The Warburg effect and its cancer therapeutic implications

Melatonin antiproliferative effects require active mitochondrial function in embryonal carcinoma cells

Although melatonin oncostatic and cytotoxic effects have been described in different types of cancer cells, the specific mechanisms leading to its antitumoral effects and their metabolic context specificity are still not completely understood. Here, we evaluated the effects of melatonin in P19 embryonal carcinoma stem cells (CSCs) and in their differentiated counterparts, cultured in either high glucose medium or in a galactose (glucose-free) medium which leads to glycolytic suppression and increased mitochondrial metabolism. We found that highly glycolytic P19 CSCs were less susceptible to melatonin antitumoral effects while cell populations relying on oxidative metabolism for ATP production were more affected. The observed antiproliferative action of melatonin was associated with an arrest at S-phase, decreased oxygen consumption, down-regulation of BCL-2 expression and an increase in oxidative stress culminating with caspase-3-independent cell death. Interestingly, the combined treatment of melatonin and dichloroacetate had a synergistic effect in cells grown in the galactose medium and resulted in an inhibitory effect in the highly resistant P19 CSCs. Melatonin appears to exert its antiproliferative activity in P19 carcinoma cells through a mitochondrially-mediated action which in turn allows the amplification of the effects of dichloroacetate, even in cells with a more glycolytic phenotype.

Metabolomics identifies the intersection of phosphoethanolamine with menaquinone-triggered apoptosis in an in vitro model of leukemia

Altered metabolism is increasingly acknowledged as an important aspect of cancer, and thus serves as a potentially fertile area for the identification of therapeutic targets or leads. Our recent work using transcriptional data to predict metabolite levels in cancer cells led to preliminary evidence of the antiproliferative role of menaquinone (vitamin K2) in the Jurkat cell line model of acute lymphoblastic leukemia. However, nothing is known about the direct metabolic impacts of menaquinone in cancer, which could provide insights into its mechanism of action. Here, we used metabolomics to investigate the process by which menaquinone exerts antiproliferative activity on Jurkat cells. We first validated the dose-dependent, semi-selective, pro-apoptotic activity of menaquinone treatment on Jurkat cells relative to non-cancerous lymphoblasts. We then used mass spectrometry-based metabolomics to identify systems-scale changes in metabolic dynamics that are distinct from changes induced in non-cancerous cells or by other chemotherapeutics. One of the most significantly affected metabolites was phosphoethanolamine, which exhibited a two-fold increase in menaquinone-treated Jurkat cells compared to vehicle-treated cells at 24 h, growing to a five-fold increase at 72 h. Phosphoethanolamine elevation was observed prior to the induction of apoptosis, and was not observed in menaquinone-treated lymphoblasts or chemotherapeutic-treated Jurkat cells. We also validated the link between menaquinone and phosphoethanolamine in an ovarian cancer cell line, suggesting potentially broad applicability of their relationship. This metabolomics-based work is the first detailed characterization of the metabolic impacts of menaquinone treatment and the first identified link between phosphoethanolamine and menaquinone-induced apoptosis.

Malate-aspartate shuttle inhibitor aminooxyacetic acid leads to decreased intracellular ATP levels and altered cell cycle of C6 glioma cells by inhibiting glycolysis

NADH shuttles, including malate-aspartate shuttle (MAS) and glycerol-3-phosphate shuttle, can shuttle the reducing equivalents of cytosolic NADH into mitochondria. It is widely accepted that the major function of NADH shuttles is to increase mitochondrial energy production. Our study tested the hypothesis that the novel major function of NADH shuttles in cancer cells is to maintain glycolysis by decreasing cytosolic NADH/NAD(+) ratios. We found that AOAA, a widely used MAS inhibitor, led to decreased intracellular ATP levels, altered cell cycle and increased apoptosis and necrosis of C6 glioma cells, without affecting the survival of primary astrocyte cultures. AOAA also decreased the glycolytic rate and the levels of extracellular lactate and pyruvate, without affecting the mitochondrial membrane potential of C6 cells. Moreover, the toxic effects of AOAA were completely prevented by pyruvate treatment. Collectively, our study has suggested that AOAA may be used to selectively decrease glioma cell survival, and the major function of MAS in cancer cells may be profoundly different from its major function in normal cells: The major function of MAS in cancer cells is to maintain glycolysis, instead of increasing mitochondrial energy metabolism.

High expression of hexokinase domain containing 1 is associated with poor prognosis and aggressive phenotype in hepatocarcinoma

Rapid progress and metastasis remain the major treatment failure modes of hepatocarcinoma (HCC). Unfortunately, the underlying molecular mechanisms of hepatoma cell proliferation and migration are poorly understood. Metabolic abnormalities play critical roles in tumorigenesis and progression. Hexokinase domain containing 1 (HKDC1) catalyzes the phosphorylation of glucose. However, the functions and mechanisms of HKDC1 in cancer remain unknown. In this study, real-time RT-PCR and Western blotting assays were used to detect the HKDC1 expression levels in HCC tissues and cell lines. The Oncomine™ Cancer Microarray Database was applied to analysis the correlations between HKDC1 expression and HCC clinical characteristics. MTT and Transwell migration assays were performed to determine the functions of HKDC1 in HCC cells. The effect of HKDC1 on Wnt/β-catenin signaling pathway was assessed using Western blotting assay. In this study, we found that HKDC1 expression levels were elevated in HCC tissues compared with the adjacent tissues. HCC patients with high expression levels of HKDC1 had poor overall survival (OS). Furthermore, higher HKDC1 levels also predicted a worse OS of patients within solitary, elevated pre-operated serum alpha fetoprotein (AFP) level and higher tumor diameter. Moreover, silencing HKDC1 suppressed HCC cells proliferation and migration in vitro. Downregulated HKDC1 expression repressed β-Catenin and c-Myc expression, which indicates that silencing HKDC1 may reduce proliferation and migration via inhibiting the Wnt/β-catenin signaling pathway in HCC. In summary, HKDC1 provides further insight into HCC tumor progression and may provide a novel prognostic biomarker and therapeutic target for HCC treatment.

Metabolic alterations and drug sensitivity of tyrosine kinase inhibitor resistant leukemia cells with a FLT3/ITD mutation

Internal tandem duplication (ITD) of the juxtamembrane region of FMS-like tyrosine kinase-3 (FLT3) receptor is a common type of mutation in adult acute myeloid leukemia (AML), and patient response to FLT3 inhibitors appears to be transient due to the emergence of drug resistance. We established two sorafenib-resistant cell lines carrying FLT3/ITD mutations, including the murine BaF3/ITD-R and human MV4-11-R cell lines. Gene expression profile analysis of the resistant and parental cells suggests that the highest ranked molecular and cellular functions of the differentially expressed genes are related to mitochondrial dysfunction. Both murine and human resistant cell lines display a longer doubling time, along with a significant inhibition of mitochondrial respiratory chain activity and substantial upregulation of glycolysis. The sorafenib-resistant cells exhibit increased expression of a majority of glycolytic enzymes, including hexokinase 2, which is also highly expressed in the mitochondrial fraction and is associated with resistance to apoptotic cell death. The sorafenib-resistant cells are collaterally sensitive to a number of glycolytic inhibitors including 2-deoxyglucose and 3-bromopyruvate propylester. Our study reveals a metabolic signature of sorafenib-resistant cells and suggests that glycolytic inhibition may override such resistance and warrant further clinical investigation.

