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Inhibition of angiogenic factor- and tumour-induced angiogenesis by gamma linolenic acid.

Angiogenesis, the formation of new blood vessels, is an essential feature of malignant tumour development. Gamma linolenic acid (GLA), a n-6 polyunsaturated fatty acid (PUFA), inhibits the growth and metastasis of a variety of tumour cells, including breast, prostate, pancreatic cancer and hepatoma cells and also has anti-metastatic effects on endothelial cells. In the current study, we tested whether GLA inhibited angiogenesis induced by tumour cells. A rat aortic ring assay and in vitro tube formation of human vascular endothelial cells were used to determine angiogenesis (spontaneous, angiogenic factor- and tumour cells-induced). Inclusion of GLA in this 3-D matrix culture system significantly inhibited angiogenesis from aortic rings in a concentration-dependent manner. The results from tube formation of vascular endothelial cell further confirmed that GLA suppressed angiogenesis. Furthermore, in the cell motility assay (phagokinetic assay and endothelial wounding assay), a significant reduction of the motility of vascular endothelial cells by GLA was seen. It is concluded that gamma linolenic acid inhibits angiogenic factor and tumour-induced angiogenesis in vitro at least in part via its inhibitory effect on the motility of vascular endothelial cells.

Angiogenesis Inducing Agents↗

[Angiogenesis, lymphangiogenesis, and tumor progression].

Angiogenesis plays an important role for the growth and metastasis of malignant tumors. The "angiogenic switch" may even precede the development of other traits that contribute to the malignant phenotype. The switch to the angiogenic phenotype is thought to be induced by a change in the balance of positive and negative regulators of angiogenesis. The main emphasis of this review is to discuss the role of two potent endogenous inhibitors, thrombospondin-(TSP-)1 and TSP-2, for the development and progression of tumors. The recent identification of specific growth factors for lymphatic vessels and of new lymphatic-specific markers provided evidence for an active role of the lymphatic system during the metastasis process. Endogenous inhibitors of lymphangiogenesis have not yet been detected and until recently it was unclear whether or not the known endogenous angiogenesis inhibitors may also have some additional effects on lymphangiogenesis. The data provided indicate that angiogenesis inhibitors specifically inhibit tumor progression but fail to block the conversion of premalignant to malignant tumors. Moreover, angiogenesis inhibitors may have some elective effects on the formation of blood vessels but not on lymphatic vessels. These results will have implications for the further development and clinical use of angiogenesis inhibitors since they indicate that inhibitors might most efficiently be used to target early stages of tumor progression and in combination with specific inhibitors of lymphangiogenesis.

Angiogenesis Inhibitors↗

Wound-induced angiogenesis and its pharmacologic inhibition in a murine model.

BACKGROUND: A novel synthetic compound, SU5416, inhibits subcutaneous tumor growth of cells. Because angiogenesis in tumor growth and wound healing involves similar mechanisms, we examined whether SU5416 inhibits wound-induced angiogenesis. METHODS: Sixteen female BALB/c mice were randomized to receive either SU5416 (n = 8) or vehicle alone (n = 8) on day -2. On day 0, transparent window chambers were implanted into the dorsal skin flap. Treatment was stopped on day 7. On days 1, 7, and 14, micrographs of the windows were taken and microvessel density was estimated. RESULTS: On day 1, no statistically significant difference was noted between the microvessel density in controls and treatments. After the mice underwent treatment from day -2 to day 7 and microvessel densities were analyzed on day 7, angiogenesis was significantly inhibited in the SU5416 group (P <.001). Seven days after cessation of treatment, however, the SU5416 group showed complete recovery in angiogenesis. The increase in microvessel density in the SU5416 group on day 14 from day 7 was not significantly different from that of the control group (P >.05). CONCLUSIONS: We observed that SU5416, a known inhibitor of tumor-induced angiogenesis, also inhibited wound-induced angiogenesis in our murine wound model. This inhibitory effect is significant while the mice are undergoing treatment.

Angiogenesis Inhibitors↗

Hepatocyte growth factor/scatter factor mediates angiogenesis through positive VEGF and negative thrombospondin 1 regulation.

