Oxidative phosphorylation is impaired by prolonged hypoxia in breast and possibly in cervix carcinoma

Characterizing heterogeneity along EMT and metabolic axes in colorectal cancer reveals underlying consensus molecular subtype-specific trends

Colorectal cancer (CRC) is highly heterogeneous with variable survival outcomes and therapeutic vulnerabilities. A commonly used classification system in CRC is the Consensus Molecular Subtypes (CMS) based on gene expression patterns. However, how these CMS categories connect to axes of phenotypic plasticity and heterogeneity remains unclear. Here, in our analysis of CMS-specific TCGA data and 101 bulk transcriptomic datasets, we found the epithelial phenotype score to be consistently positively correlated with scores of glycolysis, OXPHOS and FAO pathways, while PD-L1 activity scores positively correlated with mesenchymal phenotype scoring, revealing possible interconnections among plasticity axes. Single-cell RNA-sequencing analysis of patient samples revealed that that CMS2 and CMS3 subtype samples were relatively more epithelial as compared to CMS1 and CMS4. CMS1 revealed two subpopulations: one close to CMS4 (more mesenchymal) and the other closer to CMS2 or CMS3 (more epithelial), indicating a partial EMT-like behavior. Consistent observations were made in single-cell analysis of metabolic axes and PD-L1 activity scores. Together, our results quantify the patterns of two functional interconnected axes of phenotypic heterogeneity - EMT and metabolic reprogramming - in a CMS-specific manner in CRC.

Oxygen and Iron Availability Shapes Metabolic Adaptations of Cancer Cells

The dynamic changes between glycolysis and oxidative phosphorylation (OXPHOS) for adenosine triphosphate (ATP) output, along with glucose, glutamine, and fatty acid utilization, etc., lead to the maintenance and selection of growth advantageous to tumor cell subgroups in an environment of iron starvation and hypoxia. Iron plays an important role in the three major biochemical reactions in nature: photosynthesis, nitrogen fixation, and oxidative respiration, which all require the participation of iron-sulfur proteins, such as ferredoxin, cytochrome b, and the complex I, II, III in the electron transport chain, respectively. Abnormal iron-sulfur cluster synthesis process or hypoxia will directly affect the function of mitochondrial electron transfer and mitochondrial OXPHOS. More research results have indicated that iron metabolism, oxygen availability and hypoxia-inducible factor mutually regulate the shift between glycolysis and OXPHOS. In this article, we make a perspective review to provide novel opinions of the regulation of glycolysis and OXPHOS in tumor cells.

Mitochondrial Proteins as Metabolic Biomarkers and Sites for Therapeutic Intervention in Primary and Metastatic Cancers

Accelerated aerobic glycolysis is one of the main metabolic alterations in cancer, associated with malignancy and tumor growth. Although glycolysis is one of the most studied properties of tumor cells, recent studies demonstrate that oxidative phosphorylation (OxPhos) is the main ATP provider for the growth and development of cancer. In this last regard, the levels of mRNA and protein of OxPhos enzymes and transporters (including glutaminolysis, acetate and ketone bodies catabolism, free fatty acid β-oxidation, Krebs Cycle, respiratory chain, phosphorylating system- ATP synthase, ATP/ADP translocator, Pi carrier) are altered in tumors and cancer cells in comparison to healthy tissues and organs, and non-cancer cells. Both energy metabolism pathways are tightly regulated by transcriptional factors, oncogenes, and tumor-suppressor genes, all of which dictate their protein levels depending on the micro-environmental conditions and the type of cancer cell, favoring cancer cell adaptation and growth. In the present review paper, variation in the mRNA and protein levels as well as in the enzyme/ transporter activities of the OxPhos machinery is analyzed. An integral omics approach to mitochondrial energy metabolism pathways may allow for identifying their use as suitable, reliable biomarkers for early detection of cancer development and metastasis, and for envisioned novel, alternative therapies.

Targeting Glucose Metabolism in Cancer Cells as an Approach to Overcoming Drug Resistance

The "Warburg effect" consists of a metabolic shift in energy production from oxidative phosphorylation to glycolysis. The continuous activation of glycolysis in cancer cells causes rapid energy production and an increase in lactate, leading to the acidification of the tumour microenvironment, chemo- and radioresistance, as well as poor patient survival. Nevertheless, the mitochondrial metabolism can be also involved in aggressive cancer characteristics. The metabolic differences between cancer and normal tissues can be considered the Achilles heel of cancer, offering a strategy for new therapies. One of the main causes of treatment resistance consists of the increased expression of efflux pumps, and multidrug resistance (MDR) proteins, which are able to export chemotherapeutics out of the cell. Cells expressing MDR proteins require ATP to mediate the efflux of their drug substrates. Thus, inhibition of the main energy-producing pathways in cancer cells, not only induces cancer cell death per se, but also overcomes multidrug resistance. Given that most anticancer drugs do not have the ability to distinguish normal cells from cancer cells, a number of drug delivery systems have been developed. These nanodrug delivery systems provide flexible and effective methods to overcome MDR by facilitating cellular uptake, increasing drug accumulation, reducing drug efflux, improving targeted drug delivery, co-administering synergistic agents, and increasing the half-life of drugs in circulation.

Integration with Transcriptomic and Metabolomic Analyses Reveals the In Vitro Cytotoxic Mechanisms of Chinese Poplar Propolis by Triggering the Glucose Metabolism in Human Hepatocellular Carcinoma Cells

Natural products serve as a valuable reservoir of anticancer agents. Chinese poplar propolis (CP) has exhibited remarkable antitumor activities, yet its precise mechanisms of action remain elusive. This study aims to elucidate the in vitro cytotoxic mechanisms of CP in human hepatocellular carcinoma cells (HepG2) through comprehensive transcriptomic and metabolomic analyses. Our evidence suggested that CP possesses a great potential to inhibit the proliferation of HepG2 cells by targeting the glucose metabolism. Notably, CP exhibited a dose- and time-dependent reduction in the viability of HepG2 cells. Transcriptome sequencing unveiled significant alterations in the cellular metabolism, particularly within glucose metabolism pathways. CP effectively restrained glucose consumption and lactic acid production. Moreover, the CP treatment led to a substantial decrease in the mRNA expression levels of key glucose transporters (GLUT1 and GLUT3) and glycolytic enzymes (LDHA, HK2, PKM2, and PFK). Correspondingly, CP suppressed some key protein levels. Cellular metabolomic analysis demonstrated a marked reduction in intermediary products of glucose metabolism, specifically fructose 1,6-bisphosphate and acetyl-CoA, following CP administration. Finally, key compounds in CP were screened, and apigenin, pinobanksin, pinocembrin, and galangin were identified as potential active agents against glycolysis. It indicates that the effectiveness of propolis in inhibiting liver cancer is the result of the combined action of several components. These findings underscore the potential therapeutic value of propolis in the treatment of liver cancer by targeting glycolytic pathways.

