Ras regulation of vascular endothelial growth factor and angiogenesis

Guajadial inhibits NSCLC growth and migration following activation of the VEGF receptor-2

Guajadial, one of natural dialdehyde meroterpenoids, demonstrated significant antineoplasmic activity. The present research was to investigate the inhibitory effects of guajadial by using two NSCLC cells (A549 and H1650) proliferation and migration. Western blotting was employed to explore the underlying mechanisms of VEGF receptor (VEGFR)2-mediated. This research indicated that guajadial not only inhibited endothelial cell proliferation and migration but also suppress tumor growth in human NSCLC xenograft mouse models. It is also suggested that guajadial inhibited A549 proliferation via blocking the Ras/MAPK pathway.

Distinct molecular subtypes of gastric cancer: from Laurén to molecular pathology

In Western countries the majority of gastric cancers (GC) are usually diagnosed in advanced stages reporting a 5-year survival rate of only 26%. The Laurén classification of GC was most widely used in clinical practice since it reflects GC morphology, epidemiology, tumor biology, clinical management and outcome. Despite the initial promise of individualizing antitumor treatment, the management of GC still remains relatively broad and general. Apart from clinical staging, molecular profiling enables targeting of the identified underlying alterations, rather than histology. In contrast to breast carcinoma, molecular classification of GC does not yet imply treatment modality. Molecular classifications of GC and their therapeutic implications are therefore extensively studied. The current proposed molecular divisions of GC come from three different parts of the world where different standard treatment modalities for advanced GC are recommended. Wider use of GC molecular subtyping may solve problems, such as susceptibility to novel systemic therapy regimens or selection of patients for aggressive surgery and targeted adjuvant/conversion therapy. In any case, the rapid entry of novel molecular targeted therapies into routine oncology practice clearly underscores the urgent need for clinicians to be aware of these new possibilities.

Wogonoside inhibits angiogenesis in breast cancer via suppressing Wnt/β-catenin pathway

Wogonoside, a main flavonoid component derived from the root of Scutellaria baicalensis Georgi, has been reported to have anti-angiogenesis and anti-leukemia activities. However, whether it can inhibit tumor angiogenesis is unclear. In this study, we investigate the inhibitory effect of wogonoside on angiogenesis in breast cancer and its underlying mechanisms. ELISA assay shows that wogonoside (25, 50, and 100 µM) decreases the secretion of VEGF in MCF-7 cells by 30.0%, 35.4%, and 40.1%, respectively. We find it inhibits angiogenesis induced by the conditioned media from MCF-7 cells in vitro and in vivo by migration, tube formation, rat aortic ring, and chicken chorioallantoic membrane (CAM) assay. Meanwhile, wogonoside can inhibit the growth and angiogenesis of MCF-7 cells xenografts in nude mice. The reduction of tumor weight can be found both in wogonoside (80 mg/kg) and bevacizumab (20 mg/kg) treated group, and the tumor inhibition rate is 42.1% and 48.7%, respectively. In addition, mechanistic studies demonstrate that wogonoside suppresses the activation of Wnt/β-catenin pathway in MCF-7 cells. Wogonoside (100 µM) decreases the intracellular level of Wnt3a, increases the expression of GSK-3β, AXIN, and promotes the phosphorylation of β-catenin for proteasome degradation significantly. Furthermore, the nuclear accumulation of β-catenin and the DNA-binding activity of β-catenin/TCF/Lef complex are inhibited by 49.2% and 28.7%, respectively, when treated with 100 µM wogonoside. Taken together, our findings demonstrate that wogonoside is a potential inhibitor of tumor angiogenesis and can be developed as a therapeutic agent for breast cancer. © 2015 Wiley Periodicals, Inc.

Targeted Therapy for Metastatic Renal Carcinoma: an Update

Conventional chemotherapy is associated with poor outcomes in metastatic renal cell carcinoma (RCC). Advances in the understanding of tumor molecular biology and the implementation of new drugs that target these molecular pathways have increased the arsenal against advanced RCC and improved outcomes in these patients. Herein, we briefly describe the latest data on targeted therapies used in the treatment of advanced renal cell carcinoma. Search strategy was performed according to PRISMA guidelines. Abstracts of relevant studies published in PubMed between 2000 and 2014 were analyzed by two authors. Abstracts were selected if they were published in English, data reported was of phase II or III clinical trials, and outcomes followed FDA approval. If consensus between the two authors was achieved, they were included in the review. Key words used were “target therapy” and “metastatic renal cell carcinoma”. The results of the studies analyzed in this review support the benefits of targeted therapy in metastatic RCC. These include improved progression-free survival, overall survival, and quality of life as well as reduced toxicities compared to immunotherapy. The improvement in outcomes in metastatic RCC makes these drugs a preferred option as a primary treatment for these patients.

