Beyond Warburg effect--dual metabolic nature of cancer cells

Cancer cells change their glucose metabolism to overcome increased ROS: One step from cancer cell to cancer stem cell?

Cancer cells can adapt to low energy sources in the face of ATP depletion as well as to their high levels of ROS by altering their metabolism and energy production networks which might also have a role in determining cell fate and developing drug resistance. Cancer cells are generally characterized by increased glycolysis. This is while; cancer stem cells (CSCs) exhibit an enhanced pentose phosphate pathway (PPP) metabolism. Based on the current literature, we suggest that cancer cells when encountering ROS, first increase the glycolysis rate and then following the continuation of oxidative stress, the metabolic balance is skewed from glycolysis to PPP. Therefore, we hypothesize in this review that in cancer cells this metabolic deviation during persistent oxidative stress might be a sign of cancer cells' shift towards CSCs, an issue that might be pivotal in more effective targeting of cancer cells and CSCs.

Mechanisms of Metastasis and Cell Mobility - The Role of Metabolism

Tumour metastasis is responsible for more than 90% of tumour-associated mortality. About one third of breast cancer patients in the early stage develop metastases. The transformation in tumour development referred to as the "metastatic cascade" or "metastatic cycle" is a complex and multi-stage event. While it is generally recognised that epithelial-mesenchymal transformation (EMT) plays a crucial role in cancer progression and metastasis, the metabolic events in this process have received little attention to date. We would therefore like to provide a brief overview here of the influence of the metabolism on the progression and metastasis of tumours.

HIF-1α and HIF-2α Differently Regulate the Radiation Sensitivity of NSCLC Cells

The hypoxia-inducible transcription factors (HIF)-1/2α are the main oxygen sensors which regulate the adaptation to intratumoral hypoxia. The aim of this study was to assess the role of the HIF proteins in regulating the radiation response of a non-small cell lung cancer (NSCLC) in vitro model. To directly assess the unique and overlapping functions of HIF-1α and HIF-2α, we use CRISPR gene-editing to generate isogenic H1299 non-small cell lung carcinoma cells lacking HIF-1α, HIF-2α or both. We found that in HIF1 knockout cells, HIF-2α was strongly induced by hypoxia compared to wild type but the reverse was not seen in HIF2 knockout cells. Cells lacking HIF-1α were more radiation resistant than HIF2 knockout and wildtype cells upon hypoxia, which was associated with a reduced recruitment of γH2AX foci directly after irradiation and not due to differences in proliferation. Conversely, double-HIF1/2 knockout cells were most radiation sensitive and had increased γH2AX recruitment and cell cycle delay. Compensatory HIF-2α activity in HIF1 knockout cells is the main cause of this radioprotective effect. Under hypoxia, HIF1 knockout cells uniquely had a strong increase in lactate production and decrease in extracellular pH. Using genetically identical HIF-α isoform-deficient cells we identified a strong radiosensitizing of HIF1, but not of HIF2, which was associated with a reduced extracellular pH and reduced glycolysis.

Long non-coding RNA-NEF targets glucose transportation to inhibit the proliferation of non-small-cell lung cancer cells

Long non-coding RNA (lncRNA)-NEF is a newly discovered lncRNA, which exhibits an inhibitory function on the metastasis of hepatocellular carcinoma, while its involvement in other types of malignancy are unknown. In the present study, tumor and adjacent healthy tissues were obtained from patients with non-small-cell lung cancer (NSCLC), and blood was obtained from patients with NSCLC and healthy individuals. Expression levels of lncRNA-NEF in tumor tissue samples, healthy tissue samples and serum were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Receiver operating characteristic curve analysis and survival curve analysis were performed to evaluate the diagnostic and prognostic value of serum lncRNA-NEF for NSCLC. The effects of lncRNA-NEF overexpression in NSCLC cell lines on tumor cell proliferation, glucose uptake, glucose transporter 1 (GLUT1) protein expression and mRNA expression were investigated by Cell Counting kit-8 assay, glucose uptake assay, western blot analysis and RT-qPCR, respectively. It was identified that lncRNA-NEF was downregulated in NSCLC tissues, compared with healthy controls, and the serum level of lncRNA-NEF was negatively associated with primary tumor stage. Therefore, serum lncRNA-NEF may be a sensitive diagnostic and prognostic marker for NSCLC. Overexpression of lncRNA-NEF inhibited NSCLC cell proliferation and glucose uptake, and downregulated GLUT1 expression. Therefore, it can be concluded that lncRNA-NEF can target glucose transportation to inhibit the proliferation of NSCLC cells.

The Effects of Systemic and Local Acidosis on Insulin Resistance and Signaling

Most pathological conditions that cause local or systemic acidosis by overcoming the buffering activities of body fluids overlap with those diseases that are characterized by glucose metabolic disorders, including diabetes mellitus, inflammation, and cancer. This simple observation suggests the existence of a strong relationship between acidosis and insulin metabolism or insulin receptor signaling. In this review, we summarized the current knowledge on the activity of insulin on the induction of acidosis and, vice versa, on the effects of changes of extracellular and intracellular pH on insulin resistance. Insulin influences acidosis by promoting glycolysis. Although with an unclear mechanism, the lowering of pH, in turn, inhibits insulin sensitivity or activity. In addition to ketoacidosis that is frequently associated with diabetes, other important and more complex factors are involved in this delicate feedback mechanism. Among these, in this review we discussed the acid-mediated inhibiting effects on insulin binding affinity to its receptor, on glycolysis, on the recycling of glucose transporters, and on insulin secretion via transforming growth factor β (TGF-β) activity by pancreatic β-cells. Finally, we revised current data available on the mutual interaction between insulin signaling and the activity of ion/proton transporters and pH sensors, and on how acidosis may enhance insulin resistance through the Nuclear Factor kappa B (NF-κB) inflammatory pathway.

Lactic Acid Accumulation in the Tumor Microenvironment Suppresses 18F-FDG Uptake

The process by which tumor cells take up 2-[¹⁸F]fluoro-2-deoxy-D-glucose (FDG) is heterogeneous and influenced by a multitude of factors. In mouse tumor grafts, the core of the tumor often presents lower FDG uptake than the periphery. Whether this pattern is caused by the intrinsic avidity of individual cells for FDG, the density of viable cells in the tumor, or the perfusion of the radiotracer remains unknown. In this study, we used radioluminescence microscopy to measure FDG uptake in single cells isolated from the core and periphery of the tumor and found that differences in FDG uptake persist on the level of single cells. Single cells from the core of 4T1 and MDA-MB-231 tumors grafts took up 26% to 84% less FDG than those from the periphery. These differences were observed in mice with large tumors (>8 mm diameter) but not in those with smaller tumors. To explain the origin of these differences, we examined the influence of three microenvironmental factors on FDG uptake. Hypoxia was ruled out as a possible explanation because its presence in the core would increase and not decrease FDG uptake. Higher cell proliferation in the periphery was consistent with higher FDG uptake, but there was no evidence of a causal relationship. Finally, lactate was higher in the core of the tumor, and it suppressed FDG uptake in a dose-dependent fashion. We therefore conclude that lactic acidosis-the combination of lactate ion buildup and acidic pH-can increase the heterogeneity of FDG uptake in MDA-MB-231 and 4T1 tumor grafts. SIGNIFICANCE: Analysis of single cells from heterogeneous tumors reveals the role played by the tumor microenvironment, lactic acidosis in particular, on the uptake by tumor cells of ¹⁸F-FDG, a PET imaging agent.

