Molecular and cellular regulation of glucose transporter (GLUT) proteins in cancer

Fundamentals of molecular imaging: rationale and applications with relevance for radiation oncology

Molecular imaging allows for the visualization and quantification biologic processes at cellular levels. This article focuses on positron emission tomography as one readily available tool for clinical molecular imaging. To prove its clinical utility in oncology, molecular imaging will ultimately have to provide valuable information in the following 4 pertinent areas: staging; assessment of extent of disease; target delineation for radiation therapy planning; response prediction and assessment and differentiation between treatment sequelae and recurrent disease. These issues are addressed in other contributions in this issue of Seminars in Nuclear Medicine. In contrast, this article will focus on the biochemical principles of cancer metabolism that provide the rationale for positron emission tomography imaging in radiation oncology.

Dematin and adducin provide a novel link between the spectrin cytoskeleton and human erythrocyte membrane by directly interacting with glucose transporter-1

Dematin and adducin are actin-binding proteins located at the spectrin-actin junctions, also called the junctional complex, in the erythrocyte membrane. Here we propose a new model whereby dematin and adducin link the junctional complex to human erythrocyte plasma membrane. Using a combination of surface labeling, immunoprecipitation, and vesicle proteomics approaches, we have identified glucose transporter-1 as the receptor for dematin and adducin in the human erythrocyte membrane. This finding is the first description of a transmembrane protein that binds to dematin and adducin, thus providing a rationale for the attachment of the junctional complex to the lipid bilayer. Because homologues of dematin, adducin, and glucose transporter-1 exist in many non-erythroid cells, we propose that a conserved mechanism may exist that couples sugar and other related transporters to the actin cytoskeleton.

Axin and GSK3- control Smad3 protein stability and modulate TGF- signaling

The broad range of biological responses elicited by transforming growth factor-beta (TGF-beta) in various types of tissues and cells is mainly determined by the expression level and activity of the effector proteins Smad2 and Smad3. It is not fully understood how the baseline properties of Smad3 are regulated, although this molecule is in complex with many other proteins at the steady state. Here we show that nonactivated Smad3, but not Smad2, undergoes proteasome-dependent degradation due to the concerted action of the scaffolding protein Axin and its associated kinase, glycogen synthase kinase 3-beta (GSK3-beta). Smad3 physically interacts with Axin and GSK3-beta only in the absence of TGF-beta. Reduction in the expression or activity of Axin/GSK3-beta leads to increased Smad3 stability and transcriptional activity without affecting TGF-beta receptors or Smad2, whereas overexpression of these proteins promotes Smad3 basal degradation and desensitizes cells to TGF-beta. Mechanistically, Axin facilitates GSK3-beta-mediated phosphorylation of Smad3 at Thr66, which triggers Smad3 ubiquitination and degradation. Thr66 mutants of Smad3 show altered protein stability and hence transcriptional activity. These results indicate that the steady-state stability of Smad3 is an important determinant of cellular sensitivity to TGF-beta, and suggest a new function of the Axin/GSK3-beta complex in modulating critical TGF-beta/Smad3-regulated processes during development and tumor progression.

Hypoxia and the presence of human vascular endothelial cells affect prostate cancer cell invasion and metabolism

Tumor progression and metastasis are influenced by hypoxia, as well as by interactions between cancer cells and components of the stroma, such as endothelial cells. Here, we have used a magnetic resonance (MR)-compatible invasion assay to further understand the effects of hypoxia on human prostate cancer cell invasion and metabolism in the presence and absence of human umbilical vein endothelial cells (HUVECs). Additionally, we compared endogenous activities of selected proteases related to invasion in PC-3 cells and HUVECs, profiled gene expression of PC-3 cells by microarray, and evaluated cell proliferation of PC-3 cells and HUVECs by flow cytometry, under hypoxic and oxygenated conditions. The invasion of less-invasive DU-145 cells was not affected by either hypoxia or the presence of HUVECs. However, hypoxia significantly decreased the invasion of PC-3 cells. This hypoxia-induced decrease was attenuated by the presence of HUVECs, whereas under oxygenated conditions, HUVECs did not alter the invasion of PC-3 cells. Cell metabolism changed distinctly with hypoxia and invasion. The endogenous activity of selected extracellular proteases, although altered by hypoxia, did not fully explain the hypoxia-induced changes in invasion. Gene expression profiling indicated that hypoxia affects multiple cellular functions and pathways.

Under normoxia, 2-deoxy-D-glucose elicits cell death in select tumor types not by inhibition of glycolysis but by interfering with N-linked glycosylation

In tumor cells growing under hypoxia, inhibiting glycolysis with 2-deoxy-d-glucose (2-DG) leads to cell death, whereas under normoxic conditions cells similarly treated survive. Surprisingly, here we find that 2-DG is toxic in select tumor cell lines growing under normal oxygen tension. In contrast, a more potent glycolytic inhibitor, 2-fluorodeoxy-d-glucose, shows little or no toxicity in these cell types, indicating that a mechanism other than inhibition of glycolysis is responsible for their sensitivity to 2-DG under normoxia. A clue to this other mechanism comes from previous studies in which it was shown that 2-DG interferes with viral N-linked glycosylation and is reversible by exogenous addition of mannose. Similarly, we find that 2-DG interferes with N-linked glycosylation more potently in the tumor cell types that are sensitive to 2-DG under normoxia, which can be reversed by exogenous mannose. Additionally, 2-DG induces an unfolded protein response, including up-regulation of GADD153 (C/EBP-homologous protein), an unfolded protein response-specific mediator of apoptosis, more effectively in 2-DG-sensitive cells. We conclude that 2-DG seems to be toxic in select tumor cell types growing under normoxia by inhibition of N-linked glycosylation and not by glycolysis. Because in a phase I study 2-DG is used in combination with an anticancer agent to target hypoxic cells, our results raise the possibility that in certain cases, 2-DG could be used as a single agent to selectively kill both the aerobic (via interference with glycosylation) and hypoxic (via inhibition of glycolysis) cells of a solid tumor.

The cellular adaptations to hypoxia as novel therapeutic targets in childhood cancer

Exposure of tumour cells to reduced levels of oxygen (hypoxia) is a common finding in adult tumours. Hypoxia induces a myriad of adaptive changes within tumour cells which result in increased anaerobic glycolysis, new blood vessel formation, genetic instability and a decreased responsiveness to both radio and chemotherapy. Hypoxia correlates with disease stage and outcome in adult epithelial tumours and increasingly it is becoming apparent that hypoxia is also important in paediatric tumours. Despite its adverse effects upon tumour response to treatment hypoxia offers several avenues for new drug development. Bioreductive agents already exist, which are preferentially activated in areas of hypoxia, and thus have less toxicity for normal tissue. Additionally the adaptive cellular response to hypoxia offers several novel targets, including vascular endothelial growth factor (VEGF), carbonic anhydrase, and the central regulator of the cellular response to hypoxia, hypoxia inducible factor-1 (HIF-1). Novel agents have emerged against all of these targets and are at various stages of clinical and pre-clinical development. Hypoxia offers an exciting opportunity for new drug development that can include paediatric tumours at an early stage.

Cellular localization of facilitated glucose transporter 1 (GLUT-1) in the cochlear stria vascularis: its possible contribution to the transcellular glucose pathway

Immunoreactivity for the facilitated glucose transporter 1 (GLUT-1) has been found in the cochlear stria vascularis, but whether the strial marginal cells are immunopositive for GLUT-1 remains uncertain. To determine the cellular localization of GLUT-1 and to clarify the glucose pathway in the stria vascularis of rats and guinea pigs, immunohistochemistry was performed on sections, dissociated cells, and whole-tissue preparations. Immunoreactivity for GLUT-1 in sections was observed in the basal side of the strial tissue and in capillaries in both rats and guinea pigs. However, the distribution of the positive signals within the guinea pig strial tissue was more diffuse than that in rats. Immunostaining of dissociated guinea pig strial cells revealed GLUT-1 in the basal cells and capillary endothelial cells, but not in the marginal cells. These results indicated that GLUT-1 was not expressed in the marginal cells, and that another isoform of GLUT was probably expressed in these cells. Three-dimensional observation of whole-tissue preparations demonstrated that cytoplasmic prolongations from basal cells extended upward to the apical surface of the stria vascularis from rats and guinea pigs, and that the marginal cells were surrounded by these protrusions. We speculate that these upward extensions of basal cells have been interpreted as basal infoldings of marginal cells in previous reports from other groups. The three-dimensional relationship between marginal cells and basal cells might contribute to the transcellular glucose pathway from perilymph to intrastrial space.

