Lactate dehydrogenase 5 (LDH5) relates to up-regulated hypoxia inducible factor pathway and metastasis in colorectal cancer

Upregulation of glycolytic enzymes in proteins secreted from human colon cancer cells with 5-fluorouracil resistance

5-Fluorouracil (5-FU) is the most commonly used chemotherapeutic agent for colorectal cancer (CRC). However, resistance to this drug is a major obstacle in CRC chemotherapy. Accurate prediction of response to 5-FU would avoid unnecessary chemotherapy and allow the selection of other effective drugs. To identify a candidate predictor of 5-FU resistance, we isolated secreted proteins that were up- or downregulated in a 5-FU-resistant cancer cell line, compared with the parent cell line (SNU-C4), using a stable isotope-coded labeling protocol. For validating the clinical applicability of this method, levels of the identified proteins were determined in the sera of 46 patients treated with 5-FU. In total, 238 proteins with molecular weights ranging from 50 to 75 kDa were identified. Among these, 45 and 35 secreted proteins were up- and downregulated in the 5-FU-resistant cell line, respectively. We observed significant upregulation of glycolytic enzymes, including glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase M2 (PK-M2), transketolase, and NADP(+)-dependent malic enzyme 1. In particular, the level of PK-M2, a key enzyme in the glycolytic pathway, showed an increasing tendency in both sera and tissues from CRC patients displaying no response to 5-FU-based chemotherapy (progressive and stable disease cases), compared with that in complete or partial responders to 5-FU-based chemotherapy; however, it did not reach the statistical significance. In conclusion, increasing pattern of PK-M2 observed with 5-FU resistance induced in vitro and in sera and tissues from CRC patients displaying poor response to 5-FU-based chemotherapy suggest the relevance of dysregulated glycolysis and 5-FU-resistant CRC.

Tumor cell energy metabolism and its common features with yeast metabolism

During the last decades a considerable amount of research has been focused on cancer. A number of genetic and signaling defects have been identified. This has allowed the design and screening of a number of anti-tumor drugs for therapeutic use. One of the main challenges of anti-cancer therapy is to specifically target these drugs to malignant cells. Recently, tumor cell metabolism has been considered as a possible target for cancer therapy. It is widely accepted that tumors display an enhanced glycolytic activity and oxidative phosphorylation down-regulation (Warburg effect). Therefore, it seems reasonable that disruption of glycolysis might be a promising candidate for specific anti-cancer therapy. Nonetheless, the concept of aerobic glycolysis as the paradigm of tumor cell metabolism has been challenged, as some tumor cells use oxidative phosphorylation. Mitochondria are of special interest in cancer cell energy metabolism, as their physiology is linked to the Warburg effect. Besides, their central role in apoptosis makes these organelles a promising "dual hit target" for selectively eliminate tumor cells. Thus, it is desirable to have an easy-to-use and reliable model in order to do the screening for energy metabolism-inhibiting drugs to be used in cancer therapy. From a metabolic point of view, the fermenting yeast Saccharomyces cerevisiae and tumor cells share several features. In this paper we will review these common metabolic properties and we will discuss the possibility of using S. cerevisiae as an early screening test in the research for novel anti-tumor compounds used for the inhibition of tumor cell metabolism.

Fumarate hydratase deficiency in renal cancer induces glycolytic addiction and hypoxia-inducible transcription factor 1alpha stabilization by glucose-dependent generation of reactive oxygen species

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to biallelic inactivation of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH). Individuals with HLRCC are at risk to develop cutaneous and uterine leiomyomas and an aggressive form of kidney cancer. Pseudohypoxic drive-the aberrant activation of cellular hypoxia response pathways despite normal oxygen tension-is considered to be a likely mechanism underlying the etiology of this tumor. Pseudohypoxia requires the oxygen-independent stabilization of the alpha subunit of the hypoxia-inducible transcription factor (HIF-1alpha). Under normoxic conditions, proline hydroxylation of HIF-1alpha permits VHL recognition and subsequent targeting for proteasomal degradation. Here, we demonstrate that inactivating mutations of FH in an HLRCC-derived cell line result in glucose-mediated generation of cellular reactive oxygen species (ROS) and ROS-dependent HIF-1alpha stabilization. Additionally, we demonstrate that stable knockdown of FH in immortalized renal epithelial cells results in ROS-dependent HIF-1alpha stabilization. These data reveal that the obligate glycolytic switch present in HLRCC is critical to HIF stabilization via ROS generation.

Immunotherapeutic strategies in kidney cancer--when TKIs are not enough

FDA approval of the multitargeted, antiangiogenic tyrosine kinase inhibitors (TKIs) sunitinib and sorafenib, and the serine and threonine mammalian target of rapamycin inhibitor, temsirolimus, has revolutionized the management of metastatic clear-cell renal-cell carcinoma (CC-RCC). The inability of these targeted therapies to provide durable complete responses, however, is a serious limiting factor to their clinical usefulness. Although immunotherapeutic approaches in advanced disease are increasingly regarded as a historical treatment paradigm, we propose that a fundamental understanding of immunobiology in CC-RCC can improve the selection of patients for high-dose intravenous interleukin 2 and facilitate the development of novel immunotherapeutic strategies. In our opinion, immunotherapeutic strategies have an important place in the management of advanced CC-RCC in the era of biological targeted therapy.

