Molecular pathways of angiogenesis inhibition

Impact of Polypyridyl Ru Complexes on Angiogenesis-Contribution to Their Antimetastatic Activity

The use of polypyridyl Ru complexes to inhibit metastasis is a novel approach, and recent studies have shown promising results. We have reported recently that Ru (II) complexes gathering two 4,7-diphenyl-1,10-phenanthroline (dip) ligands and the one being 2,2'-bipyridine (bpy) or its derivative with a 4-[3-(2-nitro-1H-imidazol-1-yl)propyl (bpy-NitroIm) or 5-(4-{4'-methyl-[2,2'-bipyridine]-4-yl}but-1-yn-1-yl)pyridine-2-carbaldehyde semicarbazone (bpy-SC) moieties can alter the metastatic cascade, among others, by modulating cell adhesion properties. In this work, we show further studies of this group of complexes by evaluating their effect on HMEC-1 endothelial cells. While all the tested complexes significantly inhibited the endothelial cell migration, Ru-bpy additionally interrupted the pseudovessels formation. Functional changes in endothelial cells might arise from the impact of the studied compounds on cell elasticity and expression of proteins (vinculin and paxillin) involved in focal adhesions. Furthermore, molecular studies showed that complexes modulate the expression of cell adhesion molecules, which has been suggested to be one of the factors that mediate the activation of angiogenesis. Based on the performed studies, we can conclude that the investigated polypyridyl Ru (II) complexes can deregulate the functionality of endothelial cells which may lead to the inhibition of angiogenesis.

Curcumin improves angiogenesis in the heart of aged rats: Involvement of TSP1/NF-κB/VEGF-A signaling

BACKGROUND

Cardiac aging is an irreversible process that is determined by a number of slowly deleterious changes in morphological and physiological properties of the heart. We investigated the effects of curcumin on cardiac angiogenesis, in old male rats.

MATERIALS AND METHODS

Rats randomly divided into young, age (rats of 26-28 months of age) and curcumin-age (rats of 26-28 months of age treatment with curcumin 50mg/kg). Finally, the expression of VEGF, NF-κB, and TSP-1 were assessed by ELISA in cardiac tissue. Also, angiogenesis was determined by immunostaining for PECAM-1/CD31 and apoptosis was evaluated by TUNEL.

RESULTS

After 2 months, curcumin-age had significantly higher cardiac VEGF-A and NF-κB and lower cardiac TSP-1 expression levels in comparison with age and young. A significant increase in levels of NF-κB and TSP-1 were observed in the age group.

CONCLUSION

Results suggest that curcumin through regulation of cardiogenic mediators and improving cardiac angiogenesis can promote heart performance in the senescent rats.

Matrix Metalloproteinases' Role in Tumor Microenvironment

Cancer cells evolve in the tumor microenvironment (TME) by the acquisition of characteristics that allow them to initiate their passage through a series of events that constitute the metastatic cascade. For this purpose, tumor cells maintain a crosstalk with TME non-neoplastic cells transforming them into their allies. "Corrupted" cells such as cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and tumor-associated neutrophils (TANs) as well as neoplastic cells express and secrete matrix metalloproteinases (MMPs). Moreover, TME metabolic conditions such as hypoxia and acidification induce MMPs' synthesis in both cancer and stromal cells. MMPs' participation in TME consists in promoting events, for example, epithelial-mesenchymal transition (EMT), apoptosis resistance, angiogenesis, and lymphangiogenesis. MMPs also facilitate tumor cell migration through the basement membrane (BM) and extracellular matrix (ECM). The aim of the present chapter is to discuss MMPs' contribution to the evolution of cancer cells, their cellular origin, and their influence in the main processes that take place in the TME.

Soluble Mediators Produced by Pro-Resolving Macrophages Inhibit Angiogenesis

Different subtypes of macrophages have been shown to participate in different stages of inflammation and tissue repair. In the late stage of tissue repair, the macrophages, following their engulfment of apoptotic neutrophils, acquire a new phenotype termed alternatively activated macrophages. These macrophages produce growth factors, such as vascular endothelial growth factor (VEGF), that facilitate the angiogenic response as part of tissue restoration. Then, in the later stages of tissue healing, capillary regression takes place. It is presently unknown whether macrophages play an antiangiogenic role in the final stages of tissue repair. Here, we examined whether soluble mediators secreted by pro-resolving CD11b^low macrophages (Mres) inhibit angiogenesis in the context of the resolution of tissue repair. Our findings indicate that soluble mediators produced by ex vivo generated Mres (CM-Mres) attenuate angiogenesis in vitro by inhibiting human umbilical vein endothelial cell (HUVEC) proliferation by lowering their cyclin D1 expression. In addition, CM-Mres lowered HUVEC survival by inducing caspase 3/7 activation, and also inhibited VEGFR2 activation via VEGF. HUVEC migration and differentiation to tubular-like structure was also inhibited by CM-Mres. Similarly, CM-Mres significantly inhibited neovascularization as depicted ex vivo by utilizing the rat aorta ring assay and in vivo by utilizing the chick chorioallantoic membrane assay. Notably endostatin, which was shown previously to exert its antiangiogenic effect by inhibiting proliferation, survival, motility, and morphogenesis of endothelial cells via inhibition of VEGFR2 activation, is produced by Mres. Taken together, our results suggest that a specialized subset of macrophages that appear during the resolution of inflammation can produce antiangiogenic mediators, such as endostatin. These mediators can halt angiogenesis, thereby restoring tissue structure.

The Challenges of Recombinant Endostatin in Clinical Application: Focus on the Different Expression Systems and Molecular Bioengineering

Angiogenesis plays an essential role in rapid growing and metastasis of the tumors. Inhibition of angiogenesis is a putative strategy for cancer therapy. Endostatin (Es) is an attractive anti-angiogenesis protein with some clinical application challenges including; short half-life, instability in serum and requirement to high dosage. Therefore, production of recombinant endostatin (rEs) is necessary in large scale. The production of rEs is difficult because of its structural properties and is high-cost. Therefore, this review focused on the different expression systems that involved in rEs production including; mammalian, baculovirus, yeast, and Escherichia coli (E. coli) expression systems. The evaluating of the results of different expression systems declared that none of the mentioned systems can be considered to be generally superior to the other. Meanwhile with considering the advantages and disadvantage of E. coli expression system compared with other systems beside the molecular properties of Es, E. coli expression system can be a preferred expression system for expressing of the Es in large scale. Also, the molecular bioengineering and sustained release formulations that lead to improving of its stability and bioactivity will be discussed. Point mutation (P125A) of Es, addition of RGD moiety or an additional zinc biding site to N-terminal of Es , fusing of Es to anti-HER2 IgG or heavy-chain of IgG, and finally loading of the endostar by PLGA and PEG- PLGA nanoparticles and gold nano-shell particles are the effective bioengineering methods to overcome to clinical changes of endostatin.

