Antiangiogenic therapy against experimental glioblastoma using genetically engineered cells producing interferon-alpha, angiostatin, or endostatin

Nanocarriers and nonviral methods for delivering antiangiogenic factors for glioblastoma therapy: the story so far

Angiogenesis, the formation of new blood vessels, is an essential component of glioblastoma (GB) progression. The development of angiogenesis inhibitor therapy, including treatments targeting vascular endothelial growth factor (VEGF) in particular, raised new hopes for the treatment of GB, but no Phase III clinical trial to date has reported survival benefits relative to standard treatment. There are several possible reasons for this limited efficacy, including VEGF-independent angiogenesis, induction of tumor invasion, and inefficient antiangiogenic factor delivery to the tumor. Efforts have been made to overcome these limitations by identifying new angiogenesis inhibitors that target angiogenesis through different mechanisms of action without inducing tumor invasion, and through the development of viral and nonviral delivery methods to improve antiangiogenic activity. Herein, we describe the nonviral methods, including convection-enhanced delivery devices, implantable polymer devices, nanocarriers, and cellular vehicles, to deliver antiangiogenic factors. We focus on those evaluated in intracranial (orthotopic) animal models of GB, the most relevant models of this disease, as they reproduce the clinical scenario of tumor progression and therapy response encountered in GB patients.

Current role of anti-angiogenic strategies for glioblastoma

OPINION STATEMENT

Glioblastoma, an incurable, malignant, and highly vascular tumor, is a seemingly ideal target for anti-angiogenic therapies such as bevacizumab, an anti-vascular endothelial growth factor (VEGF) monoclonal antibody. Phase II trials in recurrent glioblastoma demonstrated bevacizumab was associated with clinical benefits, including decreases in brain edema and corticosteroids use resulting from reduced vascular permeability, as well as radiographic responses in 25 %-40 % of patients. In newly diagnosed disease, a phase III trial (AVAglio) showed adding bevacizumab to standard chemoradiotherapy improved progression free survival (PFS), with preservation of quality of life, and reduced corticosteroids use, but did not improve overall survival (OS). Another similar phase III trial (RTOG 0825) found similar PFS and OS trends, but suggested that the addition of bevacizumab resulted in more frequent cognitive decline compared with standard chemoradiotherapy. However, interpretation of those findings is limited by the fact that progressing patients were not evaluated, and patients remained longer on study in the bevacizumab arm. It is possible that the observed cognitive decline represented unrecognized tumor progression, rather than deleterious bevacizumab effects. Regardless, even if real, it is difficult to ascertain how improvements in PFS and quality of life compare with the associated economic costs and increased toxicities of bevacizumab, in the setting of no survival benefit. Further studies in recurrent disease are being conducted; preliminary results of a randomized trial showed favorable results with the combination with CCNU, and final results are awaited. Meanwhile, outside the realm of clinical trials, the current trend appears to be to reserve bevacizumab for use in recurrent disease, or for patients with moderate or severe neurologic symptoms, either in the newly diagnosed or recurrent setting. Further research efforts are needed to determine optimal candidates for this treatment from a molecular standpoint, as well as to develop imaging tools capable of accurately identifying response and progression, and to establish new drug combinations that could result in unquestionable clinical benefit and improved survival in these patients.

Plasmacytoid dendritic cells in the tumor microenvironment: immune targets for glioma therapeutics

Adenovirus-mediated delivery of the immune-stimulatory cytokine Flt3L and the conditionally cytotoxic thymidine kinase (TK) induces tumor regression and long-term survival in preclinical glioma (glioblastoma multiforme [GBM]) models. Flt3L induces expansion and recruitment of plasmacytoid dendritic cells (pDCs) into the brain. Although pDCs can present antigen and produce powerful inflammatory cytokines, that is, interferon α (IFN-α), their role in tumor immunology remains debated. Thus, we studied the role of pDCs and IFN-α in Ad.TK/GCV+ Ad.Flt3L-mediated anti-GBM therapeutic efficacy. Our data indicate that the combined gene therapy induced recruitment of plasmacytoid DCs (pDCs) into the tumor mass; which were capable of in vivo phagocytosis, IFN-α release, and T-cell priming. Thus, we next used either pDCs or an Ad vector encoding IFN-α delivered within the tumor microenvironment. When rats were treated with Ad.TK/GCV in combination with pDCs or Ad-IFN-α, they exhibited 35% and 50% survival, respectively. However, whereas intracranial administration of Ad.TK/GCV + Ad.Flt3L exhibited a high safety profile, Ad-IFN-α led to severe local inflammation, with neurologic and systemic adverse effects. To elucidate whether the efficacy of the immunotherapy was dependent on IFN-α-secreting pDCs, we administered an Ad vector encoding B18R, an IFN-α antagonist, which abrogated the antitumoral effect of Ad.TK/GCV + Ad.Flt3L. Our data suggest that IFN-α release by activated pDCs plays a critical role in the antitumor effect mediated by Ad.TK/GCV + Ad.Flt3L. In summary, taken together, our results demonstrate that pDCs mediate anti-GBM therapeutic efficacy through the production of IFN-α, thus manipulation of pDCs constitutes an attractive new therapeutic target for the treatment of GBM.

