Modification of vascular tone using iNOS under the control of a radiation-inducible promoter

Metabolism in atherosclerotic plaques: immunoregulatory mechanisms in the arterial wall

Over the last decade, there has been a growing interest to understand the link between metabolism and the immune response in the context of metabolic diseases but also beyond, giving then birth to a new field of research. Termed 'immunometabolism', this interdisciplinary field explores paradigms of both immunology and metabolism to provided unique insights into different disease pathogenic processes, and the identification of new potential therapeutic targets. Similar to other inflammatory conditions, the atherosclerotic inflammatory process in the artery has been associated with a local dysregulated metabolic response. Thus, recent studies show that metabolites are more than just fuels in their metabolic pathways, and they can act as modulators of vascular inflammation and atherosclerosis. In this review article, we describe the most common immunometabolic pathways characterised in innate and adaptive immune cells, and discuss how macrophages' and T cells' metabolism may influence phenotypic changes in the plaque. Moreover, we discuss the potential of targeting immunometabolism to prevent and treat cardiovascular diseases (CVDs).

Radiogenic Therapy: Novel Approaches for Enhancing Tumor Radiosensitivity

Radiotherapy (RT) is a well established modality for treating many forms of cancer. However, despite many improvements in treatment planning and delivery, the total radiation dose is often too low for tumor cure, because of the risk of normal tissue damage. Gene therapy provides a new adjunctive strategy to enhance the effectiveness of RT, offering the potential for preferential killing of cancer cells and sparing of normal tissues. This specificity can be achieved at several levels including restricted vector delivery, transcriptional targeting and specificity of the transgene product. This review will focus on those gene therapy strategies that are currently being evaluated in combination with RT, including the use of radiation sensitive promoters to control the timing and location of gene expression specifically within tumors. Therapeutic transgenes chosen for their radiosensitizing properties will also be reviewed, these include:

gene correction therapy, in which normal copies of genes responsible for radiation-induced apoptosis are transfected to compensate for the deletions or mutated variants in tumor cells (p53 is the most widely studied example). enzymes that synergize the radiation effect, by generation of a toxic species from endogenous precursors ( e.g., inducible nitric oxide synthase) or by activation of non toxic prodrugs to toxic species ( e.g., herpes simplex virus thymidine kinase/ganciclovir) within the target tissue. conditionally replicating oncolytic adenoviruses that synergize the radiation effect. membrane transport proteins ( e.g., sodium iodide symporter) to facilitate uptake of cytotoxic radionuclides.

The evidence indicates that many of these approaches are successful for augmenting radiation induced tumor cell killing with clinical trials currently underway.

Study of the combined treatment of lung cancer using gene-loaded immunomagnetic albumin nanospheres in vitro and in vivo

Combination therapy for lung cancer has garnered widespread attention. Radiation therapy, gene therapy, and molecular targeted therapy for lung cancer have certain effects, but the disadvantages of these treatment methods are evident. Combining these methods can decrease their side effects and increase their curative effects. In this study, we constructed a pYr-ads-8-5HRE-cfosp-iNOS-IFNG plasmid (a gene circuit that can express IFNγ), which is a gene circuit, and used that plasmid together with C225 (cetuximab) to prepare gene-loaded immunomagnetic albumin nanospheres (IMANS). Moreover, we investigated the therapeutic effects of gene-loaded IMANS in combination with radiation therapy on human lung cancer in vitro and in vivo. The results showed that this gene circuit was successively constructed and confirmed that the expression of INFγ was increased due to the gene circuit. Gene-loaded IMANS combined with radiation therapy demonstrated improved results in vitro and in vivo. In conclusion, gene-loaded IMANS enhanced the efficacy of combination therapy, solved problems related to gene transfer, and specifically targeted lung cancer cells.

Evaluation of p21 promoter for interleukin 12 radiation induced transcriptional targeting in a mouse tumor model

BACKGROUND

Radiation induced transcriptional targeting is a gene therapy approach that takes advantage of the targeting abilities of radiotherapy by using radio inducible promoters to spatially and temporally limit the transgene expression. Cyclin dependent kinase inhibitor 1 (CDKN1A), also known as p21, is a crucial regulator of the cell cycle, mediating G1 phase arrest in response to a variety of stress stimuli, including DNA damaging agents like irradiation. The aim of the study was to evaluate the suitability of the p21 promoter for radiation induced transcriptional targeting with the objective to test the therapeutic effectiveness of the combined radio-gene therapy with p21 promoter driven therapeutic gene interleukin 12.