Osteoclast precursors display dynamic metabolic shifts toward accelerated glucose metabolism at an early stage of RANKL-stimulated osteoclast differentiation

Mature osteoclasts have an increased citric acid cycle and mitochondrial respiration to generate high ATP production and ultimately lead to bone resorption. However, changes in metabolic pathways during osteoclast differentiation have not been fully illustrated. We report that glycolysis and oxidative phosphorylation characterized by glucose and oxygen consumption as well as lactate production were increased during receptor activator of nuclear factor-kappaB ligand (RANKL)-induced osteoclastogenesis from RAW264.7 and bone marrow-derived macrophage cells. Cell proliferation and differentiation varied according to glucose concentrations (0 to 100 mM). Maximal cell growth occurred at 20 mM glucose concentration and differentiation occurred at 5 mM concentration. Despite the similar growth rates exhibited when cultured cells were exposed to either 5 mM or 40 mM glucose, their differentiation was markedly decreased in high glucose concentrations. This finding suggests the possibility that osteoclastogenesis could be regulated by changes in metabolic substrate concentrations. To further address the effect of metabolic shift on osteoclastogenesis, we exposed cultured cells to pyruvate, which is capable of promoting mitochondrial respiration. Treatment of pyruvate synergistically increased osteoclastogenesis through the activation of RANKL-stimulated signals (ERK and JNK). We also found that osteoclastogenesis was retarded by blocking ATP production with either the inhibitors of mitochondrial complexes, such as rotenone and antimycin A, or the inhibitor of ATP synthase, oligomycin. Taken together, these results indicate that glucose metabolism during osteoclast differentiation is accelerated and that a metabolic shift towards mitochondrial respiration allows high ATP production and induces enhanced osteoclast differentiation.

Regulation of GLUT3 and glucose uptake by the cAMP signalling pathway in the breast cancer cell line ZR-75

Increased glucose uptake as a principal energy source is a requirement for the continued survival of tumour cells. Facilitative glucose transporter-1 (GLUT1) and -3 (GLUT3) have been previously shown to be present and regulated in breast cancer cells and are associated with poor patient prognosis. In cancer cells, the cAMP secondary messenger pathway is known to potentiate described glucose transporter activators and regulate cell fate. However, no regulation of the glucose transporters in breast cancer cells by cAMP has previously been examined. Herein, we determined in the well-characterized breast cancer cell line ZR-75, if the cAMP analogue 8-br-cAMP was capable of regulating GLUT1 and GLUT3 expression and thus glucose uptake. We demonstrated that 8-br-cAMP transiently up-regulates GLUT3 mRNA levels. The use of actinomycin-D and the cloning of 1,200 bp upstream of the human GLUT3 promoter demonstrated that this regulation was transcriptional. Immunocytochemistry and Western blotting confirmed that the increase in mRNA was reflected by an increase in protein levels. No notable regulation of GLUT1 in the presence of 8-br-cAMP was detected. Finally, we determined using the non-metabolizable glucose analogue 2-DOG if this up-regulation in GLUT3 increased glucose uptake. We observed the presence of two uptake components, one corresponding to the Km of GLUT1/4 and the other to GLUT3. A doubling in the uptake velocity was observed only at the Km corresponding to GLUT3. In conclusion, we demonstrate and characterize for the first time, an up-regulation of GLUT3 mRNA, protein and glucose uptake by the cAMP pathway in breast cancer cells.

GLUT1 and GLUT9 as major contributors to glucose influx in HepG2 cells identified by a high sensitivity intramolecular FRET glucose sensor

Genetically encoded FRET glucose nanosensors have proven to be useful for imaging glucose flux in HepG2 cells. However, the dynamic range of the original sensor was limited and thus it did not appear optimal for high throughput screening of siRNA populations for identifying proteins involved in regulation of sugar flux. Here we describe a hybrid approach that combines linker-shortening with fluorophore-insertion to decrease the degrees of freedom for fluorophore positioning leading to improved nanosensor dynamics. We were able to develop a novel highly sensitive FRET nanosensor that shows a 10-fold higher ratio change and dynamic range (0.05-11 mM) in vivo, permitting analyses in the physiologically relevant range. As a proof of concept that this sensor can be used to screen for proteins playing a role in sugar flux and its control, we used siRNA inhibition of GLUT family members and show that GLUT1 is the major glucose transporter in HepG2 cells and that GLUT9 contributes as well, however to a lower extent. GFP fusions suggest that GLUT1 and 9 are preferentially localized to the plasma membrane and thus can account for the transport activity. The improved sensitivity of the novel glucose nanosensor increases the reliability of in vivo glucose flux analyses, and provides a new means for the screening of siRNA collections as well as drugs using high-content screens.

Complex N-glycan and metabolic control in tumor cells

Golgi beta1,6N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched complex N-glycans on cell surface glycoproteins that bind to galectins and promote surface residency of glycoproteins, including cytokine receptors. Carcinoma cells from polyomavirus middle T (PyMT) transgenic mice on a Mgat5-/- background have reduced surface levels of epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) receptors and are less sensitive to acute stimulation by cytokines in vitro compared with PyMT Mgat5+/+ tumor cells but are nonetheless tumorigenic when injected into mice. Here, we report that PyMT Mgat5-/- cells are reduced in size, checkpoint impaired, and following serum withdrawal, fail to down-regulate glucose transport, protein synthesis, reactive oxygen species (ROS), and activation of Akt and extracellular signal-regulated kinase. To further characterize Mgat5+/+ and Mgat5-/- tumor cells, a screen of pharmacologically active compounds was done. Mgat5-/- tumor cells were comparatively hypersensitive to the ROS inducer 2,3-dimethoxy-1,4-naphthoquinone, hyposensitive to tyrosine kinase inhibitors, to Golgi disruption by brefeldin A, and to mitotic arrest by colcemid, hydroxyurea, and camptothecin. Finally, regulation of ROS, glucose uptake, and sensitivities to EGF and TGF-beta were rescued by Mgat5 expression or by hexosamine supplementation to complex N-glycan biosynthesis in Mgat5-/- cells. Our results suggest that complex N-glycans sensitize tumor cells to growth factors, and Mgat5 is required to balance responsiveness to growth and arrest cues downstream of metabolic flux.

PPARgamma and GLUT-4 expression as developmental regulators/markers for preadipocyte differentiation into an adipocyte

In this document, we have integrated knowledge about two major cellular markers found in cells of the adipocyte lineage (an adipogenic marker and a metabolic marker). This review provides information as to how differentiation of a cell (such as an adipofibroblast, fibroblast or preadipocyte) to become a viable (and new) adipocyte is under different regulation than that experienced by an immature adipocyte that is just beginning to accumulate lipid. The differentiation, prior to lipid-filling, involves PPARgamma. Subsequently, lipid-filling of the adipocyte relies on a late subset of genes and, depending on depot specificity, involves GLUT-4 or any number of other metabolic markers.

