Abstract 20347: Does Electrophysiological Toxicity Limit the Therapeutic Window of Serca2a Gene Therapy?

Abstract

Rescue of SERCA2a expression by gene transfer to the endstage failing heart improves its mechanical and electrophysiological (EP) function. However the safety profile of SERCA2a gene therapy as a preventive measure in patients at early stages of remodeling prior to SERCA2a downregulation is unknown. Examination of the EP consequences of SERCA2a gene therapy in non-failing hearts is imperative in determining its potential EP toxicity. Hypothesis: SERCA2a upregulation using high titer adeno associated virus type 9 (AAV9) mediated gene transfer to normal rats may promote arrhythmogenic triggers, thereby limiting the therapeutic window for this approach. Methods: Using high resolution optical action potential (AP) imaging, we investigated the EP substrate 6 weeks post gene transfer of 5E11 AAV9.SERCA2a (N=13) or AAV9.GFP (N=6) to normal rats. Arrhythmia susceptibility was determined under conditions that promoted Ca overload by burst pacing & ischemia reperfusion (IR) injury. Results: AAV9.SERCA2a hearts exhibited a 50% increase in SERCA2a expression at the mRNA and protein levels compared to AAV9.GFP. No differences in heart weight to body weight were found between groups (3.85 vs 3.74 mg/g). During baseline perfusion, AAV9.GFP hearts exhibited significantly prolonged (by 30%, p<0.05) AP durations (APD) and a strong trend (p=0.07) towards greater APD heterogeneity. Challenge with rapid pacing resulted in the onset of sustained VF in 4/6 AAV9.GFP and 0/13 AAV9.SERCA2a hearts (p=0.004). Despite significant SERCA2a upregulation, APD and conduction velocity were identical in AAV9.SERCA2a compared to normal hearts indicating lack of EP toxicity. During prolonged low flow ischemia, AAV9.SERCA2a hearts exhibited a trend towards higher incidence of arrhythmias compared to normal hearts, but differences were not statistically significant (p=0.08). Finally, all AAV9.SERCA2a hearts exhibited rapid recovery of APD and excitability upon reperfusion following 10 min of no flow ischemia. Conclusions: High titer gene transfer of AAV9.GFP but not AAV9.SERCA2a elicits adverse EP remodeling in normal rat myocardium. The lack of an EP phenotype of AAV9.SERCA2a despite 50% upregulation in SERCA2a levels is consistent with a wide safety margin for this therapy.