Bombesin – Potent natural agonist of the mammalian receptor GRPR
Bombesin (BBN) is a 14-amino acid neuropeptide originally isolated from the skin of Bombina bombina1. The bombesin-related family comprises three other peptides, the amphibian homologs alytesin and Neuromedin C (NMC), and the mammalian peptide named Gastrin-Releasing Peptide (GRP). Bombesin and bombesin-related peptides are characterized by a region of homology at the carboxy-terminus ending with Gly-His-Leu-Met-NH2, in which resides their biological activity2,3 .
Bombesin is active in mammals and affects a broad range of biological functions including smooth muscle contraction, cell growth, blood pressure, plasma glucose, as well as gastric secretions2. These effects are mediated by the interaction of Bombesin peptide with G protein-coupled receptors (GPCRs) called bombesin receptors that are well represented in the gastrointestinal tract and in the central nervous system (CNS)2.
Bombesin peptide is a potent natural agonist of the mammalian Gastrin Releasing Peptide Receptor (GRPR) also know as bombesin receptor 2 (BB2), whose endogenous ligand is the Gastrin Releasing Peptide (GRP). Bombesin has demonstrated a high affinity for human Gastrin-Releasing Peptide Receptors (hGRPR) in both human cells containing native GRP receptors and murine cells stably expressing human GRP receptors (IC50 = 0.17±0.01 nM and 0.07 ± 0.01 nM, respectively)3.There is increased interest in targeting the bombesinreceptors to explore their roles in pathophysiological processes, and for diagnostic imaging of human cancers over-expressing Gastrin-Releasing Peptide Receptors (GRPR), such as prostate, breast, and small-cell lung carcinoma2,3. Bombesin peptide is investigated as targeting peptide to deliver radiotracers and therapeutic agents into tumors. Moreover, many synthetic agonist analogs of the biologically active COOH terminus of bombesin-related peptides have been synthesized to develop more metabolically stable and selective ligands for Bombesin receptors2.
Viene descritto l’isolamento e il chiarimento della struttura della bombesina e della alytesina due tetradecapeptidi attivi a struttura analoga presenti nella pelle fresca rispettivamente della Bombina e dell’Alytes, anfibi europei della famiglia dei discoglossidi. I due polipeptidi manifestano azioni farmacologiche similari sulla pressione del sangue, su svariati organi a muscoli lisci, sulla secrezione gastrica e sulla glicemia.
2-Ramos-Álvarez, I. et al., Peptides 72, 128–144 (2015)
This following article is written for Prof. Abba Kastin’s Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin’s Handbook of Biological Active Peptides [137,138,331].
3-Uehara, H. et al., Peptides 32, 1685–1699 (2011)
The mammalian bombesin (Bn)-receptor family [gastrin-releasing peptide-receptor (GRPR-receptor), neuromedin B-receptor (NMB receptor)], their natural ligands, GRP/NMB, as well as the related orphan receptor, BRS-3, are widely distributed, and frequently overexpressed by tumors. There is increased interest in agonists for this receptor family to explore their roles in physiological/pathophysiological processes, and for receptor-imaging/cytotoxicity in tumors. However, there is minimal data on human pharmacology of Bn receptor agonists and most results are based on nonhuman receptor studies, particular rodent-receptors, which with other receptors frequently differ from human-receptors. To address this issue we compared hNMB-/GRP-receptor affinities and potencies/efficacies of cell activation (assessing phospholipase C activity) for 24 putative Bn-agonists (12 natural, 12 synthetic) in four different cells with these receptors, containing native receptors or receptors expressed at physiological densities, and compared the results to native rat GRP-receptor containing cells (AR42J-cells) or rat NMB receptor cells (C6-glioblastoma cells). There were close correlations (r=0.92-99, p<0.0001) between their affinities/potencies for the two hGRP- or hNMB-receptor cells. Twelve analogs had high affinities (≤ 1 nM) for hGRP receptor with 15 selective for it (greatest=GRP, NMC), eight had high affinity/potencies for hNMB receptors and four were selective for it. Only synthetic Bn analogs containing β-alanine(11) had high affinity for hBRS-3, but also had high affinities/potencies for all GRP-/hNMB-receptor cells. There was no correlation between affinities for human GRP receptors and rat GRP receptors (r=0.131, p=0.54), but hNMB receptor results correlated with rat NMB receptor (r=0.71, p<0.0001). These results elucidate the human and rat GRP-receptor pharmacophore for agonists differs markedly, whereas they do not for NMB receptors, therefore potential GRP-receptor agonists for human studies (such as Bn receptor-imaging/cytotoxicity) must be assessed on human Bn receptors. The current study provides affinities/potencies on a large number of potential agonists that might be useful for human studies.
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