Enhancement of glucose transporter expression of brain endothelial cells by vascular endothelial growth factor derived from glioma exposed to hypoxia

Increased need for glycolysis and glucose uptake for ATP production is observed in tumor cells, particularly in cells lacking of oxygen supply. Because glucose is transported from blood to tumor, glucose molecules must be delivered across glucose transporters of the vascular endothelium and tumor cells. Here we found that glioma suffered from hypoxic insults can secrete factor(s) to regulate glucose transporter expression in brain endothelium. It was found that conditioned medium from rat C6 glioma cells under hypoxia up-regulated glucose transporter type 1 (GLUT1) expression in rat brain endothelial cells, whereas conditioned medium from C6 cells under normoxia caused no significant effect. We further investigated whether the observed potentiating effect was caused by vascular endothelial growth factor (VEGF) production from C6 cells, because secreted VEGF was markedly increased under hypoxic condition. By transfection of C6 cells with VEGF small interfering RNA, it was found that conditioned medium from transfected cells under hypoxia no longer up-regulated GLUT1 expression of endothelial cells. Moreover, the addition of VEGF-neutralizing antibody to the hypoxic conditioned medium could also exert similar inhibitory effects. Furthermore, it was found that the VEGF-induced increase of GLUT1 expression in endothelial cells was mediated by the phosphoinositide-3 kinase/Akt pathway. Our results indicate that hypoxic brain glioma may secrete VEGF to increase glucose transport across blood-brain barrier.

Expression of glucose transporter protein-1 (Glut-1) in ocular surface squamous neoplasia

PURPOSE

To examine the expression of glucose transporter protein-1 (GLUT-1) in ocular surface squamous neoplasia and to study its relationship with degree of neoplasia and cell proliferation index (Ki-67 labeling index).

METHODS

Twelve cases diagnosed as ocular surface squamous neoplasia (4 invasive and 8 intraepithelial tumors) at Inonu University Faculty of Medicine, Department of Pathology, were included in this study. There were 3 squamous cell carcinomas, 1 basosquamous cell carcinoma, and 8 conjunctival intraepithelial neoplasms. Immunohistochemically, GLUT-1 and Ki-67 antibody staining were performed.

RESULTS

GLUT-1 membranous immunoreactivity was seen in all tumors except in 1 case. GLUT-1 immunostaining was observed in all layers of the neoplastic epithelium of squamous cell carcinoma. Intense staining for GLUT-1 was determined in the upper two thirds of the severe dysplastic squamous epithelium. Although immunoreactivity for Ki-67 nuclear antigen was present throughout the epithelium, it was higher in the lower two thirds. Ki-67 labeling index ranged between 6% and 80%, and the mean value was 35% for invasive tumors and 20% for intraepithelial tumors.

CONCLUSIONS

Marked GLUT-1 and Ki-67 immunoreactive cells throughout the neoplastic epithelium of ocular surface squamous neoplasia were observed. In most cases, it was observed that GLUT-1 expression was severe in cases having >10% Ki-67 labeling index. These findings indicate that glucose uptake was increased in dysplastic cells, especially by GLUT-1. To our knowledge, this is the first study on the subject in the literature, and further studies with more cases are needed with GLUT-1 and other GLUT members.

Glucosylated heparin derivatives as non-toxic anti-cancer drugs

Heparin, which has been widely used as an anti-coagulant agent, has potential anti-tumor effects; in particular, low molecular weight heparin (LMWH) may inhibit tumor angiogenesis and/or metastasis with reduced toxicity. For decades, it has been known that malignant cancer cells display abnormally enhanced glucose uptake rates and overexpress glucose transporters (GLUTs) compared to normal cells. With these findings in mind, we introduced a glucose moiety to heparin for the purpose of increasing the concentration of heparin at the tumor site by targeting GLUTs. Three glucosylated heparin (GH) derivatives were prepared by conjugation of glucosamine and heparin in different mole ratios. To evaluate the potential of GH derivatives as anti-cancer drugs, their anti-coagulant activities, inhibitory effects on glucose analog uptake, cellular interactions, tumor growth inhibitory effects and sub-acute toxicities were investigated. The anti-coagulant activities of GH derivatives decreased proportionally to the degree of glucosylation. In vitro, GH derivatives inhibited HUVEC proliferation to a greater extent than heparin. GH derivatives mainly existed outside of cells and interacted with GLUTs on the cell surface, thereby inhibiting glucose uptake into cells. In vivo, GH derivatives significantly suppressed tumor growth compared to control, without systemic toxicity. Therefore, GH derivatives are proposed as potent non-toxic anti-cancer drugs.

Targeting mitochondria in the treatment of human cancer: a coordinated attack against cancer cell energy metabolism and signalling

Mitochondria have major roles in bioenergetics and vital signalling of the mammalian cell. Consequently, these organelles have been implicated in the process of carcinogenesis, which includes alterations of cellular metabolism and cell death pathways. Multiple molecular routes of malignant transformation appear to result in the common ability of many tumours to take up large amounts of glucose. This metabolic twist has been explained by phenomena such as aerobic glycolysis and impaired mitochondrial function, and is linked to tumour growth potential via major cellular signalling pathways. This paper reviews the literature on central mechanisms through which energy metabolism merges with growth, proliferation and death signalling, which tend to include mitochondria at some level. These processes can potentially be targeted by pharmacological agents for therapeutic and chemosensitising purposes.

Controlling cell growth and survival through regulated nutrient transporter expression

Although all cells depend upon nutrients they acquire from the extracellular space, surprisingly little is known about how nutrient uptake is regulated in mammalian cells. Most nutrients are brought into cells by means of specific transporter proteins. In yeast, the expression and trafficking of a wide variety of nutrient transporters is controlled by the TOR (target of rapamycin) kinase. Consistent with this, recent studies in mammalian cells have shown that mTOR (mammalian TOR) and the related protein, PI3K (phosphoinositide 3-kinase), play central roles in coupling nutrient transporter expression to the availability of extrinsic trophic and survival signals. In the case of lymphocytes, it has been particularly well established that these extrinsic signals stimulate cell growth and proliferation in part by regulating nutrient transporter expression. The ability of growth factors to control nutrient access may also play an important role in tumour suppression: the non-homoeostatic growth of tumour cells requires that nutrient transporter expression is uncoupled from trophic factor availability. Also supporting a link between nutrient transporter expression levels and oncogenesis, several recent studies demonstrate that nutrient transporter expression drives, rather than simply parallels, cellular metabolism. This review summarizes the evidence that regulated nutrient transporter expression plays a central role in cellular growth control and highlights the implications of these findings for human disease.

Expression of GLUT1 in primary renal tumors: morphologic and biologic implications

This study aimed to assess whether glucose transporter 1 (GLUT1) is useful in prognostication or differential diagnosis of renal tumors. GLUT1 immunostain for 228 renal tumors showed a membranous or cytoplasmic pattern. The membranous pattern was seen in 86.2% of 145 clear cell renal cell carcinomas (RCCs) and 100% of 11 transitional cell carcinomas (TCCs) but in no oncocytomas, other subtypes of RCC, or sarcomatoid areas of RCCs. The cytoplasmic pattern was seen in 55.2% of 145 clear cell RCCs, 38% of papillary RCCs (11/29), 13% of chromophobe RCCs (2/16), 22% of oncocytomas (5/23), and 82% of TCCs (9/11). Western blot showed a markedly increased GLUT1 protein content in clear cell RCCs compared with a low level in papillary RCCs and normal kidney specimens. GLUT1 expression in clear cell RCC was not significantly correlated with patient survival, tumor grade, or tumor stage. GLUT1 may be a novel target for immunotherapy and a useful marker in the differential diagnosis and classification of renal tumors.

The potential role of intrinsic hypoxia markers as prognostic variables in cancer

Tumor hypoxia is related to tumor progression and therapy resistance, which leads to poor patient outcome. It has been suggested that measuring the hypoxic status of a tumor helps to predict patient outcome and to select more targeted treatment. However, current methods using needle electrodes or exogenous markers have limitations due to their invasiveness or necessity for preinjection. Recent studies showed that hypoxia-regulated genes could be alternatively used as endogenous hypoxia markers. This is a review of 15 hypoxia-regulated genes, including hypoxia-inducible factor-1 and its targets, and their correlation with tumor hypoxia and patient outcome from 213 studies. Though most of the studies showed significance of these genes in predicting prognosis, there was no definitive prognostic and hypoxia marker. In conclusion, this review suggests the need for further studies with standardized methods to examine gene expression, as well as the use of multiple gene expressions.

