Preparation and primary evaluation of [11C]CSC as a possible tracer for mapping adenosine A2A receptors by PET.

A 11C labeled selective adenosine A2A antagonist, (E)-8-(3-chlorostyryl)-1,3-dimethyl-7-[11C]methylxanthine [11C]CSC) was prepared by the reaction of (E)-8-(3-chlorostyryl)-1,3-dimethylxanthine and [11C]methyl iodide. The decay-corrected radiochemical yield was 32.3% with a radiochemical purity of 99%, a specific activity of 1.85-5.55 GBq/mumol and a preparation time of 1 h. A primary evaluation of [11C]CSC as a potential tracer for mapping adenosine A2A receptors by positron emission tomography (PET) is also presented. Biodistribution and autoradiographic studies were carried out on Swiss mice and domestic rabbits. In mice the lung showed the highest uptake at 10 min after i.v. injection, followed by the liver, kidney, heart and brain. Inside the brain a high level of radioactivity accumulated in the striatum, in accordance with previous findings on the specific spatial distribution of A2A adenosine receptors and also in the medulla oblongata. Dynamic PET studies on rabbits showed a fast brain uptake of CSC, reaching a maximum in less then 2 min. On the basis of competition experiments with the unlabeled ligand [11C]CSC proves to bind specifically to the appropriate receptor.

[11C-methionine: an effective radio-tracer for PET scan in the detection of tumors of low proliferating capacity]. / 11C-metionin: hatékony radiofarmakon az alacsony proliferatív kapacitású daganatok PET-vizsgálatához.

11C-methyl-methionine is available at the PET Center of University Medical School Debrecen since June, 1996. The first 5 oncological examinations were indicated for clinically suspected recurrent/residual tumorous tissue of low-grade/low proliferative capacity, following the negative or inconclusive results of previous 18F-deoxyglucose (FDG) examinations. In these situations, the methionine examinations provided conclusive results in 4 cases (out of the total of 5 examinations). On the basis of published data and own experience, the authors recommend methionine PET investigations for diagnosis, differential diagnosis and therapy monitoring of tumours of low-grade/low proliferative capacity following inconclusive results of previous FDG examination.