Current and future directions for Phase II trials in high-grade glioma

Despite surgery, radiation and chemotherapy, the prognosis for high-grade glioma (HGG) is poor. Our understanding of the molecular pathways involved in gliomagenesis and progression has increased in recent years, leading to the development of novel agents that specifically target these pathways. Results from most single-agent trials have been modest at best, however. Despite the initial success of antiangiogenesis agents in HGG, the clinical benefit is short-lived and most patients eventually progress. Several novel agents, multi-targeted agents and combination therapies are now in clinical trials for HGG and several more strategies are being pursued.

DCA increases the antitumor effects of capecitabine in a mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft

PURPOSE

Capecitabine is one of the few chemotherapy drugs with high oral availability. Recently, sodium dichloroacetate (DCA) has shown great potential as an anticancer agent. In the present study, we assessed the anticancer effect of DCA in combination with capecitabine for cancers that modestly expressed TP.

METHODS

A mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft were used to assess the effect of DCA and capecitabine combined treatment. Histology and immunohistochemistry were used to detect the apoptosis and proliferation of cancer cells. Real-time PCR and Western blot were carried out to detect the expression of TP and caspases, respectively.

RESULTS

For the first time, we report that DCA increased the antitumor effects of capecitabine in a mouse B16 allograft and a human A549 xenograft by promoting apoptosis of tumor cells. DCA has little effect on the expression of TP.

CONCLUSIONS

Our finding suggests that DCA in combination with capecitabine might be potential as a new therapeutic regimen against some cancers.

Antitumor and chemosensitizing action of dichloroacetate implicates modulation of tumor microenvironment: a role of reorganized glucose metabolism, cell survival regulation and macrophage differentiation

Targeting of tumor metabolism is emerging as a novel therapeutic strategy against cancer. Dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase (PDK), has been shown to exert a potent tumoricidal action against a variety of tumor cells. The main mode of its antineoplastic action implicates a shift of glycolysis to oxidative metabolism of glucose, leading to generation of cytotoxic reactive oxygen intermediates. However, the effect of DCA on tumor microenvironment, which in turn regulates tumor cell survival; remains speculative to a large extent. It is also unclear if DCA can exert any modulatory effect on the process of hematopoiesis, which is in a compromised state in tumor-bearing hosts undergoing chemotherapy. In view of these lacunas, the present study was undertaken to investigate the so far unexplored aspects with respect to the molecular mechanisms of DCA-dependent tumor growth retardation and chemosensitization. BALB/c mice were transplanted with Dalton's lymphoma (DL) cells, a T cell lymphoma of spontaneous origin, followed by administration of DCA with or without cisplatin. DCA-dependent tumor regression and chemosensitization to cisplatin was found to be associated with altered repertoire of key cell survival regulatory molecules, modulated glucose metabolism, accompanying reconstituted tumor microenvironment with respect to pH homeostasis, cytokine balance and alternatively activated TAM. Moreover, DCA administration also led to an alteration in the MDR phenotype of tumor cells and myelopoietic differentiation of macrophages. The findings of this study shed a new light with respect to some of the novel mechanisms underlying the antitumor action of DCA and thus may have immense clinical applications.

Metabolism modifications and apoptosis induction after Cellfood™ administration to leukemia cell lines

Background

Cellfood™ (CF) is a nutritional supplement containing deuterium sulphate, minerals, amino acids, and enzymes, with well documented antioxidant properties. Its organic and inorganic components are extracted from the red algae Lithothamnion calcareum, whose mineral extract has shown growth-inhibitory effect both on in vitro and in vivo models. The purpose of this study was to evaluate the antiproliferative effects of CF on leukemic cells. In fact, according to its capacity to modulate O₂ availability and to improve mitochondrial respiratory metabolism, we wondered if CF could affect cancer cell metabolism making cells susceptible to apoptosis.

Methods

Three leukemic cell lines, Jurkat, U937, and K562, were treated with CF 5 μl/ml up to 72 hours. Cell viability, apoptosis (i.e. caspase-3 activity and DNA fragmentation), hypoxia inducible factor 1 alpha (HIF-1α) concentration, glucose transporter 1 (GLUT-1) expression, lactate dehydrogenase (LDH) activity and lactate release in the culture medium were detected and compared with untreated cells.

Results

CF significantly inhibited leukemic cell viability by promoting cell apoptosis, as revealed by caspase-3 activation and DNA laddering. In particular, CF treated cells showed lower HIF-1α levels and lower GLUT-1 expression as compared to untreated cells. At the same time, CF was able to reduce LDH activity and, consequently, the amount of lactate released in the extracellular environment.

Conclusions

We supplied evidence for an antiproliferative effect of CF on leukemia cell lines by inducing cell death through an apoptotic mechanism and by altering cancer cell metabolism through HIF-1α and GLUT-1 regulation. Thanks to its antioxidative and proapoptotic properties, CF might be a good candidate for cancer prevention.

HIF-1 mediates metabolic responses to intratumoral hypoxia and oncogenic mutations

Hypoxia occurs frequently in human cancers and induces adaptive changes in cell metabolism that include a switch from oxidative phosphorylation to glycolysis, increased glycogen synthesis, and a switch from glucose to glutamine as the major substrate for fatty acid synthesis. This broad metabolic reprogramming is coordinated at the transcriptional level by HIF-1, which functions as a master regulator to balance oxygen supply and demand. HIF-1 is also activated in cancer cells by tumor suppressor (e.g., VHL) loss of function and oncogene gain of function (leading to PI3K/AKT/mTOR activity) and mediates metabolic alterations that drive cancer progression and resistance to therapy. Inhibitors of HIF-1 or metabolic enzymes may impair the metabolic flexibility of cancer cells and make them more sensitive to anticancer drugs.

Altered glucose metabolism in Harvey-ras transformed MCF10A cells

Metabolic reprogramming that alters the utilization of glucose including the "Warburg effect" is critical in the development of a tumorigenic phenotype. However, the effects of the Harvey-ras (H-ras) oncogene on cellular energy metabolism during mammary carcinogenesis are not known. The purpose of this study was to determine the effect of H-ras transformation on glucose metabolism using the untransformed MCF10A and H-ras oncogene transfected (MCF10A-ras) human breast epithelial cells, a model for early breast cancer progression. We measured the metabolite fluxes at the cell membrane by a selective micro-biosensor, [(13)C6 ]glucose flux by (13)C-mass isotopomer distribution analysis of media metabolites, intracellular metabolite levels by NMR, and gene expression of glucose metabolism enzymes by quantitative PCR. Results from these studies indicated that MCF10A-ras cells exhibited enhanced glycolytic activity and lactate production, decreased glucose flux through the tricarboxylic acid (TCA) cycle, as well as an increase in the utilization of glucose in the pentose phosphate pathway (PPP). These results provide evidence for a role of H-ras oncogene in the metabolic reprogramming of MCF10A cells during early mammary carcinogenesis.