Plumbagin inhibits tumour angiogenesis and tumour growth through the Ras signalling pathway following activation of the VEGF receptor-2

BACKGROUND AND PURPOSE

Angiogenesis-based therapy is an effective anti-tumour strategy and previous reports have shown some beneficial effects of a naturally occurring bioactive compound plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone). Here, we sought to determine the biological effects of plumbagin on signalling mechanisms during tumour angiogenesis.

EXPERIMENTAL APPROACH

The effects of plumbagin were evaluated in various in vitro assays which utilised human umbilical vein endothelial cells (HUVEC) proliferation, migration and tube formation. Plumbagin was also evaluated in vivo using chicken embryo chorioallantoic membrane (CAM) and mouse corneal micropocket models., Human colon carcinoma and prostate cancer xenograft mouse models were used to evaluate the effects of plumbagin on angiogenesis. Immunofluorescence, GST pull-down and Western blotting were employed to explore the underlying mechanisms of VEGF receptor (VEGFR)2-mediated Ras signalling pathways.

KEY RESULTS

Plumbagin not only inhibited endothelial cell proliferation, migration and tube formation but also suppressed chicken chorioallantoic membrane neovascularzation and VEGF-induced mouse corneal angiogenesis. Moreover, plumbagin suppressed tumour angiogenesis and tumour growth in human colon carcinoma and prostate cancer xenograft mouse models. At a molecular level, plumbagin blocked the Ras/Rac/cofilin and Ras/MEK signalling pathways mediated by VEGFR2 in HUVECs.

CONCLUSIONS AND IMPLICATIONS

Plumbagin inhibited tumour angiogenesis and tumour growth by interference with the VEGFR2-mediated Ras signalling pathway in endothelial cells. Our findings demonstrate a molecular basis for the effects of plumbagin and suggest that this compound might have therapeutic ant-tumour effects.

Newly developed reconstituted high-density lipoprotein containing sphingosine-1-phosphate induces endothelial tube formation

Reconstituted high-density lipoprotein (rHDL) has been shown to produce a rapid regression of atherosclerosis in animal models and humans. Sphingosine-1-phosphate (S1P), which is a bioactive lipid in HDL, plays a role in mitogenesis, endothelial cell motility, and cell survival, as well as organization and differentiation into a vessel. In this study, we examined the direct role of a newly developed rHDL, [POPC(1-palmitoyl-2-oleoyl phosphatidylcholine)/S1P/apolipoproteinA-I(A-I)]rHDL containing S1P in tube formation in endothelial cells (ECs) as well as cholesterol efflux in macrophage. The effect of (POPC/S1P/A-I)rHDL on cholesterol efflux in macrophage was similar to that of conventional rHDL, (POPC/A-I)rHDL. In addition, (POPC/S1P/A-I)rHDL induced EC proliferation through the activation of phospho-Akt and phospho-extracellular-signal-regulated kinases (p-ERK) 1/2 and EC tube formation, and this effect was blocked by inhibitors of Akt, ERK and endothelial nitric-oxide synthase (eNOS). In addition, (POPC/S1P/A-I)rHDL-induced p-ERK1/2 activation and EC tube formation can be mainly attributed to S1P-stimulated signaling through S1P2 and S1P3 as determined by an anti-sense strategy. In conclusion, (POPC/S1P/A-I)rHDL induces cholesterol efflux independently of S1P but has additional S1P-mediated effects on EC tube formation mediated by Akt/ERK/NO through S1P2 and S1P3. In the future, these new discs may be useful for the treatment of atherosclerotic and ischemic cardiovascular disease, such as acute coronary syndrome and atherosclerosis obliterans.

Pathological angiogenesis is induced by sustained Akt signaling and inhibited by rapamycin

Endothelial cells in growing tumors express activated Akt, which when modeled by transgenic endothelial expression of myrAkt1 was sufficient to recapitulate the abnormal structural and functional features of tumor blood vessels in nontumor tissues. Sustained endothelial Akt activation caused increased blood vessel size and generalized edema from chronic vascular permeability, while acute permeability in response to VEGF-A was unaffected. These changes were reversible, demonstrating an ongoing requirement for Akt signaling for the maintenance of these phenotypes. Furthermore, rapamycin inhibited endothelial Akt signaling, vascular changes from myrAkt1, tumor growth, and tumor vascular permeability. Akt signaling in the tumor vascular stroma was sensitive to rapamycin, suggesting that rapamycin may affect tumor growth in part by acting as a vascular Akt inhibitor.

Angiogenesis in malignant glioma--a target for antitumor therapy?

The prognosis of malignant gliomas is still dismal despite aggressive treatment attempts. Thus, alternative therapy strategies are needed. Malignant gliomas are upon the best vascularized tumors in humans and their proliferation is hallmarked by a distinct proliferative vascular component. Hence it seems to be a logical consequence to apply anti-angiogenic treatment strategies to malignant gliomas. These treatment strategies have shown promising effects in animal models and some experimental clinical studies. This review gives a short introduction into the molecules involved in angiogenesis of malignant gliomas, it provides an overview of the latest experimental developments of glioma angiogenesis inhibition and discusses the results of clinical anti-angiogenic trials in patients with high grade glioma. Additionally the problem of monitoring the treatment success of an anti-angiogenic therapy is addressed.