Differential role of gene hypermethylation in adenocarcinomas, squamous cell carcinomas and cervical intraepithelial lesions of the uterine cervix

Cervical cancer is the third most common cancer in women worldwide. The hypermethylation of P16, TSLC-1 and TSP-1 genes was analyzed in squamous cell carcinomas (SCC), cervical intraepithelial lesions (CIN) and adenocarcinomas (ADC) of the uterine cervix (total 181 lesions). Additionally human papillomavirus (HPV) type, EPB41L3, RASSF1 and RASSF2 hypermethylation were tested in ADC and the results were compared with those obtained previously by our group in SCC. P16, TSLC-1 and TSP-1 hypermethylation was more frequent in SCCs than in CINs. These percentages and the corresponding ones for EPB41L3, RASSF1 and RASSF2 genes were also higher in SCCs than in ADCs, except for P16. The presence of HPV in ADCs was lower than reported previously in SCC and CIN. Patients with RASSF1A hypermethylation showed significantly longer disease-free survival (P = 0.015) and overall survival periods (P = 0.009) in ADC patients. To our knowledge, this is the first description of the EPB41L3 and RASSF2 hypermethylation in ADCs. These results suggest that the involvement of DNA hypermethylation in cervical cancer varies depending on the histological type, which might contribute to explaining the different prognosis of patients with these types of tumors.

Nuclear factor κB-dependent regulation of angiogenesis, and metastasis in an in vivo model of thyroid cancer is associated with secreted interleukin-8

CONTEXT

Development of novel strategies in the treatment of advanced thyroid cancer are needed. Our laboratory has previously identified a role for nuclear factor κB (NF-κB) signaling in human thyroid cancer cell growth, survival, and invasion.

OBJECTIVE

Our goal was to establish the role of NF-κB signaling on thyroid cancer growth and metastases in vivo and to begin to dissect mechanisms regulating this effect.

SETTING AND DESIGN

We examined tumor formation of five thyroid cancer cell lines in an in vivo model of thyroid cancer and observed tumor establishment in two of the cell lines (8505C and BCPAP).

RESULTS

Inhibition of NF-κB signaling by overexpression of a dominant-negative IκBα (mIκBα) significantly inhibited thyroid tumor growth in tumors derived from both cell lines. Further studies in an experimental metastasis model demonstrated that NF-κB inhibition impaired growth of tumor metastasis and prolonged mouse survival. Proliferation (mitotic index) was decreased in 8505C tumors, but not in BCPAP tumors, while in vitro angiogenesis and in vivo tumor vascularity were significantly inhibited by mIkBα only in the BCPAP cells. Cytokine antibody array analysis demonstrated that IL-8 secretion was blocked by mIκBα expression. Interestingly, basal NF-κB activity and IL-8 levels were significantly higher in the two tumorigenic cell lines compared with the nontumorigenic lines. Furthermore, IL-8 transcript levels were elevated in high-risk human tumors, suggesting that NF-κB and IL-8 are associated with more aggressive tumor behavior.

CONCLUSIONS

These studies suggest that NF-κB signaling is a key regulator of angiogenesis and growth of primary and metastatic thyroid cancer, and that IL-8 may be an important downstream mediator of NF-κB signaling in advanced thyroid cancer growth and progression.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

Angiostatin inhibits activation and migration of neutrophils

There is a critical need to identify molecules that modulate the biology of neutrophils because activated neutrophils, though necessary for host defense, cause exuberant tissue damage through production of reactive oxygen species and increased lifespan. Angiostatin, an endogenous anti-angiogenic cleavage product of plasminogen, binds to integrin αvβ3, ATP synthase and angiomotin and its expression is increased in inflammatory conditions. We test the hypothesis that angiostatin inhibits neutrophil activation, induces apoptosis and blocks recruitment in vivo and in vitro. The data show immuno-reactivity for plasminogen/angiostatin in resting neutrophils. Angiostatin conjugated to FITC revealed that angiostatin was endocytozed by activated mouse and human neutrophils in a lipid raft-dependent fashion. Co-immunoprecipitation of human neutrophil lysates, confocal microscopy of isolated mouse and human neutrophils and functional blocking experiments showed that angiostatin complexes with flotillin-1 along with integrin αvβ3 and ATP synthase. Angiostatin inhibited fMLP-induced neutrophil polarization, as well as caused inhibition of hsp-27 phosphorylation and stabilization of microtubules. Angiostatin treatment, before or after LPS-induced neutrophil activation, inhibited phosphorylation of p38 and p44/42 MAPKs, abolished reactive oxygen species production and released the neutrophils from suppressed apoptosis, as indicated by expression of activated caspase-3 and morphological evidence of apoptosis. Finally, intravital microscopy and myeloperoxidase assay showed inhibition of neutrophil recruitment in post-capillary venules of TNFα-treated cremaster muscle in mouse. These in vitro and in vivo data demonstrate angiostatin as a broad deactivator and silencer of neutrophils and an inhibitor of their migration. These data potentially open new avenues for the development of anti-inflammatory drugs.

Angiostatin inhibits acute lung injury in a mouse model

Acute lung injury is marked by profound influx of activated neutrophils, which have delayed apoptosis, along with fluid accumulation that impairs lung function and causes high mortality. Inflammatory and antimicrobial molecules, such as reactive oxygen species from activated neutrophils with prolonged lifespan, cause tissue damage and contribute to lung dysfunction. Angiostatin, an endogenous antiangiogenic molecule, is expressed in the lavage fluid of patients with acute respiratory distress syndrome and modifies neutrophil infiltration in a mouse model of peritonitis. Our aim was to investigate the therapeutic role of angiostatin in acute lung injury. We analyzed bronchoalveolar lavage and lung tissues from C57BL/6 mouse model of Escherichia coli LPS-induced acute lung injury to assess the effects of angiostatin treatment. Subcutaneous angiostatin administered at 5 h after LPS treatment reduces histological signs of inflammation, protein accumulation, lung Gr1+ neutrophils, myeloperoxidase activity, and expression of phosphorylated p38 MAPK in lung tissues and peripheral blood neutrophils, while increasing the number of apoptotic cells in the lungs without affecting the levels of macrophage inflammatory protein-1 α, IL-1β, keratinocyte chemoattractant, and monocyte chemoattractant protein-1 in lavage and lung homogenates at 9 and 24 h after LPS treatment. In contrast, angiostatin administered intravenously 5 h after LPS treatment did not reduce histological sign of inflammation, BAL cell recruitment, and protein concentration at 9 h of LPS treatment. We conclude that angiostatin administered subcutaneously after LPS challenge inhibits acute lung inflammation up to 24 h after LPS treatment.

