Therapeutic targets in cancer cell metabolism and autophagy

The metabolism of cancer cells is reprogrammed both by oncogene signaling and by dysregulation of metabolic enzymes. The resulting altered metabolism supports cellular proliferation and survival but leaves cancer cells dependent on a continuous supply of nutrients. Thus, many metabolic enzymes have become targets for new cancer therapies. Recently, two processes—expression of specific isoforms of metabolic enzymes and autophagy—have been shown to be crucial for the adaptation of tumor cells to changes in nutrient availability. An increasing number of approved and experimental therapeutics target these two processes. A better understanding of the molecular basis of cancer-associated metabolic changes may lead to improved cancer therapies.

Comparison of spheroids formed by rat glioma stem cells and neural stem cells reveals differences in glucose metabolism and promising therapeutic applications

Cancer stem cells (CSCs) are thought to be partially responsible for cancer resistance to current therapies and tumor recurrence. Dichloroacetate (DCA), a compound capable of shifting metabolism from glycolysis to glucose oxidation, via an inhibition of pyruvate dehydrogenase kinase was used. We show that DCA is able to shift the pyruvate metabolism in rat glioma CSCs but has no effect in rat neural stem cells. DCA forces CSCs into oxidative phosphorylation but does not trigger the production of reactive oxygen species and consecutive anti-cancer apoptosis. However, DCA, associated with etoposide or irradiation, induced a Bax-dependent apoptosis in CSCs in vitro and decreased their proliferation in vivo. The former phenomenon is related to DCA-induced Foxo3 and p53 expression, resulting in the overexpression of BH3-only proteins (Bad, Noxa, and Puma), which in turn facilitates Bax-dependent apoptosis. Our results demonstrate that a small drug available for clinical studies potentiates the induction of apoptosis in glioma CSCs.

Normal and cancer cell metabolism: lymphocytes and lymphoma

Recent studies of normal and neoplastic lymphocytes have revealed overlapping metabolic rewiring in activated T cells and Myc-transformed lymphocytes. Myc expression is attenuated in normal lymphocytes that return to the basal state, but Notch-activated or Myc-transformed lymphocytes persistently express Myc, which activates genes involved in glucose and glutamine metabolism. Although this difference could provide a therapeutic window for the treatment of cancers, the overlapping metabolic profiles suggest a potential for immunosuppression by metabolic inhibitors.

Novel molecular mechanisms of antitumor action of dichloroacetate against T cell lymphoma: Implication of altered glucose metabolism, pH homeostasis and cell survival regulation

Pyruvate dehydrogenase kinase (PDK) inhibits pyruvate dehydrogenase (PDH) activity and thus promotes energetic switch from mitochondrial glucose oxidation to cytoplasmic glycolysis in cancerous cells (a phenomenon known as the 'Warburg effect') for their energy need, which facilitates the cancer progression by resisting induction of apoptosis and promoting tumor metastasis. Thus, in the present investigation, we explored the molecular mechanisms of the tumoricidal action of dichloroacetate (DCA), a pyruvate dehydrogenase kinase inhibitor, on cells of a murine T cell lymphoma, designated as Dalton's lymphoma (DL). In vitro treatment of tumor cells with DCA inhibited their survival accompanied by a modulation of the biophysical composition of tumor-conditioned medium with respect to pH, glucose and lactate. DCA treatment also altered expression of HIF1-α and pH regulators: VATPase and MCT1 and production of cytokines: IL-10, IL-6 and IFN-γ. Moreover, we also observed an alteration in the expression of other apoptosis and cell survival regulatory molecules: PUMA, GLUT1, Bcl2, p53, CAD, caspase-3 and HSP70. The study discusses the role of novel molecular mechanisms underlying DCA-dependent inhibition of tumor cell survival. This study shows for the first time that DCA-dependent alteration of tumor cell survival involves altered pH homeostasis and glucose metabolism. Thus, these findings will provide a new insight for therapeutic applications of DCA as a novel antineoplastic agent against T cell lymphoma.

Analysis of tumor metabolism reveals mitochondrial glucose oxidation in genetically diverse human glioblastomas in the mouse brain in vivo

Dysregulated metabolism is a hallmark of cancer cell lines, but little is known about the fate of glucose and other nutrients in tumors growing in their native microenvironment. To study tumor metabolism in vivo, we used an orthotopic mouse model of primary human glioblastoma (GBM). We infused (13)C-labeled nutrients into mice bearing three independent GBM lines, each with a distinct set of mutations. All three lines displayed glycolysis, as expected for aggressive tumors. They also displayed unexpected metabolic complexity, oxidizing glucose via pyruvate dehydrogenase and the citric acid cycle, and using glucose to supply anaplerosis and other biosynthetic activities. Comparing the tumors to surrounding brain revealed obvious metabolic differences, notably the accumulation of a large glutamine pool within the tumors. Many of these same activities were conserved in cells cultured ex vivo from the tumors. Thus GBM cells utilize mitochondrial glucose oxidation during aggressive tumor growth in vivo.

HOT models in flux: mitochondrial glucose oxidation fuels glioblastoma growth

Cancer cells in culture obtain ATP and biosynthetic precursors primarily by aerobic glycolysis, not by mitochondrial glucose oxidation. In this issue of Cell Metabolism, Marin-Valencia et al. (2012) demonstrate that glioblastoma, an aggressive and, in culture, highly glycolytic cancer, primarily uses glucose oxidation to meet energetic and biosynthetic demands in vivo.

The pyruvate dehydrogenase complex as a therapeutic target for age-related diseases

Considerable research has been conducted on mitochondrial biology as it pertains to aging. However, relatively little attention has been accorded the pyruvate dehydrogenase complex (PDC) relative to how we grow old and acquire age-related diseases. The purpose of this review is threefold: first, to describe the physiological chemistry of the PDC and define its place in normal cellular bioenergetics; second, to compare and contrast the pathogenesis and clinical features of congenital PDC deficiency with discrete examples of age-associated dysfunction of the complex; and third, to summarize recent findings in Caenorhabditis elegans that shed additional new light on the significance of the PDC to the aging process.

