Tumor Cell Oxygen Research Articles

Abstract 1140: PI3K/Akt inhibition decreases oxygen consumption In tumor cells by phosphorylating and inactivating pyruvate dehydrogenase PDH E1α subunit

Abstract The PI3K/mTOR pathway plays a central role in coupling metabolic processes to the cellular proliferative state. Pharmacologic inhibitors of the PI3K/mTOR pathway or genetic inhibition of Akt/PI3K decreased the oxygen consumption rate (OCR) in transformed cell lines in vitro by 30-40%. Pharmacologic inhibition of this pathway increased phosphorylation of the E1α subunit of the pyruvate dehydrogenase (PDH) complex on Ser293, an inhibitory modification of this critical gatekeeper of mitochondrial respiration. Expressing wild type PTEN in a doxycycline-inducible manner in a glioblastoma cell line with mutant PTEN led to an increase in PDH E1α phosphorylation and a decrease in OCR. The decrease in OCR with PI3K/Akt/mTOR inhibition was recapitulated by knocking down PDH E1α expression using siRNA. Pre-treatment with dichloroacetate (DCA), a known inhibitor of the pyruvate dehydrogenase kinases (PDKs) that phosphorylate PDH E1α, prevented the upregulation in PDH E1α phosphorylation, induced by inhibition of the pathway and also blunted the decrease in OCR. Likewise, introduction of exogenous PDH-E1α that contains serine to alanine mutations, which can no longer be regulated by phosphorylation, also blunted the decrease in OCR seen with PI3K/mTOR inhibition. Our findings highlight an association between the PI3K/mTOR pathway and tumor cell oxygen consumption that is regulated in part by PDH phosphorylation. These results have important implications for understanding the effects PI3K pathway activation in tumor metabolism and also in designing cancer therapy trials that use inhibitors of this pathway. Citation Format: George John Cerniglia, Souvik Day, Shannon M. Gallagher-Colombo, Natalie Daurio, Stephen Tuttle, Theresa M. Busch, Theresa M. Busch, Alexander Lin, Tatiana V. Esipova, Sergei A. Vinogradov, Constantinos Koumenis, Amit Maity. PI3K/Akt inhibition decreases oxygen consumption In tumor cells by phosphorylating and inactivating pyruvate dehydrogenase PDH E1α subunit. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1140. doi:10.1158/1538-7445.AM2015-1140

Abstract B05: PI3K/mTOR pathway-dependent regulation of oxygen metabolism via pyruvate dehydrogenase (PDH)-E1alpha phosphorylation

Abstract The PI3K/mTOR pathway plays a central role in coupling metabolic processes to the cellular proliferative state. In the current study we show that pharmacological inhibition of this pathway leads to a decrease in hypoxia within SQ20B human head and neck cancer xenografts. The mechanism underlying the effect appears in part to be due to reduced tumor cell oxygen consumption induced by the drug. Pharmacologic inhibitors of the PI3K/mTOR pathway or genetic inhibition of Akt/PI3K decreased the oxygen consumption rate (OCR) in transformed cell lines in vitro by 30-40%. Pharmacologic inhibition of this pathway increased phosphorylation of the E1alpha subunit of the pyruvate dehydrogenase (PDH) complex on Ser293, an inhibitory modification of this critical gatekeeper of mitochondrial respiration. Expressing wild type PTEN in a doxycycline-inducible manner in a glioblastoma cell line with mutant PTEN led to an increase in PDH-E1alpha phosphorylation and a decrease in OCR. The decrease in OCR with PI3K/Akt/mTOR inhibition was recapitulated by knocking down PDH-E1alpha expression using siRNA. Pre-treatment with dichloroacetate (DCA), a known inhibitor of the pyruvate dehydrogenase kinases (PDKs) that phosphorylate PDH-E1alpha prevented the upregulation in PDH-E1alpha phosphorylation, induced by inhibition of the pathway and also blunted the decrease in OCR. Our findings highlight an association between the PI3K/mTOR pathway and tumor cell oxygen consumption and reveal a novel link between this pathway and PDH phosphorylation. These results have important implications for understanding the effects PI3K pathway activation in tumor metabolism and also in the use of inhibitors of this pathway in cancer therapy Citation Format: George Cerniglia, Souvik Dey, Shannon M. Gallagher-Colombo, Natalie Daurio, Stephen Tuttle, Theresa M. Busch, Alexander Lin, Tatiana V. Esipova, Sergei Vinogradov, Constantinos Koumenis, Amit Maity. PI3K/mTOR pathway-dependent regulation of oxygen metabolism via pyruvate dehydrogenase (PDH)-E1alpha phosphorylation. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B05.

