Glucose deprivation activates a metabolic and signaling amplification loop leading to cell death

Multistability maintains redox homeostasis in human cells

Cells metabolize nutrients through a complex metabolic and signaling network that governs redox homeostasis. At the core of this, redox regulatory network is a mutually inhibitory relationship between reduced glutathione and reactive oxygen species (ROS)-two opposing metabolites that are linked to upstream nutrient metabolic pathways (glucose, cysteine, and glutamine) and downstream feedback loops of signaling pathways (calcium and NADPH oxidase). We developed a nutrient-redox model of human cells to understand system-level properties of this network. Combining in silico modeling and ROS measurements in individual cells, we show that ROS dynamics follow a switch-like, all-or-none response upon glucose deprivation at a threshold that is approximately two orders of magnitude lower than its physiological concentration. We also confirm that this ROS switch can be irreversible and exhibits hysteresis, a hallmark of bistability. Our findings evidence that bistability modulates redox homeostasis in human cells and provide a general framework for quantitative investigations of redox regulation in humans.

SERS monitoring of local pH in encapsulated therapeutic cells

Microencapsulation of therapeutic cells has widely advanced toward the development of treatments for various diseases, in particular seeking the protection of cell transplants from immune rejection. However, several challenges in cell therapy remain due to the lack of suitable methods to monitor in vivo microcapsule tracking, microcapsule stability and/or altered cell viability and proliferation upon transplantation. We propose in this work the incorporation of contrast agents in microcapsules, which can be easily visualized by SERS imaging. By placing SERS probes in the alginate extracellular layer, a high contrast can be obtained with negligible toxicity. Specifically, we used a pH-sensitive SERS tracking probe consisting of gold nanostars encoded with a pH-sensitive Raman-active molecule, and protected by a layer of biocompatible polymer coating, grafted on the nanoparticles via electrostatic interactions. This nanomaterial is highly sensitive within the biologically relevant pH range, 5.5-7.8. We demonstrate that this SERS-based pH sensor can provide information about cell death of microencapsulated cells, in a non-invasive manner. As a result, we expect that this approach should provide a general strategy to study biological interactions at the microcapsule level.

Metabolic stress regulates genome-wide transcription in a PTEN-dependent manner

PTEN is implicated in a wide variety of pathophysiological conditions and traditionally studied in the context of the PIK3-AKT-mTOR axis. Recent studies from our group and others have reported a novel role of PTEN in the regulation of transcription at the genome-wide scale. This emerging role of PTEN on global transcriptional regulation is providing a better understanding of various diseases, including cancer. Because cancer progression is an energy-demanding process and PTEN is known to regulate metabolic processes, we sought to understand the role of PTEN in transcriptional regulation under metabolic stress, a condition often developing in the tumor microenvironment. In the present study, we demonstrate that PTEN modulates genome-wide RNA Polymerase II occupancy in cells undergoing glucose deprivation. The glucose-deprived PTEN null cells were found to continue global gene transcription, which may activate a survival mode. However, cells with constitutive PTEN expression slow transcription, an evolutionary mechanism that may save cellular energy and activate programmed cell death pathways, in the absence of glucose. Interestingly, alternative exon usage by PTEN null cells is increased under metabolic stress in contrast to PTEN-expressing cells. Overall, our study demonstrates distinct mechanisms involved in PTEN-dependent genome-wide transcriptional control under metabolic stress. Our findings provide a new insight in understanding tumor pathology and how PTEN loss of function, whether by genetic or non-genetic mechanisms, can contribute to a favorable transcriptional program employed by tumor cells to escape apoptosis, hence developing more aggressive and metastatic phenotypes.

Metabolic reprogramming in chondrocytes to promote mitochondrial respiration reduces downstream features of osteoarthritis

Metabolic dysfunction in chondrocytes drives the pro-catabolic phenotype associated with osteoarthritic cartilage. In this study, substitution of galactose for glucose in culture media was used to promote a renewed dependence on mitochondrial respiration and oxidative phosphorylation. Galactose replacement alone blocked enhanced usage of the glycolysis pathway by IL1β-activated chondrocytes as detected by real-time changes in the rates of proton acidification of the medium and changes in oxygen consumption. The change in mitochondrial activity due to galactose was visualized as a rescue of mitochondrial membrane potential but not an alteration in the number of mitochondria. Galactose-replacement reversed other markers of dysfunctional mitochondrial metabolism, including blocking the production of reactive oxygen species, nitric oxide, and the synthesis of inducible nitric oxide synthase. Of more clinical relevance, galactose-substitution blocked downstream functional features associated with osteoarthritis, including enhanced levels of MMP13 mRNA, MMP13 protein, and the degradative loss of proteoglycan from intact cartilage explants. Blocking baseline and IL1β-enhanced MMP13 by galactose-replacement in human osteoarthritic chondrocyte cultures inversely paralleled increases in markers associated with mitochondrial recovery, phospho-AMPK, and PGC1α. Comparisons were made between galactose replacement and the glycolysis inhibitor 2-deoxyglucose. Targeting intermediary metabolism may provide a novel approach to osteoarthritis care.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.

Age and sex modify cellular proliferation responses to oxidative stress and glucocorticoid challenges in baboon cells

Aging is associated with progressive loss of cellular homeostasis resulting from intrinsic and extrinsic challenges. Lack of a carefully designed, well-characterized, precise, translational experimental model is a major limitation to understanding the cellular perturbations that characterize aging. Here, we tested the feasibility of primary fibroblasts isolated from nonhuman primates (baboons) as a model of cellular resilience in response to homeostatic challenge. Using a real-time live-cell imaging system, we precisely defined a protocol for testing effects of prooxidant compounds (e.g., hydrogen peroxide (H₂O₂), paraquat), thapsigargin, dexamethasone, and a low glucose environment on cell proliferation in fibroblasts derived from baboons across the life course (n = 11/sex). Linear regression analysis indicated that donor age significantly reduced the ability of cells to proliferate following exposure to H₂O₂ (50 and 100 µM) and paraquat (100 and 200 µM) challenges in cells from males (6.4-21.3 years; average lifespan 21 years) but not cells from females (4.3-15.9 years). Inhibitory effects of thapsigargin on cell proliferation were dependent on challenge duration (2 vs 24 h) and concentration (0.1 and 1 µM). Cells from older females (14.4-15.9 years) exhibited greater resilience to thapsigargin (1 µM; 24 h) and dexamethasone (500 µM) challenges than did those from younger females (4.3-6.7 years). The cell proliferation response to low glucose (1 mM) was reduced with age in both sexes. These data indicate that donor's chronological age and sex are important variables in determining fibroblast responses to metabolite and other challenges.

Targeting hepatocyte carbohydrate transport to mimic fasting and calorie restriction

The pervasion of three daily meals and snacks is a relatively new introduction to our shared experience and is coincident with an epidemic rise in obesity and cardiometabolic disorders of overnutrition. The past two decades have yielded convincing evidence regarding the adaptive, protective effects of calorie restriction (CR) and intermittent fasting (IF) against cardiometabolic, neurodegenerative, proteostatic, and inflammatory diseases. Yet, durable adherence to intensive lifestyle changes is rarely attainable. New evidence now demonstrates that restricting carbohydrate entry into the hepatocyte by itself mimics several key signaling responses and physiological outcomes of IF and CR. This discovery raises the intriguing proposition that targeting hepatocyte carbohydrate transport to mimic fasting and caloric restriction can abate cardiometabolic and perhaps other fasting-treatable diseases. Here, we review the metabolic and signaling fates of a hepatocyte carbohydrate, identify evidence to target the key mediators within these pathways, and provide rationale and data to highlight carbohydrate transport as a broad, proximal intervention to block the deleterious sequelae of hepatic glucose and fructose metabolism.

