Expression of 5-fluorouracil-related enzymes in lung cancer: ELISA characterizes enzyme activity and messenger RNA expression

The enzymes thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and orotate phosphoribosyl transferase (OPRT) are involved in the metabolism of the anticancer drug 5-fluorouracil (FU). Expression of TS, DPD and OPRT in cancer tissue has been reported to be associated with sensitivity and/or resistance to 5-FU therapy. However, the role of TS, DPD and OPRT expression in lung cancer has not been fully established. Furthermore, among several measuring methods, it is not clear which method effectively predicts the response to 5-FU therapy. The aim of this study was to analyze the expression of 5-FU-related enzymes using enzyme-linked immunosorbent assay (ELISA) and to examine the correlation of ELISA and the results obtained using different measuring methods such as reverse transcript polymerase chain reaction (RT-PCR), immunohistochemistry, and enzymatic activity. Lung cancer specimens were obtained from 134 patients who underwent curative resection for lung cancer. As a pilot study, enzyme expression of 11 samples was measured using 4 different methods for DPD: RT-PCR, immunohistochemistry, enzymatic activity and ELISA. The relationships between pairs of results were compared, and then enzyme protein expression was measured using ELISA in 119 patients with adenocarcinoma. Of the 4 independent methods, the highest correlation was observed between protein expression measured by ELISA and enzyme activity. The correlation of gene expression and ELISA was also significant. The protein level in stage I adenocarcinoma measured using ELISA was 13.0±24.8 ng/mg protein for TS, 362.2±264.3 ng/mg protein for DPD and 4.5±2.0 ng/mg protein for OPRT. The predictive value of the enzymes for prognosis and the effectiveness of 5-FU was not determined as few recurrences were observed during the short follow-up period. In conclusion, ELISA is a simple and reliable method to measure key enzymes related to 5-FU therapy.