Effect of differential deprivation of nutrients on cellular proliferation, oxidative stress, mitochondrial function, and cell migration in MDA-MB-231, HepG2, and HeLa cells

Cancerous cells display metabolic engineering through enhanced utilization of nutrients to support their increased requirements for proliferation, bioenergetics, biosynthesis, redox homeostasis, and cell signaling. To investigate the extent to which malignant cells rely on glycolysis and glutaminolysis, the effects of differential deprivation of nutrients such as d-glucose, l-glutamine, and pyruvate on proliferation, morphology, cell cycle, oxidative stress, mitochondrial function, autophagic vacuole formation, and migration in MDA-MB-231, HepG2, and HeLa cells were investigated in this study. Cell viability assay,  cell morphology, and ATP assay showed higher dependence of MDA-MB-231 and HepG2 cells on glucose and glutamine, respectively, for cell survival, growth, ATP production, and proliferation, while HeLa cells were equally dependent on both. However, the combination of all three nutrients displayed maximum proliferation. Differential deprivation of glucose in the absence of glutamine resulted in G0/G1 plus G2/M arrest in MDA-MB-231, whereas G0/G1 arrest in HepG2 and S-phase arrest in HeLa cells occurred at 48 h. Although the differential withdrawal of nutrients revealed a varying degree of effect dependent on cell type, nutrient type, nutrient concentrations, and deprivation time, a general trend of increased oxidative stress, loss of mitochondrial membrane potential, and ATP and antioxidant (GSH) depletion led to mitochondrial dysfunction in all three cell lines and inhibition of cell migration in MDA-MB-231 and HeLa cells at 48 h. Extreme deprivation of nutrients formed autophagic vacuoles. Importantly, normal cells (HEK293) remained unaffected under most of the nutrient-deprived conditions examined. This study enhances our understanding of the impact of differential nutrient deprivation on critical characteristics of cancer cells, contributing to the development of metabolism-based effective anticancer strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03759-w.

Mutations in Structural Genes of the Mitochondrial Complex IV May Influence Breast Cancer

Although it has gained more attention in recent years, the relationship between breast cancer (BC) and mitochondrial oxidative phosphorylation (OXPHOS) is still not well understood. Importantly, Complex IV or Cytochrome C Oxidase (COX) of OXPHOS is one of the key players in mitochondrial balance. An in silico investigation of mutations in structural genes of Complex IV was conducted in BC, comprising 2107 samples. Our findings show four variants (rs267606614, rs753969142, rs199476128 and rs267606884) with significant pathogenic potential. Moreover, we highlight nine genes (MT-CO1, MT-CO2, MT-CO3, CO4I2, COX5A, COX5B, COX6A2, COX6C and COX7B2) with a potential impact on BC.

Fluorescence microscopy imaging of mitochondrial metabolism in cancer cells

Mitochondrial metabolism is an important contributor to cancer cell survival and proliferation that coexists with enhanced glycolytic activity. Measuring mitochondrial activity is useful to characterize cancer metabolism patterns, to identify metabolic vulnerabilities and to identify new drug targets. Optical imaging, especially fluorescent microscopy, is one of the most valuable tools for studying mitochondrial bioenergetics because it provides semiquantitative and quantitative readouts as well as spatiotemporal resolution of mitochondrial metabolism. This review aims to acquaint the reader with microscopy imaging techniques currently used to determine mitochondrial membrane potential (ΔΨm), nicotinamide adenine dinucleotide (NADH), ATP and reactive oxygen species (ROS) that are major readouts of mitochondrial metabolism. We describe features, advantages, and limitations of the most used fluorescence imaging modalities: widefield, confocal and multiphoton microscopy, and fluorescent lifetime imaging (FLIM). We also discus relevant aspects of image processing. We briefly describe the role and production of NADH, NADHP, flavins and various ROS including superoxide and hydrogen peroxide and discuss how these parameters can be analyzed by fluorescent microscopy. We also explain the importance, value, and limitations of label-free autofluorescence imaging of NAD(P)H and FAD. Practical hints for the use of fluorescent probes and newly developed sensors for imaging ΔΨm, ATP and ROS are described. Overall, we provide updated information about the use of microscopy to study cancer metabolism that will be of interest to all investigators regardless of their level of expertise in the field.

Single-cell transcriptomics of human-skin-equivalent organoids

Several methods for generating human-skin-equivalent (HSE) organoid cultures are in use to study skin biology; however, few studies thoroughly characterize these systems. To fill this gap, we use single-cell transcriptomics to compare in vitro HSEs, xenograft HSEs, and in vivo epidermis. By combining differential gene expression, pseudotime analyses, and spatial localization, we reconstruct HSE keratinocyte differentiation trajectories that recapitulate known in vivo epidermal differentiation pathways and show that HSEs contain major in vivo cellular states. However, HSEs also develop unique keratinocyte states, an expanded basal stem cell program, and disrupted terminal differentiation. Cell-cell communication modeling shows aberrant epithelial-to-mesenchymal transition (EMT)-associated signaling pathways that alter upon epidermal growth factor (EGF) supplementation. Last, xenograft HSEs at early time points post transplantation significantly rescue many in vitro deficits while undergoing a hypoxic response that drives an alternative differentiation lineage. This study highlights the strengths and limitations of organoid cultures and identifies areas for potential innovation.

Estimation of energy pathway fluxes in cancer cells - Beyond the Warburg effect

Glycolytic and respiratory fluxes were analyzed in cancer and non-cancer cells. The steady-state fluxes in energy metabolism were used to estimate the contributions of aerobic glycolytic and oxidative phosphorylation (OxPhos) pathways to the cellular ATP supply. The rate of lactate production - corrected for the fraction generated by glutaminolysis - is proposed as the appropriate way to estimate glycolytic flux. In general, the glycolytic rates estimated for cancer cells are higher than those found in non-cancer cells, as originally observed by Otto Warburg. The rate of basal or endogenous cellular O₂ consumption corrected for non-ATP synthesizing O₂ consumption, measured after inhibition by oligomycin (a specific, potent and permeable ATP synthase inhibitor), has been proposed as the appropriate way to estimate mitochondrial ATP synthesis-linked O₂ flux or net OxPhos flux in living cells. Detecting non-negligible oligomycin-sensitive O₂ consumption rates in cancer cells has revealed that the mitochondrial function is not impaired, as claimed by the Warburg effect. Furthermore, when calculating the relative contributions to cellular ATP supply, under a variety of environmental conditions and for different types of cancer cells, it was found that OxPhos pathway was the main ATP provider over glycolysis. Hence, OxPhos pathway targeting can be successfully used to block in cancer cells ATP-dependent processes such as migration. These observations may guide the re-design of novel targeted therapies.

Milk yield variation partially attributed to blood oxygen-mediated neutrophil activation in lactating dairy goats

Blood oxygen is an essential component for numerous biological processes of mammalian animals. Milk production of ruminants largely relies on the supply of nutrients, such as glucose, amino acids and fatty acids. To define the regulatory role of blood oxygen availability in regard to milk production, seventy-five healthy Guanzhong dairy goats with similar body weight, days in milk and parities were selected. For each animal, milk yield was recorded and milk sample was collected to determine compositions. Milk vein blood was collected to determine parameters including blood gas, physio-biochemistry and haematology. Another blood sample was prepared for transcriptome and RT-qPCR. Results showed that both pressure of oxygen (pO₂) in the milk vein (positively) and numbers of neutrophils in mammary vein (negatively) were associated with milk yield of the animals. To learn the role of pO₂ in blood cell functionality, twelve animals (six with higher yield (H-group) and six with lower yield (L-group)) from seventy-five goats were selected. Compared with animals in L-group, goats in H-group were higher in pO₂ but lower in pCO₂, lactate, lactate dehydrogenase activity and neutrophil abundance in milk vein, compared with L-group. The blood transcriptome analysis suggested that compared with L-group, animals in H-group were depressed in functionality including neutrophil activation and metabolic pathways including glycolysis, NF-κB and HIF-1. Our result revealed that lower milk production could be associated with neutrophil activation responding to low pO₂ in the mammary vein. In the meantime, we highlighted the potential importance of blood oxygen as a milk yield regulator.