Functional insights into nucleotide-metabolizing ectoenzymes expressed by bone marrow-resident cells in patients with multiple myeloma

Human myeloma cells grow in a hypoxic acidic niche in the bone marrow. Cross talk among cellular components of this closed niche generates extracellular adenosine, which promotes tumor cell survival. This is achieved through the binding of adenosine to purinergic receptors into complexes that function as an autocrine/paracrine signal factor with immune regulatory activities that i) down-regulate the functions of most immune effector cells and ii) enhance the activity of cells that suppress anti-tumor immune responses, thus facilitating the escape of malignant myeloma cells from immune surveillance. Here we review recent findings confirming that the dominant phenotype for survival of tumor cells is that where the malignant cells have been metabolically reprogrammed for the generation of lactic acidosis in the bone marrow niche. Adenosine triphosphate and nicotinamide-adenine dinucleotide extruded from tumor cells, along with cyclic adenosine monophosphate, are the main intracellular energetic/messenger molecules that serve as leading substrates in the extracellular space for membrane-bound ectonucleotidases metabolizing purine nucleotides to signaling adenosine. Within this mechanistic framework, the adenosinergic substrate conversion can vary significantly according to the metabolic environment. Indeed, the neoplastic expansion of plasma cells exploits both enzymatic networks and hypoxic acidic conditions for migrating and homing to a protected niche and for evading the immune response. The expression of multiple specific adenosine receptors in the niche completes the profile of a complex regulatory framework whose signals modify multiple myeloma and host immune responses.

Native-mimicking in vitro microenvironment: an elusive and seductive future for tumor modeling and tissue engineering

Human connective tissues are complex physiological microenvironments favorable for optimal survival, function, growth, proliferation, differentiation, migration, and death of tissue cells. Mimicking native tissue microenvironment using various three-dimensional (3D) tissue culture systems in vitro has been explored for decades, with great advances being achieved recently at material, design and application levels. These achievements are based on improved understandings about the functionalities of various tissue cells, the biocompatibility and biodegradability of scaffolding materials, the biologically functional factors within native tissues, and the pathophysiological conditions of native tissue microenvironments. Here we discuss these continuously evolving physical aspects of tissue microenvironment important for human disease modeling, with a focus on tumors, as well as for tissue repair and regeneration. The combined information about human tissue spaces reflects the necessities of considerations when configuring spatial microenvironments in vitro with native fidelity to culture cells and regenerate tissues that are beyond the formats of 2D and 3D cultures. It is important to associate tissue-specific cells with specific tissues and microenvironments therein for a better understanding of human biology and disease conditions and for the development of novel approaches to treat human diseases.

Loss of function of miR-342-3p results in MCT1 over-expression and contributes to oncogenic metabolic reprogramming in triple negative breast cancer

Triple-negative breast cancer (TNBC) is a heterogeneous and aggressive neoplasia lacking the expression of hormonal receptors and human epidermal growth factor receptor-2. Accumulating evidence has highlighted the importance of miRNAs dysregulation in the establishment of cancer programs, but the functional role of many miRNAs remains unclear. The description of miRNAs roles might provide novel strategies for treatment. In the present work, an integrated analysis of miRNA transcriptional landscape was performed (N = 132), identifying the significant down-modulation of miR-342-3p in TNBC, probably because of the aberrant activity of estrogen receptor, which serves as a transcription factor of the miRNA, as demonstrated by a siRNA-knockdown approach. The enhanced expression of miR-342-3p significantly decreased cell proliferation, viability and migration rates of diverse TN cells in vitro. Bioinformatic and functional analyses revealed that miR-342-3p directly targets the monocarboxylate transporter 1 (MCT1), which promotes lactate and glucose fluxes alteration, thus disrupting the metabolic homeostasis of tumor cells. Optical metabolic imaging assay defined a higher optical redox ratio in glycolytic cells overexpressing miR-342-3p. Furthermore, we found that hypoxic conditions and glucose starvation attenuate miR-342-3p expression, suggesting a crosstalk program between these metabolic factors. Consistently, miR-342-3p down-modulation is associated with an increased MCT1 expression level and glycolytic score in human triple negative tumors. Overall, we described for the first time the regulatory activity of miR-342-3p on relevant metabolic carcinogenic pathways in TN breast cancers.

Cancer cell specific inhibition of Wnt/β-catenin signaling by forced intracellular acidification

Use of the diabetes type II drug Metformin is associated with a moderately lowered risk of cancer incidence in numerous tumor entities. Studying the molecular changes associated with the tumor-suppressive action of Metformin we found that the oncogene SOX4, which is upregulated in solid tumors and associated with poor prognosis, was induced by Wnt/β-catenin signaling and blocked by Metformin. Wnt signaling inhibition by Metformin was surprisingly specific for cancer cells. Unraveling the underlying specificity, we identified Metformin and other Mitochondrial Complex I (MCI) inhibitors as inducers of intracellular acidification in cancer cells. We demonstrated that acidification triggers the unfolded protein response to induce the global transcriptional repressor DDIT3, known to block Wnt signaling. Moreover, our results suggest that intracellular acidification universally inhibits Wnt signaling. Based on these findings, we combined MCI inhibitors with H⁺ ionophores, to escalate cancer cells into intracellular hyper-acidification and ATP depletion. This treatment lowered intracellular pH both in vitro and in a mouse xenograft tumor model, depleted cellular ATP, blocked Wnt signaling, downregulated SOX4, and strongly decreased stemness and viability of cancer cells. Importantly, the inhibition of Wnt signaling occurred downstream of β-catenin, encouraging applications in treatment of cancers caused by APC and β-catenin mutations.

Lactic acid induces lactate transport and glycolysis/OXPHOS interconversion in glioblastoma

The Warburg effect is a dominant phenotype of most tumor cells. Recent reports have shown that the Warburg effect can be reprogrammed by the tumor microenvironment. Lactic acidosis and glucose deprivation are the common adverse microenvironments in solid tumor. The metabolic reprogramming induced by lactic acid and glucose deprivation remains to be elucidated in glioblastoma. Here, we show that, under glucose deprivation, lactic acid can preserve high ATP levels and resist cell death in U251 cells. At the same time, we find that MCT1 and MCT4 are significantly highly expressed. The metabolic regulation factor HIF-1α decreased and C-MYC increased. Nuclear respiratory factor 1 (NRF1) and oxidative phosphorylation (OXPHOS)-related proteins (NDUFB8, ND1) are all distinctly increased. Therefore, lactic acid can induce lactate transport and convert the dominant Warburg effect to OXPHOS. Through bioinformatics analysis, the high expression of HIF-1α, MCT1 or MCT4 indicate a poor prognosis in glioblastoma. In addition, in glioblastoma tissue, HIF-1α, MCT4 and LDH are highly expressed in the interior region, and their expression is decreased in the lateral region. MCT1 can not be detected in the interior region and is highly expressed in the lateral region. Hence, different regions of glioblastoma have diverse energy metabolic pathways. Glycolysis occurs mainly in the interior region and OXPHOS in the lateral region. In general, lactic acid can induce regional energy metabolic reprogramming and assist tumor cells to adapt and resist adverse microenvironments. This study provides new ideas for furthering understanding of the metabolic features of glioblastoma. It may promote the development of new therapeutic strategies in GBM.

