Synthesis of a [18F]fluoroethyltriazolylthymidine radiotracer from [18F]2-fluoroethyl azide and 5-ethynyl-2′-deoxyuridine

An improved synthesis for a fluoroethyltriazolylthymidine analog has been developed by employing the copper(I)-catalyzed click chemistry reaction between 5-ethynyl-2'-deoxyuridine (EDU) and [F-19/18]2-fluoroethyl azide. When compared with the previously reported protocol the radiochemical yield has been increased from 3 to 32.5 +/- 2.5%. The synthesis time was 130 min and the specific activity ranged from 70.3 to 129.5 GBq/mu mol. The tracer was found to be stable in human plasma and was subsequently evaluated in an A431 tumor model in BALB/c nude mice. Dynamic image acquisition using the Mosaic small animal PET scanner showed that the tumor to muscle ratio reached a maximum value of 2.1 from 22 min postinjection. These results indicate, that the fluoroethyltriazolylthymidine synthesized can be a promising radiotracer for tumor cell proliferation and thus become an important tool for treatment evaluation in oncology.