Vascular endothelial growth factor (VEGF) induces plasminogen activators and plasminogen activator inhibitor-1 in microvascular endothelial cells

Analysis of coagulation cascade and endothelial cell activation during inhibition of vascular endothelial growth factor/vascular endothelial growth factor receptor pathway in cancer patients

OBJECTIVE

The angiogenesis inhibitor SU5416 is a potent inhibitor of vascular endothelial growth factor (VEGF) receptor-1 and -2. VEGF may be involved in hemostasis by altering the hemostatic properties of endothelial cells. We analyzed the effects of SU5416 on the coagulation cascade and the vessel wall in patients with advanced cancer.

METHODS AND RESULTS

Markers for thrombin generation, activation of the protein C pathway, fibrinolysis, and endothelial cell activation were measured in patients with renal cell carcinoma, soft tissue sarcoma, or melanoma on days 0, 14, and 28 of treatment with SU5416. Three of 17 sampled patients developed a thromboembolic event in the fifth week of treatment. Markers for thrombin generation and fibrinolysis did not show significant changes. We observed a significant increase in endogenous thrombin potential and of parameters reflecting endothelial cell activation (von Willebrand antigen, soluble tissue factor, and soluble E-selectin) in all patients (P< or =0.001). In patients experiencing a thromboembolic event, endogenous thrombin potential, soluble tissue factor, and soluble E-selectin increased to a significantly greater extent (P=0.029, P=0.021, and P=0.007, respectively).

CONCLUSIONS

VEGF is not only a permeability, proliferation, and migration factor, but it is also a maintenance and protection factor for endothelial cells.

Vascular endothelial growth factor (VEGF) is expressed by neoplastic Hodgkin-Reed-Sternberg cells in Hodgkin's disease

Vascular endothelial growth factor (VEGF) is involved in tumour angiogenesis, an important process for the growth and metastatic potential of solid tumours. Numerous studies have demonstrated up-regulation of VEGF at both mRNA and protein level in various tumours and a correlation with advanced stage and prognosis has been demonstrated in some cases. Limited information exists about its role in lymphoid malignancies and in particular, Hodgkin's disease. The present study examined the immunohistochemical expression of VEGF using the monoclonal antibody VG1 in a series of 61 cases of Hodgkin's disease, including both classical Hodgkin's disease and the nodular lymphocyte predominance variant, and correlated these results with microvessel density, using an anti-CD31 monoclonal antibody. In 41 cases (70.6%) of classical Hodgkin's disease and one of the three cases of nodular lymphocyte predominance Hodgkin's disease, the neoplastic Reed-Sternberg and Hodgkin cells expressed VEGF. The staining observed was cytoplasmic, either diffuse or with a focal paranuclear distribution. Macrophages were always positive, while reactive lymphocytes showed occasional positivity. A variable amount of strong extracellular staining was also observed in the tissue stroma and intravascular plasma staining was prominent. There was no statistically significant relationship between VEGF expression and the subtype of Hodgkin's disease or microvessel density. In vitro studies using the Reed-Sternberg cell lines L428 and KM-H2 were also performed in both normoxia and hypoxia and VEGF protein production was assessed by flow cytometry (FACS), immunoassay of cell culture supernatant, and RT-PCR. Analysis by FACS demonstrated a subset of cells in both cell lines reacting with VG1 and analysis of secreted VEGF (pg/ml per 1x10(6) cells) in cell culture supernatant confirmed the normoxic production in both cell lines and significant hypoxic induction (p<0.005). Additionally, both cell lines expressed VEGF mRNA, as demonstrated using the RT-PCR method. In conclusion, neoplastic cells express VEGF in Hodgkin's disease, as is the case in solid tumours, and this expression may be induced by hypoxia. The presence of VEGF in reactive macrophages and in the extracellular matrix might facilitate tumour progression.

Expression of angiogenesis and angiogenic factors in human aortic vascular disease

BACKGROUND

This paper presents an investigation into the expression of endothelial cells and vascular endothelial growth factor (VEGF) in the aortic wall in vascular diseases such as atherosclerotic abdominal aortic aneurysm (AAAA), inflammatory abdominal aortic aneurysm (IAAA), and aortic occlusive disease (AOD) to determine whether the differences in both neovascularization and angiogenic factor expression are related to the pathogenesis of aortic vascular disease.

MATERIALS AND METHODS

Surgical specimens of aorta (10 IAAA, 13 AAAA, 6 AOD) were studied pathologically and immunohistochemically. Representative sections of aorta were stained with hematoxylin-eosin, elastica von Gieson, CD34, and VEGF antibody. CD34-positive microvessels and VEGF-positive cells in the media and adventitia were counted, respectively.

RESULTS

CD34-positive microvessels were detected in IAAA > AAAA > AOD (one-way analysis of variance (ANOVA), P < 0.0001). VEGF expression was widely detected in macrophages, monocytes, and smooth muscle cells of IAAA and AAAA; however, it was hardly recognized in AOD. VEGF-positive cells were detected in IAAA > AAAA > AOD specimens (ANOVA, P < 0.0001).

CONCLUSIONS

VEGF is known to be a regulator of angiogenesis and to simultaneously stimulate elastolytic proteinases. The results of this study suggest that an angiogenic factor, such as VEGF, may play an important role in the degeneration of the aortic wall and could be strongly related to the pathogenesis of IAAA, AAAA, and AOD.

Vascular endothelial growth factor (VEGF)-induced angiogenesis in herniated disc resorption

Intervertebral disc herniation is a major cause of low back pain and sciatica. Spontaneous resorption of herniated disc (HD) is frrequently detected by magnetic resonance imaging (MRI). Marked infiltration by macrophages and neo-vascularization are observed upon histogical examination of HD. In addition, enhanced MRI studies suggest that HD resorption occurs more frequently in those completely exposed to the epidural space and that this correlates with their degree of vascularization. We have postulated that the angiogenic factor, vascular endothelial growth factor (VEGF), may be implicated in the neo-vascularization of HD tissues. Here we demonstrate that VEGF and its receptors VEGFR-1 and VEGFR-2 are expressed in human surgical samples of HD. Using a co-culture system comprised of murine peritoneal macrophages and intervertebral disc tissue as a model of the acute phase of HD developed previously, an increase in macrophage VEGF protein and mRNA expression was observed upon exposure to disc tissue. Tumor necrosis factor alpha (TNF-alpha) was required for this induction of VEGF. Use of a novel angiogenesis assay revealed that addition of the conditioned media from the co-culture system resulted in an increase of vascular tubule formation. This effect was strongly inhibited by anti-VEGF antibody, but augmented by recombinant VEGF. We conclude that VEGF induction, under the co-culture conditions tested can result in neo-vascularization of intervertebral disc tissue and may thus play a role in the resorption of HD.

Mechanisms of normal and tumor-derived angiogenesis

Often those diseases most evasive to therapeutic intervention usurp the human body's own cellular machinery or deregulate normal physiological processes for propagation. Tumor-induced angiogenesis is a pathological condition that results from aberrant deployment of normal angiogenesis, an essential process in which the vascular tree is remodeled by the growth of new capillaries from preexisting vessels. Normal angiogenesis ensures that developing or healing tissues receive an adequate supply of nutrients. Within the confines of a tumor, the availability of nutrients is limited by competition among actively proliferating cells, and diffusion of metabolites is impeded by high interstitial pressure (Jain RK. Cancer Res 47: 3039-3051, 1987). As a result, tumor cells induce the formation of a new blood supply from the preexisting vasculature, and this affords tumor cells the ability to survive and propagate in a hostile environment. Because both normal and tumor-induced neovascularization fulfill the essential role of satisfying the metabolic demands of a tissue, the mechanisms by which cancer cells stimulate pathological neovascularization mimic those utilized by normal cells to foster physiological angiogenesis. This review investigates mechanisms of tumor-induced angiogenesis. The strategies used by cancer cells to develop their own blood supply are discussed in relation to those employed by normal cells during physiological angiogenesis. With an understanding of blood vessel growth in both normal and abnormal settings, we are better suited to design effective therapeutics for cancer.