Mitochondrial activation by inhibition of PDKII suppresses HIF1a signaling and angiogenesis in cancer

Most solid tumors are characterized by a metabolic shift from glucose oxidation to glycolysis, in part due to actively suppressed mitochondrial function, a state that favors resistance to apoptosis. Suppressed mitochondrial function may also contribute to the activation of hypoxia-inducible factor 1α (HIF1α) and angiogenesis. We have previously shown that the inhibitor of pyruvate dehydrogenase kinase (PDK) dichloroacetate (DCA) activates glucose oxidation and induces apoptosis in cancer cells in vitro and in vivo. We hypothesized that DCA will also reverse the 'pseudohypoxic' mitochondrial signals that lead to HIF1α activation in cancer, even in the absence of hypoxia and inhibit cancer angiogenesis. We show that inhibition of PDKII inhibits HIF1α in cancer cells using several techniques, including HIF1α luciferase reporter assays. Using pharmacologic and molecular approaches that suppress the prolyl-hydroxylase (PHD)-mediated inhibition of HIF1α, we show that DCA inhibits HIF1α by both a PHD-dependent mechanism (that involves a DCA-induced increase in the production of mitochondria-derived α-ketoglutarate) and a PHD-independent mechanism, involving activation of p53 via mitochondrial-derived H(2)O(2), as well as activation of GSK3β. Effective inhibition of HIF1α is shown by a decrease in the expression of several HIF1α regulated gene products as well as inhibition of angiogenesis in vitro in matrigel assays. More importantly, in rat xenotransplant models of non-small cell lung cancer and breast cancer, we show effective inhibition of angiogenesis and tumor perfusion in vivo, assessed by contrast-enhanced ultrasonography, nuclear imaging techniques and histology. This work suggests that mitochondria-targeting metabolic modulators that increase pyruvate dehydrogenase activity, in addition to the recently described pro-apoptotic and anti-proliferative effects, suppress angiogenesis as well, normalizing the pseudo-hypoxic signals that lead to normoxic HIF1α activation in solid tumors.

The molecular basis for novel therapies

The era of targeted therapy for glioblastoma has arrived, but results have been modest thus far. This review highlights the challenges inherent to treating glioblastoma with targeted therapy and delves into the complex signaling networks that form the molecular basis of novel therapies. Past failures, current challenges, and future possibilities are discussed in the context of the classic "oncogenic" signaling network, as well as the "nononcogenic" stress response network.

From tumor cell metabolism to tumor immune escape

Tumorigenesis implies adaptation of tumor cells to an adverse environment. First, developing tumors must acquire nutrients to ensure their rapid growth. Second, they must escape the attack from the host immune system. Recent studies suggest that these phenomena could be related and that tumor cell metabolism may propel tumor immune escape. Tumor cell metabolism tends to avoid mitochondrial activity and oxidative phosphorylation (OXPHOS), and largely relies on glycolysis to produce energy. This specific metabolism helps tumor cells to avoid the immune attack from the host by blocking or avoiding the immune attack. By changing their metabolism, tumor cells produce or sequester a variety of amino acids, lipids and chemical compounds that directly alter immune function therefore promoting immune evasion. A second group of metabolism-related modification targets the major histocompatibility complex-I (MHC-I) and related molecules. Tumor MHC-I presents tumor-associated antigens (TAAs) to cytotoxic T-cells (CTLs) and hence, sensitizes cancer cells to the cytolytic actions of the anti-tumor adaptive immune response. Blocking tumor mitochondrial activity decreases expression of MHC-I molecules at the tumor cell surface. And peroxynitrite (PNT), produced by tumor-infiltrating myeloid cells, chemically modifies MHC-I avoiding TAA expression in the plasma membrane. These evidences on the role of tumor cell metabolism on tumor immune escape open the possibility of combining drugs designed to control tumor cell metabolism with new procedures of anti-tumor immunotherapy. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Mitochondria-targeted drugs synergize with 2-deoxyglucose to trigger breast cancer cell death

Cancer cells are long known to exhibit increased aerobic glycolysis, but glycolytic inhibition has not offered a viable chemotherapeutic strategy in part because of the systemic toxicity of antiglycolytic agents. However, recent studies suggest that a combined inhibition of glycolysis and mitochondrial function may help overcome this issue. In this study, we investigated the chemotherapeutic efficacies of mitochondria-targeted drugs (MTD) in combination with 2-deoxy-d-glucose (2-DG), a compound that inhibits glycolysis. Using the MTDs, termed Mito-CP and Mito-Q, we evaluated relative cytotoxic effects and mitochondrial bioenergetic changes in vitro. Interestingly, both Mito-CP and Mito-Q synergized with 2-DG to decrease ATP levels in two cell lines. However, with time, the cellular bioenergetic function and clonogenic survival were largely restored in some cells. In a xenograft model of human breast cancer, combined treatment of Mito-CP and 2-DG led to significant tumor regression in the absence of significant morphologic changes in kidney, liver, or heart. Collectively, our findings suggest that dual targeting of mitochondrial bioenergetic metabolism with MTDs and glycolytic inhibitors such as 2-DG may offer a promising chemotherapeutic strategy.

Necrosis of cervical carcinoma by dichloroacetate released from electrospun polylactide mats

It is still a great challenge to apply therapeutic concentration of anti-cancer drugs to the tumor site with low system toxicity. An in situ administration strategy was applied to reverse the aerobic glycolysis of tumor in vivo for the first time. Controlled release of therapeutic concentration of dichloroacetate (DCA) from polylactide (PLA) electrospun mats covering the solid tumor locally was designed to suppress the cervical carcinoma in vivo. A dramatic decrease in the volume and weight of tumors was observed for 19 days in tumor-bearing mice, and a totally 96% of the tumor suppression degree was obtained even the initial tumor volume was around 200 mm(3). Half of the mice recovered in less than 3 weeks. Necrosis was examined rather than apoptosis on the tumor cells as the main process of cell death induced by the DCA-loaded electrospun mats. A proposed necroptosis mechanism was presented to explain the signal pathways that were induced by the metabolic remodeling of DCA. It provided support for this strategy that target the bio-energy metabolism of the cervical carcinoma locally is a quick and effective pathway to cure the advanced-carcinoma of cervical.

Flow cytometric evaluation of the effects of 3-bromopyruvate (3BP) and dichloracetate (DCA) on THP-1 cells: a multiparameter analysis

Two human leukemia cells K562 and THP-1, the breast cancer lines MCF-7 and ZR-75-1, and the melanoma line MDA-MB-435S were compared by flowcytometry for their behaviour at increasing levels of 3BP. K562 and THP-1 responded to 3BP by membrane depolarization and increased ROS; MCF-7 and ZR-75-1 showed decreased polarization and low ROS increase; MDA-MB-435S had limited depolarization and no ROS increase. THP-1 cells exposed to a range of 3BP concentrations in combination with DCA showed increase of polarization, slight ROS increase, and weakened nuclear integrity. 3BP and DCA show no synergism, but have complementary destructive effects on THP-1 cells. The data led to the conclusion that the THP-1 cells do not carry a functional membrane monocarboxylate transporter (MCT) or that 3BP circumvents MCT binding and can enter these cells independently.

Pyruvate kinase M2-specific siRNA induces apoptosis and tumor regression

Knockdown of pyruvate kinase M2 induces apoptosis and tumor regression of multiple cancer types.

The development of cancer-specific therapeutics has been limited because most healthy cells and cancer cells depend on common pathways. Pyruvate kinase (PK) exists in M1 (PKM1) and M2 (PKM2) isoforms. PKM2, whose expression in cancer cells results in aerobic glycolysis and is suggested to bestow a selective growth advantage, is a promising target. Because many oncogenes impart a common alteration in cell metabolism, inhibition of the M2 isoform might be of broad applicability. We show that several small interfering (si) RNAs designed to target mismatches between the M2 and M1 isoforms confer specific knockdown of the former, resulting in decreased viability and increased apoptosis in multiple cancer cell lines but less so in normal fibroblasts or endothelial cells. In vivo delivery of siPKM2 additionally causes substantial tumor regression of established xenografts. Our results suggest that the inherent nucleotide-level specificity of siRNA can be harnessed to develop therapeutics that target isoform-specific exons in genes exhibiting differential splicing patterns in various cell types.