[REPROGRAMMING OF MITOCHONDRIAL ENERGY METABOLISM IN MALIGNANT NEOPLASMS]

The novel ideas of fundamental role of mitochondria in the maintenance of viability of malignant cells have been reviewed. The modern state of research is considered in detail, including: mitochondrial control of the cellular redox state, sites of reactive oxygen species (ROS) production in inner mitochondrial membrane and antioxidant protection systems. Specificities of the structural-functional mitochondrial remodelling in malignant tumors, the mechanisms of the energy metabolism reprogramming, enhancement of the ROS production and adaptation to the hypoxic conditions and metabolic stress are analyzed. The available data including our research on transplanted tumors indicate that cytotoxic action of sodium dichloroacetate (the inhibitor of pyruvate dehydrogenase kinase) depends on biological properties of tumors and intensity of structural-functional mitochondrial rearrangement. Dichloroacetate turned out to be effective for sarcoma 37, but not for Lewis lung carcinoma.

Role of mitochondrial dysfunction in cancer progression

Deregulated cellular energetics was one of the cancer hallmarks. Several underlying mechanisms of deregulated cellular energetics are associated with mitochondrial dysfunction caused by mitochondrial DNA mutations, mitochondrial enzyme defects, or altered oncogenes/tumor suppressors. In this review, we summarize the current understanding about the role of mitochondrial dysfunction in cancer progression. Point mutations and copy number changes are the two most common mitochondrial DNA alterations in cancers, and mitochondrial dysfunction induced by chemical depletion of mitochondrial DNA or impairment of mitochondrial respiratory chain in cancer cells promotes cancer progression to a chemoresistance or invasive phenotype. Moreover, defects in mitochondrial enzymes, such as succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase, are associated with both familial and sporadic forms of cancer. Deregulated mitochondrial deacetylase sirtuin 3 might modulate cancer progression by regulating cellular metabolism and oxidative stress. These mitochondrial defects during oncogenesis and tumor progression activate cytosolic signaling pathways that ultimately alter nuclear gene expression, a process called retrograde signaling. Changes in the intracellular level of reactive oxygen species, Ca(2+), or oncometabolites are important in the mitochondrial retrograde signaling for neoplastic transformation and cancer progression. In addition, altered oncogenes/tumor suppressors including hypoxia-inducible factor 1 and tumor suppressor p53 regulate mitochondrial respiration and cellular metabolism by modulating the expression of their target genes. We thus suggest that mitochondrial dysfunction plays a critical role in cancer progression and that targeting mitochondrial alterations and mitochondrial retrograde signaling might be a promising strategy for the development of selective anticancer therapy.

Metabolism-related enzyme alterations identified by proteomic analysis in human renal cell carcinoma

The renal cell carcinoma (RCC) is one of the most common types of kidney neoplasia in Western countries; it is relatively resistant to conventional chemotherapy and radiotherapy. Metabolic disorders have a profound effect on the degree of malignancy and treatment resistance of the tumor. However, the molecular characteristics related to impaired metabolism leading to the initiation of RCC are still not very clear. In this study, two-dimensional electrophoresis (2-DE) and mass spectra (MS) technologies were utilized to identify the proteins involved in energy metabolism of RCC. A total of 73 proteins that were differentially expressed in conventional RCC, in comparison with the corresponding normal kidney tissues, were identified. Bioinformatics analysis has shown that these proteins are involved in glycolysis, urea cycle, and the metabolic pathways of pyruvate, propanoate, and arginine/proline. In addition, some were also involved in the signaling network of p53 and FAS. These results provide some clues for new therapeutic targets and treatment strategies of RCC.

Cancer stem cells, metabolism, and therapeutic significance

Cancer stem cells (CSCs) have attracted much attention of the research community in the recent years. Due to their highly tumorigenic and drug-resistant properties, CSCs represent important targets for developing novel anticancer agents and therapeutic strategies. CSCs were first described in hematopoietic malignancies and subsequently identified in various types of solid tumors including brain, breast, lung, colon, melanoma, and ovarian cancer. CSCs possess special biological properties including long-term self-renewal capacity, multi-lineage differentiation, and resistance to conventional chemotherapy and radiotherapy. As such, CSCs are considered as a major source of residual disease after therapy leading to disease occurrence. Thus, it is very important to understand the cellular survival mechanisms specific to CSCs and accordingly develop effective therapeutic approaches to eliminate this subpopulation of cancer cells in order to improve the treatment outcome of cancer patients. Possible therapeutic strategies against CSCs include targeting the self-renewal pathways of CSCs, interrupting the interaction between CSCs and their microenvironment, and exploiting the unique metabolic properties of CSCs. In this review article, we will provide an overview of the biological characteristics of CSCs, with a particular focus on their metabolic properties and potential therapeutic strategies to eliminate CSCs.

Evidence-based support for the use of proton pump inhibitors in cancer therapy

‘We can only cure what we can understand first’, said Otto H. Warburg, the 1931 Nobel laureate for his discovery on tumor metabolism. Unfortunately, we still don’t know too much the mechanisms underlying of cancer development and progression. One of the unsolved mystery includes the strategies that cancer cells adopt to cope with an adverse microenvironment. However, we knew, from the Warburg’s discovery, that through their metabolism based on sugar fermentation, cancer cells acidify their microenvironment and this progressive acidification induces a selective pressure, leading to development of very malignant cells entirely armed to survive in the hostile microenvironment generated by their own metabolism. One of the most mechanism to survive to the acidic tumor microenvironment are proton exchangers not allowing intracellular acidification through a continuous elimination of H⁺ either outside the cells or within the internal vacuoles. This article wants to comment a translational process through which from the preclinical demonstration that a class of proton pump inhibitors (PPI) exploited worldwide for peptic ulcer treatment and gastroprotection are indeed chemosensitizers as well, we have got to the clinical proof of concept that PPI may well be included in new anti-cancer strategies, and with a solid background and rationale.

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.