[Anti-angiogenic strategies in glioblastoma]

INTRODUCTION

Glioblastoma, a highly angiogenic tumor, has poor prognosis despite aggressive conventional therapies combining surgery, chemotherapy and radiotherapy. Anti-angiogenic strategies that have recently come to the clinic, are the most promising therapeutic approaches for these tumors.

STATE OF ART

Tumor hypoxia is the main trigger of angiogenesis processes driven primarily by vascular endothelial growth factor (VEGF). Clinical data indicate that inhibitors of VEGF such as bevacizumab or VEGF receptors such as tyrosine kinase inhibitors are of potential interest in the treatment of recurrent glioblastoma, with an acceptable toxicity. However, despite high rate of initial radiological response and rapid clinical improvement in about half of patients, therapeutic failure is the rule. Mechanisms of resistance remain poorly understood but an invasive phenotype and alternative angiogenesis factors may contribute to tumor escape.

CONCLUSIONS AND PERSPECTIVES

Anti-angiogenic strategies already play an important role in the management of recurrent glioblastoma. However, optimal combination and schedules of angiogenic inhibitors with radiotherapy and chemotherapy remain to be established. Important randomized clinical trials currently investigate therapeutic combinations for newly diagnosed glioblastoma.

Glioma stem cells targeted by oncolytic virus carrying endostatin-angiostatin fusion gene and the expression of its exogenous gene in vitro

The development of the cancer stem cell (CSCs) niche theory has provided a new target for the treatment of gliomas. Gene therapy using oncolytic viral vectors has shown great potential for the therapeutic targeting of CSCs. To explore whether a viral vector carrying an exogenous Endo-Angio fusion gene (VAE) can infect and kill glioma stem cells (GSCs), as well as inhibit their vascular niche in vitro, we have collected surgical specimens of human high-grade glioma (world health organization, WHO Classes III-VI) from which we isolated and cultured GSCs under conditions originally designed for the selective expansion of neural stem cells. Our results demonstrate the following: (1) Four lines of GSCs (isolated from 20 surgical specimens) could grow in suspension, were multipotent, had the ability to self-renew and expressed the neural stem cell markers, CD133 and nestin. (2) VAE could infect GSCs and significantly inhibit their viability. (3) The Endo-Angio fusion gene was expressed in GSCs 48 h after VAE infection and could inhibit the proliferation of human brain microvascular endothelial cells (HBMEC). (4) Residual viable cells lose the ability of self-renewal and adherent differentiation. In conclusion, VAE can significantly inhibit the activity of GSCs in vitro and the expression of exogenous Endo-Angio fusion gene can inhibit HBMEC proliferation. VAE can be used as a novel virus-gene therapy strategy for glioma.

Nano to micro delivery systems: targeting angiogenesis in brain tumors

Treating brain tumors using inhibitors of angiogenesis is extensively researched and tested in clinical trials. Although anti-angiogenic treatment holds a great potential for treating primary and secondary brain tumors, no clinical treatment is currently approved for brain tumor patients. One of the main hurdles in treating brain tumors is the blood brain barrier - a protective barrier of the brain, which prevents drugs from entering the brain parenchyma. As most therapeutics are excluded from the brain there is an urgent need to develop delivery platforms which will bypass such hurdles and enable the delivery of anti-angiogenic drugs into the tumor bed. Such delivery systems should be able to control release the drug or a combination of drugs at a therapeutic level for the desired time. In this mini-review we will discuss the latest improvements in nano and micro drug delivery platforms that were designed to deliver inhibitors of angiogenesis to the brain.

Functional genomics of endothelial cells treated with anti-angiogenic or angiopreventive drugs

Angiogenesis is a highly regulated physiological process that has been studied in considerable detail given its importance in several chronic pathologies. Many endogenous factors and hormones intervene in the regulation of angiogensis and classical as well as targeted drugs have been developed for its control. Angiogenesis inhibition has come off the bench and entered into clinical application for cancer therapy, particularly for metastatic disease. While the clinical benefit is currently in terms of months, preclinical data suggest that novel drugs and drug combinations could lead to substantial improvement. The many targets of endogenous angiogenesis inhibitors reflect the complexity of the process; in contrast, current clinical therapies mainly target the vascular endothelial growth factor system. Cancer chemopreventive compounds can retard tumor insurgence and delay or prevent metastasis and many of these molecules hinder angiogenesis, a mechanism that we termed angioprevention. Angiopreventive drugs appear to prevalently act through the inhibition of the pro-inflammatory and anti-apoptotic player NFkappaB, thus contrasting inflammation dependent angiogenesis. Relatively little is known concerning the effects of these angiogenesis inhibitors on gene expression of endothelial cells, the main target of many of these molecules. Here we provide an exhaustive list of anti-angiogenic molecules, and summarize their effects, where known, on the transcriptome and functional genomics of endothelial cells. The regulation of specific genes can be crucial to preventive or therapeutic intervention. Further, novel targets might help to circumvent resistance to anti-angiogenic therapy. The studies we review are relevant not only to cancer but also to other chronic degenerative diseases involving endothelial cells, such as cardiovascular disorders, diabetes, rheumatoid arthritis and retinopaties, as well as vessel aging.

