Metabolic studies of 18F-labeled 5-fluoro-2'-deoxyuridine(FdUrd), 5-fluorouridine(FUrd) and
5-fluorouracil (FUra) were performed in
tumor-bearing rats and mice. Also, the usefulness of 18F-FdUrd and 3H-deoxythymidine (dThd) for
tumor detection was compared. In the
tumor, 2 h after the injection of the 18F-pyrimidines, 3%-11% and 6%-14% of the 18F was present in the nuclear and microsomal fractions, respectively, and 17%-34% and 19%-24% of the 18F was incorporated into the
acid-insoluble and
nucleotide fractions, respectively. Of the three 18F-pyrimidines, 18F-FUrd demonstrated the highest incorporation rate, while 18F-FUra showed the lowest incorporation rate. The incorporation in the spleen, small intestine, and liver was less than that in the
tumor. 3H-dThd and 18F-FdUrd were injected into the same mice. The 3H-dThd was accumulated in the spleen, small intestine, and
tumor, and in these three tissues significant amounts of the 3H were incorporated into
acid-insoluble materials. However, the clearance of 18F-FdUrd was slow in the
tumor but rapid in the spleen and small intestine. In the autoradiograms of the
tumor, 18F and 3H showed a slightly different distribution. Both distribution patterns were unchanged when the soluble materials were rinsed out with
perchloric acid. For
tumor detection, 18F-FdUrd gives the same information as radio-dThd, and further information can be obtained by positron-emission tomography.