Microenvironment acidity as a major determinant of tumor chemoresistance: Proton pump inhibitors (PPIs) as a novel therapeutic approach

Despite the major progresses in biomedical research and the development of novel therapeutics and treatment strategies, cancer is still among the dominant causes of death worldwide. One of the crucial challenges in the clinical management of cancer is primary (intrinsic) and secondary (acquired) resistance to both conventional and targeted chemotherapeutics. Multiple mechanisms have been identifiedthat underlie intrinsic and acquired chemoresistance: these include impaired drug uptake, increased drug efflux, deletion of receptors, altered drug metabolism, quantitative and qualitative alterations in drug targets, increased DNA damage repair and various mechanisms of anti-apoptosis. The fast efflux of anticancer drugs mediated by multidrug efflux pumps and the partial or complete reversibility of chemoresistance combined with the absence of genetic mutations suggests a multifactorial process. However, a growing body of recent evidence suggests that chemoresistance is often triggered by the highly acidic microenvironment of tumors. The vast majority of drugs, including conventional chemotherapeutics and more recent biological agents, are weak bases that are quickly protonated and neutralized in acidic environments, such as the extracellular microenvironment and the acidic organelles of tumor cells. It is therefore essential to develop new strategies to overcome the entrapment and neutralization of weak base drugs. One such strategy is the use of proton pump inhibitors which can enhance tumor chemosensitivity by increasing the pH of the tumor microenvironment. Recent clinical trials in animals with spontaneous tumors have indicated that patient alkalization is capable of reversing acquired chemoresistance in a large percentage of tumors that are refractory to chemotherapy. Of particular interest was the benefit of alkalization for patients undergoing metronomic regimens which are becoming more widely used in veterinary medicine. Overall, these results provide substantial new evidence that altering the acidic tumor microenvironment is an effective, well tolerated and low cost strategy for the overcoming of anticancer drug resistance.

Energy metabolism determines the sensitivity of human hepatocellular carcinoma cells to mitochondrial inhibitors and biguanide drugs

Human hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide particularly in Asia. Deregulation of cellular energetics was recently included as one of the cancer hallmarks. Compounds that target the mitochondria in cancer cells were proposed to have therapeutic potential. Biguanide drugs which inhibit mitochondrial complex I and repress mTOR signaling are clinically used to treat type 2 diabetes mellitus patients (T2DM) and were recently found to reduce the risk of HCC in T2DM patients. However, whether alteration of energy metabolism is involved in regulating the sensitivity of HCC to biguanide drugs is still unclear. In the present study, we treated four HCC cell lines with mitochondrial inhibitors (rotenone and oligomycin) and biguanide drugs (metformin and phenformin), and found that the HCC cells which had a higher mitochondrial respiration rate were more sensitive to these treatments; whereas the HCC cells which exhibited higher glycolysis were more resistant. When glucose was replaced by galactose in the medium, the altered energy metabolism from glycolysis to mitochondrial respiration in the HCC cells enhanced the cellular sensitivity to mitochondrial inhibitors and biguanides. The energy metabolism change enhanced AMP-activated protein kinase (AMPK) activation, mTOR repression and downregulation of cyclin D1 and Mcl-1 in response to the mitochondrial inhibitors and biguanides. In conclusion, our results suggest that increased mitochondrial oxidative metabolism upregulates the sensitivity of HCC to biguanide drugs. Enhancing the mitochondrial oxidative metabolism in combination with biguanide drugs may be a therapeutic strategy for HCC.

Multifaceted roles of HSF1 in cancer

Heat shock transcription factor 1 (HSF1) is the master regulator of the heat shock response. Accumulating evidence shows that HSF1 is overexpressed in a variety of human cancers, is associated with cancer aggressiveness, and could serve as an independent diagnostic or prognostic biomarker. In this review, we will provide an overview of the multifaceted roles of HSF1 in cancer, with a special focus on the four underlying molecular mechanisms involved. First, HSF1 regulates the expression of heat shock proteins (HSPs) including HSP90, HSP70, and HSP27. Second, HSF1 regulates cellular metabolism, including glycolysis and lipid metabolism. Third, HSF1 serves as a regulator of different signaling pathways, such as HuR-HIF-1, Slug, protein kinase C (PKC), nuclear factor-kappaB (NF-κB), PI3K-AKT-mTOR, and mitogen-activated protein kinase (MAPK) pathways. Finally, HSF1 regulates microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Overall, HSF1 plays many important roles in cancer via regulating cell proliferation, anti-apoptosis, epithelial-mesenchymal transition (EMT), migration, invasion, and metastasis and may be a potential therapeutic target for human cancers.

Molecular Analysis by Gene Expression of Mitochondrial ATPase Subunits in Papillary Thyroid Cancer: Is ATP5E Transcript a Possible Early Tumor Marker?

BACKGROUND

Cancer development involves an "injury" to the respiratory machinery (Warburg effect) due to decreased or impaired mitochondrial function. This circumstance results in a down regulation of some of the ATPase subunits of the malignant tissue. The objective of this work was to assess and compare the relative expression of mRNA of mitochondrial ATPase subunits between samples of thyroid cancer and benign nodules.

MATERIAL AND METHODS

Samples from 31 patients who had an operation for PTC at the General Hospital of Mexico were snap-frozen and stored at -70°C. Thirty-five patients who had an operation for benign tumors were also included in the study. mRNA expression levels of alpha, beta, gamma, and epsilon subunits of F1 and "c12" of subunit Fo were determined by real-time RT-PCR (by duplicate), in order to determine if abnormal expression of these genes could partially explain the Warburg effect in papillary thyroid cancer (PTC).

RESULTS

ATP5E transcript alteration (down-expression) was highly associated to PTC diagnosis OR=11.76 (95% confidence interval, 1.245-237.98; p=0.04).

CONCLUSIONS

Relative down-expression of ATP5E transcript was highly associated with PTC diagnosis. This transcript alteration may be used as a tumoral marker in papillary thyroid cancer.

Proton pump inhibitors while belonging to the same family of generic drugs show different anti-tumor effect

CONTEXT

Tumor acidity represents a major cause of chemoresistance. Proton pump inhibitors (PPIs) can neutralize tumor acidity, sensitizing cancer cells to chemotherapy.

OBJECTIVE

To compare the anti-tumor efficacy of different PPIs in vitro and in vivo.

MATERIALS AND METHODS

In vitro experiments PPIs anti-tumor efficacy in terms of cell proliferation and cell death/apoptosis/necrosis evaluation were performed. In vivo PPIs efficacy experiments were carried out using melanoma xenograft model in SCID mice.

RESULTS

Lansoprazole showed higher anti-tumor effect when compared to the other PPIs. The lansoprazole effect lasted even upon drug removal from the cell culture medium and it was independent from the lipophilicity of the PPIs formulation.

DISCUSSION

These PPIs have shown different anti-tumoral efficacy, and the most effective at low dose was lansoprazole.

CONCLUSION

The possibility to contrast tumor acidity by off-label using PPIs opens a new field of oncology investigation.

Expression of pyruvate dehydrogenase is an independent prognostic marker in gastric cancer

AIM: To investigate the expression and prognostic role of pyruvate dehydrogenase (PDH) in gastric cancer (GC).

METHODS: This study included 265 patients (194 male, 71 female, mean age 59 years (range, 29-81 years) with GC who underwent curative surgery at the First Affiliated Hospital of China Medical University from January 2006 to May 2007. All patients were followed up for more than 5 years. Patient-derived paraffin embedded GC specimens were collected for tissue microarrays (TMAs). We examined PDH expression by immunohistochemistry in TMAs containing tumor tissue and matched non-neoplastic mucosa. Immunoreactivity was evaluated independently by two researchers. Overall survival (OS) rates were determined using the Kaplan-Meier estimator. Correlations with other clinicopathologic factors were evaluated by two-tailed χ² tests or a two-tailed t-test. The Cox proportional-hazard model was used in univariate analysis and multivariate analysis to identify factors significantly correlated with prognosis.