Hepatocyte growth factor/scatter factor (HGF/SF), acting through the Met receptor, plays an important role in most human solid tumors, and inappropriate expression of this ligand-receptor pair is often associated with poor prognosis. The molecular basis for the malignant potential of the HGF/SF-Met signal in cancer cells has mostly been attributed to its mitogenic and invasive properties. However, HGF/SF also induces angiogenesis, but the signaling mechanism has not been fully explained, nor has this activity been directly associated with HGF/SF-Met-mediated tumorigenesis. It is known that HGF/SF induces in vitro expression of vascular endothelial growth factor (VEGF), a key agonist of tumor angiogenesis; by contrast, thrombospondin 1 (TSP-1) is a negative regulator of angiogenesis. Here, we show that, in the very same tumor cells, in addition to inducing VEGF expression, HGF/SF dramatically down-regulates TSP-1 expression. We show that TSP-1 shut-off plays an important, extrinsic role in HGF/SF-mediated tumor development, because ectopic expression of TSP-1 markedly inhibits tumor formation through the suppression of angiogenesis. Interestingly, although VEGF-induced expression is sensitive to inhibitors of several pathways, including mitogen-activated protein kinase, phosphoinositide 3-kinase, and signal transducer and activator of transcription 3, TSP-1 shut-off by HGF/SF is prevented solely by inhibiting mitogen-activated protein kinase activation. These studies identify HGF/SF as a key switch for turning on angiogenesis. They suggest that TSP-1 is a useful antagonist to tumor angiogenesis and that it may have therapeutic value when used in conjunction with inhibitors of VEGF.

Angiogenesis Inhibitors↗

Isolation of a nonmitogenic angiogenesis factor from wound fluid.

Angiogenesis, or new capillary growth, is essential to normal growth and wound healing. It is also active in several pathologic states, including the growth of malignant tumors. An extracellular, nonneoplastic angiogenesis factor has been isolated from cell-free rabbit wound fluid by pore-limit dialysis and chromatography on a size-exclusion HPLC column. The isolated angiogenesis factor was purified 9,600-fold with a yield of 81% and has a molecular weight between 2,000 and 14,000. Wound fluid angiogenesis factor was completely separated from the mitogenic activity of wound fluid; it did not increase the number of capillary endothelial cells in vitro or stimulate [3H]thymidine uptake by these cells. The isolated angiogenesis factor stimulated endothelial cell migration in vitro, and less than 200 ng of the factor stimulated angiogenesis in vivo in the corneal implant assay.

Angiogenesis Inducing Agents↗

Bone marrow angiogenesis and progression in multiple myeloma: clinical significance and therapeutic approach.

It is now well established that solid tumors depend on angiogenesis. Promoters and inhibitors of angiogenesis are in balance and antiangiogenic strategies aim at repressing the angiogenic process, thus retarding solid tumor progression. Recent data suggest the importance of angiogenesis in hematologic malignancies and several studies reveal an increased angiogenesis in active multiple myeloma. Angiogenesis seems to be a prominent feature of MM progression, and seems to be correlated with the prognosis and the resistance of MM to chemotherapy. Numerous cell populations and cytokines are involved in angiogenesis in multiple myeloma and antiangiogenic therapy with thalidomide is effective in patients with refractory or relapsed disease. The combination of thalidomide and of other immunomodulatory agents with other therapeutic regimens could lead to more effective management of patients with multiple myeloma.

Angiogenesis Inhibitors↗

Production of a heparin-binding angiogenesis factor by the embryonic kidney.

