Genetically-defined metabolic reprogramming in cancer

Preclinical efficacy of CBR-5884 against epithelial ovarian cancer cells by targeting the serine synthesis pathway

Reprogramming of the serine synthesis pathway (SSP) is intricately linked to the progression of epithelial ovarian cancer (EOC). CBR-5884, a selective small-molecule inhibitor targeting phosphoglycerate dehydrogenase (PHGDH), effectively impedes the de novo synthesis of serine within cancer cells. This study aimed to evaluate the inhibitory effect of CBR-5884 on EOC cells and delineate its specific mechanism, thereby proposing a novel therapeutic approach for treating EOC. The suppression of serine biosynthesis after CBR-5884 treatment was evaluated using RNA sequencing and a serine assay kit, and the results showed that CBR-5884 effectively downregulated serine biosynthesis in EOC cells, particularly those expressing high levels of PHGDH. In vitro studies revealed that CBR-5884 demonstrated significant antitumor effects and suppressed migration and invasion of EOC cells through down-regulation of the integrin subunit beta 4 (ITGB4)/extracellular signal-regulated kinase (ERK)/epithelial-mesenchymal transition signal axis. Additionally, CBR-5884 mitigated the stemness of EOC cells and heightened their sensitivity to chemotherapy. Moreover, in vivo studies revealed that CBR-5884 significantly delayed tumor growth, with histological analysis indicating the safety profile of CBR-5884. Finally, the patient-derived organoid (PDO) models were utilized to explore the preclinical efficacy of CBR-5884 against EOC cells, and the results unveiled that CBR-5884 impeded proliferation and downregulated the expression of ITGB4 in EOC PDO models. Our findings supports the anticancer properties of CBR-5884 in EOC cells exhibiting high PHGDH expression, manifesting through the suppression of proliferation, migration, and invasion, while enhancing chemotherapy sensitivity, suggesting that CBR-5884 holds promise as an efficacious strategy for the treatment of EOC.

PHGDH is Key to a Prognostic Multigene Signature and a Potential Therapeutic Target in Acute Myeloid Leukemia

As a rate-limiting enzyme for the serine biosynthesis pathway (SSP) in the initial step, phosphoglycerate dehydrogenase (PHGDH) is overexpressed in many different tumors, and pharmacological or genetic inhibition of PHGDH promotes antitumor effects. In the present research, by analyzing several acute myeloid leukemia (AML) datasets in the Gene Expression Omnibus (GEO), we identified prognosis-related genes and constructed a multigene signature by univariate, multivariate Cox regression and LASSO regression. Subsequently, the multigene signature was confirmed through Cox, Kaplan-Meier, and ROC analyses in the validation cohort. Moreover, PHGDH acted as a risk factor and was correlated with inferior overall survival. We further analysed other datasets and found that PHGDH was overexpressed in AML. Importantly, the expression of PHGDH was higher in drug-resistant AML compared to drug-sensitive ones. In vitro experiments showed that inhibition of PHGDH induced apoptosis and reduced proliferation in AML cells, and these antitumor effects could be related to the Bcl-2/Bax signaling pathway by the noncanonical or nonmetabolic functions of PHGDH. In summary, we constructed a twenty-gene signature that could predicate prognosis of AML patients and found that PHGDH may be a potential target for AML treatment.

Succinate metabolism: a promising therapeutic target for inflammation, ischemia/reperfusion injury and cancer

Succinate serves as an essential circulating metabolite within the tricarboxylic acid (TCA) cycle and functions as a substrate for succinate dehydrogenase (SDH), thereby contributing to energy production in fundamental mitochondrial metabolic pathways. Aberrant changes in succinate concentrations have been associated with pathological states, including chronic inflammation, ischemia/reperfusion (IR) injury, and cancer, resulting from the exaggerated response of specific immune cells, thereby rendering it a central area of investigation. Recent studies have elucidated the pivotal involvement of succinate and SDH in immunity beyond metabolic processes, particularly in the context of cancer. Current scientific endeavors are concentrated on comprehending the functional repercussions of metabolic modifications, specifically pertaining to succinate and SDH, in immune cells operating within a hypoxic milieu. The efficacy of targeting succinate and SDH alterations to manipulate immune cell functions in hypoxia-related diseases have been demonstrated. Consequently, a comprehensive understanding of succinate's role in metabolism and the regulation of SDH is crucial for effectively targeting succinate and SDH as therapeutic interventions to influence the progression of specific diseases. This review provides a succinct overview of the latest advancements in comprehending the emerging functions of succinate and SDH in metabolic processes. Furthermore, it explores the involvement of succinate, an intermediary of the TCA cycle, in chronic inflammation, IR injury, and cancer, with particular emphasis on the mechanisms underlying succinate accumulation. This review critically assesses the potential of modulating succinate accumulation and metabolism within the hypoxic milieu as a means to combat various diseases. It explores potential targets for therapeutic interventions by focusing on succinate metabolism and the regulation of SDH in hypoxia-related disorders.

Energy metabolism pathways in breast cancer progression: The reprogramming, crosstalk, and potential therapeutic targets

Breast cancer (BC) is a malignant tumor that seriously endangers health in women. BC, like other cancers, is accompanied by metabolic reprogramming. Among energy metabolism-related pathways, BC exhibits enhanced glycolysis, tricarboxylic acid (TCA) cycle, pentose phosphate pathway (PPP), glutamate metabolism, and fatty acid metabolism activities. These pathways facilitate the proliferation, growth and migration of BC cells. The progression of BC is closely related to the alterations in the activity or expression level of several metabolic enzymes, which are regulated by the intrinsic factors such as the key signaling and transcription factors. The metabolic reprogramming in the progression of BC is attributed to the aberrant expression of the signaling and transcription factors associated with the energy metabolism pathways. Understanding the metabolic mechanisms underlying the development of BC will provide a druggable potential for BC treatment and drug discovery.

Reprogramming of sentinel lymph node microenvironment during tumor metastasis

Metastasis is a major cause of death in patients with cancer. The two main routes for cancer cell dissemination are the blood and lymphatic systems. The underlying mechanism of hematogenous metastasis has been well characterized in the past few decades. However, our understanding of the molecular basis of lymphatic metastasis remains at a premature stage. Conceptually, cancer cells invade into lymphatic capillary, passively move to collecting lymphatic vessels, migrate into sentinel lymph node (SLN;, the first lymph node to which cancer cells spread from the primary tumor), and enter the blood circulatory system via the subclavian vein. Before arriving, cancer cells release specific soluble factors to modulate the microenvironment in SLN to establish a beachhead for successful colonization. After colonization, cancer cells inhibit anti-tumor immunity by inducing the recruitment of regulatory T cell and myeloid-derived suppressor cells, suppressing the function of dendritic cell and CD8⁺ T cell, and promoting the release of immunosuppressive cytokines. The development of novel strategies to reverse cancer cell-triggered SLN remodeling may re-activate immunity to reduce beachhead buildup and distant metastasis. In addition to being a microanatomic location for metastasis, the SLN is also an important site for immune modulation. Nanotechnology-based approaches to deliver lymph node-tropic antibodies or drug-conjugated nanoparticles to kill cancer cells on site are a new direction for cancer treatment. Conversely, the induction of stronger immunity by promoting antigen presentation in lymph nodes provides an alternate way to enhance the efficacy of immune checkpoint therapy and cancer vaccine. In this review article, we summarize recent findings on the reprogramming of SLN during lymphatic invasion and discuss the possibility of inhibiting tumor metastasis and eliciting anti-tumor immunity by targeting SLN.

