Endothelial Cell Growth Factor Receptor Research Articles

The CUL3-SPOP-DAXX axis is a novel regulator of VEGFR2 expression in vascular endothelial cells

Vascular endothelial cell growth factor receptor 2 (VEGFR2) is an essential receptor for the homeostasis of endothelial cells. In this study, we showed that NEDD8-conjugated Cullin3 (CUL3)-based ubiquitin E3 (UbE3) ligase plays a crucial role in VEGFR2 mRNA expression. Human umbilical vein endothelial cells treated with MLN4924, an inhibitor of NEDD8-activating enzyme, or with CUL3 siRNA drastically lost their response to VEGF due to the intense decrease in VEGFR2 expression. Moreover, speckle-type POZ protein (SPOP) and death-domain associated protein (DAXX) were involved in the CUL3 UbE3 ligase complex as a substrate adaptor and a substrate, respectively. Knockdown of SPOP and CUL3 led to the upregulation of DAXX protein and downregulation of VEGFR2 levels. These levels were inversely correlated with one another. In addition, simultaneous knockdown of SPOP and DAXX completely reversed the downregulation of VEGFR2 levels. Moreover, the CUL3-SPOP-DAXX axis had the same effects on NOTCH1, DLL4 and NRP1 expression. Taken together, these findings suggest that the CUL3-SPOP-DAXX axis plays a very important role in endothelial cell function by targeting key angiogenic regulators.

P18 peptide, a functional fragment of pigment epithelial-derived factor, inhibits angiogenesis in hepatocellular carcinoma via modulating VEGF/VEGFR2 signalling pathway.

The P18 peptide is a functional fragment of pigment epithelial-derived factor (PEDF), which is an endogenic angiogenesis inhibitor. This study sought to determine the anti-angiogenic bioactivity of the P18 peptide in hepatocellular carcinoma (HCC) and to elucidate the underlying mechanism. Xenograft tumour growth assays demonstrated the P18 peptide suppressed angiogenesis of HCC in vivo. Wound healing, Transwell and Matrigel-culture assays indicated that the P18 peptide inhibited the cell migration and tube formation of endothelial cells (ECs) in vitro. Cell viability and apoptosis assessed by Cell Counting Kit-8 (CCK-8) and flow cytometry assays suggested that the P18 peptide inhibited angiogenesis by inducing apoptosis of ECs. Angiogenesis- and signal transduction-associated molecules analysed by western blot demonstrated that the P18 peptide targets vascular endothelial cell growth factor receptor 2 (VEGFR2) on ECs. In conclusion, by inhibiting the phosphorylation of VEGFR2, the P18 peptide modulates signalling transduction between VEGF/VEGFR2 and suppresses activation of the PI3K/Akt cascades, leading to an increase in mitochondrial-mediated apoptosis and anti-angiogenic activity. This bioactivity of the P18 peptide may represent a novel therapeutic strategy for the treatment of HCC.

Integrin-Linked Kinase Senses Hypoxia During Scar Angiogenesis.

Integrin-linked kinase (ILK) mediates signal transduction between cells and the extracellular matrix, regulating cell proliferation, migration, angiogenesis, and apoptosis. However, its roles in the formation of hypertrophic scars are not yet clear. In this study, we found that ILK was predominantly expressed on the microvascular endothelial cells and the epidermal basal cells of human hypertrophic scars. The proliferation, migration and angiogenesis of primary human scar microvascular endothelial cells (HSMECs) were significantly inhibited after ILK was silenced. The ILK inhibitor QLT0267 had the same effect of impeding angiogenesis in vitro by blocking ILK activity. Both siRNA and QLT0267 markedly decreased the expression of vascular endothelial growth factor, but not its receptors, such as human vascular endothelial cell growth factor receptor 1 or kinase insert domain-containing receptor. We also showed that the expression of ILK was enhanced by inducing mild hypoxia with CoCl2, but it was suppressed under serious hypoxia. Thus, ILK regulates HSMEC proliferation and angiogenesis and participates in the formation of hypertrophic scars, in which mild hypoxia may be the mechanism of action.

β-Lapachone Induces NAD(P)H:Quinone Oxidoreductase-1- and Oxidative Stress-Dependent Heat Shock Protein 90 Cleavage and Inhibits Tumor Growth and Angiogenesis.

