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

M, K M, Dey T, Zargar MI, Singh J. Recent advance of herbal medicines in cancer- a molecular approach

Bioactive compounds are crucial for an extensive range of therapeutic uses, and some exhibit anticancer activity. Scientists advocate that phytochemicals modulate autophagy and apoptosis, involved in the underlying pathobiology of cancer development and regulation. The pharmacological aiming of the autophagy-apoptosis signaling pathway using phytocompounds hence offers an auspicious method that is complementary to conventional cancer chemotherapy. The current review aims to explore the molecular level of the autophagic-apoptotic pathway to know its implication in the pathobiology of cancer and explore the essential cellular process as a druggable anticancer target and therapeutic emergence of naturally derived phytocompound-based anticancer agents. The data in the review were collected from scientific databases such as Google search, Web of Science, PubMed, Scopus, Medline, and Clinical Trials. With a broad outlook, we investigated their cutting-edge scientifically revealed and/or searched pharmacologic effects, a novel mechanism of action, and molecular signaling pathway of phytochemicals in cancer therapy. In this review, the evidence is focused on molecular pharmacology, specifically caspase, Nrf2, NF-kB, autophagic-apoptotic pathway, and several mechanisms to understand their role in cancer biology.

Effect of α-Tocopheryloxy Acetic Acid on the Infection of Mice with Plasmodium berghei ANKA In Vivo and Humans with P. falciparum In Vitro

PURPOSE

Malarial parasites are susceptible to oxidative stress. The effects of α-tocopheryloxy acetic acid (α-TEA), a vitamin E analog, on infection by Plasmodium berghei ANKA and P. falciparum in mice and human red blood cells (RBCs), respectively, were examined in this study.

METHODS

For in vivo studies in mice, RBCs infected with P. berghei ANKA were inoculated via intraperitoneal injection and α-TEA was administered to C57BL/6 J male mice after infection. The blood-brain barrier (BBB) permeability was examined by Evans blue staining in experimental cerebral malaria at 7 days after infection. The in vitro inhibitory effect of α-TEA on P. falciparum 3D7 (chloroquine-sensitive strain) and K1 (multidrug-resistant strain) was tested using a SYBR Green I-based assay.

RESULTS

When 1.5% α-TEA was administered for 14 days after infection, 88% of P. berghei ANKA-infected mice survived during the experimental period. Nevertheless, all the control mice died within 12 days of infection. Furthermore, the Evans blue intensity in α-TEA-treated mice brains was less than that in untreated mice, indicating that α-TEA might inhibit the destruction of the BBB and progression of cerebral malaria. The in vitro experiment revealed that α-TEA inhibited the proliferation of both the 3D7 and K1 strains.

CONCLUSION

This study showed that α-TEA is effective against murine and human malaria in vivo and in vitro, respectively. Although α-TEA alone has a sufficient antimalarial effect, future research could focus on the structure-activity relationship to achieve better pharmacokinetics and decrease the cytotoxicity and/or the combined effect of α-TEA with existing drugs. In addition, the prophylactic antimalarial activity of premedication with α-TEA may also be an interesting perspective in the future.

Mitochondrial mutations and mitoepigenetics: Focus on regulation of oxidative stress-induced responses in breast cancers

Epigenetic regulation of mitochondrial DNA (mtDNA) is an emerging and fast-developing field of research. Compared to regulation of nucler DNA, mechanisms of mtDNA epigenetic regulation (mitoepigenetics) remain less investigated. However, mitochondrial signaling directs various vital intracellular processes including aerobic respiration, apoptosis, cell proliferation and survival, nucleic acid synthesis, and oxidative stress. The later process and associated mismanagement of reactive oxygen species (ROS) cascade were associated with cancer progression. It has been demonstrated that cancer cells contain ROS/oxidative stress-mediated defects in mtDNA repair system and mitochondrial nucleoid protection. Furthermore, mtDNA is vulnerable to damage caused by somatic mutations, resulting in the dysfunction of the mitochondrial respiratory chain and energy production, which fosters further generation of ROS and promotes oncogenicity. Mitochondrial proteins are encoded by the collective mitochondrial genome that comprises both nuclear and mitochondrial genomes coupled by crosstalk. Recent reports determined the defects in the collective mitochondrial genome that are conducive to breast cancer initiation and progression. Mutational damage to mtDNA, as well as its overproliferation and deletions, were reported to alter the nuclear epigenetic landscape. Unbalanced mitoepigenetics and adverse regulation of oxidative phosphorylation (OXPHOS) can efficiently facilitate cancer cell survival. Accordingly, several mitochondria-targeting therapeutic agents (biguanides, OXPHOS inhibitors, vitamin-E analogues, and antibiotic bedaquiline) were suggested for future clinical trials in breast cancer patients. However, crosstalk mechanisms between altered mitoepigenetics and cancer-associated mtDNA mutations remain largely unclear. Hence, mtDNA mutations and epigenetic modifications could be considered as potential molecular markers for early diagnosis and targeted therapy of breast cancer. This review discusses the role of mitoepigenetic regulation in cancer cells and potential employment of mtDNA modifications as novel anti-cancer targets.