Embryonic mouse kidneys induce angiogenesis when transplanted on the quail chorioallantoic membrane (Ekblom, P., H. Sariola, M. Karkinen, and L. Saxén, 1982, Cell Differ., 11:35-39). In these experiments all blood vessels were derived from the quail host, suggesting that kidney endothelium is derived from outside blood vessels. We have now analyzed whether kidney angiogenesis is regulated by kidney-derived soluble factors that stimulate the growth of new blood vessels. In the rabbit cornea, 11-d embryonic kidneys induced angiogenesis, whereas uninduced 11-d kidney mesenchymes did not. To characterize and purify this activity from an embryonic organ, we dissected between 600 and 1,000 14-17-d-old embryonic mouse kidneys for each purification experiment. Growth factor activity for capillary endothelial cells was found to bind to heparin-Sepharose and eluted at 0.9-1.1 M sodium chloride. Gel filtration revealed a molecular weight of 16,000-20,000 of this factor. A major 18,000-mol-wt band was seen after gel electrophoresis and silver staining of partially purified growth factor material. The chromatographed factor is mitogenic for endothelial cells but not for smooth muscle cells and stimulates angiogenesis in vivo in the rabbit cornea. Adult kidneys contained two heparin-binding endothelial cell growth factors. The differentiation-dependent production of an angiogenesis factor by the embryonic kidney suggests an important role of angiogenesis in organogenesis.

Angiogenesis Inducing Agents↗

A simple quantitative method for evaluation of angiogenesis activity.

Angiogenesis plays a major role in many physiological and pathological processes. Pathological development of diseased conditions like growth and metastasis of solid tumors and psoriasis is associated with angiogenesis. Assays developed, thus far, for evaluation of angiogenesis activity are qualitative or semiquantitative. In vivo angiogenesis assays are more physiologically relevant than in vitro models and, however, time-consuming, labor-intensive, and expensive. The ex vivo rat aorta tube formation model has been demonstrated to correlate well to the physiological conditions. The present study established a reproducible and quantitative assay for evaluating angiogenesis with rat aorta ring cultures. Rat thoracic aortas were harvested, cross-sectioned into rings of 1-mm thickness using a set of aligned blades, and cultured in a three-dimensional extracellular matrix. Endothelial cells outgrow consistently from the aorta rings cultured in endothelial cell growth medium. Angiogenic activity was quantified by a colorimetric 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2H-tetrazolium/phenazine methosulfate method. The colorimetric assay was reproducible, and its results were compared in parallel with that of the imaging analysis method. IC(50) values of several known antiangiogenics, SU5416, suramin, paclitaxel, and 2-methoxyestradiol, were determined and were comparable to those obtained using the imaging analysis method. We have established a simple, reproducible, and quantitative assay for evaluation of angiogenesis activity with the cultured rat aorta ring, which can be used to screen for angiogenics and angiostatics.

Algorithms↗

Liver regeneration is an angiogenesis- associated phenomenon.

OBJECTIVE: To investigate whether liver regeneration is an angiogenesis-associated phenomenon. SUMMARY BACKGROUND DATA: Angiogenesis is predominantly known for its pivotal role in tumor growth. However, angiogenesis could also play a role in physiologic processes involving tissue repair, such as liver regeneration. METHODS: Mice subjected to 70% partial hepatectomy were treated with human angiostatin (100 mg/kg body weight). Regeneration-induced hepatic angiogenesis was determined by assessing intrahepatic microvascular density using CD31 staining of frozen liver sections. Liver regeneration was evaluated by assessing wet liver weights and BrdU incorporation in DNA at regular intervals after partial hepatectomy. Possible direct effects of angiostatin on hepatocytes were studied by assessment of liver enzymes (ASAT, ALAT, bilirubin, lactate dehydrogenase), MTT assay (cytotoxicity), aminophenol production (metabolic function), and TUNEL (apoptosis). RESULTS: In a regenerating liver, microvascular density increased by 38%. Angiostatin significantly inhibited this response by 60%. In addition, angiostatin inhibited liver regeneration by 50.4% and 24.9% on postoperative days 7 and 14, respectively. In control mice liver weights regained normalcy in 8 days, whereas those in angiostatin-treated mice normalized after 21 days. In angiostatin-treated mice, the maximal BrdU incorporation was decreased and delayed. Direct adverse effects of angiostatin on cultured and in vivo hepatocytes were not observed. Angiostatin neither induced necrosis on hematoxylin and eosin staining nor affected serum levels of liver enzymes. CONCLUSIONS: Liver regeneration is accompanied by intrahepatic angiogenesis. Antiangiogenic treatment using angiostatin inhibits both phenomena. The authors conclude that liver regeneration is, at least in part, an angiogenesis-dependent phenomenon.

Analysis of Variance↗

Tumor angiogenesis, vascularization, and contrast-enhanced magnetic resonance imaging.

