What, if anything, is an angiogenic factor?

Human iPSC-derived mesodermal progenitor cells preserve their vasculogenesis potential after extrusion and form hierarchically organized blood vessels

Post-fabrication formation of a proper vasculature remains an unresolved challenge in bioprinting. Established strategies focus on the supply of the fabricated structure with nutrients and oxygen and either rely on the mere formation of a channel system using fugitive inks or additionally use mature endothelial cells and/or peri-endothelial cells such as smooth muscle cells for the formation of blood vesselsin vitro.Functional vessels, however, exhibit a hierarchical organization and multilayered wall structure that is important for their function. Human induced pluripotent stem cell-derived mesodermal progenitor cells (hiMPCs) have been shown to possess the capacity to form blood vesselsin vitro, but have so far not been assessed for their applicability in bioprinting processes. Here, we demonstrate that hiMPCs, after formulation into an alginate/collagen type I bioink and subsequent extrusion, retain their ability to give rise to the formation of complex vessels that display a hierarchical network in a process that mimics the embryonic steps of vessel formation during vasculogenesis. Histological evaluations at different time points of extrusion revealed the initial formation of spheres, followed by lumen formation and further structural maturation as evidenced by building a multilayered vessel wall and a vascular network. These findings are supported by immunostainings for endothelial and peri-endothelial cell markers as well as electron microscopic analyses at the ultrastructural level. Moreover, endothelial cells in capillary-like vessel structures deposited a basement membrane-like matrix at the basal side between the vessel wall and the alginate-collagen matrix. After transplantation of the printed constructs into the chicken chorioallantoic membrane (CAM) the printed vessels connected to the CAM blood vessels and get perfusedin vivo. These results evidence the applicability and great potential of hiMPCs for the bioprinting of vascular structures mimicking the basic morphogenetic steps ofde novovessel formation during embryogenesis.

Effect of enriched environment on angiogenesis and neurological functions in rats with focal cerebral ischemia

The purpose of this study was to investigate the effect of enriched environment (EE) on cerebral angiogenesis after ischemia-reperfusion injury. Middle cerebral artery occlusion (MCAO) followed by reperfusion was performed in rats to set up an animal model of ischemia-reperfusion injury. In a set of behavioral tests, we demonstrated that the animals in the IEE (ischemia + enriched environment) group exhibited significantly improved neurological functions compared to those in the standard housing condition group. In consistent with the functional tests, smaller infarction volumes were observed in the animals of IEE group. Laser scanning confocal microscopy and 3D quantitative analysis of cerebral microvessels revealed that EE treatment increased the total vessel surface area and number of branch point in the ischemic boundary zone. IgG extraction assay showed that the blood brain barrier (BBB) leakage in the ischemic brain was attenuated after EE treatment. EE treatment also enhanced endothelial cells (ECs) proliferation and increased the expression levels of VEGF and its receptor Flk-1 after ischemia-reperfusion injury. Analyses of Spearman's correlation coefficients indicated a correlation of mNSS scores with enhanced cerebral angiogenesis. Together, the results suggest that EE treatment-induced cerebral angiogenesis may contribute to the improved neurological outcome of stroke animals after ischemia-reperfusion injury.

Selection, Analysis and Improvement of Anti-Angiogenesis Compounds Identified by an Anti-HIF-1α Screening and Validation System

Cancer cells resort to activating hypoxia-inducible factor-1 (HIF-1) as one of several responses to hypoxic conditions. Overexpression of HIF-1, the transcriptional regulator for a group of malignant-pathway related genes including vascular endothelial growth factor (VEGF), is associated with increased tumor growth, vascularization, and metastasis. HIF-1 is composed of an inducible subunit, HIF-1α and a constitutively expressed subunit, HIF-1ß. HIF-1 activity is mainly dependent on the level of HIF-1α protein, the inducible and regulatory subunit of the HIF-1 heterodimer complex; thus, identification of novel anti-HIF-1α agents will lead to effective blockage of the HIF-1 (HIF-1α)-mediated "switch-on" function for those malignant-pathway related genes and suppression of the HIF-1α/VEGF-mediated signaling pathway that promotes cancer progression and metastasis. While there is an extremely large number of small molecule compounds in the database (compound libraries), the currently existing screening system is inefficient and time-consuming; or, at best, the application of the existing screening system is very limited as it is usually not coupled with biological validation processes. The further development of potential drugs is partly hindered due to the cumbersome steps in between the primary screen and consequent validation: the slow, exhausted and sometimes lack of a linked biological validation process contributes to the dismal fate of scant compounds uncovered in the primary screen. To improve upon the status quo, we developed a prototype screening system that is coupled anti-HIF-1α primary screen with secondary anti-VEGF/anti-angiogenesis validation screens. We used breast cancer cells as the model to select potent anti-HIF-1α small-molecule compounds by their abilities to inhibit transactivation of a VEGF promoter fused to a luciferase reporter gene under hypoxia. Positive compounds were then validated by a series of assays that confirm compounds' anti-HIF-1α activities including measurement of their effects on HIF-1α downstream VEGF gene expression and angiogenic ability of breast cancer cells. Moreover, we demonstrated that we could further improve the compound's potency of anti-HIF-1α and anti-angiogenesis by modifying the identified lead to synthesize a superior (novel) drug.

The effect of impaired angiogenesis on intestinal function following massive small bowel resection

PURPOSE

Intestinal adaptation involves villus lengthening, crypt deepening, and increased capillary density following small bowel resection (SBR). Mice lacking the proangiogenic chemokine CXCL5 have normal structural adaptation but impaired angiogenesis. This work evaluates the impact of incomplete adaptive angiogenesis on the functional capacity of the intestine after SBR.

