Hypoxia-inducible factor 1α/vascular endothelial growth factor axis in astrocytomas. Associations with microvessel morphometry, proliferation and prognosis

HIF-1α inhibition by siRNA or chetomin in human malignant glioma cells: effects on hypoxic radioresistance and monitoring via CA9 expression

Background

Hypoxia induces activation of the HIF-1 pathway and is an essential characteristic of malignant gliomas. Hypoxia has been linked to tumor progression, therapy resistance and poor prognosis. However, little is known about the impact of HIF-1α inhibition on radioresistance of malignant glioma.

Methods

In this study, we investigated the effects of the inhibition of HIF-1α on cell survival and radiosensitivity in U251MG and U343MG glioma cells, using two different strategies. HIF-1α inhibition was achieved by siRNA targeting of HIF-1α or via chetomin, a disruptor of interactions between HIF-1α and p300. The inhibition of the HIF-1 pathway was monitored by quantitative real-time PCR and Western blot analyses of the expression levels of HIF-1α and CA9. CA9 expression was investigated as a potential indicator of the efficacy of HIF-1 inhibition and the resulting radiosensitivity of malignant glioma cell lines was determined by clonogenic assay after irradiation under normoxic (2-10 Gy) or hypoxic (2-15 Gy) conditions.

Results

Although siRNA and chetomin show distinct modes of action, both attenuated the hypoxia-induced radioresistance of malignant glioma cell lines U251MG (DMF₁₀: 1.35 and 1.18) and U343MG (DMF₁₀: 1.78 and 1.48). However, siRNA and chetomin showed diverse effects on radiosensitivity under normoxic conditions in U251MG (DMF₁₀: 0.86 and 1.35) and U343MG (DMF₁₀: 1.33 and 1.02) cells.

Conclusions

Results from this in vitro study suggest that inhibition of HIF-1α is a promising strategy to sensitize human malignant gliomas to radiotherapy and that CA9 could serve as an indicator of effective HIF-1-related radiosensitization.

HIF1alpha isoforms in benign and malignant prostate tissue and their correlation to neuroendocrine differentiation

Background

Neuroendocrine (NE) differentiation in prostate cancer has been correlated with a poor prognosis and hormone refractory disease. In a previous report, we demonstrated the presence of immunoreactive cytoplasmic hypoxia inducible factor 1α (HIF1α), in both benign and malignant NE prostate cells. HIF1α and HIF1β are two subunits of HIF1, a transcription factor important for angiogenesis. The aim of this study was to elucidate whether the cytoplasmic stabilization of HIF1α in androgen independent NE differentiated prostate cancer is due to the presence of certain HIF1α isoforms.

Methods

We studied the HIF1α isoforms present in 8 cases of benign prostate hyperplasia (BPH) and 43 cases of prostate cancer with and without NE differentiation using RT-PCR, sequencing analysis, immunohistochemistry and in situ hybridization.

Results

We identified multiple isoforms in both benign and malignant prostate tissues. One of these isoforms, HIF1α1.2, which was previously reported to be testis specific, was found in 86% of NE-differentiated prostate tumors, 92% of HIF1α immunoreactive prostate tumors and 100% of cases of benign prostate hyperplasia. Immunohistochemistry and in situ hybridization results showed that this isoform corresponds to the cytoplasmic HIF1α present in androgen-independent NE cells of benign and malignant prostate tissue and co-localizes with immunoreactive cytoplasmic HIF1β.

Conclusion

Our results indicate that the cytoplasmic stabilization of HIF1α in NE-differentiated cells in benign and malignant prostate tissue is due to presence of an HIF1α isoform, HIF1α1.2. Co-localization of this isoform with HIF1β indicates that the HIF1α1.2 isoform might sequester HIF1β in the cytoplasm.

Hypoxia-inducible factor 1α expression is a prognostic biomarker in patients with astrocytic tumors associated with necrosis on MR image

Hypoxia-inducible factor (HIF)-1α and HIF-2α expression were investigated immunohistochemically as determinants of prognosis in 42 cases of astrocytic tumors associated with necrosis grade on magnetic resonance (MR) imaging. Expression of HIF-1α was determined immunohistologically. The degree of necrosis on MR images was divided into four grades. Kaplan-Meier analysis revealed a significant effect of necrosis grade on MR images on cumulative overall survival. Median survival times were 26, 14, and 13 months for patients with necrosis grades 1, 2, and 3, respectively (not defined for grade 0). Kaplan-Meier analysis revealed a significant effect of HIF-1α expression on cumulative overall survival. Median survival time of patients with HIF-1α expression was 17 months, whereas it was 80 months for patients without HIF-1α expression. However, overexpression of HIF-2α did not correlate with malignant features, for example angiogenesis or necrosis, and had no impact on overall survival of patients with glial tumors. In conclusion, HIF-1α, but not HIF-2α, is a useful prognostic factor in astrocytic tumor associated with necrosis on MR images.

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

Adaptation of cancer cells to their microenvironment is an important driving force in the clonal selection that leads to invasive and metastatic disease. O2 concentrations are markedly reduced in many human cancers compared with normal tissue, and a major mechanism mediating adaptive responses to reduced O2 availability (hypoxia) is the regulation of transcription by hypoxia-inducible factor 1 (HIF-1). This review summarizes the current state of knowledge regarding the molecular mechanisms by which HIF-1 contributes to cancer progression, focusing on (1) clinical data associating increased HIF-1 levels with patient mortality; (2) preclinical data linking HIF-1 activity with tumor growth; (3) molecular data linking specific HIF-1 target gene products to critical aspects of cancer biology and (4) pharmacological data showing anticancer effects of HIF-1 inhibitors in mouse models of human cancer.