Vascular endothelial growth factor (VEGF) and platelet (PF-4) factor 4 inputs modulate human microvascular endothelial signaling in a three-dimensional matrix migration context

The process of angiogenesis is under complex regulation in adult organisms, particularly as it often occurs in an inflammatory post-wound environment. As such, there are many impacting factors that will regulate the generation of new blood vessels which include not only pro-angiogenic growth factors such as vascular endothelial growth factor, but also angiostatic factors. During initial postwound hemostasis, a large initial bolus of platelet factor 4 is released into localized areas of damage before progression of wound healing toward tissue homeostasis. Because of its early presence and high concentration, the angiostatic chemokine platelet factor 4, which can induce endothelial anoikis, can strongly affect angiogenesis. In our work, we explored signaling crosstalk interactions between vascular endothelial growth factor and platelet factor 4 using phosphotyrosine-enriched mass spectrometry methods on human dermal microvascular endothelial cells cultured under conditions facilitating migratory sprouting into collagen gel matrices. We developed new methods to enable mass spectrometry-based phosphorylation analysis of primary cells cultured on collagen gels, and quantified signaling pathways over the first 48 h of treatment with vascular endothelial growth factor in the presence or absence of platelet factor 4. By observing early and late signaling dynamics in tandem with correlation network modeling, we found that platelet factor 4 has significant crosstalk with vascular endothelial growth factor by modulating cell migration and polarization pathways, centered around P38α MAPK, Src family kinases Fyn and Lyn, along with FAK. Interestingly, we found EphA2 correlational topology to strongly involve key migration-related signaling nodes after introduction of platelet factor 4, indicating an influence of the angiostatic factor on this ambiguous but generally angiogenic signal in this complex environment.

Differential gene hypermethylation in genital lichen sclerosus and cancer: a comparative study

AIMS

Lichen sclerosus (LS) is a chronic inflammatory disease of the genital skin of unknown aetiology. The role of LS in penile squamous cell carcinogenesis is not well characterized. HPV has been implicated in both, as have epigenetic changes. The presence of HPV and hypermethylation of the MGMT, p16, RASSF1, RASSF2, TSLC1 and TSP1 genes were studied in penile LS; MGMT, RASSF2 and TSLC1 hypermethylation in penile cancer and TSLC1 hypermethylation in vulvar LS and cancer extends previous results reported by our group.

METHODS AND RESULTS

Thirty-seven HPV genotypes and hypermethylation were evaluated by PCR/reverse-line-blot and methylation-specific PCR respectively, in 27 preputial LS, 24 penile SCC, 30 vulvar SCC, 21 vulvar LS and 22 normal skin cases. HPV66 was present in 3.7% of penile LS cases, and p16 and RASSF2 hypermethylation were more frequent in penile cancer than in penile LS. p16, RASSF1, RASSF2 and TSP1 hypermethylation were similar in penile and vulvar LS.

CONCLUSIONS

Gene hypermethylation is a common event in penile LS, and occurs approximately as frequently as in vulvar LS. Certain genes can be hypermethylated as an early or late event in LS or cancer, respectively. This suggests a possible sequential role for these alterations in the transition from benign to malignant lesions.

Histamine synergistically promotes bFGF-induced angiogenesis by enhancing VEGF production via H1 receptor

Histamine, a major mediator present in mast cells that is released into the extracellular milieu upon degranulation, is well known to possess a wide range of biological activities in several classic physiological and pathological processes. However, whether and how it participates in angiogenesis remains obscure. In the present study, we observed its direct and synergistic action with basic fibroblast growth factor (bFGF), an important inducer of angiogenesis, on in vitro angiogenesis models of endothelial cells. Data showed that histamine (0.1, 1, 10 µM) itself was absent of direct effects on the processes of angiogenesis, including the proliferation, migration, and tube formation of endothelial cells. Nevertheless, it could concentration-dependently enhance bFGF-induced angiogenesis as well as production of vascular endothelial growth factor (VEGF) from endothelial cells. The synergistic effect of histamine on VEGF production could be reversed by pretreatments with diphenhydramine (H1-receptor antagonist), SB203580 (selective p38 mitogen-activated protein kinase (MAPK) inhibitor) and L-NAME (nitric oxide synthase (NOS) inhibitor), but not with cimetidine (H2-receptor antagonist) and indomethacin (cyclooxygenase (COX) inhibitor). Moreover, histamine could augment bFGF-incuced phosphorylation and degradation of IκBα, a key factor accounting for the activation and translocation of nuclear factor κB (NF-κB) in endothelial cells. These findings indicated that histamine was able to synergistically augment bFGF-induced angiogenesis, and this action was linked to VEGF production through H1-receptor and the activation of endothelial nitric oxide synthase (eNOS), p38 MAPK, and IκBα in endothelial cells.

An imbalance between VEGF and endostatin underlies impaired angiogenesis in gastric mucosa of aging rats

Gastric mucosa of aging individuals exhibits increased susceptibility to injury and delayed healing. Our previous studies in young rats showed that healing of mucosal injury depends on and is critically dependent on VEGF and angiogenesis. Since angiogenesis in aging gastric mucosa has not been examined before, in this study we examined the extent to which angiogenesis is impaired in gastric mucosa of aging vs. young rats and determined the underlying mechanisms with a focus on mucosal expression of VEGF (proangiogenic factor) and endostatin (antiangiogenic factor). Aging rats had significantly impaired gastric angiogenesis by ~12-fold, 5-fold, 4-fold, and 3-fold, respectively (vs. young rats; all P < 0.001) at 24, 48, 72, and 120 h following ethanol-induced gastric injury and reduced and delayed healing of mucosal erosions. In gastric mucosa of aging (vs. young) rats at baseline, VEGF expression was significantly reduced, whereas endostatin levels were significantly increased (P < 0.05 and P < 0.01, respectively). In contrast to young rats, gastric mucosal VEGF levels did not increase following ethanol-induced injury in aging rats. MMP-9 enzyme activity was significantly higher in gastric mucosa of aging vs. young rats both at baseline (2.7-fold) and 24 h (3.8-fold) after ethanol injury (both P < 0.001). Since endostatin is generated from collagen XVIII by MMP-9, this finding can explain the mechanism of increased endostatin expression in aging gastric mucosa. The above findings demonstrate that reduced VEGF and increased endostatin result in the impaired angiogenesis and delayed injury healing in gastric mucosa of aging rats.