Arterial Spin Labeling Perfusion in Determining the IDH1 Status and Ki-67 Index in Brain Gliomas

The aim of the study was to evaluate the relationship between tumor blood flow (TBF) measured by the pseudo-continuous arterial spin labeling (PCASL) method and IDH1 mutation status of gliomas as well as Ki-67 proliferative index. Methods. The study included 116 patients with newly diagnosed gliomas of various grades. They received no chemotherapy or radiotherapy before MRI. IDH1 status assessment was performed after tumor removal in 106 cases—48 patients were diagnosed with wildtype gliomas (Grade 1−2—6 patients, Grade 3−4—42 patients) and 58 patients were diagnosed with mutant forms of gliomas (Grade 1−2—28 patients, Grade 3−4—30 patients). In 64 cases out of 116 Ki-67 index was measured. Absolute and normalized tumor blood flow values were measured on 3D PCASL maps. Results. TBF and normalized TBF (nTBF) in wildtype gliomas were significantly higher than in IDH1-mutant gliomas (p < 0.001). ASL perfusion showed high values of sensitivity and specificity in the differential diagnosis of gliomas with distinct IDH1 status (for TBF: specificity 75%, sensitivity 77.6%, AUC 0.783, cutoff 80.57 mL/100 g/min, for nTBF: specificity 77.1%, sensitivity 79.3%, AUC 0.791, cutoff 4.7). TBF and nTBF in wildtype high-grade gliomas (HGG) were significantly higher than in mutant forms (p < 0.001). ASL perfusion showed the following values of sensitivity and specificity in the diagnosis of mutant HGG and wildtype HGG (for TBF: specificity 83.3%, sensitivity 60%, AUC 0.719, cutoff 84.18 mL/100 g/min, for nTBF: specificity 88.1%, sensitivity 60%, AUC 0.729, cutoff 4.7). There was a significant positive correlation between tumor blood flow and Ki-67 (for TBF Rs = 0.63, for nTBF Rs = 0.61). Conclusion. ASL perfusion may be an informative factor in determining the IDH1 status in brain gliomas preoperative and tumor proliferative activity.

Dynamic transcriptome profiling reveals essential roles of the Receptor Tyrosine Kinases (RTK) family in feather development of duck

1. Chicken primary myoblasts (CPMs) are precursors that form muscle fibres. The proliferation and differentiation of CPMs is an essential stage in muscle development. Previous RNA-seq analysis showed that phosphoglycerate dehydrogenase (PHGDH) is a differentially expressed gene in chicken muscle tissue at different growth stages. Therefore, the following study explored the effect of PHGDH on the proliferation and differentiation of CPMs.2. The effect on the proliferation of CPMs by RT-qPCR, CCK-8, and EdU assays after the overexpression and knockdown of PHGDH was evaluated. RT-qPCR, western blotting, and indirect immunofluorescence were used to detect the effect of PHGDH on the differentiation of the CPMs. The expression was observed at different time points for differentiation induced by the CPMs.3. The results showed that PHGDH significantly promoted proliferation and differentiation in CPMs. The results showed that overexpression of PHGDH significantly upregulated CPM proliferation, while knockdown had the opposite effect. Marker genes showed that overexpression of PHGDH significantly upregulated the expression of P21, MYOG and MYOD genes, significantly downregulated the expression of the MSTN gene and promoted the expression of the MYHC protein. In contrast, PHGDH knockdown had the opposite effect.4. Desmin immunofluorescence analysis of myotube differentiation in primary myoblasts showed that overexpression of PHGDH significantly increased the area of myotube differentiation and promoted the proliferation and differentiation of myoblasts. Knockdown of PHGDH had the opposite effect.5. In summary, PHGDH was shown to play a positive role in regulating myoblast proliferation and differentiation. This provided a theoretical basis for further analysis of the regulatory mechanism of the PHGDH gene in chicken muscle development and for improving poultry production.

PHGDH promotes the proliferation and differentiation of primary chicken myoblasts

1. Chicken primary myoblasts (CPMs) are precursors that form muscle fibres. The proliferation and differentiation of CPMs is an essential stage in muscle development. Previous RNA-seq analysis showed that phosphoglycerate dehydrogenase (PHGDH) is a differentially expressed gene in chicken muscle tissue at different growth stages. Therefore, the following study explored the effect of PHGDH on the proliferation and differentiation of CPMs.2. The effect on the proliferation of CPMs by RT-qPCR, CCK-8, and EdU assays after the overexpression and knockdown of PHGDH was evaluated. RT-qPCR, western blotting, and indirect immunofluorescence were used to detect the effect of PHGDH on the differentiation of the CPMs. The expression was observed at different time points for differentiation induced by the CPMs.3. The results showed that PHGDH significantly promoted proliferation and differentiation in CPMs. The results showed that overexpression of PHGDH significantly upregulated CPM proliferation, while knockdown had the opposite effect. Marker genes showed that overexpression of PHGDH significantly upregulated the expression of P21, MYOG and MYOD genes, significantly downregulated the expression of the MSTN gene and promoted the expression of the MYHC protein. In contrast, PHGDH knockdown had the opposite effect.4. Desmin immunofluorescence analysis of myotube differentiation in primary myoblasts showed that overexpression of PHGDH significantly increased the area of myotube differentiation and promoted the proliferation and differentiation of myoblasts. Knockdown of PHGDH had the opposite effect.5. In summary, PHGDH was shown to play a positive role in regulating myoblast proliferation and differentiation. This provided a theoretical basis for further analysis of the regulatory mechanism of the PHGDH gene in chicken muscle development and for improving poultry production.

Identification of a novel PHGDH covalent inhibitor by chemical proteomics and phenotypic profiling

The first rate-limiting enzyme of the serine synthesis pathway (SSP), phosphoglycerate dehydrogenase (PHGDH), is hyperactive in multiple tumors, which leads to the activation of SSP and promotes tumorigenesis. However, only a few inhibitors of PHGDH have been discovered to date, especially the covalent inhibitors of PHGDH. Here, we identified withangulatin A (WA), a natural small molecule, as a novel covalent inhibitor of PHGDH. Affinity-based protein profiling identified that WA could directly bind to PHGDH and inactivate the enzyme activity of PHGDH. Biolayer interferometry and LC-MS/MS analysis further demonstrated the selective covalent binding of WA to the cysteine 295 residue (Cys295) of PHGDH. With the covalent modification of Cys295, WA blocked the substrate-binding domain (SBD) of PHGDH and exerted an allosteric effect to induce PHGDH inactivation. Further studies revealed that with the inhibition of PHGDH mediated by WA, the glutathione synthesis was decreased and intracellular levels of reactive oxygen species (ROS) were elevated, leading to the inhibition of tumor proliferation. This study indicates WA as a novel PHGDH covalent inhibitor, which identifies Cys295 as a novel allosteric regulatory site of PHGDH and holds great potential in developing anti-tumor agents for targeting PHGDH.

Expression of Glucose Metabolism-Related Proteins in Adrenal Neoplasms

PURPOSE

The aim of this study was to investigate the expression patterns of glucose metabolism-related proteins and their clinicopathologic implications in adrenal cortical neoplasms (ACN) and pheochromocytoma (PCC).

METHODS

Immunohistochemical staining was performed to evaluate glucose metabolism-related proteins (GLUT1, CAIX, hexokinase II, G6PDH, PHGDH, and SHMT1) in 132 ACN cases (115 adrenal cortical adenoma [ACA] and 17 adrenal cortical carcinoma [ACC]) and 189 PCC cases.

RESULTS

Expression levels of GLUT1 in tumor cells ([T]; p < 0.001), GLUT1 in stromal cells ([S]; p < 0.001), G6PDH (p < 0.001), and SHMT1 (p = 0.002) were higher in ACN than in PCC. GLUT1 (T; p = 0.045) and PHGDH (p = 0.043) levels were higher in ACC than in ACA. In a univariate analysis of ACN, GLUT1 (T; p = 0.017), CAIX (S; p = 0.003), and PHGDH (p = 0.009) levels were correlated with a shorter overall survival (OS). GLUT1 (T; p = 0.001) and PHGDH (p < 0.001) were related to a shorter OS in PCC. GLUT1 (T) positivity (p = 0.043) in ACN predicted a poor OS in a multivariate Cox analysis. In PCC, high GAPP score (p = 0.026), GLUT1 (T; p = 0.002), and PHGDH (p < 0.001) were independent prognostic factors for poor OS.

CONCLUSIONS

The adrenal gland tumors ACN and PCC had different expression patterns of glucose metabolism-related proteins (GLUT1, G6PDH, and SHMT1), with higher expression levels in ACN than in PCC. GLUT1 and PHGDH were significant prognostic factors in these adrenal neoplasms.

