Binding characteristics of [3H]ucb 30889 to levetiracetam binding sites in rat brain.
Levetiracetam (2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA, a novel antiepileptic drug, has been shown to bind to a specific binding site located in brain (levetiracetam binding site [Eur. J. Pharmacol. 286 (1995) 137]). However, [3H]levetiracetam displayed only micromolar affinity for these sites making it an unsuitable probe for further characterization. The present study describes the binding properties of an analogue of levetiracetam: [3H]ucb 30889, (2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide. [3H]ucb 30889 binds reversibly to specific binding sites in rat brain. Kinetics at 4 degrees C were biphasic with half-times of association and dissociation of, respectively, 3 and 4 min for the fast component and 47 and 61 min for the slow component. [3H]ucb 30889 saturation binding curves were compatible with the labelling of a homogenous population of binding sites having a B(max) of 4496+/-790 fmol/mg protein (mean+/-S.D., n=5) and a K(d) of 62+/-20 nM (mean+/-S.D., n=5), a 20-fold increase in affinity compared to [3H]levetiracetam. Competition binding curves with ligands known to interact with levetiracetam binding sites and tissue distribution restricted to the brain indicated that [3H]ucb 30889 and [3H]levetiracetam bind to the same site. Although levetiracetam binding sites and GABA(A) (gamma-aminobutyric acid) receptors share some ligands such as pentobarbital and pentylenetetrazol, experiments performed with [35S]TBPS (tert-butyl-bicyclo[2.2.2]phosporothionate), a probe for the GABA(A) Cl(-) channel do not support the hypothesis that levetiracetam binding sites are part of the GABA(A) receptor complex. Preliminary autoradiography studies in rat brain revealed that [3H]ucb 30889 labels specific sites in all brain regions and that this binding is concentration-dependently displaced by levetiracetam.
Gillard
Michel
M
UCB S A., Pharma Sector, In vitro Pharmacology, Building R4, Chemin du Foriest, B-1420 Braine-l'Alleud, Belgium. michel.gillard@ucb-group.com
Fuks
Bruno
B
Michel
Philippe
P
Vertongen
Pascale
P
Massingham
Roy
R
Chatelain
Pierre
P
D000818:Animals; D000927:Anticonvulsants / Q000737:chemistry / Q000378:metabolism*; D001386:Azides / Q000737:chemistry / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D000077287:Levetiracetam; D008297:Male; D010889:Piracetam / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D011759:Pyrrolidines / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution / Q000187:drug effects / Q000502:physiology; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
C487592:(2S)-2-(4-(3-azidophenyl)-2-oxopyrrolidin-1-yl)butanamide; D000927:Anticonvulsants; D001386:Azides; D011759:Pyrrolidines; D014316:Tritium; D000077287:Levetiracetam; D005680:gamma-Aminobutyric Acid; D010889:Piracetam