Mechanisms of action of FdUMP[10]: metabolite activation and thymidylate synthase inhibition

Oncol Rep. 2007 Jul;18(1):287-91. doi: 10.3892/or.18.1.287.


FdUMP[10] is a multimer of FdUMP, a suicide inhibitor of thymidylate synthase (TS), and was designed to bypass resistance to 5-fluorouracil (5FU). The aim of the study was to compare the effect of FdUMP[10] with 5FU and 5-fluoro-2-deoxyuridine (FUdR) in their efficacy to inhibit their target TS in resistant cells. Therefore cell lines FM3A/0, FM3A/TK- (deficient in thymidine kinase) and FM3A/TS- (deficient in thymidylate synthase) were used to determine TK dependency and specificity for TS inhibition. FdUMP[10] inhibited cell growth with greater potency than 5FU and FdUMP. Direct folate-based inhibitors Raltitrexed, GW1843U89 and Pemetrexed were also evaluated using these cell lines. In TK-deficient cells these folate-based inhibitors had greater potency than the fluoropyrimidines (FPs). Surprisingly, Pemetrexed even inhibited cell growth in TS-deficient cells. Incubation with nucleotidase and phosphatase inhibitors resulted in a reduction of cytotoxicity of FdUMP[10], indicating that the drug can be degraded outside the cells. In the TS in situ inhibition assay (TSIA) 24 h exposure of FM3A cells to 0.5 microM FdUMP and 0.05 microM FdUMP[10] decreased TSIA to 7 and 1% of control. Inhibition of nucleotidase and phosphatase activities reduced the effect of FdUMP[10], while the inhibitory effect was lower in cells lacking TK. FdUMP[10] can enter the cells intact, but also to some extent after dephosphorylation. In conclusion, FdUMP[10] can bypass resistance to FUdR by direct inhibition of TS.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Drug Screening Assays, Antitumor
  • Enzyme Inhibitors / pharmacology
  • Fluorodeoxyuridylate / pharmacology*
  • Fluorouracil / pharmacology*
  • Folic Acid Antagonists / pharmacology*
  • Glutamates / pharmacology
  • Guanine / analogs & derivatives
  • Guanine / pharmacology
  • Mammary Neoplasms, Experimental / drug therapy*
  • Mammary Neoplasms, Experimental / enzymology
  • Mammary Neoplasms, Experimental / pathology
  • Mice
  • Molecular Structure
  • Pemetrexed
  • Quinazolines / pharmacology
  • Thiophenes / pharmacology
  • Thymidylate Synthase / antagonists & inhibitors*
  • Thymidylate Synthase / metabolism
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Enzyme Inhibitors
  • Folic Acid Antagonists
  • Glutamates
  • Quinazolines
  • Thiophenes
  • Pemetrexed
  • Fluorodeoxyuridylate
  • Guanine
  • Thymidylate Synthase
  • raltitrexed
  • Fluorouracil