Effect of α-tocopheryloxy acetic acid, a vitamin E derivative mitocan, on the experimental infection of mice with Plasmodium yoelii

Background

Malaria parasites are known to be vulnerable to oxidative stress. In this study, the effects of the administration of α-tocopheryloxy acetic acid (α-TEA), which is a vitamin E analogue mitocan, on Plasmodium yoelii infection in mice were examined.

Methods

Alpha-TEA was mixed with diet and fed to C57BL/6J mice before and/or after infection. For parasite infection, 4 × 10⁴ red blood cells infected with P. yoelii (strain 17XL) were inoculated by intraperitoneal injection. In another series of experiment, the effect of the oral administration of α-TEA on P. yoelii 17XL infection in mice was examined. Finally, the combined effect of α-TEA and dihydroartemisinin or chloroquine on P. yoelii 17XL infection was examined.

Results

When 0.25% α-TEA was mixed with the diet for 7 days before infection and 14 days after infection (in total for 21 days), for 14 days after infection, and for 11 days from the third day after infection, all P. yoelii 17XL-infected mice survived during the observation period. However, all control mice died within 12 days after infection. These results indicated that α-TEA functions effectively even when administered post-infection. The oral administration of α-TEA for P. yoelii 17XL infection was also significant. Although the infected mice in the solvent control died within 10 days after infection, 90% of the mice infected with P. yoelii 17XL survived during the observation period when treated with 10 mg/head/day of α-TEA for 3 days from day 3 after infection. Although the combined effect of α-TEA and dihydroartemisinin (DHA) or chloroquine on P. yoelii 17XL infection was significant, no synergistic or additive effects were observed from the survival curve.

Conclusions

This study showed the beneficial effects of α-TEA on the experimental infection of mice with P. yoelii 17XL. The stimulatory action of α-TEA on mitochondria and the accompanying reactions, such as reactive oxygen species production, and induction of apoptosis might have some effect on malarial infection.

Vitamin E Derivative with Modified Side Chain Induced Apoptosis by Modulating the Cellular Lipids and Membrane Dynamics in MCF7 Cells

The vitamin E derivative with side chain modification (TC6OAc) has been shown to possess anticancer activity in our earlier in vivo studies. It was hypothesized that, as Vitamin E (VE) and VE derivative are fat soluble lipophilic molecules, they exert their function by modulating the lipid metabolism and related pathways. This study aimed to evaluate the cellular impact of this VE derivative (2,5,7,8-Tetramethyl-2-(4'-Methyl-3'-Pentenyl)-6-Acetoxy Chromane-TC6OH), using α-tocopherol as a reference compound throughout the experiments. Their effects on the cellular metabolism, the biophysical properties of cellular lipids and the functional characteristics of cells were monitored in human estrogen receptor (ER) positive breast cancer cells. It has been documented that TC6OH treatment induces tumor cell apoptosis by dissipating the mitochondrial membrane potential, modulating the lipid, transportation and degradation as well as downregulating certain anti-apoptotic and growth factor related proteins. Due to resistance of ER positive cells to the established therapies, the findings of this study are of translational value.

