Separation of metabolic supply and demand: aerobic glycolysis as a normal physiological response to fluctuating energetic demands in the membrane

L-type amino acid transporter 1 is associated with chemoresistance in breast cancer via the promotion of amino acid metabolism

¹⁸F-FDG PET/CT has been used as an indicator of chemotherapy effects, but cancer cells can remain even when no FDG uptake is detected, indicating the importance of exploring other metabolomic pathways. Therefore, we explored the amino acid metabolism, including L-type amino acid transporter-1 (LAT1), in breast cancer tissues and clarified the role of LAT1 in therapeutic resistance and clinical outcomes of patients. We evaluated LAT1 expression before and after neoadjuvant chemotherapy and examined the correlation of glucose uptake using FDG-PET with the pathological response of patients. It revealed that LAT1 levels correlated with proliferation after chemotherapy, and amino acid and glucose metabolism were closely correlated. In addition, LAT1 was considered to be involved in treatment resistance and sensitivity only in luminal type breast cancer. Results of in vitro analyses revealed that LAT1 promoted amino acid uptake, which contributed to energy production by supplying amino acids to the TCA cycle. However, in MCF-7 cells treated with chemotherapeutic agents, oncometabolites and branched-chain amino acids also played a pivotal role in energy production and drug resistance, despite decreased glucose metabolism. In conclusion, LAT1 was involved in drug resistance and could be a novel therapeutic target against chemotherapy resistance in luminal type breast cancer.

Resveratrol's Anti-Cancer Effects through the Modulation of Tumor Glucose Metabolism

Simple Summary

The prevention and treatment of cancer is an ongoing medical challenge. In the context of personalized medicine, the well-studied polyphenol resveratrol could complement classical tumor therapy. It may affect key processes such as inflammation, angiogenesis, proliferation, metastasis, glucose metabolism, and apoptosis in various cancers because resveratrol acts as a multi-targeting agent by modulating multiple signal transduction pathways. This review article focuses on resveratrol’s ability to modify tumor glucose metabolism and its associated therapeutic capacity. Resveratrol reduces glucose uptake and glycolysis by affecting Glut1, PFK1, HIF-1α, ROS, PDH, and the CamKKB/AMPK pathway. It also inhibits cell growth, invasion, and proliferation by targeting NF-kB, Sirt1, Sirt3, LDH, PI-3K, mTOR, PKM2, R5P, G6PD, TKT, talin, and PGAM. In addition, resveratrol induces apoptosis by targeting integrin, p53, LDH, and FAK. In conclusion, resveratrol has many potentials to intervene in tumor processes if bioavailability can be increased and this natural compound can be used selectively.

Abstract

Tumor cells develop several metabolic reprogramming strategies, such as increased glucose uptake and utilization via aerobic glycolysis and fermentation of glucose to lactate; these lead to a low pH environment in which the cancer cells thrive and evade apoptosis. These characteristics of tumor cells are known as the Warburg effect. Adaptive metabolic alterations in cancer cells can be attributed to mutations in key metabolic enzymes and transcription factors. The features of the Warburg phenotype may serve as promising markers for the early detection and treatment of tumors. Besides, the glycolytic process of tumors is reversible and could represent a therapeutic target. So-called mono-target therapies are often unsafe and ineffective, and have a high prevalence of recurrence. Their success is hindered by the ability of tumor cells to simultaneously develop multiple chemoresistance pathways. Therefore, agents that modify several cellular targets, such as energy restriction to target tumor cells specifically, have therapeutic potential. Resveratrol, a natural active polyphenol found in grapes and red wine and used in many traditional medicines, is known for its ability to target multiple components of signaling pathways in tumors, leading to the suppression of cell proliferation, activation of apoptosis, and regression in tumor growth. Here, we describe current knowledge on the various mechanisms by which resveratrol modulates glucose metabolism, its potential as an imitator of caloric restriction, and its therapeutic capacity in tumors.

The bioenergetics of neuronal morphogenesis and regeneration: Frontiers beyond the mitochondrion

The formation of axons and dendrites during development, and their regeneration following injury, are energy intensive processes. The underlying assembly and dynamics of the cytoskeleton, axonal transport mechanisms, and extensive signaling networks all rely on ATP and GTP consumption. Cellular ATP is generated through oxidative phosphorylation (OxP) in mitochondria, glycolysis and "regenerative" kinase systems. Recent investigations have focused on the role of the mitochondrion in axonal development and regeneration emphasizing the importance of this organelle and OxP in axon development and regeneration. In contrast, the understanding of alternative sources of ATP in neuronal morphogenesis and regeneration remains largely unexplored. This review focuses on the current state of the field of neuronal bioenergetics underlying morphogenesis and regeneration and considers the literature on the bioenergetics of non-neuronal cell motility to emphasize the potential contributions of non-mitochondrial energy sources.

Relevance of the Warburg Effect in Tuberculosis for Host-Directed Therapy

Tuberculosis (TB) was responsible for more deaths in 2019 than any other infectious agent. This epidemic is exacerbated by the ongoing development of multi-drug resistance and HIV co-infection. Recent studies have therefore focused on identifying host-directed therapies (HDTs) that can be used in combination with anti-mycobacterial drugs to shorten the duration of TB treatment and improve TB outcomes. In searching for effective HDTs for TB, studies have looked toward immunometabolism, the study of the role of metabolism in host immunity and, in particular, the Warburg effect. Across a variety of experimental paradigms ranging from in vitro systems to the clinic, studies on the role of the Warburg effect in TB have produced seemingly conflicting results and contradictory conclusions. To reconcile this literature, we take a historical approach to revisit the definition of the Warburg effect, re-examine the foundational papers on the Warburg effect in the cancer field and explore its application to immunometabolism. With a firm context established, we assess the literature investigating metabolism and immunometabolism in TB for sufficient evidence to support the role of the Warburg effect in TB immunity. The effects of the differences between animal models, species of origin of the macrophages, duration of infection and Mycobacterium tuberculosis strains used for these studies are highlighted. In addition, the shortcomings of using 2-deoxyglucose as an inhibitor of glycolysis are discussed. We conclude by proposing experimental criteria that are essential for future studies on the Warburg effect in TB to assist with the research for HDTs to combat TB.

Ectonucleotidase CD73 and CD39 expression in non-small cell lung cancer relates to hypoxia and immunosuppressive pathways

AIMS

Adenosine triphosphate (ATP) is released at a high concentration in the tumor microenvironment. The overexpression of ectonucleotidases in non-small-cell lung cancer (NSCLC), metabolizing ΑΤP to the immunosuppressive adenosine, is studied.

MATERIALS AND METHODS

We examined the expression of the ectonucleotidases CD73 and CD39 in NSCLC in parallel with immunological parameters and markers of hypoxia and anaerobic metabolism. In vitro experiments with A549 and H1299 lung cancer cell lines were also conducted.

RESULTS

CD73 and CD39 were not expressed by normal bronchial and alveolar epithelium. In contrast, these were overexpressed by cancer cells, cancer-associated fibroblasts (CAFs), and tumor-infiltrating lymphocytes (TILs). High CD73 cancer cell expression was directly linked with lactate dehydrogenase LDH5 and with hypoxia-inducible factor HIF1α expression by cancer cells. The expression of CD39 by CAFs was directly linked with PD-L1 expression by cancer cells. A significant abundance of FOXP3+ and PD-1+ TILs was noted in tumors with high CD73 and CD39 stroma expression. In in vitro experiments, hypoxia and acidity induced CD73 mRNA and protein levels in cancer cell lines. Exposure of cancer cell lines to adenosine induced the expression of PD-L1 and LDHA mRNA and protein levels.

CONCLUSION

Ectonucleotidases are up-regulated in cancer cells, CAFs, and TILs in lung tumors. Such overexpression is linked with regulatory TIL-phenotype and PD-L1 up-regulation by cancer cells. Overexpression of LDH5 is up-regulated by adenosine, creating a vicious cycle, as the high amounts of ATP produced by LDH5-mediated anaerobic glycolysis promote the production of adenosine by a tumor microenvironment rich in ectonucleotidases.

