Protein phosphatase 4 dephosphorylates phosphofructokinase-1 to regulate its enzymatic activity

Most cancer cells utilize glucose at a high rate to produce energyand precursors for the biosynthesis of macromolecules such as lipids, proteins, and nucleic acids. This phenomenon is called the Warburg effect or aerobic glycolysis- this distinct characteristic is an attractive target for developing anticancer drugs. Here, we found that Phosphofructokinase-1 (PFK-1) is a substrate of the Protein Phosphatase 4 catalytic subunit (PP4C)/PP4 regulatory subunit 1 (PP4R1) complex by using immunoprecipitation and in vitro assay. While manipulation of PP4C/PP4R1 does not have a critical impact on PFK-1 expression, the absence of the PP4C/PP4R1 complex increases PFK-1 activity. Although PP4C depletion or overexpression does not cause a dramatic change in the overall glycolytic rate, PP4R1 depletion induces a considerable increase in both basal and compensatory glycolytic rates, as well as the oxygen consumption rate, indicating oxidative phosphorylation. Collectively, the PP4C/PP4R1 complex regulates PFK-1 activity by reversing its phosphorylation and is a promising candidate for treating glycolytic disorders and cancers. Targeting PP4R1 could be a more efficient and safer strategy to avoid pleiotropic effects than targeting PP4C directly. [BMB Reports 2023; 56(11): 618-623].

Mitochondrial Uncoupling Inhibits Reductive Carboxylation in Cancer Cells

When the electron transport chain (ETC) function is impaired, cancer cells rely on reductive carboxylation (RC) to convert α-ketoglutarate (αKG) to citrate for macromolecular synthesis, thereby promoting tumor growth. Currently, there is no viable therapy to inhibit RC for cancer treatment. In this study, we demonstrate that the mitochondrial uncoupler treatment effectively inhibits RC in cancer cells. Mitochondrial uncoupler treatment activates the ETC and increases the NAD+/NADH ratio. Using U-13C-glutamine and 1-13C-glutamine tracers, we show that mitochondrial uncoupling accelerates the oxidative tricarboxylic acid (TCA) cycle and blocks RC under hypoxia, in von Hippel-Lindau (VHL) tumor suppressor-deficient kidney cancer cells, or under anchorage-independent growth condition. Together, these data demonstrate that mitochondrial uncoupling redirects α-KG from RC back to the oxidative TCA cycle, highlighting that the NAD+/NADH ratio is one key switch that determines the metabolic fate of α-KG. Inhibiting RC could be a key mechanism by which mitochondrial uncouplers inhibit tumor growth.

IMPLICATIONS

Mitochondrial uncoupling is a novel strategy to target RC in cancer.

Phytochemicals targeting glycolysis in colorectal cancer therapy: effects and mechanisms of action

Colorectal cancer (CRC) is the third most common malignant tumor in the world, and it is prone to recurrence and metastasis during treatment. Aerobic glycolysis is one of the main characteristics of tumor cell metabolism in CRC. Tumor cells rely on glycolysis to rapidly consume glucose and to obtain more lactate and intermediate macromolecular products so as to maintain growth and proliferation. The regulation of the CRC glycolysis pathway is closely associated with several signal transduction pathways and transcription factors including phosphatidylinositol 3-kinases/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR), adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), hypoxia-inducible factor-1 (HIF-1), myc, and p53. Targeting the glycolytic pathway has become one of the key research aspects in CRC therapy. Many phytochemicals were shown to exert anti-CRC activity by targeting the glycolytic pathway. Here, we review the effects and mechanisms of phytochemicals on CRC glycolytic pathways, providing a new method of drug development.

Refractory Lactic Acidosis and Hypoglycemia in a Patient With Metastatic Esophageal Cancer Due to the Warburg Effect

The Warburg effect describes a phenomenon in which tumor cells switch their metabolic machinery towards a glycolytic state even in the presence of normal oxygen concentration, resulting in excess lactate production. Lactic acidosis due to the Warburg effect in malignancy is a rare but potentially life-threatening emergency mainly described in hematological malignancies but can occur in non-hematological solid malignancies. To our knowledge, we present the first reported case of lactic acidosis due to the Warburg effect in metastatic esophageal cancer. A 44-year-old male was found to have an esophageal mass and likely hepatic metastases during his hospitalization for altered mental status due to severe hypercalcemia. He was re-admitted two days after discharge for persistent vomiting and an inability to tolerate an oral diet. The lab revealed elevated lactate levels (5.2 mmol/L), metabolic acidosis (pH 7.23), and hypoglycemia (48 mg/dL), all of which were persistent throughout hospitalization despite treatment with intravenous (IV) infusions of dextrose in sodium bicarbonate, IV boluses of dextrose, and IV thiamine. An esophagogastroduodenoscopy with a biopsy of the esophageal mass revealed squamous cell carcinoma of the esophagus. Given the presence of stage IV disease and poor functional status, the patient opted for in-patient hospice, where he passed away. Since prompt diagnosis and initiation of chemotherapy, if possible, are the only effective interventions for this potentially fatal complication, it is important to increase awareness of this underrecognized metabolic and oncologic emergency among physicians.

miR-140-3p/usp36 axis mediates ubiquitination to regulate PKM2 and suppressed the malignant biological behavior of breast cancer through Warburg effect

Breast cancer is a phenomenon in which breast epithelial cells proliferate out of control under the action of various carcinogenic factors. However, the role of USP36 in breast cancer is unknown. We analyzed the expression of USP36 in breast cancer and its association with poor prognosis in breast cancer patients. The effect of USP36 on malignant biological behavior of breast cancer was verified by cell functional experiments. The upstream regulatory mechanism of USP36 was analyzed by Western blot and quantitative RT-qPCR. The influence of USP36 on the Warburg effect of breast cancer was analyzed by detecting the metabolism of cellular energy substances. We found that USP36 is highly expressed in breast tumor tissues and breast cancer cell lines. High expression of USP36 predicts poor prognosis in patients with breast cancer. Effectively reducing the expression of USP36 can significantly inhibit the proliferation, invasion and migration of breast cancer cells, and promote the apoptosis of breast cancer cells. Meanwhile, inhibiting the expression of USP36 can significantly inhibit the production of ATP, lactate, pyruvate and glucose uptake in breast cancer cells. miR-140-3p is an upstream regulator of USP36, which can partially reverse the regulatory effect of USP36 on breast cancer cells. Importantly, USP36 regulates the expression of PKM2 through ubiquitination, which plays a role in regulating the Warburg effect. We confirmed that miR-140-3p regulates the expression of USP36, which mediates ubiquitination and regulates the expression of PKM2, and regulates the malignant biological behavior of breast cancer through the energy metabolism process.

Fetal oxygenation in the last weeks of pregnancy evaluated through the umbilical cord blood gas analysis

Introduction

Embryo and fetus grow and mature over the first trimester of pregnancy in a dynamic hypoxic environment, where placenta development assures an increased oxygen availability. However, it is unclear whether and how oxygenation changes in the later trimesters and, more specifically, in the last weeks of pregnancy.

Methods

Observational study that evaluated the gas analysis of the umbilical cord blood collected from a cohort of healthy newborns with gestational age ≥37 weeks. Umbilical venous and arterial oxygen levels as well as fetal oxygen extraction were calculated to establish whether oxygenation level changes over the last weeks of pregnancy. In addition, fetal lactate, and carbon dioxide production were analyzed to establish whether oxygen oscillations may induce metabolic effects in utero.

Results

This study demonstrates a progressive increase in fetal oxygenation levels from the 37th to the 41st weeks of gestation (mean venous PaO₂ approximately from 20 to 25 mmHg; p < 0.001). This increase is largely attributable to growing umbilical venous PaO₂, regardless of delivery modalities. In neonates born by vaginal delivery, the increased oxygen availability is associated with a modest increase in oxygen extraction, while in neonates born by cesarean section, it is associated with reduced lactate production. Independently from the type of delivery, carbon dioxide production moderately increased. These findings suggest a progressive shift from a prevalent anaerobic metabolism (Warburg effect) towards a growing aerobic metabolism.

Conclusion

This study confirms that fetuses grow in a hypoxic environment that becomes progressively less hypoxic in the last weeks of gestation. The increased oxygen availability seems to favor aerobic metabolic shift during the last weeks of intrauterine life; we hypothesize that this environmental change may have implications for fetal maturation during intrauterine life.

Reduced Level of Prolylhydroxyproline in the Nail Clippings of Oral Cancer Patients and its Role as an Activator of Phospholipase C-β2

BACKGROUND

The oral cancer microenvironment plays an important role in the development and progression of the disease which depicts the heterogeneous nature of diseases. Several cellular and non-cellular factors, including dipeptides, have been reported to drive tumor progression and metastasis. Among various secreted molecules in the tumor microenvironment, prolylhydroxyproline (Pro-Hyp) is a collagen-degraded product with specific relevance to fibrosis and oral cancer. However, the detection of Pro-Hyp in the nails of oral cancer patients is a potential biomarker, and our understanding of the biological relevance of Pro-Hyp is highly limited.

