Melanocortin 2 Receptor Antagonists in ACTH-Dependent Hypercortisolism: In Vitro Study in Canine Primary Adrenocortical Cell Culture

Presentation Number: MON 368
Date of Presentation: April 3rd, 2017

Karin Sanders*, Jan A. Mol, Hans S. Kooistra and Sara Galac
Utrecht University, Utrecht, Netherlands

Abstract

Hypercortisolism (Cushing’s syndrome) is one of the most frequently diagnosed endocrinopathies in dogs. As in humans, hypercortisolism in dogs is ACTH-dependent in the majority of cases, mostly due to an ACTH-secreting pituitary adenoma (Cushing’s disease). The resemblances between Cushing’s disease in dogs and humans bring potential for the dog as an animal model for the human disease. In ACTH-dependent hypercortisolism, the clinical signs are the result of excessive binding of ACTH to its receptor: the melanocortin 2 receptor (MC2R). Antagonism of this receptor could therefore be an interesting treatment target to selectively inhibit cortisol production in this type of hypercortisolism.

The aim of this study was to determine the effectiveness of two different compounds, BIM-22776 (776) and BIM-22A299 (299), as MC2R antagonists, on canine primary adrenocortical cell culture. Primary adrenocortical cell cultures (n=8) of normal canine adrenal glands were incubated with 50 nM synthetic ACTH (Synacthen®) to mimic ACTH-dependent hypercortisolism. Subsequently, 50, 500, and 5000 nM of compounds 776 and 299 were added. After 24 hours of incubation, effects were determined by cortisol measurements in the culture media, and mRNA relative expression of steroidogenic enzymes, MC2R and melanocortin 2 receptor accessory protein (MRAP) with RT-qPCR analysis.

Compound 299 significantly inhibited ACTH-stimulated cortisol production with a mean drop in cortisol production of 79% at 500 nM (p=0.004) and 91% at 5000 nM (p<0.0001). Compound 776 was less effective with a mean drop in cortisol production of 38% at 5000 nM (p=0.002). Compound 299 significantly inhibited ACTH-stimulated mRNA expression of StAR (p<0.00001), CYP11A1(p=0.001), CYP17A1(p<0.00001), 3βHSD2 (p<0.001), CYP21 (p<0.001), CYP11B (p=0.019), MC2R (p=0.010) and MRAP (p<0.001).

These results indicate that compound 299 is an effective MC2R antagonist in vitro and could become a promising new treatment option for ACTH-dependent hypercortisolism.

 

Nothing to Disclose: KS, JAM, HSK, SG