Metabolomics of human cerebrospinal fluid identifies signatures of malignant glioma

Cerebrospinal fluid is routinely collected for the diagnosis and monitoring of patients with neurological malignancies. However, little is known as to how its constituents may change in a patient when presented with a malignant glioma. Here, we used a targeted mass-spectrometry based metabolomics platform using selected reaction monitoring with positive/negative switching and profiled the relative levels of over 124 polar metabolites present in patient cerebrospinal fluid. We analyzed the metabolic profiles from 10 patients presenting malignant gliomas and seven control patients that did not present malignancy to test whether a small sample size could provide statistically significant signatures. We carried out multiple unbiased forms of classification using a series of unsupervised techniques and identified metabolic signatures that distinguish malignant glioma patients from the control patients. One subtype identified contained metabolites enriched in citric acid cycle components. Newly diagnosed patients segregated into a different subtype and exhibited low levels of metabolites involved in tryptophan metabolism, which may indicate the absence of an inflammatory signature. Together our results provide the first global assessment of the polar metabolic composition in cerebrospinal fluid that accompanies malignancy, and demonstrate that data obtained from high throughput mass spectrometry technology may have suitable predictive capabilities for the identification of biomarkers and classification of neurological diseases.

Cancer metabolism: current perspectives and future directions

Cellular metabolism influences life and death decisions. An emerging theme in cancer biology is that metabolic regulation is intricately linked to cancer progression. In part, this is due to the fact that proliferation is tightly regulated by availability of nutrients. Mitogenic signals promote nutrient uptake and synthesis of DNA, RNA, proteins and lipids. Therefore, it seems straight-forward that oncogenes, that often promote proliferation, also promote metabolic changes. In this review we summarize our current understanding of how 'metabolic transformation' is linked to oncogenic transformation, and why inhibition of metabolism may prove a cancer's 'Achilles' heel'. On one hand, mutation of metabolic enzymes and metabolic stress sensors confers synthetic lethality with inhibitors of metabolism. On the other hand, hyperactivation of oncogenic pathways makes tumors more susceptible to metabolic inhibition. Conversely, an adequate nutrient supply and active metabolism regulates Bcl-2 family proteins and inhibits susceptibility to apoptosis. Here, we provide an overview of the metabolic pathways that represent anti-cancer targets and the cell death pathways engaged by metabolic inhibitors. Additionally, we will detail the similarities between metabolism of cancer cells and metabolism of proliferating cells.

Metabolic reprogramming of the tumor

Cancer is classically considered as a genetic and, more recently, epigenetic multistep disease. Despite seminal studies in the 1920s by Warburg showing a characteristic metabolic pattern for tumors, cancer bioenergetics has often been relegated to the backwaters of cancer biology. This review aims to provide a historical account on cancer metabolism research, and to try to integrate and systematize the metabolic strategies in which cancer cells engage to overcome selective pressures during their inception and evolution. Implications of this renovated view on some common concepts and in therapeutics are also discussed.

Cotreatment with dichloroacetate and omeprazole exhibits a synergistic antiproliferative effect on malignant tumors

It has been reported that treating cancer cells with dichloroacetate (DCA), an approved treatment for congenital lactic acidosis, reverses the Warburg effect and inhibits tumor growth). Furthermore, omeprazole (OMP) is a well-known agent that enhances the effects of anticancer drugs. The aim of this study was to find clinically-used drugs that enhance the effects of DCA. The combination of DCA and OMP exhibited a more potent antitumor activity than DCA alone in HT1080 fibrosarcoma cells and RKO colon cancer cells, while the drugs did not affect the proliferation of WI-38 human fibroblasts. The inhibitory effect of DCA combined with OMP was reversed with vitamin E and Z-VAD-FMK; therefore conventional caspase-dependent cell growth inhibition through superoxide production was suggested as the mechanism for inhibition. The combination of these drugs also had an effect on HT1080 fibrosarcoma cells inoculated into mice. Since OMP and DCA may be administered orally and have been used clinically for several years without major side effects, we believe that this combination therapy could be readily translated to treat malignant tumors.

Dichloroacetate Induces Different Rates of Cell Death in Cancer and Noncancer Cell Lines in Vitro

Aims and Background

The pyruvate mimetic dichloroacetate (DCA) has been shown to induce cell death in cancer cells. A number of studies in vitro and in vivo have suggested this molecule may serve as an anticancer agent, but some cells are resistant. Here we wanted to examine the effects of DCA on cancerous and noncancerous cells grown in culture for a prolonged period of exposure and at increasing concentrations.

Methods

Six cancer cell lines (A549, SK-HEP-1, HCT116, UPCI:SCC070, HeLa and MES-SA) and three noncancerous lines (RPE, GM03349B and HEK293) were exposed to 0.5 mM DCA for seven days and cell counts were taken every day to determine viability and cell cycle progression. The same cell lines were also exposed to higher doses of DCA up to 10 mM and viability was scored.

Results

Five cancer cell lines showed high levels of cell death early in the trial, but three of the lines showed a second delayed increase in cell death at later stages. HCT116 cells were unaffected by 0.5 mM DCA. GM03349B and RPE cells also died when treated with DCA. At high concentrations, all cell lines exhibited high rates of death. No specific cell cycle arrest of the cells was observed.

Conclusion

We found that there is considerable difference in the way cancer cells are affected by DCA. Some have populations that are highly resistant to treatment, while others have stronger rates of death only after prolonged exposure. We also found noncancerous cells are not all resistant to DCA, a significant finding that has not previously been observed in other in vitro DCA trials.

A personalized life: biomarker monitoring from cradle to grave

Considering the holy grail of future medical treatment being personalized medicines, biomarker research will become more and more the focus for attention not only to develop new medical treatment regimes, based on changes in biomarker patterns, but also for nutritional advice to guarantee a lifelong optimized health condition. The current review gives an outline of how personalized medicine can become established for actual medical treatment using new biomarker concepts. Starting from the development of biomarker research using mainly immunological techniques, the review gives an overview about biomarkers of prediction evolved and focuses on new methodology for the identification of biomarkers using hyphenated analytical techniques like metabolomics and lipidomics. The actual use of multivariate statistical methods in combination with metabolomics and lipidomics is discussed not only for medical treatment but also for precautionary risk identification in human biomonitoring studies.

