Binding of 1,4-benzodiazepines to a novel [3H]Ro15-4513 binding site in the rat spinal cord.
An alpidem-insensitive benzodiazepine binding site in the rat spinal cord has recently been identified in our laboratory. We report here the binding of 23 1,4-benzodiazepines to this site using [3H]Ro15-4513 (ethyl-8-azido-6-dihydro-5-methyl-4H-imidazo[1,2- a][1,4]benzodiazepine-3-carboxylate) in the presence of 65 microM alpidem (6-chloro-2-(4-chlorophenyl)-N,N- dipropylimidazo[1,2-a]pyridine-3-acetamide). This binding site displays a wide affinity for 1,4-benzodiazepines, most of which show much higher affinity for benzodiazepine receptors in various brain regions and transfected cell systems. The highest affinity ligands are: brotizolam (1-bromo-4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2- f][1,2,4]triazolo[4,3-a][1,4]diazepine) (4.3 nM), Ro15-4513 (5.0 nM), Ro42-8773 (7-chloro-3-[3-(cyclopropylmethoxy)-1-propynyl]-4,5-dihydro- 5-methyl-6H-imidazo[1,5-a][1,4]benzodiazepine-6-one) (5.7 nM), Ro16-6028 (t-butyl (s)-8-bromo-11,12,13,13a-tetrahydro-9-oxo-9H- imidazo[1,5-a][1,4]benzodiazepine-1-carboxylate) (5.9 nM) and triazolam (8-chloro-6-(2-chlorophenyl)-1-methyl-4H- [1,2,4]triazolo[4,3-a][1,4]benzodiazepine) (7.9 nM). The structural feature common to these compounds is an imidazo- or triazolo-ring on the 1- and 2-position of the benzodiazepine. However, the presence of this feature does not guarantee high affinity binding as Ro15-1788 (8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5- a][1,4]benzodiazepine-3-carboxylic acid ethyl ester) (100 nM) and Ro23-0364 (6-[2-chlorophenyl]-4H- imidazo[1,5-a][1,4]benzodiazepine-3-carboxamide) (360 nM) display much lower affinity for this site. Studies are currently underway to investigate the functional significance of this unusual benzodiazepine binding site.
Maguire
P A
PA
Molecular Research Institute, Palo Alto, CA 94304, USA.
Davies
M F
MF
Loew
G H
GH
D000345:Affinity Labels; D000818:Animals; D001386:Azides / Q000378:metabolism*; D001569:Benzodiazepines / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D003001:Cloning, Molecular; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D008024:Ligands; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism
D000345:Affinity Labels; D001386:Azides; D007093:Imidazoles; D008024:Ligands; D011725:Pyridines; D011963:Receptors, GABA-A; D001569:Benzodiazepines; C042957:Ro 15-4513; C052036:alpidem