18FDG uptake in oesophageal adenocarcinoma: linking biology and outcome

PURPOSE

Variable uptake of 18FDG has been noticed in positron emission tomography (PET) studies of patients with oesophageal adenocarcinoma. The aim of the present study was to investigate biological parameters involved in 18FDG uptake in oesophageal adenocarcinoma for selection of patients with increased 18FDG uptake and prediction of prognostic value of 18FDG PET.

PATIENTS AND METHODS

Preoperative PET scans were performed in 26 patients with histologically proven oesophageal adenocarcinoma. 18FDG uptake was semiquantitatively measured by SUV(BSAg. )Tumour sections were stained by immunohistochemistry for angiogenic markers (VEGF, CD31), glucose transporter-1 (Glut-1), hexokinase (HK) isoforms, for proliferation marker (Ki67), for macrophage marker (CD68) and for apoptosis marker (cleaved caspase-3). Cell densities, differentiation grade, degree of necrosis and mucus, T-stage and tumour size were assessed. In addition follow-up was analysed.

RESULTS

No association was found between 18FDG uptake and angiogenic markers. In contrast, a significant correlation was found between 18FDG uptake and Glut-1 expression. No correlations were found between 18FDG uptake and HK isoforms, Ki67 or cleaved caspase-3. Also, no correlations were found between 18FDG uptake and cell density, differentiation grade, CD68, mucus and necrosis. However, there was a significant correlation between 18FDG uptake and tumour size and between 18FDG uptake and tumour recurrence.

CONCLUSIONS

Glut-1 expression and tumour size seem parameters associated with 18FDG uptake in patients with biopsy proven oesophageal adenocarcinoma, and may be used to select oesophageal cancer patients in whom 18FDG-PET is of diagnostic value and may predict disease outcome.

Glucose metabolism in lymphoid and inflammatory cells and tissues

PURPOSE OF REVIEW

To examine the role of glucose as a fuel for immune cells and the influence of glucose supply on immune-cell functional responses.

RECENT FINDINGS

Immune cells express the insulin receptor and a range of glucose-transporter isoforms. Glucose transporters are responsive to both immune stimulation and insulin. The pattern of glucose-transporter upregulation differs among different types of immune cell. In-vitro studies reveal that both hypo- and hyperglycaemia impair immune-cell functions and promote inflammatory responses. Clamp studies have revealed proinflammatory effects of hyperglycaemia and antiinflammatory and immune-promoting effects of insulin.

SUMMARY

Glucose is readily utilized by cells of the immune system and is used to generate energy and biosynthetic precursors. Activation of immune cells is associated with increased glucose utilization and this is facilitated, in part, by increased expression of glucose transporters. Immune cells express the insulin receptor and respond to insulin. Both hypo- and hyperglycaemia impair immune-cell functions and promote inflammatory responses. Insulin therapy in hyperglycaemic subjects may be of benefit through effects of both insulin itself and lowered glucose concentration. Excessive lowering of blood glucose concentration may also be harmful to the immune response.

Glycolytic metabolism confers resistance to combined all-trans retinoic acid and arsenic trioxide-induced apoptosis in HL60rho0 cells

Glycolytic cancers are resistant to many forms of chemotherapy and some respond poorly to differentiation therapies. Here, we investigate the effects of exposure to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) on differentiation and cell survival in the human leukemia cell line, HL60 and its mitochondrial gene knockout mutant, HL60rho0. Glycolytic HL60rho0 cells exposed to single and combined treatments expressed less CD15, in most cases, but produced a stronger respiratory burst than parental HL60 cells. HL60rho0 cells were also significantly more resistant to apoptosis after combined ATO+ATRA treatment compared with HL60 cells, and this was associated with failure to upregulate Fas expression.

Energy metabolism in tumor cells

In early studies on energy metabolism of tumor cells, it was proposed that the enhanced glycolysis was induced by a decreased oxidative phosphorylation. Since then it has been indiscriminately applied to all types of tumor cells that the ATP supply is mainly or only provided by glycolysis, without an appropriate experimental evaluation. In this review, the different genetic and biochemical mechanisms by which tumor cells achieve an enhanced glycolytic flux are analyzed. Furthermore, the proposed mechanisms that arguably lead to a decreased oxidative phosphorylation in tumor cells are discussed. As the O(2) concentration in hypoxic regions of tumors seems not to be limiting for the functioning of oxidative phosphorylation, this pathway is re-evaluated regarding oxidizable substrate utilization and its contribution to ATP supply versus glycolysis. In the tumor cell lines where the oxidative metabolism prevails over the glycolytic metabolism for ATP supply, the flux control distribution of both pathways is described. The effect of glycolytic and mitochondrial drugs on tumor energy metabolism and cellular proliferation is described and discussed. Similarly, the energy metabolic changes associated with inherent and acquired resistance to radiotherapy and chemotherapy of tumor cells, and those determined by positron emission tomography, are revised. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors.

The maximum uptake of (18)F-deoxyglucose on positron emission tomography scan correlates with survival, hypoxia inducible factor-1alpha and GLUT-1 in non-small cell lung cancer

The purpose of this study was to investigate the relation between the standardised uptake value (SUV) on (18)F-fluoro-2-deoxy-glucose-positron emission tomography scan and hypoxia related markers (HIF-1alpha and CAIX), a proliferation-related marker (Ki-67) and glucose transporters (GLUT-1 and GLUT-3) in non-small cell lung cancer (NSCLC). One hundred and two patients, scheduled for complete resection, received a PET scan in Leuven or Maastricht/Aachen. The maximal SUV (SUV(max)) was correlated with survival and immunohistochemical staining patterns. The actuarial survival was worse for patients showing a high SUV(max), the best discriminative value being 8.0 (Leuven, p=0.032) and 11.0 (Maastricht, p=0.007). Tumours with a high SUV(max) expressed in a higher proportion HIF-1alpha (63.1% versus 37.9%, p=0.024) and GLUT-1 (82.9% versus 62.5%, p=0.025), than tumours with a low SUV(max). No significant difference was found in the expression of CAIX, Ki-67 and GLUT-3. This study supports preclinical data that hypoxia is associated with a higher uptake of FDG.

mTOR Complex1-S6K1 signaling: at the crossroads of obesity, diabetes and cancer

Recent studies demonstrate that the mammalian target of rapamycin (mTOR) and its effector, S6 kinase 1 (S6K1), lie at the crossroads of a nutrient-hormonal signaling network that is involved in specific pathological responses, including obesity, diabetes and cancer. mTOR exists in two complexes: mTOR Complex1, which is rapamycin-sensitive and phosphorylates S6K1 and initiation factor 4E binding proteins (4E-BPs), and mTOR Complex2, which is rapamycin-insensitive and phosphorylates protein kinase B (PKB, also known as Akt). Both mTOR complexes are stimulated by mitogens, but only mTOR Complex1 is under the control of nutrient and energy inputs. Thus, to orchestrate the control of homeostatic responses, mTOR Complex1 must integrate signals from distinct cues. Here, we review recent findings concerning the regulation and pathophysiology associated with mTOR Complex1 and S6K1.

Down-regulation of N-acetylglucosaminyltransferase-V induces ER stress by changing glycosylation and function of GLUT1

N-Acetylglucosaminyltransferase-V (GnT-V) is a key enzyme in the processing of N-glycans during synthesis of glycoproteins. We have reported that down-regulating GnT-V could induce endoplasmic reticulum stress (ER stress) in 7721 cells, a human hepatocarcinoma cell line. In a search for mechanisms of ER stress, we found that there was a prominent decline of glucose uptake in antisense GnT-V transfectant, furthermore, a decrease of tri- or tetra-antannary sugar chain of glucose transporter 1 (GLUT1). However, distribution of GLUT1 in antisense GnT-V transfectant was not affected. Glucose deprivation has been known to activate ER stress in tumor cells. Therefore, the data presented in this study indicate that the glycosylation change and decrease of transport activity of GLUT1 may be one possible mechanism of ER stress induced by down-regulating GnT-V, and GnT-V may contribute to the regulation of glucose uptake by modifying glycosylation of GLUT1 in some tumor cells.