Therapeutic potential of AMPK signaling targeting in lung cancer: Advances, challenges and future prospects

Lung cancer (LC) is a leading cause of death worldwide with high mortality and morbidity. A wide variety of risk factors are considered for LC development such as smoking, air pollution and family history. It appears that genetic and epigenetic factors are also potential players in LC development and progression. AMP-activated protein kinase (AMPK) is a signaling pathway with vital function in inducing energy balance and homeostasis. An increase in AMP:ATP and ADP:ATP ratio leads to activation of AMPK signaling by upstream mediators such as LKB1 and CamKK. Dysregulation of AMPK signaling is a common finding in different cancers, particularly LC. AMPK activation can significantly enhance LC metastasis via EMT induction. Upstream mediators such as PLAG1, IMPAD1, and TUFM can regulate AMPK-mediated metastasis. AMPK activation can promote proliferation and survival of LC cells via glycolysis induction. In suppressing LC progression, anti-tumor compounds including metformin, ginsenosides, casticin and duloxetine dually induce/inhibit AMPK signaling. This is due to double-edged sword role of AMPK signaling in LC cells. Furthermore, AMPK signaling can regulate response of LC cells to chemotherapy and radiotherapy that are discussed in the current review.

Codon Bias Can Determine Sorting of a Potassium Channel Protein

Due to the redundancy of the genetic code most amino acids are encoded by multiple synonymous codons. It has been proposed that a biased frequency of synonymous codons can affect the function of proteins by modulating distinct steps in transcription, translation and folding. Here, we use two similar prototype K⁺ channels as model systems to examine whether codon choice has an impact on protein sorting. By monitoring transient expression of GFP-tagged channels in mammalian cells, we find that one of the two channels is sorted in a codon and cell cycle-dependent manner either to mitochondria or the secretory pathway. The data establish that a gene with either rare or frequent codons serves, together with a cell-state-dependent decoding mechanism, as a secondary code for sorting intracellular membrane proteins.

KLF4 Regulates Metabolic Homeostasis in Response to Stress

Cancerous cells are detrimental to the human body and can be incredibly resilient against treatments because of the complexities of molecular carcinogenic pathways. In particular, cancer cells are able to sustain increased growth under metabolic stress due to phenomena like the Warburg effect. Krüppel-like factor 4 (KLF4), a context-dependent transcription factor that can act as both a tumor suppressor and an oncogene, is involved in many molecular pathways that respond to low glucose and increased reactive oxygen species (ROS), raising the question of its role in metabolic stress as a result of increased proliferation of tumor cells. In this study, metabolic assays were performed, showing enhanced efficiency of energy production in cells expressing KLF4. Western blotting showed that KLF4 increases the expression of essential glycolytic proteins. Furthermore, we used immunostaining to show that KLF4 increases the localization of glucose transporter 1 (GLUT1) to the cellular membrane. 2',7'-Dichlorodihydrofluorescein diacetate (H2DCF-DA) was used to analyze the production of ROS, and we found that KLF4 reduces stress-induced ROS within cells. Finally, we demonstrated increased autophagic death in KLF4-expressing cells in response to glucose starvation. Collectively, these results relate KLF4 to non-Warburg metabolic behaviors that support its role as a tumor suppressor and could make KLF4 a target for new cancer treatments.

A small-molecule pan-class I glucose transporter inhibitor reduces cancer cell proliferation in vitro and tumor growth in vivo by targeting glucose-based metabolism

BACKGROUND

Cancer cells drastically increase the uptake of glucose and glucose metabolism by overexpressing class I glucose transporters (GLUT1-4) to meet their energy and biomass synthesis needs and are very sensitive and vulnerable to glucose deprivation. Although targeting glucose uptake via GLUTs has been an attractive anticancer strategy, the relative anticancer efficacy of multi-GLUT targeting or single GLUT targeting is unclear. Here, we report DRB18, a synthetic small molecule, is a potent anticancer compound whose pan-class I GLUT inhibition is superior to single GLUT targeting.

METHODS

Glucose uptake and MTT/resazurin assays were used to measure DRB18's inhibitory activities of glucose transport and cell viability/proliferation in human lung cancer and other cancer cell lines. Four HEK293 cell lines expressing GLUT1-4 individually were used to determine the IC₅₀ values of DRB18's inhibitory activity of glucose transport. Docking studies were performed to investigate the potential direct interaction of DRB18 with GLUT1-4. Metabolomics analysis was performed to identify metabolite changes in A549 lung cancer cells treated with DRB18. DRB18 was used to treat A549 tumor-bearing nude mice. The GLUT1 gene was knocked out to determine how the KO of the gene affected tumor growth.

RESULTS

DRB18 reduced glucose uptake mediated via each of GLUT1-4 with different IC₅₀s, which match with the docking glidescores with a correlation coefficient of 0.858. Metabolomics analysis revealed that DRB18 altered energy-related metabolism in A549 cells by changing the abundance of metabolites in glucose-related pathways in vitro and in vivo. DRB18 eventually led to G1/S phase arrest and increased oxidative stress and necrotic cell death. IP injection of DRB18 in A549 tumor-bearing nude mice at 10 mg/kg body weight thrice a week led to a significant reduction in the tumor volume compared with mock-treated tumors. In contrast, the knockout of the GLUT1 gene did not reduce tumor volume.

CONCLUSIONS

DRB18 is a potent pan-class I GLUT inhibitor in vitro and in vivo in cancer cells. Mechanistically, it is likely to bind the outward open conformation of GLUT1-4, reducing tumor growth through inhibiting GLUT1-4-mediated glucose transport and metabolisms. Pan-class I GLUT inhibition is a better strategy than single GLUT targeting for inhibiting tumor growth.

Multi-omics tumor profiling technologies to develop precision medicine in multiple myeloma

Multiple myeloma (MM), the second most common hematologic cancer, is caused by accumulation of aberrant plasma cells in the bone marrow. Its molecular causes are not fully understood and its great heterogeneity among patients complicates therapeutic decision-making. In the past decades, development of new therapies and drugs have significantly improved survival of MM patients. However, resistance to drugs and relapse remain the most common causes of mortality and are the major challenges to overcome. The advent of high throughput omics technologies capable of analyzing big amount of clinical and biological data has changed the way to diagnose and treat MM. Integration of omics data (gene mutations, gene expression, epigenetic information, and protein and metabolite levels) with clinical histories of thousands of patients allows to build scores to stratify the risk at diagnosis and predict the response to treatment, helping clinicians to make better educated decisions for each particular case. There is no doubt that the future of MM treatment relies on personalized therapies based on predictive models built from omics studies. This review summarizes the current treatments and the use of omics technologies in MM, and their importance in the implementation of personalized medicine.

