Horváth, András

Abstract Background Short QT syndrome type 1 (SQT1) is a genetic channelopathy caused by gain-of-function variants in the KCNH2-encoded Kv11.1 potassium channel, responsible for the repolarising IKr current. These variants lead to pathologically shortened cardiac repolarisation and QT intervals on 12-lead ECG, predisposing patients to life-threatening ventricular arrhythmias and sudden cardiac death. Purpose To investigate the therapeutic efficacy of our KCNH2-specific suppression-replacement gene therapy (KCNH2-SupRep) in transgenic SQT1 rabbits generated by cardiac-specific overexpression of KCNH2-N588K. Methods KCNH2-SupRep was developed by combining a custom-designed KCNH2 shRNA with its corresponding shRNA-immune KCNH2 cDNA, packaged into a single AAV9 vector and delivered directly into the aortic root via a Swan Ganz catheter (1E10 vg/kg). Therapeutic efficacy was evaluated in vivo by 12-lead ECG recordings pre- and three weeks post-therapy, ex vivo by optical voltage mapping, and at the cellular level by patch-clamp, calcium imaging, and qPCR in ventricular cardiomyocytes (VCMs) isolated from adult transgenic SQT1 and wild-type (WT) rabbits. Results In vivo, KCNH2-SupRep normalized the heart-rate corrected QT interval (QTc) in transgenic SQT1 rabbits towards WT levels (baseline-SQT1: 153±4ms vs SupRep-SQT1: 167±5ms, p=0.0002; Fig. 1A), without adversely impacting repolarisation heterogeneity. No such QTc changes were observed in sham-treated SQT1 rabbits (sham-SQT1) (baseline-SQT1: 155±4ms vs sham-SQT1: 146±5ms, p=0.1422). Ex vivo, at a 2.5Hz stimulation frequency, KCNH2-SupRep therapeutically prolonged the APD90 in SupRep-SQT1 hearts (176±4ms) near WT levels (179±4ms), compared to untreated (UT)-SQT1 (154±4), and resolved the pathologically increased apicobasal APD90 heterogeneity observed in UT-SQT1 hearts, supporting an anti-arrhythmic effect of KCNH2-SupRep (Fig. 1B). At the cellular level, at a 1Hz stimulation frequency, KCNH2-SupRep prolonged the APD90 in VCMs isolated from SupRep-SQT1 rabbits (363±11ms) closer to WT levels (404±14ms) as compared to UT- (314±12ms) and sham-SQT1 (322±11ms; Fig. 1C). Moreover, KCNH2-SupRep restored the cellular surrogate of the electro-mechanical window (cEMW, Ca2+ transient duration – APD) and normalized IKr in nearly 50% of VCMs (Fig. 1D), in line with a 50-60% suppression of the mutant KCNH2 transcript. This partial therapeutic effect on IKr may explain the incomplete APD90 normalization in individual VCMs. Nonetheless, both in vivo and ex vivo, this partial therapeutic effect was sufficient to completely restore the electrical properties. Conclusion This proof-of-concept study is the first to demonstrate the efficacy of gene therapy in treating SQT1 in a medium-sized animal model. KCNH2-SupRep rescued the disease phenotype in vivo, ex vivo and at cellular levels in transgenic SQT1 rabbits.Therapeutic efficacy of KCNH2-SupRep

Abstract Background Long-QT syndrome type 1 (LQT1) is a genetic channelopathy characterized by loss-of-function variants in the repolarizing potassium channel KCNQ1/IKs which lead to QT-prolongation and predisposes patients to adverse events such as cardiac arrhythmias. Clincally, during catecholamine infusion or exercise stress test, patients with LQT1 present a paradoxical QT prolongation. Purpose To investigate whether a gene-therapy approach targeting the defective K+-channel, through a KCNQ1 suppression-and-replacement (SupRep) strategy, can restore the healthy phenotype at baseline and under catecholamine infusion in LQT1 transgenic rabbits. Methods Our proprietary dual component suppression-and-replacement (SupRep) gene therapy was created by combining a custom-designed KCNQ1 shRNA and a shRNA-immune (shIMM) KCNQ1 cDNA into AAV9. In vivo KCNQ1-SupRep gene therapy was performed by targeted intra-aortic root injection during balloon occlusion. Two or three weeks post gene therapy, 12-lead ECGs were assessed in adult transgenic LQT1 (KCNQ1-Y315S, loss-of IKs) and wild-type (WT) rabbits to determine the effect of SupRep gene therapy on QT-duration at baseline and under catecholamine infusion (10nM isoproterenol, 5mL/h). Ventricular cardiomyocytes (VCMs) were isolated to investigate the effect of SupRep gene therapy on action potential duration (APD) and calcium transients (Ca2+T) at baseline and under isoproterenol infusion. Results At the cellular level, VCMs isolated from SupRep treated LQT1 rabbits showed a significant shortening of the APD90 as compared to UT-LQT1 (p<0.0001). At the whole animal level, at baseline, the QTi (%) of the UT-LQT1 transgenic rabbits (122±3) was significantly longer compared to the WT rabbits (105±2, p<0.0001). Treatment with AAV9-KCNQ1-SupRep shortened significantly the QTi of the transgenic LQT1 rabbits as compared to the UT-LQT1 rabbits (111±2, p=0.0115). To further investigate the effect of SupRep gene therapy, 12-lead ECGs were obtained in UT-LQT1, sham-treated LQT1, SupRep-treated LQT1, and WT rabbits under ISO infusion. While reaching a 20% increase in heart rate during ISO stimulation, the UT-LQT1 and the sham treated LQT1 rabbits showed a marked QT prolongation, with ΔQTi of 31.4% and 24.5%, respectively, as compared to baseline. In contrast, the SupRep-treated LQT1 rabbit behaved nearly identical to the WT rabbit during ISO infusion, showing a ΔQTi of 16.9% as compared to 16.5% in the WT rabbit. Similarly, in contrast to the UT-LQT1, VCMs isolated from SupRep-treated LQT1 rabbits demonstrated a normalization of the APD and Ca2+T under ISO stimulation, showing a significantly shortened APD90 (p<0.0001) and Ca2+T90 (p=0.0025) which was similar to what was observed in WT VCMs. Conclusion In vivo KCNQ1 suppression-and-replacement gene therapy normalizes the pathologically prolonged APD/QT interval and restores a physiological response to catecholamine infusion in treated LQT1 transgenic rabbits.