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

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 c ompare these with the 50% growth inhibition concentrations (GI(50)) from th e National Cancer Institute database. Experimental Design: Thymidine kinase (TK) activity was assessed by convers ion of [H-3]thymidine to [H-3]TMP. Thymidylate synthase (TS) protein expres sion was determined by Western analysis. TS and dihydropyrimidine dehydroge nase (DPD) mRNA expression were measured by quantitative reverse transcript ion-PCR, Results: The median (range) for the targets were as follows: 5-FU GI(50), 2 0.8 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 correlati on was noted between 5-FU and FdUrd GI(50)s (r = 0.60), whereas a week-mode rate 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 signific antly more sensitive to 5-FU and FdUrd, Conclusions: The lack of correlation may in part be attributable to the inf luence of downstream factors such as p53, the observation that the more sen sitive 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) d rug exposure.