Bombesin, a peptide of 14 amino acids, is an amphibian homolog to the mammalian gastrin-releasing peptide (GRP), that has been extensively studied as a targeting ligand for diagnosis and therapy of GRP positive tumors, such as breast, pancreas, lungs and prostate cancers. Bombesin binds to and activates G-protein coupled receptors, known as gastrin releasing peptide receptor (GRPR).

Bombesin, a tetradecapeptide isolated from the skin of the frog Bombina bombina, have shown broad spectrum of biological activities. The BBS activates three G protein-coupled receptors: bombesin receptor 1 (BB₁), bombesin receptor 2 (BB₂), and bombesin receptor 3 (BB₃). BBS-like peptides-Neuromedin B (NB) and gastrin releasing peptide (GRP) are natural ligand of the BB1 and BB2 receptors, respectively.

In mammals, BBS receptors and BBS-like peptides are distributed in the Central Nervous System (CNS) including regions involved in the cardiorespiratory control.

The mammalian bombesin G-protein-coupled receptor subfamily comprises three structurally related members, the receptors for neuromedin B (NMBR or BB1), gastrin-releasing peptide (GRPR or BB2), and bombesin receptor subtype-3 (BRS-3 or BB3).

Bombesin receptor subtype-3 (BRS-3) is an orphan G protein-coupled receptor implicated in the regulation of energy homeostasis.