The biological significance of cancer: mitochondria as a cause of cancer and the inhibition of glycolysis with citrate as a cancer treatment

Metabolic Control During Macrophage Polarization by a Citrate-Functionalized Scaffold for Maintaining Bone Homeostasis

Metabolites, as markers of phenotype at the molecular level, can regulate the function of DNA, RNA, and proteins through chemical modifications or interactions with large molecules. Citrate is an important metabolite that affects macrophage polarization and osteoporotic bone function. Therefore, a better understanding of the precise effect of citrate on macrophage polarization may provide an effective alternative strategy to reverse osteoporotic bone metabolism. In this study, a citrate functional scaffold to control the metabolic pathway during macrophage polarization based on the metabolic differences between pro-inflammatory and anti-inflammatory phenotypes for maintaining bone homeostasis, is fabricated. Mechanistically, only outside M1 macrophages are accumulated high concentrations of citrate, in contrast, M2 macrophages consume massive citrate. Therefore, citrate-functionalized scaffolds exert more sensitive inhibitory effects on metabolic enzyme activity during M1 macrophage polarization than M2 macrophage polarization. Citrate can block glycolysis-related enzymes by occupying the binding-site and ensure sufficient metabolic flux in the TCA cycle, so as to turn the metabolism of macrophages to oxidative phosphorylation of M2 macrophage, largely maintaining bone homeostasis. These studies indicate that exogenous citrate can realize metabolic control of macrophage polarization for maintaining bone homeostasis in osteoporosis.

Beta hydroxybutyrate induces lung cancer cell death, mitochondrial impairment and oxidative stress in a long term glucose-restricted condition

BACKGROUND

Metabolic plasticity gives cancer cells the ability to shift between signaling pathways to facilitate their growth and survival. This study investigates the role of glucose deprivation in the presence and absence of beta-hydroxybutyrate (BHB) in growth, death, oxidative stress and the stemness features of lung cancer cells.

METHODS AND RESULTS

A549 cells were exposed to various glucose conditions, both with and without beta-hydroxybutyrate (BHB), to evaluate their effects on apoptosis, mitochondrial membrane potential, reactive oxygen species (ROS) levels using flow cytometry, and the expression of CD133, CD44, SOX-9, and β-Catenin through Quantitative PCR. The activity of superoxide dismutase, glutathione peroxidase, and malondialdehyde was assessed using colorimetric assays. Treatment with therapeutic doses of BHB triggered apoptosis in A549 cells, particularly in cells adapted to glucose deprivation. The elevated ROS levels, combined with reduced levels of SOD and GPx, indicate that oxidative stress contributes to the cell arrest induced by BHB. Notably, BHB treatment under glucose-restricted conditions notably decreased CD133 expression, suggesting a potential inhibition of cell survival through the downregulation of CD133 levels. Additionally, the simultaneous decrease in mitochondrial membrane potential and increase in ROS levels indicate the potential for creating oxidative stress conditions to impede tumor cell growth in such environmental settings.

CONCLUSION

The induced cell death, oxidative stress and mitochondria impairment beside attenuated levels of cancer stem cell markers following BHB administration emphasize on the distinctive role of metabolic plasticity of cancer cells and propose possible therapeutic approaches to control cancer cell growth through metabolic fuels.

Petiveria alliacea Reduces Tumor Burden and Metastasis and Regulates the Peripheral Immune Response in a Murine Myeloid Leukemia Model

The poor response, adverse effects and drug resistance to treatment of acute myeloid leukemia (AML) have led to searching for safer and more effective therapeutic alternatives. We previously demonstrated that the alcoholic extract of Petiveria alliacea (Esperanza) has a significant in vitro antitumor effect on other tumor cells and also the ability to regulate energy metabolism. We evaluated the effect of the Esperanza extract in vitro and in vivo in a murine model of AML with DA-3/ER-GM cells. First, a chemical characterization of the extract was conducted through liquid and gas chromatography coupled with mass spectrometry. In vitro findings showed that the extract modulates tumor metabolism by decreasing glucose uptake and increasing reactive oxygen species, which leads to a reduction in cell proliferation. Then, to evaluate the effect of the extract in vivo, we standardized the mouse model by injecting DA-3/ER-GM cells intravenously. The animals treated with the extract showed a lower percentage of circulating blasts, higher values of hemoglobin, hematocrit, and platelets, less infiltration of blasts in the spleen, and greater production of cytokines compared to the control group. These results suggest that the antitumor activity of this extract on DA-3/ER-GM cells can be attributed to the decrease in glycolytic metabolism, its activity as a mitocan, and the possible immunomodulatory effect by reducing tumor proliferation and metastasis.

