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

In primary malignant brain tumors increased vascularity and marked edema strongly suggest a possible role of the vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). This was confirmed by earlier in situ hybridization studies, by analysis of the expression of the mitogen in different subsets of glioblastoma cells, and by the fact that the VEGF/VPF receptor flt-1 (fms-like tyrosine kinase) is up-regulated in tumor cells in vivo. To assess and quantify the expression of the VEGF/VPF gene and of the receptor gene, 26 surgical specimens of brain tumor tissue from 24 patients were analyzed. In most malignant gliomas, the expression level of the VEGF/VPF gene is elevated and can be increased up to 20- to 50-fold in comparison with low-grade tumors. Using polymerase chain reaction-based amplification, it could be shown that the messenger RNAs of three different VEGF/VPF forms are synthesized in tumor tissue samples. Northern blot studies revealed that in some samples a significant expression of the gene coding for placenta growth factor, a growth factor closely related to VEGF/VPF, was observed. In addition, using a radioreceptor assay it was possible to detect high VEGF/VPF-like activity in the cyst fluids of brain tumors, indicating the accumulation of the mitogen and permeability factor in brain tumor cysts. Further investigations revealed that astrocytoma and glioblastoma cells in culture express the VEGF/VPF gene and secrete the VEGF/VPF protein, whereas gene expression of the two known VEGF/VPF receptors, kinase insert domain-containing receptor and flt-1, could not be detected. These data support previous reports, which stated that VEGF/VPF acts as a paracrine growth and permeability factor in brain tumors and may contribute to tumor growth by initiating tumor angiogenesis.
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PMID:Detection and quantification of vascular endothelial growth factor/vascular permeability factor in brain tumor tissue and cyst fluid: the key to angiogenesis? 752 59

Key growth factor-receptor interactions involved in angiogenesis are possible targets for therapy of CNS tumors. Vascular endothelial growth factor (VEGF) is a highly specific endothelial cell mitogen that has been shown to stimulate angiogenesis, a requirement for solid tumor growth. The expression of VEGF, the closely related placental growth factor (PIGF), the newly cloned endothelial high affinity VEGF receptors KDR and FLT1, and the endothelial orphan receptors FLT4 and Tie were analyzed by in situ hybridization in normal human brain tissue and in the following CNS tumors: gliomas, grades II, III, IV; meningiomas, grades I and II; and melanoma metastases to the cerebrum. VEGF mRNA was up-regulated in the majority of low grade tumors studied and was highly expressed in cells of malignant gliomas. Significantly elevated levels of Tie, KDR, and FLT1 mRNAs, but not FLT4 mRNA, were observed in malignant tumor endothelia, as well as in endothelia of tissues directly adjacent to the tumor margin. In comparison, there was little or no receptor expression in normal brain vasculature. Our results are consistent with the hypothesis that these endothelial receptors are induced during tumor progression and may play a role in tumor angiogenesis.
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PMID:Expression of endothelial cell-specific receptor tyrosine kinases and growth factors in human brain tumors. 785 49

The growth factor receptors expressed on endothelial cells are of special interest because of their potential to program endothelial cell growth and differentiation during development and neovascularization in various pathological states, such as wound healing and angiogenesis associated with tumorigenesis. Vascular endothelial growth factor ([VEGF] also known as vascular permeability factor) is a potent mitogen and permeability factor, which has been suggested to play a role in embryonic and tumor angiogenesis. The newly cloned FLT4 receptor tyrosine kinase gene encodes a protein related to the VEGF receptors FLT1 and KDR/FLK-1. We have here studied the expression of FLT4 and the other two members of this receptor family in human fetal tissues by Northern and in situ hybridization. These results were also compared with the sites of expression of VEGF and the related placenta growth factor (PlGF). Our results reveal FLT4 mRNA expression in vascular endothelial cells in developing vessels of several organs. A comparison of FLT4, FLT1 and KDR/FLK-1 receptor mRNA signals shows overlapping, but distinct expression patterns in the tissues studied. Certain endothelia lack one or two of the three receptor mRNAs. These data suggest that the receptor tyrosine kinases encoded by the FLT gene family may have distinct functions in the regulation of the growth/differentiation of blood vessels.
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PMID:The related FLT4, FLT1, and KDR receptor tyrosine kinases show distinct expression patterns in human fetal endothelial cells. 824 83