Transgelin as a suppressor is associated with poor prognosis in colorectal carcinoma patients

We performed comparative proteomic analysis of colorectal cancer to investigate potential target proteins correlated with carcinogenesis and prognosis. Among them, transgelin, a 22 kDa protein also called SM22, was identified as a novel tumor suppressor protein, but little is known about this protein in tumors so far. A remarkable reduced expression of transgelin was found in colorectal cancer samples compared with normal colorectal mucosa. The effect of 5-aza-2'-deoxycytidine as a demethylation agent would obviously restore the original expression level of transgelin, implicating DNA hypermethylation of transgelin is important in the regulation of transgelin transcription in colorectal cancer. As a control, the investigation at cell line level confirms that transgelin protein comes from epithelium but not mesenchymal cells. Further, immunohistochemical staining for transgelin was performed on paraffin sections of 62 and 126 cases of normal colorectal mucosa and colorectal cancer specimens, respectively. As compared to normal colorectal tissue, we observed a significantly lower transgelin expression in colorectal cancer samples (P<0.001). Survival analysis demonstrated that patients without transgelin expression had shorter overall survival, whereas patients with transgelin expression had better survival (P=0.006). Multivariate analysis showed that negative transgelin expression was an independent prognostic indicator for patient's survival. Our results suggest that transgelin as a suppressor may serve as important biomarker of malignancy. Loss of transgelin involves gene promoter hypermethylation and is closely associated with poor overall survival in colorectal cancer patients.

The bioenergetics of cancer: is glycolysis the main ATP supplier in all tumor cells?

The molecular mechanisms by which tumor cells achieve an enhanced glycolytic flux and, presumably, a decreased oxidative phosphorylation are analyzed. As the O(2) concentration in hypoxic regions of tumors seems not limiting for oxidative phosphorylation, the role of this mitochondrial pathway in the ATP supply is re-evaluated. Drugs that inhibit glycoysis and oxidative phosphorylation are analyzed for their specificity toward tumor cells and effect on proliferation. The energy metabolism mechanisms involved in the use of positron emission tomography are revised and updated. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

Colon cancer cells maintain low levels of pyruvate to avoid cell death caused by inhibition of HDAC1/HDAC3

Human colon cancer cells and primary colon cancer silence the gene coding for LDH (lactate dehydrogenase)-B and up-regulate the gene coding for LDH-A, resulting in effective conversion of pyruvate into lactate. This is associated with markedly reduced levels of pyruvate in cancer cells compared with non-malignant cells. The silencing of LDH-B in cancer cells occurs via DNA methylation, with involvement of the DNMTs (DNA methyltransferases) DNMT1 and DNMT3b. Colon cancer is also associated with the expression of pyruvate kinase M2, a splice variant with low catalytic activity. We have shown recently that pyruvate is an inhibitor of HDACs (histone deacetylases). Here we show that pyruvate is a specific inhibitor of HDAC1 and HDAC3. Lactate has no effect on any of the HDACs examined. Colon cancer cells exhibit increased HDAC activity compared with non-malignant cells. HDAC1 and HDAC3 are up-regulated in colon cancer cells and in primary colon cancer, and siRNA (small interfering RNA)-mediated silencing of HDAC1 and HDAC3 in colon cancer cells induces apoptosis. Colon cancer cells silence SLC5A8, the gene coding for a Na(+)-coupled pyruvate transporter. Heterologous expression of SLC5A8 in the human colon cancer cell line SW480 leads to inhibition of HDAC activity when cultured in the presence of pyruvate. This process is associated with an increase in intracellular levels of pyruvate, increase in the acetylation status of histone H4, and enhanced cell death. These studies show that cancer cells effectively maintain low levels of pyruvate to prevent inhibition of HDAC1/HDAC3 and thereby to evade cell death.

Lactate promotes glioma migration by TGF-beta2-dependent regulation of matrix metalloproteinase-2

Lactate dehydrogenase type A (LDH-A) is a key metabolic enzyme catalyzing pyruvate into lactate and is excessively expressed by tumor cells. Transforming growth factor-beta2 (TGF-beta2) is a key regulator of invasion in high-grade gliomas, partially by inducing a mesenchymal phenotype and by remodeling the extracellular matrix. In this study, we tested the hypothesis that lactate metabolism regulates TGF-beta2-mediated migration of glioma cells. Small interfering RNA directed against LDH-A (siLDH-A) suppresses, and lactate induces, TGF-beta2 expression, suggesting that lactate metabolism is strongly associated with TGF-beta2 in glioma cells. Here we demonstrate that TGF-beta2 enhances expression, secretion, and activation of matrix metalloproteinase-2 (MMP-2) and induces the cell surface expression of integrin alpha(v)beta(3) receptors. In spheroid and Boyden chamber migration assays, inhibition of MMP-2 activity using a specific MMP-2 inhibitor and blocking of integrin alpha(v)beta(3) abrogated glioma cell migration stimulated by TGF-beta2. Furthermore, siLDH-A inhibited MMP2 activity, leading to inhibition of glioma migration. Taken together, we define an LDH-A-induced and TGF-beta2-coordinated regulatory cascade of transcriptional regulation of MMP-2 and integrin alpha(v)beta(3). This novel interaction between lactate metabolism and TGF-beta2 might constitute a crucial mechanism for glioma migration.

