Evaluation of anionic polymer-coated siRNA lipoplexes prepared using a modified ethanol injection method.

Cationic liposomes are useful carriers for delivering small interfering RNA (siRNA). In our previous study, a simple and efficient modified ethanol injection (MEI) method was developed for the preparation of cationic siRNA lipoplexes. However, non-specific interactions between cationic lipoplexes and biological components, including erythrocytes, induce aggregation, and thus, siRNA is not delivered to the target site after intravenous injection. In the present study, an anionic polymer coating was applied to cationic lipoplexes prepared using the MEI method, and their gene knockdown effect and biodistribution in mice were evaluated. The gene knockdown effect of cationic lipoplexes was preserved after coating with anionic polymers [hyaluronan (HA), chondroitin sulfate (CS) and polyglutamic acid (PGA)], although anionic polymer-coated lipoplexes showed lower cellular association than cationic lipoplexes. Coating of cationic lipoplexes with high-molecular-weight HA, CS and PGA reduced agglutination with erythrocytes. Following intravenous injection, CS- or PGA-coated lipoplexes exhibited lower pulmonary accumulation than cationic lipoplexes, whereas hepatic accumulation of CS- or PGA-coated lipoplexes increased. Collectively, cationic lipoplexes prepared using the MEI method were successfully coated with anionic polymers. Notably, CS or PGA coating of lipoplexes reduced non-specific interactions with erythrocytes, and CS- or PGA-coated lipoplexes could be potential vectors for in vivo siRNA delivery to the liver.