RESULTS: Immunohistochemistry showed that 35.47% of total cancer tissue specimens had cytoplasmic PDH staining. PDH expression was much higher in normal mucosa specimens (75.09%; P = 0.001). PDH expression was correlated with Lauren grade (70.77% in intestinal type vs 40.0% in diffuse type; P = 0.001), lymph node metastasis (65.43% with no metastasis vs 51.09% with metastasis; P = 0.033), lymphatic invasion (61.62% with no invasion vs 38.81% with invasion; P = 0.002), histologic subtypes (70.77% in intestinal type vs 40.0% in diffuse type; P = 0.001) and tumor-node-metastasis (TNM) stage (39% in poorly differentiated vs 65.91% in well differentiated and 67.11% in moderately differentiated; P = 0.001) in GC. PDH expression in cancer tissue was significantly associated with higher OS (P < 0.001). The multivariate analysis adjusted for age, Lauren classification, TNM stage, lymph node metastasis, histological type, tumor size, depth of invasion and lymphatic invasion showed that the PDH expression in GC was an independent prognostic factor for higher OS (HR = 0.608, 95%CI: 0.504-0.734, P < 0.001).

CONCLUSION: Our study indicated that PDH expression is an independent prognostic factor in GC patients and that positive expression of PDH may be predictive of favorable outcomes.

Screening of novel inhibitors targeting lactate dehydrogenase A via four molecular docking strategies and dynamics simulations

Lactate dehydrogenase A (LDHA) is a metabolic enzyme which catalyzes the interconversion of lactate and pyruvate in the glycolysis pathway, thus playing key roles in aerobic glycolysis. The inhibition of LDHA by small molecules has become an attractive strategy for anticancer therapy in recent years. However, very few LDHA inhibitors have been reported, even though a great deal of effort has directed into identifying LDHA inhibitors using structure-based approaches. Therefore, high-throughput and high-accuracy screening approaches are still urgently needed in order to target LDHA effectively. In the present work, after establishing that our docking strategies performed well using test datasets, we screened 32791 Specs products for their docking scores with the substrate-binding pocket and, separately, the cofactor-binding pocket of LDHA. We subsequently identified 76 hits (i.e., ligands that show low docking scores) for the cofactor-binding pocket and 27 hits for the substrate-binding pocket. Two representative compounds, ZINC20036549 and ZINC19369718, were then chosen for further MD simulation analysis, and we found that these compounds maintained their inhibitory activity during the MD simulations. Meanwhile, we found that ZINC19369718 interacts with a novel binding site close to the active site, and that this interaction may inhibit the catalytic activity of LDHA. Together, these results offer not only a new paradigm for identifying Specs drug-like products for novel therapeutic use but they also provide further opportunity to adopt LDHA inhibition as a strategy for cancer therapy.

Functional and dynamic state of inner mitochondrial membrane of sarcoma 37 in mice under administration of sodium dichloroacetate

The activity of enzymes of the respiratory chain and structural-dynamic properties of the inner mitochondrial membrane (IMM) of sarcoma 37 (S37) in mice under sodium dichloroacetate (SDA) administration in a daily dose of 86 mg/kg of body weight starting from the 2nd day after tumor transplantation were investigated. The dynamic and structural state of the IMM components was determined using the fluorescent probes. With S37 growth the intensification of glycolytic metabolism occurred on the background of suppressed functional capacity of mitochondrial respiratory chain enzymes. The changes of conformational properties of protein molecules and the increase of IMM lipid phase microviscosity were shown. The administration of SDA promotes the decrease of lactate content and the increase of pyruvate dehydrogenase activity in S37. This was accompanied by further suppression of the functional activity of the respiratory chain complexes and H+-ATPase coupled with conformational modification ofprotein molecules and changes of the structural orderliness of the IMM lipid phase, possibly due to intensification of reactive oxygen species generation.

Mitochondria: The ketogenic diet--A metabolism-based therapy

Mitochondria are the energy-producing organelles of the cell, generating ATP via oxidative phosphorylation mainly by using pyruvate derived from glycolytic processing of glucose. Ketone bodies generated by fatty acid oxidation can serve as alternative metabolites for aerobic energy production. The ketogenic diet, which is high in fat and low in carbohydrates, mimics the metabolic state of starvation, forcing the body to utilize fat as its primary source of energy. The ketogenic diet is used therapeutically for pharmacoresistant epilepsy and for "rare diseases" of glucose metabolism (glucose transporter type 1 and pyruvate dehydrogenase deficiency). As metabolic reprogramming from oxidative phosphorylation toward increased glycolysis is a hallmark of cancer cells; there is increasing evidence that the ketogenic diet may also be beneficial as an adjuvant cancer therapy by potentiating the antitumor effect of chemotherapy and radiation treatment. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

Evaluating the evidence for targeting FOXO3a in breast cancer: a systematic review

Background

Tumour cells show greater dependency on glycolysis so providing a sufficient and rapid energy supply for fast growth. In many breast cancers, estrogen, progesterone and epidermal growth factor receptor-positive cells proliferate in response to growth factors and growth factor antagonists are a mainstay of treatment. However, triple negative breast cancer (TNBC) cells lack receptor expression, are frequently more aggressive and are resistant to growth factor inhibition. Downstream of growth factor receptors, signal transduction proceeds via phosphatidylinositol 3-kinase (PI3k), Akt and FOXO3a inhibition, the latter being partly responsible for coordinated increases in glycolysis and apoptosis resistance. FOXO3a may be an attractive therapeutic target for TNBC. Therefore we have undertaken a systematic review of FOXO3a as a target for breast cancer therapeutics.

Methods

Articles from NCBI were retrieved systematically when reporting primary data about FOXO3a expression in breast cancer cells after cytotoxic drug treatment.

Results

Increased FOXO3a expression is common following cytotoxic drug treatment and is associated with apoptosis and cell cycle arrest. There is some evidence that metabolic enzyme expression is also altered and that this effect is also elicited in TNBC cells. FOXO3a expression serves as a positive prognostic marker, especially in estrogen (ER) receptor positive cells.

Discussion

FOXO3a is upregulated by a number of receptor-dependent and -independent anti-cancer drugs and associates with apoptosis. The identification of microRNA that regulate FOXO3a directly suggest that it offers a tangible therapeutic target that merits wider evaluation.

Histopathological determinants of tumor resistance: a special look to the immunohistochemical expression of carbonic anhydrase IX in human cancers

Intrinsic and acquired drug resistance of tumor cells still causes the failure of treatment regimens in advanced human cancers. It may be driven by intrinsic tumor cells features, or may also arise from micro environmental influences. Hypoxia is a microenvironment feature associated with the aggressiveness and metastasizing ability of human solid cancers. Hypoxic cancer cells overexpress Carbonic Anhydrase IX (CA IX). CA IX ensures a favorable tumor intracellular pH, while contributing to stromal acidosis, which facilitates tumor invasion and metastasis. The overexpression of CA IX is considered an epiphenomenon of the presence of hypoxic, aggressive tumor cells. Recently, a relationship between CA IX overexpression and the cancer stem cells (CSCs) population has been hypothesized. CSCs are strictly regulated by tumor hypoxia and drive a major non-mutational mechanism of cancer drug-resistance. We reviewed the current data concerning the role of CA IX overexpression in human malignancies, extending such information to the expression of the stem cells markers CD44 and nestin in solid cancers, to explore their relationship with the biological behavior of tumors. CA IX is heavily expressed in advanced tumors. A positive trend of correlation between CA IX overexpression, tumor stage/grade and poor outcome emerged. Moreover, stromal CA IX expression was associated with adverse events occurrence, maybe signaling the direct action of CA IX in directing the mesenchymal changes that favor tumor invasion; in addition, membranous/cytoplasmic co-overexpression of CA IX and stem cells markers were found in several aggressive tumors. This suggests that CA IX targeting could indirectly deplete CSCs and counteract resistance of solid cancers in the clinical setting.

