How to optimize in vivo gene transfer to cardiac myocytes: mechanical or pharmacological procedures?

Gene therapy for heart failure: A novel treatment for the age old disease

Across the globe, cardiovascular disease (CVD) is the leading cause of mortality. According to reports, around 6.2 million people in the United states have heart failure. Current standards of care for heart failure can delay but not prevent progression of disease. Gene therapy is one of the novel treatment modalities that promises to fill this limitation in the current standard of care for Heart Failure. In this paper we performed an extensive search of the literature on various advances made in gene therapy for heart failure till date. We review the delivery methods, targets, current applications, trials, limitations and feasibility of gene therapy for heart failure. Various methods have been employed till date for administering gene therapies including but not limited to arterial and venous infusion, direct myocardial injection and pericardial injection. Various strategies such as AC6 expression, S100A1 protein upregulation, VEGF-B and SDF-1 gene therapy have shown promise in recent preclinical trials. Furthermore, few studies even show that stimulation of cardiomyocyte proliferation such as through cyclin A2 overexpression is a realistic avenue. However, a considerable number of obstacles need to be overcome for gene therapy to be part of standard treatment of care such as definitive choice of gene, gene delivery systems and a suitable method for preclinical trials and clinical trials on patients. Considering the challenges and taking into account the recent advances in gene therapy research, there are encouraging signs to indicate gene therapy for heart failure to be a promising treatment modality for the future. However, the time and feasibility of this option remains in a situation of balance.

Meeting Contemporary Challenges: Development of Nanomaterials for Veterinary Medicine

In recent decades, nanotechnology has been rapidly advancing in various fields of human activity, including veterinary medicine. The review presents up-to-date information on recent advancements in nanotechnology in the field and an overview of the types of nanoparticles used in veterinary medicine and animal husbandry, their characteristics, and their areas of application. Currently, a wide range of nanomaterials has been implemented into veterinary practice, including pharmaceuticals, diagnostic devices, feed additives, and vaccines. The application of nanoformulations gave rise to innovative strategies in the treatment of animal diseases. For example, antibiotics delivered on nanoplatforms demonstrated higher efficacy and lower toxicity and dosage requirements when compared to conventional pharmaceuticals, providing a possibility to solve antibiotic resistance issues. Nanoparticle-based drugs showed promising results in the treatment of animal parasitoses and neoplastic diseases. However, the latter area is currently more developed in human medicine. Owing to the size compatibility, nanomaterials have been applied as gene delivery vectors in veterinary gene therapy. Veterinary medicine is at the forefront of the development of innovative nanovaccines inducing both humoral and cellular immune responses. The paper provides a brief overview of current topics in nanomaterial safety, potential risks associated with the use of nanomaterials, and relevant regulatory aspects.

Barriers in Heart Failure Gene Therapy and Approaches to Overcome Them

With the growing prevalence and incidence of heart failure worldwide, investigation and development of new therapies to address disease burden are of great urgency. Gene therapy is one promising approach for the management of heart failure, but several barriers currently exclude safe and efficient gene delivery to the human heart. These barriers include the anatomical and biological difficulty of specifically targeting cardiomyocytes, the vascular endothelium, and immunogenicity against administered vectors and the transgene. We review approaches taken to overcome these barriers with a focus on vector modification, evasion of immune responses, and heart-targeted delivery techniques. While various modifications proposed to date show promise in managing some barriers, continued investigation into improvements to existing therapies is required to address transduction efficiency, duration of transgene expression, and immune response.

Cardiac Gene Delivery in Large Animal Models: Selective Retrograde Venous Injection

Delivery of viral vectors to the heart represents a challenging endeavor. Besides vector design, the route of substrate administration is significantly influencing gene delivery success. The selective retrograde venous injection (SRVI) represents one of the most efficient percutaneous delivery strategies for transduction of the anterior left ventricular myocardium. In this chapter, we discuss the advantages and limitations of this vector delivery approach and provide a protocol for selective retrograde venous injection in a preclinical large animal model. As limited transgene expression frequently hampers generation of reliable proof-of-principle data and thus translation, this technique provides a valuable tool to ensure high myocardial transduction in preclinical research.

Cardiac Gene Delivery in Large Animal Models: Antegrade Techniques

Percutaneous antegrade coronary injection is among the least invasive cardiac selective gene delivery methods. However, the transduction efficiency of a simple bolus antegrade injection is quite low. In order to improve transduction efficiency in antegrade intracoronary delivery, several additional approaches have been proposed.In this chapter, we will describe the important elements associated with intracoronary delivery methods and present protocols for three different catheter-based antegrade gene delivery techniques in a preclinical large animal model. This is the second edition of this chapter, and it includes modifications we have made over the past several years that further enhance transduction efficacy.

Magnetofection In Vivo by Nanomagnetic Carriers Systemically Administered into the Bloodstream

Nanoparticle-based technologies are rapidly expanding into many areas of biomedicine and molecular science. The unique ability of magnetic nanoparticles to respond to the magnetic field makes them especially attractive for a number of in vivo applications including magnetofection. The magnetofection principle consists of the accumulation and retention of magnetic nanoparticles carrying nucleic acids in the area of magnetic field application. The method is highly promising as a clinically efficient tool for gene delivery in vivo. However, the data on in vivo magnetofection are often only descriptive or poorly studied, insufficiently systematized, and sometimes even contradictory. Therefore, the aim of the review was to systematize and analyze the data that influence the in vivo magnetofection processes after the systemic injection of magnetic nanostructures. The main emphasis is placed on the structure and coating of the nanomagnetic vectors. The present problems and future trends of the method development are also considered.

Left Ventricular Unloading Using an Impella CP Improves Coronary Flow and Infarct Zone Perfusion in Ischemic Heart Failure

Background

Delivering therapeutic materials, like stem cells or gene vectors, to the myocardium is difficult in the setting of ischemic heart failure because of decreased coronary flow and impaired microvascular perfusion (MP). The aim of this study was to determine if mechanical left ventricular (LV) unloading with the Impella increases coronary flow and MP in a subacute myocardial infarction.

Methods and Results

Anterior transmural myocardial infarction (infarct size, 26.0±3.4%) was induced in Yorkshire pigs. At 2 weeks after myocardial infarction, 6 animals underwent mechanical LV unloading by Impella, whereas 4 animals underwent pharmacological LV unloading using sodium nitroprusside for 2 hours. LV unloading with Impella significantly reduced end‐diastolic volume (−16±11mL, P=0.02) and end‐diastolic pressure (EDP; −32±23 mm Hg, P=0.03), resulting in a significant decrease in LV end‐diastolic wall stress (EDWS) (infarct: 71.6±14.7 to 43.3±10.8 kdynes/cm² [P=0.02]; remote: 66.6±20.9 to 40.6±13.3 kdynes/cm² [P=0.02]). Coronary flow increased immediately and remained elevated after 2 hours in Impella‐treated pigs. Compared with the baseline, MP measured by fluorescent microspheres significantly increased within the infarct zone (109±81%, P=0.003), but not in the remote zone. Although sodium nitroprusside effectively reduced LV‐EDWS, 2 (50%) of sodium nitroprusside–treated pigs developed profound systemic hypotension. A significant correlation was observed between the infarct MP and EDWS (r²=0.43, P=0.03), suggesting an important role of EDWS in regulating MP during LV unloading in the infarcted myocardium.

