Synthesis and evaluation of a thymidine analog for positron emission tomography study of tumor DNA proliferation in vivo.

This study describes the synthesis, radiolabelling and biological evaluation of 5-(2,4-difluoro-5-[18F]fluoromethyl-phenyl)-2-hydroxymethyl-tetrahydrofuran-3-ol, 13. Radiolabelling was achieved by reaction of the tosylate 3 with K[18F] in the presence of Kryptofix 222. Good stability in saline and serum solutions at physiological temperatures in vitro was observed. A cell incorporation study of 13 using SW1222 tumor cells showed a linear uptake, unfortunately, in vivo studies indicated that 13 was undergoing defluorination. Rapid defluorination of the radiotracer was confirmed by an in vitro stability study in blood plasma. Finally, a comparison between the DNA uptake of 13 and tritiated thymidine was performed in vitro to asses the potential utility of more stable analogs. These studies showed that 13 and its analogs are unsuitable as potential tracers to image DNA proliferation and highlighted the difficulty in predicting the in vivo stability of novel radiotracers.