Inhibition of vascular smooth muscle cell proliferation and neointimal accumulation by adenovirus-mediated gene transfer of cytosine deaminase

Luciferase-based reporting of suicide gene activity in murine mesenchymal stem cells

Due to their ease of isolation, gene modification and tumor-homing properties, mesenchymal stem cells (MSCs) are an attractive cellular vehicle for the delivery of toxic suicide genes to a variety of cancers in pre-clinical models. In addition, the incorporation of suicide genes in stem cell-derived cell replacement therapies improves their safety profile by permitting graft destruction in the event of unexpected tumorigeneses or unwanted differentiation. Due to the functional requirement of ATP for the Firefly luciferase gene Luc2 to produce light, luciferase-based reporting of cytotoxicity can be engineered into potential cell therapies. Consequently, we nucleofected mammalian expression plasmids containing both the Luc2 and the yeast fusion cytosine deaminase uracil phosphoribosyltransferase (CDUPRT) genes for expression in murine MSCs to assess luciferase as a reporter of suicide gene cytotoxicity, and MSC as vehicles of suicide gene therapy. In vitro bioluminescence imaging (BLI) showed that following the addition of the non-toxic prodrug fluorocytosine (5-FC), CDUPRT-expressing MSCs displayed enhanced cytotoxicity in comparison to Luc2 reporter MSC controls. This study demonstrates the utility of luciferase as a reporter of CDUPRT-mediated cytotoxicity in murine MSC using BLI.

Local Endovascular Delivery, Gene Therapy, and Cell Transplantation for Peripheral Arterial Disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

The metamorphosis of vascular stents: passive structures to smart devices

The role of nanotechnology enabled techniques in the evolution of vascular stents.

Nanoparticle drug- and gene-eluting stents for the prevention and treatment of coronary restenosis

Percutaneous coronary intervention (PCI) has become the most common revascularization procedure for coronary artery disease. The use of stents has reduced the rate of restenosis by preventing elastic recoil and negative remodeling. However, in-stent restenosis remains one of the major drawbacks of this procedure. Drug-eluting stents (DESs) have proven to be effective in reducing the risk of late restenosis, but the use of currently marketed DESs presents safety concerns, including the non-specificity of therapeutics, incomplete endothelialization leading to late thrombosis, the need for long-term anti-platelet agents, and local hypersensitivity to polymer delivery matrices. In addition, the current DESs lack the capacity for adjustment of the drug dose and release kinetics appropriate to the disease status of the treated vessel. The development of efficacious therapeutic strategies to prevent and inhibit restenosis after PCI is critical for the treatment of coronary artery disease. The administration of drugs using biodegradable polymer nanoparticles as carriers has generated immense interest due to their excellent biocompatibility and ability to facilitate prolonged drug release. Despite the potential benefits of nanoparticles as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of nanoparticle materials, as well as to their size and shape. This review describes the molecular mechanism of coronary restenosis, the use of DESs, and progress in nanoparticle drug- or gene-eluting stents for the prevention and treatment of coronary restenosis.

Gene therapy for restenosis: biological solution to a biological problem

Coronary artery disease remains a significant health threat afflicting millions of individuals worldwide. Despite the development of a variety of technologies and catheter based interventions, post-procedure restenosis is still a significant concern. Gene therapy has emerged as a promising approach aimed at modification of cellular processes that give rise to restenosis. When juxtaposed alongside the failure of traditional pharmacotherapeutics to eliminate restenosis, gene therapy has engendered great expectations for cubing coronary restenosis. In this review we have discussed an overview of gene therapy approaches that hve been utilized to reduce restenosis in preclinical and clinical studies, current status of anti-restenosis gene therapy and perspectives on its future application. For brevity, we have limited our discussion on anti-restenosis gene therapy to the introduction of a nucleic acid to the cell, tissue, organ or organism in order to give rise to the expression of a protein, the function of which will confer therapeutic effect. For the purpose of this review, we have focused ou discussion on two relevant anti-restenosis strategies, anti-proliferative and pro-endothelialization.

