Abstract

PURPOSE
The cytotoxicity by 5-fluorouracil (5-FU) is mediated by inhibition of thymi- dylate synthase (TS), which is a rate-limiting enzyme for DNA synthesis. To test whether the resistance to 5-FU would be associated with cellular TS activity, we analyzed TS gene expression from human gastrointestinal cancer cell lines.
MATERIALS AND METHODS
We established the experimental conditions for quantitating TS mRNA expression by competitive RT-PCR using mimic DNA. Based on this method, we compared TS mRNA expression between 5-FU resistant cell line and parent cell line and investigated the expression of TS mRNA following 5-FU administration in 6 human gas- trointestinal cancer cell lines.
RESULTS
Competitive RT-PCR using mimic DNA seemed to be more effective than Northern blot analysis for quantitation of TS gene expression. The quantity of TS mRNA and IC50 value of 5-FU in 5-FU resistant H630 was found to be 2.5 and 10 times higher than in parent cell line, respectively. And also, we observed linear relationship between TS mRNA level and IC50 value of 5-FU (r 0.76) in 6 gastrointestinal cancer cell lines.
CONCLUSION
These results suggest that overexpression of TS mRNA may play a role in the development of 5-FU resistance in human gastrointestinal malignancies

• Keywords: Thymidylate synthase;Drug resistance