β-Lapachone [β-lap; 3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b]pyran-5,6-dione] is a novel anticancer drug currently under investigation in phase I/II clinical trials. However, the mechanism underlying its clinical efficacy remains unclear. In this study, we found that β-lap provoked the cleavage of heat shock protein 90 (Hsp90) in quinone oxidoreductase-1 (NQO1)-expressing lung and prostate cancer cells as well as in primary human umbilical vein endothelial cells (HUVECs). These actions of β-lap were different from that of the conventional Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin. As a consequence of Hsp90 cleavage, Hsp90-associated oncoproteins, such as receptor-interacting protein, Raf-1, AKT, and CDK4, were degraded in treated cancer cells, and key receptor tyrosine kinases such as vascular endothelial cell growth factor receptor-2 and Her-2 were degraded in treated HUVECs through a proteasomal system. Further results revealed that specific inhibitors of NQO1 and reactive oxygen species could dramatically reduce β-lap-mediated Hsp90 cleavage. In addition to its cytotoxicity, β-lap effectively inhibited angiogenesis by suppressing tube formation and the invasion of HUVECs in vitro, rat aortic microvascular sprouts ex vivo, and mouse corneal neovascularization in vivo. Furthermore, β-lap markedly suppressed the growth and angiogenesis of human lung cancer xenografts in nude mice and decreased the levels of receptor-interacting protein, AKT, CDK4, and CD31 in the solid tumors. Unlike other NQO1-dependent cytotoxic quinones, such as streptonigrin, menadione, mitomycin, and 17-allylamino-17-demethoxygeldanamycin, β-lap was the only agent that could cause Hsp90 cleavage. Taken together, our results suggest a crucial mechanism underlying the antitumor efficacy of β-lap.

Heparanase-induced shedding of syndecan-1/CD138 in myeloma and endothelial cells activates VEGFR2 and an invasive phenotype: prevention by novel synstatins.

Multiple myeloma arises when malignant plasma cells invade and form multiple tumors in the bone marrow. High levels of heparanase (HPSE) correlate with poor prognosis in myeloma patients. A likely target of the enzyme is the heparan sulfate (HS) proteoglycan syndecan-1 (Sdc1, CD138), which is highly expressed on myeloma cells and contributes to poor prognosis in this disease. We find that HPSE promotes an invasive phenotype mediated by the very late antigen-4 (VLA-4, or α4β1 integrin) in myeloma cells plated on either fibronectin (FN) or vascular endothelial cell adhesion molecule-1 (VCAM-1), ligands that are prevalent in the bone marrow. The phenotype depends on vascular endothelial cell growth factor receptor-2 (VEGFR2), which is aberrantly expressed in myeloma, and is characterized by a highly protrusive lamellipodium and cell invasion. HPSE-mediated trimming of the HS on Sdc1 and subsequent matrix metalloproteinase-9-mediated shedding of the syndecan exposes a juxtamembrane site in Sdc1 that binds VEGFR2 and VLA-4, thereby coupling VEGFR2 to the integrin. Shed Sdc1 can be mimicked by recombinant Sdc1 ectodomain or by a peptide based on its binding motif, which causes VLA-4 to re-orient from the lagging edge (uropod) to the leading edge of migrating cells, couple with and activate VEGFR2. Peptides (called 'synstatins') containing only the VLA-4 or VEGFR2 binding sites competitively inhibit invasion, as they block coupling of the receptors. This mechanism is also utilized by vascular endothelial cells, in which it is also activated by HPSE, during endothelial cell tube formation. Collectively, our findings reveal for the first time the mechanism through which HPSE modulates Sdc1 function to promote both tumor cell invasion and angiogenesis, thereby driving multiple myeloma progression. The inhibitory synstatins, or inhibitors of HPSE enzyme activity, are likely to show promise as therapeutics against myeloma extravasation and spread.

Arf6 regulates tumour angiogenesis and growth through HGF-induced endothelial β1 integrin recycling.