Conclusions

LV unloading using an Impella decreased EDWS and increased infarct MP without hemodynamic decompensation. Mechanical LV unloading is a novel and efficient approach to increase infarct MP in patients with subacute myocardial infarction.

The present and future role of ultrasound targeted microbubble destruction in preclinical studies of cardiac gene therapy

Multiple limitations for cardiac pharmacologic therapies like intolerance, individual variation in effectiveness, side effects, and high cost still remain, despite the recent progress in diagnosis and health support. Gene therapy is poised to be an attractive alternative in various ways for the future, refractory cardiac diseases being one aspect of it. As a novel therapy to deliver the objective gene to organs of living animals, ultrasound targeted microbubble destruction (UTMD) has therapeutic potential in cardiovascular disorders. UTMD, which binds microbubbles with DNA or RNA carriers into the shell and destroys the located microbubbles with low frequency and high mechanical index ultrasound can release target agents to specific organs. UTMD has the ability to transfect markedly through sonoporation, cavitation and other effects by way of intravenous injection that is minimally invasive and highly specific for gene deliverance. Here, we have summarized the present role of UTMD in pre-clinical studies of cardiac gene therapy which covers myocardial infarction, regeneration, ischaemia/reperfusion injury, hypertension, diabetic cardiomyopathy, adriamycin cardiomyopathy and some discussion for further studies.

In Situ Heart Isolation Featuring Closed Loop Recirculation: The Gold Standard for Optimum Cardiac Gene Transfer?

The concept of delivering nucleic material encoding a therapeutic gene to the heart has arduously moved from hypothesis to a variety of high potential clinical applications. Despite the promise however, the results achieved have yet to be realized due to several problems that persist in the clinic. One of these identified problems is the need for an efficient delivery method which facilitates complete cardiotropism and minimizes collateral effects. Additional parameters impacting gene delivery that most need to be improved have been identified as follows: (1) Increasing the contact time of vector in coronary circulation permitting transfer, (2) Sustained intravascular flow rate and perfusion pressure to facilitate proper kinetics, (3) Modulation of cellular permeability to increase uptake efficiency, and once in the cells (4) Enhancing transcription and translation within the transfected cardiac cells, and (5) Obtaining the global gene distribution for maximum efficacy. Recently it was hypothesized that use of cardiopulmonary bypass may facilitate cardiac-selective gene transfer and permit vector delivery in the arrested heart in isolated "closed loop" recirculating model. This system was named molecular cardiac surgery with recirculating delivery (MCARD). The key components of this approach include: isolation of the heart from systemic organs, multiple pass recirculation of vector through the coronary vasculature, and removing the residual vector from the coronary circulation to minimize collateral expression. These attributes unique to a surgical approach such as MCARD can effectively increase vector transduction efficiency in coronary vasculature.

Cardiac Gene Delivery in Large Animal Models: Antegrade Techniques

Percutaneous antegrade coronary injection is among the least invasive cardiac selective gene delivery methods. However, transduction efficiency is quite low with a simple bolus antegrade injection. In order to improve the transduction efficiency using antegrade delivery, several additional approaches have been proposed.In this chapter, we briefly discuss important elements associated with intracoronary delivery methods and present protocols for three different catheter-based antegrade delivery techniques in a preclinical large animal model. Despite the lower transduction efficacy relative to more invasive delivery techniques, antegrade techniques have the advantage of being clinically well established and having safer profiles which is important when treating patients with cardiac disease.

Ultrasound-Targeted Microbubble Destruction Enhances Gene Expression of microRNA-21 in Swine Heart via Intracoronary Delivery

BACKGROUND

Ultrasound-targeted microbubble destruction (UTMD) has proved to be a promising method for gene delivery. However, the feasibility and efficacy of UTMD-mediated gene delivery to the heart of large animals remain unclear. The present study was to explore the probability of increasing the transfection of microRNA-21 (miR-21) in swine heart by UTMD, and to search for the most suitable transfection conditions.

METHODS

We first optimized ultrasound intensity for successful miR-21 delivery. After intravenous injection of miR-21/microbubble mixture (miR-21/MB), transthoracic ultrasound irradiation (US) was applied from the left anterior chest using different intensities (1, 2, and 3 W/cm(2)). Then the efficacy of UTMD-mediated miR-21 delivery into myocardium via intracoronary injection was explored. Solution of miR-21/MB was infused intravenously or intracoronarily with US over the heart. Swine undergoing phosphate-buffered saline (PBS) injection, miR-21/MB injection via ear vein or coronary artery without US served as the control. The dynamic changes of left ventricular ejection fraction (LVEF) and serum troponin I (cTnI) after UTMD were detected, then the left ventricular myocardium was harvested for hematoxylin and eosin (H&E) staining 4 days later; the expression levels of miR-21 and programmed cell death 4 (PDCD4) were detected by quantitative real time polymerase chain reaction (qRT-PCR) and Western blot, respectively.

RESULTS

Results showed that pulse ultrasound at an intensity of 2 W/cm(2) and a 50% duty ratio for 20 minutes, there was no increase in serum cTnI, no histological sign of myocardial damage, and no noted cardiac dysfunction with relatively higher miR-21 expression (P < 0.05). Compared to miR-21/MB alone, UTMD significantly increased gene expression in myocardium regardless of the delivery routes (P < 0.05). Interestingly, the transfection efficiency was found to be a little bit higher with intracoronary injection than that with intravenous injection, though the dose for intracoronary injection was half of the intravenous injection (P < 0.05).

CONCLUSION

Under suitable conditions, UTMD can efficiently enhance gene expression in swine heart regardless of the delivery routes. The intravenous injection might be superior to intracoronary injection with less invasiveness and lower requirement of the technique. And for those undergoing percutaneous coronary intervention, intracoronary injection seems to be another alternative.

Anti-inflammatory loaded poly-lactic glycolic acid nanoparticle formulations to enhance myocardial gene transfer: an in-vitro assessment of a drug/gene combination therapeutic approach for direct injection

Background

Cardiac gene therapy for heart disease is a major translational research area with potential, yet problems with safe and efficient gene transfer into cardiac muscle remain unresolved. Existing methodology to increase vector uptake include modifying the viral vector, non-viral particle encapsulation and or delivery with device systems. These advanced methods have made improvements, however fail to address the key problem of inflammation in the myocardium, which is known to reduce vector uptake and contribute to immunogenic adverse events. Here we propose an alternative method to co-deliver anti-inflammatory drugs in a controlled release polymer with gene product to improve therapeutic effects.