METHODS

To test the inducibility of the p21 promoter, three reporter gene experimental models with green fluorescent protein (GFP) under the control of p21 promoter were established by gene electrotransfer of plasmid DNA: stably transfected cells, stably transfected tumors, and transiently transfected muscles. Induction of reporter gene expression after irradiation was determined using a fluorescence microplate reader in vitro and by non-invasive fluorescence imaging using fluorescence stereomicroscope in vivo. The antitumor effect of the plasmid encoding the p21 promoter driven interleukin 12 after radio-gene therapy was determined by tumor growth delay assay and by quantification of intratumoral and serum levels of interleukin 12 protein and intratumoral concentrations of interleukin 12 mRNA.

RESULTS

Using the reporter gene experimental models, p21 promoter was proven to be inducible with radiation, the induction was not dose dependent, and it could be re-induced. Furthermore radio-gene therapy with interleukin 12 under control of the p21 promoter had a good antitumor therapeutic effect with the statistically relevant tumor growth delay, which was comparable to that of the same therapy using a constitutive promoter.

CONCLUSIONS

In this study p21 promoter was proven to be a suitable candidate for radiation induced transcriptional targeting. As a proof of principle the therapeutic value was demonstrated with the radio-inducible interleukin 12 plasmid providing a synergistic antitumor effect to radiotherapy alone, which makes this approach feasible for the combined treatment with radiotherapy.

Gamma irradiation and targeted radionuclides enhance the expression of the noradrenaline transporter transgene controlled by the radio-inducible p21(WAF1/CIP1) promoter

The use of radiation-inducible promoters to drive transgene expression offers the possibility of temporal and spatial regulation of gene activation. This study assessed the potential of one such promoter element, p21(WAF1/CIP1) (WAF1), to drive expression of the noradrenaline transporter (NAT) gene, which conveys sensitivity to radioiodinated meta-iodobenzylguanidine (MIBG). An expression vector containing NAT under the control of the radiation-inducible WAF1 promoter (pWAF/NAT) was produced. The non-NAT expressing cell lines UVW (glioma) and HCT116 (colorectal cancer) were transfected with this construct to assess radiation-controlled WAF1 activation of the NAT gene. Transfection of UVW and HCT cells with pWAF/NAT conferred upon them the ability to accumulate [(131)I]MIBG, which led to increased sensitivity to the radiopharmaceutical. Pretreatment of transfected cells with γ radiation or the radiopharmaceuticals [(123)I]MIBG or [(131)I]MIBG induced dose- and time-dependent increases in subsequent [(131)I]MIBG uptake and led to enhanced efficacy of [(131)I]MIBG-mediated cell kill. Gene therapy using WAF1-driven expression of NAT has the potential to expand the use of this therapeutic modality to tumors that lack a radio-targetable feature.

[Construction of A eukaryotic expression vector carrying the iNOS gene and its effect on A549 lung cancer cells]

背景与目的

iNOS与NO介导的抗肿瘤效应有关。本研究旨在构建pVAX-iNOS载体并转染A549肺癌细胞，检测其基因的表达并初步探讨iNOS基因表达增高后对A549肺癌细胞的抗肿瘤作用。

方法

应用RT-PCR方法扩增人iNOS编码序列的CDS片段，构建pVAX-iNOS载体后转染肺癌A549细胞，通过RT-PCR和Western blot方法检测目的基因的表达；采用MTT法、Hoechst 3235染色和划痕实验分别检测iNOS高表达在体外对肺癌A549细胞增殖、凋亡和迁移作用的影响。

结果

真核表达质粒载体pVAX-iNOS构建成功，iNOS蛋白在转染后的A549细胞中表达升高。pVAX-iNOS转染A549肺癌细胞后能明显诱导细胞发生凋亡并抑制肿瘤细胞的生长和迁移。

结论

本研究成功构建pVAX-iNOS真核表达质粒，高表达iNOS能明显抑制A549细胞的增殖、迁移并促进细胞发生凋亡。本研究有望为临床治疗肺癌提供一个新的有效策略。

Transcriptional regulation of inducible nitric oxide synthase gene therapy: targeting early stage and advanced prostate cancer

BACKGROUND

Using the tumour type specific human osteocalcin (hOC) promoter, we have previously reported strong promoter activation in hormone independent prostate cancer cells in vitro. In the present study, we present a comparative study of the tissue specific promoter prostate specific membrane antigen (PSMA), and the tumour-type specific hOC promoter driving the inducible nitric oxide synthase (iNOS) transgene using both in vitro and in vivo models.

