Delayed radioprotection by NFkappaB-mediated induction of Sod2 (MnSOD) in SA-NH tumor cells after exposure to clinically used thiol-containing drugs.
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 IkappaBalpha gene mutated at serines 32 and 36, which prevents the inducible phosphorylation of these residues and the subsequent activation of NFkappaB (SA-NH+mIkappaBalpha1), 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 NFKB activation in SA-NH+mIkappaBalpha1 cells were determined by a gel shift assay, and changes in Sod2 protein levels in these cells 24 h after exposure to 40 microM or 4 mM WR-1065 were measured by Western blot analysis and compared with wild-type cells exposed to the NFkappaB 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 NFKB 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+mIkappaBalpha1 cells, indicating that interference with thiol-induced NFKB 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.
Murley
Jeffrey S
JS
Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois 60637, USA. jmurley@rover.uchicago.edu
Kataoka
Yasushi
Y
Cao
Dingcai
D
Li
Jian Jian
JJ
Oberley
Larry W
LW
Grdina
David J
DJ
D000111:Acetylcysteine / Q000494:pharmacology; D004999:Amifostine / Q000494:pharmacology; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002216:Captopril / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D020672:I-kappa B Proteins / Q000378:metabolism; D008624:Mercaptoethylamines / Q000494:pharmacology; D015080:Mesna / Q000494:pharmacology; D051379:Mice; D009154:Mutation; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D020011:Protective Agents / Q000494:pharmacology; D011837:Radiation-Protective Agents / Q000494:pharmacology; D012694:Serine / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D000099156:Superoxide Dismutase 2
D000111:Acetylcysteine; D004999:Amifostine; D000806:Angiotensin-Converting Enzyme Inhibitors; D002216:Captopril; D020672:I-kappa B Proteins; D008624:Mercaptoethylamines; D015080:Mesna; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B; D020011:Protective Agents; D011837:Radiation-Protective Agents; D012694:Serine; D013438:Sulfhydryl Compounds; D013482:Superoxide Dismutase; D000099156:Superoxide Dismutase 2; C000606205:Nfkbia protein, mouse; C020174:N-(2-mercaptoethyl)-1,3-diaminopropane