Local endovascular delivery, gene therapy, and cell transplantation for peripheral arterial disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

Intratumoural administration of dendritic cells: hostile environment and help by gene therapy

Like paratroopers in special operations, dendritic cells (DCs) can be deployed behind the enemy borders of malignant tissue to ignite an antitumour immune response. 'Cross-priming T cell responses' is the code name for their mission, which consists of taking up antigen from transformed cells or their debris, migrating to lymphoid tissue ferrying the antigenic cargo, and meeting specific T cells. This must be accomplished in such an immunogenic manner that specific T lymphocytes would mount a robust enough response as to fully reject the malignancy. To improve their immunostimulating activity, local gene therapy can be very beneficial, either by transfecting DCs with genes enhancing their performance, or by preparing tumour tissue with pro-inflammatory mediators. In addition, endogenous DCs from the tumour host can be attracted into the malignant tissue following transfection of certain chemokine genes into tumour cells. On their side, tumour stroma and malignant cells set up a hostile immunosuppressive environment for artificially released or attracted DCs. This milieu is usually rich in transforming growth factor-beta, vascular endothelial growth factor, and IL-10, -6 and -8, among other substances that diminish DC performance. Several molecular strategies are being devised to interfere with the immunosuppressive actions of these substances and to further enhance the level of anticancer immunity achieved after artificial release of DCs intratumourally.

Molecular biology and gene transfer in atherosclerosis in the stenting era

Atherosclerosis is the major cause of death in the developed world. Understanding the pathogenesis of atherosclerosis has been a major challenge to cardiovascular research over the past several decades. During this period a number of advances in various scientific disciplines has increased our understanding of this disease. These include improved understanding of the structural and functional components of normal vessel wall and more recently the use of cell biology and molecular biology techniques to elucidate the pathogenesis of atherosclerosis. None of these advances has been more dramatic nor has potentially more far reaching consequences as the application of molecular biology and gene technology to the practice of cardiovascular medicine. These developments have already opened new and exciting areas of vascular research and may in the future provide for earlier identification of genetic predisposition to atherosclerosis, strategic planning of preventive therapy and more tailored pharmacologic approaches for established disease.

Adenoviral delivery of a constitutively active retinoblastoma mutant inhibits neointima formation in a human explant model for vein graft disease

Intimal hyperplasia resulting from vascular injury remains a major obstacle in the long-term success of coronary artery bypass grafts. Inhibition of smooth muscle cell (SMC) proliferation using adenoviral gene transfer of cell cycle inhibitors resulted in reduced neointima formation in various animal models. However, little is known about the effect on human SMCs and neointima formation. Here we report the effects of infection with an adenoviral vector encoding a constitutively active form of the retinoblastoma gene (Ad. delta Rb) on proliferation of human saphenous vein SMCs (HSVSMCs) and neointima formation in organ cultures of human saphenous vein. Proliferation of SMCs was inhibited dose-dependently after infection with Ad. delta Rb. A near-total inhibition was found at an Ad. delta Rb concentration of 10(8) pfu/ml. Organ cultures of human saphenous vein segments were used to evaluate the effect of Ad. delta Rb infection on neointima formation and vein graft disease. Segments cultured for 4 weeks develop a neointima that is morphologically highly similar to early initimal lesions found in pathological vein grafts in vivo. Infection of saphenous vein segments with 2 x 10(9) pfu/ml Ad. delta Rb resulted in a 59% reduction of neointimal area when compared to uninfected counterparts, whereas infection with control adenovirus, Ad.LacZ, had no significant effect. The results of this study show that Ad. delta Rb gene transfer might be an efficient approach to prevent neointima formation in human saphenous vein grafts.

Gene therapy in cardiovascular disease. Current status

Cardiovascular disease is the leading cause of mortality and morbidity in developed countries. Most conventional therapy is often inefficacious and tends to treat the symptoms rather than the underlying causes of the disorder. Gene therapy offers a novel approach for prevention and treatment of cardiovascular diseases. Technical advances in viral vector systems and the development of fusigenic liposome vectors have been crucial to the development of effective gene therapy strategies directed at the vasculature and myocardium in animal models. Gene transfer techniques are being evaluated as potential treatment alternatives for both genetic (familial hypercholesterolemia) and acquired occlusive vascular diseases (atherosclerosis, restenosis, arterial thrombosis) as well as for cardiac disorders including heart failure, myocardial ischemia, graft coronary arteriosclerosis and hypertension. Continued technologic advances in vector systems and promising results in human and animal gene transfer studies make the use of gene therapy a promising strategy for the treatment of cardiovascular disorders.

