Heterogeneity of the angiogenic response induced in different normal adult tissues by vascular permeability factor/vascular endothelial growth factor

In vivo laser speckle imaging reveals microvascular remodeling and hemodynamic changes during wound healing angiogenesis

Laser speckle contrast imaging (LSCI) is a high-resolution and high contrast optical imaging technique often used to characterize hemodynamic changes in short-term physiological experiments. In this study, we demonstrate the utility of LSCI for characterizing microvascular remodeling and hemodynamic changes during wound healing angiogenesis in vivo. A 2 mm diameter hole was made in the mouse ear and the periphery of the wound imaged in vivo using LSCI over 12 days. We were able to visualize and quantify the vascular and perfusion changes that accompanied wound healing in the microenvironment proximal to the wound, and validated these changes with histology. We found that consistent with the stages of wound healing, microvessel density increased during the initial inflammatory phase (i.e., day 0-3), stayed elevated through the tissue formation phase (i.e., until day 7) and returned to baseline during the tissue remodeling phase (i.e., by day 12). Concomitant "wide area mapping" of blood flow revealed that tissue perfusion in the wound periphery initially decreased, gradually increased from day 3-7, and subsided as healing completed. Interestingly, some regions exhibited a reestablishment of tissue perfusion approximately 6 days earlier than the ~18 days usually reported for the long term remodeling phase. The results from this study demonstrate that LSCI is an ideal platform for elucidating in vivo changes in microvascular hemodynamics and angiogenesis, and has the potential to offer invaluable insights in a range of disease models involving abnormal hemodynamics, such as diabetes and tumors.

Endogenous vascular endothelial growth factor-A (VEGF-A) maintains endothelial cell homeostasis by regulating VEGF receptor-2 transcription

Vascular endothelial growth factor A (VEGF-A) is one of the most important factors controlling angiogenesis. Although the functions of exogenous VEGF-A have been widely studied, the roles of endogenous VEGF-A remain unclear. Here we focused on the mechanistic functions of endogenous VEGF-A in endothelial cells. We found that it is complexed with VEGF receptor 2 (VEGFR-2) and maintains a basal expression level for VEGFR-2 and its downstream signaling activation. Endogenous VEGF-A also controls expression of key endothelial specific genes including VEGFR-2, Tie-2, and vascular endothelial cadherin. Of importance, endogenous VEGF-A differs from exogenous VEGF-A by regulating VEGFR-2 transcription through mediation of FoxC2 binding to the FOX:ETS motif, and the complex formed by endogenous VEGF-A with VEGFR-2 is localized within the EEA1 (early endosome antigen 1) endosomal compartment. Taken together, our results emphasize the importance of endogenous VEGF-A in endothelial cells by regulating key vascular proteins and maintaining the endothelial homeostasis.

Taming of the wild vessel: promoting vessel stabilization for safe therapeutic angiogenesis

VEGF (vascular endothelial growth factor) is the master regulator of blood vessel growth. However, it displayed substantial limitations when delivered as a single gene to restore blood flow in ischaemic conditions. Indeed, uncontrolled VEGF expression can easily induce aberrant vascular structures, and short-term expression leads to unstable vessels. Targeting the second stage of the angiogenic process, i.e. vascular maturation, is an attractive strategy to induce stable and functional vessels for therapeutic angiogenesis. The present review discusses the limitations of VEGF-based gene therapy, briefly summarizes the current knowledge of the molecular and cellular regulation of vascular maturation, and describes recent pre-clinical evidence on how the maturation stage could be targeted to achieve therapeutic angiogenesis.

Transgenic insulin-like growth factor-1 stimulates activation of COX-2 signaling in mammary glands

Studies show that elevated insulin-like growth factor-1 (IGF-1) levels are associated with an increased risk of breast cancer; however, mechanisms through which IGF-1 promotes mammary tumorigenesis in vivo have not been fully elucidated. To assess the possible involvement of COX-2 signaling in the pro-tumorigenic effects of IGF-1 in mammary glands, we used the unique BK5.IGF-1 mouse model in which transgenic (Tg) mice have significantly increased incidence of spontaneous and DMBA-induced mammary cancer compared to wild type (WT) littermates. Studies revealed that COX-2 expression was significantly increased in Tg mammary glands and tumors, compared to age-matched WTs. Consistent with this, PGE(2) levels were also increased in Tg mammary glands. Analysis of expression of the EP receptors that mediate the effects of PGE(2) showed that among the four G-protein-coupled receptors, EP3 expression was elevated in Tg glands. Up-regulation of the COX-2/PGE(2) /EP3 pathway was accompanied by increased expression of VEGF and a striking enhancement of angiogenesis in IGF-1 Tg mammary glands. Treatment with celecoxib, a selective COX-2 inhibitor, caused a 45% reduction in mammary PGE(2) levels, attenuated the influx of mast cells and reduced vascularization in Tg glands. These findings indicate that the COX-2/PGE(2) /EP3 signaling pathway is involved in IGF-1-stimulated mammary tumorigenesis and that COX-2-selective inhibitors may be useful in the prevention or treatment of breast cancer associated with elevated IGF-1 levels in humans. © 2011 Wiley Periodicals, Inc.

Principles and mechanisms of vessel normalization for cancer and other angiogenic diseases

Despite having an abundant number of vessels, tumours are usually hypoxic and nutrient-deprived because their vessels malfunction. Such abnormal milieu can fuel disease progression and resistance to treatment. Traditional anti-angiogenesis strategies attempt to reduce the tumour vascular supply, but their success is restricted by insufficient efficacy or development of resistance. Preclinical and initial clinical evidence reveal that normalization of the vascular abnormalities is emerging as a complementary therapeutic paradigm for cancer and other vascular disorders, which affect more than half a billion people worldwide. Here, we discuss the mechanisms, benefits, limitations and possible clinical translation of vessel normalization for cancer and other angiogenic disorders.

Glomeruloid microvascular proliferation is associated with lack of response to chemotherapy in breast cancer

Background:

Glomeruloid microvascular proliferation (GMP), a novel histology-based angiogenesis marker, has been associated with decreased survival in several human cancers.

Methods:

In this study, we evaluated the ability of GMP to predict clinical response to neoadjuvant chemotherapy in a series of locally advanced breast cancers (n=112).

Results:

Presence of GMP (21% of the cases) was significantly associated with high-grade tumours and TP53 mutations in addition to the basal-like and HER2 subtypes of breast cancer as defined by gene expression data. GMP was correlated to a gene expression signature for tumour hypoxia response. The GMP pattern was also significantly associated with lack of treatment response and progressive disease (P=0.004).

Interpretation:

The findings suggest that GMP might be able to predict the lack of response to neoadjuvant chemotherapy in locally advanced breast cancer. Whether GMP may be an independent predictor compared with other factors including TP53 mutation status and tumour grade needs confirmation in larger studies.

Tumor microenvironment and progression

Tumor blood vessels are heterogeneous, of at least six distinct types, are induced primarily by vascular endothelial growth factor-A (VEGF-A), and provide a potentially useful therapeutic target. Breast cancer is characterized by changes in the microenvironment that result in altered tensional homeostasis. Also, breast cancers arise as the result of epigenetic as well as genetic changes. Tumor blood vessel pericytes result, in part, from bone marrow precursor cells, and VEGF is a negative regulator of glioblastoma tumor cell invasion.