Anti-angiogenic drugs targeting vascular endothelial cell growth factor receptor have provided modest clinical benefit, in part, owing to the actions of additional angiogenic factors that stimulate tumour neoangiogenesis in parallel. To overcome this redundancy, approaches targeting these other signalling pathways are required. Here we show, using endothelial cell-targeted mice, that the small GTPase Arf6 is required for hepatocyte growth factor (HGF)-induced tumour neoangiogenesis and growth. Arf6 deletion from endothelial cells abolishes HGF-stimulated β1 integrin recycling. Pharmacological inhibition of the Arf6 guanine nucleotide exchange factor (GEF) Grp1 efficiently suppresses tumour vascularization and growth. Grp1 as well as other Arf6 GEFs, such as GEP100, EFA6B and EFA6D, regulates HGF-stimulated β1 integrin recycling. These findings provide insight into the mechanism of HGF-induced tumour angiogenesis and offer the possibility that targeting the HGF-activated Arf6 signalling pathway may synergize with existing anti-angiogenic drugs to improve clinical outcomes.

Differential sensitivity of prostate tumor derived endothelial cells to sorafenib and sunitinib.

BackgroundProstate cancer is the second leading cause of male cancer death in developed countries. Although the role of angiogenesis in its progression is well established, the efficacy of anti-angiogenic therapy is not clearly proved. Whether this could depend on differential responses between tumor and normal endothelial cells has not been tested.MethodsWe isolated and characterized three lines of endothelial cells from prostate cancer and we tested the effect of Sunitinib and Sorafenib, and the combined treatment with the anti-androgen Casodex, on their angiogenic functions.ResultsEndothelial cells isolated from prostate tumors showed angiogenic properties and expression of androgen and vascular endothelial cell growth factor receptors. Sunitinib affected their proliferation, survival and motility while Sorafenib only showed a minor effect. At variance, Sunitinib and Sorafenib showed similar cytotoxic and anti-angiogenic effects on normal endothelial cells. Sorafenib and Sunitinib inhibited vascular endothelial cell growth factor receptor2 phosphorylation of prostate cancer endothelial cells, while they differentially modulated Akt phosphorylation as no inhibitory effect of Sorafenib was observed on Akt activation. The combined treatment of Casodex reverted the observed resistance to Sorafenib both on cell viability and on Akt activation, whereas it did not modify the response to Sunitinib.ConclusionsOur study demonstrates a resistant behavior of endothelial cells isolated from prostate cancer to Sorafenib, but not Sunitinib. Moreover, it shows the benefit of a multi-target therapy combining anti-angiogenic and anti-hormonal drugs to overcome resistance.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2407-14-939) contains supplementary material, which is available to authorized users.

AIP1 Mediates Vascular Endothelial Cell Growth Factor Receptor-3–Dependent Angiogenic and Lymphangiogenic Responses

To investigate the novel function of ASK1-interacting protein-1 (AIP1) in vascular endothelial cell growth factor receptor (VEGFR)-3 signaling, and VEGFR-3-dependent angiogenesis and lymphangiogenesis. AIP1, a signaling scaffold protein, is highly expressed in the vascular endothelium. We have previously reported that AIP1 functions as an endogenous inhibitor in pathological angiogenesis by blocking VEGFR-2 activity. Surprisingly, here we observe that mice with a global deletion of AIP1-knockout mice (AIP1-KO) exhibit reduced retinal angiogenesis with less sprouting and fewer branches. Vascular endothelial cell (but not neuronal)-specific deletion of AIP1 causes similar defects in retinal angiogenesis. The reduced retinal angiogenesis correlates with reduced expression in VEGFR-3 despite increased VEGFR-2 levels in AIP1-KO retinas. Consistent with the reduced expression of VEGFR-3, AIP1-KO show delayed developmental lymphangiogenesis in neonatal skin and mesentery, and mount weaker VEGF-C-induced cornea lymphangiogenesis. In vitro, human lymphatic endothelial cells with AIP1 small interfering RNA knockdown, retinal endothelial cells, and lymphatic endothelial cells isolated from AIP1-KO all show attenuated VEGF-C-induced VEGFR-3 signaling. Mechanistically, we demonstrate that AIP1 via vegfr-3-specific miR-1236 increases VEGFR-3 protein expression and that, by directly binding to VEGFR-3, it enhances VEGFR-3 endocytosis and stability. Our in vivo and in vitro results provide the first insight into the mechanism by which AIP1 mediates VEGFR-3-dependent angiogenic and lymphangiogenic signaling.

