Modulation of fluorouracil cytotoxicity by interferon-α and -γ

A. S.A. Ismail, C. J. Van Groeningen, A. Hardcastle, Q. F. Ren, G. W. Aherne, F. Geoffroy, C. J. Allegra, J. L. Grem

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Abstract

Because interferons (IFN)-α and -γ individually have increased fluorouracil (FUra) cytotoxicity in several in vitro models, we studied the effects of FUra combined with IFN-α + γ in HT29 colon cancer cells. A 96- hr exposure to IFN-α (500 units/ml) plus IFN-γ (10 units/ml) and a 72-hr exposure to 0.25-1 μM FUra (hr 24-96) inhibited cell growth and colony formation in an additive or more-than-additive fashion. When cells were exposed to IFN-α + γ and FUra, free FdUMP levels became detectable, whereas [3H]FUra-RNA incorporation decreased. Exposure to IFN-α + γ FUra, or the combination decreased dTTP pools to 58%, 43%, and 17% of control, respectively. A marked increase in the dATP to dTTP ratio was seen with FUra with or without IFN-α + γ. Thymidylate synthase catalytic activity was reduced to 28% and 24% of control with FUra with or without IFN-α + γ, suggesting that the enhanced dTTP depletion must be due to another mechanism. FUra-mediated thymidylate synthase inhibition was accompanied by a 124-fold increase in total deoxyuridylate immunoreactivity and a 31-fold increase in dUTP pools, but the addition of IFN-α + γ attenuated the accumulation. Treatment with IFN-α + γ and FUra individually interfered with nascent DNA chain elongation, whereas the three-drug combination produced the most striking effects. IFN-α + γ plus FUra produced the greatest amount of single-strand breaks in nascent DNA and dramatically decreased net DNA synthesis. IFN-α + γ with or without FUra produced double-strand breaks in parental DNA. These results suggest that dTTP depletion, dATP/dTTP imbalance, pronounced inhibition of DNA synthesis, and damage to nascent and parental DNA contribute to the enhanced cytotoxicity with the triple combination.

Original languageEnglish (US)
Pages (from-to)252-261
Number of pages10
JournalMolecular pharmacology
Volume53
Issue number2
DOIs
Publication statusPublished - Feb 1998

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ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

Cite this

Ismail, A. S. A., Van Groeningen, C. J., Hardcastle, A., Ren, Q. F., Aherne, G. W., Geoffroy, F., ... Grem, J. L. (1998). Modulation of fluorouracil cytotoxicity by interferon-α and -γ. Molecular pharmacology, 53(2), 252-261. https://doi.org/10.1124/mol.53.2.252