Molecular mechanisms underlying effects of epidermal growth factor receptor inhibition on invasion, proliferation, and angiogenesis in experimental glioma

PURPOSE

Epidermal growth factor receptor (EGFR) signal transduction pathways are implicated in malignant glioma aggressiveness and promote tumor cell invasion, proliferation, and angiogenesis. Nevertheless, response to EGFR tyrosine kinase inhibitor gefitinib (Iressa, ZD1839) has been disappointing in clinical trials. One potential explanation may come from the diversity of molecular alterations seen in gliomas. To validate that hypothesis, we have investigated responses to gefitinib on various tumor parameters in human malignant gliomas that exhibited different molecular alterations.

EXPERIMENTAL DESIGN

We used a panel of six human malignant gliomas from established xenografts characterized for their genetic (EGFR, PTEN, TP53, and CDKN2A) and molecular (EGFR, PTEN, ERK, and Akt) alterations. Tumors were treated with gefitinib (1 or 10 micromol/L) for prolonged periods (8 or 16 days) in an organotypic brain slice model that allowed quantification of invasion, proliferation, and angiogenesis.

RESULTS

In nontreated tumors, EGFR amplification was associated with profuse tumor cell invasion. After treatment, invasion was inhibited in tumors with EGFR amplification in a dose-dependent manner. Treatment had only antiproliferative effect in two of three tumors with EGFR amplification. Tumors with PTEN loss were resistant to treatment. We did not observe shrinkage of the tumors after treatment. None of the tumors had mutations of the EGFR kinase domain. Gefitinib had similar antiangiogenic effect in all of the tumors.

CONCLUSIONS

Gefitinib reduces cell invasion in EGFR amplified tumors. PTEN loss of expression seems to be a determinant of resistance. Interestingly, inhibition of angiogenesis by gefitinib seems independent on the EGFR genetic status of the tumors.

Altered gene expression and miRNA expression associated with cancerous IEC-6 cell transformed by MNNG

Background

Tumorigenesis is thought to be the consequence of gene mutation and disordered gene expression. However, the detailed molecular mechanism underlying the development and progress of colon cancer have not been elucidate completely. This study aimed to find out the genes associated with cancer biological pathways involved in transformation and tumorigenesis.

Methods

Normal intestinal cell line 6 (IEC-6) cells were transformed to cancer cells by treatment with cancerogenic agent of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and Phorbol 12-myristate 13 acetate (PMA). Then we investigated the altered gene expression of transformed IEC-6 cells by the microarray containing 113 genes associated with cancer pathway. Also the altered miRNAs of transformed IEC-6 cells were analyzed by array hybridization (miRCURY Array v9.2, Exiqon). The levels of acetylated histone H3 in transformed IEC-6 cells was evaluated by western blot.

Results

Cell proliferation was significantly increased as IEC-6 cells were transformed and tumor xenografts could be detected in animals as transformed IEC-6 cells were inoculated subcutaneously in nude mice. Result of microarray showed nine genes were increased and two decreased, as well as 13 miRNA were increased and 97 decreased. Verification by real-time PCR implies that the data obtained from microarray analysis were reliable. Western blot showed the levels of acetylated histone H3 were increased dramatically after MNNG/PMA treatment.

Conclusion

Our results showed many important biological pathways and miRNAs were involved in transformation and tumorigenesis of IEC-6 cells, which suggested the transformation of normal cells was involved with large mount of genetic and epigenetic variation.

Novel technologies for antiangiogenic drug delivery in the brain

Antiangiogenic therapies aimed at inhibiting the formation of tumor vasculature hold great promise for cancer therapy, with multiple compounds currently undergoing clinical trials. As with many forms of chemotherapy, antiangiogenic drugs face numerous hurdles in their translation to clinical use. Many such promising agents exhibit a short half-life, low solubility, poor bioavailability and multiple toxic side effects. Furthermore, when targeting malignant brain tumors the blood-brain barrier represents a formidable obstacle, preventing drugs from penetrating into the central nervous system (CNS). In this review, we discuss several preclinical antiangiogenic therapies and describe issues related to the unique conditions in the brain with regard to cancer treatment and neurotoxicity. We focus on the limitations of antiangiogenic drugs in the brain, along with numerous solutions that involve novel biomaterials and nanotechnological approaches. We also discuss an example in which modifying the properties of an antiangiogenic compound enhanced its clinical efficacy in treating tumors while simultaneously mitigating undesirable neurological side-effects.

