Periadventitial angiopoietin-1 gene transfer induces angiogenesis in rabbit carotid arteries

Future directions for therapeutic strategies in post-ischaemic vascularization: a position paper from European Society of Cardiology Working Group on Atherosclerosis and Vascular Biology

Modulation of vessel growth holds great promise for treatment of cardiovascular disease. Strategies to promote vascularization can potentially restore function in ischaemic tissues. On the other hand, plaque neovascularization has been shown to associate with vulnerable plaque phenotypes and adverse events. The current lack of clinical success in regulating vascularization illustrates the complexity of the vascularization process, which involves a delicate balance between pro- and anti-angiogenic regulators and effectors. This is compounded by limitations in the models used to study vascularization that do not reflect the eventual clinical target population. Nevertheless, there is a large body of evidence that validate the importance of angiogenesis as a therapeutic concept. The overall aim of this Position Paper of the ESC Working Group of Atherosclerosis and Vascular biology is to provide guidance for the next steps to be taken from pre-clinical studies on vascularization towards clinical application. To this end, the current state of knowledge in terms of therapeutic strategies for targeting vascularization in post-ischaemic disease is reviewed and discussed. A consensus statement is provided on how to optimize vascularization studies for the identification of suitable targets, the use of animal models of disease, and the analysis of novel delivery methods.

Soluble vascular endothelial growth factor receptor-1 improves therapeutic efficacy of suicide gene therapy in an angiogenesis-independent manner

Abstract Malignant gliomas (MGs) are highly vascularized, aggressive brain cancers carrying a dismal prognosis. Because of their high vascularity, anti-angiogenic therapy is a potential treatment option. Indeed, the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab has demonstrated promising results in clinical trials. Similarly, adenovirus-medicated Herpes simplex virus thymidine kinase and ganciclovir (AdHSV-tk/GCV) suicide gene therapy has established itself in clinical trials as a potential novel therapeutic strategy for MGs. In this study, we demonstrate the feasibility of combining adenovirus-mediated soluble VEGF receptor-1 anti-angiogenic gene therapy with AdHSV-tk/GCV suicide gene therapy to treat experimental MGs. Our results reveal that, apart from inhibiting angiogenesis, other anti-tumor mechanisms, such as reduction of infiltration by tumor-associated macrophages/microglia, may contribute to the improved therapeutic benefit of combination therapy.

The angiopoietin:Tie 2 interaction: a potential target for future therapies in human vascular disease

Angiopoietin-1 and -2 are endogenous ligands for the vascular endothelial receptor tyrosine kinase Tie2. Signalling by angiopoietin-1 promotes vascular endothelial cell survival and the sprouting and reorganisation of blood vessels, as well as inhibiting activation of the vascular endothelial barrier to reduce leakage and leucocyte migration into tissues. Angiopoietin-2 generally has an opposing action, and is released naturally at times of vascular growth and inflammation. There is a significant body of emerging evidence that promoting the actions of angiopoietin-1 through Tie2 is of benefit in pathologies of vascular activation, such as sepsis, stroke, diabetic retinopathy and asthma. Similarly, methods to inhibit the actions of angiopoietin-2 are emerging and have been demonstrated to be of preclinical and clinical benefit in reducing tumour angiogenesis. Here the author reviews the evidence for potential benefits of modulation of the interaction of angiopoietins with Tie2, and the potential applications. Additionally, methods for delivery of the complex protein angiopoietin-1 are discussed, as well as potentially deleterious consequences of administering angiopoietin-1.

Measurement of angiogenic phenotype by use of two-dimensional mesenteric angiogenesis assay