Multi-omics tumor profiling technologies to develop precision medicine in multiple myeloma

Multiple myeloma (MM), the second most common hematologic cancer, is caused by accumulation of aberrant plasma cells in the bone marrow. Its molecular causes are not fully understood and its great heterogeneity among patients complicates therapeutic decision-making. In the past decades, development of new therapies and drugs have significantly improved survival of MM patients. However, resistance to drugs and relapse remain the most common causes of mortality and are the major challenges to overcome. The advent of high throughput omics technologies capable of analyzing big amount of clinical and biological data has changed the way to diagnose and treat MM. Integration of omics data (gene mutations, gene expression, epigenetic information, and protein and metabolite levels) with clinical histories of thousands of patients allows to build scores to stratify the risk at diagnosis and predict the response to treatment, helping clinicians to make better educated decisions for each particular case. There is no doubt that the future of MM treatment relies on personalized therapies based on predictive models built from omics studies. This review summarizes the current treatments and the use of omics technologies in MM, and their importance in the implementation of personalized medicine.

A septin GTPase scaffold of dynein-dynactin motors triggers retrograde lysosome transport

The metabolic and signaling functions of lysosomes depend on their intracellular positioning and trafficking, but the underlying mechanisms are little understood. Here, we have discovered a novel septin GTPase-based mechanism for retrograde lysosome transport. We found that septin 9 (SEPT9) associates with lysosomes, promoting the perinuclear localization of lysosomes in a Rab7-independent manner. SEPT9 targeting to mitochondria and peroxisomes is sufficient to recruit dynein and cause perinuclear clustering. We show that SEPT9 interacts with both dynein and dynactin through its GTPase domain and N-terminal extension, respectively. Strikingly, SEPT9 associates preferentially with the dynein intermediate chain (DIC) in its GDP-bound state, which favors dimerization and assembly into septin multimers. In response to oxidative cell stress induced by arsenite, SEPT9 localization to lysosomes is enhanced, promoting the perinuclear clustering of lysosomes. We posit that septins function as GDP-activated scaffolds for the cooperative assembly of dynein-dynactin, providing an alternative mechanism of retrograde lysosome transport at steady state and during cellular adaptation to stress.

Prodrug-Based Nanoreactors with Tumor-Specific In Situ Activation for Multisynergistic Cancer Therapy

Efficient drug delivery into tumor cells while bypassing many biological barriers is still a challenge for cancer therapy. By taking advantage of the palladium (Pd)-mediated in situ activation of a prodrug and the glucose oxidase (GOD)-based β-d-glucose oxidation reaction, we developed a multisynergistic cancer therapeutic platform that combined doxorubicin (DOX)-induced chemotherapy with GOD-mediated cancer-orchestrated oxidation therapy and cancer starvation therapy. In the present work, we first synthesized DOX prodrugs (pDOXs) and temporarily assembled them with β-cyclodextrins to reduce their toxic side effects. Then, a nanoreactor was constructed by synthesizing Pd⁰ nanoparticles in situ within the pores of mesoporous silica nanoparticles for the conversion of pDOX into the active anticancer drug. Furthermore, GOD was introduced to decrease the pH of the tumor microenvironment and induce cancer-orchestrated oxidation/starvation therapy by catalyzing β-d-glucose oxidation to form hydrogen peroxide (H₂O₂) and gluconic acid. Our study provides a new strategy that employs a cascade chemical reaction to achieve combined orchestrated oxidation/starvation/chemotherapy for the synergistic killing of cancer cells and the suppression of tumor growth.

Lower Lactate Levels and Lower Intracellular pH in Patients with IDH-Mutant versus Wild-Type Gliomas

BACKGROUND AND PURPOSE

Preclinical evidence points toward a metabolic reprogramming in isocitrate dehydrogenase (IDH) mutated tumor cells with down-regulation of the expression of genes that encode for glycolytic metabolism. We noninvasively investigated lactate and Cr concentrations, as well as intracellular pH using ¹H/phosphorus 31 (³¹P) MR spectroscopy in a cohort of patients with gliomas.

MATERIALS AND METHODS

Thirty prospectively enrolled, mostly untreated patients with gliomas met the spectral quality criteria (World Health Organization II [n = 7], III [n = 16], IV [n = 7]; IDH-mutant [n = 23]; IDH wild-type [n = 7]; 1p/19q codeletion [n = 9]). MR imaging protocol included 3D ³¹P chemical shift imaging and ¹H single-voxel spectroscopy (point-resolved spectroscopy sequence at TE = 30 ms and TE = 97 ms with optimized echo spacing for detection of 2-hydroxyglutarate) from the tumor area. Values for absolute metabolite concentrations were calculated (phantom replacement method). Intracellular pH was determined from ³¹P chemical shift imaging.

RESULTS

At TE = 97 ms, lactate peaks can be fitted with little impact of lipid/macromolecule contamination. We found a significant difference in lactate concentrations, lactate/Cr ratios, and intracellular pH when comparing tumor voxels of patients with IDH-mutant with those of patients with IDH wild-type gliomas, with reduced lactate levels and near-normal intracellular pH in patients with IDH-mutant gliomas. We additionally found evidence for codependent effects of 1p/19q codeletion and IDH mutations with regard to lactate concentrations for World Health Organization tumor grades II and III, with lower lactate levels in patients exhibiting the codeletion. There was no statistical significance when comparing lactate concentrations between IDH-mutant World Health Organization II and III gliomas.

CONCLUSIONS

We found indirect evidence for metabolic reprogramming in IDH-mutant tumors with significantly lower lactate concentrations compared with IDH wild-type tumors and a near-normal intracellular pH.

AKT but not MYC promotes reactive oxygen species-mediated cell death in oxidative culture

Oncogenes can create metabolic vulnerabilities in cancer cells. We tested how AKT (herein referring to AKT1) and MYC affect the ability of cells to shift between respiration and glycolysis. Using immortalized mammary epithelial cells, we discovered that constitutively active AKT, but not MYC, induced cell death in galactose culture, where cells rely on oxidative phosphorylation for energy generation. However, the negative effects of AKT were temporary, and AKT-expressing cells recommenced growth after ∼15 days in galactose. To identify the mechanisms regulating AKT-mediated cell death, we used metabolomics and found that AKT-expressing cells that were dying in galactose culture had upregulated glutathione metabolism. Proteomic profiling revealed that AKT-expressing cells dying in galactose also upregulated nonsense-mediated mRNA decay, a marker of sensitivity to oxidative stress. We therefore measured levels of reactive oxygen species (ROS) and discovered that galactose-induced ROS exclusively in cells expressing AKT. Furthermore, ROS were required for galactose-induced death of AKT-expressing cells. We then confirmed that galactose-induced ROS-mediated cell death in breast cancer cells with upregulated AKT signaling. These results demonstrate that AKT but not MYC restricts the flexibility of cancer cells to use oxidative phosphorylation.This article has an associated First Person interview with the first author of the paper.

