title: Allosteric and orthosteric binding modes of two nonpeptide human gonadotropin-releasing hormone receptor antagonists.
abstract: Nonpeptide antagonists of the human gonadotropin-releasing hormone receptor (GnRH-R) have been the subject of considerable interest because of their potential as a new class of oral therapeutics for the treatment of sex hormone-dependent diseases and infertility. While many classes of competitive GnRH-R antagonists have been described, we present here the first characterization of an allosteric nonpeptide GnRH-R antagonist. Previously, 5-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-ylmethyl)furan-2-carboxylic acid (2,4,6-trimethoxyphenyl)amide (here called Furan-1) had been demonstrated to be a potent GnRH-R antagonist both in vitro and in vivo. Using mutagenesis, the binding sites for Furan-1 and another potent nonpeptide antagonist (NBI-42902) have been mapped and are shown to be adjacent but nonoverlapping. Furan-1 is shown to affect the binding kinetics of radiolabeled peptide agonists as well as radiolabeled NBI-42902, and the kinetic data fit the allosteric ternary complex model. Furan-1 is considerably negatively cooperative with the nonpeptide antagonist and extremely negatively cooperative with the peptide agonist [125I-His5,d-Tyr6]GnRH so that it is nearly indistinguishable from an orthosteric competitive compound. Taken together, these data were used to develop a model of the nonpeptides bound to the GnRH-R binding site consistent with the current data.
authors.affiliation: Department of Pharmacology, California 92130, USA.
authors.forename: Susan K
authors.initials: SK
authors.lastname: Sullivan
authors.forename: Michael S
authors.initials: MS
authors.lastname: Brown
authors.forename: Yinghong
authors.initials: Y
authors.lastname: Gao
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Loweth
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Lio
authors.forename: Paul D
authors.initials: PD
authors.lastname: Crowe
authors.forename: R Scott
authors.initials: RS
authors.lastname: Struthers
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Betz
mesh_terms: D000494:Allosteric Regulation / Q000235:genetics; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive / Q000235:genetics; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D005663:Furans / Q000378:metabolism* / Q000494:pharmacology; D006727:Hormone Antagonists / Q000378:metabolism*; D006801:Humans; D020128:Inhibitory Concentration 50; D016297:Mutagenesis, Site-Directed; D011869:Radioligand Assay; D051381:Rats; D011966:Receptors, LHRH / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D013237:Stereoisomerism; D013941:Thymine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
chemical_list: C498569:3-(2-amino-2-phenylethyl)-1-(2,6-difluorobenzyl)-5-(2-fluoro-3-methoxyphenyl)-6-methylpyrimidin-2,4-dione; D005663:Furans; C484844:GNRHR protein, human; D006727:Hormone Antagonists; D011966:Receptors, LHRH; D013941:Thymine; C039281:furan