5-HT4 receptor agonists:: similar but not the same

5-Hydroxytryptamine(4) (5-HT4) receptors are an interesting target for the management of patients in need of gastrointestinal (GI) promotility treatment. They have proven therapeutic potential to treat patients with GI motility disorders. Lack of selectivity for the 5-HT4 receptor has limited the clinical success of the agonists used until now. For instance, next to their affinity for 5-HT4 receptors, both cisapride and tegaserod have appreciable affinity for other receptors, channels or transporters [e.g. cisapride: human ether-a-go-go-related gene (hERG) is K+ channel and tegaserod: 5-HT1 and 5-HT2 receptors]. Adverse cardiovascular events observed with these compounds are not 5-HT4 receptor-related. Recent efforts have led to the discovery of a series of selective 5-HT4 receptor ligands, with prucalopride being the most advanced in clinical development. The selectivity of these new compounds clearly differentiates them from the older generation compounds by minimizing the potential of target-unrelated side effects. The availability of selective agonists enables the focus to shift to the exploration of 5-HT4 receptor-related differences between agonists. Based on drug- and tissue-related properties (e.g. differences in receptor binding, receptor density, effectors, coupling efficiency), 5-HT4 receptor agonists are able to express tissue selectivity, i.e. behave as a partial agonist in some and as a full agonist in other tissues. Furthermore, the concept of ligand-directed signalling offers great opportunities for future drug development by enlarging the scientific basis for the generation of agonist-specific effects in different cell types, tissues or organs. Selective 5-HT4 receptor agonists might thus prove to be innovative drugs with an attractive safety profile for better treatment of patients suffering from hypomotility disorders.