Successful therapeutic angiogenesis requires an understanding of how the milieu of growth factors available combine to form a mature vascular bed. This requires a model in which multiple physiological and cell biological parameters can be identified. The adenoviral-mediated mesenteric angiogenesis assay as described here is ideal for that purpose. Adenoviruses expressing growth factors (vascular endothelial growth factor [VEGF] and angiopoietin 1 [Ang-1]) were injected into the mesenteric fat pad of adult male Wistar rats. The clear, thin, and relatively avascular mesenteric panel was used to measure increased vessel perfusion by intravital microscopy. In addition, high-powered microvessel analysis was carried out by immunostaining of features essential for the study of angiogenesis (endothelium, pericyte, smooth muscle cell area, and proliferation), allowing functional data to be obtained in conjunction with high-power microvessel ultrastructural analysis. A combination of individual growth factors resulted in a distinct vascular phenotype from either factor alone, with all treatments increasing the functional vessel area. VEGF produced shorter, narrow, highly branched, and sprouting vessels with normal pericyte coverage. Ang-1 induced broader, longer neovessels with no apparent increase in branching or sprouting. However, Ang-1-induced blood vessels displayed a significantly higher pericyte ensheathment. Combined treatment resulted in higher perfusion, larger and less-branched vessels, with normal pericyte coverage, suggesting them to be more mature. This model can be used to show that Ang-1 and VEGF use different physiological mechanisms to enhance vascularisation of relatively avascular tissue.

Antiangiogenic gene therapy with soluble VEGFR-1, -2, and -3 reduces the growth of solid human ovarian carcinoma in mice

We studied antiangiogenic and antilymphangiogenic effects of sVEGFR-1 (sFlt-1), sVEGFR-2 (sFlk-1/KDR), and sVEGFR-3 (sFlt-4) gene transfers and their combinations in intraperitoneal ovarian cancer xenograft mice (Balb/c-Anu, n = 55). Gene therapy was initiated when the presence of sizable tumors was confirmed in magnetic resonance imaging (MRI). Adenovirus-mediated gene transfer was performed intravenously via tail vein as follows: AdLacZ as a control (group I), AdsFlt-1 (group II), AdsKDR (group III), AdsFlt-4 (group IV) and two combination groups of AdsFlt-1 and AdsFlt-4 (group V) and AdsFlt-1, AdsKDR, and AdsFlt-4 (group VI). Antitumor effectiveness was assessed by sequential MRI, immunohistochemistry, microvessel density, overall tumor growth, and survival time. In combination group VI, intraperitoneal tumors were significantly smaller than in the control group at the end of the follow-up (P < 0.001). Furthermore, in group VI the microvessel density (microvessels/mm(2)) in tumor tissue and the total area of tumors covered by microvessels were significantly smaller than in the controls. One mouse in group V was cured. The combined antiangiogenic gene therapy with soluble VEGFRs reduced tumor growth, tumor vascularity, and ascites formation in ovarian cancer xenografts. The results suggest that the combined antiangiogenic gene therapy is a potential approach for the treatment of ovarian cancer patients.

Angiopoietin: a TIE(d) balance in tumor angiogenesis

Angiopoietins (ANG-1 and ANG-2) and their TIE-2 receptor tyrosine kinase have wide-ranging effects on tumor malignancy that includes angiogenesis, inflammation, and vascular extravasation. These multifaceted pathways present a valuable opportunity in developing novel inhibition strategies for cancer treatment. However, the regulatory role of ANG-1 and ANG-2 in tumor angiogenesis remains controversial. There is a complex interplay between complementary yet conflicting roles of both the ANGs in shaping the outcome of angiogenesis. Embryonic vascular development suggests that ANG-1 is crucial in engaging interaction between endothelial and perivascular cells. However, recruitment of perivascular cells by ANG-1 has recently been implicated in its antiangiogenic effect on tumor growth. It is becoming clear that TIE-2 signaling may function in a paracrine and autocrine manner directly on tumor cells because the receptor has been increasingly found in tumor cells. In addition, alpha(5)beta(1) and alpha(v)beta(5) integrins were recently recognized as functional receptors for ANG-1 and ANG-2. Therefore, both the ligands may have wide-ranging functions in cellular activities that affect overall tumor development. Collectively, these TIE-2-dependent and TIE-2-independent activities may account for the conflicting findings of ANG-1 and ANG-2 in tumor angiogenesis. These uncertainties have impeded development of a clear strategy to target this important angiogenic pathway. A better understanding of the molecular basis of ANG-1 and ANG-2 activity in the pathophysiologic regulation of angiogenesis may set the stage for novel therapy targeting this pathway.

