[H-3] GR 113808

GR 113808 is a synthetic ester derivative that acts as a potent, competitive antagonist at serotonin 5-HT4 receptors. By binding to these receptors, it inhibits 5-HT4-mediated adenylyl cyclase stimulation and cAMP accumulation, thereby blocking downstream serotonergic signaling in both central and peripheral tissues.

GR 113808 selectively targets 5-HT4 receptors by occupying their orthosteric binding site with high complementary structural fit, preventing endogenous serotonin (5-HT) or synthetic agonists from binding. Its chemical structure confers extreme target specificity, leaving other serotonin receptor families completely uninhibited at therapeutic research concentrations.

GR 113808 exhibits sub-nanomolar binding affinity for 5-HT4 receptors, with an reported equilibrium dissociation constant (Kd) or affinity constant (pKB) typically ranging around 9.0 to 9.5 (Kd = 0.3-1.0 nM) across human and animal tissue preparations.

GR 113808 is exceptionally selective, displaying greater than 1,000-fold higher affinity for 5-HT4 receptors over other serotonin receptor subtypes (5-HT1, 5-HT2, 5-HT3, 5-HT6, and 5-HT7). This makes it significantly more selective for 5-HT4 than older generation or broader-spectrum serotonergic antagonists like tropisetron or metoclopramide.

In preclinical neuroscience and gastroenterology, GR 113808 is used to investigate 5-HT4-mediated neurotransmitter release, gastrointestinal promotility mechanisms, and cognitive processes like memory consolidation. Radiolabeled [3H]-GR 113808}$ is also widely employed as a golden-standard ligand in radioreceptor binding assays and autoradiography to map 5-HT4 receptor distribution in brain and peripheral tissues.

While GR 113808 itself remains a laboratory research tool, clinical drugs targeting 5-HT4 receptors generally act as agonists (such as prucalopride) to promote gastrointestinal motility rather than antagonists. However, 5-HT4 antagonists related to GR 113808 have been investigated preclinically for potential therapeutic roles in treating cardiac arrhythmias, irritable bowel syndrome, and anxiety disorders.

Although both are research antagonists developed by Glaxo, GR 113808 is a selective blocker for the 5-HT4 receptor subtype, whereas GR 125743 selectively targets and blocks 5-HT1B and 5-HT1D receptors. Consequently, they regulate entirely distinct physiological pathways and intracellular signaling cascades (cAMP stimulation vs. Gi/Go-mediated inhibition).