METHODS

CXCL5 knockout (KO) and C57BL/6 wild-type (WT) mice underwent 50% SBR. Magnetic resonance imaging measured weekly body composition. Intestinal absorptive capacity was evaluated through fecal fat analysis. Gene expression profiles for select macronutrient transporters were measured via RT-PCR. Postoperative crypt and villus measurements were assessed for structural adaptation. Submucosal capillary density was measured through CD31 immunohistochemistry.

RESULTS

Comparable postoperative weight gain occurred initially. Diminished weight gain, impaired fat absorption, and elevated steatorrhea occurred in KO mice after instituting high-fat diet. Greater postoperative upregulation of ABCA1 fat transporter occurred in WT mice, while PEPT1 protein transporter was significantly downregulated in KO mice. KO mice had impaired angiogenesis but intact structural adaptation.

CONCLUSION

After SBR, KO mice display an inefficient intestinal absorption profile with perturbed macronutrient transporter expression, impaired fat absorption, and slower postoperative weight gain. In addition to longer villi and deeper crypts, an intact angiogenic response may be required to achieve functional adaptation to SBR.

CXCL5 is required for angiogenesis, but not structural adaptation after small bowel resection

PURPOSE

Intestinal adaptation is the compensatory response to massive small bowel resection (SBR) and characterized by lengthening of villi and deepening of crypts, resulting in increased mucosal surface area. Previous studies have demonstrated increased villus capillary blood vessel density after SBR, suggesting a role for angiogenesis in the development of resection-induced adaptation. Since we have previously shown enhanced expression of the proangiogenic chemokine CXCL5 after SBR, the purpose of this study was to determine the effect of disrupted CXCL5 expression on intestinal adaptation.

METHODS

CXCL5 knockout (KO) and C57BL/6 wild type (WT) mice were subjected to either a 50% proximal SBR or sham operation. Ileal tissue was harvested on postoperative day 7. To assess for adaptation, villus height and crypt depth were measured. Submucosal capillary density was measured by CD31 immunohistochemistry.

RESULTS

Both CXCL5-KO and WT mice demonstrated normal structural features of adaptation. Submucosal capillary density increased in the WT but not in the KO mice following SBR.

CONCLUSION

CXCL5 is required for increased intestinal angiogenesis during resection-induced adaptation. Since adaptive villus growth occurs despite impaired CXCL5 expression and enhanced angiogenesis, this suggests that the growth of new blood vessels is not needed for resection-induced mucosal surface area expansion following massive SBR.

p16 Modulates VEGF expression via its interaction with HIF-1alpha in breast cancer cells

The degree of tumor progression (such as growth, angiogenesis, and metastasis) directly correlates with the expression of vascular endothelial growth factor (VEGF), but inversely correlates with the expression of tumor-suppressor gene p16, therefore we examined whether the restoration of p16 in breast cancer cells would modulate VEGF expression. Adenoviral-mediated p16 expression downregulated VEGF gene expression in breast cancer cells, and inhibited breast cancer cell-induced angiogenesis by a dorsal air sac model in mice. Moreover, p16 appears to form a complex with HIF-1a, the transcription factor for the VEGF gene promoter. Taken together, the binding between p16 and HIF-1a protein may alter HIF-1a's ability to transactivate VEGF expression.

Epidermal growth factor receptor signaling modulates chemokine (CXC) ligand 5 expression and is associated with villus angiogenesis after small bowel resection

BACKGROUND

Adaptive villus growth after a massive small bowel resection (SBR) is an important response to the loss of intestinal surface area and is regulated via epidermal growth factor receptor (EGFR) signaling. Increased levels of the proangiogenic chemokine ligand 5 (CXCL5) have been found within the adapting bowel in which angiogenesis is increased. We sought to determine whether CXCL5 was expressed specifically in the villus mesenchymal zone (area of increased blood vessel growth) and whether this expression was affected by EGF.

METHODS

C57BL/6J mice were subjected to sham operation (bowel transaction with reanastomosis) or 50% proximal SBR. The remnant intestine was harvested, and the villus lamina propria was isolated by laser capture microdissection. The expression of CXCL5 messenger RNA (mRNA) was analyzed using real-time polymerase chain reaction (RT-PCR). Furthermore, CXCL5 mRNA levels were determined in EGF-stimulated human umbilical vein endothelial cells (HUVECs).

RESULTS

A 2.39-fold increase (P < .05) in CXCL5 mRNA occurred in the lamina propria after SBR. In addition, villus height was found to be related directly to the degree of CXCL5 mRNA (R(2) = 0.97) expression. HUVECs treated with EGF demonstrated a 9-fold increase in CXCL5 mRNA expression.

CONCLUSION

The villus growth observed in resection-induced adaptation is associated with increased expression of the chemokine CXCL5 within the lamina propria. Because EGF enhances CXCL5 expression directly in endothelial cells, EGFR-directed proangiogenic gene expression may be a critical mechanism for adaptive ileal villus growth.

Tristetraprolin inhibits Ras-dependent tumor vascularization by inducing vascular endothelial growth factor mRNA degradation

Vascular endothelial growth factor (VEGF) is one of the most important regulators of physiological and pathological angiogenesis. Constitutive activation of the extracellular signal-regulated kinase (ERK) pathway and overexpression of VEGF are common denominators of tumors from different origins. We have established a new link between these two fundamental observations converging on VEGF mRNA stability. In this complex phenomenon, tristetraprolin (TTP), an adenylate and uridylate-rich element-associated protein that binds to VEGF mRNA 3'-untranslated region, plays a key role by inducing VEGF mRNA degradation, thus maintaining basal VEGF mRNA amounts in normal cells. ERKs activation results in the accumulation of TTP mRNA. However, ERKs reduce the VEGF mRNA-destabilizing effect of TTP, leading to an increase in VEGF expression that favors the angiogenic switch. Moreover, TTP decreases RasVal12-dependent VEGF expression and development of vascularized tumors in nude mice. As a consequence, TTP might represent a novel antiangiogenic and antitumor agent acting through its destabilizing activity on VEGF mRNA. Determination of TTP and ERKs status would provide useful information for the evaluation of the angiogenic potential in human tumors.

