Influence of DNMT inhibitors on radiation-induced γH2AX foci. A549 and U373MG cells growing in chamber slides were exposed to DNMT inhibitors for 18 hours, irradiated, and fixed at specific times for immunocytochemical analyses of nuclear γH2AX foci. Open columns, data from cells receiving radiation alone; grey columns, data from cells that were exposed to psammaplin A and radiation; filled columns, data from cells that were exposed to 5-aza-2'-deoxycytidine and radiation; hatched columns, data from cells that were exposed to zebularine and radiation. Cells with more than five foci per nucleus were classified as positive for radiation-induced γH2AX. Foci were evaluated in 50 nuclei. Bars, SE. *p < 0.01 as determined by a logistic regression compared with radiation alone (6 Gy) group.