Endothelial cell-specific expression of tumor necrosis factor-alpha from the KDR or E-selectin promoters following retroviral delivery

Targeted polymeric nanoparticles for cancer gene therapy

In this article, advances in designing polymeric nanoparticles for targeted cancer gene therapy are reviewed. Characterization and evaluation of biomaterials, targeting ligands, and transcriptional elements are each discussed. Advances in biomaterials have driven improvements to nanoparticle stability and tissue targeting, conjugation of ligands to the surface of polymeric nanoparticles enable binding to specific cancer cells, and the design of transcriptional elements has enabled selective DNA expression specific to the cancer cells. Together, these features have improved the performance of polymeric nanoparticles as targeted non-viral gene delivery vectors to treat cancer. As polymeric nanoparticles can be designed to be biodegradable, non-toxic, and to have reduced immunogenicity and tumorigenicity compared to viral platforms, they have significant potential for clinical use. Results of polymeric gene therapy in clinical trials and future directions for the engineering of nanoparticle systems for targeted cancer gene therapy are also presented.

Bacteriophage-derived vectors for targeted cancer gene therapy

Cancer gene therapy expanded and reached its pinnacle in research in the last decade. Both viral and non-viral vectors have entered clinical trials, and significant successes have been achieved. However, a systemic administration of a vector, illustrating safe, efficient, and targeted gene delivery to solid tumors has proven to be a major challenge. In this review, we summarize the current progress and challenges in the targeted gene therapy of cancer. Moreover, we highlight the recent developments of bacteriophage-derived vectors and their contributions in targeting cancer with therapeutic genes following systemic administration.

IL10 released by a new inflammation-regulated lentiviral system efficiently attenuates zymosan-induced arthritis

Administration of anti-inflammatory cytokines is a common therapeutic strategy in chronic inflammatory diseases. Gene therapy is an efficient method for delivering therapeutic molecules to target cells. Expression of the cell adhesion molecule E-selectin (ESEL), which is expressed in the early stages of inflammation, is controlled by proinflammatory cytokines, making its promoter a good candidate for the design of inflammation-regulated gene therapy vectors. This study describes an ESEL promoter (ESELp)-based lentiviral vector (LV) that drives localized transgene expression during inflammation. Mouse matrigel plug assays with ESELp-transduced endothelial cells showed that systemic lipopolysaccharide (LPS) administration selectively induces ESELp-controlled luciferase expression in vivo. Inflammation-specific induction was confirmed in a mouse model of arthritis, showing that this LV is repeatedly induced early in acute inflammation episodes and is downregulated during remission. Moreover, the local acute inflammatory response in this animal model was efficiently blocked by expression of the anti-inflammatory cytokine interleukin-10 (IL10) driven by our LV system. This inflammation-regulated expression system has potential application in the design of new strategies for the local treatment of chronic inflammatory diseases such as cardiovascular and autoimmune diseases.

Physiological and tissue-specific vectors for treatment of inherited diseases

After more than 1500 gene therapy clinical trials in the past two decades, the overall conclusion is that for gene therapy (GT) to be successful, the vector systems must still be improved in terms of delivery, expression and safety. The recent development of more efficient and stable vector systems has created great expectations for the future of GT. Impressive results were obtained in three primary immunodeficiencies and other inherited diseases such as congenital blindness, adrenoleukodystrophy or junctional epidermolysis bullosa. However, the development of leukemia in five children included in the GT clinical trials for X-linked severe combined immunodeficiency and the silencing of the therapeutic gene in the chronic granulomatous disease clearly showed the importance of improving safety and efficiency. In this review, we focus on the main strategies available to achieve physiological or tissue-specific expression of therapeutic transgenes and discuss the importance of controlling transgene expression to improve safety. We propose that tissue-specific and/or physiological viral vectors offer the best balance between efficiency and safety and will be the tools of choice for future clinical trials in GT of inherited diseases.

