Perspective of gene therapy for heart failure

Tyumen State Medical University, Russia

Chronic heart failure remains one of the most prevalent reasons of global mortality despite the fact that modern drugs slow the progression of the disease. There is a need of a new therapeutic approach for heart failure treatment. Recent achievements in understanding the molecular basis of myocardial dysfunction caused by heart failure provide more effective gene transfer technologies allowing accessible gene-based therapy emergence. Nowadays heart failure gene therapy moves from experimental tool to the threshold of becoming viable clinical option.

Possible options of gene therapy are:

• 1.    Targeting the β-adrenergic system – Several genebased experiments tested the hypothesis that genetic manipulation of the myocardial β-AR system can enhance cardiac function.

• a.    Overexpression of β-AR: Overexpression of β-AR was initially tested as a simple way to overcome β-AR downregulation. Transgenic mice overexpressing the human β1-ARs suffered from severe cardiomyopathy [1]. In contrast, mice with cardiac overexpression of β2-AR demonstrated increased basal myocardial adenylyl cyclase activity with increased left ventricular function [2]. Both direct and intracoronary myocardial delivery of Adenovirus containing the human β2-AR transgene has resulted in enhanced cardiac performance in rodents and mammalian models 8990.

• b.    Inhibition of G protein-coupled receptor kinases (GRKs): GRK2 is the most expressed GRK in the heart. It has been implicated in the pathogenesis of dysfunctional cardiac β-AR signaling accounting for a deleterious activity in the failing heart [3]. Using intracoronary adenovirus-mediated βARKct transgene delivery to rabbits 3 weeks after induced myocardial infarction demonstrated a marked reversal of ventricular dysfunction [4]. More recent studies have focused on overexpressing βARKct in large animal models [5].

• c.    Activation of cardiac adenylycyclase (AC) expression: Overexpression of AC VI in transgenic mice resulted in improved cardiac function in response to adrenergic stimulation along with increased cyclic adenosine monophosphate production in isolated cardiac myocytes [6]. The favorable effects of AC VI in preclinical studies are encouraging and this approach is currently under investigation for initiation of clinical trials in patients with heart failure (HF) [7].

• 2.    Targeting Ca2+ cycling proteins-HF is characterized by multiple defects in Ca2-handling proteins involved

in excitation-contraction coupling. Reversal of those defects by gene therapy techniques has shown very promising results.

• a.    Overexpression of sarcoplasmic reticulum Ca2– ATPase (SERCA2a): Long-term overexpression of SER-CA2a by intracoronary delivery of adeno-associated virus (AAV) carrying SERCA2a has been associated with preserved systolic function and improved ventricular remodeling in a swine volume-overload model of HF [8]. Beyond their effects on enhancing contractility, SERCA2a gene transfer has been shown to restore the energetic state of the heart [9-12] both in terms of energy supply and utilization, decrease ventricular arrhythmias [13, 14], and enhance coronary flow through activation of eNOS in endothelial cells [15].

• b.    Phospholamban (PLN) inhibition: Decreasing PLN in human cardiac myocytes showed an improvement in contraction and relaxation velocities similar to the benefit seen with gene transfer of SERCA2a [16].

• c.    Active Inhibitor-1 (I-1) and Inhibition of phosphatase 1 (PP1): HF is associated with elevated PP1 activity in humans resulting in dephosphorylation of PLN. Overexpression of PP1 or ablation of I-1 in murine hearts has been associated with decreased β-AR-mediated contractile responses, depressed cardiac function and premature death consistent with HF [17-19]. I-1 expression ameliorated ischemia/reperfusion-induced injury by reducing the infarct size and improving contractile recovery in addition to decreasing biomarkers of apoptosis and ER stress response [17-19].

• d.    S100A1: S100 is part of a family of Ca2-modulated proteins implicated in intracellular regulatory activities. It promotes cardiac contractile and relaxation function through enhancing the activity of both RYRs and SER-CA2a [16]. In a rat model of HF, AAV6-mediated longterm expression of S100A1 resulted in a sustained in vivo reversal of LV dysfunction and remodeling [21, 22]. More recently AAV9 gene transfer of S100A1 in a pre-clinical model of ischemic cardiomyopathy induced dramatic improvements in contractile function reinforcing the rationale that a clinical trial of S100A1 gene therapy for human heart failure should be forthcoming.

• e.    SUMO1: SUMOs are a family of peptides that alter the function of other proteins in cells through a post-translational modification described as sumoylation. Sumoylation is involved in the modulation of various intracellular processes. Increasing SUMO1 levels by AAV9 gene transfer led to a restoration of SERCA2a levels, improved hemodynamic performance, and reduced mortality among the animals with heart failure [23].