PET-Specific Parameters and Radiotracers in Theoretical Tumour Modelling

The innovation of computational techniques serves as an important step toward optimized, patient-specific management of cancer. In particular, in silico simulation of tumour growth and treatment response may eventually yield accurate information on disease progression, enhance the quality of cancer treatment, and explain why certain therapies are effective where others are not. In silico modelling is demonstrated to considerably benefit from information obtainable with PET and PET/CT. In particular, models have successfully integrated tumour glucose metabolism, cell proliferation, and cell oxygenation from multiple tracers in order to simulate tumour behaviour. With the development of novel radiotracers to image additional tumour phenomena, such as pH and gene expression, the value of PET and PET/CT data for use in tumour models will continue to grow. In this work, the use of PET and PET/CT information in in silico tumour models is reviewed. The various parameters that can be obtained using PET and PET/CT are detailed, as well as the radiotracers that may be used for this purpose, their utility, and limitations. The biophysical measures used to quantify PET and PET/CT data are also described. Finally, a list of in silico models that incorporate PET and/or PET/CT data is provided and reviewed.

Abstract 4314: Metabolic manipulation of hypoxia and radiotherapy response by electron transport inhibitors

Abstract The presence of hypoxia in solid tumors is correlated with poor treatment outcome. Even small population of hypoxic cells within tumors can significantly decrease the efficacy of radiation therapy. One approach to treating hypoxia in tumours is to reduce overall tumor cell oxygen consumption by modulating mitochondrial respiration. This could reoxygenate hypoxic cells within the tumor and restore radiation sensitivity. To guide in vivo application we tested the effects of three respiratory chain inhibitors; the biguanides metformin and phenformin and rotenone on oxygen consumption in 3D tissue engineered discs. Experiments were carried out to evaluate the effect of respiratory inhibition on the hypoxic fraction of HCT116 and HT29 tissue discs using immunostaining with the hypoxic cell marker pimonidazole. An oxygen sensing phosphorescence lifetime probe assessed pO2 on the basal side of the disc as a function of time after inhibitors were exposed to the apical surface. Clonogenic assays were then performed to confirm the radiosensitization of hypoxic cells within the tissue discs. Pimonidazole staining and direct pO2 sensing confirmed that all three electron transfer inhibitors decrease the hypoxic fraction by reducing cellular oxygen consumption. Rotenone was found to completely eliminate the hypoxic fraction at nanomolar concentrations compared to metformin and phenformin which require milli to micromolar concentrations respectively. Furthermore, rotenone was found to have an effect on oxygen utilization within minutes of drug exposure compared to both metformin and phenformin, which took hours to be effective. In addition, clonogenics assays determined that all three electron transfer inhibitors radiosensitize tumor cells with rotenone being the most efficient compound on a molar basis. The mitochondrial inhibitors of complex I metformin, phenformin and rotenone decrease oxygen utilization by tumor cells in a concentration dependent manner resulting in reduction of the hypoxic fraction and increased radiosensitivity. Citation Format: Maria Jose Gandolfo, Alastair H. Kyle, Andrew I. Minchinton. Metabolic manipulation of hypoxia and radiotherapy response by electron transport inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4314. doi:10.1158/1538-7445.AM2014-4314

Mechanisms of coagulative necrosis in malignant epithelial tumors (Review).