Glucose transporter expression on the plasma membrane of resting and activated white blood cells

BACKGROUND

In white blood cells (WBC), the increase in glucose utilization is a prominent feature during immune response and this depends on the function of specific glucose transporter (GLUT) isoforms. The objective was to examine the effects of activation by Phorbol 12-myristate 13-acetate (PMA) or lipopolysaccharide (LPS) and insulin on the expression of GLUT isoforms in all subpopulations of WBC.

MATERIALS AND METHODS

Blood was withdrawn from 27 healthy subjects. The expression of GLUT1, GLUT3 and GLUT4 on the plasma membrane of resting and activated monocytes, T- and B-lymphocytes and polymorphonuclear cells (PMNs) was determined in the absence and presence of physiological concentrations of insulin, by flow cytometry.

RESULTS

GLUT1 did not respond to insulin in either resting or PMA/LPS activated state. In the resting state, monocytes and B-lymphocytes increased the abundance of GLUT3 and GLUT4 on their plasma membrane in response to insulin; in contrast, T-lymphocytes and PMNs were unresponsive to insulin. In the activated state, monocytes, B- and T- lymphocytes increased the expression of all three GLUT isoforms on their plasma membrane, whilst PMNs increased only GLUT1 and GLUT3; in all WBC, insulin augmented the expression of GLUT4 and GLUT3 isoforms in addition to the stimulation provided by the PMA or LPS treatment alone.

CONCLUSION

Activation of WBC leads to increased expression of GLUT1, GLUT3 and GLUT4 isoforms on their plasma membrane; this process was further augmented by insulin. During infection, these mechanisms may help to redistribute glucose as a potential source of energy away from peripheral tissues and direct it towards cells that mediate the immune response and are therefore crucial to survival.

Hypoxia-inducible factor-1alpha is a key regulator of metastasis in a transgenic model of cancer initiation and progression

Adaptation to hypoxia is a critical step in tumor progression and is, in part, regulated by the transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha). Xenograft models have been extensively used to characterize the role of HIF-1alpha in experimental cancers. Although these models provide an understanding of tumor growth at terminal stages of malignancy, they do not address tumor initiation or metastatic progression. To elucidate these roles, HIF-1alpha was conditionally deleted in the mammary epithelium of a transgenic mouse model for metastatic breast cancer. Conditional deletion of HIF-1alpha in the mammary epithelium resulted in delayed tumor onset and retarded tumor growth; this was correlated with decreased tumor cell proliferation. Tumors with conditional deletion of HIF-1alpha were also less vascular during early tumor progression. Perhaps most surprisingly, deletion of HIF-1alpha in the mammary epithelium resulted in decreased pulmonary metastasis. These results show that whereas HIF-1alpha is not required for the initiation of breast tumor growth or tumor cell metastasis, the transcriptional activity of HIF-1alpha is a significant positive regulator of tumor progression and metastatic potential.

Cytokine stimulation promotes glucose uptake via phosphatidylinositol-3 kinase/Akt regulation of Glut1 activity and trafficking

Cells require growth factors to support glucose metabolism for survival and growth. It is unclear, however, how noninsulin growth factors may regulate glucose uptake and glucose transporters. We show that the hematopoietic growth factor interleukin (IL)3, maintained the glucose transporter Glut1 on the cell surface and promoted Rab11a-dependent recycling of intracellular Glut1. IL3 required phosphatidylinositol-3 kinase activity to regulate Glut1 trafficking, and activated Akt was sufficient to maintain glucose uptake and surface Glut1 in the absence of IL3. To determine how Akt may regulate Glut1, we analyzed the role of Akt activation of mammalian target of rapamycin (mTOR)/regulatory associated protein of mTOR (RAPTOR) and inhibition of glycogen synthase kinase (GSK)3. Although Akt did not require mTOR/RAPTOR to maintain surface Glut1 levels, inhibition of mTOR/RAPTOR by rapamycin greatly diminished glucose uptake, suggesting Akt-stimulated mTOR/RAPTOR may promote Glut1 transporter activity. In contrast, inhibition of GSK3 did not affect Glut1 internalization but nevertheless maintained surface Glut1 levels in IL3-deprived cells, possibly via enhanced recycling of internalized Glut1. In addition, Akt attenuated Glut1 internalization through a GSK3-independent mechanism. These data demonstrate that intracellular trafficking of Glut1 is a regulated component of growth factor-stimulated glucose uptake and that Akt can promote Glut1 activity and recycling as well as prevent Glut1 internalization.

Positron emission tomography of the brain

Positron emission tomography (PTE) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceutical used for assessing various physiologic parameters pertaining to tumor metabolism.

Down-regulation of type I insulin-like growth factor receptor increases sensitivity of breast cancer cells to insulin

The type I insulin-like growth factor receptor (IGF1R) and insulin receptor (IR) are structurally and functionally related heterotetrameric receptors. Activation of IGF1R has been shown to regulate breast cancer cell biology, and it has become an attractive therapeutic target. Most strategies have focused on targeting IGF1R alone without affecting IR levels given the known physiologic functions of IR. Human breast cancer cell lines and tissues revealed mRNA expression of both IGF1R and IR. Because alphabeta chains of IGF1R and IR form hybrid receptors, we hypothesized that agents solely targeting IGF1R may affect tumor biology mediated by IGF1R/IR hybrids and IR. We used small interfering RNA (siRNA) technology to specifically down-regulate IGF1R by 60% to 80% in the MDA-435/LCC6 cell line, which was sufficient to diminish activation of IGF1R by IGF-I. IGF1R down-regulation by siRNA did not affect IR levels but, interestingly, sensitized cells to insulin activation of downstream signaling pathways in several breast cancer cell lines. IGF1R siRNA treatment diminished hybrid receptor formation, suggesting that specific down-regulation of IGF1R resulted in enhanced holo-IR formation. In addition, IGF1R down-regulation increased insulin binding consistent with the formation of an increased number of holo-IR on the cell surface. Accordingly, insulin-stimulated glucose uptake was enhanced on IGF1R down-regulation. In conclusion, our data suggest that specific siRNA targeting of IGF1R alone in breast cancer increases insulin sensitivity. Because IR also activates signaling pathways similar to IGF1R in breast cancer cells, agents targeting both receptors may be necessary to disrupt the malignant phenotype regulated by this growth factor system.

Assessment of quantitative FDG PET data in primary colorectal tumours: which parameters are important with respect to tumour detection?

PURPOSE

The impact of quantitative parameters on the differentiation of primary colorectal tumours from normal colon tissue was assessed. Dynamic PET data (DPET) were acquired, and compartment and non-compartment modelling applied. The discriminant power of single parameters and the combination of PET parameters was assessed. All lesions were confirmed by histology.

METHODS

FDG DPET studies were acquired in 22 patients with colorectal tumours prior to surgery. Five of these patients also had liver metastases at the time of the PET study. The SUV 56-60 min p.i. was included in the evaluation. A two-tissue compartment model was applied and the parameters k1-k4 as well as the fractional blood volume (VB) were obtained. The FDG influx was calculated from the compartment data. Non-compartment modelling was used to calculate the fractal dimension (FD) of the time-activity data.

RESULTS

FD, SUV, influx and k3 were the most important single parameters for lesion differentiation. The highest accuracy was achieved for FD (88.78%). The overall tracer uptake was mainly dependent on k3 and not on k1 or VB. The support vector machines (SVM) algorithm was used to predict the classification based on the combination of individual PET parameters. The overall accuracy was 97.3%, with only one false positive case and no false negative results. The analysis of the subgroup of five patients with primary tumours and synchronous metastases revealed no significant differences for the individual PET parameters. However, VB tended to be lower while k1 and k2 were higher in patients with synchronous metastases. The SVM classification analysis predicted the presence of metastases based on the PET data of the primary tumour in three of five patients.

