PDGF-BB induces MAP kinase phosphorylation and VEGF expression in neurofibroma-derived cultured cells from patients with neurofibromatosis 1

Activated androgen receptor accelerates angiogenesis in cutaneous neurofibroma by regulating VEGFA transcription

Accumulating evidence has demonstrated the significant progression of cutaneous neurofibroma (cNF) without necrosis during puberty. However, the molecular events involved in this process remain unclear. The alteration of the steroid hormone levels during puberty has led to the investigation of the expression levels of the androgen receptor (AR). A positive correlation between AR expression and microvessel density has been reported in human cNF tissues in combination with enhanced endothelial cell tube formation in vitro. In addition, activated AR signaling can promote neurofibroma cell growth in vivo and in vitro and tube formation in vitro. In the present study, AR was shown to bind directly to the promoter of vascular endothelial growth factor A (VEGFA), a key factor involved in angiogenesis, and to sequentially induce its expression. Furthermore, the AR inhibitor, MDV3100, downregulated VEGFA expression and abolished endothelial cell recruitment and tube formation. Taken collectively, the findings of this study revealed that AR signaling enhanced tumor growth and angiogenesis in cNF by regulating VEGFA transcription. However, whether AR can be regarded a therapeutic target for cNF requires further investigation.

Neurofibromin Deficiency Induces Endothelial Cell Proliferation and Retinal Neovascularization

Purpose

Neurofibromatosis type 1 (NF1) is the result of inherited mutations in the NF1 tumor suppressor gene, which encodes the protein neurofibromin. Eye manifestations are common in NF1 with recent reports describing a vascular dysplasia in the retina and choroid. Common features of NF1 retinopathy include tortuous and dilated feeder vessels that terminate in capillary tufts, increased endothelial permeability, and neovascularization. Given the retinal vascular phenotype observed in persons with NF1, we hypothesize that preserving neurofibromin may be a novel strategy to control pathologic retinal neovascularization.

Methods

Nf1 expression in human endothelial cells (EC) was reduced using small hairpin (sh) RNA and EC proliferation, migration, and capacity to form vessel-like networks were assessed in response to VEGF and hypoxia. Wild-type (WT), Nf1 heterozygous (Nf1^+/−), and Nf1^flox/+;Tie2cre pups were subjected to hyperoxia/hypoxia using the oxygen-induced retinopathy model. Retinas were analyzed quantitatively for extent of retinal vessel dropout, neovascularization, and capillary branching.

Results

Neurofibromin expression was suppressed in response to VEGF, which corresponded with activation of Mek-Erk and PI3-K-Akt signaling. Neurofibromin-deficient EC exhibited enhanced proliferation and network formation in response to VEGF and hypoxia via an Akt-dependent mechanism. In response to hyperoxia/hypoxia, Nf1^+/− retinas exhibited increased vessel dropout and neovascularization when compared with WT retinas. Neovascularization was similar between Nf1^+/− and Nf1^flox/+;Tie2cre retinas, but capillary drop out in Nf1^flox/+;Tie2cre retinas was significantly reduced when compared with Nf1^+/− retinas.

Conclusions

These data suggest that neurofibromin expression is essential for controlling endothelial cell proliferation and retinal neovascularization and therapies targeting neurofibromin-deficient EC may be beneficial.

Pivotal role of vascular endothelial growth factor pathway in tumor angiogenesis

The shaping of new blood vessels is a significant event in cancer growth and metastasis. Therefore, the molecular system of cancer angiogenesis has garnered considerable interest in cancer research. The vascular endothelial growth factor (VEGF) and VEGF receptor pathway are recognized as the key regulators of the angiogenic process. Activation of the VEGF/VEGF-receptor pathway initiates signaling cascades that promote endothelial cell growth, migration, and differentiation. Recently, VEGF was shown to play a role in the recruitment of bone marrow-derived endothelial progenitor cells to neovascularization sites. The role of VEGF in promoting tumor angiogenesis and the occurrence of human cancers has led to the rational design and development of agents that selectively target this pathway. Moreover, these anti-VEGF/VEGF receptor agents show therapeutic potential by inhibition of angiogenesis and tumor growth in preclinical models. In this review, we summarize the role of the VEGF pathway during tumor angiogenesis.