Evidence of drug-response heterogeneity rapidly generated from a single cancer cell

One cancer cell line is believed to be composed of numerous clones with different drug sensitivity. We sought to investigate the difference of drug-response pattern in clones from a cell line or from a single cell. We showed that 22 clones derived from 4T1 cells were drastically different from each other with respect to drug-response pattern against 11 anticancer drugs and expression profile of 19 genes associated with drug resistance or sensitivity. Similar results were obtained using daughter clones derived from a single 4T1 cell. Each daughter clone showed distinct drug-response pattern and gene expression profile. Similar results were also obtained using Bcap37 cells. We conclude that a single cancer cell can rapidly produce a population of cells with high heterogeneity of drug response and the acquisition of drug-response heterogeneity is random.

Tumor Microenvironment-Enabled Nanotherapy

Cancer is now one of the world's leading threats to human health. With the development of oncology in both biology and biomedicine, it has been demonstrated that abnormal physiochemical conditions and dysregulated biosynthetic intermediates in tumor microenvironment (TME) play a pivotal role in enabling tumor cells to defend or evade the damage by traditional clinical tumor therapeutics including surgery, chemotherapy, radiotherapy, etc. The fast advances of TME-enabled theranostic nanomedicine have offered promising perspectives, strategies, and approaches for combating cancer based on the novel concept of TME-enabled nanotherapy. In this comprehensive review, the origins of TME (e.g., enhanced permeability and retention effect, overexpressed biosynthetic intermediates, mild acidic nature, redox potentials, hypoxia) are initially introduced and discussed, followed by detailed discussion and overview on the state-of-the-art progresses in TME-enabled antitumor nanotherapies (e.g., chemo/chemodynamic therapy, photodynamic therapy, radiotherapy). Finally, the obstacles and challenges of future development on TME-enabled nanotherapies for further clinical translation are outlooked.

SLC2A5 promotes lung adenocarcinoma cell growth and metastasis by enhancing fructose utilization

The metabolism of cancer cells is highly plastic. Cancer cells can change their preference for nutrient uptake under nutrient stress. Fructose is one of the most common carbohydrates in diet and its metabolism is also involved in the development and progression of tumors. GLUT5, encoded by SLC2A5, is the specific fructose transporter in mammalian cells. In this study, we found that SLC2A5 is significantly upregulated in lung adenocarcinoma (LUAD) patients and overexpression of SLC2A5 is highly correlated with poor prognosis of LUAD patients. The expression of SLC2A5 determined fructose uptake and utilization efficacy in LUAD cells. GLUT5 is critical for the survival of LUAD cells in fructose-containing culture medium. Depletion of SLC2A5 undermined cell proliferation and invasion meanwhile increased cell apoptosis. Overexpression of SLC2A5 enhances cell proliferation, migration, invasion, and tumorigenic. Compared to glucose, fructose is prone to strengthen intracellular-free fatty acid accumulation and ATP production. Moreover, inhibition of GLUT5 by specific small chemical inhibitor sensitizes LUAD cells to paclitaxel treatment. Taken together, our results suggest that GLUT5 could be a potential target alone or combination with other treatment for lung cancer therapy.

Hexokinase 2 is a molecular bridge linking telomerase and autophagy

Autophagy is systematically regulated by upstream factors and nutrients. Recent studies reported that telomerase and hexokinase 2 [HK2) regulate autophagy through mTOR and that telomerase has the capacity to bind to the HK2 promoter. However, the molecular linkage among telomerase, HK2, and autophagy is not fully understood. Here, we show that HK2 connects telomerase to autophagy. HK2 inhibition in HepG2 cells suppressed TERT-induced autophagy activation and further enhancement by glucose deprivation. The HK2 downstream factor mTOR was responsible for the TERT-induced autophagy activation under glucose deprivation, implying that TERT promotes autophagy through an HK2-mTOR pathway. TERC played a role similar to that of TERT, and simultaneous expression of TERT and TERC synergistically enhanced HK2 expression and autophagy. At the gene level, TERT bound to the HK2 promoter at a specific region harboring the telomerase-responsive sequence ‘TTGGG.’ Mutagenesis of TERC and the TERT-responsive element in the HK2 promoter revealed that TERC is required for the binding of TERT to the HK2 promoter. We demonstrate the existence of a telomerase-HK2-mTOR-autophagy axis and suggest that inhibition of the interaction between telomerase and the HK2 promoter diminishes glucose starvation-induced autophagy.

Unusual cis-diprotonated forms and fluorescent aggregates of non-peripherally alkoxy-substituted metallophthalocyanines

Protonation and aggregation of two metallophthalocyanines (zinc and magnesium) non-peripherally substituted with 1,4,7-trioxanonyl moieties were studied by steady-state and time-resolved optical spectroscopy. Both compounds are easily protonated in organic solvents, but the central metal ion strongly affects the character of this process. In particular, the magnesium derivative forms the cis-diprotonated isomer observed for the first time in phthalocyanines, in contrast to its zinc counterpart which forms the typical trans-diprotonated isomer. In addition, studies performed on phthalocyanines substituted with n-butoxy groups at their non-peripheral positions indicated that the formation of the cis-diprotonated forms is a more common feature of alkoxy-substituted magnesium metallophthalocyanines, in contrast to derivatives with other metal ions. The cis-diprotonated forms of the magnesium derivatives are formed at much lower proton concentrations than the trans-diprotonated forms of their zinc counterparts. The cis-isomers were also found to have more advantageous photophysical properties for photoactive applications than the trans-isomers. Aggregation studies of the trioxanonyl phthalocyanines revealed that the magnesium derivative aggregates much more easily in non-coordinating solvents than its zinc counterpart. Both the derivatives form fluorescent aggregates, which is typically attributed to the presence of oxygen-to-metal intermolecular coordination preventing the formation of non-fluorescent face-to-face stacks. The results indicate that the oxygen-to-metal coordination plays a significant role in the studied systems and the stronger oxygen-coordination ability of magnesium ions compared to zinc ions may underlie the observed differences between the phthalocyanines metallated with these two ions.

MtDNA depleted PC3 cells exhibit Warburg effect and cancer stem cell features

Reducing mtDNA content was considered as a critical step in the metabolism restructuring for cell stemness restoration and further neoplastic development. However, the connections between mtDNA depletion and metabolism reprograming-based cancer cell stemness in prostate cancers are still lack of studies. Here, we demonstrated that human CRPC cell line PC3 tolerated high concentration of the mtDNA replication inhibitor ethidium bromide (EtBr) and the mtDNA depletion triggered a universal metabolic remodeling process. Failure in completing that process caused lethal consequences. The mtDNA depleted (MtDP) PC3 cells could be steadily maintained in the special medium in slow cycling status. The MtDP PC3 cells contained immature mitochondria and exhibited Warburg effect. Furthermore, the MtDP PC3 cells were resistant to therapeutic treatments and contained greater cancer stem cell-like subpopulations: CD44+, ABCG2+, side-population and ALDH^bright. In conclusion, these results highlight the association of mtDNA content, mitochondrial function and cancer cell stemness features.

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

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

Lactic acidosis switches cancer cells from aerobic glycolysis back to dominant oxidative phosphorylation

While transformation of normal cells to cancer cells is accompanied with a switch from oxidative phosphorylation (OXPHOS) to aerobic glycolysis, it is interesting to ask if cancer cells can revert from Warburg effect to OXPHOS. Our previous works suggested that cancer cells reverted to OXPHOS, when they were exposed to lactic acidosis, a common factor in tumor environment. However, the conclusion cannot be drawn unless ATP output from glycolysis and OXPHOS is quantitatively determined. Here we quantitatively measured ATP generation from glycolysis and OXPHOS in 9 randomly selected cancer cell lines. Without lactic acidosis, glycolysis and OXPHOS generated 23.7% − 52.2 % and 47.8% − 76.3% of total ATP, respectively; with lactic acidosis (20 mM lactate with pH 6.7), glycolysis and OXPHOS provided 5.7% − 13.4% and 86.6% − 94.3% of total ATP. We concluded that cancer cells under lactic acidosis reverted from Warburg effect to OXPHOS phenotype.