Iron chelates in the anticancer therapy

Iron plays a significant role in the metabolism of cancer cells. In comparison with normal cells, neoplastic ones exhibit enhanced vulnerability to iron. Ferric ions target tumor via the ferroptotic death pathway—a process involving the iron-mediated lipid oxidation. Ferric ion occurs in complex forms in the physiological conditions. Apart from iron, ligands are the other factors to affect the biological activity of the iron complexes. In recent decades the role of iron chelates in targeting the growth of the tumor was extensively examined. The ligand may possess a standalone activity to restrict cancer’s growth. However, a wrong choice of the ligand might lead to the enhanced cancer cell’s growth in in vitro studies. The paper aims to review the role of iron complex compounds in the anticancer therapy both in the experimental and clinical applications. The anticancer properties of the iron complex rely both on the stability constant of the complex and the ligand composition. When the stability constant is high, the properties of the drug are unique. However, when the stability constant remains low, both components—ferric ions and ligands, act separately on the cells. In the paper we show how the difference in complex stability implies the action of ligand and ferric ions in the cancer cell. Iron complexation strategy is an interesting attempt to transport the anticancer Fe2+/3+ ions throughout the cell membrane and release it when the pH of the microenvironment changes. Last part of the paper summarizes the results of clinical trials and in vitro studies of novel iron chelates such as: PRLX 93,936, Ferumoxytol, Talactoferrin, DPC, Triapine, VLX600, Tachypyridine, Ciclopiroxamine, Thiosemicarbazone, Deferoxamine and Deferasirox.

A ketogenic diet attenuates proliferation and stemness of glioma stem‑like cells by altering metabolism resulting in increased ROS production

Abnormal metabolism serves a critical role in the development and progression of different types of malignancies including glioblastoma (GBM), and may therefore serve as a promising target for treatment of cancer. Preclinical studies have indicated that a ketogenic diet (KD) may exhibit beneficial effects in patients with GBM; however, the underlying mechanisms remain incompletely understood. The aim of the present study was to evaluate the effects of a KD on glioma stem‑like cells (GSCs), by culturing patient‑derived primary GSCs as well as a GSC cell line in glucose‑restricted, β‑hydroxybutyrate‑containing medium (BHB‑Glow) which was used to mimic clinical KD treatment. GSCs cultured in BHB‑Glow medium exhibited reduced proliferation and increased apoptosis compared with cells grown in the control medium. Furthermore, decreased expression of stem cell markers, diminished self‑renewal in vitro, and reduced tumorigenic capacity in vivo, providing evidence that the stemness of GSCs was compromised. Mechanistically, culturing in BHB‑Glow medium reduced glucose uptake and inhibited glycolysis in GSCs. Furthermore, culturing in the BHB‑Glow medium resulted in morphological and functional disturbances to the mitochondria of GSCs. These metabolic changes may have reduced ATP production, promoted lactic acid accumulation, and thus, increased the production of reactive oxygen species (ROS) in GSCs. The expression levels and activation of mammalian target of rapamycin, hypoxia‑inducible factor 1 and B‑cell lymphoma 2 were decreased, consistent with the reduced proliferation of GSCs in BHB‑Glow medium. ROS scavenging reversed the inhibitory effects of a KD on GSCs. Taken together, the results demonstrate that treatment with KD inhibited proliferation of GSCs, increased apoptosis and attenuated the stemness in GSCs by increasing ROS production.