Recent advances in understanding the metabolic plasticity of ovarian cancer: A systematic review

Epithelial ovarian cancer (EOC) is a gynecologic malignancy with a poor prognosis due to resistance to first-line chemotherapeutic agents. Some cancer cells are primarily dependent on glycolysis, but others favor mitochondrial oxidative phosphorylation (OXPHOS) over glycolysis. Changes in metabolic reprogramming have been reported to be involved in cancer cell survival. In this review, we summarize the metabolic profiles (e.g., metabolic heterogeneity, plasticity, and reprogramming) and adaptation to the dynamic tumor microenvironment and discuss potential novel therapeutic strategies. A literature search was performed between January 2000 and March 2022 in the PubMed and Google Scholar databases using a combination of specific terms. Ovarian cancer cells, including cancer stem cells, depend on glycolysis, OXPHOS, or both for survival. Several environmental stresses, such as nutrient starvation or glucose deprivation, hypoxic stress, acidification, and excessive reactive oxygen species (ROS) generation, reprogram the metabolic pathways to adapt. The interaction between tumors and adjacent stromal cells allows cancer cells to enhance mitochondrial energy metabolism. The metabolic reprogramming varies depending on genomic and epigenetic alterations of metabolism-related genes and the metabolic environment. Developing accurate and non-invasive methods for early identification of metabolic alterations could facilitate optimal cancer diagnosis and treatment. Cancer metabolism research has entered an exciting era where novel strategies targeting metabolic profiling will become more innovative.

Tumor glycolysis, an essential sweet tooth of tumor cells

Cancer cells undergo metabolic alterations to meet the immense demand for energy, building blocks, and redox potential. Tumors show glucose-avid and lactate-secreting behavior even in the presence of oxygen, a process known as aerobic glycolysis. Glycolysis is the backbone of cancer cell metabolism, and cancer cells have evolved various mechanisms to enhance it. Glucose metabolism is intertwined with other metabolic pathways, making cancer metabolism diverse and heterogeneous, where glycolysis plays a central role. Oncogenic signaling accelerates the metabolic activities of glycolytic enzymes, mainly by enhancing their expression or by post-translational modifications. Aerobic glycolysis ferments glucose into lactate which supports tumor growth and metastasis by various mechanisms. Herein, we focused on tumor glycolysis, especially its interactions with the pentose phosphate pathway, glutamine metabolism, one-carbon metabolism, and mitochondrial oxidation. Further, we describe the role and regulation of key glycolytic enzymes in cancer. We summarize the role of lactate, an end product of glycolysis, in tumor growth, and the metabolic adaptations during metastasis. Lastly, we briefly discuss limitations and future directions to improve our understanding of glucose metabolism in cancer.

Upregulation of Succinate Dehydrogenase (SDHA) Contributes to Enhanced Bioenergetics of Ovarian Cancer Cells and Higher Sensitivity to Anti-Metabolic Agent Shikonin

We discovered that the overexpression of mitochondrial enzyme succinate dehydrogenase (SDHA) is particularly prevalent in ovarian carcinoma and promotes highly metabolically active phenotype. Succinate dehydrogenase deficiency has been previously studied in some rare disorders. However, the role of SDHA upregulation and its impact on ovarian cancer metabolism has never been investigated, emphasizing the need for further research. We investigated the functional consequences of SDHA overexpression in ovarian cancer. Using proteomics approaches and biological assays, we interrogated protein content of metabolic pathways, cell proliferation, anchorage-independent growth, mitochondrial respiration, glycolytic function, and ATP production rates in those cells. Lastly, we performed a drug screening to identify agents specifically targeting the SDHA overexpressing tumor cells. We showed that SDHA overexpressing cells are characterized by enhanced energy metabolism, relying on both glycolysis and oxidative phosphorylation to meet their energy needs. In addition, SDHA-high phenotype was associated with cell vulnerability to glucose and glutamine deprivation, which led to a substantial reduction of ATP yield. We also identified an anti-metabolic compound shikonin with a potent efficacy against SDHA overexpressing ovarian cancer cells. Our data underline the unappreciated role of SDHA in reprogramming of ovarian cancer metabolism, which represents a new opportunity for therapeutic intervention.

Heterogeneity in NK Cell Subpopulations May Be Involved in Kidney Cancer Metastasis

Although substantial progress has been made in the immunotherapy of kidney cancer, its efficacy varies from patient to patient, with many responding suboptimally or even developing metastases. Thus, research on the tumour immune microenvironment and immune cell heterogeneity is essential for kidney cancer treatment. In this study, natural killer (NK) cell populations were isolated using signature genes from the single-cell sequencing data of clear cell renal cell carcinoma (ccRCC) and normal kidney tissues and divided into three subpopulations according to the differences in gene expression profiles: NK(GZMH), NK(EGR1), and NK(CAPG). Gene set enrichment analysis revealed that NK(EGR1) and NK(CAPG) were closely related to tumour metastasis, as shown by kidney cancer metastasis to Hodgkin lymphoma, T-cell leukaemia, and Ki-1+ anaplastic large cell lymphoma. Thus, these two NK cell subpopulations are promising targets for inhibiting metastasis in ccRCC. Our findings revealed heterogeneity in the infiltrating NK cells of kidney cancer, which can serve as a reference for the mechanisms underlying metastasis in kidney cancer.

The Interplay of Hypoxia Signaling on Mitochondrial Dysfunction and Inflammation in Cardiovascular Diseases and Cancer: From Molecular Mechanisms to Therapeutic Approaches

Simple Summary

The regulation of hypoxia has recently emerged as having a central impact in mitochondrial function and dysfunction in various diseases, including the major disorders threatening worldwide: cardiovascular diseases and cancer. Despite the studies in this matter, its effective role in protection and disease progression even though its direct molecular mechanism in both disorders is still to be elucidated. This review aims to cover the current knowledge about the effect of hypoxia on mitochondrial function and dysfunction, and inflammation, in cardiovascular diseases and cancer, and reports further therapeutic strategies based on the modulation of hypoxic pathways.

Abstract

Cardiovascular diseases (CVDs) and cancer continue to be the primary cause of mortality worldwide and their pathomechanisms are a complex and multifactorial process. Insufficient oxygen availability (hypoxia) plays critical roles in the pathogenesis of both CVDs and cancer diseases, and hypoxia-inducible factor 1 (HIF-1), the main sensor of hypoxia, acts as a central regulator of multiple target genes in the human body. Accumulating evidence demonstrates that mitochondria are the major target of hypoxic injury, the most common source of reactive oxygen species during hypoxia and key elements for inflammation regulation during the development of both CVDs and cancer. Taken together, observations propose that hypoxia, mitochondrial abnormality, oxidative stress, inflammation in CVDs, and cancer are closely linked. Based upon these facts, this review aims to deeply discuss these intimate relationships and to summarize current significant findings corroborating the molecular mechanisms and potential therapies involved in hypoxia and mitochondrial dysfunction in CVDs and cancer.

Targeting the metabolism of cancer stem cells by energy disruptor molecules

Cancer stem cells (CSCs) have been identified in various tumor types. CSCs are believed to contribute to tumor metastasis and resistance to conventional therapy. So targeting these cells could be an effective strategy to eliminate tumors and a promising new type of cancer treatment. Alterations in metabolism play an essential role in CSC biology and their resistance to treatment. The metabolic properties pathways in CSCs are different from normal cells, and to some extent, are different from regular tumor cells. Interestingly, CSCs can use other nutrients for their metabolism and growth. The different metabolism causes increased sensitivity of CSCs to agents that disrupt cellular homeostasis. Compounds that interfere with the central metabolic pathways are known as energy disruptors and can reduce CSC survival. This review highlights the differences between regular cancer cells and CSC metabolism and discusses the action mechanisms of energy disruptors at the cellular and molecular levels.

Conditions for maintenance of hepatocyte differentiation and function in 3D cultures

Spheroid cultures of primary human hepatocytes (PHH) are used in studies of hepatic drug metabolism and toxicity. The cultures are maintained under different conditions, with possible confounding results. We performed an in-depth analysis of the influence of various culture conditions to find the optimal conditions for the maintenance of an in vivo like phenotype. The formation, protein expression, and function of PHH spheroids were followed for three weeks in a high-throughput 384-well format. Medium composition affected spheroid histology, global proteome profile, drug metabolism and drug-induced toxicity. No epithelial-mesenchymal transition was observed. Media with fasting glucose and insulin levels gave spheroids with phenotypes closest to normal PHH. The most expensive medium resulted in PHH features most divergent from that of native PHH. Our results provide a protocol for culture of healthy PHH with maintained function - a prerequisite for studies of hepatocyte homeostasis and more reproducible hepatocyte research.

