title: [(76) Br]BMK-152, a nonpeptide analogue, with high affinity and low nonspecific binding for the corticotropin-releasing factor type 1 receptor.
abstract: Corticotropin-releasing factor (CRF), a neuropeptide, regulates endocrine and autonomic responses to stress through G-protein coupled receptors, CRF(1) or CRF(2) . A PET ligand able to monitor changes in CRF(1) receptor occupancy in vivo would aid in understanding the pathophysiology of stress-related diseases as well as in the clinical development of nonpeptide antagonists with therapeutic value. We have radiolabeled the CRF(1) receptor ligand, [8-(4-bromo-2,6-dimethoxyphenyl)-2,7-dimethylpyrazolo[1,5-α][1,3,5]triazin-4-yl]-N,N-bis-(2-methoxyethyl)amine (BMK-152) (ClogP = 2.6), at both the 3 and 4 position with [(76) Br]. Using in vitro autoradiography saturation studies the 4-[(76) Br]BMK-152 exhibited high affinity binding to both rat (K(d) = 0.23 ± 0.07 nM; n = 3) and monkey frontal cortex (K(d) = 0.31 ± 0.08 nM; n = 3) consistent with CRF(1) receptor regional distribution whereas with the 3-[(76) Br]BMK-152, the K(d) s could not be determined due to high nonspecific binding. In vitro autoradiography competition studies using [(125) I]Tyr(0) -o-CRF confirmed that 3-Br-BMK-152 (K(i) = 24.4 ± 4.9 nM; n = 3) had lower affinity (70-fold) than 4-Br-BMK-152 (K(i) = 0.35 ± 0.07 nM; n = 3) in monkey frontal cortex and similiar studies using [(125) I]Sauvagine confirmed CRF(1) receptor selectivity. In vivo studies with P-glycoprotein (PGP) knockout mice (KO) and their wild-type littermates (WT) showed that the brain uptake of 3-[(76) Br]BMK/4-[(76) Br]BMK was increased less than twofold in KO versus WT indicating that 3-[(76) Br]BMK-152/4-[(76) Br]BMK was not a Pgp substrate. Rat brain uptakes of 4-[(76) Br] BMK-152 from ex vivo autoradiography studies showed regional localization consistent with known published CRF(1) receptor distribution and potential as a PET ligand for in vivo imaging of CRF(1) receptors.
authors.affiliation: PET Radiochemistry Group, NIBIB, National Institutes of Health, Bethesda, Maryland 20892-1088, USA. ejagoda@mail.nih.gov
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Jagoda
authors.forename: Lixin
authors.initials: L
authors.lastname: Lang
authors.forename: Karen
authors.initials: K
authors.lastname: McCullough
authors.forename: Carlo
authors.initials: C
authors.lastname: Contoreggi
authors.forename: B Moon
authors.initials: BM
authors.lastname: Kim
authors.forename: Ying
authors.initials: Y
authors.lastname: Ma
authors.forename: Kenner C
authors.initials: KC
authors.lastname: Rice
authors.forename: Lawrence P
authors.initials: LP
authors.lastname: Szajek
authors.forename: William C
authors.initials: WC
authors.lastname: Eckelman
authors.forename: Dale O
authors.initials: DO
authors.lastname: Kiesewetter
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000172:deficiency; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000172:deficiency; D000818:Animals; D001345:Autoradiography; D001465:Barium Radioisotopes / Q000493:pharmacokinetics; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D008024:Ligands; D008253:Macaca mulatta; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding / Q000187:drug effects; D011743:Pyrimidines / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D018019:Receptors, Corticotropin-Releasing Hormone / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D014227:Triazines / Q000737:chemistry; D000099052:CRF Receptor, Type 1
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001465:Barium Radioisotopes; C101628:CP 154526; D008024:Ligands; C476980:MJL 1-109-2; D011743:Pyrimidines; D011758:Pyrroles; D018019:Receptors, Corticotropin-Releasing Hormone; D014227:Triazines; D000099052:CRF Receptor, Type 1; C095122:multidrug resistance protein 3