METHODS

Here, the authors have attempted to use a novel and in-house vertical tube gel electrophoresis (VTGE) protocol to evaluate the level of Pro-Hyp in the nails of oral cancer patients and healthy subjects. Furthermore, we employed molecular docking and molecular dynamics (MD) simulations to predict the biological function of Pro-Hyp. ADME profiles such as the druglikeness and leadlikeness of Pro-Hyp and a known PLC-β2 activator, m-3M3FBS, were evaluated by the SWISS-ADME server.

RESULTS

We report that among various key metabolites, Pro-Hyp, a dipeptide, is reduced in the nails of oral cancer patients. Molecular docking and MD simulations helped to suggest the potential role of Pro-Hyp as an activator of Phospholipase C-β2 (PLC-β2). Pro-Hyp displayed good binding affinity (-7.6 kcal/mol) with specific interactions by a conventional hydrogen bond with key residues, such as HIS311, HIS312, VAL641, and GLU743. MD simulations showed that the activator binding residues and stability of complexes are similar to the well-known activator m-3M3FBS of PLC-β2. ADME profiles such as the druglikeness and leadlikeness of Pro-Hyp were found to be highly comparable and even better than those of m-3M3FBS.

CONCLUSION

This study is one of the first reports on Pro-Hyp as a metabolite biomarker in the nails of oral cancer patients. Furthermore, the implications of Pro-Hyp are proposed to activate PLC-β2 as a pro-tumor signaling cascade. In the future, diagnostic and therapeutic approaches may be explored as biomarkers and mimetic of Pro-Hyp.

Small extracellular vesicles in metabolic remodeling of tumor cells: Cargos and translational application

Warburg effect is characterized by excessive consumption of glucose by the tumor cells under both aerobic and hypoxic conditions. This metabolic reprogramming allows the tumor cells to adapt to the unique microenvironment and proliferate rapidly, and also promotes tumor metastasis and therapy resistance. Metabolic reprogramming of tumor cells is driven by the aberrant expression and activity of metabolic enzymes, which results in the accumulation of oncometabolites, and the hyperactivation of intracellular growth signals. Recent studies suggest that tumor-associated metabolic remodeling also depends on intercellular communication within the tumor microenvironment (TME). Small extracellular vesicles (sEVs), also known as exosomes, are smaller than 200 nm in diameter and are formed by the fusion of multivesicular bodies with the plasma membrane. The sEVs are instrumental in transporting cargoes such as proteins, nucleic acids or metabolites between the tumor, stromal and immune cells of the TME, and are thus involved in reprogramming the glucose metabolism of recipient cells. In this review, we have summarized the biogenesis and functions of sEVs and metabolic cargos, and the mechanisms through they drive the Warburg effect. Furthermore, the potential applications of targeting sEV-mediated metabolic pathways in tumor liquid biopsy, imaging diagnosis and drug development have also been discussed.

Discovery of highly potent and selective 7-ethyl-10-hydroxycamptothecin-glucose conjugates as potential anti-colorectal cancer agents

7-Ethyl-10-hydroxycamptothecin (SN38), a highly potent metabolite of irinotecan, has an anticancer efficacy 100-1000 folds more than irinotecan in vitro. However, the clinical application of SN38 has been limited due to the very narrow therapeutic window and poor water solubility. Herein, we report the SN38-glucose conjugates (Glu-SN38) that can target cancer cells due to their selective uptake via glucose transporters, which are overexpressed in most cancers. The in vitro antiproliferative activities against human cancer cell lines and normal cells of Glu-SN38 were investigated. One of the conjugates named 5b showed high potency and selectivity against human colorectal cancer cell line HCT116. Furthermore, 5b remarkably inhibited the growth of HCT116 in vivo. These results suggested that 5b could be a promising drug candidate for treating colorectal cancer.

Pathological implications of metabolic reprogramming and its therapeutic potential in medulloblastoma

Tumor-specific alterations in metabolism have been recognized to sustain the production of ATP and macromolecules needed for cell growth, division and survival in many cancer types. However, metabolic heterogeneity poses a challenge for the establishment of effective anticancer therapies that exploit metabolic vulnerabilities. Medulloblastoma (MB) is one of the most heterogeneous malignant pediatric brain tumors, divided into four molecular subgroups (Wingless, Sonic Hedgehog, Group 3 and Group 4). Recent progresses in genomics, single-cell sequencing, and novel tumor models have updated the classification and stratification of MB, highlighting the complex intratumoral cellular diversity of this cancer. In this review, we emphasize the mechanisms through which MB cells rewire their metabolism and energy production networks to support and empower rapid growth, survival under stressful conditions, invasion, metastasis, and resistance to therapy. Additionally, we discuss the potential clinical benefits of currently available drugs that could target energy metabolism to suppress MB progression and increase the efficacy of the current MB therapies.

Mutant TP53 driving the Warburg Effect in Mantle Cell lymphoma

The p53 mutation R273H in tumor cells leads to increased glucose uptake, lactic acidosis, and accelerated tumor growth, as was previously shown in mice. We here present a patient with mantle cell lymphoma harboring this p53_R273H mutation, whose clinical course is characterized by severe lactic acidosis, hypoglycemia, and aggressive disease.

HLA complex P5 upregulation is correlated with poor prognosis and tumor progression in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a deadly malignant tumor that threatens human health. Long noncoding RNA (lncRNA) is widely expressed in eukaryotes and is closely associated with human disease progression. However, its role in ESCC remains incompletely understood. In this study, we analyzed the results of three gene expression omnibus (GEO) databases containing lncRNA expression data of ESCC and normal tissues. The results showed that HCP5 was significantly overexpressed in ESCC tissues, which was further verified in our collected ESCC samples. The functional study suggested that HCP5 knockdown inhibited ESCC cell proliferation and invasion. Regarding the mechanism, HCP5 was able to directly interact with YTHDF1, a N6-methyladenosine (m⁶A) reader, enhancing the binding of YTHDF1 to m⁶A-modified HK2 mRNA, leading to increasing HK2 stability, thereby promoting the Warburg effect (aerobic glycolysis) of ESCC cells. The nude mice model showed that the knockdown of HCP5 in vivo remarkably reduced tumor size. Clinically, high HCP5 was positively correlated with larger tumor volume, higher TNM stage and lymph node metastasis. Moreover, ESCC patients with high HCP5 exerted shorter survival time than patients with low HCP5. These findings uncover the importance of HCP5 in human ESCC progression; the turbulence of HCP5/YTHDF1/HK2 axis may be responsible for ESCC carcinogenicity.

PKM2 Is Essential for Bladder Cancer Growth and Maintenance

Pyruvate kinase M2 (PKM2) has been shown to promote tumorigenesis by facilitating the Warburg effect and enhancing the activities of oncoproteins. However, this paradigm has recently been challenged by studies in which the absence of PKM2 failed to inhibit and instead accelerated tumorigenesis in mouse models. These results seem inconsistent with the fact that most human tumors overexpress PKM2. To further elucidate the role of PKM2 in tumorigenesis, we investigated the effect of PKM2 knockout in oncogenic HRAS-driven urothelial carcinoma. While PKM2 ablation in mouse urothelial cells did not affect tumor initiation, it impaired the growth and maintenance of HRAS-driven tumors. Chemical inhibition of PKM2 recapitulated these effects. Both conditions substantially reduced complex formation of PKM2 with STAT3, their nuclear translocation, and HIF1α- and VEGF-related angiogenesis. The reduction in nuclear STAT3 in the absence of PKM2 also correlated with decreased autophagy and increased apoptosis. Time-controlled, inducible PKM2 overexpression in simple urothelial hyperplasia did not trigger tumorigenesis, while overexpression of PKM2, but not PKM1, in nodular urothelial hyperplasia with angiogenesis strongly accelerated tumorigenesis. Finally, in human patients, PKM2 was overexpressed in low-grade nonmuscle-invasive and high-grade muscle-invasive bladder cancer. Based on these data, PKM2 is not required for tumor initiation but is essential for tumor growth and maintenance by enhancing angiogenesis and metabolic addiction. The PKM2-STAT3-HIF1α/VEGF signaling axis may play a critical role in bladder cancer and may serve as an actionable therapeutic target.

SIGNIFICANCE

Genetic manipulation and pharmacologic inhibition of PKM2 in mouse urothelial lesions highlight its essential role in promoting angiogenesis and metabolic addiction, events indispensable for tumor growth and maintenance.