CONCLUSION

Quantitative FDG PET studies provide very accurate data for the differentiation of primary colorectal tumours from normal tissue. The use of quantitative data has the advantage that the detection of a colorectal tumour is not primarily dependent on the individual assessment and experience of the physician evaluating the FDG PET data only visually. The results suggest that the presence of metastatic lesions may be predicted by analysis of the dynamic PET data of the corresponding primary tumour. Further studies are needed to assess this aspect in detail.

Positron Emission Tomography of the Brain

Positron emission tomography (PET) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceuticals used for assessing various physiologic parameters pertaining to tumor metabolism.

The metabolic syndrome: A high-risk state for cancer?

The metabolic syndrome is composed of cardiovascular risk factors including increased body mass index/waist circumference, blood pressure, plasma glucose, and triglycerides, as well as decreased high-density lipoprotein cholesterol. The essence of the metabolic syndrome lies in the clustering of these risk factors, which are associated with cardiovascular disease. Interestingly, most of the components of the metabolic syndrome have individually been linked in some way to the development of cancer. However, epidemiological studies linking the metabolic syndrome to cancer are scarce. Nevertheless, two such studies indicate that the clustering of metabolic syndrome components significantly increases the risk of colon cancer mortality compared with the individual components. The purpose of this review is to further explore the potential relationship between the metabolic syndrome and cancer risk. Specifically, we examine the hypothesis that individual components of the metabolic syndrome contribute to the development of several processes, including insulin resistance, aromatase activity, adipokine production, angiogenesis, glucose utilization, and oxidative stress/DNA damage, which can work together to increase cancer risk beyond that of the individual components alone. We propose that the metabolic syndrome be considered as a high-risk state for certain types of cancer and that this relationship should be systematically explored across cancer types.

A gene expression signature predicts survival of patients with stage I non-small cell lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related death in the United States. Nearly 50% of patients with stages I and II non-small cell lung cancer (NSCLC) will die from recurrent disease despite surgical resection. No reliable clinical or molecular predictors are currently available for identifying those at high risk for developing recurrent disease. As a consequence, it is not possible to select those high-risk patients for more aggressive therapies and assign less aggressive treatments to patients at low risk for recurrence.

METHODS AND FINDINGS

In this study, we applied a meta-analysis of datasets from seven different microarray studies on NSCLC for differentially expressed genes related to survival time (under 2 y and over 5 y). A consensus set of 4,905 genes from these studies was selected, and systematic bias adjustment in the datasets was performed by distance-weighted discrimination (DWD). We identified a gene expression signature consisting of 64 genes that is highly predictive of which stage I lung cancer patients may benefit from more aggressive therapy. Kaplan-Meier analysis of the overall survival of stage I NSCLC patients with the 64-gene expression signature demonstrated that the high- and low-risk groups are significantly different in their overall survival. Of the 64 genes, 11 are related to cancer metastasis (APC, CDH8, IL8RB, LY6D, PCDHGA12, DSP, NID, ENPP2, CCR2, CASP8, and CASP10) and eight are involved in apoptosis (CASP8, CASP10, PIK3R1, BCL2, SON, INHA, PSEN1, and BIK).

CONCLUSIONS

Our results indicate that gene expression signatures from several datasets can be reconciled. The resulting signature is useful in predicting survival of stage I NSCLC and might be useful in informing treatment decisions.

Glucose transporter type 1 expression are associated with poor prognosis in patients with salivary gland tumors

The objective of this study was to investigate the expression of Glucose transporter type 1 (GLUT1) and its relation to clinicopathologic parameters in patients with salivary gland tumors. Tissue samples were 49 cases of malignant tumors, 38 cases of benign tumors, mainly pleomorphic adenoma and 10 cases of normal salivary glands. Immunohistochemically, GLUT1 Labeling Index of malignant tumor was significantly higher than benign tumor. In RT-PCR assay, GLUT1 mRNA level in malignant tumor were higher than that of normal tissue. In malignant tumors, expression of GLUT1 correlated significantly with tumor size (p=0.002) and distant metastasis (p=0.007). Cumulative survival rate of high expression group was significantly lower than that of low (p<0.001). In multivariable analysis, overall survival significantly correlated with lymph node metastasis (p=0.042) and GLUT1 expression (p=0.022). These results suggest that GLUT1 expression may provide useful prognostic information in patients with salivary gland carcinoma.

Hexokinase II: cancer's double-edged sword acting as both facilitator and gatekeeper of malignancy when bound to mitochondria

A key hallmark of many cancers, particularly the most aggressive, is the capacity to metabolize glucose at an elevated rate, a phenotype detected clinically using positron emission tomography (PET). This phenotype provides cancer cells, including those that participate in metastasis, a distinct competitive edge over normal cells. Specifically, after rapid entry of glucose into cancer cells on the glucose transporter, the highly glycolytic phenotype is supported by hexokinase (primarily HK II) that is overexpressed and bound to the outer mitochondrial membrane via the porin-like protein voltage-dependent anion channel (VDAC). This protein and the adenine nucleotide transporter move ATP, newly synthesized by the inner membrane located ATP synthase, to active sites on HK II. The abundant amounts of HK II bind both the ATP and the incoming glucose producing the product glucose-6-phosphate, also at an elevated rate. This critical metabolite then serves both as a biosynthetic precursor to support cell proliferation and as a precursor for lactic acid, the latter exiting cancer cells causing an unfavorable environment for normal cells. Although helping facilitate this chemical warfare, HK II via its mitochondrial location also suppresses the death of cancer cells, thus increasing their possibility for metastasis and the ultimate death of the human host. For these reasons, targeting this key enzyme is currently being investigated in several laboratories in a strategy to develop novel therapies that may turn the tide on the continuing struggle to find effective cures for cancer. One such candidate is 3-bromopyruvate that has been shown recently to eradicate advanced stage, PET positive hepatocellular carcinomas in an animal model without apparent harm to the animals.

Mitochondrial DNA mutations in human cancer

Somatic mitochondrial DNA (mtDNA) mutations have been increasingly observed in primary human cancers. As each cell contains many mitochondria with multiple copies of mtDNA, it is possible that wild-type and mutant mtDNA can co-exist in a state called heteroplasmy. During cell division, mitochondria are randomly distributed to daughter cells. Over time, the proportion of the mutant mtDNA within the cell can vary and may drift toward predominantly mutant or wild type to achieve homoplasmy. Thus, the biological impact of a given mutation may vary, depending on the proportion of mutant mtDNAs carried by the cell. This effect contributes to the various phenotypes observed among family members carrying the same pathogenic mtDNA mutation. Most mutations occur in the coding sequences but few result in substantial amino acid changes raising questions as to their biological consequence. Studies reveal that mtDNA play a crucial role in the development of cancer but further work is required to establish the functional significance of specific mitochondrial mutations in cancer and disease progression. The origin of somatic mtDNA mutations in human cancer and their potential diagnostic and therapeutic implications in cancer are discussed. This review article provides a detailed summary of mtDNA mutations that have been reported in various types of cancer. Furthermore, this review offers some perspective as to the origin of these of mutations, their functional consequences in cancer development, and possible therapeutic implications.

Testicular Germ Cell Tumors: A Paradigm for the Successful Treatment of Solid Tumor Stem Cells

Treatment of testicular germ cell tumors (TGCTs) has been a success primarily due to the exquisite responsiveness of this solid tumor to cisplatin-based therapy. Despite the promise of cure for the majority of TGCT patients, the effectiveness of therapy for some patients is limited by toxicity and the problem of resistance. There is compelling rationale to further understand the biology of TGCTs in order to better treat other solid tumors and to address the shortcomings of present TGCT therapies. TGCTs contain undifferentiated pluripotent stem cells, known as embryonal carcinoma, that share many properties with human embryonic stem cells. The importance of cancer stem cells in the initiation, progression and treatment of solid tumors is beginning to emerge. We discuss TGCTs in the context of solid tumor curability and targeted cancer stem cell therapy.