Targeting the metabolic microenvironment of tumors

The observation of aerobic glycolysis by tumor cells in 1924 by Otto Warburg, and subsequent innovation of imaging glucose uptake by tumors in patients with PET-CT, has incited a renewed interest in the altered metabolism of tumors. As tumors grow in situ, a fraction of it is further away from their blood supply, leading to decreased oxygen concentrations (hypoxia), which induces the hypoxia response pathways of HIF1α, mTOR, and UPR. In normal tissues, these responses mitigate hypoxic stress and induce neoangiogenesis. In tumors, these pathways are dysregulated and lead to decreased perfusion and exacerbation of hypoxia as a result of immature and chaotic blood vessels. Hypoxia selects for a glycolytic phenotype and resultant acidification of the tumor microenvironment, facilitated by upregulation of proton transporters. Acidification selects for enhanced metastatic potential and reduced drug efficacy through ion trapping. In this review, we provide a comprehensive summary of preclinical and clinical drugs under development for targeting aerobic glycolysis, acidosis, hypoxia and hypoxia response pathways. Hypoxia and acidosis can be manipulated, providing further therapeutic benefit for cancers that feature these common phenotypes.

A mathematical model for the glucose-lactate metabolism of in vitro cancer cells

We propose a mathematical model of tumor cell nutrient uptake governed by the presence of two key biomolecular fuels: glucose and lactate. The model allows us to describe, in a remarkably simple way, different in vitro scenarios previously reported in experiments of tumor cell metabolism using distinct energy sources. The predictions of our model show good agreement with all the examined tumor cell lines (cervix, colon, and glioma) and provide a first step toward the development of more comprehensive frameworks accounting for in vivo cancer dynamics under complex spatial heterogeneities.

Mitochondria as therapeutic targets for the treatment of malignant disease

SIGNIFICANCE

Mitochondria exert vital functions during normal physiology and are also centrally involved in the regulation of various modes of cell death. Thus, engaging the mitochondrial apoptosis pathway presents an attractive possibility to activate lethal effectors in cancer cells.

RECENT ADVANCES

Compounds that directly target mitochondria offer the advantage to initiate mitochondrial outer membrane permeabilization independently of upstream signal transduction elements that are frequently impaired in human cancers. As a consequence, mitochondrion-targeted agents may bypass some forms of drug resistance.

CRITICAL ISSUES

An ever-increasing number of compounds, including natural compounds and rationally designed drugs, has been shown to directly act on mitochondria.

FUTURE DIRECTIONS

Forthcoming insights into the fine regulation of mitochondrial apoptosis will likely open future perspectives for cancer drug development.

Regulation of mitochondrial function by voltage dependent anion channels in ethanol metabolism and the Warburg effect

Voltage dependent anion channels (VDAC) are highly conserved proteins that are responsible for permeability of the mitochondrial outer membrane to hydrophilic metabolites like ATP, ADP and respiratory substrates. Although previously assumed to remain open, VDAC closure is emerging as an important mechanism for regulation of global mitochondrial metabolism in apoptotic cells and also in cells that are not dying. During hepatic ethanol oxidation to acetaldehyde, VDAC closure suppresses exchange of mitochondrial metabolites, resulting in inhibition of ureagenesis. In vivo, VDAC closure after ethanol occurs coordinately with mitochondrial uncoupling. Since acetaldehyde passes through membranes independently of channels and transporters, VDAC closure and uncoupling together foster selective and more rapid oxidative metabolism of toxic acetaldehyde to nontoxic acetate by mitochondrial aldehyde dehydrogenase. In single reconstituted VDAC, tubulin decreases VDAC conductance, and in HepG2 hepatoma cells, free tubulin negatively modulates mitochondrial membrane potential, an effect enhanced by protein kinase A. Tubulin-dependent closure of VDAC in cancer cells contributes to suppression of mitochondrial metabolism and may underlie the Warburg phenomenon of aerobic glycolysis. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism.

Metabolic targeting of lactate efflux by malignant glioma inhibits invasiveness and induces necrosis: an in vivo study

Glioblastoma multiforme (GBM) are the most malignant among brain tumors. They are frequently refractory to chemotherapy and radiotherapy with mean patient survival of approximately 6 months, despite surgical intervention. The highly glycolytic nature of glioblastomas describes their propensity to metabolize glucose to lactic acid at an elevated rate. To survive, GBMs efflux lactic acid to the tumor microenvironment through transmembrane transporters denoted monocarboxylate transporters (MCTs). We hypothesized that inhibition of MCT function would impair the glycolytic metabolism and affect both glioma invasiveness and survival. We examined the effect on invasiveness with α-cyano-4-hydroxy-cinnamic acid (ACCA, 4CIN, CHCA), a small-molecule inhibitor of lactate transport, through Matrigel-based and organotypic (brain) slice culture invasive assays using U87-MG and U251-MG glioma cells. We then conducted studies in immunodeficient rats by stereotaxic intracranial implantation of the glioma cells followed by programmed orthotopic application of ACCA through osmotic pumps. Effect on the implanted tumor was monitored by small-animal magnetic resonance imaging. Our assays indicated that glioma invasion was markedly impaired when lactate efflux was inhibited. Convection-enhanced delivery of inhibitor to the tumor bed caused tumor necrosis, with 50% of the animals surviving beyond the experimental end points (3 months after inhibitor exhaustion). Most importantly, control animals did not display any adverse neurologic effects during orthotopic administration of ACCA to brain through programmed delivery. These results indicate the clinical potential of targeting lactate efflux in glioma through delivery of small-molecule inhibitors of MCTs either to the tumor bed or to the postsurgical resection cavity.

Targeting metabolism with arsenic trioxide and dichloroacetate in breast cancer cells

BACKGROUND

Cancer cells have a different metabolic profile compared to normal cells. The Warburg effect (increased aerobic glycolysis) and glutaminolysis (increased mitochondrial activity from glutamine catabolism) are well known hallmarks of cancer and are accompanied by increased lactate production, hyperpolarized mitochondrial membrane and increased production of reactive oxygen species.

METHODS

In this study we target the Warburg effect with dichloroacetate (DCA) and the increased mitochondrial activity of glutaminolysis with arsenic trioxide (ATO) in breast cancer cells, measuring cell proliferation, cell death and mitochondrial characteristics.

RESULTS

The combination of DCA and ATO was more effective at inhibiting cell proliferation and inducing cell death than either drug alone. We examined the effect of these treatments on mitochondrial membrane potential, reactive oxygen species production and ATP levels and have identified new molecular mechanisms within the mitochondria for both ATO and DCA: ATO reduces mitochondrial function through the inhibition of cytochrome C oxidase (complex IV of the electron transport chain) while DCA up-regulates ATP synthase β subunit expression. The potentiation of ATO cytotoxicity by DCA is correlated with strong suppression of the expression of c-Myc and HIF-1α, and decreased expression of the survival protein Bcl-2.

CONCLUSION

This study is the first to demonstrate that targeting two key metabolic hallmarks of cancer is an effective anti-cancer strategy with therapeutic potential.

