Cytotoxic synergism of methioninase in combination with 5-fluorouracil and folinic acid.
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.
Machover
D
D
Hematology and Oncology Department, Hospital Paul-Brousse, 12-14 Avenue Paul Vaillant-Couturier, F-94804, Villejuif, France. david.machovere@pbr.ap-hop-paris.fr
Zittoun
J
J
Broët
P
P
Metzger
G
G
Orrico
M
M
Goldschmidt
E
E
Schilf
A
A
Tonetti
C
C
Tan
Y
Y
Delmas-Marsalet
B
B
Luccioni
C
C
Falissard
B
B
Hoffman
R M
RM
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D013437:Carbon-Sulfur Lyases / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D002955:Leucovorin / Q000494:pharmacology*; D008715:Methionine / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D013763:Tetrahydrofolates / Q000378:metabolism; D013940:Thymidylate Synthase / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D011994:Recombinant Proteins; D013763:Tetrahydrofolates; C013123:5,10-methylenetetrahydrofolic acid; C030371:5,6,7,8-tetrahydrofolic acid; D008715:Methionine; D013940:Thymidylate Synthase; D013437:Carbon-Sulfur Lyases; C021558:L-methionine gamma-lyase; D002955:Leucovorin; D005472:Fluorouracil