The von Hippel-Lindau tumor suppressor gene product interacts with Sp1 to repress vascular endothelial growth factor promoter activity

Deciphering von Hippel-Lindau (VHL/Vhl)-associated pancreatic manifestations by inactivating Vhl in specific pancreatic cell populations

The von Hippel-Lindau (VHL) syndrome is a pleomorphic familial disease characterized by the development of highly vascularized tumors, such as hemangioblastomas of the central nervous system, pheochromocytomas, renal cell carcinomas, cysts and neuroendocrine tumors of the pancreas. Up to 75% of VHL patients are affected by VHL-associated pancreatic lesions; however, very few reports in the published literature have described the cellular origins and biological roles of VHL in the pancreas. Since homozygous loss of Vhl in mice resulted in embryonic lethality, this study aimed to characterize the functional significance of VHL in the pancreas by conditionally inactivating Vhl utilizing the Cre/LoxP system. Specifically, Vhl was inactivated in different pancreatic cell populations distinguished by their roles during embryonic organ development and their endocrine lineage commitment. With Cre recombinase expression directed by a glucagon promoter in alpha-cells or an insulin promoter in beta-cells, we showed that deletion of Vhl is dispensable for normal functions of the endocrine pancreas. In addition, deficiency of VHL protein (pVHL) in terminally differentiated alpha-cells or beta-cells is insufficient to induce pancreatic neuroendocrine tumorigenesis. Most significantly, we presented the first mouse model of VHL-associated pancreatic disease in mice lacking pVHL utilizing Pdx1-Cre transgenic mice to inactivate Vhl in pancreatic progenitor cells. The highly vascularized microcystic adenomas and hyperplastic islets that developed in Pdx1-Cre;Vhl f/f homozygous mice exhibited clinical features similar to VHL patients. Establishment of three different, cell-specific Vhl knockouts in the pancreas have allowed us to provide evidence suggesting that VHL is functionally important for postnatal ductal and exocrine pancreas, and that VHL-associated pancreatic lesions are likely to originate from progenitor cells, not mature endocrine cells. The novel model systems reported here will provide the basis for further functional and genetic studies to define molecular mechanisms involved in VHL-associated pancreatic diseases.

Use of the tyrosine kinase inhibitor sunitinib in a patient with von Hippel-Lindau disease: targeting angiogenic factors in pheochromocytoma and other von Hippel-Lindau disease-related tumors

CONTEXT

von Hippel-Lindau disease is characterized by highly vascularized tumors of multiple organs.

EVIDENCE ACQUISITION

We present a patient with von Hippel-Lindau disease with multiple renal and pancreatic tumors and a malignant pheochromocytoma infiltrative of the sacrum and associated with lymph nodule metastases. The pheochromocytoma expressed high protein level of vascular endothelial growth factor and platelet-derived growth factor-beta receptor. The patient presented with a poor performance status, severe pelvic pain, weight loss, and manifestations of catecholamine excess.

EVIDENCE SYNTHESIS

Treatment against malignant pheochromocytoma with surgery, chemotherapy, or participation in clinical trials was not feasible because of the patient's poor performance status, the presence of multiple tumors, and the extension of the pheochromocytoma into the bones. Patient was treated with sunitinib, a potent tyrosine kinase inhibitor of vascular endothelial growth factor, platelet-derived growth factor, RET, c-KIT, and FLT-3 receptors. Six months of treatment with sunitinib was associated with normalization of the patient's performance status and blood pressure, absence of symptoms of catecholamine excess, weight gain, disappearance of pain, shrinkage of each of the tumors (50% in the largest renal tumor, 38% in the largest islet cell tumor, 21% in the pelvic malignant pheochromocytoma), and reduction of plasma normetanephrines and chromogranin A.

CONCLUSION

This study provides evidence that targeting tyrosine kinase receptors such as the vascular endothelial growth factor pathway and the platelet-derived growth factor-beta receptor may have value in the treatment of VHL-related tumors including pheochromocytoma.

Transcriptional control of the tumor- and hypoxia-marker carbonic anhydrase 9: A one transcription factor (HIF-1) show?

Transcriptional activation by hypoxia is mediated by the hypoxia-inducible factor (HIF) via binding to the hypoxia-responsive element (HRE). Hypoxia in solid tumors associates with poorer outcome of the disease and reliable cellular markers of tumor hypoxia would represent a valuable diagnostic marker and a potential therapeutic target. In this category, carbonic anhydrase IX (CAIX) is one of the most promising candidates. Here, we summarize the knowledge about transcriptional regulation of CA9. The HRE is the central regulatory element in the CA9 promoter, whereas other elements are limited to lesser roles of amplification of signals received at the HRE. The analysis of known mechanisms of activation of CA9 reveals the prominent role of the HIF-1 pathway. Experimental paradigms with uncoupled HIF-1alpha stability and transcriptional activity (pericellular hypoxia, proteasomal inhibitor) provide evidence that CA9 expression monitors transcriptional activity of HIF-1, rather than the abundance of HIF-1alpha. Furthermore, these paradigms could provide a corollary to some of the apparently discordant cases (CAIX+, HIF-1alpha-) or (CAIX-, HIF-1alpha+) observed in vivo. In conclusion, the existing data support the notion that CA9, due to the unique structure of its promoter, is one of the most sensitive endogenous sensors of HIF-1 activity.

Deletion of the von Hippel-Lindau gene in pancreatic beta cells impairs glucose homeostasis in mice

Defective insulin secretion in response to glucose is an important component of the beta cell dysfunction seen in type 2 diabetes. As mitochondrial oxidative phosphorylation plays a key role in glucose-stimulated insulin secretion (GSIS), oxygen-sensing pathways may modulate insulin release. The von Hippel-Lindau (VHL) protein controls the degradation of hypoxia-inducible factor (HIF) to coordinate cellular and organismal responses to altered oxygenation. To determine the role of this pathway in controlling glucose-stimulated insulin release from pancreatic beta cells, we generated mice lacking Vhl in pancreatic beta cells (betaVhlKO mice) and mice lacking Vhl in the pancreas (PVhlKO mice). Both mouse strains developed glucose intolerance with impaired insulin secretion. Furthermore, deletion of Vhl in beta cells or the pancreas altered expression of genes involved in beta cell function, including those involved in glucose transport and glycolysis, and isolated betaVhlKO and PVhlKO islets displayed impaired glucose uptake and defective glucose metabolism. The abnormal glucose homeostasis was dependent on upregulation of Hif-1alpha expression, and deletion of Hif1a in Vhl-deficient beta cells restored GSIS. Consistent with this, expression of activated Hif-1alpha in a mouse beta cell line impaired GSIS. These data suggest that VHL/HIF oxygen-sensing mechanisms play a critical role in glucose homeostasis and that activation of this pathway in response to decreased islet oxygenation may contribute to beta cell dysfunction.

The von Hippel-Lindau tumour suppressor protein: O2 sensing and cancer

The von Hippel-Lindau disease is caused by inactivating germline mutations of the VHL tumour suppressor gene and is associated with an increased risk of a variety of tumours in an allele-specific manner. The role of the heterodimeric transcription factor hypoxia-inducible factor (HIF) in the pathogenesis of VHL-defective tumours has been more firmly established during the past 5 years. In addition, there is now a greater appreciation of HIF-independent VHL functions that are relevant to tumour development, including maintenance of the primary cilium, regulation of extracellular matrix formation and turnover, and modulation of cell death in certain cell types following growth factor withdrawal or in response to other forms of stress.