Methods

A robust, double emulsion production process was developed to encapsulate drugs into nanoparticles. Briefly in this proof of concept study, aspirin and prednisolone anti-inflammatory drugs were encapsulated in various poly-lactic glycolic acid polymer (PLGA) formulations. The resultant particle systems were characterized, co-delivered with GFP plasmid, and evaluated in harvested myocytes in culture for uptake.

Results

High quality nanoparticles were harvested from multiple production runs, with an average 64 ± 10 mg yield. Four distinct particle drug system combinations were characterized and evaluated in vitro: PLGA(50:50) Aspirin, PLGA(65:35) Prednisolone, PLGA(65:35) Aspirin and PLGA(50:50) Prednisolone Particles consisted of spherical shape with a narrow size distribution 265 ± 104 nm as found in scanning electron microscopy imaging. Prednisolone particles regardless of PLGA type were found on average ≈ 100 nm smaller than the aspirin types. All four groups demonstrated high zeta potential stability and re-constitution testing prior to in vitro. In vitro results demonstrated co uptake of GFP plasmid (green) and drug loaded particles (red) in culture with no incidence of toxicity.

Conclusions

Nano formulated anti-inflammatories in combination with standalone gene product therapy may offer a clinical solution to maximize cardiac gene therapy product effects while minimizing the risk of the host response in the inflammatory myocardial environment.

Gene therapy delivery systems for enhancing viral and nonviral vectors for cardiac diseases: current concepts and future applications

Gene therapy is one of the most promising fields for developing new treatments for the advanced stages of ischemic and monogenetic, particularly autosomal or X-linked recessive, cardiomyopathies. The remarkable ongoing efforts in advancing various targets have largely been inspired by the results that have been achieved in several notable gene therapy trials, such as the hemophilia B and Leber's congenital amaurosis. Rate-limiting problems preventing successful clinical application in the cardiac disease area, however, are primarily attributable to inefficient gene transfer, host responses, and the lack of sustainable therapeutic transgene expression. It is arguable that these problems are directly correlated with the choice of vector, dose level, and associated cardiac delivery approach as a whole treatment system. Essentially, a delicate balance exists in maximizing gene transfer required for efficacy while remaining within safety limits. Therefore, the development of safe, effective, and clinically applicable gene delivery techniques for selected nonviral and viral vectors will certainly be invaluable in obtaining future regulatory approvals. The choice of gene transfer vector, dose level, and the delivery system are likely to be critical determinants of therapeutic efficacy. It is here that the interactions between vector uptake and trafficking, delivery route means, and the host's physical limits must be considered synergistically for a successful treatment course.

Gene therapy for cardiovascular disease mediated by ultrasound and microbubbles

Gene therapy provides an efficient approach for treatment of cardiovascular disease. To realize the therapeutic effect, both efficient delivery to the target cells and sustained expression of transgenes are required. Ultrasound targeted microbubble destruction (UTMD) technique has become a potential strategy for target-specific gene and drug delivery. When gene-loaded microbubble is injected, the ultrasound-mediated microbubble destruction may spew the transported gene to the targeted cells or organ. Meanwhile, high amplitude oscillations of microbubbles increase the permeability of capillary and cell membrane, facilitating uptake of the released gene into tissue and cell. Therefore, efficiency of gene therapy can be significantly improved. To date, UTMD has been successfully investigated in many diseases, and it has achieved outstanding progress in the last two decades. Herein, we discuss the current status of gene therapy of cardiovascular diseases, and reviewed the progress of the delivery of genes to cardiovascular system by UTMD.

Myocardial gene transfer: routes and devices for regulation of transgene expression by modulation of cellular permeability

Heart diseases are major causes of morbidity and mortality in Western society. Gene therapy approaches are becoming promising therapeutic modalities to improve underlying molecular processes affecting failing cardiomyocytes. Numerous cardiac clinical gene therapy trials have yet to demonstrate strong positive results and advantages over current pharmacotherapy. The success of gene therapy depends largely on the creation of a reliable and efficient delivery method. The establishment of such a system is determined by its ability to overcome the existing biological barriers, including cellular uptake and intracellular trafficking as well as modulation of cellular permeability. In this article, we describe a variety of physical and mechanical methods, based on the transient disruption of the cell membrane, which are applied in nonviral gene transfer. In addition, we focus on the use of different physiological techniques and devices and pharmacological agents to enhance endothelial permeability. Development of these methods will undoubtedly help solve major problems facing gene therapy.

Mechanistic, technical, and clinical perspectives in therapeutic stimulation of coronary collateral development by angiogenic growth factors

Stimulation of collateral vessel development in the heart by angiogenic growth factor therapy has been tested in animals and humans for almost two decades. Discordance between the outcome of preclinical studies and clinical trials pointed to the difficulties of translation from animal models to patients. Lessons learned in this process identified specific mechanistic, technical, and clinical hurdles, which need to be overcome. This review summarizes current understanding of the mechanisms leading to the establishment of a functional coronary collateral network and the biological processes growth factor therapies should stimulate even under conditions of impaired natural adaptive vascular response. Vector delivery methods are recommended to maximize angiogenic gene therapy efficiency and reduce side effects. Optimization of clinical trial design should include the choice of clinical end points which provide mechanistic proof-of-concept and also reflect clinical benefits (e.g., surrogates to assess increased collateral flow reserve, such as myocardial perfusion imaging). Guidelines are proposed to select patients who may respond to the therapy with high(er) probability. Both short and longer term strategies are outlined which may help to make therapeutic angiogenesis (TA) work in the future.

Minimally invasive closed-chest ultrasound-guided substance delivery into the pericardial space in mice

Organ-directed gene transfer remains an attractive method for both gaining a better understanding of heart disease and for cardiac therapy. However, virally mediated transfer of gene products into cardiac cells requires prolonged exposure of the myocardium to the viral substrate. Pericardial injection of viral vectors has been proposed and used with some success to achieve myocardial transfection and may be a suitable approach for transfection of atrial myocardium. Indeed, such an organ-specific method would be particularly useful to reverse phenotypes in young and adult genetically altered murine models of cardiac disease. We therefore sought to develop a minimally invasive technique for pericardial injection of substances in mice. Pericardial access in anaesthetised, spontaneously breathing mice was achieved using continuous high-resolution ultrasound guidance. We could demonstrate adequate delivery of injected substances into the murine pericardium. Atrial epicardial and myocardial cells were transfected in approximately one third of mice injected with enhanced green fluorescent protein-expressing adenovirus. Cellular expression rates within individual murine atria were limited to a maximum of 20 %; therefore, expression efficiency needs to be further improved. Minimally invasive, ultrasound-guided injection of viral material appears a technically challenging yet feasible method for selective transfection of atrial epi- and myocardium. This pericardial injection method may be useful in the evaluation of potential genetic interventions aimed at rescuing atrial phenotypes in transgenic mouse models.