Adenovirus-mediated transfer of ribozyme targeting platelet-derived growth factor A-chain mRNA inhibits growth of vascular smooth muscle cells from spontaneously hypertensive rats

Platelet-derived growth factor (PDGF) is a potent stimulator of growth of vascular smooth muscle cells (VSMCs). VSMCs from spontaneously hypertensive rats (SHRs) show exaggerated growth and increasingly express PDGF A-chain messenger RNA (mRNA). To examine adenovirus-mediated transfer of a ribozyme targeting the PDGF A-chain mRNA as a possible gene therapy for vascular proliferative diseases, a recombinant adenovirus vector encoding a ribozyme that targets rat PDGF A-chain mRNA (Ad. ribozyme) was designed and synthesized and its effect on the growth of VSMCs from SHRs was investigated. This vector dose-dependently inhibited DNA synthesis in VMSCs from SHRs, whereas an adenovirus vector encoding the Escherichia coli LacZ gene (Ad. LacZ) did not affect DNA synthesis. Ad. ribozyme significantly suppressed proliferation of VSMCs from SHRs in a dose-dependent manner. Ad. LacZ had no effect. Ad. ribozyme significantly inhibited expression of PDGF A-chain mRNA and PDGF-AA protein in VSMCs from SHRs. Ad. LacZ had no effect. These results demonstrated that adenovirus-mediated transfer of a ribozyme targeting the PDGF A-chain mRNA effectively and specifically inhibited the growth of VSMCs from SHRs with suppression of PDGF A-chain mRNA and PDGF-AA protein expression. Adenovirus-mediated transfer of ribozyme targeting PDGF A-chain mRNA may be a feasible gene therapy for vascular proliferative diseases.

Local gene delivery to the vessel wall

This review will provide an overview of delivery strategies that are being evaluated for vascular gene therapy. We will limit our discussion to those studies that have been demonstrated, utilizing in vivo model systems, to limit post-interventional restenosis. We also discuss the efficacy of the vectors and methods currently being used to transfer genetic material to the vessel wall. The efficiency of these techniques is a critical issue for the successful application of gene therapy.

The future of human gene therapy

Human gene therapy (HGT) is defined as the transfer of nucleic acids (DNA) to somatic cells of a patient which results in a therapeutic effect, by either correcting genetic defects or by overexpressing proteins that are therapeutically useful. In the past, both the professional and the lay community had high (sometimes unreasonably high) expectations from HGT because of the early promise of treating or preventing diseases effectively and safely by this new technology. Although the theoretical advantages of HGT are undisputable, so far HGT has not delivered the promised results: convincing clinical efficacy could not be demonstrated yet in most of the trials conducted so far, while safety concerns were raised recently as the consequence of the "Gelsinger Case" in Philadelphia. This situation resulted from the by now well-recognized disparity between theory and practice. In other words, the existing technologies could not meet the practical needs of clinically successful HGT so far. However, over the past years, significant progress was made in various enabling technologies, in the molecular understanding of diseases and the manufacturing of vectors. HGT is a complex process, involving multiple steps in the human body (delivery to organs, tissue targeting, cellular trafficking, regulation of gene expression level and duration, biological activity of therapeutic protein, safety of the vector and gene product, to name just a few) most of which are not completely understood. The prerequisite of successful HGT include therapeutically suitable genes (with a proven role in pathophysiology of the disease), appropriate gene delivery systems (e.g., viral and non-viral vectors), proof of principle of efficacy and safety in appropriate preclinical models and suitable manufacturing and analytical processes to provide well-defined HGT products for clinical investigations. The most promising areas for gene therapy today are hemophilias, for monogenic diseases, and cardiovascular diseases (more specifically, therapeutic angiogenesis for myocardial ischemia and peripheral vascular disease, restenosis, stent stenosis and bypass graft failure) among multigenic diseases. This is based on the relative ease of access of blood vessels for HGT, and also because existing gene delivery technologies may be sufficient to achieve effective and safe therapeutic benefits for some of these indications (transient gene expression in some but not all affected cells is required to achieve a therapeutic effect at relatively low [safe] dose of vectors). For other diseases (including cancer) further developments in gene delivery vectors and gene expression systems will be required. It is important to note, that there will not be a "universal vector" and each clinical indication may require a specific set of technical hurdles to overcome. These will include modification of viral vectors (to reduce immunogenicity, change tropism and increase cloning capacity), engineering of non-viral vectors by mimicking the beneficial properties of viruses, cell-based gene delivery technologies, and development of innovative gene expression regulation systems. The technical advances together with the ever increasing knowledge and experience in the field will undoubtedly lead to the realization of the full potential of HGT in the future.