Correlation of VEGF and angiopoietin expression with disruption of blood-brain barrier and angiogenesis after focal cerebral ischemia

In an effort to elucidate the molecular mechanisms underlying cerebral vascular alteration after stroke, the authors measured the spatial and temporal profiles of blood-brain barrier (BBB) leakage, angiogenesis, vascular endothelial growth factor (VEGF), associated receptors, and angiopoietins and receptors after embolic stroke in the rat. Two to four hours after onset of ischemia, VEGF mRNA increased, whereas angiopoietin 1 (Ang 1) mRNA decreased. Three-dimensional immunofluorescent analysis revealed spatial coincidence between increases of VEGF immunoreactivity and BBB leakage in the ischemic core. Two to 28 days after the onset of stroke, increased expression of VEGF/VEGF receptors and Ang/Tie2 was detected at the boundary of the ischemic lesion. Concurrently, enlarged and thin-walled vessels were detected at the boundary of the ischemic lesion, and these vessels developed into smaller vessels via sprouting and intussusception. Three-dimensional quantitative analysis of cerebral vessels at the boundary zone 14 days after ischemia revealed a significant (P < 0.05) increase in numbers of vessels (n = 365) compared with numbers (n = 66) in the homologous tissue of the contralateral hemisphere. Furthermore, capillaries in the penumbra had a significantly smaller diameter (4.8 +/- 2.0 microm) than capillaries (5.4 +/- 1.5 microm) in the homologous regions of the contralateral hemisphere. Together, these data suggest that acute alteration of VEGF and Ang 1 in the ischemic core may mediate BBB leakage, whereas upregulation of VEGF/VEGF receptors and Ang/Tie2 at the boundary zone may regulate neovascularization in ischemic brain.

Dose-finding and pharmacokinetic study of cisplatin, gemcitabine, and SU5416 in patients with solid tumors

PURPOSE

To investigate the feasibility and pharmacokinetics of the combination cisplatin, gemcitabine, and SU5416.

PATIENTS AND METHODS

Patients received cisplatin 80 mg/m(2) on day 1, gemcitabine 1,250 mg/m(2) on days 1 and 8, repeated every 3 weeks, and SU5416 (85 and 145 mg/m(2)) intravenously twice weekly. Pharmacokinetics of all three agents, side effects, and antitumor response were investigated in patients with solid tumors amenable to therapy with cisplatin/gemcitabine.

RESULTS

In the first cohort of three patients entered at the 85 mg/m(2) dose, no dose-limiting toxicities were observed. In the next cohort (145 mg/m(2)), three patients developed a thromboembolic event. After entry was restricted to patients with low thromboembolic risk, three additional patients enrolled at 145 mg/m(2) developed a thromboembolic event. The dose was then reduced to 85 mg/m(2) in all patients still on the study, and three additional patients were entered on this dose level. In 19 treated patients, eight patients developed nine thromboembolic events (three transient ischemic attacks, two cerebrovascular accidents, and four deep venous thromboses). The most common toxicities observed were those previously reported for SU5416 alone (headache and phlebitis) and for this chemotherapy regimen (nausea, thrombocytopenia, and leucopenia). No significant pharmacologic interaction among the three drugs was observed. Response rates were similar to those expected in the patient population selected for this study. Analysis of variables of the coagulation cascade and of vessel wall activation was performed in three patients and showed significant increases in thrombin generation and endothelial cell perturbation in a treatment cycle-dependent manner.

CONCLUSION

The incidence of thromboembolic events, possibly related to the particular regimen tested in this study, discourages further investigation of this regimen.

Dose-finding and pharmacokinetic study of cisplatin, gemcitabine, and SU5416 in patients with solid tumors

PURPOSE

To investigate the feasibility and pharmacokinetics of the combination cisplatin, gemcitabine, and SU5416.

PATIENTS AND METHODS

Patients received cisplatin 80 mg/m(2) on day 1, gemcitabine 1,250 mg/m(2) on days 1 and 8, repeated every 3 weeks, and SU5416 (85 and 145 mg/m(2)) intravenously twice weekly. Pharmacokinetics of all three agents, side effects, and antitumor response were investigated in patients with solid tumors amenable to therapy with cisplatin/gemcitabine.

RESULTS

In the first cohort of three patients entered at the 85 mg/m(2) dose, no dose-limiting toxicities were observed. In the next cohort (145 mg/m(2)), three patients developed a thromboembolic event. After entry was restricted to patients with low thromboembolic risk, three additional patients enrolled at 145 mg/m(2) developed a thromboembolic event. The dose was then reduced to 85 mg/m(2) in all patients still on the study, and three additional patients were entered on this dose level. In 19 treated patients, eight patients developed nine thromboembolic events (three transient ischemic attacks, two cerebrovascular accidents, and four deep venous thromboses). The most common toxicities observed were those previously reported for SU5416 alone (headache and phlebitis) and for this chemotherapy regimen (nausea, thrombocytopenia, and leucopenia). No significant pharmacologic interaction among the three drugs was observed. Response rates were similar to those expected in the patient population selected for this study. Analysis of variables of the coagulation cascade and of vessel wall activation was performed in three patients and showed significant increases in thrombin generation and endothelial cell perturbation in a treatment cycle-dependent manner.

CONCLUSION

The incidence of thromboembolic events, possibly related to the particular regimen tested in this study, discourages further investigation of this regimen.

Stabilization of vascular endothelial growth factor mRNA by hypoxia-inducible factor 1

Hypoxia regulates expression of vascular endothelial growth factor (VEGF) by increasing its transcription and by stabilizing its mRNA. Despite the pivotal role of hypoxia-inducible factor 1 (HIF-1) in transcriptional activation of hypoxia-responsive genes, it is not known whether HIF-1 mediates hypoxia-induced stabilization of VEGF mRNA. We constructed adenoviral vectors expressing either the wild-type HIF-1 alpha (Ad2/HIF-1 alpha/FL), a constitutively stable hybrid form of HIF-1 alpha (Ad2/HIF-1 alpha/VP16), or no transgene (Ad2/CMVEV). In rat glioma (C6) cells and human cardiac, vascular smooth muscle, and endothelial cells, infection with Ad2/HIF-1 alpha/VP16 or Ad2/HIF-1 alpha/FL increased VEGF expression at both the mRNA and protein levels. Under normoxic conditions, the half-life of VEGF mRNA was 42 min in C6 cells. Hypoxia and Ad2/HIF-1 alpha/VP16 increased the half-life of VEGF mRNA to 3.3 and 2.7 h, respectively, while Ad2/CMVEV had no effect. These studies are the first to demonstrate that overexpression of HIF-1 alpha increases VEGF mRNA stability. Our results also suggest that stabilization of VEGF mRNA by hypoxia is mediated, at least in part, by HIF-1.

Cell adhesion regulates the plasminogen activator inhibitor-1 gene expression in anchorage-dependent cells

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of both tissue- and urokinase-type plasminogen activators (t-PA, u-PA). PAI-1 also regulates the attachment of cells to the adhesive glycoprotein vitronectin (VN). PAI-1 gene expression has been observed in various cell types, and many regulatory factors have been identified to play a role in PAI-1 gene transcription. The complete picture of how the PAI-1 gene is expressed when cells adhere to a culture plate has not been fully elucidated. We found that in anchorage-dependent cells, PAI-1 gene was up-regulated when cells were beginning to attach to a culture dish and was down-regulated when cells had attached completely. The PAI-1 gene expression was induced only in adhered cells but not in non-adhered cells. The regulation of PAI-1 protein was also found in both culture medium and cell lysate when cells were attached to a culture dish. Our experiment indicates that vitronectin and fibronectin, as components of ECM, may be the factors involved in the regulation of PAI-1 gene expression. PAI-1, as an inhibitor of the interaction between vitronectin and integrin alphavbeta3, may also be a regulator of its own expression.

