In Depth Review,Gastrin-releasing peptide receptor (GRPR

The intricate signaling pathways within the human body are orchestrated by a variety of molecules, among which peptides play a crucial role. Two such peptides that have garnered significant scientific attention are gastrin-releasing peptide (GRP) and bombesin. While often discussed in tandem, understanding their distinct origins, functions, and interactions, particularly concerning the gastrin-releasing peptide receptor ([GRPR]), is key to appreciating their broader biological implications.

Bombesin, a decapeptide, was first isolated from the skin of the European frog, *Bombina bombina*. Its discovery marked the beginning of research into a family of homologous amphibian peptides. In mammals, including humans, the functional equivalent of bombesin is gastrin-releasing peptide (GRP). GRP is a 27-amino acid peptide that shares significant structural and functional similarities with bombesin, leading to their frequent grouping as bombesin-like peptides (BLPs). The gene encoding GRP (gastrin-releasing peptide) produces a preproprotein that, after signal peptide cleavage, undergoes further processing to yield the mature releasing peptide.

The biological effects of bombesin and its mammalian analog, gastrin-releasing peptide, are diverse and far-reaching. They influence a multitude of physiological processes, including gut motility and secretion, hormone release, and pancreatic enzyme secretion. Notably, bombesin-like peptides have profound effects on thermoregulation, with injections of GRP or neuromedin B (NMB) often leading to decreased body temperature in experimental models. Furthermore, bombesin is a neuropeptide with various biological actions, such as stimulating pancreatic enzyme secretion and inhibiting gastric emptying. In some contexts, bombesin is a putative antibacterial peptide, highlighting its potential role beyond mammalian physiology.

A central element in the action of bombesin and GRP is their interaction with specific receptors. The primary receptor for bombesin and GRP in mammals is the gastrin-releasing peptide receptor (GRPR), also known as the bombesin receptor 2 (BRS1, BB2, BBR-2). This G protein-coupled receptor belongs to the bombesin receptor family, which also includes the neuromedin B receptor (NMBR) and bombesin receptor subtype 3 (BRS-3). The gastrin-releasing peptide receptor (GRPR) is particularly noteworthy due to its overexpression in various cancer types. This makes the gastrin-releasing peptide receptor (GRPR) a promising target for cancer diagnosis and therapy. Indeed, the gastrin-releasing peptide receptor is overexpressed in many cancers, including breast and prostate cancers, with the gastrin-releasing peptide receptor being overexpressed in over 80% of estrogen receptor-positive breast cancers and up to 100% of primary prostate cancers.

The therapeutic potential of targeting the gastrin-releasing peptide receptor (GRPR) has spurred the development of various agents. For instance, bombesin/gastrin releasing peptide (BN/GRP) antagonists, such as RC-3095, have been investigated for their ability to block certain receptor-mediated pathways. Research continues into novel radioligands targeting the gastrin-releasing peptide receptor, aiming to improve imaging and therapeutic delivery for cancers expressing this receptor. The development of specific assay kits, like the Simple Plex Human Pro-GRP/Gastrin-releasing Peptide/Bombesin assay kit, further aids in the study and quantification of these crucial peptides.

While bombesin itself has not been identified in mammals, its evolutionary lineage has led to the development of gastrin-releasing peptide (GRP), the mammalian homologue of bombesin. This intricate relationship between gastrin, releasing peptide, and bombesin underscores the complex signaling networks that regulate fundamental biological processes. The ongoing exploration of gastrin-releasing peptide bombesin interactions and their associated receptors continues to unveil new insights into physiology and disease, offering potential avenues for innovative medical interventions.