Defining the role of hypoxia-inducible factor 1 in cancer biology and therapeutics

Frataxin participates to the hypoxia-induced response in tumors

Defective expression of frataxin is responsible for the degenerative disease Friedreich's ataxia. Frataxin is a protein required for cell survival since complete knockout is lethal. Frataxin protects tumor cells against oxidative stress and apoptosis but also acts as a tumor suppressor. The molecular bases of this apparent paradox are missing. We therefore sought to investigate the pathways through which frataxin enhances stress resistance in tumor cells. We found that frataxin expression is upregulated in several tumor cell lines in response to hypoxic stress, a condition often associated with tumor progression. Moreover, frataxin upregulation in response to hypoxia is dependent on hypoxia-inducible factors expression and modulates the activation of the tumor-suppressor p53. Importantly, we show for the first time that frataxin is in fact increased in human tumors in vivo. These results show that frataxin participates to the hypoxia-induced stress response in tumors, thus implying that modulation of its expression could have a critical role in tumor cell survival and/or progression.

Recently identified biomarkers that promote lymph node metastasis in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous cancer that arises in the upper aerodigestive tract. Despite advances in knowledge and treatment of this disease, the five-year survival rate after diagnosis of advanced (stage 3 and 4) HNSCC remains approximately 50%. One reason for the large degree of mortality associated with late stage HNSCC is the intrinsic ability of tumor cells to undergo locoregional invasion. Lymph nodes in the cervical region are the primary sites of metastasis for HNSCC, occurring before the formation of distant metastases. The presence of lymph node metastases is strongly associated with poor patient outcome, resulting in increased consideration being given to the development and implementation of anti-invasive strategies. In this review, we focus on select proteins that have been recently identified as promoters of lymph node metastasis in HNSCC. The discussed proteins are involved in a wide range of critical cellular functions, and offer a more comprehensive understanding of the factors involved in HNSCC metastasis while additionally providing increased options for consideration in the design of future therapeutic intervention strategies.

Genome-wide identification and annotation of HIF-1α binding sites in two cell lines using massively parallel sequencing

We identified 531 and 616 putative HIF-1α target sites by ChIP-Seq in the cancerous cell line DLD-1 and the non-cancerous cell line TIG-3, respectively. We also examined the positions and expression levels of transcriptional start sites (TSSs) in these cell lines using our TSS-Seq method. We observed that 121 and 48 genes in DLD-1 and TIG-3 cells, respectively, had HIF-1α binding sites in proximal regions of the previously reported TSSs that were up-regulated at the transcriptional level. In addition, 193 and 123 of the HIF-1α target sites, respectively, were located in proximal regions of previously uncharacterized TSSs, namely, TSSs of putative alternative promoters of protein-coding genes or promoters of putative non-protein-coding transcripts. The hypoxic response of DLD-1 cells was more significant than that of TIG-3 cells with respect to both the number of target sites and the degree of induced changes in transcript expression. The Nucleosome-Seq and ChIP-Seq analyses of histone modifications revealed that the chromatin formed an open structure in regions surrounding the HIF-1α binding sites, but this event occurred prior to the actual binding of HIF-1α. Different cellular histories may be encoded by chromatin structures and determine the activation of specific genes in response to hypoxic shock.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s11568-011-9150-9) contains supplementary material, which is available to authorized users.

Impact of a low-oxygen environment on the efficacy of antimicrobials against intracellular Chlamydia trachomatis

Emergence of chronic inflammation in the urogenital tract induced by Chlamydia trachomatis infection in females is a long-standing concern. To avoid the severe sequelae of C. trachomatis infection, such as pelvic inflammatory diseases (PID), ectopic pregnancies, and tubal infertility, antibiotic strategies aim to eradicate the pathogen even in asymptomatic and uncomplicated infections. Although first-line antimicrobials have proven successful for the treatment of C. trachomatis infection, treatment failures have been observed in a notable number of cases. Due to the obligate intracellular growth of C. trachomatis, reliable antimicrobial susceptibility assays have to consider environmental conditions and host cell-specific factors. Oxygen concentrations in the female urogenital tract are physiologically low and decrease further during an inflammatory process. We compared MIC testing and time-kill curves (TKC) for doxycycline, azithromycin, rifampin, and moxifloxacin under hypoxia (2% O2) and normoxia (20% O2). While low oxygen availability only moderately decreased the antichlamydial activity of azithromycin in conventional MIC testing (0.08 μg/ml versus 0.04 μg/ml; P<0.05), TKC analyses revealed profound divergences for antibiotic efficacies between the two conditions. Thus, C. trachomatis was significantly less rapidly killed by doxycycline and azithromycin under hypoxia, whereas the efficacies of moxifloxacin and rifampin remained unaffected using concentrations at therapeutic serum levels. Chemical inhibition of multidrug resistance protein 1 (MDR-1), but not multidrug resistance-associated protein 1 (MRP-1), restored doxycycline activity against intracellular C. trachomatis under hypoxia. We suggest careful consideration of tissue-specific characteristics, including oxygen availability, when testing antimicrobial activities of antibiotics against intracellular bacteria.

