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Synthesis of opiate receptor radioligand 11C-carfentanil and its biodistribution in rats

Objective To establish an automatic synthesis method for 11C-carfentanil (CFN) as an novel opiate receptor radioligand and study its biodistribution in rats. Methods 11C-Triflate-CH3 was bubbled into 0.5 mg precursor desmethyl-CFN (which was dissolved in 0.15 ml DMSO) to generate 11C-CFN in a V-tube at room temperature. Sep-Pak C2 column was used for purification of 11C-CFN, which was eluted by 3ml binary system aqueous solution, 10 ml water thrice, and then I ml ethanol. The biodistribution (% ID/g) of 11C-CFN in SD rats was studied. SPSS 13.0 was used for statistical analysis. Non-normal distribution data were analyzed using nonparametric test. Results The synthesis time for 11C-CFN was 20 min (end of bombardment, EOB). The synthesis yield was (35.5 ± 2.2) % on average (n = 12, uncorrected)with the radiochemical purity over 98%. Biodistribution study in rats showed that the tracer had a high brain uptake, rapid blood clearance, and a metabolic pathway via liver and kidney. The highest tracer uptake was in thalamus (4.26 ± 0.89) % ID/g and striatum (4.05 ± 1.08) % ID/g at 5 min after injection, followed by cerebral cortex (2.63±0.89) %ID/g, pons (2.26 ±0.57) % ID/g, hippocampus (2. 17 ±0.55) %ID/g and cerebellum (2. 15 ±0.39) %ID/g. Conclusions The automatic synthesis of 11C-CFN is fast and reliable, and this radioligand can be used for opiate receptor imaging. 
 
Key words: 
Receptors, opioid, mu;  Carfentanil;  Carbon radioisotopes;  Rats