Absorption of Antisense Oligonucleotides in Rat Intestine: Effect of Chemistry and Length

An in situ single-pass perfusion model was used to assess the effect of chemical modification and length on permeability and absorption of various oligonucleotides in rat intestine. Phosphorothioate oligodeoxynucleotides (PS-ODN) were compared with oligoribonucleotides with 2‵-methoxyethyl (MOE) or 2‵-0-methyl (OMe) modifications. A 25-mer PS-OMe-modified oligonucleotide showed relatively poor permeability in this model, as did unmodified 20-mer PS-ODN (permeability coefficient [Peff] = 2-8 X 10-6cm/sec). Modifying some or all of the oligonucleotides with 2‵-MOE groups on deoxyribose and 5‵-methylation of the cytosines substantially increased intestinal permeability of oligonucleotides. Both partially and fully modified PS-MOE oligonucleotides showed a 2–4-fold increase in permeability as compared with unmodified PS-ODN. The presence of a phosphodiester backbone in MOE-modified compounds led to further increases in intestinal permeability. PS-MOE composed of 6,8,10,12,14,16,18,20, and 22 nucleotides were also examined. It was found that the permeability of these oligonucleotides increased linearly with decreasing length.