Tumor angiogenesis and anti-angiogenic therapy in malignant gliomas revisited

The cellular and molecular mechanisms of tumor angiogenesis and its prospects for anti-angiogenic cancer therapy are major issues in almost all current concepts of both cancer biology and targeted cancer therapy. Currently, (1) sprouting angiogenesis, (2) vascular co-option, (3) vascular intussusception, (4) vasculogenic mimicry, (5) bone marrow-derived vasculogenesis, (6) cancer stem-like cell-derived vasculogenesis and (7) myeloid cell-driven angiogenesis are all considered to contribute to tumor angiogenesis. Many of these processes have been described in developmental angiogenesis; however, the relative contribution and relevance of these in human brain cancer remain unclear. Preclinical tumor models support a role for sprouting angiogenesis, vascular co-option and myeloid cell-derived angiogenesis in glioma vascularization, whereas a role for the other four mechanisms remains controversial and rather enigmatic. The anti-angiogenesis drug Avastin (Bevacizumab), which targets VEGF, has become one of the most popular cancer drugs in the world. Anti-angiogenic therapy may lead to vascular normalization and as such facilitate conventional cytotoxic chemotherapy. However, preclinical and clinical studies suggest that anti-VEGF therapy using bevacizumab may also lead to a pro-migratory phenotype in therapy resistant glioblastomas and thus actively promote tumor invasion and recurrent tumor growth. This review focusses on (1) mechanisms of tumor angiogenesis in human malignant glioma that are of particular relevance for targeted therapy and (2) controversial issues in tumor angiogenesis such as cancer stem-like cell-derived vasculogenesis and bone-marrow-derived vasculogenesis

A dominant-negative FGF1 mutant (the R50E mutant) suppresses tumorigenesis and angiogenesis.

Fibroblast growth factor-1 (FGF1) and FGF2 play a critical role in angiogenesis, a formation of new blood vessels from existing blood vessels. Integrins are critically involved in FGF signaling through crosstalk. We previously reported that FGF1 directly binds to integrin αvβ3 and induces FGF receptor-1 (FGFR1)-FGF1-integrin αvβ3 ternary complex. We previously generated an integrin binding defective FGF1 mutant (Arg-50 to Glu, R50E). R50E is defective in inducing ternary complex formation, cell proliferation, and cell migration, and suppresses FGF signaling induced by WT FGF1 (a dominant-negative effect) in vitro. These findings suggest that FGFR and αvβ3 crosstalk through direct integrin binding to FGF, and that R50E acts as an antagonist to FGFR. We studied if R50E suppresses tumorigenesis and angiogenesis. Here we describe that R50E suppressed tumor growth in vivo while WT FGF1 enhanced it using cancer cells that stably express WT FGF1 or R50E. Since R50E did not affect proliferation of cancer cells in vitro, we hypothesized that R50E suppressed tumorigenesis indirectly through suppressing angiogenesis. We thus studied the effect of R50E on angiogenesis in several angiogenesis models. We found that excess R50E suppressed FGF1-induced migration and tube formation of endothelial cells, FGF1-induced angiogenesis in matrigel plug assays, and the outgrowth of cells in aorta ring assays. Excess R50E suppressed FGF1-induced angiogenesis in chick embryo chorioallantoic membrane (CAM) assays. Interestingly, excess R50E suppressed FGF2-induced angiogenesis in CAM assays as well, suggesting that R50E may uniquely suppress signaling from other members of the FGF family. Taken together, our results suggest that R50E suppresses angiogenesis induced by FGF1 or FGF2, and thereby indirectly suppresses tumorigenesis, in addition to its possible direct effect on tumor cell proliferation in vivo. We propose that R50E has potential as an anti-cancer and anti-angiogenesis therapeutic agent ("FGF1 decoy")

