Absolute bioavailability of 2 '-O-(2-methoxyethyl)-modified antisense oligonucleotides following intraduodenal instillation in rats

Three modified 20-mer antisense oligonucleotides targeted to human intercel lular adhesion molecule-1 mRNA were characterized for their presystemic sta bility and oral bioavailability compared with a first-generation phosphorot hioate oligodeoxynucleotide (PS ODN), ISIS 2302. The three modified oligonu cleotides contained 2'-O-(2-methoxyethyl) (2'-O-MOE) ribose sugar modificat ions on a portion, or on all of the nucleotides in the antisense sequence. In vitro metabolism studies conducted in various gastrointestinal and diges tive tissue preparations indicated substantial improvement in stability of 2'-O-MOE-modified oligonucleotides. In addition, in vivo presystemic stabil ity of these oligonucleotides was monitored in rats following intraduodenal administration. By 8 h after administration, only chain-shortened metaboli tes of the PS ODN were recovered in the gastrointestinal contents. In contr ast, approximately 50% of the 2'-O-MOE ribose-modified (partial) compound r emained intact (20-mer) by 8 h following administration. Both of the fully modified compounds (2'-O-MOE PO and PS) were completely stable with no meas urable metabolites observed within 8 h of administration. The rank order of bioavailability was ISIS 11159 (full PS, full MOE), ISIS 2302 (PS ODN), IS IS 16952 (full PO, full MOE), ISIS 14725 (full PS, partial MOE); the absolu te plasma concentration bioavailability was measured in reference to intrav enous dosing in the rat and was estimated at 0.3, 1.2, 2.1, and 5.5%, respe ctively. The optimal oligonucleotide chemistry for improved permeability an d resulting bioavailability was the partially modified 3' hemimer 2'-O-MOE phosphorothioate oligonucleotide (ISIS 14725). Improved presystemic stabili ty coupled with improved permeability were likely responsible for the remar kable improvement in the oral bioavailability of this compound.