Histological tumor necrosis (TN) has been reported to indicate a poor prognosis for different human cancers. It is generally accepted that TN results from chronic ischemic injury due to rapid tumor growth. However, whether insufficient tumor vascularization and inadequate tumor cell oxygenation are the only factors causing TN remains controversial. Mitotic catastrophe is considered to occur as a result of dysregulated/failed mitosis, leading to cell death. We hypothesize that mitotic catastrophe, induced by hypoxic stress, may lead to the TN which is observed in high grade carcinomas. The current review describes the morphological features of TN in malignant epithelial tumors. In addition, evidence regarding the involvement of mitotic catastrophe in the induction of TN in human carcinomas is discussed.

Treatment with erythropoiesis-stimulating agents in chronic kidney disease patients with cancer

Treatment of anemia remains an important component in the care of patients with nondialysis chronic kidney disease (CKD) and end-stage renal disease (ESRD). Erythropoietin-stimulating agents (ESAs) remains a key anemia treatment strategy in this patient population. However, anemia management in this group can become more complicated by prior or current history of malignancy. There has been a great deal of work both scientifically and in clinical trials in oncology that have revealed certain concerns and risks of ESA use in patients with cancer. In this review, we will bring together knowledge from nephrology and oncology literature to help nephrologists understand the implications for ESA treatment when CKD/ESRD is complicated by cancer. We also suggest an approach to the management of anemia in this patient group with active or previous malignancy.

Prognostic impact of the combination of erythropoiesis-stimulating agents to cancer treatment: literature review

Cancer patients commonly develop anaemia. Erythropoiesis-stimulating agents (ESAs) are frequently used in cancer treatment. Numerous controlled studies indicate that ESAs can raise haemoglobin levels, reduce transfusion requirements and improve quality of life in anaemic cancer patients receiving chemotherapy. They were previously used to enhance response to radiation therapy, via increasing tumour cell oxygenation. Since the 2002 guideline, there has been increasing attention to the safety of ESA treatment in patients with cancer. Two placebo-controlled phase III randomised clinical trials published in 2003 showed evidence of harmful effects of ESAs on survival and/or tumour outcomes. Subsequently, recent trials and several large meta-analyses have confirmed negative impact on survival and/or disease progression. To comprehensively examine whether ESA use affects safety outcomes in cancer patients in different settings (chemotherapy, radiotherapy and targeted therapies), we conducted a literature review of all clinical trials, small and large meta-analyses from 1990 to 2012.

In vivo intracellular oxygen dynamics in murine brain glioma and immunotherapeutic response of cytotoxic T cells observed by fluorine-19 magnetic resonance imaging.

Noninvasive biomarkers of anti-tumoral efficacy are of great importance to the development of therapeutic agents. Tumor oxygenation has been shown to be an important indicator of therapeutic response. We report the use of intracellular labeling of tumor cells with perfluorocarbon (PFC) molecules, combined with quantitative 19F spin-lattice relaxation rate (R1) measurements, to assay tumor cell oxygen dynamics in situ. In a murine central nervous system (CNS) GL261 glioma model, we visualized the impact of Pmel-1 cytotoxic T cell immunotherapy, delivered intravenously, on intracellular tumor oxygen levels. GL261 glioma cells were labeled ex vivo with PFC and inoculated into the mouse striatum. The R1 of 19F labeled cells was measured using localized single-voxel magnetic resonance spectroscopy, and the absolute intracellular partial pressure of oxygen (pO2) was ascertained. Three days after tumor implantation, mice were treated with 2×107 cytotoxic T cells intravenously. At day five, a transient spike in pO2 was observed indicating an influx of T cells into the CNS and putative tumor cell apoptosis. Immunohistochemistry and quantitative flow cytometry analysis confirmed that the pO2 was causally related to the T cells infiltration. Surprisingly, the pO2 spike was detected even though few (∼4×104) T cells actually ingress into the CNS and with minimal tumor shrinkage. These results indicate the high sensitivity of this approach and its utility as a non-invasive surrogate biomarker of anti-cancer immunotherapeutic response in preclinical models.

