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

Rational Drug Design of Targeted and Enzyme-Cleavable Vitamin E Analogs as a Neoadjuvant to Chemotherapy: In Vitro and In Vivo Evaluation on Reduction of the Cardiotoxicity Side Effect of Doxorubicin

Traditional drug design focuses on specific biological targets where specific receptors or biomarkers are overexpressed by cancer cells. Cancer cells circumvent the interventions by activating survival pathways and/or downregulating cell death pathways for their survival. A priori activation of apoptosis pathways of tumor (AAAPT) is a novel tumor-sensitizing technology that sensitizes tumor cells that are not responding well to the current treatments by targeting specific survival pathways involved in the desensitization of tumor cells and tries to revive them selectively in cancer cells, sparing normal cells. Several vitamin E derivatives (AMP-001, AMP-002, AMP-003, and AMP-004) were synthesized, characterized, and studied for their anti-tumorigenic properties and their synergistic potential with the standard chemotherapy doxorubicin in various cancer cells including brain cancer stem cells in vitro. Preliminary studies revealed that AAAPT drugs (a) reduced the invasive potential of brain tumor stem cells, (b) synergized with Federal Drug Application-approved doxorubicin, and (c) enhanced the therapeutic index of doxorubicin in the triple-negative breast cancer tumor rat model, preserving the ventricular function compared to cardiotoxic doxorubicin alone at therapeutic dose. The AAAPT approach has the advantage of inhibiting survival pathways and activating cell death pathways selectively in cancer cells by using targeting, linkers cleavable by tumor-specific Cathepsin B, and PEGylation technology to enhance the bioavailability. We propose AAAPT drugs as a neoadjuvant to chemotherapy and not as stand-alone therapy, which is shown to be effective in expanding the therapeutic index of doxorubicin and making it work at lower doses.

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

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

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

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

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A novel tocopheryl ester mainly induces lipolysis of accumulated lipids.

Reactive Oxygen Species-Responsive Miktoarm Amphiphile for Triggered Intracellular Release of Anti-Cancer Therapeutics

Reactive oxygen species (ROS)-responsive nanocarriers have received considerable research attention as putative cancer treatments because their tumor cell targets have high ROS levels. Here, we synthesized a miktoarm amphiphile of dithioketal-linked ditocopheryl polyethylene glycol (DTTP) by introducing ROS-cleavable thioketal groups as linkers between the hydrophilic and hydrophobic moieties. We used the product as a carrier for the controlled release of doxorubicin (DOX). DTTP has a critical micelle concentration (CMC) as low as 1.55 μg/mL (4.18 × 10⁻⁴ mM), encapsulation efficiency as high as 43.6 ± 0.23% and 14.6 nm particle size. The DTTP micelles were very responsive to ROS and released their DOX loads in a controlled manner. The tocopheryl derivates linked to DTTP generated ROS and added to the intracellular ROS in MCF-7 cancer cells but not in HEK-293 normal cells. In vitro cytotoxicity assays demonstrated that DOX-encapsulated DTTP micelles displayed strong antitumor activity but only slightly increased apoptosis in normal cells. This ROS-triggered, self-accelerating drug release device has high therapeutic efficacy and could be a practical new strategy for the clinical application of ROS-responsive drug delivery systems.

Nutritional Interventions for Patients with Melanoma: From Prevention to Therapy-An Update

Melanoma is an aggressive skin cancer, whose incidence rates have increased over the past few decades. Risk factors for melanoma are both intrinsic (genetic and familiar predisposition) and extrinsic (environment, including sun exposure, and lifestyle). The recent advent of targeted and immune-based therapies has revolutionized the treatment of melanoma, and research is focusing on strategies to optimize them. Obesity is an established risk factor for several cancer types, but its possible role in the etiology of melanoma is controversial. Body mass index, body surface area, and height have been related to the risk for cutaneous melanoma, although an 'obesity paradox' has been described too. Increasing evidence suggests the role of nutritional factors in the prevention and management of melanoma. Several studies have demonstrated the impact of dietary attitudes, specific foods, and nutrients both on the risk for melanoma and on the progression of the disease, via the effects on the oncological treatments. The aim of this narrative review was to summarize the main literature results regarding the preventive and therapeutic role of nutritional schemes, specific foods, and nutrients on melanoma incidence and progression.

Nutrition and melanoma prevention

There has been considerable research in recent years on dietary factors and/or nutritional elements that might impact melanoma risk. A wide variety of dietary compounds have been studied, but only a selected group will be discussed in this review. Many have promising in vitro evidence supporting their potential, and some have been associated with decreased melanoma risk in epidemiologic studies; however, data from randomized controlled trials in humans are lacking. Future studies may be able to clarify the potential role of dietary components in melanoma risk reduction.

