In vivo KCNQ1-suppression-replacement gene therapy in transgenic LQT1 rabbits restores a physiological QT interval at baseline and under catecholamine infusion
Authors: Giammarino L , Bains S , Louradour J , Nimani S , Alerni N , Tester D , Christoforou N , Horvath A , Beslac O , Koren G , Brunner M , Casoni D , Haeberlin A , Ackerman M J , Odening K E 
Published: May 2024

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&lt;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&lt;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&lt;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.