High incidence of MGMT and RARbeta promoter methylation in primary glioblastomas: association with histopathological characteristics, inflammatory mediators and clinical outcome

Glioblastomas, the most frequent primary brain tumors in adults, are characterized by a highly aggressive, inflammatory and angiogenic phenotype. Methylation of CpG islands in cancer-related genes may serve as an epigenetic biomarker for glioblastoma diagnosis and prognosis. The aim of this study was to analyze the methylation status of four critical tumor-associated genes (MGMT, RARbeta, RASSF1A, CDH13), and investigate possible links with inflammatory (interleukin [IL]-6, IL-8) and angiogenic mediators (vascular endothelial growth factor [VEGF], cyclooxygenase [COX]-2) and clinical outcome in 23 glioma samples (6 grade II astrocytomas, 17 grade IV glioblastomas). RARbeta and MGMT genes were more frequently methylated in 70.58% and 58.8% of glioblastomas, respectively. RASSF1A and CDH13 displayed a similar methylation frequency (23.52%) in glioblastomas. No gene methylation was observed in grade II astrocytomas. Tumor grade correlated positively with MGMT and RARbeta methylation (P = 0.005 and P = 0.019, respectively) and the extent of necrosis (P = 0.001 and P = 0.003). Interestingly, the marker of chronic inflammation, IL-6, was positively associated with methylation of MGMT (P = 0.004), RARbeta (P = 0.002), and RASSF1A (P = 0.0081) as well as the total number of methylated genes (P < 0.0001), indicating the important role of IL-6 in maintaining promoter methylation of these genes. VEGF expression correlated positively with MGMT and RARbeta methylation although these relationships were of marginal significance (P = 0.0679 and P = 0.0757). Kaplan-Meier univariate survival analysis indicated an unfavorable survival period in patients with MGMT methylation compared with those without methylation (P = 0.0474). Our study highlights the implication of MGMT and RARbeta methylation in the aggressive phenotype of primary glioblastomas. The association of MGMT methylation with clinical outcome indicates its potential prognostic value.

Analysis of interleukin (IL)-8 expression in human astrocytomas: associations with IL-6, cyclooxygenase-2, vascular endothelial growth factor, and microvessel morphometry

Malignant astrocytomas are highly vascular neoplasms with potent angiogenic activity. The present study aimed to investigate peripheral and local expression of interleukin (IL)-8 in astrocytomas with possible associations to IL-6, cyclooxygenase-2 (COX-2), vascular endothelial growth factor (VEGF) expression, and microvessel morphometry. IL-6- and IL-8-secreting peripheral blood monocytes (PBMCs) were evaluated in 17 glioblastoma (WHO grade IV), 5 anaplastic astrocytoma (WHO grade III), and 6 diffuse astrocytoma patients (WHO grade II), in parallel with 23 healthy controls using enzyme-linked immunosorbent spot (ELISPOT) assay. The IL-8 expression was assessed immunohistochemically in patients' tumor tissue sections and correlated with the expression of COX-2, VEGF, IL-6, and microvessel morphometry (assessed using CD34 antibody). Eighteen cases were also stained for CD31 and used as an additional vessel marker to validate our results regarding microvessel morphometry. IL-6 and IL-8 were highly secreted in the PBMCs of glioma patients compared with controls (p = 0.0001, p < 0.0001, respectively), with a positive correlation between IL-8 expression and secretion levels (p = 0.001). IL-8 immunoreactivity was detected in malignant cells or macrophages in perivascular areas and in pseudopalisading cells around necrosis and was positively correlated with histological grade (p = 0.0175) and tumor necrosis (p = 0.0793). IL-6 and IL-8 expression levels were positively correlated (p = 0.0036) and associated with COX-2 and VEGF expression (IL-6: p = 0.0133, p = 0.065; IL-8: p = 0.0139, p = 0.0101), but not with microvessel morphometry, by either CD31 or CD34. The coordinate expression and topographical relationship of IL-6, IL-8, COX-2, and VEGF in the same tumor areas (e.g., perinecrotic areas) attest to their intimate liaison in terms of cancer-induced angiogenesis, which is probably secondary to the induction of multiple interdependent molecular pathways. Moreover, our study seems to be the first attempt to link IL-8 expression by tumor cells with histological grade, implicating its potent role in gliomagenesis.

Regulation of cancer cell metabolism by hypoxia-inducible factor 1

The induction of hypoxia-inducible factor 1 (HIF-1) activity, either as a result of intratumoral hypoxia or loss-of-function mutations in the VHL gene, leads to a dramatic reprogramming of cancer cell metabolism involving increased glucose transport into the cell, increased conversion of glucose to pyruvate, and a concomitant decrease in mitochondrial metabolism and mitochondrial mass. Blocking these adaptive metabolic responses to hypoxia leads to cell death due to toxic levels of reactive oxygen species. Targeting HIF-1 or metabolic enzymes encoded by HIF-1 target genes may represent a novel therapeutic approach to cancer.