CircLPAR3 knockdown suppresses esophageal squamous cell carcinoma cell oncogenic phenotypes and Warburg effect through miR-873-5p/LDHA axis

BACKGROUND

Circular RNAs (circRNAs) have been identified to participate in regulating multiple malignancies. Herein, this study aimed to explore the clinical significance, biological function, and regulatory mechanisms of circRNA lysophosphatidic acid receptor 3 (circLPAR3) in esophageal squamous cell carcinoma (ESCC) cell malignant phenotypes and Warburg effect.

METHODS

The qRT-PCR and Western blot were used to detect the levels of genes and proteins. Glucose uptake and lactate production were detected to determine the Warburg effect. The effects of circLPAR3 on ESCC cell proliferation, apoptosis, and metastasis were evaluated by MTT, 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, wound healing, and transwell assays. The binding interaction between miR-873-5p and circLPAR3 or lactate dehydrogenase A (LDHA) was verified using dual-luciferase reporter and RIP assays. Xenograft mice models were established to conduct in vivo analysis.

RESULTS

CircLPAR3 is a stable circRNA and was increased in ESCC tissues and cells. Functionally, circLPAR3 knockdown suppressed ESCC cell Warburg effect, proliferation, metastasis, and induced apoptosis in vitro, and impeded xenograft tumor growth and Warburg effect in ESCC mice models. Mechanistically, circLPAR3 served as a sponge for miR-873-5p, which targeted LDHA. Moreover, circLPAR3 could regulate LDHA expression by sponging miR-873-5p. Thereafter, rescue experiments suggested that miR-873-5p inhibition reversed the anticancer effects of circLPAR3 silencing on ESCC cells. Furthermore, miR-873-5p overexpression restrained ESCC cell Warburg effect and oncogenic phenotypes, which were abolished by LDHA up-regulation.

CONCLUSION

CircLPAR3 knockdown suppressed ESCC cell growth, metastasis, and Warburg effect by miR-873-5p/LDHA axis, implying a promising molecular target for ESCC therapy.

Hydrogen Sulfide Ameliorates Angiotensin II-Induced Atrial Fibrosis Progression to Atrial Fibrillation Through Inhibition of the Warburg Effect and Endoplasmic Reticulum Stress

Atrial fibrosis is the basis for the occurrence and development of atrial fibrillation (AF) and is closely related to the Warburg effect, endoplasmic reticulum stress (ERS) and mitochondrion dysfunctions-induced cardiomyocyte apoptosis. Hydrogen sulfide (H₂S) is a gaseous signalling molecule with cardioprotective, anti-myocardial fibrosis and improved energy metabolism effects. Nevertheless, the specific mechanism by which H₂S improves the progression of atrial fibrosis to AF remains unclear. A case-control study of patients with and without AF was designed to assess changes in H₂S, the Warburg effect, and ERS in AF. The results showed that AF can significantly reduce cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate thiotransferase (3-MST) expression and the H₂S level, induce cystathionine-β-synthase (CBS) expression; increase the Warburg effect, ERS and atrial fibrosis; and promote left atrial dysfunction. In addition, AngII-treated SD rats had an increased Warburg effect and ERS levels and enhanced atrial fibrosis progression to AF compared to wild-type SD rats, and these conditions were reversed by sodium hydrosulfide (NaHS), dichloroacetic acid (DCA) or 4-phenylbutyric acid (4-PBA) supplementation. Finally, low CSE levels in AngII-induced HL-1 cells were concentration- and time-dependent and associated with mitochondrial dysfunction, apoptosis, the Warburg effect and ERS, and these effects were reversed by NaHS, DCA or 4-PBA supplementation. Our research indicates that H₂S can regulate the AngII-induced Warburg effect and ERS and might be a potential therapeutic drug to inhibit atrial fibrosis progression to AF.

Immune metabolism in allergies, does it matter?-A review of immune metabolic basics and adaptations associated with the activation of innate immune cells in allergy

Type I allergies are pathological, type 2 inflammatory immune responses against otherwise harmless environmental allergens that arise from complex interactions between different types of immune cells. Activated immune cells undergo extensive changes in phenotype and function to fulfill their effector functions. Hereby, activation, differentiation, proliferation, migration, and mounting of effector responses require metabolic reprogramming. While the metabolic changes associated with activation of dendritic cells, macrophages, and T cells are extensively studied, data about the metabolic phenotypes of the other cell types critically involved in allergic responses (epithelial cells, eosinophils, basophils, mast cells, and ILC2s) are rather limited. This review briefly covers the basics of cellular energy metabolism and its connection to immune cell function. In addition, it summarizes the current state of knowledge in terms of dendritic cell and macrophage metabolism and subsequently focuses on the metabolic changes associated with activation of epithelial cells, eosinophils, basophils, mast cells, as well as ILC2s in allergy. Interestingly, the innate key cell types in allergic inflammation were reported to change their metabolic phenotype during activation, shifting to either glycolysis (epithelial cells, M1 macrophages, DCs, eosinophils, basophils, acutely activated mast cells), oxidative phosphorylation (M2 macrophages, longer term activated mast cells), or fatty acid oxidation (ILC2s). Therefore, immune metabolism is of relevance in allergic diseases and its connection to immune cell effector function needs to be considered to better understand induction and maintenance of allergic responses. Further progress in this field will likely improve both our understanding of disease pathology and enable new treatment targets/strategies.

Pan-Cancer Analysis of Glycolytic and Ketone Bodies Metabolic Genes: Implications for Response to Ketogenic Dietary Therapy

Background

The Warburg effect, also termed "aerobic glycolysis", is one of the most remarkable and ubiquitous metabolic characteristics exhibited by cancer cells, representing a potential vulnerability that might be targeted for tumor therapy. Ketogenic diets (KDs), composed of high-fat, moderate-protein and low carbohydrates, are aimed at targeting the Warburg effect for cancer treatment, which have recently gained considerable attention. However, the efficiency of KDs was inconsistent, and the genotypic contribution is still largely unknown.

Methods

The bulk RNA-seq data from The Cancer Genome Atlas (TCGA), single cell RNA sequencing (scRNA-seq), and microarray data from Gene Expression Omnibus (GEO) and Cancer Cell Line Encyclopedia (CCLE) were collected. A joint analysis of glycolysis and ketone bodies metabolism (KBM) pathway was performed across over 10,000 tumor samples and nearly 1,000 cancer cell lines. A series of bioinformatic approaches were combined to identify a metabolic subtype that may predict the response to ketogenic dietary therapy (KDT). Mouse xenografts were established to validate the predictive utility of our subtypes in response to KDT.

Results

We first provided a system-level view of the expression pattern and prognosis of the signature genes from glycolysis and KBM pathway across 33 cancer types. Analysis by joint stratification of glycolysis and KBM revealed four metabolic subtypes, which correlated extensively but diversely with clinical outcomes across cancers. The glycolytic subtypes may be driven by TP53 mutations, whereas the KB-metabolic subtypes may be mediated by CTNNB1 (β-catenin) mutations. The glycolytic subtypes may have a better response to KDs compared to the other three subtypes. We preliminarily confirmed the idea by literature review and further performed a proof-of-concept experiment to validate the predictive value of the metabolic subtype in liver cancer xenografts.

Conclusions

Our findings identified a metabolic subtype based on glycolysis and KBM that may serve as a promising biomarker to predict the clinical outcomes and therapeutic responses to KDT.

Metabolic Acidosis in Leukemia

In 2020, the incidence of leukemia was 474,519 with 311,594 mortality worldwide. In 2021, the American Cancer Society (ACS) has estimated 61,090 new cases of leukemia to occur within the United States. It has also been reported that the most common cause of death in children from one to fourteen years old is oncological, with leukemia being the most frequent cause. A phenomenon known as the Warburg effect has been affiliated with cancer. The Warburg effect is a metabolic abnormality of lactic acidosis in malignancies, with most cases presenting as hematological malignancies such as leukemia. Although many theories have been formulated to clarify the role of the Warburg effect, the exact role still remains uncertain. Four suggested theories on why the Warburg effect happens to include cell signaling, adenosine triphosphate (ATP) synthesis, biosynthesis, and the tumor microenvironment. The Warburg effect occurs in leukemia with the help of enzymes such as pyruvate kinases M2 (PKM2), lactate dehydrogenase A (LDHA), pyruvate dehydrogenase kinase 1 (PDK1), and fibroblast growth factor receptor 1 (FGFR1). In this literature, we explain the proposed hypotheses of the Warburg effect, along with the molecular mechanism of how leukemia is able to produce lactic acid, with the intent to better understand this phenomenon.

LncRNA HCG11 promotes 5-FU resistance of colon cancer cells through reprogramming glucose metabolism by targeting the miR-144-3p-PDK4 axis

BACKGROUND

Colorectal cancer (CRC), one of the most common human malignancies, is a leading cause of the cancer-related mortality. 5-FU is a first-line chemotherapeutic agent against CRC. Although CRC patients responded to 5-FU therapy initially, a part of patients succumbed to CRC due to the acquired drug resistance. Thus, investigating molecular mechanisms underlying chemoresistance will contribute to developing novel strategies against colorectal cancer.