• 3.    Homing of stem cells—The SDF1/CXCR4 complex has emerged as a therapeutic target in ischemic heart failure [24] due to the ability of the SDF-1-CXCR4 system to promote the homing of stem cells to infracted myocardium. A clinical trial is underway to investigate the therapeutic benefit of SDF-1 overexpression in ischemic cardiomyopathy [25]. One recent report has shown increased ischemia-reperfusion injury in rat hearts overexpressing CXCR4 [26], while another report investigated the modulation of beta-adrenergic receptor signaling by SDF-1 and CXCR4 [27], raising interrogations over the potential complex interaction between these chemokines and the cardiovascular

• 4. Targeting cell death—In models of acute and subacute ischemia/reperfusion, overexpression of the anti-apoptotic protein Bcl-2, Akt or PI3 kinase reduces the rate of cardiomyocyte apoptosis and improved heart function [30]. In ischemia/reperfusion injury where apoptosis plays an important part of myocardial damage gene therapy with pro-survival factors appears to be amenable to intervention, it is less clear if other forms of cardiac injury such as hypertrophy and HF can benefit from anti-apoptotic strategies. For these situations, sophisticated promoters with oxygen sensing and modified HIF1αpromoters have been designed to induce survival factors in the setting of ischemia [31].

system. Pim-1 kinase has also been shown to enhance survival, proliferation, trafficking, lineage commitment, and functional engraftment of cardiac progenitor cells [28, 29]. Pim-1 is unique as it mediates not only proliferation, but also lineage commitment, and functional engraftment in hearts [28, 29].

Expected results of gene therapy:

• 1)    Regeneration of contractile performance of the failing heart due to peripheral perfusion improvement;

• 2)    Subsequent reversal of neurohormonal overdrive and cardiac remodelling.

It has been shown that level GRK2 protein can be considered as an independent predictor of prognosis of patients with heart failure [32].

SERCA2a treatment has positive inotrope effect and do not have negative effects of accelerating in energy consumption [33].

The phase 1/2 CUPID trial was launched in 2007 [34]. The CUPID trial is a multicenter. The Phase 1 portion is an open-label, sequential dose escalation study (MYDICAR® Very Low, Low, Mild, and High Doses). The Phase 2 portion is a randomized, double-blind, place-bocontrolled, parallel-group, dose ranging, feasibility trial that compares the use of intra-coronary administered AAV1/SERCA2a at 2 or 3 dose levels with placebo [35].

MYDICAR® is the drug targeting SERCA2a replacement therapy that is now being tested in a phase 2b study (CUPID-2), which can potentially open a new era in treatment of Heart failure . Recently it has been discovered that rAAV is a good vector for a drug. In human models rAAV1 seems to do its best. Still AAV is not good enough vector (because it doesn’t have high affinity to heart cells) and further studies are required.

CUPID 1 (phase 2a) study states that SERCA2a treatment has effect of restoring lucitropic and inotropic function of the heart while also corrects cardiac metabolism which results in improvement of cardiac function [36].

In CUPID-1 study AAV1/SERCA2a were used as a vector for injecting drug to 39 patients intracoronary. Efficiency of the drug was measured by 5 parameters that were divided in 4 domains.

• 1)    Symptoms (New York Heart Association Class, Minnesota Living with Heart Failure Questionnaire),

• 2)    Functional status (6-minute walk test, peak maximum oxygen consumption),

• 3)    Biomarker (N-terminal prohormone brain natriuretic peptide),

• 4)    Left ventricular function/remodeling (left ventricular ejection fraction, left ventricular end-systolic volume)

• 5)    Additionally clinical outcomes.

Success point was mentioned as clinical improvement in those parameters and no worsening of them in 6 months. In 12 month cardiovascular events fervency decreased (0 in MYDICAR® group while 2 in control group). Duration of cardiovascular hospitalization in 12 month decreased also. As a result, patients with High dosage of drug meets all the requirements of the study success.

The problem of eligibility of patients to this study rises as there were no patients with undetectable neutralizing antibodies against AAV1 (titer 1:2), which can block entry of the vector into the target cells. Which is measured by approximately 50% of population.

Notably no cellular immune response were noticed but humoral immune response has developed which means that re-injection of drug is possible

CUPID 1 showed that MYDICAR® could be considered as a potential drug but lager study is needed – (CUPID 2)

CUPID 2 though completely failed to meet endpoint success requirements. No improvements of any of previously stated efficiency parameters were noted.

In analyzing differences of two studies. No obvious important differences in study population characteristics were recorded between the trials, except for a higher use of cardiac resynchronisation treatment in CUPID 1.

Also a review of manufacturing processes identified a difference in the proportion of empty viral capsids (containing only the protein capsid and not the single-stranded DNA) between CUPID 1 (85%) and CUPID 2 (25%), which could have affected transduction efficiency, thus leading to smaller proportion of transduced cells [37].