Lactate Modulates Cellular Metabolism Through Histone Lactylation-Mediated Gene Expression in Non-Small Cell Lung Cancer

Lactate has been observed to fuel TCA cycle and is associated with cancer progression in human lung cancer, the leading cause of cancer deaths worldwide, but the effect of lactate on lung cancer metabolism is rarely reported. In this study, disordered metabolism in non-small cell lung cancer was demonstrated by increased G6PD and SDHA protein levels via immunofluorescence, and up-regulated lactate dehydrogenase was found to be associated with poor prognosis. Then flow cytometry and Seahorse XFe analyzer were utilized to detect the effect of lactate on glycolysis and mitochondrial function in non-small cell lung cancer cells. The results show that in non-small cell lung cancer cells lactate attenuates glucose uptake and glycolysis while maintaining mitochondrial homeostasis as indicated by improved mitochondrial membrane potential. Further exploration found that mRNA levels of glycolytic enzymes (HK-1, PKM) and TCA cycle enzymes (SDHA, IDH3G) are respectively down-regulated and up-regulated by lactate, and increased histone lactylation was observed in promoters of HK-1 and IDH3G via chromatin immunoprecipitation assay. Taken together, the above results indicate that lactate modulates cellular metabolism at least in part through histone lactylation-mediated gene expression in non-small cell lung cancer.

Single-cell profiling of D-2-hydroxyglutarate using surface-immobilized resazurin analogs

D-2-hydroxyglutarate (D2HG) is over-produced as an oncometabolite due to mutations in isocitrate dehydrogenases (IDHs). Accumulation of D2HG can cause the dysfunction of many enzymes and genome-wide epigenetic alterations, which can promote oncogenesis. Quantification of D2HG at single-cell resolution can help understand the phenotypic signatures of IDH-mutant cancers and identify effective therapeutics. In this study, we developed an analytical method to detect D2HG levels in single cancer cells by adapting cascade enzymatic reactions on a resazurin-based fluorescence reporter. The resazurin probe was immobilized to the sensing surface via biotin-streptavidin interaction. This surface chemistry was rationally optimized to translate the D2HG levels to sensitive fluorescence readouts efficiently. This D2HG assay demonstrated good selectivity and high sensitivity toward D2HG, and it was compatible with the previously developed single-cell barcode chip (SCBC) technology. Using the SCBC platform, we performed simultaneous single-cell profiling of D2HG, glucose uptake, and critical oncogenic signaling proteins in single IDH-mutant glioma cells. The results unveiled the complex interplays between metabolic and oncogenic signaling and led to the identification of effective combination targeted therapy against these IDH-mutant glioma cells.

Identification of PDHX as a metabolic target for esophageal squamous cell carcinoma

The metabolism in tumors is reprogrammed to meet its energetic and substrate demands. However, this metabolic reprogramming creates metabolic vulnerabilities, providing new opportunities for cancer therapy. Metabolic vulnerability as a therapeutic target in esophageal squamous cell carcinoma (ESCC) has not been adequately clarified. Here, we identified pyruvate dehydrogenase (PDH) component X (PDHX) as a metabolically essential gene for the cell growth of ESCC. PDHX expression was required for the maintenance of PDH activity and the production of ATP, and its knockdown inhibited the proliferation of cancer stem cells (CSCs) and in vivo tumor growth. PDHX was concurrently upregulated with the CD44 gene, a marker of CSCs, by co-amplification at 11p13 in ESCC tumors and these genes coordinately functioned in cancer stemness. Furthermore, CPI-613, a PDH inhibitor, inhibited the proliferation of CSCs in vitro and the growth of ESCC xenograft tumors in vivo. Thus, our study provides new insights related to the development of novel therapeutic strategies for ESCC by targeting the PDH complex-associated metabolic vulnerability.

3-Phosphoglycerate dehydrogenase: a potential target for cancer treatment

BACKGROUND

Metabolic changes have been recognized as an important hallmark of cancer cells. Cancer cells can promote their own growth and proliferation through metabolic reprogramming. Particularly, serine metabolism has frequently been reported to be dysregulated in tumor cells. 3-Phosphoglycerate dehydrogenase (PHGDH) catalyzes the first step in the serine biosynthesis pathway and acts as a rate-limiting enzyme involved in metabolic reprogramming. PHGDH upregulation has been observed in many tumor types, and inhibition of PHGDH expression has been reported to inhibit the proliferation of PHGDH-overexpressing tumor cells, indicating that it may be utilized as a target for cancer treatment. Recently identified inhibitors targeting PHGDH have already shown effectiveness. A further in-depth analysis and concomitant development of PHGDH inhibitors will be of great value for the treatment of cancer.

CONCLUSIONS

In this review we describe in detail the role of PHGDH in various cancers and inhibitors that have recently been identified to highlight progression in cancer treatment. We also discuss the development of new drugs and treatment modalities based on PHGDH targets. Overexpression of PHGDH has been observed in melanoma, breast cancer, nasopharyngeal carcinoma, parathyroid adenoma, glioma, cervical cancer and others. PHGDH may serve as a molecular biomarker for the diagnosis, prognosis and treatment of these cancers. The design and development of novel PHGDH inhibitors may have broad implications for cancer treatment. Therapeutic strategies of PHGDH inhibitors in combination with traditional chemotherapeutic drugs may provide new perspectives for precision medicine and effective personalized treatment for cancer patients.

The oncometabolite L-2-hydroxyglutarate is a common product of dipteran larval development

The oncometabolite L-2-hydroxyglutarate (L-2HG) is considered an abnormal product of central carbon metabolism that is capable of disrupting chromatin architecture, mitochondrial metabolism, and cellular differentiation. Under most circumstances, mammalian tissues readily dispose of this compound, as aberrant L-2HG accumulation induces neurometabolic disorders and promotes renal cell carcinomas. Intriguingly, Drosophila melanogaster larvae were recently found to accumulate high L-2HG levels under normal growth conditions, raising the possibility that L-2HG plays a unique role in insect metabolism. Here we explore this hypothesis by analyzing L-2HG levels in 18 insect species. While L-2HG was present at low-to-moderate levels in most of these species (<100 pmol/mg; comparable to mouse liver), dipteran larvae exhibited a tendency to accumulate high L-2HG concentrations (>100 pmol/mg), with the mosquito Aedes aegypti, the blow fly Phormia regina, and three representative Drosophila species harboring concentrations that exceed 1 nmol/mg - levels comparable to those measured in mutant mice that are unable to degrade L-2HG. Overall, our findings suggest that one of the largest groups of animals on earth commonly generate high concentrations of an oncometabolite during juvenile growth, hint at a role for L-2HG in the evolution of dipteran development, and raise the possibility that L-2HG metabolism could be targeted to restrict the growth of key disease vectors and agricultural pests.

Phosphorylation of PDHA by AMPK Drives TCA Cycle to Promote Cancer Metastasis

Cancer metastasis accounts for the major cause of cancer-related deaths. How disseminated cancer cells cope with hostile microenvironments in secondary site for full-blown metastasis is largely unknown. Here, we show that AMPK (AMP-activated protein kinase), activated in mouse metastasis models, drives pyruvate dehydrogenase complex (PDHc) activation to maintain TCA cycle (tricarboxylic acid cycle) and promotes cancer metastasis by adapting cancer cells to metabolic and oxidative stresses. This AMPK-PDHc axis is activated in advanced breast cancer and predicts poor metastasis-free survival. Mechanistically, AMPK localizes in the mitochondrial matrix and phosphorylates the catalytic alpha subunit of PDHc (PDHA) on two residues S295 and S314, which activates the enzymatic activity of PDHc and alleviates an inhibitory phosphorylation by PDHKs, respectively. Importantly, these phosphorylation events mediate PDHc function in cancer metastasis. Our study reveals that AMPK-mediated PDHA phosphorylation drives PDHc activation and TCA cycle to empower cancer cells adaptation to metastatic microenvironments for metastasis.