Hypoxia-regulated protein expression, patient characteristics, and preoperative imaging as predictors of survival in adults with glioblastoma multiforme

BACKGROUND

Regions of hypoxia within glioblastoma multiforme (GBM) are common and may influence a tumor's aggressiveness, response to treatment, and the patient's overall survival. In this study, the authors examined 4 markers of hypoxia (hypoxia-inducible factor 1 [HIF-1alpha], glucose transporter 1 [GLUT-1], vascular endothelial growth factor [VEGF], and carbonic anhydrase 9 [CA IX]), cellular proliferation and microvascular density (MVD) indices, extent of surgical resection, and preoperative imaging characteristics and compared them with the overall survival rates of adults with GBM.

METHODS

In this retrospective cohort study, patients who had lower grade astrocytomas were compared with patients who had GBM to verify that the methods used could establish differences between tumor grades. By using preoperative imaging, the amount of necrosis was established versus the overall tumor area. The authors also compared preoperative images with postoperative images to define the amount of tumor resected; and they compared molecular markers, proliferation, MVD, and imaging studies with survival among patients who had GBM.

RESULTS

The hypoxia-regulated molecules (HRMs) and indices for MVD and cellular proliferation were associated significantly with tumor grade. Survival was improved when >or=95% of the tumor was resected. Although the total tumor area was associated with overall survival, no differences were observed when the amount of necrosis or a tumor necrosis index (area of necrosis/area of tumor) was compared with survival. The findings indicated that GLUT-1 and VEGF were correlated with survival after controlling for age.

CONCLUSIONS

Tumor grade was differentiated with HRMs, MVD, and proliferation, but only GLUT-1 predicted survival in this group of patients with GBM. The results suggested that GLUT-1 may be an important independent prognostic indicator.

Expression of hypoxia inducible factor-1alpha in tumors of patients with glioblastoma multiforme and transitional meningioma

Hypoxia-inducible factor-1 alpha (HIF-1alpha) is the major transcriptional factor involved in the adaptive response to hypoxia. The aim of this study was to assess HIF-1alpha in 22 patients with transitional meningioma (TM) and 26 patients with glioblastoma multiforme (GBM). HIF-1alpha was assessed using a commercially available enzyme-linked immunosorbent assay-based HIF-1 transcription factor assay. Levels of HIF-1alpha in TM and GBM were measured using optical density at 450nm, and median values were found to be 0.35 for TM and 0.37 OD for GBM, respectively. There was no statistically significant difference between the two types of tumor (p=0.264). These findings indicate that HIF-1alpha is elevated in both TM and GBM, suggesting that although hypoxia is one of the most important and powerful stimuli for HIF-1alpha elevation and consequently angiogenesis, other mechanisms may play roles in HIF-1alpha stimulation in benign brain tumors such as TM.

Gene expression profile analysis of primary glioblastomas and non-neoplastic brain tissue: identification of potential target genes by oligonucleotide microarray and real-time quantitative PCR

The prognosis of glioblastomas is still extremely poor and the discovery of novel molecular therapeutic targets can be important to optimize treatment strategies. Gene expression analyses comparing normal and neoplastic tissues have been used to identify genes associated with tumorigenesis and potential therapeutic targets. We have used this approach to identify differentially expressed genes between primary glioblastomas and non-neoplastic brain tissues. We selected 20 overexpressed genes related to cell cycle, cellular movement and growth, proliferation and cell-to-cell signaling and analyzed their expression levels by real time quantitative PCR in cDNA obtained from microdissected fresh tumor tissue from 20 patients with primary glioblastomas and from 10 samples of non-neoplastic white matter tissue. The gene expression levels were significantly higher in glioblastomas than in non-neoplastic white matter in 18 out of 20 genes analyzed: P < 0.00001 for CDKN2C, CKS2, EEF1A1, EMP3, PDPN, BNIP2, CA12, CD34, CDC42EP4, PPIE, SNAI2, GDF15 and MMP23b; and NFIA (P: 0.0001), GPS1 (P: 0.0003), LAMA1 (P: 0.002), STIM1 (P: 0.006), and TASP1 (P: 0.01). Five of these genes are located in contiguous loci at 1p31-36 and 2 at 17q24-25 and 8 of them encode surface membrane proteins. PDPN and CD34 protein expression were evaluated by immunohistochemistry and they showed concordance with the PCR results. The present results indicate the presence of 18 overexpressed genes in human primary glioblastomas that may play a significant role in the pathogenesis of these tumors and that deserve further functional investigation as attractive candidates for new therapeutic targets.

Time course of imaging changes of GBM during extended bevacizumab treatment

Glioblastoma multiforme (GBM) are morphologically heterogeneous tumors, with varying amounts of necrosis, and edema. Previous studies have shown that treatments incorporating the VEGF antibody bevacizumab can reduce edema and tumor burden in GBM. Additionally it has been suggested that bevacizumab regimen treatment reduces the percent of tumoral necrosis. Therefore we sought to (1) determine the time course of change in necrosis, tumor, and edema volume in patients who respond to bevacizumab regimen treatment and (2) determine if GBM that progress following a response to bevacizumab regimen treatment are morphologically different from their appearance at prior tumor progression. Therefore, we retrospectively assessed tumor, necrosis, and edema volumes on MRI scans from 15 patients with recurrent GBM who responded to bevacizumab regimen treatment, and had extended (>7 month) follow-up. We found that the median time to best tumor response was 158 days (range, 16-261, SD = 63). The median best response was 72.1% reduction in tumor volume and 72.8% reduction in peritumoral edema. Most tumors (77.8%) showed resolution of necrotic areas. The relative reduction of edema and necrosis was sustained, even in patients (n = 7) who developed tumor progression. Thus the mean ratio of edema-to-tumor volume at progression on bevacizumab regimen treatment was 38.4% lower than that for the same tumors seen on progression scans following prior chemotherapy. The percentage of necrotic tumor also was diminished following progression on bevacizumab regimen treatment. These findings illustrate the time course of changes in edema and tumor volume with prolonged bevacizumab regimen treatment, and support the conclusion that the morphology of recurrent GBM following bevacizumab regimen therapy is distinct from that on other chemotherapy.

