Comparison of anti‐inflammatory activities of ruscogenin,a major steroidal sapogenin from Radix Ophiopogon japonicus,and Its succinylated derivative,RUS‐2HS

Ruscogenin (RUS), first isolated from Ruscus aculeatus, is also a major steroidal sapogenin of the traditional Chinese herb Radix Ophiopogon japonicus. It has robust anti‐inflammatory activities. In previous studies, a ruscogenin affinity column, derived from succinylated ruscogenin (RUS‐2HS), was used to purify an antibody of ruscogenin. A ruscogenin affinity column can also be used to explore its protein targets. However, until now there have been no related pharmacological reports about ruscogenin derivatives. Whether the activity groups of ruscogenin have been blocked during the derivation process remains unknown. The present study was performed to compare the anti‐inflammatory activities in vitro of RUS‐2HS and ruscogenin. Both compounds reduced tumor necrosis factor‐α (TNF‐α)‐induced adhesion of human pro‐myelocytic leukemia cells (HL‐60) to endothelial ECV304 cells with IC₅₀ values of 6.90 nM and 7.45 nM, respectively. They were also inhibited overexpression of ICAM‐1 in ECV304 cells at the mRNA level as evaluated by real‐time PCR and at the protein level evaluated by flow cytometry with similar potency. Such data demonstrate that the functional groups of ruscogenin were not blocked by derivation, suggesting further use of the ruscogenin affinity column for target investigation. Meanwhile, RUS‐2HS was found to have remarkable anti‐inflammatory activity for the first time, indicating it would be a new lead compound with improved bioavailability. Drug Dev Res 69: 196–202, 2008. © 2008 Wiley‐Liss, Inc.     

Insulin-like growth factor binding protein-7 (IGFBP7) blocks vascular endothelial cell growth factor (VEGF)-induced angiogenesis in human vascular endothelial cells

Insulin-like growth factor binding protein-7 (IGFBP7) and vascular endothelial growth factor (VEGF) are expressed in vascular endothelial cells in several tumor types. In this study, we examined the effect of IGFBP7 on VEGF-induced tube formation in cultured human umbilical vein endothelial cells (HUVECs) and its potential action in the modulation of VEGF signaling in vascular cells. IGFBP7 treatment suppressed VEGF-induced tube formation, proliferation, and the phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) 1/2 in HUVECs. IGFBP7 attenuated VEGF-enhanced cyclooxygenase (COX)-2 and VEGF mRNA expression, and prostaglandin E₂ secretion. Knocking down endogenous IGFBP7 enhanced COX-2 and VEGF mRNA expression. A significant increase in IGFBP7-induced caspases was not observed in the presence of VEGF. These findings indicate that IGFBP7 can modulate the stimulatory effect of VEGF on angiogenesis by interfering with VEGF expression as well as VEGF signaling and not by inducing apoptosis.     

In vivoand in vitrostructure and relationship analysis of andrographolide derivatives:Identifying AGL-2 as a novel anti-angiogenesis agent

OBJECTIVE To analyse structure and relationship of several andrographolide derivatives in multiple in vivo and in vitro angiogenesis assays,and to demonstrate a novel compound named AGL-2as a potential anti-angiogenesis agent.METHODS Human umbilical vein endothelial cells(HUVECs)in vitro and zebrafish(Danio rerio)in vivo models were used to screen and identify the anti-angiogenesis activities of six andrographolide derivatives;namely,AGL-1,AGL-2,AGS-72,AGS-72 a,AGS-79 and AGP-151.RESULTS AGL-2exhibited the strongest anti-angiogenic activity among all the derivatives in zebrafish model.Interestingly,another compound named AGS-72 showed stronger anti-angiogenic activity than AGL-2 in VEGF-induced HUVECs proliferation,migration,invasion and tube formation assays.In addition,AGL-2 was found to suppress the VEGF-induced VEGFR-2auto-phosphorylation and inhibit the activity of VEGFR-2 mediated signaling cascades in a dose-dependent manner.CONCLUSION AGL-2was demonstrated to be a promising anti-angiogenic agent among all the tested derivatives.The mechanism underlying the anti-angiogenic activity of AGL-2 probably involve VEGFR-2 signaling pathway.Even though,how some of chemical structure alterations result in discrepancy between in vivo and in vitro activities still remains to be resolved,this study shall provide new insight into how modification of the chemical structure of andrographolide affects this newly identified anti-angiogenesis activity.Meanwhile,AGL-2 can be exploited as a potential therapeutic agent for the treatment of angiogenesis-related diseases.     