Nitrogen Trapping as a Therapeutic Strategy in Tumors with Mitochondrial Dysfunction

Under conditions of inherent or induced mitochondrial dysfunction, cancer cells manifest overlapping metabolic phenotypes, suggesting that they may be targeted via a common approach. Here, we use multiple oxidative phosphorylation (OXPHOS)-competent and incompetent cancer cell pairs to demonstrate that treatment with α-ketoglutarate (aKG) esters elicits rapid death of OXPHOS-deficient cancer cells by elevating intracellular aKG concentrations, thereby sequestering nitrogen from aspartate through glutamic-oxaloacetic transaminase 1 (GOT1). Exhaustion of aspartate in these cells resulted in immediate depletion of adenylates, which plays a central role in mediating mTOR inactivation and inhibition of glycolysis. aKG esters also conferred cytotoxicity in a variety of cancer types if their cell respiration was obstructed by hypoxia or by chemical inhibition of the electron transport chain (ETC), both of which are known to increase aspartate and GOT1 dependencies. Furthermore, preclinical mouse studies suggested that cell-permeable aKG displays a good biosafety profile, eliminates aspartate only in OXPHOS-incompetent tumors, and prevents their growth and metastasis. This study reveals a novel cytotoxic mechanism for the metabolite aKG and identifies cell-permeable aKG, either by itself or in combination with ETC inhibitors, as a potential anticancer approach. SIGNIFICANCE: These findings demonstrate that OXPHOS deficiency caused by either hypoxia or mutations, which can significantly increase cancer virulence, renders tumors sensitive to aKG esters by targeting their dependence upon GOT1 for aspartate synthesis. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/17/3492/F1.large.jpg.

Carbamazepine, cadmium chloride and polybrominated diphenyl ether-47, synergistically modulate the expression of antioxidants and cell cycle biomarkers, in the marine fish cell line SAF-1

A wide range of contaminants, industrial by-products, plastics, and pharmaceutics belonging to various categories, have been found in sea water. Although these compounds are detected at concentrations that might be considered as sub-lethal, under certain conditions they could act synergistically producing unexpected effects in term of toxicity or perturbation of biochemical markers leading to standard pathway. In this study, the Sparus aurata fibroblast cell line SAF-1, was exposed to increasing concentrations of carbamazepine (CBZ), polybrominated diphenyl ether 47 (BDE-47) and cadmium chloride (CdCl₂) until 72 h, to evaluate the cytotoxicity and the expression of genes related to antioxidant defense, cell cycle and energetic balance. In general, both vitality and gene expression were affected by the exposure to the different toxicants, in terms of antioxidant defense and cell cycle control, showing the most significant effects in cells exposed to the mixture of the three compounds, respect to the single compounds separately. The synergic effect of the compounds on the analyzed biomarkers, underlie the potential negative impact of the contaminants on health of marine organisms.

Decoupling of Nrf2 Expression Promotes Mesenchymal State Maintenance in Non-Small Cell Lung Cancer

Epithelial mesenchymal transition is a common mechanism leading to metastatic dissemination and cancer progression. In an effort to better understand this process we found an intersection of Nrf2/NLE2F2 (Nrf2), epithelial mesenchymal transition (EMT), and metabolic alterations using multiple in vitro and in vivo approaches. Nrf2 is a key transcription factor controlling the expression of redox regulators to establish cellular redox homeostasis. Nrf2 has been shown to exert both cancer inhibitory and stimulatory activities. Using multiple isogenic non-small cell lung cancer (NSCLC) cell lines, we observed a reduction of Nrf2 protein and activity in a prometastatic mesenchymal cell state and increased reactive oxygen species. Knockdown of Nrf2 promoted a mesenchymal phenotype and reduced glycolytic, TCA cycle and lipogenic output from both glucose and glutamine in the isogenic cell models; while overexpression of Nrf2 promoted a more epithelial phenotype and metabolic reactivation. In both Nrf2 knockout mice and in NSCLC patient samples, Nrf2^low was co-correlated with markedly decreased expression of glycolytic, lipogenic, and mesenchymal RNAs. Conversely, Nrf2^high was associated with partial mesenchymal epithelial transition and increased expression of metabolic RNAs. The impact of Nrf2 on epithelial and mesenchymal cancer cell states and metabolic output provide an additional context to Nrf2 function in cancer initiation and progression, with implications for therapeutic inhibition of Nrf2 in cancer treatment.

Sub-lethal doses of polybrominated diphenyl ethers affect some biomarkers involved in energy balance and cell cycle, via oxidative stress in the marine fish cell line SAF-1

Polybrominated diphenyl ethers (PBDEs) are a class of persistent contaminants which are found all over the world in the marine environment. Sparus aurata fibroblast cell line (SAF-1) was exposed to increasing concentrations of PBDEs 47 and 99, until 72 h to evaluate the cytotoxicity, reactive oxygen species (ROS) production and the expression of some selected molecular markers related to cell cycle, cell signaling, energetic balance and oxidative stress (p53, erk-1, hif-1α and nrf-2), by real-time PCR. Furthermore, SAF-1 cells were exposed for 7 and 15 days to sub-lethal concentrations, in order to evaluate the response of some biomarkers by immunoblotting (p53, ERK-1, AMPK, HIF-1α and NRF-2). After 48 and 72 h, the cells showed a significant decrease of cell vitality as well as an increase of intracellular ROS production. Gene expression analysis showed that sub-lethal concentrations of BDE-99 and 47, after 72 h, up-regulated cell cycle and oxidative stress biomarkers, although exposure to 100 μmol L^-1 down-regulated the selected markers related to cell cycle, cell signaling, energetic balance. After 7 and 15 days of sub-lethal doses exposure, all the analyzed markers resulted affected by the contaminants. Our results suggest that PBDEs influence the cells homeostasis first of all via oxidative stress, reducing the cell response and defense capacity and affecting its energetic levels. This situation of stress and energy imbalance could represents a condition that, modifying some of the analyzed biochemical pathways, would predispose to cellular transformation.

Sub-lethal Doses of Polybrominated Diphenyl Ethers, in Vitro, Promote Oxidative Stress and Modulate Molecular Markers Related to Cell Cycle, Antioxidant Balance and Cellular Energy Management

In the present study, we evaluated the effects of different concentrations of the polybrominated diphenyl ethers (PBDEs) BDE-209, BDE-47 and BDE-99, on the vitality and oxidative stress of a HS-68 human cell culture exposed to the compounds for three days. The results showed that for this exposure time, only the highest concentrations produced a significant vitality reduction and oxidative stress induction (p < 0.05), measured as reactive oxygen species (ROS). Subsequently, in order to verify the effects of sub-lethal doses, cells were exposed for a longer time and data collected, after 12 and 20 days, to study ROS production and some molecular markers related to cell cycle and stress (p53, pRB, PARP, c-Jun and c-Fos), antioxidant status and proliferation (ERK, c-Jun and c-Fos), energy balance (NRF2, AMPK, HIF). Most of the biomarkers were influenced by the treatments, indicating that sub-lethal doses of PBDEs, for longer time, can enhance the production of ROS, altering the energetic metabolism, cell cycle and antioxidant balance, determining possible negative effects on the cell proliferation equilibrium.

Stable Isotope Labeling Highlights Enhanced Fatty Acid and Lipid Metabolism in Human Acute Myeloid Leukemia

Background: In Acute Myeloid Leukemia (AML), a complete response to chemotherapy is usually obtained after conventional chemotherapy but overall patient survival is poor due to highly frequent relapses. As opposed to chronic myeloid leukemia, B lymphoma or multiple myeloma, AML is one of the rare malignant hemopathies the therapy of which has not significantly improved during the past 30 years despite intense research efforts. One promising approach is to determine metabolic dependencies in AML cells. Moreover, two key metabolic enzymes, isocitrate dehydrogenases (IDH1/2), are mutated in more than 15% of AML patient, reinforcing the interest in studying metabolic reprogramming, in particular in this subgroup of patients. Methods: Using a multi-omics approach combining proteomics, lipidomics, and isotopic profiling of [U-¹³C] glucose and [U-¹³C] glutamine cultures with more classical biochemical analyses, we studied the impact of the IDH1 R132H mutation in AML cells on lipid biosynthesis. Results: Global proteomic and lipidomic approaches showed a dysregulation of lipid metabolism, especially an increase of phosphatidylinositol, sphingolipids (especially few species of ceramide, sphingosine, and sphinganine), free cholesterol and monounsaturated fatty acids in IDH1 mutant cells. Isotopic profiling of fatty acids revealed that higher lipid anabolism in IDH1 mutant cells corroborated with an increase in lipogenesis fluxes. Conclusions: This integrative approach was efficient to gain insight into metabolism and dynamics of lipid species in leukemic cells. Therefore, we have determined that lipid anabolism is strongly reprogrammed in IDH1 mutant AML cells with a crucial dysregulation of fatty acid metabolism and fluxes, both being mediated by 2-HG (2-Hydroxyglutarate) production.