Tumor acidosis enhances cytotoxic effects and autophagy inhibition by salinomycin on cancer cell lines and cancer stem cells

Sustained autophagy contributes to the metabolic adaptation of cancer cells to hypoxic and acidic microenvironments. Since cells in such environments are resistant to conventional cytotoxic drugs, inhibition of autophagy represents a promising therapeutic strategy in clinical oncology. We previously reported that the efficacy of hydroxychloroquine (HCQ), an autophagy inhibitor under clinical investigation is strongly impaired in acidic tumor environments, due to poor uptake of the drug, a phenomenon widely associated with drug resistance towards many weak bases. In this study we identified salinomycin (SAL) as a potent inhibitor of autophagy and cytotoxic agent effective on several cancer cell lines under conditions of transient and chronic acidosis. Since SAL has been reported to specifically target cancer-stem cells (CSC), we used an established model of breast CSC and CSC derived from breast cancer patients to examine whether this specificity may be associated with autophagy inhibition. We indeed found that CSC-like cells are more sensitive to autophagy inhibition compared to cells not expressing CSC markers. We also report that the ability of SAL to inhibit mammosphere formation from CSC-like cells was dramatically enhanced in acidic conditions. We propose that the development and use of clinically suitable SAL derivatives may result in improved autophagy inhibition in cancer cells and CSC in the acidic tumor microenvironment and lead to clinical benefits.

Targeting Metabolic Cross Talk between Cancer Cells and Cancer-Associated Fibroblasts

Although tumorigenesis has classically been regarded as a genetic disease of uncontrolled cell growth, the importance of the tumor microenvironment (TME) is continuously emphasized by the accumulating evidence that cancer growth is not simply dependent on the cancer cells themselves [1, 2] but also dependent on angiogenesis [3–6], inflammation [7, 8], and the supporting roles of cancer-associated fibroblasts (CAFs) [9, 10]. After the discovery that CAFs are able to remodel the tumor matrix within the TME and provide the nutrients and chemicals to promote cancer cell growth [11], many studies have aimed to uncover the cross talk between cancer and CAFs. Moreover, a new paradigm in cancer metabolism shows how cancer cells act like “metabolic parasites” to uptake the high-energy metabolites, such as lactate, ketone bodies, free fatty acid, and glutamine from supporting cells, including CAFs and cancer-associated adipocytes (CAAs) [12, 13]. This chapter provides an overview of the metabolic coupling between CAFs and cancer to further define the therapeutic options to disrupt the CAF-cancer cell interactions.

Cell Microenvironment pH Sensing in 3D Microgels Using Fluorescent Carbon Dots

We report here a 3D cell culture microgel-based system containing carbon dots capable of sensing the pH changes in the cellular microenvironment. We have utilized a simple droplet-based microfluidics methodology for encapsulating cells and fluorescent pH sensitive carbon dots in polyethylene glycol microgels. Since the microfluidics assembly is developed from simple components that can be modified easily to yield microgels of different size, composition, and architecture, it can be utilized to develop complex 3D cell culture scaffolds of desired composition along with spatial control on the polymer composition. The synthesized pH sensitive carbon dots possess green fluorescence emission, which increases as the pH is lowered from neutral to acidic. Since the probe sensitivity to pH change is well within the physiologically relevant range (pH 5.8-7.7), the probe can be used for detecting a lowering of pH as the cells proliferate or undergo various biological processes. We demonstrate that the nanoprobes as well as the process of forming the microgel beads with nanoprobes and mammalian cells is biocompatible, and the cells easily proliferate inside the microgels. The changes in pH as the mammalian cells grow in the microgels is easily monitored via fluorescence microscopy, suggesting that the platform can be used to study time dependent changes in cellular microenvironment pH and can be easily utilized to monitor cellular growth, disease progression, etc.

Quantification of lactate from various metabolic pathways and quantification issues of lactate isotopologues and isotopmers

¹³C-labeled glucose combined with chromatography and mass spectrometry enables us to decipher the percentage of lactate generated from various metabolic pathways. We showed that lactate derived from glycolysis, pentose phosphate pathway, Krebs cycle, and other sources accounted for 82-90%, 6.0-11%, 0.67-1.8% and 1.5-7.9%, respectively, depending on different types of cells. When using glucose isotopomers ([1-¹³C]-, [3-¹³C]-, [4-¹³C]-, and [6-¹³C]glucose) or isotopologues ([1,2-¹³C₂]- and [1,2,3-¹³C₃]glucose) for tracing, the ratio of lactate derived from glucose carbon 1, 2, 3 over 4, 5, 6 via glycolysis varied significantly, ranging from 1.6 (traced with [1,2-¹³C₂]glucose) to 0.85 (traced with [6-¹³C]glucose), but the theoretical ratio should be 1. The odd results might be caused by intramolecular ¹³C, which may significantly affect lactate fragmentation under tandem mass spectrometry condition, leading to erroneous quantification. Indeed, the fragmentation efficiency of [U-¹³C]lactate, [2,3-¹³C]lactate, and [3-¹³C]lactate were 1.4, 1.5 and 1.2 folds higher than lactate, respectively, but [1-¹³C]lactate was similar to lactate, suggesting that carbon-13 at different positions could differentially influence lactate fragmentation. This observed phenomenon was inconsistent with the data based on theoretical calculation, according to which activation energies for all lactate isotopomers and isotopologues are nearly identical. The inconsistency suggested a need for further investigation. Our study suggests that calibration is required for quantifying metabolite isotopolugues and isotopomers.

Impact of extracellular alkalinization on the survival of human CD24-/CD44+ breast cancer stem cells associated with cellular metabolic shifts

Cancer stem cells reside in a distinct region within the tumor microenvironment that it is believed to play a fundamental role in regulating stemness, proliferation, survival, and metabolism of cancer cells. This study aimed to analyze the effect of extracellular alkalinization on metabolism and survival of human CD24-/CD44+ breast cancer stem cells (BCSCs). BCSCs were cultured in alkalinized DMEM-F12 and incubated at 37°C, 5% CO2, and 20% O2 for 30 min, 6, 24, and 48 h. After each incubation period, we analyzed the modulation of various mRNA expressions related to pH and cellular metabolic regulation using the qRT-PCR. Metabolic state was measured using colorimetric and fluorometric assays. To examine cell proliferation and apoptosis, we used trypan blue and annexin V/propidium iodide assay, respectively. This study demonstrated that alkalinization could stimulate extracellular carbonic anhydrase (CAe) activity, as well as CA9 and HIF1α expression. Under alkaline pH and HIF1α regulation, glucose consumption, extracellular lactate production, and LDH activity of BCSCs were upregulated while O2 consumption was downregulated. These metabolic shifts seemed to promote apoptosis and suppress the proliferation of BCSCs. To conclude, modulation of the extracellular environment through alkalinization could change the metabolic states of BCSCs, which in turn affect the cell survival.