Stimulation of vascular endothelial growth factor gene transcription by all trans retinoic acid through Sp1 and Sp3 sites in human bronchioloalveolar carcinoma cells

In this study, we examined the effects of all trans-retinoic acid (at-RA) on the vascular endothelial growth factor (VEGF) expression in human bronchioloalveolar carcinoma NCI-H322 cells to evaluate the potential of at-RA to affect tumor progression. Northern blot and enzyme-linked immunosorbent assay analyses indicate that VEGF production is significantly increased by 1 microM of at-RA. A series of 5'-deletion and site-directed mutation analyses indicated that G+C-rich sequence located at -81 and -52 was required for at-RA- and retinoic acid receptor alpha-mediated induction of VEGF promoter. Electrophoretic mobility shift and supershift assays showed that major constituents of nuclear factors binding to G+C-rich sequences are Sp1 and Sp3. Pretreatment with cycloheximide, a protein synthesis inhibitor, prevented the at-RA-mediated induction of VEGF mRNA expression. Likewise, at-RA-mediated VEGF expression was completely blocked in the presence of genistein, an inhibitor for tyrosine kinases. These results suggest that an increase in transcription of the VEGF promoter by at-RA is mediated through Sp1 site, and both new protein synthesis and tyrosine kinase activation are necessary for this induction. Because VEGF can promote neovascularization in cancer cells, an induction of VEGF by at-RA may preclude the therapeutic application of at-RA to cancer patients.

Vascular endothelial growth factor in porcine-derived extracellular matrix

An extracellular matrix (ECM) derived from the submucosa of the porcine small intestine (SIS) has been shown to induce angiogenesis and host tissue remodeling when used as a xenogeneic bioscaffold in animal models of wound repair. In the present study, we compared the in vitro effects of SIS ECM extracts to several purified angiogenic growth factors on human dermal microvascular endothelial cell (HMEC) growth patterns. The SIS ECM was shown to induce tube formation from HMEC in a three-dimensional fibrin-based angiogenesis assay in a manner similar to that caused by the addition of vascular endothelial growth factor (VEGF). This tube formation was blocked in the presence of anti-VEGF neutralizing antibody. Western blots and ELISA procedures showed that the SIS ECM contains as much as 0.77 ng VEGF/g SIS. The closely related endothelial cell mitogen, platelet-derived growth factor (PDGF), was not detectable in the SIS extracts. We conclude that VEGF is present in the SIS extracellular matrix. The role of VEGF in SIS-induced wound repair remains unknown, but its presence in the ECM makes it a possible contributor to the angiogenic effect of SIS when this ECM is used as a tissue repair scaffold in animal models of wound repair.

Prognostic significance of the expression of vascular endothelial growth factor (VEGF) and VEGF-C in gastric carcinoma

BACKGROUND AND OBJECTIVES

Angiogenic factors play a major role in tumor growth and metastasis. The purpose of this study was to clarify the prognostic significance of the expression of vascular endothelial growth factor (VEGF) and VEGF-C in gastric carcinoma.

METHODS

Formalin-fixed and paraffin embedded sections of tumor tissue were obtained from 76 patients who underwent curative gastrectomy for gastric carcinoma. Immunohistochemical staining for VEGF and VEGF-C was performed.

RESULTS

VEGF and VEGF-C were positively expressed in 39 and 45% of the patients, respectively. No correlation existed between VEGF and VEGF-C expressions. VEGF expression was significantly correlated with venous invasion. VEGF-C expression was significantly correlated with lymphatic and venous invasion. Patients with positive staining for VEGF showed a significantly lower survival rate than VEGF negative patients. After subdivision, according to the combination of VEGF and VEGF-C expression, VEGF-C expression had a significant unfavorable impact on prognosis among patients with negative staining for VEGF. The expression of VEGF and/or VEGF-C was independent prognostic determinant by the multivariate survival analysis.

CONCLUSIONS

The positive expression for VEGF and/or VEGF-C was an important prognostic determinant after curative gastrectomy for gastric carcinoma. VEGF-C may stimulate the tumor progression in the absence of VEGF.

Vascular endothelial growth factor in chronic subdural haematomas

OBJECTIVE

To elucidate molecular aspects of the mechanisms of expansion of chronic subdural haematomas (CSH), we examined the expression of two representative angiogenic factors, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in CSH.

METHODS

We quantified VEGF and bFGF in haematoma fluid and serum of 20 patients with CSH using an enzyme-linked immunosorbent assay. Mean concentrations of VEGF in the haematoma fluid (10277 pg/ml) and in serum, (355 pg/ml) were much greater than those of bFGF (haematoma, 3.04 pg/ml; serum, 4.74 pg/ml). Surgical specimens, including dura and the outer membrane of the CSH were analysed by in situ hybridisation to detect VEGF mRNA. Macrophages and vascular endothelial cells in the outer membrane over expressed VEGF mRNA.

CONCLUSIONS

Enhanced production of VEGF by macrophages and vascular endothelial cells in the outer membrane is thought to be pathogenetically important in CSH.

Age and growth factors in porcine full-thickness wound healing

It has been recognized that the rate of cutaneous wound healing declines with age, yet the molecular processes that affect this decline remain poorly understood. The purpose of this study was to compare reepithelialization and contraction rates, and growth factor profiles in full-thickness wounds in swine of various ages. Multiple full-thickness excisional wounds were created on the dorsum of 24-month-old (n=2), 4-month-old (n=2), and 2-month-old (n=2) Yucatan Minipigs. The extent of reepithelialization was shown to decrease with increasing age in a manner that was statistically significant among the 2-month-old (79%), 4-month-old (48%), and 24-month-old pigs (22%). Enzyme-linked immunosorbent assay results showed that endogenous vascular endothelial growth factor concentrations in the 2- and 4-month-old animals peaked on day 4, reaching levels of 482 pg/ml and 420 pg/ml, respectively. In the 24-month-old pigs the vascular endothelial growth factor concentration peaked later (day 6), and was present at a lower level (229 pg/ml). On day 4 the vascular endothelial growth factor levels in the older pigs reached only 120 pg/ml, representing a four-fold decrease in concentration compared to the younger pigs. A comparison of platelet-derived growth factor-BB concentrations across the age groups showed similar patterns in the 2- and 4-month-old pigs (peaks of 77 and 91 pg/ml on days 2 and 3, respectively), and levels in the 24-month-old were below the sensitivity level (31.5 pg/ml) of the assay. Transforming growth factor-beta1 levels across the age groups did not differ in a manner that was statistically significant, and all age groups peaked on day 9. Wound contraction showed no statistical differences among the age groups from days 3 to 9. On day 11, however, wound contraction in 2-month-old pigs was about 10% faster than in 24-month-old pigs (p < 0.05). These data suggest a possible new algorithm for treating wounds in aged skin, by which exogenous growth factors can be added to the wound microenvironment in doses and at times that match the growth factor profiles observed in wounds made in younger skin.