Angiogenesis, the process by which new blood vessels are generated, occurs during wound healing, in the female reproductive system during ovulation and gestation, and during embryonic development. The process is carefully controlled with positive and negative regulators, because several vital physiological functions require angiogenesis. The consequences of abnormal angiogenesis are either excessive or insufficient blood vessel growth. Ulcers, strokes, and heart attacks can result from the absence of angiogenesis normally required for natural healing, whereas excessive blood vessel proliferation may favor tumor growth and dissemination, blindness, and arthritis. In this review, the process of angiogenesis and the characteristics of the resulting tumor vasculature are outlined. Contrast-enhanced magnetic resonance imaging techniques that currently are available for basic research and clinical applications to study various aspects of tumor angiogenesis and neovascularization are discussed.

Angiogenesis Inducing Agents↗

Angiogenesis in lymphoproliferative disorders: a therapeutic target?

PURPOSE OF REVIEW: Several recent studies have focused on the role of angiogenesis in hematologic malignancies. This review specifically discusses angiogenesis in lymphoproliferative disorders, with a special emphasis on the most recent publications. The novel therapeutic strategies arising from advances in this field are reviewed, and the potential pitfalls of these therapies are also discussed. RECENT FINDINGS: Recent publications confirm that angiogenesis and angiogenic factors are increased in lymphoproliferative disorders. In addition, several studies have demonstrated that angiogenesis is directly involved in the pathogenesis of these disorders. SUMMARY: Knowledge of angiogenesis in lymphoproliferative disorders has increased substantially in the past few years. Angiogenic factors such as vascular endothelial growth factor have been shown to be important in the progression or maintenance of lymphoproliferative disorders. Targeting of these factors is therefore a promising new therapeutic approach. Hematopoietic angiogenesis is a nascent field, however, and its concepts are still evolving. A systematic approach to understanding and characterizing the angiogenic phenotype is required for the design of efficacious antiangiogenic therapeutic regimens.

Angiogenesis Inhibitors↗

The use of vascular biomarkers and imaging studies in the early clinical development of anti-tumour agents targeting angiogenesis.

Recent findings about the pathomechanisms of tumour angiogenesis have led to new therapeutic options in the treatment of malignant tumours. During the development of anti-angiogenic drugs, reporting ranged from healing cancer to completely ineffective drugs. In 2003 the first anti-angiogenic drug was approved. Several anti-angiogenic drugs are still in the clinical phase of development. In contrast to identifying the maximal tolerable dose, determination of the optimal biological dose--reaching biological activity at lower doses--has become the main target in the early development of anti-angiogenic agents. This has been evaluated by different biomarker techniques. As a new standard in anti-tumour treatment, a better understanding of imaging in the treatment monitoring for anti-angiogenic agents is important. Studies of tumour angiogenesis by tissue sampling rely on invasive procedures, adequate sampling and painstaking estimation of histological microvessel density. Attempts to develop wound healing assays to correlate angiogenesis in wounds with angiogenesis in tumour have been made but are still considered invasive and correlation of healthy with malignant tissue is still of limited validity. Several soluble markers of tumour angiogenesis were detected in various malignant diseases and were evaluated for assessing their use as surrogate markers in tumour angiogenesis. Further, soluble markers were investigated for visualizing them as imaging tools. Combining both, new soluble markers and imaging techniques, developing anticancer drugs and monitoring of therapy success becomes a dynamic process in which finally the patients' individual response can be achieved soon. Time-consuming delays for anatomically based restaging procedures can be avoided. Characterization of soluble biomarkers as well as different imaging techniques such as ultrasound, computed tomography (CT), magnetic resonance imaging and positron emission tomography combined with or without CT are reviewed in this manuscript.

Angiogenesis Inhibitors↗

Tumor angiogenesis in the bone marrow of multiple myeloma patients and its alteration by thalidomide treatment.