Endogenous angiogenin in endothelial cells is a general requirement for cell proliferation and angiogenesis

Angiogenin is an angiogenic protein that undergoes nuclear translocation in endothelial cells where it accumulates in the nucleolus and stimulates rRNA transcription, a rate-limiting step in ribosome biogenesis, protein translation, and cell growth. Here, we report that angiogenin is required for cell proliferation induced by various other angiogenic proteins including acidic and basic fibroblast growth factors (aFGF and bFGF), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF). Downregulation of angiogenin in endothelial cells by small interfering RNA (siRNA) and antisense results in a decrease in rRNA transcription, ribosome biogenesis, and cell proliferation induced by these angiogenic factors. Inhibitors of the nuclear translocation of angiogenin abolish the angiogenic activities of these factors. Stable angiogenin antisense transfection in HeLa cells reduces tumor angiogenesis in athymic mice despite the elevated expression level of bFGF and VEGF. Thus, nuclear angiogenin assumes an essential role in endothelial cell proliferation and is necessary for angiogenesis induced by other angiogenic factors. Angiogenin-stimulated rRNA transcription in endothelial cells may thus serve as a crossroad in the process of angiogenesis induced by various angiogenic factors.

Inhibition of growth and metastasis of human gastric cancer implanted in nude mice by d-limonene

AIM: To investigate the effects and mechanism of d-limonene on the growth and metastasis of gastric cancer in vivo.

METHODS: Metastatic model simulating human gastric cancer was established by orthotopic implantation of histologically intact human tumor tissue into gastric wall of nude mice. One percent d-limonene was orally administered at dose of 15 ml/kg every other day for seven weeks. Eight weeks after implantation, tumor weight, inhibition rate, apoptotic index (AI), microvessel density (MVD), vascular endothelial growth factor (VEGF), variation of ultrastructure, and the presence of metastasis were evaluated, respectively, after the mice were sacrificed.

RESULTS: The tumor weight was significantly reduced in 5-FU group (2.55 ± 0.28 g), d-limonene group (1.49 ± 0.09 g) and combined treatment group (1.48 ± 0.21 g) compared with the control group(2.73 ± 0.23 g, P < 0.05). In 5-FU group, d-limonene group, combined treatment group, the inhibition rates were 2.60%, 47.58% and 46.84% and 0, respectively; AI was (3.31 ± 0.33)%, (8.26 ± 1.21)%, (20.99 ± 1.84)% and (19.34 ± 2.19)%, respectively; MVD was (8.64 ± 2.81), (16.77 ± 1.39), (5.32 ± 4.26) and (5.86 ± 2.27), respectively; VEGF expression was (45.77 ± 4.79), (41.34 ± 5.41), (29.71 ± 8.92) and (28.24 ± 8.55), respectively. The incidences of peritoneal metastasis also decreased significantly in 5-FU group(77.8%), d-limonene group (20.0%) and combined group (22.2%) compared with control group (100%) versus 62.5%, 30% and 22.2%) (P < 0.05). Liver metastasis was also inhibited and the incidences decreased significantly in 5-FU group, d-limonene group and combined group than that in control group (87.5% vs 55.5%, 20.0% and 22.2% respectively) (P < 0.05). The incidence of ascites in control group, 5-FU group, d-limonene group and combined group was 25.0%, 22.2%, 0, 0, respectively and 12.5%, 11.1% 0, 0, with respect to the metastasis rate to other organs.

CONCLUSION: d-limonene has antiangiogenic and proapoptotic effects on gastric cancer, thereby inhibits tumor growth and metastasis. Combination of d-limonene with cytotoxic agents may be more effective.

VEGF protects human cerebral hybrid neurons from in vitro ischemia

Vascular endothelial growth factor (VEGF), the most potent angiogenic peptide, protects the neurons against experimental ischemia. However, its neuroprotective effect on human brain is unknown. The present study attempted to determine whether VEGF can protect human cerebral neurons in vitro. A1 human hybrid clonal neurons (human cerebral neuron + neuroblastoma cell) were exposed to hypoxia with glucose deprivation. Pretreatment with VEGF reduced the A1 cell death, and VEGFR-2/Flk-1 and VEGF increased with a neuroprotective effect. However, the human neuroblastoma or neuroglioma cells failed to show these findings. Our results suggest that VEGF can protect human cerebral neurons from cell death after an ischemic insult in vitro, which is correlated to both increased expression of VEGFR-2/Flk-1 and VEGF within the cells.

Angiogenesis-related growth factors in brain tumors

Numerous growth factors have been implicated in glioma angiogenesis. This chapter focuses on the role of scatter factor/hepatocyte growth factor, fibroblast growth factor, platelet-derived growth factor and transforming growth factor beta. We review the expression pattern of these factors in gliomas, their functional contribution to tumor angiogenesis - also in relation to vascular endothelial growth factor, and the effects resulting from their inhibition or overexpression in gliomas in vivo.