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3D spheroid cultures were established in 384-well format

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Eight different media variants were used to optimize the 3D cultures

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Optimized William's medium was as good as expensive commercial medium

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The 3D cultures were used to study drug metabolism and toxicity

Interplay between Mitochondrial Metabolism and Cellular Redox State Dictates Cancer Cell Survival

Mitochondria are the main powerhouse of the cell, generating ATP through the tricarboxylic acid cycle (TCA) and oxidative phosphorylation (OXPHOS), which drives myriad cellular processes. In addition to their role in maintaining bioenergetic homeostasis, changes in mitochondrial metabolism, permeability, and morphology are critical in cell fate decisions and determination. Notably, mitochondrial respiration coupled with the passage of electrons through the electron transport chain (ETC) set up a potential source of reactive oxygen species (ROS). While low to moderate increase in intracellular ROS serves as secondary messenger, an overwhelming increase as a result of either increased production and/or deficient antioxidant defenses is detrimental to biomolecules, cells, and tissues. Since ROS and mitochondria both regulate cell fate, attention has been drawn to their involvement in the various processes of carcinogenesis. To that end, the link between a prooxidant milieu and cell survival and proliferation as well as a switch to mitochondrial OXPHOS associated with recalcitrant cancers provide testimony for the remarkable metabolic plasticity as an important hallmark of cancers. In this review, the regulation of cell redox status by mitochondrial metabolism and its implications for cancer cell fate will be discussed followed by the significance of mitochondria-targeted therapies for cancer.

Steroid receptor RNA activator gene footprint in the progression and drug resistance of colorectal cancer through oxidative phosphorylation pathway

BACKGROUND

The steroid receptor RNA activator 1 (SRA1) gene is involved in the progression of various cancers via different molecular mechanisms mediated by long non-coding RNA SRA (lncRNA SRA). This study aimed to evaluate the lncRNA SRA effect on the tumor progression of colorectal cancer (CRC).

METHODS

SRA1 expression was assessed in the cancer genome atlas datasets, CRC cell lines, and tumor specimens. Meta-analysis and gene co-expression network analysis were performed to identify pathways related to SRA1. RNA interference and cell treatment were utilized to examine the role of SRA1 expression in HT-29 and Caco-2 cell lines. Also, the effect of SRA1 expression was investigated on drug resistance, clinical parameters, and mutations in CRC samples.

RESULTS

The SRA1 transcripts, especially lncRNA SRA, were dysregulated in CRC tissue samples compared with normal tissue samples. Furthermore, SRA1 depletion decreased colony formation and proliferation while induced apoptosis in HT-29 and Caco-2 cells. In silico analyses indicated that SRA1 level was correlated with expression levels of oxidative phosphorylation (OXPHOS) genes. LncRNA SRA expression increased in response to the increased oxidative capacity, and when lncRNA SRA was knocked down, the expression level of OXPHOS pathway genes, including NDUFB5 and ATP5F1B, was changed. Also, KRAS-mutant samples had the highest SRA1 expression level.

CONCLUSIONS

LncRNA SRA could function as an oncogene through the OXPHOS pathway in CRC, and serve as a potential biomarker for identifying CRC subtype with KRAS mutations. The findings suggest that lncRNA SRA might be a therapeutic target to inhibit cell proliferation in CRC.

VDAC Modulation of Cancer Metabolism: Advances and Therapeutic Challenges

Most anionic metabolites including respiratory substrates, glycolytic adenosine triphosphate (ATP), and small cations that enter mitochondria, and mitochondrial ATP moving to the cytosol, cross the outer mitochondrial membrane (OMM) through voltage dependent anion channels (VDAC). The closed states of VDAC block the passage of anionic metabolites, and increase the flux of small cations, including calcium. Consequently, physiological or pharmacological regulation of VDAC opening, by conditioning the magnitude of both anion and cation fluxes, is a major contributor to mitochondrial metabolism. Tumor cells display a pro-proliferative Warburg phenotype characterized by enhanced aerobic glycolysis in the presence of partial suppression of mitochondrial metabolism. The heterogeneous and flexible metabolic traits of most human tumors render cells able to adapt to the constantly changing energetic and biosynthetic demands by switching between predominantly glycolytic or oxidative phenotypes. Here, we describe the biological consequences of changes in the conformational state of VDAC for cancer metabolism, the mechanisms by which VDAC-openers promote cancer cell death, and the advantages of VDAC opening as a valuable pharmacological target. Particular emphasis is given to the endogenous regulation of VDAC by free tubulin and the effects of VDAC-tubulin antagonists in cancer cells. Because of its function and location, VDAC operates as a switch to turn-off mitochondrial metabolism (closed state) and increase aerobic glycolysis (pro-Warburg), or to turn-on mitochondrial metabolism (open state) and decrease glycolysis (anti-Warburg). A better understanding of the role of VDAC regulation in tumor progression is relevant both for cancer biology and for developing novel cancer chemotherapies.

Celecoxib and dimethylcelecoxib block oxidative phosphorylation, epithelial-mesenchymal transition and invasiveness in breast cancer stem cells

BACKGROUND

Drug resistance and invasiveness developed by breast cancer stem cells (BCSC) are considered the major hurdles for successful cancer treatment. <P> Objective: As these two processes are highly energy-dependent, the identification of the main ATP supplier required for stem cell viability may result advantageous in the design of new therapeutic strategies to deter malignant carcinomas. <P> Methods: The energy metabolism (glycolysis and oxidative phosphorylation, OxPhos) was systematically analyzed by assessing relevant protein contents, enzyme activities and pathway fluxes in BCSC. Once identified the main ATP supplier, selective energy inhibitors and canonical breast cancer drugs were used to block stem cell viability and their metastatic properties. <P> Results: OxPhos and glycolytic protein contents, as well as HK and LDH activities were several times higher in BCSC than in their parental line, MCF-7 cells. However, CS, GDH, COX activities and both energy metabolism pathway fluxes were significantly lower (38-86%) in BCSC than in MCF-7 cells. OxPhos was the main ATP provider (>85%) in BCSC. Accordingly, oligomycin (a specific and potent canonical OxPhos inhibitor) and other non-canonical drugs with inhibitory effect on OxPhos (celecoxib, dimethylcelecoxib) significantly decreased BCSC viability, levels of epithelial-mesenchymal transition proteins, invasiveness, and induced ROS over-production, with IC50 values ranging from 1 to 20 µM in 24 h treatment. In contrast, glycolytic inhibitors (gossypol, iodoacetic acid, 3-bromopyruvate, 2-deoxyglucose) and canonical chemotherapeutic drugs (paclitaxel, doxorubicin, cisplatin) were much less effective against BCSC viability (IC50> 100 µM). <P> Conclusion: These results indicated that the use of some NSAIDs may be a promising alternative therapeutic strategy to target BCSC.

