 protein, which was high in Met-5A cells, while the level of Trx-1 mRNA was similar in all cell lines. Downregulation of Trx-1 further sensitised Met-5A cells to TRAIL but not to alpha-TOS. Our data suggest that the role of Trx-1 in apoptosis modulation is unrelated to its anti-oxidant properties.

Protective effect of a synthetic anti-oxidant on neuronal cell apoptosis resulting from experimental hypoxia re-oxygenation injury

Oxidative stress is associated with the pathology of acute and chronic neurodegenerative disease. Cultured neuronal cells exposed to hypoxia-reoxygenation (H/R) injury, as a model for stroke, yield a burst of reactive oxygen species (ROS) as measured with electron paramagnetic resonance (EPR) spectroscopy in combination with spin trapping. Added superoxide dismutase inhibited spin-adduct formation verifying that superoxide radical anion was formed in neuronal cells following H/R injury. The intracellular ADP/ATP ratio increased rapidly over the first 5 h following injury and this was due primarily to the decreased cellular pools of ATP, consistent with the notion that H/R promotes mitochondrial dysfunction leading to decreased ATP reserve and increased ROS formation. As an early response to the enhanced oxidative stress, genes encoding for hypoxia-inducible factor 1-alpha (HIF1-alpha), inducible haemoxygenase-1 (HO-1), and the oxygen-sensor neuroglobin increased significantly. Up-regulation of the HO-1 gene was paralleled by increased HO protein expression and activity. Despite this cellular response, apoptosis increased significantly following H/R injury indicating that the endogenous anti-oxidant defenses were unable to protect the cells. In contrast, addition of a phenolic anti-oxidant, bisphenol (BP), prior to H/R injury, inhibited ROS production and gene regulation and significantly decreased neuronal cell apoptosis. Added BP was converted stoichiometrically to the corresponding diphenoquinone indicating the synthetic anti-oxidant effectively decreased oxidative stress through a radical scavenging mechanism. Together, these data indicate that BP has the potential to act as a neuro-protective drug.