Tumor Angiogenesis

It has long been appreciated that angiogenesis can contribute to the induction or progression of several diseases, including retinopathies, arthritis, psoriasis, and cancer.1,2 Because endothelial cells typically exist in a quiescent state in normal vessels, the molecular changes required for these cells to become proliferative and invasive have long been considered potential targets for the control of both neovascularization and the accompanying pathology. To this end, over the past 3 decades, several novel effectors of angiogenesis have been characterized, ranging from growth factors, such as vascular endothelial cell growth factor (VEGF),3 to signaling effectors, such as RasGAPs,4 to cell adhesion molecules,5,6 including the αv integrins featured in the article by Steri et al.7 Nonetheless, as an aggregate, the efficacy of antiangiogenic agents has only produced a modest impact on disease.8 Article, see p 79 We and others have demonstrated that antagonists of αv integrins target and suppress pathological angiogenesis, resulting in decreased tumor growth,9,10 inflammatory disease,9,11 and retinal disease.5 In glioblastoma patients treated with these agents, some clinical efficacy was noted,12 although overall survival was not significantly impacted in recently announced phase III trials. Studies by Hynes et al showed that mice deficient in either αv or β3 showed robust blood vessel development.13,14 In fact, these animals displayed enhanced endothelial cell VEGF receptor (VEGFR) expression associated with increased tumor angiogenesis. This led the authors to conclude that αvβ3 plays a negative role in angiogenesis. How, then, can one reconcile the fact that αvβ3 antagonists suppress angiogenesis in mice and humans? In an elegant series of …

Inverse correlation of phospho-KDR/Flk-1 expression and stage of colorectal cancer: implication of the significance of neoangiogenesis in activated VEGFR-2 expressing early stage colorectal adenocarcinomas.

The activation of vascular endothelial cell growth factor receptors (VEGFRs) plays an essential role in cancer progression. In this study, we investigated the expression of phosphorylated VEGFR-2 (or phospho-KDR/Flk-1), the activated form of VEGFR-2, in human colorectal adenomas and colorectal adenocarcinomas. Phospho-KDR/Flk-1 showed weak expression in the normal colorectal tissue. Phospho-KDR/Flk-1 was mainly stained in the cytoplasm of colorectal adenomas, and was stained in both the cytoplasm and nuclei colorectal adenocarcinomas. There was no indication of increased phospho-KDR/Flk-1 expression in the colorectal adenocarcinomas, as compared to that of colorectal adenomas. Furthermore, there was an inverse relationship of phospho-KDR/Flk-1 expression with cancer stage (p < 0.0001), lymph node metastasis (p = 0.011), and distant metastasis (p = 0.021) of the colorectal adenocarcinomas. Our results indicate that early stage colorectal adenocarcinomas with highly activated (phosphorylated) VEGFR-2 expression may indicate the significance of neoangiogenesis of the tumors.

Prognostic factors and status of hormone receptors and angiogenic factors in uterine carcinosarcoma

To determine novel prognostic factors and treatment modalities for uterine carcinosarcoma (UCS). We performed immunohistochemical staining of estrogen receptor (ER)-α, ER-β, progesterone receptor, gonadotropin-releasing hormone receptor, vascular endothelial growth factor (VEGF), platelet-derived endothelial cell growth factor (PD-ECGF) and platelet-derived growth factor receptor (PDGFR)-β in a clinicopathological study of 15 UCS patients. No significant differences were found between the sarcomatous and carcinomatous components with respect to expression of ER-α, ER-β and progesterone receptor. However, VEGF was significantly more frequently expressed in the carcinomatous component, while PD-ECGF and PDGFR-β were significantly more frequently expressed in the sarcomatous component. Only one patient showed gonadotropin-releasing hormone receptor expression in the sarcomatous component. Moreover, ER-β expression in resected specimens, increased serum levels of carbohydrate antigen (CA)-125 and C-reactive protein (CRP), and thrombocytosis were determined as significant UCS prognostic factors. Combination of anti-VEGF therapy and anti-PD-ECGF or anti-PDGFR-β therapy would be expected in advanced or recurrent UCS. Furthermore, careful monitoring for early detection of recurrence should be performed when UCS patients showed preoperative increase in serum CA-125 levels, CRP and platelet counts, and ER-β expression in biopsied or surgically resected specimens.

