Thymidine kinase, thymidylate synthase, and dihydropyrimidine dehydrogenase profiles of cell lines of the national cancer institute's anticancer drug screen

Purpose: To determine the expression of three targets of 5- fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) in human tumor cell lines and to compare these with the 50% growth inhibition concentrations (GI(50)) from the National Cancer Institute database. Experimental Design: Thymidine kinase (TK) activity was assessed by conversion of [H-3]thymidine to [H- 3]TMP. Thymidylate synthase (TS) protein expression was determined by Western analysis. TS and dihydropyrimidine dehydrogenase (DPD) mRNA expression were measured by quantitative reverse transcription-PCR, Results: The median (range) for the targets were as follows: 5-FU GI(50), 20.8 muM (0.8-536); FdUrd GI(50), 0.75 muM (0.25-237); TK, 0.93 nmol/min/mg (0.16-5.7); in arbitrary units: TS protein, 0.41 (0.05-2.95); TS mRNA, 1.05 (0.12-6.41); and DPD mRNA, 1.09 (0.00-24.4). A moderately strong correlation was noted between 5-FU and FdUrd GI(50)s (r = 0.60), whereas a week-moderate correlation was seen between TS mRNA and protein expression (r = 0.45). Neither TS expression nor TK activity correlated with 5-FU or FdUrd GI(50)s, whereas lines with lower DPD expression tended to be more sensitive to 5-FU, Cell lines with faster doubling times and wild-type p53 were significantly more sensitive to 5-FU and FdUrd, Conclusions: The lack of correlation may in part be attributable to the influence of downstream factors such as p53, the observation that the more sensitive cell lines with faster doubling times also had higher TS levels, and the standard procedure of the screen that uses a relatively short (48-h) drug exposure.

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