In vivo suppression of restenosis in balloon-injured rat carotid artery by adenovirus-mediated gene transfer of the cell surface-directed plasmin inhibitor ATF.BPTI

Injury-induced neointimal development results from migration and proliferation of vascular smooth muscle cells (SMC). Cell migration requires controlled proteolytic degradation of extracellular matrix surrounding the cell. Plasmin is a major contributor to this process by degrading various matrix proteins directly, or indirectly by activating matrix metalloproteinases. This makes it an attractive target for inhibition by gene transfer. An adenoviral vector, Ad.ATF.BPTI, was constructed encoding a hybrid protein, which consists of the aminoterminal fragment (ATF) of urokinase-type plasminogen activator (u-PA) linked to bovine pancreas trypsin inhibitor (BPTI), a potent inhibitor of plasmin. This hybrid protein binds to the u-PA receptor, thereby inhibiting plasmin activity at the cell surface, and was found to be a potent inhibitor of cell migration in vitro. Local infection with Ad.ATF.BPTI of balloon-injured rat carotid artery resulted in detectable expression of ATF.BPTI mRNA and protein in the vessel wall. Morphometric analysis of arterial cross-sections revealed that delivery of Ad.ATF.BPTI to the carotid artery wall at the time of balloon injury inhibited neointima formation by 53% (P < 0.01) at 14 days and 19% (P = NS) at 28 days after injury when compared with control vector-infected arteries. Intima/media ratios were decreased by 60% (P < 0.01) and 35% (P < 0.05) at 14 and 28 days, respectively, when compared with control vector-infected arteries. Furthermore, a small but significant increase in medial area was found in the Ad.ATF.BPTI-treated arteries at 28 days (P < 0.05). These results show that local infection of the vessel wall with Ad.ATF.BPTI reduces neointima formation, presumably by inhibiting SMC migration, thereby offering a novel therapeutic approach to inhibiting neointima development.

Gene therapy in heart disease

Application of gene therapy to the field of cardiovascular disorders has been the subject of intensive work over the recent period. Gene therapy for cardiovascular disorders is now fast developing with most therapies being devoted to the consequences (ischemia) rather than the causes of atherosclerotic diseases. Recent human clinical trials have shown that injection of naked DNA encoding vascular endothelial growth factor promotes collateral vessel development in patients with critical limb ischemia or chronic myocardial ischemia. Promising studies in animals have also fueled enthusiasm for treatment of human restenosis by gene therapy, but clinical applications are warranted. Application of gene transfer to other cardiovascular diseases will require the coordinated development of a variety of new technologies, as well as a better definition of cellular and gene targets.

Restenosis and gene therapy

Atherosclerosis is one of the main causes of mortality and morbidity in westernised countries. Treatment of symptomatic atherosclerosis by angioplasty involves major vascular responses such as neointima formation and constrictive vascular remodelling leading to restenosis. Stent placement prevents vasoconstriction but is associated with in-stent neointima formation. Therefore, stent placement requires adjunctive therapy. In this review we discuss the potential of local gene therapy for restenosis. More particularly, we focus on strategies to inhibit smooth muscle cell (SMC) proliferation and migration, prevent thrombosis, decrease oxidative stress in the arterial wall and enhance re-endothelialisation associated with adaptive remodelling. The potential of different vector systems and devices for local gene transfer in the arterial wall is discussed.

Gene Therapy for Cardiovascular Disease

During the past decade, gene therapy for the treatment of many inherited and acquired medical problems has become the subject of increasing focus in both the scientific litera ture and the lay press. This review examines the history and current status of gene therapy for advanced chronic periph eral and myocardial ischemia.

Downregulation of CXCR4 gene expression in primary human endothelial cells following infection with E1(-)E4(+) adenovirus gene transfer vectors

Infection of human endothelial cells with first-generation E1(-)E4(+) adenovirus (Ad) vectors leads to prolonged cell survival and changes in the cell phenotype to a more quiescent stage. Based on the concept that the CXCR4, the receptor for the endothelial chemoattractant stromal-derived factor-&alpha (SDF-alpha), is constitutively expressed by quiescent, resting endothelial cells, the present study analyzes the effect of Ad vector infection on CXCR4 expression and SDF-alpha responses of human umbilical vein endothelial cells (HUVEC). CXCR4 transcripts were markedly downregulated in E1(-)E4(+) Ad-infected cells 48 h following infection, but not in uninfected control cells or when the cells were infected with an E1(-)E4(-) Ad vector. Analysis of surface CXCR4 expression by flow cytometry demonstrated marked reduction of the CXCR4 receptor on cells infected with E1(-)E4(+) Ad compared to uninfected control cells or E1(-)E4(-) Ad-infected cells. Infection of other cell types which express CXCR4, such as dendritic cells and myeloma cells, did not exhibit CXCR4 receptor downregulation following infection with E1(-)E4(+) Ad. Consistent with the observed downregulation of CXCR4 mRNA and surface protein, infection of the endothelial cells with an E1(-)E4(+) Ad rendered the cells unresponsive to the chemoattractant SDF-alpha compared to naive or E1(-)E4(-) Ad-infected cells. Together, the data suggest that first-generation Ad vectors, likely the E4 region, modify the ability of endothelial cells to respond to at least one important chemoattractant.