OBJECTIVE

Accumulation evidence revealed pivotal roles of long non-coding RNAs (lncRNAs) in tumorigenesis and chemoresistance of CRC. However, the precise roles and molecular mechanisms of lncRNA-HCG11 in CRC remain unclear. This study aimed to investigate the biological roles and underlying mechanisms of HCG11 as well as its molecular targets in regulating the cellular metabolism processes, which facilitate the chemoresistance of CRC.

METHODS AND RESULTS

This study uncovers that HCG11 was significantly upregulated in CRC tumors tissues and cell lines. Moreover, HCG11 was elevated in 5-FU resistant CRC tumors. Silencing HCG11 inhibited colon cancer cell proliferation, migration, invasion and glucose metabolism and sensitized CRC cells to 5-FU. In addition, we detected increased HCG11 expression level and glucose metabolism in the established 5-FU resistant CRC cell line (DLD-1 5-FU Res). Furthermore, microRNA-microArray, RNA pull-down and luciferase assays demonstrated that HCG11 inhibited miR-144-3p which displays suppressive roles in colon cancer via sponging it to form a ceRNA network. We identified pyruvate dehydrogenase kinase 4 (PDK4), which is a glucose metabolism key enzyme, was directly targeted by miR-144-3p in CRC cells. Rescue studies validated that the miR-144-3p-inhibited glucose metabolism and 5-FU sensitization were through targeting PDK4. Finally, restoration of miR-144-3p in HCG11-overexpressing DLD-1 5-FU resistant cells successfully overcame the HCG11-faciliated 5-FU resistance via targeting PDK4.

CONCLUSION

In summary, this study reveals critical roles and molecular mechanisms of the HCG11-mediated 5-FU resistance through modulating the miR-144-3p-PDK4-glucose metabolism pathway in CRC.

The nexus between redox state and intermediary metabolism

Reactive oxygen species (ROS) are not just a by-product of cellular metabolic processes but act as signalling molecules that regulate both physiological and pathophysiological processes. A close connection exists in cells between redox homeostasis and cellular metabolism. In this review, we describe how intracellular redox state and glycolytic intermediary metabolism are closely coupled. On the one hand, ROS signalling can control glycolytic intermediary metabolism by direct regulation of the activity of key metabolic enzymes and indirect regulation via redox-sensitive transcription factors. On the other hand, metabolic adaptation and reprogramming in response to physiological or pathological stimuli regulate intracellular redox balance, through mechanisms such as the generation of reducing equivalents. We also discuss the impact of these intermediary metabolism-redox circuits in physiological and disease settings across different tissues. A better understanding of the mechanisms regulating these intermediary metabolism-redox circuits will be crucial to the development of novel therapeutic strategies.

A Root in Synapsis and the Other One in the Gut Microbiome-Brain Axis: Are the Two Poles of Ketogenic Diet Enough to Challenge Glioblastoma?

Glioblastoma is the most frequent and aggressive brain cancer in adults. While precision medicine in oncology has produced remarkable progress in several malignancies, treatment of glioblastoma has still limited available options and a dismal prognosis. After first-line treatment with surgery followed by radiochemotherapy based on the 2005 STUPP trial, no significant therapeutic advancements have been registered. While waiting that genomic characterization moves from a prognostic/predictive value into therapeutic applications, practical and easy-to-use approaches are eagerly awaited. Medical reports on the role of the ketogenic diet in adult neurological disorders and in glioblastoma suggest that nutritional interventions may condition outcomes and be associated with standard therapies. The acceptable macronutrient distribution of daily calories in a regular diet are 45-65% of daily calories from carbohydrates, 20-35% from fats, and 10-35% from protein. Basically, the ketogenic diet follows an approach based on low carbohydrates/high fat intake. In carbohydrates starvation, body energy derives from fat storage which is used to produce ketones and act as glucose surrogates. The ketogenic diet has several effects: metabolic interference with glucose and insulin and IGF-1 pathways, influence on neurotransmission, reduction of oxidative stress and inflammation, direct effect on gene expression through epigenetic mechanisms. Apart from these central effects working at the synapsis level, recent evidence also suggests a role for microbiome and gut-brain axis induced by a ketogenic diet. This review focuses on rationales supporting the ketogenic diet and clinical studies will be reported, looking at future possible perspectives.

The Warburg Effect on Cancer Cells Survival: The Role of Sugar Starvation in Cancer Therapy

BACKGROUND

Cancer is not just one disease; it is a group of diseases either genetic or metabolic due to the malfunction of mitochondria. Thus, metabolic pathways are reprogrammed to satisfy tumor cell proliferation and survival requirements.

METHODS

We undertook a structured search of bibliographic databases for peer-reviewed research literature dealing with these metabolic pathways.

RESULTS

It was found that cancer cells prefer fermentation as a source of energy even in the presence of oxygen, this altered metabolism of cancer cells may confer a selective advantage for survival and proliferation according to the Warburg effect. Furthermore, some molecules like HIF, PKM2, NADPH and others are essential to the survival of cancer cells in the hypoxic abnormal environment which has limited glucose sources.

CONCLUSION

As cancer cells use glucose for aerobic glycolysis as a preferred substrate for energyyielding metabolism, we discuss in this review the Warburg effect and a strategy of starving cancer cells from glucose to prevent cancer cell survival and induce apoptosis in various types of cancer which could be the key to future treatment.

The Effect of a New Glucose-Methotrexate Conjugate on Acute Lymphoblastic Leukemia and Non-Hodgkin's Lymphoma Cell Lines

Patients with hematologic malignancies require intensive therapies, including high-dose chemotherapy. Antimetabolite-methotrexate (MTX) has been used for many years in the treatment of leukemia and in lymphoma patients. However, the lack of MTX specificity causes a significant risk of morbidity, mortality, and severe side effects that impairs the quality of patients' life. Therefore, novel targeted therapies based on the malignant cells' common traits have become an essential treatment strategy. Glucose transporters have been found to be overexpressed in neoplastic cells, including hematologic malignancies. In this study, we biologically evaluated a novel glucose-methotrexate conjugate (Glu-MTX) in comparison to a free MTX. The research aimed to assess the effectiveness of Glu-MTX on chosen human lymphoma and leukemia cell lines. Cell cytotoxicity was verified by MTT viability test and flow cytometry. Moreover, the cell cycle and cellular uptake of Glu-MTX were evaluated. Our study reveals that conjugation of methotrexate with glucose significantly increases drug uptake and results in similar cytotoxicity of the synthesized compound. Although the finding has been confined to in vitro studies, our observations shed light on a potential therapeutic approach that increases the selectivity of chemotherapeutics and can improve leukemia and lymphoma patients' outcomes.

Metabolically Supported Chemotherapy for Managing End-Stage Breast Cancer: A Complete and Durable Response

Breast cancer accounts for significant morbidity and mortality worldwide. Currently, treatment options in metastatic breast cancer consist of chemotherapy, along with endocrine, radiation, and/or biological therapies. Although advances in management have improved overall survival times, the treatment options for women with end-stage disease are mostly limited to supportive care. Herein, we present a case report that highlights the response of a 47-year-old premenopausal woman with end-stage (T4N3M1) breast cancer treated with metabolically supported chemotherapy (MSCT), ketogenic diet (KD), hyperthermia (HT), and hyperbaric oxygen therapy (HBOT). The patient first noticed a right breast mass in late 2016, which was initially evaluated and ruled out as a cyst. Skin ulceration was observed in the region of the suspected cyst in May 2017. Subsequent bilateral breast ultrasound identified masses in both breasts and an enlarged right axillary lymph node. The diagnosis following biopsy was grade 3, estrogen receptor-positive (ER+), progesterone receptor-positive (PR+), human epidermal growth factor receptor 2 negative (HER2-), invasive ductal carcinoma of the breast. Initially, the patient refused to receive conventional chemotherapy because of its potential for side effects and toxicity, but she sought medical treatment in August 2018 following extensive disease progression and deterioration of general health. On reevaluation, the patient was considered ineligible for conventional treatment due to her advanced end-stage disease, poor performance status (Eastern Cooperative Oncology Group score: 3), and advanced respiratory symptoms. Exploring other options, the patient was admitted to the ChemoThermia Oncology Center, Istanbul, Turkey in November 2018. At that time, the patient weighed 38 kg (body mass index: 18.1 kg/m²) and had extensive metastatic disease with lesions in the brain, lungs, mediastinum, liver, abdomen, and bones that were detected by magnetic resonance imaging of the brain (with contrast) and whole-body (18F)-fluorodeoxyglucose-positron emission tomography-computed tomography. The patient received a six-month treatment protocol comprised of MSCT, KD, HT, and HBOT, which eliminated all detectable lesions. The therapeutic response was sustained for two years with maintenance treatment comprising KD, dietary supplements, and repurposed medications. This single case report presents evidence of a complete and durable response to a treatment protocol combining MSCT and a novel metabolic therapy in a patient with end-stage breast cancer.

