Inhibition Of Vascular Endothelial Growth Factor Signaling Research Articles

Abstract LB-315: Suppression of tumor invasion and metastasis by inhibition of c-MET and VEGF signaling together

Abstract Treatment with inhibitors that block vascular endothelial growth factor (VEGF) signaling can make tumors more aggressive in preclinical models. The mechanism underlying this form of resistance is not fully understood, but vascular pruning, intratumoral hypoxia, and increased expression of c-MET, the tyrosine kinase receptor for hepatocyte growth factor (HGF), could be contributing factors. We found that treatment of pancreatic neuroendocrine tumors in RIP-Tag2 mice with a neutralizing anti-VEGF antibody or with sunitinib, a receptor tyrosine kinase inhibitor that blocks VEGFR and related receptors, reduced tumor burden and vascularity but increased intratumoral hypoxia, HIF-1alpha, and expression and activation of c-MET. Invasion into the exocrine pancreas and metastasis to the liver also increased. Importantly, administration of either of two c-MET inhibitors, PF-04217903 or crizotinib (PF-02341066), together with anti-VEGF therapy reduced tumor growth and vascularity and also significantly decreased local invasion and liver metastasis. Similar benefits were found after treatment with cabozantinib (XL184), a multitargeted tyrosine kinase inhibitor that simultaneously blocks c-MET and VEGF receptors. Together, these results indicate that inhibition of VEGF signaling can promote vascular pruning, intratumoral hypoxia, HIF-1alpha accumulation, and activation of c-MET. Concurrent inhibition of c-MET and VEGF signaling not only can slow tumor growth but also can reduce invasion and metastasis. Inhibition of c-MET and VEGF signaling pathways together combines the favorable tumor growth-slowing effects of inhibiting angiogenesis with suppression of invasion and metastasis, despite the intratumoral hypoxia due to vascular pruning. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-315. doi:1538-7445.AM2012-LB-315

Abstract 1378: Concurrent inhibition of c-Met and VEGF signaling suppresses tumor invasion in orthotopic Panc-1 pancreatic carcinomas in mice

Abstract Multiple factors can contribute to evasive resistance that develops during treatment with angiogenesis inhibitors that target the vascular endothelial growth factor (VEGF) pathway. Evidence from studies of neuroendocrine tumors in RIP-Tag2 transgenic mice indicates that hypoxia-induced activation of pro-invasive pathways involving the receptor for hepatocyte growth factor, c-Met, can participate. The present study sought to determine whether this mechanism also applies to other types of tumors. Our approach was to ask whether growth and invasiveness of Panc-1 pancreatic adenocarcinomas implanted orthotopically in nude mice were reduced by inhibition of c-Met during concurrent treatment with an angiogenesis inhibitor for 3 weeks. Panc-1 tumors in mice treated with the angiogenesis inhibitor sunitinib, a tyrosine kinase inhibitor that blocks VEGFR and related receptors, had a 75% reduction in vascularity and grew more slowly than controls but had twice as much of intratumoral hypoxia, assessed by pimonidazole staining. Unlike the faint c-Met immunoreactivity in most tumor cells of vehicle-treated Panc-1 tumors, c-Met staining was stronger in tumor cells after treatment with sunitinib. Tumors in mice treated with the selective c-Met inhibitor PF-04217903 alone had little change in tumor vascularity or intratumoral hypoxia and grew faster than those treated with sunitinib. However, tumors treated with sunitinib plus PF-04217903 together grew more slowly than after sunitinib alone but had similar amounts of vascular pruning and hypoxia. Tumor invasiveness, reflected by amylase-positive acinar cells of the exocrine pancreas located within tumors, was exaggerated after sunitinib treatment but, importantly, was significantly less in tumors treated with sunitinib plus PF-04217903. These findings indicate that sunitinib used alone reduced the growth of Panc-1 tumors but increased intratumoral hypoxia, c-Met expression, and local invasion into the surrounding normal pancreas. By comparison, sunitinib administered concurrently with the c-Met inhibitor PF-04217903 resulted in further slowing of tumor growth and less tumor invasiveness. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1378. doi:1538-7445.AM2012-1378