Nickel‐induced VEGF expression via regulation of Akt,ERK1/2, NFκB,and AMPK pathways in H460 cells

Prospective cohort studies have indicated that a highly nickel‐polluted environment may severely affect human health, resulting in such conditions as respiratory tract cancers. Such exposure can trigger vascular endothelial growth factor (VEGF) expression. However, the signal transduction pathways leading to VEGF induction by nickel compounds are not well understood. This study revealed the occurrence of VEGF induction in human non‐small‐cell lung cancer H460 cells exposed to NiCl₂. Moreover, exposing H460 cells to NiCl₂ activated extracellular signal‐regulated protein kinase (ERK), nuclear factor kappa B (NFκB), and protein kinase B (Akt) as well as downregulated AMP activated protein kinase (AMPK) expression. The mitogen‐activated protein kinase (MAPK) and ERK inhibitor significantly blocked NiCl₂‐induced ERK activation and VEGF production. Pretreating H460 cells with a PI3K/Akt inhibitor substantially inhibited NiCl₂‐induced VEGF expression and reduced Akt, ERK, and NFκB phosphorylation. Furthermore, 5‐aminoimidazole‐4‐carboxamide ribonucleoside‐induced AMPK activation improved VEGF expression in NiCl₂‐treated H460 cells significantly. These results indicate that NiCl₂ induces VEGF production through Akt, ERK, NFκB activation and AMPK suppression and mediates various types of pathophysiological angiogenesis.     

The chorioallantoic membrane: A novel approach to extrapolate data from a well-established method

The chorioallantoic membrane (CAM) of the chicken embryo is a highly vascularized extra-embryonic structure that has been widely used as an in vivo model for the evaluation of angiogenesis. This study was designed to optimize data extrapolation from the most exploited experimental protocol to improve its efficiency and the reliability of the obtainable results. In our study, we followed the most common procedure for CAM assay, employing retinoic acid and vascular endothelial growth factor as standards. CAMs were photographed at t₀, t₂₄, and t₄₈; then, the main parameters of the predefined vascular network/area were evaluated. Subsequently, their variations in each CAM were calculated comparing them within the same CAM over the course of the whole treatment (t₂₄ and t₄₈), also comparing the treated CAMs respect to the untreated ones. Thus, we provide a novel approach aimed at extrapolating data from CAM assay that allows to (i) have a greater reliability and richness of data; (ii) better estimate the potential pro- and anti-angiogenic activity of new candidate drugs; (iii) save both eggs and time for the experiments.     

In vitro and in vivo evaluation of the anti-angiogenic actions of 4-hydroxybenzyl alcohol

BACKGROUND AND PURPOSE

4-Hydroxybenzyl alcohol (HBA) is a phenolic plant compound, which has been shown to influence many cellular mechanisms. In the present study, we analysed in vitro and in vivo the anti-angiogenic actions of this pleiotropic agent.

EXPERIMENTAL APPROACH

Migration and protein expression of HBA- and vehicle-treated endothelial-like eEND2 cells was assessed by cell migration assay and Western blot analyses. HBA action on vascular sprouting was analysed in an aortic ring assay. In vivo anti-angiogenic actions of HBA were studied in the dorsal skinfold chamber model of endometriosis in mice.

KEY RESULTS

Western blot analyses demonstrated that HBA inhibited proliferation of eEND2 cells, as indicated by down-regulation of proliferating cell nuclear antigen expression, and reduced expression of vascular endothelial growth factor and matrix metalloproteinase 9. HBA suppressed the migration of eEND2 cells, accompanied by inhibition of actin filament reorganization, revealed by fluorescence staining of the cytoskeleton. In addition, HBA reduced vascular sprouting in the aortic ring assay. Finally, we found, in the dorsal skinfold chamber model in vivo using intravital fluorescence microscopy, that HBA inhibited the vascularization of developing endometriotic lesions, as indicated by a decreased functional capillary density of lesions in HBA-treated mice and a reduced lesion size, compared with control animals.

CONCLUSIONS AND IMPLICATIONS

HBA targets several angiogenic mechanisms and therefore represents a promising anti-angiogenic agent for the treatment of angiogenic diseases, such as endometriosis.     

