T S Lawrence1, M A Davis, J Maybaum. 1. Department of Radiation Oncology, University of Michigan Medical Center, Ann Arbor 48109.
Abstract
PURPOSE: Although 5-fluorouracil (FUra) has been demonstrated to be a radiation sensitizer both in the laboratory and the clinic, it is not known whether radiosensitization results primarily from FUra's DNA or RNA-directed effects. METHODS AND MATERIALS: We studied the radiosensitizing effects of FUra +/- thymidine (dThd)) on HT29 human colon cancer cells, which are relatively sensitive to the DNA-directed action of FUra, in comparison to SW620 and HuTu80 human colon cancer cells, which are relatively resistant to FUra's DNA-directed effects. We hypothesized that if FUra were acting chiefly through DNA dependent mechanisms, HT29 cells would (a) show greater radiosensitization than SW620 and HuTu80 cells under the same conditions of exposure; and (b) demonstrate selective reversal of radiation sensitivity (compared to cytotoxicity) in the presence of FUra + dThd, compared to FUra alone. RESULTS: We found that the enhancement ratio produced by a 24 h exposure to 10 microM FUra was significantly greater in HT29 cells compared to SW620 and HuTu80 cells (enhancement ratios of 2.1 +/- 0.1; 1.1 +/- 0.1, and 1.3 +/- 0.1, respectively). Furthermore, in HT29 cells, dThd blocked FUra-mediated radiosensitization to a greater extent than FUra-mediated cytotoxicity. Thus, our hypotheses were confirmed. CONCLUSION: These findings support the concept that the manipulation of FUra's DNA-dependent actions, for example, through modulators of thymidylate synthase (TS) activity, may increase radiosensitization in clinical trials in the treatment of gastrointestinal cancers. However, since resistance to the DNA-directed effects of fluoropyrimidines can result from mechanisms unrelated to TS inhibition, additional strategies will be required to potentiate fluoropyrimidine-mediated radiosensitization.
PURPOSE: Although 5-fluorouracil (FUra) has been demonstrated to be a radiation sensitizer both in the laboratory and the clinic, it is not known whether radiosensitization results primarily from FUra's DNA or RNA-directed effects. METHODS AND MATERIALS: We studied the radiosensitizing effects of FUra +/- thymidine (dThd)) on HT29 humancolon cancer cells, which are relatively sensitive to the DNA-directed action of FUra, in comparison to SW620 and HuTu80 humancolon cancer cells, which are relatively resistant to FUra's DNA-directed effects. We hypothesized that if FUra were acting chiefly through DNA dependent mechanisms, HT29 cells would (a) show greater radiosensitization than SW620 and HuTu80 cells under the same conditions of exposure; and (b) demonstrate selective reversal of radiation sensitivity (compared to cytotoxicity) in the presence of FUra +dThd, compared to FUra alone. RESULTS: We found that the enhancement ratio produced by a 24 h exposure to 10 microM FUra was significantly greater in HT29 cells compared to SW620 and HuTu80 cells (enhancement ratios of 2.1 +/- 0.1; 1.1 +/- 0.1, and 1.3 +/- 0.1, respectively). Furthermore, in HT29 cells, dThd blocked FUra-mediated radiosensitization to a greater extent than FUra-mediated cytotoxicity. Thus, our hypotheses were confirmed. CONCLUSION: These findings support the concept that the manipulation of FUra's DNA-dependent actions, for example, through modulators of thymidylate synthase (TS) activity, may increase radiosensitization in clinical trials in the treatment of gastrointestinal cancers. However, since resistance to the DNA-directed effects of fluoropyrimidines can result from mechanisms unrelated to TS inhibition, additional strategies will be required to potentiate fluoropyrimidine-mediated radiosensitization.
Authors: Mary Ellen Urick; Eun Joo Chung; William P Shield; Naamit Gerber; Ayla White; Anastasia Sowers; Angela Thetford; Kevin Camphausen; James Mitchell; Deborah E Citrin Journal: Clin Cancer Res Date: 2011-06-20 Impact factor: 12.531
Authors: Tiffany S Stolworthy; Aaron M Korkegian; Candice L Willmon; Andressa Ardiani; Jennifer Cundiff; Barry L Stoddard; Margaret E Black Journal: J Mol Biol Date: 2008-01-11 Impact factor: 5.469