Vascularisation of tissue-engineered grafts: the regulation of angiogenesis in reconstructive surgery and in disease states

Angiogenesis (the formation of new blood vessels) is essential for the growth of new tissue, tissue repair and wound healing. Tissue engineering, the construction of new tissue and organs for reparative purposes, relies on angiogenesis for the vascularisation of these new grafts. In tissue engineering, the emphasis to date has been on vascularisation of newly constructed tissue grafts by an extrinsic blood supply, and relatively little attention has been given to the possibility of building these grafts around an intrinsic blood supply. However, there are many disease processes, notably tumour growth, where excess angiogenesis can be a major problem. The purposes of this review are, first, to examine various methods of vascularising tissue-engineered grafts, and, second, to compare the role of angiogenesis in tissue engineering, where stimulation of angiogenesis is paramount, with pathological states, such as tumour growth, where angiogenesis needs to be inhibited.

Anti-angiogenic agents for the treatment of brain tumors

It is accepted that novel therapeutic approaches are needed for the majority of patients with malignant brain tumors. The vascularity of many primary brain tumors and the encouraging preclinical studies suggest that antiangiogenic agents have the potential to become an important component of multimodality treatment of patients with brain tumors. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of brain tumor neovasculature. Neuroimaging techniques evaluating the angiogenic process and the impact of antiangiogenic agents will be an important tool for the rapid development of these novel therapeutic agents.

Antiangiogenic and antitumor effects of a protein kinase Cbeta inhibitor in human breast cancer and ovarian cancer xenografts

In cell culture, the compound 317615 2HCl, a potent inhibitor of VEGF-stimulated HUVEC proliferation, was not very effective against MX-1 breast cancer cells (IC50= 8.1 microM) or SKOV-3 ovarian carcinoma cells (IC50 = 9.5 microM). Exposure to combinations of paclitaxel or carboplatin and 317615 x 2HCl with MX-1 cells in culture resulted in cell survival that reflected primarily additivity of the two agents. Exposure of SKOV-3 cells to paclitaxel or carboplatin along with 317615 2HCl resulted in cell survivals that reflected additivity of 317615 x 2HCl with paclitaxel and greater-than-additive cytotoxicity with carboplatin. Administration of 317615 x 2HCI orally twice daily to nude mice bearing subcutaneous MX-1 tumors or SKOV-3 tumors resulted in a decreased number of intratumoral vessels as determined by CD31 and CD105 staining with decreases of 35% and 43% in MX-1 tumors and 60% and 75% in SKOV-3 tumors, respectively. 317615 x 2HCl was an active antitumor agent against the MX-1 xenograft and increased the tumor growth delay produced by paclitaxel by 1.7-fold and the tumor growth delay produced by carboplatin by 3.8-fold. Administration of 317615 x 2HCl also increased the tumor growth delay produced by fractionated radiation therapy in the MX-1 tumor. Treatment with 317615 x 2HCl alone increased the lifespan of animals bearing intraperitoneal SKOV-3 xenografts by 1.9 fold compared with untreated control animals. The combination of paclitaxel and 317615 x 2HCl resulted in 100% 120-day survival of SKOV-3 bearing animals. Administration of 317615 x 2HCl along with carboplatin to animals bearing the SKOV-3 tumor produced a 1.8-fold increase in lifespan compared with carboplatin alone. 317615 x 2HCl is a promising new antiangiogenic agent that is in early phase clinical testing.

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor promotes collateral development in a rabbit model of hind limb ischemia

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor (bFGF), a new strategy for the treatment of chronic vascular occlusive disease, was examined in a rabbit model of hind limb ischemia. The left femoral artery was completely excised to induce an ischemic state in the hind limb of male rabbits. Simultaneously, a skin section was resected from the wound, and host fibroblasts were cultured. The cultured fibroblasts were infected with adenovirus vector containing modified human bFGF cDNA with the secretory signal sequence (AxCAMAssbFGF) or LacZ cDNA (AxCALacZ). At 21 days after femoral artery excision, the gene-transduced fibroblasts were administered through the left internal iliac artery. The fibroblasts significantly accumulated in the ischemic hind limb, and the AxCAMAssbFGF-treated cells secreted bFGF for less than 14 days without elevation of systemic bFGF level. At 28 days after cell administration, calf blood pressure ratio, angiographic score, capillary density of muscle tissue and blood flow of the left internal iliac artery were determined, and animals with AxCAMAssbFGF-treated cells showed significantly greater development of collateral vessels, as compared with those with AxCALacZ-treated cells. These findings suggest that adenovirus-mediated ex vivo gene transfer of bFGF was effective for improvement of chronic limb ischemia.

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.

Genes that regulate metastasis and angiogenesis

Genetic instability and an accumulation of genetic and epigenetic changes during tumor progression lead to an increasingly aggressive and treatment-resistant phenotype, and ultimately metastasis. In recent years it has become well established that angiogenesis, the process by which new vasculature is formed from pre-existing vessels, is an essential component to primary tumor growth and distant metastasis. A greater understanding of the complex multitude of factors involved in tumor angiogenesis and metastasis is fundamental to the development of potential therapeutics to treat malignant disease. As highlighted throughout this review, angiogenesis and metastasis share many common cellular and molecular features. We will briefly discuss the pertinent genes involved in the regulation of angiogenesis and metastasis.