Glomerular VEGF resistance induced by PKCδ/SHP‐1 activation and contribution to diabetic nephropathy

This study characterizes the effect of glucose-induced activation of protein kinase Cδ (PKCδ) and Src homology-2 domain-containing phosphatase-1 (SHP-1) expression on vascular endothelial growth factor (VEGF) actions in glomerular podocytes in cultures and in glomeruli of diabetic rodents. Elevation of glucose levels induced PKCδ and p38 mitogen-activated protein kinase (p38 MAPK) to increase SHP-1 expression, increased podocyte apoptosis, and inhibited VEGF activation in podocytes and glomerular endothelial cells. The adverse effects of high glucose levels can be negated by molecular inhibitors of PKCδ, p38MAPK, and SHP-1 and only partially reduced by antioxidants and nuclear factor-κB (NF-κB) inhibitor. Increased PKCδ activation and SHP-1 expression correlated with loss of VEGF signaling and podocyte numbers in the glomeruli of diabetic rats and mice. In contrast, diabetic PKCδ-knockout (Prkcd(-/-)) mice did not exhibit activation of p38 MAPK and SHP-1 or inhibition of VEGF signaling in renal glomeruli. Functionally, diabetic Prkcd(-/-) mice had decreased expressions of TGFβ, VEGF, and extracellular matrix and less albuminuria than diabetic Prkcd(+/+) mice. Hyperglycemia and diabetes can cause glomerular podocyte apoptosis and endothelial dysfunction partly due to increased PKCδ/p38 MAPK activation and the expression of SHP-1 to cause VEGF resistance, independent of NF-κB activation.

Antitumor effect of FP3 in combination with cetuximab on patient-derived tumor tissue xenograft models of primary colon carcinoma and related lymphatic and hepatic metastases

FP3 is an engineered protein which contains the extracellular domain 2 of vascular endothelial growth factor (VEGF) receptor 1 (Flt-1) and the extracellular domain 3 and 4 of VEGF receptor 2 (Flk-1, KDR) fused to the Fc portion of human immunoglobulin G1. Previous studies have demonstrated its antiangiogenic effects in vitro and in vivo, and its antitumor activity in vivo. Cetuximab is a monoclonal antibody against epidermal growth factor (EGF) receptor. Combined inhibition of VEGF and EGF signaling may act additively or synergistically. In this study, patient-derived tumor tissue (PDTT) xenograft models of primary colon carcinoma and lymphatic and hepatic metastases were established for assessment of the antitumor activity of FP3 in combination with cetuximab. Xenografts were treated with FP3 and cetuximab, alone or in combination. After tumor growth was confirmed, volume and microvessel density in tumors were evaluated. Levels of VEGF, EGFR and PCNA in the tumor were examined by immunohistochemical staining, and levels of related cell signaling pathway proteins were examined by western blotting. FP3 in combination with cetuximab showed significant antitumor activity in three xenograft models (primary colon carcinoma, lymphatic metastasis and hepatic metastasis). The microvessel density in tumor tissues treated with FP3 in combination with cetuximab was lower compared to that of the control. Antitumor activity of FP3 in combination with cetuximab was significantly higher than that of each agent alone in two xenograft models (colon carcinoma lymphatic metastasis and hepatic metastasis). This study indicated that addition of FP3 to cetuximab significantly improved tumor growth inhibition in the PDTT xenograft models of colon carcinoma lymphatic and hepatic metastases. Combination anti-VEGF (FP3) and anti-EGFR (cetuximab) therapies may represent a novel therapeutic strategy for the management of metastatic colon carcinoma.