Ischemia-reperfusion increases transfection efficiency of intracoronary adenovirus type 5 in pig heart in situ

Efficiency of intracoronary (IC) adenoviral vector transfection is impaired by the vascular endothelium. Ischemia and substances that increase vascular permeability (sodium nitroprusside, nitroglycerin) may augment adenoviral vector transfection efficiency (TE). We tested whether TE of adenoviral vector following IC infusion is improved by nitrates or by ischemia. Fluoroscopically guided angioplasty balloon catheters occluded the coronary artery in Yorkshire pigs and delivered adenoviral type 5 vector encoding the luciferase gene (Ad5Luc, 10(11) viral particles). TE (luciferase activity) was minimal and was not augmented by IC co-administration of 50 μg/min sodium nitroprusside to nonischemic myocardium. Two (but not one) 3-min episodes of occlusion tended to increase luciferase activity (p=0.06), and luciferase activity was further increased by IC co-administration of nitroglycerin (p<0.001). After 75 min of coronary artery occlusion, luciferase activity was greater than with shorter periods of ischemia, and was significantly greater in the ischemia-reperfused zone compared to the border zone 3 and 14 days after infusion; there was no transfection in nonischemic myocardium. IC delivery of Ad5Luc into post-ischemic myocardium caused no local inflammation or hemodynamic instability. We conclude that the uptake of IC Ad5 to ischemic reperfused myocardium validates use of IC Ad5 delivery protocols in future human gene therapy trials in patients following myocardial ischemia.

Percutaneous methods of vector delivery in preclinical models

Cardiovascular disease remains a leading cause of hospitalization and mortality worldwide. Conventional heart failure treatment is making steady and substantial progress to reduce the burden of disease. Nevertheless novel therapies and especially cardiac gene therapy have been emerging in the past and successfully made their way into first clinical trials. Gene therapy was initially a visionary treatment strategy for inherited, monogenetic diseases but has now developed to have potential for polygenic diseases as atherosclerosis, arrhythmias and heart failure. These novel therapeutic strategies require testing in clinically relevant animal models to transition from 'bench to bedside'. One of the major hurdles for effective cardiovascular gene therapy is the delivery of the viral vectors to the heart. In this review we present the currently available vector-mediated cardiac gene delivery methods in vivo considering the specific merits and deficiencies.

Gene delivery technologies for cardiac applications

Ischemic heart disease (IHD) and heart failure (HF) are major causes of morbidity and mortality in the Western society. Advances in understanding the molecular pathology of these diseases, the evolution of vector technology, as well as defining the targets for therapeutic interventions has placed these conditions within the reach of gene-based therapy. One of the cornerstones of limiting the effectiveness of gene therapy is the establishment of clinically relevant methods of genetic transfer. Recently there have been advances in direct and transvascular gene delivery methods with the use of new technologies. Current research efforts in IHD are focused primarily on the stimulation of angiogenesis, modify the coronary vascular environment and improve endothelial function with localized gene-eluting catheters and stents. In contrast to standard IHD treatments, gene therapy in HF primarily targets inhibition of apoptosis, reduction in adverse remodeling and increase in contractility through global cardiomyocyte transduction for maximal efficacy. This article will review a variety of gene-transfer strategies in models of coronary artery disease and HF and discuss the relative success of these strategies in improving the efficiency of vector-mediated cardiac gene delivery.

Concomitant intravenous nitroglycerin with intracoronary delivery of AAV1.SERCA2a enhances gene transfer in porcine hearts

SERCA2a gene therapy improves contractile and energetic function of failing hearts and has been shown to be associated with benefits in clinical outcomes, symptoms, functional status, biomarkers, and cardiac structure in a phase 2 clinical trial. In an effort to enhance the efficiency and homogeneity of gene uptake in cardiac tissue, we examined the effects of nitroglycerin (NTG) in a porcine model following AAV1.SERCA2a gene delivery. Three groups of Göttingen minipigs were assessed: (i) group A: control intracoronary (IC) AAV1.SERCA2a (n = 6); (ii) group B: a single bolus IC injection of NTG (50 µg) immediately before administration of intravenous (IV) AAV1.SERCA2a (n = 6); and (iii) group C: continuous IV NTG (1 µg/kg/minute) during the 10 minutes of AAV1.SERCA2a infusion (n = 6). We found that simultaneous IV infusion of NTG and AAV1.SERCA2a resulted in increased viral transduction efficiency, both in terms of messenger RNA (mRNA) as well as SERCA2a protein levels in the whole left ventricle (LV) compared to control animals. On the other hand, IC NTG pretreatment did not result in enhanced gene transfer efficiency, mRNA or protein levels when compared to control animals. Importantly, the transgene expression was restricted to the heart tissue. In conclusion, we have demonstrated that IV infusion of NTG significantly improves cardiac gene transfer efficiency in porcine hearts.

A translatable, closed recirculation system for AAV6 vector-mediated myocardial gene delivery in the large animal

Current strategies for managing congestive heart failure are limited, validating the search for an alternative treatment modality. Gene therapy holds tremendous promise as both a practical and translatable technology platform. Its effectiveness is evidenced by the improvements in cardiac function observed in vector-mediated therapeutic transgene delivery to the murine myocardium. A large animal model validating these results is the likely segue into clinical application. However, controversy still exists regarding a suitable method of vector-mediated cardiac gene delivery that provides for efficient, global gene transfer to the large animal myocardium that is also clinically translatable and practical. Intramyocardial injection and catheter-based coronary delivery techniques are attractive alternatives with respect to their clinical applicability; yet, they are fraught with numerous challenges, including concerns regarding collateral gene expression in other organs, low efficiency of vector delivery to the myocardium, inhomogeneous expression, and untoward immune response secondary to gene delivery. Cardiopulmonary bypass (CPB) delivery with dual systemic and isolated cardiac circuitry precludes these drawbacks and has the added advantage of allowing for control of the pharmacological milieu, multiple pass recirculation through the coronary circulation, the selective addition of endothelial permeabilizing agents, and an increase in vector residence time. Collectively, these mechanics significantly improve the efficiency of global, vector-mediated cardiac gene delivery to the large animal myocardium, highlighting a potential therapeutic strategy to be extended to some heart failure patients.

