Gene therapy for restenosis: are we ready?

Enhancing the expression of a key mitochondrial enzyme at the inception of ischemia-reperfusion injury can boost recovery and halt the progression of acute kidney injury

Hydrodynamic fluid delivery has shown promise in influencing renal function in disease models. This technique provided pre-conditioned protection in acute injury models by upregulating the mitochondrial adaptation, while hydrodynamic injections of saline alone have improved microvascular perfusion. Accordingly, hydrodynamic mitochondrial gene delivery was applied to investigate the ability to halt progressive or persistent renal function impairment following episodes of ischemia-reperfusion injuries known to induce acute kidney injury (AKI). The rate of transgene expression was approximately 33% and 30% in rats with prerenal AKI that received treatments 1 (T1hr) and 24 (T24hr) hours after the injury was established, respectively. The resulting mitochondrial adaptation via exogenous IDH2 (isocitrate dehydrogenase 2 (NADP+) and mitochondrial) significantly blunted the effects of injury within 24 h of administration: decreased serum creatinine (≈60%, p < 0.05 at T1hr; ≈50%, p < 0.05 at T24hr) and blood urea nitrogen (≈50%, p < 0.05 at T1hr; ≈35%, p < 0.05 at T24hr) levels, and increased urine output (≈40%, p < 0.05 at T1hr; ≈26%, p < 0.05 at T24hr) and mitochondrial membrane potential, Δψm, (≈ by a factor of 13, p < 0.001 at T1hr; ≈ by a factor of 11, p < 0.001 at T24hr), despite elevated histology injury score (26%, p < 0.05 at T1hr; 47%, p < 0.05 at T24hr). Therefore, this study identifies an approach that can boost recovery and halt the progression of AKI at its inception.

Cardiovascular Gene Therapy: Past, Present, and Future

Cardiovascular diseases remain a large global health problem. Although several conventional small-molecule treatments are available for common cardiovascular problems, gene therapy is a potential treatment option for acquired and inherited cardiovascular diseases that remain with unmet clinical needs. Among potential targets for gene therapy are severe cardiac and peripheral ischemia, heart failure, vein graft failure, and some forms of dyslipidemias. The first approved gene therapy in the Western world was indicated for lipoprotein lipase deficiency, which causes high plasma triglyceride levels. With improved gene delivery methods and more efficient vectors, together with interventional transgene strategies aligned for a better understanding of the pathophysiology of these diseases, new approaches are currently tested for safety and efficacy in clinical trials. In this article, we integrate a historical perspective with recent advances that will likely affect clinical development in this research area.

Recent advances in drug eluting stents

One of the most common medical interventions to reopen an occluded vessel is the implantation of a coronary stent. While this method of treatment is effective initially, restenosis, or the re-narrowing of the artery frequently occurs largely due to neointimal hyperplasia of smooth muscle cells. Drug eluting stents were developed in order to provide local, site-specific, controlled release of drugs that can inhibit neointima formation. By implementing a controlled release delivery system it may be possible to control the time release of the pharmacological factors and thus be able to bypass some of the critical events associated with stent hyperplasia and prevent the need for subsequent intervention. However, since the advent of first-generation drug eluting stents, long-term adverse effects have raised concerns regarding their safety. These limitations in safety and efficacy have triggered considerable research in developing biodegradable stents and more potent drug delivery systems. In this review, we shed light on the current state-of-the-art in drug eluting stents, problems related to them and highlight some of the ongoing research in this area.

The management of enthusiasm: motives and expectations in cardiovascular medicine

Debates about appropriate action in medicine often turn on finding the right emotional orientation to new developments. In this article enthusiasm emerges as a key term in a professional 'vocabulary of motive' around innovation, complicating current sociological interest in expectations. The negative associations that adhere to this word among clinical researchers indicate awareness with the difficulty of managing hype and public hopes, but analysis of its use by cardiologists over the past two decades also reveals tension around more specific professional dangers, including 'credulity' and inappropriate activism. An emphasis on clinical trials offers one resolution, but additional narrative strategies can be identified when discussing when to start such trials here illustrated for stem cells for cardiac repair. In particular, while some suggest delaying trials until there is good knowledge of mechanism gained in the laboratory, others support early clinical research through gestures of therapeutic and epistemic modesty.

Catheter-mediated delivery of adenoviral vectors expressing beta-adrenergic receptor kinase C-terminus inhibits intimal hyperplasia and luminal stenosis in rabbit iliac arteries

BACKGROUND

Previous studies have shown that incubation of balloon-injured rat carotid arteries with adenoviral vectors encoding the carboxyl terminus of the beta-adrenergic receptor kinase (Ad2/betaARKct) for 30 min reduces neointima formation. However, it is unclear whether this beneficial effect of betaARKct could be achieved using a catheter-based vector delivery system and whether the observed inhibition of neointima formation translated into a reduction of vessel stenosis.

METHODS

In this study, Ad2/betaARKct was infused into the balloon-injured site of rabbit iliac arteries using a porous infusion catheter over 2 min. Twenty-eight days after gene transfer, angiographic and histological assessments were performed.

