Adenovirus-mediated delivery of a soluble form of the VEGF receptor Flk1 delays the growth of murine and human pancreatic adenocarcinoma in mice

Targeting the IGF-Axis for Cancer Therapy: Development and Validation of an IGF-Trap as a Potential Drug

The insulin-like growth factor (IGF)-axis was implicated in cancer progression and identified as a clinically important therapeutic target. Several IGF-I receptor (IGF-IR) targeting drugs including humanized monoclonal antibodies have advanced to phase II/III clinical trials, but to date, have not progressed to clinical use, due, at least in part, to interference with insulin receptor signaling and compensatory signaling by the insulin receptor (IR) isoform A that can bind IGF-II and initiate mitogenic signaling. Here we briefly review the current state of IGF-targeting biologicals, discuss some factors that may be responsible for their poor performance in the clinic and outline the stepwise bioengineering and validation of an IGF-Trap—a novel anti-cancer therapeutic that could bypass these limitations. The IGF-Trap is a heterotetramer, consisting of the entire extracellular domain of the IGF-IR fused to the Fc portion of human IgG₁. It binds human IGF-I and IGF-II with a three-log higher affinity than insulin and could inhibit IGF-IR driven cellular functions such as survival, proliferation and invasion in multiple carcinoma cell models in vitro. In vivo, the IGF-Trap has favorable pharmacokinetic properties and could markedly reduce metastatic outgrowth of colon and lung carcinoma cells in the liver, outperforming IGF-IR and ligand-binding monoclonal antibodies. Moreover, IGF-Trap dose-response profiles correlate with their bio-availability profiles, as measured by the IGF kinase receptor-activation (KIRA) assay, providing a novel, surrogate biomarker for drug efficacy. Our studies identify the IGF-Trap as a potent, safe, anti-cancer therapeutic that could overcome some of the obstacles encountered by IGF-targeting biologicals that have already been evaluated in clinical settings.

The IGF-Trap: Novel Inhibitor of Carcinoma Growth and Metastasis

The IGFI receptor promotes malignant progression and has been recognized as a target for cancer therapy. Clinical trials with anti-IGFIR antibodies provided evidence of therapeutic efficacy but exposed limitations due in part to effects on, and the compensatory function of, the insulin receptor system. Here, we report on the production, characterization, and biologic activity of a novel, IGF-targeting protein (the IGF-Trap) comprising a soluble form of hIGFIR and the Fc portion of hIgG1. The IGF-Trap has a high affinity for hIGFI and hIGFII but low affinity for insulin, as revealed by surface plasmon resonance. It efficiently blocked IGFIR signaling in several carcinoma cell types and inhibited tumor cell proliferation, migration, and invasion in vitro. In vivo, the IGF-Trap showed favorable pharmacokinetic properties and could suppress the growth of established breast carcinoma tumors when administered therapeutically into tumor-bearing mice, improving disease-free survival. Moreover, IGF-Trap treatment markedly reduced experimental liver metastasis of colon and lung carcinoma cells, increasing tumor cell apoptosis and reducing angiogenesis. Finally, when compared with an anti-IGFIR antibody or IGF-binding protein-1 that were used at similar or higher concentrations, the IGF-Trap showed superior therapeutic efficacy to both inhibitors. Taken together, we have developed a targeted therapeutic molecule with highly potent anticancer effects that could address limitations of current IGFIR-targeting agents.

Gene therapy in pancreatic cancer

Pancreatic cancer (PC) is a highly lethal disease and notoriously difficult to treat. Only a small proportion of PC patients are eligible for surgical resection, whilst conventional chemoradiotherapy only has a modest effect with substantial toxicity. Gene therapy has become a new widely investigated therapeutic approach for PC. This article reviews the basic rationale, gene delivery methods, therapeutic targets and developments of laboratory research and clinical trials in gene therapy of PC by searching the literature published in English using the PubMed database and analyzing clinical trials registered on the Gene Therapy Clinical Trials Worldwide website (http://www. wiley.co.uk/genmed/ clinical). Viral vectors are main gene delivery tools in gene therapy of cancer, and especially, oncolytic virus shows brighter prospect due to its tumor-targeting property. Efficient therapeutic targets for gene therapy include tumor suppressor gene p53, mutant oncogene K-ras, anti-angiogenesis gene VEGFR, suicide gene HSK-TK, cytosine deaminase and cytochrome p450, multiple cytokine genes and so on. Combining different targets or combination strategies with traditional chemoradiotherapy may be a more effective approach to improve the efficacy of cancer gene therapy. Cancer gene therapy is not yet applied in clinical practice, but basic and clinical studies have demonstrated its safety and clinical benefits. Gene therapy will be a new and promising field for the treatment of PC.

Sustained production of a soluble IGF-I receptor by gutless adenovirus-transduced host cells protects from tumor growth in the liver

The IGF-I receptor (IGF-IR) has an important role in malignant disease and is the target of several drugs presently in clinical trials. Gene therapy has been explored as cancer treatment, mainly for delivery of genes that induce cell death or enhance the immunological response to cancer. Previously, we have shown that the implantation of autologous bone-marrow stromal cells producing a soluble form of IGF-IR (sIGFIR) inhibited experimental liver metastasis of several tumor types in mice. Here, we evaluated the utility of adenovirus-based gene delivery for generating therapeutically effective plasma levels of this decoy. We constructed a third generation gutless adenovirus expressing sIGFIR and found that HEK-293 cells transduced by this, but not control adenoviruses, secreted soluble receptor protein that blocked IGF-I-induced tumor cell migration, proliferation and survival in vitro. Following virus injection in vivo, viral DNA was detectable by PCR in several host organs, particularly the liver, and this resulted in the production of measurable sIGFIR plasma levels for up to 21 days post injection. In mice producing virus-encoded sIGFIR, experimental liver metastasis was inhibited, indicating that sIGFIR levels were therapeutically effective. The results show that adenovirus-based delivery of inhibitory soluble proteins can provide an effective anticancer strategy.