Cancer Acidity and Hypertonicity Contribute to Dysfunction of Tumor-Associated Dendritic Cells: Potential Impact on Antigen Cross-Presentation Machinery

Macrophages (MΦ) and dendritic cells (DC), major players of the mononuclear phagocyte system (MoPh), are potent antigen presenting cells that steadily sense and respond to signals from the surrounding microenvironment, leading to either immunogenic or tolerogenic outcomes. Next to classical MHC-I/MHC-II antigen-presentation pathways described in the vast majority of cell types, a subset of MoPh (CD8⁺, XCR1⁺, CLEC9A⁺, BDCA3⁺ conventional DCs in human) is endowed with a high competence to cross-present external (engulfed) antigens on MHC-I molecules to CD8⁺ T-cells. This exceptional DC function is thought to be a crucial crossroad in cytotoxic antitumor immunity and has been extensively studied in the past decades. Biophysical and biochemical fingerprints of tumor micromilieus show significant spatiotemporal differences in comparison to non-neoplastic tissue. In tumors, low pH (mainly due to extracellular lactate accumulation via the Warburg effect and via glutaminolysis) and high oncotic and osmotic pressure (resulting from tumor debris, increased extracellular matrix components but in part also triggered by nutritive aspects) are—despite fluctuations and difficulties in measurement—likely the most constant general hallmarks of tumor microenvironment. Here, we focus on the influence of acidic and hypertonic micromilieu on the capacity of DCs to cross-present tumor-specific antigens. We discuss complex and in part controversial scientific data on the interference of these factors with to date reported mechanisms of antigen uptake, processing and cross-presentation, and we highlight their potential role in cancer immune escape and poor clinical response to DC vaccines.

Selenium deficiency-induced redox imbalance leads to metabolic reprogramming and inflammation in the liver

Selenium (Se) intake disequilibrium is associated with many human diseases (e.g., Keshan disease and type 2 diabetes). To understand the mechanism of Se deficiency-induced hepatic pathogenesis, a pure line pig model was established by feeding a diet with either 0.07 mg/kg Se or 0.3 mg/kg Se for 16 weeks. The hepatic metabolome, lipidome, global proteome, and whole transcriptome were analyzed. Se deficiency causes a redox imbalance via regulation of selenoproteins at both the mRNA and protein level, and blocks the glutathione anti-oxidant system along with enhanced glutathione synthesis and catabolism. The Warburg effect was observed by enhanced activation of the glycolysis and phosphate pentose pathways. The tricarboxylic acid cycle was dysfunctional since the preliminary metabolites decreased and shifted from using glycolysis origin substrates to a glutamine catabolism-preferred metabolic mode. The reprogrammed central carbon metabolism induced widely restrained lipid synthesis. In addition, a Se deficiency initiated inflammation by activating the NF-κB pathway through multiple mechanisms. These results identified the potential metabolic vulnerability of the liver in response to a Se deficiency-induced redox imbalance and possible therapeutic or intervention targets.

Excessive supply of glucose elicits an NF-κB2-dependent glycolysis in lactating goat mammary glands

During lactation, an improper glucose supply often threatens mammary gland (MG) health. However, information is limited on the metabolic trajectories and molecules that regulate lactating MGs with an excessive glucose supply. Based on the network analysis of transcriptome and microRNAs, we found that the oversupply of glucose-induced severe glucose metabolic disorders in MGs of lactating goats, shifting lactose synthesis to acute fermentative glycolysis which caused increased flux of glucose metabolism into lactate. Moreover, NF-κB2 played a key role in regulating glycolysis, exhibiting a metabolic shift when MGs had an excessive supply of glucose. In primary mammary epithelial cells, fermentative glycolysis, and intracellular concentration of reactive oxygen species (ROS) were reduced by ganoderic acid A through blocking NF-κB2, while activation of NF-κB2 with phorbol myristate acetate (PMA) upregulated fermentative glycolysis and increased cellular ROS accumulation under excessive glucose. Thus, we established an NF-κB2-targeting method to reform the metabolic shift toward glycolysis caused by glucose oversupply by integrating NF-κB2 blockade and intracellular ROS scavenging.

How DNA methylation affects the Warburg effect

Significant enhancement of the glycolysis pathway is a major feature of tumor cells, even in the presence of abundant oxygen; this enhancement is known as the Warburg effect, and also called aerobic glycolysis. The Warburg effect was discovered nearly a hundred years ago, but its specific mechanism remains difficult to explain. DNA methylation is considered to be a potential trigger for the Warburg effect, as the two processes have many overlapping links during tumorigenesis. Based on a widely recognized potential mechanism of the Warburg effect, we here summarized the relationship between DNA methylation and the Warburg effect with regard to cellular energy metabolism factors, such as glycolysis related enzymes, mitochondrial function, glycolysis bypass pathways, the tumor oxygen sensing pathway and abnormal methylation conditions. We believe that clarifying the relationship between these different mechanisms may further help us understand how DNA methylation works on tumorigenesis and provide new opportunities for cancer therapy.

Metabolic regulation of calcium pumps in pancreatic cancer: role of phosphofructokinase-fructose-bisphosphatase-3 (PFKFB3)

BACKGROUND

High glycolytic rate is a hallmark of cancer (Warburg effect). Glycolytic ATP is required for fuelling plasma membrane calcium ATPases (PMCAs), responsible for extrusion of cytosolic calcium, in pancreatic ductal adenocarcinoma (PDAC). Phosphofructokinase-fructose-bisphosphatase-3 (PFKFB3) is a glycolytic driver that activates key rate-limiting enzyme Phosphofructokinase-1; we investigated whether PFKFB3 is required for PMCA function in PDAC cells.

METHODS

PDAC cell-lines, MIA PaCa-2, BxPC-3, PANC1 and non-cancerous human pancreatic stellate cells (HPSCs) were used. Cell growth, death and metabolism were assessed using sulforhodamine-B/tetrazolium-based assays, poly-ADP-ribose-polymerase (PARP1) cleavage and seahorse XF analysis, respectively. ATP was measured using a luciferase-based assay, membrane proteins were isolated using a kit and intracellular calcium concentration and PMCA activity were measured using Fura-2 fluorescence imaging.

RESULTS

PFKFB3 was highly expressed in PDAC cells but not HPSCs. In MIA PaCa-2, a pool of PFKFB3 was identified at the plasma membrane. PFKFB3 inhibitor, PFK15, caused reduced cell growth and PMCA activity, leading to calcium overload and apoptosis in PDAC cells. PFK15 reduced glycolysis but had no effect on steady-state ATP concentration in MIA PaCa-2.

CONCLUSIONS

PFKFB3 is important for maintaining PMCA function in PDAC, independently of cytosolic ATP levels and may be involved in providing a localised ATP supply at the plasma membrane.

Causes and Consequences of Variable Tumor Cell Metabolism on Heritable Modifications and Tumor Evolution

When cancer research advanced into the post-genomic era, it was widely anticipated that the sought-after cure will be delivered promptly. Instead, it became apparent that an understanding of cancer genomics, alone, is unable to translate the wealth of information into successful cures. While gene sequencing has significantly improved our understanding of the natural history of cancer and identified candidates for therapeutic targets, it cannot predict the impact of the biological response to therapies. Hence, patients with a common mutational profile may respond differently to the same therapy, due in part to different microenvironments impacting on gene regulation. This complexity arises from a feedback circuit involving epigenetic modifications made to genes by the metabolic byproducts of cancer cells. New insights into epigenetic mechanisms, activated early in the process of carcinogenesis, have been able to describe phenotypes which cannot be inferred from mutational analyses per se. Epigenetic changes can propagate throughout a tumor via heritable modifications that have long-lasting consequences on ensuing phenotypes. Such heritable epigenetic changes can be evoked profoundly by cancer cell metabolites, which then exercise a broad remit of actions across all stages of carcinogenesis, culminating with a meaningful impact on the tumor's response to therapy. This review outlines some of the cross-talk between heritable epigenetic changes and tumor cell metabolism, and the consequences of such changes on tumor progression.