RESULTS

Angiographic and histological assessments indicate significant (p < 0.05) inhibition of iliac artery neointima formation and lumen stenosis by Ad2/betaARKct. Our studies demonstrate that an inhibitory effect of Ad2/betaARKct on neointima formation is achievable using a catheter-based vector delivery system and that the inhibition of neointima formation translates into a gain in the vessel minimal luminal diameter. The extent of inhibition (35%) was comparable to that observed with adenoviral-mediated expression of thymidine kinase plus ganciclovir treatment, a cytotoxic gene therapy approach for restenosis.

CONCLUSIONS

These results suggest that adenoviral-mediated gene transfer of betaARKct is a clinically viable cytostatic gene therapy strategy for the treatment of restenosis.

Designing gene delivery vectors for cardiovascular gene therapy

Genetic therapy in the cardiovascular system has been proposed for a variety of diseases ranging from prevention of vein graft failure to hypertension. Such diversity in pathogenesis requires the delivery of therapeutic genes to diverse cell types in vivo for varying lengths of time if efficient clinical therapies are to be developed. Data from extensive preclinical studies have been compiled and a certain areas have seen translation into large-scale clinical trials, with some encouraging reports. It is clear that progress within a number of disease areas is limited by a lack of suitable gene delivery vector systems through which to deliver therapeutic genes to the target site in an efficient, non-toxic manner. In general, currently available systems, including non-viral systems and viral vectors such as adenovirus (Ad) or adeno-associated virus (AAV), have a propensity to transduce non-vascular tissue with greater ease than vascular cells thereby limiting their application in cardiovascular disease. This problem has led to the development and testing of improved vector systems for cardiovascular gene delivery. Traditional viral and non-viral systems are being engineered to increase their efficiency of vascular cell transduction and diminish their affinity for other cell types through manipulation of vector:cell binding and the use of cell-selective promoters. It is envisaged that future use of such technology will substantially increase the efficacy of cardiovascular gene therapy.

Local RAD50 gene delivery induces regression of preformed porcine coronary in-stent neointimal hyperplasia

BACKGROUND

Recently, we observed that overexpression of human RAD50 (hRAD50) induced p21-dependent cytotoxicity in various cultured cells, and rat and mouse tumor models. This study investigated the characteristics of endothelial cell (EC) death by hRAD50 and the potential utility of hRAD50 in the development of gene therapies for vascular restenosis.

METHODS

We studied the effects of transient hRAD50 gene transfer using nonliposomal lipid on the survival of primary cultured human coronary arterial EC and smooth muscle cells (SMC). Palmaz-Schatz stents were deployed in two epicardial coronary arteries in each pig (n = 10). Two weeks later, the patency of the stented arteries was documented by coronary angiography, and the hRAD50 construct or empty vector mixed with lipid was delivered to one of the stented arteries in each pig using a Dispatch catheter. Coronary angiography was repeated 2 weeks after gene delivery and histological examination was performed.

RESULTS

Lipid-mediated hRAD50 gene transfer resulted in the death of EC and SMC. It also increased endothelial nitric oxide synthase (eNOS) expression and nitrite production as well as p21 expression. Pretreatment with NOS and pan-caspase inhibitors completely prevented EC death by hRAD50. In the hRAD50-delivered arteries, the percentage of diameter stenosis, neointimal area, and pathologic area of stenosis were significantly smaller than in the control arteries. eNOS expression increased in the hRAD50-delivered arteries. Systemic hematologic and chemical values were not affected by gene delivery.

CONCLUSIONS

Significant regression of preformed in-stent neointimal hyperplasia was induced by local hRAD50 gene delivery to stented porcine coronary arteries without apparent systemic toxicity.

Adrenomedullin gene delivery inhibits neointima formation in rat artery after balloon angioplasty

Adrenomedullin (AM) is a potent vasodilator expressed in tissues relevant to cardiovascular function. AM peptide has been shown to inhibit the proliferation and migration of vascular smooth muscle cells in vitro. However, the effect of AM on blood vessels after vascular injury in vivo has not been elucidated. In order to explore the potential roles of AM in vascular biology, we evaluated the effect of AM by local gene delivery on neointima formation in balloon-injured rat artery. Adenovirus carrying the human AM cDNA under the control of cytomegalovirus promoter/enhancer (Ad.CMV-hAM) was generated by homologous recombination. After delivery of Ad.CMV-hAM into rat left carotid artery, we identified the expression of human AM mRNA in the left carotid artery, but not in the right carotid artery, heart or kidney by reverse transcription-polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Following local AM gene delivery, we observed a 51% reduction in intima/media ratio at the injured site as compared with that of control rats injected with the luciferase gene (n=7, P<0.01). AM gene transfer resulted in regeneration of endothelium as compared to the control. AM gene delivery significantly increased cGMP levels in balloon-injured arteries. These results indicate that AM contributes to reduction of neointima formation by promotion of re-endothelialization and inhibition of vascular smooth muscle cell proliferation via cGMP-dependent signaling pathway.

