Retargeting of adenoviral vector using basic fibroblast growth factor ligand for malignant glioma gene therapy

CXCL12 retargeting of an adenovirus vector to cancer cells using a bispecific adapter

Ad vectors are promising delivery vehicles for cancer therapeutic interventions. However, their application is limited by promiscuous tissue tropism and hepatotoxicity. This limitation can be avoided by altering the native tropism of Ads so that they can be redirected to the target cells through alternate cellular receptors. The CXCR4 chemokine receptor belongs to a large superfamily of G-protein-coupled receptors and is known to be upregulated in a wide variety of cancers, including breast cancer and melanoma. These receptors have been associated with cancer cell survival, progression, and metastasis. In the current study, an Ad to cancer cells overexpressing CXCR4 by using a bispecific adapter, sCAR-CXCL12, was retargeted. The sCAR-CXCL12 adapter contained the soluble ectodomain form of the native Ad5 receptor (sCAR), which was fused to a mature human chemokine ligand, CXCL12, through a short peptide linker. A dramatic increase in the infectivity of cancer cells using a targeted Ad vector compared with an untargeted vector was observed. Furthermore, sCAR-CXCL12 attenuated Ad infection of liver ex vivo and in vivo and enhanced Ad vector infection of xenograft tumors implanted in immunodeficient SCID-bg mice. Thus, the sCAR-CXCL12 adapter could be used to retarget Ad vectors to chemokine receptor-positive tumors.

Epithelial membrane protein-2 (EMP2) activates Src protein and is a novel therapeutic target for glioblastoma

Despite recent advances in molecular classification, surgery, radiotherapy, and targeted therapies, the clinical outcome of patients with malignant brain tumors remains extremely poor. In this study, we have identified the tetraspan protein epithelial membrane protein-2 (EMP2) as a potential target for glioblastoma (GBM) killing. EMP2 had low or undetectable expression in normal brain but was highly expressed in GBM as 95% of patients showed some expression of the protein. In GBM cells, EMP2 enhanced tumor growth in vivo in part by up-regulating αvβ3 integrin surface expression, activating focal adhesion kinase and Src kinases, and promoting cell migration and invasion. Consistent with these findings, EMP2 expression significantly correlated with activated Src kinase in patient samples and promoted tumor cell invasion using intracranial mouse models. As a proof of principle to determine whether EMP2 could serve as a target for therapy, cells were treated using specific anti-EMP2 antibody reagents. These reagents were effective in killing GBM cells in vitro and in reducing tumor load in subcutaneous mouse models. These results support the role of EMP2 in the pathogenesis of GBM and suggest that anti-EMP2 treatment may be a novel therapeutic treatment.

The evolution of adenoviral vectors through genetic and chemical surface modifications

A long time has passed since the first clinical trial with adenoviral (Ad) vectors. Despite being very promising, Ad vectors soon revealed their limitations in human clinical trials. The pre-existing immunity, the marked liver tropism and the high toxicity of first generation Ad (FG-Ad) vectors have been the main challenges for the development of new approaches. Significant effort toward the development of genetically and chemically modified adenoviral vectors has enabled researchers to create more sophisticated vectors for gene therapy, with an improved safety profile and a higher transduction ability of different tissues. In this review, we will describe the latest findings in the high-speed, evolving field of genetic and chemical modifications of adenoviral vectors, a field in which different disciplines, such as biomaterial research, virology and immunology, co-operate synergistically to create better gene therapy tools for modern challenges.