Anti-Angiogenic Activity of Selected Receptor Tyrosine Kinase Inhibitors, PD166285 and PD173074: Implications for Combination Treatment with Photodynamic Therapy

Angiogenesis, the formation of new blood vessels from an existing vasculature, is requisite for tumor growth. It entails intercellular coordination of endothelial and tumor cells through angiogenic growth factor signaling. Interruption of these events has implications in the suppression of tumor growth. PD166285, a broad-spectrum receptor tyrosine kinase (RTK) inhibitor, and PD173074, a selective FGFR₁TK inhibitor, were evaluated for their anti-angiogenic activity and anti-tumor efficacy in combination with photodynamic therapy (PDT). To evaluate the anti-angiogenic and anti-tumor activities of these compounds, RTK assays, in vitro tumor cell growth and microcapillary formation assays, in vivo murine angiogenesis and anti-tumor efficacy studies utilizing RTK inhibitors in combination with photodynamic therapy were performed. PD166285 inhibited PDGFR--, EGFR-, and FGFR₁TKs and c-src TK by 50% (IC₅₀) at concentrations between 7–85nM. PD173074 displayed selective inhibitory activity towards FGFR₁TK at 26nM. PD173074 demonstrated (>100 fold) selective growth inhibitory action towards human umbilical vein endothelial cells compared with a panel of tumor cell lines. Both PD166285 and PD173074 (at 10nM) inhibited the formation of microcapillaries on Matrigel-coated plastic. In vivo anti-angiogenesis studies in mice revealed that oral administration (p.o.) of either PD166285 (1–25 mg/kg) or PD173074 (25–100 mg/kg) generated dose dependent inhibition of angiogenesis. Against a murine mammary 16c tumor, significantly prolonged tumor regressions were achieved with daily p.o. doses of PD166285 (5–10 mg/kg) or PD173074 (30–60 mg/kg) following PDT compared with PDT alone (p<0.001). Many long-term survivors were also noted in combination treatment groups. PD166285 and PD173074 displayed potent anti-angiogenic and anti-tumor activity and prolonged the duration of anti-tumor response to PDT. Interference in membrane signal transduction by inhibitors of specific RTKs (e.g. FGFR₁TK) should result in new chemotherapeutic agents having the ability to limit tumor angiogenesis and regrowth following cytoreductive treatments such as PDT.     

Galbanic Acid Isolated from Ferula assafoetida Exerts In Vivo Anti-tumor Activity in Association with Anti-angiogenesis and Anti-proliferation

Purpose

To investigate whether galbanic acid (GBA) exerts anti-angiogenic and anti-cancer activities.

Methods

Using human umbilical vein endothelial cell (HUVEC) model, we analyzed effects of GBA on cellular and molecular events related to angiogenesis. We tested its direct anti-proliferative action on mouse Lewis lung cancer (LLC) cells and established its in vivo anti-angiogenic and anti-tumor efficacy using LLC model.

Results

GBA significantly decreased vascular endothelial growth factor (VEGF)-induced proliferation and inhibited VEGF-induced migration and tube formation of HUVECs. These effects were accompanied by decreased phosphorylation of p38-mitogen-activated protein kinase (MAPK), c-jun N-terminal kinase (JNK), and AKT, and decreased expression of VEGFR targets endothelial nitric oxide synthase (eNOS) and cyclin D1 in VEGF-treated HUVECs. GBA also decreased LLC proliferation with an apparent G2/M arrest, but did not induce apoptosis. In vivo, inclusion of GBA in Matrigel plugs reduced VEGF-induced angiogenesis in mice. Galbanic acid given by daily i.p. injection (1 mg/kg) inhibited LLC-induced angiogenesis in an intradermal inoculation model and inhibited the growth of s.c. inoculated LLC allograft in syngenic mice. Immunohistochemistry revealed decreased CD34 microvessel density index and Ki-67 proliferative index in GBA-treated tumors.

Conclusions

GBA exerts anti-cancer activity in association with anti-angiogenic and anti-proliferative actions.     