Iris neovascularization and neovascular glaucoma in neurofibromatosis type 1: report of 3 cases in children

PURPOSE

To report the clinical findings and outcomes in 3 patients with neurofibromatosis 1 (NF1) and retinal vascular abnormalities that resulted in angle closure secondary to iris neovascularization and describe the histopathologic abnormalities in 1 case.

PATIENTS AND METHODS

Retrospective case series of patients with NF1 and angle closure due to iris neovascularization secondary to retinal vascular abnormalities. Histopathologic analysis of an enucleated eye in 1 case.

RESULTS

Three children whose age ranged from 5 to 10 years at presentation, developed unilateral retinal vascular abnormalities that resulted in iris neovascularization and angle closure with a wide range of intraocular pressures. Two patients had retinal vasoproliferative lesions of which the affected eye became blind in 1 patient and the other retained useful vision after treatment with intracameral Bevacizumab, ablation of the retinal lesions, and surgical treatment of the neovascular glaucoma. The third patient underwent enucleation and had pathologic evidence of retinal ischemia.

CONCLUSIONS

A variety of retinal vascular lesions occurring in NF1 are capable of producing iris neovascularization, ectropion uvea, and neovascular glaucoma. Although a spectrum of serious complications resulting in total vision loss can occur, retention of useful vision is possible, in some cases, with aggressive treatment of the retinal lesions and associated neovascular glaucoma. This report highlights the need for careful examination of the posterior segment with special attention to peripheral retinal vascular abnormalities or tumors in young patients with NF1.

Vascular endothelial growth factor receptor tyrosine kinase inhibitors in non-small-cell lung cancer

Angiogenesis is essential for cancer growth and progression. Vascular endothelial growth factor (VEGF) plays a crucial role in angiogenesis. The addition of bevacizumab, an antibody to vascular endothelial growth factor (VEGF), to paclitaxel and carboplatin improves survival compared with chemotherapy alone in patients with previously untreated metastatic nonsquamous non-small-cell lung cancer (NSCLC). Vascular endothelial growth factor receptor tyrosine kinase inhibitors (VEGFR TKIs) are a new class of drugs that target the TK domain of the VEGF receptors. To evaluate the role of this class of agents in the treatment of NSCLC, some phase II and phase III studies using these agents alone or in combination with other agents have been completed. This review summarizes the currently available data on VEGFR TKIs in the treatment of NSCLC.

Expression of pro- and anti-angiogenic isoforms of VEGF is differentially regulated by splicing and growth factors

Vascular endothelial growth factor A (VEGFA; hereafter referred to as VEGF) is a key regulator of physiological and pathological angiogenesis. Two families of VEGF isoforms are generated by alternate splice-site selection in the terminal exon. Proximal splice-site selection (PSS) in exon 8 results in pro-angiogenic VEGFxxx isoforms (xxx is the number of amino acids), whereas distal splice-site selection (DSS) results in anti-angiogenic VEGFxxxb isoforms. To investigate control of PSS and DSS, we investigated the regulation of isoform expression by extracellular growth factor administration and intracellular splicing factors. In primary epithelial cells VEGFxxxb formed the majority of VEGF isoforms (74%). IGF1, and TNFalpha treatment favoured PSS (increasing VEGFxxx) whereas TGFbeta1 favoured DSS, increasing VEGFxxxb levels. TGFbeta1 induced DSS selection was prevented by inhibition of p38 MAPK and the Clk/sty (CDC-like kinase, CLK1) splicing factor kinase family, but not ERK1/2. Clk phosphorylates SR protein splicing factors ASF/SF2, SRp40 and SRp55. To determine whether SR splicing factors alter VEGF splicing, they were overexpressed in epithelial cells, and VEGF isoform production assessed. ASF/SF2, and SRp40 both favoured PSS, whereas SRp55 upregulated VEGFxxxb (DSS) isoforms relative to VEGFxxx. SRp55 knockdown reduced expression of VEGF165b. Moreover, SRp55 bound to a 35 nucleotide region of the 3'UTR immediately downstream of the stop codon in exon 8b. These results identify regulation of splicing by growth and splice factors as a key event in determining the relative pro-versus anti-angiogenic expression of VEGF isoforms, and suggest that p38 MAPK-Clk/sty kinases are responsible for the TGFbeta1-induced DSS selection, and identify SRp55 as a key regulatory splice factor.