Selective stimulation of VEGFR2 accelerates progressive renal disease

Vascular endothelial growth factor A (VEGF-A) can play both beneficial and deleterious roles in renal diseases, where its specific function might be determined by nitric oxide bioavailability. The complexity of VEGF-A in renal disease could in part be accounted for by the distinct roles of its two receptors; VEGFR1 is involved in the inflammatory responses, whereas VEGFR2 predominantly mediates angiogenesis. Because nondiabetic chronic renal disease is associated with capillary loss, we hypothesized that selective stimulation of VEGFR2 could be beneficial in this setting. However, VEGFR2 activation may be deleterious in the presence of nitric oxide deficiency. We systematically overexpressed a mutant form of VEGF-A binding only VEGFR2 (Flk-sel) using an adeno-associated virus-1 vector in wild-type and eNOS knockout mice and then induced renal injury by uninephrectomy. Flk-sel treatment increased angiogenesis and lowered blood pressure in both mouse types. Flk-sel overexpression caused mesangial injury with increased proliferation associated with elevated expression of PDGF, PDGF-β receptor, and VEGFR2; this effect was greater in eNOS knockout than in wild-type mice. Flk-sel also induced tubulointerstitial injury, with some tubular epithelial cells expressing α-smooth muscle actin, indicating a phenotypic evolution toward myofibroblasts. In conclusion, prestimulation of VEGFR2 can potentiate subsequent renal injury in mice, an effect enhanced in the setting of nitric oxide deficiency.

Proteolytic cleavage of versican and involvement of ADAMTS-1 in VEGF-A/VPF-induced pathological angiogenesis

Malignant tumors and chronic inflammatory diseases induce angiogenesis by overexpressing vascular endothelial growth factor A (VEGF-A/VPF). VEGF-A-induced pathological angiogenesis can be mimicked in immunoincompetent mice with an adenoviral vector expressing VEGF-A(164) (Ad-VEGF-A(164)). The initial step is generation of greatly enlarged "mother" vessels (MV) from preexisting normal venules by a process involving degradation of their rigid basement membranes. Immunohistochemical and Western blot analyses revealed that versican, an extracellular matrix component in the basement membranes of venules, is degraded early in the course of MV formation, resulting in the appearance of a versican N-terminal DPEAAE fragment associated with MV endothelial cells. The protease ADAMTS-1, known to cleave versican near its N terminus to generate DPEAAE, is also upregulated by VEGF-A in parallel with MV formation and localizes to the endothelium of the developing MV. The authors also show that MMP-15 (MT-2 MMP), a protease that activates ADAMTS-1, is upregulated by VEGF-A in endothelial cells in vitro and in vivo. These data suggest VEGF-A initiates MV formation, in part, by inducing the expression of endothelial cell proteases such as ADAMTS-1 and MMP-15 that act in concert to degrade venular basement membrane versican. Thus, versican is actively processed during the early course of VEGF-A-induced pathological angiogenesis.

Adeno associated viral vector-delivered and hypoxia response element-regulated CD151 expression in ischemic rat heart

AIM

The aim of this study was to improve the delivery efficacy and target specificity of the pro-angiogenic gene CD151 to the ischemic heart.

METHODS

To achieve the inducible expression of adeno-associated viral (AAV)-delivered CD151 gene in only the ischemic myocardium, we generated an AAV construct in which CD151 expression can be controlled by the hypoxia response element (HRE) sequence from the human Enolase gene. The function of this vector was examined in rat H9C2 cardiac myoblasts and in ischemic rat myocardium. The expression of CD151 in the areas of ischemic myocardium was confirmed at the mRNA level by real-time PCR and on the protein level by Western blot, whereas the CD151 expression in the microvessels within the areas of ischemic myocardium was detected by immunohistochemistry.

RESULTS

HRE significantly enhances the expression of CD151 under hypoxic conditions or in the ischemic myocardium, and forced CD151 expression increases the number of microvessels in the ischemic myocardium.

CONCLUSION

The AAV-mediated, HRE regulated delivery of the CD151 gene shows higher expression in the ischemic myocardium and more efficiently targets CD151 to the hypoxic regions after myocardial infarction.

Endothelial-specific intron-derived miR-126 is down-regulated in human breast cancer and targets both VEGFA and PIK3R2

Endothelial cells are the key components of vascular intima and play pivotal roles in vasculogenesis, angiogenesis, and tumor growth. Using Northern blot and real-time PCR, we confirmed that miR-126 and its host gene EGF-like domain 7 (EGFL7) were widely expressed in rat tissues but strictly expressed in endothelial cells. In mammals, miR-126 gene is embedded in intron7 of EGFL7. To explore the biogenesis of miR-126, plasmid EGFL7(126)-pEGFPc1 containing segment of exon7-intron7-exon8 of EGFL7 was constructed and expressed in 293T. Expression of spliced exon7-8 and excised mature miR-126 was detected by PCR and Northern blot. Knocking-down of endothelial endogenous miR-126 did not affect EGFL7 expression at mRNA or protein level. To investigate the possible roles of miR-126, PicTar, miRBase, miRanda, Bibiserv, and Targetscan were used to screen the targets. VEGFA and PIK3R2 were confirmed as the targets of miR-126 by luciferase reporter assay and Western blot. Interestingly, Northern blot and western blot showed that miR-126 was down-regulated in breast tumors where the VEGF/PI3K/AKT signaling pathway was activated. Introduction of miR-126 mimics into MCF-7 could effectively decrease VEGF/PI3K/AKT signaling activity. In summary, miR-126 was strictly expressed in endothelial cells and excised from EGFL7 pre-mRNA without affecting splicing and expression of its host gene. In addition, miR-126 could target both VEGFA and PIK3R2, and its expression was decreased in human breast cancer, implying that miR-126 may play a role in tumor genesis and growth by regulating the VEGF/PI3K/AKT signaling pathway.

Effect of 8-O-acetyl shanzhiside methylester increases angiogenesis and improves functional recovery after stroke

We investigated whether 8-O-acetyl shanzhiside methylester (ND01) regulates angiogenesis and thereby improves functional outcome after stroke. Adult male rats were subjected to 1 hr of middle cerebral artery occlusion (MCAO) and reperfusion, and treated with or without different doses (5 and 10 mg/kg) of ND01, starting 24 hr after ischaemia and reperfusion (I/R) and by intravenous injection daily for 14 days. Neurological functional tests were performed and cerebral Evans blue extravasation was measured. Angiogenesis and angiogenic factor expression were measured by immunohistochemistry and Western blot, respectively. The results indicated that ND01 significantly promoted angiogenesis in the ischaemic brain and improved functional outcome after stroke. ND01 also significantly increased vascularization compared with vehicle treatment. ND01 increased the expression of VEGF, Ang1, phosphorylation of Tie2 and Akt VEGF. The Ang1/Tie2 axis and Akt pathways appear to mediate ND01-induced angiogenesis.