Transcranial near-infrared laser therapy applied to promote clinical recovery in acute and chronic neurodegenerative diseases

One of the most promising methods to treat neurodegeneration is noninvasive transcranial near-infrared laser therapy (NILT), which appears to promote acute neuroprotection by stimulating mitochondrial function, thereby increasing cellular energy production. NILT may also promote chronic neuronal function restoration via trophic factor-mediated plasticity changes or possibly neurogenesis. Clearly, NILT is a treatment that confers neuroprotection or neurorestoration using pleiotropic mechanisms. The most advanced application of NILT is for acute ischemic stroke based upon extensive preclinical and clinical studies. In laboratory settings, NILT is also being developed to treat traumatic brain injury, Alzheimer's disease and Parkinson's disease. There is some intriguing data in the literature that suggests that NILT may be a method to promote clinical improvement in neurodegenerative diseases where there is a common mechanistic component, mitochondrial dysfunction and energy impairment. This article will analyze and review data supporting the continued development of NILT to treat neurodegenerative diseases.

Matrix metalloproteinases: potential therapy to prevent the development of second malignancies after breast radiotherapy

Radiotherapy is widely used in the treatment of patients with breast cancer, but ionizing radiation-induced carcinogenesis has been described in several studies. Matrix metalloproteinases (MMPs) are a wide family of proteases secreted by tumour and microenvironmental cells that are directly linked with invasion and metastasis through complete extracellular matrix (ECM) breakage. In the past decade, MMPs have been associated with other carcinogenesis steps, including tumour growth and angiogenesis promotion. Moreover, in vitro studies have demonstrated an enhanced migration, invasiveness, and angiogenic ability of cancer cells after radiation exposure through an increase in MMP activity. These findings are consistent with clinical observations of breast cancer metastases raised in bone, lung and brain tissues after radiotherapy. The aim of this review was to analyse the current state of research on MMPs and report new insights into the potential of MMP-targeted therapy in combination with radiotherapy to decrease the risk of radiation-induced second malignancies and to improve the overall survival of breast cancer patients.

Antiangiogenic and antivascular effects of a recombinant tumstatin-derived peptide in a corneal neovascularization model

Tumstatin, a cleavage fragment of collagen IV, is a potent endogenous inhibitor of angiogenesis. Tumstatin-derived peptide T8 possesses all angiostatic properties of full-length tumstatin and indirectly suppresses tumor growth. The potential of T8 to block pathological angiogenesis in the eye has not been explored yet. Here we assess antiangiogenic effects of a recombinant T8 peptide in rabbit corneal neovascularization models. The fusion protein consisting of T8 and thioredoxin was synthesized in a highly efficient Escherichia coli expression system, isolated using ion-exchange chromatography and cleaved with TEV (tobacco etch virus) protease. The target peptide was purified on an anion-exchange resin and by reversed phase high-performance liquid chromatography. The recombinant peptide suppressed the proliferation of basic fibroblast growth factor-induced SVEC-4-10 endothelial cells (simian virus 40-immortalized murine endothelial cells) and inhibited tube formation in these cells in a dose-dependent manner. In rabbit corneal neovascularization models T8 demonstrated the ability to prevent pathological angiogenesis (when injected simultaneously with the induction of neovascularization) and, moreover, to promote the regression of newly-formed blood vessels (when injected on day 8 after angiogenesis stimulation). Our results suggest that T8 may have a therapeutic potential in the treatment of ocular neovascular diseases.

How can grafted breast cancer models be optimized?

Breast cancer is the most frequent spontaneous malignancy diagnosed in women and is characterized by a broad histological diversity. Progression of the disease has a metastasizing trend and can be resistant to hormonal and chemotherapy. Animal models have provided some understanding of these features and have allowed new treatments to be proposed. However, these models need to be revised because they have some limitations in predicting the clinical efficacy of new therapies. In this review, we discuss the biological criteria to be taken into account for a realistic animal model of breast cancer graft (tumor implantation site, animal immune status, histological diversity, modern imaging). We emphasize the need for more stringent monitoring criteria, and suggest adopting the human RECIST (Response Evaluation Criteria in Solid Tumors) criteria to evaluate treatments in animal models.

Plasminogen K5 activates mitochondrial apoptosis pathway in endothelial cells by regulating Bak and Bcl-x(L) subcellular distribution

Plasminogen Kringle 5(K5) is a proteolytic fragment of plasminogen, which displays potent anti-angiogenic activities. K5 has been shown to induce apoptosis in proliferating endothelial cells; however the exact mechanism has not been well explored. The present study was designed to elucidate the possible molecular mechanism of K5-induced endothelial cell apoptosis. Our results showed that K5 inhibited basic fibroblast growth factors activated in human umbilical vein endothelial cells (HUVECs), indicating proliferation in a dose-dependent manner and induced endothelial cell death via apoptosis. K5 exposure activated caspase 7, 8 and 9. These results suggested that both the intrinsic mitochondrial apoptosis pathway and extrinsic pathway might be involved in K5-induced apoptosis. K5 reduced mitochondrial membrane potential (MMP) of HUVECs, demonstrating mitochondrial depolarization in HUVECs. K5 increased the ratio of Bak to Bcl-x(L) on mitochondria, decreased the ratio in cytosol, and had no effect on the total amounts of these proteins. K5 also did not effect on Bax/Bcl-2 distribution. K5 increased the ratio of Bak to Bcl-x(L) on mitochondrial that resulted in mitochondrial depolarization, cytochrome c release and consequently the cleavage of caspase 9. These results suggested that K5 induces endothelial cell apoptosis at least in part via activating mitochondrial apoptosis pathway. The regulation of K5 on Bak and Bcl-x(L) distribution may play an important role in endothelial cell apoptosis. These results provide further insight into the anti-angiogenesis roles of K5 in angiogenesis-related ocular diseases and solid tumors.

Angiogenesis gene expression in murine endothelial cells during post-pneumonectomy lung growth

Although blood vessel growth occurs readily in the systemic bronchial circulation, angiogenesis in the pulmonary circulation is rare. Compensatory lung growth after pneumonectomy is an experimental model with presumed alveolar capillary angiogenesis. To investigate the genes participating in murine neoalveolarization, we studied the expression of angiogenesis genes in lung endothelial cells. After left pneumonectomy, the remaining right lung was examined on days 3, 6, 14 and 21days after surgery and compared to both no surgery and sham thoracotomy controls. The lungs were enzymatically digested and CD31⁺ endothelial cells were isolated using flow cytometry cell sorting. The transcriptional profile of the CD31⁺ endothelial cells was assessed using quantitative real-time polymerase chain reaction (PCR) arrays. Focusing on 84 angiogenesis-associated genes, we identified 22 genes with greater than 4-fold regulation and significantly enhanced transcription (p <.05) within 21 days of pneumonectomy. Cluster analysis of the 22 genes indicated that changes in gene expression did not occur in a single phase, but in at least four waves of gene expression: a wave demonstrating decreased gene expression more than 3 days after pneumonectomy and 3 sequential waves of increased expression on days 6, 14, and 21 after pneumonectomy. These findings indicate that a network of gene interactions contributes to angiogenesis during compensatory lung growth.