Autocrine activity of soluble Flt-1 controls endothelial cell function and angiogenesis

BACKGROUND

The negative feedback system is an important physiological regulatory mechanism controlling angiogenesis. Soluble vascular endothelial growth factor (VEGF) receptor-1 (sFlt-1), acts as a potent endogenous soluble inhibitor of VEGF- and placenta growth factor (PlGF)-mediated biological function and can also form dominant-negative complexes with competent full-length VEGF receptors.

METHODS AND RESULTS

Systemic overexpression of VEGF-A in mice resulted in significantly elevated circulating sFlt-1. In addition, stimulation of human umbilical vein endothelial cells (HUVEC) with VEGF-A, induced a five-fold increase in sFlt-1 mRNA, a time-dependent significant increase in the release of sFlt-1 into the culture medium and activation of the flt-1 gene promoter. This response was dependent on VEGF receptor-2 (VEGFR-2) and phosphoinositide-3'-kinase signalling. siRNA-mediated knockdown of sFlt-1 in HUVEC stimulated the activation of endothelial nitric oxide synthase, increased basal and VEGF-induced cell migration and enhanced endothelial tube formation on growth factor reduced Matrigel. In contrast, adenoviral overexpression of sFlt-1 suppressed phosphorylation of VEGFR-2 at tyrosine 951 and ERK-1/-2 MAPK and reduced HUVEC proliferation. Preeclampsia is associated with elevated placental and systemic sFlt-1. Phosphorylation of VEGFR-2 tyrosine 951 was greatly reduced in placenta from preeclamptic patients compared to gestationally-matched normal placenta.

CONCLUSION

These results show that endothelial sFlt-1 expression is regulated by VEGF and acts as an autocrine regulator of endothelial cell function.

Inhibitory effects of a chimeric anti-VEGFR-2 Fab antibody on tumor growth and angiogenesis in an orthotopic xenograft mouse model of hepatocellular carcinoma

AIM: To investigate the inhibitory effects of a mouse chimeric anti-VEGFR-2 Fab antibody on tumor growth and angiogenesis in an orthotopic xenograft mouse model of hepatocellular carcinoma.

METHODS: The antigen-binding activity of cFab antibody was assessed by ELISA. An orthotopic xenograft mouse model of hepatocellular carcinoma was created by direct injection of H22 cells into the liver parenchyma of ICR mice. Twenty-four ICR mice bearing orthotopic HCC were divided into two groups: control group (treated with normal saline) and cFab group (treated with cFab antibody). After the treatment, tumor weight and mouse survival time were compared between the two groups. Histological changes and microvessel density (MVD) in tumors were also evaluated.

RESULTS: The chimeric anti-VEGFR-2 Fab antibody exhibited a strong binding activity to VEGFR-2. Tumor size in the cFab group was significantly decreased compared with the control group (313.9 mm³ ± 41.9 mm³vs 635.4 mm³ ± 70.1 mm³, P < 0.05); and the mice of the cFab group had a significantly longer survival time (20.0 d vs 13.0 d, Long-rank test χ² = 4.611, P = 0.032). The MVD in the cFab group was also significantly lower than that in the control group (34.48 ± 1.39 vs 9.56 ± 1.26,P < 0.05).

CONCLUSION: The chimeric anti-VEGFR-2 Fab antibody can inhibit tumor growth in an orthotopic xenograft mouse model of hepatocellular carcinoma possibly by inhibiting tumor angiogenesis.

Pancreatic cancer: gene therapy approaches and gene delivery systems

IMPORTANCE OF THE FIELD

Due to the absence of early diagnosis, the highly invasive and metastatic features and the lack of effective therapeutic modalities, the prognosis of patients with pancreatic cancer is poor. Gene therapy is currently regarded as a potential and promising therapeutic modality for pancreatic cancer.

AREAS COVERED IN THIS REVIEW

This article summarizes an update of gene therapy approaches and reviews the latest progress in gene delivery systems that have been tested on pancreatic cancer.

WHAT THE READER WILL GAIN

The treatment effectiveness of gene combination therapy is better than that of the regulation of single-gene or single gene therapy approaches. Naked DNA is limited because of degradation by intracellular and extracellular nucleases. Virus vectors show high transfection efficiency but are limited due to immunogenicity, inflammatory response and potential carcinogenicity. Non-viral vectors, such as cationic polymers or inorganic nanoparticles, show an important feature that they can be easily modified, and the progress of materials science will provide more and better non-viral vectors, accordingly improving the efficiency and safety of gene therapy, which will make them the most promising vectors for pancreatic cancer.

A decrease in maternal plasma concentrations of sVEGFR-2 precedes the clinical diagnosis of preeclampsia

OBJECTIVE

The aim of this study was to examine if maternal plasma concentrations of soluble vascular endothelial growth factor receptor (sVEGFR)-2 change prior to the diagnosis of preeclampsia.

STUDY DESIGN

A longitudinal study was conducted in normal pregnant women (n = 160) and patients with preeclampsia (n = 40). Blood samples were collected at 7 gestational age intervals from 6 weeks to term. Plasma concentrations of sVEGFR-2 were determined by enzyme-linked immunosorbent assay. Analysis was performed with cross-sectional and longitudinal (mixed effects model) approaches.

RESULTS

Mothers destined to develop preeclampsia have lower plasma sVEGFR-2 concentrations than those who will have a normal pregnancy (longitudinal approach; P < .05). Cross-sectional analysis suggested that the median plasma sVEGFR-2 concentration in women destined to develop preeclampsia was significantly lower than that in normal pregnant women from 28-31 weeks of gestation (P = .001) or 6-10 weeks prior to the diagnosis (P < .001).

CONCLUSION

A lower maternal plasma sVEGFR-2 concentration precedes the development of preeclampsia, both term and preterm.

