ABSTRACT
OBJECTIVE: To investigate whether gemcitabine (dFdC) at the non-cytotoxic concentration enhances the effect of irradiation on human squamous carcinoma cells of the uterine cervix (HeLa) in vitro, and to evaluate the mechanism by which dFdC at the non-cytotoxic concentration [24 h 10% inhibiting concentration (IC(10))] is able to enhance radiation-induced cytotoxicity to HeLa in vitro. METHODS: The non-cytotoxic concentration (24 h IC(10)) of dFdC was determined by methyl thiazolyl tetrazolium (MTT). After exposure to the non-cytotoxic concentration (0.01 micro mol/L) for 4, 8, 12 and 24 hours followed by immediate irradiation (4, 6 and 8 Gy), the surviving fraction was counted and the radiation enhancement ratio (RER) was evaluated. Cell cycle distribution and apoptosis were analyzed by flow cytometry. The expressions of p53, bcl-2 and bax were studied by western blot. RESULTS: After exposure to non-cytotoxic concentration (0.01 micro mol/L) for 4, 8, 12 and 24 hours followed by immediate irradiation, the RER was 1.19, 1.35, 1.72 and 1.93, respectively. After exposed to dFdC, HeLa cells showed an S phase block. The proportion of S phase cells was elevated with the increase of exposure duration (P < 0.01). The S-phase proportion increased to 51.8% at 24 hours of exposure. Meanwhile, compared with the single-agent treatments, combination of dFdC and radiation did not additionally increase the number of apoptotic cells and expression of proteins related to apoptosis such as p53, bcl-2 and bax (P > 0.05). CONCLUSIONS: HeLa cells were radiosensitive at IC(10) concentration of dFdC. The radiosensitization effect depends on the exposure duration to dFdC. There appears a strong association between the radiosensitization and the progression of cells into S-phase after dFdC treatment. Combination of dFdC and radiation did not increase apoptosis of HeLa cells.