Mitochondrial dysfunction in gliomas

Mitochondrial (mt) dysfunction in gliomas has been linked to abnormalities of mt energy metabolism, marked by a metabolic shift from oxidative phosphorylation to glycolysis ("Warburg effect"), disturbances in mt membrane potential regulation and apoptotic signaling, as well as to somatic mutations involving the Krebs cycle enzyme isocitrate dehydrogenase. Evolving biological concepts with potential therapeutic implications include interaction between microtubule proteins and mitochondria (mt) in the control of closure of voltage-dependent anion channels and in the regulation of mt dynamics and the mt-endoplasmic reticulum network. The cytoskeletal protein βIII-tubulin, which is overexpressed in malignant gliomas, has emerged as a prosurvival factor associated in part with mt and also as a marker of chemoresistance. Mt-targeted therapeutic strategies that are discussed include the following: (1) metabolic modulation with emphasis on dichloroacetate, a pyruvate dehydrogenase kinase inhibitor; (2) tumor cell death via apoptosis induced by tricyclic antidepressants, microtubule-modulating drugs, and small molecules or compounds capable of inflicting reactive oxygen species-dependent tumor cell death; and (3) pretreatment mt priming and mt-targeted prodrug cancer therapy.

Metformin decreases glucose oxidation and increases the dependency of prostate cancer cells on reductive glutamine metabolism

Metformin inhibits cancer cell proliferation, and epidemiology studies suggest an association with increased survival in patients with cancer taking metformin; however, the mechanism by which metformin improves cancer outcomes remains controversial. To explore how metformin might directly affect cancer cells, we analyzed how metformin altered the metabolism of prostate cancer cells and tumors. We found that metformin decreased glucose oxidation and increased dependency on reductive glutamine metabolism in both cancer cell lines and in a mouse model of prostate cancer. Inhibition of glutamine anaplerosis in the presence of metformin further attenuated proliferation, whereas increasing glutamine metabolism rescued the proliferative defect induced by metformin. These data suggest that interfering with glutamine may synergize with metformin to improve outcomes in patients with prostate cancer.

Manipulation of PK-M mutually exclusive alternative splicing by antisense oligonucleotides

Alternative splicing of the pyruvate kinase M gene involves a choice between mutually exclusive exons 9 and 10. Use of exon 10 to generate the M2 isoform is crucial for aerobic glycolysis (the Warburg effect) and tumour growth. We previously demonstrated that splicing enhancer elements that activate exon 10 are mainly found in exon 10 itself, and deleting or mutating these elements increases the inclusion of exon 9 in cancer cells. To systematically search for new enhancer elements in exon 10 and develop an effective pharmacological method to force a switch from PK-M2 to PK-M1, we carried out an antisense oligonucleotide (ASO) screen. We found potent ASOs that target a novel enhancer in exon 10 and strongly switch the splicing of endogenous PK-M transcripts to include exon 9. We further show that the ASO-mediated switch in alternative splicing leads to apoptosis in glioblastoma cell lines, and this is caused by the downregulation of PK-M2, and not by the upregulation of PK-M1. These data highlight the potential of ASO-mediated inhibition of PK-M2 splicing as therapy for cancer.

Pyruvate Dehydrogenase Kinases in the Nervous System: Their Principal Functions in Neuronal-glial Metabolic Interaction and Neuro-metabolic Disorders

Metabolism is involved directly or indirectly in all processes conducted in living cells. The brain, popularly viewed as a neuronal-glial complex, gets most of its energy from the oxygen-dependent metabolism of glucose, and the mitochondrial pyruvate dehydrogenase complex (PDC) plays a key regulatory role during the oxidation of glucose. Pyruvate dehydrogenase kinase (also called PDC kinase or PDK) is a kinase that regulates glucose metabolism by switching off PDC. Four isoforms of PDKs with tissue specific activities have been identified. The metabolisms of neurons and glial cells, especially, those of astroglial cells, are interrelated, and these cells function in an integrated fashion. The energetic coupling between neuronal and astroglial cells is essential to meet the energy requirements of the brain in an efficient way. Accumulating evidence suggests that alterations in the PDKs and/or neuron-astroglia metabolic interactions are associated with the development of several neurological disorders. Here, the authors review the results of recent research efforts that have shed light on the functions of PDKs in the nervous system, particularly on neuron-glia metabolic interactions and neuro-metabolic disorders.

Exploiting metabolic differences in glioma therapy

Brain function depends upon complex metabolic interactions amongst only a few different cell types, with astrocytes providing critical support for neurons. Astrocyte functions include buffering the extracellular space, providing substrates to neurons, interchanging glutamate and glutamine for synaptic transmission with neurons, and facilitating access to blood vessels. Whereas neurons possess highly oxidative metabolism and easily succumb to ischemia, astrocytes rely more on glycolysis and metabolism associated with synthesis of critical intermediates, hence are less susceptible to lack of oxygen. Astrocytoma and higher grade glioma cells demonstrate both basic metabolic mechanisms of astrocytes as well as tumors in general, e.g. they show a high glycolytic rate, lactate extrusion, ability to proliferate even under hypoxia, and opportunistic use of mechanisms to enhance metabolism and blood vessel generation, and suppression of cell death pathways. There may be differences in metabolism between neurons, normal astrocytes and astrocytoma cells, providing therapeutic opportunities against astrocytomas, including a wide range of enzyme and transporter differences, regulation of hypoxia-inducible factor (HIF), glutamate uptake transporters and glutamine utilization, differential sensitivities of monocarboxylate transporters, presence of glycogen, high interlinking with gap junctions, use of NADPH for lipid synthesis, utilizing differential regulation of synthetic enzymes (e.g. isocitrate dehydrogenase, pyruvate carboxylase, pyruvate dehydrogenase, lactate dehydrogenase, malate-aspartate NADH shuttle) and different glucose uptake mechanisms. These unique metabolic susceptibilities may augment conventional therapeutic attacks based on cell division differences and surface receptors alone, and are starting to be implemented in clinical trials.

Targeting the latest hallmark of cancer: another attempt at 'magic bullet' drugs targeting cancers' metabolic phenotype

The metabolism of tumors is remarkably different from the metabolism of corresponding normal cells and tissues. Metabolic alterations are initiated by oncogenes and are required for malignant transformation, allowing cancer cells to resist some cell death signals while producing energy and fulfilling their biosynthetic needs with limiting resources. The distinct metabolic phenotype of cancers provides an interesting avenue for treatment, potentially with minimal side effects. As many cancers show similar metabolic characteristics, drugs targeting the cancer metabolic phenotype are, perhaps optimistically, expected to be 'magic bullet' treatments. Over the last few years there have been a number of potential drugs developed to specifically target cancer metabolism. Several of these drugs are currently in clinical and preclinical trials. This review outlines examples of drugs developed for different targets of significance to cancer metabolism, with a focus on small molecule leads, chemical biology and clinical results for these drugs.