Roflumilast inhibits leukocyte-endothelial cell interactions, expression of adhesion molecules and microvascular permeability

BACKGROUND AND PURPOSE: The present study addressed the effects of the investigational PDE4 inhibitor roflumilast on leukocyte-endothelial cell interactions and endothelial permeability in vivo and in vitro. EXPERIMENTAL APPROACH: In vivo, intravital video-microscopy was used to determine effects of roflumilast p.o. on leukocyte-endothelial cell interactions and microvascular permeability in rat mesenteric venules. In vitro, the effects of roflumilast N-oxide, the active metabolite of roflumilast in humans, and other PDE4 inhibitors on neutrophil adhesion to tumour necrosis factor alpha (TNFalpha)-activated human umbilical vein endothelial cells (HUVEC), E-selectin expression and thrombin-induced endothelial permeability was evaluated. Flow cytometry was used to determine the effect of roflumilast on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced CD11b upregulation on human neutrophils. KEY RESULTS: In vivo, roflumilast, given 1 h before lipopolysaccharide (LPS), dose-dependently reduced leukocyte-endothelial cell interactions in rat mesenteric postcapillary venules. It also diminished histamine-induced microvascular permeability. Immunohistochemical analyses revealed that roflumilast prevented LPS-induced endothelial P- and E-selectin expression. In vitro, roflumilast N-oxide concentration-dependently suppressed neutrophil adhesion to TNFalpha-activated HUVEC and CD11b expression on fMLP-stimulated neutrophils. It also reduced TNFalpha-induced E-selectin expression on HUVEC, when PDE3 activity was blocked. HUVEC permeability elicited by thrombin was concentration-dependently suppressed by roflumilast N-oxide. While roflumilast N-oxide was as potent as roflumilast at inhibiting stimulated endothelial cell and neutrophil functions, both compounds were significantly more potent than the structurally unrelated PDE4 inhibitors, rolipram or cilomilast. CONCLUSIONS AND IMPLICATIONS: These findings further support earlier observations on the inhibition of inflammatory cell influx and protein extravasation by roflumilast in vivo.     

Pseudolarix acid B inhibits angiogenesis by antagonizing the vascular endothelial growth factor-mediated anti-apoptotic effect

Angiogenesis is controlled by a number of growth factors, including vascular endothelial growth factor (VEGF). In this study, pseudolarix acid B, isolated from the traditional Chinese medicinal plant Pseudolarix kaempferi and originally identified as an early pregnancy-terminating agent, was evaluated for its potential as an angiogenesis inhibitor, using in vitro and in vivo models. After exposure to pseudolarix acid B 0.625-5 microM for 72 h, the proliferation of human umbilical vein endothelial cells was significantly inhibited. Pseudolarix acid B 0.313-2.5 microM for 24 h potently blocked the VEGF-induced tube formation of human umbilical vein endothelial cells in a dose-dependent manner. Matrigel plug assays disclosed that pseudolarix acid B reduced angiogenesis induced by VEGF in vivo. In addition, pseudolarix acid B antagonized VEGF-mediated anti-apoptotic effects on serum-deprived human umbilical vein endothelial cells and increased apoptosis of endothelial cells induced by VEGF in Matrigel plug assays. Moreover, pseudolarix acid B significantly inhibited VEGF-induced tyrosine phosphorylation of kinase insert domain-containing receptor/fetal liver kinase-1 (KDR/flk-1), in correlation with a marked decrease in the phosphorylation of Akt and extracellular signal-regulated kinases (ERK). These findings collectively suggest that pseudolarix acid B possesses anti-angiogenic activity. One of the main anti-angiogenesis mechanisms of pseudolarix acid B may involve antagonism of the VEGF-mediated anti-apoptosis effect via inhibition of KDR/flk-1, ERK1/2, and Akt phosphorylation in endothelial cells.     

In vitro inhibition of angiogenesis by hydroalcoholic extract of oak (Quercus infectoria) acorn shell via suppressing VEGF,MMP-2, and MMP-9 secretion

Context: Angiogenesis is an essential factor for cancer progression. Although more attention is paid in angiogenesis on its role in cancer biology, many other non-neoplastic diseases are also angiogenic-dependent. Recently, there is motivation to control cancer via inhibition of angiogenesis.

Objective: Quercus infectoria Olivier var (Fagaceae) (oak) is a plant whose different parts, such as its fruit shell, have been used extensively as a traditional drug in the west part of Iran. Although some biological properties of oak are determined, its effects on angiogenesis are unclear. So, we investigated the antiangiogenic effects of oak acorn shell.