2-Deoxy-D-glucose treatment changes the Golgi apparatus architecture without blocking synthesis of complex lipids

The classic Golgi apparatus organization, an arrangement of highly ordered cisternal stacks with tubular-vesicular membrane specializations on both sides, is the functional image of a continuous flow of contents and membranes with input, metabolization, and output in a dynamic steady state. In response to treatment with 2-deoxy-D-glucose (2-DG), which lowers the cellular ATP level by about 70% within minutes, this organization is rapidly replaced by tubular-glomerular membrane convolutes described as Golgi networks and bodies. 2-DG is a non-metabolizable glucose analogue and competitive inhibitor of glycolysis, which has become attractive in the context of therapeutic approaches for several kinds of tumors specifically targeting glycolysis in cancer. With the question of whether the functions of the Golgi apparatus in lipid synthesis would be influenced by the 2-DG-induced Golgi apparatus reorganization, we focused on lipid metabolism within the Golgi bodies. For this, we applied a fluorophore-labeled short-chain ceramide (BODIPY-Cer) in various combinations with 2-DG treatment to HepG2 cell cultures and followed uptake, enrichment and metabolization to higher ordered lipids. The cellular ATP status in each experiment was controlled with a bioluminescence assay, and the response of the Golgi apparatus was tracked by immunostaining of the trans-Golgi network protein TGN46. For electron microscopy, the fluorescent BODIPY-Cer signals were converted into electron-dense precipitates by photooxidation of diaminobenzidine (DAB); DAB precipitates labeled trans-Golgi areas in control cultures but also compartments at the periphery of the Golgi bodies formed in response to 2-DG treatment, thus indicating that concentration of ceramide takes place in spite of the Golgi apparatus reorganization. Lipid analyses by thin-layer chromatography (TLC) performed in parallel showed that BODIPY-Cer is not only concentrated in compartments of the 2-DG-induced Golgi bodies but is partly metabolized to BODIPY-sphingomyelin. Both, uptake and condensation of BODIPY-Cer and its conversion to complex lipids indicate that functions of the Golgi apparatus in the cellular lipid metabolism persist although the classic Golgi apparatus organization is abolished.

The α-tocopherol derivative ESeroS-GS induces cell death and inhibits cell motility of breast cancer cells through the regulation of energy metabolism

Cancer cells are known to exhibit different hallmarks compared with normal cells. Therefore, targeting these features may improve the response to cancer therapy. In this study, we provided direct evidence that the α-tocopherol derivative ESeroS-GS inhibited the viability, migration, and invasion of breast cancer cells. ESeroS-GS induced cell death in different cancer cells in a dose-dependent manner but showed no significant effects on MCF-10A mammary epithelial cells. Although the ESeroS-GS-induced cell death in MDA-MB-231 breast cancer cells was accompanied with the generation of reactive oxygen species and the down regulation of mitochondrial membrane potential (MMP), no such effect on reactive oxygen species and MMP was seen in MCF-10A cells. Further studies indicated that ESeroS-GS down-regulated the expression of hexokinase II, SDH B, UQCRC2 and COX II in MDA-MB-231 cells but not in MCF-10A cells. The down-regulation of these enzymes accounts for the decreased oxidative phosphorylation (OXPHOS) and glycolysis in MDA-MB-231 cells upon ESeroS-GS treatment. We also found that sub-toxic concentration of ESeroS-GS treatment resulted in the impairment of F-actin cytoskeleton assembly and the consequently decreased migratory and invasive ability of MDA-MB-231 cells, which might be due to the inhibition of cellular energy metabolism. These results indicate that ESeroS-GS shows potential to become a novel anti-cancer agent by targeting the energy metabolism of cancer cells.

Profilin-1 suppresses tumorigenicity in pancreatic cancer through regulation of the SIRT3-HIF1α axis

Background

Tumor cells exhibit abnormal actin remodeling profiles, which involve the altered expressions of several important actin-binding proteins. Profilin1 (Pfn1), originally identified as an actin-associated protein, has been linked to several human malignancies. Our recent studies suggested that Pfn1 facilitates apoptosis in pancreatic cancer cells. Here, we investigated the exact role of Profilin1 (Pfn1) in pancreatic adenocarcinoma (PDAC) and the underlying mechanisms.

Methods

Pfn1 protein expression in PDAC specimens was analyzed by immunohistochemistry using a tissue microarray (TMA) containing PDAC tumor tissue and corresponding normal tissue samples from 72 patients. The effect of Pfn1 expression on cancer proliferation was assessed in cells by up- and down-regulation of Pfn1 in vitro and in vivo. Immunoprecipitation and mass spectrometry were used to identify the Pfn1-associated proteins and potential pathways.

Results

Pfn1 was downregulated in clinical pancreatic adenocarcinoma specimens compared with the surrounding benign tissues. Univariate survival analysis of the PDAC cohorts showed that low expression of Pfn1 was significantly correlated with shortened patient survival (mean 14.2 months versus 20.9 months, P < 0.05). Restoration of Pfn1 in pancreatic cancer cells with low endogenous Pfn1 expression resulted in a nontumorigenic phenotype, suggesting that Pfn1 may be a negative regulator of pancreatic cancer progression. Overexpression of Pfn1 in vivo decreased the tumor volume in orthotopic xenograft nude mice models. Pfn1 upregulated the expression of SIRT3, leading to HIF1α destabilization. This data revealed that aberrant Pfn1 expression contributes to pancreatic cancer progression.

Conclusions

Our data suggest that Pfn1 is a tumor suppressor in pancreatic cancer that acts via a novel mechanism of regulating the SIRT3-HIF1α axis, independently of its cytoskeleton-related activity.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-187) contains supplementary material, which is available to authorized users.

