Improvement of in vivo stability of phosphodiester oligonucleotide using anionic liposomes in mice

Antisense phosphodiester oligonucleotides (ODN) are unstable in biological fluids due to nuclease-mediated degradation and therefore cannot be sued in most antisense therapeutic applications. We describe here in vitro and in vivo stabilization of a 15 mer phosphodiester sequence using anionic liposo mes. Two formulations have been studied: DOPC/OA/CHOL and DOPE/OA/CHOL (pH- sensitive liposomes). Our in vitro findings reveal the same stabilization e ffect in mouse plasma for both anionic liposomes. In vivo investigation sho wed a great protective effect for both formulations after intravenous admin istration to mice. By contrast with in vitro results, a higher protection o f ODN was observed with DOPC/OA/CHOL liposomes compared to the DOPE/OA/CHOL formulation. The latter was degraded in blood (75% of the injected dose at 5 min) probably due to interactions with blood components, and the remaini ng (25% at 5 min) was distributed mostly to the liver and spleen. DOPC lipo somes were remarkably stable in blood and were distributed more slowly to a ll studied organs (liver, spleen, kidneys and lungs). Intact ODN was still observed in some organs (liver, spleen, lungs), but not in blood, 24 hours after DOPC liposome administration. These results suggest that this antisen se strategy using carrier systems may be applicable to the treatment of dis eases involving the reticuloendothelial system. (C) 2000 Elsevier Science I nc. All rights reserved.