Plasminogen activator inhibitor-1 as a measure of vascular remodelling in breast cancer

The generation of urokinase plasminogen activator (uPA) by tumours is an important pathway for neoplastic cell invasion and metastasis. Indeed in several tumour types, elevated levels of uPA, its receptor (uPAR) or its inhibitor plasminogen activator inhibitor-1 (PAI-1) is associated with a poorer prognosis. Since endothelial cells also use this proteolytic system to remodel the extracellular matrix during angiogenesis and since angiogenesis, as assessed by microvessel density, is also a predictor of patient survival, this study was designed to investigate the relationship between angiogenesis and the urokinase system in breast tumours. The aims were to assess whether the uPA, uPAR and/or PAI-1 correlates with angiogenic activity and could therefore be a useful objective clinical measure of tumour neovascularization; and to clarify whether the poor outcome associated with high levels of the urokinase system is due to its association with angiogenesis. The study also sought to examine the relationship between the uPA system and vessel remodelling using loss of a basement membrane epitope (LH39) normally associated with established capillaries. The cytosolic levels of uPA, PAI-1 and uPAR were therefore measured by enzyme linked immunoabsorbent assay, together with tumour vascularity, in 136 well-characterized invasive breast carcinomas. There were significant relationships between uPA and uPAR (Spearman r=0.37, p<0.0001), uPA and PAI-1 (Spearman r=0.19, p=0.03) and between uPAR and PAI-1 (Spearman r=0.23 p=0.01). A significant correlation was also observed between PAI-1 and vessel remodelling (Spearman r=0.34, p=0.04), patient age (p=0.01), nodal status (p=0.047) and tumour grade (p=0.04), but no association between tumour vascularity and PAI (p=0.96), uPA (p=0.69) or uPAR (p=0.81) was present. No significant association was seen between any of the urokinase variables and expression of the angiogenic factor thymidine phosphorylase. Furthermore, no significant associations were found between any of the studied parameters and overall survival in a univariate analysis of the cancer patients. A multivariate Cox proportional hazard model of overall survival showed that uPA (p=0.15), but not uPAR (p=0.52) or PAI-1 (p=0.61), gave no additional prognostic information. These findings show that uPA may work via an independent pathway to angiogenesis and therefore combined blockade of uPA and angiogenesis may have additional therapeutic benefits. It also shows, as recently demonstrated in animal models, that PAI-1 may be a key regulator of vascular remodelling in human cancer.

The hemostatic system and angiogenesis in malignancy

Coagulopathy and angiogenesis are among the most consistent host responses associated with cancer. These two respective processes, hitherto viewed as distinct, may in fact be functionally inseparable as blood coagulation and fibrinolysis, in their own right, influence tumor angiogenesis and thereby contribute to malignant growth. In addition, tumor angiogenesis appears to be controlled through both standard and non-standard functions of such elements of the hemostatic system as tissue factor, thrombin, fibrin, plasminogen activators, plasminogen, and platelets. "Cryptic" domains can be released from hemostatic proteins through proteolytic cleavage, and act systemically as angiogenesis inhibitors (e.g., angiostatin, antiangiogenic antithrombin III aaATIII). Various components of the hemostatic system either promote or inhibit angiogenesis and likely act by changing the net angiogenic balance. However, their complex influences are far from being fully understood. Targeted pharmacological and/or genetic inhibition of pro-angiogenic activities of the hemostatic system and exploitation of endogenous angiogenesis inhibitors of the angiostatin and aaATIII variety are under study as prospective anti-cancer treatments.

The tubulogenic activity associated with an activated form of Flt-1 kinase is dependent on focal adhesion kinase

Focal adhesion kinase (FAK) is known to be located at the intersection between extracellular matrix and growth factor signaling pathways to regulate cell motility. We have shown previously that an activated form (BCR-FLTm1) of Flt-1 kinase, a receptor for vascular endothelial growth factor, had a tubulogenic activity not only in endothelial cells but also in fibroblastic cells. Here we show that tubulogenesis by BCR-FLTm1 depends on FAK and that FAK tyrosine phosphorylation and association with an activated Flt-1 receptor complex is increased after vascular endothelial growth factor stimulation of NIH3T3 cells overexpressing Flt-1.

Urokinase receptor and vascular endothelial growth factor are synergistically associated with the liver metastasis of colorectal cancer

Considering recent findings that the urokinase plasniinogen activation (PA) system is involved in invasion and vascular endothelial growth factor (VEGF) is involved in angiogenesis of colorectal cancer, we evaluated these factors in the liver metastasis of primary colorectal cancer. Cancer tissues from 71 colorectal cancer patients were assayed quantitatively for antigen levels of urokinase type plasminogen activator (uPA), uPA receptor (uPAR), and plasminogen activator inhibitor‐1 and ‐2 (PAI‐1, PAI‐2), and were also assayed immunohistochemically for expression of VEGF protein. Among the PA system factors, both the levels of uPAR and PAI‐1 were significantly higher in larger tumors than in smaller ones, and were also significantly higher in tumors that invaded subserosa, serosa or adjacent organs than in mucosal, submucosal tumors or in tumors that invaded the muscle layer. The uPAR levels were significantly higher in tumors with liver metastasis than in those without. VEGF overexpression was significantly more frequent in tumors with lymph node involvement or liver metastasis than in those without. Among the PA system factors, the uPAR levels were significantly higher in tumors with VEGF overexpression and a multivariate analysis revealed that high uPA level and VEGF overexpression were independent risk factors for liver metastasis. The combination of high uPAR level and overexpression of VEGF was associated with the worst prognosis in patients with colorectal cancer. These results suggest that uPAR and VEGF might contribute Synergistically to the liver metastasis of colorectal cancer.

Identification and cloning of an 85-kDa protein homologous to RING3 that is upregulated in proliferating endothelial cells

A central event in angiogenesis is proliferation of blood vessels, which plays a major role in the progression of a number of inflammatory and neoplastic diseases. It is responsible for the switch of endothelial cells from an antiangiogenic to an angiogenic phenotype. To identify novel activated/proliferating-related proteins in human endothelial cells, a subtractive immunization approach was used to elicit a host antibody response against human dermal microvascular endothelial cells (HDMECs) stimulated with a potent angiogenic cytokine such as VPF/VEGF165. In this study, a new mAb, LY9, which is highly specific to VPF/VEGF165-activated HDMECs, was isolated. Stimulation of HDMECs by VPF/VEGF165 or basic fibroblast growth factor (bFGF) resulted in a dose-dependent and time-dependent increase in the binding of LY9. On Western-blot analysis, LY9 identified an 85-kDa protein (p85) in the lysates of several endothelial cells derived from microvascular or large vessel sources, the expression of which is dramatically increased by VPF/VEGF165. The mAb also identified p85 in primary cell cultures of human foreskin keratinocytes but failed to recognize human fibroblasts (MRC5) and a number of different human tumor cell lines, including MG63 osteosarcoma and MCF7 breast carcinoma cells. Immunological screening of a human keratinocyte lambdagt11 cDNA expression library with LY9 identified a partial cDNA clone of 750 bp. DNA sequencing of this clone and predicted amino acids showed more than 93% homology to RING3 kinase, a member of a newly described family of bromodomain-containing proteins that transactivates in the nucleus the promoters of a number of the E2F family of transcription factors. This molecule may represent a new signaling target activated by VPF/VEGF165 and bFGF that allows endothelial cells to enter the proliferative phase of the angiogenic process.

Somatic gene therapy in the cardiovascular system

This review surveys a range of approaches using plasmid DNA encoding the 165-amino-acid isoform of vascular endothelial growth factor (phVEGF165) to therapeutically modulate micro- or macrovascular endothelial cells, focusing on strategies to augment postnatal collateral circulation in arterial insufficiency or to accelerate re-endothelialization after balloon angioplasty to prevent restenosis. We focus on intra-arterial and intramuscular/intramyocardial gene transfer of the VEGF165 gene, the options that have been most thoroughly studied to date in patients. We review developmental and postnatal significance of the endothelial-cell-specific mitogen VEGF that has stimulated these studies and present limitations of current knowledge as well as challenges for the future.