Nutrient transporters in cancer: relevance to Warburg hypothesis and beyond

Tumor cells have an increased demand for nutrients; this demand is met by increased availability of nutrients through vasculogenesis and by enhanced cellular entry of nutrients through upregulation of specific transporters. This review focuses on three groups of nutrient transporters relevant to cancer: glucose transporters, lactate transporters, and amino acid transporters. Tumor cells enhance glucose uptake via induction of GLUT1 and SGLT1, and coordinate the increased entry of glucose with increased glycolysis. Since enhanced glycolysis in cancer is associated with lactate production, tumor cells must find a way to eliminate lactic acid to prevent cellular acidification. This is achieved by the upregulation of MCT4, a H+-coupled lactate transporter. In addition, the Na+-coupled lactate transporter SMCT1 is silenced in cancer. SMCT1 also transports butyrate and pyruvate, which are inhibitors of histone deacetylases. The silencing of SMCT1 occurs in cancers of a variety of tissues. Re-expression of SMCT1 in cancer cell lines leads to growth arrest and apoptosis in the presence of butyrate or pyruvate, suggesting that the transporter may function as a tumor suppressor. Tumor cells meet their amino acid demands by inducing xCT/4F2hc, LAT1/4F2hc, ASCT2, and ATB0,+. xCT/4F2hc is related primarily to glutathione status, protection against oxidative stress, and cell cycle progression, whereas the other three transporters are related to amino acid nutrition. Pharmacologic blockade of LAT1/4F2hc, xCT/4F2hc, or ATB0,+ leads to inhibition of cancer cell growth. Since tumor cells selectively regulate these nutrient transporters to support their rapid growth, these transporters have potential as drug targets for cancer therapy.

The impact of hypoxia on the activity of lactate dehydrogenase in two different pre-clinical tumour models

AIM

To investigate the direct relationship between tumour hypoxia and lactate dehydrogenase (Ldh) levels in serum and tumour in two different pre-clinical murine models.

MATERIALS AND METHODS

Experiments were performed in CDF1 or C3H/ Km mice implanted with a C3H mammary carcinoma and SCCVII squamous cell carcinoma, respectively. Low oxygen breathing for 1-72 h was used to increase tumour hypoxia. Ldh activity was measured in the serum and tumour cytosole with a colorimetric method. Tumour Ldha mRNA levels were assessed with RT-PCR. RESULTS; The serum Ldh in non-tumour bearing CDF1 mice and C3H/km mice was 10.592 U/ml and 1292 U/ml, respectively. For C3H mammary carcinoma bearing mice, a positive correlation between tumour volume and tumour and serum Ldh was found. Tumour Ldh in SCCVII carcinomas also increased with increasing tumour volume, but no volume dependence of serum Ldh was found. Low oxygen breathing caused a 2-3 fold increase in tumour Ldha mRNA in both tumour models. In C3H mammary carcinoma bearing mice, serum and tumour Ldh significantly increased after 48 and 72 hours of hypoxia, respectively. Low oxygen breathing did not change serum and tumour Ldh in SCCVII carcinoma bearing mice. Reoxygenation for 4 or 24 hours had no additional effect on Ldh activity in any of the models.

DISCUSSION

Serum Ldh activity can be a marker for tumour burden in certain types of cancer. The relationship between serum and tumour Ldh and tumour hypoxia has not been confirmed. However, Ldha mRNA may be a potential new marker of tumour hypoxia and should be further investigated.

Evaluation of lactate and alanine as metabolic biomarkers of prostate cancer using 1H HR-MAS spectroscopy of biopsy tissues

The goal of this study was to investigate the use of lactate and alanine as metabolic biomarkers of prostate cancer using (1)H high-resolution magic angle spinning (HR-MAS) spectroscopy of snap-frozen transrectal ultrasound (TRUS)-guided prostate biopsy tissues. A long-echo-time rotor-synchronized Carr-Purcell-Meiboom-Gill (CPMG) sequence including an electronic reference to access in vivo concentrations (ERETIC) standard was used to determine the concentrations of lactate and alanine in 82 benign and 16 malignant biopsies (mean 26.5% +/- 17.2% of core). Low concentrations of lactate (0.61 +/- 0.28 mmol/kg) and alanine (0.14 +/- 0.06 mmol/kg) were observed in benign prostate biopsies, and there was no significant difference between benign predominantly glandular (N = 54) and stromal (N = 28) biopsies between patients with (N = 38) and without (N = 44) a positive clinical biopsy. In biopsies containing prostate cancer there was a highly significant (P < 0.0001) increase in lactate (1.59 +/- 0.61 mmol/kg) and alanine (0.26 +/- 0.07 mmol/kg), and minimal overlap with lactate concentrations in benign biopsies. This study demonstrates for the first time very low concentrations of lactate and alanine in benign prostate biopsy tissues. The significant increase in the concentration of both lactate and alanine in biopsy tissue containing as little as 5% cancer could be exploited in hyperpolarized (13)C spectroscopic imaging (SI) studies of prostate cancer patients.

