Absolute Bioavailability of 2Ј-O-(2-Methoxyethyl)-Modified Antisense Oligonucleotides following Intraduodenal Instillation in Rats

ABSTRACT Three modified 20-mer antisense oligonucleotides targeted to human intercellular adhesion molecule-1 mRNA were characterized for their presystemic stability and oral bioavailability compared with a first-generation phosphorothioate oligodeoxynucleotide (PS ODN), ISIS 2302. The three modified oligonucleotides contained 2Ј-O-(2-methoxyethyl) (2Ј-O-MOE) ribose sugar modifications on a portion, or on all of the nucleotides in the antisense sequence. In vitro metabolism studies conducted in various gastrointestinal and digestive tissue preparations indicated substantial improvement in stability of 2Ј-O-MOE-modified oligonucleotides. In addition, in vivo presystemic stability of these oligonucleotides was monitored in rats following intraduodenal administration. By 8 h after administration, only chain-shortened metabolites of the PS ODN were recovered in the gastrointestinal contents. In contrast, approximately 50% of the 2Ј-O-MOE ribose-modified (partial) compound remained intact (20-mer) by 8 h following administration. Both of the fully modified compounds (2Ј-O-MOE PO and PS) were completely stable with no measurable metabolites observed within 8 h of administration. The rank order of bioavailability was ISIS 11159 (full PS, full MOE) Ͻ ISIS 2302 (PS ODN) Ͻ ISIS 16952 (full PO, full MOE) Ͻ ISIS 14725 (full PS, partial MOE); the absolute plasma concentration bioavailability was measured in reference to intravenous dosing in the rat and was estimated at 0.3, 1.2,