Evaluation of HIF-1 inhibitors as anticancer agents

Hypoxia-inducible factor 1 (HIF-1) regulates the transcription of many genes involved in key aspects of cancer biology, including immortalization, maintenance of stem cell pools, cellular dedifferentiation, genetic instability, vascularization, metabolic reprogramming, autocrine growth factor signaling, invasion/metastasis, and treatment failure. In animal models, HIF-1 overexpression is associated with increased tumor growth, vascularization, and metastasis, whereas HIF-1 loss-of-function has the opposite effect, thus validating HIF-1 as a target. In further support of this conclusion, immunohistochemical detection of HIF-1alpha overexpression in biopsy sections is a prognostic factor in many cancers. A growing number of novel anticancer agents have been shown to inhibit HIF-1 through a variety of molecular mechanisms. Determining which combination of drugs to administer to any given patient remains a major obstacle to improving cancer treatment outcomes.

Expression of hypoxia-related tissue factors in astrocytic gliomas. A multivariate survival study with emphasis upon carbonic anhydrase IX

Carbonic anhydrase IX (CAIX) is a transmembrane enzyme involved in the reversible metabolism of carbon dioxide to carbonic acid and, hence, in physiological pH regulation. It also participates in cellular differentiation and proliferation, its expression being absent in most normal tissues. It has been recently postulated that the hypoxia-inducible factor (HIF-1) pathway up-regulated by hypoxia accounts for CAIX overexpression in most human tumors. In the present study, we examined the expression of this enzyme in diffuse gliomas of astrocytic origin in relation to vascular endothelial growth factor (VEGF) and HIF-1alpha expression, proliferation rate (as assessed with Ki-67 antigen), microvessel morphology, and survival. Of 84 cases analyzed, 61 cases (72.6%) displayed strong membrane and/or cytoplasmic expression of CAIX and were grouped as positive. Immunoreactivity tended to have a perinecrotic distribution and increased in parallel with the extent of necrosis (P < .001) and histologic grade (P < .001). A positive correlation was also noted with HIF-1alpha and VEGF expression (P < .001), proliferation rate (P = .010), microvessel density (P = .004), and microvessel caliber parameters (P = .014-.038). In univariate survival analysis, increased CAIX expression was associated with shortened survival in the entire cohort (P < .0001), along with VEGF (P = .0205) and HIF-1alpha levels (P = .0190). Multivariate analysis selected the interaction model of CAIX, with grade and age as the only parameters independently affecting survival. CAIX expression was also the only significant parameter for the survival of patients with grades II/III. We conclude that CAIX may be used as a prognostic indicator in diffuse astrocytomas to refine the information provided by grade. Given the role of CAIX in the acidification of tumor environment and its up-regulation by hypoxia, it is thought that CAIX expression may be linked to resistance of tumor cells to radiotherapy by allowing them to acclimatize to a hypoxic and acidic microenvironment.

Analysis of hypoxia-inducible factor 1alpha expression and its effects on invasion and metastasis

Hypoxia-inducible factor 1 (HIF-1) plays an important role in human cancer cell invasion and metastasis. As a result, overexpression of the HIF-1alpha subunit in biopsy specimens is associated with increased patient mortality in several common cancers, including breast adenocarcinoma and oropharyngeal squamous cell carcinoma. Here, we describe methods for immunohistochemical detection of HIF-1alpha in tumor biopsy sections and ex vivo assays for analyzing the effects of hypoxia and HIF-1 on cancer cell invasiveness and cell-cell adhesion.

Upregulation of frizzled 9 in astrocytomas

Wnt/frizzled (FZD) cascades play important roles in controlling cell fate, proliferation, migration, tissue architecture and organogenesis during embryonic development and in adult organisms. The potential involvement of this pathway in tumorigenesis has been established in several types of cancers. Frizzled 9 (FZD9) is expressed in brain and its aberrant expression in gastric cancer was observed. However, its association with astrocytomas remains unknown therefore we studied FZD9 expression in astrocytomas of different malignancy. In the present study, FZD9 expression in 25 astrocytomas was investigated using immunohistochemistry with specific antibodies. Further FZD9 expression in native human brain tissue and glioblastoma cell line were analysed using real-time reverse transcription polymerase chain reaction (RT-PCR). In human astrocytomas, FZD9 immunoreactivity (IR) was observed in both microvessels and neoplastic cells. The percentage of FZD9+ microvessels in relation to FZD9+ vessels was significantly higher in malignant astrocytomas than in low-grade astrocytomas and positively correlated with the astrocytoma World Health Organization (WHO) grading (r = 1, P = 0.04). Furthermore, the FZD9 IR scores positively correlated with astrocytoma WHO grading (r = 1, P = 0.04) and proliferating activity (r = 0.77, P < 0.001). Real-time RT-PCR data showed that FZD9 expression in human glioblastoma was significant higher than in normal brain (P < 0.05) but FZD9 expression was only slightly induced in cobalt chloride-treated human glioblastoma T98G cells compared with untreated cells (P > 0.05). FZD9 is upregulated in astrocytomas, suggesting that FZD9 could be important in the tumorigenesis of human astrocytomas.

