Neuronal and glial cell type-specific promoters within adenovirus recombinants restrict the expression of the apoptosis-inducing molecule Fas ligand to predetermined brain cell types, and abolish peripheral liver toxicity

Applications of tissue-specific and cancer-selective gene promoters for cancer diagnosis and therapy

Current treatment of solid tumors with standard of care chemotherapies, radiation therapy and/or immunotherapies are often limited by severe adverse toxic effects, resulting in a narrow therapeutic index. Cancer gene therapy represents a targeted approach that in principle could significantly reduce undesirable side effects in normal tissues while significantly inhibiting tumor growth and progression. To be effective, this strategy requires a clear understanding of the molecular biology of cancer development and evolution and developing biological vectors that can serve as vehicles to target cancer cells. The advent and fine tuning of omics technologies that permit the collective and spatial recognition of genes (genomics), mRNAs (transcriptomics), proteins (proteomics), metabolites (metabolomics), epiomics (epigenomics, epitranscriptomics, and epiproteomics), and their interactomics in defined complex biological samples provide a roadmap for identifying crucial targets of relevance to the cancer paradigm. Combining these strategies with identified genetic elements that control target gene expression uncovers significant opportunities for developing guided gene-based therapeutics for cancer. The purpose of this review is to overview the current state and potential limitations in developing gene promoter-directed targeted expression of key genes and highlights their potential applications in cancer gene therapy.

A Cre-Dependent CRISPR/dCas9 System for Gene Expression Regulation in Neurons

Site-specific genetic and epigenetic targeting of distinct cell populations is a central goal in molecular neuroscience and is crucial to understand the gene regulatory mechanisms that underlie complex phenotypes and behaviors. While recent technological advances have enabled unprecedented control over gene expression, many of these approaches are focused on selected model organisms and/or require labor-intensive customization for different applications. The simplicity and modularity of clustered regularly interspaced short palindromic repeats (CRISPR)-based systems have transformed genome editing and expanded the gene regulatory toolbox. However, there are few available tools for cell-selective CRISPR regulation in neurons. We designed, validated, and optimized CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) systems for Cre recombinase-dependent gene regulation. Unexpectedly, CRISPRa systems based on a traditional double-floxed inverted open reading frame (DIO) strategy exhibited leaky target gene induction even without Cre. Therefore, we developed an intron-containing Cre-dependent CRISPRa system (SVI-DIO-dCas9-VPR) that alleviated leaky gene induction and outperformed the traditional DIO system at endogenous genes in HEK293T cells and rat primary neuron cultures. Using gene-specific CRISPR sgRNAs, we demonstrate that SVI-DIO-dCas9-VPR can activate numerous rat or human genes (GRM2, Tent5b, Fos, Sstr2, and Gadd45b) in a Cre-specific manner. To illustrate the versatility of this tool, we created a parallel CRISPRi construct that successfully inhibited expression from a luciferase reporter in HEK293T cells only in the presence of Cre. These results provide a robust framework for Cre-dependent CRISPR-dCas9 approaches across different model systems, and enable cell-specific targeting when combined with common Cre driver lines or Cre delivery via viral vectors.

In vivo methods for acute modulation of gene expression in the central nervous system

Accurate and timely expression of specific genes guarantees the healthy development and function of the brain. Indeed, variations in the correct amount or timing of gene expression lead to improper development and/or pathological conditions. Almost forty years after the first successful gene transfection in in vitro cell cultures, it is currently possible to regulate gene expression in an area-specific manner at any step of central nervous system development and in adulthood in experimental animals in vivo, even overcoming the very poor accessibility of the brain. Here, we will review the diverse approaches for acute gene transfer in vivo, highlighting their advantages and disadvantages with respect to the efficiency and specificity of transfection as well as to brain accessibility. In particular, we will present well-established chemical, physical and virus-based approaches suitable for different animal models, pointing out their current and future possible applications in basic and translational research as well as in gene therapy.

Characterization of neural stem cells modified with hypoxia/neuron-specific VEGF expression system for spinal cord injury

Spinal cord injury (SCI) is an incurable disease causing an ischemic environment and functional defect, thus a new therapeutic approach is needed for SCI treatment. Vascular endothelial growth factor (VEGF) is a potent therapeutic gene to treat SCI via angiogenesis and neuroprotection, and both tissue-specific gene expression and high gene delivery efficiency are important for successful gene therapy. Here we design the hypoxia/neuron dual-specific gene expression system (pEpo-NSE) and efficient gene delivery platform can be achieved by the combination ex vivo gene therapy with erythropoietin (Epo) enhancer, neuron-specific enolase (NSE) promoter and neural stem cells (NSCs). An in vitro model, NSCs transfected with pEpo-NSE were consistently and selectively overexpressing therapeutic genes in response to neural differentiation and hypoxic conditions. Also, in SCI model, ex vivo gene therapy using pEpo-NSE system with NSCs significantly enhanced gene delivery efficiency compared with pEpo-NSE system gene therapy alone. However, microarray analysis reveals that introducing exogenous pEpo-NSE and VEGF triggers biological pathways in NSCs such as glycolysis and signaling pathways such as Ras and mitogen-activated protein kinase, leading to cell proliferation, differentiation and apoptosis. Collectively, it indicates that the pEpo-NSE gene expression system works stably in NSCs and ex vivo gene therapy using pEpo-NSE system with NSCs improves gene expression efficiency. However, exogenously introduced pEpo-NSE system has an influence on gene expression profiles in NSCs. Therefore, when we consider ex vivo gene therapy for SCI, the effects of changes in gene expression profiles in NSCs on safety should be investigated.

Targeted toxins for glioblastoma multiforme: pre-clinical studies and clinical implementation

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. GBM is very aggressive due to its poor cellular differentiation and invasiveness, which makes complete surgical resection virtually impossible. Therefore, GBM's invasive nature as well as its intrinsic resistance to current treatment modalities makes it a unique therapeutic challenge. Extensive examination of human GBM specimens has uncovered that these tumors overexpress a variety of receptors that are virtually absent in the surrounding non-neoplastic brain. Human GBMs overexpress receptors for cytokines, growth factors, ephrins, urokinase-type plasminogen activator (uPA), and transferrin, which can be targeted with high specificity by linking their ligands with highly cytotoxic molecules, such as Diptheria toxin and Pseudomonas exotoxin A. We review the preclinical development and clinical translation of targeted toxins for GBM. In view of the clinical experience, we conclude that although these are very promising therapeutic modalities for GBM patients, efforts should be focused on improving the delivery systems utilized in order to achieve better distribution of the immuno-toxins in the tumor/resection cavity. Delivery of targeted toxins using viral vectors would also benefit enormously from improved strategies for local delivery.

Two-photon scanning microscopy of in vivo sensory responses of cortical neurons genetically encoded with a fluorescent voltage sensor in rat

A fluorescent voltage sensor protein “Flare” was created from a Kv1.4 potassium channel with YFP situated to report voltage-induced conformational changes in vivo. The RNA virus Sindbis introduced Flare into neurons in the binocular region of visual cortex in rat. Injection sites were selected based on intrinsic optical imaging. Expression of Flare occurred in the cell bodies and dendritic processes. Neurons imaged in vivo using two-photon scanning microscopy typically revealed the soma best, discernable against the background labeling of the neuropil. Somatic fluorescence changes were correlated with flashed visual stimuli; however, averaging was essential to observe these changes. This study demonstrates that the genetic modification of single neurons to express a fluorescent voltage sensor can be used to assess neuronal activity in vivo.

