Effects of a Novel Cardioselective ATP-Sensitive Potassium Channel Antagonist, 1-[[5-[2-(5-Chloro-o-anisamido)ethyl]- - methoxyethoxyphenyl]sulfonyl]-3-methylthiourea, Sodium Salt (HMR 1402), on Susceptibility to Ventricular Fibrillation Induced by Myocardial Ischemia: In Vitro and in Vivo Studies

In the present study, a novel sulfonylthiourea, 1-[[5-[2-(5chloro-o-anisamido)ethyl]-methoxyethoxyphenyl]sulfonyl]-3methylthiourea, sodium salt (HMR 1402), was investigated using in vitro and in vivo systems. HMR 1402 inhibited rilmakaliminduced currents in rat and guinea pig myocytes (IC50 60 and 509 nM, respectively). Hypoxia-induced shortening of action potential duration at 90% repolarization was also significantly attenuated by HMR 1402 (68.1 3.9% of control at 0.3 M). In contrast, HMR 1402 had a smaller effect on pancreatic -cells (rat insuloma cells, RINm5F) hyperpolarized with 100 M diazoxide (IC50 3.9 M, compared with glibenclamide IC50 9 nM). In a similar manner, hypoxia induced increases in coronary flow in isolated guinea pig hearts were only slightly reduced by HMR 1402. These data strongly suggest that HMR 1402 has pharmacological selectivity for cardiac myocytes and, therefore, may protect against ischemically induced ventricular fibrillation (VF) without the untoward effects of nonselective compounds. To test this hypothesis, VF was induced in 8 dogs with healed myocardial infarctions by a 2-min coronary occlusion during the last minute of exercise. On a subsequent day, the exercise plus ischemia test was repeated after HMR 1402 (3.0 mg/kg i.v., n 4, infusion 4 g/kg/min for 1 h before exercise, n 4). This drug significantly reduced the incidence of VF protecting seven of eight animals (p 0.0007) without altering plasma insulin, blood glucose, or the increases in mean coronary blood flow induced by either exercise or 15-s coronary occlusions. Thus, the ATP-sensitive potassium channel antagonist HMR 1402 can prevent ischemically induced VF without altering coronary blood flow or blood glucose. Sudden cardiac death due to ventricular tachyarrhythmias remains the leading cause of death in most industrially developed countries, accounting for between 300,000 and 500,000 deaths each year in the United States alone (Abildstrom et al., 1999; Zheng et al., 2001). Although only a small number of these patients had a known history of heart disease before the collapse, up to 90% of these individuals were subsequently shown to have underlying coronary artery disease (Abildstrom et al., 1999). Therefore, myocardial ischemia almost certainly plays a crucial role in the induction of the lethal arrhythmias in these patients. It is well established that myocardial ischemia is accompanied by rapid increases in the extracellular potassium concentration (for reviews, see Billman, 1994; Coronel, 1994). The resulting depolarization of the surrounding tissue, reductions in action potential duration, and heterogeneity of repolarization facilitates reentrant conduction and the induction of ventricular fibrillation (Billman, 1994). An accumulating body of evidence demonstrates that the activation (opening) of ATPsensitive potassium (KATP) channel is largely responsible for potassium efflux and the accompanying electrophysiological changes elicited by myocardial ischemia (for reviews, see Billman, 1994; Coronel, 1994). For example, the KATP antagonist glibenclamide attenuated extracellular potassium accumulation and prevented shortening of action potential duration provoked by hypoxia or myocardial ischemia (Benndorf et al., 1991; Nakaya et al., 1991; Dhein et al., 2000). In a Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. DOI: 10.1124/jpet.103.061416. ABBREVIATIONS: KATP, ATP-sensitive potassium; SUR, sulfonylurea receptor; APD90, action potential duration at 90% repolarization; MES, 2-[N-morpholino(ethanesulfonic acid)monohydrate; LVDP, left ventricular diastolic pressure; LVP, left ventricular systolic pressure; HMR 1402,1[[5-[2-(5-chloro-o-anisamido)ethyl]-methoxyethoxyphenyl]sulfonyl]-3-methylthiourea; HMR 1883, 1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea. 0022-3565/04/3091-182–192$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 309, No. 1 Copyright © 2004 by The American Society for Pharmacology and Experimental Therapeutics 61416/1133602 JPET 309:182–192, 