The Warburg Effect 97 Years after Its Discovery

High-Contrast Fluorescence Diagnosis of Cancer Cells/Tissues Based on β-Lapachone-Triggered ROS Amplification Specific in Cancer Cells

Discrimination of cancer cells/tissues from normal ones is of critical importance for early diagnosis and treatment of cancers. Herein, we present a new strategy for high-contrast fluorescence diagnosis of cancer cells/tissues based on β-Lapachone (β-Lap, an anticancer agent) triggered ROS (reactive oxygen species) amplification specific in cancer cells/tissues. With the strategy, a wide range of cancer cells/tissues, including surgical tissue specimens harvested from patients, were distinguished from normal ones by using a combination of β-Lap and a Si-rhodamine-based NIR fluorescent ROS probe PSiR3 developed in this work with average tumor-to-normal (T/N) ratios up to 15 in cell level and 24 in tissue level, far exceeding the clinically acceptable threshold of 2.0. What's more, the strategy allowed the fluorescence discrimination of tumor tissues from inflammatory ones based on whether a marked fluorescence enhancement could be induced when treated with PSiR3 and β-Lap/PSiR3 combination, respectively.

Implications of Standardized Uptake Values of Oral Squamous Cell Carcinoma in PET-CT on Prognosis, Tumor Characteristics and Mitochondrial DNA Heteroplasmy

Under aerobic conditions, some cancers switch to glycolysis to cover their energy requirements. Taking advantage of this process, functional imaging techniques such as PET-CT can be used to detect and assess tumorous tissues. The aim of this study was to investigate standardized uptake values and mitochondrial DNA mutations in oral squamous cell carcinoma. A cohort of 57 patients underwent 18[F]FDG-PET-CT and standardized uptake values were collected. In 15 patients, data on mitochondrial DNA mutations of the tumor were available. Kaplan-Meier curves were calculated, and correlation analyses as well as univariate Cox proportional hazard models were performed. Using ROC analysis to determine a statistical threshold for SUVmax in PET investigations, a cut-off value was determined at 9.765 MB/mL. Survival analysis for SUVmax in these groups showed a Hazard Ratio of 4 (95% CI 1.7-9) in the high SUVmax group with 5-year survival rates of 23.5% (p = 0.00042). For SUVmax and clinicopathological tumor features, significant correlations were found. A tendency towards higher mtDNA heteroplasmy levels in high SUVmax groups could be observed. We were able to confirm the prognostic value of SUVmax in OSCC, showing higher survival rates at lower SUVmax levels. Correlations between SUVmax and distinct tumor characteristics were highly significant, providing evidence that SUVmax may act as a reliable diagnostic parameter. Correlation analysis of mtDNA mutations suggests an influence on metabolic activity in OSCC.

Part-time cancers and role of melatonin in determining their metabolic phenotype

This brief review describes the association of the endogenous pineal melatonin rhythm with the metabolic flux of solid tumors, particularly breast cancer. It also summarizes new information on the potential mechanisms by which endogenously-produced or exogenously-administered melatonin impacts the metabolic phenotype of cancer cells. The evidence indicates that solid tumors may redirect their metabolic phenotype from the pathological Warburg-type metabolism during the day to the healthier mitochondrial oxidative phosphorylation on a nightly basis. Thus, they function as cancer cells only during the day and as healthier cells at night, that is, they are only part-time cancerous. This switch to oxidative phosphorylation at night causes cancer cells to exhibit a reduced tumor phenotype and less likely to rapidly proliferate or to become invasive or metastatic. Also discussed is the likelihood that some solid tumors are especially aggressive during the day and much less so at night due to the nocturnal rise in melatonin which determines their metabolic state. We further propose that when melatonin is used/tested in clinical trials, a specific treatment paradigm be used that is consistent with the temporal metabolic changes in tumor metabolism. Finally, it seems likely that the concurrent use of melatonin in combination with conventional chemotherapies also would improve cancer treatment outcomes.

