Cisapride (R 51619): Nonselective 5-HT4 Agonist and hERG Channel Inhibitor

Executive Summary: Cisapride (R 51619) is a nonselective 5-HT4 receptor agonist and a potent inhibitor of the hERG potassium channel, used primarily in research on cardiac electrophysiology and gastrointestinal (GI) motility (Grafton et al., 2021). It is chemically defined as 4-amino-5-chloro-N-[1-[3-(4-fluorophenoxy)propyl]-3-methoxypiperidin-4-yl]-2-methoxybenzamide, with a molecular weight of 465.95 and a purity of ≥99.70% (ApexBio). Cisapride is highly soluble in DMSO (≥23.3 mg/mL) and ethanol (≥3.47 mg/mL) but insoluble in water. It is stored at -20°C for stability, and long-term storage of solutions is not recommended. Cisapride is routinely used in phenotypic screening assays, especially with iPSC-derived cardiomyocytes, to model hERG-related proarrhythmic risk (Grafton et al., 2021).

Biological Rationale

Cisapride (R 51619) was originally developed as a prokinetic agent for GI motility disorders, acting as a nonselective 5-HT4 receptor agonist (ApexBio). The 5-HT4 receptor is a G protein-coupled receptor (GPCR) expressed in the enteric and central nervous systems, as well as in cardiac tissue. Activation of 5-HT4 receptors enhances GI motility by increasing acetylcholine release in the myenteric plexus (ApexBio). However, cisapride’s off-target inhibition of the hERG (human ether-à-go-go-related gene) potassium channel has made it a reference tool for studying drug-induced QT prolongation and arrhythmogenesis (Grafton et al., 2021). hERG encodes the Kv11.1 channel, which is critical for cardiac repolarization. Blockade of hERG can lead to acquired long QT syndrome and torsades de pointes, a potentially fatal ventricular arrhythmia. The dual activity profile of cisapride makes it valuable for dissecting both prokinetic and proarrhythmic mechanisms in modern phenotypic screening workflows.

Mechanism of Action of Cisapride (R 51619)

Cisapride acts as a nonselective agonist at the 5-HT4 receptor, promoting cyclic AMP (cAMP) accumulation and downstream signaling in enteric neurons (ApexBio). This results in increased neurotransmitter release, enhancing peristalsis and GI transit. At the cardiac level, cisapride potently inhibits the hERG potassium channel by binding to its central cavity (Grafton et al., 2021). hERG inhibition delays repolarization of the cardiac action potential, resulting in QT interval prolongation on the electrocardiogram. This mechanistic action has been exploited to benchmark cardiotoxicity models, especially those using iPSC-derived cardiomyocytes, where cisapride induces robust, reproducible phenotypic changes. The compound’s high affinity for hERG is a primary reason for its withdrawal from clinical use, but it remains a gold-standard tool compound in research.

Evidence & Benchmarks

• Cisapride induces concentration-dependent QT prolongation by inhibiting hERG potassium channels in both native cardiac tissue and iPSC-derived cardiomyocyte models (Grafton et al., 2021).
• In high-content phenotypic screens using iPSC-derived cardiomyocytes, cisapride produces a robust cardiotoxicity signal, serving as a positive control for hERG-related arrhythmia risk (Grafton et al., 2021).
• Cisapride’s solubility in DMSO (≥23.3 mg/mL) and ethanol (≥3.47 mg/mL) enables high-throughput screening and dosing flexibility (ApexBio).
• Batch-to-batch purity of ≥99.70% is confirmed by HPLC, NMR, and MSDS, ensuring reproducibility in research applications (ApexBio).
• Phenotypic screening platforms leveraging deep learning readily classify cisapride as a cardiotoxic agent in blinded testing (Grafton et al., 2021).

This article extends the discussion in "Cisapride (R 51619): Precision Tool for Cardiotoxicity and GI Motility Research" by providing updated evidence from deep-learning phenotypic screens and reinforced benchmarks for hERG inhibition. For a mechanistic focus, see "Cisapride (R 51619): Mechanistic Insights for Cardiac Electrophysiology", which this article updates with structured, machine-readable benchmarks. For translational perspectives, "Cisapride (R 51619): Mechanistic Insight and Strategic Guidance" offers a broader strategic synthesis; this article focuses on empirical evidence and technical integration.

Applications, Limits & Misconceptions

Research Applications:

• Cardiac electrophysiology research, especially modeling hERG-related arrhythmia risk.
• Phenotypic screening for cardiotoxicity using iPSC-derived cardiomyocytes.
• Dissection of 5-HT4 receptor-mediated GI motility signaling.
• Tool compound to benchmark proarrhythmic liability in early-stage drug discovery (Grafton et al., 2021).

Common Pitfalls or Misconceptions

• Cisapride is not selective for the 5-HT4 receptor; it also inhibits hERG channels at clinically relevant concentrations.
• It is not suitable for in vivo applications in humans due to the risk of fatal arrhythmias.
• Long-term storage of cisapride solutions is not recommended; stability is optimal for the solid form at -20°C (ApexBio).
• Cisapride is insoluble in water, limiting its use in aqueous-only systems.
• hERG inhibition is not unique to cisapride; other compounds may produce similar phenotypes, necessitating appropriate controls.

Workflow Integration & Parameters

Cisapride (R 51619) is supplied as a solid with a molecular weight of 465.95 and a purity of ≥99.70%. For experimental use, it is typically dissolved in DMSO or ethanol at concentrations up to the solubility limits (DMSO: ≥23.3 mg/mL; ethanol: ≥3.47 mg/mL). The compound is stored at -20°C to maintain stability; solutions should be prepared fresh or used within a short period to avoid degradation. In high-throughput screening and cardiac safety assays, cisapride is commonly used as a positive control for hERG channel inhibition and QT prolongation. iPSC-derived cardiomyocyte assays provide human-relevant phenotypic readouts, with deep learning analytics further enhancing sensitivity and specificity for cardiotoxicity detection (Grafton et al., 2021).

For detailed product specifications, refer to the Cisapride (R 51619) B1198 kit page. For precision modeling protocols, see the update in "Cisapride (R 51619): Precision Modeling of Cardiac Risk in iPSC-Derived Systems"; this article details newer integration and deep-learning analysis strategies.

Conclusion & Outlook

Cisapride (R 51619) remains a benchmark compound for modeling drug-induced cardiotoxicity via hERG inhibition, supporting advancements in predictive cardiac safety and GI motility research. Its robust chemical profile and consistent biological activity make it indispensable for phenotypic screening, especially in iPSC-derived cardiomyocyte platforms integrated with deep learning. Future work will likely focus on refining selectivity and developing analogs with improved safety, but cisapride’s role as a positive control and mechanistic probe in translational research is firmly established (Grafton et al., 2021).