Impact of Five Succinate Dehydrogenase Inhibitors on DON Biosynthesis of Fusarium asiaticum, Causing Fusarium Head Blight in Wheat

Deoxynivalenol (DON) is a class of mycotoxin produced in cereal crops infected with Fusarium graminearum species complex (FGSC). In China, FGSC mainly includes Fusarium asiaticum and F. graminearum. DON belongs to the trichothecenes and poses a serious threat to the safety and health of humans and animals. Succinate dehydrogenase inhibitors (SDHIs) are a class of fungicides that act on succinate dehydrogenase and inhibit the respiration of pathogenic fungi. In this study, the fungicidal activities of five SDHIs, including fluopyram, flutolanil, boscalid, benzovindiflupyr, and fluxapyroxad, against FGSC were determined based on mycelial growth and spore germination inhibition methods. The five SDHIs exhibited better inhibitory activities in spore germination than mycelial growth. Fluopyram exhibited a higher inhibitory effect in mycelial growth and spore germination in comparison to the other four SDHIs. In addition, the biological characteristics of F. asiaticum as affected by the five SDHIs were determined. We found that these five SDHIs decreased DON, pyruvic acid and acetyl-CoA production, isocitrate dehydrogenase mitochondrial (ICDHm) and SDH activities, and NADH and ATP content of F. asiaticum but increased the citric acid content. In addition, TRI5 gene expression was inhibited, and the formation of toxisomes was disrupted by the five SDHIs, further confirming that SDHIs can decrease DON biosynthesis of F. asiaticum. Thus, we concluded that SDHIs may decrease DON biosynthesis of F. asiaticum by inhibiting glycolysis and the tricarboxylic acid (TCA) cycle. Overall, the findings from the study will provide important references for managing Fusarium head blight (FHB) caused by FGSC and reducing DON contamination in F. asiaticum-infected wheat grains.

NMR-based metabolomic techniques identify potential urinary biomarkers for early colorectal cancer detection

Better early detection methods are needed to improve the outcomes of patients with colorectal cancer (CRC). Proton nuclear magnetic resonance spectroscopy (¹H-NMR), a potential non-invasive early tumor detection method, was used to profile urine metabolites from 55 CRC patients and 40 healthy controls (HCs). Pattern recognition through orthogonal partial least squares-discriminant analysis (OPLS-DA) was applied to ¹H-NMR processed data. Model specificity was confirmed by comparison with esophageal cancers (EC, n=18). Unique metabolomic profiles distinguished all CRC stages from HC urine samples. A total of 16 potential biomarker metabolites were identified in stage I/II CRC, indicating amino acid metabolism, glycolysis, tricarboxylic acid (TCA) cycle, urea cycle, choline metabolism, and gut microflora metabolism pathway disruptions. Metabolite profiles from early stage CRC and EC patients were also clearly distinguishable, suggesting that upper and lower gastrointestinal cancers have different metabolomic profiles. Our study assessed important metabolomic variations in CRC patient urine samples, provided information complementary to that collected from other biofluid-based metabolomics analyses, and elucidated potential underlying metabolic mechanisms driving CRC. Our results support the utility of NMR-based urinary metabolomics fingerprinting in early diagnosis of CRC.

Key Roles of Glutamine Pathways in Reprogramming the Cancer Metabolism

Glutamine (GLN) is commonly known as an important metabolite used for the growth of cancer cells but the effects of its intake in cancer patients are still not clear. However, GLN is the main substrate for DNA and fatty acid synthesis. On the other hand, it reduces the oxidative stress by glutathione synthesis stimulation, stops the process of cancer cachexia, and nourishes the immunological system and the intestine epithelium, as well. The current paper deals with possible positive effects of GLN supplementation and conditions that should be fulfilled to obtain these effects. The analysis of GLN metabolism suggests that the separation of GLN and carbohydrates in the diet can minimize simultaneous supply of ATP (from glucose) and NADPH2 (from glutamine) to cancer cells. It should support to a larger extent the organism to fight against the cancer rather than the cancer cells. GLN cannot be considered the effective source of ATP for cancers with the impaired oxidative phosphorylation and pyruvate dehydrogenase inhibition. GLN intake restores decreased levels of glutathione in the case of chemotherapy and radiotherapy; thus, it facilitates regeneration processes of the intestine epithelium and immunological system.