α-Tocopherol Acetate Attenuates Mitochondrial Oxygen Consumption and Maintains Primitive Cells within Mesenchymal Stromal Cell Population

We present here the data showing, in standard cultures exposed to atmospheric O₂ concentration, that alpha-tocopherol acetate (α-TOA) has a positive impact on primitive cells inside mesenchymal stromal cell (MstroC) population, by maintaining their proliferative capacity. α-TOA decreases the O₂ consumption rate of MStroC probably by impacting respiratory chain complex II activity. This action, however, is not associated with a compensatory increase in glycolysis activity, in spite of the fact that the degradation of HIF-1α was decreased in presence of α-TOA. This is in line with a moderate enhancement of mtROS upon α-TOA treatment. However, the absence of glycolysis stimulation implies the inactivity of HIF-1α which might - if it were active - be related to the maintenance of stemness. It should be stressed that α-TOA might act directly on the gene expression as well as the mtROS themselves, which remains to be elucidated. Alpha-tocopherol acetate (α-TOA), a synthetic vitamin E ester, attenuates electron flow through electron transport chain (ETC) which is probably associated with a moderate increase in mtROS in Mesenchymal Stromal Cells. α-TOA action results in enhancement of the proliferative capacity and maintenance of the differentiation potential of the mesenchymal stem and progenitor cells.

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.

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.

The Combination of α-Tocopheryl Succinate and Sodium Selenite on Breast Cancer: A Merit or a Demerit?

α-Tocopheryl succinate (α-TOS), a mitochondria-targeting agent, induces apoptosis in malignant cells in vitro and in vivo. Selenite is a nutritional supplement that has been shown to stimulate apoptosis in cancer cells. This study was designed to investigate the cytotoxic effect of combined treatment of α-TOS and sodium selenite (SSe) in vitro and in vivo and to explore their effect on apoptosis and autophagy in breast cancer. The type of interaction between α-TOS and SSe was evaluated and levels of oxidative stress and apoptotic and autophagic markers were determined. SSe alone showed varying degrees of cytotoxicity on all the tested cell lines. Its combination with α-TOS was antagonistic in vitro in MCF7 and in vivo in mice bearing Ehrlich tumor compared to α-TOS-treated one. Combination of TOS with 2 μM of SSe increased the level of glutathione without changes in antiapoptotic markers Bcl-2 and Mcl-1 at 16 and 48 hrs. SSe decreased caspase 3 activity and protein level of caspases 7 and 9, while it increased autophagic markers beclin-1 and LC3B protein levels of MCF7 cells treated with α-TOS. In conclusion, SSe antagonizes α-TOS-induced apoptosis via inhibition of oxidative stress and promoting prosurvival machinery of autophagy.

Effect of Oncoxin Oral Solution in HER2-Overexpressing Breast Cancer

One of the most aggressive breast cancer subtypes includes tumors with high expression of HER2. Gene expression and functional studies have shown a link between HER2 overexpression and oxidative stress. Because of this, we hypothesized that Oncoxin Oral Solution (OOS), a composite product that contains several antioxidants, could have an antitumoral effect against HER2+ tumors. Dose-response studies, biochemical and cytometric assessment of the effect of OOS on cell cycle and apoptosis, and drug combination analyses were performed on BT474 and SKBR3 cells, 2 HER2-overexpressing breast cancer cell lines. OOS reduced the proliferation of these cells, and augmented the action of lapatinib, a HER2 inhibitor used in the breast cancer clinic. Moreover, OOS decreased growth of HER2+ tumors in mice. Mechanistically, OOS provoked cell cycle blockade through upregulation of p27 expression and downregulation of cyclin D levels. OOS also caused apoptotic cell death in HER2+ breast cancer cells, as indicated by increases in PARP cleavage as well as upregulation of caspase 8 and caspase 3 activities. These results demonstrate an antitumoral action of OOS in preclinical models of HER2+ breast cancer and suggest that it can be used with anti-HER2 therapies currently adopted as standard of care in the oncology clinic.

Trastuzumab-based chemotherapy modulates systemic redox homeostasis in women with HER2-positive breast cancer