Mitochondria-acting carrier-free nanoplatform self-assembled by α-tocopheryl succinate carrying cisplatin for combinational tumor therapy

Unsatisfactory drug loading capability, potential toxicity of the inert carrier and the limited therapeutic effect of a single chemotherapy drug are all vital inhibitory factors of carrier-assisted drug delivery systems for chemotherapy. To address the above obstacles, a series of carrier-free nanoplatforms self-assembled by dual-drug conjugates was constructed to reinforce chemotherapy against tumors by simultaneously disrupting intratumoral DNA activity and inhibiting mitochondria function. In this nanoplatform, the mitochondria-targeting small-molecular drug, α-tocopheryl succinate (TOS), firstly self-assembled into nanoparticles, which then were used as the carrier to conjugate cisplatin (CDDP). Systematic characterization results showed that this nanoplatform exhibited suitable particle size and a negative surface charge with good stability in physicochemical environments, as well as pH-sensitive drug release and efficient cellular uptake. Due to the combined effects of reactive oxygen species (ROS) generation by TOS and DNA damage by CDDP, the developed nanoplatform could induce mitochondrial dysfunction and elevated cell apoptosis, resulting in highly efficient anti-tumor outcomes in vitro. Collectively, the combined design principles adopted for carrier-free nanodrugs construction in this study aimed at targeting different intracellular organelles for facilitating ROS production and DNA disruption can be extended to other carrier-free nanodrugs-dependent therapeutic systems.

A review of the most important natural antioxidants and effective medicinal plants in traditional medicine on prostate cancer and its disorders

Herbal plants can be used to treat and prevent life-threatening diseases, such as prostate cancer, infections and other diseases. The findings from traditional medicine and the use of medicinal plants can help control and treat most problems due to prostate diseases. The aim of this study was to identify and report the most important medicinal plants that affect prostate disorders. Based on the results of the review of numerous articles indexed in the databases ISI, Scopus, PubMed, Google Scholar, etc., a number of plants have been reported to be used in the treatment and prevention of diseases, inflammation, infection, and cancer of the prostate gland. The plants include Panax ginseng, Arum palaestinum, Melissa officinalis, Syzygium paniculatum, Coptis chinensis, Embelia ribes, Scutellaria baicalensis, Tripterygium wilfordii, Salvia triloba, Ocimum tenuiflorum, Psidium guajava, Ganoderma lucidum, Litchi chinensis, Saussurea costus, Andrographis paniculata, Magnolia officinalis and Prunus africana. Phytochemical investigations have examined the therapeutic effects of medicinal plants effective on prostate cancer and their possible mechanisms of action and clinical effects as well as the use of active flavonoids in production of herbal drugs. Due to the active ingredients and important flavonoids of these plants, they can be used in production of herbal drugs that prevent and treat infections, inflammation and cancer of the prostate gland, and reduce the metastasis of prostate cancer cells, reducing the patients’ suffering and pain.

Alpha-tocopheryl succinate improves encapsulation, pH-sensitivity, antitumor activity and reduces toxicity of doxorubicin-loaded liposomes

Doxorubicin (DOX) plays an important role in cancer treatment; however, high cardiotoxicity and low penetration in solid tumors are the main limitations of its use. Liposomal formulations have been developed to attenuate the DOX toxicity, but the technological enhancement of the liposomal formulation as well as the addition of another agent with antitumor properties, like alpha-tocopheryl succinate (TS), a semi-synthetic analog of vitamin E, could certainly bring benefits. Thus, in this study, it was proposed the development of liposomes composed of DOX and TS (pHSL-TS-DOX). A new DOX encapsulation method, without using the classic ammonium sulfate gradient with high encapsulation percentage was developed. Analysis of Small Angle X-ray Scattering (SAXS) and release study proved the pH-sensitivity of the developed formulation. It was observed stabilization of tumor growth using pHSL-TS-DOX when compared to free DOX. The toxicity tests showed the safety of this formulation since it allowed body weight initial recovery after the treatment and harmless to heart and liver, main target organs of DOX toxicity. The developed formulation also avoided the occurrence of myelosuppression, a typical adverse effect of DOX. Therefore, pHSL-TS-DOX is a promising alternative for the treatment of breast cancer since it has adequate antitumor activity and a safe toxicity profile.

A pH-sensitive prodrug strategy to co-deliver DOX and TOS in TPGS nanomicelles for tumor therapy

This work has presented a novel strategy for designing pH-sensitive TOS-H-DOX prodrug-loaded TPGS nanomicelles for co-delivery TOS and DOX to enhance tumor therapy and reduce the toxic side effects. DOX was covalently conjugated to the vitamin E succinate through hydrazone bond to produce an pH-sensitive prodrug TOS-H-DOX (amido bond as a control, TOS-A-DOX), which was responsive to the acidic environment in tumor cells, and the prodrugs were subsequently encapsulated in the core of TPGS nanomicelles via hydrophobic effects with a significant drug loading capacity. The pH-sensitive prodrug nanomicelles TOS-H-DOX/TPGS exhibited potent release of DOX in acidic media relative to the pH-insensitive prodrug nanomicelles TOS-A-DOX/TPGS, and further studies of their intracellular uptake and intracellular localization demonstrated that TOS-H-DOX/TPGS nanomicelles can be effectively taken up by cells and drugs can be released. In vitro results confirmed that TOS-H-DOX/TPGS nanomicelles exhibited significant antitumor cell proliferation activity compared to TOS-A-DOX/TPGS and free DOX, TPGS. Furthermore, in vivo studies further confirmed an excellent synergistic antitumor efficacy in MCF-7 tumor-bearing nude mice model. More importantly, the H&E staining of the heart, liver, kidney tissue sections of experimental nude mice showed that TOS-H-DOX/TPGS nanomicelles can reduce damage to them.