Shaping functional gut microbiota using dietary bioactives to reduce colon cancer risk

Colon cancer is a multifactorial disease associated with a variety of lifestyle factors. Alterations in the gut microbiota and the intestinal metabolome are noted during colon carcinogenesis, implicating them as critical contributors or results of the disease process. Diet is a known determinant of health, and as a modifier of the gut microbiota and its metabolism, a critical element in maintenance of intestinal health. This review summarizes recent evidence demonstrating the role and responses of the intestinal microbiota during colon tumorigenesis and the ability of dietary bioactive compounds and probiotics to impact colon health from the intestinal lumen to the epithelium and systemically. We first describe changes to the intestinal microbiome, metabolome, and epithelium associated with colon carcinogenesis. This is followed by a discussion of recent evidence indicating how specific classes of dietary bioactives, prebiotics, or probiotics affect colon carcinogenesis. Lastly, we briefly address the prospects of using multiple 'omics' techniques to integrate the effects of diet, host, and microbiota on colon tumorigenesis with the goal of more fully appreciating the interconnectedness of these systems and thus, how these approaches can be used to advance personalized nutrition strategies and nutrition research.

Mycobacterial heat shock protein 65 mediated metabolic shift in decidualization of human endometrial stromal cells

Successful implantation is dependent on the appropriate decidualization of endometrial stromal cells for the establishment of pregnancy in women. Mycobacterial heat shock protein 65 (HSP65) is involved in pathogenesis of the genital tuberculosis (GTB), one of the common causes of infertility in emerging countries. Though implantation failure appears to be the major cause, understanding the status of decidualizaiton process in women diagnosed with GTB has not been thoroughly addressed. We, therefore, explored the effect of HSP65 protein on the endometrial cell metabolism during in vitro decidualization. In order to identify the cellular metabolism of decidual cells with and without HSP65 treatment, proton NMR based characterization of metabolites extracted from cells and culture media were performed. In presence of HSP65, significant reduction in the decidual phenotype of endometrial stromal cells and prolactin expression is suggestive of impairment in decidualization. The intracellular and extracellular metabolic changes in HSP65 treated endometrial stromal cells produced a distinct pattern, reflecting the interaction between the protein and cellular metabolism. HSP65 mediated dysregulation in cellular metabolism is associated with poor decidualization. Besides enriching the present knowledge on metabolic changes underlying stromal cells decidualization, these findings assist in identifying potential molecular causes for decidualization failure in GTB women.

Overexpression of the human DEK oncogene reprograms cellular metabolism and promotes glycolysis

The DEK oncogene is overexpressed in many human malignancies including at early tumor stages. Our reported in vitro and in vivo models of squamous cell carcinoma have demonstrated that DEK contributes functionally to cellular and tumor survival and to proliferation. However, the underlying molecular mechanisms remain poorly understood. Based on recent RNA sequencing experiments, DEK expression was necessary for the transcription of several metabolic enzymes involved in anabolic pathways. This identified a possible mechanism whereby DEK may drive cellular metabolism to enable cell proliferation. Functional metabolic Seahorse analysis demonstrated increased baseline and maximum extracellular acidification rates, a readout of glycolysis, in DEK-overexpressing keratinocytes and squamous cell carcinoma cells. DEK overexpression also increased the maximum rate of oxygen consumption and therefore increased the potential for oxidative phosphorylation (OxPhos). To detect small metabolites that participate in glycolysis and the tricarboxylic acid cycle (TCA) that supplies substrate for OxPhos, we carried out NMR-based metabolomics studies. We found that high levels of DEK significantly reprogrammed cellular metabolism and altered the abundances of amino acids, TCA cycle intermediates and the glycolytic end products lactate, alanine and NAD+. Taken together, these data support a scenario whereby overexpression of the human DEK oncogene reprograms keratinocyte metabolism to fulfill energy and macromolecule demands required to enable and sustain cancer cell growth.

[Monocarboxylate transporter 1 enhances the sensitivity of breast cancer cells to 3-bromopyruvate in vitro]

OBJECTIVE

To investigate the role of monocarboxylate transporter 1 (MCT1) in enhancing the sensitivity of breast cancer cells to 3-bromopyruvate (3-BrPA).

METHODS

The inhibitory effect of 3-BrPA on the proliferation of breast cancer cells was assessed with MTT assay, and brominated propidium bromide single staining flow cytometry was used for detecting the cell apoptosis. An ELISA kit was used to detect the intracellular levels of hexokinase II, lactate dehydrogenase, lactate, and adenosine triphosphate, and Western blotting was performed to detect the expression of MCT1. MDA-MB-231 cells were transiently transfected with MCT1 cDNA for over-expressing MCT1, and the effect of 3-BrPA on the cell proliferation and adenosine triphosphate level was deteced.

RESULTS

3-BrPA did not produce significant effects on the proliferation and apoptosis of MDA-MB-231 cells, and the cells treated with 200 µmol/L 3-BrPA for 24 h showed an inhibition rate and an apoptosis rate of only 8.72% and 7.8%, respectively. The same treatment, however, produced an inhibition rate and an apoptosis rate of 84.6% and 82.3% in MCF-7 cells, respectively. In MDA-MB-231 cells with MCT1 overexpression, 200 µmol/L 3-BrPA resulted in an inhibition rate of 72.44%, significantly higher than that in the control cells (P<0.05); treatment of the cells with 25, 50, 100, and 200 µmol/L 3-BrPA for 6 h resulted in intracellular adenosine triphosphate levels of 96.98%, 88.44%, 43.3% and 27.56% relative to the control level respectively.

CONCLUSION

MCT1 can enhance the sensitivity of breast cancer cells to 3-BrPA possibly by transporting 3-BrPA into cells to inhibit cell glycolysis.

[Monocarboxylate transporter 1 enhances the sensitivity of breast cancer cells to 3-bromopyruvate in vitro]

OBJECTIVE

To investigate the role of monocarboxylate transporter 1 (MCT1) in enhancing the sensitivity of breast cancer cells to 3-bromopyruvate (3-BrPA).

METHODS

The inhibitory effect of 3-BrPA on the proliferation of breast cancer cells was assessed with MTT assay, and brominated propidium bromide single staining flow cytometry was used for detecting the cell apoptosis. An ELISA kit was used to detect the intracellular levels of hexokinase II, lactate dehydrogenase, lactate, and adenosine triphosphate, and Western blotting was performed to detect the expression of MCT1. MDA-MB-231 cells were transiently transfected with MCT1 cDNA for over-expressing MCT1, and the effect of 3-BrPA on the cell proliferation and adenosine triphosphate level was deteced.

RESULTS

3-BrPA did not produce significant effects on the proliferation and apoptosis of MDA-MB-231 cells, and the cells treated with 200 µmol/L 3-BrPA for 24 h showed an inhibition rate and an apoptosis rate of only 8.72% and 7.8%, respectively. The same treatment, however, produced an inhibition rate and an apoptosis rate of 84.6% and 82.3% in MCF-7 cells, respectively. In MDA-MB-231 cells with MCT1 overexpression, 200 µmol/L 3-BrPA resulted in an inhibition rate of 72.44%, significantly higher than that in the control cells (P<0.05); treatment of the cells with 25, 50, 100, and 200 µmol/L 3-BrPA for 6 h resulted in intracellular adenosine triphosphate levels of 96.98%, 88.44%, 43.3% and 27.56% relative to the control level respectively.

CONCLUSION

MCT1 can enhance the sensitivity of breast cancer cells to 3-BrPA possibly by transporting 3-BrPA into cells to inhibit cell glycolysis.