New insights in the transcriptional activity and coregulator molecules in the arterial wall

A number of vascular diseases are associated with abnormal expression of genes that contribute to their pathophysiological and clinical manifestations, but at the same time offer potential therapeutic targets. One of the promising therapeutic approaches targets the pathophysiological pathways leading to aberrant gene activation, namely transcriptional activity and its molecular modulators (agonists, antagonists, coregulators, and nuclear receptors). The transcription factors can be divided into four classes (I-IV) classified by structural elements, like basic leucine zipper (bZIP) or basic helix-loop-helix (bHLH), which mediate their DNA binding activity but also determine the classes of drugs that can affect their activity. For example, statins modulate activation of the class-I transcription factor sterol responsive element-binding protein (SREBP), whose target genes including hydroxyl-methyl-glutaryl acetyl Coenzyme-A (HMG-CoA) reductase, HMG-CoA synthase, and the low-density lipoprotein receptor, all of which are involved in cholesterol and fatty acid metabolism. Similarly, insulin-like drugs target the nuclear receptor peroxisome-proliferator-activator-receptor (PPAR)-gamma (class-II), several anti-inflammatory drugs inhibit activation of nuclear factor kappa B (NFkappaB) (class-IV), while others (e.g. flavopiridol, rapamycin, and paclitaxel) target regulation of cell-cycle proteins. Increased understanding of the genetic and molecular basis of disease (e.g. transcriptional activity and its coregulation) will potentially enhance future diagnosis, treatment, and prevention of vascular diseases.

Local delivery of single low-dose of C-type natriuretic peptide, an endogenous vascular modulator, inhibits neointimal hyperplasia in a balloon-injured rabbit iliac artery model

C-type natriuretic peptide (CNP) is an endogenous vascular modulator. In addition to vasodilation, CNP exerts multifunctions including anti-thrombus and anti-proliferation actions against vascular smooth muscle cells and myofibroblasts. Therefore, CNP is a potential therapeutic agent for the prevention of restenosis following angioplasty. The current study investigated whether local delivery of CNP, even at microgram levels about three orders of magnitude lower than doses (high milligram levels) used for systemic administration in the previous study, attenuates neointimal hyperplasia. The rabbit iliac artery was denuded, and then CNP (100 microg, n = 5) or control vehicle (n = 5) was administered locally over 20 min, via a local drug delivery catheter. During drug delivery, blood pressure was monitored with a high-fidelity micromanometer catheter. There was no significant decrease in arterial pressure immediately after the CNP administration. Four weeks after the treatment, computer-assisted morphometric analysis revealed significant reduction in the intimal area (CNP 0.44 +/- 0.27 versus control 0.96 +/- 0.20 mm2, p < 0.01), but no changes in the medial area (CNP 0.93 +/- 0.23 versus control 0.79 +/- 0.29 mm2, p = NS). This resulted in a significant decrease in the ratio of the intimal area to the medial area in CNP-treated vessels compared with control vessels (CNP 0.45 +/- 0.26 versus control 1.40 +/- 0.66, p < 0.05). Local delivery of a single low dose of CNP effectively inhibits neointimal hyperplasia with a minimal likelihood of compromising hemodynamics. Considering its multipotent actions and its role as an important regulator of the vascular system, this treatment may have a therapeutic advantage for clinical use.

Coronary in-stent restenosis: current status and future strategies

In-stent restenosis (ISR) is a novel pathobiologic process, histologically distinct from restenosis after balloon angioplasty and comprised largely of neointima formation. As percutaneous coronary intervention increasingly involves the use of stents, ISR is also becoming correspondingly more frequent. In this review, we examine the available studies of the histology and pathogenesis of ISR, with particular reference to porcine and other animal models. An overview of mechanical treatments is then provided, which includes PTCA, directional coronary atherectomy and high speed rotational atherectomy. Radiation-based therapies are discussed, including a summary of current problems associated with this modality of treatment. Finally, novel strategies for the prevention of ISR are addressed, including novel developments in stents and stent coatings, conventional drugs, nucleic acid-based drugs and gene transfer. Until recently, limited pharmacologic and mechanical treatment options have been available for both treatment and prevention of ISR. However, recent advances in gene modification and gene transfer therapies and, more particularly, in local stent-based drug delivery systems make it conceivable that the incidence of ISR will now be seriously challenged.

Enhancement of Fas ligand-induced inhibition of neointimal formation in rabbit femoral and iliac arteries by coexpression of p35