Metabolism and bioenergetics in the right ventricle and pulmonary vasculature in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary vascular cross sectional area and compliance are reduced by vasoconstriction, vascular remodeling, and inflammation. Vascular remodeling results in part from increased proliferation and impaired apoptosis of vascular cells. The resulting increase in afterload promotes right ventricular hypertrophy (RVH) and RV failure. Recently identified mitochondrial-metabolic abnormalities in PAH, notably pyruvate dehydrogenase kinase-mediated inhibition of pyruvate dehydrogenase (PDH), result in aerobic glycolysis in both the lung vasculature and RV. This glycolytic shift has diagnostic importance since it is detectable early in experimental PAH by increased lung and RV uptake of ¹⁸F-fluorodeoxyglucose on positron emission tomography. The metabolic shift also has pathophysiologic and therapeutic relevance. In RV myocytes, the glycolytic switch reduces contractility while in the vasculature it renders cells hyperproliferative and apoptosis-resistant. Reactivation of PDH can be achieved directly by PDK inhibition (using dichloroacetate), or indirectly via activating the Randle cycle, using inhibitors of fatty acid oxidation (FAO), trimetazidine and ranolazine. In experimental PAH and RVH, PDK inhibition increases glucose oxidation, enhances RV function, regresses pulmonary vascular disease by reducing proliferation and enhancing apoptosis, and restores cardiac repolarization. FAO inhibition increases RV glucose oxidation and RV function in experimental RVH. The trigger for metabolic remodeling in the RV and lung differ. In the RV, metabolic remodeling is likely triggered by ischemia (due to microvascular rarefaction and/or reduced coronary perfusion pressure). In the vasculature, metabolic changes result from redox-mediated activation of transcription factors, including hypoxia-inducible factor 1α, as a consequence of epigenetic silencing of SOD2 and/or changes in mitochondrial fission/fusion. Randomized controlled trials are required to assess whether the benefits of enhancing glucose oxidation are realized in patients with PAH.

Strategies for isolating and enriching cancer stem cells: well begun is half done

Cancer stem cells (CSCs) constitute a subpopulation of cancer cells that have the potential for self-renewal, multipotent differentiation, and tumorigenicity. Studies on CSC biology and CSC-targeted therapies depend on CSC isolation and/or enrichment methodologies. Scientists have conducted extensive research in this field since John Dick's group successfully isolated CSCs based on the expression of the CD34 and CD38 surface markers. Progress in CSC research has been greatly facilitated by the enrichment and isolation of these cells. In this review, we summarize the current strategies used in our and other laboratories for CSC isolation and enrichment, including methods based on stem cell surface markers, intracellular enzyme activity, the concentration of reactive oxygen species, the mitochondrial membrane potential, promoter-driven fluorescent protein expression, autofluorescence, suspension/adherent culture, cell division, the identification of side population cells, resistance to cytotoxic compounds or hypoxia, invasiveness/adhesion, immunoselection, and physical property. Although many challenges remain to be overcome, it is reasonable to believe that more reliable, efficient, and convenient methods will be developed in the near future.

Uncoupling protein 2 deficiency mimics the effects of hypoxia and endoplasmic reticulum stress on mitochondria and triggers pseudohypoxic pulmonary vascular remodeling and pulmonary hypertension

RATIONALE

Mitochondrial signaling regulates both the acute and the chronic response of the pulmonary circulation to hypoxia, and suppressed mitochondrial glucose oxidation contributes to the apoptosis-resistance and proliferative diathesis in the vascular remodeling in pulmonary hypertension. Hypoxia directly inhibits glucose oxidation, whereas endoplasmic reticulum (ER)-stress can indirectly inhibit glucose oxidation by decreasing mitochondrial calcium (Ca²⁺m levels). Both hypoxia and ER stress promote proliferative pulmonary vascular remodeling. Uncoupling protein 2 (UCP2) has been shown to conduct calcium from the ER to mitochondria and suppress mitochondrial function.

OBJECTIVE

We hypothesized that UCP2 deficiency reduces Ca²⁺m in pulmonary artery smooth muscle cells (PASMCs), mimicking the effects of hypoxia and ER stress on mitochondria in vitro and in vivo, promoting normoxic hypoxia inducible factor-1α activation and pulmonary hypertension.

METHODS AND RESULTS

Ucp2 knockout (KO)-PASMCs had lower mitochondrial calcium than Ucp2 wildtype (WT)-PASMCs at baseline and during histamine-stimulated ER-Ca²⁺ release. Normoxic Ucp2KO-PASMCs had mitochondrial hyperpolarization, lower Ca²⁺-sensitive mitochondrial enzyme activity, reduced levels of mitochondrial reactive oxygen species and Krebs' cycle intermediates, and increased resistance to apoptosis, mimicking the hypoxia-induced changes in Ucp2WT-PASMC. Ucp2KO mice spontaneously developed pulmonary vascular remodeling and pulmonary hypertension and exhibited a pseudohypoxic state with pulmonary vascular and systemic hypoxia inducible factor-1α activation (increased hematocrit), not exacerbated further by chronic hypoxia.

CONCLUSIONS

This first description of the role of UCP2 in oxygen sensing and in pulmonary hypertension vascular remodeling may open a new window in biomarker and therapeutic strategies.

Salinomycin induces activation of autophagy, mitophagy and affects mitochondrial polarity: differences between primary and cancer cells

The molecular mechanism of Salinomycin's toxicity is not fully understood. Various studies reported that Ca(2+), cytochrome c, and caspase activation play a role in Salinomycin-induced cytotoxicity. Furthermore, Salinomycin may target Wnt/β-catenin signaling pathway to promote differentiation and thus elimination of cancer stem cells. In this study, we show a massive autophagic response to Salinomycin (substantially stronger than to commonly used autophagic inducer Rapamycin) in prostrate-, breast cancer cells, and to lesser degree in human normal dermal fibroblasts. Interestingly, autophagy induced by Salinomycin is a cell protective mechanism in all tested cancer cell lines. Furthermore, Salinomycin induces mitophagy, mitoptosis and increased mitochondrial membrane potential (∆Ψ) in a subpopulation of cells. Salinomycin strongly, and in time-dependent manner decreases cellular ATP level. Contrastingly, human normal dermal fibroblasts treated with Salinomycin show some initial decrease in mitochondrial mass, however they are largely resistant to Salinomycin-triggered ATP-depletion. Our data provide new insight into the molecular mechanism of preferential toxicity of Salinomycin towards cancer cells, and suggest possible clinical application of Salinomycin in combination with autophagy inhibitors (i.e. clinically-used Chloroquine). Furthermore, we discuss preferential Salinomycins toxicity in the context of Warburg effect.

