Radiolytic cyclization of stem-and-loop structured oligodeoxynucleotide with neighboring arrangement of α,ω-bis-disulfides

Upon X-ray irradiation of hypoxic aqueous solution, modified oligodeoxynucleotides (ODNs) bearing a pair of disulfides at both ends of the strand that forms a stem-and-loop structure with a neighboring arrangement of α,ω-bis-disulfides underwent efficient cyclization via an intramolecular exchange reaction at the disulfide moieties with a multiple turnover process. Mechanistic studies revealed that hydrogen atoms generated in the radiolysis of water are key active species initiating a chain reaction to produce cyclic ODN disulfides, in which addition of hydrogen atom results in dissociation of the original disulfide bond to generate a thiyl radical intermediate as the chain carrier for the succeeding disulfide exchange into cyclization. The properties were also assessed for the resultant cyclic ODN disulfide that has several favorable features for use in the transcriptional decoy strategy. The cyclic ODN disulfides produced by the present radiolytic method showed high thermal stability, resistance to nuclease, and high binding activity to a representative transcriptional factor of nuclear factor κB.