Bedaquiline, an FDA-approved drug, inhibits mitochondrial ATP production and metastasis in vivo, by targeting the gamma subunit (ATP5F1C) of the ATP synthase

Here, we provide evidence that high ATP production by the mitochondrial ATP-synthase is a new therapeutic target for anticancer therapy, especially for preventing tumor progression. More specifically, we isolated a subpopulation of ATP-high cancer cells which are phenotypically aggressive and demonstrate increases in proliferation, stemness, anchorage-independence, cell migration, invasion and multi-drug resistance, as well as high antioxidant capacity. Clinically, these findings have important implications for understanding treatment failure and cancer cell dormancy. Using bioinformatic analysis of patient samples, we defined a mitochondrial-related gene signature for metastasis, which features the gamma-subunit of the mitochondrial ATP-synthase (ATP5F1C). The relationship between ATP5F1C protein expression and metastasis was indeed confirmed by immunohistochemistry. Next, we used MDA-MB-231 cells as a model system to functionally validate these findings. Importantly, ATP-high MDA-MB-231 cells showed a nearly fivefold increase in metastatic capacity in vivo. Consistent with these observations, ATP-high cells overexpressed (i) components of mitochondrial complexes I-V, including ATP5F1C, and (ii) markers associated with circulating tumor cells (CTCs) and metastasis, such as EpCAM and VCAM1. Knockdown of ATP5F1C expression significantly reduced ATP-production, anchorage-independent growth, and cell migration, as predicted. Similarly, therapeutic administration of the FDA-approved drug, Bedaquiline, downregulated ATP5F1C expression in vitro and prevented spontaneous metastasis in vivo. In contrast, Bedaquiline had no effect on the growth of non-tumorigenic mammary epithelial cells (MCF10A) or primary tumors in vivo. Taken together, our results suggest that mitochondrial ATP depletion is a new therapeutic strategy for metastasis prophylaxis, to avoid treatment failure. In summary, we conclude that mitochondrial ATP5F1C is a promising new biomarker and molecular target for future drug development, for the prevention of metastatic disease progression.

Metabolic Reprogramming of Colorectal Cancer Cells and the Microenvironment: Implication for Therapy

Colorectal carcinoma (CRC) is one of the most frequently diagnosed carcinomas and one of the leading causes of cancer-related death worldwide. Metabolic reprogramming, a hallmark of cancer, is closely related to the initiation and progression of carcinomas, including CRC. Accumulating evidence shows that activation of oncogenic pathways and loss of tumor suppressor genes regulate the metabolic reprogramming that is mainly involved in glycolysis, glutaminolysis, one-carbon metabolism and lipid metabolism. The abnormal metabolic program provides tumor cells with abundant energy, nutrients and redox requirements to support their malignant growth and metastasis, which is accompanied by impaired metabolic flexibility in the tumor microenvironment (TME) and dysbiosis of the gut microbiota. The metabolic crosstalk between the tumor cells, the components of the TME and the intestinal microbiota further facilitates CRC cell proliferation, invasion and metastasis and leads to therapy resistance. Hence, to target the dysregulated tumor metabolism, the TME and the gut microbiota, novel preventive and therapeutic applications are required. In this review, the dysregulation of metabolic programs, molecular pathways, the TME and the intestinal microbiota in CRC is addressed. Possible therapeutic strategies, including metabolic inhibition and immune therapy in CRC, as well as modulation of the aberrant intestinal microbiota, are discussed.

Regulatory Mechanisms and Functional Roles of Hypoxia-Induced Long Non-Coding RNA MTORT1 in Breast Cancer Cells

Long non-coding RNAs (lncRNAs) have been found to participate in multiple genetic pathways in cancer. Also, mitochondria-associated lncRNAs have been discovered to modulate mitochondrial function and metabolism. Previously, we identified oxygen-responsive lncRNAs in MCF-7 breast cancer cells under different oxygen concentrations. Among them, a novel mitochondria-encoded lncRNA, mitochondrial oxygen-responsive transcript 1 (MTORT1), was chosen for further investigation. Nuclear, cytoplasmic, and mitochondrial fractionation assays were performed to evaluate the endogenous expression levels of MTORT1 in breast cancer cells. In vitro proliferation and migration assays were conducted to investigate the functions of MTORT1 in breast cancer cells by knockdown of MTORT1. RNA immunoprecipitation and luciferase reporter assays were used to examine the physical binding between MTORT1 and microRNAs. Our results showed that MTORT1 had low endogenous expression levels in breast cancer cells and was mainly located in the mitochondria. Knockdown of MTORT1 enhanced cell proliferation and migration, implying a tumor suppressor role of this novel mitochondrial lncRNA. MTORT1 served as sponge of miR-26a-5p to up-regulate its target genes, CREB1 and STK4. Our findings shed some light on the characterization, function, and regulatory mechanism of the novel hypoxia-induced mitochondrial lncRNA MTORT1, which functions as a microRNA sponge and may inhibit breast cancer progression. These data suggest that MTORT1 may be a candidate for therapeutic targeting of breast cancer progression.

Design, synthesis and biological evaluation of novel thiazole-derivatives as mitochondrial targeting inhibitors of cancer cells

Mitochondria are pivotal energy production sources for cells to maintain necessary metabolism activities. Targeting dysfunctional mitochondrial features has been a hotspot for mitochondrial-related disease researches. Investigation with cancerous mitochondrial metabolism is a continuing concern within tumor therapy. Herein, we set out to assess the anti-cancer activities of a novel family of TPP-thiazole derivatives based on our earlier research on mitochondrial targeting agents. Specifically, we designed and synthesized a series of TPP-thiazole derivatives and revealed by the MTT assay that most synthesized compounds effectively inhibited three cancer cell lines (HeLa, PC3 and MCF-7). After structure modifications, we explored the SAR relationships and identified the most promising compound R13 (IC₅₀ of 5.52 μM) for further investigation. In the meantime, we performed ATP production assay to assess the selected compounds inhibitory effect on HeLa cells energy production. The results displayed the test compounds significantly restrained ATP production of cancer cells. Overall, we have designed and synthesized a series of compounds which exhibited significant cytotoxicity against cancer cells and effectively inhibited mitochondrial energy production.

Oxygen gradient and tumor heterogeneity: The chronicle of a toxic relationship

The commencement of cancer is attributed to one or a few cells that become rogue and attain the property of immortality. The inception of distinct cancer cell clones during the hyperplastic and dysplastic stages of cancer progression is the utimate consequence of the dysregulated cellular pathways and the proliferative potential itself. Furthermore, a critical factor that adds a layer of complexity to this pre-existent intra-tumoral heterogeneity (ITH) is the foundation of an oxygen gradient, that is established due to the improper architecture of the tumor vasculature. Therefore, as a resultant effect, the poorly oxygenated regions thus formed and characterized as hypoxic, promote the emergence of aggressive and treatment-resistant cancer cell clones. The extraordinary property of the hypoxic cancer cells to exist harmoniously with cancerous and non-cancerous cells in the tumor microenvironment (TME) further increases the intricacies of ITH. Here in this review, the pivotal influence of differential oxygen concentrations in shaping the ITH is thoroughly discussed. We also emphasize on the vitality of the interacting networks that govern the overall fate of oxygen gradient-dependent origin of tumor heterogeneity. Additionally, the implications of less-appreciated reverse Warburg effect, a symbiotic metabolic coupling, and the associated epigenetic regulation of rewiring of cancer metabolism in response to oxygen gradients, have been highlighted as critical influencers of ITH.

Phospholipid-Gold Nanorods Induce Energy Crisis in MCF-7 Cells: Cytotoxicity Evaluation Using LC-MS-Based Metabolomics Approach

Phospholipid-modified gold nanorods (phospholipid-GNRs) have demonstrated drastic cytotoxicity towards MCF-7 breast cancer cells compared to polyethylene glycol-coated GNRs (PEG-GNRs). In this study, the mechanism of cytotoxicity of phospholipid-GNRs towards MCF-7 cells was investigated using mass spectrometry-based global metabolic profiling and compared to PEGylated counterparts. The results showed that when compared to PEG-GNRs, phospholipid-GNRs induced significant and more pronounced impact on the metabolic profile of MCF-7 cells. Phospholipid-GNRs significantly decreased the levels of metabolic intermediates and end-products associated with cellular energy metabolisms resulting in dysfunction in TCA cycle, a reduction in glycolytic activity, and imbalance of the redox state. Additionally, phospholipid-GNRs disrupted several metabolism pathways essential for the normal growth and proliferation of cancer cells including impairment in purine, pyrimidine, and glutathione metabolisms accompanied by lower amino acid pools. On the other hand, the effects of PEG-GNRs were limited to alteration of glycolysis and pyrimidine metabolism. The current work shed light on the importance of metabolomics as a valuable analytical approach to explore the molecular effects of GNRs with different surface chemistry on cancer cell and highlights metabolic targets that might serve as promising treatment strategy in cancer.

