**2. Therapeutic options: why gene therapy?**

Most frequently, four main clinical forms are described, meaning hypertrophic, dilated, and restrictive types as well as arrhythmogenic CM. These diseases have many causes, signs, symptoms, and treatments. We exclude ischemic cardiopathies from this overview, and focus more precisely on disorders of the heart muscle of non-ischemic origin. This does, however, not exclude anomalies of the perfusion of the myocardium, because pathophysiology of these

Diagnosis of non-ischemic CM is a challenging process that influences patient morbidity and mortality. Multiple biomarkers and imaging tools contribute to the adequate ranking of the clinical presentation of these diseases. More recently, nuclear magnetic resonance (NMR) imaging appeared as a robust diagnostic tool that offers various techniques to assess the structure, function, perfusion, and scarring of myocardial tissue, thus providing better understanding of the underlying causes of CMs [9–12]. At a molecular level, genotyping identifies precisely the causal mutations in inherited forms of CMs. Moreover, a systems biology approach can investigate more fully the molecular profiles of different phenotypic

From a pathophysiological and diagnostic perspective, it might be useful to consider a stratification of CMs slightly different from the clinical classification. Considering the various genes that can trigger the development and evolution of a CM, we propose to group inherited diseases as cytoskeletal CMs or cytoskeletalopathies, sarcomeric CMs or sarcomyopathies, and

Different structural alterations of the myocardium contribute in varying degrees to the different forms of the diseases, but common features may represent as many therapeutic targets.

The focus of more extensive cellular degeneration is one of the histological hallmarks of CM [13,14]. Necrosis is not the only mechanism leading to cell death. Apoptosis, or programmed cell death, is a highly regulated and active process that contributes to the maintenance of adult cardiac tissue [15]. Myocyte cell death is implicated in the architectural rearrangement occurring in the surviving myocardium. This remodelling leads to heterogeneity in the myocardial structure, created by the altered behaviour of non-myocyte cells, particularly cardiac fibroblasts, which are responsible for myocardial collagen metabolism and fibrous tissue accumulation. It may largely explain the appearance of diastolic and/or systolic myocardial failure [15]. Adverse left ventricular remodelling leads to alteration in the structure (dimension, mass, shape) of the heart that might at the beginning of the process be considered as compensatory for the disease process, but at the end will severely impair cardiac function. Remodelling is also a prominent feature of electrophysiological properties of the myocardium, translated as clinical presentation such as atrial fibrillation, flutter, complete heart

Considering the remodelling process as a deleterious end effect, one can raise the question of potential reverse remodelling. Could that be an option for remission or cure of CM? It has been shown that prolonged mechanical unloading of failing hearts can preserve myocardial contractility but impairs relaxation. Could gene therapy provide new therapeutic options for

diseases is usually complex, interleaving different mechanisms.

170 In Vivo and Ex Vivo Gene Therapy for Inherited and Non-Inherited Disorders

stages of CM.

those patients?

finally ion channel CMs or channelopathies.

block, ventricular ectopic pacing, and tachycardia.

Many medicines are used to treat CM and CHF, but despite this, CM and CHF remain leading causes of morbidity and mortality even in developed countries. Correcting hemodynamic imbalances, such as fluid control (preload) or vascular resistance control (afterload), remains primordial, but cannot change the myocardial contractility *per se* (**Figure 1**). Fundamentally, determinants of cardiac output are the same as those of myocardial energy consumption. Therefore, tackling the problem of decreased contractility raises in parallel the problem of increased energy requirements. Several attempts to increase inotropism on a chronic basis led to overall negative results because energy consumption exceeded production. Gene therapy might offer new therapeutic options. The pressure–volume relationship demonstrates the contracting and relaxing portions of the cardiac cycle (**Figure 2**). The slope of the end-systolic

**Figure 1.** Determinants of cardiac output (CO). CO is the resultant of stroke volume, the difference between enddiastolic and end-systolic volumes times the heart rate. According to the Frank–Starling law, preload influences CO positively. With developing heart failure, CO is negatively influenced by afterload. Contractility represents the primary inotropic capacity of the myocardium.

pressure–volume relationship represents the most objective measure of the intrinsic contractile capacity of the myocardium.

Similarly, management of CHF patients frequently takes advantage of rhythm control (pharmacologic or pacemakers/implantable cardioverter defibrillator). Gene therapy might represent a new way to address this topic by recreating new endogenous biological pacemakers rather than relying on electronic devices.