Central role of Sp1-regulated CD39 in hypoxia/ischemia protection

Hypoxia is common to several inflammatory diseases, where multiple cell types release adenine-nucleotides (particularly adenosine triphosphate/adenosine diphosphate). Adenosine triphosphate/adenosine diphosphate is metabolized to adenosine through a 2-step enzymatic reaction initiated by CD39 (ectonucleoside-triphosphate-diphosphohydrolase-1). Thus, extracellular adenosine becomes available to regulate multiple inflammatory endpoints. Here, we hypothesized that hypoxia transcriptionally up-regulates CD39 expression. Initial studies revealed hypoxia-dependent increases in CD39 mRNA and immunoreactivity on endothelia. Examination of the human CD39 gene promoter identified a region important in hypoxia inducibility. Multiple levels of analysis, including site-directed mutagenesis, chromatin immunoprecipitation, and inhibition by antisense, revealed a critical role for transcription-factor Sp1 in hypoxia-induction of CD39. Using a combination of cd39(-/-) mice and Sp1 small interfering RNA in in vivo cardiac ischemia models revealed Sp1-mediated induction of cardiac CD39 during myocardial ischemia. In summary, these results identify a novel Sp1-dependent regulatory pathway for CD39 and indicate the likelihood that CD39 is central to protective responses to hypoxia/ischemia.

Current insights on the biology and clinical aspects of VEGF regulation

Vascular endothelial growth factor (VEGF) is a key molecule that orchestrates the formation and function of vascular networks. Impaired regulation of angiogenesis is implicated in a number of pathologic states. For instance, neoplasias exhibit uncontrolled angiogenesis, whereas ischemia and states of vascular insufficiency involve reduced VEGF activity. As the role of VEGF has been elucidated in these disease processes, its therapeutic role has been developed. The Food and Drug Administration has approved several anti-VEGF agents for treating colorectal, lung, and kidney cancer. VEGF-inducing agents have also been used experimentally to induce angiogenesis in patients with critical limb ischemia. As more knowledge is gathered about the biology of VEGF and its receptors, there is greater promise for therapeutic modulation of VEGF expression. The purpose of this review is to describe the various therapeutic and biologic factors that regulate the expression of VEGF.

Overexpression of vascular endothelial growth factor and the development of post-transplantation cancer

Cancer is an increasing and major problem after solid organ transplantation. In part, the increased cancer risk is associated with the use of immunosuppressive agents, especially calcineurin inhibitors. We propose that the effect of calcineurin inhibitors on the expression of vascular endothelial growth factor (VEGF) leads to an angiogenic milieu that favors tumor growth. Here, we used 786-0 human renal cancer cells to investigate the effect of cyclosporine (CsA) on VEGF expression. Using a full-length VEGF promoter-luciferase construct, we found that CsA markedly induced VEGF transcriptional activation through the protein kinase C (PKC) signaling pathway, specifically involving PKC zeta and PKC delta isoforms. Moreover, CsA promoted the association of PKC zeta and PKC delta with the transcription factor Sp1 as observed by immunoprecipitation assays. Using promoter deletion constructs, we found that CsA-mediated VEGF transcription was primarily Sp1 dependent. Furthermore, CsA-induced and PKC-Sp1-mediated VEGF transcriptional activation was partially inhibited by von Hippel-Lindau protein. CsA also promoted the progression of human renal tumors in vivo, wherein VEGF is overexpressed. Finally, to evaluate the in vivo significance of CsA-induced VEGF overexpression in terms of post-transplantation tumor development, we injected CT26 murine carcinoma cells (known to form angiogenic tumors) into mice with fully MHC mismatched cardiac transplants. We observed that therapeutic doses of CsA increased tumor size and VEGF mRNA expression and also enhanced tumor angiogenesis. However, coadministration of a blocking anti-VEGF antibody inhibited this CsA-mediated tumor growth. Collectively, these findings define PKC-mediated VEGF transcriptional activation as a key component in the progression of CsA-induced post-transplantation cancer.

Kruppel-like factor 5 is required for perinatal lung morphogenesis and function

The transition to air breathing after birth requires both anatomic and biochemical maturation of the lung. Lung morphogenesis is mediated by complex paracrine interactions between respiratory epithelial cells and mesenchymal cells that direct transcriptional programs guiding patterning and cytodifferentiation of the lung. In the present study, transgenic mice were generated in which the Kruppel-like factor 5 gene (Klf5) was conditionally deleted in respiratory epithelial cells in the fetal lung. Lack of KLF5 inhibited maturation of the lung during the saccular stage of development. Klf5(Delta/Delta) mice died of respiratory distress immediately after birth. Abnormalities in lung maturation and morphogenesis were observed in the respiratory epithelium, the bronchiolar smooth muscle, and the pulmonary vasculature. Respiratory epithelial cells of both the conducting and peripheral airways were immature. Surfactant phospholipids were decreased and lamellar bodies, the storage form of surfactant, were rarely found. mRNA microarray analysis demonstrated that KLF5 influenced the expression of genes regulating surfactant lipid and protein homeostasis, vasculogenesis, including Vegfa, and smooth muscle cell differentiation. KLF5 regulates genes controlling paracrine interactions during lung morphogenesis, as well as those regulating the maturation of the respiratory epithelium that is required for lung function after birth.

CUL2 is required for the activity of hypoxia-inducible factor and vasculogenesis

CULLIN 2 (CUL2) is a component of the ElonginB/C-CUL2-RBX-1-Von Hippel-Lindau (VHL) tumor suppressor complex that ubiquitinates and degrades hypoxia-inducible factor alpha (HIFalpha). HIFalpha is a transcription factor that mediates the expression of hypoxia-sensitive genes, including vascular endothelial growth factor (VEGF), which in turn regulates vasculogenesis. Whereas CUL2 participates in the degradation of HIFalpha, the potential role of CUL2 in the regulation of other cellular processes is less well established. In the present study, suppression of CUL2 expression by Cul2 siRNA inhibited HIFalpha transcriptional activation of the VEGF gene in vitro, indicating that CUL2 plays a role distinct from its known function in HIFalpha degradation. Because ARNT heterodimerizes with HIFalpha, we assessed whether CUL2 influenced ARNT expression. Cul2 siRNA inhibited the expression of endogenous ARNT. Ectopically expressed ARNT reversed the inhibition of HIF activity by Cul2 siRNA in the VEGF promoter, suggesting that CUL2 regulates HIF activation through ARNT. In 786-O cells lacking VHL, Cul2 siRNA suppressed the expression of both ARNT and VEGF, indicating that CUL2 regulates HIF activity independently of VHL. In transgenic zebrafish expressing GFP driven by the Flk promoter (a known HIF target), zCul2 morpholino blocked embryonic vasculogenesis in a manner similar to that caused by inhibition of VEGF-A. In the zebrafish embryos, zCul2 inhibited the expression of CUL2, VEGF, and Flk-GFP protein, indicating that CUL2 is required for expression of other vasculogenic HIF targets. Taken together, CUL2 is required for normal vasculogenesis, at least in part mediated by its regulation of HIF-mediated transcription.