Urokinase-type plasminogen activator receptor transcriptionally controlled adenoviruses eradicate pancreatic tumors and liver metastasis in mouse models

Treatment options for pancreatic cancer have shown limited success mainly owing to poor selectivity for pancreatic tumor tissue and to a lack of activity in the tumor. In this study, we describe the ability of the urokinase-type plasminogen activator receptor (uPAR) promoter to efficiently and selectively target pancreatic tumors and metastases, which enables the successful management of pancreatic cancer. We have generated a replication-defective reporter adenovirus, AduPARLuc, and a conditionally replicating adenovirus, AduPARE1A, and we have studied the selectivity and antitumoral efficacy in pancreatic tumors and metastases. Toxicity was studied on intravascular delivery. We demonstrate that the uPAR promoter is highly active in pancreatic tumors but very weak in normal tissues. Tumor specificity is evidenced by a 100-fold increase in the tumor-to-liver ratio and by selective targeting of liver metastases (P < .001). Importantly, the AduPARE1A maintains the oncolytic activity of the wild-type virus, with reduced toxicity, and exhibits significant antitumoral activity (25% tumor eradication) and prolonged survival in pancreatic xenograft models (P < .0001). Furthermore, upon intravascular delivery, we demonstrate complete eradication of liver metastasis in 33% of mice, improving median survival (P = 5.43 x 10(-5)). The antitumoral selective activity of AduPARE1A shows the potential of uPAR promoter-based therapies in pancreatic cancer treatment.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

Spatiotemporal expression of flk-1 in pulmonary epithelial cells during lung development

Vascular endothelial growth factor-A (VEGF-A) responsive effects mediated via the receptors fetal liver kinase-1 (flk-1) and fms-like tyrosine kinase (flt-1), are key processes of pulmonary vascular development. Flk-1 has been shown to be involved in early embryonic lung epithelial to endothelial crosstalk and branching morphogenesis. Recent reports suggested a role of VEGF-A in lung epithelial cell function. Based on these observations, we hypothesize that epithelial flk-1 has a unique function in pulmonary development. Thus, the aim of this study is to elucidate spatiotemporal expression of flk-1 during lung development with respect to the epithelial system. Embryonic lungs were screened for flk-1 messenger RNA and protein at daily intervals, including postnatal stages. From Embryonic Day (ED) 12.5 through ED 15.5, flk-1 expression was restricted to the early vascular primitive network, while from ED 16.5 on flk-1 was detectable in the epithelial system and persisted there postnatally. At postnatal stages, flk-1 expression was increasingly restricted to individual cells in the alveolar septa. Isolation and in vitro cultivation of alveolar epithelial cells confirmed flk-1 expression and showed VEGF secretion into the supernatant. To our knowledge, this is the first murine study characterizing epithelial flk-1 expression at different stages throughout lung organogenesis until birth and at postnatal stages. To confirm epithelial flk-1 expression, we performed reporter gene analysis of the flk-1 promoter in vivo. Investigations on transgenic mouse strains, containing either a complete or incomplete flk-1 promoter driving expression of the lacZ reporter gene, suggested differential flk-1 regulation in endothelial and epithelial cells.

Recombinant adenovirus as a methodology for exploration of physiologic functions of growth factor pathways

The use of recombinant adenoviruses (Ad) to express secreted antagonists of growth factors represents a powerful strategy for studying physiologic functions of growth factor pathways in experimental animals. Indeed, a single adenoviral injection can produce characteristic high-level and persistent plasma expression of soluble receptor ectodomains or secreted protein antagonists, allowing highly stringent conditional inactivation of target pathways in vivo. In this review, we describe our experience using recombinant Ad to inactivate growth factor pathways in vivo and discuss their advantages and limitations. Using our studies on vascular endothelial growth factor and Wnt systems as examples, we further describe how recombinant Ad can unveil previously unknown physiological roles of signaling pathways. Finally, we discuss the potential physiological and therapeutic relevance of our findings.

Non-viral delivery of interleukin-2 and soluble Flk-1 inhibits metastatic and primary tumor growth in renal cell carcinoma

Treatments for renal cell carcinoma, while promising, are still limited by toxicity and cost. In the hopes of finding a novel compound or combination, we developed a plasmid containing the genes for interleukin-2 (IL-2) and soluble vascular endothelial growth factor receptor 2 (msFlk1). The plasmid, p2CMVIL2/msFlk1, demonstrated similar in vitro transgene expression of IL-2 or msFlk1 compared to their single-agent counterparts. Subcutaneous tumor growth was significantly inhibited in the p2CMVIL2/msFlk1 group when delivered locally by the non-viral water soluble polymer, WSLP and exhibited a 50% increase in survival over glucose and single-agent controls. In vivo experimentation demonstrated that WSLP/msFlk1 decreased microvessel density in pCMVmsFlk1 and p2CMVIL2/msFlk1 treated groups. Furthermore, tumor-infiltrating lymphocytes expressing CD45RO and CD68 were increased within the tumor microenvironment upon p2CMVIL2/msFlk1 treatment. To determine the effects of p2CMVIL2/msFlk1 in an experimental RENCA lung metastases model, therapeutic DNA was delivered systemically following complexation with the angiogenic endothelial-targeting polymer PEI-g-PEG-RGD. The p2CMVIL2/msFlk1 treatment significantly reduced metastases by 56% over single-agent therapy and increased survival proportions by 50% over all groups. Our work clearly demonstrates that non-viral delivery of p2CMVIL2/msFlk1 can inhibit RENCA growth in a synergistic manner and may represent a new treatment for renal carcinoma.

DNA vaccination against VEGF receptor 2 reduces atherosclerosis in LDL receptor-deficient mice

OBJECTIVE

Similarities between neovascular ingrowth in atherosclerotic plaques and angiogenesis in tumors suggest that antiangiogenic factors that target tumor expansion may prove efficacious in the treatment of atherosclerosis. This study examined whether an oral DNA vaccine against the murine VEGF receptor 2 (Flk-1) with demonstrated antitumor effect through inhibition of pathological neovascularization can prevent or retard progression of atherosclerosis in hyperlipidemic low density lipoprotein receptor-deficient (LDLr-/-) mice.

