Intracellular thymidylate synthase inhibition by trifluorothymidine in FM3A cells

Nucleosides Nucleotides Nucleic Acids. 2004 Oct;23(8-9):1491-4. doi: 10.1081/NCN-200027707.


Trifluorothymidine (TFT) can be phosphorylated by thymidine kinase (TK) to TFTMP which can inhibit thymidylate synthase (TS), resulting in depletion of thymidine nucleotides. TFT can be degraded by thymidine phosphorylase (TP) which can be inhibited by thymidine phosphorylase inhibitor (TPI). Using the TS in situ Inhibition Assay (TSIA) FM3A breast cancer cells were exposed 4 h or 24 h to TFT and 5-Fluorouracil (5FU). TS activity reduced to 9% (0.1 microM TFT) and 58% (1 microM 5FU) after 4 h exposure and to 6% (TFT) and 21% (5FU) after 24 h exposure. TPI did not affect TS inhibition by TFT. FM3A cells lacking TK or TS activity (FM3A/TK-) were far less sensitive to TFT compared to FM3A cells.

Conclusion: TFT can be taken up and activated very rapidly by FM3A cancer cells, probably due to favourable TK enzyme properties, and TPI did not influence this.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites, Antineoplastic / pharmacology
  • Cell Line, Tumor
  • Enzyme Inhibitors / pharmacology*
  • Humans
  • Inhibitory Concentration 50
  • Phosphorylation
  • Thymidine / chemistry
  • Thymidine Phosphorylase
  • Thymidylate Synthase / antagonists & inhibitors*
  • Time Factors
  • Trifluridine / pharmacology*


  • Antimetabolites, Antineoplastic
  • Enzyme Inhibitors
  • Thymidylate Synthase
  • Thymidine Phosphorylase
  • Trifluridine
  • Thymidine