RNAi screening in glioma stem-like cells identifies PFKFB4 as a key molecule important for cancer cell survival

The concept of cancer stem-like cells (CSCs) has gained considerable attention in various solid tumors including glioblastoma, the most common primary brain tumor. This sub-population of tumor cells has been intensively investigated and their role in therapy resistance as well as tumor recurrence has been demonstrated. In that respect, development of therapeutic strategies that target CSCs (and possibly also the tumor bulk) appears a promising approach in patients suffering from primary brain tumors. In the present study, we utilized RNA interference (RNAi) to screen the complete human kinome and phosphatome (682 and 180 targets, respectively) in order to identify genes and pathways relevant for the survival of brain CSCs and thereby potential therapeutical targets for glioblastoma. We report of 46 putative candidates including known survival-related kinases and phosphatases. Interestingly, a number of genes identified are involved in metabolism, especially glycolysis, such as PDK1 and PKM2 and, most prominently PFKFB4. In vitro studies confirmed an essential role of PFKFB4 in the maintenance of brain CSCs. Furthermore, high PFKFB4 expression was associated with shorter survival of primary glioblastoma patients. Our findings support the importance of the glycolytic pathway in the maintenance of malignant glioma cells and brain CSCs and imply tumor metabolism as a promising therapeutic target in glioblastoma.

Prenatal and postnatal expression of glutathione transferase ζ 1 in human liver and the roles of haplotype and subject age in determining activity with dichloroacetate

Glutathione transferase ζ 1 (GSTZ1), also known as maleylacetoacetate isomerase, catalyzes the penultimate step of tyrosine catabolism and metabolizes several α-halocarboxylic acids, including dichloroacetic acid (DCA), an investigational drug used for lactic acidosis and, recently, solid tumors. Age-related differences have been suggested in DCA pharmacotoxicology, but no information is available on GSTZ1 ontogeny in humans. Here, we investigated the cytosolic GSTZ1 developmental expression pattern and the influence of haplotype on GSTZ1 activity with DCA by using human livers from donors between 10 weeks gestation and 74 years. GSTZ1 expression was very low in fetal livers (<2 pmol of GSTZ1/mg cytosol). The expression began to increase after birth in an age-dependent manner until age 7 years. GSTZ1 was then sustained at stable, yet variable, levels (median, 20.0 pmol/mg cytosol; range, 4.8-47.3 pmol/mg cytosol) until age 74 years. GSTZ1 activity with DCA was strongly associated with haplotype and expression level. Samples homozygous or heterozygous for GSTZ1A exhibited ∼3-fold higher DCA dechlorinating activity than samples carrying other alleles at a given level of expression. The correlations (r²) between activity and expression were 0.90 and 0.68, respectively, for GSTZ1A carriers (n = 11) and noncarriers (n = 61). GSTZ1 is expressed in mitochondria in addition to cytosol. The GSTZ1A allele exhibited similar effects in the mitochondrial fraction by conferring a higher activity with DCA. In summary, we report a neonatal onset and an age-related increase in GSTZ1 protein expression during human liver development. Haplotype influenced GSTZ1 activity with DCA but not protein expression.

The role of Nogo and the mitochondria-endoplasmic reticulum unit in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is caused by excessive proliferation of vascular cells, which occlude the lumen of pulmonary arteries (PAs) and lead to right ventricular failure. The cause of the vascular remodeling in PAH remains unknown, and the prognosis of PAH remains poor. Abnormal mitochondria in PAH PA smooth muscle cells (SMCs) suppress mitochondria-dependent apoptosis and contribute to the vascular remodeling. We hypothesized that early endoplasmic reticulum (ER) stress, which is associated with clinical triggers of PAH including hypoxia, bone morphogenetic protein receptor II mutations, and HIV/herpes simplex virus infections, explains the mitochondrial abnormalities and has a causal role in PAH. We showed in SMCs from mice that Nogo-B, a regulator of ER structure, was induced by hypoxia in SMCs of the PAs but not the systemic vasculature through activation of the ER stress-sensitive transcription factor ATF6. Nogo-B induction increased the distance between the ER and mitochondria and decreased ER-to-mitochondria phospholipid transfer and intramitochondrial calcium. In addition, we noted inhibition of calcium-sensitive mitochondrial enzymes, increased mitochondrial membrane potential, decreased mitochondrial reactive oxygen species, and decreased mitochondria-dependent apoptosis. Lack of Nogo-B in PASMCs from Nogo-A/B-/- mice prevented these hypoxia-induced changes in vitro and in vivo, resulting in complete resistance to PAH. Nogo-B in the serum and PAs of PAH patients was also increased. Therefore, triggers of PAH may induce Nogo-B, which disrupts the ER-mitochondria unit and suppresses apoptosis. This could rescue PASMCs from death during ER stress but enable the development of PAH through overproliferation. The disruption of the ER-mitochondria unit may be relevant to other diseases in which Nogo is implicated, such as cancer or neurodegeneration.

7β-Hydroxycholesterol-induced energy stress leads to sequential opposing signaling responses and to death of C6 glioblastoma cells

7β-Hydroxycholesterol cytotoxicity has been shown in vivo and in vitro to be dependent on the accumulation of its esters. We show in our study, using a detergent-free raft preparation and LC/MS lipid content analysis, that membrane microdomains isolated from 7β-hydroxycholesterol-treated C6 cells have a reduced cholesterol: cholesterol ester ratio and accumulate 7keto-hydroxycholesterol, 7β-hydroxycholesterol and 7β-hydroxycholesterol esters. These modifications in lipid content are accompanied by a redistribution of flotillin-1 in the lipid rafts. Transient increases of AMPK phosphorylation and mitochondrial activity during the first 12 h of 7β-hydroxycholesterol treatment indicate that C6 cells undergo energy stress and increase oxidative phosphorylation. Even so, ATP levels are maintained during 15 h until glucose uptake decreases. The cell's answers to raft modifications and energy stress are sequential activations of different signaling pathways such as ERK, AMPK and PI3K/Akt. These pathways, known to be activated under energy stress conditions, are transiently activated at 6 h (ERK, AMPK) and 12 h (Akt) of treatment respectively suggesting a shift from cell survival to cell proliferation. The persistence of 7β-hydroxycholesterol-induced stress led after 24 h to P38 activation, loss of GSK3β activation and to cell death. Finally we demonstrate that the observed signaling responses depend on 7β-hydroxycholesterol esterification, confirming that esterification of 7β-hydroxycholesterol is essential for cytotoxicity.

D-amino acid oxidase gene therapy sensitizes glioma cells to the antiglycolytic effect of 3-bromopyruvate

Glioma tumors are refractory to conventional treatment. Glioblastoma multiforme is the most aggressive type of primary brain tumors in humans. In this study, we introduce oxidative stress-energy depletion (OSED) therapy as a new suggested treatment for glioblastoma. OSED utilizes D-amino acid oxidase (DAO), which is a promising therapeutic protein that induces oxidative stress and apoptosis through generating hydrogen peroxide (H2O2). OSED combines DAO with 3-bromopyruvate (3BP), a hexokinase II (HK II) inhibitor that interferes with Warburg effect, a metabolic alteration of most tumor cells that is characterized by enhanced aerobic glycolysis. Our data revealed that 3BP induced depletion of energetic capabilities of glioma cells. 3BP induced H2O2 production as a novel mechanism of its action. C6 glioma transfected with DAO and treated with D-serine together with 3BP-sensitized glioma cells to 3BP and decreased markedly proliferation, clonogenic power and viability in a three-dimensional tumor model with lesser effect on normal astrocytes. DAO gene therapy using atelocollagen as an in vivo transfection agent proved effective in a glioma tumor model in Sprague-Dawley (SD) rats, especially after combination with 3BP. OSED treatment was safe and tolerable in SD rats. OSED therapy may be a promising therapeutic modality for glioma.