Tumor angiogenesis in chronic pancreatitis and pancreatic adenocarcinoma: impact of K-ras mutations

Chronic pancreatitis (CP) is one condition in which epidemiologic studies have demonstrated a definite association with pancreatic adenocarcinoma (PAC). The pathophysiologic and molecular events that either predispose to the development of, or potentiate the growth of, PAC are unknown. Mutation of the codon 12 K-ras gene is one genetic aberration commonly associated with development of PAC. Tumor angiogenesis, or microvascular proliferation of new capillaries, is another pathophysiologic alteration associated with PAC. Although activated ras oncogenes modulate tumor angiogenesis/neovascularization in some tumors, the importance of tumor angiogenesis and the role of K-ras mutation in regulating angiogenesis in CP and PAC are unknown. The aim of this study was to elucidate the relationship between angiogenesis and K-ras mutations in CP and PAC. Tumor angiogenesis and K-ras mutations were evaluated in resected specimens from 25 CP (23 CP plus two CP with PAC) and 16 PAC patients. Tumor angiogenesis was determined using immunohistochemistry of factor VIII-related antigen (FVIIIRAg) and ras mutations were identified by enriched-nested polymerase chain reaction. The mean number of FVIIIRAg-positive blood vessels was significantly (p < 0.005) higher in PAC (23.0 +/- 7.5), CP with a mutant K-ras genome (17.7 +/- 2.8) and CP with a normal K-ras genome (6.5 +/- 3.8), compared to unaffected areas. Codon 12 K-ras mutations were detected in three of 25 CP specimens (12%) and in 15 of 16 PAC specimens (94%). In CP patients with mutant K-ras in their genome, microvessel density was significantly (p < 0.01) elevated, compared to patients with a normal K-ras genome. Statistical analyses (Spearman rank-difference correlation coefficient, Student t test, and chi2 analysis) indicated a significant association between codon 12 K-ras mutations and tumor angiogenesis in both CP and PAC. This study demonstrates a significant association between angiogenesis and K-ras mutation in both PAC and CP. At a minimum, K-ras mutation is associated with the events that increase angiogenesis and it may potentiate or promote tumor angiogenesis.

Hypoxia-induced vascular endothelial growth factor expression precedes neovascularization after cerebral ischemia

We investigated the hypothesis that hypoxia induces angiogenesis and thereby may counteract the detrimental neurological effects associated with stroke. Forty-eight to seventy-two hours after permanent middle cerebral artery occlusion we found a strong increase in the number of newly formed vessels at the border of the infarction. Using the hypoxia marker nitroimidazole EF5, we detected hypoxic cells in the ischemic border of the neocortex. Expression of vascular endothelial growth factor (VEGF), which is the main regulator of angiogenesis and is inducible by hypoxia, was strongly up-regulated in the ischemic border, at times between 6 and 24 hours after occlusion. In addition, both VEGF receptors (VEGFRs) were up-regulated at the border after 48 hours and later in the ischemic core. Finally, the two transcription factors, hypoxia-inducible factor-1 (HIF-1) and HIF-2, known to be involved in the regulation of VEGF and VEGFR gene expression, were increased in the ischemic border after 72 hours, suggesting a regulatory function for these factors. These results strongly suggest that the VEGF/VEGFR system, induced by hypoxia, leads to the growth of new vessels after cerebral ischemia. Exogenous support of this natural protective mechanism might lead to enhanced survival after stroke.

Differential ability of heparan sulfate proteoglycans to assemble the fibroblast growth factor receptor complex in situ

Fibroblast growth factors (FGFs) require heparan sulfate proteoglycans (HSPGs) as cofactors for signaling. The heparan sulfate chains (HS) mediate stable high affinity binding of FGFs to their receptor tyrosine kinases (FR) and may specifically regulate FGF activity. A novel in situ binding assay was developed to examine the ability of HSPGs to promote FGF/FR binding using a soluble FR fusion construct (FR1-AP). This fusion protein probe forms a dimer in solution, simulating the dimerization or oligomerization that is thought to occur at the cell surface physiologically. In frozen sections of human skin, FGF-2 binds to keratinocytes and basement membranes of epidermis and dermal blood vessels. In contrast, in skin preincubated with FGF-2, FR1-AP binds avidly to FGF-2 immobilized on keratinocyte cell surfaces, but fails to bind to basement membranes at the dermo-epidermal junction or dermal microvessels despite the fact that these structures bind large amounts of FGF-2. Apparently, basement membrane and cell surface HSPGs differ in their ability to mediate the assembly of a FGF/FR signaling complex presumably due to structural differences of the heparan sulfate chains.

Antiangiogenic Gene Therapy in Cancer

One of the most recent and exciting approaches in cancer gene therapy is the ability to target the developing blood supply of the tumor. An appealing feature of antiangiogenic gene therapy is that the tumor vasculature is a readily accessible target, particularly when the carrier and its gene are administered systemically. This is in contrast to several other gene therapy approaches in which the tumor vasculature represents a major obstacle to achieving high levels of transfection of the tumor cells. Several gene-based viral or non-viral therapies that target tumor angiogenesis have shown efficacy in pre-clinical models. Genes that encode antiangiogenic polypeptides such as angiostatin and endostatin have significantly inhibited tumor growth, inducing a microscopic dormant state. The products of these genes are thought to act extracellularly to inhibit angiogenesis. An alternative approach that investigators have used successfully in tumor-bearing mice is to target angiogenic growth factors or their receptors that are essential for tumor growth. Levels of angiogenic factors such as vascular endothelial growth factor (VEGF) have been reduced by either antisense methods or the use of genes encoding truncated angiogenic decoy receptors. Despite these promising findings of tumor reduction with antiangiogenic gene therapy, advances in the viral and/or non-viral delivery systems are essential for this therapy to have clinical utility. In this review, we will discuss the mechanisms of angiogenesis/antiangiogenesis, and the current status and future directions of antiangiogenic gene therapy.

Enzymatic rationale and preclinical support for a potent protein kinase C beta inhibitor in cancer therapy

The macrocyclic bisindolylmaleimide, LY333531, selectively inhibits protein kinase C beta 1 and beta 2 isoforms with an approximate IC50 of 5 nanomolar. The efficacy of LY333531 administered alone and in combination with cytotoxic cancer therapies in models of non-small cell lung carcinoma and brain tumors was determined in vivo. In the Lewis lung carcinoma, administration of LY333531 enhanced the activity of paclitaxel and fractionated radiation and, to a lesser degree, carboplatin and gemcitabine. In the human T98G glioblastoma multiforme xenograft, the addition of LY333531 to treatment with carmustine (BCNU) resulted in enhanced tumor response in a nodule grown subcutaneously and increased life-span in animals bearing an intracranial tumor from 37 days in the control animals to 64 days in the BCNU treated animals, and to 104 days in the LY333531 plus BCNU treated animals with 4 out of 5 animals being long-term survivors.