Abstract B7: Hypoxia-inducible factor 1 mediates thrombosis-associated cancer progression

Abstract Background. Cancer patients are up to 50 times more likely to suffer from lethal venous thromboembolism compared with non-cancer patients, but mechanisms that regulate the positive correlation between these conditions are unclear. Our primary aim was to test whether hypoxia within cells contained in the thrombus and adjacent vein leads to upregulation of hypoxia-inducible factor 1 (HIF1), which in turn stimulates the production of factors that mediate tumor growth and metastasis. Methods. Systemic or endothelial and myeloid HIF1 levels were altered (via administration of HIF1 agonist L-mimosine or via cre-Tie2 driven HIF1 deletion respectively) in established mouse models of thrombosis and breast cancer (inferior vena cava stenosis or polyoma middle T mutation driven by mouse mammary tumour virus respectively). Protein arrays were used to quantify the expression of 25 factors that regulate coagulation, thrombosis, and cancer progression. Adhesion and migration assays were used to characterise tumor and endothelial cell behaviour on thrombotic surfaces; while endothelial and tumor cell oxygen consumption rate was measured before and after thrombin treatment. Image analysis was also used to quantify intra-tumor thrombus formation. Results. Thrombus formation or upregulation of HIF1 increased the circulating expression of 10 factors that mediate tumor growth and remodelling including vascular endothelial growth factor (VEGF, 2±1 vs 1±0.2pg/ml in controls, n=6/group, P<0.05), hepatocyte growth factor (HGF, 10±5 vs 7±2% in controls, n=8/group, P<0.05), and stromal cell-derived factor 1 (SDF1, 14±6 vs 2±1% in controls, n=8/group, P<0.05). Hypoxia (1% oxygen) tended to attenuate endothelial cell migration on fibrin (100±13 vs 64±10 cells in controls, n=6/group, P=0.05); while HIF1 deletion in Lewis lung cancer cells abolished their hypoxia-induced increase in adhesion onto fibrin (n=5/group, P<0.05). Thrombin administration reduced the oxygen consumption rate of Lewis lung cancer cells (59±13 vs 79±16 pMol/min in controls, n=5/group, P<0.005) but not endothelial cells (P=0.06). Deposition of fibrin in mammary tumours was reduced following endothelial and myeloid HIF1 deletion (5±1 vs 13±3% in controls, n=7/group, P<0.05) and this was associated with reduced tumour size (n=14, R=0.7, P<0.01). Conclusions. HIF1 regulates the progression of venous thrombosis and cancer, and could also be responsible for the positive association between these conditions. Cell and tissue-specific HIF1 is an attractive therapeutic target for treatments that aim to reduce thrombosis-associated cancer progression. Citation Format: Colin E. Evans, Cristina Branco-Price, Julia Humphries, Ashar Wadoodi, Prakash Saha, Jung-whan Kim, Mattias Belting, Alberto Smith, Randall S. Johnson. Hypoxia-inducible factor 1 mediates thrombosis-associated cancer progression. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B7.

Increasing Oxygen in Hypoxic Tumors

Background: Tumors are frequently hypoxic, affecting both chemotherapy and radiotherapy. Trans sodium crocetinate (TSC), a novel pharmaceutical agent, causes increases in oxygen levels of hypoxic tissues. It has also been shown, in animal models of cancer, that radiotherapy is more effective when used in conjunction with TSC. An increase in tumor oxygen should also affect the HIF-1α pathway. Thus, an in vitro study of that pathway in human glioblastoma cells was performed. Methods: This study involved the use of quantitative real time polymerase chain reaction technology and human glioblastoma multiforme cells. The cells were cultured under both hypoxic and normoxic conditions. Results: The inclusion of TSC in the media of the cells resulted in some genes in the HIF-1α pathway being either up- or down-regulated in a statistically-significant manner. These changes were opposite to those which occurred when the same cells were grown under hypoxic conditions but without TSC. In addition, those same genes reacted in an opposite manner when the cells were grown with TSC but under a normal oxygen environment. Conclusions: These results support previous observations that TSC reduces hypoxia in tumor cells. Since TSC caused statistical differences in gene expression under hypoxia different from those caused under normoxia, it suggests that there is not a direct effect of TSC on the HIF-1α pathway. Rather, TSC alters the gene expression due to a change in the response of the genes to different oxygen levels. These data also correlate with previous in vivo studies which show that TSC increases oxygen to hypoxic tissue but not to normal tissue. Thus, these data, combined with previous studies of animal cancer models, strongly suggest that TSC has the ability to increase cellular oxygen in tumor cells. Such a physiological change can be beneficial with combined with radiotherapy for cancer.