Successful inhibition of intracranial human glioblastoma multiforme xenograft growth via systemic adenoviral delivery of soluble endostatin and soluble vascular endothelial growth factor receptor-2: laboratory investigation

OBJECT

Glioblastoma multiforme (GBM) is characterized by neovascularization, raising the question of whether angiogenic blockade may be a useful therapeutic strategy for this disease. It has been suggested, however, that, to be useful, angiogenic blockade must be persistent and at levels sufficient to overcome proangiogenic signals from tumor cells. In this report, the authors tested the hypothesis that sustained high concentrations of 2 different antiangiogenic proteins, delivered using a systemic gene therapy strategy, could inhibit the growth of established intracranial U87 human GBM xenografts in nude mice.

METHODS

Mice harboring established U87 intracranial tumors received intravenous injections of adenoviral vectors encoding either the extracellular domain of vascular endothelial growth factor receptor-2-Fc fusion protein (Ad-VEGFR2-Fc) alone, soluble endostatin (Ad-ES) alone, a combination of Ad-VEGFR2-Fc and Ad-ES, or immunoglobulin 1-Fc (Ad-Fc) as a control.

RESULTS

Three weeks after treatment, magnetic resonance imaging-based determination of tumor volume showed that treatment with Ad-VEGFR2-Fc, Ad-ES, or Ad-VEGFR2-Fc in combination with Ad-ES, produced 69, 59, and 74% growth inhibition, respectively. Bioluminescent monitoring of tumor growth revealed growth inhibition in the same treatment groups to be 62, 74, and 72%, respectively. Staining with proliferating cell nuclear antigen and with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling showed reduced tumor cell proliferation and increased apoptosis in all antiangiogenic treatment groups.

CONCLUSIONS

These results suggest that systemic delivery and sustained production of endostatin and soluble VEGFR2 can slow intracranial glial tumor growth by both reducing cell proliferation and increasing tumor apoptosis. This work adds further support to the concept of using antiangiogenesis therapy for intracranial GBM.

Glioblastoma multiforme: an emerging paradigm of anti-VEGF therapy

BACKGROUND

Adults with malignant glioma, especially the most common subtype, glioblastoma multiforme, have an unacceptably poor outcome with current therapies. Malignant gliomas are amongst the most angiogenic of cancers, and VEGF is the dominant angiogenic mediator in these tumors.

OBJECTIVE

To summarize the clinical experience of VEGF-directed treatment for malignant glioma.

METHODS

We reviewed the completed, ongoing and planned clinical trials evaluating anti-VEGF strategies for malignant glioma patients.

RESULTS/CONCLUSIONS

Recent studies incorporating anti-VEGF agents plus cytotoxic therapy among recurrent malignant glioma patients have achieved unprecedented improvements in radiographic response, time to progression and survival. Furthermore, acceptable toxicity was observed. Hence, a major current focus in neuro-oncology is to further develop antiangiogenic strategies for this desperate patient population.

Antiangiogenic and anti-invasive effects of sunitinib on experimental human glioblastoma

Angiogenesis inhibitors appear to be promising therapies for highly vascularized tumors such as glioblastoma multiforme (GBM). Sunitinib is an oral multitargeted tyrosine kinase inhibitor with both antiangiogenic and antitumor activities due to selective inhibition of various receptor tyrosine kinases, including those important for angiogenesis (vascular endothelial growth factor receptors and platelet-derived growth factor receptors). Here we evaluated the antitumor activities of sunitinib on orthotopic models of GBM in vitro and in vivo. Sunitinib potently inhibited angiogenesis that was stimulated by implantation of U87MG and GL15 cells into organotypic brain slices at concentrations as low as 10 nM. At high dose (10 microM), sunitinib induced direct antiproliferative and proapoptotic effects on GL15 cells and decreased invasion of these cells implanted into brain slices by 49% (p < 0.001). Treatment was associated with decreases in Src (35%) and focal adhesion kinase (44%) phosphorylation. However, anti-invasive activity was not observed in vivo at the highest dose level utilized (80 mg/kg per day). Survival experiments involving athymic mice bearing intracerebral U87MG GBM demonstrated that oral administration of 80 mg/kg sunitinib (five days on, two days off) improved median survival by 36% (p < 0.0001). Sunitinib treatment caused a 74% reduction in microvessel density (p < 0.05), an increase in tumor necrosis, and a decrease in number of GBM cells positive for MIB antibody. Sunitinib exhibited potent antiangiogenic activity that was associated with a meaningful prolongation of survival of mice bearing intracerebral GBM. These data support the potential utility of sunitinib in the treatment of GBM.

