Vol. 296, Issue 3, 898-904, March 2001

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

Richard S. Geary, Oleg Khatsenko, Keith Bunker, Rosanne Crooke, Max Moore, Todd Burckin, LoAnne Truong, Henri Sasmor and Arthur A. Levin

Isis Pharmaceuticals, Inc., Carlsbad, California

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 2'-O-(2-methoxyethyl) (2'-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 2'-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 2'-O-MOE ribose-modified (partial) compound remained 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 measurable metabolites observed within 8 h of administration. The rank order of bioavailability was ISIS 11159 (full PS, full MOE) < ISIS 2302 (PS ODN) < ISIS 16952 (full PO, full MOE) < 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, 2.1, and 5.5%, respectively. The optimal oligonucleotide chemistry for improved permeability and resulting bioavailability was the partially modified 3' hemimer 2'-O-MOE phosphorothioate oligonucleotide (ISIS 14725). Improved presystemic stability coupled with improved permeability were likely responsible for the remarkable improvement in the oral bioavailability of this compound.