Suppression of antitumor T cell immunity by the oncometabolite (R)-2-hydroxyglutarate

The oncometabolite (R)-2-hydroxyglutarate (R-2-HG) produced by isocitrate dehydrogenase (IDH) mutations promotes gliomagenesis via DNA and histone methylation. Here, we identify an additional activity of R-2-HG: tumor cell-derived R-2-HG is taken up by T cells where it induces a perturbation of nuclear factor of activated T cells transcriptional activity and polyamine biosynthesis, resulting in suppression of T cell activity. IDH1-mutant gliomas display reduced T cell abundance and altered calcium signaling. Antitumor immunity to experimental syngeneic IDH1-mutant tumors induced by IDH1-specific vaccine or checkpoint inhibition is improved by inhibition of the neomorphic enzymatic function of mutant IDH1. These data attribute a novel, non-tumor cell-autonomous role to an oncometabolite in shaping the tumor immune microenvironment.

Targeting of stress response pathways in the prevention and treatment of cancer

The hallmarks of tumor tissue are not only genetic aberrations but also the presence of metabolic and oxidative stress as a result of hypoxia and lactic acidosis. The stress activates several prosurvival pathways including metabolic remodeling, autophagy, antioxidant response, mitohormesis, and glutaminolysis, whose upregulation in tumors is associated with a poor survival of patients, while their activation in healthy tissue with statins, metformin, physical activity, and natural compounds prevents carcinogenesis. This review emphasizes the dual role of stress response pathways in cancer and suggests the integrative understanding as a basis for the development of rational therapy targeting the stress response.

A metabolic core model elucidates how enhanced utilization of glucose and glutamine, with enhanced glutamine-dependent lactate production, promotes cancer cell growth: The WarburQ effect

Cancer cells share several metabolic traits, including aerobic production of lactate from glucose (Warburg effect), extensive glutamine utilization and impaired mitochondrial electron flow. It is still unclear how these metabolic rearrangements, which may involve different molecular events in different cells, contribute to a selective advantage for cancer cell proliferation. To ascertain which metabolic pathways are used to convert glucose and glutamine to balanced energy and biomass production, we performed systematic constraint-based simulations of a model of human central metabolism. Sampling of the feasible flux space allowed us to obtain a large number of randomly mutated cells simulated at different glutamine and glucose uptake rates. We observed that, in the limited subset of proliferating cells, most displayed fermentation of glucose to lactate in the presence of oxygen. At high utilization rates of glutamine, oxidative utilization of glucose was decreased, while the production of lactate from glutamine was enhanced. This emergent phenotype was observed only when the available carbon exceeded the amount that could be fully oxidized by the available oxygen. Under the latter conditions, standard Flux Balance Analysis indicated that: this metabolic pattern is optimal to maximize biomass and ATP production; it requires the activity of a branched TCA cycle, in which glutamine-dependent reductive carboxylation cooperates to the production of lipids and proteins; it is sustained by a variety of redox-controlled metabolic reactions. In a K-ras transformed cell line we experimentally assessed glutamine-induced metabolic changes. We validated computational results through an extension of Flux Balance Analysis that allows prediction of metabolite variations. Taken together these findings offer new understanding of the logic of the metabolic reprogramming that underlies cancer cell growth.

Hallmarks describing common key events in initiation, maintenance and progression of cancer have been identified. One hallmark deals with rewiring of metabolic reactions required to sustain enhanced cell proliferation. The availability of molecular, mechanistic models of cancer hallmarks will mightily improve optimized personal treatment and new drug discovery. Metabolism is the only hallmark for which it is currently possible to derive large scale mathematical models, which have predictive ability. In this paper, we exploit a constraint-based model of the core metabolism required for biomass conversion of the most relevant nutrients—glucose and glutamine—to clarify the logic of control of cancer metabolism. We newly report that, when available oxygen is not sufficient to fully oxidize available glucose and glutamine carbons–a situation compatible with that observed under normal oxygen conditions in human and in cancer cells growing in vitro—utilization of glutamine by reductive carboxylation and conversion of glucose and glutamine to lactate confer advantage for biomass production. Redox homeostasis can be maintained through the use of different alternative pathways. In conclusion, this paper offers a logic interpretation to the link between metabolic rewiring and enhanced proliferation, which may offer new approaches to targeted drug discovery and utilization.

Benzo[a]pyrene-induced metabolic shift from glycolysis to pentose phosphate pathway in the human bladder cancer cell line RT4

Benzo[a]pyrene (B[a]P), a well-known polyaromatic hydrocarbon, is known for its lung carcinogenicity, however, its role in bladder cancer development is still discussed. Comparative two-dimensional blue native SDS-PAGE analysis of protein complexes isolated from subcellular fractions of 0.5 µM B[a]P-exposed cells indicated a differential regulation of proteins involved in carbohydrate, fatty acid, and nucleotide metabolism, suggesting a possible metabolic flux redistribution. It appeared that B[a]P exposure led to a repression of enzymes (fructose-bisphosphate aldolase A, glucose-6-phosphate isomerase, lactate dehydrogenase) involved in glycolysis, and an up-regulation of proteins (glucose-6-phosphate 1-dehydrogenase, 6-phosphogluconolactonase) catalyzing the pentose phosphate pathway and one carbon metabolism (10-formyltetrahydrofolate dehydrogenase, bifunctional purine biosynthesis protein). Untargeted metabolomics further supported the proteomic data, a lower concentration of glycolytic metabolite was observed as compared to glutamine, xylulose and fatty acids. The analysis of the glutathione and NADPH/NADP⁺ content of the cells revealed a significant increase of these cofactors. Concomitantly, we did not observe any detectable increase in the production of ROS. With the present work, we shed light on an early phase of the metabolic stress response in which the urothelial cells are capable of counteracting oxidative stress by redirecting the metabolic flux from glycolysis to pentose phosphate pathway.

Oncometabolite succinate promotes angiogenesis by upregulating VEGF expression through GPR91-mediated STAT3 and ERK activation

Altered cellular metabolism is now generally acknowledged as a hallmark of cancer cells, the resultant abnormal oncometabolites cause both metabolic and nonmetabolic dysregulation and potential transformation to malignancy. A subset of cancers have been found to be associated with mutations in succinate dehydrogenase genes which result in the accumulation of succinate. However, the function of succinate in tumorigenesis remains unclear. In the present study, we aim to investigate the role of oncometabolite succinate in tumor angiogenesis. Our data demonstrated the accumulation of markedly elevated succinate in gastric cancer tissues compared with that in paracancerous tissues. Moreover, succinate was able to increase the chemotactic motility, tube-like structure formation and proliferation of primary human umbilical vascular endothelial cells (pHUVECs) in vitro, as well as promoting the blood vessel formation in transgenic zebrafish. Our mechanistic studies reveal that succinate upregulates vascular endothelial growth factor (VEGF) expression by activation of signal transducer and activator of transcription 3 (STAT3) and extracellular regulated kinase (ERK)1/2 via its receptor GPR91 in a HIF-1α independent mechanism. Taken together, these data indicate an important role of the succinate-GPR91 axis in tumor angiogenesis, which may enable development of a novel therapeutic strategy that targets cancer metabolism.

Succinate: An initiator in tumorigenesis and progression

As an intermediate metabolite of the tricarboxylic acid cycle in mitochondria, succinate is widely investigated for its role in metabolism. In recent years, an increasing number of studies have concentrated on the unanticipated role of succinate outside metabolism, acting as, for instance, an inflammatory signal or a carcinogenic initiator. Actually, succinate dehydrogenase gene mutations and abnormal succinate accumulation have been observed in a battery of hereditary and sporadic malignancies. In this review, we discuss the unexpected role of succinate and possible mechanisms that may contribute to its accumulation. Additionally, we describe how the high concentration of succinate in the tumor microenvironment acts as an active participant in tumorigenesis, rather than a passive bystander or innocent victim. Focusing on mechanism-based research, we summarize some targeted therapies which have been applied to the clinic or are currently under development. Furthermore, we posit that investigational drugs with different molecular targets may expand our horizon in anticancer therapy.

