Abstract 507: Elevated manganese superoxide dismutase (SOD2) activity as a mechanism for the low dose dadiation- and thiol-induced adaptive responses in human RKO36 colon carcinoma cells and BFS2C mouse fibrosarcoma cells

Abstract

Abstract 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.