In Vitro Cardiac Safety Profiling of a Novel Benzyl-Ethylamine Compound

Abstract

When developing novel compounds for any clinical indication, the possibility of untoward cardiovascular effects must be addressed. To evaluate the cardiac electrophysiologic effects of A-674563 ((S)-1-benzyl-2-[5-(3-methyl-1H-indazol-5-yl)-pyridin-3-yloxy]-ethylamine), a novel benzyl-ethylamine, we profiled the compound in a series of cellular and tissue assays. In canine Purkinje fibers (30 min exposure; 2 sec BCL), A-674563 elicited concentration dependent depolarization with shouldering of the terminal repolarization phase (20 μM) and increased abnormal automaticity (60 μM). In papillary muscles, concentration dependent depolarization was also seen, but the effect was much less potent; 60 μM induced shouldering of the terminal phase of repolarization. Contractility was assessed using percent changes in fractional shortening of sarcomere length (FS) in rabbit left ventricular myocytes. A-674563 reduced FS in a concentration dependent manner; 10% at 2 μM and 47% at 20 μM. Effects on ionic currents were further evaluated using heterologously expressed cardiac ion channel cell lines. A-674563 inhibited Cav1.2, expressed in HEK cells, with an IC50 of 20 μM, suggesting that the decreased contractility seen in native cells is due to L-type calcium channel block. The compound reduced Nav1.5 (HEK cells) by 50% at 20 μM and inhibited Kir2.1 (tSA201 cells) with an IC50 of 35 μM. Block of these channels would be expected to reduce the upstroke velocity, depolarize the cellular membrane and lead to abnormal automaticity as was seen in the tissue assays. Although A-674563 caused minimal prolongation of action potential duration in tissues up to 60 μM, it inhibited hERG (HEK cells) with an IC50 of 0.7 μM. This potent block was most likely offset by the concomitant block of multiple cardiac ion channels. In conclusion, A-674563 affects multiple cardiac ion channels to elicit depolarization and increased automaticity in native cardiac tissues.