From scourge to cure: tumour-selective viral pathogenesis as a new strategy against cancer

Tumour mutations corrupt cellular pathways, and accumulate to disrupt, dysregulate, and ultimately avoid mechanisms of cellular control. Yet the very changes that tumour cells undergo to secure their own growth success also render them susceptible to viral infection. Enhanced availability of surface receptors, disruption of antiviral sensing, elevated metabolic activity, disengagement of cell cycle controls, hyperactivation of mitogenic pathways, and apoptotic avoidance all render the malignant cell environment highly supportive to viral replication. The therapeutic use of oncolytic viruses (OVs) with a natural tropism for infecting and subsequently lysing tumour cells is a rapidly progressing area of cancer research. While many OVs exhibit an inherent degree of tropism for transformed cells, this can be further promoted through pharmacological interventions and/or the introduction of viral mutations that generate recombinant oncolytic viruses adapted to successfully replicate only in a malignant cellular environment. Such adaptations that augment OV tumour selectivity are already improving the therapeutic outlook for cancer, and there remains tremendous untapped potential for further innovation.

Beyond Gene Delivery: Strategies to Engineer the Surfaces of Viral Vectors

Viral vectors have been extensively studied due to their great transduction efficiency compared to non-viral vectors. These vectors have been used extensively in gene therapy, enabling the comprehension of, not only the advantages of these vectors, but also the limitations, such as the activation of the immune system after vector administration. Moreover, the need to control the target of the vector has led to the development of chemical and non-chemical modifications of the vector surface, allowing researchers to modify the tropism and biodistribution profile of the vector, leading to the production of viral vectors able to target different tissues and organs. This review describes recent non-genetic modifications of the surfaces of viral vectors to decrease immune system activation and to control tissue targeting. The developments described herein provide opportunities for applications of gene therapy to treat acquired disorders and genetic diseases and to become useful tools in regenerative medicine.

Oncolytic virotherapy for malignant glioma: translating laboratory insights into clinical practice

Glioblastoma multiforme, one of the most common and aggressive brain tumors in adults, is highly resistant to currently available therapies and often recurs. Due to its poor prognosis and difficult management, there is an urgent need for the development and translation of new anti-glioma therapeutic approaches into the clinic. In this context, oncolytic virotherapy arises as an exciting treatment option for glioma patients. These natural or genetically engineered viruses are able to effectively infect cancer cells, inducing a specific anti-tumor cytotoxic effect. In addition, some viruses have been redesigned to modulate glioma microenvironment, to express cytokines to boost a systemic anti-glioma immune response and to incorporate angiostatic genes to decrease glioma vasculature. Although recent clinical trials have confirmed the safety of oncolytic virotherapies in the brain, their moderate clinical efficacy has not yet matched the encouraging preclinical laboratory results. In this review, we will discuss the leading anti-glioma virotherapy approaches that are presently under preclinical and clinical evaluation. We will also review different delivery methods, in vivo virus behavior, fate, replication, intratumoral spread, activation of anti-tumor immune response, and targeting of glioma stem cells. We will focus on the advantages and limitations of each therapeutic approach and how to overcome these hurdles to effectively translate exciting laboratory results into promising clinical trials.

Sstr2A: a relevant target for the delivery of genes into human glioblastoma cells using fiber-modified adenoviral vectors

Glioblastomas are the most aggressive of the brain tumors occurring in adults and children. Currently available chemotherapy prolongs the median survival time of patients by only 4 months. The low efficiency of current treatments is partly owing to the blood-brain barrier, which restricts the penetration of most drugs into the central nervous system. Locoregional treatment strategies thus become mandatory. In this context, viral tools are of great interest for the selective delivery of genes into tumoral cells. Gliomas express high levels of type 2 somatostatin receptors (sstr2A), pinpointing them as suitable targets for the improvement of transduction efficiency in these tumors. We designed a new adenoviral vector based on the introduction of the full-length somatostatin (SRIF (somatotropin release-inhibiting factor)) sequence into the HI loop of the HAdV fiber protein. We demonstrate that (i) HAdV-5-SRIF uptake into cells is mediated by sstr2A, (ii) our vector drives high levels of gene expression in cells expressing endogenous sstr2A, with up to 65-fold enhancement and (iii) low doses of HAdV-5-SRIF are sufficient to infect high-grade human primary glioblastoma cells. Adenoviral vectors targeting SRIF receptors might thus represent a promising therapeutic approach to brain tumors.