METHODS AND RESULTS

Vaccination against Flk-1 resulted in T cell activation, suppression of neoangiogenesis, and a marked reduction in atherosclerosis which was independent of hypercholesterolemia in both male and female mice. Immunohistochemical characterization of aortic sinus lesions showed that the decreased lesion area was not associated with reduced plaque stability and had a lower density of microvessels.

CONCLUSIONS

These findings demonstrate for the first time that a DNA vaccine targeting activated endothelial cells in atherosclerotic lesions provides direct atheroprotective effects.

The use of tissue inhibitors of matrix metalloproteinases to increase the efficacy of a tumor necrosis factor/interferonγ antitumor therapy

Owing to its impressive ability to kill tumor cells, especially in combination with interferon-gamma (IFNgamma), tumor necrosis factor (TNF) is widely appreciated as being a potential systemic therapeutic for the treatment of cancer. On the other hand, owing to its proinflammatory activities, administration of TNF leads to many systemic side effects and eventually to a potentially lethal systemic inflammatory response syndrome (SIRS). However, systemic treatment of tumor-bearing mice with TNF/IFNgamma in combination with BB-94 (a broad-spectrum metalloproteinase inhibitor) confers protection against TNF/IFNgamma-induced mortality, whereas preserving the antitumor activity. In this study, we investigated the effect of the adenoviral delivery of human tissue inhibitors of matrix metalloproteinase (hTIMP)-1 and hTIMP-2 genes on the outcome of TNF/IFNgamma antitumor therapy. The dose of adenovirus was limited to 10(8) PFU per mouse owing to the additive toxicity of combining it with TNF/IFNgamma therapy. Nevertheless, this dose was sufficient to achieve highly efficient adenoviral transfer and expression of hTIMP-1 and hTIMP-2 in the liver, but not the tumor. Treatment with this low dose of AdhTIMP-1 or AdhTIMP-2 was not enough to protect the host against the toxic effects of TNF/IFNgamma. However, it was sufficient to show a synergistic effect of hTIMPs with TNF/IFNgamma such that tumors regressed significantly faster. Interestingly, only AdTIMP-2 was able to prevent relapses after treatment.

Integrin alphavbeta5 regulates lung vascular permeability and pulmonary endothelial barrier function

Increased lung vascular permeability is an important contributor to respiratory failure in acute lung injury (ALI). We found that a function-blocking antibody against the integrin alphavbeta5 prevented development of lung vascular permeability in two different models of ALI: ischemia-reperfusion in rats (mediated by vascular endothelial growth factor [VEGF]) and ventilation-induced lung injury (VILI) in mice (mediated, at least in part, by transforming growth factor-beta [TGF-beta]). Knockout mice homozygous for a null mutation of the integrin beta5 subunit were also protected from lung vascular permeability in VILI. In pulmonary endothelial cells, both the genetic absence and blocking of alphavbeta5 prevented increases in monolayer permeability induced by VEGF, TGF-beta, and thrombin. Furthermore, actin stress fiber formation induced by each of these agonists was attenuated by blocking alphavbeta5, suggesting that alphavbeta5 regulates induced pulmonary endothelial permeability by facilitating interactions with the actin cytoskeleton. These results identify integrin alphavbeta5 as a central regulator of increased pulmonary vascular permeability and a potentially attractive therapeutic target in ALI.

Systemic inhibition of tumor growth by soluble Flk-1 gene therapy combined with cisplatin

Soluble Flk-1, a soluble vascular endothelial growth factor (VEGF) receptor, is a potent inhibitor of angiogenesis, which could restrain growth and metastasis of some experimental tumors. However, antiangiogenic agents alone cannot eradicate tumor completely, and should be combined with other therapy to enhance their effects. In this study, we evaluated the antitumor activity of the combination therapy in the immunocompetent BALB/c mice bearing H22 hepatoma and Meth A fibrosarcoma, respectively. Mice were treated with either msFlk-1 i.m. at 100 microg/mouse once every 3 days for four times from day 3 after the tumor cell injection, cisplatin cycled twice (2 mg/kg i.p. on days 4 and 11 after the tumor cell inoculation), or both agents together. Tumor growth and survival time were continually observed. Antiangiogenesis in vivo was determined by CD31 immunohistochemistry. Assessment of apoptotic cells and histological analysis was also conducted in tumor tissues. Our results showed that the combination therapy could evidently improve antitumor efficacy, including tumor growth suppression, mice survival prolongation, tumor cell apoptosis augmentation as well as neovascularization inhibition as compared with controls, without serious adverse effects. Our data suggest that the combination of DDP with msFlk-1 is more effective to suppress tumor growth in mice than either agent alone, and this combination regimen showed its potential for future clinical application.

Activation of the stress protein response prevents the development of pulmonary edema by inhibiting VEGF cell signaling in a model of lung ischemia-reperfusion injury in rats

Lung endothelial damage is a characteristic morphological feature of ischemia-reperfusion (I/R) injury, although the molecular steps involved in the loss of endothelial integrity are still poorly understood. We tested the hypothesis that the activation of vascular endothelial growth factor (VEGF) cell signaling would be responsible for the increase in lung vascular permeability seen early after the onset of I/R in rats. Furthermore, we hypothesized that the I/R-induced pulmonary edema would be significantly attenuated in rats by the activation of the stress protein response. Pretreatment with Ad Flk-1, an adenovirus encoding for the soluble VEGF receptor type II, prevented I/R-mediated increase in lung vascular permeability in rats. Furthermore, the I/R-induced lung injury was significantly decreased by prior activation of the stress protein response with geldanamycin or pyrrolidine dithiocarbamate. In vitro studies demonstrated that VEGF caused an increase in protein permeability across primary cultures of bovine macro- and microvascular lung endothelial cell monolayers that were associated with a phosphorylation of VE- and E-cadherin and the formation of actin stress fibers. Activation of the stress protein response prevented the VEGF-mediated changes in protein permeability across these cell monolayers and reduced the phosphorylation of VE-and E-cadherins, as well as the formation of actin stress fibers in these cells.

