Biodegradable nanoparticles with sustained release of functional siRNA in skin.

A key challenge in developing RNAi-based therapeutics is efficient delivery of functional short interfering RNA (siRNA) to target cells. To address this need, we have used a supercritical CO(2) process to incorporate siRNA in biodegradable polymer nanoparticles (NPs) for in vivo sustained release. By this means we have obtained complete encapsulation of the siRNA with minimal initial burst effect from the surface of the NPs. The slow release of a fluorescently labeled siRNA mimic (siGLO Red) was observed for up to 80 days in vivo after intradermal injection into mouse footpads. In vivo gene silencing experiments were also performed, showing reduction of GFP signal in the epidermis of a reporter transgenic mouse model, which demonstrates that the siRNA retained activity following release from the polymer NPs.