Angiogenesis in solid tumors is important to tumor growth, invasion and metastasis. Recently, it has been suggested that angiogenesis plays a certain role in the development of hematopoietic malignancies, including leukemia and multiple myeloma. We evaluated tumor angiogenesis in the bone marrow (BM) of multiple myeloma (MM) patients by calculating microvessel density (MVD) in needle-biopsy specimens obtained from 51 cases of untreated MM or monoclonal gammopathy of undetermined significance (MGUS). The MVD in the BM of donors for transplantation and patients with non-hematological diseases was calculated as a control. There was an obvious increase in MVD in the BM of MM patients, and the MVD correlated with the grade of myeloma cell invasion of the BM in the untreated MM cases. It was recently reported that thalidomide might be effective for the treatment of MM. We assessed the effect of thalidomide on angiogenesis in BM treatment of 11 patients with refractory MM. The concentration of M-protein in the serum or urine of seven of the 11 patients was reduced by at least 30% after thalidomide treatment, and MVD in the BM decreased in three of these seven cases in response to thalidomide. Increased plasma concentrations of basic fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF) were observed in all 11 cases before thalidomide administration and both levels were reduced after treatment with thalidomide. Augmented angiogenesis in the bone marrow of MM patients was confirmed in the present study. It seems that thalidomide is effective in the treatment of MM through the impairment of angiogenesis by decreasing FGF-2 and VEGF production. This is the first report on pathological evidence in the bone marrow of MM before and after thalidomide treatment, in Japan.

Adult↗

Effect of pharmacologic plasminogen activator inhibitor-1 inhibition on cell motility and tumor angiogenesis.

BACKGROUND: Plasminogen activator inhibitor-1 (PAI-1) is integrally involved in tumorigenesis by impacting on both proteolytic activity and cell migration during angiogenesis. OBJECTIVES: We hypothesized that an orally active small molecule inhibitor of PAI-1 (PAI-039; tiplaxtinin) could affect smooth muscle cell (SMC) attachment and migration in vitro on a vitronectin matrix, and exhibit antiangiogenic activity in vivo. METHODS: In vitro assays were used to assess the mechanism of inhibition of PAI-1 by PAI-039 using wild-type PAI-1 in the presence or absence of vitronectin and wild-type PAI-1 and specific PAI-1 mutants in SMC adhesion and migration assays. An in vivo tumor angiogenesis model was used to assess the effect of PAI-039 administration on neovascularization in a Matrigel implant. RESULTS: PAI-039 dose-dependently inhibited soluble, but not vitronectin-bound, PAI-1. Cell adhesion assays using PAI-1 mutants unable to bind vitronectin (PAI-1K) or inactivate proteases (PAI-1R) further suggested that PAI-039 inactivated PAI-1 by binding near its vitronectin domain. In a tumor angiogenesis model, PAI-039 treatment of wild-type mice dose-dependently decreased hemoglobin concentration and endothelial cell staining within the Matrigel implant, indicating reduced angiogenesis, but exhibited no in vivo efficacy in PAI-1 null mice. CONCLUSIONS: Administration of an orally active PAI-1 inhibitor prevented angiogenesis in a Matrigel implant. The lack of activity of PAI-039 against wild-type PAI-1 bound to vitronectin and PAI-1K suggests PAI-039 binding near the vitronectin-binding site. Our studies further substantiate a role for PAI-1 in cellular motility and tumor angiogenesis, and suggest for the first time that these effects can be modulated pharmacologically.

Angiogenesis Inhibitors↗

Angiogenesis.

Angiogenesis inhibitors for the treatment of cancer have now been approved by the Food and Drug Administration in the United States, and in 28 other countries including China. Clinical application of this new class of drugs is informed by certain principles from angiogenesis research. Oncogenic mutations initiate tumorigenesis, but angiogenesis is necessary for expansion of tumor mass. Two angiogenesis inhibitors have been developed that have a broad spectrum of anticancer activity, yet virtually no side effects. Endogenous angiogenesis inhibitors act as tumor suppressor proteins. The angiogenic response in vivo is based on the genetic background of the host. Several types of angiogenesis inhibitors reveal a biphasic, U-shaped curve of efficacy. "Antiangiogenic chemotherapy" is a novel approach to the treatment of drug resistance.

Angiogenesis Inhibitors↗

Tumor inflammatory angiogenesis and its chemoprevention.