Targeting the Fas/FasL signaling pathway in cancer therapy

INTRODUCTION

The Fas/FasL system plays a significant role in tumorigenesis. Research has shown that its impairment in cancer cells may lead to apoptosis resistance and contribute to tumor progression. Thus, the development of effective therapies targeting the Fas/FasL system may play an important role in the fight against cancer.

AREAS COVERED

In this review the recent literature on targeting the Fas/FasL system for therapeutic exploitation at different levels is reviewed. Promising pre-clinical approaches and various exceptions are highlighted. The potential of combined therapies is also explored, whereby tumor sensitivity to Fas-mediated apoptosis is restored, before an effective targeted therapy is employed.

EXPERT OPINION

The success of the Fas/FasL system targeting for therapeutics will require a better understanding of the alterations conferring resistance, in order to use the most appropriate sensitizing chemotherapeutic or radiotherapeutic agents in combination with effective targeted therapies.

Optical imaging for stem cell differentiation to neuronal lineage

In regenerative medicine, the prospect of stem cell therapy holds great promise for the recovery of injured tissues and effective treatment of intractable diseases. Tracking stem cell fate provides critical information to understand and evaluate the success of stem cell therapy. The recent emergence of in vivo noninvasive molecular imaging has enabled assessment of the behavior of grafted stem cells in living subjects. In this review, we provide an overview of current optical imaging strategies based on cell- or tissue-specific reporter gene expression and of in vivo methods to monitor stem cell differentiation into neuronal lineages. These methods use optical reporters either regulated by neuron-specific promoters or containing neuron-specific microRNA binding sites. Both systems revealed dramatic changes in optical reporter imaging signals in cells differentiating into a neuronal lineage. The detection limit of weak promoters or reporter genes can be greatly enhanced by adopting a yeast GAL4 amplification system or an engineering-enhanced luciferase reporter gene. Furthermore, we propose an advanced imaging system to monitor neuronal differentiation during neurogenesis that uses in vivo multiplexed imaging techniques capable of detecting several targets simultaneously.

Mechanisms Conferring Resistance to Pro-Apoptotic Cancer Gene Therapy

Recently, we have described a novel approach to the treatment of cancer that employs a series of vectors that encode surface expressed chimeric proteins in which the cytoplasmic death domain of Fas is fused in-frame to the extracellular domain of one of a number of cell surface receptors that recognize and bind various ligands that are differentially expressed within the tumor microenvironment. Although the majority of tumor cells transduced with such vectors are killed in the presence of the corresponding cognate ligand, a small percentage survive and in vivo may go on to repopulate a treated tumor. In order to understand the mechanisms employed by tumors to escape the cytotoxic effects of pro-apoptotic signals triggered via Fas, we isolated a large number of 293 tumor cell clones that survive following transfection with a plasmid vector encoding Flk-1/Fas, a chimeric receptor that induces tumor cell death in the presence of the pro-angiogenic cytokine VEGF. Characterization of Flk-1/Fas-positive clones revealed that while survival can most often be attributed simply to the down-regulation of VEGF ligand expression, in cells that express both receptor and ligand, other proteins involved in the regulation of apoptosis may be targeted. Specifically, a Flk-1/Fas-positive, VEGF-positive clone was identified in which expression of APAF-1 was almost completely abrogated.

Engineering death receptor ligands for cancer therapy

CD95, TNFR1, TRAILR1 and TRAILR2 belong to a subgroup of TNF receptors which is characterized by a conserved cell death-inducing protein domain that connects these receptors to the apoptotic machinery of the cell. Activation of death receptors in malignant cells attracts increasing attention as a principle to fight cancer. Besides agonistic antibodies the major way to stimulate death receptors is the use of their naturally occurring "death ligands" CD95L, TNF and TRAIL. However, dependent from the concept followed to develop a death ligand-based therapy various limiting aspects have to be taken into consideration on the way to a "bedside" usable drug. Problems arise in particular from the cell associated transmembrane nature of the death ligands, the poor serum half life of the soluble fragments derived from the transmembrane ligands, the ubiquitous expression of the death receptors and the existence of additional non-death receptors of the death ligands. Here, we summarize strategies how these limitations can be overcome by genetic engineering.

Tropism-modification strategies for targeted gene delivery using adenoviral vectors

Achieving high efficiency, targeted gene delivery with adenoviral vectors is a long-standing goal in the field of clinical gene therapy. To achieve this, platform vectors must combine efficient retargeting strategies with detargeting modifications to ablate native receptor binding (i.e. CAR/integrins/heparan sulfate proteoglycans) and “bridging” interactions. “Bridging” interactions refer to coagulation factor binding, namely coagulation factor X (FX), which bridges hepatocyte transduction in vivo through engagement with surface expressed heparan sulfate proteoglycans (HSPGs). These interactions can contribute to the off-target sequestration of Ad5 in the liver and its characteristic dose-limiting hepatotoxicity, thereby significantly limiting the in vivo targeting efficiency and clinical potential of Ad5-based therapeutics. To date, various approaches to retargeting adenoviruses (Ad) have been described. These include genetic modification strategies to incorporate peptide ligands (within fiber knob domain, fiber shaft, penton base, pIX or hexon), pseudotyping of capsid proteins to include whole fiber substitutions or fiber knob chimeras, pseudotyping with non-human Ad species or with capsid proteins derived from other viral families, hexon hypervariable region (HVR) substitutions and adapter-based conjugation/crosslinking of scFv, growth factors or monoclonal antibodies directed against surface-expressed target antigens. In order to maximize retargeting, strategies which permit detargeting from undesirable interactions between the Ad capsid and components of the circulatory system (e.g. coagulation factors, erythrocytes, pre-existing neutralizing antibodies), can be employed simultaneously. Detargeting can be achieved by genetic ablation of native receptor-binding determinants, ablation of “bridging interactions” such as those which occur between the hexon of Ad5 and coagulation factor X (FX), or alternatively, through the use of polymer-coated “stealth” vectors which avoid these interactions. Simultaneous retargeting and detargeting can be achieved by combining multiple genetic and/or chemical modifications.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Gene therapy for brain cancer: combination therapies provide enhanced efficacy and safety

Glioblastoma multiforme (GBM) is the most common primary brain cancer in adults. Despite significant advances in treatment and intensive research, the prognosis for patients with GBM remains poor. Therapeutic challenges for GBM include its invasive nature, the proximity of the tumor to vital brain structures often preventing total resection, and the resistance of recurrent GBM to conventional radiotherapy and chemotherapy. Gene therapy has been proposed as a useful adjuvant for GBM, to be used in conjunction with current treatment. Work from our laboratory has shown that combination of conditional cytotoxic with immunotherapeutic approaches for the treatment of GBM elicits regression of large intracranial tumor masses and anti-tumor immunological memory in syngeneic rodent models of GBM. In this review we examined the currently available animal models for GBM, including rodent transplantable models, endogenous rodent tumor models and spontaneous GBM in dogs. We discuss non-invasive surrogate end points to assess tumor progression and therapeutic efficacy, such as behavioral tests and circulating biomarkers. Growing preclinical and clinical data contradict the old dogma that cytotoxic anti-cancer therapy would lead to an immune-suppression that would impair the ability of the immune system to mount an anti-tumor response. The implications of the findings reviewed indicate that combination of cytotoxic therapy with immunotherapy will lead to synergistic antitumor efficacy with reduced neurotoxicity and supports the clinical implementation of combined cytotoxic-immunotherapeutic strategies for the treatment of patients with GBM.