METHODS

In vitro cytotoxicity was assessed by clonogenic assay. Quantification of nitric oxide expression was determined by the Griess test. In vivo anti-tumour efficacy was determined by tumour growth delay following direct intra-tumoural injection of the constructs into PC3 xenografts. In addition, tumours were dissected post mortem and examined for morphological differences as well as changes in apoptotic protein expression.

RESULTS

PSMA/iNOS produced cytotoxicity in both androgen dependant and independent cell lines. Nitric oxide quantification confirmed that increased cytotoxicity was directly associated with nitric oxide production. Tumour growth delays were observed in all groups treated with the iNOS-expressing constructs ranging from 10.7 days for the hOC/iNOS single dose treatment group to a maximum of 52.2 days for the hOC/iNOS multiple dose group. Intra-tumoural assessment of iNOS and cleaved poly (ADP-ribose) polymerase protein expression demonstrated a significant up-regulation of both proteins, indicating cytotoxicity mediated through the intrinsic apoptotic pathway.

CONCLUSIONS

Highly significant tumour growth delay coupled with no detrimental side-effects were observed following treatment with the PSMA/iNOS and hOC/iNOS constructs. We consider that these findings provide a basis for the development of systemically delivered PSMA/iNOS or hOC/iNOS targeting early stage and advanced prostate cancer.

Enhancement of artificial promoter activity by ultrasound-induced oxidative stress

We previously developed artificial promoters that were activated in response to X-ray irradiation. Sonication with 1.0MHz ultrasound that causes intracellular oxidative stress was found to activate some of these promoters though to lesser degrees. The most sensitive one among these promoters showed intensity- and duration-dependent activations by sonication. In addition, its activation by sonication was attenuated when N-acetyl cysteine was present, suggesting the involvement of intracellular oxidative stress in the activation mechanism. Improved promoters for sensitivity to X-ray irradiation were also found more sensitive to sonication. The most improved one showed 6.0 fold enhancement after sonication with 1.0MHz ultrasound at 1.0W/cm2 for 60s. This enhancement was also attenuated with the presence of N-acetyl cysteine. When stably transfected HeLa cells with the most sensitive promoter were transplanted on to mice and sonicated, luciferase activity by the promoter increased to 1.35 fold in average though it was not statistically significant compared to control. Although gene regulation in vivo by sonication was not clear, this is the first report on artificially constructed promoters responsive to ultrasound.

The tissue plasminogen activator gene promoter: a novel tool for radiogenic gene therapy of the prostate?

BACKGROUND

Radiation therapy is a treatment modality routinely used in cancer management so it is not unexpected that radiation-inducible promoters have emerged as an attractive tool for controlled gene therapy. The human tissue plasminogen activator gene promoter (t-PA) has been proposed as a candidate for radiogenic gene therapy, but has not been exploited to date. The purpose of this study was to evaluate the potential of this promoter to drive the expression of a reporter gene, the green fluorescent protein (GFP), in response to radiation exposure.

METHODS

To investigate whether the promoter could be used for prostate cancer gene therapy, we initially transfected normal and malignant prostate cells. We then transfected HMEC-1 endothelial cells and ex vivo rat tail artery and monitored GFP levels using Western blotting following the delivery of single doses of ionizing radiation (2, 4, 6 Gy) to test whether the promoter could be used for vascular targeted gene therapy.

RESULTS

The t-PA promoter induced GFP expression up to 6-fold in all cell types tested in response to radiation doses within the clinical range.

CONCLUSIONS

These results suggest that the t-PA promoter may be incorporated into gene therapy strategies driving therapeutic transgenes in conjunction with radiation therapy.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.