A pharmacokinetic analysis of molecular cardiac surgery with recirculation mediated delivery of βARKct gene therapy: developing a quantitative definition of the therapeutic window

BACKGROUND

Two major problems for translating gene therapy for heart failure therapy are: safe and efficient delivery and the inability to establish a relationship between vector exposure and in vivo effects. We present a pharmacokinetics (PK) analysis of molecular cardiac surgery with recirculating delivery (MCARD) of scAAV6-βARKct. MCARD's stable cardiac specific delivery profile was exploited to determine vector exposure, half-life, and systemic clearance.

METHODS AND RESULTS

Five naive sheep underwent MCARD with 10(14) genome copies of scAAV6-βARKct. Blood samples were collected over the recirculation interval time of 20 minutes and evaluated with quantitative polymerase chain reaction (qPCR). C(t) curves were generated and expressed on a log scale. The exposure, half-life, and clearance curves were generated for analysis. qPCR and Western blots were used to determine biodistribution. Finally, all in vivo transduction data was plotted against MCARD's PK to determine if a relationship existed. Vector concentrations at each time point were (cardiac and systemic, respectively): 5 minutes: 9.16 ± 0.15 and 3.21 ± 0.38; 10 minutes: 8.81 ± 0.19 and 3.62 ± 0.37; 15 minutes: 8.75 ± 0.12 and 3.69 ± 0.31; and 20 minutes: 8.66 ± 0.22 and 3.95 ± 0.26; P < .00001. The half life of the vector was 2.66 ± 0.24 minutes. PK model data revealed that only 0.61 ± 0.43% of the original dose remained in the blood after delivery, and complete clearance from the system was achieved at 1 week. A PK transfer function revealed a positive correlation between exposure and in vivo transduction. Robust βARKct expression was found in all cardiac regions with none in the liver.

CONCLUSION

MCARD may offer a viable method to establish a relationship between vector exposure and in vivo transduction. Using this methodology, it may be possible to address a critical need for establishing an effective therapeutic window.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Method of gene delivery in large animal models of cardiovascular diseases

Cardiovascular disease is a major cause of morbidity and mortality in contemporary societies. While progress in conventional treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore new and potentially therapeutic approaches. Gene therapy, which was initially envisioned as a treatment strategy for inherited monogenic disorders, has been found to hold broader potential that also includes acquired polygenic diseases, such as atherosclerosis, arrhythmias, and heart failure. Advances in the understanding of the molecular basis of conditions such as these, together with the evolution of increasingly efficient gene transfer technology, have placed some cardiovascular pathophysiologies within the reach of gene-based therapy. In fact, gene therapy holds great promise as a targeted treatment for cardiovascular diseases. One of the major hurdles for effective cardiovascular gene therapy is the delivery of the viral vectors to the heart. In this chapter, we will present the various types of delivery techniques in preclinical, large animal models of cardiovascular diseases.

Current strategies for myocardial gene delivery

Existing methods of cardiac gene delivery can be classified by the site of injection, interventional approach and type of cardiac circulation at the time of transfer. General criteria to assess the efficacy of a given delivery method include: global versus regional myocardial transduction, technical complexity and the pathophysiological effects associated with its use, delivery-related collateral expression and the delivery-associated inflammatory and immune response. Direct gene delivery (intramyocardial, endocardial, epicardial) may be useful for therapeutic angiogenesis and for focal arrhythmia therapy but with gene expression which is primarily limited to regions in close proximity to the injection site. An often unappreciated limitation of these techniques is that they are frequently associated with substantial systemic vector delivery. Percutaneous infusion of vector into the coronary arteries is minimally invasive and allows for transgene delivery to the whole myocardium. Unfortunately, efficiency of intracoronary delivery is highly variable and the short residence time of vector within the coronary circulation and significant collateral organ expression limit its clinical potential. Surgical techniques, including the incorporation of cardiopulmonary bypass with isolated cardiac recirculation, represent novel delivery strategies that may potentially overcome these limitations; yet, these techniques are complex with inherent morbidity that must be thoroughly evaluated before safe translation into clinical practice. Characteristics of the optimal technique for gene delivery include low morbidity, increased myocardial transcapillary gradient, extended vector residence time in the coronary circulation and exclusion of residual vector from the systemic circulation after delivery to minimize extracardiac expression and to mitigate a cellular immune response. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Treatment of heart failure by calcium cycling gene therapy

Heart failure is a major cause of morbidity and mortality in Western countries. While progress in conventional treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore new and potentially therapeutic approaches. Gene therapy, for example, was initially envisioned as a treatment strategy for inherited monogenic disorders. It is now apparent that gene therapy has broader potential, which also includes acquired polygenic diseases such as heart failure. Advances in the understanding of the molecular basis of conditions such as these, together with the evolution of increasingly efficient gene transfer technology, has placed congestive heart failure within the reach of gene-based therapy.

Cardiac gene therapy: optimization of gene delivery techniques in vivo

Vector-mediated cardiac gene therapy holds tremendous promise as a translatable platform technology for treating many cardiovascular diseases. The ideal technique is one that is efficient and practical, allowing for global cardiac gene expression, while minimizing collateral expression in other organs. Here we survey the available in vivo vector-mediated cardiac gene delivery methods--including transcutaneous, intravascular, intramuscular, and cardiopulmonary bypass techniques--with consideration of the relative merits and deficiencies of each. Review of available techniques suggests that an optimal method for vector-mediated gene delivery to the large animal myocardium would ideally employ retrograde and/or anterograde transcoronary gene delivery,extended vector residence time in the coronary circulation, an increased myocardial transcapillary gradient using physical methods, increased endothelial permeability with pharmacological agents, minimal collateral gene expression by isolation of the cardiac circulation from the systemic, and have low immunogenicity.

Human studies of angiogenic gene therapy

Despite significant advances in medical, interventional, and surgical therapy for coronary and peripheral arterial disease, the burden of these illnesses remains high. To address this unmet need, the science of therapeutic angiogenesis has been evolving for almost two decades. Early preclinical studies and phase I clinical trials achieved promising results with growth factors administered as recombinant proteins or as single-agent gene therapies, and data accumulated through 10 years of clinical trials indicate that gene therapy has an acceptable safety profile. However, more rigorous phase II and phase III clinical trials have failed to unequivocally demonstrate that angiogenic agents are beneficial under the conditions and in the patients studied to date. Investigators have worked to understand the biology of the vascular system and to incorporate their findings into new treatments for patients with ischemic disease. Recent gene- and cell-therapy trials have demonstrated the bioactivity of several new agents and treatment strategies. Collectively, these observations have renewed interest in the mechanisms of angiogenesis and deepened our understanding of the complexity of vascular regeneration. Gene therapy that incorporates multiple growth factors, approaches that combine cell and gene therapy, and the administration of "master switch" agents that activate numerous downstream pathways are among the credible and plausible steps forward. In this review, we examine the clinical development of angiogenic gene therapy, summarize several of the lessons learned during the conduct of these trials, and suggest how this prior experience may guide the conduct of future preclinical investigations and clinical trials.

