Antisense thymidylate synthase electrogene transfer to increase uptake of radiolabeled iododeoxyuridine in a murine model.
In vitro and in vivo experiments from our laboratory and others have suggested that the combination of thymidylate synthase (TS) inhibitor and radiolabeled iododeoxyuridine (IdUrd) is synergistic. Efficacy is limited by drug resistance, which is often mediated by TS overexpression. We designed an in vivo electrogene transfer (EGT) model for delivering antisense TS plasmid (ATS) into tumor to increase the subsequent efficacy of (131)I-IdUrd therapy.


METHODS
Plasmid complementary to nucleotide 531-710 in the coding region of the mouse TS (mTS) mRNA was constructed. TS activity and (131)I-IdUrd DNA incorporation were determined 48 h after in vitro EGT of ATS to CT26 cells. In vivo therapeutic effect and radioactivity retained in tumor after various combinations of EGT ATS, 5-fluorouracil (5-FU), and continuous infusion of (131)I-IdUrd by osmotic minipump were determined.


RESULTS
A reduction of TS activity was achieved after in vitro EGT ATS. Flow cytometry analysis indicated that ATS-treated cells were arrested at S phase. In the in vivo tumor model, the combination of EGT ATS and 5-FU was able to partially overcome 5-FU drug resistance. Sixty percent of tumors can be eradicated by the combination of EGT ATS, 5-FU, and infusion of (131)I-IdUrd. The tumors treated by EGT ATS had higher radioactivity retained 1 wk after (131)I-IdUrd therapy than after EGT of control plasmid.


CONCLUSIONS
In situ EGT ATS can downregulate TS and increase the therapeutic effect of radiolabeled IdUrd therapy. The combination of EGT ATS, 5-FU, and (131)I-IdUrd may result in tumor eradication.
Chi
Kwan-Hwa
KH
Cancer Center, Veterans General Hospital-Taipei, National Yang-Ming University, Taipei, Taiwan. M006565@ms.skh.org.tw
Wang
Hsin-Ell
HE
Wang
Yu-Shan
YS
Chou
Shun-Lan
SL
Yu
Hung-Man
HM
Tseng
Yu-Hua
YH
Hwang
Ing-Ming
IM
Lui
Wing-Yiu
WY
D000230:Adenocarcinoma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D000818:Animals; D041702:BALB 3T3 Cells; D002453:Cell Cycle / Q000528:radiation effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy; D016373:DNA, Antisense / Q000008:administration & dosage* / Q000235:genetics / Q000627:therapeutic use*; D018274:Electroporation / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D018014:Gene Transfer Techniques; D007065:Idoxuridine / Q000493:pharmacokinetics / Q000627:therapeutic use*; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D051379:Mice; D011836:Radiation Tolerance / Q000187:drug effects; D013940:Thymidylate Synthase / Q000235:genetics / Q000378:metabolism*
D016373:DNA, Antisense; D007457:Iodine Radioisotopes; D013940:Thymidylate Synthase; D007065:Idoxuridine