Materials and methods: Fresh oak acorns were collected, and after authentication; hydroalcoholic extract of acorn shells (5, 10, 20, 30, 40, 60, 80, and 100 μg/ml) was used for evaluation of its cytotoxicity, antiproliferative, and antiangiogenic effects in vitro. Also, effects of the extract on vascular endothelial growth factor (VEGF), matrix metalloproteinase-2 (MMP-2) and MMP-9 secretion were assayed using enzyme-linked immunosorbent assay (ELISA) and gelatin zymography. Results: Treatment with hydroalcoholic extract in eight doses resulted in a significant decrease of endothelial cell proliferation and angiogenesis with an IC₅₀ value of ~20 μg/ml, without any toxic effect. At 40 μg/ml, the extract inhibited MMP-9 activity; however, a dose-dependent reduction (60–80 µg/ml) in MMP-2 activity was seen. VEGF secretion was decreased with increase in the concentration of the extract from 5 to 100 μg/ml.

Discussion and conclusion: This study indicated that hydroalcoholic extract of oak acorn shell acts as a potent antiangiogenic agent which exerts its inhibitory effect mainly through downregulation of essential mediators such as VEGF and MMPs.     

A superoxide anion-scavenger, 1,3-selenazolidin-4-one suppresses serum deprivation-induced apoptosis in PC12 cells by activating MAP kinase

Synthetic organic selenium compounds, such as ebselen, may show glutathione peroxidase-like antioxidant activity and have a neurotrophic effect. We synthesized 1,3-selenazolidin-4-ones, new types of synthetic organic selenium compounds (five-member ring compounds), to study their possible applications as antioxidants or neurotrophic-like molecules. Their superoxide radical scavenging effects were assessed using the quantitative, highly sensitive method of real-time kinetic chemiluminescence. At 166 μM, the O₂⁻ scavenging activity of 1,3-selenazolidin-4-ones ranged from 0 to 66.2%. 2-[3-(4-Methoxyphenyl)-4-oxo-1,3-selenazolidin-2-ylidene]malononitrile (compound b) showed the strongest superoxide anion-scavenging activity among the 6 kinds of 2-methylene-1,3-selenazolidin-4-ones examined. Compound b had a 50% inhibitory concentration (IC₅₀) at 92.4 μM and acted as an effective and potentially useful O₂⁻ scavenger in vitro. The effect of compound b on rat pheochromocytome cell line PC12 cells was compared with that of ebselen or nerve growth factor (NGF) by use of the MTT [3-(4, 5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide] assay. When ebselen was added at 100 μM or more, toxicity toward PC12 cells was evident. On the contrary, compound b suppressed serum deprivation-induced apoptosis in PC12 cells more effectively at a concentration of 100 μM. The activity of compound b to phosphorylate mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) 1/2 (MAP kinase) in PC12 cells was higher than that of ebselen, and the former at 100 μM induced the phosphorylation of MAP kinase to a degree similar to that induced by NGF. From these results, we conclude that this superoxide anion-scavenger, compound b, suppressed serum deprivation-induced apoptosis by promoting the phosphorylation of MAP kinase.     

Cordycepin Attenuates Neointimal Formation by Inhibiting Reactive Oxygen Species–Mediated Responses in Vascular Smooth Muscle Cells in Rats

We determined the action mechanism of cordycepin, a major bioactive component of Cordyceps militaris, on responses of rat aortic smooth muscle cells (RASMCs) and on vascular disorders, especially neointimal formation. Cordycepin inhibited platelet-derived growth factor-BB (PDGF-BB)-induced RASMCs migration and proliferation in a dose-dependent manner. However, pre-treatment with N^ω-nitro-L-arginine methyl ester, a nitric oxide synthase (NOS) inhibitor, and 1,3-dipropyl-8-sulphophenylxanthine (DPSPX), an A₁/A₂ adenosine– receptor antagonist, abolished the inhibitory role of cordycepin. Cordycepin suppressed the phosphorylation of p38 mitogen–activated protein kinase (p38 MAPK) and heat shock protein 27 (Hsp27), but not that of extracellular signal-regulated kinase (ERK) 1/2 in RASMCs stimulated by PDGF-BB. The production of reactive oxygen species (ROS), O₂^? and H₂O₂, induced by PDGF-BB was abolished by the treatment of cordycepin. Moreover, the sprout outgrowth of aortic rings by PDGF-BB was inhibited by cordycepin. In vivo neointimal formation evoked by balloon-injury was significantly attenuated by the administration of cordycepin. These results demonstrate that cordycepin may exert inhibitory effects on PDGF-BB–induced migration and proliferation via interfering with adenosine receptor–mediated NOS pathways, thus resulting in the attenuation of neointima formation. In conclusion, cordycepin may be a potent, promising anti-atherosclerosis agent.     