Tumour vascularity is of prognostic significance in adult, but not paediatric astrocytomas

Astrocytomas are the commonest type of brain tumours in adults and children. Although the most reliable prognostic indicators have been shown consistently to be patient age and tumour histological grade, biological progression in these tumours is inevitable and the overall prognosis has remained poor. Due to the evidence that vascular changes are important histological features of astrocytomas, the aim of this study was to investigate prognostic significance of tumour vascularity in paediatric and adult astrocytomas. Study population consisted of 70 patients (45 adult and 25 children) with histologically proven diagnosis of astrocytoma with no history of previous therapy. Histological quantification of tumour vascularity was performed using three different methods: microvessel density, vascular grading and Chalkley counting. Histological classification and grading were also assessed using the World Health Organization system. In contrast to the results in paediatric astrocytomas, tumour vascularity in adult tumours correlated significantly with postoperative survival by univariate analysis (P < 0.05). Microvessel density appeared to be an independent indicator of prognosis by multivariate analysis (P = 0.001). Likewise, patients with microvessel density of 70 or greater had significantly shorter survival than the remaining group (P < 0.001). Patient age and tumour histological grade were also correlated with survival. We conclude that histological quantification of tumour vascularity is a significant prognosticator in adult astrocytomas, but not in children. Our data do not support the validity of applications of antiangiogenic agents in paediatric astrocytic tumours, particularly pilocytic astrocytomas.

Prognostic factors for anaplastic astrocytomas

Anaplastic astrocytomas (WHO grade III) constitute about 10% of all gliomas. Definitive data on predictive and prognostic factors are lacking for these neoplasms that are considered the most enigmatic entity among the whole spectrum of astrocytic tumors because of their unclear biologic behavior and variable clinical outcome. Currently, only few factors have been identified as useful for prognosis of anaplastic astrocytoma: age and Karnofsky Performance Status. Attempts have been made to identify biological prognostic factors for response to therapy and clinical outcome, as well as potential targets for new therapies. Potential prognostic biomarkers concern tumor suppressor genes on chromosome 9q that are involved in the RB1 pathway; PTEN, the PI3k/Akt/p70s6k cascade, survivin gene, Formylpeptide receptor, minichromosome maintenance protein 3 and genes on chromosome 7. Furthermore, some angiogenic factors (e.g. hypoxia-inducible factor-1alpha, vascular endothelial growth factor and scatter factor/hepatocyte growth factor) and the methylation status of O6-methylguanine-DNA methyltransferase gene (one of the main effectors of DNA repair system) are emerging novel putative determinants of prognosis. Moreover, recent studies on magnetic resonance imaging characteristics give prognostic significance to the presence of necrosis and enhancement. The state of the art pictured here underlie the recent interest on gene expression profile to identify aberrations useful to understand the biologic behavior of astrocytic tumors. Our knowledge in this field is still limited, and remains an issue of great concern.

Development of novel therapeutic strategies that target HIF-1

Activity of hypoxia-inducible factor 1 (HIF-1) is increased in human cancers as a result of the physiological induction of HIF-1alpha in response to intratumoural hypoxia and as a result of genetic alterations that activate oncogenes and inactivate tumour suppressor genes. In many cancer types, increased HIF-1alpha expression is associated with increased risk of patient mortality. HIF-1 plays important roles in every major aspect of cancer biology through the transcriptional regulation of hundreds of genes. The efficacy of many novel anticancer agents that target signal transduction pathways may be due in part to their indirect inhibition of HIF-1. Several novel compounds with anticancer activity have been shown to inhibit HIF-1 and may be useful as components of individualised multidrug therapeutic regimens chosen based on molecular analyses of tumour biopsies.

E2F1 identified by promoter and biochemical analysis as a central target of glioblastoma cell-cycle arrest in response to ras inhibition

Active Ras contributes to the malignant phenotype of glioblastoma multiforme. Recent studies showed that the Ras inhibitor farnesyl thiosalicylic acid downregulates the transcription factor hypoxia-inducible factor-1alpha, causing shutdown of glycolysis in U87 glioblastoma cells. Farnesyl thiosalicylic acid also inhibited the growth of U87 cells. The way in which Ras inhibition affects U87 cell proliferation was not clear. Here we applied a computational method in which gene expression profile clustering is combined with promoter sequence analysis to obtain global dissection of the transcriptional response to farnesyl thiosalicylic acid in U87 cells. The analysis revealed a prominent Ras-dependent cell-cycle arrest response, in which a major component is highly enriched for the binding-site signature of the transcription factor E2F1. Electrophoretic mobility shift assays together with E2F-luciferase reporter assays showed that E2F1 was inactivated by the Ras inhibitor. Inhibition of Ras by farnesyl thiosalicylic acid promoted proteasomal degradation of cyclin D1, with a concomitant decrease in phosphorylated retinoblastoma protein accompanied by downregulation of E2F1 and decreased expression of key E2F1-regulated genes critical for cell-cycle progression. U87 cell growth arrest induced by farnesyl thiosalicylic acid was overridden by constitutive expression of E2F1. Thus, downregulation of E2F1 and of hypoxia-inducible factor-1alpha represents 2 distinct arms of the antioncogenic effect of Ras inhibitors in glioblastoma.

