title: Development of bombesin analogs with conformationally restricted amino acid substitutions with enhanced selectivity for the orphan receptor human bombesin receptor subtype 3.
abstract: The human bombesin receptor subtype 3 (hBRS-3) orphan receptor, which has a high homology to bombesin (Bn) receptors [gastrin-releasing peptide (GRP) and neuromedin B (NMB) receptors], is widely distributed in the rat central nervous system. Its natural ligand or role in physiology is unknown due to lack of selective ligands. Its target disruption leads to obesity, diabetes, and hypertension. A synthetic high-affinity agonist, [D-Tyr6,beta-Ala11,Phe13,Nle14]Bn(6-14), has been described, but it is nonselective for hBRS-3 over other Bn receptors; however, substitution of (R)- or (S)-amino-3-phenylpropionic acid (Apa) for beta-Ala11 resulted in a modestly selective ligand. In the present study, we have attempted to develop a more selective hBRS-3 ligand by using two strategies: substitutions on phenyl ring of Apa11 and the substitution of other conformationally restricted amino acids into position 11 of [D-Tyr6,beta-Ala11,Phe13,Nle14]Bn(6-14). Fifteen analogs were synthesized and affinities were determined for hBRS-3 and Bn receptors (hGRP-R and hNMB-R). Selective analogs were tested for their ability to activate each receptor by stimulating phospholipase C. One analog, [D-Tyr6,Apa-4Cl,Phe13,Nle14]Bn(6-14), retained high affinity for the hBRS-3 (Ki=8 nM) and had enhanced selectivity (>230-fold) for hBRS-3 over hGRP-R or hNMB-R. This analog specifically interacted with hBRS-3, fully activated hBRS-3 receptors, and was a potent agonist at the hBRS-3 receptor. This enhanced selectivity should allow this analog to be useful for investigating the possible role of hBRS-3 in physiological or pathological processes.
authors.affiliation: Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 10, Room 9C-103, 10 Center Dr., MSC 1804, Bethesda, MD 20892-1804l, USA.
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Mantey
authors.forename: David H
authors.initials: DH
authors.lastname: Coy
authors.forename: Laurence K
authors.initials: LK
authors.lastname: Entsuah
authors.forename: Robert T
authors.initials: RT
authors.lastname: Jensen
mesh_terms: D016475:3T3 Cells; D019943:Amino Acid Substitution; D000818:Animals; D001839:Bombesin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D011487:Protein Conformation; D051381:Rats; D018004:Receptors, Bombesin / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D018004:Receptors, Bombesin; C107120:bombesin receptor subtype 3; D001839:Bombesin