Morphological and molecular analysis of angiogenesis after intramyocardial transplantation of autologous bone marrow mononuclear cells

We studied the peculiarities of angiogenesis in the postinfarction period after transmyocardial laser revascularization and intramyocardial implantation of mononuclear bone marrow cells into the pericicatrical zone of the left ventricular myocardium in dogs. Morphological manifestation of angiogenesis in the myocardium after application of laser and cell technologies are angiomatosis, formation of large thin-wall vessels and sinusoids. The angiogenic effect of implanted mononuclear bone marrow cells is determined by high content (43-47%) of CD31+ cells in both adherent and nonadherent fractions. More pronounced angiogenic potential of nonadherent cells is determined by intensive expression of cytokine VEGF-B and D mRNA essential for arterial vessels growth. Immunohistochemical studies showed that about 90% cells of the nonadherent fraction are endothelial precursors expressing endothelial cell markers isolectin B4 and VEGF-R2. It was found that the use of adherent mononuclear bone marrow cells during the postinfarction period induces ossification of the epicardium and subepicardial myocardium layer, formation of cartilage plates, and focal calcification. Implantation of nonadherent mononuclear bone marrow cells into transmyocardial laser channels did not induce ectopic ossification of the myocardium.

Vascularization of the dermal support enhances wound re-epithelialization by in situ delivery of epidermal keratinocytes

Despite significant advances in management of severe wounds such as burns and chronic ulcers, autologous split-thickness skin grafts are still the gold standard of care. The main problems with this approach include pain and discomfort associated with harvesting autologous tissue, limited availability of donor sites, and the need for multiple surgeries. Although tissue engineering has great potential to provide alternative approaches for tissue regeneration, several problems have hampered progress in translating technological advances to clinical reality. Specifically, engineering of skin substitutes requires long culture times and delayed vascularization after implantation compromises graft survival. To address these issues we developed a novel two-prong strategy for tissue regeneration in vivo: (1) vascularization of acellular dermal scaffolds by infiltration of angiogenic factors; and (2) generation of stratified epidermis by in situ delivery of epidermal keratinocytes onto the prevascularized dermal support. Using athymic mouse as a model system, we found that incorporation of angiogenic factors within acellular human dermis enhanced the density and diameter of infiltrating host blood vessels. Increased vascularization correlated with enhanced proliferation and stratification of the neoepidermis originating from the fibrin-keratinocyte cell suspension. This strategy promoted tissue regeneration in vivo with no need for engineering skin substitutes; therefore, it may be useful for treatment of major wounds when skin donor sites are scarce and rapid wound coverage is required.

Requirement of the nuclear localization of transcription enhancer factor 3 for proliferation, migration, tube formation, and angiogenesis induced by vascular endothelial growth factor

Transcription enhancer factor 3 (TEF3) is known to regulate the expression of muscle-specific genes and to play important roles in muscle development and diseases. However, little is known about its role in vascular endothelial growth factor (VEGF)-induced angiogenesis. Most recently, we discovered a novel function of TEF3, in which TEF3 is required for the up-regulation of a proangiogenic factor, Down syndrome candidate region 1 isoform 1L (DSCR1-1L), induced by VEGF-A(165) in endothelial cells. Overexpression of TEF3 isoform 1 (TEF3-1) is sufficient to induce DSCR1-1L expression. Here, we report that knocking down the expression of TEF3 almost completely inhibits VEGF-A(165)-induced proliferation, migration, tube formation, formation of F-actin stress fiber, and in vivo Matrigel angiogenesis. This inhibition cannot be rescued by DSCR1-1L overexpression. Further, overexpression of TEF3-1, but not its nuclear localization signal-deletion mutant (TEF3-ΔNLS), induces human umbilical vein endothelial cell proliferation, migration, tube formation, and formation of F-actin stress fiber, even in the absence of VEGF-A(165) stimulation, which is partially inhibited by DSCR1-1L silencing. Our data demonstrate that TEF3, mainly its nuclear localization, is required for VEGF-A(165)-induced endothelial proliferation, migration, tube formation, and in vivo Matrigel angiogenesis.

Regulation of vascular endothelial growth factor receptor 2 trafficking and angiogenesis by Golgi localized t-SNARE syntaxin 6

Vascular endothelial growth factor receptor 2 (VEGFR2) plays a key role in physiologic and pathologic angiogenesis. Plasma membrane (PM) levels of VEGFR2 are regulated by endocytosis and secretory transport through the Golgi apparatus. To date, the mechanism whereby the VEGFR2 traffics through the Golgi apparatus remains incompletely characterized. We show in human endothelial cells that binding of VEGF to the cell surface localized VEGFR2 stimulates exit of intracellular VEGFR2 from the Golgi apparatus. Brefeldin A treatment reduced the level of surface VEGFR2, confirming that VEGFR2 traffics through the Golgi apparatus en route to the PM. Mechanistically, we show that inhibition of syntaxin 6, a Golgi-localized target membrane-soluble N-ethylmaleimide attachment protein receptor (t-SNARE) protein, interferes with VEGFR2 trafficking to the PM and facilitates lysosomal degradation of the VEGFR2. In cell culture, inhibition of syntaxin 6 also reduced VEGF-induced cell proliferation, cell migration, and vascular tube formation. Furthermore, in a mouse ear model of angiogenesis, an inhibitory form of syntaxin 6 reduced VEGF-induced neovascularization and permeability. Our data demonstrate the importance of syntaxin 6 in the maintenance of cellular VEGFR2 levels, and suggest that the inhibitory form of syntaxin 6 has good potential as an antiangiogenic agent.

Gene expression profiling identifies inflammation and angiogenesis as distinguishing features of canine hemangiosarcoma

Background

The etiology of hemangiosarcoma remains incompletely understood. Its common occurrence in dogs suggests predisposing factors favor its development in this species. These factors could represent a constellation of heritable characteristics that promote transformation events and/or facilitate the establishment of a microenvironment that is conducive for survival of malignant blood vessel-forming cells. The hypothesis for this study was that characteristic molecular features distinguish hemangiosarcoma from non-malignant endothelial cells, and that such features are informative for the etiology of this disease.

Methods

We first investigated mutations of VHL and Ras family genes that might drive hemangiosarcoma by sequencing tumor DNA and mRNA (cDNA). Protein expression was examined using immunostaining. Next, we evaluated genome-wide gene expression profiling using the Affymetrix Canine 2.0 platform as a global approach to test the hypothesis. Data were evaluated using routine bioinformatics and validation was done using quantitative real time RT-PCR.

Results

Each of 10 tumor and four non-tumor samples analyzed had wild type sequences for these genes. At the genome wide level, hemangiosarcoma cells clustered separately from non-malignant endothelial cells based on a robust signature that included genes involved in inflammation, angiogenesis, adhesion, invasion, metabolism, cell cycle, signaling, and patterning. This signature did not simply reflect a cancer-associated angiogenic phenotype, as it also distinguished hemangiosarcoma from non-endothelial, moderately to highly angiogenic bone marrow-derived tumors (lymphoma, leukemia, osteosarcoma).