Adenovirus-mediated gene transfer of Fas ligand (FasL) inhibits neointimal formation in balloon-injured rat carotid arteries. Vascular smooth muscle (VSM) cells coexpressing murine FasL and p35, a baculovirus gene that inhibits caspase activity, are not susceptible to FasL-mediated apoptosis in vitro but are capable of inducing apoptosis of VSM cells that do not express p35. We reasoned that coexpression of p35 in FasL-transduced VSM cells in vivo would promote their survival, enhance FasL-induced apoptosis of adjacent VSM cells, and thereby facilitate a greater inhibition of neointimal formation. In balloon-injured rabbit femoral arteries, either Ad2/FasL/p35 or Ad2/FasL was infused into the injured site and withdrawn 20 min later. Both vectors induced a dose-dependent reduction (p < 0.05) of the neointima-to-media ratio when assessed 14 days later. However, Ad2/FasL/p35 exhibited a significantly greater inhibition of neointimal formation than Ad2/FasL. In a more clinically relevant model of restenosis, rabbit iliac arteries were injured with an angioplasty catheter under fluoroscopic guidance. Adenoviral vectors were delivered locally to the injured site over a period of 2 min, using a porous infusion balloon catheter. Twenty-eight days after gene transfer angiographic and histologic assessments indicated a significant (p < 0.05) inhibition of iliac artery lumen stenosis and neointimal formation by Ad2/FasL/p35 (5 x 10(11) particles per artery). The extent of inhibition was comparable to that achieved with Ad2/TK, an adenoviral vector encoding thymidine kinase (5 x 10(11) particles per artery) and coadministration of ganciclovir for 7 days. These data suggest that coexpression of p35 in FasL-transduced VSM cells is more potent at inhibiting neointimal formation and as such represents an improved gene therapy approach for restenosis.

Dominant negative c-jun gene transfer inhibits vascular smooth muscle cell proliferation and neointimal hyperplasia in rats

We previously reported that activator protein-1 (AP-1), containing c-Jun, is rapidly activated in balloon-injured artery. Therefore, we examined the role of c-Jun in vascular smooth muscle cell (SMC) proliferation, by using in vitro and in vivo gene transfer techniques. (1) Serum (2%) stimulation significantly increased AP-1 DNA binding activity in aortic SMCs, followed by the increase in both 3H-thymidine incorporation and cell number. Aortic SMCs were infected with recombinant adenovirus containing TAM67, a dominant negative c-Jun lacking transactivation domain of wild c-Jun (Ad-DN-c-Jun), to specifically inhibit AP-1. Ad-DN-c-Jun significantly inhibited serum-induced SMC proliferation, by inhibiting the entrance of SMC into S phase. (2) The effect of DN-c-Jun was examined on balloon injury-induced intimal hyperplasia in rats. Before balloon injury, DN-c-Jun was transfected into rat carotid artery using the hemagglutinating virus of Japan-liposome method. In vivo transfection of DN-c-Jun significantly inhibited vascular SMC proliferation in the intima and the media and subsequently prevented intimal thickening at 14 days after balloon injury. We obtained the first evidence that DN-c-Jun gene transfer prevented vascular SMC proliferation in vitro and in vivo, and c-Jun was involved in balloon injury-induced intimal hyperplasia. Thus, AP-1 seems to be the new therapeutic target for treatment of vascular diseases.

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.

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.

Nitric oxide and postangioplasty restenosis: pathological correlates and therapeutic potential

Balloon angioplasty revolutionized interventional cardiology as a nonsurgical procedure to clear a diseased artery of atherosclerotic blockage. Despite its procedural reliability, angioplasty's long-term outcome can be compromised by restenosis, the recurrence of arterial blockage in response to balloon-induced vascular trauma. Restenosis constitutes an important unmet medical need whose pathogenesis has yet to be understood fully and remains to be solved therapeutically. The radical biomediator, nitric oxide (NO), is a natural modulator of several processes contributing to postangioplasty restenosis. An arterial NO deficiency has been implicated in the establishment and progression of restenosis. Efforts to address the restenosis problem have included trials evaluating a wide range of NO-based interventions for their potential to inhibit balloon-induced arterial occlusion. All types of NO-based interventions yet investigated benefit at least one aspect of balloon injury to a naive vessel in a laboratory animal without inducing significant side effects. The extent to which this positive, albeit largely descriptive, body of experimental data can be translated into the clinic remains to be determined. Further insight into the pathogenesis of restenosis and the molecular mechanisms by which NO regulates vascular homeostasis would help bridge this gap. At present, NO supplementation represents a unique and potentially powerful approach to help control restenosis, either alone or as a pharmaceutical adjunct to a vascular device.

Microbubble-enhanced ultrasound for vascular gene delivery

Progress in cardiovascular gene therapy has been hampered by concerns over the safety and practicality of viral vectors and the inefficiency of current nonviral transfection techniques. We have previously reported that ultrasound exposure (USE) enhances transgene expression in vascular cells by up to 10-fold after naked DNA transfection, and enhances lipofection by up to three-fold. We report here that performing USE in the presence of microbubble echocontrast agents enhances acoustic cavitation and is associated with approximately 300-fold increments in transgene expression after naked DNA transfections. This approach also enhances by four-fold the efficiency of polyplex transfection, yielding transgene expression levels approximately 3000-fold higher than after naked DNA alone. These data indicate an important role for acoustic cavitation in the effects of USE. Ultrasound can be focused upon almost any organ and hence this approach holds promise as a means to deliver targeted gene therapy in cardiovascular conditions such as such angioplasty restenosis and in many other clinical situations.