In Vitro Effects of Paralytic Shellfish Toxins and Lytic Extracellular Compounds Produced by Alexandrium Strains on Hemocyte Integrity and Function in Mytilus edulis

Harmful effects caused by the exposure to paralytic shellfish toxins (PSTs) and bioactive extracellular compounds (BECs) on bivalves are frequently difficult to attribute to one or the other compound group. We evaluate and compare the distinct effects of PSTs extracted from Alexandrium catenella (Alex5) cells and extracellular lytic compounds (LCs) produced by A. tamarense (NX-57-08) on Mytilus edulis hemocytes. We used a 4 h dose–response in vitro approach and analyzed how these effects correlate with those observed in a previous in vivo feeding assay. Both bioactive compounds caused moderated cell death (10–15%), being dose-dependent for PST-exposed hemocytes. PSTs stimulated phagocytic activity at low doses, with a moderate incidence in lysosomal damage (30–50%) at all tested doses. LCs caused a dose-dependent impairment of phagocytic activity (up to 80%) and damage to lysosomal membranes (up to 90%). PSTs and LCs suppressed cellular ROS production and scavenged H₂O₂ in in vitro assays. Neither PSTs nor LCs affected the mitochondrial membrane potential in hemocytes. In vitro effects of PST extracts on M. edulis hemocytes were consistent with our previous study on in vivo exposure to PST-producing algae, while for LCs, in vivo and in vitro results were not as consistent.     

Effect of β-escin sodium on endothelial cells proliferation, migration and apoptosis

β-Escin, the major active compound in extracts of the horse chestnut Aesculus hippocastanum seed, has shown clinically significant activity in chronic venous insufficiency (CVI). Our previous studies had shown that β-escin sodium inhibited angiogenesis in chick chorioallantoic membrane (CAM) and in aortic disk assay. In this study, we explored the direct effect of β-escin sodium on proliferation, migration and apoptosis in human umbilical vein endothelial cells (HUVECs) and ECV304 cells. Sulforhodamine B (SRB) assay showed that β-escin sodium (10, 20, 40 μg/ml) inhibited endothelial cells (ECs) proliferation dose-dependently. β-escin sodium also induced ECs apoptosis at 40 μg/ml. Cell migration was evaluated by an improved wound assay: barren spot assay. And the direct effect on cell motility excluding influence of cell proliferation was examined by High Content Screening (HCS, Cellomics) assay. The data indicated that β-escin sodium suppressed ECs migration and cell motility. Western blot results suggested that β-escin sodium acts on ECs possibly by increasing expression of thrombospondin-1 (TSP-1), and decreasing expression of PKC-α and activation of p44/42 mitogen-activated protein kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK). Our findings give the evidence that β-escin sodium might have potential anti-angiogenic activity via its direct effects on ECs.     

Arsenite suppresses angiogenesis of vascular endothelial cells mediated by Platelet Derived Growth Factor Receptor-beta

The present study aimed to investigate the effects of sodium arsenite (NaAsO₂) on the angiogenesis of human umbilical vein endothelial cells (HUVECs) and the mechanism involved. Firstly, a Matrigel-based in vitro angiogenesis assay demonstrated that arsenite suppressed the angiogenesis of HUVECs in a dose-dependent manner. Then by using a global inhibitor for multiple growth factor receptors (E7080) and a specific inhibitor of PDGFR-beta (CP-673451), we found that E7080 completely prevented and CP-673451 significantly decreased the angiogenesis of HUVECs. This suggested that angiogenesis of HUVECs depends on the signal pathway mediated by tyrosine kinase receptors and that among them, PDGFR-beta has an important regulatory function. Finally by using porcine aortic endothelial cells which stably express human PDGFR-beta, we found that arsenite suppressed the angiogenesis mediated by PDGFR-beta. Based on these results, we conclude that arsenite suppressed the angiogenesis of the vascular endothelial cells, that this effect is mediated by PDGFR-beta, and postulate that it might contribute to the injuries of blood vessel in arsenism.     