Cyclooxygenase-2 expression in astrocytomas. Relationship with microvascular parameters, angiogenic factors expression and survival

OBJECTIVE

Cyclooxygenase-2 (COX-2) is the enzyme isoform involved in the synthesis of prostaglandins (PGs) and thromboxane from arachidonic acid. The role of the up-regulation of COX-2 in the formation and progression of gliomas has been dealt with in earlier reports, which describe increased levels of PGs within gliomas. In the present study, we examined the expression of COX-2 in diffuse gliomas of astrocytic origin in relation to microvascular parameters, angiogenic factors and survival.

MATERIALS AND METHODS

A total of 83 cases of diffuse astrocytomas (grade II-IV) were analyzed by immunohistochemistry for the presence of COX-2.

RESULTS

COX-2 expression was detected in 79 cases (95%) with an increased expression in grade IV as compared to grades II/III (p=0.024). A positive correlation occurred between COX-2 and angiogenic factors such as vascular endothelial growth factor (VEGF) (p<0.0001) and hypoxia inducible factor (HIF)-1alpha (p=0.005), as well as the tumours' proliferative activity (expressed as the percentage of Ki-67 positive cells) (p=0.032), and total vascular area (TVA) (p=0.040). In univariate analysis, COX-2 was associated with shortened survival (p = 0.050). Multivariate survival analysis showed that the interaction model of COX-2 with grade along with age were the only significant prognostic indicators.

CONCLUSION

These results implicate COX-2 in the angiogenesis and biological aggressiveness of diffuse astrocytomas, and suggest that it would be worthwhile to examine how the inhibition of COX-2 expression may influence astrocytoma patients' survival.

Effect of brain tumor neovasculature defined by rCBV on BOLD fMRI activation volume in the primary motor cortex

We utilized blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) and MR perfusion imaging methods to study the influence of brain tumor neovascularity on the BOLD fMRI activation volume in the primary motor cortex (PMC). The results from 57 brain tumor cases demonstrated that, for grade IV gliomas only, decreases in the BOLD fMRI activation volumes within the ipsilateral PMC, when compared with that observed in the contralateral PMC, correlated with increases in the relative regional cerebral blood volume (rCBV) in the PMC. In addition, relative increases in the activation volumes, corresponding to decreases in the rCBV, exhibited a linear dependence on the distance between the grade IV glioma and PMC. These findings lend support to the hypothesis that decreases in the fMRI activation volumes adjacent to a GBM may, in part, be due to the increased contribution of aberrant tumor neovascularity, with the resultant de-coupling of blood flow from neuronal activity. The nature of the relationship between the resulting activation volumes and adjacent tumor characteristics is complex, but is found to be dependent on the tumor grade and type, as well as the distance of the tumor to the PMC.

Regulation of angiogenesis by hypoxia-inducible factor 1

Hypoxia is an imbalance between oxygen supply and demand that occurs in cancer and in ischemic cardiovascular disease. Hypoxia-inducible factor 1 (HIF-1) was originally identified as the transcription factor that mediates hypoxia-induced erythropoietin expression. More recently, the delineation of molecular mechanisms of angiogenesis has revealed a critical role for HIF-1 in the regulation of angiogenic growth factors. In this review, we discuss the role of HIF-1 in developmental, adaptive and pathological angiogenesis. In addition, potential therapeutic interventions involving modulation of HIF-1 activity in ischemic cardiovascular disease and cancer will be discussed.

Inhibition of hypoxia inducible factor-1α (HIF-1α) decreases vascular endothelial growth factor (VEGF) secretion and tumor growth in malignant gliomas

INTRODUCTION

Hypoxia inducible factor-1alpha (HIF-1alpha) regulates vascular endothelial growth factor (VEGF), the presumed principal mediator of angiogenesis in malignant gliomas, under normal physiologic conditions. We examined the effect of HIF-1alpha on VEGF secretion, tumor growth, and angiogenesis in malignant gliomas.

METHODS

We examined 175 human gliomas for expression of HIF-1alpha and its downstream-regulated proteins. HIF-1alpha expression and VEGF secretion in glioma cell lines under normoxia and hypoxia were examined using ELISA and Western blot. Malignant glioma cell lines were transfected with dominant-negative HIF-1alpha (DN-HIF-1alpha) expression vector or siRNA constructs against the HIF-1alpha gene. Growth studies were conducted on cells with the highest VEGF/HIF-1alpha inhibition isolated from stable transfected cell lines. MIB-1-labeling index and microvascular density (MVD) measurements were performed on the in vivo tumors.

RESULTS

HIF-1 expression correlates with malignant glioma phenotype and was not confined to perinecrotic, pseudopalisading cells. VEGF and HIF-1 expression was high in glioma cell lines even under normoxia, and increased after exposure to hypoxia or growth factor stimulation. Cells transfected with DN-HIF-1alpha or HIF-1alpha siRNA demonstrated decreased HIF-1alpha and VEGF secretion. In vivo but not in vitro growth decreased in response to VEGF and HIF-1 inhibition. HIF-1 siRNA studies showed decreased VEGF secretion and in vitro and in vivo growth of glioma cell lines. MVD was unchanged but MIB-1 proliferation index decreased for both types of HIF-1 inhibition.