Photodynamic therapy induces apoptosis in intimal hyperplastic arteries

Photodynamic therapy (PDT) generates free radicals through the absorption of light by photosensitizers. PDT shows promise in the treatment of intimal hyperplasia, which contributes to restenosis, by completely eradicating cells in the vessel wall. This study investigates the mechanisms of PDT-induced cell death. PDT, using the photosensitizer chloroaluminum-sulfonated phthalocyanine (1 mg/kg) and laser light (lambda = 675 nm) 100 J/cm(2) was administered to rat carotid arteries after balloon injury-induced intimal hyperplasia. Apoptosis was determined by cell morphology with light microscopy and transmission electron microscopy, DNA cleavage by terminal dUTP nick-end labeling staining, and nucleosomal fragmentation (ladder pattern) by DNA agarose gel electrophoresis. Four hours after PDT, apoptosis was observed in vascular cells, as evidenced by terminal dUTP nick-end labeling staining and transmission electron microscopy. Within 24 hours no cells were present in the neointima and media. Immunofluorescence using an alpha-smooth muscle cell actin antibody confirmed the disappearance of all neointimal and medial cells within 24 hours. No inflammatory cell infiltrate was observed during this time frame. Apoptosis was sharply confined to the PDT treatment field. These data demonstrate that vascular PDT induces apoptosis as a mechanism of rapid, complete, and precise cell eradication in the artery wall. These findings and the lack of inflammatory reaction provide the basis for understanding and developing PDT for a successful clinical application in the treatment of hyperplastic conditions such as restenosis.

Endothelial cell delivery for cardiovascular therapy

Obstructive atherosclerotic vascular disease stands as one of the greatest public health threats in the world. While a number of therapies have been developed to combat vascular disease, endothelial cell delivery has emerged as a distinct therapeutic modality. In this article, we will review the anatomy of the normal blood vessel and the biology of the intact endothelium, focusing upon its centrality in vascular biology and control over the components of the vascular response to injury so as to understand better the motivation for a cell-based form of therapy. Our discussion of cell delivery for cardiovascular therapy will be divided into surgical and interventional approaches. We will briefly recount the development of artificial grafts for surgical vascular bypass before turning our attention towards endothelial cell seeded vascular grafts, in which endothelial cells effectively provide local delivery of endogenous endothelial secretory products to maintain prosthetic integrity after surgical implantation. New techniques in tissue and genetic engineering of vascular grafts and whole blood vessels will be presented. Methods for percutaneous interventions will be examined as well. We will evaluate results of endoluminal endothelial cell seeding for treatment of restenosis and gene therapy approaches to enhance endogenous re-endothelialization. Finally, we will examine some innovations in endothelial cell delivery that may lead to the development of endothelial cell implants as a novel therapy for controlling proliferative vascular arteriopathy.

The French Randomized Optimal Stenting Trial: a prospective evaluation of provisional stenting guided by coronary velocity reserve and quantitative coronary angiography. F.R.O.S.T. Study Group

OBJECTIVES

We sought to make a prospective comparison of systematic stenting with provisional stenting guided by Doppler measurements of coronary velocity reserve and quantitative coronary angiography.

BACKGROUND

Despite the increasing use of stents during percutaneous transluminal coronary angioplasty, it is unclear whether systematic stenting is superior to a strategy of provisional stenting in which stents are placed only in patients with unsatisfactory results or as a bail-out procedure.

METHODS

Two hundred fifty-one patients undergoing elective coronary angioplasty were randomly assigned either to provisional stenting (group 1, in which stenting was performed if postangioplasty coronary velocity reserve was <2.2 and/or residual stenosis > or =35% or as bail-out) or to systematic stenting (group 2). The primary end point was the six-month angiographic minimal lumen diameter (MLD). Major adverse cardiac events were secondary end points (death, acute myocardial infarction and target lesion revascularization).

RESULTS

Stenting was performed in 48.4% of patients in group 1 and 100% of patients in group 2 (p<0.01). Six months after angioplasty, the MLD did not differ between groups (1.90+/-0.79 mm vs. 1.99+/-0.70 mm, p = 0.39), as was the rate of binary restenosis (27.1% vs. 21.4%, p = 0.37). Among patients with restenosis, 13/32 (40.6%) in group 1 but 100% (25/25) in group 2 had in-stent restenosis (p<0.01). Target lesion revascularization (15.1% vs. 14.4% in groups 1 and 2 respectively, p = 0.89) and major adverse cardiac events (15.1% vs. 16.0%, p = 0.85) were not significantly different.

CONCLUSIONS

Systematic stenting does not provide superior angiographic results at six months as compared with provisional stenting.

Gene therapy for atherosclerotic cardiovascular disease: a time for optimism and caution

Cardiovascular disease is the leading cause of death in the Western world, and gene therapy approaches to several cardiovascular disorders have been proposed. One of the major stumbling blocks to be overcome before widespread clinical use of this technology is how to deliver DNA efficiently and safely to cells in vivo. While delivery of DNA alone is inefficient, use of viral vectors may overcome this problem. Adenoviral vectors are most commonly used in cardiovascular gene delivery, but toxicity related to these vectors remains a concern. In addition, duration of gene expression with use of these vectors is limited, which may be advantageous in settings in which transient expression is satisfactory to obtain a therapeutic effect. Gene therapy has been suggested as an approach to multiple conditions, including restenosis after angioplasty, therapeutic neovascularization, and bypass graft restenosis. Phase 1 clinical trials were recently reported. While proof of principle has been established in preclinical animal models, convincing efficacy data in humans do not yet exist. Improvements in vector technology and methods of catheter-mediated vascular gene delivery are needed before widespread clinical application of this therapy.

