Characterization of putative GRP- and NMB-receptor antagonist's interaction with human receptors.
The mammalian bombesin (Bn) peptides neuromedin B (NMB) and gastrin-releasing peptide (GRP) actions are mediated by two receptors (NMB-receptor, GRP-receptor) which are widely distributed in the GI tract and CNS. From primarily animal studies NMB/GRP-receptor activation has physiological/pathophysiological effects in the CNS and GI tract including stimulating of growth of cancers and normal tissues. Whereas these Bn-receptors' effects have been extensively studied in nonhuman cells and animals, little is known of the physiological/pathological role(s) in humans, largely due to lack of potent antagonists. To address this issue we compared NMB/GRP-receptor affinity/potency of 10 chemical classes of putative antagonists (35 compounds) for human Bn-receptors by performing binding studies or assessing abilities to activate hGRP/hNMB-receptor [assessing phospholipase C activation] in four different cells containing native Bn-receptors or transfected receptors. From binding studies 23 were GRP-receptor-preferring, 4 were NMB-receptor, and 8 nonselective. For the hGRP-receptor-preferring analogues none showed hGRP-receptor agonist activity, but 13 were full or partial hNMB-receptor agonists at hNMB-receptors. For hNMB-receptor-preferring analogues none were agonists. Analogue #24 ([(3-Ph-Pr(6)), His(7), d-Ala(11), d-Pro(13), Psi(13-14), Phe(14)]Bn(6-14)NH2) and analogue #7 [d-Phe(6), Leu(13), Psi(CH(2)NH), Cpa(14)]Bn(6-14) were the most potent (0.2-1.4nM) and selective (>10,000-fold) for the hGRP-receptor with analogue #7.5 [d-Tpi(6), Leu(13), Psi(CH2NH), Leu(14)]Bn(6-14)[RC-3095] (0.2-1.4nM) slightly less selective. Analogue #34 (PD168368) had the highest affinity for hNMB-receptor (1.32-1.58nM) and the greatest selectivity (2298-6952-fold) for the hNMB-receptor. These results demonstrate numerous putative hGRP/hNMB-receptor antagonists identified in nonhuman cells and/or animals have agonist activity at the hNMB-receptor, limiting their potential usefulness. However, a number were identified which were potent/selective for human Bn-receptors and should be useful for investigating their roles in human physiological/pathophysiological conditions.
González
Nieves
N
Digestive Diseases Branch, NIDDK, and Department of Health and Human Services, National Institutes of Health, Bethesda, MD 20892-1804, United States.
Mantey
Samuel A
SA
Pradhan
Tapas K
TK
Sancho
Veronica
V
Moody
Terry W
TW
Coy
David H
DH
Jensen
Robert T
RT
D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D051379:Mice; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D018004:Receptors, Bombesin / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
D007295:Inositol Phosphates; D010455:Peptides; D018004:Receptors, Bombesin; D010738:Type C Phospholipases