Designing heart performance by gene transfer

The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.

Enhanced thoracic gene delivery by magnetic nanobead-mediated vector

BACKGROUND

Systemic gene delivery is limited by the adverse hydrodynamic conditions on the collection of gene carrier particles to the specific area. In the present study, a magnetic field was employed to guide magnetic nanobead (MNB)/polymer/DNA complexes after systemic administration to the left side of the mouse thorax in order to induce localized gene expression.

METHODS

Nonviral polymer (poly ethyleneimine, PEI) vector-gene complexes were conjugated to MNBs with the Sulfo-NHS-LC-Biotin linker. In vitro transfection efficacy of MNB/PEI/DNA was compared with PEI/DNA in three different cell lines as well as primary endothelial cells under magnetic field stimulation. In vivo, MNB/PEI/DNA complexes were injected into the tail vein of mice and an epicardial magnet was employed to attract the circulating MNB/PEI/DNA complexes.

RESULTS

Endocytotic uptake of MNB/PEI/DNA complexes and intracellular gene release with nuclear translocation were observed in vitro, whereas the residues of MNB/PEI complexes were localized at the perinuclear region. Compared with PEI/DNA complexes alone, MNB/PEI/DNA complexes had a 36- to 85-fold higher transfection efficiency under the magnetic field. In vivo, the epicardial magnet effectively attracted MNB/PEI/DNA complexes in the left side of the thorax, resulting in strong reporter and therapeutic gene expression in the left lung and the heart. Gene expression in the heart was mainly within the endothelium.

CONCLUSIONS

MNB-mediated gene delivery could comprise a promising method for gene delivery to the lung and the heart.

Animal models for target diseases in gene therapy--using DNA and siRNA delivery strategies

Nanoparticles, including lipopolyamines leading to lipoplexes, liposomes, and polyplexes are targeted drug carrier systems in the current search for a successful delivery system for polynucleic acids. This review is focused on the impact of gene and siRNA delivery for studies of efficacy, pharmacodynamics, and pharmacokinetics within the setting of the wide variety of in vivo animal models now used. This critical appraisal of the recent literature sets out the different models that are currently being investigated to bridge from studies in cell lines through towards clinical reality. Whilst many scientists will be familiar with rodent (murine, fecine, cricetine, and musteline) models, few probably think of fish as a clinically relevant animal model, but zebrafish, madake, and rainbow trout are all being used. Larger animal models include rabbit, cat, dog, and cow. Pig is used both for the prevention of foot-and-mouth disease and human diseases, sheep is a model for corneal transplantation, and the horse naturally develops arthritis. Non-human primate models (macaque, common marmoset, owl monkey) are used for preclinical gene vector safety and efficacy trials to bridge the gap prior to clinical studies. We aim for the safe development of clinically effective delivery systems for DNA and RNAi technologies.

Advances in gene-based therapy for heart failure

Heart failure is a major cause of morbidity and mortality in western countries. While progress in current treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore novel therapeutic strategies. Clinicians and researchers alike have thus looked towards novel adjunctive therapeutic strategies, including gene-based therapy for congestive heart failure (CHF). Advances in the understanding of the molecular basis of CHF, combined to the evolution of increasingly efficient gene transfer technology, have placed congestive heart failure within reach of gene-based therapy. This review will discuss issues related to gene vector systems, gene delivery strategies, and gene targets for intervention in the setting of CHF.

Gene-therapy delivery strategies in cardiology

Clinical gene-therapy approaches in cardiology have not fulfilled their promise in randomized, controlled trials, so far, despite striking effects in preclinical models. Lack of clinical success appears not to be related to an unexpected low potency of the therapeutic factors itself in humans, but has rather been attributed to limitations of the vector systems used to transfer the DNA, as well as application modes of the vector itself. Therefore, novel delivery strategies are required with increased efficiency and increased specificity. Recent improvements of vectors using targeting approaches in addition to the development of novel application strategies for cardiac or vascular gene transfer will improve gene delivery in future clinical approaches.

Cardio-specific long-term gene expression in a porcine model after selective pressure-regulated retroinfusion of adeno-associated viral (AAV) vectors

Cornerstone for an efficient cardiac gene therapy is the need for a vector system, which enables selective and long-term expression of the gene of interest. In rodent animal models adeno-associated viral (AAV) vectors like AAV-6 have been shown to efficiently transduce cardiomyocytes. However, since significant species-dependent differences in transduction characteristics exist, large animal models are of imminent need for preclinical evaluations. We compared gene transfer efficiencies of AAV-6 and heparin binding site-deleted AAV-2 vectors in a porcine model. Application of the AAVs was performed by pressure-regulated retroinfusion of the anterior interventricular cardiac vein, which has been previously shown to efficiently deliver genes to the myocardium (3.5 x 10(10) viral genomes per animal; n=5 animals per group). All vectors harbored a luciferase reporter gene under control of a cytomegalovirus (CMV)-enhanced 1.5 kb rat myosin light chain promoter (CMV-MLC2v). Expression levels were evaluated 4 weeks after gene transfer by determining luciferase activities. To rule out a systemic spillover peripheral tissue was analyzed by PCR for the presence of vector genomes. Selective retroinfusion of AAV serotype 6 vectors into the anterior cardiac vein substantially increased reporter gene expression in the targeted distal left anterior descending (LAD) territory (65 943+/-31 122 vs control territory 294+/-69, P<0.05). Retroinfusion of AAV-2 vectors showed lower transgene expression, which could be increased with coadministration of recombinant human vascular endothelial growth factor (1365+/-707 no vascular endothelial growth factor (VEGF) vs 38 760+/-2448 with VEGF, P<0.05). Significant transgene expression was not detected in other organs than the heart, although vector genomes were detected also in the lung and liver. Thus, selective retroinfusion of AAV-6 into the coronary vein led to efficient long-term myocardial reporter gene expression in the targeted LAD area of the porcine heart. Coapplication of VEGF significantly increased transduction efficiency of AAV-2.

Targeted high-efficiency, homogeneous myocardial gene transfer

Myocardial gene therapy continues to show promise as a tool for investigation and treatment of cardiac disease. Progress toward clinical approval has been slowed by limited in vivo delivery methods. We investigated the problem in a porcine model, with an objective of developing a method for high efficiency, homogeneous myocardial gene transfer that could be used in large mammals, and ultimately in humans. Eighty-one piglets underwent coronary catheterization for delivery of viral vectors into the left anterior descending artery and/or the great cardiac vein. The animals were followed for 5 or 28 days, and then transgene efficiency was quantified from histological samples. The baseline protocol included treatment with VEGF, nitroglycerin, and adenosine followed by adenovirus infusion into the LAD. Gene transfer efficiency varied with choice of viral vector, with use of VEGF, adenosine, or nitroglycerin, and with calcium concentration. The best results were obtained by manipulation of physical parameters. Simultaneous infusion of adenovirus through both left anterior descending artery and great cardiac vein resulted in gene transfer to 78+/-6% of myocytes in a larger target area. This method was well tolerated by the animals. We demonstrate targeted, homogeneous, high efficiency gene transfer using a method that should be transferable for eventual human usage.