Active adenoviral vascular penetration by targeted formation of heterocellular endothelial-epithelial syncytia

The endothelium imposes a structural barrier to the extravasation of systemically delivered oncolytic adenovirus (Ad). Here, we introduced a transendothelial route of delivery in order to increase tumor accumulation of virus particles (vp) beyond that resulting from convection-dependent extravasation alone. This was achieved by engineering an Ad encoding a syncytium-forming protein, gibbon ape leukemia virus (GALV) fusogenic membrane glycoprotein (FMG). The expression of GALV was regulated by a hybrid viral enhancer-human promoter construct comprising the human cytomegalovirus (CMV) immediate-early enhancer and the minimal human endothelial receptor tyrosine kinase promoter (“eTie1”). Endothelial cell-selectivity of the resulting Ad-eTie1-GALV vector was demonstrated by measuring GALV mRNA transcript levels. Furthermore, Ad-eTie1-GALV selectively induced fusion between infected endothelial cells and uninfected epithelial cells in vitro and in vivo, allowing transendothelial virus penetration. Heterofusion of infected endothelium to human embryonic kidney 293 (HEK 293) cells, in mixed in vitro cultures or in murine xenograft models, permitted fusion-dependent transactivation of the replication-deficient Ad-eTie1-GALV, due to enabled access to viral E1 proteins derived from the HEK 293 cytoplasm. These data provide evidence to support our proposed use of GALV to promote Ad penetration through tumor-associated vasculature, an approach that may substantially improve the efficiency of systemic delivery of oncolytic viruses to disseminated tumors.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

Shear stress-induced transcriptional regulation via hybrid promoters as a potential tool for promoting angiogenesis

Among the key effects of fluid shear stress on vascular endothelial cells is modulation of gene expression. Promoter sequences termed shear stress response elements (SSREs) mediate the responsiveness of endothelial genes to shear stress. While previous studies showed that shear stress responsiveness is mediated by a single SSRE, these endogenous promoters often encode for multiple SSREs. Moreover, hybrid promoters encoding a single SSRE rarely respond to shear stress at the same magnitude as the endogenous promoter. Thus, to better understand the interplay between the various SSREs, and between SSREs and endothelial-specific sequences (ESS), we generated a series of constructs regulated by SSREs cassettes alone, or in combination with ESS, and tested their response to shear stress and endothelial specific expression. Among these constructs, the most responsive promoter (NR1/2) encoded a combination of two GAGACC/SSREs, the Sp1/Egr1 sequence, as well as a TPA response element (TRE). This construct was four- to five-fold more responsive to shear stress than a promoter encoding a single SSRE. The expression of constructs containing other SSRE combinations was unaffected or suppressed by shear stress. Addition of ESS derived from the Tie2 promoter, either 5' or 3' to NR1/2 resulted in shear stress transcriptional suppression, yet retained endothelial specific expression. Thus, the combination and localization order of the various SSREs in a single promoter is crucial in determining the pattern and degree of shear stress responsiveness. These shear stress responsive cassettes may prove beneficial in our attempt to time the expression of an endothelial transgene in the vasculature.

Endothelial dysfunction: from molecular mechanisms to measurement, clinical implications, and therapeutic opportunities

Endothelial dysfunction has been implicated as a key factor in the development of a wide range of cardiovascular diseases, but its definition and mechanisms vary greatly between different disease processes. This review combines evidence from cell-culture experiments, in vitro and in vivo animal models, and clinical studies to identify the variety of mechanisms involved in endothelial dysfunction in its broadest sense. Several prominent disease states, including hypertension, heart failure, and atherosclerosis, are used to illustrate the different manifestations of endothelial dysfunction and to establish its clinical implications in the context of the range of mechanisms involved in its development. The size of the literature relating to this subject precludes a comprehensive survey; this review aims to cover the key elements of endothelial dysfunction in cardiovascular disease and to highlight the importance of the process across many different conditions.

Cancer gene therapy with iCaspase-9 transcriptionally targeted to tumor endothelial cells