Antitumor effect of free rhodium (II) citrate and rhodium (II) citrate-loaded maghemite nanoparticles on mice bearing breast cancer: a systemic toxicity assay

Breast cancer is one of the most prevalent cancer types among women. The use of magnetic fluids for specific delivery of drugs represents an attractive platform for chemotherapy. In our previous studies, it was demonstrated that maghemite nanoparticles coated with rhodium (II) citrate (Magh-Rh2Cit) induced in vitro cytotoxicity and in vivo antitumor activity, followed by intratumoral administration in breast carcinoma cells. In this study, our aim was to follow intravenous treatment to evaluate the systemic antitumor activity and toxicity induced by these formulations in Balb/c mice bearing orthotopic 4T1 breast carcinoma. Female Balb/c mice were evaluated with regard to toxicity of intravenous treatments through analyses of hemogram, serum levels of alanine aminotransferase, iron, and creatinine and liver, kidney, and lung histology. The antitumor activity of rhodium (II) citrate (Rh2Cit), Magh-Rh2Cit, and maghemite nanoparticles coated with citrate (Magh-Cit), used as control, was evaluated by tumor volume reduction, histology, and morphometric analysis. Magh-Rh2Cit and Magh-Cit promoted a significant decrease in tumor area, and no experimental groups presented hematotoxic effects or increased levels of serum ALT and creatinine. This observation was corroborated by the histopathological examination of the liver and kidney of mice. Furthermore, the presence of nanoparticles was verified in lung tissue with no morphological changes, supporting the idea that our nanoformulations did not induce toxicity effects. No studies about the systemic action of rhodium (II) citrate-loaded maghemite nanoparticles have been carried out, making this report a suitable starting point for exploring the therapeutic potential of these compounds in treating breast cancer.

A novel potential biocompatible hyperbranched polyspermine for efficient lung cancer gene therapy

The clinical successful application of gene therapy critically depends upon the development of non-toxic and efficient delivery system. Although polycationic non-viral vectors hold great promise in nanomedicine, the exploring of application in clinics still remains a big challenge. To develop a non-toxic and efficient non-viral gene delivery system, two kinds of endogenous substance, citric acid (CA) and spermine (SPE), were used to prepare a new low charge density hyperbranched polyspermine (HPSPE) by one-pot polymerization. The biocompatibility evaluated by hemolytic activity and red blood cell (RBC) aggregation indicated that HPSPE was highly biocompatible without causing hemolysis and RBC aggregation compared with PEI as well as SPE. The MTS assay also demonstrated that the cell viability of HPSPE was above 90% even at 200 μg/mL at different time (24 and 72 h), which much higher than PEI 25K. Besides, HPSPE showed high transfection efficiency without any toxic effect after aerosol delivery to the mice. Moreover, aerosol delivery of HPSPE/Akt1 shRNA significantly reduced tumor size and numbers and efficiently suppressed lung tumorigenesis ultimately in K-ras(LA1) lung cancer model mice. These results suggest that low charge density as well as endogenous substance skeleton endow HPSPE with great potential for toxicity-free and efficient gene therapy.

Citrate kills tumor cells through activation of apical caspases

Most tumor cells exhibit a glycolytic phenotype. Thus, inhibition of glycolysis might be of therapeutic value in antitumor treatment. Among the agents that can suppress glycolysis is citrate, a member of the Krebs cycle and an inhibitor of phosphofructokinase. Here, we show that citrate can trigger cell death in multiple cancer cell lines. The lethal effect of citrate was found to be related to the activation of apical caspases-8 and -2, rather than to the inhibition of cellular energy metabolism. Hence, increasing concentrations of citrate induced characteristic manifestations of apoptosis, such as caspase-3 activation, and poly-ADP-ribose polymerase cleavage, as well as the release of cytochrome c. Apoptosis induction did not involve the receptor-mediated pathway, since the processing of caspase-8 was not attenuated in cells deficient in Fas-associated protein with Death Domain. We propose that the activation of apical caspases by citrate could be explained by its kosmotropic properties. Caspase-8 is activated by proximity-induced dimerization, which might be facilitated by citrate through the stabilization of intermolecular interactions between the proteins.

