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1 November 2004 Delayed Radioprotection by NFκB-Mediated Induction of Sod2 (MnSOD) in SA-NH Tumor Cells after Exposure to Clinically Used Thiol-Containing Drugs
Jeffrey S. Murley, Yasushi Kataoka, Dingcai Cao, Jian Jian Li, Larry W. Oberley, David J. Grdina
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Abstract

Murley, J. S., Kataoka, Y., Cao, D., Li, J. J., Oberley, L. W. and Grdina, D. J. Delayed Radioprotection by NFκB-Mediated Induction of Sod2 (MnSOD) in SA-NH Tumor Cells after Exposure to Clinically Used Thiol-Containing Drugs. Radiat. Res. 162, 536–546 (2004).

The ability of thiol-containing reducing agents to activate transcription factors leading to changes in gene expression and enzyme activities provides an additional mechanism to potentially protect against radiation-induced cell killing. Manganese superoxide dismutase (Sod2) is one such gene whose expression levels have been shown to be elevated after exposure to the thiol compounds WR-1065 and N-acetyl-l-cysteine (NAC), resulting in an increase in radiation resistance. To further characterize this effect, SA-NH sarcoma cells, both wild-type and a clone stably transfected with a plasmid containing an IκBα gene mutated at serines 32 and 36, which prevents the inducible phosphorylation of these residues and the subsequent activation of NFκB (SA-NH mIκBα1), were grown to confluence and then exposed to amifostine's free thiol WR-1065 at a concentration of 4 mM for 30 min. Effects of thiol exposure on NFκB activation in SA-NH mIκBα1 cells were determined by a gel shift assay, and changes in Sod2 protein levels in these cells 24 h after exposure to 40 μM or 4 mM WR-1065 were measured by Western blot analysis and compared with wild-type cells exposed to the NFκB inhibitor BAY 11-7082. Changes in radiation response, measured immediately after thiol exposure or 24 h later, were determined using a colony-forming assay and were correlated with NFκB activation and Sod2 protein levels. The effects of captopril, mesna and NAC, each at a dose of 4 mM, on radiation response were also determined and contrasted with those of WR-1065. Only WR-1065 and captopril protected SA-NH cells when present during irradiation, i.e. 1.57 and 1.31 times increase in survival at 2 Gy, respectively. All four thiols were protective if irradiation with 2 Gy occurred 24 h later; i.e. increases in survival of 1.40, 1.22, 1.35, and 1.25 times were found for WR-1065, captopril, mesna and NAC, respectively. This delayed radioprotective effect correlated with elevated Sod2 protein levels in wild-type SA-NH tumor cells but was not observed in SA-NH mIκBα1 cells, indicating that interference with thiol-induced NFκB activation abrogates this delayed radioprotective effect. Because the delayed radioprotective effect is readily demonstrable at a radiation dose of 2 Gy 24 h after exposure to clinically approved thiol-containing drugs such as amifostine, captopril, mesna and NAC, it suggests a new potential concern regarding the issue of tumor protection and the use of these agents in cancer therapy.

Jeffrey S. Murley, Yasushi Kataoka, Dingcai Cao, Jian Jian Li, Larry W. Oberley, and David J. Grdina "Delayed Radioprotection by NFκB-Mediated Induction of Sod2 (MnSOD) in SA-NH Tumor Cells after Exposure to Clinically Used Thiol-Containing Drugs," Radiation Research 162(5), 536-546, (1 November 2004). https://doi.org/10.1667/RR3256
Received: 21 October 2003; Accepted: 1 July 2004; Published: 1 November 2004
JOURNAL ARTICLE
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