Inhibition of p38 MAPK Reduces Expression of Vascular Endothelial Growth Factor in Allergic Airway Disease

The p38 mitogen-activated protein kinase (MAPK) appears to play an important role in various pathophysiological responses and has been suggested to be involved in many processes considered critical to the inflammatory response and tissue remodeling. Bronchial asthma is a chronic inflammatory disorder of the airway accompanied by increased vascular permeability. Vascular endothelial growth factor (VEGF) is a potent stimulator of bronchial inflammation, airway remodeling, and physiologic dysregulation that augments antigen sensitization and T-helper type 2 cell (Th2)-mediated inflammation in allergic airway diseases. However, there are little data on the relationship between p38 MAPK signaling and VEGF expression in allergic airway disease. This study aimed to investigate the role of p38 MAPK on the pathogenesis of allergic airway disease, more specifically in VEGF expression. Using ovalbumin (OVA)-inhaled mice and a selective p38 MAPK inhibitor, SB 239063, the involvement of p38 MAPK in allergen-induced VEGF expression in the airway was evaluated. The increases of phosphorylation of p38 MAPK, VEGF protein expression, and vascular permeability in the lung after OVA inhalation were decreased substantially by the administration of SB 239063. In addition, SB 239063 significantly reduced the increase of Th2 cytokines and OVA-specific IgE. The inhibition of p38 MAPK or VEGF signaling prevented and also decreased the increases in the number of inflammatory cells and airway hyperresponsiveness in OVA-induced allergic airway disease. These results indicate that inhibition of p38 MAPK may attenuate allergen-induced airway inflammation and vascular leakage through modulation of VEGF expression in mice.

Anti-inflammatory and anti-angiogenic effects of flavonoids isolated from Lycium barbarum Linnaeus on human umbilical vein endothelial cells

Anti-inflammatory and anti-angiogenic effects of flavonoids isolated from Lycium barbarum fruits, a traditional Chinese medicine, on human umbilical vein endothelial cells (HUVECs) were investigated. Initially, flavonoids were extracted with 80% ethanol and separated using a Cosmosil 140 C18-OPN column, with the acidic fraction eluted with deionized water being composed of chlorogenic acid, caffeoyl quinic acid, caffeic acid and p-coumaric acid and the neutral fraction eluted with methanol composed of quercetin-diglycoside, rutin and kaempferol-O-rutinoside. Flavonoid extract was effective in inhibiting expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule (VCAM-1) induced by TNF-α in HUVECs. The RT-PCR analysis indicated that ICAM-1 mRNA induced by TNF-α was inhibited by flavonoid extract. The flavonoid extract attenuated TNF-α-induced IκB phosphorylation as well as NF-κB, p65 and p50 translocation from cytosol to nucleus, through inhibition on TNF-α- and H(2)O(2)-induced intracellular reactive oxygen species (ROS) production. For the anti-angiogenic study, the flavonoid extract inhibited vascular endothelial growth factor (VEGF)-induced cell proliferation and migration in HUVECs, as well as angiogenesis. However, the flavonoid extract did not inhibit VEGF signaling. Surprisingly, HUVECs adhesion to the extracellular matrix was compromised and adhesion-induced signaling was retarded by the flavonoid extract.

Bevacizumab for glioblastoma refractory to vascular endothelial growth factor receptor inhibitors

Glioblastoma (GBM) is a highly vascular tumor dependent on angiogenesis through the vascular endothelial growth factor (VEGF) signaling cascade. Inhibition of VEGF signaling is an important therapeutic strategy. We report our experience with bevacizumab (BEV), a VEGF targeting antibody, following failure of a VEGF receptor targeting tyrosine kinase inhibitor (TKI). We retrospectively identified patients treated on clinical trials with VEGFR-TKIs for recurrent GBM followed by BEV at next recurrence. Survival was estimated by the Kaplan-Meier method. Fourteen patients were identified (six women; median age 57). All received VEGFR-TKIs (sunitinib 11, cediranib 2, sorafenib 1) then BEV at next recurrence. There were no radiographic responses to VEGFR-TKIs; best response was stable disease in 50% (7/14). Patients received BEV alone (21%, 3/14) or in combination with chemotherapy (79%, 11/14). On BEV, 29% (4/14) had a partial response, and 36% (5/14) stabilized. Of evaluable patients, 42% (5/12) had neurological improvement and 56% (5/9) reduced corticosteroid requirement. Median survival on BEV was 7.8 months (95% CI 4.0-15.8), median progression-free survival (PFS) was 4.0 months (95% CI 1.6-10.5), and the 6-month PFS rate was 29% (95% CI 9-52). Our radiographic and survival outcomes with BEV following progression after VEGFR-TKIs are similar to data from studies of BEV as initial salvage therapy, although our sample size was small. Prior exposure to VEGFR-TKIs may not preclude response to BEV, but sensitivity to BEV may be lower following more robust VEGFR inhibition.

