Structure Activity Optimization of Ryanodine Receptor Modulators for the Treatment of Catecholaminergic Polymorphic Ventricular Tachycardia.

ABSTRACT

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia disorder associated with potentially lethal arrhythmias. Most CPVT cases are caused by inherited variants in the ryanodine receptor type-2 (RYR2) gene. OBJECTIVE: To investigate the structure activity relationship of tetracaine derivatives and test a lead compound in a mouse model of CPVT. METHODS: We synthesized >200 tetracaine derivatives and characterized 11 of those. The effects of these compounds on Ca2+ handling in cardiomyocytes from R176Q/+ mice was tested using confocal microscopy. The effects of lead compound MSV1302 on arrhythmia inducibility and cardiac contractility were tested using programmed electrical stimulation and echocardiography, respectively. Plasma and microsomal stability and cytotoxicity assays were also performed. RESULTS: Ca2+ imaging revealed that 4 of 11 compounds suppressed sarcoplasmic reticulum Ca2+ leak through mutant RyR2. Two compounds selected for further testing exhibited an EC50 of 146 nM (MSV1302) and 49 nM (MSV1406), respectively. While neither compound altered baseline ECG intervals, only MSV1302 suppressed stress- and pacing-induced ventricular tachycardia in vivo in R176Q/+ mice. Echocardiography revealed that the lead compound MSV1302 did not negatively impact cardiac inotropy and chronotropy. Finally, compound MSV1302 did not block INa, ICa,L, or IKr, exhibited excellent stability in plasma and microsomes, and was not cytotoxic. CONCLUSION: Structure activity relationship studies of second generation tetracaine derivatives identified lead compound MSV1302 with a favorable pharmacokinetic profile. MSV1302 normalized aberrant RyR2 activity in vitro and in vivo, without altering cardiac inotropy, chronotropy or off-target effects on other ion channels. This compound may be a strong candidate for future clinical studies to determine its efficacy in CPVT patients.