Percutaneous intracoronary delivery of SERCA gene increases myocardial function: a tissue Doppler imaging echocardiographic study

The aim of this study was to examine the efficiency of adenovirus-mediated overexpression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1a) gene in a realistic model based on percutaneous intracoronary delivery and on noninvasive functional monitoring. Catheter-based selective coronary delivery of saline or adenoviruses (Ad.CMV.SERCA1a or Ad.CMV.lacZ, 10(10) plaque-forming units) was performed in the circumflex artery of rabbits. Effects were assessed and compared by using serial Doppler echocardiography, hemodynamics, and measurements of SERCA protein and Ca(2+) uptake activity. On day 3, a 21% increase in SERCA proteins and a 37% increase in the maximal rate of Ca(2+) uptake were observed in the transfected left ventricular (LV) walls of Ad.CMV.SERCA1a rabbits. Baseline hemodynamics and conventional echographic measurements of global LV function were poorly affected. In contrast, tissue Doppler imaging (TDI) was able to assess a strong increase in the baseline function of transfected LV walls, as assessed with maximal wall velocities (+32% and +43%, respectively) and strain rates (+18% and +30%, respectively). TDI parameters were closely related to the maximal rate of Ca(2+) uptake (r(2) = 0.68 for the systolic strain rate). Serial TDI analysis during follow-up showed that the effects lasted for 7 days and were no longer detectable 15 days after adenoviruses injection. In conclusion, LV function can be increased by adenovirus-mediated overexpression of SERCA in a clinically relevant model, and TDI provides an accurate and noninvasive tool for monitoring effects on global as well as regional myocardial function.

Transthoracic direct current shock facilitates intramyocardial transfection of naked plasmid DNA infused via coronary vessels in canines

Catheter-mediated, percutaneous, transluminal delivery of naked plasmid DNA (pDNA) into myocardium may offer a valuable strategy to heart diseases. Here, we examined whether clinically available transthoracic direct current (DC) shock improves intracoronary naked DNA transfection into myocardium. Plasmid vector encoding the GL3 luciferase was infused retrogradely into the coronary veins of beagle dogs, whereas another pDNA solution was infused into the left coronary artery. During and after these procedures, the coronary venous sinus was occluded by balloon, and transthoracic DC shock of 200 J was applied immediately after the infusions. Without DC shock, no remarkable increase in luciferase activity was demonstrated in any part of the left ventricular myocardium. In the presence of DC pulsation, significant luciferase expression was detected in the regions that were supplied by left anterior descending coronary artery (LAD), whereas the gene expression in the right coronary artery (RCA) regions was much less drastic. X-gal (5-bromo-4-chloro-3-indolyl-beta-D-galactoside) staining of cardiac cross-sections also revealed regional expression of beta-galactosidase. Immunohistochemical examinations of heart cryosections revealed that cardiomyocytes in LAD regions successfully expressed transgene product. The present system may enable a new strategy for myocardial gene therapy, without any special device or technique other than cardiac catheterization and DC cardioversion that are generally performed in ordinary hospitals.

Catheter-mediated subselective intracoronary gene delivery to the rabbit heart: introduction of a novel method

BACKGROUND

Recent studies suggest that gene therapy using replication-deficient adenoviruses will benefit treatment of cardiovascular diseases including heart failure. A persistent hurdle is the effective and reproducible delivery of a transgene to the myocardium with minimal iatrogenic morbidity. In this study, we sought to design a relatively non-invasive percutaneous gene delivery system that would maximize cardiac transgene expression and minimize mortality after intracoronary adenovirus injection.

METHODS

Adult rabbits received a left circumflex coronary artery (LCx) infusion of 5x10(11) total viral particles of an adenovirus containing the marker transgene beta-galactosidase (Adeno-betaGal) via either a continuous infusion method utilizing an oxygenated, normothermic, physiologic pH Krebs solution driven by a Langendorff apparatus (n=12) or a timed bolus and set concentration at a constant infusion rate to the LCx (n=12). Six rabbits underwent global transgene delivery via an invasive method involving intraventricular delivery and aortic root cross-clamping. The efficacy of transgene expression via these three distinct delivery methods was determined in the left ventricle at 5 days by histological staining and colorimetric quantification assay.

RESULTS

While the open-chest, aortic cross-clamping method provides the highest level of gene expression throughout the heart, the morbidity of this procedure is clinically prohibitive. Percutaneous LCx delivery of Adeno-betaGal using the Langendorff apparatus was associated with the lowest morbidity and mortality while still supporting significant myocardial gene expression.

CONCLUSIONS

Percutaneous delivery of an adenovirus solution using a continuous infusion of oxygenated Krebs solution via a Langendorff apparatus appears to be a gene delivery modality offering the best compromise of gene expression and clinical utility to maximize any potential therapeutic outcome.

Catheter-based antegrade intracoronary viral gene delivery with coronary venous blockade

The purpose of this study is to evaluate the feasibility of percutaneous antegrade myocardial gene transfer (PAMGT). A consistent and safe technique for in vivo gene transfer is required for clinical application of myocardial gene therapy. PAMGT with concomitant coronary venous blockade was performed in 12 swine. The myocardium was preconditioned with 1 min of occlusion of the left anterior descending and left circumflex arteries. The anterior interventricular vein was occluded during left anterior descending artery delivery, and the great cardiac vein at the entrance of the middle cardiac vein was occluded during left circumflex artery delivery. With arterial and venous balloons inflated (3 min) and after adenosine (25 mug) injection, PAMGT was performed by antegrade injection of an adenoviral solution (1 ml of 10(11) plaque-forming units in each coronary artery) carrying beta-galactosidase or saline through the center lumen of the angioplasty balloon. In one set of animals, PAMGT was performed with selective coronary vein blockade (n = 9); in another set of animals, PAMGT was performed without coronary vein blockade (n = 5). At 1 wk after gene delivery, the animals were killed. Quantitative beta-galactosidase analysis was performed in the left and right ventricular walls. PAMGT was successfully performed in all animals with and without concomitant occlusion of the coronary veins. Quantitative beta-galactosidase analysis showed that PAMGT with coronary blockade was superior to PAMGT without coronary blockade. beta-Galactosidase activity increased significantly in the beta-galactosidase group compared with the saline group: 1.34 +/- 0.18 vs. 0.81 +/- 0.1 ng (P </= 0.01) in the left ventricular wall and 0.91 +/- 0.1 vs. 0.66 +/- 0.07 ng (P </= 0.05) in the right ventricular wall. PAMGT with selective coronary venous blockade is feasible, reproducible, and safely achieved in a large-animal model.