Dichloroacetate inhibits aerobic glycolysis in multiple myeloma cells and increases sensitivity to bortezomib

Background:

Dichloroacetate (DCA), through the inhibition of aerobic glycolysis (the ‘Warburg effect') and promotion of pyruvate oxidation, induces growth reduction in many tumours and is now undergoing several clinical trials. If aerobic glycolysis is active in multiple myeloma (MM) cells, it can be potentially targeted by DCA to induce myeloma growth inhibition.

Methods:

Representative multiple myeloma cell lines and a myeloma-bearing mice were treated with DCA, alone and in combination with bortezomib.

Results:

We found that aerobic glycolysis occurs in approximately half of MM cell lines examined, producing on average 1.86-fold more lactate than phorbol myristate acetate stimulated-peripheral blood mononuclear cells and is associated with low-oxidative capacity. Lower doses of DCA (5–10 mℳ) suppressed aerobic glycolysis and improved cellular respiration that was associated with activation of the pyruvate dehydrogenase complex. Higher doses of DCA (10–25 mℳ) induced superoxide production, apoptosis, suppressed proliferation with a G_0/1 and G₂M phase arrest in MM cell lines. In addition, DCA increased MM cell line sensitivity to bortezomib, and combinatorial treatment of both agents improved the survival of myeloma-bearing mice.

Conclusion:

Myeloma cells display aerobic glycolysis and DCA may complement clinically used MM therapies to inhibit disease progression.

Dichloroacetate improves immune dysfunction caused by tumor-secreted lactic acid and increases antitumor immunoreactivity

The activation of oncogenic signaling pathways induces the reprogramming of glucose metabolism in tumor cells and increases lactic acid secretion into the tumor microenvironment. This is a well-known characteristic of tumor cells, termed the Warburg effect, and is a candidate target for antitumor therapy. Previous reports show that lactic acid secreted by tumor cells is a proinflammatory mediator that activates the IL-23/IL-17 pathway, thereby inducing inflammation, angiogenesis and tissue remodeling. Here, we show that lactic acid, or more specifically the acidification it causes, increases arginase I (ARG1) expression in macrophages to inhibit T-cell proliferation and activation. Accordingly, we hypothesized that counteraction of the immune effects by lactic acid might suppress tumor development. We show that dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinases, targets macrophages to suppress activation of the IL-23/IL-17 pathway and the expression of ARG1 by lactic acid. Furthermore, lactic acid-pretreated macrophages inhibited CD8+ T-cell proliferation, but CD8+ T-cell proliferation was restored when macrophages were pretreated with lactic acid and DCA. DCA treatment decreased ARG1 expression in tumor-infiltrating immune cells and increased the number of IFN-γ-producing CD8+ T cells and NK cells in tumor-bearing mouse spleen. Although DCA treatment alone did not suppress tumor growth, it increased antitumor immunotherapeutic activity of Poly(IC) in both CD8+ T cell- and NK cell-sensitive tumor models. Therefore, DCA acts not only on tumor cells to suppress glycolysis but also on immune cells to improve the immune status modulated by lactic acid and to increase the effectiveness of antitumor immunotherapy.

Antitumor activity of dichloroacetate on C6 glioma cell: in vitro and in vivo evaluation

Dichloroacetate (DCA), a small molecule mitochondria-targeting agent, can penetrate the blood-brain barrier, showing potential therapeutic effects on brain tumors. Considering the effects of DCA on tumor cellular metabolism, penetrating across the blood-brain barrier, as well as having potential antitumor activity on brain tumors, the purpose of this study is to investigate the antitumor activity of DCA on C6 glioma cells in vitro and in vivo. DCA inhibited C6 glioma cell proliferation, induced C6 cell apoptosis, and arrested C6 cells in S phase. DCA can inhibit the expression of heat shock proteins 70 (Hsp70) in a dose-dependent and time-dependent manner (P < 0.01). Our in vivo antitumor effect results indicated that DCA markedly inhibited the growth of C6 glioma tumors in both C6 brain tumor-bearing rats and C6 tumor-bearing nude mice (P < 0.01). DCA significantly induced the ROS production and decreased the mitochondrial membrane potential in tumor tissues. Our in vivo antitumor effect results also indicated that DCA has potential antiangiogenic effects. In conclusion, DCA may be a viable therapeutic agent in the treatment of gliomas.

Pyruvate dehydrogenase kinase as a novel therapeutic target in oncology

Current drug development in oncology is non-selective as it typically focuses on pathways essential for the survival of all dividing cells. The unique metabolic profile of cancer, which is characterized by increased glycolysis and suppressed mitochondrial glucose oxidation (GO) provides cancer cells with a proliferative advantage, conducive with apoptosis resistance and even increased angiogenesis. Recent evidence suggests that targeting the cancer-specific metabolic and mitochondrial remodeling may offer selectivity in cancer treatment. Pyruvate dehydrogenase kinase (PDK) is a mitochondrial enzyme that is activated in a variety of cancers and results in the selective inhibition of pyruvate dehydrogenase, a complex of enzymes that converts cytosolic pyruvate to mitochondrial acetyl-CoA, the substrate for the Krebs' cycle. Inhibition of PDK with either small interfering RNAs or the orphan drug dichloroacetate (DCA) shifts the metabolism of cancer cells from glycolysis to GO and reverses the suppression of mitochondria-dependent apoptosis. In addition, this therapeutic strategy increases the production of diffusible Krebs' cycle intermediates and mitochondria-derived reactive oxygen species, activating p53 or inhibiting pro-proliferative and pro-angiogenic transcription factors like nuclear factor of activated T cells and hypoxia-inducible factor 1α. These effects result in decreased tumor growth and angiogenesis in a variety of cancers with high selectivity. In a small but mechanistic clinical trial in patients with glioblastoma, a highly aggressive and vascular form of brain cancer, DCA decreased tumor angiogenesis and tumor growth, suggesting that metabolic-targeting therapies can be translated directly to patients. More recently, the M2 isoform of pyruvate kinase (PKM2), which is highly expressed in cancer, is associated with suppressed mitochondrial function. Similar to DCA, activation of PKM2 in many cancers results in increased mitochondrial function and decreased tumor growth. Therefore, reversing the mitochondrial suppression with metabolic-modulating drugs, like PDK inhibitors or PKM2 activators holds promise in the rapidly expanding field of metabolic oncology.

Targeting metabolism to induce cell death in cancer cells and cancer stem cells

Abnormal metabolism and the evasion of apoptosis are considered hallmarks of cancers. Accumulating evidence shows that cancer stem cells are key drivers of tumor formation, progression, and recurrence. A successful therapy must therefore eliminate these cells known to be highly resistant to apoptosis. In this paper, we describe the metabolic changes as well as the mechanisms of resistance to apoptosis occurring in cancer cells and cancer stem cells, underlying the connection between these two processes.

