Advantages of the circular dumbbell decoy in gene therapy and studies of gene regulation

Decoy oligodeoxynucleotides (ODN) that can reduce the trans-activity of transcription factors may be highly useful in gene therapy and the study of transcriptional regulation. Several different types of these double-stranded DNA decoys have been developed, including unmodified oligonucleotide duplexes, alphabeta-anomeric oligonucleotides, and oligonucleotide duplexes with methylphosphonate- and phosphorothioate-modified linkages. The latter ODNs have been particularly extensively studied but suffer from a number of limitations, including their insensitivity to polymerases, their lack of sequence specificity, and their tendency to activate immune responses. To resolve these problems, circular dumbbell (CD) double-stranded ODNs were developed. These CD ODNs are constructed by the circularization of the 3' and 5' ends of the oligonucleotides and enzymatic ligation. They exhibit high resistance to nucleases, are easily taken up by cells, and have a nontoxic unmodified backbone that resembles natural DNA. In this article, we review the method of constructing CD ODNs and their advantages compared to other modified ODNs for use as transcription decoys.