Antiangiogenic therapies have shown varying results partly because each tumor type secretes a distinct panel of angiogenic factors to sustain its own microvascular network. In addition, recent evidence demonstrated that tumors develop resistance to antiangiogenic therapy by turning on alternate angiogenic pathways when one pathway is therapeutically inhibited. Here, we test the hypothesis that expression of a caspase-based artificial death switch in tumor-associated endothelial cells will disrupt tumor blood vessels and slow down tumor progression irrespective of tumor type. Adenoviral vectors expressing inducible Caspase-9 (iCaspase-9) under transcriptional regulation with the endothelial cell-specific vascular endothelial growth factor receptor-2 (VEGFR2) promoter (Ad-hVEGFR2-iCaspase-9) induced apoptosis of proliferating human dermal microvascular endothelial cells (HDMECs), but not human tumor cells (UM-SCC-17B, head and neck squamous cell carcinoma; HepG2, hepatocellular carcinoma; PC-3, prostate adenocarcinoma; SLK, Kaposi's sarcoma; MCF-7, breast adenocarcinoma). Notably, apoptosis was dependent upon activation of iCaspase-9 with the dimerizer drug AP20187. Local delivery of Ad-hVEGFR2-iCaspase-9 followed by intraperitoneal injection of AP20187 ablated tumor microvessels and inhibited xenografted tumor growth in all tumor models evaluated here. We conclude that a cancer gene therapy strategy based on a transcriptionally targeted viral vector expressing an inducible caspase allows for selective and controlled ablation of microvessels of histopathologically diverse tumor types.

Vascular damage and anti-angiogenic effects of tumor vessel-targeted adenovirus-mediated herpes simplex virus thymidine kinase gene

AIM: To explore the therapeutic efficacy and mechanism of herpes simplex virus-thymidine kinase (HSV-tk) targeting angiogenesis against hepatocellular carcinoma in vivio and in vitro.

METHODS: Recombinant adenovirus containing kinase domain insert with receptor (KDR) or cytomegalovirus (CMV) promoter-controlled HSV-tk gene (AdKDR-tk and AdCMV-tk) was constructed using pAdeasy system. The expression of KDR antigen in human umbilical venous endothelial cells (HUVEC) and HepG2 was detected with histological analysis of cells. The virus was used to infect HUVEC and HepG2. Following administration of ganciclovir (GCV), the survival rate of gene-transfected HUVEC and HepG2 was evaluated by MTT method. To develop hepatocarcinomas in 32 Balb/C mice with HepG2 cells, the mice were divided into four groups: ganciclovir group (I), Ad group (II), AdCMV-tk group (III) and AdKDR-tk group (IV). Then selective administration of recombinant adenovirus or Ad via the intratumorial was given to all rats. Ganciclovir (GCV) was given at a dose of 100 mg·kg^-1·d^-1 (ip) started on the following day and lasted 10 d. Microvessel density (MVD) of tumor in all the treated animals were examined by the immunohistochemical methods and tumor burden was evaluated 10 d before and after the last GCV dose.

RESULTS: Immunocytochemical staining indicated the expression of KDR antigen in HUVEC. Under adenovirus infection index of 100, with increasing GCV concentration from 0 up to 50 mg/L, the survival rate of AdKDR-tk-transfected HUVEC and HepG2 decreased from 100% to (28.94 ± 5.67)% and (75.45 ± 2.91)% at proper order, respectively (P < 0.01), while the survival rate of AdCMV-tk-transfected HUVEC and HepG2 declined from 100% to (17.56 ± 2.48)% and (23.15 ± 5.72)%, respectively (P > 0.05). Compared with groupI, there was a decrease of tumor weight by 14.7% in group III and by 23.6% in group IV. And there was a distinct difference between group III and IV (P < 0.05). The median MVD for all groups was 37.4 ± 8.6, 30.6 ± 7.8, 27.6 ± 7.1, and 10.7 ± 4.1 (microvessels/mm²) in groupI, II, III and IV, respectively. And there was a marked difference between group III and II (P < 0.05), IV and II (P < 0.01), and IV and III (P < 0.01).

CONCLUSION: KDR promoter-HSV-tk gene may effectually restrain the growth of tumor via targeting angiogenesis for hepatocellular carcinoma with treatment of GCV.

Gene therapy targeting to tumor endothelium

Tumor-associated vasculature is a relatively accessible component of solid cancers that is essential for tumor survival and growth, providing a vulnerable target for cancer gene therapy administered by intravenous injection. Several features of tumor-associated vasculature are different from normal vasculature, including overexpression of receptors for angiogenic growth factors, markers of vasculogenesis, upregulation of coagulation cascades, aberrant expression of adhesion molecules and molecular consequences of hypoxia. Many of these differences provide candidate targets for tumor-selective 'transductional targeting' of genetically- or chemically modified vectors and upregulated gene expression can also enable 'transcriptional targeting', regulating tumor endothelia-selective expression of transgenes following nonspecific gene delivery. Tumor vasculature also represents an important site of therapeutic action by the secreted products of antiangiogenic gene therapies that are expressed in non-endothelial cells. In this review we assess the challenges faced and the vectors that may be suitable for gene delivery to exploit these targets. We also overview some of the strategies that have been developed to date and highlight the most promising areas of research.