Expression of vascular endothelial growth factor receptors in human prostate cancer

OBJECTIVES

We recently reported the expression and cytokine regulation of vascular endothelial growth factor (VEGF) in human prostate cancer (PCa). VEGF exerts its angiogenic and pro-tumorigenic properties by way of two high affinity receptors, fms-like tyrosine kinase 1 (FLT-1) and fetal liver kinase 1 (FLK-1). We hypothesized that these receptors are expressed and control VEGF functions in the PCa microenvironment. Herein, we evaluate the expression of these receptors in ex vivo PCa tissue, benign prostatic hypertrophy (BPH) tissue, and cultured PCa cell lines.

METHODS

Ex vivo PCa specimens were obtained from patients undergoing radical retropubic prostatectomy. Specimens were selected to contain both PCa and BPH tissue (n = 15). Immunohistochemical analysis using antihuman FLT-1 and FLK-1 was performed and specimens were analyzed to characterize the expression and distribution of both receptors. Immunocytochemical analysis for FLT-1 and FLK-1 was also performed on cultured PCa cell lines (DU-145 and LNCaP).

RESULTS

PCa cells expressed the VEGF receptor FLT-1 in 100% of specimens evaluated. Expression of FLK-1 was variable and related to tumor grade; high-grade tumors displayed little or no FLK-1 expression. Vascular endothelial cells (VECs) within areas of PCa consistently expressed both FLT-1 and FLK-1 receptors. FLT-1 and FLK-1 were both expressed in BPH tissue. FLT-1 was expressed in the glandular epithelial cells in BPH, but in most cases FLK-1 was localized specifically to the basal cell layer of hypertrophic glands. FLT-1, but not FLK-1, was expressed by the DU-145 and LNCaP cell lines.

CONCLUSIONS

Although they are differentially expressed, both FLT-1 and FLK-1 are present in PCa and BPH. Expression of receptors on VECs of tumor vessels supports the well-established role of VEGF in paracrine stimulation of VECs in the tumor microenvironment. The expression of FLT-1 and FLK-1 on tumor cells themselves suggests a potential autocrine function for VEGF (such as regulating tumor cell proliferation). These findings imply that a novel dual role may exist for VEGF, such that it is involved in tumor cell activation (autocrine), in addition to paracrine actions whereby it regulates endothelial cell functions and subsequent neovascular development.

Vascular development in the mouse embryonic pancreas and lung

PURPOSE

The purpose of this study was to analyze the formation of blood vessels in the developing mouse pancreas and lung by studying two ligands, angiopoietin-1 (ang1) and angiopoietin-2 (ang2), which are thought to play a role as angiogenesis-activating factors in development. Understanding the role of vasculogenic peptides in normal embryonic development also may have important implications for common clinical problems regarding neonatal pulmonary vasculature.

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) as well as Southern blotting was used to determine the ontogeny of angiopoietin-1 and angiopoietin-2 gene expression in the embryonic mouse pancreas and lung. Immunohistochemistry was performed for von Willebrand factor, a known marker of endothelial cells, to chronicle the development of the vasculature in these organs.

RESULTS

The authors determined the temporal expression of angiopoietin-1 and angiopoietin-2 as a function of gestational age. RT-PCR data demonstrated expression of ang1 and ang2 in the developing mouse lung between gestational day E9.5 and postnatal day 1, and in the developing pancreas between gestational days E12.5 and E18.5. Southern blot analysis confirmed PCR data for ang2 expression in both the lung and pancreas. The authors also traced the spatial development of the vascular system by von Willebrand factor staining. For both lung and pancreas specimens, no blood vessels were identifiable by immunohistochemistry until embryonic day 12.5. With increased gestational age, the blood vessel networks grew larger.

CONCLUSION

The authors have demonstrated that ang1 and ang2 may be involved in the mechanisms of vascular development in the embryonic mouse lung and pancreas.

Paracrine or virus-mediated induction of decorin expression by endothelial cells contributes to tube formation and prevention of apoptosis in collagen lattices

Resting endothelial cells express the small proteoglycan biglycan, whereas sprouting endothelial cells also synthesize decorin, a related proteoglycan. Here we show that decorin is expressed in endothelial cells in human granulomatous tissue. For in vitro investigations, the human endothelium-derived cell line, EA.hy 926, was cultured for 6 or more days in the presence of 1% fetal calf serum on top of or within floating collagen lattices which were also populated by a small number of rat fibroblasts. Endothelial cells aligned in cord-like structures and developed cavities that were surrounded by human decorin. About 14% and 20% of endothelial cells became apoptotic after 6 and 12 days of co-culture, respectively. In the absence of fibroblasts, however, the extent of apoptosis was about 60% after 12 days, and cord-like structures were not formed nor could decorin production be induced. This was also the case when lattices populated by EA.hy 926 cells were maintained under one of the following conditions: 1) 10% fetal calf serum; 2) fibroblast-conditioned media; 3) exogenous decorin; or 4) treatment with individual growth factors known to be involved in angiogenesis. The mechanism(s) by which fibroblasts induce an angiogenic phenotype in EA.hy 926 cells is (are) not known, but a causal relationship between decorin expression and endothelial cell phenotype was suggested by transducing human decorin cDNA into EA.hy 926 cells using a replication-deficient adenovirus. When the transduced cells were cultured in collagen lattices, there was no requirement of fibroblasts for the formation of capillary-like structures and apoptosis was reduced. Thus, decorin expression seems to be of special importance for the survival of EA.hy 926 cells as well as for cord and tube formation in this angiogenesis model.