Gene transfer into rat brain using adenoviral vectors

Viral vector-mediated gene delivery is an attractive procedure for introducing genes into the brain, both for purposes of basic neuroscience research and to develop gene therapy for neurological diseases. Replication-defective adenoviruses possess many features which make them ideal vectors for this purpose-efficiently transducing terminally differentiated cells such as neurons and glial cells, resulting in high levels of transgene expression in vivo. Also, in the absence of anti-adenovirus immunity, these vectors can sustain very long-term transgene expression within the brain parenchyma. This unit provides protocols for the stereotactic injection of adenoviral vectors into the brain, followed by protocols to detect transgene expression or infiltrates of immune cells by immunocytochemistry or immunofluorescence. ELISPOT and neutralizing antibody assay methodologies are provided to quantitate the levels of cellular and humoral immune responses against adenoviruses. Quantitation of adenoviral vector genomes within the rat brain using qPCR is also described.

Targeting cancer by transcriptional control in cancer gene therapy and viral oncolysis

Cancer-specificity is the key requirement for a drug or treatment regimen to be effective against malignant disease--and has rarely been achieved adequately to date. Therefore, targeting strategies need to be implemented for future therapies to ensure efficient activity at the site of patients' tumors or metastases without causing intolerable side-effects. Gene therapy and viral oncolysis represent treatment modalities that offer unique opportunities for tumor targeting. This is because both the transfer of genes with anti-cancer activity and viral replication-induced cell killing, respectively, facilitate the incorporation of multiple mechanisms restricting their activity to cancer. To this end, cellular mechanisms of gene regulation have been successfully exploited to direct therapeutic gene expression and viral cell lysis to cancer cells. Here, transcriptional targeting has been the role model and most widely investigated. This approach exploits cellular gene regulatory elements that mediate cell type-specific transcription to restrict the expression of therapeutic genes or essential viral genes, ideally to cancer cells. In this review, we first discuss the rationale for such promoter targeting and its limitations. We then give an overview how tissue-/tumor-specific promoters are being identified and characterized. Strategies to apply and optimize such promoters for the engineering of targeted viral gene transfer vectors and oncolytic viruses-with respect to promoter size, selectivity and activity in the context of viral genomes-are described. Finally, we discuss in more detail individual examples for transcriptionally targeted virus drugs. First highlighting oncolytic viruses targeted by prostate-specific promoters and by the telomerase promoter as representatives of tissue-targeted and pan-cancer-specific virus drugs respectively, and secondly recent developments of the last two years.

Death receptors as targets for anti-cancer therapy

Human tumour cells are characterized by their ability to avoid the normal regulatory mechanisms of cell growth, division and death. The classical chemotherapy aims to kill tumour cells by causing DNA damage-induced apoptosis. However, as many tumour cells possess mutations in intracellular apoptosis-sensing molecules like p53, they are not capable of inducing apoptosis on their own and are therefore resistant to chemotherapy. With the discovery of the death receptors the opportunity arose to directly trigger apoptosis from the outside of tumour cells, thereby circumventing chemotherapeutic resistance. Death receptors belong to the tumour necrosis factor receptor superfamily, with tumour necrosis factor (TNF) receptor-1, CD95 and TNF-related apoptosis-inducing ligand-R1 and -R2 being the most prominent members. This review covers the current knowledge about these four death receptors, summarizes pre-clinical approaches engaging these death receptors in anti-cancer therapy and also gives an overview about their application in clinical trials conducted to date.

Gene transfer into neural cells in vitro using adenoviral vectors

Adenoviral vectors are excellent vehicles to transfer genes into the nervous system due to their ability to transduce dividing and nondividing cells, their ability to be grown to very high titers, and their relatively large insert capacity. Also, adenoviral vectors can sustain very long-term transgene expression in the CNS of rodents and in neurons and glial cells in culture. Successful gene transfer into the nervous system is dependent on the development, production, and quality control of vector preparations, which need to be of the highest quality. This unit provides protocols to clone, rescue, amplify, and purify first-generation adenoviral vectors. Detailed quality control assays are provided to ensure that vector preparations are devoid of contamination from replication-competent adenovirus and lipopolysaccharides. Also included are methodologies related to adenoviral-mediated gene transfer into neurons and glial cells in culture, and the analysis of transgene expression using immunocytochemistry, enzymatic assays, and fluorescence-activated cell sorting (FACS) analysis.

Gene transfer into rat brain using adenoviral vectors

Recombinant adenovirus vectors are attractive vehicles to deliver genes into the brain for the purposes of neurobiological research and for gene therapy of neurological diseases. This unit provides a comprehensive set of protocols for adenovirus vector-mediated gene transfer to the brain, including introduction of the vector into the brain by stereotaxic injection and preparation and processing of brain tissue for the evaluation of gene transfer. The potential side-effects of administering adenovirus vectors to the brain are discussed in detail. The unit also provides protocols for evaluating these side-effects (e.g., demyelination, inflammation, vector-mediated cytotoxicity, etc.). Finally, critical parameters for obtaining optimal gene transfer with minimum side-effects are presented.

Targeting malignant gliomas with a glial fibrillary acidic protein (GFAP)-selective oncolytic adenovirus

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein abundantly expressed in malignant gliomas. We have constructed a novel oncolytic adenovirus, Ad5-gfa2(B)3-E1, for treatment of these tumors. In this construct, the E1 region is under control of the tissue-specific GFAP promoter (gfa2) with three additional copies of the glial specific 'B' enhancer. Infection of a GFAP-positive cell line with Ad5-gfa2(B)3-E1 resulted in E1A and E1B expression at 75% and 30% of the levels obtained after wtAd5 infection. Q-PCR showed that Ad5-gfa2(B)3-E1 replicated 4.5 times more efficiently in the GFAP-positive than in the GFAP-negative cell lines. Cell viability assays showed efficient elimination of GFAP-positive cells by Ad5-gfa2(B)3-E1, in some cell lines as efficiently as wtAd5, while the elimination was attenuated in GFAP-negative cell lines. When tested in human tumor xenografts in nude mice, Ad5-gfa2(B)3-E1 effectively suppressed the growth of GFAP-positive SNB-19 glial tumors but not of GFAP-negative A549 lung tumors. In Ad5-gfa2(B)3-E1, the E3 region was deleted to create space for future insertion of heterologous therapeutic genes. Experiments with dl7001, an E3-deleted variant of wtAd5, confirmed that the specificity of Ad5-gfa2(B)3-E1 replication was based on the promoter driving E1 and not on the E3 deletion. Strategies to further improve the efficacy of Ad5-gfa2(B)3-E1 for the treatment of malignant gliomas include the insertion of therapeutic genes in E3 or retargeting to receptors that are more abundantly expressed on primary glioma cells than CAR.