Vascular Wall Maturation and Prolonged Angiogenic Effect by Endothelial-Specific Platelet-Derived Growth Factor Expression

BACKGROUND

The implementation of angiogenic gene therapy at clinics is hindered by the transience of the therapeutic effect. Recruiting vascular wall smooth muscle cells, a process termed 'maturation', can stabilize newly formed vessels.

OBJECTIVE

To induce angiogenesis followed by vessel maturation in a murine ischemic limb model by endothelial cell-specific promoter regulated expression of vascular endothelial growth factor (VEGF) and platelet-derived growth factor-BB (PDGF-BB).

METHODS

We constructed adenoviral vectors containing angiogenic factors VEGF and PDGF-B regulated by a modified preproendothelin-1 (PPE-1-3x) promoter and investigated their angiogenic effect in a murine ischemic limb model.

RESULTS

VEGF gene therapy increased perfusion and the vessel density in the limb shortly after expression with PPE-1-3x promoter or cytomegalovirus (CMV) promoter vectors, but only PPE-1-3xVEGF treatment exhibited a sustained effect. Expression of PDGF-B by PPE-1-3x promoter resulted in morphological maturation of the vasculature and further increased the perfusion, while nonspecific expression of PDGF-B with CMV promoter had no therapeutic effect. Regulation of dual therapy with VEGF and PDGF-B by PPE-1-3x promoter resulted in an early-onset, sustained angiogenic effect accompanied by vessel maturation.

CONCLUSIONS

Systemic gene therapy with the angiogenic factors VEGF and PDGF-B under angiogenic- endothelial cell-specific regulation was effective in inducing functionally and morphologically mature vasculature.

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.

Delivery of viral vectors to tumor cells: extracellular transport, systemic distribution, and strategies for improvement

It is a challenge to deliver therapeutic genes to tumor cells using viral vectors because (i) the size of these vectors are close to or larger than the space between fibers in extracellular matrix and (ii) viral proteins are potentially toxic in normal tissues. In general, gene delivery is hindered by various physiological barriers to virus transport from the site of injection to the nucleus of tumor cells and is limited by normal tissue tolerance of toxicity determined by local concentrations of transgene products and viral proteins. To illustrate the obstacles encountered in the delivery and yet limit the scope of discussion, this review focuses only on extracellular transport in solid tumors and distribution of viral vectors in normal organs after they are injected intravenously or intratumorally. This review also discusses current strategies for improving intratumoral transport and specificity of viral vectors.

Conditionally replicative adenoviral vectors for malignant glioma

High-grade gliomas constitute an important challenge to modern medicine, and although great effort has been made to prolong patient survival, the prognosis for this disease remains poor. Due to recent discoveries in the molecular basis of gliomas, gene therapy is becoming a promising alternative. In this review, we discuss the use of conditionally replicative adenoviral vectors (CRAd) and their applications in neuro-oncology. Such vectors, when rendered conditionally replicative via transductional and transcriptional modifications, offer great promise for patients with malignant brain tumours. We review data from preclinical and clinical studies utilising such vectors and discuss the limitations and future perspectives of CRAd oncolytic therapy for malignant glioma.

Characterisation of systemic dissemination of nonreplicating adenoviral vectors from tumours in local gene delivery

Systemic virus dissemination is a potential problem during local gene delivery in solid tumours. However, the kinetics and pathways of the dissemination have not been well characterised during the first 24 h after the infusion is started. To this end, we infused adenoviral vectors for luciferase or enhanced green fluorescence protein into three different tumour models in mice. During and/or after the infusion, we determined the amount of adenoviruses in the tumour, blood, and liver, and examined the transgene expression in the liver, lung, blood, and tumour. In addition, we intravenously injected tumour cells expressing luciferase and examined the biodistribution of these cells in the body. We observed transgene expression in the liver and tumour at 24 h after the infusion, but could not detect transgene expression in the blood and lung. The peak concentration of viral vectors in the plasma occurred during the intratumoral infusion. At 10 min after the infusion, few viral vectors remained in the blood and the ratio of copy numbers of adenoviruses between liver and tumour was >2 in 80% and ⩾10 in 40% of the mice. Most tumour cells injected intravenously accumulated in the lung within the first 24 h. Taken together, these data indicated that systemic virus dissemination occurred mainly during the first 10 min after the intratumoral infusion was started, and that the dissemination was due to infusion-induced convective transport of viral vectors into leaky tumour microvessels.