Using Phosphatidylinositol Phosphorylation as Markers for Hyperglycemic Related Breast Cancer

Studies have suggested that type 2 diabetes (T2D) is associated with a higher incidence of breast cancer and related mortality rates. T2D postmenopausal women have an ~20% increased chance of developing breast cancer, and women with T2D and breast cancer have a 50% increase in mortality compared to breast cancer patients without diabetes. This correlation has been attributed to the general activation of insulin receptor signaling, glucose metabolism, phosphatidylinositol (PI) kinases, and growth pathways. Furthermore, the presence of breast cancer specific PI kinase and/or phosphatase mutations enhance metastatic breast cancer phenotypes. We hypothesized that each of the breast cancer subtypes may have characteristic PI phosphorylation profiles that are changed in T2D conditions. Therefore, we sought to characterize the PI phosphorylation when equilibrated in normal glycemic versus hyperglycemic serum conditions. Our results suggest that hyperglycemia leads to: 1) A reduction in PI3P and PIP3, with increased PI4P that is later converted to PI(3,4)P2 at the cell surface in hormone receptor positive breast cancer; 2) a reduction in PI3P and PI4P with increased PIP3 surface expression in human epidermal growth factor receptor 2-positive (HER2+) breast cancer; and 3) an increase in di- and tri-phosphorylated PIs due to turnover of PI3P in triple negative breast cancer. This study begins to describe some of the crucial changes in PIs that play a role in T2D related breast cancer incidence and metastasis.

Inhibition of glycogenolysis prolongs action potential repriming period and impairs muscle function in rat skeletal muscle

KEY POINTS

Muscle glycogen content is associated with muscle function, but the physiological link between the two is poorly understood. This study investigated the effects of inhibiting glycogenolysis, while maintaining high overall energy status, on different aspects of muscle function. We demonstrate here that Na⁺ ,K⁺ -ATPase activity depends on glycogenolytically derived ATP regardless of high global ATP, with a decrease in activity leading to reduced force production and accelerated fatigue development. The results support the concept of compartmentalized energy transfer with glycogen metabolism playing a crucial role in intramuscular ATP resynthesis and ion regulation. This study gives specific insights into muscular function and may help towards a better understanding of glycogen storage diseases and muscle fatigue.

ABSTRACT

Skeletal muscle glycogen content is associated with muscle function and fatigability. However, little is known about the physiological link between glycogen content and muscle function. Here we aimed to investigate the importance of glycogenolytically derived ATP per se on muscle force and action potential (AP) repriming period, i.e. the time before a second AP can be produced (indicative of Na⁺ ,K⁺ -ATPase activity). Single fibres from rat extensor digitorum longus muscles were isolated and mechanically skinned in order to investigate force production and the AP repriming period while global ATP and PCr concentrations were kept high. The importance of glycogenolytically derived ATP was studied by inhibition of glycogen phosphorylase (1,4-dideoxy-1,4-imino-d-arabinitol (DAB; 2 mm) or CP-316,819 (CP; 10 µm)) or glycogen removal (amyloglucosidase, 20 U ml^-1 ). Tetanic force decreased by (mean (SD)) 21 (15)% (P < 0.001) and 76 (28)% (DAB) or 94 (6)% (CP, P < 0.001) in well-polarized and partially depolarized fibres, respectively. In depolarized fibres, twitch force decreased by 16 (10)% and 55 (26)% with DAB and CP, respectively, with no effect in well-polarized fibres (84 (10)%, P = 0.14). There was no effect of glycogen phosphorylase inhibition on repriming period in well-polarized fibres (median (25th, 75th percentile): 5 (4, 5) vs. 4 (4, 5) ms, P = 0.26), while the repriming period was prolonged from 6 (5, 7) to 8 (7, 10) ms (P = 0.01) in partially depolarized fibres. In line with this, glycogen removal increased repriming period from 5 (5, 6) to 6 (5, 7) ms (P = 0.003) in depolarized fibres. Together, these data strongly indicate that blocking glycogenolysis attenuates Na⁺ ,K⁺ -ATPase activity, which in turn increases the repriming period and reduces force, demonstrating a functional link between glycogenolytically derived ATP and force production.

Cutting off the fuel supply to calcium pumps in pancreatic cancer cells: role of pyruvate kinase-M2 (PKM2)

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has poor survival and treatment options. PDAC cells shift their metabolism towards glycolysis, which fuels the plasma membrane calcium pump (PMCA), thereby preventing Ca2+-dependent cell death. The ATP-generating pyruvate kinase-M2 (PKM2) is oncogenic and overexpressed in PDAC. This study investigated the PKM2-derived ATP supply to the PMCA as a potential therapeutic locus.

METHODS

PDAC cell growth, migration and death were assessed by using sulforhodamine-B/tetrazolium-based assays, gap closure assay and poly-ADP ribose polymerase (PARP1) cleavage, respectively. Cellular ATP and metabolism were assessed using luciferase/fluorescent-based assays and the Seahorse XFe96 analyzer, respectively. Cell surface biotinylation identified membrane-associated proteins. Fura-2 imaging was used to assess cytosolic Ca2+ overload and in situ Ca2+ clearance. PKM2 knockdown was achieved using siRNA.

RESULTS

The PKM2 inhibitor (shikonin) reduced PDAC cell proliferation, cell migration and induced cell death. This was due to inhibition of glycolysis, ATP depletion, inhibition of PMCA and cytotoxic Ca2+ overload. PKM2 associates with plasma membrane proteins providing a privileged ATP supply to the PMCA. PKM2 knockdown reduced PMCA activity and reduced the sensitivity of shikonin-induced cell death.

CONCLUSIONS

Cutting off the PKM2-derived ATP supply to the PMCA represents a novel therapeutic strategy for the treatment of PDAC.

Sodium homeostasis in the tumour microenvironment

The concentration of sodium ions (Na+) is raised in solid tumours and can be measured at the cellular, tissue and patient levels. At the cellular level, the Na+ gradient across the membrane powers the transport of H+ ions and essential nutrients for normal activity. The maintenance of the Na+ gradient requires a large proportion of the cell's ATP. Na+ is a major contributor to the osmolarity of the tumour microenvironment, which affects cell volume and metabolism as well as immune function. Here, we review evidence indicating that Na+ handling is altered in tumours, explore our current understanding of the mechanisms that may underlie these alterations and consider the potential consequences for cancer progression. Dysregulated Na+ balance in tumours may open opportunities for new imaging biomarkers and re-purposing of drugs for treatment.

Mathematical Modeling of p53 Pathways

Cells have evolved balanced systems that ensure an appropriate response to stress. The systems elicit repair responses in temporary or moderate stress but eliminate irreparable cells via apoptosis in detrimental conditions of prolonged or severe stress. The tumor suppressor p53 is a central player in these stress response systems. When activated under DNA damage stress, p53 regulates hundreds of genes that are involved in DNA repair, cell cycle, and apoptosis. Recently, increasing studies have demonstrated additional regulatory roles of p53 in metabolism and mitochondrial physiology. Due to the inherent complexity of feedback loops between p53 and its target genes, the application of mathematical modeling has emerged as a novel approach to better understand the multifaceted functions and dynamics of p53. In this review, we discuss several mathematical modeling approaches in exploring the p53 pathways.

Co-Operation between Aneuploidy and Metabolic Changes in Driving Tumorigenesis

Alterations from the normal set of chromosomes are extremely common as cells progress toward tumourigenesis. Similarly, we expect to see disruption of normal cellular metabolism, particularly in the use of glucose. In this review, we discuss the connections between these two processes: how chromosomal aberrations lead to metabolic disruption, and vice versa. Both processes typically result in the production of elevated levels of reactive oxygen species, so we particularly focus on their role in mediating oncogenic changes.