Effect of percutaneous adenovirus-mediated Gax gene delivery to the arterial wall in double-injured atheromatous stented rabbit iliac arteries

Though the efficacy of intravascular gene transfer has been demonstrated in native vessels following acute injury, this methodology has not been validated in complex models of vascular injury that more closely mimic clinical angioplasty procedures. Previous studies have shown that Gax gene overexpression modulates the injury-induced remodeling of the vessel in rat carotid and normal rabbit iliac arteries. Here, we evaluated the effect of the Gax gene delivery in atheromatous stented vessels. Rabbits were fed 120 g daily of 1% cholesterol diet for 3 weeks. At 1 week they underwent initial injury on the external iliac artery, then balloon angioplasty was performed at 3 weeks at the same site with a 2.5 mm diameter channel balloon catheter (three times 1 min at 6 atm). Either saline (n = 4) or the control viral construct Ad-CMVluc (5 x 109 p.f.u.) (n = 5) or Ad-CMVGax (5 x 10(9) p.f.u.) (n = 4) was delivered with a poloxamer mixture via a channel balloon (6 atm, 30 min), and a 15 mm long Palmaz-Schatz stent (PS154) was then deployed at the site (1 min, 8 atm). Arteries were analyzed 1 month later. At 1 month, the Ad-CMVGax treated arteries exhibited a lower maximal intimal area (1. 15+/-0.1 mm2) than saline (1.87+/-0.15 mm2, P = 0.007) or Ad-CMVluc-treated vessels (1.98+/-0.31 mm2, P = 0.04). Likewise Ad-CMVGax-treated vessels displayed a lower maximal percentage cross-sectional area narrowing (35.1+/-3.5%) than saline (65.3+/-9.4%, P = 0.01) or Ad-CMVluc-treated vessels (62.7+/-6.7%, P = 0.02). Angiographic analysis revealed larger minimal lumen diameter in Ad-CMVGax treated arteries (2.0+/-0.1 mm) than saline (1.14+/-0.36 mm, P = 0.06) or Ad-CMVluc-treated vessels (1.23+/-0.25 mm, P = 0.02). Overexpression of the Gax gene inhibits neointimal hyperplasia and lumen loss in atheromatous stented rabbit iliac arteries.

Biocompatibility of cardiovascular gene delivery catheters with adenovirus vectors: an important determinant of the efficiency of cardiovascular gene transfer

Gene therapy approaches hold promise for the treatment of a wide variety of cardiovascular diseases. Many strategies for cardiovascular gene therapy involve catheter-mediated vector delivery via intramyocardial injection, intracoronary infusion, or direct gene transfer into the vessel wall. Several different gene delivery catheters have been developed and utilized in preclinical and clinical studies of cardiovascular gene therapy. However, rigorous studies of the biocompatibility of these catheters with gene therapy vectors have not yet been reported. In this report, we have examined the compatibility of cardiovascular gene therapy catheters and catheter constituents with first-generation E1/E3-deleted adenovirus vectors. We show that (i) currently available catheters rapidly and efficiently inactivate adenovirus vector infectivity; (ii) this inactivation is mediated by a variety of commonly used catheter constituents including stainless steel, nitinol, and polycarbonate; (iii) catheter-mediated inactivation of adenovirus vectors can be prevented by preflushing catheters with solutions of serum albumin; and (iv) it is possible to identify a set of catheter materials that are compatible with current adenovirus vectors. These results underscore the importance of catheter/vector compatibility and suggest methods for increasing the efficiency of catheter-mediated cardiovascular gene therapy.

Insights into the molecular pathogenesis of atherosclerosis and therapeutic strategies using gene transfer

Gene therapy for the treatment of atherosclerosis and related diseases has shown its potential in animal models and in the first human trials. Gene transfer to the vascular system can be performed both via intravascular and extravascular periadventitial routes. Intravascular gene transfer can be done with several types of catheters under fluoroscopic control. Extravascular gene transfer, on the other hand, provides a well-targeted gene delivery route available during vascular surgery. It can be done with direct injection or by using perivascular cuffs or surgical collagen sheets. Ex vivo gene delivery via transfected smooth muscle cells or endothelial cells might be useful for the production of secreted therapeutic compounds. Gene transfer to the liver has been used for the treatment of hyperlipidemia. The first clinical trials for the induction of therapeutic angiogenesis in ischemic myocardium or peripheral muscles with VEGF or FGF gene transfer are under way and preliminary results are promising. VEGF has also been used for the prevention of postangioplasty restenosis because of its capability to induce endothelial repair and production of NO and prostacyclin. However, further basic research is needed to fully understand the pathophysiological mechanisms involved in conditions related to atherosclerosis. Also, further development of gene transfer vectors and gene delivery techniques will improve the efficacy and safety of human gene therapy.

