Premium
[ 76 Br]BMK‐152, a nonpeptide analogue, with high affinity and low nonspecific binding for the corticotropin‐releasing factor type 1 receptor
Author(s) -
Jagoda Elaine M.,
Lang Lixin,
Mccullough Karen,
Contoreggi Carlo,
Kim B. Moon,
Ma Ying,
Rice Kenner C.,
Szajek Lawrence P.,
Eckelman William C.,
Kiesewetter Dale O.
Publication year - 2011
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.20919
Subject(s) - receptor , in vivo , medicine , ligand (biochemistry) , chemistry , endocrinology , in vitro , biology , biochemistry , microbiology and biotechnology
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. Synapse 2011. Published 2011 Wiley‐Liss, Inc.