A possible primary cause of cancer: deficient cellular interactions in endocrine pancreas

Background

Cancer is a devastating type of disease. New and innovative ways to tackle cancers that have so far proved refractive to conventional therapies is urgently needed. It is becoming increasingly clear that, in addition to conventional therapeutics targeting by small molecules, that tumor cell metabolism presents new opportunities to target selectively specific cancer cell populations. Metabolic defects in cancer cells can be manifested in many ways that might not be readily apparent, such as altering epigenetic gene regulation for example.

The complex rewiring of metabolic pathways gives tumor cells a special advantage over differentiated cells, since they deplete body stores as fuel for their growth and proliferation. Tumor metabolism looks simpler when we consider that some enzymatic switches are in a neoglucogenic direction thereby depleting body stores. However, these pathways may be inadequately switched on by catabolic hormones (glucagon, epinephrine and cortisol) in a specific situation where anabolism is activated by, for example insulin released from beta pancreatic cells or IGF, inducing mitosis and synthesis that are powered by glucose catabolism. Such a hybrid metabolic situation would be reached if a pancreatic beta cell mechanism, mediated by GABA, failed to silence neighboring alpha cells and delta cells. The inhibitory transmitter GABA hyperpolarizes alpha and delta cells via their GABA A receptors, and blocks the release of glucagon and somatostatin. Alternatively, an anomaly of alpha cell channels, would lead to a similar situation. Whatever is the alteration, anabolism fails to silence catabolism and enzymatic switches controlled by kinases and phosphatases adopt an inadequate direction, leading to a hybrid metabolic rewiring found in cancer. It is daring to formulate such a hypothesis as this. However, it is quite possible that the starting point in cancer is an alteration of the endocrine pancreas, suppressing the mechanism by which beta cells silence the neighboring alpha and delta cells, with GABA and Zn²⁺.

Anticancer agents that counteract tumor glycolysis

Can we consider cancer to be a "metabolic disease"? Tumors are the result of a metabolic selection, forming tissues composed of heterogeneous cells that generally express an overactive metabolism as a common feature. In fact, cancer cells have increased needs for both energy and biosynthetic intermediates to support their growth and invasiveness. However, their high proliferation rate often generates regions that are insufficiently oxygenated. Therefore, their carbohydrate metabolism must rely mostly on a glycolytic process that is uncoupled from oxidative phosphorylation. This metabolic switch, also known as the Warburg effect, constitutes a fundamental adaptation of tumor cells to a relatively hostile environment, and supports the evolution of aggressive and metastatic phenotypes. As a result, tumor glycolysis may constitute an attractive target for cancer therapy. This approach has often raised concerns that antiglycolytic agents may cause serious side effects toward normal cells. The key to selective action against cancer cells can be found in their hyperbolic addiction to glycolysis, which may be exploited to generate new anticancer drugs with minimal toxicity. There is growing evidence to support many glycolytic enzymes and transporters as suitable candidate targets for cancer therapy. Herein we review some of the most relevant antiglycolytic agents that have been investigated thus far for the treatment of cancer.

The use of variations in proteomes to predict, prevent, and personalize treatment for clinically nonfunctional pituitary adenomas

Pituitary adenomas account for ∼10% of intracranial tumors, and they cause the compression of nearby structures and the inappropriate expression of pituitary hormones. Unlike functional pituitary adenomas, nonfunctional (NF) pituitary adenomas account for ∼30% of pituitary tumors, and are large enough to cause blindness; because they do not cause any clinical hormone hypersecretion, they are difficult to detect at an early stage; and hypopituitarism results. No effective molecular biomarkers or chemical therapy have been approved for the clinical setting. Because an NF pituitary adenoma is highly heterogeneous, differences in the proteins (the proteome) can distinguish among those heterogeneity structures. The components of a proteome dynamically change as an NF adenoma progresses. Changes in protein expression and protein modifications, individually or in combination, might be biomarkers to predict the disease, monitor the tumor progression, and develop an accurate molecular classification for personalized patient treatment. The modalities of proteomic variation might also be useful in the interventional prevention and personalized treatment of patients to halt the occurrence and progression of NF pituitary adenomas.