Conclusions

The data show that inflammation and angiogenesis are important processes in the pathogenesis of vascular tumors, but a definitive ontogeny of the cells that give rise to these tumors remains to be established. The data do not yet distinguish whether functional or ontogenetic plasticity creates this phenotype, although they suggest that cells which give rise to hemangiosarcoma modulate their microenvironment to promote tumor growth and survival. We propose that the frequent occurrence of canine hemangiosarcoma in defined dog breeds, as well as its similarity to homologous tumors in humans, offers unique models to solve the dilemma of stem cell plasticity and whether angiogenic endothelial cells and hematopoietic cells originate from a single cell or from distinct progenitor cells.

Dextran sulfate sodium leads to chronic colitis and pathological angiogenesis in Endoglin heterozygous mice

BACKGROUND

Pathological angiogenesis is an intrinsic component of chronic intestinal inflammation, which results in remodeling and expansion of the gut microvascular bed. Endoglin is essential for endothelial cell function and physiological angiogenesis. In this study we investigated its potential role in the regulation of inflammation by testing the response of Endoglin heterozygous (Eng(+/-)) mice to experimental colitis.

METHODS

C57BL/6 Eng(+/-) and littermate control mice drank water supplemented with 3% dextran sulfate sodium (DSS) for 5 days and were monitored for up to 26 days for clinical signs of colitis. Inflammation, crypt damage, and angiogenic index were scored on histological sections of distal colon. Levels of the vascular endothelial growth factor (VEGF) and angiopoietins were measured by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and/or Western blots. Vascular permeability was assessed using Evans Blue.

RESULTS

Eng(+/-) and control mice developed acute colitis, which peaked at day 9. While control mice recovered by days 19-26, Eng(+/-) mice progressed to chronic colitis and showed numerous vascular protrusions penetrating into the serosa of the inflamed distal colon. Prior to DSS induction, VEGF levels and vascular permeability were higher in the distal colon of Eng(+/-) mice, while angiopoietin 1 and 2 levels were unchanged. In the chronic phase of colitis, VEGF levels were increased in both groups of mice and remained significantly higher in the Eng(+/-) mice.

CONCLUSIONS

Higher VEGF levels and increased vascular permeability in the distal colon may predispose Eng(+/-) mice to progress to chronic and persistent bowel inflammation, associated with pathological angiogenesis.

VEGF stimulates PKD-mediated CREB-dependent orphan nuclear receptor Nurr1 expression: role in VEGF-induced angiogenesis

New vessel formation is critical for solid tumor growth and it is primarily stimulated by the most potent angiogenic factor vascular endothelial growth factor (VEGF or VEGF-A165). VEGF promotes endothelial cell proliferation by initiating signaling cascades to increase gene transcription. Recent works showed that VEGF potently and rapidly induces expression of orphan nuclear receptor Nurr1 in endothelial cells. However, the signaling pathway for VEGF-induced Nurr1 expression and its role in VEGF-induced endothelial cell proliferation and angiogenic response have not been examined. In our study, we first show that VEGF significantly induces expression of Nurr1 mRNA, protein and its promoter activity in cultured endothelial cells. Furthermore, the promoter analysis shows that deletion of the putative cAMP-responsive element binding protein (CREB) site in the proximal region of the promoter markedly reduces VEGF-induced promoter activity whereas deletion of the upstream NF-κB site has moderate effect. Transfection of a dominant negative CREB mutant (K-CREB) or mutation of this putative CREB site in the Nurr1 promoter attenuates VEGF-induced Nurr1 expression. VEGF also stimulates the binding of nuclear CREB protein to its site in the Nurr1 promoter in vitro and in vivo. Moreover, using pharmacological inhibitors and molecular approaches, we show that VEGF-induced CREB activation is largely mediated by protein kinase C-dependent protein kinase D activation. Finally, our data indicate that knockdown of endogenous Nurr1 expression attenuates VEGF-induced endothelial cell proliferation, migration and in vivo matrigel angiogenesis, suggesting its potential importance in mediating VEGF-induced tumor angiogenesis.

The role of angiogenesis in the transformation of plexiform neurofibroma into malignant peripheral nerve sheath tumors in children with neurofibromatosis type 1

PURPOSE

The role of angiogenesis in the transformation of peripheral neurofibroma (PNF) to malignant peripheral nerve sheath tumor (MPNST) in neurofibromatosis type 1 (NF1) remains elusive and forms the objective of this study.

EXPERIMENTAL DESIGN

Archival tissue from 5 children with NF1 and PNF, who developed MPNST between the ages of 8 and 15 years were analyzed for differences in microvasculature. The role of proangiogenic growth factors such as Vascular Endothelial Growth Factor (VEGF), and its receptors Flk-1 and Flt-1, and vessel maturity, defined as von Willebrand factor (vWf), α-smooth muscle actin+ (SMA+), were evaluated by immuno-histochemistry.

RESULTS

A qualitative evaluation of the vasculature showed predominantly α-SMA+/vWf+ more stable vessels in PNF, and an irregular meshwork of α-SMA-/vWf+ endothelial cells structures in MPNST. In NF and PNF tumor cells were VEGF-, in contrast to VEGF+ tumor cells in MPNST. If present, the VEGF stain was confined mainly to the perivascular spaces in PNF, unlike the mainly stromal VEGF stain in MPNST. VEGF receptors also manifested a tumor stage-specific pattern. Flk-1 and Flt-1 were restricted to the mature, well-formed vasculature in PNF, but exhibited a diffuse pattern in MPNST.

CONCLUSION

Our study provides a rare opportunity to document consistent and histologically detectable differences in the vascular organization of PNF and MPNST. It permits a pair-wise evaluation of the malignant conversion of benign PNF into its malignant counterpart, in the same patients. The phenotypic variations and characteristics of the vessels in these tumors are consistent with the idea that a strong proangiogenic drive contributes to the progressive growth in MPNST.

Blood vessel endothelial VEGFR-2 delays lymphangiogenesis: an endogenous trapping mechanism links lymph- and angiogenesis

Angio- and lymphangiogenesis are inherently related processes. However, how blood and lymphatic vessels regulate each other is unknown. This work introduces a novel mechanism explaining the temporal and spatial relation of blood and lymphatic vessels. Vascular endothelial growth factor-A (VEGF-A) surprisingly reduced VEGF-C in the supernatant of blood vessel endothelial cells, suggesting growth factor (GF) clearance by the growing endothelium. The orientation of lymphatic sprouting toward angiogenic vessels and away from exogenous GFs was VEGF-C dependent. In vivo molecular imaging revealed higher VEGF receptor (R)-2 in angiogenic tips compared with normal vessels. Consistently, lymphatic growth was impeded in the angiogenic front. VEGF-C/R-2 complex in the cytoplasm of VEGF-A-treated endothelium indicated that receptor-mediated internalization causes GF clearance from the extracellular matrix. GF clearance by receptor-mediated internalization is a new paradigm explaining various characteristics of lymphatics.