Antiangiogenic gene therapy: disruption of neovascular networks mediated by inducible caspase-9 delivered with a transcriptionally targeted adenoviral vector

The activation of an inducible caspase (iCaspase-9) mediates apoptosis of neovascular endothelial cells, and overcomes the prosurvival effect of vascular endothelial growth factor or basic fibroblast growth factor. The potential utilization of direct activation of caspases as an antiangiogenic strategy for treatment of angiogenesis-dependent diseases (eg cancer) requires expression of the inducible caspase primarily in the tumor endothelium. The objective of this work was to develop and characterize a transcriptionally targeted adenoviral vector that mediates expression of iCaspase-9 specifically in neovascular endothelial cells. We observed that adenoviral vectors containing the human VEGFR2 promoter induced reporter gene expression primarily in proliferating human dermal microvascular endothelial cells (HDMEC). HDMEC transduced with recombinant adenoviral vectors containing iCaspase-9 under regulation of the VEGFR2 promoter (Ad-hVEGFR2-iCaspase-9) and exposed to a cell-permeable dimerizer drug (AP20187), presented higher caspase-3 activity and apoptosis than controls (P < or = 0.05). Using the SCID Mouse Model of Human Angiogenesis, we observed that local delivery of Ad-hVEGFR2-iCaspase-9 followed by intraperitoneal injection of AP20187 resulted in endothelial cell apoptosis and local ablation of microvessels. We believe that this constitutes the first report of a transcriptionally targeted antiangiogenic adenoviral vector that mediates neovascular disruption upon activation of a caspase-based artificial death switch.

Gene therapy for head and neck cancer

The prognosis of patients with advanced head and neck cancer has not changed significantly in the last twenty years, despite concerted efforts to optimize treatment using conventional modalities such as surgery, radiotherapy and chemotherapy. Novel therapeutic approaches based on our increasing understanding of the molecular changes that underlie the development of cancer have the potential to alter this situation. Gene therapy involves the delivery of genetic sequences in to tumour or normal cells for a therapeutic purpose. A number of viral and non-viral vectors have been developed that have the ability to deliver therapeutic genes specifically to tumours. These therapeutic genes can exert their effects by correcting existing genetic abnormalities, by killing cells directly or indirectly through recruitment of the immune system. In this review, the various gene therapy strategies that are under development are presented with particular reference to the treatment of head and neck cancer.

Endothelium-Targeted Gene and Cell-Based Therapies for Cardiovascular Disease

Most common cardiovascular diseases are accompanied by endothelial dysfunction. Because of its predominant role in the pathogenesis of cardiovascular disease, the vascular endothelium is an attractive therapeutic target. The identification of promoter sequences capable of rendering endothelial-specific transgene expression together with the recent development of vectors with enhanced tropism for endothelium may offer opportunities for the design of new strategies for modulation of endothelial function. Such strategies may be useful in the treatment of chronic diseases such as hypertension, atherosclerosis, and ischemic artery disease, as well as in acute myocardial infarction and during open heart surgery for prevention of ischemia and reperfusion (I/R)-induced injury. The recent identification of putative endothelial progenitor cells in peripheral blood may allow the design of autologous cell-based strategies for neovascularization of ischemic tissues and for the repair of injured blood vessels and bioengineering of vascular prosthesis. "Proof-of-concept" for some of these strategies has been established in animal models of cardiovascular disease. However the successful translation of these novel strategies into clinical application will require further developments in vector and delivery technologies. Further characterization of the processes involved in mobilization, migration, homing, and incorporation of endothelial progenitor cells into the target tissues is necessary, and the optimal conditions for therapeutic application of these cells need to be defined and standardized.