Evaluation of a series of naphthamides as potent, orally active vascular endothelial growth factor receptor-2 tyrosine kinase inhibitors

We have previously shown N-arylnaphthamides can be potent inhibitors of vascular endothelial growth factor receptors (VEGFRs). N-Alkyl and N-unsubstituted naphthamides were prepared and found to yield nanomolar inhibitors of VEGFR-2 (KDR) with an improved selectivity profile against a panel of tyrosine and serine/threonine kinases. The inhibitory activity of this series was retained at the cellular level. Naphthamides 3, 20, and 22 exhibited good pharmacokinetics following oral dosing and showed potent inhibition of VEGF-induced angiogenesis in the rat corneal model. Once-daily oral administration of 22 for 14 days led to 85% inhibition of established HT29 colon cancer and Calu-6 lung cancer xenografts at doses of 10 and 20 mg/kg, respectively.

Beyond the hypoxia-inducible factor-centric tumour suppressor model of von Hippel-Lindau

PURPOSE OF REVIEW

To provide an overview of the recent advances in the understanding of the molecular mechanisms governing the tumour suppressor functions of the von Hippel-Lindau protein.

RECENT FINDINGS

von Hippel-Lindau is a vital component of an E3 ubiquitin ligase complex involved in the oxygen-dependent targeting of hypoxia-inducible factor for ubiquitin-mediated destruction. Recent reports have linked von Hippel-Lindau to the regulation of diverse biological processes including cell adhesion, extracellular matrix assembly and ciliogenesis in a manner dependent and/or independent of hypoxia-inducible factor.

SUMMARY

The tumour suppressor function of von Hippel-Lindau has remained hypoxia-inducible factor-centric since the discovery of von Hippel-Lindau as a bona fide negative regulator of the ubiquitous oxygen-sensing pathway. Emerging evidence supports this hypothesis with the elucidation of fundamental cellular processes deregulated upon the inactivation of the von Hippel-Lindau-hypoxia-inducible factor pathway, but has also proved compelling on the hypoxia-inducible factor-independent tumour suppressor role of von Hippel-Lindau. These and continuing studies into the molecular pathways and mechanisms governing the tumour suppressor functions of von Hippel-Lindau will ultimately afford new avenues for anticancer strategies for the improved treatment of a diverse array of cancers.

Predicting outcome to VEGF-targeted therapy in metastatic clear-cell renal cell carcinoma: data from recent studies

Attempts to predict outcome in patients with metastatic clear-cell renal cell carcinoma (RCC) have conventionally been based on pretherapy clinical factors such as performance status, disease-free interval, number of metastatic sites and several laboratory variables. These factors were developed before the era of VEGF-targeted therapy. Recent analysis from trials with anti-VEGF agents indicate that these factors continue to be of major importance in patient prognostication. Additionally, several serum and molecular markers, many of which relate to certain alterations of the von Hippel-Lindau pathway, are currently being investigated. Responses to VEGF-targeted agents appear to be related to a greater modulation of serum VEGF and soluble VEGF receptor levels. The impact of von Hippel-Lindau gene status on response to VEGF-targeted therapy was tested in a large study and was not found to predict a higher response rate to these agents. However, a subset of von Hippel-Lindau mutations that predict a 'loss of function' of the von Hippel-Lindau gene seem to have the best response to these agents. Future prognostic models will incorporate molecular markers with clinical variables to refine prognosis and prediction in metastatic clear-cell RCC patients treated with novel VEGF-targeted agents. These models, if externally and prospectively validated, will culminate in the rational selection of patients for specific VEGF-directed therapeutics.

Therapeutic inhibition of Sp1 expression in growing tumors by mithramycin a correlates directly with potent antiangiogenic effects on human pancreatic cancer

BACKGROUND

Human pancreatic cancer over expresses the transcription factor Sp1. However, the role of Sp1 in pancreatic cancer angiogenesis and its use as target for antiangiogenic therapy remain unexplored.

METHODS

Archived human pancreatic cancer specimens were used to assess gene expression and microvessel density (MVD) status by immunohistochemistry: Small-interfering RNA (siRNA) was used to determine the impact of altered Sp1 expression on tumor growth and angiogenesis, and mithramycin A (MIT) was used to evaluate Sp1-targeted antiangiogenic treatment of human pancreatic cancer in animal models.

RESULTS

The expression level of Sp1 was correlated directly with the MVD status (P < .001) and the expression level of vascular endothelial growth factor (VEGF) (P < .05). Knockdown of Sp1 expression did not affect the growth of pancreatic cancer cells in vitro but inhibited their growth and metastasis in mouse models. This antitumor activity was consistent with the in vitro and in vivo antiangiogenic activity resulting from Sp1 knockdown. Subcutaneous and intraperitoneal injection of MIT significantly suppressed the growth of human pancreatic cancer in mouse models. This tumor suppression was correlated with the suppression of Sp1 expression in growing tumors but not in normal tissues. Moreover, treatment with MIT reduced tumor MVD, which was consistent with the down-regulation of VEGF, platelet-derived growth factor, and epidermal growth factor receptor.

CONCLUSIONS

Both clinical and experimental evidence indicated that Sp1 is a critical regulator of human pancreatic cancer angiogenesis and the antitumor activity of MIT is a result, at least in part, of the suppression of Sp1 expression and consequent down-regulation the downstream targets of Sp1 that are key to angiogenesis.

Clinical factors associated with outcome in patients with metastatic clear-cell renal cell carcinoma treated with vascular endothelial growth factor-targeted therapy

BACKGROUND

Therapy targeted against the vascular endothelial growth factor (VEGF) pathway is a standard of care for patients with metastatic renal cell carcinoma (RCC). The identification of patients who are more likely to benefit from these agents is warranted.

METHODS

In total, 120 patients with metastatic clear-cell RCC received bevacizumab, sorafenib, sunitinib, or axitinib on 1 of 9 prospective clinical trials at the Cleveland Clinic. Clinical features associated with outcome were identified by univariate analysis; then, a stepwise modeling approach based on Cox proportional hazards regression was used to identify independent prognostic factors and to form a model for progression-free survival (PFS). A bootstrap algorithm was used to provide internal validation.

RESULTS

The overall median PFS was 13.8 months, and the objective response according to the Response Criteria in Solid Tumors was 34%. Multivariate analysis identified time from diagnosis to current treatment <2 years; baseline platelet and neutrophil counts >300 K/microL and >4.5 K/microL, respectively; baseline corrected serum calcium <8.5 mg/dL or >10 mg/dL; and initial Eastern Cooperative Oncology Group performance status >0 as independent, adverse prognostic factors (PF) for PFS. Three prognostic subgroups were formed based on the number of adverse prognostic factors present. The median PFS in patients with 0 or 1 adverse prognostic factor was 20.1 months compared with 13 months in patients with 2 adverse prognostic factors and 3.9 months in patients with >2 adverse prognostic factors.

CONCLUSIONS

Five independent prognostic factors for predicting PFS were identified and were used to categorize patients with metastatic RCC who received VEGF-targeted therapies into 3 risk groups. These prognostic factors can be incorporated into patient care and clinical trials that use such novel, VEGF-targeted agents.

Vascular endothelial growth factor in astroglioma stem cell biology and response to therapy

Malignant astrogliomas are among the most aggressive, highly vascular and infiltrating tumours bearing a dismal prognosis, mainly due to their resistance to current radiation treatment and chemotherapy. Efforts to identify and target the mechanisms that underlie astroglioma resistance have recently focused on candidate cancer stem cells, their biological properties, interplay with their local microenvironment or 'niche', and their role in tumour progression and recurrence. Both paracrine and autocrine regulation of astroglioma cell behaviour by locally produced cytokines such as the vascular endothelial growth factor (VEGF) are emerging as key factors that determine astroglioma cell fate. Here, we review these recent rapid advances in astroglioma research, with emphasis on the significance of VEGF in astroglioma stem-like cell biology. Furthermore, we highlight the unique DNA damage checkpoint properties of the CD133-marker-positive astroglioma stem-like cells, discuss their potential involvement in astroglioma radioresistance, and consider the implications of this new knowledge for designing combinatorial, more efficient therapeutic strategies.