Phase II trial of sunitinib in patients with metastatic colorectal cancer after failure of standard therapy

PURPOSE

Sunitinib is an oral, multitargeted receptor tyrosine kinase inhibitor of the vascular endothelial growth factor receptor and multiple other growth factor receptors. We assessed the safety and efficacy of sunitinib in patients with metastatic colorectal cancer after failure of standard therapy.

PATIENTS AND METHODS

Eighty-four patients were enrolled onto this two-stage phase II trial and were stratified by whether they had received prior bevacizumab (n = 43) or not (n = 41). Treatment comprised sunitinib 50 mg orally daily for 4 weeks, followed by 2 weeks off treatment, in repeated 6-week cycles.

RESULTS

By Response Evaluation Criteria in Solid Tumors criteria, one patient, who was in the prior bevacizumab cohort, achieved a partial response, and 13 patients (two in the prior bevacizumab cohort and 11 in the no prior bevacizumab cohort) achieved stable disease lasting > or = 22 weeks. Median time to progression in the prior bevacizumab and bevacizumab-naïve cohorts was 2.2 months (95% CI, 1.9 to 2.3 months) and 2.5 months (95% CI, 2.3 to 3.1 months), respectively, whereas median overall survival time was 7.1 months (95% CI, 4.9 to 10.6 months) and 10.2 months (95% CI, 8.2 to 15.3 months), respectively. The most common adverse events were fatigue, diarrhea, nausea, vomiting, and anorexia. Twenty-six patients (32%) required dose reduction to 37.5 mg/d, and one patient required dose reduction to 25 mg/d.

CONCLUSION

Sunitinib did not demonstrate a meaningful single-agent objective response rate in colorectal cancer refractory to standard chemotherapy. However, the mechanisms of action and acceptable safety profile of sunitinib warrant further study in combination with standard regimens for metastatic colorectal cancer.

Hypoxia-inducible factor 1alpha is regulated by the mammalian target of rapamycin (mTOR) via an mTOR signaling motif

Tumors that form as a result of heightened mammalian target of rapamycin (mTOR) signaling are highly vascularized. This process of angiogenesis is regulated through hypoxia-inducible factor (HIF)-mediated transcription of angiogenic factors. It is recognized that inhibition of mTOR with rapamycin can diminish the process of angiogenesis. Our work shows that activation of mTOR by Ras homologue enriched in brain (Rheb) overexpression potently enhances the activity of HIF1alpha and vascular endothelial growth factor (VEGF)-A secretion during hypoxia, which is reversed with rapamycin. Mutants of Rheb, which do not bind guanine nucleotide (D60K, D60V, N119I, and D122N) and are unable to activate mTOR, inhibit the activity of HIF when overexpressed. We show that regulatory associated protein of mTOR (Raptor) interacts with HIF1alpha and requires an mTOR signaling (TOS) motif located in the N terminus of HIF1alpha. Furthermore, a mutant of HIF1alpha lacking this TOS motif dominantly impaired HIF activity during hypoxia and was unable to bind to the co-activator CBP/p300. Rapamycin treatments do not affect the stability of HIF1alpha and modulate HIF activity via a Von Hippel-Lindau (VHL)-independent mechanism. We demonstrate that the high levels of HIF activity in cells devoid of TSC2 can be reversed by treatments with rapamycin or the readdition of TSC2. Our work explains why human cancers with aberrant mTOR signaling are prone to angiogenesis and suggests that inhibition of mTOR with rapamycin might be a suitable therapeutic strategy.

Hitting the mark in hamartoma syndromes

The missed mark or hamartia underlying each hamartoma syndrome is a mutation in a tumor suppressor gene. This sets the stage for the development of frequent and early tumors in multiple organs. Loss of function of the tumor suppressor in neoplastic cells leads to dysregulation of signaling pathways and tumor growth. The convergence of these signaling pathways to the mTOR pathway suggests that rapamycin or rapamycin-like drugs have potential for treatment, perhaps in combination with drugs targeting other signaling pathways. Haploinsufficient cells also play significant roles in tumor formation. Disrupting interactions between neoplastic cells and surrounding haploinsufficient cells using antiangiogenesis therapies represent an additional approach for treatment. It is hoped that the debilitating effects of these syndromes soon will be alleviated or even reversed though targeted therapies.