Peroxisome Proliferator-Activated Receptor-gamma Ligands: Potential Pharmacological Agents for Targeting the Angiogenesis Signaling Cascade in Cancer

Peroxisome proliferator-activated receptor-γ (PPAR-γ) has currently been considered as molecular target for the treatment of human metabolic disorders. Experimental data from in vitro cultures, animal models, and clinical trials have shown that PPAR-γ ligand activation regulates differentiation and induces cell growth arrest and apoptosis in a variety of cancer types. Tumor angiogenesis constitutes a multifaceted process implicated in complex downstream signaling pathways that triggers tumor growth, invasion, and metastasis. In this aspect, accumulating in vitro and in vivo studies have provided extensive evidence that PPAR-γ ligands can function as modulators of the angiogenic signaling cascade. In the current review, the crucial role of PPAR-γ ligands and the underlying mechanisms participating in tumor angiogenesis are summarized. Targeting PPAR-γ may prove to be a potential therapeutic strategy in combined treatments with conventional chemotherapy; however, special attention should be taken as there is also substantial evidence to support that PPAR-γ ligands can enhance angiogenic phenotype in tumoral cells.

Endothelial cells regulate cardiomyocyte development from embryonic stem cells

The molecules and environment that direct pluripotent stem cell differentiation into cardiomyocytes are largely unknown. Here, we determined a critical role of receptor tyrosine kinase, EphB4, in regulating cardiomyocyte generation from embryonic stem (ES) cells through endothelial cells. The number of spontaneous contracting cardiomyocytes, and the expression of cardiac-specific genes, including alpha-MHC and MLC-2V, was significantly decreased in EphB4-null ES cells. EphB4 was expressed in endothelial cells underneath contracting cardiomyocytes, but not in cardiomyocytes. Angiogenic inhibitors, including endostatin and angiostatin, inhibited endothelial cell differentiation and diminished cardiomyogenesis in ES cells. Generation of functional cardiomyocytes and the expression of cardiac-specific genes were significantly enhanced by co-culture of ES cells with human endothelial cells. Furthermore, the defects of cardiomyocyte differentiation in EphB4-deficient ES cells were rescued by human endothelial cells. For the first time, our study demonstrated that endothelial cells play an essential role in facilitating cardiomyocyte differentiation from pluripotent stem cells. EphB4 signaling is a critical component of the endothelial niche to regulate regeneration of cardiomyocytes.

Angiogenesis as a therapeutic target in urothelial carcinoma

In the last few years, angiogenesis has confirmed its critical role in the development of malignant neoplasms. Antiangiogenic drugs, mainly bevacizumab, sorafenib, or sunitinib, are currently approved in a wide number of tumor types, such as breast, colorectal, liver, or kidney cancer, and have changed dramatically the evolution of our patients. Unfortunately, in urothelial carcinoma, which is a very common neoplasm, antiangiogenic agents are still in a very preliminary phase of clinical research. In this study, we focus on the biological basis of angiogenesis in urothelial tumors, its influence in the prognosis of these malignancies, and the available evidence about the use of antiangiogenic drugs in urothelial carcinoma.

Inhibition of transcription, expression, and secretion of the vascular epithelial growth factor in human epithelial endometriotic cells by romidepsin

OBJECTIVE

To investigate whether the histone deacetylase (HDAC) inhibitor romidepsin down-regulates VEGF (vascular endothelial growth factor) gene expression and abrogates VEGF protein secretion in human epithelial endometriotic cells.

DESIGN

In vitro study with human immortalized epithelial endometriotic cells.

SETTING

University hospital.

PATIENT(S)

Not applicable.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Real-time reverse-transcriptase polymerase chain reaction to evaluate VEGF gene expression, immunoblot analysis to evaluate protein expression, and enzyme-linked immunosorbent assay to evaluate VEGF protein secretion into the culture medium.

RESULT(S)

Treatment of 11z human endometriotic cells with romidepsin statistically significantly inhibited VEGF gene transcription and down-regulated VEGF protein expression. Moreover, romidepsin abrogated the secretion of VEGF protein into the culture medium. Romidepsin also reduced the expression of hypoxia-inducible factor-1α (HIF-1α), which is implicated in the transcription of the VEGF gene, in cobalt chloride-pretreated (to mimic hypoxic conditions) 11z cultures.

CONCLUSION(S)

Romidepsin targets VEGF at the transcriptional level, which subsequently leads to the reduction of secreted VEGF (the "active" form of VEGF). Therefore, romidepsin may be a potential therapeutic candidate against angiogenesis in endometriosis.

NF-kappaB in lung cancer, a carcinogenesis mediator and a prevention and therapy target

Lung cancer ranks as the first malignant tumor killer worldwide. Despite the knowledge that carcinogens from tobacco smoke and the environment constitute the main causes of lung cancer, the mechanisms for lung carcinogenesis are still elusive. Cancer development and progression depend on the balance between cell survival and death signals. Common cell survival signaling pathways are activated by carcinogens as well as by inflammatory cytokines, which contribute substantially to cancer development. As a major cell survival signal, nuclear factor-kappaB (NF-kappaB) is involved in multiple steps in carcinogenesis and in cancer cell's resistance to chemo- and radio-therapy. Recent studies with animal models and cell culture systems have established the links between NF-kappaB and lung carcinogenesis, highlighting the significance of targeting NF-kappa signaling pathway for lung cancer treatment and chemoprevention. In this review, we summarize progresses in understanding the NF-kappaB pathway in lung cancer development as well as in modulating NF-kappaB for lung cancer prevention and therapy.

Expression profile and regulation of telomerase reverse transcriptase on oxygen-induced retinal neovascularization

PURPOSE

Telomerase is critical for the control of replicative capacity, which plays a major role in proliferative retinal neovascularization. In this study, we investigated the expression profiles of telomerase reverse transcriptase (Tert) in a mouse model of oxygen-induced retinal neovascularization and explored the possibility of inhibiting a retinal Tert expression with small interfering RNAs (SiRNA) as a novel potential approach to suppress proliferative retinopathy.

METHODS

The mouse oxygen-induced retinal neovascularization model was used to examine expression profiles in different developmental phases and to assess the anti-angiogenic activity of Tert-SiRNA. Recombinant SiRNA plasmids were injected intravitreously into mice with or without pathological retinal neovascularization. Fluorescein angiography, vessel counting, and the expression levels of Tert mRNA and protein were used to evaluate the anti-angiogenic effects.

RESULTS

Retinal Tert expression, as assessed by both mRNA and protein levels, was significantly up-regulated during the proliferative phase of oxygen-induced retinal neovascularization. Intravitreous injection of Tert-SiRNA effectively suppressed the expression of Tert mRNA and proteins and inhibited retinal neovascularization, as confirmed by retinal flat angiography and vessel counting.

