Effects of SZV-2649, a new multiple ion channel inhibitor mexiletine analogue

Abstract

The antiarrhythmic and cardiac electrophysiological effects of SZV-2649 that contains a 2,6-diiodophenoxy moiety but lacks the benzofuran ring system present in amiodarone, were studied in mammalian cell line, rat and dog cardiac preparations. SZV-2649 exerted antiarrhythmic effects against coronary artery occlusion/reperfusion induced ventricular arrhythmias in rats and in acetylcholine- and burst stimulation induced atrial fibrillation in dogs. SZV-2649 inhibited hERG and GIRK currents in HEK cells (IC₅₀: 342 and 529 nM, respectively). In canine ventricular myocytes, SZV-2649 (10 µM) decreased the densities of I_Kr, and I_to outward and I_NaL and I_CaL inward currents. The compound (2.5-10 µM) elicited Class IB type V_max reducing and Class III type action potential duration prolonging effects in dog right ventricular muscle preparations. In canine atrial muscle, SZV-2629 (2.5-10 µM) moderately prolonged action potential duration and this effect was greatly augmented in preparations pretreated with 1 µM carbachol. In conclusion, SZV-2649, has antiarrhythmic effects based on its multiple ion channel blocking properties. Since its chemical structure substantially differs from that of amiodarone, it is expected that SZV-2649 would exhibit fewer adverse effects than the currently used most effective multichannel inhibitor drug amiodarone and may be a promising molecule for further development.

Fig. 1

Chemical structure of SZV-2649 [4-(2-aminopropoxy)-3,5-diiodobenzonitrile hydrochloride].

Fig. 2

Effects of SZV-2649 on GIRK (a) and on hERG (b) currents in HEK cell lines. Top panels display original recordings of GIRG (a) and hERG (b) currents treated with 100 nM, 300 nM, 1000 nM and 3000 nM SZV-2649. Propafenone (1 µM) and amitriptyline (10 µM) were applied as reference inhibitors for GIRK (a) and hERG (b), respectively. Insets show the voltage protocols. Bottom panels display concentration-response curves of SZV-2649 inhibitory activity on GIRK (a) and hERG (b) channels. The dashed lines indicate zero current levels. Data are expressed as means ± SEM.

Fig. 3

Effect of SZV-2649 on the late sodium (I_NaL) and L-type calcium (I_CaL) currents in dog left ventricular myocytes. Panel a indicates the effects of 10 µM SZV-2649 administration on the I_NaL current showing original current recordings (left) and bar diagrams (right). Panel b displays current-voltage relationship of I_CaL recorded with 3000 ms pulsing cycle length in control conditions and in the presence of 10 µM SZV-2649. Inset (top) shows original current records in control conditions and after application of 10 µM SZV-2649. The dashed lines indicate zero current levels. The applied voltage protocols are displayed on the insets. Data are expressed as means ± SEM. *P < 0.05 vs. control.

Fig. 4

Effect of SZV-2649 on the rapid (I_Kr) and slow (I_Ks) delayed rectifier, the transient outward (I_to) potassium currents and on the steady state current-voltage relationship in dog left ventricular myocytes. Top panels display the tail current section of original I_Kr (a) and I_Ks (b) current traces in control conditions and in the presence of SZV-2649. Dashed lines refer to the baseline for I_Kr and I_Ks tail current levels after the test pulse at -40 mV. Bottom panels illustrates current-volatage relationship for I_Kr (a) and I_Ks (b). SZV-2649 was applied at concentrations of 1 µM and 5 µM for I_Kr and 10 µM for I_Ks current. Panel c indicates current-voltage relationship of I_to recorded with 3000 ms pulsing cycle length in control conditions and in the presence of 10 µM SZV-2649. Original current records in control conditions and after application of 10 µM SZV-2649 are displayed on the inset. Dashed lines refer to the zero current level. Panel d shows the steady state current-voltage relation recorded with 3000 ms pulsing cycle length in control conditions and in the presence of 10 µM SZV-2649. The applied voltage protocols are displayed on the inset. Data are expressed as means ± SEM. *P < 0.05 vs. control.

Fig. 5

Effect of SZV-2649 on the maximum upstroke velocity (V_max) of action potential in dog ventricular muscle and on the action potential duration (APD) in atrial preparations. Panel a indicates the effect of 10 µM SZV-2649 on V_max as a function of stimulation frequency. Panel b shows the recovery (“offset”) kinetics of SZV-2649-elicited V_max block, while panel c displays the onset kinetics of use-dependent V_max block after 10 µM SZV-2649 administration. Panel d indicates the effect of SZV-2649 on APD in the presence of carbachol in dog atrial trabecular muscle. Effects of 10 µM SZV-2649 administration on action potential after application of 1 µM carbachol are indicated showing original records (left) and bar diagrams (right). The dashed line indicates zero potential level. APD₉₀, action potential duration at 90% of repolarization; APD₇₅, action potential duration at 75% of repolarization. Data are expressed as means ± SEM. *P < 0.05 vs. control; #P < 0.05 vs. carbachol.

Fig. 6

Experimental protocol for the in vivo test system to assess ischaemia-evoked arrhythmias in anesthetized rats following treatment with the test articles (a). Heart rates before and after the administration of test articles (TA) in anesthetized rats subjected to coronary artery occlusion/reperfusion (b). Data are expressed as mean ± S.E.M., n = 8–11, *P < 0.05, **P < 0.001 as analyzed by repeated measures two-way ANOVA with Tukey’s multiple comparisons post hoc test as compared to Vehicle.

Fig. 7

Detailed arrhythmia map showing the arrhythmias in the order of severity during 6 min ischemia followed by 5 min of reperfusion in anesthetized rats induced by coronary artery occlusion and its release, respectively. Each row represents arrhythmias of each animal. The different color boxes show 1 min periods. BL, baseline; TA, test article.

Fig. 8

Grouped data showing the incidence of coronary artery occlusion/reperfusion induced ventricular fibrillation (VF) (a) and myocardial area at risk (b) in rats. n = 9–14, *P < 0.05 as analyzed by Chi-square test with Yate’s correction, pairwise compared to Vehicle (VEH, Vehicle; MEX, mexiletine; DOFE, dofetilide).

Fig. 9

Synthesis of SZV-2649.