Perinatal epidermal growth factor receptor blockade prevents peripheral nerve disruption in a mouse model reminiscent of benign world health organization grade I neurofibroma

Benign peripheral nerve tumors called neurofibromas are a major source of morbidity for patients with neurofibromatosis type 1. Some neurofibroma Schwann cells aberrantly express the epidermal growth factor receptor (EGFR). In a mouse model in which the CNPase promoter drives expression of human EGFR in Schwann cells, nerves develop hypertrophy, mast cell accumulation, collagen deposition, disruption of axon-glial interactions, characteristics of neurofibroma and are hypoalgesic. Administration of the EGFR antagonist cetuximab (IMC-C225) for 2 weeks beginning at birth in CNPase-hEGFR mice normalized all pathologies at 3 months of age as evaluated by hotplate testing or histology and by electron microscopy. Mast cell chemoattractants brain-derived neurotrophic factor, monocyte chemoattractant protein-1, and transforming growth factor-beta1, which may account for mast cell accumulation and fibrosis, were reduced by cetuximab. Later treatment was much less effective. A birth to 2-week pulse of cetuximab blocked hEGFR phosphorylation and Schwann cell prolifera-tion in perinatal mutant nerve, so CNPase-hEGFR Schwann cell numbers correlate with the cetuximab effect. A >250-fold enlarged population of EGFR(+)/p75(+) cells was detected in newborn Nf1(+/-) mouse nerves. These results suggest the existence of an EGFR(+) cell enriched in the perinatal period capable of driving complex changes characteristic of neurofibroma formation.

c-Jun kinase mediates expression of VEGF induced at transcriptional level by Rac1 and Cdc42Hs but not by RhoA

Tumour angiogenesis is mediated by increased levels of vascular endothelial growth factor (VEGF). We have studied the mechanism by which endogenous activation of Rho oncoproteins regulates VEGF expression in COS-7 and NIH3T3 cells. We carried out transient and stable transfection with constitutively activated rhoA, rac1, and cdc42 mutants in COS-7 and NIH3T3 cells, respectively in the absence of external stimuli. Western blot and inmunohistochemistry assays of those cells revealed increased VEGF protein expression. Cotransfection with constitutively activated rhoA, rac1, and cdc42 mutants and a VEGF promoter-reporter construct showed an increase in VEGF promoter transcriptional activity induced by Rho oncoproteins in COS-7 and NIH3T3. c-Jun kinase had been described as a MAPK involved in Rho oncoproteins pathways. Interestingly, we found that c-Jun kinase chemical inhibition as well as transient transactivation assays using dominant negative c-Jun kinase mutant abolished the VEGF promoter transcriptional induction by Rac1 and Cdc42 but not by RhoA. These findings indicate that Rho oncoprotein endogenously activated regulates VEGF expression through a transcriptional mechanism, and that the c-Jun kinase activity is a mediator in the expression of VEGF induced by Rac1 and Cdc42 oncoproteins, but not of that induced by RhoA.

Role of the vascular endothelial growth factor pathway in tumor growth and angiogenesis

New blood vessel formation (angiogenesis) is a fundamental event in the process of tumor growth and metastatic dissemination. Hence, the molecular basis of tumor angiogenesis has been of keen interest in the field of cancer research. The vascular endothelial growth factor (VEGF) pathway is well established as one of the key regulators of this process. The VEGF/VEGF-receptor axis is composed of multiple ligands and receptors with overlapping and distinct ligand-receptor binding specificities, cell-type expression, and function. Activation of the VEGF-receptor pathway triggers a network of signaling processes that promote endothelial cell growth, migration, and survival from pre-existing vasculature. In addition, VEGF mediates vessel permeability, and has been associated with malignant effusions. More recently, an important role for VEGF has emerged in mobilization of endothelial progenitor cells from the bone marrow to distant sites of neovascularization. The well-established role of VEGF in promoting tumor angiogenesis and the pathogenesis of human cancers has led to the rational design and development of agents that selectively target this pathway. Studies with various anti-VEGF/VEGF-receptor therapies have shown that these agents can potently inhibit angiogenesis and tumor growth in preclinical models. Recently, an anti-VEGF antibody (bevacizumab), when used in combination with chemotherapy, was shown to significantly improve survival and response rates in patients with metastatic colorectal cancer and thus, validate VEGF pathway inhibitors as an important new treatment modality in cancer therapy.

The vascular endothelial growth factor family and its receptors

This article focuses on describing the biology of vascular endothelial growth factor (VEGF) and its receptors as well as the regulation of their expression. A thorough understanding of the VEGF system is paramount in optimizing antiangiogenic therapies as a component of antineoplastic regimens.