Energetic costs regulated by cell mechanics and confinement are predictive of migration path during decision-making

Cell migration during the invasion-metastasis cascade requires cancer cells to navigate a spatially complex microenvironment that presents directional choices to migrating cells. Here, we investigate cellular energetics during migration decision-making in confined spaces. Theoretical and experimental data show that energetic costs for migration through confined spaces are mediated by a balance between cell and matrix compliance as well as the degree of spatial confinement to direct decision-making. Energetic costs, driven by the cellular work needed to generate force for matrix displacement, increase with increasing cell stiffness, matrix stiffness, and degree of spatial confinement, limiting migration. By assessing energetic costs between possible migration paths, we can predict the probability of migration choice. Our findings indicate that motility in confined spaces imposes high energetic demands on migrating cells, and cells migrate in the direction of least confinement to minimize energetic costs. Therefore, therapeutically targeting metabolism may limit cancer cell migration and metastasis.

Clonal expansion of vaccine-elicited T cells is independent of aerobic glycolysis

In contrast to responses against infectious challenge, T cell responses induced via adjuvanted subunit vaccination are dependent on interleukin-27 (IL-27). We show that subunit vaccine-elicited cellular responses are also dependent on IL-15, again in contrast to the infectious response. Early expression of interferon regulatory factor 4 (IRF4) was compromised in either IL-27- or IL-15-deficient environments after vaccination but not infection. Because IRF4 facilitates metabolic support of proliferating cells via aerobic glycolysis, we expected this form of metabolic activity to be reduced in the absence of IL-27 or IL-15 signaling after vaccination. Instead, metabolic flux analysis indicated that vaccine-elicited T cells used only mitochondrial function to support their clonal expansion. Loss of IL-27 or IL-15 signaling during vaccination resulted in a reduction in mitochondrial function, with no corresponding increase in aerobic glycolysis. Consistent with these observations, the T cell response to vaccination was unaffected by in vivo treatment with the glycolytic inhibitor 2-deoxyglucose, whereas the response to viral challenge was markedly lowered. Collectively, our data identify IL-27 and IL-15 as critical to vaccine-elicited T cell responses because of their capacity to fuel clonal expansion through a mitochondrial metabolic program previously thought only capable of supporting quiescent naïve and memory T cells.

Metabolic reprogramming in atherosclerosis: Opposed interplay between the canonical WNT/β-catenin pathway and PPARγ

Atherosclerosis, a chronic inflammatory and age-related disease, is a complex mechanism presenting a dysregulation of vessel structures. During this process, the canonical WNT/β-catenin pathway is increased whereas PPARγ is downregulated. The two systems act in an opposite manner. This paper reviews the opposing interplay of these systems and their metabolic-reprogramming pathway in atherosclerosis. Activation of the WNT/β-catenin pathway enhances the transcription of targets involved in inflammation, endothelial dysfunction, the proliferation of vascular smooth muscle cells, and vascular calcification. This complex mechanism, which is partly controlled by the WNT/β-catenin pathway, presents several metabolic dysfunctions. This phenomenon, called aerobic glycolysis (or the Warburg effect), consists of a shift in ATP production from mitochondrial oxidative phosphorylation to aerobic glycolysis, leading to the overproduction of intracellular lactate. This mechanism is partially due to the injury of mitochondrial respiration and an increase in the glycolytic pathway. In contrast, PPARγ agonists downregulate the WNT/β-catenin pathway. Therefore, the development of therapeutic targets, such as PPARγ agonists, for the treatment of atherosclerosis could be an interesting and innovative way of counteracting the canonical WNT pathway.

Molecular intricacies of aerobic glycolysis in cancer: current insights into the classic metabolic phenotype

Aerobic glycolysis is the process of oxidation of glucose into pyruvate followed by lactate production under normoxic condition. Distinctive from its anaerobic counterpart (i.e. glycolysis that occurs under hypoxia), aerobic glycolysis is frequently witnessed in cancers, popularly known as the "Warburg effect", and it is one of the earliest known evidences of metabolic alteration in neoplasms. Intracellularly, aerobic glycolysis circumvents mitochondrial oxidative phosphorylation (OxPhos), facilitating an increased rate of glucose hydrolysis. This in turn enables cancer cells to successfully compete with normal cells for glucose uptake in order to maintain uninterrupted growth. In addition, evading OxPhos mitigates excessive generation/accumulation of reactive oxygen species that otherwise may be deleterious to cells. Emerging data indicate that aerobic glycolysis in cancer also promotes glutaminolysis to satisfy the precursor requirements of certain biosynthetic processes (e.g. nucleic acids). Next, the metabolic intermediates of aerobic glycolysis also feed the pentose phosphate pathway (PPP) to facilitate macromolecular biosynthesis necessary for cancer cell growth and proliferation. Extracellularly, the extrusion of the end-product of aerobic glycolysis, i.e. lactate, alters the tumor microenvironment, and impacts cancer-associated cells. Collectively, accumulating data unequivocally demonstrate that aerobic glycolysis implicates myriad of molecular and functional processes to support cancer progression. This review, in the light of recent research, dissects the molecular intricacies of its regulation, and also deliberates the emerging paradigms to target aerobic glycolysis in cancer therapy.

Warburg effect, lactate dehydrogenase, and radio/chemo-therapy efficacy

The anaerobic metabolism of glucose by cancer cells, even under well-oxygenated conditions, has been documented by Otto Warburg as early as 1927. Micro-environmental hypoxia and intracellular pathways activating the hypoxia-related gene response, shift cancer cell metabolism to anaerobic pathways. In the current review, we focus on a major enzyme involved in anaerobic transformation of pyruvate to lactate, namely lactate dehydrogenase 5 (LDH5). The value of LDH5 as a marker of prognosis of cancer patients, as a predictor of response to radiotherapy (RT) and chemotherapy and, finally, as a major target for cancer treatment and radio-sensitization is reported and discussed. Clinical, translational and experimental data supporting the uniqueness of the LDHA gene and its product LDH5 isoenzyme are summarized and future directions for a metabolic treatment of cancer are highlighted.

Papaverine and its derivatives radiosensitize solid tumors by inhibiting mitochondrial metabolism

Tumor hypoxia reduces the effectiveness of radiation therapy by limiting the biologically effective dose. An acute increase in tumor oxygenation before radiation treatment should therefore significantly improve the tumor cell kill after radiation. Efforts to increase oxygen delivery to the tumor have not shown positive clinical results. Here we show that targeting mitochondrial respiration results in a significant reduction of the tumor cells' demand for oxygen, leading to increased tumor oxygenation and radiation response. We identified an activity of the FDA-approved drug papaverine as an inhibitor of mitochondrial complex I. We also provide genetic evidence that papaverine's complex I inhibition is directly responsible for increased oxygenation and enhanced radiation response. Furthermore, we describe derivatives of papaverine that have the potential to become clinical radiosensitizers with potentially fewer side effects. Importantly, this radiosensitizing strategy will not sensitize well-oxygenated normal tissue, thereby increasing the therapeutic index of radiotherapy.

Near-simultaneous quantification of glucose uptake, mitochondrial membrane potential, and vascular parameters in murine flank tumors using quantitative diffuse reflectance and fluorescence spectroscopy

The shifting metabolic landscape of aggressive tumors, with fluctuating oxygenation conditions and temporal changes in glycolysis and mitochondrial metabolism, is a critical phenomenon to study in order to understand negative treatment outcomes. Recently, we have demonstrated near-simultaneous optical imaging of mitochondrial membrane potential (MMP) and glucose uptake in non-tumor window chambers, using the fluorescent probes tetramethylrhodamine ethyl ester (TMRE) and 2-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG). Here, we demonstrate a complementary technique to perform near-simultaneous in vivo optical spectroscopy of tissue vascular parameters, glucose uptake, and MMP in a solid tumor model that is most often used for therapeutic studies. Our study demonstrates the potential of optical spectroscopy as an effective tool to quantify the vascular and metabolic characteristics of a tumor, which is an important step towards understanding the mechanisms underlying cancer progression, metastasis, and resistance to therapies.