Cancer stem cells: the final frontier for glioma virotherapy

Cancer stem cells (CSC) are a very small subset of all cancer cells and possess characteristics very similar to normal stem cells, in particular, the capacity for self-renewal, multipotency and relative quiescence. These chemo- and radiation resistant cells are responsible for maintaining tumor volume leading to therapy failure and recurrence. In glioblastoma multiforme (GBM), the most common primary intracranial malignancy, glioma stem cells have been implicated as one of the key players in treatment failure. Many novel treatment modalities are being investigated to specifically target this small group of cells. In this review, we shed light on one such targeted therapy, specifically, oncolytic virotherapy, and review the literature to highlight the advances and challenges in designing effective oncolytic virotherapy for glioma stem cells.

Adenoviral virotherapy for malignant brain tumors

Glioblastoma multiforme is the most common form of primary brain cancer. In the past decade, virotherapy of tumors has gained credence, particularly in glioma management, as these tumors are not completely resectable and tend to micro-metastasize. Adenoviral vectors have an advantage over other viral vectors in that they are relatively non-toxic and do not integrate in the genome. However, the lack of coxsackie and adenovirus receptors on surface of gliomas provides for inefficient transduction of wild-type adenoviral vectors in these tumors. By targeting receptors that are overexpressed in gliomas, modified adenoviral constructs have been shown to efficiently infect glioma cells. In addition, by taking advantage of tumor-specific promoter elements, oncolytic adenoviral vectors offer the promise of selective tumor-specific replication. This dual targeting strategy has enabled specificity in both laboratory and pre-clinical settings. This review examines current trends in adenoviral virotherapy of gliomas, with an emphasis on targeting modalities and future clinical applications.

EphA4 promotes cell proliferation and migration through a novel EphA4-FGFR1 signaling pathway in the human glioma U251 cell line

The Eph receptor tyrosine kinases and their ephrin ligands form a unique cell-cell contact-mediated bidirectional signaling mechanism for regulating cell localization and organization. High expression of Eph receptors in a wide variety of human tumors indicates some roles in tumor progression, which makes these proteins potential targets for anticancer therapy. For this purpose, we did gene expression profiling for 47 surgical specimens of brain tumors including 32 high-grade glioma using a microarray technique. The analysis, focused on the receptor tyrosine kinases, showed that EphA4 mRNA in the tumors was 4-fold higher than in normal brain tissue. To investigate the biological significance of EphA4 overexpression in these tumors, we analyzed EphA4-induced phenotypic changes and the signaling mechanisms using human glioma U251 cells. EphA4 promoted fibroblast growth factor 2-mediated cell proliferation and migration accompanied with enhancement of fibroblast growth factor 2-triggered mitogen-activated protein kinase and Akt phosphorylation. In addition, active forms of Rac1 and Cdc42 increased in the EphA4-overexpressing cells. Furthermore, we found that EphA4 formed a heteroreceptor complex with fibroblast growth factor receptor 1 (FGFR1) in the cells and that the EphA4-FGFR1 complex potentiated FGFR-mediated downstream signaling. Thus, our results indicate that EphA4 plays an important role in malignant phenotypes of glioblastoma by enhancing cell proliferation and migration through accelerating a canonical FGFR signaling pathway.