Type I collagen gene suppresses tumor growth and invasion of malignant human glioma cells

Background

Invasion is a hallmark of a malignant tumor, such as a glioma, and the progression is followed by the interaction of tumor cells with an extracellular matrix (ECM). This study examined the role of type I collagen in the invasion of the malignant human glioma cell line T98G by the introduction of the human collagen type I α1 (HCOL1A1) gene.

Results

The cells overexpressing HCOL1A1 were in a cluster, whereas the control cells were scattered. Overexpression of HCOL1A1 significantly suppressed the motility and invasion of the tumor cells. The glioma cell growth was markedly inhibited in vitro and in vivo by the overexpression of HCOL1A1; in particular, tumorigenicity completely regressed in nude mice. Furthermore, the HCOL1A1 gene induced apoptosis in glioma cells.

Conclusion

These results indicate that HCOL1A1 have a suppressive biological function in glioma progression and that the introduction of HCOL1A1 provides the basis of a novel therapeutic approach for the treatment of malignant human glioma.

Gene modulatory effects, pharmacokinetics, and clinical tolerance of interferon-alpha1b: a second member of the interferon-alpha family

Interferon-alpha1 (IFN-alpha1), which may have a primary role in innate immunity, differs significantly in amino-acid sequence from IFN-alpha2, the only recombinant IFN-alpha with substantial clinical evaluation. Patients with metastatic malignancies received daily subcutaneous doses of 1.5-270 mug/m(2) of recombinant IFN-alpha1b. Gene modulation, pharmacokinetics, tolerability, and disease response were determined. Significant (P<0.01) dose and gene-dependent increases of 2-10 fold occurred in IFN-stimulated genes, including four (tumor necrosis factor-related apoptosis-inducing ligand, cig 5, p56, GEM) never previously identified as increased in patients; significant increases (P<0.01) resulted at the lowest dose (1.5 microg/m(2); 1.5 x 10(4) human antiviral units/m(2)). Increases (P<0.01) were sustainable for >4 weeks. Peak levels of IFN-alpha1b were at 3 h; an increase of approximately eightfold in both C(max) and AUC occurred between 15 microg/m(2) and 270 microg/m(2). Chronic toxicities of anorexia, weight loss, and fatigue were relatively uncommon. Eighteen patients were treated for >8 weeks; none experienced >grade 1 weight loss. Three patients at the highest dose developed grade 3 fatigue after > or =3 months, which required dose reduction or discontinuation. Patient acceptability of fatigue defined a dose for initiation of Phase II trials, 270 microg/m(2). Six patients (five with renal cell carcinoma) had progression-free survival for >1 year, including two who had partial responses. IFN-alpha1b resulted in potent stimulation of IFN-regulated genes and tumor regressions in renal cell carcinoma. Unique gene modulatory effects, when coupled with the moderate severity of side effects and a potentially central role in innate immunity, provide rationale for further clinical evaluation of IFN-alpha1 in virus infections and cancer.

Identification of genes selectively regulated by IFNs in endothelial cells

IFNs are highly pleiotropic cytokines also endowed with marked antiangiogenic activity. In this study, the mRNA expression profiles of endothelial cells (EC) exposed in vitro to IFN-alpha, IFN-beta, or IFN-gamma were determined. We found that in HUVEC as well as in other EC types 175 genes were up-regulated (>2-fold increase) by IFNs, including genes involved in the host response to RNA viruses, inflammation, and apoptosis. Interestingly, 41 genes showed a >5-fold higher induction by IFN-alpha in EC compared with human fibroblasts; among them, the gene encoding the angiostatic chemokine CXCL11 was selectively induced by IFN-alpha in EC along with other genes associated with angiogenesis regulation, including CXCL10, TRAIL, and guanylate-binding protein 1. These transcriptional changes were confirmed and extended by quantitative PCR analysis and ELISA; whereas IFN-alpha and IFN-beta exerted virtually identical effects on transcriptome modulation, a differential gene regulation by type I and type II IFN emerged, especially as far as quantitative aspects were concerned. In vivo, IFN-alpha-producing tumors overexpressed murine CXCL10 and CXCL11, guanylate-binding protein 1, and TRAIL, with evidence of CXCL11 production by tumor-associated EC. Overall, these findings improve our understanding of the antiangiogenic effects of IFNs by showing that these cytokines trigger an antiangiogenic transcriptional program in EC. Moreover, we suggest that quantitative differences in the magnitude of the transcriptional activation of IFN-responsive genes could form the basis for cell-specific transcriptional signatures.