Mitochondrial metabolism inhibitors for cancer therapy

Cancer cells catabolise nutrients in a different way than healthy cells. Healthy cells mainly rely on oxidative phosphorylation, while cancer cells employ aerobic glycolysis. Glucose is the main nutrient catabolised by healthy cells, while cancer cells often depend on catabolism of both glucose and glutamine. A key organelle involved in this altered metabolism is mitochondria. Mitochondria coordinate the catabolism of glucose and glutamine across the cancer cell. Targeting mitochondrial metabolism in cancer cells has potential for the treatment of this disease. Perhaps the most promising target is the hexokinase-voltage dependent anion channel-adenine nucleotide translocase complex that spans the outer- and inner-mitochondrial membranes. This complex links glycolysis, oxidative phosphorylation and mitochondrial-mediated apoptosis in cancer cells. This review discusses cancer cell mitochondrial metabolism and the small molecule inhibitors of this metabolism that are in pre-clinical or clinical development.

Glycogen as a Putative Target for Diagnosis and Therapy in Brain Pathologies

Brain glycogen, a glucose polymer, is now considered as a functional energy store to the brain. Indeed, when neurons outpace their own possibilities to provide themselves with energy, astrocytic metabolism is in charge of feeding neurons, since brain glycogen synthesis is mainly due to astrocyte. Therefore, malfunctions or perturbations of astrocytic glycogen content, synthesis, or mobilization may be involved in processes of brain pathologies. This is the case, for example, in epilepsies and gliomas, two different situations in which, brain needs high level of energy during acute or chronic conditions. The purpose of the present paper is to demonstrate how brain glycogen might be relevant in these two pathologies and to pinpoint the possibilities of considering glycogen as a tool for diagnostic and therapeutic approaches in brain pathologies.

Rapid dissolution of ZnO nanocrystals in acidic cancer microenvironment leading to preferential apoptosis

The microenvironment of cancer plays a very critical role in the survival, proliferation and drug resistance of solid tumors. Here, we report an interesting, acidic cancer microenvironment-mediated dissolution-induced preferential toxicity of ZnO nanocrystals (NCs) against cancer cells while leaving primary cells unaffected. Irrespective of the size-scale (5 and 200 nm) and surface chemistry differences (silica, starch or polyethylene glycol coating), ZnO NCs exhibited multiple stress mechanisms against cancer cell lines (IC(50)∼150 μM) while normal human primary cells (human dermal fibroblast, lymphocytes, human umbilical vein endothelial cells) remain less affected. Flow cytometry and confocal microscopy studies revealed that ZnO NCs undergo rapid preferential dissolution in acidic (pH ∼5-6) cancer microenvironment causing elevated ROS stress, mitochondrial superoxide formation, depolarization of mitochondrial membrane, and cell cycle arrest at S/G2 phase leading to apoptosis. In effect, by elucidating the unique toxicity mechanism of ZnO NCs, we show that ZnO NCs can destabilize cancer cells by utilizing its own hostile acidic microenvironment, which is otherwise critical for its survival.

Mammalian NADH:ubiquinone oxidoreductase (Complex I) and nicotinamide nucleotide transhydrogenase (Nnt) together regulate the mitochondrial production of H₂O₂--implications for their role in disease, especially cancer

Mammalian NADH:ubiquinone oxidoreductase (Complex I) in the mitochondrial inner membrane catalyzes the oxidation of NADH in the matrix. Excess NADH reduces nine of the ten prosthetic groups of the enzyme in bovine-heart submitochondrial particles with a rate of at least 3,300 s⁻¹. This results in an overall NADH→O₂ rate of ca. 150 s⁻¹. It has long been known that the bovine enzyme also has a specific reaction site for NADPH. At neutral pH excess NADPH reduces only three to four of the prosthetic groups in Complex I with a rate of 40 s⁻¹ at 22 °C. The reducing equivalents remain essentially locked in the enzyme because the overall NADPH→O₂ rate (1.4 s⁻¹) is negligible. The physiological significance of the reaction with NADPH is still unclear. A number of recent developments has revived our thinking about this enigma. We hypothesize that Complex I and the Δp-driven nicotinamide nucleotide transhydrogenase (Nnt) co-operate in an energy-dependent attenuation of the hydrogen-peroxide generation by Complex I. This co-operation is thought to be mediated by the NADPH/NADP⁺ ratio in the vicinity of the NADPH site of Complex I. It is proposed that the specific H₂O₂ production by Complex I, and the attenuation of it, is of importance for apoptosis, autophagy and the survival mechanism of a number of cancers. Verification of this hypothesis may contribute to a better understanding of the regulation of these processes.

Targeting cancer metabolism: a therapeutic window opens

Genetic events in cancer activate signalling pathways that alter cell metabolism. Clinical evidence has linked cell metabolism with cancer outcomes. Together, these observations have raised interest in targeting metabolic enzymes for cancer therapy, but they have also raised concerns that these therapies would have unacceptable effects on normal cells. However, some of the first cancer therapies that were developed target the specific metabolic needs of cancer cells and remain effective agents in the clinic today. Research into how changes in cell metabolism promote tumour growth has accelerated in recent years. This has refocused efforts to target metabolic dependencies of cancer cells as a selective anticancer strategy.

Metabolism of glioma and IDH1/IDH2 mutations

Many known oncogenic signaling pathways involved in gliomagenesis have strong consequences on tumor cell metabolism, and promote the switch from oxidative phosphorylation to aerobic glycolysis, for ATP generation. However, the interest on metabolism has been recently renewed by the discovery of recurrent mutation of IDH1 genes by systematic sequencing of a glioblastoma series. IDH1 encodes the cytoplasmic NADP dependent isocitrate dehydrogenase1 that catalyzes the oxidative decarboxylation of isocitrate into α-ketoglutarate. IDH1, more rarely IDH2, is mutated in 40% of gliomas (roughly 70% of low-grade gliomas, 50% of grade III, and 5 to 10% of primary glioblastomas). IDH1/IDH2 mutations are associated with genomic profile, being present in nearly all the 1p19q codeleted gliomas, and virtually absent in gliomas with EGFR amplification. It is a strong and independent predictor of survival, whatever grade considered. IDH1/IDH2 mutation results in a new enzymatic activity transforming α-ketoglutarate into 2-hydroxyglutarate (2-HG). The oncometabolite 2-HG accumulates in the cell and acts as a competitive inhibitor of many α-ketoglutarate dependent cellular reactions. The cellular consequences of this mutation offer potential targets for the development of novel therapeutics.