Current status of vascular endothelial growth factor inhibition in age-related macular degeneration

Angiogenesis, the process by which new vessels are created from pre-existing vasculature, has become the subject of intense research in recent years. Increased rates of angiogenesis are associated with several disease states, including cancer, age-related macular degeneration (AMD), psoriasis, rheumatoid arthritis, and diabetic retinopathy. Vascular endothelial growth factor (VEGF) is an important modulator of angiogenesis, and has been implicated in the pathology of a number of conditions, including AMD, diabetic retinopathy, and cancer. AMD is a progressive disease of the macula and the third major cause of blindness worldwide. If not treated appropriately, AMD can progress to involve both eyes. Until recently, the treatment options for AMD have been limited, with photodynamic therapy (PDT) the mainstay of treatment. Although PDT is effective at slowing disease progression, it rarely results in improved vision. Several therapies have been or are now being developed for neovascular AMD, with the goal of inhibiting VEGF. These VEGF inhibitors include the RNA aptamer pegaptanib, partial and full-length antibodies ranibizumab and bevacizumab, the VEGF receptor decoy aflibercept, small interfering RNA-based therapies bevasiranib and AGN 211745, sirolimus, and tyrosine kinase inhibitors, including vatalanib, pazopanib, TG 100801, TG 101095, AG 013958, and AL 39324. At present, established therapies have met with great success in reducing the vision loss associated with neovascular AMD, whereas those still under investigation offer the potential for further advances. In AMD patients, these therapies slow the rate of vision loss and in some cases increase visual acuity. Although VEGF-inhibitor therapies are a milestone in the treatment of these disease states, several concerns need to be addressed before their impact can be fully realized.

Heterogeneity of the tumor vasculature

The blood vessels supplying tumors are strikingly heterogeneous and differ from their normal counterparts with respect to organization, structure, and function. Six distinctly different tumor vessel types have been identified, and much has been learned about the steps and mechanisms by which they form. Four of the six vessel types (mother vessels, capillaries, glomeruloid microvascular proliferations, and vascular malformations) develop from preexisting normal venules and capillaries by angiogenesis. The two remaining vessel types (feeder arteries and draining veins) develop from arterio-venogenesis, a parallel, poorly understood process that involves the remodeling of preexisting arteries and veins. All six of these tumor vessel types can be induced to form sequentially in normal mouse tissues by an adenoviral vector expressing vascular endothelial growth factor (VEGF)-A164. Current antiangiogenic cancer therapies directed at VEGF-A or its receptors have been of only limited benefit to cancer patients, perhaps because they target only the endothelial cells of the tumor blood vessel subset that requires exogenous VEGF-A for maintenance. A goal of future work is to identify therapeutic targets on tumor blood vessel endothelial cells that have lost this requirement.

Metronomic administration of the drug GMX1777, a cellular NAD synthesis inhibitor, results in neuroblastoma regression and vessel maturation without inducing drug resistance

High-risk neuroblastoma is a rapidly growing tumor with a survival rate below 50%. A new treatment strategy is to administer chemotherapeutic drugs metronomically, i.e., at lower doses and frequent intervals. The aim of the study was to investigate the effects of GMX1777, a chemotherapeutic drug affecting cellular energy metabolism, in a mouse model for high-risk neuroblastoma. Female SCID mice were injected s.c. with MYCN-amplified human neuroblastoma cells and randomized to either treatment with GMX1777 or vehicle. In some animals, treatment was discontinued allowing tumor relapse. Treatment response was evaluated using the pediatric preclinical testing program (PPTP). Immunohistochemistry and qRT-PCR was performed on tumor cryosections to investigate the microscopic and molecular changes in tumors in response to GMX1777. Despite an increase in vessel density, tumor regression and a high group response score according to PPTP criteria was induced by GMX1777 without inducing drug resistance. Treatment resulted in inhibition of tumor cell proliferation, vessel maturation, reduced hypoxia, increased infiltration of MHC class II negative macrophages and expansion of the nonvascular stromal compartment. Decreased stromal VEGF-A and PDGF-B mRNA in response to treatment together with the structural data suggest a "deactivation" or "silencing" of the tumor stroma as a paracrine entity. In conclusion, GMX1777 was highly efficient against high-risk neuroblastoma xenografts through modulation of both the tumor cell and stromal compartment.

Cytocompatibility of regenerated silk fibroin film: a medical biomaterial applicable to wound healing

OBJECTIVE

To explore the feasibility of using regenerated silk fibroin membrane to construct artificial skin substitutes for wound healing, it is necessary to evaluate its cytocompatibility.

METHODS

The effects of regenerated silk fibroin film on cytotoxicity, adhesion, cell cycle, and apoptosis of L929 cells, growth and vascular endothelial growth factor (VEGF) expression of ECV304 cells, and VEGF, angiopoietin-1 (Ang-1), platelet-derived growth factor (PDGF) and fibroblast growth factor 2 (FGF2) expression of WI-38 cells were assessed by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, viable cell counting, flow cytometry (FCM), and enzyme-linked immunosorbant assay (ELISA).

RESULTS

We showed that the regenerated silk fibroin film was not cytotoxic to L929 cells and had no adverse influence on their adhesion, cell cycle or apoptosis; it had no adverse influence on the growth and VEGF secretion of ECV304 cells and no effect on the secretion of VEGF, Ang-1, PDGF and FGF2 by WI-38 cells.

CONCLUSION

The regenerated silk fibroin film should be an excellent biomaterial with good cytocompatibility, providing a framework for reparation after trauma in clinical applications.

HIF-1α and VEGF are associated with disease progression in esophageal carcinoma

BACKGROUND

Hypoxia inducible factor-1alpha (HIF-1α) is a transcription factor that regulates the transcription of genes associated with cell proliferation and angiogenesis. The purpose of this study is to clarify the correlation of HIF-1α protein expression with vascular endothelial growth factor (VEGF) and inducible (iNOS), endothelial (eNOS), and neuronal nitric oxide synthase (nNOS) expression in esophageal tumors. Additionally, vascular density in tumor tissue was assessed.

MATERIALS AND METHODS

Eighty-eight esophageal carcinomas were analyzed by immunohistochemistry in paraffin embedded sections.

RESULTS

HIF-1α immunoreactivity was seen in 71.2 % of the tumors. Squamous cell carcinomas expressed more often HIF-1α than adenocarcinomas (P = 0.009). HIF-1α immunoreactivity was associated with iNOS (P = 0.049), and iNOS positivity was also more commonly seen in squamous cell carcinomas than adenocarcinomas (P = 0.016). VEGF immunoreaction tended to associate with HIF-1α (P = 0.073) and iNOS (P = 0.08). ENOS did not associate with HIF-1α, but tended to associate with VEGF (P = 0.072). T1-T2 tumors were more often VEGF negative than T3-T4 tumors (P = 0.063). In the subgroup of 78 operatively treated ECs patients with HIF-1α positivity (> +) had more often distant metastases (P = 0.036). There was no association between iNOS, eNOS, nNOS, or VEGF, and microvessel density in tumor tissue, tumor marginal zone, or in peripheral tissue.

CONCLUSIONS

These results show that there is a link in expression between HIF-1α, iNOS, (eNOS), and VEGF in esophageal cancer. This is in line with the fact of HIF-1α's function as a transcriptional factor for these angiogenic factors. Results also show that squamous cell and adenocarcinomas differ in their expression of HIF-1α and iNOS. VEGF appear to have association with depth of invasion in esophageal carcinomas. In our material HIF-1α positivity was associated with distant metastases, but not with patient survival.