Constitutive expression of vascular endothelial cell growth factor (VEGF) gene family ligand and receptors on human upper and lower airway epithelial cells

We previously reported that vascular endothelial cell growth factor (VEGF) is abundantly expressed by primary human nasal epithelial cells (PNECs) and functions to promote cell hyperplasia in polyposis. Therefore, we aimed to examine the full expression profile of other members of the VEGF gene family of ligands and receptors, which may play a role in cell growth and the development of chronic rhinosinusitis with nasal polyposis (CRSwNP). Messenger RNA (mRNA) and protein expression of VEGF genes, receptors, and co-receptors was examined from cultured PNECs (n = 4) and compared to that from primary human bronchial epithelial cells (PBECs; n = 4) and the BEAS2B cell line (n = 4) by real-time polymerase chain reaction (PCR) and flow cytometry. We report abundant expression of VEGFA, VEGFB, and VEGFC, detected by mRNA and flow cytometric analysis on PNECs. We herein report the novel finding that there is significant expression of VEGFR1, VEGFR2, VEGFR3, and both neuropilin co-receptors, NP1 and NP2, at baseline conditions on PNECs. Lower airway PBECs and BEAS2B cells displayed similar patterns of expression. PNECs express high constitutive levels of the VEGF gene family homolog of ligands and receptors. Expression of multiple VEGF ligand-receptor combinations may function as redundant pathways to promote upper and lower airway epithelial cell growth during inflammation.

Tanshinone IIA inhibits metastasis after palliative resection of hepatocellular carcinoma and prolongs survival in part via vascular normalization

BackgroundPromotion of endothelial normalization restores tumor oxygenation and obstructs tumor cells invasion, intravasation, and metastasis. We therefore investigated whether a vasoactive drug, tanshinone IIA, could inhibit metastasis by inducing vascular normalization after palliative resection (PR) of hepatocellular carcinoma (HCC).MethodsA liver orthotopic double-tumor xenograft model in nude mouse was established by implantation of HCCLM3 (high metastatic potential) and HepG2 tumor cells. After removal of one tumor by PR, the effects of tanshinone IIA administration on metastasis, tumor vascularization, and survival were evaluated. Tube formation was examined in mouse tumor-derived endothelial cells (TECs) treated with tanshinone IIA.ResultsPR significantly accelerated residual hepatoma metastases. Tanshinone IIA did not inhibit growth of single-xenotransplanted tumors, but it did reduce the occurrence of metastases. Moreover, it inhibited PR-enhanced metastases and, more importantly, prolonged host survival. Tanshinone IIA alleviated residual tumor hypoxia and suppressed epithelial-mesenchymal transition (EMT) in vivo; however, it did not downregulate hypoxia-inducible factor 1α (HIF-1α) or reverse EMT of tumor cells under hypoxic conditions in vitro. Tanshinone IIA directly strengthened tube formation of TECs, associated with vascular endothelial cell growth factor receptor 1/platelet derived growth factor receptor (VEGFR1/PDGFR) upregulation. Although the microvessel density (MVD) of residual tumor tissue increased after PR, the microvessel integrity (MVI) was still low. While tanshinone IIA did not inhibit MVD, it did dramatically increase MVI, leading to vascular normalization.ConclusionsOur results demonstrate that tanshinone IIA can inhibit the enhanced HCC metastasis associated with PR. Inhibition results from promoting VEGFR1/PDGFR-related vascular normalization. This application demonstrates the potential clinical benefit of preventing postsurgical recurrence.

CCAAT/Enhancer-binding Protein-Homologous Protein Sensitizes to SU5416 by Modulating p21 and PI3K/Akt Signal Pathway in FRO Anaplastic Thyroid Carcinoma Cells

SU5416, vascular endothelial cell growth factor receptor inhibitor, suppresses hypoxia-induced angiogenesis, growth, proliferation, and metastasis in cancer cells. CCAAT/enhancer-binding protein-homologous protein (CHOP) has pivotal roles in regulation of growth and survival. In the present study, we evaluated the effects of SU5416 on cell survival, p21, and PI3K/Akt signal pathway in FRO anaplastic thyroid carcinoma (ATC) cells. Moreover, we investigated the roles of CHOP in cell survival under condition of SU5416 treatment in FRO ATC cells. After SU5416 treatment, cell viability, PARP-1, and caspase-3 protein levels were not changed. p53 and p27 protein levels decreased while p21 protein levels increased. Phospho-Akt protein levels were not altered. In SU5416-treated situation, cell viability was not different before and after administration of either p21 siRNA or LY294002 whereas it was lessened after co-administration of p21 siRNA and LY294002. Compared to SU5416 treatment alone, cell viability was reduced with CHOP plasmid but it was unchanged with CHOP siRNA. PARP-1 and caspase-3 protein levels with CHOP plasmid were elevated whereas the protein levels with CHOP siRNA were similar. While CHOP plasmid transfection diminished p21 and phospho-Akt protein levels, CHOP siRNA transfection did not alter the protein levels. In conclusion, these results suggest that CHOP may sensitize FRO ATC cells to SU5416 thereby inhibiting cell survival by modulating p21 and PI3K/Akt signal pathway. Furthermore, these findings imply that CHOP may be a possible candidate as the chemosensitizing factor for induction of cytotoxicity in ATC cells exposed to SU5416.

