Cytogenetic Damages from Iododeoxyuridine -induced Radiosensitivity with and without Methoxyamine in Human Glioblastoma Spheroids

Received: 26/Sep/2007, Accepted: 13/Feb/2008 Objective: Iododeoxyuridine-induced Radiosensitivityi (IUdR) is a halogenated thymidine analogue recognized to be effective in vitro and in vivo radiosensitizer in human cancers. It is reported that Methoxyamine (MX) potentiates DNA damages in cancer cells with blocking the repair pathway of IUdR damages. But studies, entirely, are restricted on monolayer culture cells from human colon cancer cells. Spheroids are 3D form of cells that aggregate and grow together which resemble in vivo tumor models in several aspects and the the results of such studies can be extended to tumor in vivo. The aim of the current study was to evaluate DNA damages from IUdR and gamma rays with and without Methoxyamine in human Glioblastoma spheroids. Materials and Methods: The DNA induced damages in U87MG cell line were compared using alkaline comet assay method. Experiments were performed with two different sizes of spheroids (100μm and 300μm). Results: Evaluation of the effects of IUdR with and without MX pretreatment on spheroids following ionizing radiation showed that MX increased the cell damages of IUdR with and without irradiation in both diameters spheroids. The damages were further increased in 100μm compared with 300μm diameter. Conclusion: Comparisons of tail moments in spheroids with 100 and 300μm diameter showed that cell damages in larger spheroids, 300μm, are lesser than smaller one, 100μm. This could be due to existence of G0 cells and cells with longer cycle which IUdR was less incorporated into them. Thus, decrease in IUdR radiosensitization and base wxcision repair (BER), results in reduction of MX activities. Using agents for Inhibiting the activities of proteins which are responsible for carrying the cells to G0 may be beneficial in solving such problems.