CONCLUSIONS

The expression of Tert was up-regulated during the development of oxygen-induced retinal neovascularization. Inhibiting Tert expression with SiRNA is effective in suppressing retinal neovascularization, suggesting that telomerase may be a potential therapeutic target for treating proliferative retinopathy.

19-peptide, a fragment of tumstatin, inhibits the growth of poorly differentiated gastric carcinoma cells in vitro and in vivo

BACKGROUND AND AIM

This study investigated whether 19-peptide, a fragment of tumstatin, inhibited the growth of gastric tumor cells in vitro and in vivo.

METHODS

19-peptide was expressed in bacteria and purified with Sephadex G-15. SGC7901 gastric carcinoma cells and human umbilical-vein endothelial cells (HUVECs) were exposed to 19-peptide in vitro, and their viability was evaluated by biochemical and histopathological analysis. In vivo, pieces of solid tumor derived from SGC7901 cells were inoculated into the gastric serosa of 36 nude mice, with a biological glue to hold them in place. Twenty-eight days after injection of 19-peptide, the mice were killed. The tumors were measured and examined by western blotting, histopathology, and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assay.

RESULTS

19-peptide induced apoptosis of many SGC7901 cells but few HUVECs in vitro. In vivo, after the application of 19-peptide, significant tumor cell apoptosis was observed in the center of the tumors, tumor volume was reduced significantly (P < 0.001), and the invasion and migration of cancer cells was reduced. PTEN was increased in the treatment group and phospho-Akt (pAkt) was decreased in the control group.

CONCLUSIONS

These results suggest that 19-peptide inhibits the growth and metastases of poorly differentiated gastric carcinoma cells, primarily by inducing apoptosis. The apoptotic mechanism could be related to anoikis and the PTEN/Akt pathway.

Tumor angiogenesis: insights and innovations

Angiogenesis is a vital process resulting in the formation of new blood vessels. It is normally a highly regulated process that occurs during human development, reproduction, and wound repair. However, angiogenesis can also become a fundamental pathogenic process found in cancer and several other diseases. To date, the inhibition of angiogenesis has been researched at both the bench and the bedside. While several studies have found moderate improvements when treating with angiogenesis inhibitors, greater success is being seen when the inhibition of angiogenesis is combined with other traditional forms of available therapy. This review summarizes several important angiogenic factors, examines new research and ongoing clinical trials for such factors, and attempts to explain how this new knowledge may be applied in the fight against cancer and other angiogenic-related diseases.

Angiostatic effects of K252a, a Trk inhibitor, in murine brain capillary endothelial cells

Nerve growth factor (NGF) supports the survival and differentiation of sympathetic and sensory neurons and is also mitogenic for a variety of tumors. K252a, an antagonist of NGF receptor TrkA, was previously used as a pharmacological tool to study NGF actions and as a lead compound for developing anti-tumor drugs. Since recently, NGF was characterized as an angiogenic factor, we sought to investigate the angiostatic properties of K252a on endothelial cells (ECs). For this purpose, we used a murine brain microcapillary ECs model in which we found autocrine release of NGF in the culture medium and activation of TrkA receptor-induced downstream signaling molecules Erk1/2, Akt, and PLCgamma. In this model, we demonstrated the angiostatic property of K252a based on its ability to affect several important angiogenic steps. K252a, but not its cell membrane impermeable analogue K252b at 100 nM: (i) inhibited the proliferation of the ECs by 45 +/- 9%; (ii) reduced by 70 +/- 4% the migration of the ECs measured in a wound-closure model; (iii) reduced by 29 +/- 9% the formation of tube-like structures of the ECs cultured on Matrigel; (iv) stimulated by 100 +/- 25% the collagen deposition by the ECs, a process responsible for the increased endothelial barrier functions expressed by 22 +/- 5% reduction of paracellular permeability and by 17 +/- 3% elevation of transendothelial electrical resistance. These data suggest that NGF/TrkA may represent a target for the development of novel, K252a-derived multikinase inhibitors drugs with anti-tumor and angiostatic dual activities.

The YSNSG cyclopeptide derived from tumstatin inhibits tumor angiogenesis by down-regulating endothelial cell migration

We previously demonstrated that the CNYYSNS peptide derived from tumstatin inhibited in vivo tumor progression. The YSNS motif formed a beta-turn crucial for biological activity. More recently, a YSNSG cyclopeptide with a constrained beta-turn on the YSNS residues was designed. Intraperitoneal administration of the YSNSG cyclopeptide inhibited in vivo melanoma progression more efficiently than the native linear peptide. In the present article, we showed that the YSNSG cyclopeptide also triggered an inhibition of in vivo tumor neovascularization and we further analyzed its in vitroantiangiogenic effect. The YSNSG cyclopeptide did not alter endothelial cell proliferation but inhibited cell migration by 83% in an in vitro wound healing model. The inhibition was mediated by a decrease in active MT1-MMP at the migration front as well as a decrease in u-PA and u-PAR expression. The cyclopeptide also altered beta1-integrin distribution in endothelial cell lamellipodia, induced a strong decrease in the phosphorylated focal adhesion kinase (p125(FAK)), disorganized F-actin stress fibers and decreased the number of lamellipodia, resulting in a non migratory phenotype. Our results confirm the YSNSG cyclopeptide as a potent antitumor agent, through both the inhibition of invasive properties of tumor cells and the antiangiogenic activity.

Discrepancies between antiangiogenic and antitumor effects of recombinant human endostatin

It has been widely accepted that antiangiogenesis therapy could deprive tumor cells of nutrients and oxygen and suppress tumor growth. However, in the present study, Lewis lung carcinomas and A549 adenocarcinomas established in male C57BL/6 and BALB/c nude mice, respectively, were treated with recombinant human endostatin (rh-endostatin). Earlier studies document discrepancies in the antiangiogenic and antitumor outcomes of rh-endostatin treatment, at doses equivalent to clinical usage. Although there was no significant regression of tumor growth, tumor vasculature was widely disrupted within the first few days of treatment with rh-endostatin, as indicated by reduced blood perfusion (visualized by dynamic-contrast-enhanced magnetic resonance imaging) and reduced microvascular density. Interestingly, when rh-endostatin treatment was discontinued, there was an elevation in the diffusion of oxygen and tetramethylrhodamine isothiocyanate-dextran in both tumor classes, which was detected by hypoxyprobe (pimonidazole) and fluorescence microscopy. We conclude that the paradoxic outcomes in the antiangiogenic and antitumor properties of rh-endostatin might derive from the tumors' tolerance to antiangiogenesis inhibitors. Additionally, rh-endostatin might have the ability to transiently normalize tumor vasculature.