3D modeling of effects of increased oxygenation and activity concentration in tumors treated with radionuclides and antiangiogenic drugs

Formation of new blood vessels (angiogenesis) in response to hypoxia is a fundamental event in the process of tumor growth and metastatic dissemination. However, abnormalities in tumor neovasculature often induce increased interstitial pressure (IP) and further reduce oxygenation (pO2) of tumor cells. In radiotherapy, well-oxygenated tumors favor treatment. Antiangiogenic drugs may lower IP in the tumor, improving perfusion, pO2 and drug uptake, by reducing the number of malfunctioning vessels in the tissue. This study aims to create a model for quantifying the effects of altered pO2-distribution due to antiangiogenic treatment in combination with radionuclide therapy. Based on experimental data, describing the effects of antiangiogenic agents on oxygenation of GlioblastomaMultiforme (GBM), a single cell based 3D model, including 10(10) tumor cells, was developed, showing how radionuclide therapy response improves as tumor oxygenation approaches normal tissue levels. The nuclides studied were 90Y, 131I, 177Lu, and 211At. The absorbed dose levels required for a tumor control probability (TCP) of 0.990 are compared for three different log-normal pO2-distributions: micro1 = 2.483, sigma1 = 0.711; micro2 = 2.946, sigma2 = 0.689; micro3 = 3.689, and sigma3 = 0.330. The normal tissue absorbed doses will, in turn, depend on this. These distributions were chosen to represent the expected oxygen levels in an untreated hypoxic tumor, a hypoxic tumor treated with an anti-VEGF agent, and in normal, fully-oxygenated tissue, respectively. The former two are fitted to experimental data. The geometric oxygen distributions are simulated using two different patterns: one Monte Carlo based and one radially increasing, while keeping the log-normal volumetric distributions intact. Oxygen and activity are distributed, according to the same pattern. As tumor pO2 approaches normal tissue levels, the therapeutic effect is improved so that the normal tissue absorbed doses can be decreased by more than 95%, while retaining TCP, in the most favorable scenario and by up to about 80% with oxygen levels previously achieved in vivo, when the least favourable oxygenation case is used as starting point. The major difference occurs in poorly oxygenated cells. This is also where the pO2-dependence of the oxygen enhancement ratio is maximal. Improved tumor oxygenation together with increased radionuclide uptake show great potential for optimising treatment strategies, leaving room for successive treatments, or lowering absorbed dose to normal tissues, due to increased tumor response. Further studies of the concomitant use of antiangiogenic drugs and radionuclide therapy therefore appear merited.

Residual DNA double strand breaks in perfused but not in unperfused areas determine different radiosensitivity of tumours

PurposeMicromilieu-dependent quantification of γH2AX after irradiation in vivo and correlation with local tumour control. Materials and methodsLocal tumour control was evaluated after irradiation of FaDu and SKX xenografts with ambient single doses. γH2AX foci were quantified in perfused and unperfused regions after different irradiation doses and at different time points. ResultsThe TCD50 of FaDu was 2-times higher compared to SKX (28.0Gy [95% C.I. 24.6; 31.3Gy] for FaDu; 14.9Gy [10.9; 18.9] for SKX, p<0.001). The induction of foci did not differ between the tumour models. Residual foci were twice higher in perfused SKX regions compared to FaDu, no difference was observed in the non-perfused region between both tumour models. The number of residual foci increased with a 2-times higher slope in perfused SKX-regions compared to FaDu, while no difference was detected in unperfused regions. Already within the perfused regions, this slope decreased with distance from perfused vessels. ConclusionThe dose–response of residual γH2AX foci is highly dependent on tumour cell oxygenation in well perfused areas. This dependence decreases further away from tumour vessels. Only γH2AX evaluation in perfused tumour areas can distinguish between the different radiocurability of the two tumour models.

