Cardiac Gene Delivery in Large Animal Models: Antegrade Techniques

Atrial Gene Painting in Large Animal Model of Atrial Fibrillation

Gene therapy appears promising as a targeted treatment of cardiac diseases. Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and also a major contributor to stroke, heart failure, and death. Mechanisms that initiate and sustain AF are associated with structural and electrophysiological remodeling in the whole atria. Selection of the appropriate gene delivery method is critical for transduction efficacy. The ideal gene delivery method to manage AF should provide widespread and sufficient exposure to the transgene in atria only that safely maintains the homeostasis of the heart without off-target expression. All these requirements can be achieved using atrial gene painting that is directly applied to the atrial epicardial surface. In this chapter, we present the advantages of atrial gene painting and the experimental method, as applied to a large animal model of AF.

Updates on Cardiac Gene Therapy Research and Methods: Overview of Cardiac Gene Therapy

Gene therapy has made a significant progress in clinical translation over the past few years with several gene therapy products currently approved or anticipating approval for clinical use. Cardiac gene therapy lags behind that of other areas of diseases, with no application of cardiac gene therapy yet approved for clinical use. However, several clinical trials for gene therapy targeting the heart are underway, and innovative research studies are being conducted to close the gap. The second edition of Cardiac Gene Therapy in Methods in Molecular Biology provides protocols for cutting-edge methodologies used in these studies. In this chapter, we discuss recent updates on cardiac gene therapy studies and provide an overview of the chapters in the book.

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.

AAV Vectors for Efficient Gene Delivery to Rodent Hearts

Currently, gene therapy is one of the most promising fields in biomedicine, with great therapeutic potential for an array of inherited and acquired diseases. Adeno-associated viral (AAV) vectors have emerged as promising tools to deliver selectively a therapeutic payload to target organs, including the heart. In this chapter, we describe the production and quality control of recombinant AAV (rAAV) vectors of the serotype 9, the most cardiotropic AAV serotype when delivered systemically in rodents. We also describe the systemic administration of rAAV vectors and the local delivery of rAAV vectors by direct intramyocardial injection. Taken together, the methods described in this chapter will allow the reader to deliver efficiently therapeutic genes to the rodent heart, both globally and regionally.

The Gene Therapy Resource Program: A Decade of Dedication to Translational Research by the National Heart, Lung, and Blood Institute

Over a 10-year period, the Gene Therapy Resource Program (GTRP) of the National Heart Lung and Blood Institute has provided a set of core services to investigators to facilitate the clinical translation of gene therapy. These services have included a preclinical (research-grade) vector production core; current Good Manufacturing Practice clinical-grade vector cores for recombinant adeno-associated virus and lentivirus vectors; a pharmacology and toxicology core; and a coordinating center to manage program logistics and to provide regulatory and financial support to early-phase clinical trials. In addition, the GTRP has utilized a Steering Committee and a Scientific Review Board to guide overall progress and effectiveness and to evaluate individual proposals. These resources have been deployed to assist 82 investigators with 172 approved service proposals. These efforts have assisted in clinical trial implementation across a wide range of genetic, cardiac, pulmonary, and blood diseases. Program outcomes and potential future directions of the program are discussed.

Reduced longitudinal contraction is associated with ischemic mitral regurgitation after posterior MI

The role of left ventricular (LV) longitudinal contraction in ischemic mitral regurgitation (MR) remains unclear. We hypothesized that reduced longitudinal contraction disrupts normal mitral valve plane displacement during systole and leads to mitral valve tethering, thereby inducing ischemic MR. Twenty-three Yorkshire pigs underwent induction of different-sized posterior myocardial infarction (MI) using a percutaneous approach. The incidence of MR and its association with LV longitudinal strain were examined using speckle-tracking echocardiography at 1 mo post-MI to determine their relationship. A total of 17 pigs survived MI and completed the study. Pigs developed no more than mild MR after proximal left circumflex artery (LCx) occlusion (LCx group; n = 7). Addition of a first diagonal branch (D1) occlusion to LCx-MI (LCx + D1 group; n = 7) resulted in moderate to severe MR development 1 mo post-MI. LCx + D1 animals had lower longitudinal strain compared with the LCx group, whereas circumferential strain and LV rotation did not differ significantly. Posterolateral annular displacement toward the apex was significantly reduced in LCx + D1 animals, whereas the septal annular displacement was similar, suggesting an asymmetric mitral annular plane excursion in the LCx + D1 group. To exclude the contribution of papillary muscle infarction in MR development in our model, three pigs underwent obtuse marginal branch + D1 occlusion. None of these pigs developed significant MR after 1 mo. In conclusion, reduced longitudinal contraction contributes to the development of ischemic MR in a large posterior MI. NEW & NOTEWORTHY In this study, using our unique swine models of different-sized myocardial infarction, we showed, for the first time, that reduced longitudinal contraction contributes to the development of ischemic mitral regurgitation in a large posterior myocardial infarction. Our study adds new insights into the mechanisms of ischemic mitral regurgitation pathophysiology.

Protein Phosphatase Inhibitor-1 Gene Therapy in a Swine Model of Nonischemic Heart Failure

BACKGROUND

Increased protein phosphatase-1 in heart failure (HF) induces molecular changes deleterious to the cardiac cell. Inhibiting protein phosphatase-1 through the overexpression of a constitutively active inhibitor-1 (I-1c) has been shown to reverse cardiac dysfunction in a model of ischemic HF.

OBJECTIVES

This study sought to determine the therapeutic efficacy of a re-engineered adenoassociated viral vector carrying I-1c (BNP116.I-1c) in a preclinical model of nonischemic HF, and to assess thoroughly the safety of BNP116.I-1c gene therapy.

METHODS

Volume-overload HF was created in Yorkshire swine by inducing severe mitral regurgitation. One month after mitral regurgitation induction, pigs were randomized to intracoronary delivery of either BNP116.I-1c (n = 6) or saline (n = 7). Therapeutic efficacy and safety were evaluated 2 months after gene delivery. Additionally, 24 naive pigs received different doses of BNP116.I-1c for safety evaluation.

RESULTS

At 1 month after mitral regurgitation induction, pigs developed HF as evidenced by increased left ventricular end-diastolic pressure and left ventricular volume indexes. Treatment with BNP116.I-1c resulted in improved left ventricular ejection fraction (-5.9 ± 4.2% vs. 5.5 ± 4.0%; p < 0.001) and adjusted dP/dt maximum (-3.39 ± 2.44 s^-1 vs. 1.30 ± 2.39 s^-1; p = 0.007). Moreover, BNP116.I-1c-treated pigs also exhibited a significant increase in left atrial ejection fraction at 2 months after gene delivery (-4.3 ± 3.1% vs. 7.5 ± 3.1%; p = 0.02). In vitro I-1c gene transfer in isolated left atrial myocytes from both pigs and rats increased calcium transient amplitude, consistent with its positive impact on left atrial contraction. We found no evidence of adverse electrical remodeling, arrhythmogenicity, activation of a cellular immune response, or off-target organ damage by BNP116.I-1c gene therapy in pigs.

CONCLUSIONS

Intracoronary delivery of BNP116.I-1c was safe and improved contractility of the left ventricle and atrium in a large animal model of nonischemic HF.