Evaluation of carbon-11-labeled KF17837: a potential CNS adenosine A2a receptor ligand. 
The 11C-labeled KF17837 ([7-methyl-11C](E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxa nthine) was evaluated as a PET ligand for mapping adenosine A2a receptors in the central nervous system (CNS).  The regional brain distribution of [11C]KF17837 and the effect of adenosine antagonists on the distribution were measured in mice by the tissue sampling method.  In rats, the regional brain uptake of [11C]KF17837 and the effect of carrier KF17837 was visualized by autoradiography.  Imaging of the monkey brain with [11C]KF17837 was performed by PET.  In mice, a high uptake of [11C]KF17837 was found in the striatum in which A2a receptors were highly enriched.  The uptake was decreased by co-injection of carrier KF17837 or a xanthine-type A2a antagonist CSC but not by nonxanthine-type A2a antagonists ZM 241385 or SCH 58261, or an A1 antagonist KF15372.  In the rat brain, [11C]KF17837 was accumulated higher in the striatum than in other brain regions, and the uptake was blocked by co-injection of carrier KF17837.  In a monkey PET study, a high striatal uptake of radioactivity was observed.  Carbon-11-KF17837 binds to adenosine A2a receptors in the striatum.  However, the presence of an unknown but specific binding site for xanthine-type compounds also was suggested in the other brain regions.  The results also suggested that the in vivo receptor-binding sites of xanthine-type ligands are slightly different from those of nonxanthine-type A2a antagonists.