Gazing into the future: Parkinson's disease gene therapeutics to modify natural history

PD gene therapy clinical trials have primarily focused on increasing the production of dopamine (DA) through supplemental amino acid decarboxylase (AADC) expression, neurotrophic support for surviving dopaminergic neurons (DAN) or altering brain circuitry to compensate for DA neuron loss. The future of PD gene therapy will depend upon resolving a number of important issues that are discussed in this special issue. Of particular importance is the identification of novel targets that are amenable to early intervention prior to the substantial loss of DAN. However, for the most part the etiopathogenesis of PD is unknown making early intervention a challenge and the development of early biomarker diagnostics imperative.

Noninvasive in vivo monitoring of neuronal differentiation using reporter driven by a neuronal promoter

PURPOSE

We imaged neuronal differentiation in vivo using dual reporters (sodium iodide symporter [NIS] and luciferase) coupled to a neuron-specific enolase (NSE) promoter.

METHODS

PC12 (NSE positive) and F11 cells were transfected with a bicistronic (NIS and luciferase; pNSE-NF) or a luciferase (pNSE-Fluc) reporter coupled to the NSE promoter. Weak NSE promoter activity was overcome by a two-step transcriptional amplification (TSTA) system (pNSE-TSTA-Fluc). In vivo, NIS and luciferase expression were examined using a (99m)Tc-pertechnetate gamma camera and bioluminescence imaging, respectively.

RESULTS

pNSE-NF-transfected PC12 cells showed 3-fold higher radioiodine uptakes and >100-fold higher luciferase activity than parental cells. NIS or luciferase activity was not detected in pNSE-NF-transfected HeLa cells. When F11 cells were differentiated into neurons by db-cAMP, NIS and luciferase activities increased 4-fold compared to those without treatment, which was confirmed by Western blot and RT-PCR of NSE. In vivo in pNSE-NF-transfected F11 cells, db-cAMP treatment increased the luciferase activity but not the scintigraphic activity. In vitro, pNSE-TSTA-Fluc produced 130-fold higher luciferase activity than pNSE-Fluc and neuronal differentiation showed 4-fold higher activity from both pNSE-TSTA-Fluc and pNSE-Fluc than before differentiation. In vivo, in pNSE-TSTA-Fluc-transfected F11 cells, luciferase activity increased after neuronal differentiation. In vivo luciferase activity persisted up to 2 days after db-cAMP-induced neuronal differentiation.

CONCLUSION

NSE promoter-driven dual reporter transgenes revealed the possibility of in vivo imaging of neuronal differentiation, which was further enabled by high amplification using a TSTA system. We propose that this strategy be used to follow the transplanted stem cells during differentiation in live animals.

Targeted-simultaneous expression of Gas1 and p53 using a bicistronic adenoviral vector in gliomas

The targeted expression of transgenes is one of the principal goals of gene therapy, and it is particularly relevant for the treatment of brain tumors. In this study, we examined the effect of the overexpression of human gas1 (growth arrest specific 1) and human p53 cDNAs, both under the transcriptional control of a promoter of the human glial fibrillary acidic protein (gfa2), employing adenoviral expression vectors, in glioma cells. We showed that the targeted overexpression of gas1 and p53 (AdSGas1 and AdSp53, respectively) in rat glioma cells (C6) reduced the number of viable cells and induced apoptosis. Moreover, the adenovirally targeted expression of these genes also reduced tumor growth in vivo. Unexpectedly, there was no additive effect when both gas1 and p53 were simultaneously expressed in the same cells using a bicistronic adenoviral vector. We suggest that Gas1 does not act in combination with p53 in the C6 and U373 glioma cell lines, inducing apoptosis and cell cycle arrest. Our results indicate that the targeted expression of tumor suppressor genes (gas1 and p53) regulated by the gfa2 promoter, together with adenoviral vectors may provide an interesting approach for adjuvant selective glioma gene therapy.

Astrocyte-specific heme oxygenase-1 hyperexpression attenuates heme-mediated oxidative injury

In prior studies, we have observed that HO activity protects astrocytes from heme-mediated injury, but paradoxically increases neuronal injury. In this study, we tested the hypothesis that an adenovirus encoding the human HO-1 gene driven by an enhanced glial fibrillary acidic protein promoter (Ad-GFAP-HO-1) would increase HO-1 expression selectively in astrocytes, and provide cytoprotection. Treatment with 100 MOI Ad-GFAP-HO-1 for 24 h resulted in HO-1 expression that was 6.4-fold higher in cultured primary astrocytes than in neurons. Astrocyte HO activity was increased by approximately fourfold over baseline, which was sufficient to reduce cell death after 24-h hemin exposure by 60%, as assessed by both MTT and LDH release assays. A similar reduction in cell protein oxidation, quantified by carbonyl assay, was also observed. These results suggest that HO-1 transgene expression regulated by an enhanced GFAP promoter selectively increases HO-1 expression in astrocytes, and is cytoprotective. Further investigation of this strategy in vivo is warranted.

Oncolytic adenoviruses as antiglioma agents

The treatment for malignant gliomas is suboptimal. Oncolytic adenoviruses hold the promise of being effective agents for the treatment of solid tumors. Importantly, the first oncolytic viral therapy has just been approved for use in combination with chemotherapy for late-stage refractory nasopharyngeal cancer by the Chinese State FDA, following a successful Phase III randomized clinical trial. The concept underlying treatment with oncolytic adenoviruses is based on cancer selectivity by confining viral replication and infectivity to cancer cells. For this purpose, the main strategies used currently to modify the viruses include: functional deletions in essential viral genes; tumor- or tissue-specific promoters used to control the expression of these viral genes; and tropism modification to redirect adenovirus to the cancer cell surface. In the near future, oncolytic adenoviruses need to be optimized to fully realize their potential as critical anticancer tools and, thus, improve the prognosis for patients with malignant gliomas.

Astrocytic expression of transgene in the rat brain mediated by baculovirus vectors containing an astrocyte-specific promoter

Therapeutic gene expression in glial cells has been tested for the treatment of neurological diseases in animal models. Many of such studies used the promoter of the glial fibrillary acidic protein (GFAP) to restrict gene expression to astrocytes. We have investigated in the current study whether it is possible to improve the transcriptional activity of the cellular promoter, while maintaining its cell-type specificity. We constructed an expression cassette containing a hybrid cytomegalovirus (CMV) enhancer/GFAP promoter and placed it into baculovirus vectors, a type of viral vectors capable of transducing astrocytes. In another vector design, we used inverted terminal repeats (ITRs) from adeno-associated virus (AAV) to flank the expression cassette. The recombinant baculoviruses with the hybrid promoter improved gene expression levels over two orders of magnitude in glial cell lines and by 10-fold in the rat brain when compared to the baculoviruses with the GFAP promoter alone. The expression was further improved by ITR flanking, reaching levels higher than that mediated by the baculovirus vectors with the CMV immediate-early enhancer/promoter (CMV promoter). Using these recombinant baculoviruses, we observed extended in vivo transgene expression in the rat brain at 90 days postinjection, by which time the gene expression from baculovirus vectors with the GFAP or CMV promoter had already become undetectable. The astrocyte specificity of the GFAP promoter was preserved in the engineered expression cassette with the CMV enhancer and the AAV ITRs, as demonstrated by immunohistological analysis of brain samples and an axonal retrograde transport assay. Taken together, our findings suggest that these baculovirus vectors may serve as useful tools for astrocyte-specific gene expression in the brain.

