Simplified labeling approach for synthesizing 3′-deoxy-3′-[18F]fluorothymidine ([18F]FLT)

[F-18]FLT (3'-deoxy-3'-[F-18]fluorothymidine) turned out to be a tracer particularly suitable for FET imaging of tumor proliferation because of lacking degradation in vivo. To facilitate clinical studies with [F-18]FLT, we investigated two new easily accessible precursors, 2.3'-anhydrothymidine (AThy) and 5'-O-(4,4'-dimethoxytriphenylmethyl)-2.3-anhydrothymidine (DMTThy), using a common approach for introducing the label with nucleophilic [F-18]fluoride. Radiochemical yields were determined in dependence on substrate concentration, reaction time and temperature. In the case of AThy (10 mg), best FLT yields were 5.3%+/-1.2 (130 degrees C, 30 min). Labeling of DMTThy (10 mg) gave 14.3%+/- 3.3 at 160 degrees C within 10 minutes. Starting with an aqueous solution of 20 GBq [F-18]fluoride the new method allows to produce 1.3 GBq [F-18]FLT within 90 minutes ready for intravenous injection. The new labeling procedures allow [F-18]FLT synthesis without lengthy preparation of the precursor and with high reproducibility mandatory for clinical application.