Kinase insert domain receptor (KDR) extracellular immunoglobulin-like domains 4-7 contain structural features that block receptor dimerization and vascular endothelial growth factor-induced signaling

The vascular endothelial growth factor (VEGF) receptor tyrosine kinase subtype kinase insert domain receptor (KDR) contains seven extracellular Ig-like domains, of which the three most amino-terminal contain the necessary structural features required for VEGF binding. To clarify the functional role of KDR Ig-like domains 4-7, we compared VEGF-induced signaling in human embryonic kidney and porcine aortic endothelial cells expressing native versus mutant receptor proteins in which Ig-like domains 4-7, 4-6, or 7 had been deleted. Western blotting using an anti-receptor antibody indicated equivalent expression levels for each of the recombinant proteins. As expected, VEGF treatment robustly augmented native receptor autophosphorylation. In contrast, receptor autophosphorylation, as well as downstream signaling events, were VEGF-independent for cells expressing mutant receptors. (125)I-VEGF(165) bound with equal or better affinity to mutant versus native receptor, although the number of radioligand binding sites was significantly reduced because a significant percentage of mutant, but not native, receptors were localized to the cell interior. As was the case for native KDR, (125)I-VEGF(165) binding to the mutant receptors was dependent upon cell surface heparan sulfate proteoglycans, and (125)I-VEGF(121) bound with an affinity equal to that of (125)I-VEGF(165) to the native and mutant receptors. It is concluded that KDR Ig-like domains 4-7 contain structural features that inhibit receptor signaling by a mechanism that is independent of neuropilin-1 and heparan sulfate proteoglycans. We speculate that this provides a cellular mechanism for blocking unwanted signaling events in the absence of VEGF.

Signaling mechanisms mediating vascular protective actions of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is essential for angiogenesis in health and pathophysiology, and it is currently a major focus for drug targeting in the development of treatments for diverse human diseases. Recently, we proposed that VEGF could also play a role as a vascular protective factor in the adult vasculature and in disease. In this model, vascular protection is defined as a VEGF-induced enhancement of endothelial functions that mediate the inhibition of vascular smooth muscle cell proliferation, enhanced endothelial cell survival, suppression of thrombosis, and anti-inflammatory effects. A feature of this model is that protective effects of VEGF are essentially independent of angiogenesis or endothelial cell proliferation. VEGF-dependent cell survival and VEGF-induced synthesis of nitric oxide and prostacyclin are likely to be key mediators of a vascular protective effect. Vascular protection should help to improve insight into the underlying mechanisms of cardiovascular actions of VEGF and prove valuable for developing novel therapeutic approaches to cardiovascular disease.

A single autophosphorylation site on KDR/Flk-1 is essential for VEGF-A-dependent activation of PLC-gamma and DNA synthesis in vascular endothelial cells

KDR/Flk-1 tyrosine kinase, one of the two vascular endothelial growth factor (VEGF) receptors, induces mitogenesis and differentiation of vascular endothelial cells. To understand the mechanisms underlying the VEGF-A-induced growth signaling pathway, we constructed a series of human KDR mutants and examined their biological properties. An in vitro kinase assay and subsequent tryptic peptide mapping revealed that Y1175 and Y1214 are the two major VEGF-A-dependent autophosphorylation sites. Using an antibody highly specific to the phosphoY1175 region, we demonstrated that Y1175 is phosphorylated rapidly in vivo in primary endothelial cells. When the mutated KDRs were introduced into the endothelial cell lines by adenoviral vectors, only the Y1175F KDR, Tyr1175 to phenylalanine mutant, lost the ability to tyrosine phosphorylate phospholipase C-gamma and, significantly, reduced MAP kinase phosphorylation and DNA synthesis in response to VEGF-A. Furthermore, primary endothelial cells microinjected with anti-phosphoY1175 antibody clearly decreased DNA synthesis compared with control cells. These findings strongly suggest that autophosphorylation of Y1175 on KDR is crucial for endothelial cell proliferation, and that this region is a new target for anti-angiogenic reagents.

Sinusoidal endothelial cell proliferation and expression of angiopoietin/Tie family in regenerating rat liver

BACKGROUND/AIMS

Angiogenesis is essential in liver regeneration. However, only little is known about sinusoidal endothelial cell proliferation and the role of different angiogenic growth factors and their receptors during regeneration.

METHODS

Seventy percent hepatectomy was carried out on male rats. Serial changes in endothelial cell proliferation were evaluated by immunohistochemistry. The mRNA expressions of angiogenic growth factors (vascular endothelial growth factor (VEGF) and angiopoietins 1 and 2) and their receptors (flt-1, flk-1, Tie-1 and Tie-2) in the whole liver were evaluated by semi-quantitative RT-PCR.

RESULTS

Significant elevation of endothelial cell proliferation started at 48 h and peaked at 72 h after hepatectomy. The ratio of sinusoids to liver tissue area initially decreased at 72 h, and thereafter, significantly increased at 96 h. VEGF related factors had early peaks, which coincided with the endothelial proliferation. flt-1, flk-1 and VEGF expressions peaked at 24, 48 and 72 h, respectively. angiopoietin/Tie factors peaked at 96 h, except Ang-2, which gradually increased and peaked at 168 h.

CONCLUSIONS

During liver regeneration, hepatocyte proliferation was followed by endothelial cell proliferation. The VEGF family and angiopoietin/Tie system may have distinct roles in angiogenesis, with an enhanced expression of the VEGF family in the early phase of regeneration followed by angiopoietin/Tie expression.

The splice variants of vascular endothelial growth factor (VEGF) and their receptors

Vascular endothelial growth factor (VEGF) is a secreted mitogen highly specific for cultured endothelial cells. In vivo VEGF induces microvascular permeability and plays a central role in both angiogenesis and vasculogenesis. VEGF is a promising target for therapeutic intervention in certain pathological conditions that are angiogenesis dependent, most notably the neovascularisation of growing tumours. Through alternative mRNA splicing, a single gene gives rise to several distinct isoforms of VEGF, which differ in their expression patterns as well as their biochemical and biological properties. Two VEGF receptor tyrosine kinases (VEGFRs) have been identified, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1). VEGFR-2 seems to mediate almost all observed endothelial cell responses to VEGF, whereas roles for VEGFR-1 are more elusive. VEGFR-1 might act predominantly as a ligand-binding molecule, sequestering VEGF from VEGFR-2 signalling. Several isoform-specific VEGF receptors exist that modulate VEGF activity. Neuropilin-1 acts as a co-receptor for VEGF(165), enhancing its binding to VEGFR-2 and its bioactivity. Heparan sulphate proteoglycans (HSPGs), as well as binding certain VEGF isoforms, interact with both VEGFR-1 and VEGFR-2. HSPGs have a wide variety of functions, such as the ability to partially restore lost function to damaged VEGF(165) and thereby prolonging its biological activity.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.

Signalling properties of an HIV-encoded angiogenic peptide mimicking vascular endothelial growth factor activity

HIV-1 expresses a multifunctional protein called TAT (trans-acting transcriptional activator), the function of which in vivo is tightly correlated with the incidence of Kaposi's sarcoma in AIDS patients. TAT is angiogenic and apparently binds to receptors specific for vascular endothelial growth factor (VEGF). Amino acids 46-60 of HIV-TAT, known as the basic peptide, have been shown to be responsible for its functional interaction with VEGF receptors. To characterize further the binding properties of this peptide, its coding sequence was fused to the reading frame of bacterial thioredoxin, allowing the production of large amounts of chimaeric polypeptides in bacteria in a biologically active form. Binding of chimaeric proteins to VEGF receptors was studied in vitro in endothelial cell cultures expressing either of the two receptors. Chimaeric thioredoxin proteins carrying the basic domain of TAT bound to both VEGF receptors with affinities similar to those of HIV-TAT or VEGF. Interestingly, these polypeptides competed only partially with VEGF for receptor binding, implying different binding sites for the TAT peptide and VEGF. This suggests that TAT binds VEGF receptors at new sites that might be useful targets for pharmacological intervention during pathological angiogenesis. The thioredoxin/basic-peptide chimaeras are functional agonists that mediate VEGF receptor signalling: (1) they stimulate the growth of endothelial cells; (2) together with basic fibroblast growth factor they cause tube formation of endothelial cells in collagen gels; (3) they induce blood vessel formation on the chicken chorioallantoic membrane; and (4) they activate VEGF receptor kinase and mitogen-activated protein kinase activity.

