Caffeine-increased radiosensitivity is not dependent on a loss of G2/M arrest or apoptosis in bladder cancer cell lines

Purpose: Bladder cancer cell lines UCRU-BL-13, UCRU-BL-17/2 and UCRU-BL-28, with differing p53 status and molecular responses to irradiation, were use d to investigate possible mechanisms for caffeine-induced radiosensitizatio n. Materials and methods: After treatment with caffeine and exposure to X-radi ation, radiosensitivity was determined by clonogenic assay. Cell-cycle arre st and apoptosis were measured by flow cytometry. Results: Both BL-13 and BL-28 cells (each expressing p53 with a wild-type s equence) fail to arrest at the G2 checkpoint after radiation, but neverthel ess caffeine did induce radiosensitization. In contrast, in BL-17/2 cells ( expressing p53 with a point mutation in codon 280), caffeine treatment abro gated the radiation-induced G2 arrest but was not accompanied by radiosensi tization. No effects on radiosensitivity were seen in RT112 cells (expressi ng a functionally defective p53) at low caffeine doses (2mM), but at higher doses (4mM and 10mM) caffeine caused both abrogation of radiation-induced G2 arrest and radiosensitization. In none of the cell lines examined did ca ffeine treatment and/or irradiation result in apoptosis. Conclusions: In contrast with previous studies, the data suggest that radio sensitization induced by caffeine is not dependent on abrogation of G2 arre st or the induction of apoptosis, and is not selective for cells expressing p53 proteins with mutations.