Metabolic Cooperation and Competition in the Tumor Microenvironment: Implications for Therapy

The tumor microenvironment (TME) is an ensemble of non-tumor cells comprising fibroblasts, cells of the immune system, and endothelial cells, besides various soluble secretory factors from all cellular components (including tumor cells). The TME forms a pro-tumorigenic cocoon around the tumor cells where reprogramming of the metabolism occurs in tumor and non-tumor cells that underlies the nature of interactions as well as competitions ensuring steady supply of nutrients and anapleoretic molecules for the tumor cells that fuels its growth even under hypoxic conditions. This metabolic reprogramming also plays a significant role in suppressing the immune attack on the tumor cells and in resistance to therapies. Thus, the metabolic cooperation and competition among the different TME components besides the inherent alterations in the tumor cells arising out of genetic as well as epigenetic changes supports growth, metastasis, and therapeutic resistance. This review focuses on the metabolic remodeling achieved through an active cooperation and competition among the three principal components of the TME—the tumor cells, the T cells, and the cancer-associated fibroblasts while discussing about the current strategies that target metabolism of TME components. Further, we will also consider the probable therapeutic opportunities targeting the various metabolic pathways as well as the signaling molecules/transcription factors regulating them for the development of novel treatment strategies for cancer.

Central role of lactate and proton in cancer cell resistance to glucose deprivation and its clinical translation

Targeting common weaknesses of cancer is an important strategy for cancer therapy. Glucose is a nutrient that maintains essential cellular metabolism, supporting cancer cell survival, growth and proliferation. Depriving glucose rapidly kills cancer cells. Most cancer cells possess a feature called Warburg effect, which refers to that cancer cells even with ample oxygen exhibit an exceptionally high glycolysis rate and convert most incoming glucose to lactate. Although it is recognized that Warburg effect confers growth advantage to cancer cells when glucose supply is sufficient, this feature could be considered as a fatal weakness of cancer cells when glucose supply is a problem. As glucose supply in many solid tumors is poor, and as most cancer cells have exceptionally high glycolytic capacity, maximizing cancer cell glycolysis rate would possibly exhaust intratumoral glucose, leading cancer cell to death. Lactate and proton are two common factors in solid tumors, they jointly protect cancer cells against glucose deprivation, and they are also powerful regulators dictating glucose metabolic phenotypes of cancer cells. Disrupting the joint action of lactate and proton, for example, by means of bicarbonate infusion into tumor, could maximize cancer cell glycolytic rate to rapidly use up glucose, expose their vulnerability to glucose deprivation and ultimately kill cancer cells. A pilot clinical study demonstrated that this approach achieved a remarkable improvement in local control of large and huge hepatocellular carcinoma.

Multimodality Imaging Identifies Distinct Metabolic Profiles In Vitro and In Vivo

The study of alterations of tumor metabolism should allow the identification of new targets for innovative anticancer strategies. Metabolic alterations are generally established in vitro, and conclusions are often extrapolated to the in vivo situation without further tumor metabolic phenotyping. To highlight the key role of microenvironment on tumor metabolism, we studied the response of glycolytic and oxidative tumor models to metabolic modulations in vitro and in vivo. MDA-MB-231 and SiHa tumor models, characterized in vitro as glycolytic and oxidative, respectively, were studied. Theoretically, when passing from a hypoxic state to an oxygenated state, a Warburg phenotype should conserve a glycolytic metabolism, whereas an oxidative phenotype should switch from glycolytic to oxidative metabolism (Pasteur effect). This challenge was applied in vitro and in vivo to evaluate the impact of different oxic conditions on glucose metabolism. ¹⁸F-fluorodeoxyglucose uptake, lactate production, tumor oxygenation, and metabolic fluxes were monitored in vivo using positron emission tomography, microdialysis, electron paramagnetic resonance imaging, and ¹³C-hyperpolarizated magnetic resonance spectroscopy, respectively. In vitro, MDA-MB-231 cells were glycolytic under both hypoxic and oxygenated conditions, whereas SiHa cells underwent a metabolic shift after reoxygenation. On the contrary, in vivo, the increase in tumor oxygenation (induced by carbogen challenge) led to a similar metabolic shift in glucose metabolism in both tumor models. The major discordance in metabolic patterns observed in vitro and in vivo highlights that any extrapolation of in vitro metabolic profiling to the in vivo situation should be taken cautiously and that metabolic phenotyping using molecular imaging is mandatory in vivo.

Collagen Matrix Density Drives the Metabolic Shift in Breast Cancer Cells

Increased breast density attributed to collagen I deposition is associated with a 4-6 fold increased risk of developing breast cancer. Here, we assessed cellular metabolic reprogramming of mammary carcinoma cells in response to increased collagen matrix density using an in vitro 3D model. Our initial observations demonstrated changes in functional metabolism in both normal mammary epithelial cells and mammary carcinoma cells in response to changes in matrix density. Further, mammary carcinoma cells grown in high density collagen matrices displayed decreased oxygen consumption and glucose metabolism via the tricarboxylic acid (TCA) cycle compared to cells cultured in low density matrices. Despite decreased glucose entry into the TCA cycle, levels of glucose uptake, cell viability, and ROS were not different between high and low density matrices. Interestingly, under high density conditions the contribution of glutamine as a fuel source to drive the TCA cycle was significantly enhanced. These alterations in functional metabolism mirrored significant changes in the expression of metabolic genes involved in glycolysis, oxidative phosphorylation, and the serine synthesis pathway. This study highlights the broad importance of the collagen microenvironment to cellular expression profiles, and shows that changes in density of the collagen microenvironment can modulate metabolic shifts of cancer cells.

Expression of Cell-Surface Marker ABCB5 Causes Characteristic Modifications of Glucose, Amino Acid and Phospholipid Metabolism in the G3361 Melanoma-Initiating Cell Line

We present a pilot study aimed at determining the effects of expression of ATP-binding cassette member B5 (ABCB5), a previously described marker for melanoma-initiating cells, on cellular metabolism. Metabolic profiles for two groups of human G3361 melanoma cells were compared, i.e. wildtype melanoma cells with intact ABCB5 expression (ABCB5-WT) and corresponding melanoma cell variants with inhibited ABCB5 expression, through shRNA-mediated gene knockdown (ABCB5-KD). A comprehensive metabolomic analysis was performed by using proton and phosphorus NMR spectroscopy of cell extracts to examine water-soluble metabolites and lipids. Parametric and non-parametric statistical analysis of absolute and relative metabolite levels yielded significant differences for compounds involved in glucose, amino acid and phospholipid (PL) metabolism. By contrast, energy metabolism was virtually unaffected by ABCB5 expression. The sum of water-soluble metabolites per total protein was 17% higher in ABCB5-WT vs. ABCB5-KD G3361 variants, but no difference was found for the sum of PLs. Enhanced abundance was particularly pronounced for lactate (+ 23%) and alanine (+ 26%), suggesting an increase in glycolysis and potentially glutaminolysis. Increases in PL degradation products, glycerophosphocholine and glycerophosphoethanolamine (+ 85 and 123%, respectively), and redistributions within the PL pool suggested enhanced membrane PL turnover as a consequence of ABCB5 expression. The possibility of glycolysis modulation by an ABCB5-dependent IL1β-mediated mechanism was supported by functional studies employing monoclonal antibody (mAb)-dependent ABCB5 protein inhibition in wildtype G3361 melanoma cells. Our metabolomic results suggest that the underlying biochemical pathways may offer targets for melanoma therapy, potentially in combination with other treatment forms.