Oxidative Stress in Cancer Cell Metabolism

Reactive oxygen species (ROS) are important in regulating normal cellular processes whereas deregulated ROS leads to the development of a diseased state in humans including cancers. Several studies have been found to be marked with increased ROS production which activates pro-tumorigenic signaling, enhances cell survival and proliferation and drives DNA damage and genetic instability. However, higher ROS levels have been found to promote anti-tumorigenic signaling by initiating oxidative stress-induced tumor cell death. Tumor cells develop a mechanism where they adjust to the high ROS by expressing elevated levels of antioxidant proteins to detoxify them while maintaining pro-tumorigenic signaling and resistance to apoptosis. Therefore, ROS manipulation can be a potential target for cancer therapies as cancer cells present an altered redox balance in comparison to their normal counterparts. In this review, we aim to provide an overview of the generation and sources of ROS within tumor cells, ROS-associated signaling pathways, their regulation by antioxidant defense systems, as well as the effect of elevated ROS production in tumor progression. It will provide an insight into how pro- and anti-tumorigenic ROS signaling pathways could be manipulated during the treatment of cancer.

Cell Metabolism and DNA Repair Pathways: Implications for Cancer Therapy

DNA repair and metabolic pathways are vital to maintain cellular homeostasis in normal human cells. Both of these pathways, however, undergo extensive changes during tumorigenesis, including modifications that promote rapid growth, genetic heterogeneity, and survival. While these two areas of research have remained relatively distinct, there is growing evidence that the pathways are interdependent and intrinsically linked. Therapeutic interventions that target metabolism or DNA repair systems have entered clinical practice in recent years, highlighting the potential of targeting these pathways in cancer. Further exploration of the links between metabolic and DNA repair pathways may open new therapeutic avenues in the future. Here, we discuss the dependence of DNA repair processes upon cellular metabolism; including the production of nucleotides required for repair, the necessity of metabolic pathways for the chromatin remodeling required for DNA repair, and the ways in which metabolism itself can induce and prevent DNA damage. We will also discuss the roles of metabolic proteins in DNA repair and, conversely, how DNA repair proteins can impact upon cell metabolism. Finally, we will discuss how further research may open therapeutic avenues in the treatment of cancer.

Less Can Be More: The Hormesis Theory of Stress Adaptation in the Global Biosphere and Its Implications

A dose-response relationship to stressors, according to the hormesis theory, is characterized by low-dose stimulation and high-dose inhibition. It is non-linear with a low-dose optimum. Stress responses by cells lead to adapted vitality and fitness. Physical stress can be exerted through heat, radiation, or physical exercise. Chemical stressors include reactive species from oxygen (ROS), nitrogen (RNS), and carbon (RCS), carcinogens, elements, such as lithium (Li) and silicon (Si), and metals, such as silver (Ag), cadmium (Cd), and lead (Pb). Anthropogenic chemicals are agrochemicals (phytotoxins, herbicides), industrial chemicals, and pharmaceuticals. Biochemical stress can be exerted through toxins, medical drugs (e.g., cytostatics, psychopharmaceuticals, non-steroidal inhibitors of inflammation), and through fasting (dietary restriction). Key-lock interactions between enzymes and substrates, antigens and antibodies, antigen-presenting cells, and cognate T cells are the basics of biology, biochemistry, and immunology. Their rules do not obey linear dose-response relationships. The review provides examples of biologic stressors: oncolytic viruses (e.g., immuno-virotherapy of cancer) and hormones (e.g., melatonin, stress hormones). Molecular mechanisms of cellular stress adaptation involve the protein quality control system (PQS) and homeostasis of proteasome, endoplasmic reticulum, and mitochondria. Important components are transcription factors (e.g., Nrf2), micro-RNAs, heat shock proteins, ionic calcium, and enzymes (e.g., glutathion redox enzymes, DNA methyltransferases, and DNA repair enzymes). Cellular growth control, intercellular communication, and resistance to stress from microbial infections involve growth factors, cytokines, chemokines, interferons, and their respective receptors. The effects of hormesis during evolution are multifarious: cell protection and survival, evolutionary flexibility, and epigenetic memory. According to the hormesis theory, this is true for the entire biosphere, e.g., archaia, bacteria, fungi, plants, and the animal kingdoms.

Phytocompounds curcumin, quercetin, indole-3-carbinol, and resveratrol modulate lactate-pyruvate level along with cytotoxic activity in HeLa cervical cancer cells

Cancer cells meet their energy need by predominantly increased uptake of glucose, high rate of glycolysis, and increased production of lactate even in the presence of adequate oxygen.  This process was proposed by Otto Warburg and named after him as the Warburg effect. The development of drugs that target glucose intake and aerobic glycolysis or lactic acid secretion of cancer cells is a newer approach for drug discovery. We have tested five purified plants-derived compounds such as curcumin, quercetin, ellagic acid, resveratrol, and indole-3-carbinol in HeLa cells for cytotoxicity, inhibition of metastasis, and modulation of lactate-pyruvate metabolism. Standard biochemical methods were used for glucose, lactic acid, and pyruvic acid measurement. The cell viability was determined by MTT assay. Cell migration was checked by wound healing assay. A dose-dependent cytotoxic effect and inhibition of cell migration were observed in all the tested compounds. A decrease in the lactate and increase in pyruvate level was observed in all the tested compounds except ellagic acid. Our finding suggests that tested phytocompounds are associated with the metabolic reprogramming of cancer cells and execute the cytotoxic effect. These compounds could be used for cancer prevention and therapy.

The SIRT6-Autophagy-Warburg Effect Axis in Papillary Thyroid Cancer

As shown in our previous study, SIRT6 promotes an aggressive phenotype and the epithelial-mesenchymal transition (EMT) in papillary thyroid cancer (PTC). In this study, we focused on the regulatory axis including SIRT6, autophagy, and the Warburg effect. We innovatively confirmed that SIRT6 overexpression depleted histone H3 lysine 56 acetylation (H3K56ac) of the negative regulator of reactive oxygen species (NRROS) in vitro, thus increasing reactive oxygen species (ROS) production. The accumulated ROS then activated endoplasmic reticulum stress (ER stress) and subsequently induced autophagy. Furthermore, SIRT6 overexpression inhibited glucose transporter 1 (GLUT1) via autophagy-mediated degradation, ultimately suppressing the Warburg effect. Treatment with the ROS scavenger N-acetyl-L-cysteine (NAC, 5 mM) or the autophagy inhibitor chloroquine (CQ) both rescued the inhibition of the Warburg effect. Additionally, a higher concentration of NAC (15 mM) further inhibited the Warburg effect. These concentration-dependent bilateral effects of NAC on this process were confirmed to be due to the regulation of the AMPK signaling pathway. Finally, we further examined this mechanism in vivo by establishing subcutaneous xenografts in nude mice and analyzed the tumors using 18F radio-labeled fluorodeoxyglucose (18F-FDG) PET/CT. In conclusion, we identified a SIRT6-ROS-ER stress-autophagy-GLUT1-Warburg effect axis in PTC, which may provide a new therapeutic target. In addition, NAC (low concentration) and CQ, previously considered to be tumor inhibitors, were shown to promote tumorigenesis in PTC with high SIRT6 expression by inducing the Warburg effect.

Protein Kinase CK2 in Cancer Energetics

Protein kinase CK2 (formerly known as casein kinase 2) is abnormally elevated in many cancers. This may increase tumor aggressiveness through CK2-dependent phosphorylation of key proteins in several signaling pathways. In this work, we have compiled evidence from the literature to suggest that CK2 also modulates a metabolic switch characteristic of cancer cells that enhances resistance to death, due to either drugs or to a microenvironment deficient in oxygen or nutrients. Concurrently, CK2 may help to preserve mitochondrial activity in a PTEN-dependent manner. PTEN, widely recognized as a tumor suppressor, is another CK2 substrate in the PI3K/Akt signaling pathway that promotes cancer viability and aerobic glycolysis. Given that CK2 can regulate Akt as well as two of its main effectors, namely mTORC1 and β-catenin, we comprehensively describe how CK2 may modulate cancer energetics by regulating expression of key targets and downstream processes, such as HIF-1 and autophagy, respectively. Thus, the specific inhibition of CK2 may lead to a catastrophic death of cancer cells, which could become a feasible therapeutic strategy to beat this devastating disease. In fact, ATP-competitive inhibitors, synthetic peptides and antisense oligonucleotides have been designed as CK2 inhibitors, some of them used in preclinical models of cancer, of which TBB and silmitasertib are widely known. We will finish by discussing a hypothetical scenario in which cancer cells are "addicted" to CK2; i.e., in which many proteins that regulate signaling pathways and metabolism-linked processes are highly dependent on this kinase.