Confirmation of a linkage between H-Ras and MMP-13 expression as well as MMP-9 by chemical genomic approach

As farnesylation of the Ras protein by farnesyl transferase is a critical step for the Ras functional activity, the farnesyl transferase inhibitor could affect H-Ras functions and the inhibitors such as arteminolide, SCH66336 and LB42908 completely inhibited Ras-farnesylation. However, they did not induce apoptosis of H-Ras-transformed cells with concentration for blocking H-Ras farnesylation. To determine the antitumor effects of the inhibitors, it was analyzed through the expression profile of genes, regulated by activated H-Ras or FTIs by using cDNA microarray. On the basis of the results, the relationship between H-Ras and MMPs expression was confirmed by RT-PCR, Western bolt, zymographic analysis and angiogenesis assay. Our results suggested that activation of MMP-13 as well as MMP-9 induced by H-Ras is involved in angiogenesis and with farnesyl transferase inhibitors, in part, exerts their anticancer effects. We confirmed that MMP-13 is a critical H-Ras target gene through chemical genomic approaches with farnesyl transferase inhibitors.

Targeted agents for the treatment of advanced renal cell carcinoma

Metastatic renal cell carcinoma (RCC) is currently one of the most treatment-resistant malignancies. However, the elucidation of the molecular mechanisms underlying RCC development has led to the identification of promising targets for novel therapeutic agents. The involvement of the Von Hippel-Lindau protein pathway in clear cell RCC suggests that downstream targets of this pathway, namely, signaling through vascular endothelial growth factor (VEGF) in endothelial cells, platelet-derived growth factor (PDGF) in endothelial cells and pericytes, and the epidermal growth factor receptor (EGFR) pathway in tumor cells are all reasonable and rational therapeutic targets. A number of agents are in development that target VEGF (bevacizumab, a recombinant, humanized monoclonal antibody) or its receptor, VEGFR (PTK787, SU011248, and BAY 43-9006, all of which are small molecule inhibitors). Agents targeting EGFR also are being investigated clinically (gefitinib, cetuximab, erlotinib, and ABX-EGF). The Raf/MEK/ERK pathway is an important downstream convergence point for signaling through VEGFR, platelet-derived growth factor receptor (PDGFR), and EGFR (all have receptor tyrosine kinase activity) and also has important antiapoptotic effects, thereby providing an attractive target for intervention. In addition to inhibiting VEGFR and PDGFR-mediated angiogenic pathways, BAY 43-9006 has been shown to inhibit the Raf/MEK/ERK pathway at the level of Raf kinase. MEK-directed therapeutic approaches are also in development. Given that multiple molecular pathways are implicated in tumor cell growth, antitumor activity may be increased by using individual agents that target multiple pathways, or by combining different agents to allow vertical or horizontal inhibition of relevant pathways.

A highly potent and selective farnesyltransferase inhibitor ABT-100 in preclinical studies

Ras mutation has been detected in approximately 20-30% of all human carcinomas, primarily in pancreatic, colorectal, lung and bladder carcinomas. The indirect inhibition of Ras activity by inhibiting farnesyltransferase (FTase) function is one therapeutic intervention to control tumor growth. Here we report the preclinical anti-tumor activity of our most advanced FTase inhibitor (FTI), ABT-100, and a direct comparison with the current clinical candidates. ABT-100 is a highly selective, potent and orally bioavailable FTI. It broadly inhibits the growth of solid tumors in preclinical animal models. Thus, ABT-100 is an attractive candidate for further clinical evaluation. In addition, our results provide plausible insights to explain the impressive potency and selectivity of ABT-100. Finally, we have demonstrated that ABT-100 significantly suppresses the expression of vascular endothelial growth factor (VEGF) mRNA and secretion of VEGF protein, as well as inhibiting angiogenesis in the animal model.

Phase I study to determine the safety and pharmacokinetics of the novel Raf kinase and VEGFR inhibitor BAY 43-9006, administered for 28 days on/7 days off in patients with advanced, refractory solid tumors

BACKGROUND

BAY 43--9006, an oral multi-kinase inhibitor, targets serine-threonine kinases and receptor tyrosine kinases, and affects the tumor and vasculature in preclinical models. Based on its pharmacologic effect, it may be a useful cancer treatment. This study determined the maximum tolerated dose (MTD) of BAY 43-9006 in 42 patients with advanced, refractory metastatic or recurrent solid tumors. Dose-limiting toxicities (DLTs), safety, pharmacokinetics and tumor response were also evaluated.