TU‐E‐214‐03: Preclinical and Clinical Hypoxia Imaging: Current and Emerging Methods and Technology

The definition of tumor hypoxia is multifaceted, ranging from a simple physiological absence of molecular oxygen in tumor cells to a major factor associated with aggressive tumor phenotype; therefore, imaging of tumor hypoxia is equally poorly defined. Several compounds have been synthesized for PET hypoxia imaging studies: 18F‐fluoromisonidazole (FMISO), Cu‐diacetyl‐bis(N4‐methylthiosemicarbazone) (Cu‐ATSM), 2‐nitroimidazoles based markers such as 2‐(2‐nitroimidazol‐1[H]‐yl)‐N‐(3‐[F‐18]fluoropropyl) acetamide (EF1) and [2‐(2‐nitroimidazol‐1‐yl)‐N‐(3,3,3‐trifluoropropyl)‐acetamide], [2‐(2‐nitro‐1[H]‐imidazol‐1‐yl)‐N‐(2,2,3,3,3‐penta‐fluoropropyl)‐acetamide] (EF5), and most recently 1‐(5‐fluoro‐5‐deoxy‐alpha‐D‐arabinofuranosyl)‐2‐nitroimidazole (FAZA). All these compounds diffuse into normally oxygenated and hypoxic cells but are retained in substantially higher concentrations in hypoxic issues. Clinically most commonly used PET hypoxia tracers are FMISO and Cu‐ATSM. In this lecture, different PET hypoxia tracers will be reviewed, focusing on differences in their uptake mechanisms, which lead to differences in their clinical appearance. In addition, the most important clinical trials utilizing PET hypoxia imaging will be reviewed.Learning objectives:1. To learn about clinical PET imaging of hypoxia2. To learn about differences between various PET hypoxia tracers3. To learn about clinical trials utilizing PET hypoxia imaging

Decrease in Tumor Cell Oxygen Consumption after Treatment with Vandetanib (ZACTIMA™; ZD6474) and its Effect on Response to Radiotherapy

We investigated the early effects of vandetanib (ZACTIMA; ZD6474), an inhibitor of VEGFR-dependent angiogenesis, on tumor oxygenation and on the possible consequences of combining vandetanib with radiotherapy. Tumor oxygenation, perfusion, cellular consumption of oxygen, and radiation sensitivity were studied in transplantable liver tumors after daily doses of vandetanib (25 mg kg(-1) i.p.). Measurements of oxygenation (pO(2)) and tumor cell oxygen consumption were carried out using electron paramagnetic resonance (EPR), and perfusion parameters were assessed by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Regrowth delay assays were performed after treatment with vandetanib alone, radiation alone or a combination of both treatments. Vandetanib induced an early increase in tumor oxygenation that did not correlate with remodeling of the tumor vasculature or with changes in tumor perfusion. A decrease in tumor cell oxygen consumption was observed that could have been responsible for this increase in tumor oxygenation. Consistent with this increase in tumor oxygenation, we found that vandetanib potentiated the tumor response to radiotherapy. Our results confirm that treatment with an inhibitor of VEGFR signaling reduces oxygen consumption rate by tumor cells. The observation that vandetanib causes an early increase in tumor oxygenation has implications for the timing and sequencing of treatment with VEGF signaling inhibitors in combination with radiation.