Angiogenesis meets immunology: Cytokine gene therapy of cancer

Delivery of cytokine genes at the tumor site in pre-clinical models has been shown to recruit host inflammatory cells followed by inhibition of tumor growth. This local effect is often accompanied by systemic protection mediated by the immune system, mainly by CD8(+) T and NK cells. On this basis, cytokine gene-transduced tumor cells have widely been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Are these findings the end of the story? Possibly not, if major improvements will be attained in the coming years. These should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression, and at the level of improving immune stimulation, i.e. by co-administration of co-stimulatory molecules including B7 and CD40, or boosting the expression of tumor antigens or MHC class I molecules. Interestingly, some of the cytokines which have shown encouraging anti-tumor activity, including IFNs, IL-4, IL-12 and TNF-alpha, are endowed with anti-angiogenic or vasculotoxic effects, which may significantly contribute to local tumor control. Therapeutic exploitation of this property may result in the design of novel approaches which, by maximizing immune-stimulating and anti-angiogenic effects, could possibly lead to starvation of established tumors in patients.

Anti-angiogenic gene therapy of cancer: current status and future prospects

The discovery of endogenous inhibitors of angiogenesis has made it possible to test the hypothesis that blocking the angiogenic switch may keep tumor growth in check, and has added a new investigational arm to the field of cancer gene therapy. Angiogenesis inhibitors are heterogeneous in origin and potency, and their growing list includes proteolysis products of larger molecules with a different function, such as angiostatin, endostatin and vasostatin, modulators of vascular endothelial growth factor activity, such as sFLT-1, and some cytokines/chemokines with marked anti-endothelial activity, such as IL-12, IFN-alpha, and CXCL10. Pre-clinical studies have clearly indicated that these factors are essentially cytostatic and that they need long-term administration in order to obtain prolonged anti-tumor effects, representing a rational basis for their delivery by a gene therapy approach. The experimental approaches attempted to date, reviewed herein, indicate overall that anti-angiogenic gene therapy has efficacy mainly as an early intervention strategy and that a better understanding of the biological mechanisms underlying resistance to angiogenesis inhibition, as well as appropriate combined treatments, are required to generate a conceptual advancement which could drive the field towards successful management of established tumors.

Brainstem tumors: where are we today?

Brainstem tumors comprise 10-20% of all pediatric central nervous system tumors. The management of these tumors has evolved dramatically in the past century. Once considered uniformly fatal, it is now known that brainstem tumors have distinguishing characteristics and do not behave identically. The focality and location of the lesion is determined from the clinical history, presentation, and associated imaging. Based on these findings, it is possible to predict the behavior of the tumor and choose an appropriate intervention. Focal lesions have a good prognosis and are treated operatively while diffuse lesions have a poor prognosis and are managed medically. This article reviews the current classification of brainstem tumors, current management options and future directions for the treatment of these rare tumors.

A gene transfer comparative study of HSA-conjugated antiangiogenic factors in a transgenic mouse model of metastatic ocular cancer

Different antiangiogenic and antimetastatic recombinant adenoviruses were tested in a transgenic mouse model of metastatic ocular cancer (TRP1/SV40 Tag transgenic mice), which is a highly aggressive tumor, developed from the pigmented epithelium of the retina. These vectors, encoding amino-terminal fragments of urokinase plasminogen activator (ATF), angiostatin Kringles (K1-3), endostatin (ES) and canstatin (Can) coupled to human serum albumin (HSA) were injected to assess their metastatic and antiangiogenic activities in our model. Compared to AdCO1 control group, AdATF-HSA did not significantly reduce metastatic growth. In contrast, mice treated with AdK1-3-HSA, AdES-HSA and AdCan-HSA displayed significantly smaller metastases (1.19+/-1.19, 0.87+/-1.5, 0.43+/-0.56 vs controls 4.04+/-5.12 mm3). Moreover, a stronger inhibition of metastatic growth was obtained with AdCan-HSA than with AdK1-3-HSA (P=0.04). Median survival was improved by 4 weeks. A close correlation was observed between the effects of these viruses on metastatic growth and their capacity to inhibit tumor angiogenesis. Our study indicates that systemic antiangiogenic factors production by recombinant adenoviruses, particularly Can, might represent an effective way of delaying metastatic growth via inhibition of angiogenesis.

Interferon-alpha prevents apoptosis of endothelial cells after short-term exposure but induces replicative senescence after continuous stimulation

Although the antiangiogenic activity of type I interferons (IFN) is well known, the mechanism by which it occurs is unclear. In the present study, we have investigated effects of short-term and long-term IFN-alpha exposure on different types of endothelial cells (EC). Short-term IFN-alpha treatment resulted in a distinct reduction of apoptosis of serum and growth factor starved HUVEC and HDMEC. This was accompanied by a strong upregulation of the IFN inducible guanylate binding protein-1 (GBP-1) whereas no consistent regulation of several known antiapoptotic proteins was evident. Stable transfection of HUVEC with an expression vector for GBP-1 mimicked the protective effect of IFN-alpha, suggesting that GBP-1 may contribute to the inhibition of apoptosis. When IFN-alpha, together with serum and EC growth factors, was present continuously a decrease of population doublings by more than 40% was observed in both HDMEC and HCAEC. In addition, the cells displayed a senescent phenotype significantly earlier than control cells and showed an increased adherence for monocytes. Our findings suggest that the antiangiogenic effect of IFN-alpha is mediated by inducing EC senescence rather than EC apoptosis. Furthermore IFN-alpha released in chronic inflammatory conditions might contribute via its prosenescent activity to the pathogenesis of atherosclerosis.