Gene therapy enhances the antiproliferative effect of radiation in intimal hyperplasia

BACKGROUND

Although ionizing radiation (IR) has been demonstrated to attenuate vessel wall restenosis and intimal hyperplasia (IH), dose-related mural injury and atrophy are possible deleterious side effects. We tested the hypothesis that a radiosensitizing strategy may improve IR-induced inhibition of in vivo vascular smooth muscle cells (VSMCs) without influencing apoptotic cell death.

METHODS

In 28 New Zealand White rabbits, the right common carotid artery (CCA) was injured and subjected to low-flow conditions to promote IH. The CCA was transfected with an adenoviral vector incorporating the cytosine deaminase (CD) gene (1 x 10(9) PFU/ml). 5-Fluorocytosine (5-FC), a prodrug that is converted to the radiosensitizing agent 5-fluorouracil (5-FU) by CD, was thereafter administered intravenously. The CCA was exposed to 5 Gy IR at 24 h. Intimal/medial (I/M) area and thickness ratios were determined in the harvested CCAs at 14 days. VSMC proliferative and apoptotic indices were assessed with immunohistochemistry.

RESULTS

A 50% reduction in I/M area was found in rabbits treated with IR and IR + CD/5-FC (0.19 +/- 0.03 and 0.18 +/- 0.02) when compared with untreated controls (UC) (0.37 +/- 0.06) (P = 0.005). This finding was substantiated by attenuation of I/M thickness in the IR groups [0.47 +/- 0.13 (IR), 0.41 +/- 0.11 (IR + CD/5-FC), 0.61 +/- 0.17 (UC)] (P = 0.007). The number of proliferating VSMCs was notably smaller when IR was combined with CD/5-FC (4.17 +/- 1.16 vs 2.97 +/- 1.09 log transformed cells/mm(2), P < 0.07). Apoptosis was similar in all groups.

CONCLUSIONS

Both IR alone and IR combined with a radiosensitizing agent are effective in attenuating experimental IH. However, combination therapy is synergistic and achieves greater inhibition of VSMC proliferation and may involve selective killing of radioresistant S-phase VSMCs. IR + CD/5-FC represents a novel therapeutic strategy that offers potential for long-term control of IH.

Gene therapy of hepatocellular carcinoma in vitro and in vivo in nude mice by adenoviral transfer of the Escherichia coli purine nucleoside phosphorylase gene

Expression of viral or bacterial enzymes in tumor cells to convert nontoxic prodrugs into highly toxic metabolites is an attractive gene-therapeutic approach for the treatment of hepatocellular carcinoma (HCC). The Escherichia coli purine nucleoside phosphorylase (PNP) converts purine analogs into freely diffusible metabolites, which are highly toxic to dividing and nondividing cells. We investigated the antitumor effects of PNP in the human HCC cell lines, HepG2, Hep3B, and HuH-7, and performed a comparison with herpes simplex thymidine kinase (TK). The genes for PNP, TK, and enhanced green fluorescent protein (EGFP) were delivered to HCC cells by identical adenoviral vectors. Fludarabine and ganciclovir (GCV) served as prodrugs for PNP and TK, respectively. Expression of PNP highly sensitized HCC cells to fludarabine treatment. Fludarabine concentrations between 0.5 and 1 microg/mL killed 100% of the cells expressing PNP with no detectable toxicity in control cells expressing EGFP. Expression of PNP in as few as 10% of HCC cells induced efficient killing of most bystander cells. Expression of TK followed by GCV treatment produced a potent growth inhibition but failed to kill all TK-expressing HCC cells. More importantly, the TK system exhibited a lower degree of bystander effect. Adenoviral delivery of PNP followed by fludarabine administration prevented subcutaneous and intrahepatic tumor formation in nude mice and was also effective for the treatment of established tumors. These results demonstrate the potential of the PNP/fludarabine system for the treatment of HCC.

