Structure-activity relationship study on Tyr9 of urotensin-II(4-11): identification of a partial agonist of the UT receptor

Combination of Docking-Based and Pharmacophore-Based Virtual Screening Identifies Novel Agonists That Target the Urotensin Receptor

The urotensin receptor (UT receptor), a G-protein-coupled receptor mediating urotensin-II and urotensin-II-related peptide signaling in the urotensinergic system, has multiple pharmacological activities. However, there is no drug targeting the UT receptor currently in clinical use, and the discovery of new leads is still important. The complete crystal structure of the UT receptor has not yet been resolved and a screening strategy combining multiple methods can improve the accuracy and efficiency of drug screening. This study aimed to identify novel UT receptor agonists using a combination of docking-based, pharmacophore-based, and cell-based drug screening. First, the three-dimensional structures of the UT receptor were constructed through single-template, multi-template homologous modeling and threading strategies. After structure evaluation and ligand enrichment analysis, a model from the threading modeling was selected for docking-based virtual screening based on stepwise filtering, and 1368 positive compounds were obtained from our compound library. Second, the pharmacophore models were constructed using known ligands targeting the UT receptor for pharmacophore-based virtual screening. A model was selected after model validation, and 300 positive compounds were retrieved. Then, after intersecting the results of two different virtual screening methods with 570 compound entities from our primary screening, 14 compounds were obtained. Finally, three hits were obtained after in vitro confirmation. Furthermore, preliminary evaluation of the hits showed that they influenced glucose consumption. In summary, by integrating docking-based, pharmacophore-based, and in vitro drug screening, three new agonists targeting the UT receptor were identified which may serve as promising therapeutic agents for urotensinergic system disorders.

Functional Selectivity Revealed by N-Methylation Scanning of Human Urotensin II and Related Peptides

In accordance with their common but also divergent physiological actions, human urotensin II (1) and urotensin II-related peptide (2) could stabilize specific urotensin II receptor (UTR) conformations, thereby activating different signaling pathways, a feature referred to as biased agonism or functional selectivity. Sequential N-methylation of the amides in the conserved core sequence of 1, 2, and fragment U-II_4-11 (3) shed light on structural requirements involved in their functional selectivity. Thus, 18 N-methylated UTR ligands were synthesized and their biological profiles evaluated using in vitro competition binding assays, ex vivo rat aortic ring bioassays and BRET-based biosensor experiments. Biological activity diverged from that of the parent structures contingent on the location of amide methylation, indicating relevant hydrogen-bond interactions for the function of the endogenous peptides. Conformational analysis of selected N-methyl analogs indicated the importance of specific amide residues of 2 for the distinct pharmacology relative to 1 and 3.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Characterization of iodinated adrenomedullin derivatives suitable for lung nuclear medicine

INTRODUCTION

We have recently demonstrated the effectiveness of 99m-technetium adrenomedullin (AM) as a new molecular lung imaging agent that could provide significant advantages for the diagnosis and follow-up of disorders affecting the pulmonary circulation such as pulmonary embolism and pulmonary hypertension. Having the possibility to conjugate the targeting molecule with different radionuclides would offer more flexibility and potential advantages depending on clinical situations. Since various iodine isotopes are currently used in nuclear medicine and in pharmacological studies, we have evaluated which iodination method should be privileged in order to produce a good iodinated AM-derived nuclear medicine agent.

METHODS

Synthetic AM was labeled with iodine through chemical and lactoperoxidase oxidation methods. Position of the iodine atom on the peptide was determined by MALDI-TOF mass spectrometry analysis following cyanogen bromide cleavage and carboxypeptidase Y digestion. Binding affinity of iodinated AM analogues was evaluated by competition and saturation binding experiments on dog lung preparations.

RESULTS

In this study, we demonstrated that, upon lactoperoxidase oxidation, iodination occurred at Tyr(1) and that this radioligand retained higher binding affinity and specificity over preparations obtained through chemical oxidation.

CONCLUSIONS

These results emphasize the fact that even a small chemical modification, i.e. iodination, might deeply modify the pharmacological profile of a compound and support observations that the C-terminal tail of human AM plays an important role in the AM receptor binding process. Consequently, incorporation of a radionuclide to produce an AM-based nuclear medicine agent should privilege the N-terminus of the molecule.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.