Thymidylate synthase activity after preoperative administration of 5-FU in patients with gastric or colorectal cancer

Continuous intravenous injection of 5-FU was given at 300 mg/m2 to patients with gastric or colorectal cancer for consecutive 3 days preoperatively, and the relationships between the time until collection of samples (from final administration of 5-FU to excision of tissue samples) and total thymidylate synthase (TS total) activity, free thymidylate synthase (TS free) activity, thymidylate synthase inhibition rate (TSIR), thimidine kinase (TK) activity, and tissue 5-FU and FdUMP concentrations investigated. TS total was shown to gradually reduce with time, but the relationship between time and the other assay items could not be identified due to large variability in the data. TS total and TK also proved to be affected also by the sites at which the samples were collected, and exhibited significantly higher enzyme activity in tumor tissue than that in normal tissue.