Metabolomics Analysis of Hormone-Responsive and Triple-Negative Breast Cancer Cell Responses to Paclitaxel Identify Key Metabolic Differences

To date, no targeted therapies are available to treat triple negative breast cancer (TNBC), while other breast cancer subtypes are responsive to current therapeutic treatment. Metabolomics was conducted to reveal differences in two hormone receptor-negative TNBC cell lines and two hormone receptor-positive Luminal A cell lines. Studies were conducted in the presence and absence of paclitaxel (Taxol). TNBC cell lines had higher levels of amino acids, branched-chain amino acids, nucleotides, and nucleotide sugars and lower levels of proliferation-related metabolites like choline compared with Luminal A cell lines. In the presence of paclitaxel, each cell line showed unique metabolic responses, with some similarities by type. For example, in the Luminal A cell lines, levels of lactate and creatine decreased while certain choline metabolites and myo-inositol increased with paclitaxel. In the TNBC cell lines levels of glutamine, glutamate, and glutathione increased, whereas lysine, proline, and valine decreased in the presence of drug. Profiling secreted inflammatory cytokines in the conditioned media demonstrated a greater response to paclitaxel in the hormone-positive Luminal cells compared with a secretion profile that suggested greater drug resistance in the TNBC cells. The most significant differences distinguishing the cell types based on pathway enrichment analyses were related to amino acid, lipid and carbohydrate metabolism pathways, whereas several biological pathways were differentiated between the cell lines following treatment.

A nonrandomized cohort and a randomized study of local control of large hepatocarcinoma by targeting intratumoral lactic acidosis

Background:

Previous works suggested that neutralizing intratumoral lactic acidosis combined with glucose deprivation may deliver an effective approach to control tumor. We did a pilot clinical investigation, including a nonrandomized (57 patients with large HCC) and a randomized controlled (20 patients with large HCC) study.

Methods:

The patients were treated with transarterial chemoembolization (TACE) with or without bicarbonate local infusion into tumor.

Results:

In the nonrandomized controlled study, geometric mean of viable tumor residues (VTR) in TACE with bicarbonate was 6.4-fold lower than that in TACE without bicarbonate (7.1% [95% CI: 4.6%–10.9%] vs 45.6% [28.9%–72.0%]; p<0.0001). This difference was recapitulated by a subsequent randomized controlled study. TACE combined with bicarbonate yielded a 100% objective response rate (ORR), whereas the ORR treated with TACE alone was 44.4% (nonrandomized) and 63.6% (randomized). The survival data suggested that bicarbonate may bring survival benefit.

Conclusions:

Bicarbonate markedly enhances the anticancer activity of TACE.

Funding:

Funded by National Natural Science Foundation of China.

Clinical trial number:

ChiCTR-IOR-14005319.

Surgery is the main treatment for liver cancer, but the most common liver cancer – called hepatocellular carcinoma – can sometimes become too large to remove safely. An alternative option to kill the tumor is to block its blood supply via a process called embolization. This procedure deprives the tumor cells of oxygen and nutrients such as glucose. However, embolization also prevents a chemical called lactic acid – which is commonly found around tumors – from being removed. Lactic acid actually helps to protect cancer cells and also aids the growth of new blood vessels, and so the “trapped” lactic acid may reduce the anticancer activity of embolization.

Previous works suggested that neutralizing the acidic environment in a tumor while depriving it of glucose via embolization could become a new treatment option for cancer patients. Chao et al. now report a small clinical trial that tested this idea and involved patients with large hepatocellular carcinomas. First, a group of thirty patients received the embolization treatment together with an injection of bicarbonate – a basic compound used to neutralize the lactic acid – that was delivered directly to the tumor. The neutralization killed these large tumors more effectively than what is typically seen in patients who just undergo embolization

Chao et al. then recruited another twenty patients and randomly assigned them to receive either just the embolization or the embolization with bicarbonate treatment. This randomized trial showed that the tumors died more and patients survived for longer if they received the bicarbonate together with the embolization treatment compared to those patients that were only embolized. In fact, four patients initially assigned to, and treated in, the embolization-only group subsequently asked to cross over to, and indeed received, the bicarbonate treatment as well.

These data indicate that this bicarbonate therapy may indeed be effective for patients with large tumors that are not amenable to surgery. In future, larger clinical trials will need to be carried out to verify these initial findings.

Anticancer strategies based on the metabolic profile of tumor cells: therapeutic targeting of the Warburg effect

Tumor cells rely mainly on glycolysis for energy production even in the presence of sufficient oxygen, a phenomenon termed the Warburg effect, which is the most outstanding characteristic of energy metabolism in cancer cells. This metabolic adaptation is believed to be critical for tumor cell growth and proliferation, and a number of onco-proteins and tumor suppressors, including the PI3K/Akt/mTOR signaling pathway, Myc, hypoxia-inducible factor and p53, are involved in the regulation of this metabolic adaptation. Moreover, glycolytic cancer cells are often invasive and impervious to therapeutic intervention. Thus, altered energy metabolism is now appreciated as a hallmark of cancer and a promising target for cancer treatment. A better understanding of the biology and the regulatory mechanisms of aerobic glycolysis has the potential to facilitate the development of glycolysis-based therapeutic interventions for cancer. In addition, glycolysis inhibition combined with DNA damaging drugs or chemotherapeutic agents may be effective anticancer strategies through weakening cell damage repair capacity and enhancing drug cytotoxicity.

Cancer metabolism: a therapeutic perspective

Awareness that the metabolic phenotype of cells within tumours is heterogeneous - and distinct from that of their normal counterparts - is growing. In general, tumour cells metabolize glucose, lactate, pyruvate, hydroxybutyrate, acetate, glutamine, and fatty acids at much higher rates than their nontumour equivalents; however, the metabolic ecology of tumours is complex because they contain multiple metabolic compartments, which are linked by the transfer of these catabolites. This metabolic variability and flexibility enables tumour cells to generate ATP as an energy source, while maintaining the reduction-oxidation (redox) balance and committing resources to biosynthesis - processes that are essential for cell survival, growth, and proliferation. Importantly, experimental evidence indicates that metabolic coupling between cell populations with different, complementary metabolic profiles can induce cancer progression. Thus, targeting the metabolic differences between tumour and normal cells holds promise as a novel anticancer strategy. In this Review, we discuss how cancer cells reprogramme their metabolism and that of other cells within the tumour microenvironment in order to survive and propagate, thus driving disease progression; in particular, we highlight potential metabolic vulnerabilities that might be targeted therapeutically.

Protein Kinase A Activation Promotes Cancer Cell Resistance to Glucose Starvation and Anoikis

Cancer cells often rely on glycolysis to obtain energy and support anabolic growth. Several studies showed that glycolytic cells are susceptible to cell death when subjected to low glucose availability or to lack of glucose. However, some cancer cells, including glycolytic ones, can efficiently acquire higher tolerance to glucose depletion, leading to their survival and aggressiveness. Although increased resistance to glucose starvation has been shown to be a consequence of signaling pathways and compensatory metabolic routes activation, the full repertoire of the underlying molecular alterations remain elusive. Using omics and computational analyses, we found that cyclic adenosine monophosphate-Protein Kinase A (cAMP-PKA) axis activation is fundamental for cancer cell resistance to glucose starvation and anoikis. Notably, here we show that such a PKA-dependent survival is mediated by parallel activation of autophagy and glutamine utilization that in concert concur to attenuate the endoplasmic reticulum (ER) stress and to sustain cell anabolism. Indeed, the inhibition of PKA-mediated autophagy or glutamine metabolism increased the level of cell death, suggesting that the induction of autophagy and metabolic rewiring by PKA is important for cancer cellular survival under glucose starvation. Importantly, both processes actively participate to cancer cell survival mediated by suspension-activated PKA as well. In addition we identify also a PKA/Src mechanism capable to protect cancer cells from anoikis. Our results reveal for the first time the role of the versatile PKA in cancer cells survival under chronic glucose starvation and anoikis and may be a novel potential target for cancer treatment.

