[Level of inhibition of thymidylate synthase activity and 5-fluorouracil in tumor tissues after administration of UFT or tegafur].

The antitumor effects of tegafur and UFT, fluorinated pyrimidines, were investigated in endometrial carcinoma bearing mice. Following administration of tegafur and UFT, each at a clinical dosage, the levels of 5-fluorouracil (5-Fu) and the inhibition of thymidylate synthase (TS) activity in the tumor tissue were measured. As a result, the mean levels of 5-Fu in the tumor tissue were approximately six times higher in the UFT group (29.2 +/- 10.7 ng/g) than in the tegafur group (4.9 +/- 4.8 ng/g) (p less than 0.01). The UFT group showed a mean inhibition of TS activity in the tumor tissue significantly higher (61.60 +/- 2.02%) than did the tegafur group (56.08 +/- 4.87%) (p less than 0.05). Hence, not only the higher tumor tissue levels of 5-Fu but also the higher inhibition of TS activity in the UFT group as compared with the tegafur group suggested that UFT had more potent antitumor effect.