2004 Printed in U.S.A. 182 at A PE T Jornals on O cber 5, 2017 jpet.asjournals.org D ow nladed from similar manner, glibenclamide has also been shown to prevent ventricular fibrillation induced by myocardial ischemia in several animal models (Gwilt et al., 1992; Billman et al., 1993, 1998; Barrett and Walker, 1998; El-Reyani et al., 1999), as well as to reduce both the severity and number of arrhythmias in diabetic patients (Cacciapuoti et al., 1991; Davis et al., 1998; Aronson et al., 2003) and the incidence of ventricular fibrillation in noninsulin-dependent diabetic patients with acute myocardial infarction (Lomuscio et al., 1994). Because the KATP channels are only activated when intracellular ATP levels fall (Deutsch et al., 1991; Edwards and Weston, 1993), as during ischemia, drugs that block this channel would have minimal effects on the nonischemic myocardium, and therefore should be free of the proarrhythmic effects noted for many antiarrhythmic drugs. However, KATP channels are not located exclusively in the heart (Gribble et al., 1998; Gögelein et al., 1999; Gögelein, 2001). Indeed, glibenclamide blocks both pancreatic KATP channels and coronary vascular smooth muscle KATP channels, thereby promoting insulin release and hypoglycemia as well as reducing coronary perfusion (Gögelein et al., 1999; Gögelein, 2001), respectively. These noncardiac actions would limit the antiarrhythmic potential of glibenclamide in the clinic. Cardioselective compounds should have fewer side effects and would therefore provide a better therapeutic option than the nonselective ATP-sensitive potassium channel antagonist glibenclamide. Several different ATP-sensitive potassium channel subtypes have been identified. The ATP-sensitive potassium channel consists of a pore-forming subunit coupled to a sulfonylurea receptor (Inagaki et al., 1995; Gögelein et al., 1999; Gögelein, 2001). The functional channel forms as a heterooctomer composed of a tetramer of the pore and four sulfonyl receptor subunits. At present, two different pore-forming subunits have been identified, both of which produce an inward rectifier potassium current (Kir 6.1 and Kir 6.2; Liu et al., 2001). Three different sulfonylurea receptor subtypes have been isolated: SUR1 (on pancreatic islet cells), SUR2A (on cardiac tissue), and SUR2B (on vascular smooth muscle) (Gribble et al., 1998; Gögelein et al., 1999; Gögelein, 2001). Thus, six different potassium channel pore and sulfonylurea receptor combinations are possible. Suzuki et al. (2001) recently demonstrated that Kir 6.2 and Kir 6.1 were required for cardiac and vascular smooth muscle ATP-sensitive potassium channel activity, respectively. They concluded that Kir 6.2/SUR2A most likely forms the cardiac cell membrane ATP-sensitive potassium channel, whereas Kir 6.1/SUR2B is located on vascular smooth muscle. In a similar manner, Liu et al. (2001) demonstrated that the mitochondrial KATP channel most closely resembles Kir6.1/SUR1 subtype. It should therefore be possible to develop compounds that selectively inhibit (or activate) a particular ATP-sensitive potassium channel subtype. A drug that selectively blocks the Kir 6.2/ SUR2A subtypes should prevent ischemically induced changes in cardiac electrical properties (e.g., reductions in action potential duration), and thereby protect against arrhythmias without the untoward side effects noted for the nonselective ATP-sensitive channel antagonist glibenclamide. The novel sulfonylurea compound 1-[[5-[2-(5-chloro-o-anisamido)ethyl]methoxyethoxyphenyl]sulfonyl]-3-methylthiourea, sodium salt (HMR 1402) (Fig. 1) was developed to block myocardial KATP channels selectively. It was, therefore, the purpose of this series of studies to first evaluate the effects HMR 1402 on KATP channels in vitro, using cardiac and pancreatic preparations, and then to investigate the effects of HMR 1402 on the susceptibility to ventricular fibrillation using an unanesthetized canine model of sudden death. Materials and Methods The principles governing the care and use of animals as expressed by the Declaration of Helsinki, and as adopted by the American Physiological Society, were followed at all times during this study. In addition, The Ohio State University or the Aventis Pharma Institutional Animal Care and Use Committee approved all the procedures