Repression of Vascular Endothelial Growth Factor Expression by the Zinc Finger Transcription Factor ZNF24

Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis. Although many positive regulators of VEGF have been identified, relatively little is known regarding the negative regulation of VEGF expression. We identified a zinc finger transcription factor, ZNF24, that may repress VEGF transcription. An inverse correlation between expression of VEGF and ZNF24 was observed in a series of independent studies. ZNF24 was up-regulated in angiogenic tumor nodules where VEGF expression is significantly decreased compared with preangiogenic nodules. In human breast carcinoma cells cultured under normoxic conditions, ZNF24 levels were significantly up-regulated whereas VEGF levels were low. In contrast, VEGF was significantly increased in hypoxic cells whereas ZNF24 was down-regulated. The same inverse correlation between ZNF24 and VEGF was also observed in 70% of matched cDNA pairs of normal and malignant tissues from human colon and breast biopsies. Overexpression of ZNF24 resulted in a significant down-regulation of VEGF, whereas silencing of ZNF24 with small interfering RNA led to increased VEGF expression. Cotransfection of ZNF24 and a VEGF promoter luciferase reporter construct in MDA-MB-231 cells resulted in a significant decrease in VEGF promoter activity. Taken together, these data suggest that ZNF24 is involved in negative regulation of VEGF and may represent a novel repressor of VEGF transcription.

Expression of VACM-1/cul5 mutant in endothelial cells induces MAPK phosphorylation and maspin degradation and converts cells to the angiogenic phenotype

Vasopressin-activated calcium mobilizing receptor (VACM-1) is a member of the cullin gene family involved in ubiquitin-proteosome dependent regulation of cellular functions. Expression of VACM-1 cDNA in cos-1 cells in vitro decreases basal cAMP levels and inhibits growth. The expression of (S730A)VACM-1 mutant cDNA, which removes PKA-dependent phosphorylation site in the VACM-1 cDNA sequence, reverses this phenotype. Since the expression of VACM-1 protein in vivo localizes largely to the vascular endothelial cells, in this study, we examined the effects of (S730A)VACM-1 cDNA expression on cellular signaling in the rat endothelial cell line RAMEC. Our results indicate that expression of (S730A)VACM-1 cDNA in RAMEC promotes cellular proliferation and induces angiogenic growth patterns. Western blot analyses indicate that (S730A)VACM-1 cDNA transfected cells express increased levels of Nedd8 modified VACM-1 and have higher levels of phosphorylated MAPK protein when compared to controls. Furthermore, expression of (S730A)VACM-1 cDNA induces translocation of the endogenous early response gene, egr-1, to the nucleus and leads to morphological changes that involve actin rearrangement. Finally, expression of (S730A)VACM-1 cDNA in RAMEC decreases concentration of maspin, a putative anti-angiogenic factor with a tumor suppressor activity. These results show that VACM-1 protein regulates endothelial cell growth and may modulate angiogenesis by a mechanism that involves MAPK phosphorylation, nuclear localization of egr-1, maspin expression, and actin polymerization.

Molecular basis of the synergistic antiangiogenic activity of bevacizumab and mithramycin A

The impact of antiangiogenic therapy on the Sp1/vascular endothelial growth factor (VEGF) pathway and that of alteration of Sp1 signaling on the efficacy of antiangiogenic therapy is unclear, yet understanding their interactions has significant clinical implications. Treatment with bevacizumab, a neutralizing antibody against VEGF, suppressed human pancreatic cancer growth in nude mice. Gene expression analyses revealed that this treatment substantially up-regulated the expression of Sp1 and its downstream target genes, including VEGF and epidermal growth factor receptor, in tumor tissues, whereas it did not have this effect on pancreatic cancer cells in culture. Treatment with mithramycin A, an Sp1 inhibitor, suppressed the expression of Sp1 and its downstream target genes in both cell culture and tumors growing in nude mice. Combined treatment with bevacizumab and mithramycin A produced synergistic tumor suppression, which was consistent with suppression of the expression of Sp1 and its downstream target genes. Thus, treatment with bevacizumab may block VEGF function but activate the pathway of its expression via positive feedback. Given the fact that Sp1 is an important regulator of the expression of multiple angiogenic factors, bevacizumab-initiated up-regulation of Sp1 and subsequent overexpression of its downstream target genes may profoundly affect the potential angiogenic phenotype and effectiveness of antiangiogenic strategies for human pancreatic cancer. Therefore, this study is the first to show the significance and clinical implications of alteration of Sp1 signaling in antiangiogenic therapy for pancreatic cancer and other cancers.

Autocrine VEGF loops, signaling pathways, and acute leukemia regulation

Data obtained from animal models, and partially confirmed in pre-clinical studies, have provided clear evidence of the importance of angiogenesis for the growth of solid tumors. Similarly, in hematological cancers such as leukemias and lymphomas, the role of angiogenesis has been under intense scrutiny. However, the molecular singularities of leukemia, namely its cellular origin, have suggested a putative role for angiogenesis in these tumors may have distinct features. We and others have shown acute leukemia cells use angiogenic growth factor signaling pathways, namely those activated by vascular endothelial growth factor (VEGF) in autocrine and paracrine fashion. Autocrine and paracrine VEGF stimulation of subsets of leukemias results in cell proliferation, increased survival and migration. This review discusses recent advances in the field of leukemia angiogenesis, focusing on the role of VEGF and its receptors, acting in a paracrine or autocrine manner. We also briefly describe some of the novel anti-angiogenic compounds, namely VEGF blockers, and suggest their use to treat subsets of hematological malignancies may have clinical benefit.

Elevated expression of vascular endothelial growth factor correlates with increased angiogenesis and decreased progression-free survival among patients with low-grade neuroendocrine tumors

BACKGROUND

Vascular endothelial growth factor (VEGF) is a critical proangiogenic factor in solid tumors. However, its expression and role in human neuroendocrine tumor development and progression remains unclear.

METHODS

Using immunohistochemistry, VEGF and Sp1 expression patterns were investigated in 50 cases of human gastrointestinal neuroendocrine tumor having various clinicopathologic characteristics.

RESULTS

It was found that strong VEGF expression was detected in tumor cells, whereas no or very weak VEGF expression was detected in stromal cells surrounding or within the tumors. The levels of VEGF expression directly correlated with the expression levels of Sp1 and microvessel density. Strong, weak, and negative VEGF expression was observed in 32%, 54%, and 14% of cases, respectively. Compared with the group with negative VEGF expression, VEGF (weak/strong) expression was associated with metastasis (14% versus 58%; P = .03). The median progression-free survival (PFS) durations of patients with strong and weak VEGF expression were 29 months and 81 months, respectively. With a median follow-up duration of 50 months, the median PFS duration for the group with negative VEGF expression has not been reached. Compared with the log-rank test, VEGF expression was associated with poor PFS (P = .02). Using in vitro and in vivo models, human carcinoid cell lines were treated with bevacizumab, a monoclonal antibody targeting VEGF. Bevacizumab did not inhibit the growth of carcinoid cells in vitro but significantly reduced tumor angiogenesis and impaired tumor growth in animals.