Obesity and Androgen Receptor Signaling: Associations and Potential Crosstalk in Breast Cancer Cells

Obesity is an increasing health challenge and is recognized as a breast cancer risk factor. Although obesity-related breast cancer mechanisms are not fully understood, this association has been linked to impaired hormone secretion by the dysfunctional obese adipose tissue (hyperplasic and hypertrophic adipocytes). Among these hormones, altered production of androgens and adipokines is observed, and both, are independently associated with breast cancer development. In this review, we describe and comment on the relationships reported between these factors and breast cancer, focusing on the biological associations that have helped to unveil the mechanisms by which signaling from androgens and adipokines modifies the behavior of mammary epithelial cells. Furthermore, we discuss the potential crosstalk between the two most abundant adipokines produced by the adipose tissue (adiponectin and leptin) and the androgen receptor, an emerging marker in breast cancer. The identification and understanding of interactions among adipokines and the androgen receptor in cancer cells are necessary to guide the development of new therapeutic approaches in order to prevent and cure obesity and breast cancer.

Mechanisms of Metabolic Reprogramming in Cancer Cells Supporting Enhanced Growth and Proliferation

Cancer cells alter metabolic processes to sustain their characteristic uncontrolled growth and proliferation. These metabolic alterations include (1) a shift from oxidative phosphorylation to aerobic glycolysis to support the increased need for ATP, (2) increased glutaminolysis for NADPH regeneration, (3) altered flux through the pentose phosphate pathway and the tricarboxylic acid cycle for macromolecule generation, (4) increased lipid uptake, lipogenesis, and cholesterol synthesis, (5) upregulation of one-carbon metabolism for the production of ATP, NADH/NADPH, nucleotides, and glutathione, (6) altered amino acid metabolism, (7) metabolism-based regulation of apoptosis, and (8) the utilization of alternative substrates, such as lactate and acetate. Altered metabolic flux in cancer is controlled by tumor-host cell interactions, key oncogenes, tumor suppressors, and other regulatory molecules, including non-coding RNAs. Changes to metabolic pathways in cancer are dynamic, exhibit plasticity, and are often dependent on the type of tumor and the tumor microenvironment, leading in a shift of thought from the Warburg Effect and the “reverse Warburg Effect” to metabolic plasticity. Understanding the complex nature of altered flux through these multiple pathways in cancer cells can support the development of new therapies.

Identification of Prognostic Glycolysis-Related lncRNA Signature in Tumor Immune Microenvironment of Hepatocellular Carcinoma

Purpose: The purpose of this study was to construct a novel risk scoring model with prognostic value that could elucidate tumor immune microenvironment of hepatocellular carcinoma (HCC).

Samples and methods: Data were obtained through The Cancer Genome Atlas (TCGA) database. Univariate Cox analysis, least absolute shrinkage and selection operator (LASSO) analysis, and multivariate Cox analysis were carried out to screen for glycolysis-related long noncoding RNAs (lncRNAs) that could provide prognostic value. Finally, we established a risk score model to describe the characteristics of the model and verify its prediction accuracy. The receiver operating characteristic (ROC) curves of 1, 3, and 5 years of overall survival (OS) were depicted with risk score and some clinical features. ESTIMATE algorithm, single-sample gene set enrichment analysis (ssGSEA), and CIBERSORT analysis were employed to reveal the characteristics of tumor immune microenvironment in HCC. The nomogram was drawn by screening indicators with high prognostic accuracy. The correlation of risk signature with immune infiltration and immune checkpoint blockade (ICB) therapy was analyzed. After enrichment of related genes, active behaviors and pathways in high-risk groups were identified and lncRNAs related to poor prognosis were validated in vitro. Finally, the impact of MIR4435-2HG upon ICB treatment was uncovered.

Results: After screening through multiple steps, four glycolysis-related lncRNAs were obtained. The risk score constructed with the four lncRNAs was found to significantly correlate with prognosis of samples. From the ROC curve of samples with 1, 3, and 5 years of OS, two indicators were identified with high prognostic accuracy and were used to draw a nomogram. Besides, the risk score significantly correlated with immune score, immune-related signature, infiltrating immune cells (i.e. B cells, etc.), and ICB key molecules (i.e. CTLA4,etc.). Gene enrichment analysis indicated that multiple biological behaviors and pathways were active in the high-risk group. In vitro validation results showed that MIR4435-2HG was highly expressed in the two cell lines, which had a significant impact on the OS of samples. Finally, we corroborated that MIR4435-2HG had intimate relationship with ICB therapy in hepatocellular carcinoma.

