Bitopic Sphingosine 1-Phosphate Receptor 3 (S1P3) Antagonist Rescue from Complete Heart Block: Pharmacological and Genetic Evidence for Direct S1P3 Regulation of Mouse Cardiac Conduction

Abstract

The molecular pharmacology of the G protein-coupled receptors for sphingosine 1-phosphate (S1P) provides important insight into established and new therapeutic targets. A new, potent bitopic S1P 3 antagonist, SPM-354, with in vivo activity, has been used, together with S1P 3 -knockin and S1P 3 -knockout mice to define the spatial and functional properties of S1P 3 in regulating cardiac conduction. We show that S1P 3 is a key direct regulator of cardiac rhythm both in vivo and in isolated perfused hearts. 2-Amino-2-[2-(4-octylphenyl)ethyl] propane-1,3-diol in vivo and S1P in isolated hearts induced a spectrum of cardiac effects, ranging from sinus bradycardia to complete heart block, as measured by a surface electrocardiogram in anesthetized mice and in volume-conducted Langendorff preparations. The agonist effects on complete heart block are absent in S1P 3 -knockout mice and are reversed in wild-type mice with SPM-354, as characterized and described here. Homologous knockin of S1P 3 -mCherry is fully functional pharmacologically and is strongly expressed by immunohistochemistry confocal microscopy in Hyperpolarization Activated Cyclic Nucleotide Gated Potassium Channel 4 (HCN4)-positive atrioventricular node and His-Purkinje fibers, with relative less expression in the HCN4-positive sinoatrial node. In Langendorff studies, at constant pressure, SPM-354 restored sinus rhythm in S1P-induced complete heart block and fully reversed S1P-mediated bradycardia. S1P 3 distribution and function in the mouse ventricular cardiac conduction system suggest a direct mechanism for heart block risk that should be further studied in humans. A richer understanding of receptor and ligand usage in the pacemaker cells of the cardiac system is likely to be useful in understanding ventricular conduction in health, disease, and pharmacology.

Cardiac Safety of Ozanimod, a Novel Sphingosine‐1‐Phosphate Receptor Modulator: Results of a Thorough QT/QTc Study

“…In mice, S1P 3 receptors are expressed in cardiac Purkinje fibers, and their activation is associated with blockade of ventricular conduction. Fingolimod‐induced cardiac abnormalities are not observed in S1P 3 knockout mice and are reversed in wild‐type mice with a selective S1P 3 antagonist . In human TQT studies, results with fingolimod and 2 other S1P receptor‐targeting agents in development (ponesimod and siponimod) support a potential relationship between activity at S1P 3R and QT prolongation.…”

“…Fingolimodinduced cardiac abnormalities are not observed in S1P 3 knockout mice and are reversed in wild-type mice with a selective S1P 3 antagonist. 13 In human TQT studies, results with fingolimod and 2 other S1P receptor-targeting agents in development (ponesimod and siponimod) support a potential relationship between activity at S1P 3R and QT prolongation. In addition to the observation of QT prolongation with the nonselective agonist fingolimod, such prolongation has occurred in a TQT study of ponesimod, which has only modest selectivity for S1P 1R vs S1P 3R (18-fold).…”

“…Fingolimod, a nonselective S1P 1,3,4,5R agonist approved for treatment of RMS, can cause transient first‐ and second‐degree atrioventricular (AV) blocks and prolongation of the corrected QT interval (QTc) . It has been postulated that this QTc effect may occur via activation of S1P 3R expressed in cells of the His‐Purkinje fibers . The potential for cardiac adverse events complicates the initiation of treatment with fingolimod and requires cardiac monitoring for at least 6 hours after the first dose.…”

“…12 It has been postulated that this QTc effect may occur via activation of S1P 3R expressed in cells of the His-Purkinje fibers. 13 The potential for cardiac adverse events complicates the initiation of treatment with fingolimod and requires cardiac monitoring for at least 6 hours after the first dose. Bradycardia and first-and second-degree AV conduction blocks also have been reported for other S1P receptor agonists in clinical development for multiple sclerosis [14][15][16][17][18][19] as well as prolongation of the QTc interval.…”

Clinical pharmacology, efficacy, and safety aspects of sphingosine-1-phosphate receptor modulators

“…It was suggested that modulation of S1P 3 receptors on cardiac myocytes by fingolimod was associated with a reduction in HR by activation of G-protein-coupled inwardly rectifying potassium channels (GIRK) that regulate pacemaker activity [98] and may lead to heart block [99]. This effect was confirmed in clinical studies [100].…”