Combined therapy using TS-suppressing vector and 5-FU

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Thymidylate synthase (TS) is a target molecule of 5-FU-derived anti-tumor drugs. We found a TS overexpression to be associated with the 5-FU resistance (Nakano, et. al., Br J Cancer 2006). Therefore, in order to develop the treatment against patients with TS-overexpressing cancers, we have been studying on the combined therapy with a TS-suppressing vector and 5-FU. First, to determine the effective siRNA sequence against TS, we synthesized several siRNAs. With the transfection of the siRNA into TS-overexpressing cells, such as A549 and MAC10, using the lipofection method, we determined the most effective siRNA sequence against TS. After the synthesize of shRNA (short hairpin RNA) based on this siRNA, we constructed a TS-suppressing shRNA plasmid vector by inserting the shRNA into the pBAsi-hU6 DNA plasmid vector with the human U6 promoter. Then, using the COS-TPC method, we constructed a TS-suppressing shRNA adenoviral vector (TSshRNA-Ad5). The transfection of TSshRNA-Ad5 into TS-overexpressing.lls, A549 and MAC10, resulted in more than 90% of knockdown of the TS gene expression. Then, we concentrated and purified the TSshRNA-Ad5. Next, we performed the MTT assay to evaluate the anti-tumor efficacy of the TSshRNA-Ad5 and 5-FU in A549 and MAC10 cells. Consequently, we found that the combined therapy with both TSshRNA-Ad5 and 5-FU had a stronger anti-tumor effect than the simple treatment of TSshRNA-Ad5 or 5-FU did. In order to confirm these results, we are performing the additional in vitro experiments using 5-FU-resistant cancer cells, such as NUGC-3/5-FU. In addition, we are also performing the in vivo experiment of the combined therapy with the TS-suppressing vector and 5-FU using the tumor-bearing nude mice. Furthermore, we found an E2F1 overexpression to induce the TS expression in non-small cell lung cancer (Huang, et. Al., Clin Cancer Res 2007).