Abstract 14260: Suppression and Replacement Gene Therapy for Type 2 Long QT Syndrome

Introduction: Type 2 long QT syndrome (LQT2) is caused by loss-of-function variants in the KCNH2 -encoded K v 11.1 potassium channel which is essential for the rapid delayed rectifier channel (I Kr ) that governs phase 3 of cardiac action potential (AP). No current therapies target the molecular cause of LQT2. Methods: A dual-component “suppression-and-replacement” (SupRep) KCNH2 gene therapy was created by cloning into a single construct a custom-designed KCNH2 shRNA that produces ~80% knockdown (suppression) and a “shRNA-immune” (shIMM) KCNH2 cDNA modified by the introduction of synonymous single nucleotide substitutions within the shRNA target site (replacement). The ability of KCNH2-SupRep gene therapy to suppress and replace LQT2-causative variants in KCNH2 was evaluated via heterologous expression in TSA201 cells. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from two patients with LQT2 (KCNH2-G604S and -N633S). CRISPR-Cas9 corrected isogenic control iPSC-CMs were made. Both lines were treated with KCNH2-SupRep or non-targeting control shRNA (shCT). FluoVolt voltage dye was used to measure the APD. Results: KCNH2-SupRep achieved mutation-independent suppression of wild-type KCNH2 and both LQT2-causative variants with simultaneous replacement of KCNH2-shIMM as measured by allele-specific qRT-PCR. Treatment with KCNH2-SupRep resulted in shortening of the pathologically prolonged APD at 90% repolarization (APD 90 ) to near isogenic control APD 90 levels (G604S: isogenic controls, 424 + 39 ms and N633S: isogenic controls, 433 + 16 ms) compared to treatment with non-targeting shCT (G604S: SupRep treated, 399±105 ms vs. shCT treated, 577±39 ms, p<0.0001; N633S: SupRep treated, 432±85 ms vs. shCT treated, 483±65 ms, p<0.005). Conclusions: We provide the first proof-of-principle gene therapy for correction of LQT2. Like our sentinel discovery of SupRep gene therapy for LQT1, KCNH2-SupRep successfully suppressed and replaced KCNH2 to normal wild-type levels. In TSA201 cells, co-transfection of LQT2 variants and KCNH2-SupRep caused mutation-independent suppression-and-replacement of KCNH2 . In LQT2 iPSC-CMs, KCNH2-SupRep shortened the APD, thereby eliminating the pathognomonic feature of LQT2.