PATIENTS AND METHODS

In this open-label, phase I, dose-escalation study, BAY 43--9,006 was administered orally in repeated cycles of 35 days (28 days on/7 days off). Eight doses were investigated: from 50 mg every fourth day to 600 mg twice daily. Treatment continued until unacceptable toxicity, tumor progression or death.

RESULTS

The MTD was 400 mg twice daily. BAY 43-9006 was well tolerated, with mild to moderate toxicities; only six patients discontinued study therapy due to adverse events. DLTs consisted of hand-foot skin reaction in three of seven patients receiving 600 mg twice daily. Stable disease was achieved in 22% of patients; median duration of stable disease was 7.2 months. Consistent with its observed half-life of approximately 27 h, BAY 43-9, 006 accumulated on multiple dosing. Increases in exposure were less than proportional to the increases in dose.

CONCLUSIONS

Results indicate that further clinical investigation of BAY 43--9006 is warranted, and suggest it could be a promising future therapy for patients with cancer.

Fluvastatin synergistically enhances the antiproliferative effect of gemcitabine in human pancreatic cancer MIAPaCa-2 cells

The new combination between the nucleoside analogue gemcitabine and the cholesterol-lowering drug fluvastatin was investigated in vitro and in vivo on the human pancreatic tumour cell line MIAPaCa-2. The present study demonstrates that fluvastatin inhibits proliferation, induces apoptosis in pancreatic cancer cells harbouring a p21ras mutation at codon 12 and synergistically potentiates the cytotoxic effect of gemcitabine. The pharmacologic activities of fluvastatin are prevented by administration of mevalonic acid, suggesting that the shown inhibition of geranyl-geranylation and farnesylation of cellular proteins, including p21rhoA and p21ras, plays a major role in its anticancer effect. Fluvastatin treatment also indirectly inhibits the phosphorylation of p42ERK2/mitogen-activated protein kinase, the cellular effector of ras and other signal transduction peptides. Moreover, fluvastatin administration significantly increases the expression of the deoxycytidine kinase, the enzyme required for the activation of gemcitabine, and simultaneously reduces the 5′-nucleotidase, responsible for deactivation of gemcitabine, suggesting a possible additional role of these enzymes in the enhanced cytotoxic activity of gemcitabine. Finally, a significant in vivo antitumour effect on MIAPaCa-2 xenografts was observed with the simultaneous combination of fluvastatin and gemcitabine, resulting in an almost complete suppression and a marked delay in relapse of tumour growth. In conclusion, the combination of fluvastatin and gemcitabine is an effective cytotoxic, proapoptotic treatment in vitro and in vivo against MIAPaCa-2 cells by a mechanism of action mediated, at least in part, by the inhibition of p21ras and rhoA prenylation. The obtained experimental findings might constitute the basis for a novel translational research in humans.

Role of the vascular endothelial growth factor pathway in tumor growth and angiogenesis

New blood vessel formation (angiogenesis) is a fundamental event in the process of tumor growth and metastatic dissemination. Hence, the molecular basis of tumor angiogenesis has been of keen interest in the field of cancer research. The vascular endothelial growth factor (VEGF) pathway is well established as one of the key regulators of this process. The VEGF/VEGF-receptor axis is composed of multiple ligands and receptors with overlapping and distinct ligand-receptor binding specificities, cell-type expression, and function. Activation of the VEGF-receptor pathway triggers a network of signaling processes that promote endothelial cell growth, migration, and survival from pre-existing vasculature. In addition, VEGF mediates vessel permeability, and has been associated with malignant effusions. More recently, an important role for VEGF has emerged in mobilization of endothelial progenitor cells from the bone marrow to distant sites of neovascularization. The well-established role of VEGF in promoting tumor angiogenesis and the pathogenesis of human cancers has led to the rational design and development of agents that selectively target this pathway. Studies with various anti-VEGF/VEGF-receptor therapies have shown that these agents can potently inhibit angiogenesis and tumor growth in preclinical models. Recently, an anti-VEGF antibody (bevacizumab), when used in combination with chemotherapy, was shown to significantly improve survival and response rates in patients with metastatic colorectal cancer and thus, validate VEGF pathway inhibitors as an important new treatment modality in cancer therapy.

The vascular endothelial growth factor family and its receptors

This article focuses on describing the biology of vascular endothelial growth factor (VEGF) and its receptors as well as the regulation of their expression. A thorough understanding of the VEGF system is paramount in optimizing antiangiogenic therapies as a component of antineoplastic regimens.

Osteopontin-deficiency suppresses growth of B16 melanoma cells implanted in bone and osteoclastogenesis in co-cultures

Tumor metastasis and invasion to bone is one of major medical issues in our modern societies. Osteopontin deficiency decreased tumor invasion in bone based on knockout mouse study. In bone, osteopontin is a positive factor to increase tumor invasion.