Cellular signaling molecules as therapeutic targets in glioblastoma multiforme

Despite recent advances in operative techniques, chemotherapy, and radiotherapy, the prognosis in patients with glioblastoma multiforme (GBM) remains poor; the majority die within a year of diagnosis. Although often effective at reducing mass effect and tumor burden, surgical debulking and cytotoxic therapies have never demonstrated an unequivocally significant benefit in treating patients with GBM. This shortcoming has led to the development of molecules that target specific steps in the transduction pathways of high-grade glioma cells. In this article the authors review various cellular and extracellular signaling pathways that may prove promising in the treatment of patients with malignant glioma.

Increased VEGF levels induced by anti-VEGF treatment are independent of tumor burden in colorectal carcinomas in mice

Inhibition of vascular endothelial growth factor (VEGF) by gene transfer techniques was effectively applied to control experimental tumor growth, whereas effects on systemic VEGF levels had not been investigated. Therefore, we evaluated the effect of VEGF inhibition by adenoviral-mediated gene delivery of a dominant-negative soluble fragment of FLK-1 (sFlk-1) on systemic VEGF levels, organ-specific VEGF-RNA expression and antitumor efficacy in a murine colorectal cancer (CRC) tumor model. Vector function of AdsFlk-1 was shown by Western blot analysis and transgene expression was documented over a time period of 42 days in the serum of treated mice. Although cell supernatant of CT26 cells contained considerable levels of VEGF, systemic VEGF levels in the serum of tumor-bearing mice remained unaffected. Interestingly, mice that were systemically treated with AdsFlk-1 showed a strong upraise of circulating VEGF, whereas VEGF remained at background levels in the control. Vascular endothelial growth factor was increased not only in tumor bearing but also in healthy, tumor-free mice. Vascular endothelial growth factor determination in liver tissue homogenates showed a 16.5-fold upraise in AdsFlk-1-treated animals as compared to the AdLacZ control. Consecutively, systemic small interfering RNA injection targeted against VEGF reverted elevated VEGF levels almost back to normal levels. In spite of elevated VEGF levels, AdsFlk-1 administration showed significant antitumor effects in a subcutaneous metastatic CRC tumor model. There was no significant correlation between antitumour treatment response and VEGF levels in this model. Collectively, we conclude that the systemic administration of AdsFlk-1 had significant inhibitory effects on metastatic CRC tumor growth in spite of elevated systemic VEGF levels and that VEGF serum concentrations did not correlate to tumor burden and antitumor treatment response in this model.

Vascular endothelial growth factor blockade promotes the transition from compensatory cardiac hypertrophy to failure in response to pressure overload

Cardiac hypertrophy is associated with upregulation of vascular endothelial growth factor (VEGF) in the myocardium. Here, we evaluated the effects of a decoy VEGF receptor on heart morphology and function to a murine model of pressure overload hypertrophy. Mice were administered adenoviral vector encoding a decoy VEGF receptor (Ad-Flk), and their hearts were subjected to pressure overload by transverse aortic constriction (TAC). Treatment with Ad-Flk led to a net reduction in capillary density in hearts subjected to TAC. Ad-Flk also led to a reduction in TAC-induced cardiac hypertrophy and promoted left ventricle dilatation and a loss in contractile function. Treatment with Ad-Flk markedly increased myocardial fibrosis and collagen gene upregulation. In contrast, Ad-Flk had no effect on any of these parameters in sham-treated mice. Administration of a VEGF trap reagent diminished pressure overload cardiac hypertrophy and promoted the progression to heart failure but had no effect on sham-treated animals. These findings suggest that VEGF is required to maintain myocardial capillary density and that reductions in the vascular bed are associated with the transition from compensatory hypertrophy to failure.

A comparison of antiangiogenic therapies for the prevention of liver metastases

Angiogenesis is essential for solid tumor growth. Although successful antiangiogenic therapies have been demonstrated in animal models, a systematic comparison of the efficacy of different antiangiogenic factors has not been described in the hepatic environment. To address this issue, CT26 murine colon carcinoma cells were transfected with retroviral vectors encoding murine endostatin (mEndostatin), human angiostatin (hAngiostatin), murine-soluble vascular endothelial growth factor receptor-2, (msFlk-1), or murine-soluble Tie2 (msTie2). The transfected cells were then subjected to another round of transfection with a luciferase cDNA-encoding retroviral vector. Expression of these putative antiangiogenic proteins inhibited the proliferation of human umbilical vein endothelial cells in vitro but not tumor cells. To examine effects on tumor growth in vivo, modified cells were delivered via intrasplenic injection into BALB/c mice to induce liver metastases. Tumor burden was measured weekly by bioluminescence. Growth of hepatic metastases in vivo was significantly reduced in mice that were administered cells expressing msTie2 (76% reduction compared with control cells 21 days after intrasplenic inoculation; P < 0.05). Similar results were observed with cells that expressed msFlk-1 and hAngiostatin. However, expression of mEndostatin had no significant effect on the growth of liver metastases compared with control animals. These findings indicate that multiple antiangiogenic pathways are necessary for the growth of hepatic metastases, and each of these pathways is a potential clinically relevant antiangiogenic target for the treatment of this disease.

Serous cystadenoma of the pancreas: tumor growth rates and recommendations for treatment

OBJECTIVE

To define the natural history and optimal management of serous cystadenoma of the pancreas.

SUMMARY BACKGROUND DATA

Serous cystadenoma of the pancreas is the most common benign pancreatic neoplasm. Diagnostic criteria, potential for growth or malignancy, and outcomes are not well defined. As a result, management for patients with serous cystadenomas varies widely in current practice.