Restenosis: a challenge for pharmacology

The quest for an anti-restenotic drug continues to be a major challenge in the field of cardiovascular pharmacology because most therapies with proven efficacy in experimental neointima models have failed to limit restenosis. Some drug classes, including glycoprotein IIb/IIIa antagonists, nitric oxide donors and the antioxidant probucol, have recently demonstrated potential benefits in clinical trials. Progress in the development of local delivery systems for administration of drugs, antisense oligonucleotides or genes, in combination with an improved understanding of the pathogenesis of restenosis holds promise for ultimate pharmacotherapy of this condition.

Percutaneous gene therapy using recombinant adenoviruses encoding human herpes simplex virus thymidine kinase, human PAI-1, and human NOS3 in balloon-injured porcine coronary arteries

Local intracoronary delivery of recombinant adenoviruses expressing anti-migratory or anti-proliferative proteins including human constitutive endothelial nitric oxide synthase (NOS3), plasminogen activator inhibitor 1 (PAI-1), or herpesvirus thymidine kinase (TK) (combined with ganciclovir) was used to prevent neointimal formation in porcine coronary arteries. After balloon injury of the left anterior descending (LAD) coronary artery, animals received an intramural injection of adenovirus (1.5 X 10(9) PFU) carrying either the NOS3 cDNA (AdCMVNOS3, n = 12), the PAI-1 cDNA (AdCMVPAI-1, n = 12), the TK cDNA (AdMLPItk, n = 12), or no cDNA (AdpL+, n = 12). After 28 days, morphometric analysis was performed on coronary sections from all segments demonstrating injury. The internal elastic lamina (IEL) fracture length normalized to the IEL perimeter (initial injury) and the neointimal area normalized to the vessel area (response to injury) were used to generate linear regression lines and calculate an index of stenosis for the respective treatment groups. The response to injury was significantly smaller in AdCMVNOS3- and AdMLPItk-infected animals than in AdpL+-infected animals (slopes = 0.86 +/- 0.05 and 0.69 +/- 0.07 versus 1.11 +/- 0.06, p < 0.005 and p < 0.0001, respectively) but not in AdCMVPAI-1-infected animals (slope = 1.26 +/- 0.04, p = 0.04). No viral shedding was observed and there was no acute systemic toxicity after gene transfer. An increase in neutralizing antibody titers against Ad vectors was observed without any detectable response to the transgene products (NOS3, PAI-1). Local gene transfer of NOS3 and TK may hold promise as a safe and effective adjunctive treatment to reduce neointimal formation after percutaneous coronary intervention in humans.

Local photodynamic action of methylene blue favorably modulates the postinterventional vascular wound healing response

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizers to produce free radicals, is known to inhibit experimental intimal hyperplasia (IH). However, its clinical application has been limited by the lack of a suitable approach and a clinically appropriate photosensitizer. The aim of this study was to determine the effectiveness of a clinical approach for PDT, while testing its ability to favorably modulate the vascular wound healing response.

METHODS

Rat carotid arteries were balloon-injured (BI), and for PDT, the arteries were irradiated with thermoneutral laser light (lambda = 660 nm, 100 J/cm(2)) after the photosensitizer methylene blue (MB) was delivered locally. Control rats included BI alone and MB after BI alone. Arteries were analyzed after 2 weeks with morphometric evaluation (n = 6) and in situ hybridization for versican and procollagen type I gene expression (digitized image pixel analyses, n = 3).

RESULTS

No IH developed in PDT-treated arteries (0 +/- 0 mm(2); compared with BI, 0.192 +/- 0.006 mm(2); P <.0001). The diameters remained unchanged (PDT, 0.95 +/- 0.04 mm; BI, 0.94 +/- 0.05 mm; uninjured artery, 0.91 +/- 0.06 mm). Arterial injury resulted in an increase of versican and procollagen type I messenger RNA (mRNA) in the adventitia and neointima. In the repopulating cells of the adventitia after PDT, there was a significant decrease in versican mRNA (% of positive pixels per high-power field: PDT, 1.13% +/- 0.39%; BI, 2.93% +/- 0.61%; P <.02), but not in procollagen type I mRNA.

CONCLUSION

The decrease of versican mRNA expression of repopulating cells after PDT reflects favorable healing on a molecular level. Site-specific delivery of MB, a clinically appropriate photosensitizer, followed by PDT represents a suitable method to promote favorable healing after balloon intervention and further supports its role for inhibiting postinterventional restenosis.