CD36-TSP-HRGP interactions in the regulation of angiogenesis

Thrombospondin (TSP)-1 and -2 are potent inhibitors of angiogenesis in vivo and of microvascular endothelial cell responses to angiogenic factors in vitro. The anti-angiogenic activity of thrombospondins is contained in a structural domain known as the TSP type I repeat or TSR. TSR domains are present in many other proteins, several of which have also been shown to have anti-angiogenic activity and a peptide-mimetic drug based on the domain is in clinical trials as an anti-angiogenic anti-cancer therapy. We have identified CD36 as the endothelial cell receptor for TSP-1 and -2 and showed that it is necessary for their anti-angiogenic activity. CD36-mediated anti-angiogenic activity in endothelial cells is due to its ability to activate a specific signaling cascade that results in diversion of a pro-angiogenic response to an apoptotic response. Recently we identified a circulating protein, histidine-rich glycoprotein (HRGP), that contains a CD36 homology domain and that acts as a soluble decoy to block the anti-angiogenic activities of TSPs, thereby promoting angiogenesis. The tripartite interactions among CD36, TSR domains and HRGP in tissues may play an important role in regulating physiological and pathological angiogenesis.     

Anti-angiogenic effect of α-mangostin

Eleven known prenyl xanthones, isolated from the pericarp of Garcinia mangostana, were tested for their ability to inhibit the phosphorylation of kinase domain receptor (KDR) tyrosine kinase. α-Mangostin was found to inhibit phosphorylation of KDR. α-Mangostin also showed to inhibit phosphorylation of the Y1175 residue of KDR (10 μM). This is the first report that α-mangostin inhibited the phosphorylation of KDR tyrosine kinase and also the Y1175 residue of KDR. α-Mangostin also showed inhibitory effects on proliferation of human umbilical vein endothelial cells (HUVECs) (IC₅₀ 1.2 μM) and human umbilical artery endothelial cells (IC₅₀ 2.4 μM), as well as the migration (IC₅₀ 0.034 μM) and tubule formation (at the concentrations of 0.6 and 1.2 μM) of HUVECs. These results suggest that the inhibition of the phosphorylation of KDR tyrosine kinase is concerned in the anti-angiogenic activity of α-mangostin.     

Tumour angiogenesis: a novel therapeutic target in patients with malignant disease

Angiogenesis refers to the formation of new blood vessels from an existing vasculature and is recognised as a necessary requirement for most tumours to grow beyond 1-2 mm in diameter. Factors established as playing a role in angiogenesis may be divided into two principal groups: (a) those that stimulate endothelial cell proliferation and/or elongation, migration and vascular morphogenesis including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet derived endothelial cell growth factor (PD-ECGF) and the tie and tek receptors, and (b) proteases and their receptors involved in the breakdown of basement membranes and the extracellular matrix (ECM) including the matrix metalloproteinases (MMPs), cathepsins and those involved in the plasmin cascade. Angiogenesis has been identified as a potential target for development of anticancer agents. The discovery of a range of naturally-occurring factors which negatively regulate angiogenesis, including the thrombospondins, angiostatin and endostatin, and the tissue inhibitors of MMPs (TIMPs), has given added impetus to this approach. Synthetic anti-angiogenic compounds have been developed, including TNP-470, carboxyamidotriazole, VEGF-tyrosine kinase inhibitors and MMP inhibitors (MMPI) which, like the naturally-occurring anti-angiogenic factors, inhibit angiogenesis in vitro and in vivo, and tumour development, growth and metastasis in vivo. Anti-angiogenic agents also enhance the antitumour activity of many conventional cytotoxic chemotherapeutic agents. Such combinations may have a particular role as adjuvant therapies following surgical resection of primary tumours. Unlike tumour cells, tumour associated endothelial cells do not develop resistance to anti-angiogenic agents. Furthermore, anti-angiogenic agents are generally cytostatic rather than cytotoxic. As such, these agents are, in general, likely to be administered over long periods of time. Therefore, as well as having proven antitumour efficacy, an anti-angiogenic compound will need to be well-tolerated if it is to become established in the clinical management of patients with malignant disease.