VEGF regulates antidepressant effects of lamotrigine

The anticonvulsant drug lamotrigine has been shown to produce strong antidepressant effects in the treatment of bipolar disorder patients. Our previous studies have demonstrated that brain derived neurotrophic factor (BDNF) signaling plays an important role in regulating its behavioral actions in several rodent models of depression. The current study extends earlier work on BDNF and explores the role of another important neurotrophin vascular endothelial growth factor (VEGF) in regulating the antidepressant actions of lamotrigine. The results showed that chronic administration of 30mg/kg lamotrigine (14days) normalized the down-regulated frontal and hippocampal VEGF protein expression as well as the behavioral deficits induced by chronic unpredictable stress. In addition, pharmacological inhibition of VEGF signaling by infusion of SU5416, a selective Flk-1 receptor inhibitor, blocks the antidepressant effects of lamotrigine in all behavioral paradigms. Taken together, this study provides further evidence that VEGF is also an essential regulator for the antidepressant effects of lamotrigine.

Biomarkers in tumor angiogenesis and anti-angiogenic therapy.

Tumor angiogenesis has been identified to play a critical role in tumor growth and tumor progression, and is regulated by a balance of angiogenic and anti-angiogenic cytokines. Among them VEGF (vascular endothelial growth factor) and its signaling through its receptors are of crucial relevance. Inhibition of VEGF signaling by monoclonal antibodies or small molecules (kinase inhibitors) has already been successfully established for the treatment of different cancer entities and multiple new drugs are being tested in clinical trials. However not all patients are likely to respond to these therapies, but to date there are no reliable biomarkers available to predict therapy response. Many studies integrated biomarker programs in their study protocols, thus several potential biomarkers have been identified which are currently under clinical investigation in prospective randomized studies. This review intends to give an overview of the described potential biomarkers as well as different imaging techniques such as ultrasound and magnetic resonance imaging that can indicate benefit, resistance and toxicity to anti-angiogenic therapies.

Precise Scheduling of Chemotherapy Primes VEGF-producing Tumors for Successful Systemic Oncolytic Virotherapy

We have previously reported that a burst of vascular endothelial growth factor (VEGF) signaling to tumor-associated endothelium induces a proviral state, during which systemically delivered oncolytic reovirus can replicate in endothelium, thereby inducing immune-mediated vascular collapse and significant antitumor therapy. Using chimeric receptors, we show here that induction of the proviral state proceeds through VEGFR2, but not VEGFR1, signaling in endothelial cells. In contrast, innate immune activation by reovirus-exposed endothelial cells was predominantly through VEGFR1. By screening conventional chemotherapies for their ability to induce similar effects in combination with reovirus both in vitro and in vivo, we observed that the proviral state could also be induced in endothelial cells exposed to VEGF during rebound from paclitaxel-mediated inhibition of VEGF signaling. We translated these in vitro findings in vivo by careful scheduling of paclitaxel chemotherapy with systemic virotherapy, neither of which alone had therapeutic effects against B16 tumors. Systemic availability of reovirus during endothelial cell recovery from paclitaxel treatment allowed for endothelial replication of the virus, immune-mediated therapy, and tumor cures. Therefore, careful scheduling of combination viro- and chemotherapies, which preclinical testing suggests are individually ineffective against tumor cells, can lead to rational new clinical protocols for systemic treatments with oncolytic viruses.