Arginine methylation of ribose-5-phosphate isomerase A senses glucose to promote human colorectal cancer cell survival

Cancer cells remodel their metabolic network to adapt to variable nutrient availability. Pentose phosphate pathway (PPP) plays protective and biosynthetic roles by oxidizing glucose to generate reducing power and ribose. How cancer cells modulate PPP activity in response to glucose supply remains unclear. Here we show that ribose-5-phosphate isomerase A (RPIA), an enzyme in PPP, directly interacts with co-activator associated arginine methyltransferase 1 (CARM1) and is methylated at arginine 42 (R42). R42 methylation up-regulates the catalytic activity of RPIA. Furthermore, glucose deprivation strengthens the binding of CARM1 with RPIA to induce R42 hypermethylation. Insufficient glucose supply links to RPIA hypermethylation at R42, which increases oxidative PPP flux. RPIA methylation supports ROS clearance by enhancing NADPH production and fuels nucleic acid synthesis by increasing ribose supply. Importantly, RPIA methylation at R42 significantly potentiates colorectal cancer cell survival under glucose starvation. Collectively, RPIA methylation connects glucose availability to nucleotide synthesis and redox homeostasis.

Pro- and antitumor effects of mitochondrial reactive oxygen species

In cancer, mitochondrial functions are commonly altered. Directly involved in metabolic reprogramming, mitochondrial plasticity confers to cancer cells a high degree of adaptability to a wide range of stresses and to the harsh tumor microenvironment. Lack of nutrients or oxygen caused by altered perfusion, metabolic needs of proliferating cells, co-option of the microenvironment, control of the immune system, cell migration and metastasis, and evasion of exogenous stress (e.g., chemotherapy) are all, at least in part, influenced by mitochondria. Mitochondria are undoubtedly one of the key contributors to cancer development and progression. Understanding their protumoral (dys)functions may pave the way to therapeutic strategies capable of turning them into innocent entities. Here, we will focus on the production and detoxification of mitochondrial reactive oxygen species (mtROS), on their impact on tumorigenesis (genetic, prosurvival, and microenvironmental effects and their involvement in autophagy), and on tumor metastasis. We will also summarize the latest therapeutic approaches involving mtROS.

In vitro quantification: Long-term effect of glucose deprivation on various cancer cell lines

OBJECTIVE

Although metabolic treatment of highly glycolytic cancers and metastases is becoming an important research field, the effects of such treatments are not fully quantified yet. In this article we attempt to quantify the effect of long-term glucose deprivation (similar to ketogenic diets) on cancer cells using in vitro tests.

METHODS

Two tumorigenic cell lines were used, namely a metastatic breast and a cervical cancer cell line. The non-tumorigenic control cell line was an immortalized breast cell line. All the cell lines were stabilized at a typical average human blood glucose level of 6 mmol/L. The cell lines were then exposed to the therapeutic blood glucose level of 3 mmol/L for 90 d.

RESULTS

The tests indicated that glucose deprivation restricted the different cancer cell lines' growth more than that of non-tumorigenic cells. The different cell lines were also differentially affected, which suggests that long-term glucose deprivation will not be equally effective for different types of cancer. The highly glycolytic breast cancer cell line was most adversely affected, with cell growth decreasing to 30% after 26 d. Cell growth was stable at this level for up to 22 d. Furthermore, all of the other cancer cell lines were similarly affected.

CONCLUSIONS

This in vitro data could help to direct future human in vivo tests to find the most therapeutic time (cancer cells at their most vulnerable) for additional short-term adjuvant therapies. Partial recovery of proliferation occurred after 90 d. Therefore, as expected, the results also indicated that without an adjuvant treatment, full extinction cannot be reached with the proposed long-term metabolic treatment. The need for more clinical data on long-term glucose deprivation treatments for cancer is well described in the literature. This paper attempts to add to the available pool of knowledge.

Homotypic targeting upconversion nano-reactor for cascade cancer starvation and deep-tissue phototherapy

Cancer starvation therapy based on catalytic chemistry of glucose oxidase (GOx) offers great potential for multimodal treatment, benefiting from both nutrition shutting-off and the oxidization product hydrogen peroxide (H₂O₂). Herein, further optimization of such combined therapy was achieved by a cascade Nano-reactor, which was constructed by incorporating GOx into a bio-mimic upconversion nanosystem. The cascade began when GOx was delivered into tumor sites through homotypic targeting, facilitating selective starving of cancer cells and H₂O₂ generation. Then, upon 980 nm laser excitation, the 470 nm light emitted by upconversion nanoparticles (NaYF₄: Yb, Tm) photolyzed H₂O₂ into hydroxyl radical for phototherapy, superior to direct photolysis by blue light with limited tissue penetration depth. Meanwhile, the 800 nm emission of UCNPs was used to track the in vivo fate and tumor targeting ability of the Nano-reactor. Radionuclide imaging further confirmed the targeting of the Nano-reactor to subcutaneous 4T1 tumor and lung metastasis. Significantly enhanced therapeutic efficacy of this cascade starvation-phototherapy was validated in vitro and in vivo, suggesting the Nano-reactor as a smart, simple and strong system for cancer multimodal therapy.

Pathological Roles of Mitochondrial Oxidative Stress and Mitochondrial Dynamics in Cardiac Microvascular Ischemia/Reperfusion Injury

Mitochondria are key regulators of cell fate through controlling ATP generation and releasing pro-apoptotic factors. Cardiac ischemia/reperfusion (I/R) injury to the coronary microcirculation has manifestations ranging in severity from reversible edema to interstitial hemorrhage. A number of mechanisms have been proposed to explain the cardiac microvascular I/R injury including edema, impaired vasomotion, coronary microembolization, and capillary destruction. In contrast to their role in cell types with higher energy demands, mitochondria in endothelial cells primarily function in signaling cellular responses to environmental cues. It is clear that abnormal mitochondrial signatures, including mitochondrial oxidative stress, mitochondrial fission, mitochondrial fusion, and mitophagy, play a substantial role in endothelial cell function. While the pathogenic role of each of these mitochondrial alterations in the endothelial cells I/R injury remains complex, profiling of mitochondrial oxidative stress and mitochondrial dynamics in endothelial cell dysfunction may offer promising potential targets in the search for novel diagnostics and therapeutics in cardiac microvascular I/R injury. The objective of this review is to discuss the role of mitochondrial oxidative stress on cardiac microvascular endothelial cells dysfunction. Mitochondrial dynamics, including mitochondrial fission and fusion, are critically discussed to understand their roles in endothelial cell survival. Finally, mitophagy, as a degradative mechanism for damaged mitochondria, is summarized to figure out its contribution to the progression of microvascular I/R injury.

A synthetic lethal drug combination mimics glucose deprivation-induced cancer cell death in the presence of glucose

Metabolic reprogramming in cancer cells can increase their dependence on metabolic substrates such as glucose. As such, the vulnerability of cancer cells to glucose deprivation creates an attractive opportunity for therapeutic intervention. Because it is not possible to starve tumors of glucose in vivo, here we sought to identify the mechanisms in glucose deprivation-induced cancer cell death and then designed inhibitor combinations to mimic glucose deprivation-induced cell death. Using metabolomic profiling, we found that cells undergoing glucose deprivation-induced cell death exhibited dramatic accumulation of intracellular l-cysteine and its oxidized dimer, l-cystine, and depletion of the antioxidant GSH. Building on this observation, we show that glucose deprivation-induced cell death is driven not by the lack of glucose, but rather by l-cystine import. Following glucose deprivation, the import of l-cystine and its subsequent reduction to l-cysteine depleted both NADPH and GSH pools, thereby allowing toxic accumulation of reactive oxygen species. Consistent with this model, we found that the glutamate/cystine antiporter (xCT) is required for increased sensitivity to glucose deprivation. We searched for glycolytic enzymes whose expression is essential for the survival of cancer cells with high xCT expression and identified glucose transporter type 1 (GLUT1). Testing a drug combination that co-targeted GLUT1 and GSH synthesis, we found that this combination induces synthetic lethal cell death in high xCT-expressing cell lines susceptible to glucose deprivation. These results indicate that co-targeting GLUT1 and GSH synthesis may offer a potential therapeutic approach for targeting tumors dependent on glucose for survival.