Several groups have shown that quantitation of tumor angiogenesis by counting blood vessels in primary breast cancer gives an independent assessment of prognosis. Poor prognosis is associated with high blood vessel counts. We have shown that the rate of cell division in endothelial cells is much higher in breast tumours than in normal breast. Breast cancer cell lines and primary human breast tumours express a wide range of vascular growth factors, including VEGF, placenta growth factor, pleiotrophin, TGF beta 1, acidic and basic FGF, and platelet-derived endothelial cell growth factor. Inhibiting angiogenesis by blocking vascular growth factors would be difficult with highly specific agents, but drugs with a broader spectrum of antagonism may be effective. We have developed several suramin analogues which are less toxic than suramin in vivo but more potent in inhibiting angiogenesis, and these have been developed for Phase I. A combination of anti-angiogenesis agents with drugs activated by hypoxia may also be useful, because anti-angiogenesis alone may not kill cells, whereas activation of hypoxic drugs could synergize. New endpoints may be necessary because inhibition of new blood vessel formation may not cause tumour regression. Thus, the endpoint of stable disease and biochemical assessment of inhibition of angiogenesis may be much more important in therapeutic studies and for drug development in the future. The prognostic importance of angiogenesis suggests that this should be a major new therapeutic target.
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PMID:Breast cancer angiogenesis--new approaches to therapy via antiangiogenesis, hypoxic activated drugs, and vascular targeting. 882 27

The vascular endothelial growth factor is produced by a large variety of human tumors, including melanoma, in which it appears to play an important role in the process of tumor-induced angiogenesis. Little information is available on the role of placenta growth factor, a member of the vascular endothelial growth factor family of cytokines, in tumor angiogenesis, even though placenta growth factor/vascular endothelial growth factor heterodimers have been recently isolated from tumor cells. To investigate the role of placenta growth factor and vascular endothelial growth factor homodimers and heterodimers in melanoma angiogenesis and growth, 19 human melanoma cell lines derived from primary or metastatic tumors were characterized for the expression of these cytokines and their receptors. Release of placenta growth factor and vascular endothelial growth factor polypeptides into the supernatant of human melanoma cells was demonstrated. Reverse transcriptase polymerase chain reaction analysis showed the presence of mRNAs encoding at least three different vascular endothelial growth factor isoforms (VEGF(121), VEGF(165), and VEGF(189)) and transcripts for two placenta growth factor isoforms (PlGF-1 and PlGF-2) in human melanoma cells. In addition, placenta growth factor expression in human melanoma in vivo was detected by immunohistochemical staining of tumor specimens. Both primary and metastatic melanoma cells were found to express the mRNAs encoding for vascular endothelial growth factor and placenta growth factor receptors (KDR, Flt-1, neuropilin-1, and neuropilin-2), and exposure of melanoma cells to these cytokines resulted in a specific proliferative response, supporting the hypothesis of a role of these angiogenic factors in melanoma growth. J Invest Dermatol 115:1000-1007 2000
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PMID:Human melanoma cells secrete and respond to placenta growth factor and vascular endothelial growth factor. 1112 Nov 33

In order to grow beyond minimal size and to metastasize, tumors need to induce the growth of new blood vessels (angiogenesis). Whereas in normal tissues, vascular quiescence is maintained by the dominant influence of endogenous angiogenesis inhibitors over angiogenic stimuli, tumor angiogenesis is induced by increased secretion of angiogenic factors and/or by downregulation of angiogenesis inhibitors. Recent evidence suggests vascular endothelial growth factor (VEGF) as the major tumor angiogenesis factor, promoting tumor growth, invasion, and metastasis. Conversely, blocking of VEGF function inhibits angiogenesis and suppresses tumor growth in vivo. Newly identified members of the VEGF family of angiogenesis factors include placental growth factor, VEGF-B, VEGF-C, and VEGF-D, and show overlapping binding patterns to specific endothelial cell receptors. VEGF-C appears to play a major role as a lymphangiogenesis factor and as a growth factor for Kaposi's sarcoma. In contrast, endogenous inhibitors prevent blood vessel growth in normal tissues. In particular, thrombospondin-1 (TSP-1) and TSP-2 are expressed in normal skin and, when introduced into squamous cell carcinomas, potently inhibit malignant tumor growth via inhibition of tumor angiogenesis.
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PMID:Tumor angiogenesis. 1114 70

The vascular endothelial growth factor (VEGF)-related factor, placental growth factor (PlGF),has been shown recently to play an important role in pathological VEGF-driven angiogenesis. In this study, we examine the effects of mPlGF/PlGF-2 overexpression in tumors grown from glioma cells containing a tetracycline-regulated mPlGF cDNA. Overexpression of mPlGF leads to increased tumor growth and vascular survival. When tetracycline is used to abruptly withdraw mPlGF overexpression, we see increased apoptosis in both vascular cells and macrophages. In addition, PlGF-2 induces survival gene expression and inhibits apoptosis in vitro. Thus, we propose that PlGF-2 contributes to tumor angiogenesis by providing increased survival function to endothelial cells and macrophages.
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PMID:Placental growth factor is a survival factor for tumor endothelial cells and macrophages. 1201 48