Hypoxia and acidosis: immune suppressors and therapeutic targets

Due to imbalances between vascularity and cellular growth patterns, the tumour microenvironment harbours multiple metabolic stressors including hypoxia and acidosis, which have significant influences on remodelling both tumour and peritumoral tissues. These stressors are also immunosuppressive and can contribute to escape from immune surveillance. Understanding these effects and characterizing the pathways involved can identify new targets for therapy and may redefine our understanding of traditional anti-tumour therapies. In this review, the effects of hypoxia and acidosis on tumour immunity will be summarized, and how modulating these parameters and their sequelae can be a useful tool for future therapeutic interventions is discussed.

Regulation of Cellular Metabolism by High-Risk Human Papillomaviruses

The alteration of glucose metabolism is one of the first biochemical characteristics associated with cancer cells since most of these cells increase glucose consumption and glycolytic rates even in the presence of oxygen, which has been called “aerobic glycolysis” or the Warburg effect. Human papillomavirus (HPV) is associated with approximately 5% of all human cancers worldwide, principally to cervical cancer. E6 and E7 are the main viral oncoproteins which are required to preserve the malignant phenotype. These viral proteins regulate the cell cycle through their interaction with tumor suppressor proteins p53 and pRB, respectively. Together with the viral proteins E5 and E2, E6 and E7 can favor the Warburg effect and contribute to radio- and chemoresistance through the increase in the activity of glycolytic enzymes, as well as the inhibition of the Krebs cycle and the respiratory chain. These processes lead to a fast production of ATP obtained by Warburg, which could help satisfy the high energy demands of cancer cells during proliferation. In this way HPV proteins could promote cancer hallmarks. However, it is also possible that during an early HPV infection, the Warburg effect could help in the achievement of an efficient viral replication.

Metaboloptics: Visualization of the tumor functional landscape via metabolic and vascular imaging

Many cancers adeptly modulate metabolism to thrive in fluctuating oxygen conditions; however, current tools fail to image metabolic and vascular endpoints at spatial resolutions needed to visualize these adaptations in vivo. We demonstrate a high-resolution intravital microscopy technique to quantify glucose uptake, mitochondrial membrane potential (MMP), and SO₂ to characterize the in vivo phentoypes of three distinct murine breast cancer lines. Tetramethyl rhodamine, ethyl ester (TMRE) was thoroughly validated to report on MMP in normal and tumor-bearing mice. Imaging MMP or glucose uptake together with vascular endpoints revealed that metastatic 4T1 tumors maintained increased glucose uptake across all SO₂ (“Warburg effect”), and also showed increased MMP relative to normal tissue. Non-metastatic 67NR and 4T07 tumor lines both displayed increased MMP, but comparable glucose uptake, relative to normal tissue. The 4T1 peritumoral areas also showed a significant glycolytic shift relative to the tumor regions. During a hypoxic stress test, 4T1 tumors showed significant increases in MMP with corresponding significant drops in SO₂, indicative of intensified mitochondrial metabolism. Conversely, 4T07 and 67NR tumors shifted toward glycolysis during hypoxia. Our findings underscore the importance of imaging metabolic endpoints within the context of a living microenvironment to gain insight into a tumor’s adaptive behavior.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

Simulation of Cellular Energy Restriction in Quiescence (ERiQ)-A Theoretical Model for Aging

Cellular responses to energy stress involve activation of pro-survival signaling nodes, compensation in regulatory pathways and adaptations in organelle function. Specifically, energy restriction in quiescent cells (ERiQ) through energetic perturbations causes adaptive changes in response to reduced ATP, NAD+ and NADP levels in a regulatory network spanned by AKT, NF-κB, p53 and mTOR. Based on the experimental ERiQ platform, we have constructed a minimalistic theoretical model consisting of feedback motifs that enable investigation of stress-signaling pathways. The computer simulations reveal responses to acute energetic perturbations, promoting cellular survival and recovery to homeostasis. We speculated that the very same stress mechanisms are activated during aging in post-mitotic cells. To test this hypothesis, we modified the model to be deficient in protein damage clearance and demonstrate the formation of energy stress. Contrasting the network’s pro-survival role in acute energetic challenges, conflicting responses in aging disrupt mitochondrial maintenance and contribute to a lockstep progression of decline when chronically activated. The model was analyzed by a local sensitivity analysis with respect to lifespan and makes predictions consistent with inhibitory and gain-of-function experiments in aging.

Metabolic cooperation between co-cultured lung cancer cells and lung fibroblasts

Cooperation of cancer cells with stromal cells, such as cancer-associated fibroblasts (CAFs), has been revealed as a mechanism sustaining cancer cell survival and growth. In the current study, we focus on the metabolic interactions of MRC5 lung fibroblasts with lung cancer cells (A549 and H1299) using co-culture experiments and studying changes of the metabolic protein expression profile and of their growth and migration abilities. Using western blotting, confocal microscopy and RT-PCR, we observed that in co-cultures MRC5 respond by upregulating pyruvate dehydrogenase (PDH) and the monocarboxylate transporter MCT1. In contrast, cancer cells increase the expression of glucose transporters (GLUT1), LDH5, PDH kinase and the levels of phosphorylated/inactivated pPDH. H1299 cells growing in the same culture medium with fibroblasts exhibit a 'metastasis-like' phenomenon by forming nests within the fibroblast area. LDH5 and pPDH were drastically upregulated in these nests. The growth rate of both MRC5 and cancer cells increased in co-cultures. Suppression of LDHA or PDK1 in cancer cells abrogates the stimulatory signal from cancer cells to fibroblasts. Incubation of MRC5 fibroblasts with lactate resulted in an increase of LDHB and of PDH expression. Silencing of PDH gene in fibroblasts, or silencing of PDK1 or LDHA gene in tumor cells, impedes cancer cell's migration ability. Overall, a metabolic cooperation between lung cancer cells and fibroblasts has been confirmed in the context of direct Warburg effect, thus the fibroblasts reinforce aerobic metabolism to support the intensified anaerobic glycolytic pathways exploited by cancer cells.

Palliative treatment efficacy of glucose inhibition combined with chemotherapy for non-small cell lung cancer with widespread bone and brain metastases: A case report

Otto Warburg observed in 1924 that cancer cells were dependent exclusively on glycolysis for the production of energy even in the presence of oxygen (the 'Warburg effect'). Consequently, cancer cells require ~19 times more glucose uptake to obtain equivalent amounts of energy as normal cells. The Warburg effect is the scientific basis for positron emission tomography (PET), which has markedly improved cancer detection. During chemotherapy, cancer cells may upregulate their expression of multi-drug resistance proteins and ultimately cause treatment failure. As multi-drug resistance proteins require energy to operate, the present report evaluated the potential clinical efficacy of lowering blood glucose with insulin during chemotherapy for a patient with advanced pulmonary adenocarcinoma with multiple metastases. A 64-year-old male was admitted to the Department of Medical Oncology at Changzhou Tumor Hospital (Changzhou, China) due to an irritating cough and multiple bone pain. PET/computed tomography (CT) with F-18 fluorodeoxy glucose (18F-FDG) identified multiple hypermetabolic foci in the right hilum, right upper lung, shoulder blades, thoracic vertebrae, lumbar, sacrum, bilateral iliac crest and pelvis. Additionally, magnetic resonance imaging detected multiple metastases in the brain. The patient received 56 repeat treatments with insulin to induce hypoglycemia combined with reduced doses of chemotherapy over an 8-month period. For each treatment, insulin at 0.2 U/kg body weight was injected intravenously (i.v.), and when blood glucose level reached 2.5-3.0 mmol/l, navelbine (10 mg), cisplatin (10 mg) and fluorouracil (250 mg) were injected (i.v.) over a period of ~10 min. The patient's blood glucose level was returned to normal immediately after chemotherapy with an i.v. injection of 20 ml 50% glucose solution. During the 8-month chemotherapy regimen, the patient received two PET/CT follow-ups. The results demonstrated that the levels of 18F-FDG uptake in all lesions had been reduced. In addition, the patient exhibited improved appetite and weight gain, a reduced cough, and had less pain. The levels of tumor markers, namely carcinoembryonic antigen, carcinoma antigen 15-3, CYRA21-1, neuron-specific enolase, also declined gradually. These results suggest that controlled, mild hypoglycemia may be safely combined with low dose chemotherapy to provide clinical benefit for advanced non-small cell lung cancer.