High expression of PFTK1 in cancer cells predicts poor prognosis in colorectal cancer

The serine/threonine-protein kinase PFTAIRE 1 (PFTK1) is a member of the cyclin‑dependent kinase family that is highly expressed in several malignant tumors, including hepatocellular carcinoma, esophageal, breast and gastric cancers, and glioma. It contributes to tumor progression and influences tumor prognosis. However, the expression and clinicopathological significance of PFTK1 in human colorectal cancer (CRC) remain to be elucidated. The present study aimed to examine the expression of PFTK1 and to evaluate the clinical significance of its expression in human CRC. Reverse transcription‑quantitative polymerase chain reaction was performed on 10 fresh CRC and 10 surrounding normal tissue samples to detect and compare the expression of PFTK1 mRNA in CRC and normal colorectal tissues. Immunohistochemistry was performed on 179 CRC tissue specimens and 47 control samples of normal colorectal lesions to characterize the expression of PFTK1 protein. Kaplan‑Meier overall survival (OS) rate and Cox regression analyses were performed to evaluate the prognosis of patients with CRC. The expression of PFTK1 mRNA in CRC tissues (1.433±0.168) was significantly higher compared with normal tissues (0.853±0.107; t=1.97 ('t' was the value obtained from quantification of the mRNA data, following a paired t‑test), P=0.008). High PFTK1 expression in cancerous cells was detected in 92 of the CRC specimens (51.40%), and high levels of PFTK1 were associated with tumor node metastasis (TNM) stage (P=0.042), tumor classification (P=0.022) and preoperative carcinoembryonic antigen (CEA) level (P<0.001). Kaplan‑Meier OS rate and Cox regression analysis revealed that high PFTK1 expression level (hazard ratio (HR)=1.999; P=0.019) was an independent prognostic factor of CRC patients. The degree of differentiation (HR, 0.368, P=0.003), TNM classification (HR, 2.118, P=0.001) and preoperative CEA level (HR, 2.302, P=0.003) were also predictors of the prognosis of patients with CRC. The present study suggested that PFTK1 may be a potential anticancer target and prognostic marker in patients with CRC.

Isocitrate dehydrogenase (IDH) inhibition as treatment of myeloid malignancies: Progress and future directions

Isocitrate dehydrogenase (IDH) is an essential metabolic enzyme. Over the last two decades, there has been a growing focus on the metabolic derangements that occur with IDH1 and IDH2 mutations. The altered IDH protein leads to accumulation of 2-hydroxyglutarate (2-HG), a metabolite with oncogenic activity via epigenetic mechanisms. The advent of IDH inhibitors has engendered hope in novel and targeted therapies in IDH1/2 mutant myeloid malignancies. We here summarize the basic physiology of IDH, the metabolic and oncogenic consequences of mutant IDH1/2, and the clinical significance of IDH inhibition in hematologic malignancies. We also discuss completed and ongoing clinical trials focusing on the inhibition of IDH proteins, which have demonstrated preliminary indications of efficacy. The promise of IDH inhibition is now being further investigated as a novel therapeutic approach for AML and other myeloid malignancies.

Oncometabolites: Unconventional triggers of oncogenic signalling cascades

Cancer is a complex and heterogeneous disease thought to be caused by multiple genetic lesions. The recent finding that enzymes of the tricarboxylic acid (TCA) cycle are mutated in cancer rekindled the hypothesis that altered metabolism might also have a role in cellular transformation. Attempts to link mitochondrial dysfunction to cancer uncovered the unexpected role of small molecule metabolites, now known as oncometabolites, in tumorigenesis. In this review, we describe how oncometabolites can contribute to tumorigenesis. We propose that lesions of oncogenes and tumour suppressors are only one of the possible routes to tumorigenesis, which include accumulation of oncometabolites triggered by environmental cues.

Mutant IDH1 expression is associated with down-regulation of monocarboxylate transporters

Mutations in isocitrate dehydrogenase 1 (IDH1) are characteristic of low-grade gliomas. We recently showed that mutant IDH1 cells reprogram cellular metabolism by down-regulating pyruvate dehydrogenase (PDH) activity. Reduced pyruvate metabolism via PDH could lead to increased pyruvate conversion to lactate. The goal of this study was therefore to investigate the impact of the IDH1 mutation on the pyruvate-to-lactate flux. We used 13C magnetic resonance spectroscopy and compared the conversion of hyperpolarized [1-13C]-pyruvate to [1-13C]-lactate in immortalized normal human astrocytes expressing mutant or wild-type IDH1 (NHAIDHmut and NHAIDHwt). Our results indicate that hyperpolarized lactate production is reduced in NHAIDHmut cells compared to NHAIDHwt. This reduction was associated with lower expression of the monocarboxylate transporters MCT1 and MCT4 in NHAIDHmut cells. Furthermore, hyperpolarized lactate production was comparable in lysates of NHAIDHmut and NHAIDHwt cells, wherein MCTs do not impact hyperpolarized pyruvate delivery and lactate production. Collectively, our findings indicated that lower MCT expression was a key contributor to lower hyperpolarized lactate production in NHAIDHmut cells. The SLC16A3 (MCT4) promoter but not SLC16A1 (MCT1) promoter was hypermethylated in NHAIDHmut cells, pointing to possibly different mechanisms mediating reduced MCT expression. Finally analysis of low-grade glioma patient biopsy data from The Cancer Genome Atlas revealed that MCT1 and MCT4 expression was significantly reduced in mutant IDH1 tumors compared to wild-type. Taken together, our study shows that reduced MCT expression is part of the metabolic reprogramming of mutant IDH1 gliomas. This finding could impact treatment and has important implications for metabolic imaging of mutant IDH1 gliomas.

Molecular Imaging of Metabolic Reprograming in Mutant IDH Cells

Mutations in the metabolic enzyme isocitrate dehydrogenase (IDH) have recently been identified as drivers in the development of several tumor types. Most notably, cytosolic IDH1 is mutated in 70-90% of low-grade gliomas and upgraded glioblastomas, and mitochondrial IDH2 is mutated in ~20% of acute myeloid leukemia cases. Wild-type IDH catalyzes the interconversion of isocitrate to α-ketoglutarate (α-KG). Mutations in the enzyme lead to loss of wild-type enzymatic activity and a neomorphic activity that converts α-KG to 2-hydroxyglutarate (2-HG). In turn, 2-HG, which has been termed an "oncometabolite," inhibits key α-KG-dependent enzymes, resulting in alterations of the cellular epigenetic profile and, subsequently, inhibition of differentiation and initiation of tumorigenesis. In addition, it is now clear that the IDH mutation also induces a broad metabolic reprograming that extends beyond 2-HG production, and this reprograming often differs from what has been previously reported in other cancer types. In this review, we will discuss in detail what is known to date about the metabolic reprograming of mutant IDH cells, and how this reprograming has been investigated using molecular metabolic imaging. We will describe how metabolic imaging has helped shed light on the basic biology of mutant IDH cells, and how this information can be leveraged to identify new therapeutic targets and to develop new clinically translatable imaging methods to detect and monitor mutant IDH tumors in vivo.

AMPK-mediated energy homeostasis and associated metabolic effects on cancer cell response and resistance to cetuximab

We previously reported that cetuximab, an EGFR-blocking antibody, inhibits cancer metabolism via downregulation of HIF-1α and reverses the Warburg effect in cancer cells. Here, we report that inhibition of HIF-1 transcriptional activity by cetuximab does not necessarily lead to successful inhibition of cell proliferation. In several head and neck squamous cell carcinoma (HNSCC) cell lines, we observed a pattern of oscillating decrease and increase of intracellular ATP level after cetuximab treatment, and the magnitude and kinetics of which varied by cell line and appeared to be linked to the extent of cellular response to cetuximab. In HNSCC cells with low basal level of AMPK activity and that responded to cetuximab-induced growth inhibition, there was a transient, LKB1-dependent activation of AMPK. In contrast, HNSCC cells that had a high basal level of AMPK activity were less sensitive to cetuximab-induced growth inhibition despite effective inhibition of EGFR downstream signaling by cetuximab. Knockdown or inhibition of AMPK markedly enhanced response to cetuximab via induction of apoptosis. These findings indicate that a transient activation of AMPK is an early metabolic marker of cellular response to cetuximab and that high and sustained AMPK activity is an important mechanism by which cancer cells survive cetuximab treatment.