Biology of vascular endothelial growth factors

Angiogenesis is the process by which new blood vessels are formed from existing vessels. The vascular endothelial growth factors (VEGFs) are considered as key molecules in the process of angiogenesis. The VEGF family currently includes VEGF-A, -B, -C, -D, -E, -F and placenta growth factor (PlGF), that bind in a distinct pattern to three structurally related receptor tyrosine kinases, denoted VEGF receptor-1, -2, and -3. VEGF-C and VEGF-D also play a crucial role in the process of lymphangiogenesis. Here, we review the biology of VEGFs and evaluate their role in pathological angiogenesis and lymphangiogenesis.

Adenovirus-Mediated Gene Transfer of Placental Growth Factor to Perivascular Tissue Induces Angiogenesis via Upregulation of the Expression of Endogenous Vascular Endothelial Growth Factor-A

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that binds specifically to VEGF receptor (VEGFR)-1. However, the mechanism of PlGF- and VEGFR-1-mediated angiogenesis has remained unclear and some in vitro studies suggest that VEGF-A/VEGFR-2 signaling may also play a role in PlGF-mediated angiogenesis. To clarify these issues we evaluated angiogenic responses in a well-characterized periadventitial angiogenesis model using adenovirus-mediated PlGF-2 (AdvPlGF-2) gene transfer. We also investigated the roles of VEGFR-1 and VEGFR-2 in PlGF-2-mediated angiogenesis. Using a periadventitial collar technique, AdvPlGF-2 (1 x 10(9) plaque-forming units/ml) was transferred to the adventitia of New Zealand White rabbits alone or together with adenoviruses encoding soluble VEGFR-1 (sVEGFR-1) or soluble VEGFR-2 (sVEGFR-2). Adenoviruses encoding LacZ were used as controls. All animals were killed 7 days after gene transfer. Increased neo-vessel formation, upregulation of endogenous VEGF-A expression, and a significant inflammatory response were seen in AdvPlGF-2-transduced arteries. The neo-vessels were large and well perfused. sVEGFR-1 and sVEGFR-2 suppressed the angiogenic response of PlGF-2 by 80 and 71.7%, respectively. We conclude that adenovirus-mediated PlGF-2 gene transfer to vascular tissue increases endogenous VEGF-A expression and produces significant angiogenesis. Both sVEGFR-1 and sVEGFR-2 can inhibit PlGF-2-mediated angiogenesis. PlGF-2 is a potentially useful candidate for the induction of therapeutic angiogenesis in vivo.

VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) induced intimal hyperplasia in carotid arteries

BACKGROUND

The role of vascular endothelial growth factors (VEGFs) in intimal hyperplasia and atherogenesis remains unknown. Several studies have suggested that some members of the VEGF family reduce intimal hyperplasia, but others have proposed that VEGFs accelerate restenosis and atherosclerosis. This investigation conducted a comparative study with adenoviruses encoding different VEGFs in a rabbit carotid artery collar model of intimal hyperplasia in order to analyze the role of VEGFs in the formation of intimal hyperplasia.

MATERIALS AND METHODS

Intimal hyperplasia was induced in the carotid arteries of cholesterol fed New Zealand White rabbits using a silastic collar. Adenoviral vectors encoding VEGF-A, VEGF-B, VEGF-C, VEGF-C(DeltaNDeltaC), VEGF-D and VEGF-D(DeltaNDeltaC) were delivered to the adventitia using the collar as a gene delivery device. Adeno-LacZ was used as a control.

RESULTS

A significant (P < 0.01) increase in the intima/media ratio was observed in the arteries transduced with VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC). There was a significant increase in the number of proliferating cells in the adventitia, media and intima of the VEGF-A, VEGF-D and the VEGF-D(DeltaNDeltaC) transduced arteries. The majority of medial smooth muscle cells in these arteries had a synthetic phenotype. The presence of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the VEGF-A, VEGF-D and the VEGF-D(DeltaNDeltaC) transduced arteries was significantly increased. A significant positive correlation was observed between adventitial angiogenesis and intimal hyperplasia.

CONCLUSIONS

Adventitial delivery of adenoviruses encoding VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) increased intimal hyperplasia in the rabbit collar model. Adventitial angiogenesis correlated positively with the intimal hyperplasia. These results indicated that efficient adventitial production of VEGF-A, VEGF-D and VEGF-D(DeltaNDeltaC) can cause thickening of the inner layer of the artery in rabbits.