Dichloroacetate reverses the hypoxic adaptation to bevacizumab and enhances its antitumor effects in mouse xenografts

Inhibition of vascular endothelial growth factor increases response rates to chemotherapy and progression-free survival in glioblastoma. However, resistance invariably occurs, prompting the urgent need for identification of synergizing agents. One possible strategy is to understand tumor adaptation to microenvironmental changes induced by antiangiogenic drugs and test agents that exploit this process. We used an in vivo glioblastoma-derived xenograft model of tumor escape in presence of continuous treatment with bevacizumab. U87-MG or U118-MG cells were subcutaneously implanted into either BALB/c SCID or athymic nude mice. Bevacizumab was given by intraperitoneal injection every 3 days (2.5 mg/kg/dose) and/or dichloroacetate (DCA) was administered by oral gavage twice daily (50 mg/kg/dose) when tumor volumes reached 0.3 cm(3) and continued until tumors reached approximately 1.5-2.0 cm(3). Microarray analysis of resistant U87 tumors revealed coordinated changes at the level of metabolic genes, in particular, a widening gap between glycolysis and mitochondrial respiration. There was a highly significant difference between U87-MG-implanted athymic nude mice 1 week after drug treatment. By 2 weeks of treatment, bevacizumab and DCA together dramatically blocked tumor growth compared to either drug alone. Similar results were seen in athymic nude mice implanted with U118-MG cells. We demonstrate for the first time that reversal of the bevacizumab-induced shift in metabolism using DCA is detrimental to neoplastic growth in vivo. As DCA is viewed as a promising agent targeting tumor metabolism, our data establish the timely proof of concept that combining it with antiangiogenic therapy represents a potent antineoplastic strategy.

Metabolic response of glioma to dichloroacetate measured in vivo by hyperpolarized (13)C magnetic resonance spectroscopic imaging

BACKGROUND

The metabolic phenotype that derives disproportionate energy via glycolysis in solid tumors, including glioma, leads to elevated lactate labeling in metabolic imaging using hyperpolarized [1-(13)C]pyruvate. Although the pyruvate dehydrogenase (PDH)-mediated flux from pyruvate to acetyl coenzyme A can be indirectly measured through the detection of carbon-13 ((13)C)-labeled bicarbonate, it has proven difficult to visualize (13)C-bicarbonate at high enough levels from injected [1-(13)C]pyruvate for quantitative analysis in brain. The aim of this study is to improve the detection of (13)C-labeled metabolites, in particular bicarbonate, in glioma and normal brain in vivo and to measure the metabolic response to dichloroacetate, which upregulates PDH activity.

METHODS

An optimized protocol for chemical shift imaging and high concentration of hyperpolarized [1-(13)C]pyruvate were used to improve measurements of lactate and bicarbonate in C6 glioma-transplanted rat brains. Hyperpolarized [1-(13)C]pyruvate was injected before and 45 min after dichloroacetate infusion. Metabolite ratios of lactate to bicarbonate were calculated to provide improved metrics for characterizing tumor metabolism.

RESULTS

Glioma and normal brain were well differentiated by lactate-to-bicarbonate ratio (P = .002, n = 5) as well as bicarbonate (P = .0002) and lactate (P = .001), and a stronger response to dichloroacetate was observed in glioma than in normal brain.

CONCLUSION

Our results clearly demonstrate for the first time the feasibility of quantitatively detecting (13)C-bicarbonate in tumor-bearing rat brain in vivo, permitting the measurement of dichloroacetate-modulated changes in PDH flux. The simultaneous detection of lactate and bicarbonate provides a tool for a more comprehensive analysis of glioma metabolism and the assessment of metabolic agents as anti-brain cancer drugs.

Case report: Sodium dichloroacetate (DCA) inhibition of the "Warburg Effect" in a human cancer patient: complete response in non-Hodgkin's lymphoma after disease progression with rituximab-CHOP

The uptake of fluorodeoxyglucose Positron Emission Tomography in the tumors of various cancer types demonstrates the key role of glucose in the proliferation of cancer. Dichloroacetate is a 2-carbon molecule having crucial biologic activity in altering the metabolic breakdown of glucose to lactic acid. Human cell line studies show that dichloroacetate switches alter the metabolomics of the cancer cell from one of glycolysis to oxidative phosphorylation, and in doing so restore mitochondrial functions that trigger apoptosis of the cancer cell. Reports of dichloroacetate in human subjects are rare. The authors contacted individuals from Internet forums who had reported outstanding anti-cancer responses to self-medication with dichloroacetate. With informed consent, complete medical records were requested to document response to dichloroacetate, emphasizing the context of monotherapy with dichloroacetate. Of ten patients agreeing to such an evaluation, only one met the criteria of having comprehensive clinic records as well as pathology, imaging and laboratory reports, along with single agent therapy with dichloroacetate. That individual is the focus of this report. In this case report of a man with documented relapse after state-of-the-art chemotherapy for non-Hodgkin's lymphoma, a significant response to dichloroacetate is documented with a complete remission, which remains ongoing after 4 years. Dichloroacetate appears to be a novel therapy warranting further investigation in the treatment of cancer.

Activating oxidative phosphorylation by a pyruvate dehydrogenase kinase inhibitor overcomes sorafenib resistance of hepatocellular carcinoma

Background:

Sorafenib is the only drug approved for the treatment of hepatocellular carcinoma (HCC). The bioenergetic propensity of cancer cells has been correlated to anticancer drug resistance, but such correlation is unclear in sorafenib resistance of HCC.

Methods:

Six sorafenib-naive HCC cell lines and one sorafenib-resistant HCC cell line (Huh-7R; derived from sorafenib-sensitive Huh-7) were used. The bioenergetic propensity was calculated by measurement of lactate in the presence or absence of oligomycin. Dichloroacetate (DCA), a pyruvate dehydrogenase kinase (PDK) inhibitor, and siRNA of hexokinase 2 (HK2) were used to target relevant pathways of cancer metabolism. Cell viability, mitochondrial membrane potential, and sub-G1 fraction were measured for in vitro efficacy. Reactive oxygen species (ROS), adenosine triphosphate (ATP) and glucose uptake were also measured. A subcutaneous xenograft mouse model was used for in vivo efficacy.

Results:

The bioenergetic propensity for using glycolysis correlated with decreased sorafenib sensitivity (R²=0.9067, among sorafenib-naive cell lines; P=0.003, compared between Huh-7 and Huh-7 R). DCA reduced lactate production and increased ROS and ATP, indicating activation of oxidative phosphorylation (OXPHOS). DCA markedly sensitised sorafenib-resistant HCC cells to sorafenib-induced apoptosis (sub-G1 (combination vs sorafenib): Hep3B, 65.4±8.4% vs 13±2.9% Huh-7 R, 25.3± 5.7% vs 4.3±1.5% each P<0.0001), whereas siRNA of HK2 did not. Sorafenib (10 mg kg⁻¹ per day) plus DCA (100 mg kg⁻¹ per day) also resulted in superior tumour regression than sorafenib alone in mice (tumour size: −87% vs −36%, P<0.001).

Conclusion:

The bioenergetic propensity is a potentially useful predictive biomarker of sorafenib sensitivity, and activation of OXPHOS by PDK inhibitors may overcome sorafenib resistance of HCC.