CD95L/FasL and TRAIL in tumour surveillance and cancer therapy

The membrane-bound death ligands CD95L/FasL and TRAIL, which activate the corresponding death receptors CD95/Fas, TRAILR1 and TRAILR2, induce apoptosis in many tumour cells, but can also elicit an inflammatory response. This chapter focuses on the relevance of CD95L/FasL and TRAIL for the tumour surveillance function of natural killer cells and cytotoxic T-cells and discuss current concepts of utilizing these ligands in tumour therapy.

Production and formulation of adenovirus vectors

Adenovirus vectors have attracted considerable interest over the past decade, with ongoing clinical development programs for applications ranging from replacement therapy for protein deficiencies to cancer therapeutics to prophylactic vaccines. Consequently, considerable product, process, analytical, and formulation development has been undertaken to support these programs. For example, "gutless" vectors have been developed in order to improve gene transfer capacity and durability of expression; new cell lines have been developed to minimize recombination events; production conditions have been optimized to improve volumetric productivities; analytical techniques and scaleable purification processes have advanced towards the goal of purified adenovirus becoming a "well-characterized biological"; and liquid formulations have been developed which maintain virus infectivity at 2-8 degrees C for over 18 months. These and other advances in the production of adenovirus vectors are discussed in detail in this review. In addition, the needs for the next decade are highlighted.

Inflammatory and anti-glioma effects of an adenovirus expressing human soluble Fms-like tyrosine kinase 3 ligand (hsFlt3L): treatment with hsFlt3L inhibits intracranial glioma progression

Glioblastoma multiforme is an intracranial tumor that has very poor prognosis. Patients usually succumb to their disease 6 to 12 months after they are diagnosed despite very aggressive treatment modalities. We tested the efficacy of a potent differentiation and proliferation factor for the professional antigen-presenting dendritic cells (DCs), i.e., Flt3L, for its potential role as a novel therapy for gliomas. We investigated the ability of recombinant adenoviral vectors encoding human soluble Flt3L (hsFlt3L) to improve the survival of Lewis rats bearing intracranial syngeneic CNS-1 gliomas. We show that RAdhsFlt3L can improve survival in a dose-dependent manner. Seventy percent of rats survive when treated with 8 x 10(7) pfu RAdhsFlt3L (P < 0.0005). In addition we demonstrate in both naive Lewis rats and C57BL/6 mice the presence of increased numbers of cells bearing DC markers (OX62 and MHCII, in rats, or CD11C, 33D1, MHCII, and F4/80, but not DEC205, in mice) in sites of brain delivery of RAdhsFlt3L. These results show that expression of hsFlt3L in the brain leads to the presence of cells displaying DC markers. We demonstrate that treatment with hsFlt3L leads to inhibition of tumor growth and significantly increased life span of animals implanted with syngeneic CNS-1 glioma cells. Animals that had survived for long periods, i.e., 6 months, had eliminated the implanted tumors after neuropathological analysis; on the other hand, some of the 3-month survivors still appeared to harbor brain tumors. Our results have profound implications for immune-mediated brain tumor therapy and also suggest the ability to recruit DC-like cells within the brain parenchyma in response to the local expression of Flt3L from adenoviral vectors.

Oncolytic viral therapies

Molecular research has vastly advanced our understanding of the mechanism of cancer growth and spread. Targeted approaches utilizing molecular science have yielded provocative results in the treatment of cancer. Oncolytic viruses genetically programmed to replicate within cancer cells and directly induce toxic effect via cell lysis or apoptosis are currently being explored in the clinic. Safety has been confirmed and despite variable efficacy results several dramatic responses have been observed with some oncolytic viruses. This review summarizes results of clinical trials with oncolytic viruses in cancer.

Fas Ligand as a Tool for Immunosuppression and Generation of Immune Tolerance

The role of Fas ligand (FasL) in physiologically limiting immune responses and maintaining immune-privileged sites has led to a body of research aiming to confer protection to allogeneic grafts by expressing FasL on the allogeneic tissue or by administrating FasL-transduced donor dendritic cells. In addition, several studies have used FasL to abrogate autoimmune responses. This review presents the results of these studies and discusses the problems associated with FasL usage.

Effects of ectopic decorin in modulating intracranial glioma progression in vivo, in a rat syngeneic model

Given the failure of conventional treatments for glioblastoma, gene therapy has gained interest considerable in recent years. Gliomas are associated with a state of immunosuppression, which appears to be partially mediated by an increase in secretion of transforming growth factor-beta (TGF-beta) from glioma cells. Decorin, a small proteoglycan which can bind to and inactivate TGF-beta, has been successfully used as an antitumor strategy on stably transfected tumor cells and has been shown to cause growth suppression in neoplastic cells of various histological origins. In this paper, we investigated the use of gene therapy to deliver the decorin transgene in a site-specific manner in an experimental model of intracranial gliomas. Our aim was to inhibit the glioma-associated immunosuppressive state, and prolong the survival of tumor-bearing rats. We studied the effects of decorin gene transfer in the rat CNS-1 glioma model. To assess the effect of ectopic expression of decorin on glioma progression in vivo, stably transfected CNS-1 cells expressing decorin were implanted into the brain parenchyma of syngeneic Lewis rats. The rats implanted with CNS-1 cells expressing decorin survived significantly longer than those in the control groups which received CNS-1 cells that did not express decorin (P < .0001). We then investigated whether the survival observed with decorin expressing cells could be mimicked in vivo, using recombinant adenoviruses (RAds) expressing the decorin gene under the control of two different promoters: the human immediate-early cytomegalovirus (h-IE-CMV) and the glial fibrillary acidic protein (GFAP). In vivo results showed that administration of RAd expressing the human decorin under the control of h-IE-CMV promoter has a small, but significant effect in prolonging the survival of experimental tumor bearing rats (P < .0001). Our data indicate that ectopic decorin expression has the potential to slow glioma progression in vivo. Our results also indicate that expression of decorin has to be present in all cells which constitute the intracranial tumor mass for the inhibition of tumor growth and prolongation of the life expectancy of tumor-bearing rats to be effective.

Enhanced apoptosis of glioma cell lines is achieved by co-delivering FasL-GFP and TRAIL with a complex Ad5 vector

Brain tumors (BTs) are among the most malignant forms of human cancer. Unfortunately, current treatments are often ineffective and produce severe side effects. Cytotoxic gene therapy is an alternative treatment strategy, with the potential advantages of reduced toxicity to normal brain tissue. Apoptosis-inducing "death ligands" Fas ligand and TNF-related apoptosis-inducing ligand (TRAIL) are genes with substantial cytotoxic activity in susceptible tumor cells. Here, we compared the effectiveness of Ad vector-mediated delivery of Fas ligand-green fluorescent protein (FasL-GFP) fusion protein, human TRAIL, and both genes simultaneously. We examined a panel of 13 cell lines (eight derived from primary isolates) for susceptibility to Ad5-based vector infection and for sensitivity to FasL- and TRAIL-mediated apoptosis. All cell lines were efficiently transduced, but, as expected, varied in their sensitivity to ligand-induced apoptosis. Generally, sensitivity to FasL-GFP correlated with cell surface FasR levels, but no such correlation was seen for TRAIL and its functional receptors, DR4 and DR5. The vector expressing both FasL-GFP and TRAIL was more effective than either of the single-gene vectors at comparable transduction levels, and it was effective against a broader range of cell lines. In five cell lines, coexpression resulted in apoptosis levels greater than those predicted for strictly additive activity of the two death ligands. We believe that Ad vector-mediated delivery of multiple death ligands may be developed as a potential BT therapy, either alone or in conjunction with surgical resection of the primary tumor.