PDK-1 regulates lactate production in hypoxia and is associated with poor prognosis in head and neck squamous cancer

Here we describe the expression and function of a HIF-1-regulated protein pyruvate dehydrogenase kinase-1 (PDK-1) in head and neck squamous cancer (HNSCC). Using RNAi to downregulate hypoxia-inducible PDK-1, we found that lactate and pyruvate excretion after 16-48 h of hypoxia was suppressed to normoxic levels. This indicates that PDK-1 plays an important role in maintaining glycolysis. Knockdown had no effect on proliferation or survival under hypoxia. The immunohistochemical expression of PDK-1 was assessed in 140 cases of HNSCC. PDK-1 expression was not expressed in normal tissues but was upregulated in HNSCC and found to be predominantly cytoplasmic with occasional strong focal nuclear expression. It was strongly related to poor outcome (P=0.005 split by median). These results indicate that HIF regulation of PDK-1 has a key role in maintaining lactate production in human cancer and that the investigation of PDK-1 inhibitors should be investigated for antitumour effects.

Involvement of hypoxia-inducing factor-1alpha-dependent plasminogen activator inhibitor-1 up-regulation in Cyr61/CCN1-induced gastric cancer cell invasion

Cysteine-rich 61 (Cyr61/CCN1), one of the members of CCN family, has been implicated in the progression of human malignancies. Previously, our studies have demonstrated that Cyr61/CCN1 has a role in promoting gastric cancer cell invasion, but the mechanism is not clear yet. Here, we found that hypoxia-inducing factor-1alpha (HIF-1alpha) protein, but not mRNA, expression was significantly elevated in gastric cancer cells overexpressing Cyr61. Supportively, a profound reduction of endogenous HIF-1alpha protein was noted in one highly invasive cell line, TSGH, when transfected with antisense Cyr61. By comparison, the induction kinetics of HIF-1alpha protein by recombinant Cyr61 (rCyr61) was distinct from that of insulin-like growth factor-1 and CoCl(2) treatment, both well known for induction of HIF-1alpha. Using cycloheximide and MG132, we demonstrated that the Cyr61-mediated HIF-1alpha up-regulation was through de novo protein synthesis, rather than increased protein stability. rCyr61 could also activate the PI3K/AKT/mTOR and ERK1/2 signaling pathways, both of which were essential for HIF-1alpha protein accumulation. Blockage of HIF-1alpha activity in Cyr61-expressing cells by transfecting with a dominant negative (DN)-HIF-1alpha strongly inhibited their invasion ability, suggesting that elevation in HIF-1alpha protein is vital for Cyr61-mediated gastric cancer cell invasion. In addition, several HIF-1alpha-regulated invasiveness genes were examined, and we found that only plasminogen activator inhibitor-1 (PAI-1) showed a significant increase in mRNA and protein levels in cells overexpressing Cyr61. Treatment with PAI-1-specific antisense oligonucleotides or function-neutralizing antibodies abolished the invasion ability of the Cyr61-overexpressing cells. Transfection with dominant negative-HIF-1alpha to block HIF-1alpha activity also effectively reduced the elevated PAI-1 level. In conclusion, our data provide a detailed mechanism by which Cyr61 promoted gastric cancer cell invasive ability via an HIF-1alpha-dependent up-regulation of PAI-1.

Serum lactate dehydrogenase levels and glycolysis significantly correlate with tumor VEGFA and VEGFR expression in metastatic CRC patients

OBJECTIVES

In an attempt to elucidate the relationship between biomarkers of tumor hypoxia, glycolysis and angiogenesis, we tested the hypothesis that intratumoral gene expression of the hypoxia response (hypoxia inducible factor [HIF1 alpha and 2 alpha]), glycolysis (lactate dehydrogenase A [LDHA]), glucose metabolism (glucose transporter-1 [Glut-1]) and genes involved in angiogenesis (i.e., VEGFA, VEGFR1-3, and neuropilin [NRP]1) are upregulated in metastatic colorectal cancer (mCRC) patients with high serum lactate dehydrogenase (LDH).

PATIENTS AND METHODS

78 formalin-fixed, paraffin-embedded (FFPE) tumor samples were collected from 36 patients with mCRC. Tumor gene expression was correlated with serum LDH levels from the same group of patients. FFPE tissues were dissected using laser-captured microdissection and analyzed for gene expression using a quantitative real-time RT-PCR method.

RESULTS

Intratumoral gene expression of VEGFA and VEGFR1 showed a statistically significant correlation with serum LDH levels (p = 0.006, r = 0.45 and p = 0.004, r = 0.50, respectively). Intratumoral expression of LDHA gene showed a significant correlation with Glut-1, VEGF, HIF1 alpha, HIF2 alpha and VEGFR1 (p = 0.007, r = 0.44; p < 0.001, r = 0.57; p = 0.013, r = 0.41; p = 0.044, r = 0.34; p = 0.026, r = 0.40). Serum LDH levels also correlated with microvessel density analyzed by immunohistochemical analysis.

CONCLUSION

The results demonstrated a significant correlation between the intratumoral gene expression of LDHA, HIF1 alpha, HIF2 alpha, Glut-1, NRP1, VEGFA and VEGFR1. Patients with high serum LDH have increased intratumoral gene expression of VEGFA and VEGFR1. The results also support the hypothesis that serum LDH levels may serve as a surrogate marker for activation of the HIF-related genes in the 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.