FOXO1-mediated upregulation of pyruvate dehydrogenase kinase-4 (PDK4) decreases glucose oxidation and impairs right ventricular function in pulmonary hypertension: therapeutic benefits of dichloroacetate

Pyruvate dehydrogenase kinase (PDK) is activated in right ventricular hypertrophy (RVH), causing an increase in glycolysis relative to glucose oxidation that impairs right ventricular function. The stimulus for PDK upregulation, its isoform specificity, and the long-term effects of PDK inhibition are unknown. We hypothesize that FOXO1-mediated PDK4 upregulation causes bioenergetic impairment and RV dysfunction, which can be reversed by dichloroacetate. Adult male Fawn-Hooded rats (FHR) with pulmonary arterial hypertension (PAH) and right ventricular hypertrophy (RVH; age 6-12 months) were compared to age-matched controls. Glucose oxidation (GO) and fatty acid oxidation (FAO) were measured at baseline and after acute dichloroacetate (1 mM × 40 min) in isolated working hearts and in freshly dispersed RV myocytes. The effects of chronic dichloroacetate (0.75 g/L drinking water for 6 months) on cardiac output (CO) and exercise capacity were measured in vivo. Expression of PDK4 and its regulatory transcription factor, FOXO1, were also measured in FHR and RV specimens from PAH patients (n = 10). Microarray analysis of 168 genes related to glucose or FA metabolism showed >4-fold upregulation of PDK4, aldolase B, and acyl-coenzyme A oxidase. FOXO1 was increased in FHR RV, whereas HIF-1 α was unaltered. PDK4 expression was increased, and the inactivated form of FOXO1 decreased in human PAH RV (P < 0.01). Pyruvate dehydrogenase (PDH) inhibition in RVH increased proton production and reduced GO's contribution to the tricarboxylic acid (TCA) cycle. Acutely, dichloroacetate reduced RV proton production and increased GO's contribution (relative to FAO) to the TCA cycle and ATP production in FHR (P < 0.01). Chronically dichloroacetate decreased PDK4 and FOXO1, thereby activating PDH and increasing GO in FHR. These metabolic changes increased CO (84 ± 14 vs. 69 ± 14 ml/min, P < 0.05) and treadmill-walking distance (239 ± 20 vs. 171 ± 22 m, P < 0.05). Chronic dichloroacetate inhibits FOXO1-induced PDK4 upregulation and restores GO, leading to improved bioenergetics and RV function in RVH.

Profiling metabolic networks to study cancer metabolism

Cancer is a disease of unregulated cell growth and survival, and tumors reprogram biochemical pathways to aid these processes. New capabilities in the computational and bioanalytical characterization of metabolism have now emerged, facilitating the identification of unique metabolic dependencies that arise in specific cancers. By understanding the metabolic phenotype of cancers as a function of their oncogenic profiles, metabolic engineering may be applied to design synthetically lethal therapies for some tumors. This process begins with accurate measurement of metabolic fluxes. Here we review advanced methods of quantifying pathway activity and highlight specific examples where these approaches have uncovered potential opportunities for therapeutic intervention.

Glutathione transferases, regulators of cellular metabolism and physiology

BACKGROUND

The cytosolic glutathione transferases (GSTs) comprise a super family of proteins that can be categorized into multiple classes with a mixture of highly specific and overlapping functions.

SCOPE OF REVIEW

The review covers the genetics, structure and function of the human cytosolic GSTs with particular attention to their emerging roles in cellular metabolism.

MAJOR CONCLUSIONS

All the catalytically active GSTs contribute to the glutathione conjugation or glutathione dependant-biotransformation of xenobiotics and many catalyze glutathione peroxidase or thiol transferase reactions. GSTs also catalyze glutathione dependent isomerization reactions required for the synthesis of several prostaglandins and steroid hormones and the catabolism of tyrosine. An increasing body of work has implicated several GSTs in the regulation of cell signaling pathways mediated by stress-activated kinases like Jun N-terminal kinase. In addition, some members of the cytosolic GST family have been shown to form ion channels in intracellular membranes and to modulate ryanodine receptor Ca(2+) channels in skeletal and cardiac muscle.

GENERAL SIGNIFICANCE

In addition to their well established roles in the conjugation and biotransformation of xenobiotics, GSTs have emerged as significant regulators of pathways determining cell proliferation and survival and as regulators of ryanodine receptors that are essential for muscle function. This article is part of a Special Issue entitled Cellular functions of glutathione.

PDK1 inhibition is a novel therapeutic target in multiple myeloma

BACKGROUND

Cancer cells utilise the glycolytic pathway even when adequate oxygen is present, a phenomenon known as the Warburg effect. We examined whether this system is operative in multiple myeloma (MM) cells and whether glycolysis inhibition is a potential therapeutic modality.

METHODS

The MM cells were purified from 59 patients using CD138-immunomagnetic beads. The expression levels of genes associated with glycolysis, c-MYC, GLUT1, LDHA, HIF1A and pyruvate dehydrogenase kinase-1 (PDK1) were determined by real-time PCR. Glucose consumption and lactate production by MM cell lines were analysed. Oxamate, an LDH inhibitor, and dichloroacetate (DCA), a PDK1 inhibitor, were employed. Inhibition of PDK1 expression was achieved using a siRNA.

RESULTS

High LDHA expression was found to be an indicator of poor prognosis. It was also positively correlated with the expression of PDK1, c-MYC and GLUT1. Greater glucose consumption and lactate production in MM cells was associated with higher LDHA expression. All the glycolysis inhibitors (oxamate, DCA and PDK1 siRNA) induced apoptosis in MM cells. DCA combined with bortezomib showed additive cytotoxic effects.

CONCLUSION

The present data suggest that the Warburg effect is operative in MM cells. As PDK1 is not overexpressed in normal tissues, PDK1 inhibition could serve as a novel therapeutic approach.

Mitochondria in vascular health and disease

The eukaryote's mitochondrial network is perhaps the cell's most sophisticated and dynamic responsive sensing system. Integrating metabolic, oxygen, or danger signals with inputs from other organelles, as well as local and systemic signals, mitochondria have a profound impact on vascular function in both health and disease. This review highlights recently discovered aspects of mitochondrial function (oxygen sensing, inflammation, autophagy, and apoptosis) and discusses their role in diseases of both systemic and pulmonary vessels. We also emphasize the role of mitochondria as therapeutic targets for vascular disease. We highlight the intriguing similarities of mitochondria-driven molecular mechanisms in terms of both pathogenesis and therapies in very diverse diseases, such as atherosclerosis, pulmonary hypertension, and cancer, to support the foundation of a new field in medicine: mitochondrial medicine.