Effect of 6-Shogaol on the Glucose Uptake and Survival of HT1080 Fibrosarcoma Cells

Ginger is a plant that is native to southern China. In the last decade and research on the components of ginger has significantly increased; of these components, 6-shogaol exhibits the greatest potential antitumor capacity. However, the molecular mechanism through which 6-shogaol exerts its effects has not yet been elucidated. In this study, the effect of 6-shogaol on tumor cells that were derived from human fibrosarcoma (HT1080) was evaluated. Cell viability was determined by a (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) MTT assay testing different concentrations of 6-shogaol (2.5–150 μM). Subsequently, the effect of 6-shogaol on reactive oxygen species (ROS) production, glucose uptake, and protein expression of the signaling pathway phosphatase and tensin homolog/ protein kinase B /mammalian target of rapamycin (PTEN/Akt/mTOR) was measured. 6-Shogaol reduced the viability of the tumor cells and caused an increase in ROS production, which was attenuated with the addition of N-acetylcysteine, and the recovery of cell viability was observed. The increase in ROS production in response to 6-shogaol was associated with cell death. Similarly, glucose uptake decreased with incremental concentrations of 6-shogaol, and an increase in the expression of mTOR-p and Akt-p proteins was observed; PTEN was active in all the treatments with 6-shogaol. Thus, the results suggest that cells activate uncontrolled signaling pathways, such as phosphoinositide 3-kinase (PI3K)/Akt/mTOR, among other alternative mechanisms of metabolic modulation and of survival in order to counteract the pro-oxidant effect of 6-shogaol and the decrease in glucose uptake. Interestingly, a differential response was observed when non-cancerous cells were treated with 6-shogaol.

Palladium-Mediated Cleavage of Proteins with Thiazolidine-Modified Backbone in Live Cells

Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond-forming reactions for site-selective protein labeling are commonly used in these endeavors. Selective bond-cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium-based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin-aldehyde, which was decaged for the inhibition of deubiquitinases in live cells.

Endothelial Dysfunction: Is There a Hyperglycemia-Induced Imbalance of NOX and NOS?

NADPH oxidases (NOX) are enzyme complexes that have received much attention as key molecules in the development of vascular dysfunction. NOX have the primary function of generating reactive oxygen species (ROS), and are considered the main source of ROS production in endothelial cells. The endothelium is a thin monolayer that lines the inner surface of blood vessels, acting as a secretory organ to maintain homeostasis of blood flow. The enzymatic production of nitric oxide (NO) by endothelial NO synthase (eNOS) is critical in mediating endothelial function, and oxidative stress can cause dysregulation of eNOS and endothelial dysfunction. Insulin is a stimulus for increases in blood flow and endothelium-dependent vasodilation. However, cardiovascular disease and type 2 diabetes are characterized by poor control of the endothelial cell redox environment, with a shift toward overproduction of ROS by NOX. Studies in models of type 2 diabetes demonstrate that aberrant NOX activation contributes to uncoupling of eNOS and endothelial dysfunction. It is well-established that endothelial dysfunction precedes the onset of cardiovascular disease, therefore NOX are important molecular links between type 2 diabetes and vascular complications. The aim of the current review is to describe the normal, healthy physiological mechanisms involved in endothelial function, and highlight the central role of NOX in mediating endothelial dysfunction when glucose homeostasis is impaired.

The cystine/glutamate antiporter xCT is a key regulator of EphA2 S897 phosphorylation under glucose-limited conditions

EphA2, which belongs to the Eph family of receptor tyrosine kinases, is overexpressed in a variety of human cancers. Serine 897 (S897) phosphorylation of EphA2 is known to promote cancer cell migration and proliferation in a ligand-independent manner. In this study, we show that glucose deprivation induces S897 phosphorylation of EphA2 in glioblastoma cells. The phosphorylation requires the activity of the cystine/glutamate antiporter xCT and reactive oxygen species (ROS)-dependent ERK and RSK activation. Furthermore, depletion of EphA2 in glioblastoma cells leads to decreased cell viability under glucose starvation. Our results suggest a role of EphA2 in glioblastoma cell viability under glucose-limited conditions.

Targeting intermediary metabolism enhances the efficacy of BH3 mimetic therapy in hematologic malignancies

BH3 mimetics are novel targeted drugs with remarkable specificity, potency and enormous potential to improve cancer therapy. However, acquired resistance is an emerging problem. We report the rapid development of resistance in chronic lymphocytic leukemia cells isolated from patients exposed to increasing doses of navitoclax (ABT-263), a BH3 mimetic. To mimic such rapid development of chemoresistance, we developed simple resistance models to three different BH3 mimetics, targeting BCL-2 (ABT-199), BCL-XL (A-1331852) or MCL-1 (A-1210477), in relevant hematologic cancer cell lines. In these models, resistance could not be attributed to either consistent changes in expression levels of the anti-apoptotic proteins or interactions among different pro- and anti-apoptotic BCL-2 family members. Using genetic silencing, pharmacological inhibition and metabolic supplementation, we found that targeting glutamine uptake and its downstream signaling pathways, namely glutaminolysis, reductive carboxylation, lipogenesis, cholesterogenesis and mammalian target of rapamycin signaling resulted in marked sensitization of the chemoresistant cells to BH3 mimetic-mediated apoptosis. Furthermore, our findings highlight the possibility of repurposing widely used drugs, such as statins, to target intermediary metabolism and improve the efficacy of BH3 mimetic therapy.

Mechanisms of skeletal muscle wasting in a mouse model for myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multi-systemic disease resulting in severe muscle weakening and wasting. DM1 is caused by expansion of CTG repeats in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene. We have developed an inducible, skeletal muscle-specific mouse model of DM1 (CUG960) that expresses 960 CUG repeat-expressing animals (CUG960) in the context of human DMPK exons 11-15. CUG960 RNA-expressing mice induced at postnatal day 1, as well as adult-onset animals, show clear, measurable muscle wasting accompanied by severe histological defects including central myonuclei, reduced fiber cross-sectional area, increased percentage of oxidative myofibers, the presence of nuclear RNA foci that colocalize with Mbnl1 protein, and increased Celf1 protein in severely affected muscles. Importantly, muscle loss, histological abnormalities and RNA foci are reversible, demonstrating recovery upon removal of toxic RNA. RNA-seq and protein array analysis indicate that the balance between anabolic and catabolic pathways that normally regulate muscle mass may be disrupted by deregulation of platelet derived growth factor receptor β signaling and the PI3K/AKT pathways, along with prolonged activation of AMP-activated protein kinase α signaling. Similar changes were detected in DM1 skeletal muscle compared with unaffected controls. The mouse model presented in this paper shows progressive skeletal muscle wasting and has been used to identify potential molecular mechanisms underlying skeletal muscle loss. The reversibility of the phenotype establishes a baseline response for testing therapeutic approaches.