Recent clinical trials [17–19] have not only pinpointed the importance of inflammation but moreover the therapeutic potentialities of selectively targeting some cytokines. At a preclinical level, glycoprotein-130 (gp130) has been identified as a potential new target [20–22]. It is now established that with gp-130, the common receptor of IL-6 is elevated in patients with chronic heart failure. Hilfiker-Kleiner et al. have shown that mice carrying a cardio-specific mutation of gp-130 have a normal myocardial phenotype at baseline. However, induction of an experimental myocardial infaction leads to development of heart failure and increased mortality. Moreover, these observations were associated with increased expression of complement-activating mannose-binding lectin [23]. Thus, this animal model suggested a link between IL-6 and chronic myocardial injury induced by complement activation.

gene therapy, but nucleic acids can interfere in a very selective way with proteins. Targeting proteins of the intrinsic pathway of the coagulation might achieve safe and efficient thrombus control without the usual risk of bleeding that conventional anticoagulants share. Furthermore, one should keep in mind that initiation of the intrinsic pathway is intimately linked to inflammation via kinins and complement. Nucleic acid might represent a new class

**Figure 2.** Pressure–volume relationship. The pressure–volume curve for the left ventricle is represented as a pressure vs. volume plot. The slope of the end-systolic pressure–volume relationship indicates the intrinsic contractile capacity of the myocardium independently of the hemodynamic load conditions. Compared to a control curve (dark lines), cardiomyopathy (light lines) is characterized by a decreased slope among other hallmarks. Gene therapy would aim at

Gene Therapy for Cardiomyopathies http://dx.doi.org/10.5772/intechopen.80478

Surgery represents an important therapeutic option in the arsenal for managing CM and CHF patients. The surgical approach can consist of either specific procedures such as septal myomectomy in hypertrophic CM (HCM), coronary artery bypass graft surgery, or more generally left ventricular assist devices as a "bridge to transplant" or destination therapy [24]. Transplantation remains the reference treatment for end-stage CHF and for people who have failed other treatment options. It might be surprising to refer to surgery in the context of gene therapy, but one should not forget that most initial clinical trials have included terminally

of drugs in this context.

preserving or restoring normal contractility.

Cardiac myofibroblasts respond to a large number of proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides), and hormones (e.g. noradrenaline), the levels of which are increased in the remodelling heart. Reducing myocardial remodelling specifically via modulatory effects on cardiac fibroblasts might represent further new therapeutic targets.

Anticoagulants in the context of CHF are an important therapeutic class for those subgroups of patients at high risk for abnormal clotting. Anticoagulation might appear inappropriate for

pressure–volume relationship represents the most objective measure of the intrinsic contrac-

**Figure 1.** Determinants of cardiac output (CO). CO is the resultant of stroke volume, the difference between enddiastolic and end-systolic volumes times the heart rate. According to the Frank–Starling law, preload influences CO positively. With developing heart failure, CO is negatively influenced by afterload. Contractility represents the primary

Similarly, management of CHF patients frequently takes advantage of rhythm control (pharmacologic or pacemakers/implantable cardioverter defibrillator). Gene therapy might represent a new way to address this topic by recreating new endogenous biological pacemakers

Recent clinical trials [17–19] have not only pinpointed the importance of inflammation but moreover the therapeutic potentialities of selectively targeting some cytokines. At a preclinical level, glycoprotein-130 (gp130) has been identified as a potential new target [20–22]. It is now established that with gp-130, the common receptor of IL-6 is elevated in patients with chronic heart failure. Hilfiker-Kleiner et al. have shown that mice carrying a cardio-specific mutation of gp-130 have a normal myocardial phenotype at baseline. However, induction of an experimental myocardial infaction leads to development of heart failure and increased mortality. Moreover, these observations were associated with increased expression of complement-activating mannose-binding lectin [23]. Thus, this animal model suggested a link

Cardiac myofibroblasts respond to a large number of proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides), and hormones (e.g. noradrenaline), the levels of which are increased in the remodelling heart. Reducing myocardial remodelling specifically via modulatory effects on cardiac

Anticoagulants in the context of CHF are an important therapeutic class for those subgroups of patients at high risk for abnormal clotting. Anticoagulation might appear inappropriate for

between IL-6 and chronic myocardial injury induced by complement activation.

fibroblasts might represent further new therapeutic targets.

tile capacity of the myocardium.

inotropic capacity of the myocardium.

rather than relying on electronic devices.