Cardiovascular gene therapy

Vascular gene transfer potentially offers new treatments for cardiovascular diseases. It can be used to overexpress therapeutically important proteins and correct genetic defects, and to test experimentally the effects of various genes in a local vascular compartment. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers have improved blood flow and collateral development in ischaemic limb and myocardium. Promising therapeutic effects have been obtained in animal models of restenosis or vein-graft thickening with the transfer of genes coding for VEGF, nitric-oxide synthase, thymidine kinase, retinoblastoma, growth arrest homoeobox, tissue inhibitor of metalloproteinases, cyclin or cyclin-dependent kinase inhibitors, fas ligand and hirudin, and antisense oligonucleotides against transcription factors or cell-cycle regulatory proteins. First experiences of VEGF gene transfer and decoy oligonucleotides in human beings have been reported. However, further developments in gene-transfer vectors, gene-delivery techniques and identification of effective treatment genes will be required before the full therapeutic potential of gene therapy in cardiovascular disease can be assessed.

Effects of hydroxymethylglutaryl coenzyme A reductase inhibitor simvastatin on smooth muscle cell proliferation in vitro and neointimal formation in vivo after vascular injury

OBJECTIVES

We sought to evaluate the effects of hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors on vascular smooth muscle cell (VSMC) proliferation in vitro and neointimal formation in vivo after vascular injury.

BACKGROUND

Neointimal hyperplasia after vascular injury is responsible for restenosis after arterial stenting, whereas arterial remodeling and neointimal formation are the causes of restenosis after percutaneous transluminal coronary angioplasty.

METHODS

We assessed the effect of simvastatin on in vitro VSMC proliferation. To study the effects of simvastatin in vivo, balloon injury and stent deployment were performed in the common carotid artery of rats. Neointimal area was measured two weeks later in the balloon injury model and three weeks after stent deployment.

RESULTS

Simvastatin markedly inhibits VSMC proliferation in vitro. In vivo, simvastatin reduced, in a dose-dependent manner, the neointimal area and the neointima-media ratio after balloon injury from 0.266 +/- 0.015 mm2 to 0.080 +/- 0.026 mm2 and from 1.271 +/- 0.074 to 0.436 +/- 0.158 (p < 0.001 vs. control rats) at the highest dose. Simvastatin also significantly reduced the neointimal formation and the neointima-media ratio after stenting from 0.508 +/- 0.035 mm2 to 0.362 +/- 0.047 mm2 (p < 0.05 vs. control rats) and from 2.000 +/- 0.136 to 1.374 +/- 0.180 (p < 0.05 vs. control rats). The vessel thrombosis rate after stent deployment was 30% in the control group and 11.1% in the treated group (p = NS). Moreover, the systemic administration of simvastatin did not affect hepatic and renal functions, blood pressure or heart rate.

CONCLUSIONS

Simvastatin potently inhibits VSMC proliferation in vitro and reduces neointimal formation in a rat model of vascular injury.

Gene therapy for restenosis

This review provides an overview of candidate genes that are currently being evaluated for genetic strategies in vascular gene therapy. We discuss treatment strategies that have proven efficacious in limiting postinterventional restenosis through evaluation with in vivo model systems. The candidate strategies utilize genes that are either cytotoxic, regulate vascular smooth muscle cell differentiation or proliferation. In addition, we review oligonuclotide and ribozyme strategies that function by suppressing the expression of cell cycle regulators.

Prospects for genetic therapy of cardiovascular disease

Significant progress has been made in cardiovascular gene therapy. Further investigations are required to understand the basic science of vectors, mechanisms of gene delivery, vector-associated immunogenicity, and pathophysiology of vascular and myocardial diseases. In addition, catheter and stent devices will be required to deliver vectors to the vasculature and myocardium (Fig. 3). Despite these scientific challenges, molecular therapies for cardiovascular diseases are being implemented into clinical practice.

Gene therapy for atherosclerosis and atherosclerosis-related diseases

Gene therapy for atherosclerosis-related disorders of lipoprotein metabolism is primarily directed to liver and aims at long-lasting correction of familial hypercholesterolemia, lipoprotein / hepatic lipase deficiency, and Apolipoprotein A, B, or E -related diseases. Treatment of complications of atherosclerosis (eg, restenosis, ischemia) requires local gene transfer to arterial wall or ischemic muscle with transient gene expression. Catheter-mediated approach or direct injections have been used in clinical trials for the treatment of restenosis and for the induction of angiogenesis in ischaemic limb and myocardium. Other possible applications of local gene transfer include antithrombotic treatment and stabilization of vulnerable plaques.