Comparison of methods for measuring oxygen consumption in tumor cells in vitro

The oxygen consumption rate of tumor cells affects tumor oxygenation and response to therapies. Highly sensitive methods for determining cellular oxygen consumption are, therefore, needed to identify treatments that can modulate this parameter. We compared the performances of three different methods for measuring cellular oxygen consumption: electron paramagnetic resonance (EPR) oximetry, the Clark electrode, and the MitoXpress fluorescent assay. To compare the assays, we used K562 cells in the presence of rotenone and hydrocortisone, compounds that are known to inhibit the mitochondrial electron transport chain to different extents. The EPR method was the only one that could identify both rotenone and hydrocortisone as inhibitors of tumor cell oxygen consumption. The Clark electrode and the fluorescence assay demonstrated a significant decrease in cellular oxygen consumption after administration of the most potent inhibitor (rotenone) but failed to show any significant effect of hydrocortisone. EPR oximetry is, therefore, the most sensitive method for identifying inhibitors of oxygen consumption on cell assays, whereas the Clark electrode offers the unique opportunity to add external compounds during experiments and still shows great sensitivity in studying enzyme and chemical reactions that consume oxygen (non-cell assays). Finally, the MitoXpress fluorescent assay has the advantage of a high-sample throughput and low bulk requirements but at the cost of a lower sensitivity.

Hypoxia in Brain Tumors

Primary malignant brain tumors are estimated to have caused more than 12,800 deaths in the United States in 2006, and nearly 19,000 new cases are diagnosed annually in this country. The glial-derived neoplasm, or glioma, is the most aggressive type of brain tumor and accounts for 44% of all primary brain tumors. Among gliomas, the glioblastoma is the most commonly seen glial brain tumor in the United States and the most lethal worldwide. Despite very active investigation of new therapeutic models, more aggressive surgical approaches, novel delivery modalities and protocols for radiation, types and dosage of chemotherapy, and use of new signaling modifiers, only small improvements in patient outcomes have been achieved in this disease. The purpose of this review is to summarize the important aspects of tumor hypoxia in human glial brain tumors. We will describe the techniques used to measure tumor hypoxia, highlight what is currently known of the pathophysiologic and genetic mechanisms linking hypoxia with tumor progression and illustrate the significance of the oxygen effect and its role in tumor resistance to radiation and chemotherapy. We will also review therapeutic modalities to combat hypoxic tumor cell resistance and discuss the future of diagnosing and combating brain tumor hypoxia, emphasizing noninvasive imaging and novel hypoxia-modifying agents. At the conclusion of this article, the reader should have an up-to-date understanding of a concept, tumor cell oxygenation, which has the potential to help differentiate which malignant glioma patients are most likely to have good outcomes and respond to antihypoxia therapy.

Use of H2 15O-PET for investigating perfusion changes in pelvic tumors due to regional hyperthermia

Purpose: An increase in tumor oxygenation and perfusion due to hyperthermia has been reported for experimental tumors. The present study was performed to investigate this hypothesis in patients who underwent regional hyperthermia.Methods: Twenty-seven patients with primary or recurrent pelvic tumors were included in this study. Prior to and up to 1 h after regional hyperthermia, perfusion and partition coefficient were quantitatively determined by utilizing H2 15O-PET. First pass PET images were fused with the segmented common iliac artery from separately acquired CT scan. The arterial input function was extracted from the common iliac arteries using the dynamic PET images and the fused CT. The fused images were also used to extract tumor activity–time curves. Perfusion was calculated from the total tumor curves with correction for arterial spill-over. Changes in perfusion and partition coefficient were analyzed and correlated with various treatment parameters.Results: Heating under hyperthermia conditions significantly increased the partition coefficient for pelvic tumors (P = 0.005). The increase correlated with the duration of hyperthermia and was found in patients treated for more than 1 h and persisted for more than 1 h after the end. Significant changes in perfusion were not observed. Perfusion had recurred to initial values 20 min after heating.Conclusions: The increase in partition coefficient reflects an increased diffusion distance of radio-labeled water. Therefore water diffusion is increased due to hyperthermia. Analogous to water diffusion, the diffusion of inert gases is also facilitated, improving the oxygenation of hypoxic tumor cells. Our results suggest that tumor oxygenation can probably be enhanced by regional hyperthermia for a period of more than 1 h after heating, provided hyperthermia is applied for at least 60 min. The effect was observed to be reversible within one week.