Therapeutic inhibition of angiogenesis

Angiogenesis, or the growth of new blood vessels, has, in recent years, become an area of intense scientific research. The primary reason for this has been the realization that angiogenesis plays a key role in many common pathologies, and that its inhibition could have profound implications in the treatment of these disorders. A substantial number of anti-angiogenic agents have now been identified; however, none has, as of yet, achieved widespread acceptance in the clinic. Many agents have been identified as the result of clearly defined research programs, such as the inhibitors of the vascular endothelial growth factor transmembrane tyrosine kinase receptors, but many other simply by screening. The purpose of this article is to review the wealth of information available on known anti-angiogenic agents and to assess their future potential.

Transcription-controlled gene therapy against tumor angiogenesis

A major drawback of current approaches to antiangiogenic gene therapy is the lack of tissue-specific targeting. The aim of this work was to trigger endothelial cell-specific apoptosis, using adenoviral vector-mediated delivery of a chimeric death receptor derived from the modified endothelium-specific pre-proendothelin-1 (PPE-1) promoter. In the present study, we constructed an adenovirus-based vector that targets tumor angiogenesis. Transcriptional control was achieved by use of a modified endothelium-specific promoter. Expression of a chimeric death receptor, composed of Fas and TNF receptor 1, resulted in specific apoptosis of endothelial cells in vitro and sensitization of cells to the proapoptotic effect of TNF-alpha. The antitumoral activity of the vectors was assayed in two mouse models. In the model of B16 melanoma, a single systemic injection of virus to the tail vein caused growth retardation of tumor and reduction of tumor mass with central tumor necrosis. When the Lewis lung carcinoma lung-metastasis model was applied, i.v. injection of vector resulted in reduction of lung-metastasis mass, via an antiangiogenic mechanism. Moreover, by application of the PPE-1-based transcriptional control, a humoral immune response against the transgene was avoided. Collectively, these data provide evidence that transcriptionally controlled, angiogenesis-targeted gene therapy is feasible.

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.

The NFY transcription factor functions as a repressor and activator of the von Willebrand factor promoter

Human von Willebrand factor (VWF) gene sequences -487 to +247 function as an endothelial-specific promoter in vitro. Analysis of the activation mechanism of the VWF promoter has resulted in the identification of a number of cis-acting elements and trans-acting factors that regulate its activity. The GATA and Ets transcription factors were shown to function as activators of transcription, whereas NF1 and Oct1 were shown to repress transcription. We have reported the presence of another repressor element in exon 1 that interacted with a protein complex designated "R." In the absence of NF1 binding, inhibition of this interaction resulted in promoter activation in nonendothelial cells. We have now identified the "R" protein complex as the NFY transcription factor. Using DNA methylation interference assay and base substitution mutation analysis, we show that NFY interacts with a novel DNA sequence corresponding to nucleotides +226 to +234 in the VWF promoter that does not conform to the consensus NFY binding sequence CCAAT. The VWF gene does contain a CCAAT element that is located downstream of the TATA box and we show that the NFY factor also interacts with this CCAAT element. Using antibodies specific against the A, B, and C subunits of NFY, we demonstrate that the NFY complexes interacting with the CCAAT sequence have a composition similar to that of the repressor binding to the first exon sequences. The results of mutation analysis and transfection studies demonstrated that the interaction of NFY with the upstream CCAAT element is required for VWF promoter activation. Based on these results, we hypothesize that NFY can function both as a repressor and activator of transcription and its function may be modulated through its DNA binding sequences.

Conditional gene targeting for cancer gene therapy

Current treatment of solid tumors is limited by severe adverse effects, resulting in a narrow therapeutic index. Therefore, cancer gene therapy has emerged as a targeted approach that would significantly reduce undesired side effects in normal tissues. This approach requires a clear understanding of the molecular biology of both the malignant clone and the biological vectors that serve as vehicles to target cancer cells. In this review we discuss novel approaches for conditional gene expression in cancer cells. Targeting transgene expression to malignant tissues requires the use of specific regulatory elements including promoters based on tumor biology, tissue-specific promoters and inducible regulatory elements. We also discuss the regulation of both replication and transgene expression by conditionally-replicative viruses. These approaches have the potential to restrict the expression of transgenes exclusively to tissues of interest and thereby to increase the therapeutic index of future vectors for cancer gene therapy.

Gene transfer by viral vectors into blood vessels in a rat model of retinopathy of prematurity

AIMS

To test the feasibility of gene transfer into hyaloid blood vessels and into preretinal neovascularisation in a rat model of retinopathy of prematurity (ROP), using different viral vectors.