Near-simultaneous intravital microscopy of glucose uptake and mitochondrial membrane potential, key endpoints that reflect major metabolic axes in cancer

While the demand for metabolic imaging has increased in recent years, simultaneous in vivo measurement of multiple metabolic endpoints remains challenging. Here we report on a novel technique that provides in vivo high-resolution simultaneous imaging of glucose uptake and mitochondrial metabolism within a dynamic tissue microenvironment. Two indicators were leveraged; 2-[N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG) reports on glucose uptake and Tetramethylrhodamine ethyl ester (TMRE) reports on mitochondrial membrane potential. Although we demonstrated that there was neither optical nor chemical crosstalk between 2-NBDG and TMRE, TMRE uptake was significantly inhibited by simultaneous injection with 2-NBDG in vivo. A staggered delivery scheme of the two agents (TMRE injection was followed by 2-NBDG injection after a 10-minute delay) permitted near-simultaneous in vivo microscopy of 2-NBDG and TMRE at the same tissue site by mitigating the interference of 2-NBDG with normal glucose usage. The staggered delivery strategy was evaluated under both normoxic and hypoxic conditions in normal tissues as well as in a murine breast cancer model. The results were consistent with those expected for independent imaging of 2-NBDG and TMRE. This optical imaging technique allows for monitoring of key metabolic endpoints with the unique benefit of repeated, non-destructive imaging within an intact microenvironment.

The Warburg effect as an adaptation of cancer cells to rapid fluctuations in energy demand

To maintain optimal fitness, a cell must balance the risk of inadequate energy reserve for response to a potentially fatal perturbation against the long-term cost of maintaining high concentrations of ATP to meet occasional spikes in demand. Here we apply a game theoretic approach to address the dynamics of energy production and expenditure in eukaryotic cells. Conventionally, glucose metabolism is viewed as a function of oxygen concentrations in which the more efficient oxidation of glucose to CO₂ and H₂O produces all or nearly all ATP except under hypoxic conditions when less efficient (2 ATP/ glucose vs. about 36ATP/glucose) anaerobic metabolism of glucose to lactic acid provides an emergency backup. We propose an alternative in which energy production is governed by the complex temporal and spatial dynamics of intracellular ATP demand. In the short term, a cell must provide energy for constant baseline needs but also maintain capacity to rapidly respond to fluxes in demand particularly due to external perturbations on the cell membrane. Similarly, longer-term dynamics require a trade-off between the cost of maintaining high metabolic capacity to meet uncommon spikes in demand versus the risk of unsuccessfully responding to threats or opportunities. Here we develop a model and computationally explore the cell’s optimal mix of glycolytic and oxidative capacity. We find the Warburg effect, high glycolytic metabolism even under normoxic conditions, is represents a metabolic strategy that allow cancer cells to optimally meet energy demands posed by stochastic or fluctuating tumor environments.

Blocking LDHA glycolytic pathway sensitizes glioblastoma cells to radiation and temozolomide

PURPOSE

Up-regulation of lactate dehydrogenase LDHA, is a frequent event in human malignancies and relate to poor postoperative outcome. In the current study we examined the hypothesis that LDHA and anaerobic glycolysis, may contribute to the resistance of glioblastoma to radiotherapy and to temozolomide.

METHODS AND MATERIALS

The expression of LDH5 isoenzyme (fully encoded by the LDHA gene) was assessed in human glioblastoma tissues. Experimental in vitro studies involved the T98 and U87 glioblastoma cell lines. Their sensitivity to radiotherapy and to temozolomide, following silencing of LDHA gene or following exposure to the LDHA chemical inhibitor 'oxamate' and to the glycolysis inhibitor '2-deoxy-d-glucose' (2DG), was studied.

RESULTS

Glioblastoma tissues showed strong cytoplasmic and nuclear LDH5 expression in 0-90% (median 20%) of the neoplastic cells. T98 and U87 cell lines showed that blocking glycolysis, either with LDHA gene silencing or exposure to oxamate (30 mM) and blockage of glycolysis with 2DG (500 μM), results in enhanced radiation sensitivity, an effect that was more robust in the T98 radioresistant cell line. Furthermore, all three glycolysis targeting methods, significantly sensitized both cell lines to Temozolomide.

CONCLUSIONS

The current study provides evidence that a large subgroup of human glioblastomas are highly glycolytic, and that inhibitors of glycolysis, like LDHA targeting agents, may prove of therapeutic importance by enhancing the efficacy of radiotherapy and temozolomide against this lethal disease.

Metabolic reprogramming in the tumour microenvironment: a hallmark shared by cancer cells and T lymphocytes

Altered metabolism is a hallmark of cancers, including shifting oxidative phosphorylation to glycolysis and up-regulating glutaminolysis to divert carbon sources into biosynthetic pathways that promote proliferation and survival. Therefore, metabolic inhibitors represent promising anti-cancer drugs. However, T cells must rapidly divide and survive in harsh microenvironments to mediate anti-cancer effects. Metabolic profiles of cancer cells and activated T lymphocytes are similar, raising the risk of metabolic inhibitors impairing the immune system. Immune checkpoint blockade provides an example of how metabolism can be differentially impacted to impair cancer cells but support T cells. Implications for research with metabolic inhibitors are discussed.

A Flux Balance of Glucose Metabolism Clarifies the Requirements of the Warburg Effect

The Warburg effect, or aerobic glycolysis, is marked by the increased metabolism of glucose to lactate in the presence of oxygen. Despite its widespread prevalence in physiology and cancer biology, the causes and consequences remain incompletely understood. Here, we show that a simple balance of interacting fluxes in glycolysis creates constraints that impose the necessary conditions for glycolytic flux to generate lactate as opposed to entering into the mitochondria. These conditions are determined by cellular redox and energy demands. By analyzing the constraints and sampling the feasible region of the model, we further study how cell proliferation rate and mitochondria-associated NADH oxidizing and ATP producing fluxes are interlinked. Together this analysis illustrates the simplicity of the origins of the Warburg effect by identifying the flux distributions that are necessary for its instantiation.

Expression of enzymes related to glucose metabolism in non-small cell lung cancer and prognosis

Purpose/Aim: Cancer cells are addicted to glycolytic anaerobic pathways, in presence or in absence of a functional Krebs' cycle (phenomenon Warburg). This metabolic predilection relies on both extracellular (impaired vascularization and oxygenation) and intracellular (oncogenic activation of genes) causes.

MATERIALS AND METHODS

We investigated the expression and prognostic relevance of enzymes involved in the glucose absorption and metabolism, monocarboxylate transporter (MCT) expression, MCT1 and MCT2, pentose pathway (Glucose-6-phospahte dehydrogenase G6PD), glycogene synthesis (glycogene synthase GYS1), glycolysis (Hexokinase HXKII, phosphofructokinase PFK1, fructose biphosphate aldolase), fate of pyruvate (pyruvate dehydrogenase PDH, phosphorylated pPDH, PDH kinase PDK1, lactate dehydrogenase LDH5 and LDH1) and key Kreb's cycle enzymes (citrate synthase CSynth and isocitrate dehydrogenase IDH).