CONCLUSIONS

The data suggest that overexpression of VEGF promotes the growth of human neuroendocrine tumors in part through up-regulation of angiogenesis.

CXCR4/CXCL12 axis promotes VEGF-mediated tumor angiogenesis through Akt signaling pathway

CXC chemokine receptor 4 (CXCR4) has been shown to play a critical role in chemotaxis and homing, which are key steps in cancer metastasis. There is also increasing evidence that links this receptor to angiogenesis; however, its molecular basis remains elusive. Vascular endothelial growth factor (VEGF), one of the major angiogenic factors, promotes the formation of leaky tumor vasculatures that are the hallmarks of tumor progression. Here, we investigated whether CXCR4 induces the expression of VEGF through the PI3K/Akt pathway. Our results showed that CXCR4/CXCL12 induced Akt phosphorylation, which resulted in upregulation of VEGF at both the mRNA and protein levels. Conversely, blocking the activation of Akt signaling led to a decrease in VEGF protein levels; blocking CXCR4/CXCL12 interaction with a CXCR4 antagonist suppressed tumor angiogenesis and growth in vivo. Furthermore, VEGF mRNA levels correlated well with CXCR4 mRNA levels in patient tumor samples. In summary, our study demonstrates that the CXCR4/CXCL12 signaling axis can induce angiogenesis and progression of tumors by increasing expression of VEGF through the activation of PI3K/Akt pathway. Our findings suggest that targeting CXCR4 could provide a potential new anti-angiogenic therapy to suppress the formation of both primary and metastatic tumors.

Transcriptional Control of the HumanHigh Mobility Group A1Gene: Basal and Oncogenic Ras-Regulated Expression

Several studies have already shown that the high mobility group A1 (HMGA1) gene is up-regulated in most common types of cancer and immortalized tissue culture cell lines. HMGA1 expression is also much higher during embryonic development than in adult life. The elevated expression of HMGA1 in cancer thus likely occurs through oncofetal transcriptional mechanisms, which to date have not been well characterized. In the present study, we have cloned and functionally analyzed the TATA-less 5'-flanking regulatory region of human HMGA1. We identified two proximal regulatory regions that are important for basal transcription and in which specificity protein 1 (SP1) and activator protein 1 (AP1) transcription factors seem to be the regulating elements. In addition, we showed that the HMGA1 promoter is strongly inducible by oncogenic Ras, via a distal regulatory region. An AP1 site and three SP1-like sites are responsible for this inducible activity. An even more convincing finding for a role of oncogenic Ras in the regulation of HMGA1 in cancers is the discovery that HMGA1 up-regulation in the HCT116 colon cancer cell line is abolished when the mutated Ras allele is removed from these cells. Our data constitute the first extensive study of the regulation of basal and Ras-induced human HMGA1 gene expression and suggest that the elevated expression of HMGA1 in cancer cells requires, among others, a complex cooperation between SP1 family members and AP1 factors by the activation of Ras GTPase signaling.

The VHL tumor suppressor inhibits expression of the IGF1R and its loss induces IGF1R upregulation in human clear cell renal carcinoma

Clear cell renal cell cancer (CC-RCC) is a highly chemoresistant tumor characterized by frequent inactivation of the von Hippel-Lindau (VHL) gene. The prognosis is reportedly worse in patients whose tumors express immunoreactive type I insulin-like growth factor receptor (IGF1R), a key mediator of tumor cell survival. We aimed to investigate how IGF1R expression is regulated, and found that IGF1R protein levels were unaffected by hypoxia, but were higher in CC-RCC cells harboring mutant inactive VHL than in isogenic cells expressing wild-type (WT) VHL. IGF1R mRNA and promoter activities were significantly lower in CC-RCC cells expressing WT VHL, consistent with a transcriptional effect. In Sp1-null Drosophila Schneider cells, IGF1R promoter activity was dependent on exogenous Sp1, and was suppressed by full-length VHL protein (pVHL) but only partially by truncated VHL lacking the Sp1-binding motif. pVHL also reduced the stability of IGF1R mRNA via sequestration of HuR protein. Finally, IGF1R mRNA levels were significantly higher in CC-RCC biopsies than benign kidney, confirming the clinical relevance of these findings. Thus, we have identified a new hypoxia-independent role for VHL in suppressing IGF1R transcription and mRNA stability. VHL inactivation leads to IGF1R upregulation, contributing to renal tumorigenesis and potentially also to chemoresistance.

Non-myeloablative allogeneic stem cell transplantation for metastatic renal cell carcinoma

Between 1999 and 2004, 11 patients with metastatic renal cell carcinoma (RCC) underwent non-myeloablative stem cell transplantation (NST) with conditioning using fludarabine-based regimens in two institutions of Korea. Among 11 patients, only one patient showed partial response (response rate: 9%), three showed stable disease, and six progressive disease. Three patients developed acute graft-versus-host disease (GVHD), and among them, one developed grade III acute GVHD which caused early death at day 60 after transplantation, and this patient showed partial response at day 30. Six patients developed chronic GVHD, three limited, and three extensive GVHD, respectively. Survival after one yr was 18% in transplanted patients. Median overall survival for entire cohort was 4.3 months. Eight patients died from progressive disease and three (27%) from treatment-related mortality. Only one patient survived 51.2 months after NST with slowly progressive disease. This patient received donor lymphocyte infusion three times after NST and achieved complete donor chimerism. NST does not lead to durable response and prolonged overall survival in the majority of patients with RCC in our series.

Opportunities and obstacles to combination targeted therapy in renal cell cancer

The treatment of advanced renal cell carcinoma (RCC) has undergone a major change with the development of potent angiogenesis inhibitors and targeted agents. Several multitargeted tyrosine kinase inhibitors, sorafenib and sunitinib, have already been approved for the treatment of advanced RCC. Temsirolimus (CCI-779), a mammalian target of rapamycin inhibitor, has shown a survival advantage over IFN in advanced, poor-prognosis RCC patients. Bevacizumab, an antibody targeting vascular endothelial growth factor (VEGF) A, has also shown promising clinical activity. Benefits attributable to these agents have been recognized by high objective response rates (sunitinib), significant increases in progression-free survival (sunitinib, sorafenib and bevacizumab), or improved overall survival (temsirolimus). These agents mediate much of their effect through inhibition of the hypoxia-inducible factor (HIF)-VEGF-VEGF receptor axis. Their inhibitory activity for the signaling of platelet-derived growth factor (PDGF) receptor beta or kinases like c-Raf may contribute to the antitumor effects of the multitargeted kinase inhibitors. Nevertheless, all four single agents rarely, if ever, induce complete responses and, at present, all patients develop resistance and, ultimately, progress during therapy. A critical need exists to develop strategies that may increase the degree of the antitumor effects with the hope of inducing more complete responses impeding the onset of or elimination of refractory disease. Combinations of these and other targeted agents may overcome the resistance that develops with single-agent therapy and could be incorporated either as part of initial therapy or later when disease resistance develops. Approaches aimed at combining these agents can be based on the genetics and biology of clear cell RCC. von Hippel-Lindau loss leads to an increase in cellular levels of HIF (HIF-1alpha or HIF-2alpha) leading to increased expression of a number of hypoxia-regulated genes critical to cancer progression. Combinations of targeted agents may block several of these mediators (VEGF, epidermal growth factor receptor, and PDGF), so-called horizontal blockade. Blockade could also take place at two levels of the pathways (vertical blockade), either at HIF and VEGF or at VEGF and VEGF receptor signaling. Many of the above strategies are ongoing and will require careful phase 1 determination of toxicity and even more rigorous phase 2 analysis before moving onto phase 3 trials.