Improved glioblastoma treatment with Ad5/35 fiber chimeric conditionally replicating adenoviruses

Adenovirus type 5 (Ad5)-based vectors have been used in clinical trials for glioblastoma treatment, but the capacity of Ad5 to infect human glioma cells was questioned. Seeking to improve the adenovirus transduction, we tested four Ad5-based vectors differing only in their fiber gene on permanent and short-term cultures of glioblastoma cells. A wild-type fiber Ad5 vector (Ad5.Luc) was compared to an RGD integrin-binding motif-containing fiber adenovirus (AdlucRGD) and the two fiber chimeras Ad5/3 and Ad5/35, with vector binding redirected to the Ad3 or Ad35 receptor, respectively. Compared to Ad5, the transduction of the tested short-term glioblastoma cultures with the vector Ad5/35.Luc, AdlucRGD and Ad5/3.Luc was enhanced by approximately 72%, approximately 13% and approximately 2%, respectively. To limit adenovirus spread, we aimed to develop conditionally replicative Ad5/35 vectors by targeting the expression of the essential E1 and E4 genes; in addition, some vectors had the E1Delta24 deletion. We analyzed eleven promoters for their activity in glioblastoma cells and determined the specificity of eight replicative adenovirus vectors in vitro. We evaluated the most promising vectors with E1/E4 under the control of the GFAP/Ki67 or E2F-1/COX-2 promoters, and the native Ad5 or the chimeric Ad5/35 fiber for their antineoplastic activity in a subcutaneous and intracranial glioblastoma xenograft model. Animals treated with the Ad5/35-based vectors showed significantly smaller tumors and longer survival than those treated with the homologous Ad5 vectors; no significant toxicity was observed in the intracranial model. Our data suggest that Ad5/35-based vectors are promising tools for glioblastoma treatment.

Neuroblastomas and medulloblastomas exhibit more Coxsackie adenovirus receptor expression than gliomas and other brain tumors

Adenoviral vector-mediated treatment is a potential therapy for tumors of the central nervous system. To obtain a significant therapeutic effect by adenoviral vectors, a sufficient infection is required, the power of which depends predominantly on the level of Coxsackie adenovirus receptors. We stained surgical biopsies of central nervous system tumors and neuroblastomas for Coxsackie adenovirus receptors. For gliomas, the level of the receptor was low and markedly variable among individual tumors. By contrast, neuroblastomas and medulloblastomas exhibited a higher degree of Coxsackie adenovirus receptor expression than gliomas and other brain tumors. We conclude that neuroblastomas and medulloblastomas could be suitable for adenovirus-mediated gene therapy. Adverse effects of the treatment, however, must be considered because neurons and reactive astrocytes also express a significant amount of the receptor.

Recent developments in the use of adenoviruses and immunotoxins in cancer gene therapy

Despite setbacks in the past and apparent hurdles ahead, gene therapy is advancing toward reality. The past several years have witnessed this new field of biomedicine developing rapidly both in breadth and depth, especially for the treatment of cancer, thanks largely to the better understanding of molecular and genetic basis of oncogenesis and the development of new and improved vectors and technologies for gene delivery and targeting. This article is intended to provide a brief review of recent advances in cancer gene therapy using adenoviruses, both as vectors and as oncolytic agents, and some of the recent progress in the development of immunotoxins for use in cancer gene therapy.

Dominant-negative fibroblast growth factor receptor expression enhances antitumoral potency of oncolytic herpes simplex virus in neural tumors

PURPOSE

Oncolytic herpes simplex viruses (HSV) appear to be a promising platform for cancer therapy. However, efficacy as single agents has thus far been unsatisfactory. Fibroblast growth factor (FGF) signaling is important for the growth and migration of endothelial and tumor cells. Here, we examine the strategy of arming oncolytic HSV with a dominant-negative FGF receptor (dnFGFR) that targets the FGF signaling pathway.

EXPERIMENTAL DESIGN

A mouse Nf1:p53 malignant peripheral nerve sheath tumor (MPNST) cell line expressing dnFGFR was generated by transfection. The effects of dnFGFR expression on cell growth and migration in vitro and tumor formation in vivo were determined. The dnFGFR transgene was then inserted into oncolytic HSV G47Delta using a bacterial artificial chromosome construction system. Antitumoral and antiangiogenic activities of bG47Delta-dnFGFR were examined.