INTRODUCTION

Osteopontin is an arginine-glycine-aspartate (RGD)-containing protein and is recognized by integrin family members. Osteopontin promotes cell attachment to bone, where it is abundantly present. Because osteopontin levels were reported to be elevated in patients bearing highly metastatic tumors, this molecule has been implicated in the metastasis of tumors. However, the effect of osteopontin on the invasion of tumor cells in bone microenvironment has not been clear. The purpose of this paper is to elucidate the effect of host osteopontin on the behavior of tumor cells in bone.

MATERIALS AND METHODS

Bone marrow ablation was conducted in the femora of mice, and B16 melanoma cells were injected directly into the ablated bone marrow space of the osteopontin-deficient and wildtype mice.

RESULT

Invasion foci of B16 melanoma cells in the cortical bone was observed 7 weeks after tumor cell implantation. The number of the foci was 5-fold less in osteopontin-deficient mice compared with that in wildtype mice. In wildtype mice, trabecular bone formation was not observed in the ablated marrow space where tumor cells were injected. In contrast, significant levels of trabecular bone were observed in the marrow space of osteopontin-deficient mice even after tumor cells were injected. To examine cellular mechanisms underlying these observations, co-cultures of bone marrow cells and B16 cells were conducted. While the presence of B16 cells promoted TRACP+ cell development in wildtype bone marrow cells, such enhancement in TRACP+ cell formation by the co-cultures with B16 cells was reduced in the case of bone marrow cells from osteopontin-deficient mice.

CONCLUSIONS

Osteopontin deficiency reduced the bone loss caused by tumor cell implantation into the bone marrow space.

1alpha,25-dihydroxycholecalciferol increases the expression of vascular endothelial growth factor in C3H10T1/2 mouse embryo fibroblasts

Evidence suggests that biologically active vitamin D, 1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)], may inhibit carcinogenesis. Because angiogenesis is crucial to carcinogenesis, 1,25(OH)(2)D(3) regulation of proangiogenic vascular endothelial growth factor (VEGF) secretion was investigated in cellular models for multistage carcinogenesis. Conditioned media from 1,25(OH)(2)D(3)-treated C3H10T(1/2) mouse fibroblasts and their Harvey ras-oncogene transfected counterparts (rasneo11a cells) induced human umbilical vein endothelial cell (HUVEC) proliferation (1.3 and 0.3 times, respectively, P < 0.05), suggesting that 1,25(OH)(2)D(3) altered the angiogenic phenotype of the cells. Although rasneo11a cells secreted less VEGF than C3H10T(1/2) cells (97%, P < 0.005), 1,25(OH)(2)D(3) induced C3H10T(1/2) and rasneo11a cells to secrete 2 and 3 times, respectively, more VEGF than controls (P < 0.05). Similar effects on VEGF release occurred after 1,25(OH)(2)D(3) treatment of MCF10A and MCF10Aras cells, a human breast epithelial cell model for multistage carcinogenesis. In C3H10T(1/2) cells, 1,25(OH)(2)D(3) activated the VEGF promoter in a dose-dependent (5-100 nmol/L) manner (maximum 60%) and all doses induced VEGF secretion (P < 0.05). 1,25(OH)(2)D(3) induced VEGF mRNA expression ( approximately 50%) from 2 through 24 h; VEGF release was significantly increased at 8 h and sustained for 24 h. VEGF mRNA expression and release declined as C3H10T(1/2) cells grew more confluent, whereas the magnitude of 1,25(OH)(2)D(3)-stimulated changes in VEGF was greater in confluent (3.3 times RNA; 3.5 times release) than in subconfluent (50% RNA; 100% release) cultures (P < 0.05). Thus, 1,25(OH)(2)D(3) increases VEGF secretion, and in C3H10T(1/2) cells, this is likely through activation of the VEGF promoter and induction of gene expression. These data contribute to understanding the role 1,25(OH)(2)D(3) plays in regulation of angiogenesis in normal compared with disease states.

VEGF-null cells require PDGFR alpha signaling-mediated stromal fibroblast recruitment for tumorigenesis

We generated VEGF-null fibrosarcomas from VEGF-loxP mouse embryonic fibroblasts to investigate the mechanisms of tumor escape after VEGF inactivation. These cells were found to be tumorigenic and angiogenic in vivo in spite of the absence of tumor-derived VEGF. However, VEGF derived from host stroma was readily detected in the tumor mass and treatment with a newly developed anti-VEGF monoclonal antibody substantially inhibited tumor growth. The functional significance of stroma-derived VEGF indicates that the recruitment of stromal cells is critical for the angiogenic and tumorigenic properties of these cells. Here we identified PDGF AA as the major stromal fibroblast chemotactic factor produced by tumor cells, and demonstrated that disrupting the paracrine PDGFR alpha signaling between tumor cells and stromal fibroblasts by soluble PDGFR alpha-IgG significantly reduced tumor growth. Thus, PDGFR alpha signaling is required for the recruitment of VEGF-producing stromal fibroblasts for tumor angiogenesis and growth. Our findings highlight a novel aspect of PDGFR alpha signaling in tumorigenesis.