New approaches in angiogenic targeting for colorectal cancer

Colorectal carcinoma (CRC) is one of the leading causes of cancer death worldwide. In the last decade, the addition of irinotecan and oxaliplatin to standard fluorouracil-based chemotherapy regimens have set the new benchmark of survival for patients with metastatic CRC at approximately 20 mo. Despite these advances in the management of CRC, there is a strong medical need for more effective and well-tolerated therapies. The dependence of tumor growth and metastasis on blood vessels makes angiogenesis a rational target for therapy. One of the major pathways involved in this process is the vascular endothelial growth factor (VEGF) and its receptors (VEGFR). In 2004, the first agent targeting angiogenesis, bevacizumab (BV), was approved as an adjunct to first-line cytotoxic treatment of metastatic CRC. The role of BV as part of adjuvant treatment and in combination with other targeted therapies is the subject of ongoing trials. However, BV is associated with an increase in the risk of arterial thromboembolic events, hypertension and gastrointestinal perforations and its use must be cautious. Novel VEGFR TK inhibitors with different ranges of nanomolar potencies, selectivities, and pharmacokinetic properties are entering phase III trials for the treatment of cancer. Conversely, one of these novel agents, vatalanib, has been shown not to confer survival benefit in first and second-line treatment of advanced CRC. The basis of these findings is being extensively evaluated. Ongoing and new well-designed trials will define the optimal clinical application of the actual antiangiogenic agents, and, on the other hand, intensive efforts in basic research will identify new agents with different antiangiogenic approaches for the treatment of CRC. In this review we discuss and highlight current and future approaches in angiogenic targeting for CRC.

Patient characteristics and stratification in medical treatment studies for metastatic colorectal cancer: A proposal for standardization of patient characteristic reporting and stratification

BACKGROUND

Prognostic factors have the potential to determine the survival of patients to a greater extent than current antineoplastic agents. Despite this knowledge, there is no consensus on, first, what patient characteristics to report and, second, what stratification factors to use in metastatic colorectal cancer trials.

PATIENTS AND METHODS

Seven leading oncology and medical journals were reviewed for phase II and III publications reporting on medical treatment of metastatic colorectal cancer patients during 2001-2005. One hundred and forty-three studies with 21 214 patients were identified. The reporting of patient characteristics and use of stratification was noted.

RESULTS

Age, gender, performance status, metastases location, sites and adjuvant chemotherapy were often reported (99-63%). Laboratory values as alkaline phosphatase, lactate dehydrogenase and white blood cell count, repeatedly found to be of prognostic relevance, were rarely reported (5-9%). Stratification was used in all phase III trials; however, only study centre was used with any consistency.

CONCLUSION

There is considerable inconsistency in the reporting of patient characteristics and use of stratification factors in metastatic colorectal cancer trials. We propose a standardization of patient characteristics reporting and stratification factors. A common set of characteristics and strata will aid in trial reporting, interpretation and future meta-analyses.

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.

Design of clinical trials of radiation combined with antiangiogenic therapy

Clinical trials showing longer survival when chemotherapy is combined with antiangiogenic agents (AAs) have led to growing interest in designing combined modality protocols that exploit abnormalities in tumor vasculature. Approved agents include bevacizumab, a recombinant monoclonal antibody that binds to vascular endothelial growth factor, and two small molecule multitargeted tyrosine kinase inhibitors of angiogenesis (SU11248 and BAY-43-9006) that have been approved for therapy of renal cancer. Targeting tumor vasculature has a strong biological rationale in radiation therapy, and preclinical studies consistently show an increase in radiosensitization with combined treatment. Preclinical studies indicate that excessive damage to tumor vasculature can result in radioresistance in some situations, and early clinical data suggest that treatment sequencing may be important when combining AAs with radiation. Radiation itself appears to antagonize any hypoxia that can be induced by long-term administration of AAs. The optimal biological doses of AAs with radiotherapy are unknown, and surrogate markers of efficacy remain to be validated. Early clinical trials should therefore include studies designed to identify mechanisms of interaction and increases in tumor hypoxia. This review highlights preclinical and early clinical data that are relevant for clinical trial design. Optimal radiation planning and delivery is required to minimize the volume of irradiated normal organs and to establish safe dose-volume parameters for phase II-III clinical trials.

Hypoxia signalling controls metabolic demand

It has been known for quite some time that cancer cells undergo far-reaching modifications in their metabolism, yet a full understanding of these changes and how they come about remains elusive. Even under conditions of plentiful oxygen, cancer cells choose to switch glucose metabolism from respiration to lactic acid formation. The mystery behind the molecular mechanisms of this phenomenon, known as the Warburg effect, is now being unravelled. The reduced respiration rate and increased glucose uptake associated with lactic acid production, and acidosis of the micro-environment, are primarily due to activation of the alpha/beta hypoxia-inducible transcription factor. This distinctive metabolic nature of cancer cells is already being exploited as a diagnostic tool but is yet to be harnessed as a therapeutic intervention.