Low molecular weight catalytic metalloporphyrin antioxidant AEOL 10150 protects lungs from fractionated radiation

The objective of this study was to determine whether administration of a catalytic antioxidant, Mn(III) tetrakis(N,N'-diethylimidazolium-2-yl) porphyrin, AEOL10150, reduces the severity of long-term lung injury induced by fractionated radiation (RT). Fisher 344 rats were randomized into five groups: RT+AEOL10150 (2.5 mg/kg BID), AEOL10150 (2.5 mg/kg BID) alone, RT+ AEOL10150 (5 mg/kg BID), AEOL10150 (5 mg/kg BID) alone and RT alone. Animals received five 8 Gy fractions of RT to the right hemithorax. AEOL10150 was administered 15 min before RT and 8 h later during the period of RT treatment (5 days), followed by subcutaneous injections for 30 days, twice daily. Lung histology at 26 weeks revealed a significant decrease in lung structural damage and collagen deposition in RT+AEOL10150 (5 mg/kg BID) group, in comparison to RT alone. Immunohistochemistry studies revealed a significant reduction in tissue hypoxia (HIF1alpha, CAIX), angiogenic response (VEGF, CD-31), inflammation (ED-1), oxidative stress (8-OHdG, 3-nitrotyrosine) and fibrosis pathway (TGFbeta1, Smad3, p-Smad2/3), in animals receiving RT+ AEOL10150 (5 mg/kg BID). Administration of AEOL10150 at 5 mg/kg BID during and after RT results in a significant protective effect from long-term RT-induced lung injury. Low dose (2.5 mg/kg BID) delivery of AEOL10150 has no beneficial radioprotective effects.

The radiation-inducible pE9 promoter driving inducible nitric oxide synthase radiosensitizes hypoxic tumour cells to radiation

Driving high-level transgene expression in a tumour-specific manner remains a key requirement in the development of cancer gene therapy. We have previously demonstrated the strong anticancer effects of generating abnormally high levels of intracellular NO(*) following the overexpression of the inducible nitric oxide synthase (iNOS) gene. Much of this work has focused on utilizing exogenously activated promoters, which have been primarily induced using X-ray radiation. Here we further examine the potential of the pE9 promoter, comprising a combination of nine CArG radio-responsive elements, to drive the iNOS transgene. Effects of X-ray irradiation on promoter activity were compared in vitro under normoxic conditions and various degrees of hypoxia. The pE9 promoter generated high-level transgene expression, comparable with that achieved using the constitutively driven cytomegalovirus promoter. Furthermore, the radio-resistance of radiation-induced fibrosarcoma-1 (RIF-1) mouse sarcoma cells exposed to 0.1 and 0.01% O(2) was effectively eliminated following transfection with the pE9/iNOS construct. Significant inhibition of tumour growth was also observed in vivo following direct intratumoural injection of the pE9/iNOS construct compared to empty vector alone (P<0.001) or to a single radiation dose of 10 Gy (P<0.01). The combination of both therapies resulted in a significant 4.25 day growth delay compared to the gene therapy treatment alone (P<0.001). In summary, we have demonstrated the potential of the pE9/iNOS construct for reducing radio-resistance conferred by tumour cell hypoxia in vitro and in vivo, with greater tumour growth delay observed following the treatment with the gene therapy construct as compared with radiotherapy alone.

Human osteocalcin: a strong promoter for nitric oxide synthase gene therapy, with specificity for hormone refractory prostate cancer

BACKGROUND

Gene therapy has been identified as a promising treatment strategy for hormone refractory prostate cancer (HRPC). We report, for the first time, the use of the human osteocalcin (hOC) promoter to control inducible nitric oxide synthase (iNOS) transgene expression in HRPC.

METHODS

Human prostate carcinoma cells (PC3, DU145, LNCaP), colon cancer cells (HT29) and human microvascular endothelial cells (HMEC-1) were transfected in vitro with constitutively driven CMV/iNOS or hOC/iNOS plasmid DNA by cationic lipid vector. End points of these experiments were Western blotting, NO(.) generation using the Greiss test to measure accumulated nitrite, and clonogenic assay.

RESULTS

Transfection of the hOC/iNOS plasmid increased iNOS protein and total nitrite levels in PC3 and DU145 cells, but not LNCaP or HT29. Transfection with CMV/iNOS or hOC/iNOS resulted in no additional cytotoxicity in androgen-dependent LNCaP cells or in the non-prostate cell lines. However, transfection with either construct resulted in a greatly reduced cell survival (to 10-20%) in the androgen-independent PC3 and DU145 cell lines.