Selective replicating viral vectors : potential for use in cancer gene therapy

Treatment of cancer is limited by toxicity to normal tissue with standard approaches (chemotherapy, surgery and radiotherapy). The use of selective replicating viral vectors may enable the targeting of gene-modified viruses to malignant tissue without toxic effect. Studies of these vectors have demonstrated tumour-selective replication and minimal evidence of replication in normal tissue. The most advanced clinical results reported involve gene-modified adenoviral vectors. Several completed, histologically confirmed responses to local/regional injection have been induced, particularly in recurrent squamous cell carcinoma involving the head and neck region. Dose limiting toxicity above 10(13) viral particles per injection has been observed. Anti-tumour effect is demonstrable in animal models without evidence of significant toxicity when these vectors are used alone or in combination with chemotherapy, radiation therapy or as gene delivery vehicles. Preliminary clinical trials, particularly with E1B-deleted adenoviruses, report evidence of clinical activity in comparison with expected historical responses. Enhancement in replication selectivity to malignant tissue is also demonstrated preclinically and clinically with an E1B-deleted adenovirus utilising a prostate-specific antigen promoter. Other selective replicating viral vectors such as herpes simplex virus and vaccinia virus have also been explored clinically and suggest evidence of activity in patients with cancer. Modifications may one day enable more aggressive use of these new and exciting therapeutics as systemic gene delivery vehicles.

Glial-specific retrovirally mediated gas1 gene expression induces glioma cell apoptosis and inhibits tumor growth in vivo

We recently reported that the targeted expression of growth arrest specific 1 (Gas1) induces apoptosis in glioma cells. Because the vast majority of gliomas present genetic alterations that reduce their ability to undergo apoptosis, a gene therapy strategy aimed at reinstating apoptotic processes in glioma cells is an interesting approach for the treatment of these tumors. We used a retroviral gene transfer system to transduce C6 glioma cells with a transgene in which the expression of a full-length human gas1 cDNA is under the transcriptional control of a human promoter of the glial fibrillary acidic protein (gfa2). In vitro experiments showed that the retroviral transfer of gas1 significantly reduces the number of viable cells, and induces apoptosis in C6 cells, through the activation of caspase-3. Furthermore, retroviral-mediated transfer of gas1 to gliomas implanted in nude mice induces a significant inhibition of tumor growth, accompanied by increased caspase-3 activation. In the present experiments, we have taken advantage of the property of retrovirus to transfer transgenes exclusively to proliferating cells, together with the use of a glial specific promoter, to selectively target the expression of gas1, a pro-apoptotic gene, to glioma cells.

Delivery of GDNF by an E1,E3/E4 deleted adenoviral vector and driven by a GFAP promoter prevents dopaminergic neuron degeneration in a rat model of Parkinson's disease

A new adenoviral vector (Ad-GFAP-GDNF) (Ad=adenovirus, GFAP=glial fibrillary acidic protein, GDNF=glial cell line-derived neurotrophic factor) was constructed in which (i) the E1,E3/E4 regions of Ad5 were deleted and (ii) the GDNF transgene is driven by the GFAP promoter. We verified, in vitro, that the recombinant GDNF was expressed in primary cultures of astrocytes. In vivo, the Ad-GFAP-GDNF was injected into the striatum of rats 1 week before provoking striatal 6-OHDA lesion. After 1 month, the striatal GDNF levels were 37 pg/microg total protein. This quantity was at least 120-fold higher than in nontransduced striatum or after injection of the empty adenoviral vector. At 3 months after viral injection, GDNF expression decreased, whereas the viral DNA remained unchanged. Furthermore, around 70% of the dopaminergic (DA) neurons were protected from degeneration up to 3 months as compared to about 45% in the control groups. In addition, the amphetamine-induced rotational behavior was decreased. The results obtained in this study on DA neuron protection and rotational behavior are similar to those previously reported using vectors with viral promoters. In addition to these results, we established that a high level of GDNF was present in the striatum and that the period of GDNF expression was prolonged after injection of our adenoviral vector.

Compromised reproductive function in adult female mice selectively expressing mutant ErbB-1 tyrosine kinase receptors in astroglia

The ErbB-1 tyrosine kinase receptor plays critical roles in regulating physiological functions. This receptor-mediated signaling in astroglia has been implicated in controlling female sexual development via activating neurons that release LH-releasing hormone (LHRH), the neuropeptide required for the secretion of LH. It remains unknown whether astroglial ErbB-1 receptors are necessary for maintaining normal adult reproductive function. Here we provide genetic evidence that astroglia-specific and time-controlled disruption of ErbB-1 receptor signaling by expressing mutant ErbB-1 receptors leads to compromised reproduction due to alteration in LHRH neuron-controlled secretion of LH in adult female mice. Therefore, astroglial ErbB-1 receptors are required for controlling LHRH neuronal function and thus maintaining adult reproduction, suggesting that compromised astroglial ErbB-1 signaling may also contribute to reproductive abnormalities in aging females.

Transcriptionally targeted gene therapy to detect and treat cancer

The greatest challenge in cancer treatment is to achieve the highest levels of specificity and efficacy. Cancer gene therapy could be designed specifically to express therapeutic genes to induce cancer cell destruction. Cancer-specific promoters are useful tools to accomplish targeted expression; however, high levels of gene expression are needed to achieve therapeutic efficacy. Incorporating an imaging reporter gene in tandem with the therapeutic gene will allow tangible proof of principle that gene expression occurs at the correct location and at a sufficient level. Gene-based imaging can advance cancer detection and diagnosis. By combining the cancer-targeted imaging and therapeutic strategies, the exciting prospect of a 'one-two punch' to find hidden, disseminated cancer cells and destroy them simultaneously can potentially be realized.

Aspartylglucosaminidase (AGA) is efficiently produced and endocytosed by glial cells: implication for the therapy of a lysosomal storage disorder

BACKGROUND

Aspartylglucosaminuria (AGU) represents diseases affecting the central nervous system and is caused by a deficiency of a lysosomal enzyme, aspartylglucosaminidase (AGA). AGA, like lysosomal enzymes in general, are good targets for gene therapy since they move from cell to cell using the mannose-6-phosphate receptor. Consequently, only a minority of target cells need to be corrected. Here, we wanted to determine which cell type, neurons or glia would better produce AGA to be transported to adjacent cells for use in possible treatment strategies.

METHODS

Adenoviruses containing tissue-specific glial fibrillary acidic protein (GFAP) promoter and neuron-specific enolase (NSE) promoter were generated to target expression of AGA in Aga-deficient mouse primary glial and neuronal cell cultures. In addition an endogenous AGA promoter was used. The experimental design was planned to measure the enzymatic activities in the cells and media of neurons and glia infected with each specific virus. The endocytosis of AGA was analyzed by incubating neuronal and glial cells with media produced by each virus-cell combination.