Urinary metabonomic study on colorectal cancer

After our serum metabonomic study of colorectal cancer (CRC) patients recently published in J. Proteome Res., we profiled urine metabolites from the same group of CRC patients (before and after surgical operation) and 63 age-matched healthy volunteers using gas chromatography-mass spectrometry (GC-MS) in conjunction with a multivariate statistics technique. A parallel metabonomic study on a 1,2-dimethylhydrazine (DMH)-treated Sprague-Dawley rat model was also performed to identify significantly altered metabolites associated with chemically induced precancerous colorectal lesion. The orthogonal partial least-squares-discriminant analysis (OPLS-DA) models of metabonomic results demonstrated good separations between CRC patients or DMH-induced model rats and their healthy counterparts. The significantly increased tryptophan metabolism, and disturbed tricarboxylic acid (TCA) cycle and the gut microflora metabolism were observed in both the CRC patients and the rat model. The urinary metabolite profile of postoperative CRC subjects altered significantly from that of the preoperative stage. The significantly down-regulated gut microflora metabolism and TCA cycle were observed in postoperative CRC subjects, presumably due to the colon flush involved in the surgical procedure and weakened physical conditions of the patients. The expression of 5-hydroxytryptophan significantly decreased in postsurgery samples, suggesting a recovered tryptophan metabolism toward healthy state. Abnormal histamine metabolism and glutamate metabolism were found only in the urine samples of CRC patients, and the abnormal polyamine metabolism was found only in the rat urine. This study assessed the important metabonomic variations in urine associated with CRC and, therefore, provided baseline information complementary to serum/plasma and tissue metabonomics for the complete elucidation of the underlying metabolic mechanisms of CRC.

Signaling pathway networks mined from human pituitary adenoma proteomics data

Background

We obtained a series of pituitary adenoma proteomic expression data, including protein-mapping data (111 proteins), comparative proteomic data (56 differentially expressed proteins), and nitroproteomic data (17 nitroproteins). There is a pressing need to clarify the significant signaling pathway networks that derive from those proteins in order to clarify and to better understand the molecular basis of pituitary adenoma pathogenesis and to discover biomarkers. Here, we describe the significant signaling pathway networks that were mined from human pituitary adenoma proteomic data with the Ingenuity pathway analysis system.

Methods

The Ingenuity pathway analysis system was used to analyze signal pathway networks and canonical pathways from protein-mapping data, comparative proteomic data, adenoma nitroproteomic data, and control nitroproteomic data. A Fisher's exact test was used to test the statistical significance with a significance level of 0.05. Statistical significant results were rationalized within the pituitary adenoma biological system with literature-based bioinformatics analyses.

Results

For the protein-mapping data, the top pathway networks were related to cancer, cell death, and lipid metabolism; the top canonical toxicity pathways included acute-phase response, oxidative-stress response, oxidative stress, and cell-cycle G2/M transition regulation. For the comparative proteomic data, top pathway networks were related to cancer, endocrine system development and function, and lipid metabolism; the top canonical toxicity pathways included mitochondrial dysfunction, oxidative phosphorylation, oxidative-stress response, and ERK/MAPK signaling. The nitroproteomic data from a pituitary adenoma were related to cancer, cell death, lipid metabolism, and reproductive system disease, and the top canonical toxicity pathways mainly related to p38 MAPK signaling and cell-cycle G2/M transition regulation. Nitroproteins from a pituitary control related to gene expression and cellular development, and no canonical toxicity pathways were identified.

Conclusions

This pathway network analysis demonstrated that mitochondrial dysfunction, oxidative stress, cell-cycle dysregulation, and the MAPK-signaling abnormality are significantly associated with a pituitary adenoma. These pathway-network data provide new insights into the molecular mechanisms of human pituitary adenoma pathogenesis, and new clues for an in-depth investigation of pituitary adenoma and biomarker discovery.