Hypoxia-Induced Lactate Dehydrogenase Expression and Tumor Angiogenesis

The aim of this review is to discuss the basic science of tumor angiogenesis and recent clinical trial results with angiogenic inhibitors. Colorectal cancer (CRC) continues to be a major cause of all new cancer cases and cancer-related deaths in North America. Although advances in chemotherapy have increased overall survival for patients suffering from metastatic CRC, the survival rate continues to be poor. In order to develop new and more effective therapies for advanced CRC, it is important to understand the basic biologic processes that govern tumor growth. This review will focus on pathways involved in stimulating tumor growth and angiogenesis. Recent excitement has been generated by the clinical efficacy of targeted antiangiogenic therapy against growth factors important in angiogenesis and tumor proliferation. By presenting the basic biology of tumor growth and angiogenesis, we will attempt to explain the therapeutic effects of different angiogenesis inhibitors and speculate how combination treatments with these agents might be beneficial.

Structural and mechanistic studies on the inhibition of the hypoxia-inducible transcription factor hydroxylases by tricarboxylic acid cycle intermediates

In humans both the levels and activity of the alpha-subunit of the hypoxia-inducible transcription factor (HIF-alpha) are regulated by its post-translation hydroxylation as catalyzed by iron- and 2-oxoglutarate (2OG)-dependent prolyl and asparaginyl hydroxylases (PHD1-3 and factor-inhibiting HIF (FIH), respectively). One consequence of hypoxia is the accumulation of tricarboxylic acid cycle intermediates (TCAIs). In vitro assays were used to assess non-2OG TCAIs as inhibitors of purified PHD2 and FIH. Under the assay conditions, no significant FIH inhibition was observed by the TCAIs or pyruvate, but fumarate, succinate, and isocitrate inhibited PHD2. Mass spectrometric analyses under nondenaturing conditions were used to investigate the binding of TCAIs to PHD2 and supported the solution studies. X-ray crystal structures of FIH in complex with Fe(II) and fumarate or succinate revealed similar binding modes for each in the 2OG co-substrate binding site. The in vitro results suggest that the cellular inhibition of PHD2, but probably not FIH, by fumarate and succinate may play a role in the Warburg effect providing that appropriate relative concentrations of the components are achieved under physiological conditions.

SLC5A8 triggers tumor cell apoptosis through pyruvate-dependent inhibition of histone deacetylases

Tumor cells up-regulate glycolysis but convert pyruvate into lactate instead of oxidizing it. Here, we show that pyruvate, but not lactate, is an inhibitor of histone deacetylases (HDAC) and an inducer of apoptosis in tumor cells and that SLC5A8, a Na(+)/monocarboxylate cotransporter, is obligatory for this process. We found that SLC5A8 is expressed in nontransformed breast epithelial cell lines but silenced by DNA methylation in tumor cell lines. The down-regulation of the gene is also evident in primary breast tumors. When MCF7 breast tumor cells are transfected with SLC5A8 cDNA, the cells undergo pyruvate-dependent apoptosis. Butyrate and propionate also induce apoptosis in SLC5A8-expressing cells, whereas lactate does not. The differential ability of these monocarboxylates to cause apoptosis in SLC5A8-expressing MCF7 cells correlates with their ability to inhibit HDACs. Apoptosis induced by SLC5A8/pyruvate in MCF7 cells is associated with up-regulation of p53, Bax, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), TRAIL receptor (TRAILR) 1, and TRAILR2 and down-regulation of Bcl2 and survivin. Lactate dehydrogenase isozymes are differentially expressed in nontransformed cells and tumor cells such that the latter convert pyruvate into lactate. Silencing of SLC5A8 coupled with conversion of pyruvate into lactate in tumor cells correlates with increased HDAC activity in these cells compared with nontransformed cells. Our studies thus identify pyruvate as a HDAC inhibitor and indicate that the Na(+)-coupled pyruvate transport underlies the tumor-suppressive role of SLC5A8. We propose that tumor cells silence SLC5A8 and convert pyruvate into lactate as complementary mechanisms to avoid pyruvate-induced cell death.

Lactate dehydrogenase 5 (LDH-5) expression in endometrial cancer relates to the activated VEGF/VEGFR2(KDR) pathway and prognosis

PURPOSE

Lactate dehydrogenase (LDH-5) is a major lactate dehydrogenase isoenzyme catalyzing the transformation of pyruvate to lactate for anaerobic acquisition energy. In this study, the expression of LDH-5 was assessed in the normal and malignant endometrium. Its role in prognosis and tumor angiogenesis and hypoxia was also examined.

EXPERIMENTAL DESIGN

Tissue specimens from 68 patients with clinical stage I endometrial adenocarcinoma of the endometrioid cell type and 20 samples from normally cycling endometrium were investigated immunohistochemically for the expression of LDH-5. The vascular density and the expression of angiogenesis/hypoxia-related proteins (VEGF, HIF1alpha, HIF2alpha, phosphorylated VEGFR2/KDR, VEGF/KDR complex) were also assessed.

RESULTS

Unlike other normal epithelia, the glandular endometrial cells consistently expressed LDH-5 suggesting a role of this enzyme in the normal menstrual cycle. Endometrial adenocarcinomas displayed LDH-5 expression in 31/68 (45.5%) cases with those having a high LDH-5 expression being connected with a low lymphocytic response; this may suggest an important role of LDH-5 and, presumably, lactate release in tumor escape from host immuno-surveillance. More importantly, LDH-5 was significantly associated with the expression of phosphorylated VEGFR2/KDR receptors in cancer cells and tumor-associated vasculature. LDH-5 was one of the most powerful and independent prognostic variables.