RESULTS

AGA promoter was shown to be a very powerful glia promoter producing 32 times higher specific AGA activity in glia than in neurons. GFAP and NSE promoters also produced a clear overexpression of AGA in glia and neurons, respectively. Interestingly, both the NSE and GFAP promoters were not cell-specific in our system. The amount of exocytosed AGA was significantly higher in glial cells than neurons and glial cells were also found to have a greater capacity to endocytose AGA.

CONCLUSIONS

These data indicate the importance of glial cells in the expression and transport of AGA. Subsequently, new approaches can be developed for therapeutic intervention.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

Current and future strategies for the treatment of malignant brain tumors

Glioblastoma (GB) is the most common subtype of primary brain tumor in adults. These tumors are highly invasive, very aggressive, and often infiltrate critical neurological areas within the brain. The mean survival time after diagnosis of GB has remained unchanged during the last few decades, in spite of advances in surgical techniques, radiotherapy, and also chemotherapy; patients' survival ranges from 9 to 12 months after initial diagnosis. In the same time frame, with our increasing understanding and knowledge of the physiopathology of several cancers, meaningful advances have been made in the treatment and control of several cancers, such as breast, prostate, and hematopoietic malignancies. Although a number of the genetic lesions present in GB have been elucidated and our understanding of the progressions of this cancer has increased dramatically over the last few years, it has not yet been possible to harness this information towards developing effective cures. In this review, we will focus on the classical ways in which GB is currently being treated, and will introduce a novel therapeutic modality, i.e., gene therapy, which we believe will be used in combination with classical treatment strategies to prolong the life-span of patients and to ultimately be able to control and/or cure these brain tumors. We will discuss the use of several vector systems that are needed to introduce the therapeutic genes within either the tumor mass, if these are not resectable, or the tumor bed, after successful tumor resection. We also discuss different therapeutic modalities that could be exploited using gene therapy, i.e., conditional cytotoxic approach, direct cytotoxicity, immunotherapy, inhibition of angiogenesis, and the use of pro-apoptotic genes. The advantages and disadvantages of each of the current vector systems available to transfer genes into the CNS are also discussed. With the advances in molecular techniques, both towards the elucidation of the physiopathology of GB and the development of novel, more efficient and less toxic vectors to deliver putative therapeutic genes into the CNS, it should be possible to develop new rationale and effective therapeutic approaches to treat this devastating cancer.

Transcriptionally mediated gene targeting of gas1 to glioma cells elicits growth arrest and apoptosis

Induction of growth arrest-specific genes (gas1) prevents cell proliferation and/or leads to apoptosis in different cell types. In neurons, it has been recently reported that mild excitotoxic neuronal death is associated with gas1 induction, and that overexpression of Gas1 induces apoptosis in terminally differentiated neurons or in proliferating neuroblastoma cells. In the present study, we have analysed the effects of the transcriptionally mediated targeting of gas1 to C6 rat glioma cells. Expression of Gas1 decreased glial proliferation and induced C6 cell apoptosis. While the identity of the caspase(s) responsible for Gas1-induced apoptosis in neurons has remained elusive, in C6 glioma cells, overexpression of Gas1 reproducibly activated caspase-3. Our results support the concept of targeted expression of gas1 as a potentially useful gene therapy strategy in the treatment of human gliomas.

Oncolytic adenoviruses for treatment of brain tumours

Standard therapies are not capable of curing patients with malignant glioma; more than 90% of patients die within 2 years after diagnosis. Gene therapy appeared as a promising new approach for this disease. However, results of clinical trials with replication deficient viral vectors were disappointing. The main reasons being poor transduction efficiency of adenovirus towards glioma cells and limited spread and distribution of the vector in the tumour. With the increasing knowledge of viral genetics and its functions, an attractive alternative tool to kill malignant glioma cells has been developed: Replicating adenovirus as an oncolytic agent. This type of therapy, also referred to as virotherapy, has the potential to overcome some of the limitations connected with replication deficient adenoviral vectors. In this review the authors describe the latest developments in strategies that are being used to create a tumour- or glioma-selective replicating adenovirus. Special attention is given to the methods of viral delivery to an infiltrating tumour in the brain, regarding optimal dose and toxicity. Furthermore, the role of conventional antitumour treatments, such as irradiation and chemotherapy, in enhancing the effect of virotherapy is being emphasised.

Gene therapy of erectile dysfunction in the rat with penile neuronal nitric oxide synthase

Gene transfer to the penile corpora cavernosa of constructs of the inducible and endothelial nitric oxide synthase (NOS) cDNAs ameliorates erectile dysfunction in aged rats. In this study, we investigated whether the neuronal NOS (nNOS) variant responsible for erection, penile nNOS (PnNOS), can exert a similar effect, and whether the combination of electroporation with a helper-dependent adenovirus (AdV) improves gene transfer. PnNOS and beta-galactosidase cDNAs were cloned in plasmid (pCMV-PnNOS; pCMV-beta-gal) and "gutless" AdV (AdV-CMV-PnNOS; AdV-CMV-beta-gal) vectors, and injected into the penis of adult (beta-gal) or aged (PnNOS) rats, with or without electroporation. Penile erection was measured at different times after PnNOS cDNA injection, by electrical field stimulation of the cavernosal nerve. The expression of beta-galactosidase or PnNOS was estimated in penile tissue by either histochemistry and luminometry or Western blot, and the effects of AdV-CMV-PnNOS on mRNA expression were examined by a DNA microarray. We found that electroporation increased pCMV-beta-gal uptake, and its expression was detectable at 56 days. In the aged rats treated with pCMV-PnNOS and electroporation, the maximal intracavernosal:mean arterial pressure ratios were elevated for 11 and 18 days when compared with those in controls. Electroporation intensified penile uptake of as few as 10(6) viral particles (vp) of AdV-CMV-beta-gal, and with 10(7) vp beta-galactosidase was still detectable at 60 days. Electroporated AdV-CMV-PnNOS (10(7) vp) was effective at 18 days in stimulating the erection of aged rats, without inducing the expression of cytotoxic genes. In conclusion, intracavernosal gene therapy with PnNOS cDNA corrected the aging-related erectile dysfunction for at least 18 days when given by electroporation in a helper-dependent AdV at low viral loads.

Upregulation of the Fas receptor death-inducing signaling complex after traumatic brain injury in mice and humans

Recent studies have implicated Fas in the pathogenesis of inflammatory, ischemic, and traumatic brain injury (TBI); however, a direct link between Fas activation and caspase-mediated cell death has not been established in injured brain. We detected Fas-Fas ligand binding and assembly of death-inducing signaling complexes (DISCs) [Fas, Fas-associated protein with death domain, and procaspase-8 or procaspase-10; receptor interacting protein (RIP)-RIP-associated interleukin-1beta converting enzyme and CED-3 homolog-1/Ced 3 homologous protein with a death domain-procaspase-2] by immunoprecipitation and immunoblotting within mouse parietal cortex after controlled cortical impact. At the time of DISC assembly, procaspase-8 was cleaved and the cleavage product appeared at 48 hr in terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive neurons. Cleavage of caspase-8 was accompanied by caspase-3 processing detected at 48 hr by immunohistochemistry, and by caspase-specific cleavage of poly(ADP-ribose) polymerase at 12 hr. Fas pathways were also stimulated by TBI in human brain, because Fas expression plus Fas-procaspase-8 interaction were robust in contused cortical tissue samples surgically removed between 2 and 30 hr after injury. To address whether Fas functions as a death receptor in brain cells, cultured embryonic day 17 cortical neurons were transfected with an adenoviral vector containing the gene encoding Fas ligand. After 48 hr in culture, Fas ligand expression and Fas-procaspase-8 DISC assembly increased, and by 72 hr, cell death was pronounced. Cell death was decreased by approximately 50% after pan-caspase inhibition (Z-Val-ALa-Asp(Ome)-fluoromethylketone). These data suggest that Fas-associated DISCs assemble in neurons overexpressing Fas ligand as well as within mouse and human contused brain after TBI. Therefore, Fas may function as a death receptor after brain injury.

