UMLS:C1519670 - FACTA Search

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Query: UMLS:C1519670 (tumor angiogenesis)
6,052 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A tumor vasculature is highly unstable and immature, characterized by a high proliferation rate of endothelial cells, hyper-permeability, and chaotic blood flow. The dysfunctional vasculature gives rise to continual plasma leakage and hypoxia in the tumor, resulting in constant on-sets of inflammation and angiogenesis. Tumors are thus likened to wounds that will not heal. The lack of functional mural cells, including pericytes and vascular smooth muscle cells, in tumor vascular structure contributes significantly to the abnormality of tumor vessels. Angiopoietin-1 (Ang1) is a physiological angiogenesis promoter during embryonic development. The function of Ang1 is essential to endothelial cell survival, vascular branching, and pericyte recruitment. However, an increasing amount of experimental data suggest that Ang1-stimulated association of mural cells with endothelial cells lead to stabilization of newly formed blood vessels. This in turn may limit the otherwise continuous angiogenesis in the tumor, and consequently give rise to inhibition of tumor growth. We discuss the enigmatic role of Ang1 in tumor angiogenesis in this review.
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PMID:The enigmatic role of angiopoietin-1 in tumor angiogenesis. 1467 54

Early theories of tumor angiogenesis suggested that preexisting vessels surrounding the tumor were the principal source of the tumor vasculature but recent evidence suggests that endothelial progenitor cells (EPC) migrate from the marrow play an important role in developing the tumor blood supply. In a mouse model, in which the vascularization of a transplantable tumor was studied after bone marrow (BM) transplantation, we show that cells that express Tie-2, Sca-1, CD31 and CD45 function as both BM EPC and primitive hematopoietic stem cells. BM cells from transgenic mice expressing green fluorescent protein (GFP) under the control of the endothelial lineage-specific Tie-2 promoter (Tie-2 /GFP) were used to reconstitute irradiated (12 Gy) wild-type mice. Five donor BM cell populations were studied: (1) whole BM; (2) Sca-1-enriched BMC; (3) GFP/Tie-2+, Sca-1+ BMC; (4) GFP/Tie-2-, Sca-1+ BMC and (5) Sca-1-depleted BMC. After 4 weeks, the mice were injected with Tg.AC tumor cells. Three weeks later, sections from the tumors were stained for CD31 and examined for Tie-2-driven GFP expression. BM-derived endothelial cells were found only in mice transplanted with bone marrow containing populations of Tie-2+, Sca-1+ cells. As few as 3500 of these cells were sufficient to radioprotect lethally irradiated mice. Thus, we conclude that a rare subset of BMC (approximately 4 x 10(-3)%) with the putative properties of hemangioblasts have an active Tie-2 promoter. Selection of Tie-2+Sca-1+ BMC enriches for marrow-derived EPCs that participate in tumor angiogenesis and cells that can provide hematopoietic reconstitution of marrow-ablated mice.
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PMID:Hematopoietic stem cells and endothelial cell precursors express Tie-2, CD31 and CD45. 1475 32

Advanced stages of neuroblastoma show increased expression of matrix metalloproteinases MMP-2 and MMP-9, that have been implicated in many steps of tumor progression, suggesting that they play a contributory role. Using pharmacological and genetic approaches, we have examined the role of these MMPs in progression of SK-N-BE (2).10 human neuroblastoma tumors orthotopically xenotransplanted into immunodeficient mice. Mice treated with Prinomastat, a synthetic inhibitor of MMPs, showed an inhibition of tumor cell proliferation in implanted tumors and a prolonged survival (50 versus 39 days in control group, P < 0.035). Treatment with Prinomastat did not affect formation of liver metastases (P = 0.52) but inhibited intravascular colonization by the tumor cells in the lung by 73.8% (P = 0.03) and angiogenesis in both primary tumors and experimental liver metastases. The primary tumors from Prinomastat-treated mice showed a 39.3% reduction in endothelial area detected by PECAM/CD31 staining in tumor sections (P < 0.001), primarily due to the presence of smaller vessels (P = 0.004). MMP-2 is expressed by neuroblastoma tumor cells and stromal cells, whereas MMP-9 is exclusively expressed by stromal cells, particularly vascular cells. To examine the contribution of MMP-9 to tumor angiogenesis, we generated RAG1/MMP-9 double-deficient mice. We observed a significant inhibition of angiogenesis in the immunodeficient RAG1/MMP-9 double-deficient mice orthotopically implanted with tumor cells (P = 0.043) or implanted s.c. with a mixture of tumor cells and Matrigel (P < 0.001). Using an FITC-labeled lectin, we demonstrated an inhibition in the architecture of the tumor vasculature in MMP-9-deficient mice, resulting in fewer and smaller blood vessels. These changes were associated with a 48% decrease in pericytes present along microvessels. Taken together, the data demonstrate that in neuroblastoma, stromally derived MMP-9 contributes to angiogenesis by promoting blood vessel morphogenesis and pericyte recruitment.
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PMID:Stromal matrix metalloproteinase-9 regulates the vascular architecture in neuroblastoma by promoting pericyte recruitment. 1499 27

