Evaluation of the Extent of Cytogenetic Damage Induced by Ionizing Radiation at Different Intervals of Cell Incubation with Iudr in Spheroid Model of Glioblastoma Cell Line Using Comet Assay

5-iodo-2-deoxyuridine(Iudr) is a thymidine analog that is known as a radiosensitizer for human cancer cells in in vitro and in vivo studies. The investigations on the spheroid have shown that Iudr uptake of cells increases with the increasing Iudr incubation time. The aim of this study was to evaluate the extent of cytogenetic damage induced by ionizing radiation at different intervals of cell incubation with Iudr using comet assay. In this basic experimental study, U87MG, a Glioblastoma cell line was cultured as spheroid in two different sizes, 100 and 300µm. The spheroids were incubated with Iudr in three different volume doubling times. Then they were irradiated by 2Gy of gamma radiation of cobalt 60. The extent of DNA damage was measured using alkaline comet assay and the data were analyzed by Student's t-test. The results showed the extent of DNA damage induced by gamma radiation in combination with Iudr was greater in spheroids with 300µm of diameter than spheroids with 100µm of diameter. Investigations revealed that the DNA damage after two volume doubling times of incubation with Iudr is significantly more than one volume doubling time of incubation in two different sizes of spheroids, but the extent of damage in spheroids with 300µm of diameter was larger. However, there is no significant difference between the DNA damage after incubation for two and three volume doubling times. As it can be seen, two-volume-doubling-time incubation of cells is more suitable than one or three volume doubling times to develop radiation sensitivities.