Eleclazine exhibits enhanced selectivity for long QT syndrome type 3-associated late Na current.

Background: Eleclazine (GS-6615) is a sodium channel blocker designed to improve the selectivity for cardiac late Na current (I) over peak I.

Objectives: The goals of this study were to investigate the inhibition of late I by eleclazine using a sample of long QT syndrome type 3 (LQT3) and overlap LQT3/Brugada syndrome mutant channels; to compare the apparent binding rates for eleclazine with those for other class 1 antiarrhythmic agents; and to investigate the binding site.

Methods: Wild-type human cardiac voltage-gated sodium channel (hNa1.5) and 21 previously reported variants were studied using patch clamp recordings from a heterologous expression system.

Results: Eleclazine inhibited anemone toxin II-enhanced late I from wild-type hNa1.5 with a drug concentration that causes 50% block of 0.62 ± 0.12 μM (84-fold selectivity over peak I). The drug concentration that causes 50% block of eleclazine to inhibit the enhanced late I from LQT3 mutant channels ranged from 0.33 to 1.7 μM. At predicted therapeutic concentrations, eleclazine and ranolazine inhibited peak I to a similar degree as assessed with 4 overlap LQT3/Brugada syndrome mutations. Eleclazine was found to interact with hNa1.5 significantly faster than ranolazine and 6 other class 1 antiarrhythmic agents. Engineered mutations (F1760A/Y1767A) located within the local anesthetic binding site decreased the inhibition of late I and peak I by eleclazine.

Conclusion: At predicted therapeutic concentrations, eleclazine elicits potent inhibition of late I across a cohort of Na1.5 mutant channels. These properties are consistent with a class 1b antiarrhythmic agent that associates with unusually rapid binding/unbinding rates.