Regulation of type II transmembrane serine proteinase TMPRSS6 by hypoxia-inducible factors: new link between hypoxia signaling and iron homeostasis

Hepcidin is a liver-derived hormone with a key role in iron homeostasis. In addition to iron, it is regulated by inflammation and hypoxia, although mechanisms of hypoxic regulation remain unclear. In hepatocytes, hepcidin is induced by bone morphogenetic proteins (BMPs) through a receptor complex requiring hemojuvelin (HJV) as a co-receptor. Type II transmembrane serine proteinase (TMPRSS6) antagonizes hepcidin induction by BMPs by cleaving HJV from the cell membrane. Inactivating mutations in TMPRSS6 lead to elevated hepcidin levels and consequent iron deficiency anemia. Here we demonstrate that TMPRSS6 is up-regulated in hepatic cell lines by hypoxia and by other activators of hypoxia-inducible factor (HIF). We show that TMPRSS6 expression is regulated by both HIF-1α and HIF-2α. This HIF-dependent up-regulation of TMPRSS6 increases membrane HJV shedding and decreases hepcidin promoter responsiveness to BMP signaling in hepatocytes. Our results reveal a potential role for TMPRSS6 in hepcidin regulation by hypoxia and provide a new molecular link between oxygen sensing and iron homeostasis.

The hypoxia-inducible factor HIF-1 functions as both a positive and negative modulator of aging

In the past year and a half, five studies have independently established a direct connection between the hypoxic response transcription factor, HIF-1, and aging in Caenorhabditis elegans. These studies demonstrated that HIF-1 can both promote and limit longevity via pathways that are mechanistically distinct. Here, we review the current state of knowledge regarding modulation of aging by HIF-1 and speculate on potential aspects of HIF-1 function that could be relevant for mammalian longevity and healthspan.

Hypoxia-selective growth inhibition of cancer cells by furospinosulin-1, a furanosesterterpene isolated from an Indonesian marine sponge

It is generally accepted that cancer cells, which have adapted to the hypoxic environments in tumor tissues, aggravate cancer pathology by promoting tumor growth, angiogenesis, metastasis, and drug resistance. Therefore, compounds that selectively inhibit the growth of tumor cells in hypoxic environments are expected to provide new leads for promising anticancer drugs. Furospinosulin-1, a marine-sponge-derived furanosesterterpene, exhibited selective antiproliferative activity against DU145 human prostate cancer cells under hypoxic conditions in concentrations ranging from 1 to 100 μM. Furospinosulin-1 also demonstrated antitumor activity at 10-50 mg kg(-1) oral administration in a mouse model inoculated with sarcoma S180 cells. Mechanistic analysis revealed that furospinosulin-1 suppresses transcription of the insulin-like growth factor-2 gene (IGF-2), which is selectively induced under hypoxic conditions through prevention of the binding of nuclear proteins to the Sp1 consensus sequence in the IGF-2 promoter region.

Regulation of cancer cell metabolism

Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

The G protein-coupled receptor 30 is up-regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) in breast cancer cells and cardiomyocytes

GPR30, also known as GPER, has been suggested to mediate rapid effects induced by estrogens in diverse normal and cancer tissues. Hypoxia is a common feature of solid tumors involved in apoptosis, cell survival, and proliferation. The response to low oxygen environment is mainly mediated by the hypoxia-inducible factor named HIF-1α, which activates signaling pathways leading to adaptive mechanisms in tumor cells. Here, we demonstrate that the hypoxia induces HIF-1α expression, which in turn mediates the up-regulation of GPER and its downstream target CTGF in estrogen receptor-negative SkBr3 breast cancer cells and in HL-1 cardiomyocytes. Moreover, we show that HIF-1α-responsive elements located within the promoter region of GPER are involved in hypoxia-dependent transcription of GPER, which requires the ROS-induced activation of EGFR/ERK signaling in both SkBr3 and HL-1 and cells. Interestingly, the apoptotic response to hypoxia was prevented by estrogens through GPER in SkBr3 cells. Taken together, our data suggest that the hypoxia-induced expression of GPER may be included among the mechanisms involved in the anti-apoptotic effects elicited by estrogens, particularly in a low oxygen microenvironment.

Regulation of Aerobic Glycolysis by microRNAs in Cancer

One of the most common and profound biochemical phenotypes of animal and human cancer cells is their ability to metabolize glucose at high rates, even under aerobic conditions. Such alterations lead to establishment of tumor-specific metabolic machinery that is sufficient for supporting the biosynthetic and energy requirements of the tumor cells for facilitating rapid tumor growth and adaptation to new metastatic niches. These changes entail rapid glycolysis by the tumor cells, shifting the flux of glucose from tricarboxylic acid (TCA) cycle to glycolysis, resulting in generation of vast amounts of lactate, which is then secreted outside the tumor cells. This phenomenon is also termed as Warburg effect, as originally described by Otto Warburg. Several oncogenes and tumor suppressors have been implicated in altering tumor cell metabolism in order to facilitate tumor growth and metastasis. MicroRNAs mediate fine-tuning of the cancerassociated glycolytic pathways either directly or at the level of oncogenes. This article intends to review the mechanisms and pathways by which miRNAs regulate the aerobic glycolysis in cancer.