Angiogenesis inhibition in prostate cancer: current uses and future promises

Angiogenesis has been well recognized as a fundamental part of a multistep process in the evolution of cancer progression, invasion, and metastasis. Strategies for inhibiting angiogenesis have been one of the most robust fields of cancer investigation, focusing on the vascular endothelial growth factor (VEGF) family and its receptors. There are numerous regulatory drug approvals to date for the use of these agents in treating a variety of solid tumors. While therapeutic efficacy has been established, challenges remain with regards to overcoming resistance and assessing response to antiangiogenic therapies. Prostate cancer is the most common noncutaneous malignancy among American men and angiogenesis plays a role in disease progression. The use of antiangiogenesis agents in prostate cancer has been promising and is hereby explored.

Angiogenesis inhibition in the treatment of prostate cancer

For many men, prostate cancer is an indolent disease that, even without definitive therapy, may have no impact on their quality of life or overall survival. However for those men who are either diagnosed with or eventually develop metastatic disease, prostate cancer is a painful and universally fatal disease. Testosterone-lowering hormonal therapy may control the disease for some time, but patients eventually develop resistance and progress clinically. At this point, only docetaxel has been shown to improve survival, so clearly additional therapeutic options are needed. Angiogenesis inhibition is an active area of clinical research in prostate cancer. Without angiogenesis, tumors have insufficient nutrients and oxygen to grow larger than a few millimeters and are potentially less likely to metastasize. In prostate cancer in particular, angiogenesis plays a significant role in tumor proliferation, and markers of angiogenesis appear to have prognostic significance. Several different compounds have been developed to inhibit angiogenesis, including monoclonal antibodies, multitargeted kinase inhibitors, and fusion proteins. In addition, more traditional agents may also have an impact on angiogenesis. Trials studying antiangiogenic agents have been conducted in localized and advanced prostate cancer. There are several large, ongoing phase III trials in metastatic castration-resistant prostate cancer. The findings of these and future studies will ultimately determine the role of angiogenesis inhibitors in the treatment of prostate cancer.

Lymphoscintigraphy in angiomyomatous hamartomas and primary lower limb lymphedema

PURPOSE

Angiomyomatous hamartoma (AH) of the lymph node is a rare vascular benign disease of unknown etiology with a predisposition for the lymph nodes of the inguinal area. Only 18 cases have been described up to now in the literature and the disorder was reported to be associated with lymphedema or swelling of the ipsilateral limb in 4 patients. However, scintigraphic investigation of the lymphatic system in these patients was reported in only 2 cases.

MATERIAL AND METHODS

Five patients where the biopsy of inguinal nodes for suspected lymphadenitis led to the diagnosis of angiomyomatous hamartoma were investigated using lymphoscintigraphic techniques (1 girl aged 15; 1 boy aged 9 at the time of first biopsy and 11 at the time of the second one; and 3 men aged 30, 50, and 57). The operated limb was lymphedematous in 3 and 1 developed lymphedema after biopsy. The fifth patient developed a contralateral lymphedema after his second nodal biopsy.

RESULTS

In all cases, lymphoscintigraphic investigation of the limbs showed extensive lymph node abnormalities on the operated side and in 4 cases on the opposite side.

CONCLUSIONS

These observations support not only the hypothesis that lymphatic disturbance was involved in the pathogenesis of these tumors but also the proposition that lymphoscintigraphy should be performed in cases of inguinal lymphadenitis of unknown origin to diagnose the underlying situation of latent lymphedema.

Vascular permeability and pathological angiogenesis in caveolin-1-null mice

Caveolin-1, the signature protein of endothelial cell caveolae, has many important functions in vascular cells. Caveolae are thought to be the transcellular pathway by which plasma proteins cross normal capillary endothelium, but, unexpectedly, cav-1(-/-) mice, which lack caveolae, have increased permeability to plasma albumin. The acute increase in vascular permeability induced by agents such as vascular endothelial growth factor (VEGF)-A occurs through venules, not capillaries, and particularly through the vesiculo-vacuolar organelle (VVO), a unique structure composed of numerous interconnecting vesicles and vacuoles that together span the venular endothelium from lumen to ablumen. Furthermore, the hyperpermeable blood vessels found in pathological angiogenesis, mother vessels, are derived from venules. The present experiments made use of cav-1(-/-) mice to investigate the relationship between caveolae and VVOs and the roles of caveolin-1 in VVO structure in the acute vascular hyperpermeability induced by VEGF-A and in pathological angiogenesis and associated chronic vascular hyperpermeability. We found that VVOs expressed caveolin-1 variably but, in contrast to caveolae, were present in normal numbers and with apparently unaltered structure in cav-1(-/-) mice. Nonetheless, VEGF-A-induced hyperpermeability was strikingly reduced in cav-1(-/-) mice, as was pathological angiogenesis and associated chronic vascular hyperpermeability, whether induced by VEGF-A(164) or by a tumor. Thus, caveolin-1 is not necessary for VVO structure but may have important roles in regulating VVO function in acute vascular hyperpermeability and angiogenesis.

Tissue factor in tumour progression

The linkage between activation of the coagulation system and cancer is well established, as is deregulation of tissue factor (TF) by cancer cells, their vascular stroma and cancer-associated inflammatory cells. TF is no longer perceived as an 'alternative' coagulation factor, but rather as a central trigger of the coagulation cascade and an important cell-associated signalling receptor activated by factor VIIa, and interacting with several other regulatory entities, most notably protease-activated receptors (PAR-1 and PAR-2). Preclinical studies revealed the role of oncogenic transformation and tumour micro-environment as TF regulators in cancer, along with the impact of this receptor on gene expression, tumour growth, metastasis, angiogenesis and, possibly, formation of the cancer stem cell niche. Increasing interest surrounds the shedding of TF-containing microvesicles from cancer cells, their entry into the circulation and their role in the intercellular transfer of TF activity, cancer coagulopathy and other processes. Recent data also suggest differential roles of cell autonomous versus global effects of TF in various settings. Questions are raised regarding the consequences of TF expression by tumour cells themselves and by their associated host stroma. Progress in these areas may soon begin to impact on clinical practice and, as such, raises several important questions. Can TF be exploited as a therapeutic target in cancer? Where and when may this be safe and beneficial? Is expression of TF in various disease settings useful as a biomarker of cancer progression or the associated hypercoagulability? What clinical questions related to TF are especially worthy of further exploration, at present and in the near future? Some of these developments and questions will be discussed in this chapter.

The Contribution of Harold F. Dvorak to the Study of Tumor Angiogenesis and Stroma Generation Mechanisms

In 1983, Harold Dvorak and his colleagues were the first to show that tumor cells secreted vascular permeability factor (VPF) and that a blocking antibody to VPF could prevent the edema and fluid accumulation that is characteristic of human cancers. In 1986, Dvorak went on to demonstrate that VPF was secreted by a variety of human tumor cell lines and proposed that VPF was in part responsible for the abnormal vasculature seen in human tumors. As a result, he and other investigators demonstrated that VPF was capable of stimulating endothelial cell growth and angiogenesis. These fundamental discoveries led to additional research conducted by Napoleone Ferrara and his laboratory, confirming the cloning of VPF and renaming the protein vascular endothelial growth factor (VEGF). In 1986, Dvorak proposed that by secreting VPF, tumors induce angiogenesis by turning on the wound healing response. He noted that wounds, like tumors, secrete VPF, causing blood vessels to leak plasma fibrinogen, which stimulates blood vessel growth and provides a matrix on which they can spread. Unlike wounds, however, that turn off VPF production after healing, tumors did not turn off their VPF production and instead continued to make large amounts of VPF, allowing malignant cells to continue to induce new blood vessels and so to grow and spread. Thus, tumors behave like wounds that fail to heal. This work is again extremely significant for patients worldwide, as Dvorak's scientific research is leading his colleagues all over the world to examine how to treat a tumor through its blood supply.