Trastuzumab is an immunotargeting therapeutic against breast tumors with amplification of the human epithelial growth factor receptor 2 (HER2). HER2 patients naturally exhibit disruption in the pro-oxidant inflammatory profiling; however, the impact of trastuzumab-based chemotherapy in modulating this process is still unknown. Here we determined the systemic pro-inflammatory profile of women diagnosed with HER2-amplified tumors, undergoing trastuzumab-based chemotherapy (TZ), and compared the results with that of healthy controls (CTR) and untreated patients with HER2-amplified breast cancer (CA). The plasmatic inflammatory profile was assessed by evaluating pro-oxidant parameters such as lipid peroxidation, total antioxidant capacity (TRAP), levels of advanced oxidation protein products (AOPPs), nitric oxide (NO), C-reactive protein (CRP), and total thiol content. Markers of cardiac damage were also assessed. Our findings showed increased NO levels in TZ than that in either CA or CTR groups. Furthermore, TZ augmented TRAP and reduced total thiol than that of the CA group. Our data also revealed that AOPP levels were significantly higher in the TZ than the CA group. AOPP and the MB fraction of creatine-kinase (CKMB) levels were positively correlated in TZ patients. These findings suggest that trastuzumab-associated chemotherapy can modulate the pro-inflammatory markers of HER2-positive breast cancer patients to the levels found in healthy controls.

Targeting HER2 Positive Breast Cancer with Chemopreventive Agents

Human epidermal growth factor receptor 2-positive (HER2+) breast cancer is a subtype of breast cancer that is exhibited in approximately 20-30% of breast cancer cases. The overexpression of HER2 is typically associated with a more aggressive disease and poor prognosis. Currently, the therapeutic drugs trastuzumab and lapatinib are the most commonly used to combat HER2+ breast cancer. However, tumors can develop resistance to these drugs. A better understanding of the mechanism of how HER2+ breast cancer works will help aid the development for new therapeutic approaches which more closely target the source of the signaling dysfunction. This review summarizes four major points in the context of HER2 over-expressing breast cancer (i) HER2 as a molecular target in breast cancer therapy, (ii) current treatment options as well as ongoing clinical studies, (iii) animal and cellular models for the study of HER2 over-expressing breast cancer, and (iv) future therapies and chemopreventive agents used to target HER2+ breast cancer.

Manipulating miRNA Expression: A Novel Approach for Colon Cancer Prevention and Chemotherapy

Small non-coding RNA has been implicated in the control of various cellular processes such as proliferation, apoptosis, and differentiation. About 50% of the miRNA genes are positioned in cancer-associated genomic regions. Several studies have shown that miRNA expression is deregulated in cancer and modulating their expression has reversed the cancer phenotype. Therefore, mechanisms to modulate microRNA (miRNA) activity have provided a novel opportunity for cancer prevention and therapy. In addition, a common cause for development of colorectal cancers is environmental and lifestyle factors. One such factor, diet has been shown to modulate miRNA expression in colorectal cancer patients. In this chapter, we will summarize the work demonstrating that miRNAs are novel promising drug targets for cancer chemoprevention and therapy. Improved delivery, increased stability and enhanced regulation of off-target effects will overcome the current challenges of this exciting approach in the field of cancer prevention and therapy.

Reducing the cytotoxicity while improving the anti-cancer activity of silver nanoparticles through α-tocopherol succinate modification

α-TOS modified Ag NPs could reduce the cytotoxicity while improving the anti-cancer activity of Ag NPs.

RRR-α-tocopheryl succinate induces apoptosis in human gastric cancer cells via the NF-κB signaling pathway

To investigate the effects of the nuclear factor (NF)-κB signaling pathway on the induction of apoptosis by vitamin E succinate (RRR-α-tocopheryl succinate; VES) in human gastric carcinoma cells. Human gastric carcinoma SGC-7901 cells were treated with temperate concentrations of VES and pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB. Cell viability and apoptosis were respectively estimated by methylthiazol tetrazolium (MTT) assay and the Annexin V‑FITC method. Western blot analysis was used to evaluate the protein expressions of NF-κBp65 and Bcl-2 family members Bcl-2, Bax and cleavage of caspase-3, caspase-9, and poly (ADP-ribose) polymerase (PARP). The DNA-binding activity of NF-κBp65 was measured by electrophoretic mobility shift assay (EMSA). Reverse transcription and polymerase chain reaction (RT-PCR) was implemented to evaluate the transcription of inhibitor of apoptosis (IAP) genes. Apoptosis assessment showed that VES induces apoptotic cell death in human gastric carcinoma cells. In the following experiments, PDTC (100 µM) was used in cell treatment 2 h before VES. The decreased ratio of the nuclear and cytosolic NF-κBp65 protein level was induced by VES and PDTC reinforced this trend. PDTC treatment significantly enhanced the decrease of NF-κB-DNA binding activity induced by VES in human gastric SGC-7901. The decrease in protein expression of Bcl-2 as well as the increase in the protein expression of Bax were induced by VES treatment. The cleavage of caspase-9, caspase-3 and PARP was induced. There was no effect on the gene transcription of c-IAP-1, c-IAP-2, and x-linked IAP (XIAP) compared with the control group, whereas mRNA levels of survivin and the neuronal apoptosis inhibitory protein (NAIP) markedly decreased. Notably, pretreatment with PDTC reinforced all the above VES-induced effects. In conclusion, VES-induced apoptosis in SGC-7901 cells is accompanied by the inhibition of the NF-κB signaling pathway, including changes in Bcl-2 family members, cleavage of caspases and gene transcription of survivin and NAIP.