Multidisciplinary treatment strategies for patients with malignant brain tumors have resulted in only small gains in terms of prognosis in spite of the use of aggressive therapy. There is a growing realization that a paradigm shift is needed in the conceptual approaches to glioma therapy. Such approaches will rely on identification and modification of key cellular targets that define the biological behavior of these tumors. Among the targets for such treatment approaches, tumor angiogenesis has captured the attention of not only the medical field but also of the lay public because of its conceptual departure from traditional methods of cancer therapy. Angiogenesis and vascular proliferation are particularly important in the growth and progression of malignant gliomas and are used as indicators of the degree of malignancy. Recent studies have helped us gain a better understanding of the molecular mediators of this process. It is now evident that after the initial formation of malignancy the continued growth of a glioma is critically dependent on its angiogenic potential. Hence, several approaches to control angiogenesis are being developed and tested. Preliminary results from clinical studies have shown that angiogenesis inhibition is a valid approach as a therapeutic strategy against gliomas but it is also becoming evident that inhibition of individual modulators of this process may not yield the expected impact on prognosis. To fully realize the potential of antiangiogenic therapy, a deeper understanding of the interplay between the tumor vasculature and its environment is needed. Angiogenesis inhibitors have made the transition from preclinical studies to the clinical arena; it remains for ongoing human trials of such agents to fully explore the feasibility and efficacy of these agents in order to exploit the potential of this approach.
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PMID:Inhibition of angiogenesis as a therapeutic strategy against brain tumors. 1501 67

Targeting tumor vasculature represents an interesting approach for the treatment of solid tumors. The alpha v beta 3 integrins have been found to be specifically associated with angiogenesis in tumors. By using bacteriophage display technology, Ruoslahti et al found that a group of peptides containing the RGD (Arg-Gly-Asp) motif have high-binding affinity to the alpha v beta 3 integrins in tumors. In this study, we designed a fusion protein containing the RGD sequence and the Fc fragment of mouse IgG in order to target the Fc portion of IgG to the tumor vasculature to elicit an antiangiogenesis immune response. In vivo angiogenesis and tumor studies demonstrated that the fusion protein (RGD/mFc) inhibited tumor angiogenesis and tumor growth and improved overall survival. This approach may generate new therapeutic agents for solid tumor treatment.
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PMID:Fusion protein from RGD peptide and Fc fragment of mouse immunoglobulin G inhibits angiogenesis in tumor. 1504 60

Vascular Endothelial Growth Factor (VEGF) functions as a key regulator in tumor angiogenesis. In addition, VEGF is an important survival factor for endothelial cells under chemical or physical stress. In our report, we show that treatment of endothelial cells with the chemotherapeutic agent carboplatin significantly increased the expression of VEGF. Furthermore, neutralization of secreted VEGF with specific polyclonal anti-VEGF antibodies or monoclonal antibody sensitized endothelial cells to carboplatin treatment and increased apoptosis several-fold. Interestingly, carboplatin treatment did not alter VEGF expression in tumor cells. Similarly, antibody to VEGF did not change the chemosensitivity of tumor cells to this drug. Most importantly, tumor-bearing animals treated with carboplatin showed an increase in VEGF immunoreactivity in the tumor vasculature, confirming the in vitro studies. Based on these observations, we determined whether neutralization of VEGF could enhance the anti-tumor activity of carboplatin in an in vivo ovarian cancer model system. A combination therapy consisting of a suboptimal dose of carboplatin (32.5 mg/kg/inj., q3d x 5; i.p.) and polyclonal anti-VEGF antibody (2 mg/inj., q3d x 10; i.p.) significantly enhanced solid tumor growth inhibition over individual monotherapies and included multiple complete responses. These findings suggest that VEGF is a critical endothelial cell specific survival factor that is induced by carboplatin and contributes to the protection of tumor vasculature during chemotherapy treatment. In addition, these results provide evidence for a potential mechanism that underlies enhanced anti-tumor activity achieved with chemotherapy and anti-VEGF antibody combination treatment regimens as recently reported in a number of clinical trials. We conclude that a similar type of combination therapy may be applicable to many types of malignancies since VEGF expression was differentially induced in the tumor host environment (i.e., tumor vasculature) and not in the tumor cells themselves; hence, this phenomenon may be independent of the type and origin of the primary cancer.
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PMID:Carboplatin selectively induces the VEGF stress response in endothelial cells: Potentiation of antitumor activity by combination treatment with antibody to VEGF. 1509 98