Expression of vascular endothelial growth factor and angiopoietins in human corpus cavernosum

OBJECTIVE

To evaluate the expression of the angiogenic factors vascular endothelial growth factor (VEGF) and angiopoietins (Ang) 1 and 2, in normal human penile erectile tissue.

MATERIALS AND METHODS

Penile fragments were removed from four young healthy organ donors (aged 17-28 years), and processed for immunohistochemical studies for VEGF, Ang1 and Ang2, and their specific receptors (VEGFR1 and 2, and Tie2, respectively). Molecular analysis was used to confirm the expression of VEGF and Angs in erectile tissue.

RESULTS

VEGF and VEGFR1 expression was restricted to smooth muscle cells (SMCs). VEGFR2 was detected mainly in the endothelium lining and to a lesser extent in the SMC. Ang1 had a scattered distribution mostly in the perivascular SM layer, showing co-localization with VEGF. Tie2 was faintly detected in the endothelial cells. Ang2 was not detected by immunohistochemical studies, but the use of the same antibody in molecular analysis confirmed Ang2 expression in human corpus cavernosum.

CONCLUSIONS

We show for the first time the co-localization of VEGF and Ang1 in the SMC, suggesting an interaction for vessel stabilization. Ang2 seems to be available for neoangiogenesis, if challenged. Studies of endothelial markers, growth factors and specific receptors are useful for understanding vascular organization and angiogenesis in normal human erectile tissue. This knowledge will be fundamental for developing newer therapeutic approaches to prevent or even cure erectile dysfunction.

RGS5, a hypoxia-inducible apoptotic stimulator in endothelial cells

Endothelial cells rapidly respond to changes in oxygen homeostasis by regulating gene expression. Regulator of G protein signaling 5 (RGS5) is a negative regulator of G protein-mediated signaling that is strongly expressed in vessels during angiogenesis; however, the role of RGS5 in hypoxia has not been fully understood. Under hypoxic conditions, we found that the expression of RGS5, but not other RGS, was induced in human umbilical vein endothelial cells (HUVEC). RGS5 mRNA was increased when HUVEC were incubated with chemicals that stabilized hypoxia-inducible factor-1alpha (HIF-1alpha), whereas hypoxia-stimulated RGS5 promoter activity was absent in HIF-1beta(-/-) cells. Vascular endothelial growth factor (VEGF), which is regulated by HIF-1, did not appear to be involved in hypoxia-induced RGS5 expression; however, VEGF-mediated activation of p38 but not ERK1/2 was increased by RGS5. Overexpression of RGS5 in HUVEC exhibited a reduced growth rate without affecting the cell proliferation. Annexin V assay revealed that RGS5 induced apoptosis with significantly increased activation of caspase-3 and the Bax/Bcl-2 ratio. Small interfering RNA-specific for RGS5, caspase-3 inhibitor, and p38 inhibitor resulted in an attenuation of RGS5-stimulated apoptosis. Matrigel assay proved that RGS5 significantly impaired the angiogenic effect of VEGF and stimulated apoptosis in vivo. We concluded that RGS5 is a novel HIF-1-dependent, hypoxia-induced gene that is involved in the induction of endothelial apoptosis. Moreover, RGS5 antagonizes the angiogenic effect of VEGF by increasing the activation of p38 signaling, suggesting that RGS5 could be an important target for apoptotic therapy.

Targeting VEGF-encapsulated immunoliposomes to MI heart improves vascularity and cardiac function

Recent attempts at rebuilding the myocardium using stem cells have yielded disappointing results. The lack of a supporting vasculature may, in part, explain these disappointing findings. However, concerns over possible side effects have hampered attempts at revascularizing the infarcted myocardium using systemic delivery of proangiogenic compounds. In this study, we develop the technology to enhance the morphology and function of postinfarct neovasculature. Previously, we have shown that the up-regulated expression of endothelial cell adhesion molecules in the myocardial infarction (MI) region provides a potential avenue for selectively targeting drugs to infarcted tissue. After treatment with anti-P-selectin-conjugated liposomes containing vascular endothelial growth factor (VEGF), changes in cardiac function and vasculature post-MI were quantified in a rat MI model. Targeted delivery of VEGF to post-MI tissue resulted in significant increase in fractional shortening and improved systolic function. These functional improvements were accompanied by a 21% increase in the number of anatomical vessels and a 74% increase in the number of perfused vessels in the MI region of treated animals. No significant improvements in cardiac function were observed in untreated, systemic VEGF-treated, nontargeted liposome-treated, or blank immunoliposome-treated animals. Targeted delivery of low doses of proangiogenic compounds to post-MI tissue results in significant improvements in cardiac function and vascular structure.

Paradoxical effects of PDGF-BB overexpression in endothelial cells on engineered blood vessels in vivo

Therapeutic revascularization with either exogenous angiogenic growth factors or vascular cells has yet to demonstrate efficacy in the clinic. Injection of angiogenic growth factors often produces unstable and abnormal blood vessels. Blood vascular networks derived from implanted endothelial cells persist only transiently due to the insufficient recruitment of perivascular cells. We hypothesize that a combination of the two approaches may act synergistically to yield a better result. To enhance the recruitment of perivascular cells, human umbilical vein endothelial cells were genetically modified to overexpress platelet-derived growth factor (PDGF)-BB. PDGF-BB overexpression promoted both proliferation and migration of perivascular precursor cells (10T1/2 cells) in vitro. When mock-infected endothelial cells were implanted alone in vivo, they formed transient blood vascular networks that regressed by day 30. PDGF-BB overexpression enhanced the survival of endothelial cells in vivo. However, the PDGF-BB-expressing vessel network failed to establish patent blood flow. Co-implantation of PDGF-BB-overexpressing endothelial cells with 10T1/2 cells paradoxically resulted in the rapid regression of the vascular networks in vivo. PDGF-BB stimulated the expression of both chemokine (C-C motif) ligand 2 (CCL2) and CCL7 in 10T1/2 cells and led to the increased accumulation of macrophages in vivo. These results suggest a potential negative interaction between angiogenic growth factors and vascular cells; their use in combination should be carefully tested in vivo for such opposing effects.