Role of Endomucin in Hypoxia-Induced Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a major cause of blindness among premature, low birth weight infants as a result of pathological angiogenesis. Angiogenesis, the growth of new blood vessels from preexisting vessels, occurs in the veins and capillaries of the body. The process is highly regulated during early development and maturation. However, under abnormal conditions such as a decrease in oxygen levels or hypoxia, angiogenesis can become dysregulated and pathogenic. Currently, the best treatment for ROP is laser therapy, which does not significantly improve vision. Alternatively, glycoproteins are believed to play an important role in angiogenesis. Endomucin (EMCN), a glycoprotein, has been shown to be expressed by the venous and capillary endothelium. EMCN is believed to be associated with angiogenesis and could be a potential target for treatment of ROP. Thus, we hypothesize that EMCN is regulated by hypoxia and plays an important role in pathological angiogenesis. Human retinal endothelial cells (HRECs), representative of endothelial cells involved in retinal angiogenesis, were deprived of oxygen using a hypoxia chamber. We established the optimal oxygen dosage, determined the optimal cell density, and monitored EMCN expression at different time points after exposure to hypoxia. Changes in gene expression in response to hypoxia were compared to control cells. Our preliminary data indicates that EMCN is regulated by hypoxia. Currently, we are investigating whether EMCN has similar effects in regulating revascularization in vivo. Taken together, our study indicates a novel role for EMCN during hypoxia-induced angiogenesis which may serve as a therapeutic target

Emerging role of angiogenesis in adaptive and maladaptive right ventricular remodeling in pulmonary hypertension

Right ventricular (RV) function is the primary prognostic factor for both morbidity and mortality in pulmonary hypertension (PH). RV hypertrophy is initially an adaptive physiological response to increased overload; however, with persistent and/or progressive afterload increase, this response frequently transitions to more pathological maladaptive remodeling. The mechanisms and disease processes underlying this transition are mostly unknown. Angiogenesis has recently emerged as a major modifier of RV adaptation in the setting of pressure overload. A novel paradigm has emerged that suggests that angiogenesis and angiogenic signaling are required for RV adaptation to afterload increases and that impaired and/or insufficient angiogenesis is a major driver of RV decompensation. Here, we summarize our current understanding of the concepts of maladaptive and adaptive RV remodeling, discuss the current literature on angiogenesis in the adapted and failing RV, and identify potential therapeutic approaches targeting angiogenesis in RV failure

Bone growth following demineralized bone matrix implantation requires angiogenesis

Angiogenesis is required for endochondral ossification during development and fracture healing; however the exact mechanisms and temporal relationship between the two processes remains unclear. In this study, we utilize an in vivo model of endochondral ossification in mice by implanting demineralized bone matrix (DBM) proximal to the femur to induce ectopic bone formation. TNP-470, a drug known to be anti-angiogenic, was used to inhibit vascularization during the time course of de novo bone formation in order to define the role of angiogenesis during the chondrogenic phase of endochondral bone formation. Day 2, day 8, and day 16 post-surgery were selected time points to represent pre-chondrogenic, chondrogenic, and bone mineralization stages, respectively. Plain x-ray and micro-CT analysis showed that inhibition of angiogenesis led to decreased mineralized tissue formation. Inhibited angiogenesis was confirmed with qRT-PCR. Most striking, however, is that while stem cells are recruited and committed to the chondrogenic lineage, subsequent chondrogenesis failed to progress based on the failure of Sox5 and Sox6 expression, which directs chondrocyte commitment. This expands the role for angiogenesis to a much earlier stage than currently thought and places the necessity of angiogenesis very early in the endochondral ossification process

The regulation of miRNAs by reconstituted high-density lipoproteins in diabetes-impaired angiogenesis

Diabetic vascular complications are associated with impaired ischaemia-driven angiogenesis. We recently found that reconstituted high-density lipoproteins (rHDL) rescue diabetes-impaired angiogenesis. microRNAs (miRNAs) regulate angiogenesis and are transported within HDL to sites of injury/repair. The role of miRNAs in the rescue of diabetes-impaired angiogenesis by rHDL is unknown. Using a miRNA array, we found that rHDL inhibits hsa-miR-181c-5p expression in vitro and using a hsa-miR-181c-5p mimic and antimiR identify a novel anti-angiogenic role for miR-181c-5p. miRNA expression was tracked over time post-hindlimb ischaemic induction in diabetic mice. Early post-ischaemia when angiogenesis is important, rHDL suppressed hindlimb mmu-miR-181c-5p. mmu-miR-181c-5p was not detected in the plasma or within HDL, suggesting rHDL specifically targets mmu-miR-181c-5p at the ischaemic site. Three known angiogenic miRNAs (mmu-miR-223-3p, mmu-miR-27b-3p, mmu-miR-92a-3p) were elevated in the HDL fraction of diabetic rHDL-infused mice early post-ischaemia. This was accompanied by a decrease in plasma levels. Only mmu-miR-223-3p levels were elevated in the hindlimb 3 days post-ischaemia, indicating that rHDL regulates mmu-miR-223-3p in a time-dependent and site-specific manner. The early regulation of miRNAs, particularly miR-181c-5p, may underpin the rescue of diabetes-impaired angiogenesis by rHDL and has implications for the treatment of diabetes-related vascular complications

