Identification, Optimization, and Pharmacology of Acylurea GHS-R1a Inverse Agonists

Abstract

Ghrelin plays a major physiological role in the control of food intake, and inverse agonists of the ghrelin receptor (GHS-R1a) are widely considered to offer utility as antiobesity agents by lowering the set-point for hunger between meals. We identified an acylurea series of ghrelin modulators from high throughput screening and optimized binding affinity through structure-activity relationship studies. Furthermore, we identified specific substructural changes, which switched partial agonist activity to inverse agonist activity, and optimized physicochemical and DMPK properties to afford the non-CNS penetrant inverse agonist 22 (AZ-GHS-22) and the CNS penetrant inverse agonist 38 (AZ-GHS-38). Free feeding efficacy experiments showed that CNS exposure was necessary to obtain reduced food intake in mice, and it was demonstrated using GHS-R1a null and wild-type mice that this effect operates through a mechanism involving GHS-R1a.

2-Aminoalkyl nicotinamide derivatives as pure inverse agonists of the ghrelin receptor

“…There has been debate about the peripheral versus central actions of ghrelinR on appetite control, with some ghrelinR ligands targeting high brain penatration 21 and others targeting low brain penetration. 16,17 We support the theory that ghrelin, which is primarily produced in the stomach, exerts its orexigenic action via vagal afferent neurons, and its GH secretagogue action via vagal afferent nerves and the pituitary gland. 22 Moreover ghrelin is known to enhance gastric motility, which influences its orexigenic effects, via direct stimulation of the enteric neural pathway and afferent neurons.…”

“…19,20 We therefore explored nonaromatic rings for this site and found that morpholine (16) or tetrahydropyridine (19) rings were tolerated. Introduction of two methyl groups at the morpholine ring (17) improved the activity by one order of magnitude, which encouraged us to design a bridged ring structure (18); this demonstrated comparable potency. Interestingly, similar bridging of the tetrahydropyridine ring yielded compounds 20 and 21, which showed sub-nanomolar binding IC 50 values and <100 nM inverse agonist IC 50 values.…”

“…1). [15][16][17] We performed high-throughput screening (HTS) using the 125 I-ghrelin substitution assay system to obtain ghrelinR binders and the hits obtained were evaluated using an inverse agonist assay employing a reporter-gene system. This system was based on the fact that ghrelinR-derived Ga q signaling results in activation of the nuclear factor of activated T-cells (NFAT) and activator protein-1 (AP-1) response element, stimulating gene expression.…”

“…Interestingly, this 2-aminoalkyl nicotinamide structure showed no functional switching toward neutral antagonism or partial agonism (or even partial inverse agonism 24 ) in the entire SAR study, in contrast to the functional switching to partial agonism reported for many ghrelinR antagonists and inverse agonists with small structural modifications. 13,15,17 The concentration-response relationships of inverse agonists in the reporter-gene assay are depicted in Figure 3. A known peptidic ghrelinR inverse agonist, named substance P analog 14 ([D-Arg 1 , D-Phe 5 , D-Trp 7,9 , Leu 11 ]-substance P), almost completely suppressed the constitutive activity of this receptor, although its potency (IC 50 = 250 nM) was lower than the previously reported one for an inositol phosphate turnover assay 25 (IC 50 = 5.2 nM).…”

From Belly to Brain: Targeting the Ghrelin Receptor in Appetite and Food Intake Regulation

“…Pharmacological evaluation in obesity-induced rats revealed that a BBB penetrant inverse agonist for the GHSR-1a effectively reduced weight gain [334]. Ad libitum food intake was also reduced in mice treated with a BBB-penetrant inverse agonist (AZ-GHS-38) while a lack of efficacy was obtained in mice treated with a non- BBB-penetrant inverse agonist [335]. Therefore, a crucial determinant of the anti-obesogenic potential of GHSR-1a inverse agonists and antagonists is their ability to traverse the BBB.…”