Single-Cell Transcriptional Profiling of Cells Derived From Regenerating Alveolar Ducts

Lung regeneration occurs in a variety of adult mammals after surgical removal of one lung (pneumonectomy). Previous studies of murine post-pneumonectomy lung growth have identified regenerative “hotspots” in subpleural alveolar ducts; however, the cell-types participating in this process remain unclear. To identify the single cells participating in post-pneumonectomy lung growth, we used laser microdissection, enzymatic digestion and microfluidic isolation. Single-cell transcriptional analysis of the murine alveolar duct cells was performed using the C1 integrated fluidic circuit (Fluidigm) and a custom PCR panel designed for lung growth and repair genes. The multi-dimensional data set was analyzed using visualization software based on the tSNE algorithm. The analysis identified 6 cell clusters; 1 cell cluster was present only after pneumonectomy. This post-pneumonectomy cluster was significantly less transcriptionally active than 3 other clusters and may represent a transitional cell population. A provisional cluster identity for 4 of the 6 cell clusters was obtained by embedding bulk transcriptional data into the tSNE analysis. The transcriptional pattern of the 6 clusters was further analyzed for genes associated with lung repair, matrix production, and angiogenesis. The data demonstrated that multiple cell-types (clusters) transcribed genes linked to these basic functions. We conclude that the coordinated gene expression across multiple cell clusters is likely a response to a shared regenerative microenvironment within the subpleural alveolar ducts.

Continuous Hypoxia and Glucose Metabolism: The Effects on Gene Expression in Mcf7 Breast Cancer Cell Line

BACKGROUND

Hypoxia (deprived oxygen in tissues) may induce molecular and genetic changes in cancer cells.

OBJECTIVE

To Investigate the genetic changes of glucose metabolism in breast cancer cell line (MCF7) after exposure to continuous hypoxia (10 and 20 cycles exposure of 72 hours continuously on a weekly basis).

METHODS

Gene expression of MCF7 cells was evaluated using real-time polymerase chain reactionarray method. Furthermore, cell migration and wound healing assays were also applied.

RESULTS

It was found that 10 episodes of continuous hypoxia activated the Warburg effect in MCF7 cells, via the significant up-regulation of genes involved in glycolysis (ANOVA, p value < 0.05). The molecular changes were associated with the ability of MCF7 cells to divide and migrate. Interestingly, after 20 episodes of continuous hypoxia, the expression glycolysis mediated genes dropped significantly (from 30 to 9 folds). This could be attributed to the adaptive ability of cancer cells.

CONCLUSION

It is concluded that 10 hypoxic episodes increased the survival rate and aggressiveness of MCF7 cells and induced the Warburg effect by the up-regulation of the glycolysis mediating gene expression.

Involvement of Lactate and Pyruvate in the Anti-Inflammatory Effects Exerted by Voluntary Activation of the Sympathetic Nervous System

We recently demonstrated that the sympathetic nervous system can be voluntarily activated following a training program consisting of cold exposure, breathing exercises, and meditation. This resulted in profound attenuation of the systemic inflammatory response elicited by lipopolysaccharide (LPS) administration. Herein, we assessed whether this training program affects the plasma metabolome and if these changes are linked to the immunomodulatory effects observed. A total of 224 metabolites were identified in plasma obtained from 24 healthy male volunteers at six timepoints, of which 98 were significantly altered following LPS administration. Effects of the training program were most prominent shortly after initiation of the acquired breathing exercises but prior to LPS administration, and point towards increased activation of the Cori cycle. Elevated concentrations of lactate and pyruvate in trained individuals correlated with enhanced levels of anti-inflammatory interleukin (IL)-10. In vitro validation experiments revealed that co-incubation with lactate and pyruvate enhances IL-10 production and attenuates the release of pro-inflammatory IL-1β and IL-6 by LPS-stimulated leukocytes. Our results demonstrate that practicing the breathing exercises acquired during the training program results in increased activity of the Cori cycle. Furthermore, this work uncovers an important role of lactate and pyruvate in the anti-inflammatory phenotype observed in trained subjects.

Role of Glucose Metabolism Reprogramming in the Pathogenesis of Cholangiocarcinoma

Cholangiocarcinoma (CCA) is one of the most lethal cancers, and its rate of occurrence is increasing annually. The diagnoses of CCA patients remain elusive due to the lack of early symptoms and is misdiagnosed as HCC in a considerable percentage of patients. It is crucial to explore the underlying mechanisms of CCA carcinogenesis and development to find out specific biomarkers for early diagnosis of CCA and new promising therapeutic targets. In recent times, the reprogramming of tumor cells metabolism has been recognized as a hallmark of cancer. The modification from the oxidative phosphorylation metabolic pathway to the glycolysis pathway in CCA meets the demands of cancer cell proliferation and provides a favorable environment for tumor development. The alteration of metabolic programming in cancer cells is complex and may occur via mutations and epigenetic modifications within oncogenes, tumor suppressor genes, signaling pathways, and glycolytic enzymes. Herein we review the altered metabolism in cancer and the signaling pathways involved in this phenomena as they may affect CCA development. Understanding the regulatory pathways of glucose metabolism such as Akt/mTOR, HIF1α, and cMyc in CCA may further develop our knowledge of this devastating disease and may offer relevant information in the exploration of new diagnostic biomarkers and targeted therapeutic approaches for CCA.

Lactate Beyond a Waste Metabolite: Metabolic Affairs and Signaling in Malignancy

To sustain their high proliferation rates, most cancer cells rely on glycolytic metabolism, with production of lactic acid. For many years, lactate was seen as a metabolic waste of glycolytic metabolism; however, recent evidence has revealed new roles of lactate in the tumor microenvironment, either as metabolic fuel or as a signaling molecule. Lactate plays a key role in the different models of metabolic crosstalk proposed in malignant tumors: among cancer cells displaying complementary metabolic phenotypes and between cancer cells and other tumor microenvironment associated cells, including endothelial cells, fibroblasts, and diverse immune cells. This cell metabolic symbiosis/slavery supports several cancer aggressiveness features, including increased angiogenesis, immunological escape, invasion, metastasis, and resistance to therapy. Lactate transport is mediated by the monocarboxylate transporter (MCT) family, while another large family of G protein-coupled receptors (GPCRs), not yet fully characterized in the cancer context, is involved in lactate/acidosis signaling. In this mini-review, we will focus on the role of lactate in the tumor microenvironment, from metabolic affairs to signaling, including the function of lactate in the cancer-cancer and cancer-stromal shuttles, as well as a signaling oncometabolite. We will also review the prognostic value of lactate metabolism and therapeutic approaches designed to target lactate production and transport.

Proteomics Analysis Reveals that Warburg Effect along with Modification in Lipid Metabolism Improves In Vitro Embryo Development under Low Oxygen

The molecular mechanism regulating embryo development under reduced oxygen tension remains elusive. This study aimed to identify the molecular mechanism impacting embryo development under low oxygen conditions. Buffalo embryos were cultured under 5% or 20% oxygen and were evaluated according to their morphological parameters related to embryo development. The protein profiles of these embryos were compared using iTRAQ-based quantitative proteomics. Physiological O2 (5%) significantly promoted blastocyst yield, hatching rate, embryo quality and cell count as compared to atmospheric O2 (20%). The embryos in the 5% O2 group had an improved hatching rate of cryopreserved blastocysts post-warming (p < 0.05). Comparative proteome profiles of hatched blastocysts cultured under 5% vs. 20% O2 levels identified 43 differentially expressed proteins (DEPs). Functional analysis indicated that DEPs were mainly associated with glycolysis, fatty acid degradation, inositol phosphate metabolism and terpenoid backbone synthesis. Our results suggest that embryos under physiological oxygen had greater developmental potential due to the pronounced Warburg Effect (aerobic glycolysis). Moreover, our proteomic data suggested that higher lipid degradation, an elevated cholesterol level and a higher unsaturated to saturated fatty acid ratio might be involved in the better cryo-survival ability reported in embryos cultured under low oxygen. These data provide new information on the early embryo protein repertoire and general molecular mechanisms of embryo development under varying oxygen levels.