Conclusion: We elucidated the crucial role of risk signature in immune cell infiltration and immunotherapy, which might contribute to clinical strategies and clinical outcome prediction of HCC.

NONO-TFE3 fusion promotes aerobic glycolysis and angiogenesis by targeting HIF1A in NONO-TFE3 translocation renal cell carcinoma

BACKGROUND

NONO-TFE3 translocation renal cell carcinoma (tRCC), one of RCCs associated with Xp11.2 translocation/TFE3 gene fusion (Xp11.2 tRCCs), involves an X chromosome inversion between NONO and TFE3 with the characteristics of endonuclear aggregation of NONO-TFE3 fusion protein. Nowadays, the oncogenic mechanisms of NONO-TFE3 fusion have not been fully elucidated.

OBJECTIVE

This study aimed at investigating the mechanism of NONO-TFE3 fusion regulating HIF1A as well as the role of HIF-1α in the progression of NONO-TFE3 tRCC under hypoxia.

METHODS

Immunohistochemistry and Western Blotting assays were performed to profile HIF-1α expression in renal clear cell carcinoma (ccRCC) or in Xp11.2 tRCC. Chromatin immunoprecipitation (ChIP), luciferase reporter assay and real-time quantitative PCR (RT-qPCR) were used to evaluate the regulation of HIF1A expression by NONO-TFE3 fusion. Then, flow cytometry analysis, tube formation assays and cell migration assays were used as well as glucose or lactic acid levels were measured to establish the impact of HIF-1α on the progression of NONO-TFE3 tRCC. Besides, the effect of HIF-1α inhibitor (PX-478) on UOK109 cells was analyzed.

RESULTS

We found that HIF1A was targeting gene of NONO-TFE3 fusion. In UOK109 cells, which were isolated from NONO-TFE3 tRCC samples, NONO-TFE3 fusion promoted aerobic glycolysis and angiogenesis by up-regulating the expression of HIF-1α under hypoxia. Furthermore, inhibition of HIF-1α mediated by PX-478 suppressed the development of NONO-TFE3 tRCC under hypoxia.

CONCLUSION

HIF-1α is a potential target for therapy of NONO-TFE3 tRCC under hypoxia.

The Importance of Mitochondrial Pyruvate Carrier in Cancer Cell Metabolism and Tumorigenesis

Simple Summary

The characteristic metabolic hallmark of cancer cells is the massive catabolism of glucose by glycolysis, even under aerobic conditions—the so-called Warburg effect. Although energetically unfavorable, glycolysis provides “building blocks” to sustain the unlimited growth of malignant cells. Aberrant glycolysis is also responsible for lactate accumulation and acidosis in the tumor milieu, which fosters hypoxia and immunosuppression. One of the mechanisms used by cancer cells to increase glycolytic flow is the negative regulation of the proteins that conform the mitochondrial pyruvate carrier (MPC) complex, which transports pyruvate into the mitochondrial matrix to be metabolized in the tricarboxylic acid (TCA) cycle. Evidence suggests that MPC downregulation in tumor cells impacts many aspects of tumorigenesis, including cancer cell-intrinsic (proliferation, invasiveness, stemness, resistance to therapy) and -extrinsic (angiogenesis, anti-tumor immune activity) properties. In many cancers, but not in all, MPC downregulation is associated with poor survival. MPC regulation is therefore central to tackling glycolysis in tumors.

Abstract

Pyruvate is a key molecule in the metabolic fate of mammalian cells; it is the crossroads from where metabolism proceeds either oxidatively or ends with the production of lactic acid. Pyruvate metabolism is regulated by many enzymes that together control carbon flux. Mitochondrial pyruvate carrier (MPC) is responsible for importing pyruvate from the cytosol to the mitochondrial matrix, where it is oxidatively phosphorylated to produce adenosine triphosphate (ATP) and to generate intermediates used in multiple biosynthetic pathways. MPC activity has an important role in glucose homeostasis, and its alteration is associated with diabetes, heart failure, and neurodegeneration. In cancer, however, controversy surrounds MPC function. In some cancers, MPC upregulation appears to be associated with a poor prognosis. However, most transformed cells undergo a switch from oxidative to glycolytic metabolism, the so-called Warburg effect, which, amongst other possibilities, is induced by MPC malfunction or downregulation. Consequently, impaired MPC function might induce tumors with strong proliferative, migratory, and invasive capabilities. Moreover, glycolytic cancer cells secrete lactate, acidifying the microenvironment, which in turn induces angiogenesis, immunosuppression, and the expansion of stromal cell populations supporting tumor growth. This review examines the latest findings regarding the tumorigenic processes affected by MPC.

