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Aberrant cell cycle inhibition pattern in human colon carcinoma cell lines after exposure to 5-fluorouracil
G Pizzorno1, Z Sun, R E Handschumacher
1Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510.
Abstract:
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).
Insights
This study reveals that 5-fluorouracil (FUra) exhibits distinct DNA- and RNA-directed cytotoxicity mechanisms in colon cancer cells. HCT-8 cells show RNA-related toxicity, while HT-29 cells demonstrate DNA-directed toxicity.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- 5-fluorouracil (FUra) is a widely used chemotherapy agent.
- Understanding its precise mechanisms of cytotoxicity is crucial for optimizing cancer treatment.
- Colon carcinoma cell lines offer valuable models for investigating drug effects.
Purpose of the Study:
- To investigate the differential DNA- and RNA-directed cytotoxicity of 5-fluorouracil (FUra) in human colon carcinoma cell lines.
- To characterize the cellular responses and underlying biochemical pathways in HCT-8 and HT-29 cells upon FUra exposure.
Main Methods:
- Utilized two human colon carcinoma cell lines: HCT-8 and HT-29.
- Employed flow microfluorimetric analysis to assess DNA cell content after FUra exposure.
- Investigated the effects of RNA polymerase inhibitors and 5-fluorodeoxyuridine.
- Analyzed enzymatic activities, including uridine kinase and thymidine kinase.
Main Results:
- HT-29 cells (EC50 = 0.9 microM) were more sensitive to FUra than HCT-8 cells (EC50 = 4 microM).
- HCT-8 cells showed a disappearance of S-phase cells, suggesting RNA-related toxicity, unlike HT-29 cells which accumulated at G1-S border (DNA-directed toxicity).
- Thymidine and Leucovorin differentially modulated FUra's cytotoxicity, supporting distinct mechanisms in each cell line.
Conclusions:
- FUra exhibits distinct DNA- and RNA-directed cytotoxic mechanisms dependent on the cellular context.
- HCT-8 cells primarily undergo RNA-related toxicity, while HT-29 cells are more susceptible to DNA-directed toxicity.
- These findings highlight the importance of cell-specific responses in chemotherapy and suggest potential strategies for targeted drug efficacy.