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

Novel therapeutic approaches for the management of cystic fibrosis

Cystic fibrosis (CF) is a genetic condition characterised by the build-up of thick, sticky mucus that can damage many of the body's organs. It is a life-long disease that results in a shortened life expectancy, often due to the progression of advanced lung disease. Treatment has previously targeted the downstream symptoms such as diminished mucus clearance and recurrent infection. More recently, significant advances have been made in treating the cause of the disease by targeting the faulty gene responsible. Hope for the development of potential therapies lies with ongoing research into new pharmacological agents and gene therapy. This review gives an overview of CF, and summarises the current evidence regarding the disease management and upcoming strategies aimed at treating or potentially curing this condition.

Overview of the Components of Cardiac Metabolism

Metabolism in organs other than the liver and kidneys may play a significant role in how a specific organ responds to chemicals. The heart has metabolic capability for energy production and homeostasis. This homeostatic machinery can also process xenobiotics. Cardiac metabolism includes the expression of numerous organic anion transporters, organic cation transporters, organic carnitine (zwitterion) transporters, and ATP-binding cassette transporters. Expression and distribution of the transporters within the heart may vary, depending on the patient’s age, disease, endocrine status, and various other factors. Several cytochrome P450 (P450) enzyme classes have been identified within the heart. The P450 hydroxylases and epoxygenases within the heart produce hydroxyeicosatetraneoic acids and epoxyeicosatrienoic acids, metabolites of arachidonic acid, which are critical in regulating homeostatic processes of the heart. The susceptibility of the cardiac P450 system to induction and inhibition from exogenous materials is an area of expanding knowledge, as are the metabolic processes of glucuronidation and sulfation in the heart. The susceptibility of various transcription factors and signaling pathways of the heart to disruption by xenobiotics is not fully characterized but is an area with implications for disruption of normal postnatal development, as well as modulation of adult cardiac health. There are knowledge gaps in the timelines of physiologic maturation and deterioration of cardiac metabolism. Cross-species characterization of cardiac-specific metabolism is needed for nonclinical work of optimum translational value to predict possible adverse effects, identify sensitive developmental windows for the design and conduct of informative nonclinical and clinical studies, and explore the possibilities of organ-specific therapeutics.

A Needleless Liquid Jet Injection Delivery Approach for Cardiac Gene Therapy

Fundamentally, cardiac gene therapy clinical trials have demonstrated that route efficiency is paramount in achieving maximum myocardial expression within safety limits. Gene transfer phenomena are largely influenced by physical transport principles (i.e., pressure, residence time, dispersion trafficking, mechanical resistance) that are independent of therapeutic characteristics. An alternative to intracoronary infusion methods, in an effort to improve efficiency in terms of cardiac specificity, is direct myocardial delivery via surgical injection. Direct injection methods circumvent the blood's immunological components and the cardiac system's native anatomical barriers by directly administering product into the myocardium. In addition, this approach offers the advantage of precise site selection. Two unresolved problems with direct delivery wherein the novel needleless liquid jet approach may resolve are: (1) initial therapeutic retention and (2) subsequent host responses associated with highly focal expression.In this protocol, we present a novel approach to improve direct cardiac gene delivery using a needleless liquid jet methodology. The liquid jet application is essentially a device concept that accelerates and disperses the therapeutic at a targeted myocardial site. The core hypothesis offered is that this approach, with optimized settings, could result in increased therapeutic retention in the initial delivery phase. This would theoretically result in more total myocardial expression per dose while at the same time providing a more homogenous profile around the injection site. Therefore, this would increase efficiency in terms of transduced muscle per delivery site and offer a significant improvement to standard intramuscular injection.

Molecular Cardiac Surgery with Recirculating Delivery (MCARD): Procedure and Vector Transfer

Despite progress in clinical treatment, cardiovascular diseases are still the leading cause of morbidity and mortality worldwide. Therefore, novel therapeutic approaches are needed, targeting the underlying molecular mechanisms of disease with improved outcomes for patients. Gene therapy is one of the most promising fields for the development of new treatments for the advanced stages of cardiovascular diseases. The establishment of clinically relevant methods of gene transfer remains one of the principal limitations on the effectiveness of gene therapy. Recently, there have been significant advances in direct and transvascular gene delivery methods. The ideal gene transfer method should be explored in clinically relevant large animal models of heart disease to evaluate the roles of specific molecular pathways in disease pathogenesis. Characteristics of the optimal technique for gene delivery include low morbidity, an increased myocardial transcapillary gradient, esxtended vector residence time in the myocytes, and the exclusion of residual vector from the systemic circulation after delivery to minimize collateral expression and immune response. Here we describe myocardial gene transfer techniques with molecular cardiac surgery with recirculating delivery in a large animal model of post ischemic heart failure.

Liquid jet delivery method featuring S100A1 gene therapy in the rodent model following acute myocardial infarction

The S100A1 gene is a promising target enhancing contractility and survival post myocardial infarction (MI). Achieving sufficient gene delivery within safety limits is a major translational problem. This proof of concept study evaluates viral-mediated S100A1 overexpression featuring a novel liquid jet delivery (LJ) method. 24 rats after successful MI were divided into 3 groups (n=8 ea.): saline control (SA), ssAAV9.S100A1 (SS) delivery, and scAAV9.S100A1 (SC) delivery (both 1.2×10¹¹ viral particles). For each post MI rat, the LJ device fired three separate 100 μL injections into the myocardium. Following 10 weeks, all rats were evaluated with echocardiography, quantitative polymerase chain reaction (qPCR), and overall S100A1 and CD38 immune protein. At 10 weeks all groups demonstrated a functional decline from baseline, but the S100A1 therapy groups displayed preserved LV function with significantly higher ejection fraction %; SS group [60±3] and SC group [57±4] versus saline [46±3], p<0.05. Heart qPCR testing showed robust S100A1 in the SS [10,147±3993] and SC [35,155±5808] copies per 100 ng DNA, while off target liver detection was lower in both SS [40±40], SC [34,841±3164] respectively. Cardiac S100A1 protein expression was [4.3±0.2] and [6.1±0.3] fold higher than controls in the SS and SC groups respectively, p<0.05.

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.

The road ahead: working towards effective clinical translation of myocardial gene therapies

During the last two decades the fields of molecular and cellular cardiology, and more recently molecular cardiac surgery, have developed rapidly. The concept of delivering cDNA encoding a therapeutic gene to cardiomyocytes using a vector system with substantial cardiac tropism, allowing for long-term expression of a therapeutic protein, has moved from hypothesis to bench to clinical application. However, the clinical results to date are still disappointing. The ideal gene transfer method should be explored in clinically relevant animal models of heart disease to evaluate the relative roles of specific molecular pathways in disease pathogenesis, helping to validate the potential targets for therapeutic intervention. Successful clinical cardiovascular gene therapy also requires the use of nonimmunogenic cardiotropic vectors capable of expressing the requisite amount of therapeutic protein in vivo and in situ. Depending on the desired application either regional or global myocardial gene delivery is required. Cardiac-specific delivery techniques incorporating mapping technologies for regional delivery and highly efficient methodologies for global delivery should improve the precision and specificity of gene transfer to the areas of interest and minimize collateral organ gene expression.