Suppression and Replacement Gene Therapy for -Mediated Arrhythmias.

Background: -mediated arrhythmia syndromes are caused by loss-of-function (type 2 long QT syndrome [LQT2]) or gain-of-function (type 1 short QT syndrome [SQT1]) pathogenic variants in the -encoded K11.1 potassium channel, which is essential for the cardiac action potential.

Methods: A dual-component "suppression-and-replacement" (SupRep) gene therapy was created by cloning into a single construct a custom-designed short hairpin RNA with ~80% knockdown (suppression) and a "short hairpin RNA-immune" cDNA (replacement). Induced pluripotent stem cell-derived cardiomyocytes and their CRISPR-Cas9 variant-corrected isogenic control (IC) induced pluripotent stem cell-derived cardiomyocytes were made for 2 LQT2- (G604S, N633S) and 1 SQT1- (N588K) causative variants. All variant lines were treated with KCNH2-SupRep or non-targeting control short hairpin RNA (shCT). The action potential duration (APD) at 90% repolarization (APD) was measured using FluoVolt voltage dye.

Results: KCNH2-SupRep achieved variant-independent rescue of both pathologic phenotypes. For LQT2-causative variants, treatment with KCNH2-SupRep resulted in shortening of the pathologically prolonged APD to near curative (IC-like) APD levels (G604S IC, 471±25 ms; N633S IC, 405±55 ms) compared with treatment with shCT (G604S: SupRep-treated, 452±76 ms versus shCT-treated, 550±41 ms; <0.0001; N633S: SupRep-treated, 399±105 ms versus shCT-treated, 577±39 ms, <0.0001). Conversely, for the SQT1-causative variant, N588K, treatment with KCNH2-SupRep resulted in therapeutic prolongation of the pathologically shortened APD (IC: 429±16 ms; SupRep-treated: 396±61 ms; shCT-treated: 274±12 ms).

Conclusions: We provide the first proof-of-principle gene therapy for correction of both LQT2 and SQT1. KCNH2-SupRep gene therapy successfully normalized the pathologic APD, thereby eliminating the pathognomonic feature of both LQT2 and SQT1.