Evaluation of Nitrone Spin-Trapping Agents as Radioprotectors

The focus of this investigation was to determine whether the nitrone spin-trapping compounds α-phenyl-N-tert-butylnitrone (PBN), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) are radioprotectors. Two methods were used to assess for radioprotection: measurement of oxidative damage to DNA bases and mammalian cell survival assays. Oxidative damage to DNA was quantified by measuring the relative amounts of 8-hydroxy-2′-deoxyguanosine (8-OH-dG) produced by the reaction of hydroxyl radicals (${\rm OH}^{\bullet}$) with 2-deoxyguanosine (dG) after irradiation. PBN, DMPO and POBN, when dissolved in aqueous solutions of either dG or naked salmon sperm DNA, reduced the formation of 8-OH-dG by¹³⁷ Cs γ irradiation significantly. The spin-trapping agents, especially PBN at lower concentrations, were more effective in preventing radiation-induced formation of 8-OH-dG in naked DNA than in free dG. These data suggest that PBN, DMPO and POBN act as free radical scavengers which may associate with DNA and afford protection against γ rays. However, no enhancement of survival was observed when Chinese hamster ovary (CHO) cells were exposed to high non-toxic concentrations of PBN or POBN prior to and during irradiation with⁶⁰ Co γ rays and scored for clonogenic survival. DMPO provided only minimal protection from radiation-induced cell killing.