Celecoxib inhibits vascular endothelial growth factor expression in and reduces angiogenesis and metastasis of human pancreatic cancer via suppression of Sp1 transcription factor activity

The aggressive biology of human pancreatic adenocarcinoma has been linked with overexpression of vascular endothelial growth factor (VEGF). Constitutive activation of the transcription factor Sp1 plays a critical role in VEGF overexpression. Recent studies indicated that celecoxib, a selective cyclooxygenase-2 inhibitor, exhibits potent antitumor activity. However, the underlying molecular mechanisms of this activity remain unclear. In the present study, we used a pancreatic cancer model to determine the role of Sp1 in the antitumor activity of celecoxib. Treatment of various pancreatic cancer cells with celecoxib suppressed VEGF expression at both the mRNA and protein level in a dose-dependent manner. VEGF promoter deletion and point mutation analyses indicated that a region between nucleotide -109 and -61 and its intact Sp1-binding sites were required for the inhibition of VEGF promoter activity by celecoxib. Also, celecoxib treatment reduced both Sp1 DNA binding activity and transactivating activity. This decreased activity correlated with reduced Sp1 protein and its phosphorylation as determined using Western blot analysis. Furthermore, in an orthotopic pancreatic cancer animal model, celecoxib treatment inhibited tumor growth and metastasis. The antitumor activity was consistent with inhibition of angiogenesis as determined by evaluating tumor microvessel formation, which correlated with decreased Sp1 activity and VEGF expression. Collectively, our data provide a novel molecular mechanism for the antitumor activity of celecoxib and may help further improve its effectiveness in controlling pancreatic cancer growth and metastasis.

Angiogenesis in hepatocellular carcinoma: the retrospectives and perspectives

Hepatocellular carcinoma (HCC) is a typical hypervascular tumor. Many angiogenic factors have been studied in HCC, and several anti-angiogenic therapies have been tested in animal models and patients. This paper summarizes the latest findings, especially regarding the clinical significance of endothelial cell markers and angiogenic factors in HCC, and experimental and clinical anti-angiogenesis therapies. Further developments in this area, such as endothelial cell-oriented research and better experimental and clinical designs in the evaluation of anti-angiogenic therapies are discussed.

Regulation of endothelial cell differentiation and transformation by H-Ras

Angiogenesis is regulated by growth factors which activate tyrosine kinase receptors leading to the activation of a number of intracellular signaling pathways. The specific function of H-Ras during FGF-2 stimulated endothelial cell differentiation, defined as invasive growth and formation of branching networks in fibrin gels, was investigated by using conditionally immortalized endothelial cell lines induced to express H-Ras mutants. Expression of inhibitory N17Ras did not impair differentiation in response to FGF-2 and TNF-alpha. The farnesyltransferase inhibitor FTI-277 inhibited farnesylation of Ras but did not inhibit differentiation of human microvascular endothelial cells or mouse brain endothelial cells. In contrast, activated V12Ras inhibited endothelial cell differentiation and cells displayed a transformed phenotype with an increased rate of proliferation and loss of contact inhibited growth. Furthermore, V12Ras expressing endothelial cells grew as solid tumors when injected subcutaneously into mice. Our data suggest that, in endothelial cells, H-Ras activity is not required for differentiation. However, this activity must be tightly regulated as aberrant activity can disturb the ability of endothelial cells to undergo differentiation.

Inhibitory effects of cannabinoid CB1 receptor stimulation on tumor growth and metastatic spreading: actions on signals involved in angiogenesis and metastasis

Stimulation of cannabinoid CB1 receptors by 2-methyl-arachidonyl-2'-fluoro-ethylamide (Met-F-AEA) inhibits the growth of a rat thyroid cancer cell-derived tumor in athymic mice by inhibiting the activity of the oncogene product p21ras. Here we report that Met-F-AEA also blocks the growth of tumors previously induced in nude mice by the s.c. injection of the same rat thyroid carcinoma cells. Met-F-AEA significantly inhibited, in tumors as well as transformed cells, the expression of the vascular endothelial growth factor, an angiogenetic factor known to be up-regulated by p21ras, as well as of one of its receptors, flt-1/VEGFR-1. The levels of the cyclin-dependent kinase inhibitor p27(kip1), which is down-regulated by p21ras, were instead increased by Met-F-AEA. All these effects were antagonized by the selective CB1 receptor antagonist SR141716A. Met-F-AEA inhibited in vitro the growth of a metastasis-derived thyroid cancer cell line more potently than a primary cancer cell line. Therefore, the hypothesis that CB1 receptor stimulation interferes not only with angiogenesis but also with metastatic processes was tested in a widely used model of metastatic infiltration in vivo, the Lewis lung carcinoma (3LL) in C57Bl/6 mice. Three weeks from the paw injection of 3LL cells, Met-F-AEA reduced significantly the number of metastatic nodes, in a way antagonized by SR141716A. Our findings indicate that CB1 receptor agonists might be used therapeutically to retard tumor growth in vivo by inhibiting at once tumor growth, angiogenesis, and metastasis.