Interactions between nitric oxide and hypoxia-inducible factor signaling pathways in inflammatory disease

Induction and activation of nitric oxide (NO) synthases (NOS) and excessive production of NO are common features of almost all diseases associated with infection and acute or chronic inflammation, although the contribution of NO to the pathophysiology of these diseases is highly multifactorial and often still a matter of controversy. Because of its direct impact on tissue oxygenation and cellular oxygen (O(2)) consumption and re-distribution, the ability of NO to regulate various aspects of hypoxia-induced signaling has received widespread attention. Conditions of tissue hypoxia and the activation of hypoxia-inducible factors (HIF) have been implicated in hypoxia or in cancer biology, but are also being increasingly recognized as important features of acute and chronic inflammation. Thus, the activation of HIF transcription factors has been increasingly implicated in inflammatory diseases, and recent studies have indicated its critical importance in regulating phagocyte function, inflammatory mediator production, and regulation of epithelial integrity and repair processes. Finally, HIF also appears to contribute to important features of tissue fibrosis and epithelial-to-mesenchymal transition, processes that are associated with tissue remodeling in various non-malignant chronic inflammatory disorders. In this review, we briefly summarize the current state of knowledge with respect to the general mechanisms involved in HIF regulation and the impact of NO on HIF activation. Secondly, we will summarize the major recent findings demonstrating a role for HIF signaling in infection, inflammation, and tissue repair and remodeling, and will address the involvement of NO. The growing interest in hypoxia-induced signaling and its relation with NO biology is expected to lead to further insights into the complex roles of NO in acute or chronic inflammatory diseases and may point to the importance of HIF signaling as key feature of NO-mediated events during these disorders.

Carbon metabolism and the sign of control coefficients in metabolic adaptations underlying K-ras transformation

Metabolic adaptations are associated with changes in enzyme activities. These adaptations are characterized by patterns of positive and negative changes in metabolic fluxes and concentrations of intermediate metabolites. Knowledge of the mechanism and parameters governing enzyme kinetics is rarely available. However, the signs-increases or decreases-of many of these changes can be predicted using the signs of metabolic control coefficients. These signs require the only knowledge of the structure of the metabolic network and a limited qualitative knowledge of the regulatory dependences, which is widely available for carbon metabolism. Here, as a case study, we identified control coefficients with fixed signs in order to predict the pattern of changes in key enzyme activities which can explain the observed changes in fluxes and concentrations underlying the metabolic adaptations in oncogenic K-ras transformation in NIH-3T3 cells. The fixed signs of control coefficients indicate that metabolic changes following the oncogenic transformation-increased glycolysis and oxidative branch of the pentose-phosphate pathway, and decreased concentration in sugar-phosphates-could be associated with increases in activity for glucose-6-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase, and decrease for transketolase. These predictions were validated experimentally by measuring specific activities. We conclude that predictions based on fixed signs of control coefficients are a very robust tool for the identification of changes in enzyme activities that can explain observed metabolic adaptations in carbon metabolism.

Cancer stem cells may be mostly maintained by fluctuating hypoxia

We wonder if most cancer stem cells (CSCs) survive and are maintained in the region of fluctuating hypoxia, which protects them against differentiation. Fluctuating hypoxia, as an important and neglected factor, has been confirmed to induce malignant progression, confer to therapeutic resistance and exist extensively. The subsequent consequence is similar with the behavior of CSCs. Therefore, we cite some examples for our bases and hypothesize CSCs may be mostly maintained by fluctuating hypoxia.

Zinc downregulates HIF-1α and inhibits its activity in tumor cells in vitro and in vivo

Background

Hypoxia inducible factor-1α (HIF-1α) is responsible for the majority of HIF-1-induced gene expression changes under hypoxia and for the “angiogenic switch” during tumor progression. HIF-1α is often upregulated in tumors leading to more aggressive tumor growth and chemoresistance, therefore representing an important target for antitumor intervention. We previously reported that zinc downregulated HIF-1α levels. Here, we evaluated the molecular mechanisms of zinc-induced HIF-1α downregulation and whether zinc affected HIF-1α also in vivo.

Methodology/Principal Findings

Here we report that zinc downregulated HIF-1α protein levels in human prostate cancer and glioblastoma cells under hypoxia, whether induced or constitutive. Investigations into the molecular mechanisms showed that zinc induced HIF-1α proteasomal degradation that was prevented by treatment with proteasomal inhibitor MG132. HIF-1α downregulation induced by zinc was ineffective in human RCC4 VHL-null renal carcinoma cell line; likewise, the HIF-1αP402/P564A mutant was resistant to zinc treatment. Similarly to HIF-1α, zinc downregulated also hypoxia-induced HIF-2α whereas the HIF-1β subunit remained unchanged. Zinc inhibited HIF-1α recruitment onto VEGF promoter and the zinc-induced suppression of HIF-1-dependent activation of VEGF correlated with reduction of glioblastoma and prostate cancer cell invasiveness in vitro. Finally, zinc administration downregulated HIF-1α levels in vivo, by bioluminescence imaging, and suppressed intratumoral VEGF expression.

Conclusions/Significance

These findings, by demonstrating that zinc induces HIF-1α proteasomal degradation, indicate that zinc could be useful as an inhibitor of HIF-1α in human tumors to repress important pathways involved in tumor progression, such as those induced by VEGF, MDR1, and Bcl2 target genes, and hopefully potentiate the anticancer therapies.