CONCLUSIONS

Utilising the tumour-type specific properties of the hOC promoter in tandem with the iNOS gene, we have demonstrated target cell specificity, and transgene activation, in the androgen-independent prostate cancer cell lines (PC3 and DU145), an effect absent in normal and androgen-dependent cells. Furthermore, the levels of NO(.) generated are comparable with those seen generated with constitutively (CMV)-driven iNOS. The data obtained from this study provide a basis for future development of hOC/iNOS gene therapy.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

Radiation pneumonitis and fibrosis: Mechanisms underlying its pathogenesis and implications for future research

Radiation pneumonitis and subsequent radiation pulmonary fibrosis are the two main dose-limiting factors when irradiating the thorax that can have severe implications for patients' quality of life. In this article, the current concepts about the pathogenetic mechanisms underlying radiation pneumonitis and fibrosis are presented. The clinical course of fibrosis, a postulated acute inflammatory stage, and a late fibrotic and irreversible stage are discussed. The interplay of cells and the wide variety of molecules orchestrating the immunologic response to radiation, their interactions with specific receptors, and the cascade of events they trigger are elucidated. Finally, the implications of this knowledge with respect to the therapeutic interventions are critically presented.

p21(WAF1)-mediated transcriptional targeting of inducible nitric oxide synthase gene therapy sensitizes tumours to fractionated radiotherapy

Cancer gene therapy that utilizes toxic transgene products requires strict transcriptional targeting to prevent adverse normal tissue effects. We report on the use of a promoter derived from the cyclin dependent kinase inhibitor, p21((WAF1)), to control transgene expression. We demonstrate that this promoter is relatively silent in normal cells (L132, FSK, HMEC-1) compared to the almost constitutive expression obtained in tumour cells (DU145, LNCaP, HT29 and MCF-7) of varying p53 status, a characteristic that will be important in gene therapy protocols. In addition, we found that the p21((WAF1)) promoter could be further induced by both external beam radiation (up to eight-fold in DU145 cells), intracellular-concentrated radionuclides ([(211)At]MABG) (up to 3.5-fold in SK-N-BE(2c) cells) and hypoxia (up to four-fold in DU145 cells). We have previously achieved significant radiosensitization of tumour cells both in vitro and in vivo by using inducible nitric oxide synthase (iNOS) gene therapy to generate the potent radiosensitizer, nitric oxide (NO(.-)). Here, we report that a clinically relevant schedule of p21((WAF1))-driven iNOS gene therapy significantly sensitized both p53 wild-type RIF-1 tumours and p53 mutant HT29 tumours to fractionated radiotherapy. Our data highlight the utility of this p21((WAF1))/iNOS-targeted approach.

Plasmid engineering for controlled and sustained gene expression for nonviral gene therapy

Gene therapy requires the introduction of genetic material in diseased cells with the aim of treating or ultimately curing a disease. Since the start of gene therapy clinical trials in 1990, gene therapy has proven to be possible, but studies to date have highlighted the difficulty of achieving efficient, specific, and long-term transgene expression. Efforts to improve gene therapy strategies over the past years were mainly aimed at solving the problem of delivery, without paying much attention to the optimization of the expression cassette. With the current understanding of the eukaryotic transcription machinery and advanced molecular biology techniques at our disposition, it has now become possible to create custom-made transgene expression cassettes optimized for gene therapy applications. In this review, we will discuss several strategies that have been explored to improve the level and duration of transgene expression, to increase control over expression, or to restrict transgene expression to specific cell types or tissues. Although still in its infancy, such strategies will eventually lead to improvement of nonviral gene therapy and expansion of the range of possible therapeutic applications.

Gene manipulation to enhance MIBG-targeted radionuclide therapy

The goal of targeted radionuclide therapy is the deposition in malignant cells of sterilizing doses of radiation without damaging normal tissue. The radiopharmaceutical [(131)I]meta-iodobenzylguanidine ([(131)I]MIBG) is an effective single agent for the treatment of neuroblastoma. However, uptake of the drug in malignant sites is insufficient to cure disease. A growing body of experimental evidence indicates exciting possibilities for the integration of gene transfer with [(131)I]MIBG-targeted radiotherapy.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Current status of tumor radiogenic therapy

Although tumor gene therapy falls behind its clinical use, the combination of irradiation and gene therapy is full of promise in cancer therapy based on traditional radiotherapy, chemotherapy and surgery. We have termed it as radiogenic therapy. This review focuses on the following aspects of radiogenic therapy in recent years: improvement of gene transfer efficiency by irradiation, radiotherapy combined with cytokine gene delivery or enhancement of the immunity of tumor cells by transgene, direct stimulation by radiation to produce cytotoxic agents, increase of tumor cell radiosensitivity in gene therapy by controlling the radiosensitivity genes and adjusting the fraction dose and interval of radiation so as to achieve the optimum antitumor effect while reducing the normal tissue damage, radioprotective gene therapy enhancing radiation tumor killing effect while protecting the normal tissue and organs with transgene using transfer vectors.