Cellular glucose metabolism is essential for the reduction of cell-impermeable water-soluble tetrazolium (WST) dyes

Water-soluble tetrazolium (WST) dyes, such as WST-1 and WST-8, are widely used in cell proliferation and anti-cell-growth drug screen assays. However, the underlying determinants for WST reduction are still largely unknown. In addition, application of tetrazolium-based assays to cellular glucose metabolism studies has not been fully explored. In the present study, we show here that WST-8 reduction is dependent on cellular glucose metabolism. In order to minimize the variance of live cell number during stimulation, we treated cells with different stimuli and performed tetrazolium-based assays within 6 hours. Withdrawal of medium glucose supply greatly attenuated WST-8 reduction but not intracellular ATP levels, while re-adding glucose reconstituted WST-8 reduction, indicating the effect was not due to cell death. The role of glucose on WST-8 reduction is specific since glutamine, fructose or galactose did not substitute for the effect of glucose on WST-8 reduction. Furthermore, inhibition of glucose transporters, intracellular glucose metabolic enzymes or EGFR-PI3K-Akt signaling also attenuated WST-8 reduction. In an attempt to screen inhibitors targeting cellular glucose metabolism from hyperglycemia-associated drugs, it turned out that HIV protease inhibitor, ritonavir, could largely block WST-8 reduction, but not cellular ATP level. Interestingly, ritonavir has been shown to acutely block glucose transport in vitro and in vivo. Taken together, our studies not only demonstrate an essential role of cellular glucose metabolism on WST-8 reduction, but also propose a novel application of tetrazolium-based assays in screening for inhibitors of cellular glucose metabolism when used in combination with ATP assay.

Wilhelm Brünings' forgotten contribution to the metabolic treatment of cancer utilizing hypoglycemia and a very low carbohydrate (ketogenic) diet

The growing interest in the alterations of tumor cell metabolism and their possible therapeutic exploitation also spurred new complementary and integrative approaches such as treating patients with a ketogenic diet (KD). KDs aim at inhibiting glycolytic tumor metabolism and growth, and have therefore been proposed as adjuncts not only to standard-of-care, but also to other therapies targeting tumor metabolism. Here I describe the life and forgotten work of one of the earliest researchers who realized the importance of altered tumor cell metabolism and its possible exploitation through metabolic modifications: Wilhelm Brünings. Brünings was a German natural scientist and physician famous for his innovative contributions to the fields of physiology and otorhinolaryngology. Based on the findings of Otto Warburg and his physiological reasoning he started to experiment with insulin administration and KDs in his patients with head and neck cancers, aiming to maximally lower blood glucose concentrations. He obtained encouraging short-term results, although most tumors became refractory to treatment after several weeks. His pioneering work is worth revisiting, especially for an international readership that may be unaware of his efforts, as hypoglycemic treatments, including the use of insulin injections and KDs, are currently being re-investigated as complementary and integrative cancer treatments.

mTORC2 contributes to the metabolic reprogramming in EGFR tyrosine-kinase inhibitor resistant cells in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations are often successfully treated with EGFR tyrosine kinase inhibitor (TKI) such as erlotinib; however, treatment resistance inevitably occurs. Given tumor metabolism of glucose and therapeutic response are intimately linked, we explored the metabolic differences between isogenic erlotinib-sensitive and -resistant NSCLC cell lines. We discovered that the growth of erlotinib-resistant cells is more sensitive to glucose deprivation. Seahorse metabolic assay revealed erlotinib-resistant cells have lower spare respiratory capacity (SRC), an indicator of metabolic flexibility, compared to erlotinib-sensitive cells. Additionally, we found downstream components of mTORC2 signaling to be phosphorylated in erlotinib-resistant cells. Knockdown of an mTORC2 component, Rictor, enhanced the SRC and rescued the growth rate of erlotinib-resistant cells during glucose deprivation. Among NSCLCs with activating EGFR mutations, gene sets involved in glucose metabolism were enriched in patients with high expression of p-NDGR1, a readout of mTORC2 activity. Furthermore, overall survival was negatively correlated with p-NDRG1. Our work uncovers a link between mTORC2 and metabolic reprogramming in EGFR TKI-resistant cells and highlights the significance of mTORC2 in the progression of EGFR-mutated NSCLC.

Determination of glucose deficiency-induced cell death by mitochondrial ATP generation-driven proton homeostasis

Glucose is one of major nutrients and its catabolism provides energy and/or building bricks for cell proliferation. Glucose deficiency results in cell death. However, the underlying mechanism still remains elusive. By using our recently developed method to monitor real-time cellular apoptosis and necrosis, we show that glucose deprivation can directly elicit necrosis, which is promoted by mitochondrial impairment, depending on mitochondrial adenosine triphosphate (ATP) generation instead of ATP depletion. We demonstrate that glucose metabolism is the major source to produce protons. Glucose deficiency leads to lack of proton provision while mitochondrial electron transfer chain continues consuming protons to generate energy, which provokes a compensatory lysosomal proton efflux and resultant increased lysosomal pH. This lysosomal alkalinization can trigger apoptosis or necrosis depending on the extent of alkalinization. Taken together, our results build up a metabolic connection between glycolysis, mitochondrion, and lysosome, and reveal an essential role of glucose metabolism in maintaining proton homeostasis to support cell survival.

Expression of glycolytic enzymes in ovarian cancers and evaluation of the glycolytic pathway as a strategy for ovarian cancer treatment

BACKGROUND

Novel therapeutic approaches are required to treat ovarian cancer and dependency on glycolysis may provide new targets for treatment. This study sought to investigate the variation of expression of molecular components (GLUT1, HKII, PKM2, LDHA) of the glycolytic pathway in ovarian cancers and the effectiveness of targeting this pathway in ovarian cancer cell lines with inhibitors.

METHODS

Expression of GLUT1, HKII, PKM2, LDHA were analysed by quantitative immunofluorescence in a tissue microarray (TMA) analysis of 380 ovarian cancers and associations with clinicopathological features were sought. The effect of glycolysis pathway inhibitors on the growth of a panel of ovarian cancer cell lines was assessed by use of the SRB proliferation assay. Combination studies were undertaken combining these inhibitors with cytotoxic agents.

RESULTS

Mean expression levels of GLUT1 and HKII were higher in high grade serous ovarian cancer (HGSOC), the most frequently occurring subtype, than in non-HGSOC. GLUT1 expression was also significantly higher in advanced stage (III/IV) ovarian cancer than early stage (I/II) disease. Growth dependency of ovarian cancer cells on glucose was demonstrated in a panel of ovarian cancer cell lines. Inhibitors of the glycolytic pathway (STF31, IOM-1190, 3PO and oxamic acid) attenuated cell proliferation in platinum-sensitive and platinum-resistant HGSOC cell line models in a concentration dependent manner. In combination with either cisplatin or paclitaxel, 3PO (a novel PFKFB3 inhibitor) enhanced the cytotoxic effect in both platinum sensitive and platinum resistant ovarian cancer cells. Furthermore, synergy was identified between STF31 (a novel GLUT1 inhibitor) or oxamic acid (an LDH inhibitor) when combined with metformin, an inhibitor of oxidative phosphorylation, resulting in marked inhibition of ovarian cancer cell growth.

