Identification of small-molecule antagonists targeting the Growth Hormone Releasing Hormone Receptor (GHRHR)

Background and Purpose: Growth hormone-releasing hormone (GHRH), a 44-residue neuropeptide produced in the hypothalamus, stimulates the synthesis and release of pituitary growth hormone via binding to its cognate receptor, the growth hormone-releasing hormone receptor (GHRHR). The GHRHR belongs to Class B1 of G protein-coupled receptors (GPCRs). Class B1 GPCR peptides have been proposed to bind in a two-step model, where firstly the C-terminal region of the peptide interacts with the extracellular domain of the receptor and subsequently, the N-terminus interacts with the seven transmembrane domain of the receptor, resulting in activation. No non-peptide compounds targeting the GHRHR have been identified, despite observations indicating that it may be an effective therapeutic target due to overexpression in several disorders including prostate, breast, pancreatic and ovarian cancer, and peptide antagonists displaying promising results in many cancer models. Experimental Approach: We have utilized several computational tools to target the GHRHR and identify potential small-molecule compounds directed at this receptor. These compounds were validated in vitro using a cAMP ELISA to measure activity at the GHRHR. Key Results: In vitro results suggest that several of the novel small-molecule compounds could inhibit GHRH-induced cAMP accumulation. Preliminary analysis of the specificity/selectivity of one of the most effective hit compounds indicated that the effect was via antagonism of the GHRHR. Conclusion and Implications: We therefore report the first non-peptide antagonists of GHRHR and propose a structural basis for antagonism, which may assist in the future design of lead GHRHR compounds for treating disorders attributed to dysregulated/aberrant GHRHR signalling.