Sunitinib, Hypertension, and Heart Failure: A Model for Kinase Inhibitor-Mediated Cardiotoxicity

Kinase inhibitors have emerged as an important new class of agents for the treatment of diverse tumors. Sunitinib malate is a small-molecule, oral, multi-kinase inhibitor approved for use in treating renal cell carcinoma and gastrointestinal stromal tumor. It has also demonstrated efficacy in treating pancreatic neuroendocrine tumors and is being evaluated for the treatment of other cancers. Initially developed for its inhibition of the vascular endothelial growth factor (VEGF) signaling pathway, sunitinib has been associated with hypertension and heart failure. This review examines the incidence and severity of these adverse events, relevant findings from other agents that inhibit VEGF signaling, the mechanisms underlying these effects, and suggestions for their clinical management. Hypertension is a common adverse effect that is usually easily managed. The associated heart failure is less common; it can be reversible but must be actively monitored and managed. Mechanistic insights suggest that an attentive clinical strategy for hypertension could prevent severe cardiotoxicity.

Regulation of vascular growth and tone by hydrogen sulfide

Hydrogen sulfide (H2S) is a colourless, flammable gas with a characteristic pungent smell. Until recently, the H2S literature was focused in the toxicology of this agent. Exposure to H2S concentrations lower than 100 ppm lead to eye irritation, sore throat, dizziness, nausea, shortness of breath, and chest tightness, while exposure to 1000 ppm or more causes central nervous system toxicity and respiratory depression. In the past 5 years the interest for H2S biology has seen an upsurge, as it was accepted that low amounts of this gas are endogenously produced in most mammalian tissues. Increasing evidence shows that H2S acts as a signalling molecule in cells and is now considered the third member of the gasotransmitter family along with nitric oxide and carbon monoxide. Most of H2S is produced by two enzymes cystathionine-synthase (CBS) and cystathionine γ-lyase (CSE) that use L-cysteine as a substrate and pyridoxal phosphate as a co-factor. CBS is highly expressed in the central nervous system, while CSE is abundantly present in the heart, lung, blood vessels, liver and kidney. In the cardiovascular system, H2S has anti-apoptotic effects on cardiomyocytes, exerts cardioprotective actions and modifies vascular tone. We have recently shown that exogenously administered Na2S stimulates endothelial proliferation, migration and capillary-like network formation. These effects of H2S on migration are mediated through the activation of ATP-sensitive K+-channels (KATP) and activation of mitogen activated protein kinase pathways. Inhibition of CSE and reduction of endogenously produced H2S reduces vascular network length and branching of blood vessels in the chicken chorioallantoic membrane. Exposure of endothelial cells to vascular endothelial growth factor (VEGF) increased H2S production and genetic or pharmacological inhibition of CSE restricted VEGF signalling and VEGF-driven angiogenic responses (migration, sprouting). Thus, H2S is an endogenous activator of angiogenesis and modulation of its production might be useful in diseases characterized by aberrant or excessive angiogenesis. H2S exerts important biological actions in vascular smooth muscle cells. Originally H2S–induced vasorelaxation was believed to be mediated by potassium channels (including KATP channels). However, significant vasodilation can be observed after sulfonylurea treatment, suggesting that additional pathways are involved. We recently showed that H2S donors inhibit phosphodiesterase activity in vitro and that exposure to H2S increases cGMP levels in smooth muscle cells. The cGMP elevating effects of H2S are abolished following phosphodiesterase inhibition. Moreover, incubation of cells with H2S led to an increase in VASP phopshorylation on Ser239, suggesting that H2S activates PKG signalling pathways. More importantly, incubation of aortic rings with selective PKG-I inhibitors (DT-2, DT-3) attenuated H2S-induced vasorelaxation. Our results reinforce the notion that H2S plays important roles in vascular biology, by modulating vascular growth and tone.

An Algorithm for the Management of Hypertension in the Setting of Vascular Endothelial Growth Factor Signaling Inhibition

Vascular endothelial growth factor (VEGF) signaling is considered to be one of the key factors involved in tumor-associated angiogenesis. Inhibition of angiogenesis has significantly improved anticancer therapy making it one of the cornerstones of treatment for various solid tumors. Several antiangiogenesis inhibitory compounds (eg, bevacizumab, sunitinib, sorafenib) are now widely used in the treatment of patients with colorectal, non-small-cell lung, advanced renal cell, hepatocellular, and breast cancer. One of the most commonly observed side effects of inhibition of VEGF signaling is hypertension, which is dose-dependent and varies in incidence among the different angiogenesis inhibitor drugs. Poorly controlled hypertension not only can lead to cardiovascular events, renal disease, and stroke, but may also necessitate discontinuation of anticancer therapy, thereby potentially limiting overall clinical benefit. In contrast, hypertension induced by VEGF inhibitors has been shown to represent an important pharmacodynamic biomarker of oncologic response. For the practicing oncologist, knowledge and optimal management of this toxicity is essential. Because of the lack of controlled studies on this topic, no clear recommendations are available. In this article, we review the available preclinical and clinical data on the pathogenesis and management of hypertension resulting from anti-VEGF inhibitor therapy and propose a treatment algorithm that our group has now implemented for daily clinical practice.