Interaction between vascular endothelial growth factor (VEGF) and its cognate receptors, KDR/Flk-1 and Flt-1, of vascular endothelial cells is expected to induce an angiogenesis "switch" in tumors and other angiogenesis-associated diseases. SU5416, a selective inhibitor of the KDR/Flk-1 tyrosine kinase, is known to be a potent inhibitor of tumor angiogenesis. In this study, we first observed that SU5416 inhibited Flt-1 tyrosine kinase activity at similar doses, in addition to inhibiting KDR/Flk-1 tyrosine kinase activity in response to VEGF. SU5416 inhibited cell migration of human vascular endothelial cells expressing both Flt-1 and KDR in response to VEGF and also inhibited the cell migration in response to placenta growth factor (PIGF), a specific ligand for Flt-1. Chemotaxis of monocytes expressing only Flt-1 was also inhibited by SU5416 in a dose-dependent manner. Moreover, SU5416 was found to inhibit tyrosine kinase of Flt-1 in response to PIGF in vitro. And angiogenesis induced by PIGF in a Matrigel plug assay was inhibited by administration of SU5416. The antiangiogenic effects by this VEGF receptor-targeting compound appeared to be mediated through interference not only with KDR/Flk-1 but also with Flt-1. Cell migration of vascular endothelial cells and monocytic cells through Flt-1, thus, might play a key role in VEGF-induced tumor angiogenesis in concert with KDR/Flk-1.
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PMID:Antiangiogenic effect by SU5416 is partly attributable to inhibition of Flt-1 receptor signaling. 1248 45

To fully assess the role of VEGF-A in tumor angiogenesis, antibodies that can block all sources of vascular endothelial growth factor (VEGF) are desired. Selectively targeting tumor-derived VEGF overlooks the contribution of host stromal VEGF. Other strategies, such as targeting VEGF receptors directly or using receptor decoys, result in inhibiting not only VEGF-A but also VEGF homologues (e.g. placental growth factor, VEGF-B, and VEGF-C), which may play a role in angiogenesis. Here we report the identification of novel anti-VEGF antibodies, B20 and G6, from synthetic antibody phage libraries, which block both human and murine VEGF action in vitro. Their affinity-improved variants completely inhibit three human tumor xenografts in mice of skeletal muscle, colorectal, and pancreatic origins (A673, HM-7, and HPAC). Avastin, which only inhibits the tumor-derived human VEGF, is approximately 90% effective at inhibiting HM-7 and A673 growth but is <50% effective at inhibiting HPAC growth. Indeed, HPAC tumors contain more host stroma invasion and stroma-derived VEGF than other tumors. Thus, the functional contribution of stromal VEGF varies greatly among tumors, and systemic blockade of both tumor and stroma-derived VEGF is sufficient for inhibiting the growth of tumor xenografts.
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PMID:Cross-species vascular endothelial growth factor (VEGF)-blocking antibodies completely inhibit the growth of human tumor xenografts and measure the contribution of stromal VEGF. 1627 8

The role of placenta growth factor (PlGF) in pathologic angiogenesis is controversial. The effects of PlGF on growth, angiogenesis, and metastasis from orthotopic tumors are not known. To this end, we stably transfected three human cancer cell lines (A549 lung, HCT116 colon, and U87-MG glioblastoma) with human plgf-2 full-length cDNA. Overexpression of PlGF did not affect tumor cell proliferation or migration in vitro. The growth of PlGF-overexpressing tumors grown orthotopically or ectopically was impaired in all three tumor models. This decrease in tumor growth correlated with a decrease in tumor angiogenesis. The PlGF-overexpressing tumors had decreased vessel density and increased vessel diameter, but vessel permeability was not different from the parental tumors. Tumors overexpressing PlGF exhibited higher levels of PlGF homodimers and PlGF/vascular endothelial growth factor (VEGF) heterodimers but decreased levels of VEGF homodimers. Our study shows that PlGF overexpression decreases VEGF homodimer formation and inhibits tumor progression.
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PMID:Placenta growth factor overexpression inhibits tumor growth, angiogenesis, and metastasis by depleting vascular endothelial growth factor homodimers in orthotopic mouse models. 1661 13


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