Evaluation of a synthetic CArG promoter for nitric oxide synthase gene therapy of cancer

Nitric oxide synthase gene therapy has been shown to be effective at inducing apoptosis in experimental tumours and sensitizing them to radiotherapy. We have also shown that expression of inducible nitric oxide synthase (iNOS) can be effectively restricted to the tumour volume by the use of the radiation inducible promoter (WAF1) to drive the transgene in clinically relevant protocols. A synthetic construct (pE9), incorporating nine radiosensitive CArG elements from the Egr1 promoter, has recently been developed for cancer gene therapy. We have now investigated basal gene expression of transgenes driven by this promoter to assess its suitability for use in iNOS gene therapy protocols in vivo. Transfection of human microvascular endothelial cells (HMEC-1) with pE9iNOS, using a cationic lipid vector, resulted in progressively increasing (<5-fold) levels of iNOS protein expression up to 8 h after transfection. Transfection of an ex vivo rat artery preparation with pE9iNOS caused 83% inhibition of response to the vasoconstrictor phenylephrine (PE). CMViNOS transfection also reduced response to PE, but by only 52%. A single injection of 25 microg of pE9iNOS DNA in a lipid vector into the centre of a murine sarcoma (RIF1) induced iNOS protein expression by four-fold and increased nitrite concentration eight-fold. This caused a 7-day delay in tumour growth and was more effective than the constitutive CMV-driven construct. Our data suggest that generation of NO*, as a result of iNOS overexpression, is capable of further activating the E9 promoter, through a positive feedback loop, yielding stronger and sustained levels of NO*. This pE9iNOS combination may, therefore, be particularly useful in an anticancer gene therapy strategy as its antitumour effect in vivo was clearly superior to that of the strong constitutive promoter, CMV.

Vascular-targeted cancer gene therapy

As a consequence of the dramatic progress that has been made in recent years towards elucidating the diverse molecular events involved in the development and pathogenesis of malignant disease, there is now no shortage of genes that can be exploited or targeted in the context of cancer gene therapy. Many of these have been shown to be effective both in vitro and in various animal models, and a number have progressed to the clinic. The results of these later studies, although generally encouraging, are perhaps less dramatic than one might have hoped. Although a number of factors undoubtedly contribute to this finding, it is evident that a major reason relates to the difficulties implicit in achieving efficient in vivo gene transfer, particularly in a clinical context. Targeting gene therapy, not to the malignant population, but instead to the vasculature upon which the survival and growth of a tumour depends constitutes an alternative approach that overcomes some of the delivery problems associated with established tumour cell-directed strategies.

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.

Spatial and temporal control of transgene expression in vivo using a heat-sensitive promoter and MRI-guided focused ultrasound

BACKGROUND

Among the techniques used to induce and control gene expression, a non-invasive, physical approach based on local heat in combination with a heat-sensitive promoter represents a promising alternative but requires accurate temperature control in vivo. MRI-guided focused ultrasound (MRI-FUS) with real-time feedback control allows automatic execution of a predefined temperature-time trajectory. The purpose of this study was to demonstrate temporal and spatial control of transgene expression based on a well-defined local hyperthermia generated by MRI-FUS.

METHODS

Expression of the green fluorescent protein (GFP) marker gene was used. Two cell lines were derived from C6 glioma cells. The GFP expression of the first one is under the control of the CMV promoter, whereas it is under the control of the HSP70 promoter in the second one and thus inducible by heat. Subcutaneous tumours were generated by injection in immuno-deficient mice and rats. Tumours were subjected to temperatures varying from 42 to 50 degrees C for 3 to 25 min controlled by MRI-FUS and analyzed 24 h after the heat-shock. Endogenous HSP70 expression and C6 cell distribution were also analyzed.

RESULTS

The results demonstrate strong expression at 50 degrees C applied during a short time period (3 min) without affecting cell viability. Induced expression was also clearly shown for temperature in the range 44-48 degrees C but not at 42 degrees C.

CONCLUSIONS

Heating with MRI-FUS allows a tight and non-invasive control of transgene expression in a tumour.