Commonly used imaging techniques for diagnosis and staging

Imaging plays a vital role in the management of patients with cancer. Not only is it important for diagnosis, indicating sites of abnormality, and guiding biopsies, but it is also crucial in assessing disease extent and thereby determining treatment. In this review, conventional imaging techniques such as ultrasound, computed tomography, magnetic resonance imaging, and [18F]fluorodeoxyglucose-positron emission tomography are described, with attention to their mechanisms of action, and their strengths and weaknesses in diagnosis and staging of tumors. New developments are addressed and radiation safety issues are highlighted. In addition, we describe current and expected future uses of imaging techniques in oncology. Given that each technique has its inherent strengths and weaknesses, the combination of the methods will result in improved diagnosis, staging, and treatment prediction and monitoring.

Determining and understanding the control of glycolysis in fast-growth tumor cells. Flux control by an over-expressed but strongly product-inhibited hexokinase

Control analysis of the glycolytic flux was carried out in two fast-growth tumor cell types of human and rodent origin (HeLa and AS-30D, respectively). Determination of the maximal velocity (V(max)) of the 10 glycolytic enzymes from hexokinase to lactate dehydrogenase revealed that hexokinase (153-306 times) and phosphofructokinase-1 (PFK-1) (22-56 times) had higher over-expression in rat AS-30D hepatoma cells than in normal freshly isolated rat hepatocytes. Moreover, the steady-state concentrations of the glycolytic metabolites, particularly those of the products of hexokinase and PFK-1, were increased compared with hepatocytes. In HeLa cells, V(max) values and metabolite concentrations for the 10 glycolytic enzyme were also significantly increased, but to a much lesser extent (6-9 times for both hexokinase and PFK-1). Elasticity-based analysis of the glycolytic flux in AS-30D cells showed that the block of enzymes producing Fru(1,6)P2 (i.e. glucose transporter, hexokinase, hexosephosphate isomerase, PFK-1, and the Glc6P branches) exerted most of the flux control (70-75%), whereas the consuming block (from aldolase to lactate dehydrogenase) exhibited the remaining control. The Glc6P-producing block (glucose transporter and hexokinase) also showed high flux control (70%), which indicated low flux control by PFK-1. Kinetic analysis of PFK-1 showed low sensitivity towards its allosteric inhibitors citrate and ATP, at physiological concentrations of the activator Fru(2,6)P2. On the other hand, hexokinase activity was strongly inhibited by high, but physiological, concentrations of Glc6P. Therefore, the enhanced glycolytic flux in fast-growth tumor cells was still controlled by an over-produced, but Glc6P-inhibited hexokinase.

Glycogen synthase kinase-3β positively regulates the proliferation of human ovarian cancer cells

Although glycogen synthase kinase-3 (GSK-3) might act as a tumor suppressor since its inhibition is expected to mimic the activation of Wnt-signaling pathway, GSK-3beta may contribute to NF-kappaB activation in cancer cells leading to increased cancer cell proliferation and survival. Here we report that GSK-3beta activity was involved in the proliferation of human ovarian cancer cell both in vitro and in vivo. Inhibition of GSK-3 activity by pharmacological inhibitors suppressed proliferation of the ovarian cancer cells. Overexpressing constitutively active form of GSK-3beta induced entry into the S phase, increased cyclin D1 expression and facilitated the proliferation of ovarian cancer cells. Furthermore, GSK-3 inhibition prevented the formation of the tumor in nude mice generated by the inoculation of human ovarian cancer cells. Our findings thus suggest that GSK-3beta activity is important for the proliferation of ovarian cancer cells, implicating this kinase as a potential therapeutic target in ovarian cancer.

Dietary and genetic control of glucose transporter 2 glycosylation promotes insulin secretion in suppressing diabetes

Pancreatic beta cell-surface expression of glucose transporter 2 (Glut-2) is essential for glucose-stimulated insulin secretion, thereby controlling blood glucose homeostasis in response to dietary intake. We show that the murine GlcNAcT-IVa glycosyltransferase is required for Glut-2 residency on the beta cell surface by constructing a cell-type- and glycoprotein-specific N-glycan ligand for pancreatic lectin receptors. Loss of GlcNAcT-IVa, or the addition of glycan-ligand mimetics, attenuates Glut-2 cell-surface half-life, provoking endocytosis with redistribution into endosomes and lysosomes. The ensuing impairment of glucose-stimulated insulin secretion leads to metabolic dysfunction diagnostic of type 2 diabetes. Remarkably, the induction of diabetes by chronic ingestion of a high-fat diet is associated with reduced GlcNAcT-IV expression and attenuated Glut-2 glycosylation coincident with Glut-2 endocytosis. We infer that beta cell glucose-transporter glycosylation mediates a link between diet and insulin production that typically suppresses the pathogenesis of type 2 diabetes.

Comparison of metabolic pathways between cancer cells and stromal cells in colorectal carcinomas: a metabolic survival role for tumor-associated stroma

Understanding tumor metabolism is important for the development of anticancer therapies. Immunohistochemical evaluation of colorectal adenocarcinomas showed that cancer cells share common enzyme/transporter activities suggestive of an anaerobic metabolism [high lactate dehydrogenase 5 (LDH5)/hypoxia-inducible factor alphas (HIFalphas)] with high ability for glucose absorption and lactate extrusion [high glucose transporter 1 (GLUT1)/monocarboxylate transporter (MCT1)]. The tumor-associated fibroblasts expressed proteins involved in lactate absorption (high MCT1/MCT2), lactate oxidation (high LDH1 and low HIFalphas/LDH5), and reduced glucose absorption (low GLUT1). The expression profile of the tumor-associated endothelium indicated aerobic metabolism (high LDH1 and low HIFalphas/LDH5), high glucose absorption (high GLUT1), and resistance to lactate intake (lack of MCT1). It is suggested that the newly formed stroma and vasculature express complementary metabolic pathways, buffering and recycling products of anaerobic metabolism to sustain cancer cell survival. Tumors survive and grow because they are capable of organizing the regional fibroblasts and endothelial cells into a harmoniously collaborating metabolic domain.

Metabolism and transport of oxazaphosphorines and the clinical implications

The oxazaphosphorines including cyclophosphamide (CPA), ifosfamide (IFO), and trofosfamide represent an important group of therapeutic agents due to their substantial antitumor and immuno-modulating activity. CPA is widely used as an anticancer drug, an immunosuppressant, and for the mobilization of hematopoetic progenitor cells from the bone marrow into peripheral blood prior to bone marrow transplantation for aplastic anemia, leukemia, and other malignancies. New oxazaphosphorines derivatives have been developed in an attempt to improve selectivity and response with reduced toxicity. These derivatives include mafosfamide (NSC 345842), glufosfamide (D19575, beta-D-glucosylisophosphoramide mustard), NSC 612567 (aldophosphamide perhydrothiazine), and NSC 613060 (aldophosphamide thiazolidine). This review highlights the metabolism and transport of these oxazaphosphorines (mainly CPA and IFO, as these two oxazaphosphorine drugs are the most widely used alkylating agents) and the clinical implications. Both CPA and IFO are prodrugs that require activation by hepatic cytochrome P450 (CYP)-catalyzed 4-hydroxylation, yielding cytotoxic nitrogen mustards capable of reacting with DNA molecules to form crosslinks and lead to cell apoptosis and/or necrosis. Such prodrug activation can be enhanced within tumor cells by the CYP-based gene directed-enzyme prodrug therapy (GDEPT) approach. However, those newly synthesized oxazaphosphorine derivatives such as glufosfamide, NSC 612567 and NSC 613060, do not need hepatic activation. They are activated through other enzymatic and/or non-enzymatic pathways. For example, both NSC 612567 and NSC 613060 can be activated by plain phosphodiesterase (PDEs) in plasma and other tissues or by the high-affinity nuclear 3'-5' exonucleases associated with DNA polymerases, such as DNA polymerases and epsilon. The alternative CYP-catalyzed inactivation pathway by N-dechloroethylation generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde (CAA). Various aldehyde dehydrogenases (ALDHs) and glutathione S-transferases (GSTs) are involved in the detoxification of oxazaphosphorine metabolites. The metabolism of oxazaphosphorines is auto-inducible, with the activation of the orphan nuclear receptor pregnane X receptor (PXR) being the major mechanism. Oxazaphosphorine metabolism is affected by a number of factors associated with the drugs (e.g., dosage, route of administration, chirality, and drug combination) and patients (e.g., age, gender, renal and hepatic function). Several drug transporters, such as breast cancer resistance protein (BCRP), multidrug resistance associated proteins (MRP1, MRP2, and MRP4) are involved in the active uptake and efflux of parental oxazaphosphorines, their cytotoxic mustards and conjugates in hepatocytes and tumor cells. Oxazaphosphorine metabolism and transport have a major impact on pharmacokinetic variability, pharmacokinetic-pharmacodynamic relationship, toxicity, resistance, and drug interactions since the drug-metabolizing enzymes and drug transporters involved are key determinants of the pharmacokinetics and pharmacodynamics of oxazaphosphorines. A better understanding of the factors that affect the metabolism and transport of oxazaphosphorines is important for their optional use in cancer chemotherapy.