Delayed vascular changes after antiangiogenic therapy with antivascular endothelial growth factor antibodies in human glioma xenografts in nude mice

OBJECTIVE

The purpose of this study was to examine the delayed effects of antivascular endothelial growth factor treatment on tumor growth and vascularity in a subcutaneous mouse tumor model of human glioblastoma.

METHODS

Antivascular endothelial growth factor antibody treatment was administered for a period of 6 weeks, to suppress tumor growth. To detect late vascular effects, tumor vascular parameters for treated tumors and control tumors were analyzed 4 weeks thereafter. By that time, tumors had grown to adequate sizes (diameter, 8-10 mm) for comparison with untreated control tumors. Vascular parameters were quantified by using an image-analysis system.

RESULTS

Vascular density was significantly lower in antivascular endothelial growth factor antibody-treated tumors, compared with control tumors of similar size. The vascular architecture of treated tumors was also distinctly different, compared with control tumors, showing larger but sparser vessel structures.

CONCLUSION

These findings suggest that antiangiogenic therapy may have a prolonged effect on the vascular architecture of certain tumors, resulting in enduring changes in the tumor vessels. Because tumor vasculature plays an important role in the sensitivity to various treatment modalities, these changes are likely to influence the responses of these tumors to further therapy.

Positive and negative regulation of angiogenesis: from cell biology to the clinic

Virtually every subspecialty in medicine in one way or another deals with angiogenesis-associated physiological or pathological processes and, without exception, every organ system in the body has many diseases in which angiogenesis is an important component. This in itself makes the study of angiogenesis mandatory, in both basic science and clinical settings. Yet the study of angiogenesis does not require this justification. As a biological process it is extraordinarily rich, touching on virtually every aspect of modern cell biology, making it almost impossible for molecular biologists, biochemists and morphologists to ignore. Considerable therapeutic benefit can now be obtained through positive or negative manipulation of the angiogenic process, and this is due in large part to the rapid transfer to the clinical setting of knowledge acquired through a cell biological approach.

Impact of oncogenes in tumor angiogenesis: mutant K-ras up-regulation of vascular endothelial growth factor/vascular permeability factor is necessary, but not sufficient for tumorigenicity of human colorectal carcinoma cells

Targeted disruption of the single mutant K-ras allele in two human colorectal carcinoma cell lines (DLD-1 and HCT-116) leads to loss of tumorigenic competence in nude mice with retention of ability to grow indefinitely in monolayer culture. Because expression of the mutant K-ras oncogene in these cell lines is associated with marked up-regulation of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF), we sought to determine whether this potent angiogenesis inducer plays a role in K-ras-dependent tumorigenic competence. Transfection of a VEGF121 antisense expression vector into DLD-1 and HCT-116 cells resulted in suppression of VEGF/VPF production by a factor of 3- to 4-fold. The VEGF/VPF-deficient sublines, unlike the parental population or vector controls, were profoundly suppressed in their ability to form tumors in nude mice for as long as 6 months after cell injection. In contrast, in vitro growth of these sublines was unaffected, thus demonstrating the critical importance of VEGF/VPF as an angiogenic factor for HCT-116 and DLD-1 cells. Transfection of a full-length VEGF121 cDNA into two nontumorigenic mutant K-ras knockout sublines resulted in a weak but detectable restoration of tumorigenic ability in vivo in a subset of the transfectants, with no consistent change in growth properties in vitro. The findings indicate that mutant ras-oncogene-dependent VEGF/VPF expression is necessary, but not sufficient, for progressive tumor growth in vivo and highlight the relative contribution of oncogenes, such as mutant K-ras, to the process of tumor angiogenesis.

Role of angiogenesis in the response to anticancer therapies

Most solid tumors develop a vasculature (angiogenesis) as they increase in mass. Elucidation of the process by which blood vessels form in tumors has revealed the existence of both positive and negative regulators produced and secreted by many cell types. Angiogenesis has been identified as a critical process in mass expansion in most solid tumors, and numerous molecules have been described to be antiangiogenic agents. The question of whether antiangiogenic therapy is compatible with cytotoxic anticancer therapy has been addressed in the Lewis lung tumor with TNP-470 and minocycline along with radiation therapy and chemotherapy. Although the antiangiogenic therapy had no effect on the tumor size, administration of TNP-470/minocycline increased drug delivery to the tumor and tumor response to cytotoxic therapy increased implicating a potential role for these agents in the treatment of solid tumors.

Microvascular density in terms of number and length of microvessel segments per unit tissue volume in mammalian angiogenesis

The number and length of all the microvessel segments present per unit of tissue volume are the two determinants of microvascular density. In the present study, a microscopic interactive image-analysis method was introduced, using the length of individual microvessel segments extending between two successive points of bifurcation (Le. MS) and their number (No. MS) per unit of tissue volume in large populations of microvessel segments, which were measured using the nonsurgical rat mesenteric-window angiogenesis assay. In addition, microvessel tortuosity was quantitatively assessed. The method presented here was applied to the angiogenic response over 3 weeks to the directly acting angiogen VEGF165, which was administered i.p. at three dose levels, i.e., 4.8, 48, and 480 pM. Following the VEGF165-treatment, statistically significant changes were found not only in the No. MS but also in the distribution of Le. MS: shortening of vessels being an indicator of vessel branching and increased vessel length being an indicator of angiogenesis through elongation. The shape of the overall distribution of Le. MS was, however, basically the same on any observation occasion regardless of whether significant angiogenesis was present or not. VEGF165 induced a roughly dose-dependent angiogenic response in terms of No. MS and the length of the shortest (0-10% percentile) and/or the longest (90-100% percentile) microvessel segments. Moreover, the onset of the early stimulating effect of VEGF165 on microvessel branching was also dose-dependent. The variables which were introduced here were shown to display a very high degree of sensitivity and resolution and are apparently unrivalled when it comes to the study of density in populations of microvessels.