Hepatitis C Virus Downregulates Core Subunits of Oxidative Phosphorylation, Reminiscent of the Warburg Effect in Cancer Cells

Hepatitis C Virus (HCV) mainly infects liver hepatocytes and replicates its single-stranded plus strand RNA genome exclusively in the cytoplasm. Viral proteins and RNA interfere with the host cell immune response, allowing the virus to continue replication. Therefore, in about 70% of cases, the viral infection cannot be cleared by the immune system, but a chronic infection is established, often resulting in liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Induction of cancer in the host cells can be regarded to provide further advantages for ongoing virus replication. One adaptation in cancer cells is the enhancement of cellular carbohydrate flux in glycolysis with a reduction of the activity of the citric acid cycle and aerobic oxidative phosphorylation. To this end, HCV downregulates the expression of mitochondrial oxidative phosphorylation complex core subunits quite early after infection. This so-called aerobic glycolysis is known as the “Warburg Effect” and serves to provide more anabolic metabolites upstream of the citric acid cycle, such as amino acids, pentoses and NADPH for cancer cell growth. In addition, HCV deregulates signaling pathways like those of TNF-β and MAPK by direct and indirect mechanisms, which can lead to fibrosis and HCC.

Developments in Carbohydrate-Based Cancer Therapeutics

Cancer cells of diverse origins express extracellular tumor-specific carbohydrate antigens (TACAs) because of aberrant glycosylation. Overexpressed TACAs on the surface of tumor cells are considered biomarkers for cancer detection and have always been prioritized for the development of novel carbohydrate-based anti-cancer vaccines. In recent years, progress has been made in developing synthetic, carbohydrate-based antitumor vaccines to improve immune responses associated with targeting these specific antigens. Tumor cells also exhaust more energy for proliferation than normal cells, by consuming excessive amounts of glucose via overexpressed sugar binding or transporting receptors located in the cellular membrane. Furthermore, inspired by the Warburg effect, glycoconjugation strategies of anticancer drugs have gained considerable attention from the scientific community. This review highlights a small cohort of recent efforts which have been made in carbohydrate-based cancer treatments, including vaccine design and the development of glycoconjugate prodrugs, glycosidase inhibiting iminosugars, and early cancer diagnosis.

The Fate of Glutamine in Human Metabolism. The Interplay with Glucose in Proliferating Cells

Genome-scale models of metabolism (GEM) are used to study how metabolism varies in different physiological conditions. However, the great number of reactions involved in GEM makes it difficult to understand these variations. In order to have a more understandable tool, we developed a reduced metabolic model of central carbon and nitrogen metabolism, C2M2N with 77 reactions, 54 internal metabolites, and 3 compartments, taking into account the actual stoichiometry of the reactions, including the stoichiometric role of the cofactors and the irreversibility of some reactions. In order to model oxidative phosphorylation (OXPHOS) functioning, the proton gradient through the inner mitochondrial membrane is represented by two pseudometabolites DPH (∆pH) and DPSI (∆ψ). To illustrate the interest of such a reduced and quantitative model of metabolism in mammalian cells, we used flux balance analysis (FBA) to study all the possible fates of glutamine in metabolism. Our analysis shows that glutamine can supply carbon sources for cell energy production and can be used as carbon and nitrogen sources to synthesize essential metabolites. Finally, we studied the interplay between glucose and glutamine for the formation of cell biomass according to ammonia microenvironment. We then propose a quantitative analysis of the Warburg effect.

The Fate of Glutamine in Human Metabolism. The Interplay with Glucose in Proliferating Cells

Genome-scale models of metabolism (GEM) are used to study how metabolism varies in different physiological conditions. However, the great number of reactions involved in GEM makes it difficult to understand these variations. In order to have a more understandable tool, we developed a reduced metabolic model of central carbon and nitrogen metabolism, C2M2N with 77 reactions, 54 internal metabolites, and 3 compartments, taking into account the actual stoichiometry of the reactions, including the stoichiometric role of the cofactors and the irreversibility of some reactions. In order to model oxidative phosphorylation (OXPHOS) functioning, the proton gradient through the inner mitochondrial membrane is represented by two pseudometabolites DPH (∆pH) and DPSI (∆ψ). To illustrate the interest of such a reduced and quantitative model of metabolism in mammalian cells, we used flux balance analysis (FBA) to study all the possible fates of glutamine in metabolism. Our analysis shows that glutamine can supply carbon sources for cell energy production and can be used as carbon and nitrogen sources to synthesize essential metabolites. Finally, we studied the interplay between glucose and glutamine for the formation of cell biomass according to ammonia microenvironment. We then propose a quantitative analysis of the Warburg effect.

Mitochondrial fusion supports increased oxidative phosphorylation during cell proliferation

Proliferating cells often have increased glucose consumption and lactate excretion relative to the same cells in the quiescent state, a phenomenon known as the Warburg effect. Despite an increase in glycolysis, however, here we show that non-transformed mouse fibroblasts also increase oxidative phosphorylation (OXPHOS) by nearly two-fold and mitochondrial coupling efficiency by ~30% during proliferation. Both increases are supported by mitochondrial fusion. Impairing mitochondrial fusion by knocking down mitofusion-2 (Mfn2) was sufficient to attenuate proliferation, while overexpressing Mfn2 increased proliferation. Interestingly, impairing mitochondrial fusion decreased OXPHOS but did not deplete ATP levels. Instead, inhibition caused cells to transition from excreting aspartate to consuming it. Transforming fibroblasts with the Ras oncogene induced mitochondrial biogenesis, which further elevated OXPHOS. Notably, transformed fibroblasts continued to have elongated mitochondria and their proliferation remained sensitive to inhibition of Mfn2. Our results suggest that cell proliferation requires increased OXPHOS as supported by mitochondrial fusion.

A Barter Economy in Tumors: Exchanging Metabolites through Gap Junctions

To produce physiological functions, many tissues require their cells to be connected by gap junctions. Such diffusive coupling is important in establishing a cytoplasmic syncytium through which cells can exchange signals, substrates and metabolites. Often the benefits of connectivity become apparent solely at the multicellular level, leading to the notion that cells work for a common good rather than exclusively in their self-interest. In some tumors, gap junctional connectivity between cancer cells is reduced or absent, but there are notable cases where it persists or re-emerges in late-stage disease. Diffusive coupling will blur certain phenotypic differences between cells, which may seem to go against the establishment of population heterogeneity, a central pillar of cancer that stems from genetic instability. Here, building on our previous measurements of gap junctional coupling between cancer cells, we use a computational model to simulate the role of connexin-assembled channels in exchanging lactate and bicarbonate ions down their diffusion gradients. Based on the results of these simulations, we propose that an overriding benefit of gap junctional connectivity may relate to lactate/bicarbonate exchange, which would support an elevated metabolic rate in hypoxic tumors. In this example of barter, hypoxic cancer cells provide normoxic neighbors with lactate for mitochondrial oxidation; in exchange, bicarbonate ions, which are more plentiful in normoxic cells, are supplied to hypoxic neighbors to neutralize the H⁺ ions co-produced glycolytically. Both cells benefit, and so does the tumor.

Anti-Cancer Compounds Targeted to VDAC: Potential and Perspectives

BACKGROUND

VDAC (Voltage-Dependent Anion selective Channel) is a small family of abundant pore-forming proteins located in the outer mitochondrial membrane. Their role range from the most intuitive, the formation of a hydrophilic conduit through the membrane thanks to its beta-barrel structure, to less understood functions that make them essential actors in the cross-talk between the bioenergetics metabolism and the cytosol components. Due to this localization, VDAC1, in particular, has been reported to be involved in apoptosis, Hexokinase and tubulin binding, and in the Warburg effect. For these reasons, an involvement of VDAC in cancer is considered consequential and a number of compounds have been proposed and used in experimental trials to demonstrate the efficacy of molecules affecting the functions of VDAC.

OBJECTIVES

In this work, we thus survey the literature describing drug compounds acting on the cancerous proliferation through VDAC. Three main categories have been assigned: molecules acting on the VDAC-Hexokinase binding, molecules directly inhibiting the VDAC conductance, molecules affecting the expression levels of the VDAC gene. The application of biological peptides for this purpose is also considered.

CONCLUSION

Since the knowledges about the functional properties of VDAC protein are still insufficient, VDAC as a pharmacological target in the fight against cancer is still a very open, but very promising, field.

Bioenergetic modulators hamper cancer cell viability and enhance response to chemotherapy

Gliomas are characterized by a marked glycolytic metabolism with a consequent production of massive amounts of lactate, even in the presence of normal levels of oxygen, associated to increased invasion capacity and to higher resistance to conventional treatment. This work aimed to understand how the metabolic modulation can influence tumour aggressive features and its potential to be used as complementary therapy. We assessed the effect of bioenergetic modulators (BMs) targeting different metabolic pathways in glioma cell characteristics. The in vivo effect of BMs was evaluated using the chicken chorioallantoic membrane model. Additionally, the effect of pre-treatment with BMs in the response to the antitumour drug temozolomide (TMZ) was analysed in vitro. Cell treatment with the BMs induced a decrease in cell viability and in migratory/invasion abilities, as well as modifications in metabolic parameters (glucose, lactate and ATP) and increased the cytotoxicity of the conventional drug TMZ. Furthermore, all BMs decreased the tumour growth and the number of blood vessels in an in vivo model. Our results demonstrate that metabolic modulation has the potential to be used as therapy to decrease the aggressiveness of the tumours or to be combined with conventional drugs used in glioma treatment.