METHODS

A total of 106 patients presenting with serous cystadenoma of the pancreas from 1976-2004 were identified. Hospital records were evaluated for patient and tumor characteristics, diagnostic workup, treatment, and outcome. Twenty-four patients with serial radiographic imaging were identified, and tumor growth curves calculated.

RESULTS

Mean age at presentation was 61.5 years and 75% of patients were female. The most common symptoms were abdominal pain (25%), fullness/mass (10%), and jaundice (7%); 47% were asymptomatic. Mean tumor diameter was 4.9 +/- 3.1 cm, which did not vary by location. Tumors <4 cm were less likely to be symptomatic than were tumors > or =4 cm (22% vs. 72%, P < 0.001). The median growth rate in the patients who had serial radiography was 0.60 cm/y. For tumors <4 cm at presentation (n = 15), the rate was 0.12 cm/y, whereas for tumors > or =4 cm (n = 9), the rate was 1.98 cm/y (P = 0.0002). Overall, 86 patients underwent surgery, with one perioperative death.

CONCLUSIONS

Large (>4 cm) serous cystadenomas are more likely to be symptomatic. Although the median growth rate for this neoplasm is only 0.6 cm/y, it is significantly greater in large tumors. Whereas expectant management is reasonable in small asymptomatic tumors, we recommend resection for large serous cystadenomas regardless of the presence or absence of symptoms.

Cancer gene therapy

The prognosis of patients with some kinds of cancers whose patients are often found unresectable upon diagnosis is still dismal. In these fields, development of a new therapeutic modality is needed and gene therapy represents one promising strategy. So far, numerous cancer gene therapy clinical trials based on these principles have been carried out and have shown the safety of such modalities, but have fallen short of the initial expectations to cure cancers. In this review, we would like to make a problem-oriented discussion of current status of cancer gene therapy research by using mainly gastrointestinal cancers as an example. In order to overcome obstacles for full realization of cancer gene therapy, numerous researches have been conducted by many researchers. Various cancer-selective and non-selective genes, as well as lytic viruses themselves have been employed for gene therapy. In the context of gene delivery method, different kinds of viral and non-viral strategies have been utilized. In addition, surrogate assays, such as soluble markers and imaging, have been developed for safer and more informative clinical trials. Many experiments and clinical trials to date have figured out current obstacles for the realization of an effective cancer gene therapy modality. Tireless efforts to overcome such hurdles and continuous infusion of novel concepts into this field should lead to break through technologies and the cure of the patients.

Cotargeting tumor and tumor endothelium effectively inhibits the growth of human prostate cancer in adenovirus-mediated antiangiogenesis and oncolysis combination therapy

Tumor-endothelial interaction contributes to local prostate tumor growth and distant metastasis. In this communication, we designed a novel approach to target both cancer cells and their "crosstalk" with surrounding microvascular endothelium in an experimental hormone refractory human prostate cancer model. We evaluated the in vitro and in vivo synergistic and/or additive effects of a combination of conditional oncolytic adenovirus plus an adenoviral-mediated antiangiogenic therapy. In the in vitro study, we demonstrated that human umbilical vein endothelial cells (HUVEC) and human C4-2 androgen-independent (AI) prostate cancer cells, when infected with an antiangiogenic adenoviral (Ad)-Flk1-Fc vector secreting a soluble form of Flk1, showed dramatically inhibited proliferation, migration and tubular formation of HUVEC endothelial cells. C4-2 cells showed maximal growth inhibition when coinfected with Ad-Flk1-Fc and Ad-hOC-E1, a conditional replication-competent Ad vector with viral replication driven by a human osteocalcin (hOC) promoter targeting both prostate cancer epithelial and stromal cells. Using a three-dimensional (3D) coculture model, we found that targeting C4-2 cells with Ad-hOC-E1 markedly decreased tubular formation in HUVEC, as visualized by confocal microscopy. In a subcutaneous C4-2 tumor xenograft model, tumor volume was decreased by 40-60% in animals treated with Ad-Flk1-Fc or Ad-hOC-E1 plus vitamin D3 alone and by 90% in a combined treatment group, compared to untreated animals in an 8-week treatment period. Moreover, three of 10 (30%) pre-established tumors completely regressed when animals received combination therapy. Cotargeting tumor and tumor endothelium could be a promising gene therapy strategy for the treatment of both localized and metastatic human prostate cancer.

Effective angiostatic treatment in a murine metastatic and orthotopic hepatoma model

Vascular endothelial growth factor (VEGF) activity is correlated with a progressive tumor disease in patients with hepatocellular carcinoma (HCC). In spite of the well-recognized role of VEGF in HCC, there are few data available regarding therapeutic strategies to block VEGF activity. Therefore, we employed a recombinant adenoviral vector encoding a soluble dominant negative fragment of VEGF receptor 2 (Flk-1), AdsFlk-1, to control pre-established murine orthotopic and metastatic hepatomas. Vector function was confirmed via reverse-transcriptase polymerase chain reaction and ELISA, and angiostatic effects were analyzed in vitro and in vivo. Antitumoral effects of systemic AdsFlk-1 application were studied in a subcutaneous and orthotopic Hepa129 HCC model. Cell supernatant containing the truncated form of Flk-1 had no direct effect on cell proliferation of Hepa129 cells in vitro but reduced endothelial tube formation on matrigel matrix by approximately 80% in vitro. Endothelial-like cell infiltration into matrigel plugs in vivo was also decreased by 80%. Systemic treatment of tumor-bearing mice inhibited tumor growth by 84% compared with the corresponding control group within 16 days after vector application. Likewise, the survival rate was significantly improved in the AdsFlk-1 group compared with control. Orthotopic tumor growth was reduced by 82%, and development of malignant ascites was also retarded. In conclusion, systemic adenoviral-mediated gene transfer of an Flk-1 fragment significantly inhibited tumor growth in orthotopic and metastatic murine HCC. The data support the value of VEGF blockade as an effective target for HCC treatment.

