Efficacy and safety of HERG channel agonists for treatment of Long QT Syndrome type 8
Authors: Kukavica D , Mazzanti A , Trancuccio A , Porta-Sanchez A , Jauregui Abularach M E , Pergola V , Tarifa C , Hernandez Lopez K , Lentini G , Priori S G 
Published: October 2024

Abstract

Background
Substrate-based approach aimed at repolarization abbreviaton using mexiletine was shown to normalize the QTc interval and reduce the event rate in LQT3, and is now considered standard-of-care. Unfortunately, mexiletine is partially efficacious in other malignant forms of LQTS, such as LQT2 and LQT8. Novel compounds, such as HERG channel agonists, potentially capable of safely and efficaciously abbreviating the repolarization have not been tested in a clinically relevant model.

Purpose
To investigate the efficacy and safety of repolarization shortening using ICA-105574, the most potent compound belonging to the class of HERG channel agonists, in a clinically relevant, first-in-class porcine model of LQT8.

Methods
We used a combination of 12-lead ECG and electroanatomical mapping (EAM) to obtain data on the QTc interval, local activation time (LAT), local repolarization time (LRT) and its gradients, and reentrant vulnerability index (RVI), at baseline and after drug administration. We used LQT8 pigs of both genders weighing between 60 kg and 80 kg. All procedures were conducted following local regulations for the care and use of laboratory animals after authorization by relevant authorities. We used mixed effects linear regression model to assess the effect of ICA-105574 on the QTc interval and paired nested t-test to assess the effect of ICA-105574 on EAM-derived parameters.

Results
As a first step, we assessed the effects of ICA-105574 on the QTc interval. Compared to baseline, a single dose of 3 mg/kg of ICA-105574 resulted in an immediate and pronounced shortening of the QTc interval in all animals (∆QTc at 5 minutes post-injection: -28%, p&lt;0.001). We then investigated repeated intravenous administrations of 3 mg/kg doses at 10-minute intervals for a total of 4 doses (i.e., overall drug dose of 12 mg/kg). Importantly, we did not observe excessive QTc shortening (∆QTc 6 mg/kg: -26%; ∆QTc 9 mg/kg: -26%; ∆QTc 12 mg/kg: -30%, p&lt;0.001 for all) nor did we observe any proarrhythmic events in any of the animals studied. In a second phase of the study, we used EAM to assess the modifications in the arrhythmic substrate induced by ICA-105574. Importantly, ICA-105574 not only shortened the duration of ventricular repolarization (∆LRT: -21%, p=0.017), but also reduced the dispersion of ventricular repolarization (∆Max. LRT gradient: -69%, p=0.020). This, coupled with reduction of the activation delay as compared to baseline (∆LAT: -28%, p=0.072), had a net positive effect on the arrhythmic substrate, as evidenced by an amelioration by 30% of global RVI (∆RVIG,D: -32%, p=0.029).

Conclusions
In our LQT8 pig model, ICA-105574, a potent HERG channel agonist, safely and efficaciously ameliorated the arrhythmic substrate. These results suggest that HERG channel agonists, as a novel class of antiarrhythmics, could have clinical application as a novel substrate-based therapy for LQT8.Figure 1