We characterized the effect of potent vascular endothelial growth factor (VEGF) blockade on early-stage Wilms tumor xenograft growth, vasculature and metastasis. VEGF is a key mediator of both physiologic and tumor angiogenesis. We recently described that potent VEGF blockade induces regression of established Wilms tumor xenografts and vessels, also reducing the size but not the incidence of pre-existing metastases. In these studies, we examined the effects of potent VEGF blockade on earlier stages of experimental Wilms tumors, focusing on tumor growth, vasculature and metastasis. Athymic mice received intrarenal human Wilms tumor cell implants. Biweekly treatment with vehicle or the VEGF-Trap, a high-affinity soluble decoy receptor incorporating regions of VEGFR1 and VEGFR2, was begun 1 week later (100 or 500 micrograms/dose, n=20 in each group). Mice were euthanized at week 6 to examine tumor weight, incidence of lung metastases, vascularity and expression of angiogenic factors. A cohort of mice was examined 2 weeks after cessation of treatment. Compared to controls, VEGF-Trap treated tumors were significantly smaller (100 micrograms/dose: 92.7% smaller, p=0.0017; 500 micro g/dose: 99.0% smaller, p=0.0009). The incidence of lung metastasis also decreased significantly (p<0.0055). VEGF-Trap nearly eradicated tumor vasculature. Rare persisting vessels were characterized by large caliber, quiescence (lacking proliferation/apoptosis) and arterialization (both phenotypic and molecular). Potent VEGF blockade caused near-arrest of experimental Wilms tumor growth, resulted in nearly avascular tumors, and also decreased the incidence and size of metastases. Persistent vessels in tumors treated with VEGF-Trap displayed specific morphologic and molecular features, suggestive of arterialization. Future strategies that target these persisting vessels may enhance the efficacy of VEGF blockade therapy.
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PMID:Effects of potent VEGF blockade on experimental Wilms tumor and its persisting vasculature. 1528 55

Two of the most promising new targets in the treatment of colorectal cancer are the epithelial growth factor receptor (EGFR) and the vascular endothelial growth factor (VEGF). Agents that inhibit the EGFR or bind to VEGF have demonstrated clinical activity as single agents and in combination with chemotherapy in phase II and phase III clinical trials. The most promising of these agents are cetuximab, which blocks the binding of EGF and transforming growth factor alpha (TGF-alpha) to EGFR, and bevacizumab, which binds free VEGF. Cetuximab and irinotecan have been evaluated in two clinical studies in the USA (IMCL CP02-0141 and IMCL CP02-9923). Study IMCL CP02-0141 evaluated the antitumor activity of single-agent cetuximab in patients with irinotecan-refractory, EGFR-positive metastatic colorectal carcinoma. There were 6 partial responses in 57 treated patients, for a response rate of 10.5%. Study IMCL CP02-9923 evaluated the combination of cetuximab and irinotecan in a total of 139 patients enrolled at 27 study sites. In this trial 22.5% of patients with progressive disease on irinotecan achieved an objective response (19% by investigator assessment) showing that the combination of cetuximab and irinotecan has antitumor activity in this population. A large randomized phase II trial evaluating similar study populations in Europe confirmed these findings, demonstrating response rates for cetuximab/irinotecan and cetuximab alone of 22.9% and 10.8%, respectively. The other promising agent bevacizumab is a humanized variant of the anti-VEGF monoclonal antibody. VEGF is produced by healthy and neoplastic cells. Its activities are mediated by two receptor tyrosine kinases. VEGF signaling is often a rate-limiting step in physiologic and pathologic angiogenesis. Bevacizumab has been studied as an antiangiogenic cancer therapeutic as a single agent and in combination with chemotherapy in patients with stage III and IV colon cancer. In addition to its direct antiangiogenic effects, bevacizumab may allow more efficient delivery of chemotherapy by altering tumor vasculature and decreasing the elevated interstitial pressure common in tumors. In this regard, some of the most robust phase II data using bevacizumab are from a randomized study of chemotherapy [fluorouracil (5-FU) and leucovorin (LV)] with or without bevacizumab in metastatic colorectal cancer. In this study, treatment with bevacizumab plus 5-FU/LV resulted in higher response rates, longer median time to disease progression, and longer median survival. Recently, a phase III, multicenter, double-blind, randomized, placebo-controlled trial was designed to investigate the addition of bevacizumab to first-line irinotecan, 5-FU, and LV chemotherapy (IFL). The trial showed a higher response rate, longer time to tumor progression, and prolonged overall survival in patients with metastatic colorectal cancer. It was the first large, randomized, phase III survival trial to assess the importance of targeting VEGF and tumor angiogenesis for the treatment of human cancer. Integration of novel agents targeting VEGF and EGFR with irinotecan-based chemotherapy has shown clinical activity in patients with metastatic colorectal cancer. The goal in the future will be to predict which specific chemotherapy and targeted agent combination will most likely benefit individual patients.
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PMID:Integration of novel agents in the treatment of colorectal cancer. 1530 12