Investigation of glucose catabolism in hypoxic Mcf 7 breast cancer culture

Hypoxia plays an important role in tumor phenotype and progression and alters glycolysis, with changes in signaling pathways that develop in response to hypoxia. In this study, the effects of oxygen (normoxia/hypoxia) and of glucose levels on the glucose metabolism was investigated in MCF-7 cancer cells. Under either normoxia or hypoxia conditions, the cells were exposed to glucose at different concentrations (0, 5.5, 15 or 55 mM) for either 3, 6, 12, 24 or 48 h. In all groups, cell viability, levels of key enzymes reflecting glycolytic metabolism in cell lysates, glucose consumed in the medium and extracellular lactate levels and wound closure percentages were determined. In hypoxic cells, intracellular consumption of glucose, and extracellular lactate levels due to increased glucose concentration were observed to be higher (compared to normoxia) and as a result of prolonged exposure to hypoxia, cells were observed to develop resistance to the prolonged exposure to hypoxia. The number of glycolytic enzymes obtained at different levels proved that cells had different potential capacities and changing mechanisms for the metabolic needs of the cell depending on the glucose amount in the medium and time in adapting to the oxygen tension. This study showed that there was an important interaction between hypoxia and glucose metabolism in general, and it was concluded that metabolic processes activated by hypoxia could offer new therapeutic targets.

Glucose Metabolism in Cancer: The Warburg Effect and Beyond

Otto Warburg observed a peculiar phenomenon in 1924, unknowingly laying the foundation for the field of cancer metabolism. While his contemporaries hypothesized that tumor cells derived the energy required for uncontrolled replication from proteolysis and lipolysis, Warburg instead found them to rapidly consume glucose, converting it to lactate even in the presence of oxygen. The significance of this finding, later termed the Warburg effect, went unnoticed by the broader scientific community at that time. The field of cancer metabolism lay dormant for almost a century awaiting advances in molecular biology and genetics, which would later open the doors to new cancer therapies [2, 3].

The oncogenic and clinical implications of lactate induced immunosuppression in the tumour microenvironment

The tumour microenvironment is of critical importance in cancer development and progression and includes the surrounding stromal and immune cells, extracellular matrix, and the milieu of metabolites and signalling molecules in the intercellular space. To support sustained mitotic activity cancer cells must reconfigure their metabolic phenotype. Lactate is the major by-product of such metabolic alterations and consequently, accumulates in the tumour. Lactate actively contributes to immune evasion, a hallmark of cancer, by directly inhibiting immune cell cytotoxicity and proliferation. Furthermore, lactate can recruit and induce immunosuppressive cell types, such as regulatory T cells, tumour-associated macrophages, and myeloid-derived suppressor cells which further suppress anti-tumour immune responses. Given its roles in oncogenesis, measuring intratumoural and systemic lactate levels has shown promise as a both predictive and prognostic biomarker in several cancer types. The efficacies of many anti-cancer therapies are limited by an immunosuppressive TME in which lactate is a major contributor, therefore, targeting lactate metabolism is a priority. Developing inhibitors of key proteins in lactate metabolism such as GLUT1, hexokinase, LDH, MCT and HIF have shown promise in preclinical studies, however there is a corresponding lack of success in human trials so far. This may be explained by a weakness of preclinical models that fail to reproduce the complexities of metabolic interactions in natura. The future of these therapies may be as an adjunct to more conventional treatments.

Signaling pathways essential for triple-negative breast cancer stem-like cells

Since the discovery of breast cancer stem cells (CSCs), a significant effort has been made to identify and characterize these cells. It is a generally believe that CSCs play an important role in cancer initiation, therapy resistance, and progression of triple-negative breast cancer (TNBC), an aggressive breast cancer subtype with poor prognosis. Thus, therapies targeting these cells would be a valuable addition to standard treatments that primarily target more differentiated, rapidly dividing TNBC cells. Although several cell surface and intracellular proteins have been described as biomarkers for CSCs, none of these are specific to this population of cells. Recent research is moving toward cellular signaling pathways as targets and biomarkers for CSCs. The WNT pathway, the nuclear factor-kappa B (NF-κB) pathway, and the cholesterol biosynthesis pathway have recently been identified to play a key role in proliferation, survival, and differentiation of CSCs, including those of breast cancer. In this review, we assess recent findings related to these three pathways in breast CSC, with particular focus on TNBC CSCs, and discuss how targeting these pathways, in combination with current standard of care, might prove effective and improve the prognosis of TNBC patients.

Itaconate regulates the glycolysis/pentose phosphate pathway transition to maintain boar sperm linear motility by regulating redox homeostasis

Mammalian cells improve redox homeostasis under reactive oxygen species (ROS) stress conditions via the enhancement of the pentose phosphate pathway (PPP). However, it is not clear how the cell reprograms glucose metabolism from glycolysis to the PPP. Hence, in the present study, we used boar sperm as a model to elucidate the mechanism by which the glycolysis/PPP transition occurs under ROS stress. The boar sperm treated with moderate glucose levels for 3 h exhibited increased sperm linear motility patterns, ATP levels and GSH/GSSG ratios and decreased ROS levels compared to the boar sperm treated without glucose. In addition, the hexokinase activity, glucose-6-phosphate dehydrogenase (G6PD) activity, NADPH level, NADPH/NADP⁺ ratio and mitochondrial activity were higher in the sperm treated with moderate glucose than in those not treated with glucose. Interestingly, the enzyme activity of fructose-1,6-bisphosphate aldolase (ALDOA) was not significantly changed during the incubation. The sperm linear motility patterns were decreased by treatment with the G6PD inhibitor 6-aminonicotinamide. Moreover, moderate glucose treatment significantly increased the itaconate levels in sperm. Both endogenous and exogenous itaconate increased the total itaconate modifications and the itaconate-modified ALDOA levels in sperm, suggesting that under moderate-glucose conditions, glycolysis in the sperm was suppressed by an increase in the itaconate levels. Furthermore, the addition of itaconate improved the sperm linear motility patterns by suppressing glycolysis and enhancing oxidative phosphorylation (OXPHOS). Therefore, the itaconate generated from OXPHOS regulates the glycolysis/PPP transition to maintain redox homeostasis. In sperm, this itaconate-dependent mechanism plays an important role in maintaining their high linear motility.

The molecular mechanisms of celecoxib in tumor development

BACKGROUND

Clinical studies have shown that celecoxib can significantly inhibit the development of tumors, and basic experiments and in vitro experiments also provide a certain basis, but it is not clear how celecoxib inhibits tumor development in detail.

METHODS

A literature search of all major academic databases was conducted (PubMed, China National Knowledge Internet (CNKI), Wan-fang, China Science and Technology Journal Database (VIP), including the main research on the mechanisms of celecoxib on tumors.

RESULTS

Celecoxib can intervene in tumor development and reduce the formation of drug resistance through multiple molecular mechanisms.