Careful decoy receptor titering is required to inhibit tumor angiogenesis while avoiding adversely altering VEGF bioavailability

To inhibit tumor-induced angiogenesis, the VEGF signaling pathway was targeted using AAV vectors encoding a VEGF decoy receptor, a truncated, soluble form of the murine VEGF receptor-2 (tsFlk-1). This approach initially had significant anti-neuroblastoma efficacy in murine xenograft models of local and metastatic disease, but when higher circulating levels of tsFlk-1 were established, tumor growth was more aggressive than even in control mice. Part of the mechanism for this apparent tumor resistance was increased human VEGF expression by the tumor cells. However, further investigation revealed that although a greater amount of VEGF could be bound by higher levels of tsFlk-1, more VEGF also existed in an unbound state and was, therefore, available to support angiogenesis. This novel, tumor-independent mechanism for resistance to antiangiogenic strategies suggests that careful titering of angiogenesis inhibitors may be required to achieve maximal antitumor efficacy and avoid therapy resistance mediated, in part, by ligand bioavailability. This has important implications for therapeutic strategies that use decoy receptors and other agents, such as antibodies, to bind angiogenic factors, in an attempt to inhibit tumor neovascularization.

Enhanced antimetastatic effect of fetal liver kinase 1 extracellular domain and interferon-gamma fusion gene-modified dendritic cell vaccination

Antiangiogenic immunotherapy benefits from targeting antigens expressed on genetically stable endothelial cells and represents a novel modality for cancer treatment. Vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2, also known as flk1 in mouse) mediated VEGF signaling is the key rate-limiting step in angiogenesis. Blockade of the flk1 signaling pathway can significantly inhibit tumor cell-induced angiogenesis and lead to inhibition of tumor metastasis. Interferon-gamma (IFN-gamma) is a pleiotropic cytokine, which plays an important role in cell-mediated immunity. In this study, we tested the hypothesis that immunization of mice with soluble flk1 (sflk1) and IFN-gamma fusion gene-transfected dendritic cells (DC-sflk1-IFN-gamma) would induce a potent CTL response to flk1, leading to an inhibition of tumor-induced angiogenesis and metastasis. Our data show that immunization of mice with sflk1 gene-modified DC (DC-sflk1) could induce a CTL response to flk1, leading to profound inhibition of tumor-cell-induced angiogenesis and metastasis. However, more striking antimetastatic effects were achieved through induction of enhanced CTL response to flk1 and augmented inhibition of angiogenesis when mice were immunized with DC-sflk1-IFN-gamma. In vivo T-cell subset depletion experiments showed that CD8(+) T cells were mainly responsible for this antimetastatic effect. Our data extend the notion that DC-based active antiangiogenic immunotherapy is an effective modality for cancer treatment, and show that the antitumor efficacy of this strategy can be improved by combination with DC-based cytokine immunotherapy.

Gene therapy for proliferative ocular diseases

Proliferative ocular diseases encompass a wide variety of pathological processes with adverse cellular differentiation, proliferation and migration as common features. Pathologies may involve neovascular responses associated with diabetic retinopathy, retinopathy of prematurity or age-related macular degeneration. These diseases are quite prevalent and account for substantial visual impairment and blindness worldwide. Although treatment strategies are largely surgical, advances in our understanding of the proteins crucial to cell transdifferentiation, proliferation and migration, along with better gene transfer techniques, have greatly increased the potential for biological treatment options. In this report, the most common proliferative ocular vascular diseases and existing therapeutic modalities will be reviewed and an overview of possible gene therapy options will be discussed, along with potential candidate genes.

Adenoviral gene transfer with soluble vascular endothelial growth factor receptors impairs angiogenesis and perfusion in a murine model of hindlimb ischemia

BACKGROUND

The purpose of the current study was to examine the contribution of endogenous vascular endothelial growth factor (VEGF) to ischemia-induced angiogenesis and perfusion.

METHODS AND RESULTS

C57BL/6J mice (n=28) were subjected to unilateral hindlimb ischemia after intravenous injection of recombinant adenoviruses (10(9) plaque-forming units) encoding the ligand-binding ectodomain of VEGF receptor 1 (VEGFR1/Ad Flt1), VEGF receptor 2 (VEGFR2/Ad Flk1-Fc), a control murine IgG2alpha Fc fragment (Ad Fc), or vehicle (phosphate-buffered saline). Hindlimb perfusion was assessed by both laser Doppler and fluorescent microsphere injection 10 days after surgery. The role of endogenous VEGF in ischemia-induced angiogenesis and arteriogenesis was measured by capillary density and microangiography, respectively. Adenoviral gene transfer with soluble VEGFRs significantly attenuated hindlimb perfusion as assessed by laser Doppler and microsphere analysis (P<0.05). Furthermore, soluble VEGFRs significantly reduced ischemia-induced angiogenesis and collateral growth and inhibited histological recovery of muscle tissue. Adverse events consistent with ongoing vascular insufficiency such as limb necrosis or gangrene were observed only in animals expressing soluble VEGFRs and not in control animals.

CONCLUSIONS

Systemic, soluble receptor-mediated VEGF inhibition indicates an essential role for endogenous VEGF during postischemic angiogenesis and hindlimb perfusion.

