*6.4. Modulation of Serca2a*/*PLN*

As a result of the central role of Serca2a and PLN in cardiac calcium cycling, their necessity in the maintenance of low diastolic calcium concentration, and the changes associated with their expression and activity in DCM, this complex has become an important experimental therapeutic target in both DCM and DMD-cardiomyopathy.

## 6.4.1. Serca2a as a Target for DCM Therapy

Serca2a gene therapy has been studied extensively in a variety of heart failure models. Adenoviral gene transfer of Serca2a in isolated cardiac myocytes from failing human hearts improved peak height of contraction and relaxation rate, which could be explained by increased calcium peak height and decay rate [171]. Multiple small animal models of heart failure have also been used to study the effectiveness of Serca2a gene therapy. Aortic-banded rats with adenoviral gene delivery of Serca2a had improved systolic and diastolic function measured by *in vivo* hemodynamics [172], increased survival rate [173], normalized energetics (PCr:ATP), and more efficient oxygen utilization compared to aortic-banded rats without Serca2a treatment [173,174]. Lentiviral-mediated Serca2a gene delivery after myocardial infarction in rats led to improvement in left ventricular systolic and diastolic dimensions and fractional shortening measured by echocardiography, improved hemodynamic measurements of systolic and diastolic function, and increased survival rate [175]. Two large animal models have also been used to study the effectiveness of Serca2a gene delivery via adeno-associated viral (AAV) gene transfer. In a swine model of mitral regurgitation, AAV delivery of Serca2a led to improved LV systolic and diastolic dimensions, left ventricular ejection fraction, and +dP/dt two months after gene delivery. AAV2/1-Serca2a in sheep with rapid pacing-induced heart failure also had improvements in LV dimensions, as well as increased systolic function and improvements in the pressure-volume relationship [176,177].

As a result of its therapeutic benefit in pre-clinical models of heart failure, Serca2a gene therapy has been tested in two randomized, placebo-controlled clinical trials using intracoronary delivery of AAV1 in advanced heart failure patients. In the first trial, patients that received the highest dose of Serca2a (1 <sup>×</sup> 1013 DNase resistant particles) showed improvement in pre-defined clinical endpoints including symptomatic, functional, biomarker, and LV function and remodeling abnormalities after six months [178]. The high-dose group also had an 82% decrease in recurrent cardiovascular events after three years of follow-up [179]. This study was followed by a larger multi-center trial of 250 heart failure patients using the high dose of Serca2a. Unlike the initial trial, there was no difference between treatment and control groups in either recurrent or terminal clinical events [180]. The basis for the discrepancy in results between the two studies is uncertain. A small number of heart tissue samples

revealed low vector DNA copy number. Additionally, there were differences between the two trials in the number of total viral particles (including empty capsids) delivered [180].
