Tissue distribution of 5'-deoxy-5-fluorouridine and derived 5-fluorouracil in tumor-bearing mice and rats.

Distribution of 5-fluorouracil (5-FU) in various tissues including transplanted tumors was examined 1, 3 (or 4), and 24 hr after a single oral dose of 5'-deoxy-5-fluorouridine (5'-DFUR), Ftorafur (FT-207), or 5-FU itself to groups of mice bearing sarcoma-180 and of rats bearing Walker carcinoma-256. The levels of 5-FU derived from 5'-DFUR were highest in the tumors among the tissues examined 3 (or 4) and 24 hr after administration. At the 1st hr after dosing the 5-FU level in the small intestine was close to, but that in other tissues was much lower than, the 5-FU level in the tumor of both types. Such a selective distribution of 5-FU in tumor tissues was not observed after dosing of either FT-207 or 5-FU itself. Since the anticancer effect of 5'-DFUR is likely to be manifested after its conversion to 5-FU, the 5'-deoxyribose moiety of 5'-DFUR may be deemed as an efficient carrier by which the 5-FU moiety is conveyed selectively to cancer tissues.