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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

Identification of Bombesin Receptor Subtype-Specific Ligands: Effect of N-Methyl Scanning, Truncation, Substitution, and Evaluation of Putative Reported Selective Ligands

From the Digestive Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland (S.A.M., N.G., M.S., T.K.P., L.S., R.T.J.); and the Department of Medicine, Peptide Research, Tulane University Health Science Center, New Orleans, Louisiana (D.H.C.)

Mammalian bombesin (Bn) receptors include the gastrin-releasing peptide receptor, neuromedin B receptor, and bombesin receptor subtype 3 (BRS-3). These receptors are involved in a variety of physiological/pathologic processes, including thermoregulation, secretion, motility, chemotaxis, and mitogenic effects on both normal and malignant cells. Tumors frequently overexpress these receptors, and their presence is now used for imaging and receptor-mediated cytotoxicity. For these reasons, there is an increased need to develop synthetic, selective receptor subtype-specific ligands, especially agonists for these receptors. In this study, we used a number of strategies to identify useful receptor subtype-selective ligands, including synthesizing new analogs (N-methyl-substituted constrained analogs, truncations, and substitutions) in [D-Tyr⁶,Ala¹¹,Phe¹³,Nle¹⁴]Bn(6–14), which has high affinity for all Bn receptors and is metabolically stable, as well as completely pharmacologically characterized analogs recently reported to be selective for these receptors in [Ca²⁺]_i assays. Affinities and potencies of each analog were determined for each human Bn receptor subtype. N-Methyl substitutions in positions 14, 12, 11, 10, 9, and 8 did not result in selective analogs, with the exception of position 11, which markedly decreased affinity/potency. N-Terminal truncations or position 12 substitutions did not increase selectivity as previously reported by others. Of the four shortened analogs of [D-Phe⁶,Ala¹¹,Phe¹³,Nle¹⁴]Bn(6–14) reported to be potent selective BRS-3 ligands on [Ca²⁺]_i assays, only AcPhe,Trp,Ala,His(Bzl),Nip,Gly,Arg-NH₂ had moderate selectivity for hBRS-3; however, it was less selective than previously reported Apa¹¹ analogs, demonstrating these are still the most selective BRS-3 analogs available. However, both of these analogs should be useful templates to develop more selective BRS-3 ligands.

Address correspondence to: Dr. Robert T. Jensen, DHHS/NIH, NIDDK, DDB, Bldg. 10, Rm. 9C103, 31 Center Drive, Bethesda, MD 20892. E-mail: robertj{at}bdg10.niddk.nih.gov

This article has been cited by other articles:

				R. T. Jensen, J. F. Battey, E. R. Spindel, and R. V. Benya International Union of Pharmacology. LXVIII. Mammalian Bombesin Receptors: Nomenclature, Distribution, Pharmacology, Signaling, and Functions in Normal and Disease States Pharmacol. Rev., March 1, 2008; 60(1): 1 - 42. [Abstract] [Full Text] [PDF]

				N. Gonzalez, S. J. Hocart, S. Portal-Nunez, S. A. Mantey, T. Nakagawa, E. Zudaire, D. H. Coy, and R. T. Jensen Molecular Basis for Agonist Selectivity and Activation of the Orphan Bombesin Receptor Subtype 3 Receptor J. Pharmacol. Exp. Ther., February 1, 2008; 324(2): 463 - 474. [Abstract] [Full Text] [PDF]