Key result
ITP-2 activated hERG1a homomeric channels by causing large depolarizing shifts in voltage-dependent inactivation and hyperpolarizing shifts in activation, and could activate an LQT2 mutant.
ITP-2 is a novel small molecule activator of hERG channels that differentially modulates hERG1a and hERG1a/1b channels, representing a potential lead for LQT syndrome therapeutics.
Identifies a novel therapeutic lead for Long QT syndrome; leaves open whether this.
BACKGROUND AND PURPOSE: 11.1 (hERG) channels have potential utility in the treatment of acquired and congenital long QT (LQT) syndrome. Here, we describe a new hERG channel activator, 5-(((1H-indazol-5-yl)oxy)methyl)-N-(4-(trifluoromethoxy)phenyl)pyrimidin-2-amine (ITP-2), with a chemical structure distinct from previously reported compounds. EXPERIMENTAL APPROACH: Conventional electrophysiological methods were used to assess the effects of ITP-2 on hERG1a and hERG1a/1b channels expressed heterologously in HEK-293 cells. KEY RESULTS: 1.0 μM) and decreased tail currents. ITP-2 activated hERG1a homomeric channels primarily by causing large depolarizing shifts in the midpoint of voltage-dependent inactivation and hyperpolarizing shifts in the voltage-dependence of activation. In addition, ITP-2 slowed rates of inactivation and made recovery from inactivation faster. hERG1a/1b heteromeric channels showed reduced sensitivity to ITP-2 and their inactivation properties were differentially modulated. Effects on midpoint of voltage-dependent inactivation and rates of inactivation were less pronounced for hERG1a/1b channels. Effects on voltage-dependent activation and activation kinetics were not different from hERG1a channels. Interestingly, hERG1b channels were inhibited by ITP-2. Inactivation-impairing mutations abolished activation by ITP-2 and led to inhibition of hERG channels. ITP-2 exerted agonistic effect from extracellular side of the membrane and could activate one of the arrhythmia-associated trafficking-deficient LQT2 mutants. CONCLUSIONS AND IMPLICATIONS: ITP-2 may serve as another novel lead molecule for designing robust activators of hERG channels. hERG1a/1b gating kinetics were differentially modulated by ITP-2 leading to altered sensitivity. ITP-2 is capable of activating an LQT2 mutant and may be potentially useful in the development of LQT2 therapeutics.
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Sale et al. (2017) studied Long QT (LQT) syndrome. ITP-2 was evaluated on Electrophysiological effects on hERG1a and hERG1a/1b channels. ITP-2 activated hERG1a homomeric channels by causing large depolarizing shifts in voltage-dependent inactivation and hyperpolarizing shifts in activation, and could activate an LQT2 mutant.
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