Vitamin E succinate induces apoptosis via the PI3K/AKT signaling pathways in EC109 esophageal cancer cells

Esophageal cancer is the fourth most common gastrointestinal cancer, it generally has a poor prognosis and novel strategies are required for prevention and treatment. Vitamin E succinate (VES) is a potential chemical agent for cancer prevention and therapy as it exerts anti‑tumor effects in a variety of cancers. However, the role of VES in tumorigenesis and progression of cancer remains to be elucidated. The present study aimed to determine the effects of VES in regulating the survival and apoptosis of human esophageal cancer cells. EC109 human esophageal cancer cells were used to investigate the anti‑proliferative effects of VES. The MTT and Annexin V‑fluorescein isothiocyanate/propidium iodide assays demonstrated that VES inhibited cell proliferation and induced apoptosis in esophageal cancer cells. Furthermore, VES downregulated constitutively active basal levels of phosphorylated (p)‑serine‑threonine kinase AKT (AKT) and p‑mammalian target of rapamycin (mTOR), and decreased the phosphorylation of AKT substrates Bcl‑2‑associated death receptor and caspase‑9, in addition to mTOR effectors, ribosomal protein S6 kinase β1 and eIF4E‑binding protein 1. Phosphoinositide‑3‑kinase (PI3K) inhibitor, LY294002 suppressed p‑AKT and p‑mTOR, indicating PI3K is a common upstream mediator. The apoptosis induced by VES was increased by inhibition of AKT or mTOR with their respective inhibitor in esophageal cancer cells. The results of the present study suggested that VES targeted the PI3K/AKT signaling pathways and induced apoptosis in esophageal cancer cells. Furthermore, the current study suggests that VES may be useful in a combinational therapeutic strategy employing an mTOR inhibitor.

All roads lead to PP2A: exploiting the therapeutic potential of this phosphatase

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase involved in the regulation of many cellular processes. A confirmed tumor suppressor protein, PP2A is genetically altered or functionally inactivated in many cancers highlighting a need for its therapeutic reactivation. In this review we discuss recent literature on PP2A: the elucidation of its structure and the functions of its subunits, and the identification of molecular lesions and post-translational modifications leading to its dysregulation in cancer. A final section will discuss the proteins and small molecules that modulate PP2A and how these might be used to target dysregulated forms of PP2A to treat cancers and other diseases.

Protective Macroautophagy Is Involved in Vitamin E Succinate Effects on Human Gastric Carcinoma Cell Line SGC-7901 by Inhibiting mTOR Axis Phosphorylation

Vitamin E succinate (VES), a potential cancer therapeutic agent, potently induces apoptosis and inhibits the growth of various cancer cells. Autophagy has been supposed to promote cancer cell survival or trigger cell death, depending on particular cancer types and tumor microenvironments. The role of autophagy in the growth suppressive effect of VES on gastric cancer cell is basically unknown. We aimed to determine whether and how autophagy affected the VES-induced inhibition of SGC-7901 human gastric carcinoma cell growth. SGC-7901 cells were treated with VES or pre-treated with autophagy inhibitor, chloroquine (CQ) and 3-methyladenine (3-MA). Electron microscopy, fluorescence microscopy and Western blot were used to study whether VES induced autophagy reaction in SGC-7901 cells. Western blot evaluated the activities of the mammalian target of rapamycin (mTOR) axis. Then we used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry to detect the level of cell viability and apoptosis. Collectively, our data indeed strongly support our hypothesis that VES treatment produced cytological variations that depict autophagy, increased the amount of intracellular green fluorescent protein—microtubule associated protein 1 light chain 3 (GFP-LC3) punctate fluorescence and the number of autophagic vacuoles. It altered the expression of endogenous autophagy marker LC3. VES activated the suppression of mTOR through inhibiting upstream regulators p38 MAPK and Akt. mTOR suppression consequently inhibited the activation of mTOR downstream targets p70S6K and 4E-BP-1. The activation of the upstream mTOR inhibitor AMPK had been up-regulated by VES. The results showed that pre-treatment SGC-7901 with autophagy inhibitors before VES treatment could increase the capacity of VES to reduce cell viability and to provoke apoptosis. In conclusion, VES-induced autophagy participates in SGC-7901 cell protection by inhibiting mTOR axis phosphorylation. Our findings not only strengthen our understanding of the roles of autophagy in cancer biology, but may also be useful for developing new treatments for gastric cancer patients.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

Anticancer and antiangiogenic activity of surfactant-free nanoparticles based on self-assembled polymeric derivatives of vitamin E: structure-activity relationship