CONCLUSIONS

LDH-5 expression is an independent prognostic marker in endometrial cancer, linked with impaired host immune response and activation of VEGFR2/KDR receptors in both cancer cells and tumor-associated vasculature. Adjuvant radio-chemotherapy may, therefore, be useful in these cases, while the administration of VEGF- tyrosine kinase receptor inhibitors emerges as a therapeutic option.

Lactate dehydrogenase, not vascular endothelial growth factor or basic fibroblast growth factor, positively correlates to bone marrow vascularity in acute myeloid leukemia

BACKGROUND

Angiogenesis has been extensively studied in acute myeloid leukemia (AML). Lactate dehydrogenase (LDH), a common biochemical marker for tumor burden and anaerobic glycolysis, is a poor prognostic factor for AML. Regulated by hypoxia-induced factor, both vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are responsive to cancer-related angiogenesis. To study the roles of serum LDH, VEGF and bFGF in AML angiogenesis, we investigated bone marrow vascularity in untreated AML patients, and analyzed its relationship to serum LDH, VEGF and bFGF levels.

METHODS

Eighteen (11 males, 7 females; mean age, 57.7 years) de novo, untreated AML patients were enrolled. Bone marrow vascularity was evaluated by staining bone marrow core biopsy tissue with endothelial cell marker CD31 or CD34. Serum LDH was determined with the Wroblewski-La Due method. Serum VEGF and bFGF were determined with enzyme-linked immunoassay. The relationship of LDH, VEGF and bFGF level to bone marrow vessel numbers was examined by linear regression.

RESULTS

Log LDH significantly correlated to AML bone marrow vascularity (r = 0.61; p = 0.007). VEGF and bFGF concentrations did not correlate with AML angiogenesis.

CONCLUSION

These results suggest that serum LDH, but not VEGF and bFGF concentrations, can be used as a simple parameter for predicting vessel formation in AML bone marrow.

Oxygen and glucose consumption in gastrointestinal adenocarcinomas: correlation with markers of hypoxia, acidity and anaerobic glycolysis

This study gives an insight into tumor metabolic activity by investigating oxygen and glucose content, together with their metabolic products carbon dioxide and acids-pH, in the arterial and venous blood of a tumor. Nineteen patients with gastrointestinal adenocarcinomas undergoing surgery were studied. Biochemical analysis showed that in a large subgroup of tumors, oxygen consumption was reduced while that of glucose was increased in malignant, as compared to normal tissues; these features were more evident in tumors overexpressing lactate dehydrogenase (LDH-5) and hypoxia inducible factors (HIF1alpha/2alpha). An increase in carbon dioxide production in the tumor environment was linked with overexpression of carbonic anhydrase 9 (CA9). The simultaneous overexpression of CA9 and LDH-5 was related to very low pH levels in the veins draining the tumor, suggesting an intense acidification of the tumor microenvironment in such cases. These in vivo data confirm the importance of HIFs and their downstream regulated genes in tumor metabolism, particularly in glycolysis and carbon dioxide buffering.

Kinetic Parameters and Lactate Dehydrogenase Isozyme Activities Support Possible Lactate Utilization by Neurons

Lactate is potentially a major energy source in brain, particularly following hypoxia/ischemia; however, the regulation of brain lactate metabolism is not well understood. Lactate dehydrogenase (LDH) isozymes in cytosol from primary cultures of neurons and astrocytes, and freshly isolated synaptic terminals (synaptosomes) from adult rat brain were separated by electrophoresis, visualized with an activity-based stain, and quantified. The activity and kinetics of LDH were determined in the same preparations. In synaptosomes, the forward reaction (pyruvate + NADH + H(+ )--> lactate + NAD(+)), which had a V (max) of 1,163 micromol/min/mg protein was 62% of the rate in astrocyte cytoplasm. In contrast, the reverse reaction (lactate + NAD(+ )--> pyruvate + NADH + H(+)), which had a V (max) of 268 micromol/min/mg protein was 237% of the rate in astrocytes. Although the relative distribution was different, all five isozymes of LDH were present in synaptosomes and primary cultures of cortical neurons and astrocytes from rat brain. LDH1 was 14.1% of the isozyme in synaptic terminals, but only 2.6% and 2.4% in neurons and astrocytes, respectively. LDH5 was considerably lower in synaptic terminals than in neurons and astrocytes, representing 20.4%, 37.3% and 34.8% of the isozyme in these preparations, respectively. The distribution of LDH isozymes in primary cultures of cortical neurons does not directly reflect the kinetics of LDH and the capacity for lactate oxidation. However, the kinetics of LDH in brain are consistent with the possible release of lactate by astrocytes and oxidative use of lactate for energy in synaptic terminals.

