This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Houghton, J. A. Articles by Rahman, A. Search for Related Content PubMed PubMed Citation Articles by Houghton, J. A. Articles by Rahman, A.

Locus of the Interaction among 5-Fluorouracil, Leucovorin, and Interferon-2a in Colon Carcinoma Cells¹

Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101 [J. A. H., C. L. M., D. A. A.], and Division of Biopharmaceutics, Food and Drug Administration, Rockville, Maryland 20857 [A. R.]

Prior studies from these laboratories demonstrated 3.2-fold potentiation of 5-fluorouracil (FUra) cytotoxicity by recombinant human interferon-2a (rIFN-2a) in GC₃/cl colon adenocarcinoma cells that was significantly enhanced to 14-fold when FUra was combined with rIFN-2a + a mixture of the diasteroisomers of the biologically active (6S) and inactive (6R) leucovorin or 5-formyl-H₄PteGlu (LV), events that were reversible by thymidine (dThd). In GC₃/clTS^-c3/c3 cells, deficient in thymidylate synthase, rIFN-2a cytotoxicity was not influenced by the concentration of dThd, indicating no direct effect at the level of dThd-less stress. Direct assays of thymidylate synthase indicated no significant difference between FUra-induced accumulation of total thymidylate synthase or free or unbound thymidylate synthase in cells receiving FUra + modulators. In addition, the cytotoxic activity of CB3717, a specific quinazoline-based inhibitor of thymidylate synthase, was not potentiated by rIFN-2a. These studies suggested that thymidylate synthase was not the primary target site for rIFN-2a activity. Since data indicated that a 5-fluoropyrimidine was required in the interaction among FUra, LV, and rIFN-2a, attention was focused at the level of DNA. Both DNA single-strand breaks (SSBs) and DNA double-strand breaks (DSBs) induced by FUra were significantly elevated by rIFN-2a and LV administered as single modulators and were influenced by the concentrations of both FUra and rIFN-2a. However, when FUra was combined with LV, rIFN-2a further potentiated the frequency of DNA SSBs, and data correlated with the relative cytotoxic activity of FUra-LV-rIFN-2a combinations. No effect on CB3717-induced DNA SSBs or DSBs by rIFN-2a was demonstrated. Drug exposure for 48 h was required to detect measurable differences in DNA SSB frequency among FUra-LV-rIFN-2a treatment groups and correlated with decreased clonogenic survival under these conditions. Continuous exposure to FUra (72 h) allowed shorter exposures to LV and/or rIFN-2a (48 h) to maintain maximal cytotoxicity. Shorter exposure times for FUra during continuous exposure to the modulators were less cytotoxic. Data suggest that the primary locus of the interaction among FUra, LV, and rIFN-2a lies at the level of DNA. rIFN-2a may exert its effects via enhancement of FUra base excision or incorporation into DNA, events that subsequently become influenced by thymidylate synthase inhibition and dThd-less stress and are further potentiated by LV. Further studies will define the exact target of rIFN-2a action.

¹ Supported by National Cancer Institute awards CA23099, CA32613, CA21765 and by the American Lebanese Syrian Associated Charities.

² To whom requests for reprints should be addressed, at St. Jude Children's Research Hospital, Department of Molecular Pharmacology, 332 North Lauderdale, Memphis, TN 38101-0318.

Received 2/22/93. Accepted 7/13/93.

This article has been cited by other articles:

				E. Jonasch and F. G. Haluska Interferon in Oncological Practice: Review of Interferon Biology, Clinical Applications, and Toxicities Oncologist, February 1, 2001; 6(1): 34 - 55. [Abstract] [Full Text]

				I. Petak, D. M. Tillman, F. G. Harwood, R. Mihalik, and J. A. Houghton Fas-dependent and -independent Mechanisms of Cell Death following DNA Damage in Human Colon Carcinoma Cells Cancer Res., May 1, 2000; 60(10): 2643 - 2650. [Abstract] [Full Text]

				C. A. Presant, W. Wolf, V. Waluch, C. L. Wiseman, I. Weitz, and J. Shani Enhancement of Fluorouracil Uptake in Human Colorectal and Gastric Cancers by Interferon or by High-Dose Methotrexate: An In Vivo Human Study Using Noninvasive 19F-Magnetic Resonance Spectroscopy J. Clin. Oncol., January 14, 2000; 18(2): 255 - 255. [Abstract] [Full Text] [PDF]

				J. D. Shapiro, N. Harold, C. Takimoto, J. M. Hamilton, D. Vaughn, A. Chen, S. M. Steinberg, D. Liewehr, C. Allegra, B. Monahan, et al. A Pilot Study of Interferon {{alpha}}-2a, Fluorouracil, and Leucovorin Given with Granulocyte-Macrophage Colony Stimulating Factor in Advanced Gastrointestinal Adenocarcinoma Clin. Cancer Res., September 1, 1999; 5(9): 2399 - 2408. [Abstract] [Full Text] [PDF]

				D. M. Tillman, I. Petak, and J. A. Houghton A Fas-dependent Component in 5-Fluorouracil/Leucovorin-induced Cytotoxicity in Colon Carcinoma Cells Clin. Cancer Res., February 1, 1999; 5(2): 425 - 430. [Abstract] [Full Text] [PDF]

				J. A. Houghton, F. G. Harwood, and D. M. Tillman Thymineless death in colon carcinoma cells is mediated via Fas signaling PNAS, July 22, 1997; 94(15): 8144 - 8149. [Abstract] [Full Text] [PDF]