α-Tocopheryl succinate (α-TOS) is a well-known mitochondrially targeted anticancer compound, however, it is highly hydrophobic and toxic. In order to improve its activity and reduce its toxicity, new surfactant-free biologically active nanoparticles (NP) were synthesized. A methacrylic derivative of α-TOS (MTOS) was prepared and incorporated in amphiphilic pseudoblock copolymers when copolymerized with N-vinylpyrrolidone (VP) by free radical polymerization (poly(VP-co-MTOS)). The selected poly(VP-co-MTOS) copolymers formed surfactant-free NP by nanoprecipitation with sizes between 96 and 220 nm and narrow size distribution, and the in vitro biological activity was tested. In order to understand the structure-activity relationship three other methacrylic monomers were synthesized and characterized: MVE did not have the succinate group, SPHY did not have the chromanol ring, and MPHY did not have both the succinate group and the chromanol ring. The corresponding families of copolymers (poly(VP-co-MVE), poly(VP-co-SPHY), and poly(VP-co-MPHY)) were synthesized and characterized, and their biological activity was compared to poly(VP-co-MTOS). Both poly(VP-co-MTOS) and poly(VP-co-MVE) presented triple action: reduced cell viability of cancer cells with little or no harm to normal cells (anticancer), reduced viability of proliferating endothelial cells with little or no harm to quiescent endothelial cells (antiangiogenic), and efficiently encapsulated hydrophobic molecules (nanocarrier). The anticancer and antiangiogenic activity of the synthesized copolymers is demonstrated as the active compound (vitamin E or α-tocopheryl succinate) do not need to be cleaved to trigger the biological action targeting ubiquinone binding sites of complex II. Poly(VP-co-SPHY) and poly(VP-co-MPHY) also formed surfactant-free NP that were also endocyted by the assayed cells; however, these NP did not selectively reduce cell viability of cancer cells. Therefore, the chromanol ring of the vitamin E analogues has an important role in the biological activity of the copolymers. Moreover, when succinate moiety is substituted and vitamin E is directly linked to the macromolecular chain through an ester bond, the biological activity is maintained.

Vitamin E-based nanomedicines for anti-cancer drug delivery

This review aims to highlight the development of novel vitamin E conjugates for the vectorization of active pharmaceutical ingredients through nanotechnologies. The physico-chemical and biological properties of vitamin E derivatives offer multiple advantages in drug delivery like biocompatibility, improvement of drug solubility and anticancer activity. Nanomedicines have shown high potential in drug delivery since (i) they may offer better drug biopharmaceutical properties such as longer half-life or better bioavailability and (ii) they have shown benefits in cancer therapy by improving anticancer drug therapeutic index. Vitamin E-based nanomedicines were developed to combine the pharmaceutical properties of both vitamin E and nanomedicines for two purposes: (i) to improve water solubility of hydrophobic drugs and (ii) to enhance the therapeutic efficiency of anticancer agents. This review is divided into three parts: the first one describes the biology and the metabolic functions of vitamin E, the second one focuses on the anticancer activity of two vitamin E derivatives: vitamin E succinate (TOS) and vitamin E polyethylene glycol-succinate (TPGS). Finally, in the third part, we discuss vitamin E derivatives based-nanomedicines.

Vitamin E: tocopherols and tocotrienols as potential radiation countermeasures

Despite the potential devastating health consequences of intense total-body irradiation, and the decades of research, there still remains a dearth of safe and effective radiation countermeasures for emergency, radiological/nuclear contingencies that have been fully approved and sanctioned for use by the US FDA. Vitamin E is a well-known antioxidant, effective in scavenging free radicals generated by radiation exposure. Vitamin E analogs, collectively known as tocols, have been subject to active investigation for a long time as radioprotectors in patients undergoing radiotherapy and in the context of possible radiation accidents or terrorism scenarios. Eight major isoforms comprise the tocol group: four tocopherols and four tocotrienols. A number of these agents and their derivatives are being investigated actively as radiation countermeasures using animal models, and several appear promising. Although the tocols are well recognized as potent antioxidants and are generally thought to mediate radioprotection through 'free radical quenching', recent studies have suggested several alternative mechanisms: most notably, an 'indirect effect' of tocols in eliciting specific species of radioprotective growth factors/cytokines such as granulocyte colony-stimulating factor (G-CSF). The radioprotective efficacy of at least two tocols has been abrogated using a neutralizing antibody of G-CSF. Based on encouraging results of radioprotective efficacy, laboratory testing of γ-tocotrienol has moved from a small rodent model to a large nonhuman primate model for preclinical evaluation. In this brief review we identify and discuss selected tocols and their derivatives currently under development as radiation countermeasures, and attempt to describe in some detail their in vivo efficacy.

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.

Mitochondria: redox metabolism and dysfunction

Mitochondria are the main intracellular location for fuel generation; however, they are not just power plants but involved in a range of other intracellular functions including regulation of redox homeostasis and cell fate. Dysfunction of mitochondria will result in oxidative stress which is one of the underlying causal factors for a variety of diseases including neurodegenerative diseases, diabetes, cardiovascular diseases, and cancer. In this paper, generation of reactive oxygen/nitrogen species (ROS/RNS) in the mitochondria, redox regulatory roles of certain mitochondrial proteins, and the impact on cell fate will be discussed. The current state of our understanding in mitochondrial dysfunction in pathological states and how we could target them for therapeutic purpose will also be briefly reviewed.

Anticancer drugs targeting the mitochondrial electron transport chain

SIGNIFICANCE

Mitochondria are emerging as highly intriguing organelles showing promise but that are yet to be fully exploited as targets for anticancer drugs.

RECENT ADVANCES

A group of compounds that induce mitochondrial destabilization, thereby affecting the physiology of cancer cells, has been defined and termed 'mitocans.' Based on their mode of action of targeting in and around mitochondria, we have placed these agents into several groups including hexokinase inhibitors, compounds targeting Bcl-2 family proteins, thiol redox inhibitors, VDAC/ANT targeting drugs, electron transport chain-targeting drugs, lipophilic cations targeting the inner membrane, agents affecting the tricarboxylic acid cycle, drugs targeting mtDNA, and agents targeting other presently unknown sites.