VEGF-D Promotes Tumor Metastasis by Regulating Prostaglandins Produced by the Collecting Lymphatic Endothelium

Lymphatic metastasis is facilitated by lymphangiogenic growth factors VEGF-C and VEGF-D that are secreted by some primary tumors. We identified regulation of PGDH, the key enzyme in prostaglandin catabolism, in endothelial cells of collecting lymphatics, as a key molecular change during VEGF-D-driven tumor spread. The VEGF-D-dependent regulation of the prostaglandin pathway was supported by the finding that collecting lymphatic vessel dilation and subsequent metastasis were affected by nonsteroidal anti-inflammatory drugs (NSAIDs), known inhibitors of prostaglandin synthesis. Our data suggest a control point for cancer metastasis within the collecting lymphatic endothelium, which links VEGF-D/VEGFR-2/VEGFR-3 and the prostaglandin pathways. Collecting lymphatics therefore play an active and important role in metastasis and may provide a therapeutic target to restrict tumor spread.

Expression of Angiogenic Factors in Rat Periapical Lesions

IntroductionAngiogenic factors such as VEGFR2 (vascular endothelial cell growth factor receptor 2), Bcl-2 (a prosurvival and proangiogenic signaling molecule), and chemokine (C-X-C motif) ligand 1 (CXCL1) (a proangiogenic chemokine) may have critical roles in enhancing the establishment of apical periodontitis. To understand the role of these factors in the pathogenesis of apical periodontitis, we conducted immunohistochemical and molecular biological analysis. MethodsApical periodontitis was induced in the lower first molars of Wistar rats by making unsealed pulp exposures. After, 14, 21, and 28 days, the molars were retrieved, embedded as frozen sample blocks, and cut in a cryostat. Normal lower first molars served as controls. Immunostaining for CD31 (a marker for endothelial cells), Bcl-2, and real-time polymerase chain reaction analysis of VEGFR2, Bcl-2, CXCL1, and CXCR2 messenger RNA were performed. In the real-time polymerase chain reaction analysis, messenger RNA was extracted from CD31-stained endothelial cells that were retrieved with laser capture microdissection. For statistical analysis of immunohistochemistry, the immunostained area was plotted, and pixel counts were determined. Then, the percentage of the immunostained area in the total area was calculated. ResultsThe density of the CD31-stained area increased until 21 days after pulp exposure. On the other hand, Bcl-2–stained area showed the highest density at 14 days (active lesion expanding phase) and then decreased until 28 days (lesion stability phase). VEGFR2, Bcl-2, CXCL1, and CXCR2 messenger RNA expression in endothelial cells showed the highest levels at 14 days and then decreased until 28 days. ConclusionsThe increase in microvascular density and the up-regulation of VEGFR2, Bcl-2, CXCL1, and CXCR2 messenger RNA expression in endothelial cells took place coincidently with the expanding phase of experimentally induced periapical lesions. These data suggest that these angiogenic factors play a role in the lesion development.

Focal adhesion kinase and tumour angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones, is essential for tumour development. It is initiated and regulated by growth factors via their surface receptors, which activate several intracellular signalling pathways in endothelial cells. Cell adhesion molecules, such as integrins, also regulate angiogenesis. Despite these facts, inhibitors of endothelial cell growth factor receptors or integrins have not been as effective as initially hoped in the long-term inhibition of angiogenesis in cancer patients. Signalling downstream of growth factor receptors and integrins converge on the ubiquitously expressed non-receptor tyrosine kinase focal adhesion kinase (FAK). FAK is involved in endothelial cell proliferation, migration and survival, is up-regulated in many cancers and has recently been shown to control tumour angiogenesis. Indeed, FAK inhibitors are presently being developed for the treatment of cancer. However, recent studies have indicated the complexities of understanding the precise role for FAK in angiogenesis. Here we have summarized some of the key features of FAK, addressed some of the apparently contradictory roles of this molecule in angiogenesis and provided some perspectives for future studies.