Clinical relevance of maspin expression in bladder cancer

Transitional cell carcinoma (TCC) of the bladder is a solid tumor that induces angiogenesis to maintain nutrition and oxygenation of tumor cells. Maspin, a serpin with tumor suppressing activity, has recently been identified as an inhibitor of angiogenesis. This study examined the impact of maspin expression in the growth pattern of TCC of the bladder. Maspin was identified in a panel of normal tissues, in several bladder carcinoma cell lines, and 51 patient samples of TCC of the bladder. Expression was detected by RT-PCR and immunohistochemistry. Furthermore, the level of maspin was correlated to the growth rate of bladder tumor cell lines in vitro and in vivo. Maspin expression was found in high quantities in normal urothelium. Maspin expression was preserved in superficial bladder cancers but was significantly diminished in invasive carcinomas. Within the group of invasive TCCs, maspin expression was inversely correlated to the patient prognosis. Furthermore, low maspin expression level was coupled to an increased tumor cell growth in vivo. Down-regulation of maspin expression seems to be a specific event in the progression of invasive bladder carcinoma. Maspin might be a useful marker to determine the prognosis of invasive TCC. Furthermore, maspin re-expression might become a therapeutic option in the treatment of invasive, metastatic TCC.

PFKFB3 gene silencing decreases glycolysis, induces cell-cycle delay and inhibits anchorage-independent growth in HeLa cells

The high rate of glycolysis despite the presence of oxygen in tumor cells (Warburg effect) suggests an important role for this process in cell division. The glycolytic rate is dependent on the cellular concentration of fructose 2,6-bisphosphate (Fru-2,6-P 2), which, in turn, is controlled by the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2). The ubiquitous PFK-2 isoenzyme (uPFK-2, alternatively named UBI2K5 or ACG) coded by the pfkfb3 gene is induced by different stimuli (serum, progesterone, insulin, hypoxia, etc.) and has the highest kinase/phosphatase activity ratio amongst all PFK-2 isoenzymes discovered to date, which is consistent with its role as a powerful activator of glycolysis. uPFK-2 is expressed in brain, placenta, transformed cells and proliferating cells. In the present work, we analyze the impact of small interfering RNA (siRNA)-induced silencing of uPFK-2 on the inhibition of cell proliferation. HeLa cells treated with uPFK-2 siRNA showed a decrease in uPFK-2 RNA levels measured at 24 h. uPFK-2 protein levels were severely depleted at 48–72 h when compared with cells treated with an unrelated siRNA, correlating with decreased glycolytic activity, Fru-2,6-P 2, lactate and ATP concentrations. These metabolic changes led to reduced viability, cell-cycle delay and an increase in the population of apoptotic cells. Moreover, uPFK-2 suppression inhibited anchorage-independent growth. The results obtained highlight the importance of uPFK-2 on the regulation of glycolysis, on cell viability and proliferation and also on anchorage-independent growth. These data underscore the potential for uPFK-2 as an effective tumor therapeutic target.

DNA Damage during Reoxygenation Elicits a Chk2-Dependent Checkpoint Response

Due to the abnormal vasculature of solid tumors, tumor cell oxygenation can change rapidly with the opening and closing of blood vessels, leading to the activation of both hypoxic response pathways and oxidative stress pathways upon reoxygenation. Here, we report that ataxia telangiectasia mutated-dependent phosphorylation and activation of Chk2 occur in the absence of DNA damage during hypoxia and are maintained during reoxygenation in response to DNA damage. Our studies involving oxidative damage show that Chk2 is required for G2 arrest. Following exposure to both hypoxia and reoxygenation, Chk2-/- cells exhibit an attenuated G2 arrest, increased apoptosis, reduced clonogenic survival, and deficient phosphorylation of downstream targets. These studies indicate that the combination of hypoxia and reoxygenation results in a G2 checkpoint response that is dependent on the tumor suppressor Chk2 and that this checkpoint response is essential for tumor cell adaptation to changes that result from the cycling nature of hypoxia and reoxygenation found in solid tumors.