Multi-tracer small animal PET imaging of the tumour response to the novel pan-Erb-B inhibitor CI-1033

PURPOSE

This study was designed as "proof of concept" for a drug development model utilising multi-tracer serial small animal PET imaging to characterise tumour responses to molecularly targeted therapy.

METHODS

Mice bearing subcutaneous A431 human squamous carcinoma xenografts (n=6-8) were treated with the pan-Erb-B inhibitor CI-1033 or vehicle and imaged serially (days 0, 3 and 6 or 7) with [(18)F]fluorodeoxyglucose, [(18)F]fluoro-L: -thymidine, [(18)F]fluoro-azoazomycinarabinoside or [(18)F]fluoromisonidazole. Separate cohorts (n=3) were treated identically and tumours were assessed ex vivo for markers of glucose metabolism, proliferation and hypoxia.

RESULTS

During the study period, mean uptake of all PET tracers generally increased for control tumours compared to baseline. In contrast, tracer uptake into CI-1033-treated tumours decreased by 20-60% during treatment. Expression of the glucose transporter Glut-1 and cell cycle markers was unchanged or increased in control tumours and generally decreased with CI-1033 treatment, compared to baseline. Thymidine kinase activity was reduced in all tumours compared to baseline at day 3 but was sevenfold higher in control versus CI-1033-treated tumours by day 6 of treatment. Uptake of the hypoxia marker pimonidazole was stable in control tumours but was severely reduced following 7 days of CI-1033 treatment.

CONCLUSION

CI-1033 treatment significantly affects tumour metabolism, proliferation and hypoxia as determined by PET. The PET findings correlated well with ex vivo biomarkers for each of the cellular processes studied. These results confirm the utility of small animal PET for evaluation of the effectiveness of molecularly targeted therapies and simultaneously definition of specific cellular processes involved in the therapeutic response.

Sustained trophism of the mammary gland is sufficient to accelerate and synchronize development of ErbB2/Neu-induced tumors

Epidemiological studies indicate that parity enhances HER2/ErbB2/Neu-induced breast tumorigenesis. Furthermore, recent studies using multiparous, ErbB2/Neu-overexpressing mouse mammary tumor virus (MMTV-Neu) mice have shown that parity induces a population of cells that are targeted for ErbB2/Neu-induced transformation. Although parity accelerates mammary tumorigenesis, the pattern of tumor development in multiparous MMTV-Neu mice remains stochastic, suggesting that additional events are required for ErbB2/Neu to cause mammary tumors. Whether such events are genetic in nature or reflective of the dynamic hormonal control of the gland that occurs with pregnancy remains unclear. We postulated that young age at pregnancy initiation or chronic trophic maintenance of mammary epithelial cells might provide a cellular environment that significantly increases susceptibility to ErbB2/Neu-induced tumorigenesis. MMTV-Neu mice that were maintained pregnant or lactating beginning at 3 weeks of age demonstrated accelerated tumorigenesis, but this process was still stochastic, indicating that early pregnancy does not provide the requisite events of tumorigenesis. However, bitransgenic mice that were generated by breeding MMTV-Neu mice with a luteinizing hormone-overexpressing mouse model of ovarian hyperstimulation developed multifocal mammary tumors in an accelerated, synchronous manner compared to virgin MMTV-Neu animals. This synchrony of tumor development in the bitransgenic mice suggests that trophic maintenance of the mammary gland provides the additional events required for tumor formation and maintains the population of cells that are targeted by ErbB2/Neu for transformation. Both the synchrony of tumor appearance and the ability to characterize a window of commitment by ovariectomy/palpation studies permitted microarray analysis to evaluate changes in gene expression over a defined timeline that spans the progression from normal to preneoplastic mammary tissue. These approaches led to identification of several candidate genes whose expression changes in the mammary gland with commitment to ErbB2/Neu-induced tumorigenesis, suggesting that they may either be regulated by ErbB2/Neu and/or contribute to tumor formation.

Interaction of glucose transporter 1 with anion exchanger 1 in vitro

The facilitative glucose transporter 1 (GLUT1) mediates the passive diffusion of d-glucose across the cell membrane, providing the energy resource in glycolysis in the erythrocytes. Anion exchanger 1 (band 3) is another important membrane protein that mediates rapid exchange of CO(2) through Cl(-)/HCO(3)(-) exchange across the erythrocyte membrane. For verifying the presumption over a decade that GLUT1 and band 3 in the erythrocyte would be interacting with each other, we cloned and expressed both the cytoplasmic domains of GLUT1 and band 3 in Escherichia coli, and tested their binding ability. By coimmunoprecipitation we found that among the tested N-terminal, C-terminal, and loop fraction of GLUT1, only the C-terminal of GLUT1 can interact with cytoplasmic domain of band 3. The interaction was further verified by coimmunoprecipitation and pull-down assay using both proteins as bait and target. These results showed that GLUT1 and band 3 form a protein complex that can regulate the activities of the proteins within it.

Differential subcellular distribution of glucose transporters GLUT1–6 and GLUT9 in human cancer: Ultrastructural localization of GLUT1 and GLUT5 in breast tumor tissues

It has been proposed that the enhanced metabolic activity of tumor cells is accompanied by an increased expression of facilitative hexose transporters (GLUTs). However, a previous immunohistochemical analysis of GLUT1 expression in 154 malignant human neoplasms failed to detect the GLUT1 isoform in 87 tumors. We used 146 normal human tissues and 215 tumor samples to reassess GLUT1 expression. A similar number of samples were used to compare the expression of GLUT2-6 and 9. The classical expression of GLUT1-5 in different normal human tissues was confirmed, however, we were unable to detect GLUT2 in human pancreatic islet cells. GLUT6 was principally detected in testis germinal cells and GLUT9 was localized in kidney, liver, heart, and adrenal. In tumor samples, GLUT1, 2, and 5 were the main transporters detected. GLUT1 was the most widely expressed transporter, however, 42% of the samples had very low-to-negative expression levels. GLUT2 was detected in 31% of the samples, being mainly expressed in breast, colon, and liver carcinoma. GLUT5 was detected in 27% of breast and colon adenocarcinoma, liver carcinoma, lymphomas, and testis seminoma samples. In situ RT-PCR and ultrastructural immunohistochemistry confirmed GLUT5 expression in breast cancer. GLUT6 and 9 are not clearly over-expressed in human cancer. The extensive expression of GLUT2 and 5 (glucose/fructose and fructose transporters, respectively) in malignant human tissues indicates that fructose may be a good energy substrate in tumor cells. Our functional data obtained in vitro in different tumor cells support this hypothesis. Additionally, these results suggest that fructose uptake could be used for positron emission tomography imaging and, may possibly represent a novel target for the development of therapeutic agents in different human cancers.