Cell-specific viral gene therapy of a Hurthle cell tumor

We evaluated the effectiveness of a replication-defective adenovirus-transducing thymidine kinase (TK) gene under the control of the rat Tg (rTg) promoter (AdrTgtk) in therapy of a human Hurthle cancer (XTC-1 cell) in vitro and in vivo. The ganciclovir (GCV) sensitivity of infected XTC-1 cells was assessed in vitro by H(3)-thymidine incorporation assay and Trypan-blue exclusion, and by an in vivo tumor development assay. Proliferation was strongly inhibited by adding GCV into the culture medium of infected cells, but not uninfected cells, proving cell infection and expression of TK in the XTC-1 cells. AdrTgtk, and also viruses that have the noncell-specific cytomegalovirus (CMV) promoter-directing expression of TK (AdCMVtk), or luciferase (AdCMVLuc), were used to transduce XTC-1 cells to evaluate killing effects. After infection with AdCMVtk or AdrTgtk, followed by GCV treatment, 70% of infected cells were killed in the presence of GCV, compared with less than 20% of cells infected by AdCMVLuc and treated with GCV. In vivo toxicity was studied in BALB/c mice. When adenovirus is given iv, liver is the major organ infected. No significant changes of the serum transaminase levels and no histological abnormalities were found in animals treated with AdrTgtk/GCV given iv, compared with control animals. High levels of serum transaminases, lymphocyte infiltration, some Kupffer's cell prominence, and extensive single-cell hepatocyte death were found in AdCMVtk/GCV-treated animals, indicating severe liver damage induced, as expected, by the noncell-specific CMV promoter. XTL-1 cells (2 x 10(6)) were injected sc into BALB/c-severe combined immunodeficient mice (BALB/c-SCID), and the mice developed tumors after 3 wk. After intratumoral injection of AdrTgtk and treatment with GCV, tumors stabilized in 15 of 17 mice within 3 wk, 9 tumors remained stabilized after 5 wk of treatment, and 2 disappeared during observation. In AdCMVLuc/GCV-treated control mice, almost all tumors grew continuously. The average tumor size in AdrTgtk-treated mice was significantly smaller than that of control animals after 2 wk of treatment. Our data confirm the effectiveness and specificity of an adenovirus using rTg promoter to express TK, and support its future application to thyroid cancer gene therapy in humans.

Viral vector-mediated delivery of competing glycosyltransferases modifies epitope expression cell specifically

The glycoconjugate epitopes 3-fucosyl-N-acetyllactosamine (CD15) and sulfoglucuronylcarbohydrate (SGC) mediate cell adhesion events in several systems, and are regulated both spatially and temporally during cerebellar development. In cotransfection studies using COS-1 cells, competition between glycosyltransferases that utilize a common precursor involved in the final synthetic steps of these epitopes, can modulate epitope expression. For example, cotransfection of rat alpha1,3-fucosyltransferase IV (Fuc-TIV) and either rat glucuronic acid transferase P (GlcAT) or pig alpha1,3-galactosyltransferase (GalT) resulted in the dominance of either SGC or GalalphaGal epitope expression, respectively, with blockage of CD15 epitope expression. Viral vectors expressing these glycosyltransferases were used to determine whether competition plays a role in establishing epitope dominance in cerebellar cells, and whether overexpression of competing glycosyltransferases could be used to block epitope expression. Infection of cerebellar astrocytes with viral vectors expressing either Fuc-TIV, or Fuc-TIX, caused dramatic increases in CD15 expression in the presence of continued endogenous SGC epitope expression. Likewise, viral transduction with GalT resulted in GalalphaGal expression without affecting endogenous CD15 or SGC expression. Thus, competition between these enzymes does not appear to play a role in establishing epitope expression in astrocytes, and transduction of these enzymes does not provide a method of blocking the expression of endogenous epitopes. In contrast to what was observed for astrocytes, infection with viral vectors expressing either Fuc-T, GlcAT, or GalT did not result in significant expression of the relevant epitopes (CD15, SGC or GalalphaGal, respectively) on granule neurons. These results suggest a different complement of precursors are present in granule neurons and astrocytes, presumably due to the presence of different complements of glycosyltransferases in these cells.

Fas receptor-mediated apoptosis: a clinical application?

Fas is a membrane protein belonging to the death receptor family. Cross-linking of Fas by its ligand, FasL, or agonistic anti-Fas antibodies, induces apoptosis of cells expressing Fas on the membrane by triggering a cascade of caspases. Since many different tumours express Fas on their membrane, targeting Fas-mediated apoptosis by anti-Fas antibodies may be a promising anticancer therapy. Unfortunately, not all Fas-expressing cells are sensitive to Fas-mediated apoptosis. This has resulted in the discovery of many different inhibition mechanisms of Fas-mediated apoptosis. In addition, mutations in the Fas or p53 gene can also influence the sensitivity for Fas-mediated apoptosis. However, the role of wild-type p53 in Fas expression is still controversial. Because several different cytotoxic drugs are able to induce Fas membrane expression, combination therapy of anticancer drugs with anti-Fas antibodies or FasL is conceivable as an anticancer strategy. The efficiency of the induction of Fas-mediated apoptosis by anti-Fas antibodies, FasL-expressing cells or recombinant FasL (rFasL) in tumours has been demonstrated in vivo in solid tumours implanted in mice. Unfortunately, systemic treatment with anti-Fas antibodies or rFasL causes severe damage to the liver, so most preclinical studies are now focusing on circumvention of this problem by local administration of FasL, or on the use of inducible FasL-expressing vectors as gene therapy.

Head and neck cancer: gene therapy approaches. Part 1: adenoviral vectors

Treatment options for recurrent or refractory head and neck cancer are limited. The goal of gene therapy is to introduce new genetic material into cancer cells without affecting toxicity to surrounding malignant cells. The most common vehicles for delivery of genes are adenoviruses. Adenoviruses gain access to malignant and normal cell cytoplasm via viral ligand binding to a unique cell surface receptor (the coxsackie adenovirus receptor [CAR]). However, this receptor is not cancer specific. Genetic modification of adenoviral DNA can create cancer specific targeting. Adenoviruses can be modified to express cancer specific ligands thereby focusing binding to malignant tissue. Furthermore, adenoviral delivered genes can be put under cancer specific promoter control to further limit gene expression in malignant tissue. Increased antitumour activity from such modifications has been demonstrated preclinically and several clinical trials have been completed demonstrating safety and clinical activity of non-replicating and conditional replicating adenoviral vector thereby opening the door for gene delivery and cancer specific targeting.