Image-guided Control of Transgene Expression Based on Local Hyperthermia

Spatial and temporal control of transgene expression is one of the major prerequisites of efficient gene therapy. Recently, a noninvasive, physical approach has been presented based on local heat in combination with a heat-sensitive promoter. This strategy requires tight temperature control in vivo. Here, we use MRI-guided focused ultrasound (MRI-FUS) with real-time feedback control on a whole-body clinical MRI system for a completely automatic execution of a predefined temperature-time trajectory in the focal point. Feasibility studies on expression control were carried out on subcutaneously implanted rat tumors. A stable modified C6 glioma cell line was used carrying a fused gene coding for thymidine kinase (TK) and green fluorescent protein (GFP) under control of the human heat-shock protein 70 (HSP70) promoter. In vitro studies showed strong induction of the TK-GFP gene expression upon heat shock under various conditions and localization of the protein product in the nucleus. In vivo tumors were subjected to a 3-min temperature elevation using MRI-FUS with a constant temperature, and were analysed 24 hr after the heat shock with respect to GFP fluorescence. Preliminary results showed strong local induction in regions heated above 40°C, and a good correspondence between temperature maps at the end of the heating period and elevated expression of TK-GFP.

Radiation-induced tumour necrosis factor-alpha expression: clinical application of transcriptional and physical targeting of gene therapy

Promising data are emerging on a new anticancer agent, Ad.EGR-TNF, an adenoviral vector, which contains radio-inducible DNA sequences from the early growth response (EGR1) gene promoter and cDNA for the gene encoding human tumour necrosis factor-alpha. Ad.EGR-TNF combines the well-documented broad-spectrum anticancer activity of TNFalpha with the proven clinical usefulness of radiotherapy. Systemic delivery of the TNFalpha protein has had limited success clinically because of severe dose-limiting toxic effects. This limitation has been overcome by the use of a gene delivery approach, combined with a radiation-inducible promoter to express the TNFalpha protein in the irradiated tumour tissue. Preclinical and early phase I clinical testing indicates that effective concentrations of TNFalpha can be delivered to the tumour site without significant systemic exposure or toxic effects. The combination of radiation and TNFalpha gene delivery has produced striking antitumour effects in model systems in animals. In the clinical setting, potent anticancer activity has been observed with a high rate of complete and partial objective tumour responses. A novel mechanism of destruction of the tumour vasculature seems to be central to this distinct antitumour activity. This review summarises the rationale, mechanistic basis, preclinical data, and preliminary clinical findings for this new treatment model.

Optimizing radiation-responsive gene promoters for radiogenetic cancer therapy

We have been developing synthetic gene promoters responsive to clinical doses of ionizing radiation (IR) for use in suicide gene therapy vectors. The crucial DNA sequences utilized are units with the consensus motif CC(A/T)(6)GG, known as CArG elements, derived from the IR-responsive Egr1 gene. In this study we have investigated the parameters needed to enhance promoter activation to radiation. A series of plasmid vectors containing different enhancer/promoters were constructed, transiently transfected into tumor cells (MCF-7 breast adenocarcinoma and U-373MG glioblastoma) and expression of a downstream reporter assayed. Results revealed that increasing the number of CArG elements, up to a certain level, increased promoter radiation-response; from a fold-induction of 1.95 +/- 0.17 for four elements to 2.74 +/- 0.17 for nine CArGs of the same sequence (for MCF-7 cells). Specific alteration of the core A/T sequences caused an even greater positive response, with fold-inductions of 1.71 +/- 0.23 for six elements of prototype sequence compared with 2.96 +/- 0.52 for one of the new sequences following irradiation. Alteration of spacing (from six to 18 nucleotides) between elements had little effect, as did the addition of an adjacent Sp1 binding site. Combining the optimum number and sequence of CArG elements in an additional enhancer was found to produce the best IR induction levels. Furthermore, the improved enhancers also performed better than the previously reported prototype when used in in vitro and in vivo experimental GDEPT. We envisage such enhancers will be used to drive suicide gene expression from vectors delivered to a tumor within an irradiated field. The modest, but tight expression described in the present study could be amplified using a molecular 'switch' system as previously described using Cre/LoxP. In combination with targeted delivery, this strategy has great potential for significantly improving the efficacy of cancer treatment in the large number of cases where radiotherapy is currently employed.

