How to make siRNA lipoplexes efficient? Add a DNA cargo

Background: We recently reported an efficient formulation of siRNA targeting TNF-alpha, that was able to restore immunological balance in a mouse arthritis model following intravenous injection. Method: Since this efficient formulation included the pre association of siRNA with a DNA cargo, we decided to extensively characterise siRNA lipoplexes with or without DNA cargo, in order to better understand the DNA cargo enhancing effect. Results: We showed that addition of DNA cargo to siRNA lipoplexes led to specific gene extinction in vitro, using reduced siRNA concentration. This procedure is also applicable to other lipid vectors, like Lipofectamine or DMRIE-C. No structural modification could be observed in siRNA lipoplexes upon addition of DNA cargo using dynamic light scattering or transmission electronic microscopy. Nevertheless, we observed some slight differences, in the amount of lipid required to obtain neutrality of the complex and in stability of the complex towards incubation with heparan sulfate. Conclusions: These results suggest that the addition of DNA cargo to siRNA complexes is an easy procedure that leads to more efficient complexes to transfer siRNA at low concentration and in the presence of serum. (C) 2009 Elsevier B.V. All rights reserved.