Selective tumor cell killing by triptolide in p53 wild-type and p53 mutant ovarian carcinomas

Triptolide is a traditional Chinese medicinal herb-derived antineoplastic agent. However, its antitumor activity against gynecologic carcinomas has not yet been well described. It is the purpose of this article to investigate the effect and mechanism of triptolide in human ovarian cancer using both A2780 (p53 wild) and OVCAR-3 (p53 mutated) cells. Our results showed that triptolide exerted a potent inhibitory effect on the growth and proliferation of both cell lines in a dose- and time-dependent manner and that the effect was independent of the expression of p53. In contrast, triptolide had only a marginal cytotoxicity in noncancerous ovary cells, lung fibroblast cells, and macrophage cells, indicating differential inhibitory effects of the drug on cell growth between ovarian cancer cells and normal tissue cells. Exposure of the ovarian cancer cells to triptolide induced apoptosis, as evaluated by annexin V/propidium iodide-labeled flow cytometry. Triptolide-induced apoptosis was accompanied by cytochrome c release and caspase-3 activation and was associated with downregulation of Bcl-2 and upregulation of Bax. Cell cycle analysis demonstrated that treatment with triptolide induced cell cycle S phase arrest in A2780 cells and G2/M phase arrest in OVCAR-3 cells. Further detection by Western blotting revealed that the cell cycle arrest by triptolide in both cell lines occurred in concert with increased expression of p21(CIP1/WAF1). This study shows that triptolide selectively kills ovarian cancer cells with different p53 status predominantly through regulating the coordinate and dynamic cellular processes of proliferation and apoptosis, thereby making it a promising chemotherapeutic agent against a broad spectrum of ovarian carcinomas.

Nanomicellar carriers for targeted delivery of anticancer agents

Clinical application of anticancer drugs is limited by problems such as low water solubility, lack of tissue-specificity and toxicity. Formulation development represents an important approach to these problems. Among the many delivery systems studied, polymeric micelles have gained considerable attention owing to ease in preparation, small sizes (10-100 nm), and ability to solubilize water-insoluble anticancer drugs and accumulate specifically at the tumors. This article provides a brief review of several promising micellar systems and their applications in tumor therapy. The emphasis is placed on the discussion of the authors' recent work on several nanomicellar systems that have both a delivery function and antitumor activity, named dual-function drug carriers.

Use of anti-cancer drugs, mitocans, to enhance the immune responses against tumors

Cytotoxic drugs in cancer therapy are used with the expectation of selectively killing and thereby eliminating the offending cancer cells. If they should die in an appropriate manner, the cells can also release danger signals that promote an immune reaction that reinforces the response against the cancer. The identity of these immune-enhancing danger signals, how they work extra- and intracellularly, and the molecular mechanisms by which some anti-cancer drugs induce cell death to bring about the release of danger signals are the major focus of this review. A specific group of mitocans, the vitamin E analogs that act by targeting mitochondria to drive ROS production and also promote a more immunogenic means of cancer cell death exemplify such anti-cancer drugs. The role of reactive oxygen species (ROS) production and the events leading to the activation of the inflammasome and pro-inflammatory mediators induced by dying cancer cell mitochondria are discussed along with the evidence for their contribution to promoting immune responses against cancer. Current knowledge of how the danger signals interact with immune cells to boost the anti-tumor response is also evaluated.