Tumour cell radiosensitization using constitutive (CMV) and radiation inducible (WAF1) promoters to drive the iNOS gene: a novel suicide gene therapy

Nitric oxide (NO(*)) has many characteristics including cytotoxicity, radiosensitization and anti-angiogenesis, which make it an attractive molecule for use in cancer therapy. We have investigated the use of iNOS gene transfer, driven by both a constitutive (CMV) and X-ray inducible (WAF1) promoter, for generating high concentrations of NO(*) within tumour cells. We have combined this treatment with radiation to exploit the radiosensitizing properties of this molecule. Transfection of murine RIF-1 tumour cells in vitro with the iNOS constructs resulted in increased iNOS protein levels. Under hypoxic conditions cells were radiosensitized by delivery of both constructs so that these treatments effectively eliminated the radioresistance observed under hypoxic conditions. In vivo transfer of the CMV/iNOS construct by direct tumour injection resulted in a delay (4.2 days) in tumour growth compared with untreated controls. This was equivalent to the effect of 20 Gy X-rays alone. Combination of CMV/iNOS gene transfer with 20 Gy X-rays resulted in a dramatic 19.8 day growth delay compared with controls. Tumours treated with the CMV/iNOS showed large areas of necrosis and abundant apoptosis. We believe that iNOS gene transfer has the potential to be a highly effective treatment in combination with radiotherapy.

Molecular approaches to chemo-radiotherapy

Although radiotherapy is used to treat many solid tumours, normal tissue tolerance and inherent tumour radioresistance can hinder successful outcome. Cancer gene therapy is one approach being developed to address this problem. However, the potential of many strategies are not realised owing to poor gene delivery and a lack of tumour specificity. The use of treatment-, condition- or tumour-specific promoters to control gene-directed enzyme prodrug therapy (GDEPT) is one such method for targeting gene expression to the tumour. Here, we describe two systems that make use of GDEPT, regulated by radiation or hypoxic-responsive promoters. To ensure that the radiation-responsive promoter is be activated by clinically relevant doses of radiation, we have designed synthetic promoters based on radiation responsive CArG elements derived from the Early Growth Response 1 (Egr1) gene. Use of these promoters in several tumour cell lines resulted in a 2-3-fold activation after a single dose of 3 Gy. Furthermore, use of these CArG promoters to control the expression of the herpes simplex virus (HSV) thymidine kinase (tk) gene in combination with the prodrug ganciclovir (GCV) resulted in substantially more cytotoxicity than seen with radiation or GCV treatment alone. Effectiveness was further improved by incorporating the GDEPT strategy into a novel molecular switch system using the Cre/loxP recombinase system of bacteriophage P1. The level of GDEPT bystander cell killing was notably increased by the use of a fusion protein of the HSVtk enzyme and the HSV intercellular transport protein vp22. Since hypoxia is also a common feature of many tumours, promoters containing hypoxic-responsive elements (HREs) for use with GDEPT are described. The development of such strategies that achieve tumour targeted expression of genes via selective promoters will enable improved specificity and targeting thereby addressing one of the major limitations of cancer gene therapy.

NO-dependent vasorelaxation is impaired after gene transfer of inducible NO-synthase

Proinflammatory stimuli produce expression of inducible NO-synthase (iNOS) within blood vessels and are associated with impaired endothelium-dependent relaxation. Gene transfer of iNOS was used to test the hypothesis that expression of iNOS in blood vessels produces impairment of NO-dependent relaxation as well as contraction. An adenoviral vector containing cDNA for murine iNOS, AdCMViNOS, and a control virus, AdCMVBglII, were used for gene transfer to rabbit carotid arteries in vitro and in vivo. After gene transfer of iNOS in vitro, contractile responses to KCl, phenylephrine, and U46619 were impaired. Relaxation in response to acetylcholine, ADP, A23187, and nitroprusside was also impaired. For example, maximum relaxation of vessels to acetylcholine (10 micromol/L) was 78+/-4% (mean+/-SE) after AdBglII (10(10.5) plaque-forming units) and 34+/-5% after AdiNOS (10(10.5) plaque-forming units, P<0.05). NO-independent relaxation in response to 8-bromo-cGMP and papaverine was not impaired after AdiNOS. Contraction and relaxation were improved in carotid arteries expressing iNOS by aminoguanidine and L-N-iminoethyl lysine, inhibitors of iNOS. After intraluminal gene transfer of iNOS in vivo, contraction of vessels in vitro was normal, but responses to acetylcholine were impaired. In summary, the major finding is that NO-dependent relaxation is impaired in arteries after gene transfer of iNOS in vitro and in vivo. Thus, expression of iNOS per se impairs NO-dependent relaxation.