Plasminogen activators and inhibitors are transcribed during early macaque implantation

Plasminogen activators and inhibitors may be important early in primate implantation but evidence for this is sparse in non-human primates. We define the expression of urokinase type plasminogen activator (uPA), tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1) and type 2 (PAI-2), the receptor for uPA (uPAR) and fibrin/fibrinogen in monkey implantation sites. In situ hybridization and immuno-histochemical localization of rhesus monkey implantation sites (day 15-16 postovulation) indicate: (1) uPA mRNA is localized to placental trophoblast, epithelial plaque and endometrial stroma. (2) tPA mRNA is mainly expressed in glandular cells of endometrium. (3) PAI-1 expression is linked to a specific population of trophoblasts that confront maternal cells, adding support to our view that it has a regulatory role in trophoblast invasion. (4) Localization of tPA antigen confirms that uterine glands are the major source of tPA and that it is also closely associated with fibrin(ogen) suggesting its possible function during implantation is fibrinolysis. (5) Unlike uPA mRNA, however, the distribution of uPA protein and its cell surface receptor uPAR suggests that it mediates trophoblast invasion and plays a significant role in angiogenesis. (6) PAI-2, the inhibitor associated with pregnancy in humans, was found in unidentified cells located specifically along the maternofetal junction. This localization adjacent to areas of cell death at the maternofetal junction implies that it may have a role as a protective curtain with anti-apoptotic function. In conclusion our results suggest that gene expression of PAs and PAIs in early implantation sites are tissue-specific, location-sensitive and function-related.

Estrogen and angiogenesis: A review

Multiple lines of evidence suggest that estrogen directly modulates angiogenesis via effects on endothelial cells. Under physiological conditions, angiogenesis is routinely observed in the uterus in association with fluctuations in the levels of circulating estradiol and other sex steroids. In pathological circumstances, such as breast cancer, a clear association between estrogen, estrogen receptor expression by endothelial cells, angiogenic activity, and/or tumor invasiveness has been made. Studies performed in our laboratory have revealed that estradiol accelerates functional endothelial recovery after arterial injury. Despite these consistent observations, the mechanisms by which estrogen regulates angiogenesis under physiological and pathological circumstances have not been defined.

Fibroblast growth factor 2 activation of stromal cell vascular endothelial growth factor expression and angiogenesis

Angiogenesis is a key component of human cancer progression and metastasis. In an effort to recapitulate early events in tumor-induced angiogenesis, we have employed a subcutaneous Matrigel implant model using immunodeficient mice as hosts. Matrigel-containing fibroblast growth factor 2 (FGF-2; 1.2 microg/ml) induced stromal cell infiltration into the Matrigel/skin interface within 4 days and maximal neovascularization at 7 days. Cells staining positive for the endothelial cell marker, platelet-endothelial cell adhesion molecule 1 (PECAM-1), were present in neovessels and in isolated cells within the Matrigel matrix. Immunohistochemical analysis revealed high levels of vascular endothelial growth factor (VEGF) deposited in the stromal interface present only in the FGF-2-containing but not in control Matrigel implants. VEGF expression was confirmed with in situ hybridization. High VEGF mRNA levels were observed in the infiltrating stromal cells but not in endothelial or endothelial precursors as defined by PECAM-1 staining. In vitro analysis of FGF-2-treated embryonic fibroblasts, Balb/c 3T3 cells, showed an induction of VEGF transcription, mRNA synthesis, and protein secretion as defined by transcriptional reporter, Northern blot, and ELISA assays. The FGF-2-induced VEGF expression was not dependent on select matrix adherence or signaling components because VEGF mRNA expression induced by FGF-2 was equally activated on serum, basement membrane, and fibronectin matrix substrates. Systemic application of anti-VEGF antibodies significantly repressed FGF-2-induced angiogenesis over control antibody by 88% (p < 0.001). These data support an FGF-2 angiogenic model that is dependent on endothelial cell activation, stromal cell infiltration, and VEGF expression by the infiltrating stromal cell population.

Vascular endothelial growth factor binds to fibrinogen and fibrin and stimulates endothelial cell proliferation

Vascular development and response to injury are regulated by several cytokines and growth factors including the members of the fibroblast growth factor and vascular endothelial cell growth factor (VEGF) families. Fibrinogen and fibrin are also important in these processes and affect many endothelial cell properties. Possible specific interactions between VEGF and fibrinogen that could play a role in coordinating vascular responses to injury are investigated. Binding studies using the 165 amino acid form of VEGF immobilized on Sepharose beads and soluble iodine 125 (125I)–labeled fibrinogen demonstrated saturable and specific binding. Scatchard analysis indicated 2 classes of binding sites with dissociation constants (Kds) of 5.9 and 462 nmol/L. The maximum molar binding ratio of VEGF:fibrinogen was 3.8:1. Further studies characterized binding to fibrin using 125I-labeled VEGF- and Sepharose-immobilized fibrin monomer. These also demonstrated specific and saturable binding with 2 classes of sites havingKds of 0.13 and 97 nmol/L and a molar binding ratio of 3.6:1. Binding to polymerized fibrin demonstrated one binding site with a Kd of 9.3 nmol/L. Binding of VEGF to fibrin(ogen) was independent of FGF-2, indicating that there are distinct binding sites for each angiogenic peptide. VEGF bound to soluble fibrinogen in medium and to surface immobilized fibrinogen or fibrin retained its capacity to support endothelial cell proliferation. VEGF binds specifically and saturably to fibrinogen and fibrin with high affinity, and this may affect the localization and activity of VEGF at sites of tissue injury.

Plasminogen activator system, vascular endothelial growth factor, and colorectal cancer progression

AIMS

To plasminogen activator system (PAS) consists of the plasminogen activators (urokinase (uPA) and tissue-type (tPA) plasminogen activators), the uPA receptor (uPAR), and the plasminogen activator inhibitors (PAI-1 and PAI-2). Plasminogen activators activate plasminogen to plasmin, which can break down extracellular matrix (ECM) components. Vascular endothelial growth factor (VEGF) is a mitogen for endothelial cells and is involved in angiogenesis. VEGF has been shown to upregulate uPA and this may facilitate tumour angiogenesis further.

METHODS

PAS components and VEGF were determined by enzyme linked immunosorbent assay (ELISA) in paired colorectal tumour and normal tissue (n = 50) and correlated with pathological staging.

RESULTS

uPA, uPAR, PAI-1, and VEGF values were significantly higher in tumour tissue (for example, tumour uPA: median, 2.3 (range, 0.1-6.7) ng/mg protein v normal uPA: median, 0.2 (range, 0-2.6) ng/mg protein). tPA was significantly higher in normal mucosa and there was no difference in PAI-2. uPA, uPAR, PAI-1, and VEGF values significantly correlated with each other and with Dukes's staging (uPA in adenomas: median, 0.42 (range, 0.1-1.2) ng/mg protein; upA in Dukes's B tumours: median, 2.1 (range, 0.4-4.3) ng/mg protein; and uPA in Dukes's D tumours: median, 4.0 (range, 3.7-4.2) ng/mg protein) and lymphatic invasion. In addition PAI-1 also correlated with tumour size and differentiation.

CONCLUSION

The involvement of the PAS and VEGF in colorectal cancer appears to be complex. uPA, uPAR, PAI-1, and VEGF were upregulated in tumour tissue and this correlated with Dukes's staging and lymphatic invasion.