The importance of angiogenesis for the growth of tumors is widely recognized. Drugs that successfully target the endothelium, such as antivascular endothelial growth factor antibodies, are beginning to have an effect on the life expectancy of cancer patients. However, the endothelial cell is not the only possible target for antiangiogenic therapy or prevention of vascularization (angioprevention). It is evident from the literature that native immune cells recruited into tumors in turn stimulate the endothelium and are responsible for an indirect pathway of tumor vascularization. Inflammation-dependent angiogenesis seems to be a central force in tumor growth and expansion, a concept supported by the observation that the use of "classic" anti-inflammatory drugs, such as nonsteroidal anti-inflammatory drugs, leads to angiogenesis inhibition. The mechanisms of inflammatory angiogenesis provide new approaches to target, cure, or even better, prevent tumor angiogenesis by treatment with synthetic or natural agents with anti-inflammatory properties. We propose chemoprevention of inflammatory angiogenesis as a way of checking the cancer before it progresses.

Angiogenesis Inhibitors↗

Doxycycline suppresses cerebral matrix metalloproteinase-9 and angiogenesis induced by focal hyperstimulation of vascular endothelial growth factor in a mouse model.

BACKGROUND AND PURPOSE: A number of central nervous system (CNS) disorders are associated with abnormalities in or activation of angiogenesis, including vascular malformations. To test the hypothesis that the nonspecific matrix metalloproteinase (MMP) inhibitor, doxycycline, suppresses vascular endothelial growth factor (VEGF)-induced cerebral angiogenesis through inhibition of MMPs, we used a mouse model with enhanced cerebral angiogenesis induced by focal hyperstimulation of VEGF from adenovirus DNA (AdVEGF) transduction. METHODS: The time course study of MMP activity was performed at 7 and 14 days after AdVEGF transduction. MMP activity and expression were examined by zymography and immunohistochemistry, respectively. As an index of cerebral angiogenesis, microvessel counting was performed in the brains of 3 groups of mice (n=6): (1) control; (2) AdVEGF only; and (3) AdVEGF plus doxycycline (30 mg/kg per day). RESULTS: Brain MMP-9 activities increased 4-fold (883+/-137 versus 179+/-179; 1-sided P<0.001) at 7 days after AdVEGF transduction. VEGF transduction increased vessel counts by 19% (255+/-27 versus 215+/-15, 1-sided P<0.01). Doxycycline treatment decreased MMP-9 activity (89+/-72 versus 883+/-137; 1-sided P<0.001) and cerebral microvessel number (231+/-17 versus 255+/-27; 1-sided P<0.05). CONCLUSIONS: Doxycycline is effective in decreasing stimulated cerebral MMP-9 activity and parenchymal angiogenesis. The decrease in MMP-9 activity is associated with decreased microvessel counts. Brain pathophysiological processes that involve abnormally enhanced angiogenesis may be amenable to manipulation by MMP inhibitors, including tetracycline derivatives.

Adenoviridae↗

Vasohibin as an endothelium-derived negative feedback regulator of angiogenesis.

Negative feedback is a crucial physiological regulatory mechanism, but no such regulator of angiogenesis has been established. Here we report a novel angiogenesis inhibitor that is induced in endothelial cells (ECs) by angiogenic factors and inhibits angiogenesis in an autocrine manner. We have performed cDNA microarray analysis to survey VEGF-inducible genes in human ECs. We characterized one such gene, KIAA1036, whose function had been uncharacterized. The recombinant protein inhibited migration, proliferation, and network formation by ECs as well as angiogenesis in vivo. This inhibitory effect was selective to ECs, as the protein did not affect the migration of smooth muscle cells or fibroblasts. Specific elimination of the expression of KIAA1036 in ECs restored their responsiveness to a higher concentration of VEGF. The expression of KIAA1036 was selective to ECs, and hypoxia or TNF-alpha abrogated its inducible expression. As this molecule is preferentially expressed in ECs, we designated it "vasohibin." Transfection of Lewis lung carcinoma cells with the vasohibin gene did not affect the proliferation of cancer cells in vitro, but did inhibit tumor growth and tumor angiogenesis in vivo. We propose vasohibin to be an endothelium-derived negative feedback regulator of angiogenesis.

Amino Acid Sequence↗