Interaction of gamma interferon and 5-fluorouracil in the H630 human colon carcinoma cell line.
The antiproliferative effects and pharmacological interactions of 5-fluorouracil (5-FU) in combination with gamma interferon (IFN-gamma) were determined against the human colon carcinoma H630 cell line in vitro. H630 was 9-fold more resistant to 5-FU, as compared to a relatively sensitive human colon line (C1). IFN-gamma showed modest antiproliferative activity against the H630 line, with a 50% inhibitory concentration of 440 units/ml. Simultaneous treatment of H630 with subinhibitory concentrations of IFN-gamma and 5-FU produced a significant enhancement of the 5-FU-associated growth inhibition. The growth-inhibitory activity of the combination against H630 was prevented by the addition of 20 microM thymidine. Thymidylate synthase (TS) activity was measured by both the 5-fluoro-2'-deoxyuridine-5'-monophosphate binding and catalytic assays, using cytosolic extracts. A 24-h exposure to 1 microM 5-FU in the H630 line resulted in a 3.1-fold increase in the total amount of TS, while in the 5-FU/IFN-gamma-treated cells TS remained unchanged from non-drug-treated control levels. Moreover, we found that free thymidylate synthase in the 5-FU/IFN-gamma-treated cells was significantly decreased, as compared to the cells treated with 5-FU alone. Incorporation of 5-FU into both the RNA and DNA fractions did not change with the addition of IFN-gamma. Accumulation of the fluoropyrimidine metabolites 5-fluoro-2'-deoxyuridine-5'-monophosphate and 5-fluorouridine-5'-triphosphate remained the same for 5-FU alone and the combination treatment. These findings suggest that acute TS induction by 5-FU may provide an important mechanism by which human colon carcinoma cells express decreased sensitivity to 5-FU and that IFN-gamma can reverse the development of resistance to 5-FU in the H630 line by inhibiting the overexpression of TS that results from 5-FU exposure. These studies contribute to a growing understanding of the complex interaction between 5-FU and IFN-gamma.
Chu
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E
Division of Cancer Treatment, National Cancer Institute, Bethesda, Maryland 20892.
Zinn
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Boarman
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Allegra
C J
CJ
D000230:Adenocarcinoma / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000473:pathology*; D004247:DNA / Q000378:metabolism; D004347:Drug Interactions; D004351:Drug Resistance; D005468:Fluorodeoxyuridylate / Q000032:analysis; D005472:Fluorouracil / Q000378:metabolism / Q000494:pharmacology*; D005492:Folic Acid / Q000032:analysis; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D012313:RNA / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors; D014407:Tumor Cells, Cultured
D005468:Fluorodeoxyuridylate; D012313:RNA; D007371:Interferon-gamma; D004247:DNA; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D005472:Fluorouracil