Histone deacetylase inhibitors: the epigenetic therapeutics that repress hypoxia-inducible factors

Histone deacetylase inhibitors (HDACIs) have been actively explored as a new generation of chemotherapeutics for cancers, generally known as epigenetic therapeutics. Recent findings indicate that several types of HDACIs repress angiogenesis, a process essential for tumor metabolism and progression. Accumulating evidence supports that this repression is mediated by disrupting the function of hypoxia-inducible factors (HIF-1, HIF-2, and collectively, HIF), which are the master regulators of angiogenesis and cellular adaptation to hypoxia. Since HIF also regulate glucose metabolism, cell survival, microenvironment remodeling, and other alterations commonly required for tumor progression, they are considered as novel targets for cancer chemotherapy. Though the precise biochemical mechanism underlying the HDACI-triggered repression of HIF function remains unclear, potential cellular factors that may link the inhibition of deacetylase activity to the repression of HIF function have been proposed. Here we review published data that inhibitors of type I/II HDACs repress HIF function by either reducing functional HIF-1α levels, or repressing HIF-α transactivation activity. In addition, underlying mechanisms and potential proteins involved in the repression will be discussed. A thorough understanding of HDACI-induced repression of HIF function may facilitate the development of future therapies to either repress or promote angiogenesis for cancer or chronic ischemic disorders, respectively.

Imaging of oxygen gradients in monolayer cultured cells using green fluorescent protein

Gradients of Po2 between capillary blood and mitochondria are the driving force for diffusional O2 delivery in tissues. Hypoxic microenvironments in tissues that result from diffusional O2 gradients are especially relevant in solid tumors because they have been related to a poor prognosis. To address the impact of tissue O2 gradients, we developed a novel technique that permits imaging of intracellular O2 levels in cultured cells at a subcellular spatial resolution. This was done, with the sensitivity to O2 ≤3%, by the O2-dependent red shift of green fluorescent protein (AcGFP1) fluorescence. Measurements were carried out in a confluent monolayer of Hep3B cells expressing AcGFP1 in the cytoplasm. To establish a two-dimensional O2 diffusion model, a thin quartz glass slip was placed onto the monolayer cells to prevent O2 diffusion from the top surface of the cell layer. The magnitude of the red shift progressively increased as the distance from the gas coverslip interface increased. It reached an anoxic level in cells located at ∼220 μm and ∼690 μm from the gas coverslip boundary at 1% and 3% gas phase O2, respectively. Thus the average O2 gradient was 0.03 mmHg/μm in the present tissue model. Abolition of mitochondrial respiration significantly dampened the gradients. Furthermore, intracellular gradients of the red shift in mitochondria-targeted AcGFP1 in single Hep3B cells suggest that the origin of tissue O2 gradients is intracellular. Findings in the present two-dimensional O2 diffusion model support the crucial role of tissue O2 diffusion in defining the O2 microenvironment in individual cells.

Glioblastoma, cancer stem cells and hypoxia

Glioblastoma (GBM) prognosis remains dismal, with most patients succumbing to disease within 1 or 2 years of diagnosis. Recent studies have suggested that many solid tumors, including GBM, are maintained by a subset of cells termed cancer stem cells (CSCs). It has been shown that these cells are inherently radio- and chemotherapy resistant, and may be maintained in vivo in a niche characterized by reduced oxygen tension (hypoxia). This review examines the recently described effects of hypoxia on CSC in GBM, and the potential promise in targeting the hypoxic pathway therapeutically.

Mammea E/BB, an isoprenylated dihydroxycoumarin protonophore that potently uncouples mitochondrial electron transport, disrupts hypoxic signaling in tumor cells

The mammea-type coumarin mammea E/BB (1) was found to inhibit both hypoxia-induced and iron chelator-induced hypoxia-inducible factor-1 (HIF-1) activation in human breast tumor T47D cells with IC(50) values of 0.96 and 0.89 μM, respectively. Compound 1 suppressed the hypoxic induction of secreted VEGF protein (T47D cells) and inhibited cell viability/proliferation in four human tumor cell lines. Compound 1 (at 5 and 20 μM) inhibited human breast tumor MDA-MB-231 cell migration. While the mechanisms that underlie their biological activities have remained unknown, prenylated mammea coumarins have been shown to be cytotoxic to human tumor cells, suppress tumor growth in animal models, and display a wide variety of antimicrobial effects. Mechanistic studies revealed that 1 appears to exert an assemblage of cellular effects by functioning as an anionic protonophore that potently uncouples mitochondrial electron transport and disrupts mitochondrial signaling in human tumor cell lines.

Transcriptional regulation of BRCA1 expression by a metabolic switch

Though the linkages between germline mutations of BRCA1 and hereditary breast cancer are well known, recent evidence suggests that altered BRCA1 transcription may also contribute to sporadic forms of breast cancer. Here we show that BRCA1 expression is controlled by a dynamic equilibrium between transcriptional coactivators and co-repressors that govern histone acetylation and DNA accessibility at the BRCA1 promoter. Eviction of the transcriptional co-repressor and metabolic sensor, C terminal-binding protein (CtBP), has a central role in this regulation. Loss of CtBP from the BRCA1 promoter through estrogen induction, depletion by RNA interference or increased NAD+/NADH ratio leads to HDAC1 dismissal, elevated histone acetylation and increased BRCA1 transcription. The active control of chromatin marks, DNA accessibility and gene expression at the BRCA1 promoter by this 'metabolic switch' provides an important molecular link between caloric intake and tumor suppressor expression in mammary cells.