CONCLUSIONS

The findings of this study provide further support for targeting the glycolytic pathway in ovarian cancer and several useful combinations were identified.

Arylamine N-acetyltransferase 1 protects against reactive oxygen species during glucose starvation: Role in the regulation of p53 stability

Human arylamine N-acetyltransferase 1 (NAT1) has been associated with cancer cell growth and invasion, but the underlying molecular mechanisms remain unknown. NAT1 is located on the short arm of chromosome 8 (8p21), a region that is commonly deleted in colon cancer. Previously, it was reported that HT-29 colon cancer cells, which have a large deletion at 8p21-22, show marked morphological changes, increased E-cadherin expression and altered cell-cell contact inhibition following down-regulation of NAT1 with shRNA. By contrast, no effects on growth were observed in HeLa cells. In the present study, cellular changes following knockout of NAT1 with CRISPR/Cas9 in HT-29 and HeLa cells were compared in the presence and absence of glucose. Cell growth decreased in both cell-lines during glucose starvation, but it was enhanced in HT-29 cells following NAT1 deletion. This was due to an increase in ROS production that induced cell apoptosis. Both ROS production and cell death were prevented by the glutathione precursor N-acetylcysteine. NAT1 knockout also resulted in a loss of the gain-of-function p53 protein in HT-29 cells. When p53 expression was inhibited with siRNA in parental HT-29 cells, ROS production and apoptosis increased to levels seen in the NAT1 knockout cells. The loss of p53 may explain the decreased colony formation and increased contact inhibition previously reported following NAT1 down-regulation in these cells. In conclusion, NAT1 is important in maintaining intracellular ROS, especially during glucose starvation, by stabilizing gain-of-function p53 in HT-29 cells. These results suggest that NAT1 may be a novel target to decrease intracellular gain-of -function p53.

Glucose deprivation elicits phenotypic plasticity via ZEB1-mediated expression of NNMT

Glucose is considered the primary energy source for all cells, and some cancers are addicted to glucose. Here, we investigated the functional consequences of chronic glucose deprivation in serous ovarian cancer cells. We found that cells resistant to glucose starvation (glucose-restricted cells) demonstrated increased metabolic plasticity that was dependent on NNMT (Nicotinamide N-methyltransferase) expression. We further show that ZEB1 induced NNMT, rendered cells resistant to glucose deprivation and recapitulated metabolic adaptations and mesenchymal gene expression observed in glucose-restricted cells. NNMT depletion reversed metabolic plasticity in glucose-restricted cells and prevented de novo formation of glucose-restricted colonies. In addition to its role in glucose independence, we found that NNMT was required for other ZEB1-induced phenotypes, such as increased migration. NNMT protein levels were also elevated in metastatic and recurrent tumors compared to matched primary carcinomas, while normal ovary and fallopian tube tissue had no detectable NNMT expression. Our studies define a novel ZEB1/NNMT signaling axis, which elicits mesenchymal gene expression, as well as phenotypic and metabolic plasticity in ovarian cancer cells upon chronic glucose starvation. Understanding the causes of cancer cell plasticity is crucial for the development of therapeutic strategies to counter intratumoral heterogeneity, acquired drug resistance and recurrence in high-grade serous ovarian cancer (HGSC).

Hexokinase 2 and nuclear factor erythroid 2-related factor 2 transcriptionally coactivate xanthine oxidoreductase expression in stressed glioma cells

A dynamic network of metabolic adaptations, inflammatory responses, and redox homeostasis is known to drive tumor progression. A considerable overlap among these processes exists, but several of their key regulators remain unknown. To this end, here we investigated the role of the proinflammatory cytokine IL-1β in connecting these processes in glioma cells. We found that glucose starvation sensitizes glioma cells to IL-1β-induced apoptosis in a manner that depended on reactive oxygen species (ROS). Although IL-1β-induced JNK had no effect on cell viability under glucose deprivation, it mediated nuclear translocation of hexokinase 2 (HK2). This event was accompanied by increases in the levels of sirtuin 6 (SIRT6), nuclear factor erythroid 2-related factor 2 (Nrf2), and xanthine oxidoreductase (XOR). SIRT6 not only induced ROS-mediated cell death but also facilitated nuclear Nrf2-HK2 interaction. Recruitment of the Nrf2-HK2 complex to the ARE site on XOR promoter regulated its expression. Importantly, HK2 served as transcriptional coactivator of Nrf2 to regulate XOR expression, indicated by decreased XOR levels in siRNA-mediated Nrf2 and HK2 knockdown experiments. Our results highlight a non-metabolic role of HK2 as transcriptional coactivator of Nrf2 to regulate XOR expression under conditions of proinflammatory and metabolic stresses. Our insights also underscore the importance of nuclear activities of HK2 in the regulation of genes involved in redox homeostasis.

Extracellular acidification by lactic acid suppresses glucose deprivation-induced cell death and autophagy in B16 melanoma cells

In solid tumors, cancer cells survive and proliferate under conditions of microenvironment stress such as poor nutrients and hypoxia due to inadequate vascularization. These stress conditions in turn activate autophagy, which is important for cancer cell survival. However, autophagy has a contrary effect of inducing cell death in cancer cells cultured in vitro under conditions of glucose deprivation. In this study, we hypothesized that supplementation of lactic acid serves as a means of cell survival under glucose-deprived conditions. At neutral pH, cell death of B16 murine melanoma cells by autophagy under glucose-deprived conditions was observed. However, supplementation of lactic acid suppressed cell death and autophagy in B16 melanoma cells when cultured in glucose-deprived conditions. Sodium lactate, which does not change extracellular pH, did not inhibit cell death, while HCl-adjusted acidic pH suppressed cell death under glucose-deprived conditions. These results suggested that an acidic pH is crucial for cell survival under glucose-deprived conditions.

Lactate metabolism: historical context, prior misinterpretations, and current understanding

Lactate (La^-) has long been at the center of controversy in research, clinical, and athletic settings. Since its discovery in 1780, La^- has often been erroneously viewed as simply a hypoxic waste product with multiple deleterious effects. Not until the 1980s, with the introduction of the cell-to-cell lactate shuttle did a paradigm shift in our understanding of the role of La^- in metabolism begin. The evidence for La^- as a major player in the coordination of whole-body metabolism has since grown rapidly. La^- is a readily combusted fuel that is shuttled throughout the body, and it is a potent signal for angiogenesis irrespective of oxygen tension. Despite this, many fundamental discoveries about La^- are still working their way into mainstream research, clinical care, and practice. The purpose of this review is to synthesize current understanding of La^- metabolism via an appraisal of its robust experimental history, particularly in exercise physiology. That La^- production increases during dysoxia is beyond debate, but this condition is the exception rather than the rule. Fluctuations in blood [La^-] in health and disease are not typically due to low oxygen tension, a principle first demonstrated with exercise and now understood to varying degrees across disciplines. From its role in coordinating whole-body metabolism as a fuel to its role as a signaling molecule in tumors, the study of La^- metabolism continues to expand and holds potential for multiple clinical applications. This review highlights La^-'s central role in metabolism and amplifies our understanding of past research.