Id1 and Id3 genes are required for vascularization, growth, and metastasis of xenograft tumors. In Id-deficient mice, tumor transplantation and proangiogenic factors fail to mobilize and recruit circulating endothelial precursor cells (CEPs) and hematopoietic cells, leading to defective tumor angiogenesis in various models. To investigate the requirement of Id genes and bone marrow incorporation in spontaneous prostate tumors, we crossbred Id mutant mice with the transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Id1-/- Id3+/- TRAMP mice display delayed tumor growth at 24 weeks compared with wild-type TRAMP mice. Id1 and Id3 were strongly expressed in the endothelial cells of poorly differentiated prostate adenocarcinoma but not in the vasculature of well-differentiated tumors, a finding that is corroborated in human prostate tumor samples. In Id-deficient TRAMP mice, the poorly differentiated tumors show extensive hemorrhage, whereas well-differentiated tumors exhibit none. Transplantation with Id wild-type bone marrow significantly reduced the hemorrhage in poorly differentiated prostate adenocarcinomas with bone marrow-derived endothelial cells contributing to 14% of the tumor blood vessels. However, in well-differentiated prostate adenocarcinomas, there was little evidence of bone marrow-derived endothelial cell incorporation. These differences in the expression of Id genes, the effects of Id loss, and the recruitment of bone marrow-derived endothelial precursor cells in tumor vasculature between well-differentiated and poorly differentiated prostate adenocarcinoma suggest that tumor angiogenesis varies depending on the tumor grade.
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PMID:Utilization of bone marrow-derived endothelial cell precursors in spontaneous prostate tumors varies with tumor grade. 1534 97

We identified regulator of G-protein signaling-5 (RGS-5) as an angiogenic pericyte marker at sites of physiologic and pathologic angiogenesis. In a mouse model of pancreatic islet cell carcinogenesis, RGS-5 is specifically induced in the vasculature of premalignant lesions during the "angiogenic switch" and further elevated in tumor vessels. Similarly, RGS-5 is overexpressed in highly angiogenic astrocytomas but not in hypoxia-inducible factor-1alpha (HIF-1alpha)-deficient tumors, which grow along preexisting brain capillaries without inducing neovessels. Elevated levels of RGS-5 in pericytes are also observed during wound healing and ovulation indicating a strong correlation between RGS-5 expression and active vessel remodeling beyond tumor angiogenesis. Moreover, antitumor therapy, which reverses tumor vasculature to an almost normal morphology, results in down-regulation of RGS-5 transcription. Taken together, these data demonstrate for the first time a factor that is specific for "activated" pericytes. This further supports the notion that pericytes, like endothelial cells, undergo molecular changes during neovascularization that makes them a novel target for antiangiogenic therapy.
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PMID:Regulator of G-protein signaling-5 induction in pericytes coincides with active vessel remodeling during neovascularization. 1545 6

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