The absence of LPA receptor 2 reduces the tumorigenesis by ApcMin mutation in the intestine

Lysophosphatidic acid (LPA) is a lipid mediator that mediates several effects that promote cancer progress. The LPA receptor type 2 (LPA(2)) expression is often elevated in several types of cancers, including colorectal cancer (CRC). In this study, we investigated the role of LPA(2) in the development of intestinal adenomas by comparing Apc(Min/+) mice with Apc(Min/+)/Lpar2(-/-) mice. There were 50% fewer intestinal adenomas in Apc(Min/+)/Lpar2(-/-) mice than Apc(Min/+) mice. Smaller-size adenomas (<1 mm) were found at higher frequencies in Apc(Min/+)/Lpar2(-/-) mice compared with Apc(Min/+) mice at the two age groups examined. The expression level of LPA(2) correlated with increased size of intestinal adenomas. Reduced tumor multiplicity and size in Apc(Min/+)/Lpar2(-/-) mice correlated with decreased proliferation of intestinal epithelial cells. Apc(Min/+)/Lpar2(-/-) mice showed an increased level of apoptosis, suggesting that LPA(2)-mediated signaling stimulates intestinal tumor development and progress by regulating both cell proliferation and survival. In addition, the expression levels of Krüpple-like factor 5 (KLF5), β-catenin, cyclin D1, c-Myc, and hypoxia-inducible factor-1α (HIF-1α) were significantly altered in Apc(Min/+)/Lpar2(-/-) mice compared with Apc(Min/+) mice. In vitro studies using HCT116 cells showed that LPA induced cyclin D1, c-Myc, and HIF-1α expression, which was attenuated by knockdown of LPA(2). In summary, intestinal tumor initiated by Apc mutations is altered by LPA(2)-mediated signaling, which regulates tumor growth and survival by altering multiple targets.

Chalcone-based inhibitors against hypoxia-inducible factor 1--structure activity relationship studies

Many tumor tissues are under hypoxic conditions. Activating hypoxia-inducible factor 1 (HIF-1), a transcription factor, is a major mechanism for tumor cells to survive and even to evade other tissues. Therefore inhibiting HIF-1 is a potential strategy to help improve cancer treatment. Chalcone is a promising template to develop HIF-1 inhibitor because quite a few of chalcone-based compounds reveal moderate HIF-1 inhibitory activity and many chalcone-based compounds demonstrate promising anticancer activities in various animal models. However, there are no reports about the structure-activity relationship of chalcone compounds with respect to HIF-1 inhibition. This study reports the HIF-1 inhibitory activities of a panel of chalcones, identifies a few lead candidates of single-digit micromolar potency, and determines important structural modifications.

Molecular characterization of hypoxia and hypoxia-inducible factor 1 alpha (HIF-1α) from Taiwan voles (Microtus kikuchii)

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that senses and adapts cells to hypoxic environmental conditions. HIF-1 is composed of an oxygen-regulated α subunit (HIF-1α) and a constitutively expressed β subunit (HIF-1β). Taiwan voles (Microtus kikuchii) are an endemic species in Taiwan, found only in mountainous areas greater than 2000m above sea level. In this study, the full-length HIF-1α cDNA was cloned and sequenced from liver tissues of Taiwan voles. We found that HIF-1α of Taiwan voles had high sequence similarity to HIF-1α of other species. Sequence alignment of HIF-1α functional domains indicated basic helix-loop-helix (bHLH), PER-ARNT-SIM (PAS) and C-terminal transactivation (TAD-C) domains were conserved among species, but sequence variations were found between the oxygen-dependent degradation domains (ODDD). To measure Taiwan vole HIF-1α responses to hypoxia, animals were challenged with cobalt chloride, and HIF-1α mRNA and protein expression in brain, lung, heart, liver, kidney, and muscle was assessed by quantitative RT-PCR and Western blot analysis. Upon induction of hypoxic stress with cobalt chloride, an increase in HIF-1α mRNA levels was detected in lung, heart, kidney, and muscle tissue. In contrast, protein expression levels showed greater variation between individual animals. These results suggest that the regulation of HIF-1α may be important to the Taiwan vole under cobalt chloride treatments. But more details regarding the evolutionary effect of environmental pressure on HIF-1α primary sequence, HIF-1α function and regulation in Taiwan voles remain to be identified.

DNA strand breaks and hypoxia response inhibition mediate the radiosensitisation effect of nitric oxide donors on prostate cancer under varying oxygen conditions