Challenges for patient selection with VEGF inhibitors

As targeted therapies for cancer become increasingly integrated into standard practice, appropriate selection of the patients most likely to benefit from these therapies is now receiving critical scrutiny. Early experience with therapies directed at targets that are definitively overactive (e.g. the bcr-abl tyrosine kinase targeted by imatinib) or over-expressed [e.g. the human epidermal growth factor receptor 2 (HER2) targeted by trastuzumab] has generated the perception that pre-treatment target assessment is a pre-requisite for therapy with all targeted agents. However, emerging evidence suggests that this is not presently feasible for anti-angiogenic agents. Despite considerable evidence for the association of intratumoral and/or plasma vascular endothelial growth factor (VEGF) levels with tumor progression and/or poor prognosis, pre-treatment VEGF levels do not appear to be predictive of response to anti-angiogenic therapy. This may possibly be due to the complexity of the angiogenic pathways and the limitations associated with current methods of VEGF detection and quantification; e.g. low assay sensitivity and lack of standardized methods could prevent detection of very small increases in VEGF, which may be clinically important in patients with tumors that are highly dependent on this growth factor. In addition to a general lack of agreement as to the relative clinical relevance of circulating versus tumor VEGF levels, the absence of a 'gold standard' VEGF detection assay and the lack of a predefined, clinically relevant cut-off pose a significant hindrance to the clinical utility of VEGF measurements for therapy selection. Given the fundamental importance of angiogenesis for tumor growth and progression, and the key role of VEGF in these processes, presently it seems appropriate to view anti-VEGF agents such as bevacizumab (Avastin) as having potential utility, independently of pre-treatment screening. Further research is needed to define the relationship between potential surrogate markers of VEGF pathway activity and clinical outcomes.

Molecular pathology of eyes with von Hippel-Lindau (VHL) Disease: a review

BACKGROUND

von Hippel-Lindau Disease (VHL) is an autosomal dominant inherited systemic cancer syndrome. Recently, many advances have contributed to the understanding of VHL pathophysiology.

METHODS

In this article we review recent developments and summarize our findings in VHL molecular pathology related to retinal and optic nerve diseases.

RESULTS

Loss of heterozygosity (LOH) within the VHL gene is detected in the stromal cells surrounding the capillary endothelial cells and admixed with glial cells in ocular hemangioblastomas. This finding is in line with similar findings in VHL-associated CNS hemangioblastoma and renal clear cell carcinomas. Increases of vascular endothelial growth factor (VEGF), hypoxia induced factor (HIF), and ubiquitin are found in ocular hemangioblastomas.Interestingly, tumorlet cells, which are composed of poorly differentiated small cells with prominent dark nuclei and little cytoplasm, as well as several stem cell markers, such as erythropoietin (Epo), Epo receptor (EpoR), and CD133, are present in ocular VHL lesions. CXCR4, a CXC chemokine receptor is also expressed in retinal VHL hemangioblastomas.

CONCLUSIONS

These findings imply that VHL cells with LOH of the tumor suppressor gene, most likely originate from a hematopoietic/vascular lineage. Targeting these proteins and ischemic factors, not VEGF alone, may be a potential therapeutic approach for VHL-associated ocular hemangioblastomas.

Modulation of mRNA stability as a novel therapeutic approach

During the last decade evidence has accumulated that modulation of mRNA stability plays a central role in cellular homeostasis, including cell differentiation, proliferation and adaptation to external stimuli. The functional relevance of posttranscriptional gene regulation is highlighted by many pathologies, wherein occurrence tightly correlates with a dysregulation in mRNA stability, including chronic inflammation, cardiovascular diseases and cancer. Most commonly, the cis-regulatory elements of mRNA decay are represented by the adenylate- and uridylate (AU)-rich elements (ARE) which are specifically bound by trans-acting RNA binding proteins, which finally determine whether mRNA decay is delayed or facilitated. Regulation of mRNA decay by RNA stabilizing and RNA destabilizing factors is furthermore controlled by different intrinsic and environmental stimuli. The modulation of mRNA binding proteins, therefore, illuminates a promising approach for the pharmacotherapy of those key pathologies mentioned above and characterized by a posttranscriptional dysregulation. Most promisingly, intracellular trafficking of many of the mRNA stability regulating factors is, in turn, regulated by some major signaling pathways, including the mitogen-activated protein kinase (MAPK) cascade, the AMP-activated kinase (AMPK) and the protein kinase (PK) C (PKC) family. In this review, we present timely examples of genes regulated by mRNA stability with a special focus on signaling pathways involved in the ARE-dependent mRNA decay. A better understanding of these processes may form the basis for the development of novel therapeutics to treat major human diseases.

Phase II study of lenalidomide in patients with metastatic renal cell carcinoma

BACKGROUND

Lenalidomide (LEN) is a structural and functional analogue of thalidomide that has demonstrated enhanced immunomodulatory properties and a more favorable toxicity profile. A Phase II, open-label study of LEN in patients with metastatic renal cell carcinoma (RCC) was conducted to determine its safety and clinical activity.

METHODS

Patients with metastatic RCC received LEN orally at a dose of 25 mg daily for the first 21 days of a 28-day cycle. The primary endpoint was the objective response rate. Time to treatment failure, safety, and survival were secondary endpoints.

RESULTS

In total, 28 patients participated in the trial and were included in the current analysis. Three of 28 patients (11%) demonstrated partial responses and continued to be progression-free for >15 months. Eleven patients (39%) had stable disease that lasted >3 months, including 8 patients who had tumor shrinkage. In total, 6 patients (21%) remained on the trial, and 5 additional patients continued to be followed for survival. The median follow-up for those 11 patients was 13.5 months (range, 8.3-17.0 months). The median survival had not been reached at the time of the current report. Serious adverse events included fatigue (11%), skin toxicity (11%), and neutropenia (36%).

CONCLUSIONS

LEN demonstrated an antitumor effect in metastatic RCC, as evidenced by durable partial responses. LEN toxicities were manageable. Further studies will be required to assess the overall activity of LEN in patients with metastatic RCC.

Multiple myeloma in a murine syngeneic model:modulation of growth and angiogenesis by a monoclonal antibody to kininogen

Multiple myeloma (MM), a B-cell malignancy characterized by proliferation of monoclonal plasma cells remains incurable. Murine plasma cell tumors share common features with human MM. We used two cell lines (B38 and C11C1) derived from P3X63Ag8 myeloma cells. The new cell lines were implanted subcutaneously in the strain of origin (Balb/c mice) and used as a model to monitor the effects of C11C1 monoclonal antibody (mAb) to kininogen (HK). We assessed their behavior by intraperitoneal and subcutaneous implantation, by implanting them together and by treating B38-MM with purified mAb C11C1. We evaluated growth, microvascular density (MVD), and cellular expression of urokinase-type plasminogen activator-receptor (uPAR), fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF), bradykinin-1 receptor (B1R), bradykinin-2 receptor (B2R) and HK. We found that both MM-cell-lines are uPAR positive, that mAb C11C1 inhibits its own tumor growth in vivo, slows down B38-MM growth rate when both MM are implanted together and when mAb C11C1 is injected intraperitoneally. MAb C11C1-treated-MM showed decreased MVD and HK binding in vivo without FGF-2, B1R or B2R expression changes. We propose that the B38-extramedullary-myeloma-model is a useful tool to study the interactions of this hematopoietic tumor and its environment and that mAb C11C1 may improve the efficacy of conventional MM treatment with minimal side effects.