Polyploidy impairs human aortic endothelial cell function and is prevented by nicotinamide phosphoribosyltransferase

Polyploid endothelial cells are found in aged and atherosclerotic arteries. However, whether increased chromosome content has an impact on endothelial cell function is unknown. We show here that human aortic endothelial cells become tetraploid as they approach replicative senescence. Furthermore, accumulation of tetraploid endothelial cells was accelerated during growth in high glucose. Interestingly, induction of polyploidy was completely prevented by modest overexpression of the NAD+ regenerating enzyme, nicotinamide phosphoribosyltransferase (Nampt). To determine the impact of polyploidy on endothelial cell function, independent of replicative senescence, we induced tetraploidy using the spindle poison, nocodazole. Global gene expression analyses of tetraploid endothelial cells revealed a dysfunctional phenotype characterized by a cell cycle arrest profile (decreased CCNE2/A2, RBL1, BUB1B; increased CDKN1A) and increased expression of genes involved in inflammation (IL32, TNFRSF21/10C, PTGS1) and extracellular matrix remodeling (COL5A1, FN1, MMP10/14). The protection from polyploidy conferred by Nampt was not associated with enhanced poly(ADP-ribose) polymerase-1 or sirtuin (SIRT) 2 activity, but with increased SIRT1 activity, which reduced cellular reactive oxygen species and the associated oxidative stress stimulus for the induction of polyploidy. We conclude that human aortic endothelial cells are prone to chromosome duplication that, in and of itself, can induce characteristics of endothelial dysfunction. Moreover, the emergence of polyploid endothelial cells during replicative aging and glucose overload can be prevented by optimizing the Nampt-SIRT1 axis.

Proteomic characterization of HIV-modulated membrane receptors, kinases and signaling proteins involved in novel angiogenic pathways

Background

Kaposi's sarcoma (KS), hemangioma, and other angioproliferative diseases are highly prevalent in HIV-infected individuals. While KS is etiologically linked to the human herpesvirus-8 (HHV8) infection, HIV-patients without HHV-8 and those infected with unrelated viruses also develop angiopathies. Further, HIV-Tat can activate protein-tyrosine-kinase (PTK-activity) of the vascular endothelial growth factor receptor involved in stimulating angiogenic processes. However, Tat by itself or HHV8-genes alone cannot induce angiogenesis in vivo unless specific proteins/enzymes are produced synchronously by different cell-types. We therefore tested a hypothesis that chronic HIV-replication in non-endothelial cells may produce novel factors that provoke angiogenic pathways.

Methods

Genome-wide proteins from HIV-infected and uninfected T-lymphocytes were tested by subtractive proteomics analyses at various stages of virus and cell growth in vitro over a period of two years. Several thousand differentially regulated proteins were identified by mass spectrometry (MS) and >200 proteins were confirmed in multiple gels. Each protein was scrutinized extensively by protein-interaction-pathways, bioinformatics, and statistical analyses.

Results

By functional categorization, 31 proteins were identified to be associated with various signaling events involved in angiogenesis. 88% proteins were located in the plasma membrane or extracellular matrix and >90% were found to be essential for regeneration, neovascularization and angiogenic processes during embryonic development.

Conclusion

Chronic HIV-infection of T-cells produces membrane receptor-PTKs, serine-threonine kinases, growth factors, adhesion molecules and many diffusible signaling proteins that have not been previously reported in HIV-infected cells. Each protein has been associated with endothelial cell-growth, morphogenesis, sprouting, microvessel-formation and other biological processes involved in angiogenesis (p = 10^-4 to 10^-12). Bioinformatics analyses suggest that overproduction of PTKs and other kinases in HIV-infected cells has suppressed VEGF/VEGFR-PTK expression and promoted VEGFR-independent pathways. This unique mechanism is similar to that observed in neovascularization and angiogenesis during embryogenesis. Validation of clinically relevant proteins by gene-silencing and translational studies in vivo would identify specific targets that can be used for early diagnosis of angiogenic disorders and future development of inhibitors of angiopathies. This is the first comprehensive study to demonstrate that HIV-infection alone, without any co-infection or treatment, can induce numerous "embryonic" proteins and kinases capable of generating novel VEGF-independent angiogenic pathways.

NF-kappaB activation in endothelial cells is critical for the activity of angiostatic agents

In tumor cells, the transcription factor NF-kappaB has been described to be antiapoptotic and proproliferative and involved in the production of angiogenic factors such as vascular endothelial growth factor. From these data, a protumorigenic role of NF-kappaB has emerged. Here, we examined in endothelial cells whether NF-kappaB signaling pathway is involved in mediating the angiostatic properties of angiogenesis inhibitors. The current report describes that biochemically unrelated agents with direct angiostatic effect induced NF-kappaB activation in endothelial cells. Our data showed that endostatin, anginex, angiostatin, and the 16-kDa N-terminal fragment of human prolactin induced NF-kappaB activation in endothelial cells in both cultured human endothelial cells and in vivo in a mouse tumor model. It was also found that NF-kappaB activity was required for the angiostatic activity, because inhibition of NF-kappaB in endothelial cells impaired the ability of angiostatic agents to block sprouting of endothelial cells and to overcome endothelial cell anergy. Therefore, activation of NF-kappaB in endothelial cells can result in an unexpected antitumor outcome. Based on these data, the current approach of systemic treatment with NF-kappaB inhibitors may therefore be revisited because NF-kappaB activation specifically targeted to endothelial cells might represent an efficient strategy for the treatment of cancer.

Drug resistance associated with antiangiogenesis therapy

Neovascularization is one of the hallmarks associated with tumor growth. In the recent years, a number of angiogenesis inhibitors have been approved for clinical use in cancer patients. However, the efficacy of antiangiogenic therapy is in most cases short-lasting, with likely drug resistance developing within a few months. It is becoming clear also that there are a subset of malignant tumors that are inherently resistant to angiogenesis inhibition. The knowledge regarding resistance mechanisms towards angiogenesis inhibitors is still evolving and here we propose some theories and in some cases provide experimental evidence.

Oligomeric procyanidins inhibit cell migration and modulate the expression of migration and proliferation associated genes in human umbilical vascular endothelial cells

The consumption of flavan-3-ols has been associated with reduced risk of cardiovascular diseases and improvements in vascular function. However, the nature of the flavan-3-ols responsible and the mechanisms underlying the vascular responses are not fully understood. We used microarrays to search for molecular changes in response to the exposure to (-)-epicatechin (EC), procyanidin dimer B2, and a mixture of oligomeric procyanidins in human umbilical vein endothelial cells (HUVECs). No gene expression changes were detected in HUVECs exposed to EC or dimer B2, however, the oligomeric procyanidins induced significant gene expression changes in both resting and TNF-alpha-stimulated cells. In particular, the expression of genes such as ADAMTS1, THBS1, ANGPT2, CYR61, ET-1, EDG3, and PDE4B involved in endothelial cell migration and proliferation, were substantially over-represented. Also, exposure to the oligomers arrested the cells at the G(0)/G(1 )phase and inhibited cell migration. These data show that human endothelial cells respond to oligomeric procyanidins by exhibiting a less migratory phenotype and by a general modulation of the expression of genes that are associated with key events in the angiogenic process. The molecular changes associated with procyanidin treatment identified in this study are consistent with the beneficial effects of flavan-3-ols on vascular function.