Tumor-specific expression of the RGD-alpha3(IV)NC1 domain suppresses endothelial tube formation and tumor growth in mice

Angiogenesis plays an essential role in tumor growth. This study investigated expression of the noncollagenous domain of alpha3(IV) collagen (alpha3(IV)NC1) transduced into tumors and its inhibition of tumor growth. We hypothesized that if a human telomerase reverse transcriptase (hTERT) promoter-driven RGD motif containing alpha3(IV)NC1 (hTERT/RGD-alpha3(IV)NC1) were expressed in telomerase-expressing tumor cells, it would inhibit tumor growth by its anti-angiogenic property. Adenoviral transduction of hTERT/RGD-alpha3(IV)NC1 expressed RGD-alpha3(IV)NC1 in hTERT-positive tumor cell lines. However, hTERT/RGD-alpha3(IV)NC1 did not express RGD-alpha3(IV)NC1 in hTERT-negative cells such as keratinocytes and fibroblasts. The secreted RGD-alpha3(IV)NC1 in the conditioned medium from tumor cells inhibited cell proliferation as well as tube formation in cultured endothelial cells, but had no effect on other types of cells. In an in vivo model, adenoviral hTERT/RGD-alpha3(IV)NC1 gene therapy showed limited expression of RGD-alpha3(IV)NC1 in tumors and resulted in a significant decrease of vessel density in tumors. The growth of subcutaneous (s.c.) tumors in nude mice was significantly suppressed by treatment with hTERT/RGD-alpha3(IV)NC1. In addition, long-term inhibition of tumor growth was achieved by intermittent administration of hTERT/RGD-alpha3(IV)NC1. In conclusion, our findings demonstrate that tumor-specific anti-angiogenic gene therapy utilizing RGD-alpha3(IV)NC1 under the hTERT promoter inhibited angiogenesis in tumors, resulting in an antitumor effect.

Gene therapy of ovarian cancer with IFN-alpha-producing fibroblasts: comparison of constitutive and inducible vectors

Ovarian cancer represents a malignancy suitable for cell and gene therapy approaches owing to its containment within the peritoneal cavity, even at advanced tumor stages. As regulation of transgene expression would be preferable for conducting clinical trials for reasons of safety, we investigated whether intraperitoneal (i.p.) administration of retroviral vector-transduced fibroblasts encoding murine interferon-alpha (IFN-alpha) could have therapeutic activity, and compared its effect with the antitumor effects of fibroblasts producing IFN-alpha under a rapamycin analogue (AP21967)-inducible promoter. Human and murine fibroblasts were recruited into the solid component of transplantable ovarian cancer-grown i.p. in severe combined immunodeficiency mice. Multiple administrations of fibroblasts producing IFN-alpha in a constitutive manner showed therapeutic efficacy, leading to significant prolongation of survival in the majority of animals, associated with inhibition of tumor angiogenesis. Compared to cells transduced by the constitutive vector, fibroblasts transduced by the inducible vector released twofold higher IFN-alpha levels in vitro, following induction by AP21967, and production of the cytokine was under pharmacologic control both in vitro and in vivo. However, these cells elicited only modest therapeutic effects in vivo. Overall, these findings indicate that intracavitary IFN-alpha gene therapy using engineered fibroblasts requires sustained production of IFN-alpha to achieve durable antitumor effects.

Angiogenesis in gliomas: imaging and experimental therapeutics

Much of the interest in angiogenesis and hypoxia has led to investigating diagnostic imaging methodologies and developing efficacious agents against angiogenesis in gliomas. In many ways, because of the cytostatic effects of these agents on tumor growth and tumor-associated endothelial cells, the effects of therapy are not immediately evident. Hence finding clinically applicable imaging tools and pathologic surrogate markers is an important step in translating glioma biology to therapeutics. There are a variety of strategies in the approach to experimental therapeutics that target the hypoxia-inducible factor pathway, the endogenous antiangiogenic and proangiogenic factors and their receptors, adhesion molecules, matrix proteases and cytokines, and the existing vasculature. We discuss the rationale for antiangiogenesis as a treatment strategy, the preclinical and clinical assessment of antiangiogenic interventions and finally focus on the various treatment strategies, including combining antiangiogenic drugs with radiation and chemotherapy.