Hyperglycemia-Induced miR-467 Drives Tumor Inflammation and Growth in Breast Cancer

The tumor microenvironment contains the parenchyma, blood vessels, and infiltrating immune cells, including tumor-associated macrophages (TAMs). TAMs affect the developing tumor and drive cancer inflammation. We used mouse models of hyperglycemia and cancer and specimens from hyperglycemic breast cancer (BC) patients to demonstrate that miR-467 mediates the effects of high blood glucose on cancer inflammation and growth. Hyperglycemic patients have a higher risk of developing breast cancer. We have identified a novel miRNA-dependent pathway activated by hyperglycemia that promotes BC angiogenesis and inflammation supporting BC growth. miR-467 is upregulated in endothelial cells (EC), macrophages, BC cells, and in BC tumors. A target of miR-467, thrombospondin-1 (TSP-1), inhibits angiogenesis and promotes resolution of inflammation. Systemic injections of a miR-467 antagonist in mouse models of hyperglycemia resulted in decreased BC growth (p < 0.001). Tumors from hyperglycemic mice had a two-fold increase in macrophage accumulation compared to normoglycemic controls (p < 0.001), and TAM infiltration was prevented by the miR-467 antagonist (p < 0.001). BC specimens from hyperglycemic patients had increased miR-467 levels, increased angiogenesis, decreased levels of TSP-1, and increased TAM infiltration in malignant breast tissue in hyperglycemic vs. normoglycemic patients (2.17-fold, p = 0.002) and even in normal breast tissue from hyperglycemic patients (2.18-fold increase, p = 0.04). In malignant BC tissue, miR-467 levels were upregulated 258-fold in hyperglycemic patients compared to normoglycemic patients (p < 0.001) and increased 56-fold in adjacent normal tissue (p = 0.008). Our results suggest that miR-467 accelerates tumor growth by inducing angiogenesis and promoting the recruitment of TAMs to drive hyperglycemia-induced cancer inflammation.

Warburg's Ghost-Cancer's Self-Sustaining Phenotype: The Aberrant Carbon Flux in Cholesterol-Enriched Tumor Mitochondria via Deregulated Cholesterogenesis

Interpreting connections between the multiple networks of cell metabolism is indispensable for understanding how cells maintain homeostasis or transform into the decontrolled proliferation phenotype of cancer. Situated at a critical metabolic intersection, citrate, derived via glycolysis, serves as either a combustible fuel for aerobic mitochondrial bioenergetics or as a continuously replenished cytosolic carbon source for lipid biosynthesis, an essentially anaerobic process. Therein lies the paradox: under what conditions do cells control the metabolic route by which they process citrate? The Warburg effect exposes essentially the same dilemma—why do cancer cells, despite an abundance of oxygen needed for energy-generating mitochondrial respiration with citrate as fuel, avoid catabolizing mitochondrial citrate and instead rely upon accelerated glycolysis to support their energy requirements? This review details the genesis and consequences of the metabolic paradigm of a “truncated” Krebs/TCA cycle. Abundant data are presented for substrate utilization and membrane cholesterol enrichment in tumors that are consistent with criteria of the Warburg effect. From healthy cellular homeostasis to the uncontrolled proliferation of tumors, metabolic alterations center upon the loss of regulation of the cholesterol biosynthetic pathway. Deregulated tumor cholesterogenesis at the HMGR locus, generating enhanced carbon flux through the cholesterol synthesis pathway, is an absolute prerequisite for DNA synthesis and cell division. Therefore, expedited citrate efflux from cholesterol-enriched tumor mitochondria via the CTP/SLC25A1 citrate transporter is fundamental for sustaining the constant demand for cytosolic citrate that fuels the elevated flow of carbons from acetyl-CoA through the deregulated pathway of cholesterol biosynthesis.