Novel proteomic biomarker panel for prediction of aggressive metastatic hepatocellular carcinoma relapse in surgically resectable patients

The natural course of early HCC is unknown, and its progression to intermediate and advanced HCC can be diverse. Some early stage HCC patients enjoy prolonged disease-free survival, whereas others suffer aggressive relapse to stage IV metastatic cancer within a year. Comparative proteomics of HCC tumor tissues was carried out using 2D-DIGE and MALDI-TOF/TOF MS to identify proteins that can distinguish these two groups of stage I HCC patients. Twelve out of 148 differentially regulated protein spots were found to differ by approximately 2-fold for the relapse versus nonrelapse patient tissues. Four proteins, namely, heat shock 70 kDa protein 1, argininosuccinate synthase, isoform 2 of UTP-glucose-1-phosphate uridylyltransferase, and transketolase, were shown to have the potential to differentiate metastatic relapse (MR) from nonrelapse (NR) HCC patients after validation by western blotting and immunohistochemical assays. Subsequent TMA analysis revealed a three marker panel of HSP70, ASS1, and UGP2 to be statistically significant in stratifying the two groups of HCC patients. This combination panel achieved high levels of sensitivity and specificity, which has potential for clinical use in identifying HCC tumors prone to MR. This stratification will allow development of clinical management, including close follow-up and possibly treatment options, in the near future.

Pros and cons of bifunctional platinum(IV) antitumor prodrugs: two are (not always) better than one

This article evaluates the efficacy and applicability of bifunctional prodrugs consisting of a six-coordinate Pt(iv) octahedral core and one or more bioactive molecules. The platinum(iv) complexes release upon reduction the corresponding cytotoxic Pt(ii) agents and the bioactive molecules, able to inhibit some biochemical mechanisms of cancer growth and/or prevent the deactivation of the Pt(ii) metabolites.

Somatic alterations in mitochondrial DNA and mitochondrial dysfunction in gastric cancer progression

Energy metabolism reprogramming was recently identified as one of the cancer hallmarks. One of the underlying mechanisms of energy metabolism reprogramming is mitochondrial dysfunction caused by mutations in nuclear genes or mitochondrial DNA (mtDNA). In the past decades, several types of somatic mtDNA alterations have been identified in gastric cancer. However, the role of these mtDNA alterations in gastric cancer progression remains unclear. In this review, we summarize recently identified somatic mtDNA alterations in gastric cancers as well as the relationship between these alterations and the clinicopathological features of gastric cancer. The causative factors and potential roles of the somatic mtDNA alterations in cancer progression are also discussed. We suggest that point mutations and mtDNA copy number decreases are the two most common mtDNA alterations that result in mitochondrial dysfunction in gastric cancers. The two primary mutation types (transition mutations and mononucleotide or dinucleotide repeat instability) imply potential causative factors. Mitochondrial dysfunction-generated reactive oxygen species may be involved in the malignant changes of gastric cancer. The search for strategies to prevent mtDNA alterations and inhibit the mitochondrial retrograde signaling will benefit the development of novel treatments for gastric cancer and other malignancies.

Bringing the heavy: carbon ion therapy in the radiobiological and clinical context

Radiotherapy for the treatment of cancer is undergoing an evolution, shifting to the use of heavier ion species. For a plethora of malignancies, current radiotherapy using photons or protons yields marginal benefits in local control and survival. One hypothesis is that these malignancies have acquired, or are inherently radioresistant to low LET radiation. In the last decade, carbon ion radiotherapy facilities have slowly been constructed in Europe and Asia, demonstrating favorable results for many of the malignancies that do poorly with conventional radiotherapy. However, from a radiobiological perspective, much of how this modality works in overcoming radioresistance, and extending local control and survival are not yet fully understood. In this review, we will explain from a radiobiological perspective how carbon ion radiotherapy can overcome the classical and recently postulated contributors of radioresistance (α/β ratio, hypoxia, cell proliferation, the tumor microenvironment and metabolism, and cancer stem cells). Furthermore, we will make recommendations on the important factors to consider, such as anatomical location, in the future design and implementation of clinical trials. With the existing data available we believe that the expansion of carbon ion facilities into the United States is warranted.

Clinicopathological significance and prognostic value of lactate dehydrogenase A expression in gastric cancer patients

INTRODUCTION

LDH-A, the enzyme responsible for transforming pyruvate into lactate, has been demonstrated to be up-regulated in many types of cancer and to give rise to more aggressive behavior by regulating proliferation and anti-apoptosis. However, its expression in gastric cancer (GC) has not been characterized thoroughly. The purpose of this study was to clarify the expression and potential impact of LDH-A in GC.

METHODS

We examined LDH-A expression by immunohistochemistry on GC tissue microarray (TMA) and using Western blot on fresh GC tissues and cell lines. Prognostic value and correlation with other clinicopathologic factors were evaluated. We transfected siRNA into GC cells against LDH-A. LDH-A was analyzed by Western blotting and real-time RT-PCR. Cell growth was evaluated in vitro and in vivo. Lactate and ATP production by cells were determined.

RESULTS

There was significantly higher LDH-A expression in carcinoma than in non-neoplastic mucosa (NNM). There was a positive correlation of LDH-A expression with age, histological type and Lymph node metastases. Survival analysis demonstrated that high expression of LDH-A in GC was associated with lower overall survival (OS). When stratified by Lauren grade and histological classification, significance appeared in diffuse type and undifferentiated type GC. In multivariate analysis, the LDH-A expression in GC was an independent prognostic risk factor for OS (hazard ratio = 1.829, 95%CI 1.375-2.433,P<0.0001). Specific siRNA against LDH-A in GC cell line retarded cell growth both in vitro and in mouse models. LDH-A knockdown also reduced lactate and ATP production in GC cells.

CONCLUSIONS

Our study indicated the oncogenic role of LDH-A in GC. LDH-A expression is an independent prognostic risk factor in GC patients and up-regulated expression of LDH-A could be predictive of poor outcomes in diffuse type and undifferentiated type GC. Our results suggested that LDH-A might be a potential therapeutic target in gastric cancer.

Metabolomic heterogeneity of pulmonary arterial hypertension

Although multiple gene and protein expression have been extensively profiled in human pulmonary arterial hypertension (PAH), the mechanism for the development and progression of pulmonary hypertension remains elusive. Analysis of the global metabolomic heterogeneity within the pulmonary vascular system leads to a better understanding of disease progression. Using a combination of high-throughput liquid-and-gas-chromatography-based mass spectrometry, we showed unbiased metabolomic profiles of disrupted glycolysis, increased TCA cycle, and fatty acid metabolites with altered oxidation pathways in the human PAH lung. The results suggest that PAH has specific metabolic pathways contributing to increased ATP synthesis for the vascular remodeling process in severe pulmonary hypertension. These identified metabolites may serve as potential biomarkers for the diagnosis of PAH. By profiling metabolomic alterations of the PAH lung, we reveal new pathogenic mechanisms of PAH, opening an avenue of exploration for therapeutics that target metabolic pathway alterations in the progression of PAH.

De novo synthesize of bile acids in pulmonary arterial hypertension lung

Although multiple, complex molecular studies have been done for understanding the development and progression of pulmonary hypertension (PAH), little is known about the metabolic heterogeneity of PAH. Using a combination of high-throughput liquid-and-gas-chromatography-based mass spectrometry, we found bile acid metabolites, which are normally product derivatives of the liver and gallbladder, were highly increased in the PAH lung. Microarray showed that the gene encoding cytochrome P450 7B1 (CYP7B1), an isozyme for bile acid synthesis, was highly expressed in the PAH lung compared with the control. CYP7B1 protein was found to be primarily localized on pulmonary vascular endothelial cells suggesting de novo bile acid synthesis may be involved in the development of PAH. Here, by profiling the metabolomic heterogeneity of the PAH lung, we reveal a newly discovered pathogenesis mechanism of PAH.