Combinatorial antiangiogenic gene therapy by nonviral gene transfer using the sleeping beauty transposon causes tumor regression and improves survival in mice bearing intracranial human glioblastoma

Glioblastoma is a fatal brain tumor that becomes highly vascularized by secreting proangiogenic factors and depends on continued angiogenesis to increase in size. Consequently, a successful antiangiogenic therapy should provide long-term inhibition of tumor-induced angiogenesis, suggesting long-term gene transfer as a therapeutic strategy. In this study a soluble vascular endothelial growth factor receptor (sFlt-1) and an angiostatin-endostatin fusion gene (statin-AE) were codelivered to human glioblastoma xenografts by nonviral gene transfer using the Sleeping Beauty (SB) transposon. In subcutaneously implanted xenografts, co-injection of both transgenes showed marked anti-tumor activity as demonstrated by reduction of tumor vessel density, inhibition or abolition of glioma growth, and increase in animal survival (P = 0.003). Using luciferase-stable engrafted intracranial gliomas, the anti-tumor effect of convection-enhanced delivery of plasmid DNA into the tumor was assessed by luciferase in vivo imaging. Sustained tumor regression of intracranial gliomas was achieved only when statin-AE and sFlt-1 transposons were coadministered with SB-transposase-encoding DNA to facilitate long-term expression. We show that SB can be used to increase animal survival significantly (P = 0.008) by combinatorial antiangiogenic gene transfer in an intracranial glioma model.

Integration and long-term expression in xenografted human glioblastoma cells using a plasmid-based transposon system

Gene therapy has the potential to become an effective component of cancer treatment by transferring genes that cause immunomodulation or tumor cell death or that inhibit angiogenesis into tumor cells or tumor-associated stroma. Viral vectors have been the primary gene transfer vehicles used for intratumoral gene transfer to date. Plasmid-based vectors may be safer and more scalable than viral vectors. However, attempts at plasmid-based intratumoral gene transfer have been met with transient expression and poor gene transfer efficiency. Here we report integration and long-term expression of reporter genes in human glial tumors, growing in nude mice, using the Sleeping Beauty (SB) transposon system. A two-plasmid system was used, in which linear polyethylenimine was complexed with a GFP, NEO, or luciferase transposon plasmid and a SB transposase-expressing plasmid. SB-mediated transposition led to chromosomal integration of the NEO transgene in roughly 8% of tumor cells. SB-mediated insertions were cloned from the genomes of glial tumor cells to provide molecular proof of transposase-mediated integration. Luciferase studies showed that SB facilitated long-term expression of the transgene in glial tumors. SB-mediated intratumoral gene transfer is a novel, nonviral technique that could be used to augment conventional therapy for glioblastoma or other cancers.

Efficient human interferon-alpha gene transfer to neuroendocrine tumor cells with long-term and stable expression

Interferon (IFN)-alpha has been used in the treatment of neuroendocrine (NE) tumors; however, the feasibility of IFN-alpha gene therapy has not been evaluated in NE tumor cells. In this study, human IFN-alpha2 (hIFN-alpha2) gene has been transferred into a NE tumor cell line BON. hIFN-alpha2-expressing BON cells were subcutaneously inoculated in nude mice. The results demonstrated that hIFN-alpha2 exerted significant antiproliferative effects on NE tumor cell lines (BON and LCC18) and other tumor cell lines (CA46 and SW480) as well as porcine aorta cell line. Furthermore, hIFN-alpha2 demonstrated its antineovascular activity in mice tumor and a direct antiangiogenic effect in chicken chorioallantoic membrane assay. hIFN-alpha2-expressing BON cells had a stable and long-term expression. Mice implanted with hIFN-alpha2-expressing BON cells showed a lower incidence, a delayed development and a significantly longer doubling time of the tumor compared to both wild-type (WT) and vector group. In addition, IFN-alpha significantly inhibited cell adhesion of WT BON cells. hIFN-alpha2-expressing BON tumors had a high level of hIFN-alpha2 protein. Finally, mice implanted with a mixture of WT and hIFN-alpha2-expressing BON cells (1:1) presented a delayed tumor development and had an even lower incidence of tumors than those implanted with hIFN-alpha2-expressing BON cells only. The doubling time of tumor was also longest in the mixture group. Our data suggest that hIFN-alpha2 gene therapy might be possible to be used as a new treatment for NE tumor patients. Further studies on the regulation of hIFN-alpha expression are needed, especially in combination with other cytokines, which could lead to a better understanding and improvements of hIFN-alpha gene therapy.

Angiogenesis in hepatocellular carcinoma: the retrospectives and perspectives

Hepatocellular carcinoma (HCC) is a typical hypervascular tumor. Many angiogenic factors have been studied in HCC, and several anti-angiogenic therapies have been tested in animal models and patients. This paper summarizes the latest findings, especially regarding the clinical significance of endothelial cell markers and angiogenic factors in HCC, and experimental and clinical anti-angiogenesis therapies. Further developments in this area, such as endothelial cell-oriented research and better experimental and clinical designs in the evaluation of anti-angiogenic therapies are discussed.