CONCLUSION

Celecoxib mainly regulates the proliferation, migration, and invasion of tumor cells by inhibiting the cyclooxygenases-2/prostaglandin E2 signal axis and thereby inhibiting the phosphorylation of nuclear factor-κ-gene binding, Akt, signal transducer and activator of transcription and the expression of matrix metalloproteinase 2 and matrix metalloproteinase 9. Meanwhile, it was found that celecoxib could promote the apoptosis of tumor cells by enhancing mitochondrial oxidation, activating mitochondrial apoptosis process, promoting endoplasmic reticulum stress process, and autophagy. Celecoxib can also reduce the occurrence of drug resistance by increasing the sensitivity of cancer cells to chemotherapy drugs.

Ciclopirox activates PERK-dependent endoplasmic reticulum stress to drive cell death in colorectal cancer

Ciclopirox (CPX) modulates multiple cellular pathways involved in the growth of a variety of tumor cell types. However, the effects of CPX on colorectal cancer (CRC) and the underlying mechanisms for its antitumor activity remain unclear. Herein, we report that CPX exhibited strong antitumorigenic properties in CRC by inducing cell cycle arrest, repressing cell migration, and invasion by affecting N-cadherin, Snail, E-cadherin, MMP-2, and MMP-9 expression, and disruption of cellular bioenergetics contributed to CPX-associated inhibition of cell growth, migration, and invasion. Interestingly, CPX-induced reactive oxygen species (ROS) production and impaired mitochondrial respiration, whereas the capacity of glycolysis was increased. CPX (20 mg/kg, intraperitoneally) substantially inhibited CRC xenograft growth in vivo. Mechanistic studies revealed that the antitumor activity of CPX relies on apoptosis induced by ROS-mediated endoplasmic reticulum (ER) stress in both 5-FU-sensitive and -resistant CRC cells. Our data reveal a novel mechanism for CPX through the disruption of cellular bioenergetics and activating protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent ER stress to drive cell death and overcome drug resistance in CRC, indicating that CPX could potentially be a novel chemotherapeutic for the treatment of CRC.

Physiological Role of Glutamate Dehydrogenase in Cancer Cells

NH 4 + increased growth rates and final densities of several human metastatic cancer cells. To assess whether glutamate dehydrogenase (GDH) in cancer cells may catalyze the reverse reaction of NH 4 + fixation, its covalent regulation and kinetic parameters were determined under near-physiological conditions. Increased total protein and phosphorylation were attained in NH 4 + -supplemented metastatic cells, but total cell GDH activity was unchanged. Higher V _max values for the GDH reverse reaction vs. forward reaction in both isolated hepatoma (HepM) and liver mitochondria [rat liver mitochondria (RLM)] favored an NH 4 + -fixing role. GDH sigmoidal kinetics with NH 4 + , ADP, and leucine fitted to Hill equation showed n _H values of 2 to 3. However, the K _0.5 values for NH 4 + were over 20 mM, questioning the physiological relevance of the GDH reverse reaction, because intracellular NH 4 + in tumors is 1 to 5 mM. In contrast, data fitting to the Monod-Wyman-Changeux (MWC) model revealed lower K _m values for NH 4 + , of 6 to 12 mM. In silico analysis made with MWC equation, and using physiological concentrations of substrates and modulators, predicted GDH N-fixing activity in cancer cells. Therefore, together with its thermodynamic feasibility, GDH may reach rates for its reverse, NH 4 + -fixing reaction that are compatible with an anabolic role for supporting growth of cancer cells.

Cancer cachexia has many symptoms but only one cause: anoxia

During nearly 100 years of research on cancer cachexia (CC), science has been reciting the same mantra: it is a multifactorial syndrome. The aim of this paper is to show that the symptoms are many, but they have a single cause: anoxia. CC is a complex and devastating condition that affects a high proportion of advanced cancer patients. Unfortunately, it cannot be reversed by traditional nutritional support and it generally reduces survival time. It is characterized by significant weight loss, mainly from fat deposits and skeletal muscles. The occurrence of cachexia in cancer patients is usually a late phenomenon. The conundrum is why do similar patients with similar tumors, develop cachexia and others do not? Even if cachexia is mainly a metabolic dysfunction, there are other issues involved such as the activation of inflammatory responses and crosstalk between different cell types.  The exact mechanism leading to a wasting syndrome is not known, however there are some factors that are surely involved, such as anorexia with lower calorie intake, increased glycolytic flux, gluconeogenesis, increased lipolysis and severe tumor hypoxia. Based on this incomplete knowledge we put together a scheme explaining the molecular mechanisms behind cancer cachexia, and surprisingly, there is one cause that explains all of its characteristics: anoxia.  With this different view of CC we propose a treatment based on the physiopathology that leads from anoxia to the symptoms of CC.  The fundamentals of this hypothesis are based on the idea that CC is the result of anoxia causing intracellular lactic acidosis. This is a dangerous situation for cell survival which can be solved by activating energy consuming gluconeogenesis. The process is conducted by the hypoxia inducible factor-1α. This hypothesis was built by putting together pieces of evidence produced by authors working on related topics.

Stem metabolism: Insights from oncometabolism and vice versa

Metabolism, is a transversal hot research topic in different areas, resulting in the integration of cellular needs with external cues, involving a highly coordinated set of activities in which nutrients are converted into building blocks for macromolecules, energy currencies and biomass. Importantly, cells can adjust different metabolic pathways defining its cellular identity. Both cancer cell and embryonic stem cells share the common hallmark of high proliferative ability but while the first represent a huge social-economic burden the second symbolize a huge promise. Importantly, research on both fields points out that stem cells share common metabolic strategies with cancer cells to maintain their identity as well as proliferative capability and, vice versa cancer cells also share common strategies regarding pluripotent markers. Moreover, the Warburg effect can be found in highly proliferative non-cancer stem cells as well as in embryonic stem cells that are primed towards differentiation, while a bivalent metabolism is characteristic of embryonic stem cells that are in a true naïve pluripotent state and cancer stem cells can also range from glycolysis to oxidative phosphorylation. Therefore, this review aims to highlight major metabolic similarities between cancer cells and embryonic stem cells demonstrating that they have similar strategies in both signaling pathways regulation as well as metabolic profiles while focusing on key metabolites.

4-Hydroxychalcone Induces Cell Death via Oxidative Stress in MYCN-Amplified Human Neuroblastoma Cells

Neuroblastoma is an embryonal malignancy that arises from cells of sympathoadrenal lineage during the development of the nervous system. It is the most common pediatric extracranial solid tumor and is responsible for 15% of childhood deaths from cancer. Fifty percent of cases are diagnosed as high-risk metastatic disease with a low overall 5-year survival rate. More than half of patients experience disease recurrence that can be refractory to treatment. Amplification of the MYCN gene is an important prognostic indicator that is associated with rapid disease progression and a poor prognosis, highlighting the need for new therapeutic approaches. In recent years, there has been an increasing focus on identifying anticancer properties of naturally occurring chalcones, which are secondary metabolites with variable phenolic structures. Here, we report that 4-hydroxychalcone is a potent cytotoxin for MYCN-amplified IMR-32 and SK-N-BE (2) neuroblastoma cells, when compared to non-MYCN-amplified SH-SY5Y neuroblastoma cells and to the non-neuroblastoma human embryonic kidney cell line, HEK293t. Moreover, 4-hydroxychalcone treatment significantly decreased cellular levels of the antioxidant glutathione and increased cellular reactive oxygen species. In addition, 4-hydroxychalcone treatment led to impairments in mitochondrial respiratory function, compared to controls. In support of this, the cytotoxic effect of 4-hydroxychalcone was prevented by co-treatment with either the antioxidant N-acetyl-L-cysteine, a pharmacological inhibitor of oxidative stress-induced cell death (IM-54) or the mitochondrial reactive oxygen species scavenger, Mito-TEMPO. When combined with the anticancer drugs cisplatin or doxorubicin, 4-hydroxychalcone led to greater reductions in cell viability than was induced by either anti-cancer agent alone. In summary, this study identifies a cytotoxic effect of 4-hydroxychalcone in MYCN-amplified human neuroblastoma cells, which rationalizes its further study in the development of new therapies for pediatric neuroblastoma.