Antiangiogenic effect of capecitabine combined with ginsenoside Rg3 on breast cancer in mice

Capecitabine is a novel fluoropyrimidine carbamate, which has a broader spectrum of antitumor activity than other fluoropyrimidines, such as 5-FU, DFUR, or UFT; it has proved effective over a wide dose range. Recent research has suggested that frequent administration of lower doses of certain chemotherapeutic drugs might enhance their antiangiogenic effect. The present study investigated the antiangiogenic effect of capecitabine on breast cancer. In order to augment its efficacy, we combined capecitabine chemotherapy with ginsenoside Rg3. Our results indicate that a metronomic regimen of capecitabine inhibited angiogenesis in breast cancer, and its antiangiogenic effects may be further enhanced by the concurrent administration of ginsenoside Rg3. As an antiangiogenic method, this regimen presented better antitumor effects, less toxicity, and reduced susceptibility to drug resistance.

Tumor vasculature and microenvironment normalization: a possible mechanism of antiangiogenesis therapy

Tumor antiangiogenesis therapy has been in application for more than 30 years; however, its mechanism remains obscure. An intriguing hypothesis, which has recently gained acceptance, explores the possibility that antiangiogenesis therapy may transiently normalize tumor vasculature and its microenvironment, thus enhancing chemoradiotherapy efficacy. As the equilibrium between proangiogenesis and antiangiogenesis factors is perturbed in the tumor and tips to the former, tumor vasculature tends to exhibit abnormal structure and function. Abnormal vasculature is tightly associated with an uncharacteristic microenvironment, including uneven perfusion, hypoxia, and increased interstitial fluid pressure: This malignant microenvironment hinders the delivery of chemotherapeutics to tumor cells and desensitizes the malignant cells to radiation. Antiangiogenesis therapy can reverse the imbalance and transiently normalize this microenvironment and gives a new perspective for combining antiangiogenesis therapy and traditional chemoradiotherapy.

Role of non-neuronal nicotinic acetylcholine receptors in angiogenesis

Angiogenesis is a critical physiological process for cell survival and development. Endothelial cells, necessary for the course of angiogenesis, express several non-neuronal nicotinic acetylcholine receptors (AChRs). The most important functional non-neuronal AChRs are homomeric alpha7 AChRs and several heteromeric AChRs formed by a combination of alpha3, alpha5, beta2, and beta4 subunits, including alpha3beta4-containing AChRs. In endothelial cells, alpha7 AChR stimulation indirectly triggers the activation of the integrin alphavbeta3 receptor and an intracellular MAP kinase (ERK) pathway that mediates angiogenesis. Non-selective cholinergic agonists such as nicotine have been shown to induce angiogenesis, enhancing tumor progression. Moreover, alpha7 AChR selective antagonists such as alpha-bungarotoxin and methyllycaconitine as well as the non-specific antagonist mecamylamine have been shown to inhibit endothelial cell proliferation and ultimately blood vessel formation. Exploitation of such pharmacologic properties can lead to the discovery of new specific cholinergic antagonists as anti-cancer therapies. Conversely, the pro-angiogenic effect elicited by specific agonists can be used to treat diseases that respond to revascularization such as diabetic ischemia and atherosclerosis, as well as to accelerate wound healing. In this mini-review we discuss the pharmacological evidence supporting the importance of non-neuronal AChRs in angiogenesis. We also explore potential intracellular mechanisms by which alpha7 AChR activation mediates this vital cellular process.

Antiangiogenic drugs: current knowledge and new approaches to cancer therapy

Angiogenesis--process of new blood-vessel growth from existing vasculature--is an integral part of both normal developmental processes and numerous pathologies such as cancer, ischemic diseases and chronic inflammation. Angiogenesis plays a crucial role facilitating tumour growth and the metastatic process, and it is the result of a dynamic balance between proangiogenic and antiangiogenic factors. The potential to block tumour growth and metastases by angiogenesis inhibition represents an intriguing approach to the cancer treatment. Angiogenesis continues to be a topic of major scientific interest; and there are currently more antiangiogenic drugs in cancer clinical trials than those that fit into any other mechanistic category. Based on preclinical studies, researchers believe that targeting the blood vessels which support tumour growth could help treatment of a broad range of cancers. Angiogenic factors or their receptors, endothelial cell proliferation, matrix metalloproteinases or endothelial cell adhesion, are the main targets of an increasing number of clinical trials approved to test the tolerance and therapeutic efficacy of antiangiogenic agents. Unfortunately, contrary to initial expectations, it has been described that antiangiogenic treatment can cause different toxicities in cancer patients. The purpose of this article is to provide an overview of current attempts to inhibit tumour angiogenesis for cancer therapy.

The hemopexin domain of MMP-9 inhibits angiogenesis and retards the growth of intracranial glioblastoma xenograft in nude mice

Matrix Metalloproteinase-9 (MMP-9) consists of a prodomain, catalytic domain with 3 fibronectin-like type II modules and C-terminal hemopexin-like (PEX) domain. These domains play distinct roles in terms of proteolytic activity, substrate binding and interaction with inhibitors and receptors. To assess the potential of the MMP-9-PEX domain to interfere with tumor progression, we stably transfected human glioblastoma cells with an expression vector containing a cDNA sequence of the MMP-9-PEX. The selected clones exhibited decreased MMP-9 activity and reduced invasive capacity. We assessed how secretion of MMP-9-PEX by glioblastoma cells affects angiogenic capabilities of human microvascular endothelial cells (HMECs) in vitro. MMP-9-PEX conditioned medium treatment caused a reduction in migration of HMECs and inhibited capillary-like structure formation in association with suppression of vascular endothelial growth factor (VEGF) secretion and VEGF receptor-2 protein level. The suppression of HMECs survival by conditioned medium from MMP-9-PEX stable transfectants was associated with apoptosis induction characterized by an increase in cells with a sub-G0/G1 content, fragmentation of DNA, caspase-3, -8 and -9 activation and poly (ADP-ribose) polymerase (PARP) cleavage. A significant tumor growth inhibition was observed in intracranial implants of MMP-9-PEX stable transfectants in nude mice with attenuation of CD31 and MMP-9 protein expression. These results demonstrate that MMP-9-PEX inhibits angiogenic features of endothelial cells and retards intracranial glioblastoma growth.