Inhibition of vascular endothelial growth factor (VEGF) signaling in cancer causes loss of endothelial fenestrations, regression of tumor vessels, and appearance of basement membrane ghosts

Angiogenesis inhibitors are receiving increased attention as cancer therapeutics, but little is known of the cellular effects of these inhibitors on tumor vessels. We sought to determine whether two agents, AG013736 and VEGF-Trap, that inhibit vascular endothelial growth factor (VEGF) signaling, merely stop angiogenesis or cause regression of existing tumor vessels. Here, we report that treatment with these inhibitors caused robust and early changes in endothelial cells, pericytes, and basement membrane of vessels in spontaneous islet-cell tumors of RIP-Tag2 transgenic mice and in subcutaneously implanted Lewis lung carcinomas. Strikingly, within 24 hours, endothelial fenestrations in RIP-Tag2 tumors disappeared, vascular sprouting was suppressed, and patency and blood flow ceased in some vessels. By 7 days, vascular density decreased more than 70%, and VEGFR-2 and VEGFR-3 expression was reduced in surviving endothelial cells. Vessels in Lewis lung tumors, which lacked endothelial fenestrations, showed less regression. In both tumors, pericytes did not degenerate to the same extent as endothelial cells, and those on surviving tumor vessels acquired a more normal phenotype. Vascular basement membrane persisted after endothelial cells degenerated, providing a ghost-like record of pretreatment vessel number and location and a potential scaffold for vessel regrowth. The potent anti-vascular action observed is evidence that VEGF signaling inhibitors do more than stop angiogenesis. Early loss of endothelial fenestrations in RIP-Tag2 tumors is a clue that vessel phenotype may be predictive of exceptional sensitivity to these inhibitors.

A Naturally Occurring Soluble Form of Vascular Endothelial Growth Factor Receptor 2 Detected in Mouse and Human Plasma

Angiogenesis and vasculogenesis are regulated in large part by several different growth factors and their associated receptor tyrosine kinases (RTKs). Foremost among these is the vascular endothelial growth factor (VEGF) family including VEGF receptor (VEGFR)-2 and -1. VEGFR ligand binding and biological activity are regulated at many levels, one of which is by a soluble, circulating form of VEGFR-1 (sVEGFR-1). This sVEGFR-1 can act as a competitive inhibitor of its ligand, serve as a possible biomarker, and play important roles in cancer and other diseases such as preeclampsia. Recombinant forms of sVEGFR-2 have been shown to have antiangiogenic activity, but a naturally occurring sVEGFR-2 has not been described previously. Here, we report such an entity. Having a molecular weight of ∼160 kDa, sVEGFR-2 can be detected in mouse and human plasma with several different monoclonal and polyclonal anti-VEGFR-2 antibodies using both ELISA and immunoprecipitation techniques. In vitro studies have determined that the sVEGFR-2 fragment can be found in the conditioned media of mouse and human endothelial cells, thus suggesting that it may be secreted, similar to sVEGFR-1, or proteolytically cleaved from the cell. Potential biological activity of this protein was inferred from experiments in which mouse sVEGFR-2 could bind to VEGF-coated plates. Similar to sVEGFR-1 and other soluble circulating RTKs, sVEGFR-2 may have regulatory consequences with respect to VEGF-mediated angiogenesis as well as potential to serve as a quantitative biomarker of angiogenesis and antiangiogenic drug activity, particularly for drugs that target VEGF or VEGFR-2.

Subcutaneous metastasis at a surgical drain site after the resection of pancreatic cancer

The aggressive nature of pancreatic cancer makes surgical control of disease an arduous challenge. Tumor seeding during resection is a feared complication during operations performed for this disease. Recurrence within the peritoneal cavity commonly occurs after resection for curative intent. Cutaneous metastasis, however, is a rare event. The majority of skin metastasis reported in the literature occurred after palliative procedures, in which the tumor burden remains. In this report, we describe an unusual case of cutaneous recurrence at the site of a surgical drain after resection for curative intent and discuss the impact of surgery on tumor-growth characteristics.

Inhibition of adenovirus-mediated p27kip1 gene on growth of esophageal carcinoma cell strain

AIM: To investigate the inhibition of p27kip1 gene on the growth of esophageal carcinoma cell strain (EC9706).

METHODS: Recombinant adenovirus Ad-p27kip1 was constructed and transfected into esophageal carcinoma cell EC-9706, and its effect on p27kip1 expression, the growth of esophageal carcinoma cell, DNA replication, protein synthesis, cell multiplication and apoptosis were explored by means of cell growth count, ³H-TdR, ³H-Leucine incorporation, flow cytometry, DNA fragment analysis and TUNEL.

RESULTS: Recombinant adenovirus Ad-p27kip1 was successfully constructed with a virus titer of 1.24 × 10¹² pfu/mL. p27kip protein expression increased markedly after EC-9706 transfection, while incorporation quantity of ³H-TdR and ³H-Leucine decreased significantly. The growth of esophageal carcinoma cell was inhibited obviously. Testing of flow cytometry displayed a typical apoptosis peak, and DNA gel electrophoresis showed a typical apoptosis ladder. TUNEL showed the apoptosis rate of Ad-p27kip1 group and control group to be 37.3% and 1.26% (P < 0.001) respectively.

CONCLUSION: Ad-p27kip1 can inhibit the growth and multiplication of esophageal carcinoma cells and induce apoptosis. Therefore, enhanced p27kip1 expression may be a new way to treat esophageal carcinoma.

VEGF is necessary for exercise-induced adult hippocampal neurogenesis

Declining learning and memory function is associated with the attenuation of adult hippocampal neurogenesis. As in humans, chronic stress or depression in animals is accompanied by hippocampal dysfunction, and neurogenesis is correspondingly down regulated, in part, by the activity of the hypothalamic-pituitary-adrenal axis as well as glutamatergic and serotonergic networks. Antidepressants can reverse this effect over time but one of the most clinically effective moderators of stress or depression and robust stimulators of neurogenesis is simple voluntary physical exercise such as running. Curiously, running also elevates circulating stress hormone levels yet neurogenesis is doubled in running animals. In evaluating the signalling that running provides to the central nervous system in mice, we have found that peripheral vascular endothelial growth factor (VEGF) is necessary for the effects of running on adult hippocampal neurogenesis. Peripheral blockade of VEGF abolished running-induced neurogenesis but had no detectable effect on baseline neurogenesis in non-running animals. These data suggest that VEGF is an important element of a 'somatic regulator' of adult neurogenesis and that these somatic signalling networks can function independently of the central regulatory networks that are typically considered in the context of hippocampal neurogenesis.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.