CRITICAL ISSUES

Mitocans have a potential to prove highly efficient in suppressing various malignant diseases in a selective manner. They include compounds that are currently in clinical trial and offer substantial promise to become clinically applied drugs. Here we update and redefine the individual classes of mitocans, providing examples of the various members of these groups with a particular focus on agents targeting the electron transport chain, and indicate their potential application in clinical practice.

FUTURE DIRECTIONS

Even though reactive oxygen species induction is important for the anticancer activity of many mitocans, the precise sequence of events preceding and following this pivotal event are not yet fully clarified, and warrant further investigation. This is imperative for effective deployment of these compounds in the clinic.

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].

Vitamin E succinate inhibits survivin and induces apoptosis in pancreatic cancer cells

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States. Identifying novel chemotherapeutic and chemopreventive approaches is critical in the prevention and treatment of cancers such as pancreatic cancer. Vitamin E succinate (VES) is a redox-silent analog of the fat-soluble vitamin alpha-tocopherol. In the present study, we explored the antiproliferative action of VES and its effects on inhibitor of apoptosis proteins in pancreatic cancer cells. We show that VES inhibits cell proliferation and induces apoptosis in pancreatic cancer cells. Further, we demonstrate that VES downregulates the expression of survivin and X-linked inhibitor of apoptosis proteins. The apoptosis induced by VES was augmented by siRNA-mediated inhibition of survivin in PANC-1 cells. In summary, our results suggest that VES targets survivin signaling and induces apoptosis in pancreatic cancer cells.

Role of immunoregulatory transcription factors in differential immunomodulatory effects of tocotrienols

Tocotrienols have been shown to possess antioxidant, antitumor, cardioprotective, and antiproliferative effects. This report describes novel immunomodulatory effects of tocotrienols in murine lymphocytes. γ-Tocotrienol (GT) was more effective in suppressing concanavalin A (Con A)-induced T cell proliferation and cytokine production compared to α-tocotrienol (AT) when present continuously in the culture. GT inhibited T cell activation markers and costimulatory molecule. GT modulated intracellular glutathione in lymphocytes, and the suppressive effects of GT could not be abrogated by thiol or nonthiol antioxidants, indicating a poor link between anti-inflammatory properties of tocotrienols and cellular redox status. It was also observed that GT suppressed Con A-induced activation of NF-κB, AP-1, and NF-κB-dependent gene expression. Cellular uptake studies with tocotrienols showed higher accumulation of GT compared to AT. Similar immunosuppressive effects of GT were also observed when administered to mice. In contrast, transient exposure of lymphocytes to GT (4 h) resulted in higher survival and proliferation of lymphocytes in vitro and in vivo in syngeneic and allogeneic hosts. This was attributed to the ability of GT to induce NF-κB, AP-1, and mTOR activation in lymphocytes upon transient exposure. Our results demonstrated that antioxidants such as tocotrienols may exhibit pleiotropic effects by activating multiple mechanisms in cells.

Nano self-assembly of recombinant human gelatin conjugated with α-tocopheryl succinate for Hsp90 inhibitor, 17-AAG, delivery

A wide variety of drug delivery systems have been developed for the delivery of anticancer agents. One of the most frequently used natural biomaterials in drug delivery systems is polysaccharides; however, they are difficult to digest and to eliminate from the body after systemic administration due to their high molecular weight natures and the absence of degrading enzymes. Therefore, the development of degradable and eliminable natural biomaterials is critical for successful in vivo applications. In the present study, we report the development of self-assembled biodegradable nanoparticles based on recombinant human gelatin (rHG) modified with alpha-tocopheryl succinate (TOS). The rHG-TOS nanoparticles efficiently encapsulated 17-AAG (17-allylamino-17-demethoxygeldanamycin), a small molecular anticancer drug targeting heat shock protein 90. The formation of 17-AAG-loaded nanoparticles was confirmed using TEM and dynamic light scattering analysis and found to be within the size of 90-220 nm. The loading efficiency, sustained release pattern, and stability of 17-AAG from the rHG-TOS nanoparticles were determined using HPLC. Furthermore, the passive targeting of rHG-TOS nanoparticles to the tumor area via enhanced permeability and retention effect was examined by noninvasive live animal imaging in a tumor mouse model. Finally, the 17-AAG-loaded nanoparticles were nonimmunogenic and more efficient than free 17-AAG in manifesting an anticancer effect in the tumor model. Overall, our data demonstrate rHG-TOS as a promising tool for the delivery of 17-AAG featuring therapeutic efficacy and biocompatibility.

α-Tocopheryloxyacetic acid: a novel chemotherapeutic that stimulates the antitumor immune response

Introduction

α-Tocopheryloxyacetic acid (α-TEA) is a novel ether derivative of α-tocopherol that has generated interest as a chemotherapeutic agent because of its selective toxicity toward tumor cells and its ability to suppress tumor growth in various rodent and human xenograft models. We previously reported that oral α-TEA inhibited the growth of both a transplanted (4T1) and a spontaneous MMTV-PyMT mouse model of breast cancer.