Catalytic chemistry of glucose oxidase in cancer diagnosis and treatment

This tutorial review focuses on the state-of-the-art progress in GOx-based cancer diagnosis and treatment, including the general principles for the design and construction of GOx-based biosensors and cancer therapeutic approaches, and their biological applications in detail. Moreover, the current trends and key problems, as well as the challenges and future prospects of GOx-based catalytic systems in biomedicine are also discussed in the end.

Fasting, Fats, and Physics: Combining Ketogenic and Radiation Therapy against Cancer

Radiotherapy (RT) is a mainstay in the treatment of solid tumors and works by physicochemical reactions inducing oxidative stress in cells. Because in practice the efficacy of RT is limited by its toxicity to normal tissues, any strategy that selectively increases the radiosensitivity of tumor cells or boosts the radioresistance of normal cells is a valuable adjunct to RT. In this review, I summarize preclinical and clinical data supporting the hypothesis that ketogenic therapy through fasting and/or ketogenic diets can be utilized as such an adjunct in order to improve the outcome after RT, in terms of both higher tumor control and lower normal-tissue complication probability. The first effect relates to the metabolic shift from glycolysis towards mitochondrial metabolism, which selectively increases reactive oxygen species (ROS) production and impairs adenoside triphosphate (ATP) production in tumor cells. The second effect is based on the differential stress resistance phenomenon describing the reprogramming of normal cells, but not tumor cells, from proliferation towards maintenance and stress resistance when glucose and growth factor levels are decreased and ketone body levels are elevated. Underlying both effects are metabolic differences between normal and tumor cells. Ketogenic therapy is a non-toxic and cost-effective complementary treatment option that exploits these differences and deserves further clinical investigation.

Cystine uptake through the cystine/glutamate antiporter xCT triggers glioblastoma cell death under glucose deprivation

Oncogenic signaling in cancer cells alters glucose uptake and utilization to supply sufficient energy and biosynthetic intermediates for survival and sustained proliferation. Oncogenic signaling also prevents oxidative stress and cell death caused by increased production of reactive oxygen species. However, elevated glucose metabolism in cancer cells, especially in glioblastoma, results in the cells becoming sensitive to glucose deprivation (i.e. in high glucose dependence), which rapidly induces cell death. However, the precise mechanism of this type of cell death remains unknown. Here, we report that glucose deprivation alone does not trigger glioblastoma cell death. We found that, for cell death to occur in glucose-deprived glioblastoma cells, cystine and glutamine also need to be present in culture media. We observed that cystine uptake through the cystine/glutamate antiporter xCT under glucose deprivation rapidly induces NADPH depletion, reactive oxygen species accumulation, and cell death. We conclude that although cystine uptake is crucial for production of antioxidant glutathione in cancer cells its transport through xCT also induces oxidative stress and cell death in glucose-deprived glioblastoma cells. Combining inhibitors targeting cancer-specific glucose metabolism with cystine and glutamine treatment may offer a therapeutic approach for glioblastoma tumors exhibiting high xCT expression.

Silybin counteracts doxorubicin resistance by inhibiting GLUT1 expression

Despite significant advances in the diagnosis and treatment of cancer, the development of drug resistance still remains one of the principal causes that hampers the effectiveness of the therapy. Emerging evidences support the idea that the dysregulated metabolism could be related to drug resistance. The major goal of this study was to target cancer metabolic pathways using new pharmacological approaches coming from natural sources in order to possibly prevent or overcome this phenomenon. Firstly, the metabolic profile of human colorectal adenocarcinoma cells sensitive (LoVo WT) and resistant to doxorubicin (LoVo DOX) was delineated demonstrating that resistant cells remodel their metabolism toward a glycolytic phenotype. In particular it was observed that doxorubicin-resistant cancer cells exhibit an increased dependency from glucose for their survival, associated with overexpression of the glycolytic pathway. Moreover, both GLUT1 mRNA and protein expression significantly increased in LoVo DOX cells. Given the results about the metabolic profile, silybin, modulator of GLUTs, was selected as potential candidate to overcome doxorubicin resistance and, intriguingly, data revealed not only that silybin is more active in resistant cells than in wild type cells, but also that the combined treatment with doxorubicin and silybin presents a synergistic effect in LoVo DOX cells. Although many unanswered questions still remain about the molecular mechanism of silybin, these data suggest that targeting GLUTs may be a good strategy to restore doxorubicin sensitivity and elude drug resistance.

The influence of ketogenic therapy on the 5 R's of radiobiology

PURPOSE

Radiotherapy (RT) is a mainstay in the treatment of solid tumors and works by inducing free radical stress in tumor cells, leading to loss of reproductive integrity. The optimal treatment strategy has to consider damage to both tumor and normal cells and is determined by five factors known as the 5 R's of radiobiology: Reoxygenation, DNA repair, radiosensitivity, redistribution in the cell cycle and repopulation. The aim of this review is (i) to present evidence that these 5 R's are strongly influenced by cellular and whole-body metabolism that in turn can be modified through ketogenic therapy in form of ketogenic diets and short-term fasting and (ii) to stimulate new research into this field including some research questions deserving further study.

CONCLUSIONS

Preclinical and some preliminary clinical data support the hypothesis that ketogenic therapy could be utilized as a complementary treatment in order to improve the outcome after RT, both in terms of higher tumor control and in terms of lower normal tissue complication probability. The first effect relates to the metabolic shift from glycolysis toward mitochondrial metabolism that selectively increases ROS production and impairs ATP production in tumor cells. The second effect is based on the differential stress resistance phenomenon, which is achieved when glucose and growth factors are reduced and ketone bodies are elevated, reprogramming normal but not tumor cells from proliferation toward maintenance and stress resistance. Underlying both effects are metabolic differences between normal and tumor cells that ketogenic therapy seeks to exploit. Specifically, the recently discovered role of the ketone body β-hydroxybutyrate as an endogenous class-I histone deacetylase inhibitor suggests a dual role as a radioprotector of normal cells and a radiosensitzer of tumor cells that opens up exciting possibilities to employ ketogenic therapy as a cost-effective adjunct to radiotherapy against cancer.

Direct 1O2 optical excitation: A tool for redox biology

Molecular oxygen (O2) displays very interesting properties. Its first excited state, commonly known as singlet oxygen (1O2), is one of the so-called Reactive Oxygen Species (ROS). It has been implicated in many redox processes in biological systems. For many decades its role has been that of a deleterious chemical species, although very positive clinical applications in the Photodynamic Therapy of cancer (PDT) have been reported. More recently, many ROS, and also 1O2, are in the spotlight because of their role in physiological signaling, like cell proliferation or tissue regeneration. However, there are methodological shortcomings to properly assess the role of 1O2 in redox biology with classical generation procedures. In this review the direct optical excitation of O2 to produce 1O2 will be introduced, in order to present its main advantages and drawbacks for biological studies. This photonic approach can provide with many interesting possibilities to understand and put to use ROS in redox signaling and in the biomedical field.