Production of experimental malignant pleural effusions is dependent on invasion of the pleura and expression of vascular endothelial growth factor/vascular permeability factor by human lung cancer cells

We determined the molecular mechanisms that regulate the pathogenesis of malignant pleural effusion (PE) associated with advanced stage of human, non-small-cell lung cancer. Intravenous injection of human PC14 and PC14PE6 (adenocarcinoma) or H226 (squamous cell carcinoma) cells into nude mice yielded numerous lung lesions. PC14 and PC14PE6 lung lesions invaded the pleura and produced PE containing a high level of vascular endothelial growth factor (VEGF)-localized vascular hyperpermeability. Lung lesions produced by H226 cells were confined to the lung parenchyma with no PE. The level of expression of VEGF mRNA and protein by the cell lines directly correlated with extent of PE formation. Transfection of PC14PE6 cells with antisense VEGF165 gene did not inhibit invasion into the pleural space but reduced PE formation. H226 cells transfected with either sense VEGF 165 or sense VEGF 121 genes induced localized vascular hyperpermeability and produced PE only after direct implantation into the thoracic cavity. The production of PE was thus associated with the ability of tumor cells to invade the pleura, a property associated with expression of high levels of urokinase-type plasminogen activator and low levels of TIMP-2. Collectively, the data demonstrate that the production of malignant PE requires tumor cells to invade the pleura and express high levels of VEGF/VPF.

Vascular endothelial growth factor binds to fibrinogen and fibrin and stimulates endothelial cell proliferation

Vascular development and response to injury are regulated by several cytokines and growth factors including the members of the fibroblast growth factor and vascular endothelial cell growth factor (VEGF) families. Fibrinogen and fibrin are also important in these processes and affect many endothelial cell properties. Possible specific interactions between VEGF and fibrinogen that could play a role in coordinating vascular responses to injury are investigated. Binding studies using the 165 amino acid form of VEGF immobilized on Sepharose beads and soluble iodine 125 (125I)–labeled fibrinogen demonstrated saturable and specific binding. Scatchard analysis indicated 2 classes of binding sites with dissociation constants (Kds) of 5.9 and 462 nmol/L. The maximum molar binding ratio of VEGF:fibrinogen was 3.8:1. Further studies characterized binding to fibrin using 125I-labeled VEGF- and Sepharose-immobilized fibrin monomer. These also demonstrated specific and saturable binding with 2 classes of sites havingKds of 0.13 and 97 nmol/L and a molar binding ratio of 3.6:1. Binding to polymerized fibrin demonstrated one binding site with a Kd of 9.3 nmol/L. Binding of VEGF to fibrin(ogen) was independent of FGF-2, indicating that there are distinct binding sites for each angiogenic peptide. VEGF bound to soluble fibrinogen in medium and to surface immobilized fibrinogen or fibrin retained its capacity to support endothelial cell proliferation. VEGF binds specifically and saturably to fibrinogen and fibrin with high affinity, and this may affect the localization and activity of VEGF at sites of tissue injury.

Biological behaviour and clinical implications of micrometastases

BACKGROUND

The most important prognostic determinant in cancer is the identification of disseminated tumour burden (metastases). Micrometastases are microscopic (smaller than 2 mm) deposits of malignant cells that are segregated spatially from the primary tumour and depend on neovascular formation (angiogenesis) to propagate.

METHODS

The electronic literature (1966 to present) on micrometastases and their implications in malignant melanoma and epithelial cancers was reviewed.

RESULTS

Immunohistochemical techniques combined with serial sectioning offer the best accuracy for detection of nodal micrometastases. Molecular techniques should be reserved for blood samples or bone marrow aspirates. Detection of micrometastases in regional lymph nodes and/or bone marrow confers a poor prognosis in epithelial cancers. The concept of sentinel node biopsy combined with serial sectioning and dedicated screening for micrometastases may improve staging procedures. Strategies against angiogenesis may provide novel therapies to induce and maintain micrometastatic dormancy.

CONCLUSION

The concept of micrometastases has resulted in a paradigm shift in the staging of epithelial tumours and our overall understanding of malignant processes.

Placental vascular morphogenesis

Appropriate growth and development of the placenta is essential for fetal growth and wellbeing, and indeed may be an important factor in determining adult health. As the fetus grows its demands increase and the capacity of the placenta to facilitate transfer between the fetal and maternal circulations increases as gestation progresses. The principal units for diffusional exchange of oxygen are the terminal villi, and these develop in the third trimester. It is thought that capillary growth within the villi drives the growth of these structures which are characterized by a high proportion of their volume being occupied by fetal capillaries and extreme thinning of the trophoblast and endothelial cell layers. In the first trimester the PO2 in the intervillous space is low and rises sharply at the start of the second. Endothelial growth is influenced by a variety of soluble factors, and several of these are regulated by oxygen, for example, vascular endothelial growth factor (VEGF), angiopoietin 2, and soluble flt (a VEGF antagonist). Thus, fetal demand may regulate villous growth and differentiation by altering local PO2 which, in turn, modulates growth factors (or their antagonists) to regulate endothelial growth and vessel re-modelling.

Matrix metalloproteinases: pro- and anti-angiogenic activities

Matrix metalloproteinases (MMP) are a family of structurally related proteinases most widely recognized for their ability to degrade extracellular matrix, although recent investigations have demonstrated other biologic functions for these enzymes. MMP are typically not constitutively expressed, but are regulated by: (1) cytokines, growth factors, and cell-cell and cell-matrix interactions that control gene expression; (2) activation of their proenzyme form; and (3) the presence of MMP inhibitors [tissue inhibitors of metalloproteinases, (TIMP)]. MMP have important roles in normal processes including development, wound healing, mammary gland, and uterine involution, but are also involved in angiogenesis, tumor growth, and metastasis. Angiogenesis, characteristically defined as the establishment of new vessels from pre-existing vasculature, is required for biologic processes such as wound healing and pathologic processes such as arthritis, tumor growth, and metastasis. Blocking of MMP activity has been studied for potential therapeutic efficacy in controlling such pathologic processes. Synthetic MMP inhibitors, most notably the hydroxymates, have been engineered for this purpose and are presently in clinical trial. These inhibitors may have broad versus specific MMP inhibitory activity. As increased non-matrix degrading capabilities of MMP are recognized, however, i.e., cytokine activation, processing of proteins to molecules of distinct biologic function, it becomes less clear whether the nonselective inhibition of MMP activity for all pathologic processes involving MMP is appropriate. This review focuses upon the contribution of MMP to the process of tumor invasion and angiogenesis, and discusses the design and use of MMP inhibitors as therapeutic agents in these processes.

Vascular endothelial growth factor and its correlation with angiogenesis and p53 expression in prostate cancer

BACKGROUND

Previously it was demonstrated that in prostate tumors, angiogenesis measured as microvessel density (MVD) is associated with tumor stage as well as WHO grade and is an independent predictor of clinical outcome. Vascular endothelial growth factor (VEGF) is a major inducer of angiogenesis. There is some evidence that P53 mutations cause overexpression of VEGF. We studied VEGF expression, p53 overexpression, and P53 mutations in prostate cancer (PCA) to investigate the role of VEGF as an angiogenic marker and the possible deregulation of VEGF as a result of P53 mutations in PCA.

METHODS

Immunohistochemical staining with a polyclonal VEGF antibody was performed in 55 paraffin-embedded PCA, in which MVD had previously been determined, as well as in 5 prostatic adenomas (PA) and 20 adjacent normal prostate tissues. In addition, 37 PCA and 5 PAs were examined for p53 expression by immunohistochemistry. Temperature gradient gel electrophoresis (TGGE) was performed in 13 of these PCA to screen for P53 mutations. VEGF expression, p53 expression, and mutations were then correlated with tumor stage, grade, MVD, and clinical outcome.

RESULTS

While PA and normal prostate tissue generally showed no or only low VEGF expression, there was a significant increase in VEGF expression with tumor stage, grade, and MVD in PCA. During clinical follow-up (mean, 31.9 months), 9 of 55 patients had tumor progression. Significant differences in VEGF expression were found between patients with tumor progression and those without (P = 0.0004). Of the 37 PCA evaluated for p53 expression, 12 exhibited p53 overexpression. TGGE revealed P53 mutations in 3 of 13 PCA. However, there was no correlation between VEGF expression, p53 overexpression, and P53 mutation, respectively.