Identification of a small molecule inhibitor of 3-phosphoglycerate dehydrogenase to target serine biosynthesis in cancers

Cancer cells reprogram their metabolism to promote growth and proliferation. The genetic evidence pointing to the importance of the amino acid serine in tumorigenesis is striking. The gene encoding the enzyme 3-phosphoglycerate dehydrogenase (PHGDH), which catalyzes the first committed step of serine biosynthesis, is overexpressed in tumors and cancer cell lines via focal amplification and nuclear factor erythroid-2-related factor 2 (NRF2)-mediated up-regulation. PHGDH-overexpressing cells are exquisitely sensitive to genetic ablation of the pathway. Here, we report the discovery of a selective small molecule inhibitor of PHGDH, CBR-5884, identified by screening a library of 800,000 drug-like compounds. CBR-5884 inhibited de novo serine synthesis in cancer cells and was selectively toxic to cancer cell lines with high serine biosynthetic activity. Biochemical characterization of the inhibitor revealed that it was a noncompetitive inhibitor that showed a time-dependent onset of inhibition and disrupted the oligomerization state of PHGDH. The identification of a small molecule inhibitor of PHGDH not only enables thorough preclinical evaluation of PHGDH as a target in cancers, but also provides a tool with which to study serine metabolism.

NF-Y activates genes of metabolic pathways altered in cancer cells

The trimeric transcription factor NF-Y binds to the CCAAT box, an element enriched in promoters of genes overexpressed in tumors. Previous studies on the NF-Y regulome identified the general term metabolism as significantly enriched. We dissect here in detail the targeting of metabolic genes by integrating analysis of NF-Y genomic binding and profilings after inactivation of NF-Y subunits in different cell types. NF-Y controls de novo biosynthetic pathways of lipids, teaming up with the master SREBPs regulators. It activates glycolytic genes, but, surprisingly, is neutral or represses mitochondrial respiratory genes. NF-Y targets the SOCG (Serine, One Carbon, Glycine) and Glutamine pathways, as well as genes involved in the biosynthesis of polyamines and purines. Specific cancer-driving nodes are generally under NF-Y control. Altogether, these data delineate a coherent strategy to promote expression of metabolic genes fuelling anaerobic energy production and other anabolic pathways commonly altered in cancer cells.

Targeting Mitochondrial Function to Treat Quiescent Tumor Cells in Solid Tumors

The disorganized nature of tumor vasculature results in the generation of microenvironments characterized by nutrient starvation, hypoxia and accumulation of acidic metabolites. Tumor cell populations in such areas are often slowly proliferating and thus refractory to chemotherapeutical drugs that are dependent on an active cell cycle. There is an urgent need for alternative therapeutic interventions that circumvent growth dependency. The screening of drug libraries using multicellular tumor spheroids (MCTS) or glucose-starved tumor cells has led to the identification of several compounds with promising therapeutic potential and that display activity on quiescent tumor cells. Interestingly, a common theme of these drug screens is the recurrent identification of agents that affect mitochondrial function. Such data suggest that, contrary to the classical Warburg view, tumor cells in nutritionally-compromised microenvironments are dependent on mitochondrial function for energy metabolism and survival. These findings suggest that mitochondria may represent an “Achilles heel” for the survival of slowly-proliferating tumor cells and suggest strategies for the development of therapy to target these cell populations.

Dysregulated metabolism contributes to oncogenesis

Cancer is a disease characterized by unrestrained cellular proliferation. In order to sustain growth, cancer cells undergo a complex metabolic rearrangement characterized by changes in metabolic pathways involved in energy production and biosynthetic processes. The relevance of the metabolic transformation of cancer cells has been recently included in the updated version of the review "Hallmarks of Cancer", where dysregulation of cellular metabolism was included as an emerging hallmark. While several lines of evidence suggest that metabolic rewiring is orchestrated by the concerted action of oncogenes and tumor suppressor genes, in some circumstances altered metabolism can play a primary role in oncogenesis. Recently, mutations of cytosolic and mitochondrial enzymes involved in key metabolic pathways have been associated with hereditary and sporadic forms of cancer. Together, these results demonstrate that aberrant metabolism, once seen just as an epiphenomenon of oncogenic reprogramming, plays a key role in oncogenesis with the power to control both genetic and epigenetic events in cells. In this review, we discuss the relationship between metabolism and cancer, as part of a larger effort to identify a broad-spectrum of therapeutic approaches. We focus on major alterations in nutrient metabolism and the emerging link between metabolism and epigenetics. Finally, we discuss potential strategies to manipulate metabolism in cancer and tradeoffs that should be considered. More research on the suite of metabolic alterations in cancer holds the potential to discover novel approaches to treat it.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead

Low-dose exposures to common environmental chemicals that are deemed safe individually may be combining to instigate carcinogenesis, thereby contributing to the incidence of cancer. This risk may be overlooked by current regulatory practices and needs to be vigorously investigated.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety ‘Mode of Action’ framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

Metabolic reprogramming and dysregulated metabolism: cause, consequence and/or enabler of environmental carcinogenesis?

Environmental contributions to cancer development are widely accepted, but only a fraction of all pertinent exposures have probably been identified. Traditional toxicological approaches to the problem have largely focused on the effects of individual agents at singular endpoints. As such, they have incompletely addressed both the pro-carcinogenic contributions of environmentally relevant low-dose chemical mixtures and the fact that exposures can influence multiple cancer-associated endpoints over varying timescales. Of these endpoints, dysregulated metabolism is one of the most common and recognizable features of cancer, but its specific roles in exposure-associated cancer development remain poorly understood. Most studies have focused on discrete aspects of cancer metabolism and have incompletely considered both its dynamic integrated nature and the complex controlling influences of substrate availability, external trophic signals and environmental conditions. Emerging high throughput approaches to environmental risk assessment also do not directly address the metabolic causes or consequences of changes in gene expression. As such, there is a compelling need to establish common or complementary frameworks for further exploration that experimentally and conceptually consider the gestalt of cancer metabolism and its causal relationships to both carcinogenesis and the development of other cancer hallmarks. A literature review to identify environmentally relevant exposures unambiguously linked to both cancer development and dysregulated metabolism suggests major gaps in our understanding of exposure-associated carcinogenesis and metabolic reprogramming. Although limited evidence exists to support primary causal roles for metabolism in carcinogenesis, the universality of altered cancer metabolism underscores its fundamental biological importance, and multiple pleiomorphic, even dichotomous, roles for metabolism in promoting, antagonizing or otherwise enabling the development and selection of cancer are suggested.

Metabolic consequences of oncogenic IDH mutations

Specific point mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) occur in a variety of cancers, including acute myeloid leukemia (AML), low-grade gliomas, and chondrosarcomas. These mutations inactivate wild-type enzymatic activity and convey neomorphic function to produce d-2-hydroxyglutarate (d-2HG), which accumulates at millimolar levels within tumors. d-2HG can impact α-ketoglutarate-dependent dioxygenase activity and subsequently affect various cellular functions in these cancers. Inhibitors of the neomorphic activity of mutant IDH1 and IDH2 are currently in Phase I/II clinical trials for both solid and blood tumors. As IDH1 and IDH2 represent key enzymes within the tricarboxylic acid (TCA) cycle, mutations have significant impact on intermediary metabolism. The loss of some wild-type metabolic activity is an important, potentially deleterious and therapeutically exploitable consequence of oncogenic IDH mutations and requires continued investigation in the future. Here we review how IDH1 and IDH2 mutations influence cellular metabolism, epigenetics, and other biochemical functions, discussing these changes in the context of current efforts to therapeutically target cancers bearing these mutations.