RESULTS

A strong overexpression of the above enzymes/proteins was noted in a varying percentage of cases examined. An interesting significant correlation between the enzymes involved in glycolysis and with the LDH5 was noted. Adenocarcinomas expressed higher levels of GLUT1 and MCT2 compared to other subtypes. Stage (p = 0.0001), aldolase (p = 0.004), LDH5 (p = 0.008), GLUT2 (p = 0.008), MCT2 (p = 0.009), GSYS1 (p = 0.04), and GLUT1 (p = 0.05) were significantly related with poor disease specific overall survival. In multivariate analysis stage (p = 0.001), LDH5 (p = 0.04), pPDH (p = 0.04), and aldolase (p = 0.04) were independent prognostic variables.

CONCLUSION

It is concluded that an orchestrated activation of glucose absorption and metabolism towards anaerobic pathways characterize the majority of NSCLC, and this phenotype is strongly linked with an aggressive clinical behavior. This glycolytic addiction of lung cancer cell is revealed as a key therapeutic target.

Unravelling the complexity of signalling networks in cancer: A review of the increasing role for computational modelling

Cancer induction is a highly complex process involving hundreds of different inducers but whose eventual outcome is the same. Clearly, it is essential to understand how signalling pathways and networks generated by these inducers interact to regulate cell behaviour and create the cancer phenotype. While enormous strides have been made in identifying key networking profiles, the amount of data generated far exceeds our ability to understand how it all "fits together". The number of potential interactions is astronomically large and requires novel approaches and extreme computation methods to dissect them out. However, such methodologies have high intrinsic mathematical and conceptual content which is difficult to follow. This review explains how computation modelling is progressively finding solutions and also revealing unexpected and unpredictable nano-scale molecular behaviours extremely relevant to how signalling and networking are coherently integrated. It is divided into linked sections illustrated by numerous figures from the literature describing different approaches and offering visual portrayals of networking and major conceptual advances in the field. First, the problem of signalling complexity and data collection is illustrated for only a small selection of known oncogenes. Next, new concepts from biophysics, molecular behaviours, kinetics, organisation at the nano level and predictive models are presented. These areas include: visual representations of networking, Energy Landscapes and energy transfer/dissemination (entropy); diffusion, percolation; molecular crowding; protein allostery; quinary structure and fractal distributions; energy management, metabolism and re-examination of the Warburg effect. The importance of unravelling complex network interactions is then illustrated for some widely-used drugs in cancer therapy whose interactions are very extensive. Finally, use of computational modelling to develop micro- and nano- functional models ("bottom-up" research) is highlighted. The review concludes that computational modelling is an essential part of cancer research and is vital to understanding network formation and molecular behaviours that are associated with it. Its role is increasingly essential because it is unravelling the huge complexity of cancer induction otherwise unattainable by any other approach.

Hif-1α Knockdown Reduces Glycolytic Metabolism and Induces Cell Death of Human Synovial Fibroblasts Under Normoxic Conditions

Increased glycolysis and HIF-1α activity are characteristics of cells under hypoxic or inflammatory conditions. Besides, in normal O₂ environments, elevated rates of glycolysis support critical cellular mechanisms such as cell survival. The purpose of this study was to analyze the contribution of HIF-1α to the energy metabolism and survival of human synovial fibroblasts (SF) under normoxic conditions. HIF-1α was silenced using lentiviral vectors or small-interfering RNA (siRNA) duplexes. Expression analysis by qRT-PCR and western blot of known HIF-1α target genes in hypoxia demonstrated the presence of functional HIF-1α in normoxic SF and confirmed the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a HIF-1α target even in normoxia. HIF-1α silencing induced apoptotic cell death in cultured SF and, similarly, treatment with glycolytic, but not with OXPHOS inhibitors, induced SF death. Finally, in vivo HIF-1α targeting by siRNA showed a significant reduction in the viability of human SF engrafted into a murine air pouch. Our results demonstrate that SF are highly dependent on glycolytic metabolism and that HIF-1α plays a regulatory role in glycolysis even under aerobic conditions. Local targeting of HIF-1α provides a feasible strategy to reduce SF hyperplasia in chronic arthritic diseases.

The vicious circle of hypometabolism in neurodegenerative diseases: Ways and mechanisms of metabolic correction

Hypometabolism, characterized by decreased brain glucose consumption, is a common feature of many neurodegenerative diseases. Initial hypometabolic brain state, created by characteristic risk factors, may predispose the brain to acquired epilepsy and sporadic Alzheimer's and Parkinson's diseases, which are the focus of this review. Analysis of available data suggests that deficient glucose metabolism is likely a primary initiating factor for these diseases, and that resulting neuronal dysfunction further promotes the metabolic imbalance, establishing an effective positive feedback loop and a downward spiral of disease progression. Therefore, metabolic correction leading to the normalization of abnormalities in glucose metabolism may be an efficient tool to treat the neurological disorders by counteracting their primary pathological mechanisms. Published and preliminary experimental results on this approach for treating Alzheimer's disease and epilepsy models support the efficacy of metabolic correction, confirming the highly promising nature of the strategy. © 2017 Wiley Periodicals, Inc.

Inflammatory role of high salt level in tumor microenvironment (Review)

Chronic inflammation is known to play a critical role in cancer development and progression. High salt is known to mediate several chronic inflammatory diseases including hypertension, myocardial infarction, neurological ischemic attack, autoimmune diseases and cancers. High salt level is shown to induce angiogenesis and immune-dysfunction, both of which play a direct role in cancer proliferation. Furthermore, salt has been suggested to enhance Warburg-like metabolic phenotype in cancer cells and at the same time also induce pro-tumor MΦ2-macrophage phenotype. Recent studies have identified several molecular targets such as tonicity specific transcript factor NFAT5/TonEBP, sodium ion channel γENaC, and vascular endothelial growth factor, VEGF, which are upregulated under high salt external environment. These molecular targets offer futuristic therapeutic application in precision medicine. In this review, we discuss the current understanding of the salt mediated metabolic and immune dysfunctions playing a potential role in cancerous changes.

Quantifying intracellular rates of glycolytic and oxidative ATP production and consumption using extracellular flux measurements

Partitioning of ATP generation between glycolysis and oxidative phosphorylation is central to cellular bioenergetics but cumbersome to measure. We describe here how rates of ATP generation by each pathway can be calculated from simultaneous measurements of extracellular acidification and oxygen consumption. We update theoretical maximum ATP yields by mitochondria and cells catabolizing different substrates. Mitochondrial P/O ratios (mol of ATP generated per mol of [O] consumed) are 2.73 for oxidation of pyruvate plus malate and 1.64 for oxidation of succinate. Complete oxidation of glucose by cells yields up to 33.45 ATP/glucose with a maximum P/O of 2.79. We introduce novel indices to quantify bioenergetic phenotypes. The glycolytic index reports the proportion of ATP production from glycolysis and identifies cells as primarily glycolytic (glycolytic index > 50%) or primarily oxidative. The Warburg effect is a chronic increase in glycolytic index, quantified by the Warburg index. Additional indices quantify the acute flexibility of ATP supply. The Crabtree index and Pasteur index quantify the responses of oxidative and glycolytic ATP production to alterations in glycolysis and oxidative reactions, respectively; the supply flexibility index quantifies overall flexibility of ATP supply; and the bioenergetic capacity quantifies the maximum rate of total ATP production. We illustrate the determination of these indices using C2C12 myoblasts. Measurement of ATP use revealed no significant preference for glycolytic or oxidative ATP by specific ATP consumers. Overall, we demonstrate how extracellular fluxes quantitatively reflect intracellular ATP turnover and cellular bioenergetics. We provide a simple spreadsheet to calculate glycolytic and oxidative ATP production rates from raw extracellular acidification and respiration data.