CONCLUSIONS

VEGF and HIF-1alpha are elevated in malignant gliomas. HIF-1alpha inhibition results in VEGF secretion inhibition. HIF-1alpha expression affects glioma tumor growth, suggesting clinical applications for malignant glioma treatment.

Tailoring Ras-pathway--inhibitor combinations for cancer therapy

Constitutive activation of Ras pathways plays a critical role in cancer development and maintenance. Inhibitors of such pathways are already in use for cancer therapy, with significant but as yet only partial success in the most deadly types of human cancers, against which even combinations of Ras-pathway inhibitors with classic cytotoxic drugs or irradiation are insufficient. Combinations of farnesyl transferase inhibitors (FTI's), inhibitors of Ras pathways, are now in use in clinical trials. In this review we analyze possible reasons for the limited efficacy--including the diverse and sometimes even contradictory effects of active Ras pathways in tumor cells--and propose possible alternative methods of tailoring Ras-pathway inhibitor combinations for cancer therapy. Such tailoring is now possible thanks to increased knowledge of the complexity of Ras pathways, their cooperation with other oncogenic pathways, and their "addictive" nature. We provide examples demonstrating that this knowledge can be translated into useful drug combinations that disrupt multiple oncogenic pathways and hit a weak point of a given tumor cell. One such example is combination treatment with a Ras inhibitor and a glycolysis blocker for pancreatic tumor cells. The future design of such potential drug combination therapies and the follow-up of their outcome will undoubtedly be facilitated by gene-expression profiling and proteomic methods.

Is the hypoxia-inducible factor pathway important in gastric cancer?

Tumour hypoxia is well recognised in oncology to be a key factor resulting in treatment resistance and poor prognosis. Hypoxia leads to the expression of a number of gene products that are involved in tumour progression, invasion and metastasis formation. The most important of these proteins is thought to be hypoxia-inducible factor-1alpha (HIF-1alpha), which appears to be a master regulator of the cellular response to hypoxia. HIF-1alpha expression is associated with a poor prognosis and treatment response in a number of tumour sites. There is some evidence that the HIF-1alpha pathway might be involved in gastric carcinogenesis. Studies have shown reactive oxygen species from Helicobacter pylori, associated with the development of gastric cancer, stabilise HIF-1alpha. Non-steroidal anti-inflammatory drugs, shown to reduce the risk of gastric cancer, can decrease HIF-1alpha expression. Although a large study correlating HIF-1alpha expression with prognosis is lacking in gastric cancer, the immunohistochemical expression of HIF-1alpha target genes (Glut-1, VEGF, CA9, iNOS) is associated with a poor prognosis. In addition, the targeted inhibition of HIF-1alpha has been shown to inhibit the growth of gastric tumours in animals. Increased understanding of the importance of hypoxia and the HIF-1alpha pathways may therefore hold the key to prevention strategies, improved selection of patients for adjuvant therapy and new treatments for the disease.

Hypoxia-inducible factor 1-alpha reduces infarction and attenuates progression of cardiac dysfunction after myocardial infarction in the mouse

OBJECTIVES

The aim of this research was to test whether constitutive expression of hypoxia-inducible factor 1-alpha (HIF-1alpha) influences infarction size and cardiac performance after myocardial infarction.

BACKGROUND

A major question in clinical medicine is whether infarction size and border zone remodeling of the heart can be influenced by the overexpression of specific genes in the peri-infarction region.

METHODS

We investigated the role of constitutive HIF-1alpha expression in acute myocardial infarction using a transgenic model. Transgenic mice containing the HIF-1alpha gene under the control of the alpha-myosin heavy chain promoter were constructed. Myocardial infarction was produced by coronary ligation in HIF-1alpha transgenic mice and control animals. Extent of infarction was then quantitated by two-dimensional and M-mode echocardiography as well as by molecular and pathologic analysis of heart samples in infarct, peri-infarct, and remote heart regions at serial time points.

RESULTS

Constitutive overexpression of HIF-1alpha in the murine heart resulted in attenuated infarct size and improved cardiac function 4 weeks after myocardial infarction. Significantly, we found an increase in both capillary density as well as vascular endothelial growth factor and inducible nitric oxide synthase expression in peri-infarct and infarct regions in the hearts of constitutive HIF-1alpha-expressing animals compared to control animals.

CONCLUSIONS

These observations suggest the involvement of HIF-1alpha in myocardial remodeling and peri-infarct vascularization. Our results show that supranormal amounts of this peptide protect against extension of infarction and improve border zone survival in myocardial infarction.

A reassessment of vascular endothelial growth factor in central nervous system pathology

✓ Overexpression of vascular endothelial growth factor (VEGF) is associated with several central nervous system (CNS) diseases and abnormalities, and is often postulated as a causative factor and promising therapeutic target in these settings. The authors' goal was to reassess the contribution of VEGF to the biology and pathology of the CNS.

The authors review the literature relating to the following aspects of VEGF: 1) the biology of VEGF in normal brain; 2) the involvement of VEGF in CNS disorders other than tumors (traumatic and ischemic injuries, arteriovenous malformations, inflammation); and 3) the role of VEGF in brain tumor biology (gliomas and the associated vasogenic edema, and hemangioblastomas).