Angiogenesis in Chronic Obstructive Pulmonary Disease

Angiogenesis is a crucial component of lung pathophysiology, not only in cancer but also in other disorders, such as chronic obstructive pulmonary disease (COPD). In COPD angiogenesis is definitely able to control and orchestrate the progression of airway remodeling. Herein, we provide several remarkable translational aspects of angiogenesis in COPD, exploring both basic and clinical research in this field. Indeed, we present a number of pro- and anti-angiogenic factors, which can be also used as potential biomarkers to monitor disease progression. 

This pre-print has subsequently been published at http://www.unisa.it/uploads/7100/06.pd

The relationship between angiogenesis and cyclooxygenase-2 expression in prostate cancer

<b>OBJECTIVE</b>: To test the hypothesis that angiogenesis in prostate cancer is associated with tumour invasion and metastasis, and that this is mediated through increased cyclooxygenase-2 (COX-2) expression. <b>PATIENTS AND METHODS</b>: Angiogenesis was assessed in 105 patients with either prostate cancer (79) or benign prostatic hyperplasia (BPH, 26) and these data correlated with levels of COX-2 expression in the same dataset. The mean microvessel density (MVD) was analysed as a marker of angiogenesis, using the endothelial antigen CD34 stained by immunohistochemistry. <b>RESULTS</b>: There was no difference in MVD in progressive tumour stages compared with BPH. There was a negative correlation between MVD and COX-2 expression, but the effect of increased COX-2 expression on MVD was not marked. <b>CONCLUSION</b>: These data suggest that COX-2 drives tumour spread in prostate cancer by means other than the promotion of angiogenesis

Cholinergic neural activity directs retinal layer-specific angiogenesis and blood retinal barrier formation.

Blood vessels in the central nervous system (CNS) develop unique features, but the contribution of CNS neurons to regulating those features is not fully understood. We report that inhibiting spontaneous cholinergic activity or reducing starburst amacrine cell numbers prevents invasion of endothelial cells into the deep layers of the retina and causes blood-retinal-barrier (BRB) dysfunction in mice. Vascular endothelial growth factor (VEGF), which drives angiogenesis, and Norrin, a Wnt ligand that induces BRB properties, are decreased after activity blockade. Exogenous VEGF restores vessel growth but not BRB function, whereas stabilizing beta-catenin in endothelial cells rescues BRB dysfunction but not vessel formation. We further identify that inhibiting cholinergic activity reduces angiogenesis during oxygen-induced retinopathy. Our findings demonstrate that neural activity lies upstream of VEGF and Norrin, coordinating angiogenesis and BRB formation. Neural activity originating from specific neural circuits may be a general mechanism for driving regional angiogenesis and barrier formation across CNS development

Angiogenesis-dependent and independent phases of intimal hyperplasia.

BACKGROUND: Neointimal vascular smooth muscle cell (VSMC) proliferation is a primary cause of occlusive vascular disease, including atherosclerosis, restenosis after percutaneous interventions, and bypass graft stenosis. Angiogenesis is implicated in the progression of early atheromatous lesions in animal models, but its role in neointimal VSMC proliferation is undefined. Because percutaneous coronary interventions result in induction of periadventitial angiogenesis, we analyzed the role of this process in neointima formation. METHODS AND RESULTS: Local injury to the arterial wall in 2 different animal models induced periadventitial angiogenesis and neointima formation. Application of angiogenesis stimulators vascular endothelial growth factor (VEGF-A165) or a proline/arginine-rich peptide (PR39) to the adventitia of the injured artery induced a marked increase in neointimal thickening beyond that seen with injury alone in both in vivo models. Inhibition of either VEGF (with soluble VEGF receptor 1 [sFlt1]) or fibroblast growth factor (FGF) (with a dominant=negative form of FGF receptor 1 [FGF-R1DN]), respectively, signaling reduced adventitial thickening induced by VEGF and PR39 to the level seen with mechanical arterial injury alone. However, neither inhibitor was effective in preventing neointimal thickening after mechanical injury when administered in the absence of angiogenic growth factor. CONCLUSIONS: Our findings indicate that adventitial angiogenesis stimulates intimal thickening but does not initiate it