Role of Rac1 and Cdc42 in hypoxia induced p53 and von Hippel-Lindau suppression and HIF1alpha activation

Low oxygen tension can influence tumor progression by enhancing angiogenesis, a process that may involve Rho GTPases whose activities have been implicated in tumorigenesis and metastasis. In the present study, we show that hypoxia can increase the mRNA levels and intracellular activities of Rac1 and Cdc42 in a time-dependent manner. The hypoxia-stimulated activities of Rac1 and Cdc42 could be blocked by the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and the protein tyrosine kinase (PTK) inhibitor genistein but were not affected by the p38MAPK inhibitor SB203580 or the MEK-1 inhibitor PD98059, suggesting that the hypoxia-mediated signals were through PI3K and PTK. Correlating with the increased activities of Rac1 and Cdc42, the expression of the pro-angiogenesis factors HIF-1alpha and vascular endothelial growth factor (VEGF) was upregulated by hypoxia, whereas the expression of the tumor suppressors von Hippel-Lindau and p53 was down-regulated. Dominant negative N17Rac1 and N17Cdc42 could upregulate the expression of p53 and pVHL but downregulate that of HIF-1alpha and VEGF under hypoxia. Furthermore, the preconditioned medium from N17Rac1 or N17Cdc42-expressing gastric cancer cells was able to inhibit the proliferation of HUVECs. Our results indicate that PI3K and PTK-mediated activations of Rac1 and Cdc42 are involved in the hypoxia-induced production of angiogenesis-promoting factors and tumor suppressors, and suggest that the Rho family GTPases Rac1 and Cdc42 may contribute to the hypoxia-mediated angiogenesis.

Hypoxia-Inducible Factor-1-Dependent and -Independent Regulation of Insulin-Like Growth Factor-1-Stimulated Vascular Endothelial Growth Factor Secretion

Hypoxia-induced stress plays a central role in retinal vascular disease and cancer. Increased hypoxia-inducible factor-1 alpha (Hif-1 alpha) expression leads to HIF-1 formation and the production of vascular endothelial growth factor (VEGF). Cytokines, including insulin-like growth factor-1 (IGF-1), also stimulate VEGF secretion. In this study, we examined the relationship between IGF-1 signaling, HIF-1 alpha protein turnover and VEGF secretion in the ARPE-19 retinal pigment epithelial cell line. Northern analysis revealed that IGF-1 stimulated Hif-1 alpha message expression, whereas the hypoxia-mimetic CoCl2 did not. CoCl2 treatment increased Hif-1 alpha protein accumulation to a greater extent than IGF-1 treatment. However, IGF-1 stimulated a more significant increase in VEGF secretion. IGF-1-stimulated VEGF promoter activity was phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR (mammalian target of rapamycin)-dependent, whereas VEGF secretion was only partially reduced by inhibition of PI3K/Akt/mTOR and HIF-1 activities. Analysis of VEGF promoter truncation mutants indicated that sensitivity to CoCl2 was hypoxia response element (HRE)-dependent with the region upstream of the HRE conferring IGF-1 sensitivity. In conclusion, IGF-1 regulates VEGF expression and secretion via HIF-1-dependent and -independent pathways.

pVHL function is essential for endothelial extracellular matrix deposition

The tumor suppressor von Hippel-Lindau protein (pVHL) is critical for cellular molecular oxygen sensing, acting to target degradation of the hypoxia-inducible factor alpha transcription factor subunits under normoxic conditions. We have found that independent of its function in regulating hypoxic response, the VHL gene plays a critical role in embryonic endothelium development through regulation of vascular extracellular matrix assembly. We created mice lacking the VHL gene in endothelial cells; these conditional null mice died at the same stage as homozygous VHL-null mice, with similar vascular developmental defects. These included defective vasculogenesis in the placental labyrinth, a collapsed endocardium, and impaired vessel network patterning. The defects in embryonic vascularization were correlated with a diminished vascular fibronectin deposition in vivo and defective endothelial extracellular fibronectin assembly in vitro. We found that the impaired migration and adhesion of VHL-null endothelial cells can be partially rescued by the addition of back exogenous fibronectin, which indicates that pVHL regulation of fibronectin deposition plays an important functional role in vascular patterning and maintenance of vascular integrity.

IGF-1 induced vascular endothelial growth factor secretion in head and neck squamous cell carcinoma

Elevated vascular endothelial growth factor (VEGF) levels correlate with increased progression and poor prognosis of head and neck squamous cell carcinomas (HNSCC). VEGF expression is regulated by hypoxia and cytokines, including insulin-like growth factor-1 (IGF-1). In this report, we examined IGF-1 signaling and VEGF expression in SCC-9 cells. IGF-1 and the chemical hypoxia agent, cobalt chloride, each stimulated VEGF secretion and VEGF promoter activation. Cobalt chloride increased Hif-1alpha protein levels and HIF-1 dependent activation of the enolase promoter. IGF-1 increased these parameters only in the presence of cobalt chloride. IGF-1 stimulated PI-3K/Akt and Erk/MAPK pathways in SCC-9 cells, each contributing to Hif-1alpha expression and VEGF secretion. SCC-9 cells express the VEGF receptors Flk-1 and neuropilin-1, with VEGF treatment increasing VEGF promoter activity and VEGF secretion that was attenuated by the Flk-1 tyrosine kinase inhibitor, ZM 323881. These results demonstrate the presence of an IGF-1 regulated VEGF autocrine loop in HNSCC.

The VHL/HIF oxygen-sensing pathway and its relevance to kidney disease

Over the past decade major advances have been made in our understanding of the molecular machinery that mammalian cells use to sense and to adapt to a low-oxygen environment. A critical mediator of cellular adaptation to hypoxia is hypoxia-inducible factor (HIF), a basic helix-loop-helix transcription factor that consists of an oxygen-sensitive alpha-subunit, HIF-alpha and a constitutively expressed beta-subunit, HIF-beta. Under conditions of normal oxygen tension, the HIF-alpha subunit is hydroxylated by specific prolyl-hydroxylases and targeted for rapid proteasomal degradation by the von Hippel-Lindau (VHL) tumor suppressor, which is the substrate recognition component of an E3-ubiquitin ligase. In a hypoxic environment or in the absence of functional VHL tumor suppressor protein irrespective of oxygen concentration, HIF-alpha is not degraded and translocates to the nucleus, where it dimerizes with HIF-beta to form transcriptionally active HIF. As a transcription factor, HIF is involved in the regulation of many biological processes that facilitate both oxygen delivery and adaptation to oxygen deprivation by regulating genes that are involved in glucose uptake and energy metabolism, angiogenesis, erythropoiesis, cell proliferation and apoptosis, cell-cell and cell-matrix interactions, and barrier function. This review summarizes some of the most recent advances in the VHL/HIF field and discusses their relevance for pathogenesis and treatment of acute ischemic renal failure, renal fibrosis, and renal cancer.

Understanding the Importance of Smart Drugs in Renal Cell Carcinoma

OBJECTIVE

To understand the mode of action of the currently most investigated new drugs in renal cell carcinoma (RCC) and ultimately to analyze what should be the role of the urologist in this new therapeutic era.