Therapeutic applications of herbal medicines for cancer patients

Medicinal herbs and their derivative phytocompounds are being increasingly recognized as useful complementary treatments for cancer. A large volume of clinical studies have reported the beneficial effects of herbal medicines on the survival, immune modulation, and quality of life (QOL) of cancer patients, when these herbal medicines are used in combination with conventional therapeutics. Here, we briefly review some examples of clinical studies that investigated the use of herbal medicines for various cancers and the development of randomized controlled trials (RCTs) in this emerging research area. In addition, we also report recent studies on the biochemical and cellular mechanisms of herbal medicines in specific tumor microenvironments and the potential application of specific phytochemicals in cell-based cancer vaccine systems. This review should provide useful technological support for evidence-based application of herbal medicines in cancer therapy.

Mitochondrial-dependent anticancer activity of δ-tocotrienol and its synthetic derivatives in HER-2/neu overexpressing breast adenocarcinoma cells

Anticancer activity and mitochondrial mechanism of the vitamin E form δ-tocotrienol (δ-T3) was investigated in HER-2/neu-overexpressing human SKBR3 and murine TUBO breast cancer cells. δ-T3 was confirmed to possess high cytotoxic and apoptotic activity in SKBR3 cells as compared with all natural forms of vitamin E and several synthetic forms that included novel derivatives with the same backbone of δ-T3 such as δ-tocotrienyl-succinyl amide (δ-T3AS) and the redox-active analogue δ-tocotrienyl amine (δ-T3NH2). As observed in the case of alpha-TOS, a prototypical anticancer drug derived from α-tocopherol, succinylation of δ-T3 enhanced citotoxicity and apoptotic activity of the vitamer. δ-T3 induced apoptosis of SKBR3 cells was associated with mitochondrial destabilization, energy failure, and unbalanced activity of stress/survival MAPKs, namely p38 and ERK1/2 pathways. An increased generation of ROS followed to such a series of early events. Enhanced activity of δ-T3 in this human carcinoma cell line was characterized by the sustained uptake and oxidative transformation to the quinone derivative δ-T3Q, thereby suggesting redox effects in SKBR3 mitochondria by this vitamer. Viability and uptake data show a different pattern of responses in TUBO cells with higher response to synthetic derivatives of δ-T3 than in SKBR3 cells. In conclusion, synthetic derivatives of δ-T3 with enhanced apoptotic activity in breast carcinoma cells are investigated for the first time in this study also describing mechanistic aspects of mitochondrial effects of δ-T3. Further investigation in preclinical models of HER2/neu-high breast adenocarcinoma is underway to identify other and more effective forms of VE in this type of cancer.

α-Tocopheryloxyacetic acid is superior to α-tocopheryl succinate in suppressing HER2-high breast carcinomas due to its higher stability

Breast cancer is the number one neoplastic disease of women, with the HER2-high carcinomas presenting a considerable challenge for efficient treatment. Therefore, a search for novel agents active against this type of cancer is warranted. We tested two vitamin E (VE) analogs, the esterase-hydrolyzable α-tocopheryl succinate (α-TOS) and the non-hydrolyzable ether α-tocopheryloxyacetic acid (α-TEA) for their effects on HER2-positive breast carcinomas using a breast tumor mouse model and breast cancer cell lines. Ultrasound imaging documented that α-TEA suppressed breast carcinomas in the transgenic animals more efficiently than found for its ester counterpart. However, both agents exerted a comparable apoptotic effect on the NeuTL breast cancer cells derived from the FVB/N c-neu mice as well as in the human MBA-MD-453 and MCF7HER2-18 cells with high level of HER2. The superior anti-tumor effect of α-TEA over α-TOS in vivo can be explained by longer persistence of the former in mice, possibly due to the enhanced plasma and hepatic processing of α-TOS in comparison to the esterase-non-cleavable α-TEA. Indeed, the stability of α-TOS in plasma was inferior to that of α-TEA. We propose that α-TEA is a promising drug efficient against breast cancer, as documented by its effect on experimental HER2-positive breast carcinomas that present a considerable problem in cancer management.

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].

α-Tocopheryl succinate induces apoptosis in erbB2-expressing breast cancer cell via NF-κB pathway

AIM

to study the molecular mechanisms underlying α-tocopheryl succinate (α-TOS)-induced apoptosis in erbB2-positive breast cancer cells and to determine whether α-TOS and the human recombinant TNF-related apoptosis-inducing ligand (hrTRAIL) act synergically to induce cell death of erbB2-expressing breast cancer cells.