Targeting Toxins toward Tumors

Many cancer diseases, e.g., prostate cancer and lung cancer, develop very slowly. Common chemotherapeutics like vincristine, vinblastine and taxol target cancer cells in their proliferating states. In slowly developing cancer diseases only a minor part of the malignant cells will be in a proliferative state, and consequently these drugs will exert a concomitant damage on rapidly proliferating benign tissue as well. A number of toxins possess an ability to kill cells in all states independently of whether they are benign or malignant. Such toxins can only be used as chemotherapeutics if they can be targeted selectively against the tumors. Examples of such toxins are mertansine, calicheamicins and thapsigargins, which all kill cells at low micromolar or nanomolar concentrations. Advanced prodrug concepts enabling targeting of these toxins to cancer tissue comprise antibody-directed enzyme prodrug therapy (ADEPT), gene-directed enzyme prodrug therapy (GDEPT), lectin-directed enzyme-activated prodrug therapy (LEAPT), and antibody-drug conjugated therapy (ADC), which will be discussed in the present review. The review also includes recent examples of protease-targeting chimera (PROTAC) for knockdown of receptors essential for development of tumors. In addition, targeting of toxins relying on tumor-overexpressed enzymes with unique substrate specificity will be mentioned.

The Distinctive Serum Metabolomes of Gastric, Esophageal and Colorectal Cancers

Simple Summary

Cancer of the stomach, esophagus and colon are often fatal. Ways are being sought to establish patient-friendly screening tests that would allow these cancers to be detected earlier. Examination of the metabolomics results of cancer patient’s serum for certain metabolites unique for a particular cancer was the goal of this review. From studies conducted within the past five years several metabolites were found to be changed in cancer compared to non-cancer patients for each of the three cancers. Further confirmation of what was discovered in this review coupled with establishment of standard protocols may allow for cancer screening on patient blood samples to become routine clinical tests.

Abstract

Three of the most lethal cancers in the world are the gastrointestinal cancers—gastric (GC), esophageal (EC) and colorectal cancer (CRC)—which are ranked as third, sixth and fourth in cancer deaths globally. Early detection of these cancers is difficult, and a quest is currently on to find non-invasive screening tests to detect these cancers. The reprogramming of energy metabolism is a hallmark of cancer, notably, an increased dependence on aerobic glycolysis which is often referred to as the Warburg effect. This metabolic change results in a unique metabolic profile that distinguishes cancer cells from normal cells. Serum metabolomics analyses allow one to measure the end products of both host and microbiota metabolism present at the time of sample collection. It is a non-invasive procedure requiring only blood collection which encourages greater patient compliance to have more frequent screenings for cancer. In the following review we will examine some of the most current serum metabolomics studies in order to compare their results and test a hypothesis that different tumors, notably, from EC, GC and CRC, have distinguishing serum metabolite profiles.

Hydrogen Sulfide, an Endogenous Stimulator of Mitochondrial Function in Cancer Cells

Hydrogen sulfide (H₂S) has a long history as toxic gas and environmental hazard; inhibition of cytochrome c oxidase (mitochondrial Complex IV) is viewed as a primary mode of its cytotoxic action. However, studies conducted over the last two decades unveiled multiple biological regulatory roles of H₂S as an endogenously produced mammalian gaseous transmitter. Cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST) are currently viewed as the principal mammalian H₂S-generating enzymes. In contrast to its inhibitory (toxicological) mitochondrial effects, at lower (physiological) concentrations, H₂S serves as a stimulator of electron transport in mammalian mitochondria, by acting as an electron donor—with sulfide:quinone oxidoreductase (SQR) being the immediate electron acceptor. The mitochondrial roles of H₂S are significant in various cancer cells, many of which exhibit high expression and partial mitochondrial localization of various H₂S producing enzymes. In addition to the stimulation of mitochondrial ATP production, the roles of endogenous H₂S in cancer cells include the maintenance of mitochondrial organization (protection against mitochondrial fission) and the maintenance of mitochondrial DNA repair (via the stimulation of the assembly of mitochondrial DNA repair complexes). The current article overviews the state-of-the-art knowledge regarding the mitochondrial functions of endogenously produced H₂S in cancer cells.

