PD 118057

Pharmacologic Approach to Defective Protein Trafficking in the E637K-hERG Mutant with PD-118057 and Thapsigargin.[Pubmed:23840331]

PLoS One. 2013 Jun 19;8(6):e65481.

BACKGROUND: Treatment of LQT2 is inadequate. Many drugs which can pharmacologically rescue defective protein trafficking in LQT2 also result in potent blockade of HERG current, negating their therapeutic benefit. It is reported that PD-118057 and thapsigargin can rescue LQT2 without hERG channel blockade, but the precise mechanism of action is unknown. Furthermore, the effect of PD-118057 and thapsigargin on the dominant negative E637K-hERG mutant has not been previously investigated. OBJECTIVE: IN THIS STUDY, WE INVESTIGATED: (a) the effect of PD-118057 and thapsigargin on the current amplitudes of WT-hERG and WT/E637K-hERG channels; (b) the effect of PD-118057 and thapsigargin on the biophysical properties of WT-hERG and WT/E637K-hERG channels; (c) whether drug treatment can rescue channel processing and trafficking defects of the WT/E637K-hERG mutant. METHODS: The whole-cell Patch-clamp technique was used to assess the effect of PD-118057 and thapsigargin on the electrophysiological characteristics of the rapidly activating delayed rectifier K(+) current (Ikr) of the hERG protein channel. Western blot was done to investigate pharmacological rescue on hERG protein channel function. RESULTS: In our study, PD-118057 was shown to significantly enhance both the maximum current amplitude and tail current amplitude, but did not alter the gating and kinetic properties of the WT-hERG channel, with the exception of accelerating steady-state inactivation. Additionally, thapsigargin shows a similar result as PD-118057 for the WT-hERG channel, but with the exception of attenuating steady-state inactivation. However, for the WT/E637K-hERG channel, PD-118057 had no effect on either the current or on the gating and kinetic properties. Furthermore, thapsigargin treatment did not alter the current or the gating and kinetic properties of the WT/E637K-hERG channel, with the exception of opening at more positive voltages. CONCLUSION: Our findings illustrate that neither PD-118057 nor thapsigargin play a role in correcting the dominant-negative effect of the E637K-hERG mutant.

PD-118057 contacts the pore helix of hERG1 channels to attenuate inactivation and enhance K+ conductance.[Pubmed:19892732]

Proc Natl Acad Sci U S A. 2009 Nov 24;106(47):20075-80.

Human ether-a-go-go-related gene 1 (hERG1) K(+) channels mediate repolarization of cardiac action potentials. Unintended block of hERG1 channels by some drugs can prolong the QT interval and induce arrhythmia. Recently, hERG1 channel agonists were discovered and, based on their mechanisms of action can be classified into two types. RPR260243 [(3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5 trifluorophenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid], a type 1 agonist, binds to residues located near the intracellular end of S5 and S6 transmembrane segments and activates hERG1 channels by a dual mechanism of slowed deactivation and attenuated P-type inactivation. As defined here, type 2 agonists such as PD-118057 [2-(4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino)-benzoic acid] attenuate inactivation but do not slow deactivation. At 10 muM, PD-118057 shifted the half-point for inactivation of wild-type hERG1 channels by +19 mV and increased peak outward current by 136%. Scanning mutagenesis and functional characterization of 44 mutant channels expressed in Xenopus oocytes was used to identify the major structural determinants of the binding site for PD-118057. Single mutations of residues in the pore helix (F619) or the S6 segment (L646) of hERG1 eliminated agonist activity. Mutation of a nearby residues in the S6 segment (C643, M645) enhanced drug activity, presumably by reducing steric hindrance for drug binding. Molecular modeling indicates that PD-118057 binds to a hydrophobic pocket formed by L646 of one hERG1 subunit and F619 of an adjacent subunit. We conclude that direct interaction of PD-118057 with the pore helix attenuates fast P-type inactivation and increases open probability of hERG1 channels.

Pharmacological and biophysical isolation of K+ currents encoded by ether-a-go-go-related genes in murine hepatic portal vein smooth muscle cells.[Pubmed:16870833]

Am J Physiol Cell Physiol. 2007 Jan;292(1):C468-76.

Previous studies have shown that murine portal vein myocytes express ether-a-go-go related genes (ERGs) and exhibit distinctive currents when recorded under symmetrical K(+) conditions. The aim of the present study was to characterize ERG channel currents evoked from a negative holding potential under conditions more pertinent to a physiological scenario to assess the possible functional impact of this conductance. Currents were recorded with ruptured or perforated patch variants of the whole cell technique from a holding potential of -60 mV. Application of three structurally distinct and selective ERG channel blockers, E-4031, dofetilide, and the peptide toxin BeKM-1, all inhibited a significant proportion of the outward current and abolished inward currents with distinctive "hooked" kinetics recorded on repolarization. Dofetilide-sensitive currents at negative potentials evoked by depolarization to +40 mV had a voltage-dependent time to peak and rate of decay characteristic of ERG channels. Application of the novel ERG channel activator PD-118057 (1-10 microM) markedly enhanced the hooked inward currents evoked by membrane depolarization and hyperpolarized the resting membrane potential recorded by current clamp and the perforated patch configuration by approximately 20 mV. In contrast, ERG channel blockade by dofetilide (1 microM) depolarized the resting membrane potential by approximately 8 mV. These data are the first record of ERG channel currents in smooth muscle cells under quasi-physiological conditions that suggest that ERG channels contribute to the resting membrane potential in these cells.

Novel potent human ether-a-go-go-related gene (hERG) potassium channel enhancers and their in vitro antiarrhythmic activity.[Pubmed:15976038]

Mol Pharmacol. 2005 Sep;68(3):876-84.

A variety of drugs has been reported to cause acquired long QT syndrome through inhibition of the IKr channel. Screening compounds in early discovery and development stages against their ability to inhibit IKr or the hERG channel has therefore become an indispensable procedure in the pharmaceutical industry. In contrast to numerous hERG channel blockers discovered during screening, only (3R,4R)-4-[3-(6-methoxyquinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl) -prop-2-ynyl]-piperidine-3-carboxylic acid (RPR260243) has been reported so far to enhance the hERG current. In this article, we describe several potent mechanistically distinct hERG channel enhancers. One example is PD-118057 (2-{4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino}-benzoic acid) which produced average increases of 5.5 +/- 1.1, 44.8 +/- 3.1, and 111.1 +/- 21.7% in the peak tail hERG current at 1, 3, and 10 muM, respectively, in human embryonic kidney 293 cells. PD-118057 did not affect the voltage dependence and kinetics of gating parameters, nor did it require open conformation of the channel. In isolated guinea pig cardiomyocytes, PD-118057 showed no major effect on I(Na), I(Ca,L), I(K1), and I(Ks). PD-118057 shortened the action potential duration and QT interval in arterially perfused rabbit ventricular wedge preparation in a concentration-dependent manner. The presence of 3 muM PD-118057 prevented action potential duration and QT prolongation caused by dofetilide. "Early after-depolarizations" induced by dofetilide were also completely eliminated by 3 microM PD-118057. Although further investigation is warranted to evaluate the therapeutic value and safety profile of these compounds, our data support the notion that hERG activation by pharmaceuticals may offer a new approach in the treatment of delayed repolarization conditions, which may occur in patients with inherited or acquired long QT syndrome, congestive heart failure, and diabetes.