Objectives: Vast number of studies show the relationship between aneuploidy and cancer. Ionizing radiation in addition to induce all kinds of damages to the cells and structure of chromosomes, is also able to induce aneuploidy through direct damages to chromosome division apparatus. Also irradiation of the cells induces mutations in several genes which might be involved in cell division fidelity and play a role in reversing the effect of aneugens. Therefore, irradiation of cells and tissues might produce sensitivity to agents with aneugenic capability in irradiated cells. Methods: To investigate the persistent genomic effect of ionizing irradiation on chromosomal instability, L929 cells were gamma irradiated with the dose of 2 Gy. Cells were left to recover from the harmful effect of irradiation. They were treated with low dose of vinblastine (0.5 ng.ml-1) 72h post-gamma irradiation. Finally, the induced chromosomal abnormalities were scored using micronucleus assay in cytokinesis-blocked binucleated cells (MnBi). Results: Irradiation-recovered L929 cells treated with vinblastine showed a statistically higher frequency of MnBi compared to non-irradiated and vinblastine treated cells. Conclusion: The results indicate that gamma irradiation, in addition to direct induction of chromosomal damages, is also able to create persisting genomic sensitivity in the cells to chromosomal instability, which is detectable when exposed to the second stimulus.

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