METHODS

the annexin V binding method was used to measure apoptosis induced by α-TOS and/or hrTRAIL. RT-PCR and Western blotting were performed to detect gene and protein expression. A colorimetric assay was performed to detect caspase activity. The TransAM(TM) NF-κB p65 kit was used to assess NF-κB activation.

RESULTS

α-TOS (100 μmol/L) significantly inhibited NF-κB nuclear translocation in erbB2-expressing breast cancer cells; this inhibition is expected to result in the inactivation of NF-κB. α-TOS (50 and 100 μmol/L) inhibited the expression of Flice-like inhibitory protein (FLIP) and cellular inhibitor of apoptosis protein 1 (c-IAP1) in erbB2-positive cells. α-TOS (100 μmol/L) inhibited Akt activation and augmented the activity of caspase 3 and caspase 8 in breast cancer cells expressing erbB2. α-TOS (50 μmol/L) and hrTRAIL (30 mg/mL) acted synergically to induce apoptosis in breast cancer cells. α-TOS also decreased the hrTRAIL-induced transient activation of NF-κB .

CONCLUSION

our results suggest that α-TOS mediates the apoptosis of erbB2-positive breast cancer cells and acts synergically with hrTRAIL via the NF-κB pathway.

Micronutrient intake and breast cancer characteristics among postmenopausal women

Few studies on micronutrients and postmenopausal breast cancer have examined the association with breast cancer characteristics. The aim of this study was to investigate the associations between vitamin C, vitamin E, folate and beta-carotene from diet and supplements and risk of postmenopausal breast cancer subtypes defined by histology (ductal/lobular), estrogen receptor (ER) and progesterone receptor (PGR) status. In a prospective cohort study of 26,224 postmenopausal women information on diet, supplements and lifestyle was collected through questionnaires. One thousand seventy-two cases were identified during follow-up. Incidence rate ratios of total breast cancers and breast cancer subtypes related to micronutrient intake were calculated using Cox proportional hazard analyses. This study found no association between overall breast cancer and any micronutrients, while some effects were shown when stratifying by breast cancer subtypes: dietary but not supplemental beta-carotene showed a protective effect against lobular breast cancer [incidence rate ratio (IRR): 0.72; 95% confidence interval (CI): 0.57-0.91]. Dietary vitamin E was associated with decreased risk of ER and PGR positive breast cancer (IRR: 0.50; 95% CI: 0.25-0.98) and dietary folate was associated with increased risk of ER and PGR positive breast cancer (IRR: 1.27; 95% CI: 1.03-1.95). This study found no effect of micronutrients on overall risk of postmenopausal breast cancer, but indicated possible effects of micronutrients in subgroups of breast cancer, with a potential beneficial effect of dietary beta-carotene in lobular breast cancer and dietary vitamin E in ER + PGR+ breast cancer and a potential harmful effect of dietary folate in ER+ PGR+ breast cancer.

Oxidative stress promotes myofibroblast differentiation and tumour spreading

JunD regulates genes involved in antioxidant defence. We took advantage of the chronic oxidative stress resulting from junD deletion to examine the role of reactive oxygen species (ROS) in tumour development. In a model of mammary carcinogenesis, junD inactivation increased tumour incidence and revealed an associated reactive stroma. junD-inactivation in the stroma was sufficient to shorten tumour-free survival rate and enhance metastatic spread. ROS promoted conversion of fibroblasts into highly migrating myofibroblasts through accumulation of the hypoxia-inducible factor (HIF)-1α transcription factor and the CXCL12 chemokine. Accordingly, treatment with an antioxidant reduced the levels of HIF and CXCL12 and numerous myofibroblast features. CXCL12 accumulated in the stroma of HER2-human breast adenocarcinomas. Moreover, HER2 tumours exhibited a high proportion of myofibroblasts, which was significantly correlated to nodal metastases. Interestingly, this subset of tumours exhibited a significant nuclear exclusion of JunD and revealed an associated oxido-reduction signature, further demonstrating the relevance of our findings in human cancers. Collectively, our data uncover a new mechanism by which oxidative stress increases the migratory properties of stromal fibroblasts, which in turn potentiate tumour dissemination.

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.