Dichloroacetate inhibits neuroblastoma growth by specifically acting against malignant undifferentiated cells

The small, water soluble molecule Dichloroacetate (DCA) is recently arousing lively interests in the field of cancer therapy for it has been shown to be able to inhibit the growth of human tumors acting specifically on the mitochondria of cancer cells without perturbing the physiology of nonmalignant cells. Neuroblastoma was one of the tumor types on which DCA was considered ineffective as it is composed of cells with few recognized mitochondrial anomalies. Neuroblastoma, however, is composed of different cell types in terms of metabolism, phenotype and malignant potential. Despite the above prediction, in this work, we show that (i) DCA exhibits an unexpected anticancer effect on NB tumor cells and (ii) this effect is selectively directed to very malignant NB cells, whereas the more differentiated/less malignant NB cells are refractory to DCA treatment. This result supports the need of a detailed investigation of DCA anticancer properties against this tumor type with the final aim of its possible use as therapeutic agent.

Anticancer targets in the glycolytic metabolism of tumors: a comprehensive review

CANCER IS A METABOLIC DISEASE AND THE SOLUTION OF TWO METABOLIC EQUATIONS: to produce energy with limited resources and to fulfill the biosynthetic needs of proliferating cells. Both equations are solved when glycolysis is uncoupled from oxidative phosphorylation in the tricarboxylic acid cycle, a process known as the glycolytic switch. This review addresses in a comprehensive manner the main molecular events accounting for high-rate glycolysis in cancer. It starts from modulation of the Pasteur Effect allowing short-term adaptation to hypoxia, highlights the key role exerted by the hypoxia-inducible transcription factor HIF-1 in long-term adaptation to hypoxia, and summarizes the current knowledge concerning the necessary involvement of aerobic glycolysis (the Warburg effect) in cancer cell proliferation. Based on the many observations positioning glycolysis as a central player in malignancy, the most advanced anticancer treatments targeting tumor glycolysis are briefly reviewed.

Oncogenic K-Ras decouples glucose and glutamine metabolism to support cancer cell growth

A systems approach using 13C metabolic flux analysis (MFA), non-targeted tracer fate detection (NTFD), and transcriptional profiling was applied to investigate the role of oncogenic K-Ras in metabolic transformation.

K-Ras transformed cells exhibit an increased glycolytic rate and lower flux through the oxidative tricarboxylic acid (TCA) cycle.

K-Ras transformed cells show a relative increase in glutamine anaplerosis and reductive TCA metabolism.

Transcriptional changes driven by oncogenic K-Ras suggest control nodes associated with the metabolic reprogramming of cancer cells.

The ras and myc oncogenes drive pleiotropic changes in cell signaling, nutrient uptake, and intracellular metabolism (Chiaradonna et al, 2006b; Yuneva et al, 2007; Wise et al, 2008; Vander Heiden et al, 2009). Mutated ras proteins, identified in 25% of human cancers (Bos, 1989; Downward, 2003), correlate with an increased rate of glucose consumption, lactate accumulation, altered expression of mitochondrial genes, increased ROS production, and reduced mitochondrial activity (Bos, 1989; Downward, 2003; Vizan et al, 2005; Chiaradonna et al, 2006a; Yun et al, 2009; Baracca et al, 2010; Weinberg et al, 2010). Furthermore, K-Ras transformed cancer cells are dependent upon glucose and glutamine availability, since their withdrawal induces apoptosis and cell-cycle arrest, respectively (Ramanathan et al, 2005; Telang et al, 2006; Yun et al, 2009). However, the precise metabolic effects downstream of oncogenic Ras signaling as well as the mechanisms by which intracellular glucose and glutamine metabolism change have not been completely elucidated.

In this report, we have investigated the reprogramming of central carbon metabolism in cancer cells and its regulation by the K-ras oncogene, applying a systems level approach using ¹³C metabolic flux analysis (MFA), non-targeted tracer fate detection (NTFD), and transcriptional profiling. These data reveal a coordinated decoupling of glycolysis and the tricarboxylic acid (TCA) cycle. K-Ras transformed mouse and human cells exhibited a high glucose to lactate flux and relatively lower oxidative metabolism of pyruvate. Such changes were supported by increased expression of glycolytic genes as well as several pyruvate dehydrogenase kinases. In contrast to glucose, the contribution of glutamine carbon to TCA cycle intermediates through both oxidative and reductive metabolism was significantly increased upon K-Ras transformation. Despite this increase in glutamine anaplerosis, oxidative TCA flux was significantly decreased. Additionally, we observed elevated levels of glutamine-derived nitrogen in various biosynthetic metabolites in transformed cells, including amino acids, 5-oxoproline, and the nucleobase adenine. Consistent with these changes, we detected increased transcription of genes associated with glutamine metabolism and nucleotide biosynthesis in cells expressing oncogenic K-Ras.

Taken together, these findings indicate an important role of oncogenic K-Ras in cancer cell metabolism. The observed decoupling of glucose and glutamine metabolism enables the efficient utilization of both carbon and nitrogen from glutamine for biosynthetic processes. In accord with these alterations, oncogenic K-Ras induces gene expression changes that may drive this metabolic reprogramming. Finally, these results may enable the identification of metabolic and transcriptional targets throughout the network and allow more effective cancer therapies.

Oncogenes such as K-ras mediate cellular and metabolic transformation during tumorigenesis. To analyze K-Ras-dependent metabolic alterations, we employed ¹³C metabolic flux analysis (MFA), non-targeted tracer fate detection (NTFD) of ¹⁵N-labeled glutamine, and transcriptomic profiling in mouse fibroblast and human carcinoma cell lines. Stable isotope-labeled glucose and glutamine tracers and computational determination of intracellular fluxes indicated that cells expressing oncogenic K-Ras exhibited enhanced glycolytic activity, decreased oxidative flux through the tricarboxylic acid (TCA) cycle, and increased utilization of glutamine for anabolic synthesis. Surprisingly, a non-canonical labeling of TCA cycle-associated metabolites was detected in both transformed cell lines. Transcriptional profiling detected elevated expression of several genes associated with glycolysis, glutamine metabolism, and nucleotide biosynthesis upon transformation with oncogenic K-Ras. Chemical perturbation of enzymes along these pathways further supports the decoupling of glycolysis and TCA metabolism, with glutamine supplying increased carbon to drive the TCA cycle. These results provide evidence for a role of oncogenic K-Ras in the metabolic reprogramming of cancer cells.

Antitumor compound testing in glioblastoma organotypic brain cultures

Glioblastoma multiforme (GBM) is the most common and most aggressive type of primary brain tumor. Identification of new therapeutic regimens is urgently needed. A major challenge remains the development of a relevant in vitro model system with the necessary capacity and flexibility to profile compounds. The authors have developed and characterized a 3D culture system of brain cells (brain Hi-Spot) where GBM-derived cells can be incorporated (GBM/brain Hi-Spot). Immuno-fluorescence and electrophysiological recordings demonstrate that brain Hi-Spots recapitulate many features of brain tissue. Within this tissue, GBM-derived cell growth is monitored using a fluorescence assay. GBM-derived cells growing in Hi-Spots form tumor nodules that display properties of GBM such as 5-Ala positive staining, an acidic environment, and tumor-surrounding astrocyte activation. Temozolomide inhibits GBM growth in brain Hi-Spots, but it is not effective in 2D cultures. Other chemotherapeutics that have proven to be inefficient in GBM treatment display low activity against GBM-derived cells growing in brain Hi-Spots in comparison to their activity against GBM 2D cultures. These findings suggest that GBM/brain Hi-Spots represent a simple system to culture cells derived from brain tumors in an orthotopic environment in vitro and that the system is reliable to test GBM targeting compounds.

