5-Fluorouracil (5-FU), a fluoropyrimidine analogue, is one of the most commonly used anticancer drugs for the treatment of gastrointestinal malignancies. Some studies reported that the cytotoxicity of fluoropyrimidines is mediated, in large part, by inhibition of the thymidylate synthase (TS), an essential DNA synthetic enzyme. The aim of this study was to determine if antisense TS technology could augment the chemosensitivity of human cancer cells to 5-FU. The full length coding region of TS cDNA was inversely cloned into the eukaryotic expression vector pCDL81 and transfected into DLD-1 cells. The expression and activity of TS were significantly suppressed in the antisense TS transfected cells. Interestingly, the transfection of antisense TS alone inhibited the cellular growth in vitro. The chemosensitivity to 5-FU was significantly increased in the transfected cells. The 50% inhibition values of 5-FU on DLD-1/anti-TS were approximately one forth that on parental cells. The augmentation of chemosensitivity to 5-FU was also confirmed in a nude mice model. The tumor growth of DLD-1/anti-TS cells was suppressed significantly more than that of DLD-1 cells by the 5-FU. The expression and activity of TS in human colon cancer cells were effectively inhibited by TS antisense treatment and the effect of 5-FU to cancer cells can be augmented. The antisense TS technology could be promising for treatments of gastrointestinal cancers.

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