The authors conclude the following: first, that VEGF overexpression contributes to the phenotype associated with many CNS disorders, but VEGF is a reactive rather than a causative factor in many cases; and second, that use of VEGF as a therapeutic agent or target is complicated by the effects of VEGF not only on the cerebral vasculature, but also on astrocytes, neurons, and inflammatory cells. In many cases, therapeutic interventions targeting the VEGF/VEGF receptor axis are likely to be ineffective or even detrimental. Clinical manipulation of VEGF levels in the CNS must be approached with caution.

Advances in the biology of astrocytomas

PURPOSE OF REVIEW

Conventional surgery, radio- and chemotherapy have failed to significantly improve the prognosis of patients with malignant astrocytomas--hence the need for understanding their molecular biology. Harvesting this understanding to yield novel biological targeted therapies has approached the clinical doorstep. Therapeutic efficacy will likely require combinatorial therapy involving biologicals and conventional therapies, with small incremental efficacy in selected sub-groups. This review highlights some of the findings over the past year (June 2003-2004) that have contributed to this slow but essential journey towards our understanding of the biology of astrocytomas.

RECENT FINDINGS

The accumulation of loss and/or gain of function molecular alterations underlying astrocytoma formation, progression and key growth parameters including proliferation, angiogenesis, apoptosis, invasion and resistance are emerging. These alterations involve those regulating the growth factor/receptor and downstream signaling networks, cell cycle, immune modulators and other key biological processes. The advances are facilitated by interactions amongst clinician and basic scientists, in both academia and industry. They have incorporated high-throughput bioinformatics analysis of genomic and expression array data, the emerging field of proteomics and development of various genetically engineered models of astrocytomas.

SUMMARY

Astrocytomas, like other cancers, are a result of several molecular alterations, some of which strongly correlate to their pathological grade. However, molecular heterogeneity exists between astrocytomas of similar grades and likely between varying micro-environmental regions of a single tumor. Characterization of the molecular signature of an astrocytoma and linking with the appropriate 'tailored' therapie(s) is the hope of the future.

Evaluation of hypoxia-inducible factor 1alpha overexpression as a predictor of tumour recurrence and progression in superficial urothelial bladder carcinoma

OBJECTIVES

To investigate the possible role of hypoxia-inducible factor 1alpha (HIF-1alpha, a transcription factor important in regulating O(2) homeostasis and physiological responses to oxygen deprivation) in the recurrence and progression of superficial urothelial bladder cancer, and to examine its expression in relation to proliferation status, apoptotic activity and intratumoral angiogenesis.

PATIENTS AND METHODS

Paraffin wax-embedded tissue from 140 patients with superficial primary urothelial bladder carcinoma was immunostained for HIF-1alpha, Ki-67, single-stranded DNA antibody for apoptotic cells, p53, bcl-2, vascular endothelial growth factor and CD31 antigen. We calculated the proliferative rate, the apoptotic index and the microvessel density (MVD). The mean (sem) follow-up was 46 (3.5) months, within which 86 patients relapsed while 18 progressed to a higher tumour stage and/or grade.

RESULTS

HIF-1alpha expression was more common in high-grade superficial urothelial carcinomas. The positivity was related to increased proliferative activity (P = 0.012), apoptotic rate (P = 0.006) and MVD (P < 0.001). HIF-1alpha overexpression had a marginal adverse influence on progression-free survival (P = 0.058; univariate analysis), but when combined with p53 overexpression, the unfavourable impact was statistically important (P = 0.028). In multivariate analysis, only grade and the high Ki-67 labelling index were significant predictors of recurrence-free survival, while T-stage and the HIF-1alpha+/p53+ phenotype emerged as the only independent variables of adverse prognostic significance for time to progression.

CONCLUSIONS

HIF-1alpha overexpression combined with aberrant mutant p53 nuclear protein accumulation seem to indicate an aggressive phenotype, suggesting a potential biological model predictive of future risk of disease progression in patients with superficial urothelial bladder carcinoma. These indicators may be helpful in clinical practice to discriminate superficial bladder cancer worth a more intensive follow-up, or more aggressive treatment.

Ras Inhibition in Glioblastoma Down-regulates Hypoxia-Inducible Factor-1α, Causing Glycolysis Shutdown and Cell Death

Active Ras and phosphatidylinositol-3-kinase–dependent pathways contribute to the malignant phenotype of glioblastoma multiformes (GBM). Here we show that the Ras inhibitor trans-farnesylthiosalicylic acid (FTS) exhibits profound antioncogenic effects in U87 GBM cells. FTS inhibited active Ras and attenuated Ras signaling to extracellular signal-regulated kinase, phosphatidylinositol-3-kinase, and Akt. Concomitantly, hypoxia-inducible factor 1α (HIF-1α) disappeared, expression of key glycolysis pathway enzymes and of other HIF-1α–regulated genes (including vascular endothelial growth factor and the Glut-1 glucose transporter) was down-regulated, and glycolysis was halted. This led to a dramatic reduction in ATP, resulting in a severe energy crisis. In addition, the expression of E2F-regulated genes was down-regulated in the FTS-treated cells. Consequently, U87 cell growth was arrested and the cells died. These results show that FTS is a potent down-regulator of HIF-1α and might therefore block invasiveness, survival, and angiogenesis in GBM.