172 In Vivo and Ex Vivo Gene Therapy for Inherited and Non-Inherited Disorders

**Figure 2.** Pressure–volume relationship. The pressure–volume curve for the left ventricle is represented as a pressure vs. volume plot. The slope of the end-systolic pressure–volume relationship indicates the intrinsic contractile capacity of the myocardium independently of the hemodynamic load conditions. Compared to a control curve (dark lines), cardiomyopathy (light lines) is characterized by a decreased slope among other hallmarks. Gene therapy would aim at preserving or restoring normal contractility.

gene therapy, but nucleic acids can interfere in a very selective way with proteins. Targeting proteins of the intrinsic pathway of the coagulation might achieve safe and efficient thrombus control without the usual risk of bleeding that conventional anticoagulants share. Furthermore, one should keep in mind that initiation of the intrinsic pathway is intimately linked to inflammation via kinins and complement. Nucleic acid might represent a new class of drugs in this context.

Surgery represents an important therapeutic option in the arsenal for managing CM and CHF patients. The surgical approach can consist of either specific procedures such as septal myomectomy in hypertrophic CM (HCM), coronary artery bypass graft surgery, or more generally left ventricular assist devices as a "bridge to transplant" or destination therapy [24]. Transplantation remains the reference treatment for end-stage CHF and for people who have failed other treatment options. It might be surprising to refer to surgery in the context of gene therapy, but one should not forget that most initial clinical trials have included terminally ill patients. Thereby, in terms of therapeutic efficiency and risk/benefit ratio, initial evaluations will refer to outcomes of surgical procedures. The gene therapist should be aware of the competing therapeutic strategies.

was able to delay the onset of an overt CM. More generally, when designing a gene therapy strategy, one should consider whether the defective gene should be rescued or whether other

Gene Therapy for Cardiomyopathies http://dx.doi.org/10.5772/intechopen.80478

Delta-sarcoglycan (dSG)-deficient hamsters represent a well-characterized genetically determined model of a CM. Phenotypically these animals develop a dilated cardiomyopathy (DCM) with terminal heart failure over a rather short time span as they die as mid-aged adults [27,28]. From the perspective of gene therapy they represent a very useful model. Beyond the clear phenotype, the causal genetic mutation is known, coding sequences are readily available, and transmission is autosomal recessive. A single allele correction can correct or at least clearly improve the phenotype when administered in young animals [29]. Some authors observed even more than a simple phenotypic rescue as the lifespan of these animals seemed

However, unlike dSG, coding sequences of some normal alleles can be very extensive, the most extreme case being dystrophin with a full-length cDNA of more than 11 kb. Several strategies can be considered. Given some structural specificities, reengineering of the active pharmaceutical ingredient (API) can be performed while retaining therapeutic potential. Thus, gene therapy should not simply be considered as a substitution of defective alleles. Hence, truncated forms of dystrophin have proven to alleviate pathologic phenotypes in several experiment models [32,33].

Similarly, it was possible to show that editing the intrinsic messenger RNA can lead to coding of a functional protein. Exon skipping is used to restore the reading frame within a gene. The mechanism behind exon skipping is a mutation-specific antisense oligonucleotide. An antisense oligonucleotide is a synthesized short nucleic acid polymer that will bind to the mutation site in the pre-messenger RNA to induce exon skipping. In the context of Duchenne muscular dystrophy (DMD) the genetic mutation that leads to Becker muscular dystrophy (BMD) is an in-frame deletion. Exon skipping can induce the expression of a truncated but functional dystrophin protein and thus switch the phenotype of some DMD-type mutations

Multiple arguments in favour of the feasibility of cardiac gene therapy have been generated over time. However, these experiments raise new questions. Most non-clinical studies were carried out on well-characterized model-rescuing defective genotypes and avoiding or delaying the development of a pathological phenotype. So referring to clinical settings, this mimics

In this setting, gene therapy would basically be a prophylactic option to avoid development of a pathological phenotype, but are we ready for a gene therapy that would be mainly preventive? What would an acceptable risk/benefit ratio be in that case? Ideally in the context of preventive medicine, gene therapy of an inherited monogenic disorder should by homologous recombination correct most if not all of the affected cells without any off-target adverse effects. Gene therapy has not yet reached this level of maturity. Nevertheless, this does not

genes involved in heart failure development and progression should be targeted.

**3.2. Preclinical models of CM**

to increase [30,31].

to the phenotype of a BMD-type mutation [34,35].

mean that such options cannot be tested in the future.

mainly presymptomatic situations.

So far, none of the existing treatments have definitively changed the fate of CM and CHF. There is thus space for new drug developments and gene therapy might help to solve some of the intrinsic hurdles of CM and CHF. For instance, none of the existing treatments really change myocardial contractility without excessively increasing oxygen consumption.

Advances in gene transfer vectors, development of new vector delivery methods, and discovery of new gene targets continue to fuel our motivation to use this approach in routine bedside care [25,26].