Methods

Because little is known about the possible immunological mechanisms underlying the in vivo α-TEA effects, we evaluated the impact of α-TEA therapy on the immune response by characterizing immune cell populations infiltrating the tumor site.

Results

α-TEA treatment resulted in higher frequencies of activated T cells in the tumor microenvironment and twofold and sixfold higher ratios of CD4⁺ and CD8⁺ T cells to regulatory T cells, respectively. This finding was correlated with an increased ability of tumor-draining lymph node cells and splenocytes from α-TEA-treated mice to secrete interferon (IFN)-γ in response to CD3 or to mediate a cytolytic response in a tumor-specific fashion, respectively. That the α-TEA-mediated antitumor effect had a T cell-dependent component was demonstrated by the partial abrogation of tumor suppression when CD4⁺ and CD8⁺ T cells were depleted. We also determined the intratumoral cytokine and chemokine profile and found that α-TEA treatment increased intratumoral IFN-γ levels but decreased interleukin (IL)-4 levels, suggesting a shift toward a TH1 response. In addition, α-TEA induced higher levels of the inflammatory cytokine IL-6 and the chemokine CCL5.

Conclusions

Taken together, these data suggest that α-TEA treatment, in addition to its direct cytotoxic effects, enhanced the anti-tumor immune response. This study provides a better understanding of the mechanisms of action of α-TEA and its effect on the immune system and may prove useful in designing immune-stimulating strategies to boost the antitumor effects of α-TEA in breast cancer patients.

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.

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.

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.

Bioanalytical applications using supercritical fluid techniques

The bioanalytical applications of supercritical fluid techniques, such as supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC), are of increasing interest. The main role of these techniques is in the sample preparation and separation of biologically active compounds, particularly drugs and their metabolites, as well as endogenous compounds. An insight is given into the different types of extracting fluids and modifiers, detectors, stationary phases, mobile phases and collection strategies. A critical discussion is presented on the existing state of the art concerning the applications of SFC and SFE with a specific focus on its advantages and limitations in the bioanalytical field. New developments and the possibilities for routine work in the near future are also covered.

Anticancer actions of natural and synthetic vitamin E forms: RRR-alpha-tocopherol blocks the anticancer actions of gamma-tocopherol

Two naturally occurring dietary sources of vitamin E (i.e. RRR-alpha-tocopherol (alphaT) and RRR-gamma-tocopherol (gammaT)), the manufactured synthetic form of vitamin E, all-racemic-alpha-tocopherol (all-rac-alphaT), as well as a potent antitumor analog of vitamin E, RRR-alpha-tocopherol ether-linked acetic acid analog (alpha-TEA), were assessed for anticancer actions. Data showed that gammaT, all-rac-alphaT, and alpha-TEA but not alphaT or alphaT+gammaT significantly inhibited tumor burden of human MDA-MB-231 cells in nude mice. Immunohistochemical analyses of tumor tissue showed that all-rac-alphaT and alpha-TEA increased apoptosis and decreased proliferation in tumor cells while gammaT was associated with increased tumor cell apoptosis only. In vitro data showed alpha-TEA and gammaT but not all-rac-alphaT or alphaT to inhibit colony formation and induce apoptosis. Anticancer actions of alpha-TEA and gammaT involved death receptor 5 protein upregulation, Survivin protein downregulation and poly (ADP-ribose) polymerase cleavage, all of which were blocked by co-treatment with alphaT. In summary, both gammaT and alpha-TEA exhibited promising anticancer properties in vivo and in vitro, whereas all-rac-alphaT exhibited promising anticancer properties in vivo only. Importantly, alphaT not only failed to exhibit anticancer properties but it also reduced anticancer actions of gammaT in vivo and gammaT and alpha-TEA in vitro.

alpha-Tocopheryl succinate as a scaffold to develop potent inhibitors of breast cancer cell adhesion

This study is aimed at the pharmacological exploitation of alpha-tocopheryl succinate (1) to develop potent antiadhesion agents. Considering the structural cooperativity between the phytyl chain and the carboxylic terminus in determining the antiadhesion activity, our structural optimization led to compound 5 ([2-(4,8-dimethyl-non-1-enyl)-2,5,7,8-tetramethyl-chroman-6-yloxy]-acetic acid), which exhibited an-order-of-magnitude higher potency than 1 in blocking the adhesion of 4T1 metastatic breast cancer cells to extracellular matrix proteins (IC(50), 0.6 microM versus 10 microM). Evidence indicates that the ability of compound 5 to block cell adhesion and migration was attributable to its effect on disrupting focal adhesion and actin cytoskeletal integrity by facilitating the degradation of focal adhesion kinase. Interactions between tumor cells and the ECM in the tumor microenvironment have been increasingly recognized as critical modulators of the metastatic potential of tumor cells. Consequently, the ability of compound 5 to block such interactions provides a unique pharmacological tool to shed light onto mechanisms that govern cell adhesion and tumor metastasis.