Prostate cancer cells can exist in a hypoxic microenvironment, causing radioresistance. Nitric oxide (NO) is a radiosensitiser of mammalian cells. NO-NSAIDs are a potential means of delivering NO to prostate cancer cells. This study aimed to determine the effect and mechanism of action of NO-sulindac and radiation, on prostate cancer cells and stroma, under normoxia (21% oxygen) and chronic hypoxia (0.2% oxygen). Using clonogenic assays, at a surviving fraction of 10% the sensitisation enhancement ratios of radiation plus NO-sulindac over radiation alone on PC-3 cells were 1.22 and 1.42 under normoxia and hypoxia, respectively. 3D culture of PC-3 cells revealed significantly reduced sphere diameter in irradiated spheres treated with NO-sulindac. Neither NO-sulindac nor sulindac radiosensitised prostate stromal cells under normoxia or hypoxia. HIF-1α protein levels were reduced by NO-sulindac exposure and radiation at 21 and 0.2% oxygen. Alkaline Comet assay analysis suggested an increased rate of single strand DNA breaks and slower repair of these lesions in PC-3 cells treated with NO-sulindac prior to irradiation. There was a higher level of γ-H2AX production and hence double strand DNA breaks following irradiation of NO-sulindac treated PC-3 cells. At all radiation doses and oxygen levels tested, treatment of 2D and 3D cultures of PC-3 cells with NO-sulindac prior to irradiation radiosensitised PC-3, with minimal effect on stromal cells. Hypoxia response inhibition and increased DNA double strand breaks are potential mechanisms of action. Neoadjuvent and concurrent use of NO-NSAIDs have the potential to improve radiotherapy treatment of prostate cancer under normoxia and hypoxia.

Hypoxia-inducible factor 1-mediated regulation of PPP1R3C promotes glycogen accumulation in human MCF-7 cells under hypoxia

Hundreds of genes can be regulated by hypoxia-inducible factor 1 (HIF1) under hypoxia. Here we demonstrated a HIF1-mediated induction of protein phosphatase 1, regulatory subunit 3C gene (PPP1R3C) in human MCF7 cells under hypoxia. By mutation analysis we confirmed the presence of a functional hypoxia response element that is located 229bp upstream from the PPP1R3C gene. PPP1R3C induction correlates with a significant glycogen accumulation in MCF7 cells under hypoxia. Knockdown of either HIF1α or PPP1R3C attenuated hypoxia-induced glycogen accumulation significantly. Knockdown of HIF2α reduced hypoxia-induced glycogen accumulation slightly (but not significantly). Our results demonstrated that HIF1 promotes glycogen accumulation through regulating PPP1R3C expression under hypoxia, which revealed a novel metabolic adaptation of cells to hypoxia.

Signaling pathways in renal cell carcinoma

Renal cell carcinoma (RCC), the most lethal type of genitourinary cancer, is generally resistant to chemotherapy and radiation therapy. Surgical excision of the tumor at a localized stage remains the mainstay for curative therapy. A number of drugs developed in recent years have shown limited to significant efficacy in treating RCC. These drugs act by blocking critical signaling pathways associated with RCC tumor growth and survival, and angiogenesis. Beyond well-validated signaling targets such as VHL, VEGFR and mTOR, additional pathways including HGF/c-MET and Wnt/β-catenin have emerged as important to RCC pathogenesis. Mutations in one or more components of these signaling networks may affect tumor response to therapy. This review summarizes the state of knowledge about signaling pathways in RCC and discusses the known genetic and epigenetic alterations that underlie dysregulation of these pathways.

Genetic heterogeneity and chromatin modifiers in renal clear cell carcinoma

Evaluation of: Dalgliesh GL, Furge K, Greenman C et al.: Systematic sequencing of renal carcinoma reveals inactivation of histone modifying genes. Nature 463, 360-363 (2010). Clear cell renal cell carcinoma (ccRCC) accounts for more than 75% of all adult kidney cancer. Hereditary ccRCC in von Hippel-Lindau disease is caused by germline mutations of the VHL tumor suppressor gene. Moreover, 50% of sporadic ccRCCs harbor biallelic mutations of VHL. However, loss of VHL alone is insufficient for tumor initiation, and a minority of ccRCCs retain wild-type VHL alleles, indicating a requirement for additional or alternative genetic alterations in tumor development. This systematic study demonstrated that a fraction of ccRCCs harbored inactivating mutations in four genes encoding histone-modifying enzymes. One of these, UTX, has recently been implicated in the control of cell proliferation. Moreover, several other mutations were identified, among them NF2 truncations in a subset of VHL-positive ccRCC. The study illustrates both a vast genetic heterogeneity in ccRCC and a requirement for further systematic investigations to design a targeted treatment for different ccRCC subtypes.

Identification of novel p53 pathway activating small-molecule compounds reveals unexpected similarities with known therapeutic agents

Manipulation of the activity of the p53 tumor suppressor pathway has demonstrated potential benefit in preclinical mouse tumor models and has entered human clinical trials. We describe here an improved, extensive small-molecule chemical compound library screen for p53 pathway activation in a human cancer cell line devised to identify hits with potent antitumor activity. We uncover six novel small-molecule lead compounds, which activate p53 and repress the growth of human cancer cells. Two tested compounds suppress in vivo tumor growth in an orthotopic mouse model of human B-cell lymphoma. All compounds interact with DNA, and two activate p53 pathway in a DNA damage signaling-dependent manner. A further screen of a drug library of approved drugs for medicinal uses and analysis of gene-expression signatures of the novel compounds revealed similarities to known DNA intercalating and topoisomerase interfering agents and unexpected connectivities to known drugs without previously demonstrated anticancer activities. These included several neuroleptics, glycosides, antihistamines and adrenoreceptor antagonists. This unbiased screen pinpoints interference with the DNA topology as the predominant mean of pharmacological activation of the p53 pathway and identifies potential novel antitumor agents.