Decreased circulating soluble Tie2 levels in preeclampsia may result from inhibition of vascular endothelial growth factor (VEGF) signaling.

Recent studies have found dysregulation in circulating levels of a number of angiogenic factors and their soluble receptors in preeclampsia. In this study, we examined the mechanism of production of soluble Tie2 (sTie2) and its potential connection to the failure of vascular remodeling in preeclamptic pregnancies. Serum samples were collected prospectively from 41 pregnant subjects at five different time points throughout pregnancy. Five of these subjects developed preeclampsia. For a second study, serum and placental samples were collected at delivery from preeclamptic and gestational age-matched controls. We examined serum sTie2 levels, and angiopoietin 1, angiopoietin 2, and Tie2 mRNA expression and localization in placental samples from the central basal plate area. We also examined the effects of vascular endothelial growth factor (VEGF) and a matrix metalloproteinase (MMP) inhibitor on proteolytic shedding of Tie2 in uterine microvascular endothelial cells. Serum sTie2 levels were significantly lower in preeclamptic subjects starting at 24-28 wk of gestation and continued to be lower through the time of delivery. In culture experiments, VEGF treatment significantly increased sTie2 levels in conditioned media, whereas the MMP inhibitor completely blocked this increase, suggesting that VEGF-induced Tie2 release is MMP dependent. Our data suggest, for the first time, an interaction between VEGF and Tie2 in uterine endothelial cells and a potential mechanism for the decrease in circulating sTie2 levels in preeclampsia, likely through inhibition of VEGF signaling. Further studies on VEGF-Tie2 interactions during pregnancy should provide new insights into the mechanisms underlying the failure of vascular remodeling in preeclampsia and other pregnancy complications.

Effect of MDM2 and vascular endothelial growth factor inhibition on tumor angiogenesis and metastasis in neuroblastoma

Neuroblastoma is the most common pediatric abdominal tumor and principally a p53 wild-type, highly vascular, aggressive tumor, with limited response to anti-VEGF therapies alone. MDM2 is a key inhibitor of p53 and a positive activator of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) activity with an important role in neuroblastoma pathogenesis. We hypothesized that concurrent inhibition of both MDM2 and VEGF signaling would have cooperative anti-tumor effects, potentiating anti-angiogenic strategies for neuroblastoma and other p53 wild-type tumors. We orthotopically implanted SH-SY5Y neuroblastoma cells into nude mice (n = 40) and treated as follows: control, bevacizumab, Nutlin-3a, combination of bevacizumab plus Nutlin-3a. Expression of HIF-1α and VEGF were measured by qPCR, Western blot, and ELISA. Tumor apoptosis was measured by immunohistochemistry and caspase assay. Angiogenesis was evaluated by immunohistochemistry for vascular markers (CD-31, type-IV collagen, αSMA). Both angiogenesis and metastatic burden were digitally quantified. In vitro, Nutlin-3a suppresses HIF-1α expression with subsequent downregulation of VEGF. Bevacizumab plus Nutlin-3a leads to significant suppression of tumor growth compared to control (P < 0.01) or either agent alone. Combination treated xenograft tumors display a marked decrease in endothelial cells (P < 0.0001), perivascular basement membrane (P < 0.04), and vascular mural cells (P < 0.004). Nutlin-3a alone and in combination with bevacizumab leads to significant tumor apoptosis (P < 0.0001 for both) and significant decrease in incidence of metastasis (P < 0.05) and metastatic burden (P < 0.03). Bevacizumab plus Nutlin-3a cooperatively inhibits tumor growth and angiogenesis in neuroblastoma in vivo with dramatic effects on tumor vascularity. Concomitantly targeting VEGF and p53 pathways potently suppresses tumor growth, and these results support further clinical development of this approach.