Gene transfer of dominant negative Rho kinase suppresses neointimal formation after balloon injury in pigs

Restenosis after angioplasty still remains a major problem for which neointimal formation appears to play an important role. Recent studies in vitro suggested that Rho kinase, a target protein of Rho, is important in various cellular functions. We thus examined whether Rho kinase is involved in the restenotic changes after balloon injury. In vivo gene transfer was performed immediately after balloon injury in both sides of the porcine femoral arteries with adenoviral vector encoding either a dominant negative form of Rho kinase (AdDNRhoK) or beta-galactosidase (AdLacZ) as a control. One week after the transfer, immunohistochemistry confirmed the successful gene expression in the vessel wall, whereas 2 wk after the transfer, Western blotting showed the functional upregulation of Rho kinase at the AdLacZ site and its suppression at the AdDNRhoK site. Angiography showed the development of a stenotic lesion at the AdLacZ site where histological neointimal formation was noted, whereas those changes were significantly suppressed at the AdDNRhoK site. These results indicate that Rho kinase is involved in the pathogenesis of neointimal formation after balloon injury in vivo.

Nitric oxide (NO)-related pharmaceuticals: contemporary approaches to therapeutic NO modulation

The biologically important gaseous radical, nitric oxide (NO), is a versatile chemical entity that enters into regulatory, protective, and adverse interactions with biomolecules and cells, in some cases through NO-derived nitrogen oxide species. Both excess tissue NO and its insufficiency have been implicated in the genesis or evolution of several important disease states. The associated medical needs and commercial opportunities have fostered attempts to modulate tissue NO tone for symptomatic benefit or therapeutic gain. State-of-the-art strategies for NO modulation in contemporary drug discovery and development encompass sexual dysfunction, cardiovascular, and antiinflammatory indications. Increased understanding of NO's physiological chemistry and ways to target its pharmacology appear critical to the successful clinical exploitation of NO's diverse properties. Integration of research on both the basic science of NO's mechanistic biology and the applied science of drug discovery and development represents a millennium mandate to the pharmaceutical industry in the area of NO-related therapeutics.

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.

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.

Pathology of in-stent restenosis

The process of in-stent restenosis parallels wound healing responses. Stent deployment results in early thrombus deposition and acute inflammation, granulation tissue development, and ultimately smooth muscle cell proliferation and extracellular matrix synthesis. The severity of arterial injury during stent placement correlates with increased inflammation and late neointimal growth. These pathological findings provide useful targets for therapies aimed at reducing the incidence of in-stent restenosis.

Cell-based gene transfer to the pulmonary vasculature: Endothelial nitric oxide synthase overexpression inhibits monocrotaline-induced pulmonary hypertension

To circumvent the problems of in vivo transfection and avoid the use of viral vectors or proteins, we sought to establish whether smooth-muscle cells (SMCs) transfected ex vivo could be delivered via the systemic venous circulation into the pulmonary bed to achieve local transgene expression in the lung. Primary cultures of pulmonary artery SMCs from Fisher 344 rats were labeled with a fluorescent, membrane-impermeable dye chloromethyl trimethyl rhodamine or transfected with the beta-galactosidase (betaGal) reporter gene under the control of the cytomegalovirus (CMV) enhancer/promoter (pCMV-beta). Transfected or labeled SMCs (5 x 10(5) cells/animal) were delivered to syngeneic recipient rats by injection into the jugular vein; the animals were killed at intervals between 15 min and 2 wk; and the lungs, spleens, kidneys, and skeletal muscle were excised and examined. At 15 min after transplantation, injected cells were detected mainly in the lumen of small pulmonary arteries and arterioles, often in groups of three or more cells. After 24 h, labeled SMCs were found incorporated into the vascular wall of pulmonary arterioles, and transgene expression persisted in situ for 14 d with no evidence of immune response. Using simple geometric assumptions, it was calculated that approximately 57 +/- 5% of the labeled cells reintroduced into the venous circulation could be identified in the lungs after 15 min, 34 +/- 7% at 48 h, 16 +/- 3% at 1 wk, and 15 +/- 5% at 2 wk. Similar results were observed using cells transfected with the reporter gene betaGal. To determine whether this method of gene transfer could prove effective in inhibiting the development of pulmonary vascular disease, pulmonary artery SMCs were transfected with either the full-length coding sequence of endothelial nitric oxide synthase (NOS) under the control of the CMV enhancer/promoter or with the control vector (pcDNA3.1) and injected simultaneously with the pulmonary endothelial toxin monocrotaline. At 28 d after injection the right ventricular systolic pressure was significantly decreased from 50 +/- 4 mm Hg in animals injected with the null-transfected cells to 33 +/- 3 mm Hg in animals injected with the NOS-transfected cells (P < 0.01). These results suggest that a cell-based strategy of ex vivo transfection may provide an effective nonviral approach for the selective delivery of foreign transgenes to pulmonary microvessels in the treatment of pulmonary vascular disease.

