Fig. 4. Detection of DNA strand breaks by comet assay in Namalwa cells, 1 or 7 days after irradiation. After treatment and incubation for the desired time, cells were embedded in agarose and subjected to electrophoresis at pH 12.1. This alkaline electrophoresis allows the detection of single and double DNA strand breaks. The tail moment (% of migrated DNA x tail length) was measured using Scion image software and a comet assay macro. (A) 96% of non-irradiated Namalwa cells had a tail moment of between 2000 and 8000. (B) On day 1 after 10 Gy irradiation, nearly all of the cells had a tail moment greater than 10,000, providing evidence that DNA strand breaks were not repaired within 24 hours. (C) The vast majority of Namalwa polyploid cells (arrows) on day 7 post irradiation displayed tail moments similar to non-irradiated control cells. Overall, 75.2% of non-apoptotic cells on day 7 had tail moment values equal to those observed in controls. (D) Frequency histograms representing the distribution of tail moments in non-irradiated control Namalwa cells and cells on days 1 and 7 after 10 Gy irradiation.

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