Mathematical modeling links Wnt signaling to emergent patterns of metabolism in colon cancer

Cell-intrinsic metabolic reprogramming is a hallmark of cancer that provides anabolic support to cell proliferation. How reprogramming influences tumor heterogeneity or drug sensitivities is not well understood. Here, we report a self-organizing spatial pattern of glycolysis in xenograft colon tumors where pyruvate dehydrogenase kinase (PDK1), a negative regulator of oxidative phosphorylation, is highly active in clusters of cells arranged in a spotted array. To understand this pattern, we developed a reaction-diffusion model that incorporates Wnt signaling, a pathway known to upregulate PDK1 and Warburg metabolism. Partial interference with Wnt alters the size and intensity of the spotted pattern in tumors and in the model. The model predicts that Wnt inhibition should trigger an increase in proteins that enhance the range of Wnt ligand diffusion. Not only was this prediction validated in xenograft tumors but similar patterns also emerge in radiochemotherapy-treated colorectal cancer. The model also predicts that inhibitors that target glycolysis or Wnt signaling in combination should synergize and be more effective than each treatment individually. We validated this prediction in 3D colon tumor spheroids.

Inhibition of the pentose phosphate pathway by dichloroacetate unravels a missing link between aerobic glycolysis and cancer cell proliferation

Glucose fermentation through glycolysis even in the presence of oxygen (Warburg effect) is a common feature of cancer cells increasingly considered as an enticing target in clinical development. This study aimed to analyze the link between metabolism, energy stores and proliferation rates in cancer cells. We found that cell proliferation, evaluated by DNA synthesis quantification, is correlated to glycolytic efficiency in six cancer cell lines as well as in isogenic cancer cell lines. To further investigate the link between glycolysis and proliferation, a pharmacological inhibitior of the pentose phosphate pathway (PPP) was used. We demonstrated that reduction of PPP activity decreases cancer cells proliferation, with a profound effect in Warburg-phenotype cancer cells. The crucial role of the PPP in sustaining cancer cells proliferation was confirmed using siRNAs against glucose-6-phosphate dehydrogenase, the first and rate-limiting enzyme of the PPP. In addition, we found that dichloroacetate (DCA), a new clinically tested compound, induced a switch of glycolytic cancer cells to a more oxidative phenotype and decreased proliferation. By demonstrating that DCA decreased the activity of the PPP, we provide a new mechanism by which DCA controls cancer cells proliferation.

Acute stimulation of glucose influx upon mitoenergetic dysfunction requires LKB1, AMPK, Sirt2 and mTOR-RAPTOR

Mitochondria play a central role in cellular energy production, and their dysfunction can trigger a compensatory increase in glycolytic flux to sustain cellular ATP levels. Here, we studied the mechanism of this homeostatic phenomenon in C2C12 myoblasts. Acute (30 min) mitoenergetic dysfunction induced by the mitochondrial inhibitors piericidin A and antimycin A stimulated Glut1-mediated glucose uptake without altering Glut1 (also known as SLC2A1) mRNA or plasma membrane levels. The serine/threonine liver kinase B1 (LKB1; also known as STK11) and AMP-activated protein kinase (AMPK) played a central role in this stimulation. In contrast, ataxia-telangiectasia mutated (ATM; a potential AMPK kinase) and hydroethidium (HEt)-oxidizing reactive oxygen species (ROS; increased in piericidin-A- and antimycin-A-treated cells) appeared not to be involved in the stimulation of glucose uptake. Treatment with mitochondrial inhibitors increased NAD⁺ and NADH levels (associated with a lower NAD⁺:NADH ratio) but did not affect the level of Glut1 acetylation. Stimulation of glucose uptake was greatly reduced by chemical inhibition of Sirt2 or mTOR-RAPTOR. We propose that mitochondrial dysfunction triggers LKB1-mediated AMPK activation, which stimulates Sirt2 phosphorylation, leading to activation of mTOR-RAPTOR and Glut1-mediated glucose uptake.

Synergistic cell death in FLT3-ITD positive acute myeloid leukemia by combined treatment with metformin and 6-benzylthioinosine

Current therapy for acute myeloid leukemia (AML) primarily includes high-dose cytotoxic chemotherapy with or without allogeneic stem cell transplantation. Targeting unique cellular metabolism of cancer cells is a potentially less toxic approach. Monotherapy with mitochondrial inhibitors like metformin have met with limited success since escape mechanisms such as increased glycolytic ATP production, especially in hyperglycemia, can overcome the metabolic blockade. As an alternative strategy for metformin therapy, we hypothesized that the combination of 6-benzylthioinosine (6-BT), a broad-spectrum metabolic inhibitor, and metformin could block this drug resistance mechanism. Metformin treatment alone resulted in significant suppression of ROS and mitochondrial respiration with increased glycolysis accompanied by modest cytotoxicity (10-25%). In contrast, 6-BT monotherapy resulted in inhibition of glucose uptake, decreased glycolysis, and decreased ATP with minimal changes in ROS and mitochondrial respiration. The combination of 6-BT with metformin resulted in significant cytotoxicity (60-70%) in monocytic AML cell lines and was associated with inhibition of FLT3-ITD activated STAT5 and reduced c-Myc and GLUT-1 expression. Therefore, although the anti-tumor and metabolic effects of metformin have been limited by the metabolic reprogramming within cells, the novel combination of 6-BT and metformin targets this bypass mechanism resulting in reduced glycolysis, STAT5 inhibition, and increased cell death.

Oleanolic Acid Inhibits High Salt-Induced Exaggeration of Warburg-like Metabolism in Breast Cancer Cells

Cancer cells have a proliferative advantage by utilizing intermediates of aerobic glycolysis (Warburg effect) for their macromolecule synthesis. Although the exact causes of this Warburg effect are unclear, high osmotic stress in solid tumor microenvironment is considered one of the important factors. Oleanolic acid (OA) is known to exert anti-inflammatory and anti-cancer effect. In our current studies, using breast cancer cell lines, we determined the protective role of OA in high salt-mediated osmotic stress-induced cancer growth. Hypertonic (0.16 M NaCl) culture conditions enhanced the cancer cell growth (26 %, p < 0.05) and aerobic glycolysis as marked by increased glucose consumption (34 %, p < 0.05) and lactate production (25 %, p < 0.05) over untreated cells. This effect was associated with increased expression and activity of key rate-limiting enzymes of aerobic glycolysis, namely hexokinase, pyruvate kinase type M2, and lactate dehydrogenase A. Interestingly, this high salt-mediated enhanced expression of aerobic glycolytic enzymes was efficiently reversed by OA along with the decreased cancer cell proliferation. In cancer cells, enhanced aerobic glycolysis is associated with the decreased mitochondrial activity and mitochondrial-associated caspase activity. As expected, high salt further inhibited the mitochondrial related cytochrome oxidase and caspase-3 activity. However, OA efficiently reversed the high salt-mediated inhibition of cytochrome oxidase, caspase activity, and pro-apoptotic Bax expression, thus suggesting that OA induced mitochondrial activity and enhanced apoptosis. Taken together, our data indicate that OA efficiently reverses the enhanced Warburg-like metabolism induced by high salt-mediated osmotic stress along with potential application of OA in anti-cancer therapy.

Determining Maximum Glycolytic Capacity Using Extracellular Flux Measurements

Measurements of glycolytic rate and maximum glycolytic capacity using extracellular flux analysis can give crucial information about cell status and phenotype during normal operation, development of pathology, differentiation, and malignant transformation. They are also of great use when assessing the effects of chemical or drug treatments. Here, we experimentally define maximum glycolytic capacity, demonstrate how it differs from glycolytic rate, and provide a protocol for determining the basal glycolytic rate and maximum glycolytic capacity in cells using extracellular flux measurements. The results illustrate the power of extracellular flux analysis to describe the energetics of adherent cells in culture in a fully quantitative way.