Interleukin-1-alpha and de novo mammalian angiogenesis

In the literature, the role of interleukin-1 (IL-1) as an angiogen is controversial. The ability of IL-1-alpha to induce de novo angiogenesis in adult rats was studied using the mesenteric window angiogenesis assay (MWAA). Murine recombinant IL-1-alpha was injected intraperitoneally twice daily on Days 0 to 4 at 11.8 pM, 118 pM, and 1.18 nM and groups of animals were sacrificed on Days 7, 14, 21 and 28; controls received the vehicle. Angiogenesis was quantified in terms of microvascular spatial extension and density using technically independent microscopic techniques and image analysis. Compared with the vehicle control, the treatment with IL-1-alpha at doses of 118 pM and 1.18 nM induced statistically significant angiogenesis throughout the study period, whereas IL-1-alpha at 11.8 pM did not induce significant angiogenesis in statistical terms until Days 21 and 28. Compared with the previously reported angiogenic response to VEGF165, bFGF, IL-8, and TNF-alpha using the rat MWAA and the same standardized experimental protocol, the IL-1-alpha treatment displayed a higher degree of efficacy and potency than that of bFGF, IL-8, and TNF-alpha. Moreover, the duration of the significant response to IL-1-alpha exceeded that of bFGF, IL-8, and TNF-alpha. The present data indicate that IL-1-alpha at near-physiologic doses is a very effective angiogenic factor in the system used here. The response may well be multifactorially mediated, as is discussed, and the molecular mechanisms which are involved remain to be clarified.

Angiogenesis: new aspects relating to its initiation and control

Angiogenesis, the formation of new microvessels from parent microvessels, involves remodeling the basement membrane and interstitial extracellular matrix (ECM) using degrading proteases produced by the endothelial cells (ECs) and other adjacent cells, and the synthesis of ECM molecules by these cells. Degraded ECM releases previously bound heparin-binding cytokines (and growth factors) which are able to act as ligands to high-affinity receptors on various target cells, including ECs. The EC carries receptors for a number of cytokines which are produced by neighboring cells or released from the ECM and which can either induce or suppress the angiogenic phenotype of the EC. ECs are able to synthesize and secrete cytokines with auto- and paracrine effects. Angiogenesis, which virtually never occurs physiologically in adult tissues (except in the ovary, the endometrium and the placenta), is essential in wound healing and inflammation. Angiogenesis is, in fact, strictly controlled by a redundancy of pro- and anti-angiogenic paracrine peptide molecules, some of which have recently been described. The expression and synthesis of two distinct anti-angiogenic factors is, for example, controlled by the p53 tumor suppressor gene. In certain hypoxic conditions, chronic inflammatory diseases and syndromes, angiogenesis is of pathogenic and prognostic significance. Angiogenesis is, moreover, essential for the growth and metastatic spread of solid tumors. This indicates the potential for developing new therapeutic strategies not only for tumors but also in diseases such as rheumatoid arthritis, psoriasis, liver cirrhosis and diabetic retinopathy. Moreover, the therapeutic induction of angiogenesis in ischemic tissues using recombinant cytokines is also promising for clinical application. In fact, the first successful human gene therapy for stimulating angiogenesis has recently been reported.

Mechanisms of angiogenesis

After the developing embryo has formed a primary vascular plexus by a process termed vasculogenesis, further blood vessels are generated by both sprouting and non-sprouting angiogenesis, which are progressively pruned and remodelled into a functional adult circulatory system. Recent results, particularly from the study of mice lacking some of the signalling systems involved, have greatly improved our understanding of the molecular basis underlying these events, and may suggest new approaches for treating conditions such as cancer that depend on angiogenesis.

Manipulating angiogenesis. From basic science to the bedside

Considerable progress has been made recently in understanding the molecular mechanisms of angiogenesis, which like most other biological processes is the result of subtle and often complex interactions between molecules that have regulatory (eg, cytokines and their receptors) and effector (eg, extracellular matrix, integrins, and proteases) functions. The title of this review was chosen to reflect a recent trend in which knowledge acquired through a molecular/cell biological approach is being rapidly transferred to the clinical setting. As a result, by manipulating angiogenesis either positively or negatively, considerable therapeutic benefit can now be envisaged in physiological and pathological settings in which neovascularization is a prominent component.

Transforming growth factor-beta: vasculogenesis, angiogenesis, and vessel wall integrity

Genetic studies have recently revealed a role for transforming growth factor-beta-1 (TGF-beta 1) and its receptors (TGF-beta Rs I and II as well as endoglin) in embryonic vascular assembly and in the establishment and maintenance of vessel wall integrity. The purpose of this review is threefold: first, to reassess previous studies on TGF-beta and endothelium in the light of these recent findings; second, to describe some of the well-established as well as controversial issues concerning TGF-beta and its regulatory role in angiogenesis; and third, to explore the notion of "context' with respect to TGF-beta and endothelial cell function. Although the focus of this review will be on the endothelium, other vascular wall cells are also likely to be important in the pathogenesis of the vascular lesions revealed by genetic studies.

The role of vascular endothelial growth factor in blood vessel formation

Angiogenic growth factors and their endothelial receptors function as signalling molecules during vascular growth and development. Vascular endothelial growth factor (VEGF) and its receptors represent a key regulatory system of embryonic vascular development and of both physiological and pathological neovascularization.