Figure 5

Effect of Loratadine and Radiation on Cell Cycle Progression. HT29 cells were either treated with loratadine (75 μM, 24 hrs) prior to exposure to 8 Gy radiation, or treated with loratadine or radiation alone. Cell cycle progression was analyzed by flow cytometry. (A) After 24 hr treatment with loratadine, cells exhibited a G2 block (38%) which persisted through 36 hrs and resolved by 42 hrs. Irradiated cells also exhibited a G2 block which peaked (74%) at 12 hrs after irradiation and began to decrease 18 hrs after irradiation. Loratadine abrogated the radiation-induced G2 block at 12 hrs post-irradiation and by 18 hrs had returned to baseline. (B) Irradiation alone (open circle) increased the percentage of cells in G2/M but did not increase the percentage of loratadine-treated cells (solid circle) in G2/M compared to loratadine treatment alone (open square). The figure represents a single representative experiment.