Expression of pyruvate dehydrogenase kinase-1 in gastric cancer as a potential therapeutic target

In contrast to mitochondria in healthy cells, which utilize oxidative phosphorylation, malignant cells undergo elevated glycolysis for energy production using glucose. The objectives of this study were to evaluate whether the expression of various molecules, including pyruvate dehydrogenase kinase-1 (PDK-1), is involved in the altered glucose metabolism associated with gastric cancer prognosis and to assess the role of a therapeutic agent in targeting glucose metabolism in gastric cancer. Immunohistochemistry was performed on gastric cancer tissues obtained from 152 patients who underwent curative resection to assess the expression of hypoxia-inducible factor-1α (HIF-1α), glucose transporter-1 (GLUT-1), hexokinase-2 (HK-2) and PDK-1. In an in vitro analysis, the lactate production and glucose uptake levels, cellular viability and 5-fluorouracil (5-FU) responses were evaluated before and after treatment with dichloroacetate (DCA), a PDK-1 inhibitor, in the MKN45 and AGS gastric cancer cell lines and in the non-cancerous HEK293 cell line. GLUT-1 and PDK-1 expression was significantly associated with tumor progression, although only PDK-1 expression was an independent prognostic factor for patients who received 5-FU adjuvant treatment. There was no significant difference in cell viability between the HEK293 and gastric cancer cell lines following DCA treatment. However, DCA treatment reduced lactate production and increased responsiveness to 5-FU in MKN45 cells, which expressed high levels of PDK-1 in comparison to the other cell lines. Thus, PDK-1 may serve as a biomarker of poor prognosis in patients with gastric cancer. In addition, PDK-1 inhibitors such as DCA may be considered an additional treatment option for patients with PDK-1-expressing gastric cancers.

Metabolism of [U-13 C]glucose in human brain tumors in vivo

Glioblastomas and brain metastases demonstrate avid uptake of 2-[(18) F]fluoro-2-deoxyglucose by positron emission tomography and display perturbations of intracellular metabolite pools by (1) H MRS. These observations suggest that metabolic reprogramming contributes to brain tumor growth in vivo. The Warburg effect, excess metabolism of glucose to lactate in the presence of oxygen, is a hallmark of cancer cells in culture. 2-[(18) F]Fluoro-2-deoxyglucose-positive tumors are assumed to metabolize glucose in a similar manner, with high rates of lactate formation relative to mitochondrial glucose oxidation, but few studies have specifically examined the metabolic fates of glucose in vivo. In particular, the capacity of human brain cancers to oxidize glucose in the tricarboxylic acid cycle is unknown. Here, we studied the metabolism of human brain tumors in situ. [U-(13) C]Glucose (uniformly labeled glucose, i.e. d-glucose labeled with (13) C in all six carbons) was infused during surgical resection, and tumor samples were subsequently subjected to (13) C NMR spectroscopy. The analysis of tumor metabolites revealed lactate production, as expected. We also determined that pyruvate dehydrogenase, turnover of the tricarboxylic acid cycle, anaplerosis and de novo glutamine and glycine synthesis contributed significantly to the ultimate disposition of glucose carbon. Surprisingly, less than 50% of the acetyl-coenzyme A pool was derived from blood-borne glucose, suggesting that additional substrates contribute to tumor bioenergetics. This study illustrates a convenient approach that capitalizes on the high information content of (13) C NMR spectroscopy and enables the analysis of intermediary metabolism in diverse cancers growing in their native microenvironment.

Rapid sequential injections of hyperpolarized [1-¹³C]pyruvate in vivo using a sub-kelvin, multi-sample DNP polarizer

The development of hyperpolarized technology utilizing dynamic nuclear polarization (DNP) has enabled the rapid measurement of (13)C metabolism in vivo with very high SNR. However, with traditional DNP equipment, consecutive injections of a hyperpolarized compound in an animal have been subject to a practical minimum time between injections governed by the polarization build-up time, which is on the order of an hour for [1-(13)C]pyruvate. This has precluded the monitoring of metabolic changes occurring on a faster time scale. In this study, we demonstrated the ability to acquire in vivo dynamic magnetic resonance spectroscopy (MRS) and 3D magnetic resonance spectroscopic imaging (MRSI) data in normal rats with a 5 min interval between injections of hyperpolarized [1-(13)C]pyruvate using a prototype, sub-Kelvin dynamic nuclear polarizer with the capability to simultaneously polarize up to 4 samples and dissolve them in rapid succession. There were minimal perturbations in the hyperpolarized spectra as a result of the multiple injections, suggesting that such an approach would not confound the investigation of metabolism occurring on this time scale. As an initial demonstration of the application of this technology and approach for monitoring rapid changes in metabolism as a result of a physiological intervention, we investigated the pharmacodynamics of the anti-cancer agent dichloroacetate (DCA), collecting hyperpolarized data before administration of DCA, 1 min after administration, and 6 min after administration. Dramatic increases in (13)C-bicarbonate were detected just 1 min (as well as 6 min) after DCA administration.

The emerging paradigm of network medicine in the study of human disease

The molecular pathways that govern human disease consist of molecular circuits that coalesce into complex, overlapping networks. These network pathways are presumably regulated in a coordinated fashion, but such regulation has been difficult to decipher using only reductionistic principles. The emerging paradigm of "network medicine" proposes to utilize insights garnered from network topology (eg, the static position of molecules in relation to their neighbors) as well as network dynamics (eg, the unique flux of information through the network) to understand better the pathogenic behavior of complex molecular interconnections that traditional methods fail to recognize. As methodologies evolve, network medicine has the potential to capture the molecular complexity of human disease while offering computational methods to discern how such complexity controls disease manifestations, prognosis, and therapy. This review introduces the fundamental concepts of network medicine and explores the feasibility and potential impact of network-based methods for predicting individual manifestations of human disease and designing rational therapies. Wherever possible, we emphasize the application of these principles to cardiovascular disease.

The metabolomic signature of malignant glioma reflects accelerated anabolic metabolism

Although considerable progress has been made toward understanding glioblastoma biology through large-scale genetic and protein expression analyses, little is known about the underlying metabolic alterations promoting their aggressive phenotype. We conducted global metabolomic profiling on patient-derived glioma specimens and identified specific metabolic programs differentiating low- and high-grade tumors, with the metabolic signature of glioblastoma reflecting accelerated anabolic metabolism. When coupled with transcriptional profiles, we identified the metabolic phenotype of the mesenchymal subtype to consist of accumulation of the glycolytic intermediate phosphoenolpyruvate and decreased pyruvate kinase activity. Unbiased hierarchical clustering of metabolomic profiles identified three subclasses, which we term energetic, anabolic, and phospholipid catabolism with prognostic relevance. These studies represent the first global metabolomic profiling of glioma, offering a previously undescribed window into their metabolic heterogeneity, and provide the requisite framework for strategies designed to target metabolism in this rapidly fatal malignancy.