Gene therapy as a therapeutic intervention for vascular disease

Gene therapy for the treatment of many medical problems, including vascular disease, has become the subject of increasing discussion in both the scientific literature and the national press over the past decade. This review will examine the history and current status of gene therapy for vascular proliferative disorders and advanced chronic peripheral and cardiac ischemia.

Early cell loss after angioplasty results in a disproportionate decrease in percutaneous gene transfer to the vessel wall

Acute cell loss has been documented following angioplasty of normal rat and rabbit arteries. Here we analyzed the effects of balloon injury intensity on early cellular loss in single- and double-injury models and how it influences the efficiency of percutaneous gene delivery to the vessel wall. Rabbits underwent bilateral iliac angioplasties (n = 52) with 2.5-mm (balloon-to-artery [B/A] ratio, 1.08 to 1.13) and 3.0-mm (B/A ratio, 1.29 to 1.34) balloons. In the single-injury model, the 3.0-mm balloon induced a 61% reduction in medial cellularity at 3 days postinjury (p < 0.001) while the 2.5-mm balloon did not produce significant cell loss. In the double-injury model, the effects were more pronounced, with 35% (p < 0.01) and 91% (p < 0.001) reductions in medial cellularity at 3 days with the 2.5- and 3.0-mm balloons, respectively, but neointimal cellularity was decreased only with the 3.0-mm balloon (37% reduction, p = 0.025). Adenovirus-mediated beta-galactosidase gene delivery with a channel balloon (n = 24) revealed that larger balloon-to-artery ratios decreased both absolute levels and relative frequencies of transgene expression in the vessel wall. In the single-injury model, gene transfer efficiency was 4.2+/-1.1 and 1.3+/-0.25% (p < 0.05) for the small and large balloons, respectively. In the double-injury model, gene transfer efficiency was 6.6+/-1.6 and 2.3+/-0.8% (p < 0.05) in the neointima and 4.1+/-1.2 and 2.6+/-1.2% (p = NS) in the media for the small and large balloon, respectively. We conclude that early cell loss is dependent on the intensity of the injury in both single- and double-injury models of balloon angioplasty, with greater frequencies of cell loss occurring in the media than in the neointima. In both models, larger balloon-to-artery ratios result in disproportionate reductions in percutaneous adenovirus-mediated gene delivery.

Gene therapy for tissue repair and regeneration

This review presents a current overview of the discipline of human gene therapy. In addition, a gene therapy method is described in which plasmid genes are transferred from a structural matrix carrier into fresh wound sites so as to enhance tissue repair and regeneration. The potential to develop a gene therapy for bone regeneration is discussed in detail.

Effects of poloxamer 407 on transfection time and percutaneous adenovirus-mediated gene transfer in native and stented vessels

Reduction in transfection time and the ability to perform gene transfer in conjunction with endovascular stent implantation constitute two important challenges for percutaneous adenovirus-mediated gene transfer to vessel walls. Studies have suggested that the use of biocompatible polyol poloxamer 407 could be useful. We first evaluated the use of poloxamer 407 for percutaneous gene transfer in nonstented rabbit iliac arteries. A 200-microl mixture of Ad-RSVbetagal or Ad-CMVLuc in either phosphate-buffered saline (PBS) or 20% poloxamer was delivered. After 3 days, gene transfection was evaluated by X-Gal staining or measurement of luciferase activity. Poloxamer use resulted in a 3- to 15-fold increase in the percentage of transfected cells (X-Gal, p = 0.001) and a 16-fold increase in protein product (luciferase activity, p = 0.03), and allowed a decrease in transfection time from 30 to 5 min with minimal reduction in transfection efficiency. We then evaluated the feasibility of percutaneous gene transfer, using Ad-RSVbetagal diluted in pure PBS or 20% poloxamer, in conjunction with stent implantation. Gene delivery was performed either immediately before (pre-) or after (post-) stent implantation. When adenoviruses were diluted in PBS, gene transfer had a low efficiency (prestent, 0.3%; poststent, 0.2%; NS). With poloxamer, the efficacy was much higher (p = 0.0001) and similar "pre" (2.2%) or "post" (1.7%) stent delivery (NS).

CONCLUSIONS

(1) The use of poloxamer, rather than PBS, as a vehicle increases the efficacy of percutaneous adenovirus-mediated gene transfer and reduces transfection time; (2) gene transfer performed during stent implantation with poloxamer is feasible and achieves a significant level of gene expression. Thus percutaneous gene delivery is applicable to conventional stents and could present an attractive method by which to achieve local biological effects in a stent environment.