Ras/Raf1-dependent signal in sphingosine-1-phosphate-induced tube formation in human coronary artery endothelial cells

Since we recently reported that high density lipoprotein, which contains the bioactive lipid sphingosine-1-phosphate (S1P) [Arterioscler. Thromb. Vasc. Biol. 23 (2003) 802], induced human coronary artery endothelial cell (HCEC) tube formation mediated by a Ras/Raf/ERK (extracellular signal-activated kinase) pathway, we thought that it would be very important to evaluate whether the signal in S1P-induced tube formation is Ras-dependent or -independent. In an in vitro model of HCEC tube formation on a matrix gel, S1P-induced tube formation. ERK1/2 inhibitor (PD98059) and pertussis toxin (PTX) suppressed S1P-induced tube formation. S1P activated phospho(p)-ERK1/2, while dominant-negative RasN17 blocked S1P-induced p-ERK1/2. Moreover, RasN17 inhibited S1P-induced tube formation. S1P activated Ras/Raf1 by Ras pull-down assay and this effect was inhibited by PTX. These results demonstrate that Ras/Raf1-dependent ERK activation mediated by PTX-sensitive G protein-coupled receptors may be a potent signal in S1P-induced HCEC tube formation.

High density lipoprotein-induced angiogenesis requires the activation of Ras/MAP kinase in human coronary artery endothelial cells

OBJECTIVE

Plasma high density lipoprotein (HDL) levels have been shown to be inversely correlated with coronary artery disease, but the mechanisms of the direct protective effect of HDL on endothelial cells (ECs) are not fully understood. In this study, we investigated the role of the HDL-mediated promotion of angiogenesis in human coronary artery ECs (HCECs).

METHODS AND RESULTS

We developed an in vitro model of HCEC tube formation on a matrix gel. We optimized the maximum dose of HDL required to induce tube formation in initial experiments, in which the dose response showed that the maximum effective dose of HDL was 100 microg/mL. PD98059, an inhibitor of p42/44 mitogen-activated protein kinase (MAPK) activity, but not SB203580, an inhibitor of p38 MAPK activity, suppressed HDL-induced tube formation. Dominant-negative Ras N17 inhibited HDL-induced tube formation. HDL activated Ras according to a ras pull-down assay, and this effect was inhibited by pertussis toxin. Moreover, HDL activated phospho(p)-p42/44 MAPK, whereas Ras N17 blocked HDL-induced pp42/44 MAPK.

CONCLUSIONS

These results indicate that HDL induced a potent signal through a Ras/MAPK pathway mediated by a pertussis toxin-sensitive G-protein coupled receptor to the angiogenic phenotype in HCECs.

Transcriptional regulation of osteopontin and the metastatic phenotype: evidence for a Ras-activated enhancer in the human OPN promoter

Elevated osteopontin (OPN) transcription often correlates with increased metastatic potential of transformed cells, and in several model systems OPN--whether produced by the tumor cells or by stromal cells - has been shown to enhance metastatic ability. Sequence elements in the OPN promoter have been identified on the basis of their ability to interact with protein factors associated with the tumorigenic process in one or more cell lineages. One of these is a Ras-activated enhancer (RAE) that binds a protein, the Ras-response factor (RRF), whose ability to form a complex with the RAE is stimulated by Ras signaling in fibroblasts and epithelial cells. Another is the T cell factor-4 binding site, which in the OPN promoter can retard OPN transcription when bound by the Tcf-4 protein. In Rama 37 rat mammary epithelial cells Tcf-4 suppresses OPN transcription and the metastatic phenotype. A third promoter segment consists of two sequences in the -94 to -24 region of the human OPN promoter able to bind several known transcription factors, including Sp1, Myc and Oct-1, which may act synergistically to stimulate OPN transcription in malignant astrocytic cells. Although expression of other genes may also be regulated by these transcription factors, evidence suggests that often OPN alone can stimulate metastasis. In this communication we address two issues: (1) How does OPN facilitate the metastatic phenotype? (2) What mechanisms are responsible for the increase in OPN transcription in metastatic cells?

Inhibition of angiogenesis and promotion of melanoma dormancy by vitamin E succinate

BACKGROUND

Relapse of melanoma after surgical treatment remains a significant clinical problem in need of novel therapies. Vitamin E succinate (VES) is a promising antitumor micronutrient. We evaluated the effect of VES on melanoma dormancy and angiogenesis.

METHODS

B16F10 melanoma cells were allografted in mice. The effect of VES on melanoma dormancy was measured by monitoring tumor volume. Tumor vascularity was quantitated with CD31 immunostaining. The expression of vascular endothelial growth factor (VEGF), VEGF receptor 1, and VEGF receptor 2 in tumors was assessed by the intensity of immunostaining. VES effect on secreted VEGF protein and VEGF promoter activity was measured with enzyme-linked immunosorbent assay and transient transfection assay, respectively. Significance was determined by analysis of variance.