Cancer cell metabolism: one hallmark, many faces

Cancer cells must rewire cellular metabolism to satisfy the demands of growth and proliferation. Although many of the metabolic alterations are largely similar to those in normal proliferating cells, they are aberrantly driven in cancer by a combination of genetic lesions and nongenetic factors such as the tumor microenvironment. However, a single model of altered tumor metabolism does not describe the sum of metabolic changes that can support cell growth. Instead, the diversity of such changes within the metabolic program of a cancer cell can dictate by what means proliferative rewiring is driven, and can also impart heterogeneity in the metabolic dependencies of the cell. A better understanding of this heterogeneity may enable the development and optimization of therapeutic strategies that target tumor metabolism.

Knockdown of lactate dehydrogenase A suppresses tumor growth and metastasis of human hepatocellular carcinoma

In previous studies, lactate dehydrogenase A (LDHA) was identified as one of the leading genes that promote the proliferative and tumorigenic potential of malignancies. However, less definitive evidence was reported in hepatocellular carcinoma (HCC) cells. Furthermore, the role of LDHA in promoting metastasis of HCC, and its possible mechanism, is not clear. In this study, RNA interference (RNAi) mediated by lentiviral vectors (which induce strong down-regulation of gene expression) was used to analyze the role of LDHA in tumor growth and metastasis in HCC. We performed transient and stable RNAi knockdowns of LDHA in HCCLM3 cells, a line that over-expresses LDHA and has a high metastatic potential. Our studies reveal that previously unidentified effects of LHDA may mediate tumor growth and metastasic effects in HCC. First, HCC cell lines over-express LDHA. Second, LDHA inhibition results in increased apoptosis via production of reactive oxygen species in HCCLM3 cells. Thus, LDHA knockdown resulted in significant reduction in metastatic potential in a xenograft mouse model. Furthermore, we found that FAK, MMP-2, VEGF and E-cadherin proteins contribute to inhibitory effects on metastasis in HCC cells. These studies have important implications for understanding the mechanisms by which LDHA promotes tumor growth and metastasis.

Overexpression of pyruvate dehydrogenase kinase 1 and lactate dehydrogenase A in nerve cells confers resistance to amyloid β and other toxins by decreasing mitochondrial respiration and reactive oxygen species production

We previously demonstrated that nerve cell lines selected for resistance to amyloid β (Aβ) peptide exhibit elevated aerobic glycolysis in part due to increased expression of pyruvate dehydrogenase kinase 1 (PDK1) and lactate dehydrogenase A (LDHA). Here, we show that overexpression of either PDK1 or LDHA in a rat CNS cell line (B12) confers resistance to Aβ and other neurotoxins. Treatment of Aβ-sensitive cells with various toxins resulted in mitochondrial hyperpolarization, immediately followed by rapid depolarization and cell death, events accompanied by increased production of cellular reactive oxygen species (ROS). In contrast, cells expressing either PDK1 or LDHA maintained a lower mitochondrial membrane potential and decreased ROS production with or without exposure to toxins. Additionally, PDK1- and LDHA-overexpressing cells exhibited decreased oxygen consumption but maintained levels of ATP under both normal culture conditions and following Aβ treatment. Interestingly, immunoblot analysis of wild type mouse primary cortical neurons treated with Aβ or cortical tissue extracts from 12-month-old APPswe/PS1dE9 transgenic mice showed decreased expression of LDHA and PDK1 when compared with controls. Additionally, post-mortem brain extracts from patients with Alzheimer disease exhibited a decrease in PDK1 expression compared with nondemented patients. Collectively, these findings indicate that key Warburg effect enzymes play a central role in mediating neuronal resistance to Αβ or other neurotoxins by decreasing mitochondrial activity and subsequent ROS production. Maintenance of PDK1 or LDHA expression in certain regions of the brain may explain why some individuals tolerate high levels of Aβ deposition without developing Alzheimer disease.

A microRNA Link to Glioblastoma Heterogeneity

Glioblastomas (GBM) are one of the most malignant adult primary brain tumors. Through decades of research using various model systems and GBM patients, we have gained considerable insights into the mechanisms regulating GBM pathogenesis, but have mostly failed to significantly improve clinical outcome. For the most part GBM heterogeneity is responsible for this lack of progress. Here, we have discussed sources of cellular and microenvironmental heterogeneity in GBMs and their potential regulation through microRNA mediated mechanisms. We have focused on the role of individual microRNAs (miRNA) through their specific targets and miRNA mediated RNA-RNA interaction networks with the potential to influence various aspects of GBM heterogeneity including tumor neo-vascularization. We believe a better understanding of such mechanisms for regulation of GBM pathogenesis will be instrumental for future therapeutic options.

Anticancer agents that counteract tumor glycolysis

Can we consider cancer to be a "metabolic disease"? Tumors are the result of a metabolic selection, forming tissues composed of heterogeneous cells that generally express an overactive metabolism as a common feature. In fact, cancer cells have increased needs for both energy and biosynthetic intermediates to support their growth and invasiveness. However, their high proliferation rate often generates regions that are insufficiently oxygenated. Therefore, their carbohydrate metabolism must rely mostly on a glycolytic process that is uncoupled from oxidative phosphorylation. This metabolic switch, also known as the Warburg effect, constitutes a fundamental adaptation of tumor cells to a relatively hostile environment, and supports the evolution of aggressive and metastatic phenotypes. As a result, tumor glycolysis may constitute an attractive target for cancer therapy. This approach has often raised concerns that antiglycolytic agents may cause serious side effects toward normal cells. The key to selective action against cancer cells can be found in their hyperbolic addiction to glycolysis, which may be exploited to generate new anticancer drugs with minimal toxicity. There is growing evidence to support many glycolytic enzymes and transporters as suitable candidate targets for cancer therapy. Herein we review some of the most relevant antiglycolytic agents that have been investigated thus far for the treatment of cancer.

Use of hyperpolarized [1-13C]pyruvate and [2-13C]pyruvate to probe the effects of the anticancer agent dichloroacetate on mitochondrial metabolism in vivo in the normal rat

Development of hyperpolarized technology utilizing dynamic nuclear polarization has enabled the measurement of (13)C metabolism in vivo at very high signal-to-noise ratio (SNR). In vivo mitochondrial metabolism can, in principle, be monitored with pyruvate, which is catalyzed to acetyl-CoA via pyruvate dehydrogenase (PDH). The purpose of this work was to determine whether the compound sodium dichloroacetate (DCA) could aid the study of mitochondrial metabolism with hyperpolarized pyruvate. DCA stimulates PDH by inhibiting its inhibitor, pyruvate dehydrogenase kinase. In this work, hyperpolarized [1-(13)C]pyruvate and [2-(13)C]pyruvate were used to probe mitochondrial metabolism in normal rats. Increased conversion to bicarbonate (+181±69%, P=.025) was measured when [1-(13)C]pyruvate was injected after DCA administration, and increased glutamate (+74±23%, P=.004), acetoacetate (+504±281%, P=.009) and acetylcarnitine (+377±157%, P=.003) were detected when [2-(13)C]pyruvate was used.