Barriers to SIRNA Transfection through a Phospholipid Bilayer

Abstract

Small interfering RNA (siRNA) molecules play a pivotal role in silencing gene expression via the RNA interference (RNAi) mechanism. SiRNA offers considerable promise for gene therapy, and substantial effort has gone into developing siRNA as a therapeutic technology. A key limitation to the widespread implementation of siRNA techniques is the difficulty of delivering siRNA-based drugs to cells. We have examined structural and mechanical barriers to siRNA passage across a phospholipid bilayer using all-atom molecular dynamics (MD) simulations. We find that the electrostatic interaction between the anionic siRNA and zwitterionic head groups of phospholipid molecules induces a liquid crystalline-to-gel phase transformation. The gel phase consists of a major region of interdigitated lipid molecules and a patch of noninterdigitated lipids. Large compressive lateral stresses in the hydrocarbon chains of lipid molecules present a considerable barrier to siRNA passage across the bilayer. Steered MD simulations reveal that the siRNA transfection through the bilayer gel phase requires a force of ∼ 2 nN. We will discuss the role of multivalent cations in lowering transfection barriers.