Drug resistance in metastatic castration-resistant prostate cancer

Docetaxel in combination with prednisone is the standard of care in men with symptomatic castration-resistant prostate cancer (CRPC). However, a substantial proportion of men with CRPC do not benefit from docetaxel or other systemic therapy and those who do benefit invariably progress and die of (or with) prostate cancer. Resistance to chemotherapy in metastatic CRPC is a result of cellular mechanisms of drug resistance intrinsic to prostate cancer and general mechanisms common to different tumor types. Continued signaling from the androgen receptor, activation of oncogenic survival pathways by various receptor tyrosine kinases and crosstalk between the androgen receptor and these oncogenic survival pathways are hallmarks of progression of CRPC. General mechanisms of drug resistance include the existence of subpopulations of cancer cells with cellular mechanisms of resistance, resistance related to interactions between prostate cancer cells and their surrounding microenvironment and impaired drug delivery to the cancer cells. New therapeutics targeting these mechanisms are under evaluation in clinical trials. Drug resistance in metastatic CRPC is multifactorial and complex and development of new medical therapies remains challenging.

Oxidative phosphorylation in cancer cells

Evidence suggests that mitochondrial metabolism may play a key role in controlling cancer cells life and proliferation. Recent evidence also indicates how the altered contribution of these organelles to metabolism and the resistance of cancer mitochondria against apoptosis-associated permeabilization are closely related. The hallmarks of cancer growth, increased glycolysis and lactate production in tumours, have raised attention due to recent observations suggesting a wide spectrum of oxidative phosphorylation deficit and decreased availability of ATP associated with malignancies and tumour cell expansion. More specifically, alteration in signal transduction pathways directly affects mitochondrial proteins playing critical roles in controlling the membrane potential as UCP2 and components of both MPTP and oxphos complexes, or in controlling cells life and death as the Bcl-2 proteins family. Moreover, since mitochondrial bioenergetics and dynamics, are also involved in processes of cells life and death, proper regulation of these mitochondrial functions is crucial for tumours to grow. Therefore a better understanding of the key pathophysiological differences between mitochondria in cancer cells and in their non-cancer surrounding tissue is crucial to the finding of tools interfering with these peculiar tumour mitochondrial functions and will disclose novel approaches for the prevention and treatment of malignant diseases. Here, we review the peculiarity of tumour mitochondrial bioenergetics and the mode it is linked to the cell metabolism, providing a short overview of the evidence accumulated so far, but highlighting the more recent advances.

Pediatric and wild-type gastrointestinal stromal tumor: new therapeutic approaches

PURPOSE OF REVIEW

Pediatric gastrointestinal stromal tumor is an uncommon tumor, the rarity of which has made both laboratory research studies and clinical management very difficult. As we learn more about this disorder, what is emerging is that this rare cancer is markedly different in children and adults. One of the main biological differences is that pediatric patients lack activating mutations in the oncogenes that drive tumor formation in adults. The natural history of this disease also appears to be more indolent in children than in adults. In this review, we will discuss the differences between children and adults with gastrointestinal stromal tumor and some new potential therapeutic agents.

RECENT FINDINGS

This review discusses recent advances and the rationale for several recently identified molecular targets. In addition, we discuss the formation of a clinic at the National Institutes of Health that is dedicated to the study of this rare disorder.

SUMMARY

Collaborative efforts are underway to better define the natural history and clinical course of pediatric patients with gastrointestinal stromal tumor. When combined with innovative genomic and molecular studies, these dual approaches will allow for notable advances in this field.

Potential therapeutics specific to c-MET/RON receptor tyrosine kinases for molecular targeting in cancer therapy

Products of proto-oncogenes c-MET and RON belong to a subfamily of receptor tyrosine kinases that contribute significantly to tumorigenic progression. In primary tumors, altered c-MET/RON expression transduces signals regulating invasive growth that is characterized by cell migration and matrix invasion. These pathogenic features provide the basis for targeting c-MET/RON in cancer therapy. In the last decade, various approaches have been investigated to suppress c-MET/RON-transduced oncogenesis. Among the therapeutics developed, monoclonal antibodies (mAbs) and small-molecule inhibitors (SMIs) have emerged as promising candidates. The mechanism of these therapeutic candidates is the disruption of tumor dependency on c-MET/RON signals for survival. The mAbs specific to hepatocyte growth factor (AMG102) and c-MET (MetMAb) are both humanized and able to block c-MET signaling, leading to inhibition of tumor cell proliferation in vitro and inhibition of tumor growth in xenograft models. The mAb AMG102 neutralizes hepatocyte growth factor and enhances the cytotoxicity of various chemotherapeutics to tumors in vivo. AMG102 is currently in phase II clinical trials for patients with advanced solid tumors. IMC-41A40 and Zt/f2 are RON-specific mAbs that down-regulate RON expression and inhibit ligand-induced phosphorylation. Both mAbs inhibit tumor growth in mice mediated by colon and pancreatic cancer cells. SMIs specific to c-MET (ARQ107 and PF-02341066) are in various phases of clinical trials. Therapeutic efficacy has also been observed with dual inhibitors such as Compound I, which is specific to c-MET/RON. However, a potential issue is the emergence of acquired resistance to these inhibitors. Clearly, development of c-MET/RON therapeutics provides opportunities and challenges for combating cancer in the future.