Small mitochondria-targeting molecules as anti-cancer agents

Alterations in mitochondrial structure and functions have long been observed in cancer cells. Targeting mitochondria as a cancer therapeutic strategy has gained momentum in the recent years. The signaling pathways that govern mitochondrial function, apoptosis and molecules that affect mitochondrial integrity and cell viability have been important topics of the recent review in the literature. In this article, we first briefly summarize the rationale and biological basis for developing mitochondrial-targeted compounds as potential anti-cancer agents, and then provide key examples of small molecules that either directly impact mitochondria or functionally affect the metabolic alterations in cancer cells with mitochondrial dysfunction. The main focus is on the small molecular weight compounds with potential applications in cancer treatment. We also summarize information on the drug developmental stages of the key mitochondria-targeted compounds and their clinical trial status. The advantages and potential shortcomings of targeting the mitochondria for cancer treatment are also discussed.

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.

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.

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.

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.

Curcumin induces apoptosis through mitochondrial hyperpolarization and mtDNA damage in human hepatoma G2 cells

Curcumin, a major pigment of turmeric, is a natural antioxidant possessing a variety of pharmacological activities and therapeutic properties. But its mechanisms are unknown. In our previous study, we found that a 2-h exposure to curcumin induced DNA damage to both the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA) in HepG2 cells and that mtDNA damage was more extensive than nDNA damage. Therefore, experiments were initiated to evaluate the role of mtDNA damage in curcumin-induced apoptosis. The results demonstrated that HepG2 cells challenged with curcumin for 1 h showed a transient elevation of the mitochondrial membrane potential (DeltaPsim), followed by cytochrome c release into the cytosol and disruption of DeltaPsim after 6 h exposure to curcumin. Apoptosis was detected by Hoechst 33342 and annexin V/PI assay after 10 h treatment. Interestingly, the expression of Bcl-2 remained unchanged. A resistance to apoptosis for the corresponding rho0 counterparts confirmed a critical dependency for mitochondria during the induction of apoptosis in HepG2 cells mediated by curcumin. The effects of PEG-SOD in protecting against curcumin-induced cytotoxicity suggest that curcumin-induced cytotoxicity is directly dependent on superoxide anion O2- production. These data suggest that mitochondrial hyperpolarization is a prerequisite for curcumin-induced apoptosis and that mtDNA damage is the initial event triggering a chain of events leading to apoptosis in HepG2 cells.

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.

Targeting antioxidants to mitochondria by conjugation to lipophilic cations

Mitochondrial oxidative damage contributes to a range of degenerative diseases. Consequently, the selective inhibition of mitochondrial oxidative damage is a promising therapeutic strategy. One way to do this is to invent antioxidants that are selectively accumulated into mitochondria within patients. Such mitochondria-targeted antioxidants have been developed by conjugating the lipophilic triphenylphosphonium cation to an antioxidant moiety, such as ubiquinol or alpha-tocopherol. These compounds pass easily through all biological membranes, including the blood-brain barrier, and into muscle cells and thus reach those tissues most affected by mitochondrial oxidative damage. Furthermore, because of their positive charge they are accumulated several-hundredfold within mitochondria driven by the membrane potential, enhancing the protection of mitochondria from oxidative damage. These compounds protect mitochondria from damage following oral delivery and may therefore form the basis for mitochondria-protective therapies. Here we review the background and work to date on this class of mitochondria-targeted antioxidants.

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.

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 Apoptosis

Vitamin E is a generic term that refers to a family of compounds that is further divided into two subgroups called tocopherols and tocotrienols. All natural forms of tocopherols and tocotrienols are potent antioxidants that regulate peroxidation reactions and controls free radical production within the body. However, it is now firmly established that many of the biological actions mediated by individual vitamin E isoforms are not dependent on their antioxidant activity. Furthermore, synthetic ether derivatives of vitamin E that no longer possess antioxidant activity also display a wide range of biological activities. One of the most intriguing therapeutic applications for natural vitamin E and vitamin E derivatives currently being investigated is their use as anticancer agents. Specific forms of vitamin E display potent apoptotic activity against a wide range of cancer cell types, while having little or no effect on normal cell function or viability. Experimental studies have also determined that the intracellular mechanisms mediating the apoptotic effects of specific vitamin E compounds display great diversity in different types of caner cells and has been found to restore multidrug resistant tumor cells sensitivity to chemotherapeutic agents. These findings strongly suggest that some natural and synthetic analogues of vitamin E can be used effectively as anticancer therapy either alone or in combination to enhance the therapeutic efficacy and reduce toxicity of other anticancer agents.

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.

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.