Dichloroacetic acid (DCA) synergizes with the SIRT2 inhibitor Sirtinol and AGK2 to enhance anti-tumor efficacy in non-small cell lung cancer

Combination chemotherapy is a potentially promising approach to enhance anticancer activity, overcome drug resistance, and improve disease-free and overall survival. The current study investigates the antitumor activity of sodium dichloroacetic acid (DCA) in combination with SIRT2 inhibitor Sirtinol and AGK2. We found that combining DCA with Sirtinol produced a synergistic therapeutic benefit in A549 and H1299 NSCLC cells in vitro and in a mouse A549 xenograft model. Synergistic potentiation of oxidative phosphorylation (OXPHOS) was observed, including decreased glucose consumption, decreased lactate production, increased OCR and increased ROS generation, possibly via co-targeting pyruvate dehydrogenase alpha 1(PDHA1). Mechanically, AGK2 and Sirtinol were found to increase the lysine-acetylation and decrease the serine-phosphorylation of PDHA1, which enabled the two inhibitors to synergize with DCA to further activate PDHA1. Besides, a AMPKα-ROS feed-forward loop was notably activated after the combined treatments compared with mono-therapy. Our results indicate that the combination of DCA and SIRT2 inhibitor may provide a promising therapeutic strategy to effectively kill cancer cells.

High mobility group protein B1 controls liver cancer initiation through yes-associated protein -dependent aerobic glycolysis

Emerging studies have suggested that the Hippo pathway is involved in the tumorigenesis of hepatocellular carcinoma (HCC). However, the key regulator of the Hippo pathway in liver tumor metabolic reprogramming remains elusive. Here, we provide evidence that high mobility group box 1 (HMGB1), a chromosomal protein, plays a role in the regulation of the Hippo pathway during liver tumorigenesis. Cre/loxP recombination-mediated HMGB1 depletion in hepatocytes blocks diethylnitrosamine-induced liver cancer initiation in mice, whereas short hairpin RNA-mediated gene silencing of HMGB1 inhibits HCC cell proliferation. Mechanistically, the binding of HMGB1 to GA-binding protein alpha promotes the expression of yes-associated protein (YAP), a major downstream effector of the Hippo pathway that contributes to liver tumorigenesis by inducing hypoxia-inducible factor 1α (HIF1α)-dependent aerobic glycolysis. Like wild-type YAP-complementary DNA, YAP-5SA-S94A can restore HIF1α DNA binding activity, glycolysis-associated gene expression, and HIF1α-YAP complex formation in YAP-knockdown HCC cell lines. In contrast, verteporfin, a reagent targeting the interface between YAP and TEA domain transcription factor, has the ability to block YAP-HIF1α complex formation. Notably, genetic or pharmacologic inhibition of the HMGB1-YAP-HIF1α pathway confers protection against excessive glycolysis and tumor growth in mice.

CONCLUSION

These findings demonstrate that HMGB1 plays a novel role in modulating the YAP-dependent HIF1α pathway and shed light on the development of metabolism-targeting therapeutics for HCC chemoprevention. (Hepatology 2018;67:1823-1841).

Phytometabolites Targeting the Warburg Effect in Cancer Cells: A Mechanistic Review

Phytometabolites are functional elements derived from plants and most of them exhibit therapeutic characteristics such as anti-cancer, anti-inflammatory and anti-oxidant effects. Phytometabolites exert their anti-cancer effect by targeting multiple signaling pathways. One of the remarkable phenomena targeted by phytometabolites is the Warburg effect. The Warburg effect describes the observation that cancer cells exhibit an increased rate of glycolysis and aberrant redox activity compared to normal cells. This phenomenon promotes further cancer development and progression. Recent observations revealed that some phytometabolites could target metabolic-related enzymes (e.g. Hexokinase, Pyruvate kinase M2, HIF-1) in cancer cells, with little or no harm to normal cells. Since hyper-proliferation of cancer cells is fueled by higher cellular metabolism, phytometabolites targeting these metabolic pathways can create synergistic crosstalk with induced apoptotic pathways and sensitize cancer cells to chemotherapeutic agents. In this review, we discuss phytometabolites that target the Warburg effect and the underlying molecular mechanism that leads to tumor growth suppression.

TLR-mediated metabolic reprogramming in the tumor microenvironment: potential novel strategies for cancer immunotherapy

Cellular energy metabolism not only promotes tumor cell growth and metastasis but also directs immune cell survival, proliferation and the ability to perform specific and functional immune responses within the tumor microenvironment. A better understanding of the molecular regulation of metabolism in different cell components in the tumor-suppressive microenvironment is critical for the development of effective strategies for human cancer treatments. Toll-like receptors (TLRs) have recently been recognized as critical factors involved in tumor pathogenesis, regulating both tumor cells and tumor-infiltrating innate and adaptive immune cells. However, little is known about the molecular crosstalk between TLR signaling and tumor or/and immune cell metabolism, although there is abundant expression of TLRs in these cells. In this review, we explore the functional role of TLR signaling in reprogramming cell metabolism in the tumor microenvironment. In particular, we discuss how malignant tumors regulate metabolism to support their growth and survival, summarize more recently identified metabolic profiles of different immune cell subsets and TLR-mediated regulation of cellular metabolism in both tumor and immune cells, and further explore potential strategies targeting cell metabolism for TLR-based cancer therapy. An improved understanding of these issues should open new avenues for the development of novel strategies via TLR-mediated metabolic reprogramming of the tumor microenvironment for cancer immunotherapy.

Stimulation of the toll-like receptor 3 promotes metabolic reprogramming in head and neck carcinoma cells

In this study, a possible link between the innate immune recognition receptor TLR3 and metabolic reprogramming in Head and Neck carcinoma (HNC) cells was investigated. The effects of TLR3 stimulation/knock-down were assessed under several culture conditions in 4 HNC cell-lines by cell growth assays, targeted metabolomics, and glycolysis assays based on time-resolved analysis of proton release (Seahorse analyzer). The stimulation of TLR3 by its synthetic agonist Poly(A:U) resulted in a faster growth of HNC cells under low foetal calf serum conditions. Targeted analysis of glucose metabolism pathways demonstrated a tendency towards a shift from tricarboxylic acid cycle (Krebs cycle) to glycolysis and anabolic reactions in cells treated with Poly(A:U). Glycolysis assays confirmed that TLR3 stimulation enhanced the capacity of malignant cells to switch from oxidative phosphorylation to extra-mitochondrial glycolysis. We found evidence that HIF-1α is involved in this process: addition of the TLR3 agonist resulted in a higher cell concentration of the HIF-1α protein, even in normoxia, whereas knocking-down TLR3 resulted in a lower concentration, even in hypoxia. Finally, we assessed TLR3 expression by immunohistochemistry in a series of 7 HNSCC specimens and found that TLR3 was detected at higher levels in tumors displaying a hypoxic staining pattern. Overall, our results demonstrate that TLR3 stimulation induces the Warburg effect in HNC cells in vitro, and suggest that TLR3 may play a role in tumor adaptation to hypoxia.

PTEN dephosphorylates AKT to prevent the expression of GLUT1 on plasmamembrane and to limit glucose consumption in cancer cells

GLUT1 is the facilitative transporter playing the major role in the internalization of glucose. Basally, GLUT1 resides on vesicles located in a para-golgian area, and is translocated onto the plasmamembrane upon activation of the PI3KC1-AKT pathway. In proliferating cancer cells, which demand a high quantity of glucose for their metabolism, GLUT1 is permanently expressed on the plasmamembrane. This is associated with the abnormal activation of the PI3KC1-AKT pathway, consequent to the mutational activation of PI3KC1 and/or the loss of PTEN. The latter, in fact, could antagonize the phosphorylation of AKT by limiting the availability of Phosphatidylinositol (3,4,5)-trisphosphate. Here, we asked whether PTEN could control the plasmamembrane expression of GLUT1 also through its protein-phosphatase activity on AKT. Experiments of co-immunoprecipitation and in vitro de-phosphorylation assay with homogenates of cells transgenically expressing the wild type or knocked-down mutants (lipid-phosphatase, protein-phosphatase, or both) isoforms demonstrated that indeed PTEN physically interacts with AKT and drives its dephosphorylation, and so limiting the expression of GLUT1 at the plasmamembrane. We also show that growth factors limit the ability of PTEN to dephosphorylate AKT. Our data emphasize the fact that PTEN acts in two distinct steps of the PI3k/AKT pathway to control the expression of GLUT1 at the plasmamembrane and, further, add AKT to the list of the protein substrates of PTEN.