Nitroprusside increases gene transfer associated with intracoronary delivery of adenovirus

Efficient gene transfer by vectors that can be easily delivered to target organs is desirable in clinical gene therapy. We tested the hypothesis that intracoronary infusion of the nitric oxide donor nitroprusside would increase the efficiency of adenovirus vector-mediated gene transfer to the heart. Intracoronary delivery of an adenovirus encoding murine adenylyl cyclase type VI (Ad.AC(VI)) was performed in adult pigs with and without simultaneous intracoronary infusion of nitroprusside. Animals were killed 12-14 days after Ad.AC(VI) delivery and myocardial adenylyl cyclase activity was measured. Addition of nitroprusside during intracoronary infusion of Ad.AC(VI) was associated with a 4-fold increase in cAMP-generating capacity in the left ventricle. Transgene expression was confirmed by immunoblotting. Intracoronary nitroprusside produced mild dose-dependent changes in blood pressure and heart rate during infusion. Intracoronary nitroprusside infusion is a safe and effective means to increase the extent of cardiac gene transfer with intracoronary delivery of adenovirus vectors.

Indirect intracoronary delivery of adenovirus encoding adenylyl cyclase increases left ventricular contractile function in mice

We performed indirect intracoronary delivery of adenovirus vectors in mice and explored techniques including hypothermia and pharmacological means to increase cardiac gene transfer. Mice were maintained in a normothermic state or cooled to 25°C. The aorta or both the pulmonary artery and aorta were clamped while a needle was advanced into the left ventricular cavity to deliver adenovirus vectors encoding enhanced green fluorescent protein (EGFP) or murine adenylyl cyclase type VI (ACVI) with saline, sodium nitroprusside, acetylcholine, or serotonin. Clamping was maintained for 30 s (normothermia) or 2 min (25°C) after adenovirus administration. Mice were killed 7 or 21 days later, and hearts were examined for EGFP expression. Compared with clamping the aorta alone and with no cooling, gene transfer was increased as follows: 1) 1.3-fold with hypothermia to extend dwell time; 2) 4.5-fold by clamping the aorta and the pulmonary artery; 3) 11.4-fold with nitroprusside administration; 4) 11.8-fold with serotonin addition, and 5) 14.3-fold with acetylcholine delivery. Gene expression remained substantial at 21 days, and no significant inflammatory response was seen. Efficacy of the method was tested by performing gene transfer of adenovirus encoding ACVI. Fourteen days after gene transfer, hearts isolated from mice that received adenovirus encoding ACVIshowed increased contractile function. Indirect intracoronary delivery of adenovirus vectors in mice is associated with efficient cardiac gene transfer and increased left ventricular function after ACVIgene transfer.

Vascular transfer of adenovirus is augmented by nitric oxide in the rat heart

Reversible opening of the endothelial barrier remains a major obstacle when hearts are transfected via the coronary system. Our aim was to establish an experimental system permitting the continuous analysis of vascular transfer of virus in the intact heart. Isolated saline-perfused rat hearts were inverted and covered with a latex cap to collect interstitial transudate (IT) on the pericardial surface. Adenovirus (10(9) pfu/ml) was stably labeled with rhodamine fluorescent dye. Analysis of IT and coronary perfusate revealed that under baseline conditions, adenovirus in the IT reached 75% of its vascular concentration within 3 min. The nitric oxide-donors S-nitroso-N-acetyl penicillamine (SNAP) and bradykinin (BK) were the most effective substances to increase total IT volume and adenoviral interstitial concentration. Perfusion with 9% serum markedly reduced IT volume flow and delayed the SNAP/BK effect. Our findings demonstrate that SNAP and BK effectively increased coronary transfer of adenovirus suggesting that the inverted isolated heart is a suitable model to optimize vascular transfer of virus under standardized conditions.

A minimally invasive approach for efficient gene delivery to rodent hearts

Transcoronary gene delivery represents a desirable option to achieve global myocardial transgene expression but still requires aggressive surgical preparation in rodents. We therefore developed a catheter-based approach for cardiac gene transfer in the closed chest rat. A double-lumen balloon catheter was used to create aortic occlusion for specific infusion of adenoviral vectors carrying a beta-galactosidase transgene (1 x 10(11) PFU) into the coronaries. Simultaneously, venous return was obstructed by a second balloon catheter in the right atrium. To prolong viral incubation time, we induced a transient cardiac arrest (2 and 5 min) by a combination of acetylcholine and the beta-receptor antagonist, esmolol. At 72 h after transfection, the hearts showed a homogeneous and widespread beta-galactosidase expression, and the transduction efficiency increased and up to about 43% of cardiac myocytes (histochemistry) with a 400-fold increase of beta-galactosidase activity (luminescence assay) compared to sham-operated hearts. Pharmacological treatment aimed at increasing vascular permeability (SNAP and histamine) did not bring about synergistic effects on transfection efficiency. In addition, the method using high intracoronary pressure delivery (>300 mmHg) in a single-pass manner resulted in rather sparse beta-galactosidase expression in the myocardium (3-5% of cardiac myocytes). Therefore, the percutaneous gene delivery system described here provides a simple and minimally invasive procedure that represents a novel strategy for a homogeneous and highly efficient in vivo gene transfer to rodent hearts. Our results also suggest that prolongation of viral incubation time is an effective means for achieving highly efficient myocardial gene transduction.

Ultrasound-targeted microbubble destruction can repeatedly direct highly specific plasmid expression to the heart

BACKGROUND

Noninvasive, tissue-specific delivery of therapeutic agents would be a valuable clinical tool. We have previously shown that ultrasound-targeted microbubble destruction can direct expression of an adenoviral reporter to the heart. The present study shows that this method can be applied to selectively deliver plasmid vectors to the heart.

METHODS AND RESULTS

We used albumin and lipid microbubbles containing plasmids with a luciferase transgene to target the heart in rats. After 4 days, organs were harvested and analyzed for reporter gene expression. In a second set of experiments, the hearts of rats treated with plasmids were harvested at various time points during a 4-week period. Both luciferase activity and mRNA concentrations were measured. Luciferase transfection with plasmids showed highly specific gene expression in the heart, with hardly any activity in control organs. Time course evaluation showed high transgene expression in the first 4 days, with a rapid decline thereafter. Repeated treatment produced a second peak of transgene expression with similar decay.

CONCLUSIONS

Ultrasound-mediated destruction of microbubbles directs plasmid transgene expression to the heart with much greater specificity than viral vectors and can be regulated by repeated treatments. This noninvasive technique is a promising method for cardiac gene therapy.