Mitochondrial DNA alterations and mitochondrial dysfunction in the progression of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies and is ranked third in mortality among cancer-related diseases. Mitochondria are intracellular organelles that are responsible for energy metabolism and cellular homeostasis, and mitochondrial dysfunction has been regarded as a hallmark of cancer. Over the past decades, several types of mitochondrial DNA (mtDNA) alterations have been identified in human cancers, including HCC. However, the role of these mtDNA alterations in cancer progression is unclear. In this review, we summarize the recent findings on the somatic mtDNA alterations identified in HCC and their relationships with the clinicopathological features of HCC. Recent advances in understanding the potential roles of somatic mtDNA alterations in the progression of HCC are also discussed. We suggest that somatic mtDNA mutations and a decrease in the mtDNA copy number are common events in HCC and that a mitochondrial dysfunction-activated signaling cascade may play an important role in the progression of HCC. Elucidation of the retrograde signaling pathways in HCC and the quest for strategies to block some of these pathways will be instrumental for the development of novel treatments for this and other malignancies.

Hyperpolarized 13C NMR studies of glucose metabolism in living breast cancer cell cultures

The recent development of dissolution dynamic nuclear polarization (DNP) gives NMR the sensitivity to follow metabolic processes in living systems with high temporal resolution. In this article, we apply dissolution DNP to study the metabolism of hyperpolarized U-(13)C,(2)H7-glucose in living, perfused human breast cancer cells. Spectrally selective pulses were used to maximize the signal of the main product, lactate, whilst preserving the glucose polarization; in this way, both C1-lactate and C3-lactate could be observed with high temporal resolution. The production of lactate by T47D breast cancer cells can be characterized by Michaelis-Menten-like kinetics, with K(m) = 3.5 ± 1.5 mM and V(max) = 34 ± 4 fmol/cell/min. The high sensitivity of this method also allowed us to observe and quantify the glycolytic intermediates dihydroxyacetone phosphate and 3-phosphoglycerate. Even with the enhanced DNP signal, many other glycolytic intermediates could not be detected directly. Nevertheless, by applying saturation transfer methods, the glycolytic intermediates glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate, phosphoenolpyruvate and pyruvate could be observed indirectly. This method shows great promise for the elucidation of the distinctive metabolism and metabolic control of cancer cells, suggesting multiple ways whereby hyperpolarized U-(13)C,(2)H7-glucose NMR could aid in the diagnosis and characterization of cancer in vivo.

Regulation of the cell fate by DNA damage and hypoxia

In order to provide the means for the design of novel rational anti-cancer drug therapies research efforts are concentrated on unravelling the molecular circuits which induce programmed cell death and block proliferation of cancer cells. Modern therapeutic strategies are based on the understanding of the complexity of physiological functions such as differentiation, development, immune responses, cell-cycle arrest, DNA damage repair, apoptosis, autophagy, energy metabolism, and senescence. It has become evident that this knowledge will provide the means to target the components of the pathways involved in these processes in a specific and selective manner thus paving the way for the development of effective and personalised anti-cancer therapies. Transcription is a crucial cellular process that regulates a multitude of physiological functions, which are essential in disease progression and cellular response to therapy. Transcription factors such as the p53 tumor suppressor and the hypoxia-inducible factor-α (HIF-α) are key players in carcinogenesis and cellular response to cancer therapies. Both of these transcription factors regulate gene expression of genes involved in cell death and proliferation, in some cases cooperating towards producing the same outcome and in some others mediating opposing effects. It is thus apparent that fine tuning of the activity of these transcription factors is essential to determine the cellular response to therapeutic regimens, in other words whether tumor cells will commit to apoptosis or evade engagement with the anti-proliferative effects of drugs leading to drug resistance. Our observations support the notion that the functional crosstalk between HIF-1α and p53 pathways and thus the fine tuning of their transcriptional activity is mediated by cofactors shared between the two transcription factors such as components of the p300 co-activator multiprotein complex. In particular, there is evidence to suggest that differential composition of the co-modulatory protein complexes associated with p53 and HIF-1α under diverse types of stress conditions differentially regulate the expression of distinct subsets of p53 and HIF-1α target genes involved in processes such as cell cycle arrest, apoptosis, chronic inflammation, and cellular energy metabolism thereby determining the cellular fate under particular types of micro-environmental stress.

Cancer cachexia and diabetes: similarities in metabolic alterations and possible treatment

Cancer cachexia is a metabolic syndrome featuring many alterations typical of type 2 diabetes (T2D). While muscle wasting is a hallmark of cachexia, epidemiological evidence also supports an accelerated age-related muscle loss in T2D. Insulin resistance manifests in both conditions and impairs glucose disposal and protein anabolism by tissues. A greater contribution of gluconeogenesis to glucose production may limit amino acid availability for muscle protein synthesis, further aggravating muscle loss. In the context of inter-dependence between glucose and protein metabolism, the present review summarizes the current state of knowledge on alterations that may lead to muscle wasting in human cancer. By highlighting the similarities with T2D, a disease that has been more extensively studied, the objective of this review is to provide a better understanding of the pathophysiology of cancer cachexia and to consider potential treatments usually targeted for T2D. Nutritional approaches aimed at stimulating protein anabolism might include specially formulated food with optimal protein and amino acid composition. Because the gradual muscle loss in T2D may be attenuated by diabetes treatment, anti-diabetic drugs might be considered in cachexia treatment. Metformin emerges as a choice candidate as it acts both on reducing gluconeogenesis and improving insulin sensitivity, and has demonstrated tumour suppressor properties in multiple cancer types. Such a multimodal approach to slow or reverse muscle wasting in cachexia warrants further investigation.

Monofunctional and higher-valent platinum anticancer agents

Platinum compounds represent one of the great success stories of metals in medicine. Following the serendipitous discovery of the anticancer activity of cisplatin by Rosenberg, a large number of cisplatin variants have been prepared and tested for their ability to kill cancer cells and inhibit tumor growth. These efforts continue today with increased realization that new strategies are needed to overcome issues of toxicity and resistance inherent to treatment by the approved platinum anticancer agents. One approach has been the use of so-called "non-traditional" platinum(II) and platinum(IV) compounds that violate the structure-activity relationships that governed platinum drug-development research for many years. Another is the use of specialized drug-delivery strategies. Here we describe recent developments from our laboratory involving monofunctional platinum(II) complexes together with a historical account of the manner by which we came to investigate these compounds and their relationship to previously studied molecules. We also discuss work carried out using platinum(IV) prodrugs and the development of nanoconstructs designed to deliver them in vivo.