METHODS

Newborn rats were exposed to alternating hypoxic and hyperoxic conditions in order to induce ocular neovascularisation (ROP rats). Adenovirus, herpes simplex, vaccinia, and retroviral (MuLV based) vectors, all carrying the beta galactosidase (beta-gal) gene, were injected intravitreally on postnatal day 18 (P18). Two sets of controls were also examined: P18 ROP rats injected with saline and P18 rats that were raised in room air before the viral vectors or saline were injected. Two days after injection, the rats were killed, eyes enucleated, and beta-gal expression was examined by X-gal staining in whole mounts and in histological sections.

RESULTS

Intravitreal injection of the adenovirus and vaccinia vectors yielded marked beta-gal expression in hyaloid blood vessels in the rat ROP model. Retinal expression of beta-gal with these vectors was limited almost exclusively to the vicinity of the injection site. Injection of herpes simplex yielded a punctuate pattern of beta-gal expression in the retina but not in blood vessels. No significant beta-gal expression occurred in rat eyes injected with the retroviral vector.

CONCLUSIONS

Adenovirus is an efficient vector for gene transfer into blood vessels in an animal model of ROP. This may be a first step towards utilising gene transfer as a tool for modulating ocular neovascularisation for experimental and therapeutic purposes.

Transcriptional targeting for ovarian cancer gene therapy

Ovarian carcinoma is a leading cause of cancer death in women. Though advances in conventional therapies have been achieved, long-term survival rates for most patients diagnosed with ovarian cancer are still low. Therefore, novel molecular therapeutic strategies such as gene therapy are being intensively pursued. Such approaches are based on the enormous progress that has been achieved in the elucidation of the molecular foundations of ovarian cancer. In this regard transcriptional control elements (promoters) of genes frequently upregulated or specifically expressed in tumors can be applied in a heterologous context to drive expression of therapeutic genes in targeted gene therapy strategies. This review discusses transcriptional targeting strategies in ovarian cancer gene therapy and gives an overview of tumor-specific promoters (TSPs) that have been applied for this purpose.

Tissue-specific gene therapy directed to tumor angiogenesis

Gene therapy directed specifically to the vascular wall, particularly to angiogenic endothelial cells is a prerequisite in vascular disease treatment. Angiogenesis is a major feature in many pathological conditions including wound healing, solid tumors, developing metastases, ischemic heart diseases and diabetic retinopathy. In the present study we developed a tissue-specific gene therapy to the angiogenic blood vessels of tumor metastasis using an adeno-based vector containing the murine preproendothelin-1 (PPE-1) promoter. Genes activated by the PPE-1 promoter were highly expressed in bovine aortic endothelial cells in vitro. Systemic injection of the adenoviral vectors AdPPE-1-luciferase and AdCMV-luciferase to normal C57BL/6 mice, resulted in higher activity of PPE-1 promoter compared with CMV promoter in the aorta and vascularized tissues such as heart, kidney, lung and pancreas. Systemic administration of the adenoviral vector, in mice bearing Lewis lung carcinoma, resulted in high and specific activity of PPE-1 in the new vasculature of primary tumors and lung metastasis. Cellular distribution of the delivered gene revealed highest expression of GFP in angiogenic endothelial cells of the metastasis. We expect that this approach of 'vascular-directed' gene therapy will be applicable to both vascular diseases and cancer.

Transcriptional control: an essential component of cancer gene therapy strategies?

The therapeutic index of cancer gene therapy approaches will, at least in part, be dictated by the spatial and temporal control of expression of the therapeutic transgenes. Strategies which allow precise control of gene transcription are likely to play a crucial role in the future pre-clinical and clinical development of gene therapy. In this review, we discuss these issues as they relate to tissue and tumor specific promoters. In addition, the exciting opportunities offered by the development of regulated gene expression systems using small molecules, radiation and heat are reviewed. It is realistic to expect that the future offers the prospect of amalgamating elements of a number of these different systems in a co-ordinated gene delivery approach with the potential to increase the efficacy and reduce the toxicity of treatment.