Post-translational hydroxylation by 2OG/Fe(II)-dependent oxygenases as a novel regulatory mechanism in bacteria

Protein hydroxylation has been well-studied in eukaryotic systems. The structural importance of hydroxylation of specific proline and lysine residues during collagen biosynthesis is well established. Recently, key roles for post-translational hydroxylation in signaling and degradation pathways have been discovered. The function of hydroxylation in signaling is highlighted by its role in the hypoxic response of eukaryotic cells, where oxygen dependent hydroxylation of the hypoxia inducible transcription factor both targets it for degradation and blocks its activation. In contrast, the role of protein hydroxylation has been largely understudied in prokaryotes. Recently, an evolutionarily conserved class of ribosomal oxygenases (ROX) that catalyze the hydroxylation of specific residues in the ribosome has been identified in bacteria. ROX activity has been linked to cell growth, and has been found to have a direct impact on bulk protein translation. This discovery of ribosomal protein hydroxylation in bacteria could lead to new therapeutic targets for regulating bacterial growth, as well as, shed light on new prokaryotic hydroxylation signaling pathways. In this review, recent structural and functional studies will be highlighted and discussed, underscoring the regulatory potential of post-translational hydroxylation in bacteria.

Phosphoglycerate dehydrogenase: potential therapeutic target and putative metabolic oncogene

Exemplified by cancer cells' preference for glycolysis, for example, the Warburg effect, altered metabolism in tumorigenesis has emerged as an important aspect of cancer in the past 10–20 years. Whether due to changes in regulatory tumor suppressors/oncogenes or by acting as metabolic oncogenes themselves, enzymes involved in the complex network of metabolic pathways are being studied to understand their role and assess their utility as therapeutic targets. Conversion of glycolytic intermediate 3-phosphoglycerate into phosphohydroxypyruvate by the enzyme phosphoglycerate dehydrogenase (PHGDH)—a rate-limiting step in the conversion of 3-phosphoglycerate to serine—represents one such mechanism. Forgotten since classic animal studies in the 1980s, the role of PHGDH as a potential therapeutic target and putative metabolic oncogene has recently reemerged following publication of two prominent papers near-simultaneously in 2011. Since that time, numerous studies and a host of metabolic explanations have been put forward in an attempt to understand the results observed. In this paper, I review the historic progression of our understanding of the role of PHGDH in cancer from the early work by Snell through its reemergence and rise to prominence, culminating in an assessment of subsequent work and what it means for the future of PHGDH.

Metabolic reprogramming in transformed mouse cortical astrocytes: A proteomic study

Metabolic reprogramming is thought to play a key role in sustaining the survival and proliferation of cancer cells. These changes facilitate for example the uptake and release of nutrients required for nucleotide, protein and lipid synthesis necessary for macromolecule assembly and tumor growth. We applied a 2D-DIGE (two-dimensional differential in-gel electrophoresis) quantitative proteomic analysis to characterize the proteomes of mouse astrocytes that underwent in vitro cancerous transformation, and of their normal counterparts. Metabolic reprogramming effects on enzymatic and structural protein expression as well as associated metabolites abundance were quantified. Using enzymatic activity measurements and zymography, we documented and confirmed several changes in abundance and activity of various isoenzymes likely to participate in metabolic reprogramming. We found that after transformation, the cells increase their expression of glycolytic enzymes, thus augmenting their ability to use aerobic glycolysis (Warburg effect). An increased capacity to dispose of reducing equivalents through lactate production was also documented. Major effects on carbohydrates, amino acids and nucleotides metabolic enzymes were also observed. Conversely, the transformed cells reduced their enzymatic capacity for reactions of tricarboxylic acid oxidation, for neurotransmitter (glutamate) metabolism, for oxidative stress defense and their expression of astroglial markers.

BIOLOGICAL SIGNIFICANCE

The use of a global approach based on a 2D DIGE analysis allows obtaining a comprehensive view of the metabolic reprogramming undergone by astrocytes upon cancerous transformation. Indeed, except for a few enzymes such as pyruvate carboxylase and glutaminase that were not detected in our initial analysis, pertinent information on the abundance of most enzymes belonging to pathways relevant to metabolic reprogramming was directly obtained. In this in vitro model, transformation causes major losses of astrocyte-specific proteins and functions and the acquisition of metabolic adaptations that favor intermediate metabolites production for increased macromolecule biosynthesis. Thus our approach appears to be readily applicable for the investigation of changes in protein abundance that determine various transformed cell phenotypes. It could similarly be applied to the evaluation of the effects of treatments aimed at correcting the consequences of cell transformation.

Angiogenesis revisited - role and therapeutic potential of targeting endothelial metabolism

Clinically approved therapies that target angiogenesis in tumors and ocular diseases focus on controlling pro-angiogenic growth factors in order to reduce aberrant microvascular growth. Although research on angiogenesis has revealed key mechanisms that regulate tissue vascularization, therapeutic success has been limited owing to insufficient efficacy, refractoriness and tumor resistance. Emerging concepts suggest that, in addition to growth factors, vascular metabolism also regulates angiogenesis and is a viable target for manipulating the microvasculature. Recent studies show that endothelial cells rely on glycolysis for ATP production, and that the key glycolytic regulator 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) regulates angiogenesis by controlling the balance of tip versus stalk cells. As endothelial cells acquire a tip cell phenotype, they increase glycolytic production of ATP for sprouting. Furthermore, pharmacological blockade of PFKFB3 causes a transient, partial reduction in glycolysis, and reduces pathological angiogenesis with minimal systemic harm. Although further assessment of endothelial cell metabolism is necessary, these results represent a paradigm shift in anti-angiogenic therapy from targeting angiogenic factors to focusing on vascular metabolism, warranting research on the metabolic pathways that govern angiogenesis.

Metformin directly acts on mitochondria to alter cellular bioenergetics

BACKGROUND

Metformin is widely used in the treatment of diabetes, and there is interest in 'repurposing' the drug for cancer prevention or treatment. However, the mechanism underlying the metabolic effects of metformin remains poorly understood.

METHODS

We performed respirometry and stable isotope tracer analyses on cells and isolated mitochondria to investigate the impact of metformin on mitochondrial functions.

RESULTS

We show that metformin decreases mitochondrial respiration, causing an increase in the fraction of mitochondrial respiration devoted to uncoupling reactions. Thus, cells treated with metformin become energetically inefficient, and display increased aerobic glycolysis and reduced glucose metabolism through the citric acid cycle. Conflicting prior studies proposed mitochondrial complex I or various cytosolic targets for metformin action, but we show that the compound limits respiration and citric acid cycle activity in isolated mitochondria, indicating that at least for these effects, the mitochondrion is the primary target. Finally, we demonstrate that cancer cells exposed to metformin display a greater compensatory increase in aerobic glycolysis than nontransformed cells, highlighting their metabolic vulnerability. Prevention of this compensatory metabolic event in cancer cells significantly impairs survival.

CONCLUSIONS

Together, these results demonstrate that metformin directly acts on mitochondria to limit respiration and that the sensitivity of cells to metformin is dependent on their ability to cope with energetic stress.

The Succinated Proteome of FH-Mutant Tumours

Inherited mutations in the Krebs cycle enzyme fumarate hydratase (FH) predispose to hereditary leiomyomatosis and renal cell cancer (HLRCC). Loss of FH activity in HLRCC tumours causes accumulation of the Krebs cycle intermediate fumarate to high levels, which may act as an oncometabolite through various, but not necessarily mutually exclusive, mechanisms. One such mechanism, succination, is an irreversible non-enzymatic modification of cysteine residues by fumarate, to form S-(2-succino)cysteine (2SC). Previous studies have demonstrated that succination of proteins including glyceraldehyde 3-phosphate dehydrogenase (GAPDH), kelch-like ECH-associated protein 1 (KEAP1) and mitochondrial aconitase (ACO2) can have profound effects on cellular metabolism. Furthermore, immunostaining for 2SC is a sensitive and specific biomarker for HLRCC tumours. Here, we performed a proteomic screen on an FH-mutant tumour and two HLRCC-derived cancer cell lines and identified 60 proteins where one or more cysteine residues were succinated; 10 of which were succinated at cysteine residues either predicted, or experimentally proven, to be functionally significant. Bioinformatic enrichment analyses identified most succinated targets to be involved in redox signaling. To our knowledge, this is the first proteomic-based succination screen performed in human tumours and cancer-derived cells and has identified novel 2SC targets that may be relevant to the pathogenesis of HLRCC.