Anti-Warburg Effect of Melatonin: A Proposed Mechanism to Explain its Inhibition of Multiple Diseases

Glucose is an essential nutrient for every cell but its metabolic fate depends on cellular phenotype. Normally, the product of cytosolic glycolysis, pyruvate, is transported into mitochondria and irreversibly converted to acetyl coenzyme A by pyruvate dehydrogenase complex (PDC). In some pathological cells, however, pyruvate transport into the mitochondria is blocked due to the inhibition of PDC by pyruvate dehydrogenase kinase. This altered metabolism is referred to as aerobic glycolysis (Warburg effect) and is common in solid tumors and in other pathological cells. Switching from mitochondrial oxidative phosphorylation to aerobic glycolysis provides diseased cells with advantages because of the rapid production of ATP and the activation of pentose phosphate pathway (PPP) which provides nucleotides required for elevated cellular metabolism. Molecules, called glycolytics, inhibit aerobic glycolysis and convert cells to a healthier phenotype. Glycolytics often function by inhibiting hypoxia-inducible factor-1α leading to PDC disinhibition allowing for intramitochondrial conversion of pyruvate into acetyl coenzyme A. Melatonin is a glycolytic which converts diseased cells to the healthier phenotype. Herein we propose that melatonin's function as a glycolytic explains its actions in inhibiting a variety of diseases. Thus, the common denominator is melatonin's action in switching the metabolic phenotype of cells.

Revisiting the Warburg effect: historical dogma versus current understanding

Contrary to Warburg's original thesis, accelerated aerobic glycolysis is not a primary, permanent and universal consequence of dysfunctional or impaired mitochondria compensating for poor ATP yield per mole of glucose. Instead, in most tumours the Warburg effect is an essential part of a 'selfish' metabolic reprogramming, which results from the interplay between (normoxic/hypoxic) hypoxia-inducible factor-1 (HIF-1) overexpression, oncogene activation (cMyc, Ras), loss of function of tumour suppressors (mutant p53, mutant phosphatase and tensin homologue (PTEN), microRNAs and sirtuins with suppressor functions), activated (PI3K-Akt-mTORC1, Ras-Raf-MEK-ERK-cMyc, Jak-Stat3) or deactivated (LKB1-AMPK) signalling pathways, components of the tumour microenvironment, and HIF-1 cooperation with epigenetic mechanisms. Molecular and functional processes of the Warburg effect include: (a) considerable acceleration of glycolytic fluxes; (b) adequate ATP generation per unit time to maintain energy homeostasis and electrochemical gradients; (c) backup and diversion of glycolytic intermediates facilitating the biosynthesis of nucleotides, non-essential amino acids, lipids and hexosamines; (d) inhibition of pyruvate entry into mitochondria; (e) excessive formation and accumulation of lactate, which stimulates tumour growth and suppression of anti-tumour immunity - in addition, lactate can serve as an energy source for normoxic cancer cells and drives malignant progression and resistances to conventional therapies; (f) cytosolic lactate being mainly exported through upregulated lactate-proton symporters (MCT4), working together with other H⁺ transporters, and carbonic anhydrases (CAII, CAIX), which hydrate CO₂ from oxidative metabolism to form H⁺ and bicarbonate; (g) these proton export mechanisms, in concert with poor vascular drainage, being responsible for extracellular acidification, driving malignant progression and resistance to conventional therapies; (h) maintenance of the cellular redox homeostasis and low reactive oxygen species (ROS) formation; and (i) HIF-1 overexpression, mutant p53 and mutant PTEN, which inhibit mitochondrial biogenesis and functions, negatively impacting cellular respiration rate. The glycolytic switch is an early event in oncogenesis and primarily supports cell survival. All in all, the Warburg effect, i.e. aerobic glycolysis in the presence of oxygen and - in principle - functioning mitochondria, constitutes a major driver of the cancer progression machinery, resistance to conventional therapies, and poor patient outcome. However, as evidenced during the last two decades, in a minority of tumours primary mitochondrial defects can play a key role promoting the Warburg effect and tumour progression due to mutations in some Krebs cycle enzymes and mitochondrial ROS overproduction.