Structure-activity optimization of ryanodine receptor modulators for the treatment of catecholaminergic polymorphic ventricular tachycardia.

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia disorder associated with lethal arrhythmias. Most CPVT cases are caused by inherited variants in the gene encoding ryanodine receptor type 2 (RYR2).
Objective: The goal of this study was to investigate the structure-activity relationship of tetracaine derivatives and to 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 Ca ²⁺ handling in cardiomyocytes from R176Q/+ mice was tested with confocal microscopy. The effects of lead compound MSV1302 on arrhythmia inducibility and cardiac contractility were tested by programmed electrical stimulation and echocardiography, respectively. Plasma and microsomal stability and cytotoxicity assays were also performed.
Results: Ca ²⁺ imaging revealed that 3 of 11 compounds suppressed sarcoplasmic reticulum Ca ²⁺ leak through mutant RyR2. Two compounds selected for further testing exhibited a half-maximal effective concentration of 146 nM (MSV1302) and 49 nM (MSV1406). Whereas neither compound altered baseline electrocardiogram 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 affect cardiac inotropy and chronotropy. Finally, compound MSV1302 did not block I _Na , I _Ca,L , or I _Kr ; it exhibited excellent stability in plasma and microsomes, and it 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.
Competing Interests: Disclosures R.M.S. and X.H.T.W. are founding partners and M.S.-V., R.M.S., and X.H.T.W. were shareholders of Elex Biotech Inc, a start-up company that developed drug molecules that target ryanodine receptors to treat cardiac arrhythmia disorders. The other authors do not have relevant disclosures.
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