VEGF-A induces angiogenesis by perturbing the cathepsin-cysteine protease inhibitor balance in venules, causing basement membrane degradation and mother vessel formation

Tumors initiate angiogenesis primarily by secreting vascular endothelial growth factor (VEGF-A(164)). The first new vessels to form are greatly enlarged, pericyte-poor sinusoids, called mother vessels (MV), that originate from preexisting venules. We postulated that the venular enlargement necessary to form MV would require a selective degradation of their basement membranes, rigid structures that resist vascular expansion. To identify the specific proteases responsible for MV formation, we induced angiogenesis in mouse tissues with an adenoviral vector expressing VEGF-A(164) (Ad-VEGF-A(164)) or with VEGF-A-secreting TA3/St mammary tumors. We found that MV formation resulted from greatly increased activity of cathepsins (B>S>L) in venules transitioning into MV, as well as from a reciprocal decrease in the expression of several cysteine protease inhibitors (CPI), stefin A and cystatins B and C, by these same venules. Using a fluorescence probe that selectively binds cellular sites of cathepsin protease activity in vivo, we showed that increased cathepsin activity was localized exclusively to perivenular cells, not to venule endothelial cells. CPI strikingly inhibited angiogenesis in the Matrigel assay, and Ad-VEGF-A(164)-induced angiogenesis was reduced by approximately 50% in cathepsin B-null mice. Thus, VEGF-A, whether expressed by interstitial cells infected with an adenoviral vector or by tumor cells, upsets the normal cathepsin-CPI balance in nearby venules, leading to degradation of their basement membranes, an important first step in angiogenesis.

The role of hypoxia in canine cancer

Human oncology has clearly demonstrated the existence of hypoxic tumours and the problematic nature of those tumours. Hypoxia is a significant problem in the treatment of all types of solid tumours and a common reason for treatment failure. Hypoxia is a negative prognostic indicator of survival and is correlated with the development of metastatic disease. Resistance to radiation therapy and chemotherapy can be because of hypoxia. There are two dominant types of hypoxia recognized in tumours, static and intermittent. Both types of hypoxia are important in terms of resistance. A variety of physiological factors cause hypoxia, and in turn, hypoxia can induce genetic and physiological changes. A limited number of studies have documented that hypoxia exists in spontaneous canine tumours. The knowledge from the human literature of problematic nature of hypoxic tumours combined with the rapid growth of veterinary oncology has necessitated a better understanding of hypoxia in canine tumours.

The L6 protein TM4SF1 is critical for endothelial cell function and tumor angiogenesis

Transmembrane-4-L-six-family-1 (TM4SF1) was originally described as a cancer cell protein. Here, we show that it is highly expressed in the vascular endothelium of human cancers and in a banded pattern in the filopodia of cultured endothelial cells (EC). TM4SF1 knockdown prevented filopodia formation, inhibited cell mobility, blocked cytokinesis, and rendered EC senescent. Integrin-alpha5 and integrin-beta1 subunits gave a similar staining pattern and interacted constitutively with TM4SF1, whereas integrin subunits often associated with angiogenesis (alphaV, beta3, beta5) interacted with TM4SF1 only after vascular endothelial growth factor (VEGF)-A or thrombin stimulation. TM4SF1 knockdown substantially inhibited maturation of VEGF-A(164)-induced angiogenesis. Thus, TM4SF1 is a key regulator of EC function in vitro and of pathologic angiogenesis in vivo and is potentially an attractive target for antiangiogenesis therapy.

Vasoactive intestinal peptide in rats with focal cerebral ischemia enhances angiogenesis

We studied the effect of vasoactive intestinal peptide (VIP) on angiogenesis in the ischemic boundary area after focal cerebral ischemia. Adult male Sprague-Dawley rats underwent middle cerebral artery occlusion for 2 h. A single dose of VIP was given via i.c.v. injection at the beginning of reperfusion. Immunohistochemistry and Western blotting were performed to assay angiogenesis and brain levels of vascular endothelial growth factor (VEGF) protein, respectively. In addition, the expression of VEGF and its receptors (flt-1 and flk-1), as well as endothelial proliferation, was measured using rat brain microvascular endothelial cells. Immunohistochemical analyses revealed significant (P<0.05) increases in the numbers of bromodeoxyuridine (BrdU) positive endothelial cells and microvessels at the boundary of the ischemic lesion in rats treated with VIP compared with rats treated with saline. Western blotting analysis showed that treatment with VIP significantly (P<0.05) raised VEGF levels in the ischemic hemisphere. In addition, treatment with VIP increased flt-1 and flk-1 immunoreactivity in endothelial cells. In vitro, incubation with VIP significantly (P<0.01) increased the proliferation of endothelial cells and induced the expression of VEGF, flt-1 and flk-1 in endothelial cells. The stimulatory effect of VIP on the proliferation of endothelial cells was significantly (P<0.01) inhibited by SU5416, a selective inhibitor of VEGF receptor tyrosine kinase. Our data suggest that treatment with VIP enhances angiogenesis in the ischemic brain, and this effect may be mediated by increases in levels of VEGF and its receptors.

Why are tumour blood vessels abnormal and why is it important to know?

Tumour blood vessels differ from their normal counterparts for reasons that have received little attention. We report here that they are of at least six distinct types, we describe how each forms, and, looking forward, encourage the targeting of tumour vessel subsets that have lost their vascular endothelial growth factor-A (VEGF-A) dependency and so are likely unresponsive to anti-VEGF-A therapies.

An assay system for in vitro detection of permeability in human "endothelium"

The molecular mechanisms by which endothelial permeability occurs are often studied more readily in vitro, underscoring the importance of the use of systems that mimic human endothelium in vivo. We present an assay that accurately models human endothelium by use of primary human microvascular endothelial cells (hMVEC), because permeability primarily occurs at the microvascular level, and transwell filter units coated with Matrigel, extracellular matrix that mimics basal lamina, the matrix that is tightly associated with endothelium and is critical for its proper function. As a tracer molecule, we used 3-kDa dextran-FITC to detect leakage through the small gaps present in the early stages of permeability induction. The permeability-inducing agents IL-8 and VEGF were added to the lower chamber of the transwell units to mimic inflammatory conditions in vivo. After optimization, we were able to minimize basal permeability and to detect rapid changes in permeability stimulated by IL-8 and VEGF, similar to that observed in vivo. Furthermore, we have used this system to delineate the importance of the transactivation of VEGFR2 in IL-8-induced permeability and have confirmed the relevance of this signaling in vivo, suggesting that our permeability assay system adequately mimics the in vivo situation. Therefore, this system can be used to better understand the molecular mechanisms of human vascular permeability in a more in vivo-like setting and, thus, may be used to test effective therapeutics to prevent and treat diseases involving persistent permeability.

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.

Palomid 529, a novel small-molecule drug, is a TORC1/TORC2 inhibitor that reduces tumor growth, tumor angiogenesis, and vascular permeability

It has become clear that the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is central for promoting both tumor and tumor stroma and is therefore a major target for anticancer drug development. First- and second-generation rapalogs (prototypical mTOR inhibitors) have shown promise but, due to the complex nature of mTOR signaling, can result in counterproductive feedback signaling to potentiate upstream Akt signaling. We present a novel PI3K/Akt/mTOR inhibitor, Palomid 529 (P529), which inhibits the TORC1 and TORC2 complexes and shows both inhibition of Akt signaling and mTOR signaling similarly in tumor and vasculature. We show that P529 inhibits tumor growth, angiogenesis, and vascular permeability. It retains the beneficial aspects of tumor vascular normalization that rapamycin boasts. However, P529 has the additional benefit of blocking pAktS473 signaling consistent with blocking TORC2 in all cells and thus bypassing feedback loops that lead to increased Akt signaling in some tumor cells.