BACKGROUND: Response of Fanconi anemia (FA) cells to X-irradiation is controversial. Present study was undertaken to compare short-term and long-term responses of irradiated FA fibroblasts. MATERIAL/METHODS: Skin fibroblasts derived from FA patients were studied using the Comet assay, clonogenic survival, apoptosis and cell cycle checkpoint arrest. Fibroblasts derived from ataxia telangiectasia (AT) patients served as positive controls. RESULTS: The alkaline Comet assay showed that the initial DNA fragmentation in irradiated FA fibroblasts is similar to or even higher than in AT cells. Moreover, the DNA rejoining occurred slowly in FA fibroblasts than in AT cells. In contrast, the colony assay revealed that the survival of X-ray-irradiated FA fibroblasts is higher than that of irradiated AT cells. Unlike FA fibroblasts, which were arrested in the G1 phase of the cell cycle by X-irradiation, AT cells displayed a pronounced G2/M arrest after X-ray exposure. CONCLUSIONS: FA cells are shown to be radioresistant by clonogenic survival but display high tail moments in the Comet assay suggesting high initial DNA damage and reduced repair capacity. It is demonstrated that the colony assay can not explain the high radiosensitivity of FA patients. The Comet assay can help to obtain additional information on initial DNA damage and repair capacity.

Keywords: Ataxia Telangiectasia - metabolism, Ataxia Telangiectasia - pathology, Cell Survival - physiology, Fanconi Anemia - pathology