Bid integrates intrinsic and extrinsic signaling in apoptosis induced by alpha-tocopheryl succinate in human gastric carcinoma cells

The underlying mechanisms of alpha-tocopheryl succinate (alpha-TOS)-mediated apoptosis are not understood in detail, although the redox-silent vitamin E analog is a potent apoptogen and anti-cancer agent. Our previous studies showed the important role of Fas signaling in apoptosis induced by the mitocan. The objective of the present study was to investigate whether apoptosis triggered by alpha-TOS in gastric carcinomas cells involves both mitochondria- and death receptor-dependent pathways. alpha-TOS induced apoptosis and mitochondrial permeability transition in a concentration- and time-dependent manner. As a consequence, cytochrome c and the apoptosis-inducing factor were released and caspases were activated. Bax was translocated from the cytosol to mitochondria and Bid was cleaved into its truncated form, tBid. Knocking down Bid by RNAi and Fas antisense oligodeoxynucleotides resulted in a decreased release and cleavage. The results imply that Bid may serve as a critical integrating factor of the death receptor and mitochondrial pathway in alpha-TOS-mediated apoptosis.

Correlation between antiangiogenic activity and antioxidant activity of various components from propolis

Propolis possesses various physiological activities. In this study, we examined the antiangiogenic and antioxidant activities of various components from propolis: acacetin, apigenin, artepillin C, caffeic acid phenethyl ester, chrysin, p-coumaric acid, galangin, kaempferol, pinocembrin, and quercetin. The effects of these components were tested on in vitro models of angiogenesis, tube formation and growth of human umbilical vein endothelial cells (HUVECs). Furthermore, these components were evaluated for their antioxidant activities by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging and ferric reducing/antioxidant power (FRAP) assays. Two propolis components, caffeic acid phenethyl ester, and quercetin, possessed strong inhibitory effects on tube formation and on endothelial cell proliferation and, coincidentally, showed strong antioxidant activity. Artepillin C, galangin, and kaempferol also possessed strong antiangiogenic and antioxidant activities to a slightly less degree. In contrast, acacetin, apigenin, and pinocembrin possessed a considerable degree of antiangiogenic activities, although they showed very low antioxidant activities. From these results, we propose that components from propolis such as artepillin C, caffeic acid phenethyl ester, galangin, kaempferol, and quercetin might represent a new class of dietary-derived antioxidative compounds with antiangiogenic activities. These propolis components may have the potential to be developed into pharmaceutical drugs for the treatment of angiogenesis-dependent human diseases such as tumors.

alpha-Tocopheryl succinate and derivatives mediate the transcriptional repression of androgen receptor in prostate cancer cells by targeting the PP2A-JNK-Sp1-signaling axis

As part of our effort to understand the mechanism underlying alpha-tocopheryl succinate [vitamin E succinate (VES)]-mediated antitumor effects, we investigated the signaling pathway by which VES suppresses androgen receptor (AR) expression in prostate cancer cells. VES and, to a greater extent, its truncated derivative TS-1 mediated transcriptional repression of AR in prostate cancer cells but not in normal prostate epithelial cells; a finding that underscores the differential susceptibility of normal versus malignant cells to the antiproliferative effect of these agents. This AR repression was attributable to the ability of VES and TS-1 to facilitate the proteasomal degradation of the transcription factor Sp1. This mechanistic link was corroborated by the finding that proteasome inhibitors or ectopic expression of Sp1 protected cells against drug-induced AR ablation. Furthermore, evidence suggests that the destabilization of Sp1 by VES and TS-1 resulted from the inactivation of Jun N-terminal kinases (JNKs) as a consequence of increased phosphatase activity of protein phosphatase 2A (PP2A). Stable transfection of LNCaP cells with the dominant-negative JNK1 plasmid mimicked drug-induced Sp1 repression, whereas constitutive activation of JNK kinase activity or inhibition of PP2A activity by okadaic acid protected Sp1 from VES- and TS-1-induced degradation. From a mechanistic perspective, the ability of VES and TS-1 to activate PP2A activity underscores their broad spectrum of effects on multiple signaling mechanisms, including those mediated by Akt, mitogen-activated protein kinases, nuclear factor kappaB, Sp1 and AR. This pleiotropic effect in conjunction with low toxicity suggests the translational potential for developing TS-1 into potent PP2A-activating agents for cancer therapy.

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.

Vitamin E succinate induces ceramide-mediated apoptosis in head and neck squamous cell carcinoma in vitro and in vivo

PURPOSE

Vitamin E succinate (alpha-TOS) inhibits the growth of cancer cells without unacceptable side effects. Therefore, the mechanisms associated with the anticancer action of alpha-TOS, including ceramide-mediated apoptosis, were investigated using head and neck squamous cell carcinoma (HNSCC) in vitro and in vivo.

EXPERIMENTAL DESIGN

Five different human HNSCC cell lines (JHU-011, JHU-013, JHU-019, JHU-022, and JHU-029) were treated with alpha-TOS, and its effects on cell proliferation, cell cycle progression, ceramide-mediated apoptosis, and ceramide metabolism were evaluated. The anticancer effect of alpha-TOS was also examined on JHU-022 solid tumor xenograft growth in immunodeficient mice.

