Insight into the Mechanism of Carrier-Mediated Delivery of siRNA in the Cell Membrane Using MD Simulation.

The effective translocation of small interfering RNA (siRNA) across cell membranes has become one of the main challenges in gene silencing therapy. In this study, we have carried out molecular dynamics simulations to investigate a systematic procedure with different carriers that could be convenient for efficient siRNA delivery into the cell. Starting with poly-amido-amine (PAMAM) dendrimers and cholesterol molecules as carriers, we have found cholesterol as the most efficient carrier for siRNA when it is covalently attached with the siRNA terminal group. Our simulations show that binding of this complex in the lipid membrane alters the structure and dynamics of the nearby lipids to initiate the translocation process. Potential of mean force (PMF) was computed for siRNA with the carriers along the bilayer normal to understand the spontaneity of the process. Though all the PMF profiles show repulsive interaction inside the bilayer, the siRNA with cholesterol shows a comparative attractive interaction (∼27 kcal/mol) with respect to the siRNA-PAMAM complex. Altogether, our results demonstrate the binding interaction of the siRNA-carrier complex in the lipid membrane and propose a theoretical model for the efficient carrier by comparative study of the binding. The probable mechanism of the translocation process is also provided by the alteration of the lipid structure and dynamics for specifically siRNA-cholesterol binding.