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The effect of irradiation on mitotic and apoptotic frequency in head and neck cancer cell lines, the correlation to p53 mutations and clonogenic survival.

It was our intention to enlighten the controversy between the mainstream of studies and our previous results showing a correlation between the intrinsic radiosensitivity and the p53 allele status of 20 human head and neck squamous cell carcinoma (HNSCC) cell lines. In our study cell lines carrying a wild-type (WT) p53 allele were significantly more radioresistant than cell lines which lacked a WT gene. We observed nine HNSCC cell lines with known intrinsic radiosensitivity and p53 allele status with time-lapse video microscopy after irradiation with 2 and 3 Gy. We studied the mitotic and apoptotic frequencies and scored the apoptoses as to whether they occurred morphologically in mitosis or in interphase. Irradiation with 2 or 3 Gy did not induce apoptosis in the cell lines studied. As expected the mitotic frequency was reduced by the irradiation. This was statistically significant in the cell lines which were radiosensitive when measured with a clonogenic assay. p53 allele status did not have an independent effect on the cell lines, except that the irradiation favoured the apoptosis in mitosis in the cell lines with WT p53 and the apoptosis in the interphase in the cell lines with a mutated or non-functional p53 gene. We conclude that although the apoptosis is not induced by irradiation with 2 Gy or 3 Gy, the p53 suppressor gene seems to influence the process of apoptosis after irradiation in the cell lines studied.