The Structural Basis for the Function of Two Anti-VEGF Receptor 2 Antibodies

The anti-VEGF receptor 2 antibody IMC-1121B is a promising antiangiogenic drug being tested for treatment of breast and gastric cancer. We have determined the structure of the 1121B Fab fragment in complex with domain 3 of VEGFR2, as well as the structure of a different neutralizing anti-VEGFR2 antibody, 6.64, also in complex with VEGFR2 domain 3. The two Fab fragments bind at opposite ends of VEGFR2 domain 3; 1121B directly blocks VEGF binding, whereas 6.64 may prevent receptor dimerization by perturbing the domain 3:domain 4 interface. Mutagenesis reveals that residues essential for VEGF, 1121B, and 6.64 binding are nonoverlapping among the three contact patches.

Differences in integrin expression and signaling within human breast cancer cells

BackgroundIntegrins are used as prognostic indicators in breast cancer. Following engagement with extracellular matrix proteins, their signaling influences numerous cellular processes including migration, proliferation, and death. Integrin signaling varies between cell types through differential expression of integrin subunits, and changes within a given cell upon exposure to a cell agonist or through changes in its surroundings. These variations in signaling can profoundly affect the phenotypic, tumorogenecity and metastatic properties of cancer cells. In the present study, we investigated if there were differences in the expression of integrins, integrin structures, and integrin co-receptors within three breast cancer cells and if these differences effected integrin signaling.MethodsExpression of integrins, urokinase receptor and vascular endothelial cell growth factor receptor (VEGFR) in metastatic MDA-MB-435 and MDA-MB-231, non-metastatic MCF7 and non-breast cancer Hek-293 cells was measured by flow cytometry. Cell adhesion was assessed using collagen, fibrinogen, fibronectin and vitronectin coated plates. Changes in kinase levels following PMA stimulation, and cell adhesion-induced activation of kinases were determined by western blot analysis. Distribution of actin stress fibers and focal adhesions was assessed by immunocytochemistry.ResultsAll cells expressed αv integrins, while high β5 and αvβ5 expression was restricted to the cancer cells and high β3 and αvβ3 expression was restricted to MDA-MB-435 cells. The two metastatic cells were the least adhesive, but all cells adhered well to most proteins in the absence of PMA. All proliferating cells expressed activated pSrc, but only proliferating metastatic cells expressed high pMEK levels. PMA treatment resulted in time-dependent changes in activated kinase levels, and only MDA-MB-231 cells constitutively expressed high levels of activated pMEK. MDA-MB-435 cells formed more stress fibers and focal adhesions and only exhibited adhesion-induced activation of pMEK and pFAK. All cells expressed the urokinase receptor, but MCF7 cells had markedly higher VEGFR expression. Adhesion induced differential expression of pFAK, pMEK and pERK.ConclusionsThis study demonstrates that breast cancers vary in their expression of integrins, their capacity to form focal adhesion and to signal through integrins. These differences likely contribute to phenotypic variations between cancer lines and account for some of the heterogeneity of breast cancer.

Targeted therapy in head and neck cancer

Results of clinical studies on targeted cancer therapies are rapidly accumulating. This is also true in the field of head and neck cancer (HNC). Due to the unique multidisciplinary needs of the disease, it is of paramount importance that physicians who treat HNC are aware of the evolving changes that research is offering. Many targeted agents directed at inhibiting epithelial growth factor receptors (EGFRs) are under investigation in both curable loco-regional advanced disease in combination with standard treatments and in the recurrent metastatic setting. Human papilloma virus (HPV)-positive tumors present a distinct biological profile. Consequently, the role of targeted agents in this specific setting still needs to be refined. Herein we will briefly review the results of the most recent studies on targeted agents. Cetuximab and other monoclonal antibodies (panitumumab, zalotumumab and nimotumumab) have been already investigated in phase III studies; and some results are now available. Small molecules inhibiting EGFR have still to prove their efficacy. Other agents such as vascular endothelial cell growth factor receptor, vascular endoinsulin-like growth factor 1 receptor, MET, PI3KA and mammalian target of rapamycin inhibitor are in development. At present treatment options in HNC are changing and include targeted agents with demonstrated efficacy. A better selection based on biological factors of patients who are potentially responsive to such targeted agents is being actively pursued.