Tumor heterogeneity exists in many human cancers, and it has been shown that it can play a role in tumor progression. Indeed, cell diversity may be critically important when tumors experience selective pressures, like nutrient deprivation, hypoxia, chemotherapy. PKA, through incompletely understood mechanisms, controls several cellular processes like cell growth, cell differentiation, cell metabolism, cell migration and, as more recently observed, also cancer progression. In this work, we show that activation of PKA induces the ability of a cancer cell sub-population to survive under strong stress conditions namely nutrient deprivation and cell detachment. Indeed, PKA activation in these cells results in autophagy induction, and at the same time, in activation of glutamine metabolism and Src kinase. Importantly, blocking directly the PKA pathway, as well as the autophagy, the glutamine metabolism or the Src pathway by inhibitory drugs, almost completely prevents cell growth of this sub-population of resistant cancer cells. These results suggest that drugs, targeting especially PKA pathway as well as downstream processes like autophagy, glutamine metabolism and Src signaling, may specifically inhibit cancer cells ability to survive under selective pressure favoring cancer resistance.

Irisin immunohistochemistry in gastrointestinal system cancers

Cancer is the leading cause of morbidity and mortality worldwide. Some studies have shown that high heat kills cancer cells. Irisin is a protein involved in heat production by converting white into brown adipose tissue, but there is no information about how its expression changes in cancerous tissues. We used irisin antibody immunohistochemistry to investigate changes in irisin expression in gastrointestinal cancers compared to normal tissues. Irisin was found in human brain neuroglial cells, esophageal epithelial cells, esophageal epidermoid carcinoma, esophageal adenocarcinoma and neuroendocrine esophageal carcinoma, gastric glands, gastric adenosquamous carcinoma, gastric neuroendocrine carcinoma, gastric signet ring cell carcinoma, neutrophils in vascular tissues, intestinal glands of colon, colon adenocarcinoma, mucinous colon adenocarcinoma, hepatocytes, hepatocellular carcinoma, islets of Langerhans, exocrine pancreas, acinar cells and interlobular and interlobular ducts of normal pancreas, pancreatic ductal adenocarcinoma, and intra- and interlobular ducts of cancerous pancreatic tissue. Histoscores (area × intensity) indicated that irisin was increased significantly in gastrointestinal cancer tissues, except liver cancers. Our findings suggest that the relation of irisin to cancer warrants further investigation.

Evidence That Does Not Support Pyruvate Kinase M2 (PKM2)-catalyzed Reaction as a Rate-limiting Step in Cancer Cell Glycolysis

It has been recognized that the rate-limiting function of pyruvate kinase M2 (PKM2) in glycolysis plays an important role in distributing glycolytic intermediates for anabolic and catabolic purposes in cancer cells. However, after analysis of the catalytic capacity of PKM2 relative to other glycolytic enzymes, the regulation range of PKM2 activity, metabolic flux control, and thermodynamics, we suggest that the PKM2-catalyzed reaction is not a rate-limiting step in cancer cell glycolysis. Hexokinase and phosphofructokinase 1 (PFK1), the first and third enzyme along the pathway, are rate-limiting enzymes that limit the overall glycolytic rate, whereas PKM2 and lactate dehydrogenase, the last two enzymes in the pathway, are for the fast removal of upstream intermediates to prevent the obstruction of the pathway. The argument is in accordance with the catalytic capacity of glycolytic enzymes, regulation range of enzyme activities, metabolic flux control, and thermodynamics.

NanoLC MALDI MS/MS based quantitative metabolomics reveals the alteration of membrane biogenesis in oral cancer

We present a label-free untargeted metabolomics approach using nanoLC-MALDI MS/MS interface for the separation, identification and quantification of the metabolites from cancer biopsies.

SUN2 exerts tumor suppressor functions by suppressing the Warburg effect in lung cancer

SUN2, a key component of LINC (linker of nucleoskeleton and cytoskeleton) complex located at the inner nuclear membrane, plays unknown role in lung cancer. We found that SUN2 expression was decreased in lung cancer tissue compared with paired normal tissues and that higher SUN2 levels predicted better overall survival and first progression survival. Overexpression of SUN2 inhibits cell proliferation, colony formation and migration in lung cancer, whereas knockdown of SUN2 promotes cell proliferation and migration. Additionally, SUN2 increases the sensitivity of lung cancer to cisplatin by inducing cell apoptosis. Mechanistically, we showed that SUN2 exerts its tumor suppressor functions by decreasing the expression of GLUT1 and LDHA to inhibit the Warburg effect. Finally, our results provided evidence that SIRT5 acts, at least partly, as a negative regulator of SUN2.Taken together, our findings indicate that SUN2 is a key component in lung cancer progression by inhibiting the Warburg effect and that the novel SIRT5/SUN2 axis may prove to be useful for the development of new strategies for treating the patients with lung cancer.

Nutrient deprivation-related OXPHOS/glycolysis interconversion via HIF-1α/C-MYC pathway in U251 cells

Although the Warburg effect is a dominant metabolic phenotype observed in cancers, the metabolic changes and adaptation occurring in tumors have been demonstrated to extend beyond the Warburg effect and thus considered a secondary effect to the transformation process of carcinogenesis, including nutritional deficiencies. However, the role of nutritional deficiencies in this metabolic reprogramming (e. g., oxidative phosphorylation (OXPHOS)/glycolysis interconversion) is not completely known yet. Here, we showed that under regular culture condition, the proliferation of U251 cells, but not other tumor cell lines, preferentially performed the Warburg effect and was remarkably inhibited by oxamic acid which can inhibit the activity of lactate dehydrogenase (LDH); whereas under serum starvation, glycolysis was depressed, tricarboxylic acid cycle (TCA) was enhanced, and the activity of OXPHOS was reinforced to maintain cellular ATP content in a high level, but interestingly, we observed a decreased expression of reactive oxygen species (ROS). Moreover, the upregulated activity of mitochondrial complex I was confirmed by Western blots and showed that the mitochondrial-related protein, NDUFA9, NDUFB8, ND1, and VDAC1 were remarkably increased after serum starved. Mechanistically, nutritional deficiencies could reduce hypoxia-inducible factor α (HIF-1α) protein expression to increase C-MYC protein level, which in turn increased nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM) transcription to enhance the activity of OXPHOS, suggesting that metabolic reprogramming by the changes of microenvironment during the carcinogenesis can provide some novel therapeutic clues to traditional cancer treatments.

Radiobiological modifiers in clinical radiation oncology: current reality and future potential

Radiation therapy can successfully ablate tumors. However, the same ionization process that destroys a cancer can also permanently damage surrounding organs resulting in unwanted clinical morbidity. Therefore, modern radiation therapy attempts to minimize dose to normal tissue to prevent side effects. Still, as tumors and normal tissues intercalate, the risk of normal tissue injury often may prevent tumoricidal doses of radiation therapy to be delivered. This paper will review current outcomes and limitations of radiobiological modifiers that may selectively enhance the radiosensitivity of tumors as well as parallel techniques that may protect normal tissues from radiation injury. Future endeavors based in part upon newly elucidated genetic pathways will be highlighted.