Inhibition of tubulogenesis and of carcinogen-mediated signaling in brain endothelial cells highlight the antiangiogenic properties of a mumbaistatin analog

A better understanding of the metabolic adaptations of the vascular endothelial cells (EC) that mediate tumor vascularization would help the development of new drugs and therapies. Novel roles in cell survival and metabolic adaptation to hypoxia have been ascribed to the microsomal glucose-6-phosphate translocase (G6PT). While antitumorigenic properties of G6PT inhibitors such as chlorogenic acid (CHL) have been documented, those of the G6PT inhibitor and semi-synthetic analog AD4-015 of the polyketide mumbaistatin are not understood. In the present study, we evaluated the in vitro antiangiogenic impact of AD4-015 on human brain microvascular endothelial cells (HBMEC), which play an essential role as structural and functional components in tumor angiogenesis. We found that in vitro HBMEC migration and tubulogenesis were reduced by AD4-015 but not by CHL. The mumbaistatin analog significantly inhibited the phorbol 12-myristate 13-acetate (PMA)-induced matrix-metalloproteinase (MMP)-9 secretion and gene expression as assessed by zymography and RT-PCR. PMA-mediated cell signaling leading to cyclooxygenase (COX)-2 expression and IkappaB downregulation was also inhibited, further confirming AD4-015 as a cell signaling inhibitor in tumor promoting conditions. G6PT functions may therefore account for the metabolic flexibility that enables EC-mediated neovascularization. This process could be specifically targeted within the vasculature of developing brain tumors by G6PT inhibitors.

Pharmacokinetic/pharmacodynamic modeling identifies SN30000 and SN29751 as tirapazamine analogues with improved tissue penetration and hypoxic cell killing in tumors

PURPOSE

Tirapazamine (TPZ) has attractive features for targeting hypoxic cells in tumors but has limited clinical activity, in part because of poor extravascular penetration. Here, we identify improved TPZ analogues by using a spatially resolved pharmacokinetic/pharmacodynamic (SR-PKPD) model that considers tissue penetration explicitly during lead optimization.

EXPERIMENTAL DESIGN

The SR-PKPD model was used to guide the progression of 281 TPZ analogues through a hierarchical screen. For compounds exceeding hypoxic selectivity thresholds in single-cell cultures, SR-PKPD model parameters (kinetics of bioreductive metabolism, clonogenic cell killing potency, diffusion coefficients in multicellular layers, and plasma pharmacokinetics at well tolerated doses in mice) were measured to prioritize testing in xenograft models in combination with radiation.

RESULTS

SR-PKPD-guided lead optimization identified SN29751 and SN30000 as the most promising hypoxic cytotoxins from two different structural subseries. Both were reduced to the corresponding 1-oxide selectively under hypoxia by HT29 cells, with an oxygen dependence quantitatively similar to that of TPZ. SN30000, in particular, showed higher hypoxic potency and selectivity than TPZ in tumor cell cultures and faster diffusion through HT29 and SiHa multicellular layers. Both compounds also provided superior plasma PK in mice and rats at equivalent toxicity. In agreement with SR-PKPD predictions, both were more active than TPZ with single dose or fractionated radiation against multiple human tumor xenografts.

CONCLUSIONS

SN30000 and SN29751 are improved TPZ analogues with potential for targeting tumor hypoxia in humans. Novel SR-PKPD modeling approaches can be used for lead optimization during anticancer drug development.

Angiogenesis inhibitors in the treatment of prostate cancer

Prostate cancer remains a significant public health problem, with limited therapeutic options in the setting of castrate-resistant metastatic disease. Angiogenesis inhibition is a relatively novel antineoplastic approach, which targets the reliance of tumor growth on the formation of new blood vessels. This strategy has been used successfully in other solid tumor types, with the FDA approval of anti-angiogenic agents in breast, lung, colon, brain, and kidney cancer. The application of anti-angiogenic therapy to prostate cancer is reviewed in this article, with attention to efficacy and toxicity results from several classes of anti-angiogenic agents. Ultimately, the fate of anti-angiogenic agents in prostate cancer rests on the eagerly anticipated results of several key phase III studies.

Lipoxin A4 and its analogue suppress the tumor growth of transplanted H22 in mice: the role of antiangiogenesis

Tumor angiogenesis plays an essential role in carcinogenesis, cancer progression, and metastasis. Some studies indicate that lipoxins, endogenous anti-inflammatory lipid mediators, might be involved in tumor angiogenesis; however, the governing mechanisms are still unknown. In the present study, we examined the effects of exogenous lipoxin A(4) (LXA(4)) in mouse hepatocarcinoma cell line (H22) and H22-bearing mice model. It was found that in H22 cells, LXA(4) inhibited the production of vascular endothelial growth factor and reduced hypoxia-inducible factor-1 alpha level. In addition, its analogue, BML-111, blocked the expression of vascular endothelial growth factor in serum and tumor sections from H22-bearing mice. H&E staining and immunostaining with antibodies against CD34 revealed that BML-111 suppressed tumor-related angiogenesis in vivo, but LXA(4) could not influence the proliferation of primary cultured human umbilical vein endothelial cells. The tumor growth was also inhibited by BML-111. We also found that BML-111 enhanced the in situ apoptosis while inhibiting macrophage infiltration in tumor tissue. The results provide new evidence that LXA(4) suppresses the growth of transplanted H22 tumor in mice through inhibiting tumor-related angiogenesis.