Differential utilization of ketone bodies by neurons and glioma cell lines: a rationale for ketogenic diet as experimental glioma therapy

Background

Even in the presence of oxygen, malignant cells often highly depend on glycolysis for energy generation, a phenomenon known as the Warburg effect. One strategy targeting this metabolic phenotype is glucose restriction by administration of a high-fat, low-carbohydrate (ketogenic) diet. Under these conditions, ketone bodies are generated serving as an important energy source at least for non-transformed cells.

Methods

To investigate whether a ketogenic diet might selectively impair energy metabolism in tumor cells, we characterized in vitro effects of the principle ketone body 3-hydroxybutyrate in rat hippocampal neurons and five glioma cell lines. In vivo, a non-calorie-restricted ketogenic diet was examined in an orthotopic xenograft glioma mouse model.

Results

The ketone body metabolizing enzymes 3-hydroxybutyrate dehydrogenase 1 and 2 (BDH1 and 2), 3-oxoacid-CoA transferase 1 (OXCT1) and acetyl-CoA acetyltransferase 1 (ACAT1) were expressed at the mRNA and protein level in all glioma cell lines. However, no activation of the hypoxia-inducible factor-1α (HIF-1α) pathway was observed in glioma cells, consistent with the absence of substantial 3-hydroxybutyrate metabolism and subsequent accumulation of succinate. Further, 3-hydroxybutyrate rescued hippocampal neurons from glucose withdrawal-induced cell death but did not protect glioma cell lines. In hypoxia, mRNA expression of OXCT1, ACAT1, BDH1 and 2 was downregulated. In vivo, the ketogenic diet led to a robust increase of blood 3-hydroxybutyrate, but did not alter blood glucose levels or improve survival.

Conclusion

In summary, glioma cells are incapable of compensating for glucose restriction by metabolizing ketone bodies in vitro, suggesting a potential disadvantage of tumor cells compared to normal cells under a carbohydrate-restricted ketogenic diet. Further investigations are necessary to identify co-treatment modalities, e.g. glycolysis inhibitors or antiangiogenic agents that efficiently target non-oxidative pathways.

Overcoming temozolomide resistance in glioblastoma via dual inhibition of NAD+ biosynthesis and base excision repair

Glioblastoma multiforme (GBM) is a devastating brain tumor with poor prognosis and low median survival time. Standard treatment includes radiation and chemotherapy with the DNA alkylating agent temozolomide (TMZ). However, a large percentage of tumors are resistant to the cytotoxic effects of the TMZ-induced DNA lesion O(6)-methylguanine due to elevated expression of the repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) or a defect in the mismatch repair (MMR) pathway. Although a majority of the TMZ-induced lesions (N7-methylguanine and N3-methyladenine) are base excision repair (BER) substrates, these DNA lesions are also readily repaired. However, blocking BER can enhance response to TMZ and therefore the BER pathway has emerged as an attractive target for reversing TMZ resistance. Our lab has recently reported that inhibition of BER leads to the accumulation of repair intermediates that induce energy depletion-mediated cell death via hyperactivation of poly(ADP-ribose) polymerase. On the basis of our observation that TMZ-induced cell death via BER inhibition is dependent on the availability of nicotinamide adenine dinucleotide (NAD(+)), we have hypothesized that combined BER and NAD(+) biosynthesis inhibition will increase TMZ efficacy in glioblastoma cell lines greater than BER inhibition alone. Importantly, we find that the combination of BER and NAD(+) biosynthesis inhibition significantly sensitizes glioma cells with elevated expression of MGMT and those deficient in MMR, two genotypes normally associated with TMZ resistance. Dual targeting of these two interacting pathways (DNA repair and NAD(+) biosynthesis) may prove to be an effective treatment combination for patients with resistant and recurrent GBM.

From cancer metabolism to new biomarkers and drug targets

Great interest is presently given to the analysis of metabolic changes that take place specifically in cancer cells. In this review we summarize the alterations in glycolysis, glutamine utilization, fatty acid synthesis and mitochondrial function that have been reported to occur in cancer cells and in human tumors. We then propose considering cancer as a system-level disease and argue how two hallmarks of cancer, enhanced cell proliferation and evasion from apoptosis, may be evaluated as system-level properties, and how this perspective is going to modify drug discovery. Given the relevance of the analysis of metabolism both for studies on the molecular basis of cancer cell phenotype and for clinical applications, the more relevant technologies for this purpose, from metabolome and metabolic flux analysis in cells by Nuclear Magnetic Resonance and Mass Spectrometry technologies to positron emission tomography on patients, are analyzed. The perspectives offered by specific changes in metabolism for a new drug discovery strategy for cancer are discussed and a survey of the industrial activity already going on in the field is reported.

Mechanisms of disease: pulmonary arterial hypertension

In the past decade or so, our understanding of pulmonary arterial hypertension has undergone a paradigm shift. In this article, Dr Schermuly and colleagues discuss the known molecular mechanisms of the pathogenesis of this disease, and highlight the molecular technologies that are currently being used to further our understanding of these disease processes.

Our understanding of, and approach to, pulmonary arterial hypertension has undergone a paradigm shift in the past decade. Once a condition thought to be dominated by increased vasoconstrictor tone and thrombosis, pulmonary arterial hypertension is now seen as a vasculopathy in which structural changes driven by excessive vascular cell growth and inflammation, with recruitment and infiltration of circulating cells, play a major role. Perturbations of a number of molecular mechanisms have been described, including pathways involving growth factors, cytokines, metabolic signaling, elastases, and proteases, that may underlie the pathogenesis of the disease. Elucidating their contribution to the pathophysiology of pulmonary arterial hypertension could offer new drug targets. The role of progenitor cells in vascular repair is also under active investigation. The right ventricular response to increased pressure load is recognized as critical to survival and the molecular mechanisms involved are attracting increasing interest. The challenge now is to integrate this new knowledge and explore how it can be used to categorize patients by molecular phenotype and tailor treatment more effectively.

Pulmonary hypertension is a progressive disease of various origins, which has a poor prognosis and affects, in its different forms, more than 100 million people worldwide

Pulmonary arterial hypertension (PAH) is now considered to be a vasculopathy in which structural changes driven by excessive vascular cell growth and inflammation have a major role

A number of proproliferative signaling pathways involving growth factors, cytokines, metabolic signaling, and elastases and proteases have been identified in the pathophysiology of PAH

Clinical studies with tyrosine kinase inhibitors, serotonin antagonists, and soluble guanylate cyclase stimulators are underway in patients with PAH

The benefits of progenitor cells for vascular repair in PAH are under active investigation

The right ventricular response to increased pressure load is recognized as critical to survival in patients with PAH, and strategies for preserving myocardial function are increasingly attracting interest