RESULTS

Alpha-TOS inhibited the growth of all the HNSCC cell lines in vitro in a dose- and time-dependent manner. Thus, JHU-013 and JHU-022 cell lines were more sensitive to alpha-TOS than the other cell lines. Cellular levels of ceramide, sphingomyelinase activity, caspase-3, and p53 were elevated with increasing time of exposure to alpha-TOS. The degradation of poly(ADP-ribose) polymerase protein in JHU-022 cells treated with alpha-TOS provided evidence for apoptosis. The amounts of nuclear factor kappaB, Bcl-2, and Bcl-X(L) proteins were reduced in the cells treated with alpha-TOS for 6 hours. The levels of caspase-9, murine double minute-2, and IkappaB-alpha proteins were unchanged after alpha-TOS treatment. I.p. administration of alpha-TOS slowed tumor growth in immunodeficient mice.

CONCLUSIONS

Alpha-TOS showed promising anticancer effects to inhibit HNSCC growth and viability in vivo and in vitro. The induction of enzymes involved in ceramide metabolism by alpha-TOS suggests that ceramide-mediated apoptosis may expand therapeutic strategies in the treatment of carcinoma.

Arsenic trioxide-induced apoptosis in H9c2 cardiomyocytes: implications in cardiotoxicity

Arsenic trioxide (As(2)O(3)) achieved dramatic remissions in patients with acute promyelocytic leukaemia. Clinical reports have shown that treatment was associated with cardiotoxicity. We investigated the toxic mechanisms of As(2)O(3) in H9c2 cardiomyocytes. Clinically relevant concentrations of As(2)O(3) (2-10 microM) reduced the viability of H9c2 cells in a concentration-dependent manner. The decreased cell viability was because As(2)O(3) induced cell apoptosis (cell shrinkage, nuclear alterations and caspase-3 activation), or even necrosis at higher concentrations. Inhibition of caspase-3 with a specific inhibitor, Ac-DEVD-CHO, suppressed apoptosis induced by As(2)O(3). In addition, reactive oxygen species formation and cellular Ca(2+) overload were observed in H9c2 cells exposed to As(2)O(3), which was partly inhibited by vitamin E and verapamil. These results suggest that As(2)O(3)-induced cardiotoxicity is mediated, at least in part, by activation of caspase-3 pathway, which may be triggered by reactive oxygen species formation and intracellular Ca(2+) overload.

Critical roles for JNK, c-Jun, and Fas/FasL-Signaling in vitamin E analog-induced apoptosis in human prostate cancer cells

BACKGROUND

Alpha-tocopherol ether-linked acetic acid (alpha-TEA), an analog of vitamin E (RRR-alpha-tocopherol), is a potent pro-apoptotic agent for human cancer cells in vivo and in vitro.

METHODS

alpha-TEA-induced apoptosis was investigated in LNCaP and PC-3 human prostate cancer cells. Apoptosis was measured by DAPI-staining and FACS analyses of the sub-G1 fraction. Signaling molecules involved in apoptosis were measured by Western immunoblot analyses with or without prior immunoprecipitation, FACS analyses of cell surface membrane expression, RT-PCR analyses of mRNA levels, and chromatin immunoprecipitation. Functional significance was determined using siRNAs, dominant negative mutant, chemical inhibitor, or neutralizing antibody.

RESULTS

Alpha-TEA treatment increased Fas and Fas ligand mRNA and protein levels; as well as, levels of cell surface membrane Fas in both cell lines. Blockage of Fas signaling attenuated alpha-TEA-induced apoptosis. alpha-TEA treatment also produced prolonged, elevated levels of activated (phosphorylated) c-Jun N-terminal kinase (JNK) and its substrate c-Jun, both of which were demonstrated to be necessary for alpha-TEA-induced apoptosis. Chromatin immunoprecipitation results showed binding of c-Jun to the promoters of both Fas and FasL in alpha-TEA treated cells. Investigations of alpha-TEA-triggered apoptosis showed dual signaling from Fas with essential roles for both FADD and Daxx with FADD initiating the classical pathway mediated by caspase-8 activation and Daxx initiating an alternate pathway involving activation of JNK, c-Jun, and increased levels of Fas and FasL.

CONCLUSIONS

Collectively, data support critical roles for JNK, c-Jun, and dual signaling from Fas/FasL via FADD and Daxx in alpha-TEA-induced apoptosis of human prostate cancer cells.

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

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

Alpha-Tocopheryl succinate: toxicity and lack of anti-tumour activity in immuno-competent mice

Alpha-tocopheryl succinate (alpha-TOS), an analogue of vitamin E (VitE), inhibits peritoneal human malignant mesoethelioma xenograft development in immuno-compromised mice via the induction of apoptosis of tumour cells [Tomasetti, M., Gellert, N., Procopio, A., Neuzil, J., 2004. A vitamin E analogue suppresses malignant mesothelioma in a preclinical model: a future drug against a fatal neoplastic disease? Int. J. Cancer 109, 641-642]. We tested the effect of systemic alpha-TOS treatment in our immuno-competent and syngeneic murine mesothelioma model. VitE analogues such as alpha-TOS have been developed for clinical use as supplements mainly for the treatment of VitE deficiency and are considered safe and non-toxic when taken orally. In our murine model of mesothelioma alpha-TOS was not only ineffective at inhibiting established tumour development at the published doses, but resulted in severe side effects characterized by both behavioural changes, intra-peritoneal abnormalities and the destruction of T cells. Toxicity of alpha-TOS has not been reported to date perhaps due to a lack of studies conducted in fully immuno-competent hosts. Our results suggest that the translation of animal studies to clinical treatment with alpha-TOS requires careful consideration.

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.