Comparative molecular dynamics calculations of duplexation of chemically modified analogs of DNA used for antisense applications.

We have subjected several analogs of DNA that have been widely used as antisense oligonucleotide (ASO) inhibitors of gene expression to comparative molecular dynamics (MD) calculations of their ability to form duplexes with DNA and RNA. The analogs included in this study are the phosphorothioate (PS), peptide nucleic acid (PNA), locked nucleic acid (LNA), morpholino nucleic acid (PMO), the 2'-OMe, 2'-F, 2'-methoxyethyl (2'-MOE) and the constrained cET analogs, as well as the natural phosphodiester (PO) as control, for a total of nine structures, in both XNA-DNA and XNA-RNA duplexes. This is intended as an objective criterion for their relative ability to duplex with an RNA complement and their comparative potential for antisense applications. We have found that the constrained furanose ring analogs show increased stability when considering this study's structural and energetic parameters. The 2'-MOE modification, even though energetically stable, has an elevated dynamic range and breathing properties due to the bulkier moiety in the C2' position of the furanose. The smaller modifications in the C2' position, 2'-F, 2'-OMe and PS also form stable and energetically favored duplexes with both DNA and RNA. The morpholino moiety allows for increased tolerance in accommodating either DNA or RNA and the PNA, with the PNA being the most energetically stable, although with a preference for the B-form DNA. In summary, we can rank the overall preference of hybrid strand formations as PNA > cET/LNA > PS/2'-F/2'-OMe > morpholino > 2'-MOE for the efficacy of duplex formation.