RESULTS

MPNST 61E4 cells expressing dnFGFR grew less well than parental control cells. bG47Delta-dnFGFR showed enhanced killing of both tumor (human U87 glioma and F5 malignant meningioma cells and murine MPNST 61E4 and 37-3-18-4 cells) and proliferating endothelial cells (human umbilical vascular endothelial cell and Py-4-1) in vitro compared with the control vector bG47Delta-empty without inhibiting viral replication. In vivo, bG47Delta-dnFGFR was more efficacious than its nonexpressing parent bG47Delta-empty at inhibiting tumor growth and angiogenesis in both human U87 glioma and mouse 37-3-18-4 MPNST tumors in nude mice.

CONCLUSIONS

By using multiple therapeutic mechanisms, including destruction of both tumor cells and tumor endothelial cells, an oncolytic HSV encoding dnFGFR enhances antitumor efficacy. This strategy can be applied to other oncolytic viruses and for clinical translation.

Deletion of the intracellular domain of coxsackie and adenovirus receptor (CAR) enhances the expression of itself and boosts the efficiency of current adenovirus-mediated gene therapy in ovarian cancer cell lines in vitro

The failure of adenovirus-mediated gene therapy often derives from the absence of coxsackie and adenovirus receptor (CAR) expression in target cells. We hypothesize that the slight up-regulation of CAR expression might boost the effect of adenovirus-mediated gene therapy in ovarian cancer. To test this hypothesis, we transfected full-length and intracellular-domain-deleted (tailless) CAR plasmids into CAR-deficient ovarian cancer cell line SKOV3. We observed significant elevations of the in vitro killing effect of Adv-TK and oncolytic adenovirus-mediated cytopathic effect (CPE) in transfected sub-clones, and tailless-transfected SKOV3 showed higher CAR expressions than full-length CAR-transfected cells. We conclude that the extracellular domain of CAR is essential for adenovirus-based gene therapy and, furthermore, that its intracellular domain might play an important role in the regulation of its own expression.

Targeting the CYP2B1/Cyclophosphamide Suicide System to Fibroblast Growth Factor Receptors Results in a Potent Antitumoral Response in Pancreatic Cancer Models

The CYP2B1/cyclophosphamide (CPA) suicide gene therapy approach has been shown to be highly promising in clinical trials for the treatment of pancreatic cancer. However, delivering the therapeutic gene to a sufficient number of tumor cells able to trigger a complete response remains a challenge. Target-specific delivery of adenovirus to fibroblast growth factor receptors (FGFRs) has been obtained in a variety of tumor models and has been shown to highly increase transduction efficiency. In the present paper we have tested the therapeutic outcome of retargeting the adenoviral vector, Ad-CYP2B1, to FGFRs, using an FGF2-Fab' conjugate, in pancreatic cancer models. First, we show a heterogeneous subcellular distribution of overexpressed FGFR-1 in pancreatic cancer cells. Higher transduction efficiency was observed in five of the six cell lines studied after FGF2-AdGFPLuc infection. Interestingly, an association between FGFR-1 membrane cell expression and viral entry was found. Moreover, tumors injected with FGF2-AdGFPLuc showed enhanced and persistent transgene expression. Importantly, we demonstrate the relevant enhanced cytotoxic effect of the FGF2-Ad-CYP2B]/CPA system in four of the six cell lines studied. Moreover, retargeting Ad-CYP2B1/CPA to FGFRs resulted in a potent antitumoral effect and in an increased survival rate, in two human pancreatic xenograft models. Thus, our results indicate that redirecting adenoviruses to FGFRs highly increases the potency of the suicide system CYP2B1/CPA. Consequently, it may constitute a promising approach to the treatment of patients with pancreatic tumors, in which a high proportion of FGF receptors precisely localize to the plasma membrane.

