Discovery of a novel, orally active, small molecule gonadotropin-releasing hormone (GnRH) receptor antagonist.

Gonadotropin releasing hormone (GnRH) plays an important role in the biology of reproduction. The use of GnRH receptor antagonists has been reported in the literature for the treatment of breast, ovarian, and prostate cancers. In this article, we report the synthesis, in vitro characterization, pharmacokinetics, and pharmacodynamics of an orally bioavailable, potent, small molecule GnRH receptor antagonist N-{4,6-dimethoxy-2-[(3-morpholin-4-ylpropyl)amino]pyrimidin-5-yl}-5-[3,3,6-trimthyl-2,3-dihydro-1H-inden-5-yl)oxy]-2-furamide (compound 1).

Effect of testosterone suppression on the pharmacokinetics of a potent gnRH receptor antagonist.

PURPOSE: The expression of cytochrome P450 enzymes (CYPs) in animals and humans is under complex hormonal regulation. Chronic treatment with drugs that alter sex hormone levels such as GnRH receptor agonists or antagonists may affect the expression of hormone-dependent CYPs, and as a result the pharmacokinetics of drugs metabolized by them. METHODS: Enzyme kinetic parameters were obtained by incubating AG-045572 (0.1-30 microM) with human or rat liver microsomes, or expressed CYP3A4 and CYP3A5. The pharmacokinetics of AG-045572 (10 mg/kg i.v. or 20 mg/kg p.o.) were studied in intact male, female, castrated male and male rats pretreated with AG-045572 for 4 days. RESULTS: AG-045572 is metabolized by CYP3A in both rats and humans. The Km values were similar in male and female human, female rat liver microsomes, and expressed CYP3A4 and CYP3A5 (0.39, 0.27, 0.28, 0.25, and 0.26 microM, respectively). The Km in male rat liver microsomes was 1.5 microM, suggesting that in male and female rats AG-045572 is metabolized by different CYP3A isozymes. The oral bioavailability of AG-045572 in intact male rats was 8%, while in female or castrated male rats it was 24%. Pretreatment of intact male rats with AG-045572 i.m. for 4 days resulted in suppression of testosterone to castrate levels, accompanied by an increase in oral bioavailability of AG-045572 to 27%. In the same experiment, the male-specific pulsatile pattern of growth hormone remained unchanged with slightly elevated baseline levels. CONCLUSIONS: The potent GnRH receptor antagonist AG-045572 is metabolized by hormone-dependent CYP3A. As a result, suppression of testosterone by pretreatment with AG-045572 "feminized" its own pharmacokinetics.

Characterization of mono- and diaminopyrimidine derivatives as novel, nonpeptide gonadotropin releasing hormone (GnRH) receptor antagonists.

A novel series of derivatives of mono- and diaminopyrimidines 1 potently displaced binding of a radiolabeled GnRH analogue to human and rat GnRH receptors. Analogues from these series competitively antagonized GnRH-stimulated increases in extracellular acidification in vitro and suppressed GnRH-mediated increases in circulating luteinizing hormone (LH) in castrated rats and testosterone in intact rats. These compounds or their analogues may be useful in treating sex hormone-dependent disease.

Biological characterization of a novel, orally active small molecule gonadotropin-releasing hormone (GnRH) antagonist using castrated and intact rats.

Gonadotropin-releasing hormone (GnRH) receptor antagonists have potential in treating numerous hormone-dependent pathologies including cancers of the prostate, breast, and ovary, endometriosis, and fertility disorders. An unmet clinical need exists for an orally available GnRH receptor antagonist. Guided by structure-activity relationships, ligand-based targeted library designs, and biomarker measurements, our discovery efforts have yielded a novel, small molecule GnRH receptor antagonist, 5-[(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthalenyl)methyl]-N-(2,4,6-trimethoxyphenyl)-2-furamide (CMPD1). CMPD1 bound with low nanomolar affinities to human, rat, and mouse GnRH receptors (6.0, 3.8, and 2.2 nM, respectively). CMPD1 was more than 100-fold selective for GnRH receptors versus various G-protein-coupled receptors and other enzymes and ion channels. In cells expressing recombinant rat GnRH receptors, CMPD1 was a competitive antagonist of GnRH-stimulated increases in extracellular acidification rates in Cytosensor microphysiometer assays. In cells expressing recombinant human GnRH receptors, CMPD1 was a potent inhibitor of GnRH-stimulated total inositol phosphate accumulation. The effects of CMPD1 on circulating levels of luteinizing hormone (LH) and testosterone were studied in castrated and intact male rats, respectively. Intravenous and oral administration of CMPD1 dose dependently suppressed GnRH-mediated elevations of LH in castrated male rats and testosterone in gonad-intact male rats. Moreover, CMPD1, when given at 20 mg/kg i.v. to intact male rats, inhibited the elevations of LH and testosterone stimulated by the superagonist of GnRH, [d-Ala(6), des-Gly(10)]GnRH (GnRH-A). These data suggest that CMPD1 is a potent, selective, orally active GnRH receptor antagonist that may have potential application as a therapeutic agent for treating hormone-dependent cancers and diseases.