Aberrant cell cycle inhibition pattern in human colon carcinoma cell lines after exposure to 5-fluorouracil.
In this report, we describe the use of two human colon carcinoma cell lines, HCT-8 and HT-29, as potential models to study DNA- and RNA-directed cytotoxicity due to 5-fluorouracil (FUra) exposure by flow microfluorimetric analysis of DNA cell content. The sensitivity of the HT-29 line (EC50 = 0.9 microM) to FUra was somewhat greater than that of the HCT-8 line (EC50 = 4 microM), but each presented a dramatically different DNA histogram after exposure to FUra. In HCT-8, an unexpected and nearly complete disappearance of cells in S-phase occurred, whereas in HT-29 the expected accumulation of cells at the G1-S border was observed. The absence of HCT-8 cells in S-phase also occurred as a result of two RNA polymerase inhibitors: actinomycin D and dichloro-D-ribofuranosylbenzimidazole. However, an accumulation of cells in S-phase was observed in the presence of 5-fluorodeoxyuridine. These results suggest that in the HCT-8 cell line, FUra predominantly causes an RNA-related toxicity. By comparison, the rate of formation of 5-fluorodeoxyuridine monophosphate, the increased dUMP pool size, and low thymidylate synthase activity in the HT-29 line are consistent with its greater susceptibility to DNA-directed toxicity. Further evidence was seen in the prevention of FUra cytotoxicity by thymidine in HT-29, but not in HCT-8 cells. Similarly, Leucovorin synergized the action of FUra in HT-29 but not in HCT-8. Enzymatic correlates supporting these observations are seen in the greater activity of uridine kinase than thymidine kinase (20:1) in HCT-8 cells compared with that in HT-29 cells (4:1).
Pizzorno
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Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510.
Sun
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Handschumacher
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D002453:Cell Cycle / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000188:drug therapy; D004247:DNA / Q000096:biosynthesis; D004347:Drug Interactions; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D002955:Leucovorin / Q000494:pharmacology; D016196:S Phase; D013936:Thymidine / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects
D004247:DNA; D013940:Thymidylate Synthase; D002955:Leucovorin; D005472:Fluorouracil; D013936:Thymidine