Characterization of novel ligands for wild-type and natural mutant diazepam-insensitive benzodiazepine receptors.
A series of benzodiazepine receptor ligands with different chemical structures were evaluated for their affinities at diazepam-sensitive and diazepam-insensitive binding sites for [3H]Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo-[1,5a][1,4] benzodiazepine-3-carboxylate) in cerebellar GABAA receptors. Rats of Wistar strain and of alcohol-sensitive (ANT) and alcohol-insensitive (AT) lines were used. The ANT rats possess a single point mutation in their GABAA receptor alpha 6 subunit, which makes their diazepam-insensitive sites sensitive to benzodiazepine agonists, unlike those of AT and Wistar rats. All compounds evaluated displayed high-affinity binding to diazepam-sensitive sites (Ki < 50 nM). In contrast, a wider range of affinities were observed at diazepam-insensitive sites which depended upon the basic structure and substitutions. The 7- and 8-halogen substituted imidazobenzodiazepines and 12-halogen substituted diimidazoquinazolines displayed the highest affinities (Ki < 15 nM), while intermediate to low affinities (100 < Ki < 4000 nM) were displayed by imidazoquinazolines, thienopyrimidines, one oxoimidazoquinoxaline, and some cyclopyrrolones. The imidazoquinoxalines evaluated displayed the lowest affinity (Ki > 10000 nM). The oxoimidazoquinoxaline, 6-chloro-3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4,5-dihydro-5-isop ropyl-4-oxo-imidazo[1,5-a]quinoxaline (NNC 14-0578) and suriclone represent the first benzodiazepine receptor full agonists to bind with relatively high affinity (Ki approximately 100 nM) to diazepam-insensitive sites. The 5 position substituted methoxybenzyl, dimethylallyl, and 4-fluorobenzyl oxoimidazoquinoxaline analogs demonstrated a 58-336-fold higher affinity for ANT than AT diazepam-insensitive sites.(ABSTRACT TRUNCATED AT 250 WORDS)
Wong
G
G
Biomedical Research Center, Alko Group Ltd, Helsinki, Finland.
Uusi-Oukari
M
M
Hansen
H C
HC
Suzdak
P D
PD
Korpi
E R
ER
D000818:Animals; D001386:Azides / Q000494:pharmacology; D001569:Benzodiazepines / Q000494:pharmacology; D001667:Binding, Competitive; D002531:Cerebellum / Q000187:drug effects*; D003975:Diazepam / Q000494:pharmacology*; D000431:Ethanol; D008297:Male; D009154:Mutation; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000187:drug effects
D001386:Azides; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D000431:Ethanol; C042957:Ro 15-4513; D003975:Diazepam