Selective neointimal gene transfer in an avian model of vascular injury

Avian models of atherosclerosis helped pioneer the study of vascular biology, and offer economic and technical advantages over mammalian models. As an initial step towards investigating important molecular pathways involved in avian atherogenesis and restenosis, we developed a recombinant adenovirus (Ad) which expresses the reporter gene beta-galactosidase (beta-gal), and applied it to cultured chicken vascular smooth muscle cells (SMCs) and a rooster model of acute vascular injury. In cultured chicken SMCs, recombinant gene expression increased as a function of multiplicity of infection (MOI) and incubation time. Maximal expression occurred at an MOI of 10(4) plaque-forming units (pfu)/cell with approximately 50% of quiescent and non-quiescent chicken SMCs expressing beta-gal. Human aorta SMCs had two- to four-fold increased beta-gal expression compared with chicken SMCs at all MOI and incubation times. In vivo instillation of recombinant Ad into uninjured rooster femoral artery segments revealed low efficiency endothelial cell expression of the reporter gene. In contrast, recombinant Ad infection of rooster femoral artery segments 3-21 days after balloon injury revealed up to 60% of luminal surface beta-gal expression, confined predominantly to the neointimal layer. Peak reporter gene expression efficiencies occurred in arterial segments infected 3 days after balloon injury. Uninfected and control Ad infected arteries had no detectable beta-gal expression. Rooster neointimal cells targeted by the recombinant Ad were identified as alpha-smooth muscle actin containing cells by immunohistochemistry. We conclude that Ad-mediated gene transfer is efficient and selective for the neointima in the rooster acute vascular injury model, and offers the potential to efficiently introduce exogenous genes that may impact on the injury response. This model of acute vascular injury may also be manipulated into more established avian models of atherosclerosis, permitting the investigation of acute injury progression to chronic injury.

Percutaneous adenoviral gene transfer into porcine coronary arteries: is catheter-based gene delivery adapted to coronary circulation?

Recombinant adenoviral (Ad) vectors represent an efficient gene transfer system for targeting the cardiovascular system. Phenotypic modulation of coronary vascular cells in vivo is, however, critically dependent on the efficacy of local delivery devices. Four local drug delivery catheters were tested for intracoronary gene transfer efficiency: the Infiltrator (INF, n = 10), the Crescendo (CRE, n = 10), the Infusasleeve (SLE, n = 8), and the Remedy balloon (channel balloon [CHA], n = 8). After balloon injury of the LAD, Ad vector containing the firefly luciferase cDNA (AdCMVluc, 1.5 x 10(10) plaque-forming units) was administered at the site of injury. On day 4, tissue samples from different regions in the heart and from the liver were assayed for luciferase activity to evaluate local and systemic gene transfer. INF, CRE, and SLE catheters showed higher transduction levels of the target LAD segment than did the CHA catheter (median luciferase activity = 4.2 x 10(6), 11 x 10(6), and 1.3 x 10(6) light units [LU]/vessel versus 0.09 x 10(6) LU/vessel, respectively, p < 0.05). Luciferase activity was occasionally observed in nontarget tissues (right and left ventricular free wall, distal LAD, and liver) and was not significantly different between groups. The viral circulatory half-life was similar for the four groups (<1 min). Gene transfer efficiency was positively correlated with the degree of injury for the intralumenal catheters (CRE, SLE, and CHA) but was independent of the vessel wall injury for the intramural INF. Local drug delivery catheters enable efficient vascular gene transfer in balloon-injured coronary arteries, a prerequisite for further development of intracoronary gene therapy for restenosis.

Vascular gene transfer for the treatment of restenosis and atherosclerosis

Local gene transfer into the vascular wall offers a promising alternative to treat atherosclerosis-related diseases at cellular and molecular levels. Blood vessels are among the easiest targets for gene therapy because of novel percutaneous, catheter-based treatment methods. On the other hand, gene transfer to the artery wall can also be accomplished from adventitia, and in some situations intramuscular gene delivery is also a possibility. In most conditions, such as postangioplasty restenosis, only a temporary expression of the transfected gene will be required. Promising therapeutic effects have been obtained in animal models of restenosis with the transfer of genes for vascular endothelial growth factor, fibroblast growth factor, thymidine kinase, p53, bcl-x, nitric oxide synthase and retinoblastoma. Also, growth arrest homeobox gene and antisense oligonucleotides against transcription factors or cell cycle regulatory proteins have produced beneficial therapeutic effects. Angiogenesis is an emerging new target for gene therapy of ischemic diseases. In addition, hyperlipoproteinemias may be improved by transferring functional lipoprotein-receptor genes into hepatocytes of affected individuals. First experiences of gene transfer methods in the human vascular system have been reported. However, further studies regarding gene delivery methods, vectors and safety of the procedures are needed before a full therapeutic potential of gene therapy in vascular diseases can be evaluated.

Transfer and expression of recombinant nitric oxide synthase genes in the cardiovascular system

Gene therapy involves the transfer of a functional gene into host cells to correct the malfunction of a specific gene or to alleviate the symptoms of a disease. For gene transfer to the cardiovascular system, adenoviral vectors are the most efficient means of transfer. Recently, transfer and functional expression of recombinant nitrio oxide synthase (NOS) genes to cerebral and cardiovascular beds have been demonstrated both ex vivo and in vivo. Here, Alex Chen and colleagues review current progress in the field of vascular NOS gene transfer and the potential use of NOS gene therapy for a number of cardiovascular diseases. Although the feasibility of the NOS gene transfer approach has been demonstrated in animal models, currently available vectors have a number of technical and safety limitations that have to be solved before human NOS gene therapy for cardiovascular disease can be attempted.