title: Comparative pharmacology of bombesin receptor subtype-3, nonpeptide agonist MK-5046, a universal peptide agonist, and peptide antagonist Bantag-1 for human bombesin receptors.
abstract: Bombesin-receptor-subtype-3 (BRS-3) is an orphan G-protein-coupled receptor of the bombesin (Bn) family whose natural ligand is unknown and which does not bind any natural Bn-peptide with high affinity. It is present in the central nervous system, peripheral tissues, and tumors; however, its role in normal physiology/pathophysiology is largely unknown because of the lack of selective ligands. Recently, MK-5046 [(2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol] and Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate], a nonpeptide agonist and a peptide antagonist, respectively, for BRS-3 have been described, but there have been limited studies on their pharmacology. We studied MK-5046 and Bantag-1 interactions with human Bn-receptors-human bombesin receptor subtype-3 (hBRS-3), gastrin-releasing peptide receptor (GRP-R), and neuromedin B receptor (NMB-R)-and compared them with the nonselective, peptide-agonist [d-Tyr6,βAla11,Phe13,Nle14]Bn-(6-14) (peptide #1). Receptor activation was detected by activation of phospholipase C (PLC), mitogen-activated protein kinase (MAPK), focal adhesion kinase (FAK), paxillin, and Akt. In hBRS-3 cells, the relative affinities were Bantag-1 (1.3 nM) > peptide #1 (2 nM) > MK-5046 (37-160 nM) > GRP, NMB (>10 μM), and the binding-dose-inhibition curves were broad (>4 logs), with Hill coefficients differing significantly from unity. Curve-fitting demonstrated high-affinity (MK-5046, Ki = 0.08 nM) and low-affinity (MK-5046, Ki = 11-29 nM) binding sites. For PLC activation in hBRS-3 cells, the relative potencies were MK-5046 (0.02 nM) > peptide #1 (6 nM) > GRP, NMB, Bantag-1 (>10 μM), and MK-5046 had a biphasic dose response, whereas peptide #1 was monophasic. Bantag-1 was a specific hBRS-3-antagonist. In hBRS-3 cells, MK-5046 was a full agonist for activation of MAPK, FAK, Akt, and paxillin; however, it was a partial agonist for phospholipase A2 (PLA2) activation. The kinetics of activation/duration of action for PLC/MAPK activation of MK-5046 and peptide #1 differed, with peptide #1 causing more rapid stimulation; however, MK-5046 had more prolonged activity. Our study finds that MK-5046 and Bantag-1 have high affinity/selectivity for hBRS-3. The nonpeptide MK-5046 and peptide #1 agonists differ markedly in their receptor coupling, ability to activate different signaling cascades, and kinetics/duration of action. These results show that their hBRS-3 receptor activation is not always concordant and could lead to markedly different cellular responses.
authors.affiliation: Digestive Diseases Branch (P.M., S.M., B.N.-B., R.T.J.) and Diabetes, Endocrinology, and Obesity Branch (M.L.R.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland; Department of Metabolism, Nutrition and Hormones (N.G.), IIS-Fundación Jiménez Díaz, Madrid, Spain; Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Madrid, Spain; and Peptide Research Laboratories, Department of Medicine, Tulane Health Sciences Center, New Orleans, Louisiana (D.H.C.).
authors.forename: Paola
authors.initials: P
authors.lastname: Moreno
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Mantey
authors.forename: Bernardo
authors.initials: B
authors.lastname: Nuche-Berenguer
authors.forename: Marc L
authors.initials: ML
authors.lastname: Reitman
authors.forename: Nieves
authors.initials: N
authors.lastname: González
authors.forename: David H
authors.initials: DH
authors.lastname: Coy
authors.forename: Robert T
authors.initials: RT
authors.lastname: Jensen
mesh_terms: D016475:3T3 Cells; D000818:Animals; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D011720:Pyrazoles / Q000378:metabolism / Q000494:pharmacology*; D018004:Receptors, Bombesin / Q000819:agonists* / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C556243:1,1,1-trifluoro-2-(4-(1H-pyrazol-1-yl)phenyl)-3-(4-((1-(trifluoromethyl)cyclopropyl)methyl)-1H-imidazol-2-yl)propan-2-ol; D007093:Imidazoles; D009842:Oligopeptides; D011720:Pyrazoles; D018004:Receptors, Bombesin; C107120:bombesin receptor subtype 3
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