Hyperglycaemia-induced chemoresistance of prostate cancer cells due to IGFBP2

Clinically relevant prostate cancer (PCa) is more frequent in Westernised societies and increasingly men have co-morbidities associated with a Western lifestyle, primarily diabetes, characterised by hyperinsulinaemia and hyperglycaemia. IGFs and their binding proteins (IGFBPs) are important mediators of the effects of nutrition on growth and play a key role in the development of PCa. We used DU145, PC3 and LNCaP PCa cell lines to examine how hyperglycaemia altered their response to docetaxel. Trypan Blue dye-exclusion assay was used to determine the percentage of cell death. Protein abundance was determined using western immunoblotting. Levels of IGFBP2 were measured using an ELISA. IGFBP2 gene silencing was achieved using siRNA technology. DNA methylation was assessed using combined bisulphide restriction analysis. Acetylation status of histones H3 and H4 associated with IGFBP2 gene was assessed using chromatin immunoprecipitation assay. Hyperglycaemia reduced docetaxel-induced apoptosis by 40% for DU145 cells and by 88% for LNCaP cells. This reduced cell death was mediated by a glucose-induced up-regulation of IGFBP2, as silencing IGFBP2 negated the survival effect of high glucose. Glucose increased IGFBP2 via increasing the acetylation of histones associated with the IGFBP2 gene promoter. This finding could have important implications in relation to therapeutic strategies as epigenetic modulation could be reversible.

Parallels between embryo and cancer cell metabolism

A key characteristic of cancer cells is the ability to switch from a predominantly oxidative metabolism to glycolysis and the production of lactate even when oxygen is plentiful. This metabolic switch, known as the Warburg effect, was first described in the 1920s, and has fascinated and puzzled researchers ever since. However, a dramatic increase in glycolysis in the presence of oxygen is one of the hallmarks of the development of the early mammalian embryo; a metabolic switch with many parallels to the Warburg effect of cancers. The present review provides a brief overview of this and other similarities between the metabolism in tumours and early embryos and proposes whether knowledge of early embryo metabolism can help us to understand metabolic regulation in cancer cells.

Effective inhibition of nasopharyngeal carcinoma in vitro and in vivo by targeting glycolysis with oxamate

Elevated aerobic glycolysis in cancer cells (Warburg effect) has been observed in many tumor types including nasopharyngeal carcinoma (NPC), which can often be detected clinically using FDG-PET. However, the role of glycolysis in supporting the growth of NPC cells and its therapeutic implications still remain to be investigated. In the present study, we showed that the LDH inhibitor oxamate significantly suppressed NPC cell proliferation in vitro and tumor growth in vivo, yet exhibited minimum toxicity to normal nasopharyngeal epithelial cells in vitro and was well tolerated in mice. Moreover, oxamate exhibited cytotoxic effect in NPC cells under hypoxia. Mechanistic study showed that oxamate significantly inhibited LDH activity, leading to a substantial decrease in glucose uptake and lactate production. Combination of oxamate with a mitochondrial respiratory complex I inhibitor resulted in a significant depletion of cellular ATP and a synergistic killing of cancer cells. Our results suggest that inhibition of glycolysis by oxamate is an effective therapeutic strategy for treatment of NPC and that combination of this compound with mitochondrial-targeted agents may improve the therapeutic activity.

Emerging metabolic targets in the therapy of hematological malignancies

During the last decade, the development of anticancer therapies has focused on targeting neoplastic-related metabolism. Cancer cells display a variety of changes in their metabolism, which enable them to satisfy the high bioenergetic and biosynthetic demands for rapid cell division. One of the crucial alterations is referred to as the "Warburg effect", which involves a metabolic shift from oxidative phosphorylation towards the less efficient glycolysis, independent of the presence of oxygen. Although there are many examples of solid tumors having altered metabolism with high rates of glucose uptake and glycolysis, it was only recently reported that this phenomenon occurs in hematological malignancies. This review presents evidence that targeting the glycolytic pathway at different levels in hematological malignancies can inhibit cancer cell proliferation by restoring normal metabolic conditions. However, to achieve cancer regression, high concentrations of glycolytic inhibitors are used due to limited solubility and biodistribution, which may result in toxicity. Besides using these inhibitors as monotherapies, combinatorial approaches using standard chemotherapeutic agents could display enhanced efficacy at eradicating malignant cells. The identification of the metabolic enzymes critical for hematological cancer cell proliferation and survival appears to be an interesting new approach for the targeted therapy of hematological malignancies.

Mitochondrial dysfunction represses HIF-1α protein synthesis through AMPK activation in human hepatoma HepG2 cells

BACKGROUND

Hypoxia-inducible factor-1α (HIF-1α) is an important transcription factor that modulates cellular responses to hypoxia and also plays critical roles in cancer progression. Recently, somatic mutations and decreased copy number of mitochondrial DNA (mtDNA) were detected in hepatocellular carcinoma (HCC). These mutations were shown to have the potential to cause mitochondrial dysfunction. However, the effects and mechanisms of mitochondrial dysfunction on HIF-1α function are not fully understood. This study aims to explore the underlying mechanism by which mitochondrial dysfunction regulates HIF-1α expression.

METHODS

Human hepatoma HepG2 cells were treated with various mitochondrial respiration inhibitors and an uncoupler, respectively, and the mRNA and protein expressions as well as transactivation activity of HIF-1α were determined. The role of AMP-activated protein kinase (AMPK) was further analyzed by compound C and AMPK knock-down.

RESULTS

Treatments of mitochondrial inhibitors and an uncoupler respectively reduced both the protein level and transactivation activity of HIF-1α in HepG2 cells under normoxia or hypoxia. The mitochondrial dysfunction-repressed HIF-1α protein synthesis was associated with decreased phosphorylations of p70(S6K) and 4E-BP-1. Moreover, mitochondrial dysfunction decreased intracellular ATP content and elevated the phosphorylation of AMPK. Treatments with compound C, an AMPK inhibitor, and knock-down of AMPK partially rescued the mitochondrial dysfunction-repressed HIF-1α expression.

CONCLUSIONS

Mitochondrial dysfunctions resulted in reduced HIF-1α protein synthesis through AMPK-dependent manner in HepG2 cells.

GENERAL SIGNIFICANCE

Our results provided a mechanism for communication from mitochondria to the nucleus through AMPK-HIF-1α. Mitochondrial function is important for HIF-1α expression in cancer progression.

Receptor tyrosine kinase ErbB2 translocates into mitochondria and regulates cellular metabolism

It is well known that ErbB2, a receptor tyrosine kinase, localizes on the plasma membrane. Here we describe a novel observation that ErbB2 also localizes in mitochondria of cancer cells and patient samples. We found that ErbB2 translocates into mitochondria through the association with mtHSP70. Additionally, mitochondrial ErbB2 (mtErbB2) negatively regulates mitochondrial respiratory functions. Oxygen consumption and activities of complexes of the mitochondrial electron transport chain were decreased in mtErbB2-overexpressing cells. Mitochondrial membrane potential and the cellular ATP level also were decreased. In contrast, mtErbB2 enhanced cellular glycolysis. The translocation of ErbB2 and its impact on mitochondrial function are kinase dependent. Interestingly, cancer cells with higher levels of mtErbB2 were more resistant to ErbB2 targeting antibody trastuzumab. Our study provides a novel perspective on the metabolic regulatory function of ErbB2 and reveals that mtErbB2 plays an important role in the regulation of cellular metabolism and cancer cell resistance to therapeutics.