Potential of allospecific gene-engineered T cells in transplantation gene therapy: specific T cell activation determines transgene expression in vitro and in vivo

T lymphocytes, regardless of their specificity, are considered key targets for genetic modification in the treatment of inherited or acquired human diseases. In this study, we generated Lewis T cell lines specific for Dark Agouti rat alloantigens and tested the potential of allospecific T lymphocytes as carriers of genes encoding therapeutic proteins in transplantation gene therapy. These allospecific T lymphocytes were successfully, stably transduced with enhanced green fluorescent protein (EGFP) by an Mo-MuLV-based retrovirus vector. A novel gene delivery protocol was utilized, resulting in nearly 100% EGFP-expressing T cells. This approach enabled tracking of allospecific transduced T cells in vivo and illustrates their transgene production by fluorometric determination after ex vivo isolation. Quantitation of EGFP transgene expression was used to determine the influence of T cell receptor-specific activation on transgene regulation. A strict positive correlation between activation state and expression level was detected in vitro and in vivo. The activation-induced increase in transgene expression could be blocked by interference with T cell activation signaling pathways by cyclosporin A, anti-CD4 MAb, or CTLA4-Ig. These data provide strong evidence that direct or indirect effects caused by activation-induced transcription factors are crucial in transgene upregulation. Allospecific activation in spleens, lymph nodes, and transplanted grafts can be considered as antigen-specific targeting strategy. This activation might be useful in expressing therapeutic proteins such as TGF-beta or IL-10 specific to these sites. T lymphocyte priming and activation might be prevented or altered by modification of the local microenvironments, thereby exerting a therapeutic influence on acute and chronic graft rejection processes.

Increasing endothelial cell specific expression by the use of heterologous hypoxic and cytokine-inducible enhancers

One of the current challenges in gene therapy is to construct a vector that will target specific tissues. Targeting expression to endothelium is of particular interest in the treatment of several pathologies. We have shown previously that defined regions of the E-selectin and KDR promoters confer endothelial cell specific expression following retroviral delivery. However, the levels of expression were low. In an attempt to increase expression but to preserve the tissue specificity we have examined hypoxic and cytokine-inducible enhancer elements in combination with the KDR and E-selectin promoters. Both enhancers should be active in the tumour environment, boosting expression and giving additional specificity of gene expression in the tumour endothelium. The hypoxia response element (HRE) of the murine phosphoglycerate kinase-1 (PGK-1) promoter was used as a hypoxic enhancer and the tandem-binding site for NFKB from the murine vascular cell adhesion molecule-1 (VCAM-1) promoter as a cytokine-inducible enhancer. The HRE conferred hypoxia inducibility to the KDR and E-selectin promoters. Endothelial specificity of expression was retained with the KDR but not the E-selectin promoter. The NFKB-binding site conferred responsiveness to TNF-alpha to the KDR promoter, however the level of induction was less than that achieved with the HRE. Retrovirus combining both enhancer elements transferred inducibility by hypoxia and TNF-alpha, and reached the highest expression levels upon stimulation. These results confirm that heterologous enhancer elements may operate on a single endothelial cell specific promoter. These findings make the use of inducible enhancers a promising strategy for increasing tissue specific gene expression.

Gene therapy: designer promoters for tumour targeting

One of the biggest challenges facing cancer therapy is to generate tumour-specific treatment strategies. Gene therapy hopes to achieve this by directing the activity of therapeutic genes specifically to the sites of disease. Of paramount importance for the success of this approach is the availability of tumour-specific delivery systems: both the transductional targeting of the vector vehicle and the restriction of transgene expression to the tumour are promising strategies towards this goal. This review will focus on the recent achievements in the field of transcriptional targeting and the different strategies to improve or design promoters with the desired specificities.

Anti-angiogenesis therapy and strategies for integrating it with adjuvant therapy

Tumor angiogenesis is critical for the growth of primary cancers above 1-2 mm in diameter. A major vascular growth factor is VEGF, and approaches to inhibit VEGF have shown encouraging results in pre-clinical studies. The mechanisms involved in switching on angiogenesis involve activation of oncogenes and upregulation of the hypoxia-sensing pathway. These provide novel targets for therapy. Many anti-angiogenic drugs are in clinical trial currently and there are problems in assessing these types of drugs if they only cause disease stabilisation. It will be important to develop methods to assess inhibition of vascular growth in vivo. New generations of anti-angiogenesis drugs such as endostatin of angiostatin, which are more potent, may cause tumor regression, but this has not yet been studied in patients. These approaches for advanced disease should be more successful when applied early in an adjuvant situation. This will also require careful monitoring of long-term toxicity.