Biochemical determinants of responsiveness to 5-fluorouracil and its derivatives in xenografts of human colorectal adenocarcinomas in mice.

摘要: The level of thymidylate synthetase (EC 2.1.1.45) and its activity have been measured in a series human colorectal adenocarcinomas growing as xenografts immune-deprived mice. Enzyme varied between 8.4 124 pmol per mg protein hr; within each tumor line, this correlated with the capacity to bind [6-3H]5-fluoro-2′-deoxyuridine 5′-monophosphate ([6-3H]FdUMP), which 0.16 1.68 [6-3H]FdUMP bound g tissue. Highest lowest activities were lines that insensitive 5-fluorouracil, 5-fluorouridine, 5-fluoro-2′-deoxyuridine. ratio maximum free FdUMP concentration thymidine synthetase-binding did not differentiate fluorinated pyrimidine-responsive from those innately insensitive. Maximum potential binding vitro was without addition dl -L-5,10-methylenetetrahydrofolate (CH2FH4) cytosol two lines, both demonstrated some sensitivity pyrimidine therapy. other four required CH2FH4 be added order attain binding. Similar data obtained using nitrocellulose membrane filtration isolate covalent noncovalent complexes. Direct measurement after incubation cytosols FdUMP, or CH2FH4, showed that, nonresponsive tumors, enzyme inhibition achieved only presence exogenous cofactor. It is suggested availability cofactor may prove important formation ternary complex CH2FH4:thymidine synthetase:FdUMP when high concentrations are present for short periods time.