Cytotoxic synergism of methioninase in combination with 5-fluorouracil and folinic acid

Biochem Pharmacol. 2001 Apr 1;61(7):867-76. doi: 10.1016/s0006-2952(01)00560-3.


Potentiation of the cytotoxic activity of 5-fluorouracil (FUra) by folinic acid (5-HCO-H4folate) is due to elevation of the methylene tetrahydrofolate (CH2-H4folate) level, which increases the stability of the ternary complex of thymidylate synthase (TS), fluorodeoxyuridine monophosphate, and CH2-H4folate that inactivates the TS. Methionine deprivation results in the production of tetrahydrofolate (H4folate) and, subsequently, CH2-H4folate from methyl tetrahydrofolate, as a consequence of the induction of methionine synthesis. We hypothesized that the efficacy of FUra could be augmented by the combination of high-concentration 5-HCO-H4folate and recombinant methioninase (rMETase), a methionine-cleaving enzyme. Studies in vitro were performed with the cell line CCRF-CEM. Cytotoxic synergism of FUra + rMETase and FUra + 5-HCO-H4folate + rMETase was demonstrated with the combination index throughout a broad concentration range of FUra and rMETase. A subcytotoxic concentration of rMETase reduced the IC50 of FUra by a factor of 3.6, and by a factor of 7.5, in the absence and in the presence of 5-HCO-H4folate, respectively. 5-HCO-H4folate increased the intracellular concentrations of CH2-H4folate and H4folate from their baseline levels. Concentrations of folates were not changed by exposure to rMETase. Levels of free TS in cells treated with FUra + 5-HCO-H4folate and with FUra + rMETase were lower than those in cells exposed to FUra alone. The decrease of TS was still more pronounced in cells treated with FUra + 5-HCO-H4folate + rMETase. The synergism described in this study will be a basis for further exploration of combinations of fluoropyrimidines, folates, and rMETase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites, Antineoplastic / pharmacology
  • Carbon-Sulfur Lyases / pharmacology*
  • Cell Division / drug effects
  • Drug Screening Assays, Antitumor
  • Drug Synergism
  • Fluorouracil / pharmacology*
  • Humans
  • Leucovorin / pharmacology*
  • Methionine / metabolism
  • Recombinant Proteins / pharmacology
  • Tetrahydrofolates / metabolism
  • Thymidylate Synthase / metabolism
  • Tumor Cells, Cultured


  • Antimetabolites, Antineoplastic
  • Recombinant Proteins
  • Tetrahydrofolates
  • 5,10-methylenetetrahydrofolic acid
  • 5,6,7,8-tetrahydrofolic acid
  • Methionine
  • Thymidylate Synthase
  • Carbon-Sulfur Lyases
  • L-methionine gamma-lyase
  • Leucovorin
  • Fluorouracil