Preclinical evaluation of a radiosensitizing effect of gemcitabine in p53 mutant and p53 wild type bladder cancer cells.
OBJECTIVES: Despite clinical use, the radiosensitizing effect of gemcitabine (2'2'-difluorodeoxycytidine) in human transitional cell carcinoma (TCC) has not been shown to date. We investigated gemcitabine as a radiosensitizer for human TCC cells. METHODS: Monolayer cultures of RT112 (G1, p53 wild type), RT4 (G1-G2, p53 wild type), T24 (G3, p53, mutant type), and SUP (G4, p53 mutant type) cells were incubated in medium with gemcitabine. Electron beam radiation was applied alone, simultaneous, or 3, 6, 12, and 24 hours after gemcitabine. Jurkat leukemia cells were used as controls for radiation toxicity. Cell survival was determined 6, 12, 24, 48, and 72 hours after radiation by microculture tetrazolium assay. DNA damage was evaluated by flow cytometric assessment of poly(ADP-ribose) polymerase, and apoptosis was determined by terminal-deoxynucleotidyltransferase-mediated dUTP nick-end labeling and flow cytometric assessment after annexin-V and propidium iodide labeling. RESULTS: In all TCC cell lines, radiation alone caused only little and insignificant growth inhibitory effects at 10 Gy. Gemcitabine alone had a dose-dependent cytotoxic and apoptosis inducing effect on all TCC cell lines independent of p53 status. Assays combining radiation with gemcitabine in different dose and time schedules demonstrated no radiosensitizing effect in TCC cells. CONCLUSIONS: Gemcitabine is effective in TCC cell lines independent of p53 status. A radiosensitizing effect could not be demonstrated. Again, p53 status was not predictive of the radioresponse in the bladder cancer cell lines. Clinical studies with gemcitabine and radiotherapy might nevertheless yield different results but should be performed with utmost caution.