CONCLUSIONS

VEGF seems to be an important, clinically relevant inducer of angiogenesis in PCA. VEGF expression was shown to correlate positively with tumor stage, grade, MVD, and clinical outcome. However, regulation of VEGF in PCA appears to be independent of p53 expression.

VEGF in brain tumors

Vascular endothelial growth factor (VEGF) is a regulator of angiogenesis, vasculogenesis and vascular permeability. In this contribution, molecular and biological properties of VEGF are described. Furthermore, this article focuses on the evidence that angiogenesis in brain tumors is mediated by VEGF. Among the topics discussed are expression patterns of VEGF and its receptors in different brain tumors, possible regulatory mechanism involved in the VEGF-driven tumor angiogenesis and the involvement of VEGF in the genesis of peritumoral edema. Finally, anti-angiogenesis approaches to target VEGF/VEGF receptors are discussed.

Serum levels of vascular endothelial growth factor dependent on the stage progression of lung cancer

STUDY OBJECTIVE

In lung cancer, vascular endothelial growth factor (VEGF) is an important cytokine and is correlated with tumor vessel density, malignant pleural effusions, and coagulation-fibrinolysis factors in vitro. We investigated the correlation between serum VEGF level and stage progression in lung cancer to study the predicted value of VEGF level. We also studied whether coagulation-fibrinolysis factors and PaO(2) levels, which are also important factors for the prediction of the clinical course, are correlated with VEGF.

METHODS

Forty-nine patients with lung cancer were investigated prospectively. VEGF levels of sera and malignant effusions, and plasma concentrations of coagulation-fibrinolysis factors were measured by enzyme-linked immunosorbent assay. We measured PaO(2) levels in all patients at rest.

RESULTS

Serum levels of VEGF were increased significantly according to stage progression. Additionally, plasma concentrations of D dimer, thrombin-antithrombin complex (TAT), and tissue plasminogen activator/plasminogen activator inhibitor type I complex were elevated significantly according to stage progression. The serum VEGF level had a significant positive correlation with the TAT and D dimer levels. Serum VEGF levels had a significant negative correlation with PaO(2) levels. The incidence of cerebral vascular disorder was significantly higher in the patients with systemic hypoxemia than in those without (p<0.05). Mean VEGF levels in malignant effusions in eight patients (five with pleural effusions, two with pericardial effusions, and one with both) were extremely high, especially in pericardial effusions ([mean +/- SD] pleural effusions, 531.9+/-285.4 pg/mL; pericardial effusion, 3,071.6+/-81.3 pg/mL).

CONCLUSION

We predict that in lung cancer, VEGF production and the abnormality of the coagulation-fibrinolysis system differ depending on the stage of progression of disease. Serum VEGF levels would be affected by PaO(2) levels in lung cancer.

Inhibition of vascular endothelial growth factor activity by transfection with the soluble FLT-1 gene

Vascular endothelial growth factor (VEGF)-induced angiogenesis is involved in the etiology of some cardiovascular diseases. The soluble form of VEGF receptor, FLT-1 (sFLT-1), is a potent antagonist of VEGF. Therefore, we investigated whether transfection with the sFLT-1 gene could inhibit VEGF-induced angiogenesis. Human embryonic kidney (HEK)-293 cells were transfected with plasmids containing VEGF and sFLT-1 (pCMV-VEGF and pCMV-sFLT-1) by the calcium-phosphate co-precipitation method. VEGF- and/or sFLT-1-transfected HEK-293 cells were incubated for 24 h, and then conditioned medium was collected. The effects of conditioned medium on angiogenesis were tested by incorporation of [3H]thymidine into human umbilical vein endothelial cells (HUVECs). Expression of VEGF protein was determined by Western blotting. The conditioned medium from sFLT-1 gene-transfected HEK-293 cells significantly inhibited recombinant VEGF-induced increase in [3H]thymidine incorporation by HUVECs. VEGF gene-transfected HEK-293 cells secreted VEGF protein into conditioned medium. This conditioned medium increased [3H]thymidine incorporation by HUVECs, which was significantly inhibited by co-transfection of sFLT-1 gene with VEGF gene. These observations suggested that sFLT-1 gene transfer could inhibit VEGF-induced DNA synthesis of vascular endothelial cells.

Expression and tissue concentration of vascular endothelial growth factor, its receptors, and localization in the bovine corpus luteum during estrous cycle and pregnancy

The presence of vascular endothelial growth factor (VEGF) in the ovary has been reported in a number of species. The objective of the present study was to demonstrate the expression of VEGF, VEGF receptor (R)-1, and VEGFR-2 in detail by different methodological approaches in bovine corpora lutea (CL) obtained from different stages of the estrous cycle and during pregnancy. VEGF and VEGF receptor transcripts were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay. All components of the VEGF system were found in the bovine CL during the estrous cycle and pregnancy. Analysis of VEGF transcript by RT-PCR shows that CL tissues expressed predominantly the smallest isoforms (VEGF(121) and VEGF(165)). The highest mRNA expression for VEGF and VEGFR-2 mRNA was detected during the early luteal phase, followed by a significant decrease of expression during the mid and late luteal phase and a further decrease of VEGF mRNA after regression. During pregnancy, high levels of expression were always present. In contrast, no significant change in VEGFR-1 mRNA expression during the estrous cycle and pregnancy was found. The VEGF protein concentration in CL tissue was significantly higher (20.9-23.4 ng/g wet weight) during the early luteal phase (Days 1-7), followed by a decrease at the late luteal phase (14.3-18.7 ng/g wet weight) and, especially, after CL regression (2.8 ng/g wet weight). However, relatively high levels were found during pregnancy (10.1 ng/g wet weight). As achieved by immunohistochemistry, VEGF protein was localized predominantly in luteal cells. High VEGF protein and transcript concentrations and increased VEGFR-2 expression during the early luteal phase coincided with luteal vascularization. These results suggest an important role of VEGF in angiogenesis of the newly formed CL. The high VEGF mRNA expression and protein levels during matured vasculature in the mid-stage CL and pregnancy also suggest also a survival function for endothelial cells.

Vascular endothelial growth factor-driven glioma growth and vascularization in an orthotopic rat model monitored by magnetic resonance imaging

OBJECTIVE

The goal of the present study was to develop an orthotopic in vivo model for the investigation of vascular endothelial growth factor (VEGF)-dependent glioma growth and vascularization.

METHODS

C6 glioma cells were infected with viruses encoding sense or antisense VEGF. Expression of the transgene was controlled by Northern blot analysis, Western blot analysis, and immunohistochemistry. Spheroids generated from both clones as well as from wild-type and mock-transfected cells were implanted in the brains of Sprague-Dawley rats. Growth and vascularization were assessed using magnetic resonance imaging after 7 and 11 days. Histology was studied using hematoxylin and eosin staining, immunohistochemistry with anti-von Willebrand staining, anti-VEGF, anti-CD8, and assessment of vessel density.

RESULTS

Cell proliferation, migration, and invasion in vitro were very similar in all cell clones. Sense gliomas demonstrated by far the fastest growth in vivo, with intense contrast enhancement meeting criteria for highly malignant tumors. Histological examination revealed masses of von Willebrand- and VEGF-positive tumor vessels with a high vessel density. Antisense gliomas depicted the radiological features of low-grade gliomas, with slow growth and poor vascularization, although they were highly infiltrative. Wild-type and mock-transfected gliomas demonstrated similar growth and vascularization patterns intermediate between sense and antisense gliomas. Any influence of the allogeneic response of the hosts on different tumor sizes could be excluded.

CONCLUSION

Our model elucidates glioma growth and vascularization as strongly VEGF dependent, which is consistent with human gliomas. Thus, this model is suitable for testing antiangiogenic strategies to interfere with the VEGF/VEGF receptor system, as well as for exploring VEGF-independent mechanisms using the antisense-transfected clone.