Effective high-capacity gutless adenoviral vectors mediate transgene expression in human glioma cells

Glioblastoma multiforme (GBM) is the most common subtype of primary malignant brain tumor. Although serotype 5 adenoviral vectors (Ads) have been used successfully in clinical trials for GBM, the capacity of Ads to infect human glioma cells and the expression of adenoviral receptors in GBM cells have been challenged. In this report, we studied the expression of three molecules that have been shown to mediate adenoviral entry into cells, i.e., coxsackie and adenovirus receptor (CAR), integrin alphavbeta3 (INT), and major histocompatibility complex class I (MHCI), in rodent glioma cell lines and low-passage primary cultures and cell lines from human GBM. We correlated levels of expression of CAR, INT, and MHCI with transduction efficiency elicited by several high-capacity helper-dependent adenoviral vectors (HC-Ads). Expression levels of adenoviral receptors were variable among the different GBM cells studied. HC-Ad-mediated therapeutic gene expression was efficient, ranging between 20 and 80% of the total target cells expressing the encoded transgenes. Our results show no correlation between the levels of CAR, INT, or MHCI molecules and the levels of transgene expression or the number of GBM cells transduced. We conclude that expression levels of adenoviral receptors do not predict their transduction efficiency or biological function.

Use of replication-competent retroviral vectors in an immunocompetent intracranial glioma model

OBJECT

The authors had previously reported on a replication-competent retrovirus (RCR) that has been demonstrated to be stable, capable of effective transduction, and able to prolong survival in an intracranial tumor model in nude mice. The purpose of this study was further investigation of this gene therapy option.

METHODS

The transduction efficiency of RCR in RG2, an immunocompetent intracranial tumor model, was tested in Fischer 344 rats. The immune response to the RCR vector was expressed by the quantification of CD4, CD8, and CD11/b in tumors. The pharmaceutical efficacy of the suicide gene CD in converting prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) was measured using fluorine-19 nuclear magnetic resonance (19F-NMR) spectroscopy. Animal survival data were plotted on Kaplan-Meier survival curves. Finally, the biodistribution of RCR was determined using quantitative real-time polymerase chain reaction (RT-PCR) for the detection of retroviral env gene. There was no evidence of viral transduction in normal brain cells. Neither severe inflammation nor immunoreaction occurred after intracranial injection of RCR-green fluorescent protein compared with phosphate-buffered saline (PBS). The 19F-NMR spectroscopy studies demonstrated that RCR-CD was able to convert 5-FC to 5-FU effectively in vitro. The infection of RG2 brain tumors with RCR-CD and their subsequent treatment with 5-FC significantly prolonged survival compared with that in animals with RG2 transduced tumors treated with PBS. In contrast to the nude mouse model, evidence of virus dissemination to the systemic organs after intracranial injection was not detected using RT-PCR.

CONCLUSIONS

The RCR-mediated suicide gene therapy described in this paper effectively transduced malignant gliomas in an immunocompetent in vivo rodent model, prolonging survival, without evidence of severe intracranial inflammation, and without local transduction of normal brain cells or systemic organs.

Adenoviral vectors--how to use them in cancer gene therapy?

Gene therapy is most often described as a technique for introducing the foreign genetic material into cells with a correction of a dysfunctional gene as its final goal. Today, it is well known that cancer is one of the leading causes of mortality in the world. Besides classical methods for cancer treatment new strategies against cancer are needed. Although originally being designed as a treatment for monogenetic illness, soon after, gene therapy appeared as a potential new strategy in cancer therapy. One of the widely used vectors for cancer gene therapy is adenovirus. In this review we have described molecular biology of adenoviruses and basis for construction of adenoviral vectors. We have also described concepts for cancer gene therapy including their in vitro and in vivo application. Special attention is drawn toward retargeting of adenovirus as a new approach in vector design for cancer gene therapy, in order to restrict transgene expression in tumor tissue. This approach uses biophysical as well as genetic characteristics of tumor itself and its supporting tissue, allowing new "bypass" in cancer gene therapy.