St. Davis et Sh. Berger, VARIATION IN HUMAN THYMIDYLATE SYNTHASE IS ASSOCIATED WITH RESISTANCETO 5-FLUORO-2'-DEOXYURIDINE, Molecular pharmacology, 43(5), 1993, pp. 702-708
Two human colorectal tumor cell lines are differentially sensitive to
growth inhibition by 5-fluorodeoxyuridine (FdUrd); cell line RCA is le
ss sensitive to FdUrd than is cell line C. Thymidylate synthase (TS),
a target of FdUrd, has been purified to homogeneity from both cell lin
es. Because of differences in the avidity for a folate ligand affinity
matrix, TS forms from the cells were purified by two different proced
ures. Relative to the enzyme from C cells, the enzyme from RCA cells d
emonstrated higher K(m) values for the substrates deoxyuridylate and 5
,10-methylenetetrahydrofolate, a lower rate of association of the inhi
bitor 5-fluorodeoxyuridylate (FdUMP), a similar rate of FdUMP dissocia
tion, and lower enhancement of covalent FdUMP binding by folate deriva
tives. The activities of the enzymes in situ and the catalytic efficie
ncies of the purified enzymes were similar. Thus, a cell line that is
naturally resistant to FdUrd has been identified that expresses a TS w
ith reduced affinity for FdUMP and 5,10-methylenetetrahydrofolate, rel
ative to the enzyme expressed in a FdUrd-sensitive cell line.