Engineered Conformation-dependent VEGF Peptide Mimics Are Effective in Inhibiting VEGF Signaling Pathways

Angiogenesis, or formation of new blood vessels, is crucial to cancer tumor growth. Tumor growth, progression, and metastasis are critically influenced by the production of the pro-angiogenic vascular endothelial growth factor (VEGF). Promising anti-angiogenic drugs are currently available; however, their susceptibilities to drug resistance and long term toxicity are serious impediments to their use, thus requiring the development of new therapeutic approaches for safe and effective angiogenic inhibitors. In this work, peptides were designed to mimic the VEGF-binding site to its receptor VEGFR-2. The VEGF conformational peptide mimic, VEGF-P3(CYC), included two artificial cysteine residues, which upon cyclization constrained the peptide in a loop native-like conformation to better mimic the anti-parallel structure of VEGF. The engineered cyclic VEGF mimic peptide demonstrated the highest affinity to VEGFR-2 by surface plasmon resonance assay. The VEGF peptide mimics were evaluated as inhibitors in several in vitro assays in which VEGF-dependent signaling pathways were observed. All VEGF mimics inhibited VEGFR-2 phosphorylation with VEGF-P3(CYC) showing the highest inhibitory effects when compared with unstructured peptides. Additionally, we show in several angiogenic in vitro assays that all the VEGF mimics inhibited endothelial cell proliferation, migration, and network formation with the conformational VEGF-P3 (CYC) being the best. The VEGF-P3(CYC) also caused a significant delay in tumor development in a transgenic model of VEGF(+/-)Neu2-5(+/-). These results indicate that the structure-based design is important for the development of this peptidomimetic and for its anti-angiogenic effects.

VEGF non-angiogenic functions in adult organ homeostasis: therapeutic implications

Vascular endothelial growth factor (VEGF) is best known as an angiogenic factor essential for embryonic vasculogenesis and postnatal angiogenesis. Considerable evidence has accumulated that VEGF also has non-angiogenic functions. Early studies demonstrated that VEGF transcripts are ubiquitously expressed, and the phosphorylation of VEGF receptor is detectable in adult organs that have no feature of angiogenesis. Recent clinical studies showed that the inhibition of VEGF signaling results in diverse angiogenesis-irrelevant side effects involving the dysfunctions of many organs, suggesting non-angiogenic roles of VEGF in the regulation of organ homeostasis. On the other hand, VEGF stimulates endothelial cells (ECs) to express intercellular adhesion molecules that mediate physical interactions with adjacent tissue cells, or secreted various multifunctional substances that affect the functions of surrounding organs. Furthermore, very recent studies including ours have revealed VEGF as a potent agonist for endothelial exocytosis of Weibel-Palade bodies in which thrombogenic and inflammatory factors are stored. In this brief review, we highlight the importance of VEGF non-angiogenic functions in the modulation of tissue repair and organ regeneration, vascular homeostasis, and inflammation, and propose that the non-angiogenic functions are primarily mediated through the substances released from ECs.

Cytokine and angiogenic factor (CAF) profiling for identification of markers associated with response to cediranib in metastatic renal cell carcinoma (mRCC).

