Discovery and Pharmacological Evaluation of Growth Hormone Secretagogue Receptor Antagonists

Abstract

The discovery and pharmacological evaluation of potent, selective, and orally bioavailable growth hormone secretagogue receptor (GHS-R) antagonists are reported. Previously, 2,4-diaminopyrimidine-based GHS-R antagonists reported from our laboratories have been shown to be dihydrofolate reductase (DHFR) inhibitors. By comparing the X-ray crystal structure of DHFR docked with our GHS-R antagonists and GHS-R modeling, we designed and synthesized a series of potent and DHFR selective GHS-R antagonists with good pharmacokinetic (PK) profiles. An amide derivative 13d (Ca2+ flux IC50 = 188 nM, [brain]/[plasma] = 0.97 @ 8 h in rat) showed a 10% decrease in 24 h food intake in rats, and over 5% body weight reduction after 14-day oral treatment in diet-induced obese (DIO) mice. In comparison, a urea derivative 14c (Ca2+ flux IC50 = 7 nM, [brain]/[plasma] = 0.0 in DIO) failed to show significant effect on food intake in the acute feeding DIO model. These observations demonstrated for the first time that peripheral GHS-R blockage with small molecule GHS-R antagonists might not be sufficient for suppressing appetite and inducing body weight reduction.

In vitro selection of a peptide antagonist of growth hormone secretagogue receptor using cDNA display

“…The amino acid sequences of Trp 3 -ghrelin 1-8 , desacyl-ghrelin 1-8 , and X 1-8 are described in (B). Additional symbols and abbreviations are defined as follows: T7prom, T7 promoter; Ω, translation enhancer of tobacco mosaic virus; Kozak, Kozak sequence for translation initiation; PDO and BDA, POU-specific DNA-binding domain of Oct-1 (PDO) or B domain of protein A (BDA) as a scaffold protein; 6xHis, hexahistidine tag; Xa, the recognition site for factor Xa protease; Trp 3 -ghrelin 1-8 , desacyl-ghrelin 1-8 ; X [1][2][3][4][5][6][7][8] , eight N-terminal amino acids of the ghrelin mutant or eight randomized amino acids; ghrelin 9-28 , 20 C-terminal amino acids of ghrelin; and LHR, the hybridization region for the puromycin linker. (B) Amino acid sequences of the regions of ghrelin used in the selection process.…”

“…Therefore, GHS-R antagonists are expected to perform antiobesity functions by suppressing food intake and weight gain. In fact, small-molecule GHS-R antagonists and [D-Lys-3]-GHRP-6, which is one of the few known peptide antagonists of GHS-R, decrease food intake and weight gain via peripheral administration (7)(8)(9)(10).…”

GSK1614343, a Novel Ghrelin Receptor Antagonist, Produces an Unexpected Increase of Food Intake and Body Weight in Rodents and Dogs

“…Due to the relevant role of ghrelin in the regulation of energy balance, FI and adiposity, several research groups have been engaged in developing GHS-R1a neutral competitive antagonist and inverse agonists [23,29,30,31]. Recently, a vaccine directed against the hormone ghrelin, preventing ghrelin from reaching the CNS, has been developed [32].…”

Energy Homoeostasis: The Roles of Adipose Tissue-Derived Hormones, Peptide YY and Ghrelin

“…The use of ghrelin administration and GHS-R1a agonists in aiding weight gain in cachexia and anorexia nervosa has been investigated [138,139]. Conversely, the use of GHS-R1a antagonists in the treatment of obesity has also been explored, with antagonists such as 2,4-diaminopyrimidine showing promising results in decreasing appetite in animals [140]. However, in order to realise the full potential of ghrelin antagonism as anti-obesity treatment, GHS-R1a antagonists with better selectivity, potency, and pharmacokinetic properties are required [141].…”