137 DNA nanostructure serum stability: greater than the sum of their parts

Abstract

DNA cages hold tremendous potential to encapsulate and selectively release therapeutic drugs, and can provide useful tools to probe the size and shape dependence of nucleic acid delivery (McLaughlin & Sleiman, H. F., 2011). These structures have been shown to site-specifically present ligands, small molecule drugs, or antisense/siRNA motifs, in order to increase their therapeutic efficiency (Li & Fan, C. 2012). One of the major barriers towards their in vivo applications is the susceptibility of their strands towards nuclease degradation. A number of chemical strategies have been used to block nuclease digestion of oligonucleotides and improve potency, such as the use of a phosphorothioate backbone, 2´-O-methyl, locked nucleic acids, and short hybrid gapmers. However, the synthesis of these oligonucleotides is often complicated and expensive, driving the need for simple modifications to enhance serum stability and address in vivo biodistribution. We show here a simple method to significantly enhance the nuclease stability of DNA strands, through introduction of commercially available, single-endmodifications (Conway & Sleiman 2013). We use these oligonucleotides to construct DNA cages in a single step and in quantitative yields. Even in single-stranded form, these cages stabilize their component strands towards nucleases, with mean lifetimes as long as 62 h in 10 % (v/v) fetal bovine serum (FBS). We examine the effect of other DNA-end modifications on nuclease susceptibility. Finally, we show the ligation of these single-stranded cages into topologically interesting catenane ‘necklaces,’ with mean lifetimes in serum of ∼200 h.