title: Autoradiographic comparison of in vitro binding characteristics of various tritiated adenosine A2A receptor ligands in rat, mouse and pig brain and first ex vivo results.
abstract: The adenosine A(2A) receptor in the basal ganglia is involved in the control of movement and plays a role in movement disorders such as Parkinsonism. Developing ligands to evaluate that receptor by noninvasive methods such as positron emission tomography has a high priority. In vitro radioligand binding guides the selection of ligands for in vivo application. This study measured the binding of the adenosine A(2A) receptor antagonist [(3)H]MSX-2 (3-(3-hydroxypropyl)-8-m-methoxystyryl)-7-methyl-1-propargylxanthine) to rat, mouse and pig brain by autoradiography. Other studies measured binding to membranes from PC12 pheochromocytoma cells. Those binding parameters were compared to those of the adenosine A(2A) receptor antagonist [(3)H]ZM241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino)ethyl)phenol), the adenosine A(2A) receptor agonist [(3)H]CGS21680 (2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoadenosine) and the unselective adenosine receptor agonist [(3)H]NECA (5'N-ethylcarboxamido)adenosine). The potency order (K(d)) in the three species was [(3)H]ZM241385<[(3)H]MSX-2<[(3)H]NECA<[(3)H]CGS21680. The density of [(3)H]MSX-2 binding sites was greater in the striatum than in the cortex. Preliminary ex vivo experiments showed that by 10min after iv injection, [(3)H]MSX-2 and [(3)H]CGS21680 crossed the blood-brain barrier to the extent of almost 1% ID/g brain tissue, but [(3)H]NECA and [(3)H]ZM241385 to only 0.2% ID/g. The prior administration of unlabeled ZM241385 significantly lowered brain uptake of [(3)H]MSX-2. In conclusion, [(3)H]MSX-2 has a high affinity and sufficient selectivity for the adenosine A(2A) receptor. It penetrates the blood-brain barrier. Sensitivity to photoisomerization is a limitation. Further investigations assess its suitability as a ligand for imaging the brain adenosine A(2A) receptor.
authors: Institute of Neuroscience and Medicine, INM-5, (Nuclear Chemistry), Research Center Jülich, 52425 Jülich, Germany. w.sihver@fz-juelich.de
authors: Wiebke
authors: W
authors: Sihver
authors: Annette
authors: A
authors: Schulze
authors: Walter
authors: W
authors: Wutz
authors: Stefan
authors: S
authors: Stüsgen
authors: Ray A
authors: RA
authors: Olsson
authors: Dirk
authors: D
authors: Bier
authors: Marcus H
authors: MH
authors: Holschbach
mesh_terms: D058908:Adenosine A2 Receptor Agonists; D000818:Animals; D001345:Autoradiography; D001812:Blood-Brain Barrier / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005260:Female; D008024:Ligands; D051379:Mice; D016716:PC12 Cells; D011485:Protein Binding; D051381:Rats; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D013552:Swine; D014316:Tritium / Q000737:chemistry*; D014970:Xanthines / Q000737:chemistry / Q000378:metabolism
chemical_list: C113601:3-(3-hydroxypropyl)-8-(3-methoxystyryl)-7-methyl-1-propargylxanthine; D058908:Adenosine A2 Receptor Agonists; D008024:Ligands; D043705:Receptor, Adenosine A2A; D014970:Xanthines; D014316:Tritium