362 Background: Cediranib is a highly potent and selective signaling inhibitor of vascular endothelial growth factor (VEGF) receptors−1, −2, −3 and c-Kit. In a phase II trial, patients (pts) with mRCC were randomized 3:1 to treatment with cediranib or placebo to primarily assess the difference in change in tumor size at 12 weeks. Cediranib resulted in a significant reduction in tumor size vs. placebo (Mulders et al. ESMO. 2009). Here we investigated soluble biomarkers in serum and concentration changes during treatment. Methods: Pts received cediranib 45 mg/day PO or placebo for the first 12 weeks on treatment. At that time (or upon progression if earlier), treatment was unblinded and pts on placebo were given the option of receiving cediranib. Serum was collected from 61 pts at baseline (BL; cediranib 46, placebo 15), from 50 pts on day (D) 28, and from 45 pts on D84. Multiplex bead suspension arrays and ELISA were used to measure CAF concentrations including VEGF, placental growth factor (PlGF), sVEGFR-2, PDGFbb, HGF, MMP-9, multiple chemokines and interleukins (IL). The objectives of this exploratory analysis were to assess whether baseline CAFs were associated with changes in tumor size after 12 weeks of treatment and whether CAF levels changed while on treatment. Results: Of 39 CAFs available at BL, lower than median (‘low') concentrations of IL-10, VEGF, PlGF, stem cell factor (SCF), and monokine-induced by interferon-gamma (MIG) were associated with larger decreases in tumor size than high concentrations (independent of treatment arm), whereas the opposite trend was observed for IL-5 and TRAIL. Consistent with inhibition of VEGF signaling, cediranib treatment resulted in changes over time in VEGF (increase), sVEGFR-2 (decrease) and PlGF (increase) concentrations. In addition, SCF, a c-Kit ligand and M-CSF decreased, while VCAM-1 and TRAIL increased during cediranib treatment. Conclusions: Candidate CAFs associated with response to cediranib in mRCC such as IL-10 and VEGF were identified. Patients treated with cediranib showed distinct CAF changes compared with placebo. These results require independent validation in a larger trial. [Table: see text]

373 The oral MEK1/MEK2 inhibitor, GSK1120212, effectively inhibits the MAPK pathway: pharmacokinetic, pharmacodynamic, and clinical response relationship

Vascular endothelial cells are ordinarily quiescent in adult humans and divide less than once per decade. When tumors reach a size of about 0.2–2.0 mm in diameter, they become hypoxic and limited in size in the absence of angiogenesis. There are about 30 endogenous pro-angiogenic factors and about 30 endogenous anti-angiogenic factors. In order to increase in size, tumors undergo an angiogenic switch where the action of pro-angiogenic factors predominates, resulting in angiogenesis and tumor progression. One mechanism for driving angiogenesis results from the increased production of vascular endothelial growth factor (VEGF) following up-regulation of the hypoxia-inducible transcription factor. The human VEGF family consists of VEGF (VEGF-A), VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PlGF). The VEGF family of receptors consists of three protein-tyrosine kinases and two non-protein kinase receptors (neuropilin-1 and -2). Owing to the importance of angiogenesis in tumor progression, inhibition of VEGF signaling represents an attractive cancer treatment.

Tyrosine Kinase Inhibitor PTK/ZK Enhances the Antitumor Effects of Interferon-α/5-Fluorouracil Therapy for Hepatocellular Carcinoma Cells

There is no standardized treatment for hepatocellular carcinoma (HCC) with portal vein tumor thrombus. We previously reported the efficacy of interferon-alpha and 5-fluorouracil combination (IFN/5-FU) therapy for these patients and the potential mechanism via the regulation of vascular endothelial growth factor (VEGF). In this study, we showed the VEGF-related effects of IFN/5-FU therapy using VEGF-receptor (VEGFR) selective inhibitor, PTK787/ZK222584 (PTK/ZK), in HCC cells. Using two VEGF secreting and VEGFR expressing human HCC cell lines, PLC/PRF/5 and HuH7, we performed growth inhibitory assays in vitro and in vivo, apoptosis assay, cell cycle analysis, and Western blot analysis for the mechanism, with or without PTK/ZK in IFN/5-FU therapy. The combination of PTK/ZK and IFN/5-FU significantly inhibited cell growth in vitro and tended to reduce tumor growth in vivo in a HuH7 xenograft model in nude mice-in both cases without affecting VEGF secretion. PTK/ZK enhanced the IFN/5-FU induced apoptosis, based on increased proteins levels of Bax and reduced Bcl-xL and Bcl-2. Cell cycle analysis showed different results between the HCC cell lines following the combination therapy, possibly due to differences in p21 protein. VEGF signaling inhibition would support an antitumor effect of IFN/5-FU therapy against HCC cell lines via induction of apoptosis and cell cycle delay.