Protective effects of eicosapentaenoic acid in adipocyte-breast cancer cell cross talk

Breast cancer is the leading cause of death in women among all cancer types. Obesity is one of the factors that promote progression of breast cancer, especially in post-menopausal women. Increasingly, adipose tissue is recognized for its active role in the tumor microenvironment. We hypothesized that adipocytes conditioned medium can impact breast cancer progression by increasing inflammatory cytokines production by cancer cells, and subsequently increasing their motility. By contrast, eicosapentaenoic acid (EPA), an anti-inflammatory n-3 polyunsaturated fatty acid, reduces adipocyte-secreted inflammatory factors, leading to reduced cancer cell motility. To test these hypotheses, we investigated the direct effects of EPA on MCF-7 and MDA-MB-231 breast cancer cells and the effects of conditioned medium from 3 T3-L1 or human mesenchymal stem cells (HMSC)-derived adipocytes treated with or without EPA supplementation on breast cancer cells. We observed that conditioned medium from HMSC-derived adipocytes significantly increased mRNA transcription levels of cancer-associated genes such as FASN, STAT3 and cIAP2, while EPA-treated HMSC-derived adipocytes significantly reduced mRNA levels of these genes. However, direct EPA treatment significantly reduced mRNA content of these tumor-associated markers (FASN, STAT3, cIAP-2) only in MDA-MB-231 cells not in MCF-7 cells. Conditioned medium from EPA-treated 3 T3-L1 adipocytes further decreased inflammation, cell motility and glycolysis in cancer cells. Our data confirms that adipocytes play a significant role in promoting breast cancer progression and demonstrates that EPA-treated adipocytes reduced the negative impact of adipocyte-secreted factors on breast cancer cell inflammation and migration.

Transcriptional Regulation of Energy Metabolism in Cancer Cells

Cancer development, growth, and metastasis are highly regulated by several transcription regulators (TRs), namely transcription factors, oncogenes, tumor-suppressor genes, and protein kinases. Although TR roles in these events have been well characterized, their functions in regulating other important cancer cell processes, such as metabolism, have not been systematically examined. In this review, we describe, analyze, and strive to reconstruct the regulatory networks of several TRs acting in the energy metabolism pathways, glycolysis (and its main branching reactions), and oxidative phosphorylation of nonmetastatic and metastatic cancer cells. Moreover, we propose which possible gene targets might allow these TRs to facilitate the modulation of each energy metabolism pathway, depending on the tumor microenvironment.

Glut 1 in Cancer Cells and the Inhibitory Action of Resveratrol as A Potential Therapeutic Strategy

An important hallmark in cancer cells is the increase in glucose uptake. GLUT1 is an important target in cancer treatment because cancer cells upregulate GLUT1, a membrane protein that facilitates the basal uptake of glucose in most cell types, to ensure the flux of sugar into metabolic pathways. The dysregulation of GLUT1 is associated with numerous disorders, including cancer and metabolic diseases. There are natural products emerging as a source for inhibitors of glucose uptake, and resveratrol is a molecule of natural origin with many properties that acts as antioxidant and antiproliferative in malignant cells. In the present review, we discuss how GLUT1 is involved in the general scheme of cancer cell metabolism, the mechanism of glucose transport, and the importance of GLUT1 structure to understand the inhibition process. Then, we review the current state-of-the-art of resveratrol and other natural products as GLUT1 inhibitors, focusing on those directed at treating different types of cancer. Targeting GLUT1 activity is a promising strategy for the development of drugs aimed at treating neoplastic growth.

Resveratrol inhibits cancer cell proliferation by impairing oxidative phosphorylation and inducing oxidative stress

The resveratrol (RSV) efficacy to affect the proliferation of several cancer cell lines was initially examined. RSV showed higher potency to decrease growth of metastatic HeLa and MDA-MB-231 (IC₅₀ = 200-250 μM) cells than of low metastatic MCF-7, SiHa and A549 (IC₅₀ = 400-500 μM) and non-cancer HUVEC and 3T3 (IC₅₀≥600 μM) cells after 48 h exposure. In order to elucidate the biochemical mechanisms underlying RSV anti-cancer effects, the energy metabolic pathways and the oxidative stress metabolism were analyzed in HeLa cells as metastatic-type cell model. RSV (200 μM/48 h) significantly decreased both glycolysis and oxidative phosphorylation (OxPhos) protein contents (30-90%) and fluxes (40-70%) vs. non-treated cells. RSV (100 μM/1-5 min) also decreased at a greater extent OxPhos flux (net ADP-stimulated respiration) of isolated tumor mitochondria (> 50%) than of non-tumor mitochondria (< 50%), particularly with succinate as oxidizable substrate. In addition, RSV promoted an excessive cellular ROS (2-3 times) production corresponding with a significant decrement in the SOD activity (but not in its content) and GSH levels; whereas the catalase, glutahione reductase, glutathione peroxidase and glutathione-S-transferase activities (but not their contents) remained unchanged. RSV (200 μM/48 h) also induced cellular death although not by apoptosis but rather by promoting a strong mitophagy activation (65%). In conclusion, RSV impaired OxPhos by inducing mitophagy and ROS over-production, which in turn halted metastatic HeLa cancer cell growth.

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.

An Apoptotic and Endosymbiotic Explanation of the Warburg and the Inverse Warburg Hypotheses

Otto Warburg, a Nobel prize winner, observed that cancer cells typically “switch” from aerobic to anaerobic respiration. He hypothesized that mitochondrial damage induces neoplastic transformation. In contrast, pathological aging is observed mainly in neuron cells in neurodegenerative diseases. Oxidative respiration is particularly active in neurons. There is inverse comorbidity between cancer and neurodegenerative diseases. This led to the creation of the “inverse Warburg hypothesis”, according to which excessive mitochondrial activity induces pathological aging. The findings of our studies suggest that both the Warburg effect and the “inverse Warburg hypothesis” can be elucidated by the activation or suppression of apoptosis through oxidative respiration. The key outcome of our phylogenetic studies was the discovery that apoptosis and apoptosis-like cell death evolved due to an evolutionary “arms race” conducted between “prey” protomitochondrion and “predator” primitive eukaryotes. The ancestral protomitochondrial machinery produces and releases toxic mitochondrial proteins. Extant apoptotic factors evolved from these toxins. Our experiments indicate that the mitochondrial machinery is directly involved in adaptation to aerobic conditions. Additionally, our hypothesis is supported by the fact that different apoptotic factors are directly involved in respiration.

Metabolic Targeting of Breast Cancer Cells With the 2-Deoxy-D-Glucose and the Mitochondrial Bioenergetics Inhibitor MDIVI-1

Breast cancer cells have different requirements on metabolic pathways in order to sustain their growth. Triple negative breast cancer (TNBC), an aggressive breast cancer subtype relies mainly on glycolysis, while estrogen receptor positive (ER+) breast cancer cells possess higher mitochondrial oxidative phosphorylation (OXPHOS) levels. However, breast cancer cells generally employ both pathways to sustain their metabolic needs and to compete with the surrounding environment. In this study, we demonstrate that the mitochondrial fission inhibitor MDIVI-1 alters mitochondrial bioenergetics, at concentrations that do not affect mitochondrial morphology. We show that this effect is accompanied by an increase in glycolysis consumption. Dual targeting of glycolysis with 2-deoxy-D-glucose (2DG) and mitochondrial bioenergetics with MDIVI-1 reduced cellular bioenergetics, increased cell death and decreased clonogenic activity of MCF7 and HDQ-P1 breast cancer cells. In conclusion, we have explored a novel and effective combinatorial regimen for the treatment of breast cancer.