Establishment and characterization of 5-fluorouracil-resistant gastric cancer cells.

Two 5-fluorouracil (5-FU)-resistant cell lines from a Korean gastric cancer cell line were established by incubation of the cells with increasing concentration of 5-FU, and the resultant cell lines showed an over 800-fold increased resistance to 5-FU. To identify the mechanism of 5-FU resistance, the expressions of genes involved in 5-FU metabolism were examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Expressions of orotate phosphoribosyltransferase (OPRT), thymidine phosphorylase (TP), and uridine phosphorylase (UP) were significantly downregulated in these cell lines, resulting in low incorporation of 5-FU into nucleic acids. In contrast, an increased expression of thymidine kinase (TK) was observed in 5-FU-resistant cells. These results strongly indicate that blocking of 5-FU incorporation into nucleic acids and TK overexpression may play a major role in 5-FU resistance in these cells. Interestingly, these cell lines showed cross-resistance to paclitaxel, cisplatin, and doxorubicin, suggesting that other factors such as HSP27 and Mn-SOD could be also involved in the mechanism of multidrug resistance in these cell lines.