Exposure of cells to low non-lethal doses of ionizing radiation (≤ 10 cGy) or WR1065, the active free thiol form of amifostine, can induce pro-survival pathways that result in protection against the damaging effects of a 2 Gy dose of ionizing radiation. One such signaling pathway involves the elevation of active manganese superoxide dismutase (SOD2). SOD2 is a mitochondrial matrix protein that serves as the primary mitochondrial defense against superoxide formation. Its primary function is to facilitate the dismutation of two molecules of superoxide anion (O2) produced by normal respiratory processes or following exposure to ionizing radiation into water and hydrogen peroxide. To characterize the role of SOD2 in the radiation- and thiol-induced adaptive responses, RKO36 human colon carcinoma cells and BFS2C mouse fibrosarcoma cells were exposed to 10 cGy x-rays and 40 μM or 4 mM WR1065 and SOD2 activity measured 24 h later. Significant increases in SOD2 activity in RKO36 cells (3.7-fold, P < 0.001) and BFS2C cells (3.0-fold, P = 0.005) were observed 24 h after exposure to 10 cGy. SOD2 activity was also observed to be significantly elevated in RKO36 cells (3.5-fold, P = 0.014 and 3.4-fold, P = 0.017) and BFS2C cells (3.7-fold, P = 0.007 and 2.5 fold, P = 0.021) 24 h after treatment with 40 μM or 4 mM WR1065, respectively. The protective effect of the low dose radiation- and thiol-induced elevation in active SOD2 was examined using the endpoint of micronuclei formation as a measure of chromosomal damage. Exposure of RKO36 and BFS2C cells to 2 Gy resulted in a significant increase in the mean number of micronuclei observed relative to unirradiated control cells (8.8 versus 2.2, P < 0.001; 5.4 versus 2.1, P < 0.001, respectively). The frequency of micronuclei formation was significantly reduced in both RKO36 cells (P = 0.003) and BFS2C cells (P = 0.011) exposed to 10 cGy 24 h prior to the 2 Gy dose. A significant reduction in micronuclei formation was also observed in RKO36 and BFS2C cells treated with 40 μM or 4 mM WR1065 30 min or 24 h prior to irradiation with 2 Gy. Treatment of both cell lines with SOD2 siRNA reduced SOD2 activity relative to mock-transfected control cells which resulted in the abrogation of both the radiation- and thiol-induced protective effect. This work was supported by NIH/NCI grant R01 CA132998 and DOE grant DE- PS02-08ER08-21 (D.J.G.).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 507.