RESULTS

VES promoted melanoma dormancy (P =.0019) and inhibited melanoma angiogenesis (P <.0001). VES also significantly suppressed the expression of VEGF, VEGF receptor 1, and VEGF receptor 2 in melanoma tumors (P <.0001). Melanoma VEGF secretion (P =.0077) and melanoma VEGF promoter activity (P <.05) were significantly inhibited by VES.

CONCLUSIONS

VES promotes melanoma dormancy and inhibits melanoma angiogenesis. The mechanism of the VES antiangiogenesis effect involves the inhibition of VEGF gene transcription. These findings support future studies of VES in the prevention of melanoma metastasis.

Vascular permeability factor/vascular endothelial growth factor: a critical cytokine in tumor angiogenesis and a potential target for diagnosis and therapy

Vascular endothelial growth factor A (VEGF-A), the founding member of the vascular permeability factor (VPF)/VEGF family of proteins, is an important angiogenic cytokine with critical roles in tumor angiogenesis. This article reviews the literature with regard to VEGF-A's multiple functions, the mechanisms by which it induces angiogenesis, and its current and projected roles in clinical oncology. VEGF-A is a multifunctional cytokine that is widely expressed by tumor cells and that acts through receptors (VEGFR-1, VEGFR-2, and neuropilin) that are expressed on vascular endothelium and on some other cells. It increases microvascular permeability, induces endothelial cell migration and division, reprograms gene expression, promotes endothelial cell survival, prevents senescence, and induces angiogenesis. Recently, VEGF-A has also been shown to induce lymphangiogenesis. Measurements of circulating levels of VEGF-A may have value in estimating prognosis, and VEGF-A and its receptors are potential targets for therapy. Recognized as the single most important angiogenic cytokine, VEGF-A has a central role in tumor biology and will likely have an important role in future approaches designed to evaluate patient prognosis. It may also become an important target for cancer therapy.

Angiogenesis modulation in cancer research: novel clinical approaches

Angiogenesis--the formation of new blood vessels--is essential for tumour progression and metastasis. Consequently, the modulation of tumour angiogenesis using novel agents has become a highly active area of investigation in cancer research, from the bench to the clinic. However, the great therapeutic potential of these agents has yet to be realized, which could, in part, be because the traditional strategies that are used in clinical trials for anticancer therapies are not appropriate for assessing the efficacy of agents that modulate angiogenesis. Here, we discuss methods for monitoring the biological activity of angiogenic modulators, and innovative approaches to trial design that might facilitate the integration of these agents into anticancer therapy.

The retinoblastoma family: twins or distant cousins?

The destiny of a cell--whether it undergoes division, differentiation or death--results from an intricate balance of many regulators, including oncoproteins, tumor-suppressor proteins and cell-cycle-associated proteins. One of the better-studied tumor suppressors is the retinoblastoma protein, known as pRb or p105. Two recently identified proteins, pRb2/p130 and p107, show structural and functional similarities to pRb, and these proteins and their orthologs make up the retinoblastoma (Rb) family. Members of the family have been found in animals and plants, and a related protein is known in the alga Chlamydomonas. Members of the Rb family are bound and inactivated by viral proteins and, in turn, bind cellular transcription factors and repress their function, and can also form complexes with cyclins and cyclin-dependent kinases and with histone deacetylases. They are found in the nucleus and their subnuclear localization depends on binding to the nuclear matrix. Members of the family form part of a signal-transduction pathway called the Rb pathway, which is important in cell-cycle regulation and have roles in growth suppression, differentiation and apoptosis in different organisms and cell types.

Vascular endothelial growth factor induction of the angiogenic phenotype requires Ras activation

We investigated the role of Ras in vascular endothelial growth factor (VEGF)-mediated signal transduction and the promotion of angiogenic changes primary endothelial cells. We find that VEGF potently induces Ras activation and that this step is essential for the stimulation by VEGF of several cellular changes associated with angiogenesis, including proliferation, migration, and branching morphogenesis in three-dimensional culture. Inhibition of Ras signaling induced subtle changes in the actin architecture but had no effect on the phosphatidylinositol 3-kinase (PI3K) or p38 signaling pathways. In contrast, activation of ERK was largely dependent on Ras. Although inhibiting ERK activity completely suppressed cell proliferation and partially blocked in vitro differentiation, neither ERK nor PI3K activity was required for VEGF-induced migration. These data provide the first direct demonstration that inhibition of Ras signal transduction is anti-angiogenic. Interestingly, VEGF signal transduction bifurcates both upstream and downstream of Ras, with different Ras-dependent signals controlling endothelial cell proliferation and migration, essential components of the angiogenic response.