Abstract
Thymidylate synthase (TS) is a key enzyme in the synthesis of dTTP and a target for 5-fluorouracil (5FU), used for the treatment of colorectal cancer. The metabolite FdUMP inhibits TS by formation of a ternary complex with TS and 5, 10-methylene tetrahydrofolate (CH2 THF). Its extent of formation and stability determine the effect of 5FU. To establish a relation with antitumor activity of 5FU we measured in vitro TS activity and binding of FdUMP to TS in biopsies (immediately frozen in liquid nitrogen) of primary colon tumors and healthy mucosa from 7 patients. At optimal CH2THF concentration and 10 μM dUMP TS activity was 3-6 fold higher than at 1 μM, both in tumors and mucosa. In mucosa TS activity at 10 μM dUMP was 44-107 pmol/hr per mg protein; in tumors from the same patient TS activity was always higher, but varied considerably between 52 and 3000, which is possibly related to tumor heterogeneity. 10 nM FdUMP inhibited TS activity 70-90%. The number of FdUMP binding sites at optimal CH2THF concentrations was 0.1-0.3 pmol FdUMP/mg protein in tumors and <0.1 in mucosa, but always 2-3 fold higher in the tumor. In vivo FdUMP binding was determined in tumor biopsies of patients obtained 1.5-3 hr after treatment with 500 mg 5FU/m2. FdUMP binding to the ternary complex was still complete; all binding sites were occupied by FdUMP. Currently the FdUMP binding in samples obtained at later time-points is being measured. In conclusion; TS activity was higher in tumors; inhibition by FdUMP was not only observed in vitro but also in vivo.
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Peters, G., Laurensse, E., Van Groeningen, C. et al. 115 IN VITRO AND IN VIVO INHIBITION OF THYMIDYLATE SYNTHASE OF HUMAN COLON CANCER BY 5-FLUOROURACIL. Pediatr Res 24, 130 (1988). https://doi.org/10.1203/00006450-198807000-00139
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DOI: https://doi.org/10.1203/00006450-198807000-00139