METHODS

A comprehensive review of the peer-reviewed literature was performed on the topic of molecular pathways involved in RCC angiogenesis, vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor (VEGFR) and targeted molecular therapy for RCC.

RESULTS

Von Hippel-Lindau (VHL) disease has provided a model for understanding that the early inactivation of the VHL gene was responsible for accumulation of hypoxia-inducible factor and therefore activation of hypoxia-inducible genes such as VEGF, platelet-derived growth factor, erythropoietin, carbonic anhydrase IX and tumor growth factor alpha. The fact that such VHL inactivation also was found in up to 70% of sporadic RCC has been the rationale for developing new drugs targeting VEGF, VEGFR, platelet-derived growth factor receptor and tyrosine kinase receptors that are required for intracellular transduction.

CONCLUSION

Initial results from phase 2 trials in metastatic disease are very promising. There is a strong rationale for initiating adjuvant trials with those kind of agents in patients with high-risk localised tumors. Urologists who have a good understanding of prognostic parameters in localised RCC particularly should be involved in such new approaches.

Mechanisms of angiogenesis in gliomas

Gliomas are the most frequent primary tumors of the central nervous system in adults. Glioblastoma multiforme, the most aggressive form of astrocytic tumors, displays a rapid progression that is accompanied by particular poor prognosis of patients. Intense angiogenesis is a distinguishing pathologic characteristic of these tumors and in fact, glioblastomas are of the most highly vascularized malignant tumors. For this reason, research and therapy strategies have focused on understanding the mechanisms leading to the origin of tumor angiogenic blood vessels in order to develop new approaches that effectively block angiogenesis and cause tumor regression. We discuss here some important features of glioma angiogenesis and we present molecules and factors and their possible functions and interactions that play a role in neovascularization. In spite of the great progress that molecular biology has achieved on investigating tumor angiogenesis, many aspects remain obscure and the complexity of the angiogenic process stands for an obstacle in identifying the exact and complete molecular pathways orchestrating new blood vessels formation, which are necessary for the survival and expansion of these tumors.

Vascular endothelial growth factor antagonist modulates leukocyte trafficking and protects mouse livers against ischemia/reperfusion injury

Although hypoxia stimulates the expression of vascular endothelial growth factor (VEGF), little is known of the role or mechanism by which VEGF functions after ischemia and reperfusion (I/R) injury. In this report, we first evaluated the expression of VEGF in a mouse model of liver warm ischemia. We found that the expression of VEGF increased after ischemia but peaked between 2 and 6 hours after reperfusion. Mice were treated with a neutralizing anti-mouse VEGF antiserum (anti-VEGF) or control serum daily from day -1 (1 day before the initiation of ischemia). Treatment with anti-VEGF significantly reduced serum glutaminic pyruvic transaminase levels and reduced histological evidence of hepatocellular damage compared with controls. Anti-VEGF also markedly decreased T-cell, macrophage, and neutrophil accumulation within livers and reduced the frequency of intrahepatic apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells. Moreover, there was a reduction in the expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interferon-gamma), chemokines (interferon-inducible protein-10 and monocyte chemoattractant protein-1) and adhesion molecules (E-selectin) in parallel with enhanced expression of anti-apoptotic genes (Bcl-2/Bcl-xl and heme oxygenase-1) in anti-VEGF-treated animals. In conclusion, hypoxia-inducible VEGF expression by hepatocytes modulates leukocyte trafficking and leukocyte-induced injury in a mouse liver model of warm I/R injury, demonstrating the importance of endogenous VEGF production in the pathophysiology of hepatic I/R injury.

Lipid peroxidation and renal cell carcinoma: further supportive evidence and new mechanistic insights

We have recently proposed lipid peroxidation as a unifying mechanistic pathway by which several seemingly unrelated risk/protective factors (obesity, hypertension, diabetes, smoking, oophorectomy/hysterectomy, parity, antioxidants) affect renal cell carcinoma development. In experimental studies, increased lipid peroxidation is a principal mechanistic pathway in renal carcinogenesis induced by different chemicals. In this communication, we provide additional lines of evidence that further support a role for lipid peroxidation on renal cell cancer development. (1) Lipid peroxidation may explain the role of other risk (analgesic use, pre-eclampsia) or protective (alcohol intake, oral contraceptives) factors for renal cell carcinoma. (2) Additional experimental evidence supports lipid peroxidation as an important mechanism in renal carcinogenesis, and (3) Existing evidence support a cross-talk between the lipid peroxidation pathway and other pathways that are relevant to renal carcinogenesis, such as apoptosis, VHL, and possibly other pathways.

Clusterin is a secreted marker for a hypoxia-inducible factor-independent function of the von Hippel-Lindau tumor suppressor protein

Germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene predispose people to renal cancer, hemangioblastomas, and pheochromocytomas in an allele-specific manner. The best documented function of the VHL gene product (pVHL) relates to its ability to polyubiquitinate, and hence target for destruction, the alpha subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF). pVHL mutants linked to familial pheochromocyctoma (type 2C VHL disease), in contrast to classical VHL disease, appear to be normal with respect to HIF regulation. Using a simple method for identifying proteins that are differentially secreted by isogenic cell line pairs, we confirmed that the HIF targets IGBP3 and PAI-1 are overproduced by pVHL-defective renal carcinoma cells. In addition, cells lacking wild-type pVHL, including cells producing type 2C pVHL mutants, were defective with respect to expression and secretion of clusterin, which does not behave like a HIF target. Decreased clusterin secretion by pVHL-defective tumors was confirmed in vivo by immunohistochemistry. Therefore, clusterin is a secreted marker for a HIF-independent pVHL function that might be especially important in pheochromocytoma development.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Induction of the von Hippel-Lindau tumor suppressor gene by late hypoxia limits HIF-1 expression

Hypoxia-inducible factor (HIF) remains the central focus of oxygen sensing during hypoxia. HIF is a heterodimeric transcription factor consisting of an oxygen-regulated alpha- and a constitutively expressed beta subunit. The von Hippel-Lindau tumor suppressor (pVHL) is a component of the E3 ubiquitin ligase complex and targets HIF-alpha to proteasomal degradation, but also is known to exert a significant control on HIF transactivation activity. However, the understanding of the full interaction between HIF and pVHL has been hindered by a lack in the understanding of pVHL regulation. Here, we report that pVHL itself is induced in prolonged hypoxia in a kinetic that parallels the observed downregulation of HIF-1alpha protein under such conditions. In addition, we document direct HIF-1alpha binding to the VHL promoter and identify a functional hypoxia response element (HRE) within the VHL promoter. Such induction of pVHL in hypoxia furthermore has functional implications for the HIF dependent hypoxic response, implicating a physiologically relevant feedback mechanism. These results provide an intriguing model, whereby HIF self-regulates expression through VHL and highlight the role of pVHL as a unifying mechanism of HIF regulation.

Epidermal growth factor receptor and angiogenesis: Opportunities for combined anticancer strategies

Tumor-induced angiogenesis is essential for malignant growth. This mini review focuses on the role of vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) and their receptors in this process, and the rationale to combine inhibitors of these growth factors as anticancer therapy. Concomitantly, targeting the VEGF(R) and the EGF(R) signaling pathway may circumvent the problem of acquired resistance to EGFR inhibitors. By targeting both pathways, the antiangiogenic effect may be more pronounced, which may lead to greater antitumor activity. Preliminary efficacy data from clinical trials encourage further exploration of this combined anticancer strategy.