Radiosensitization of glioblastoma cells against accelerated charged particles

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【Purpose】 : Effects of caffeine, wortmannin and pentoxifylline on the sensitivity of glioblastoma cell lines against high LET carbon beams were analyzed on the basis that wortmannin inhibits the activity of a DNA double strand break repair enzyme DNA-PK while caffeine and pentoxifylline inhibits a cell cycle promoter cdc2 and post-radiation G2-block.【Materials and methods】 : Glioblastoma cell lines with or without mutation in p53 were used as materials. Human skin fibroblast NB1RGB was used as a control. Gamma irradiation was performed as control and 290 MeV/u carbon mono-peak beam was generated at HIMAC of NIRS. Caffeine was used at the final concentration of 5 mM. Wortmannin was added to the culture media at a final concentration of 10 μM. Pentoxifylline was added at final concentrations of 0.25, 0.5 and 1 mM to the culture media. Following irradiations, cells were incubated for 1, 3 and 5 days in the same media before fixation for flow-cytometry analysis. Fixed cells were analyzed b … More y FACScaliber^<TM> and obtained DNA histograms were analyzed by Modfit^<TM>. Standard colony formation assay was used to evaluate the effect of these chemicals on the gamma or carbon beam sensitivities of these cell lines. Western blot and kinase assay were performed to evaluate the expression and kinase activity of DNA-PK in 9 cell lines and the results were compared to their gamma sensitivities.【Results and discussion】 : Caffeine significantly inhibited post irradiation G2/M block and sensitized glioblastoma cell lines against gamma ray. Pentoxifylline had no effect on post-irradiation cell cycle change in fibroblasts and a p53 wild type cell line, while slight inhibition of G2/M-block was observed in a mutant cell line. Also pentoxifylline did not increase apoptosis in these cell lines. Expressions and kinase activities of DNA-PK were in correlation with the gamma sensitivities of gliobalstoma cell lines. Wortmannin significantly sensitized glioblastoma cells against gamma rays in clonogenic survival assay, that was compatible with those results of DNA-PK expression and kinase assay. Furthermore, wortmannin inhibited the G2-block after gamma or carbon beam irradiations. However, there was no effect on the induction of apoptosis on DNA histograms. Sensitization with these chemicals was more remarkable in p53 mutant cell lines than in wild types. It was indicated that these chemicals were in useful to sensitize glioblastoma cell against ionizing radiation, especially wortmannin demonstrated high performance in high LET radiation. Less