Multiparameter metabolic analysis reveals a close link between attenuated mitochondrial bioenergetic function and enhanced glycolysis dependency in human tumor cells

Increased conversion of glucose to lactic acid associated with decreased mitochondrial respiration is a unique feature of tumors first described by Otto Warburg in the 1920s. Recent evidence suggests that the Warburg effect is caused by oncogenes and is an underlying mechanism of malignant transformation. Using a novel approach to measure cellular metabolic rates in vitro, the bioenergetic basis of this increased glycolysis and reduced mitochondrial respiration was investigated in two human cancer cell lines, H460 and A549. The bioenergetic phenotype was analyzed by measuring cellular respiration, glycolysis rate, and ATP turnover of the cells in response to various pharmacological modulators. H460 and A549 cells displayed a dependency on glycolysis and an ability to significantly upregulate this pathway when their respiration was inhibited. The converse, however, was not true. The cell lines were attenuated in oxidative phosphorylation (OXPHOS) capacity and were unable to sufficiently upregulate mitochondrial OXPHOS when glycolysis was disabled. This observed mitochondrial impairment was intimately linked to the increased dependency on glycolysis. Furthermore, it was demonstrated that H460 cells were more glycolytic, having a greater impairment of mitochondrial respiration, compared with A549 cells. Finally, the upregulation of glycolysis in response to mitochondrial ATP synthesis inhibition was dependent on AMP-activated protein kinase activity. In summary, our results demonstrate a bioenergetic phenotype of these two cancer cell lines characterized by increased rate of glycolysis and a linked attenuation in their OXPHOS capacity. These metabolic alterations provide a mechanistic explanation for the growth advantage and apoptotic resistance of tumor cells.

Angiogenesis in colorectal cancer: prognostic and therapeutic implications

Angiogenesis is important for tumor growth and metastasis. This account reviews the clinicopathological studies conducted in the field of angiogenesis in colorectal cancer, the methods of assessing vascular-related characteristics in tissue sections and provides a background for the usefulness of antiangiogenic policies along with chemotherapy and radiotherapy. Highly angiogenic colorectal tumors are associated with aggressive histopathological features and poor patients' survival. Similarly, factors stimulating angiogenesis, such as vascular endothelial growth factor (VEGF), thymidine phosphorylase (TP), and others, are commonly related to increased vascular density (VD) and, therefore, to an unfavorable clinical course. Anti-VEGF agents have improved prognosis in patients with metastatic colorectal cancer, when added to standard chemotherapy. It is expected that, in addition to adjuvant chemotherapy and radiotherapy, agents blocking the stimulatory effect of VEGF on endothelial cells would prove beneficial to the patient.

Lactate dehydrogenase 5 expression in operable colorectal cancer: strong association with survival and activated vascular endothelial growth factor pathway--a report of the Tumour Angiogenesis Research Group

PURPOSE

Lactate dehydrogenase 5 (LDH-5) regulates, under hypoxic conditions, the anaerobic transformation of pyruvate to lactate for energy acquisition. Several studies have shown that serum LDH may be an ominous prognostic marker in malignant tumors. The clinical significance of tissue LDH-5, however, remains largely unexplored.

PATIENTS AND METHODS

We investigated the immunohistochemical expression of LDH-5 in a series of 128 stage II/III colorectal adenocarcinomas treated with surgery alone. In addition, markers of tumor hypoxia (hypoxia-inducible factor 1 alpha [HIF1alpha]), angiogenesis (vascular endothelial growth factor [VEGF] and phosporylated kinase domain receptor [pKDR]/flk-1 receptor) and the tumor vascular density (CD31 positive standard vascular density [sVD] and pKDR positive activated vascular density [aVD]) were assessed.

RESULTS

The expression of LDH-5, together with that of HIF1alpha and pKDR, was both nuclear and cytoplasmic. Assessment, with minimal interobserver variability, was achieved using a previously described scoring system. LDH-5 was significantly associated with HIF1alpha (P = .01), aVD (P = .001) and, particularly, with pKDR expression in cancer cells (P = .0001). Tissue LDH-5 expression was linked with elevated serum LDH levels, but serum levels failed to reflect tissue expression in 71% of LDH-5 positive cases. In univariate analysis tissue LDH-5 was associated with poor survival (P = .0003, HR 15.1), whereas in multivariate analysis this isoenzyme was the strongest independent prognostic factor (P = .0009). VEGF, pKDR, aVD, sVD and vascular invasion were all significantly related to unfavorable prognosis.

CONCLUSION

The immunohistochemical assessment of tissue LDH-5 and pKDR provides important prognostic information in operable colorectal cancer. The strong association between LDH-5 and pKDR expression would justify their use as surrogate markers to screen patients for tyrosine kinase inhibitor therapy.

Elevation of serum l-lactate dehydrogenase B correlated with the clinical stage of lung cancer

To identify potential biomarkers related with lung cancer metastasis, conditional media (CM) proteins collected from a primary non-small cell lung cancer (NSCLC) cell line NCI-H226 and its brain metastatic subline H226Br were analyzed by one-dimensional electrophoresis (1-D PAGE) and matrix-assisted laser desorption/time of flight mass spectrometry (MALDI-TOF-MS). Twelve biomarkers were identified, of which l-lactate dehydrogenase B (LDHB) chain was significantly up-regulated in the CM of H226Br cell and was further validated in 105 lung cancer, 93 non-lung cancer, 41 benign lung disease, as well as 65 healthy individuals sera using enzyme-linked immunosorbent assay (ELISA). It was found that the levels of LDHB were specifically elevated in NSCLC sera compared with other groups and were progressively increased with the clinical stage. At the cutoff point 0.260 (OD value) on the receiver operating characteristic (ROC) curve, LDHB could comparatively discriminate lung cancer from benign lung disease and healthy control groups with sensitivity 81%, specificity 70% and total accuracy 76%. These findings demonstrated that secretome could open up a possibility to find, identify, and characterize novel biomarkers related with invasion and metastasis.