Human DMBT1-derived cell-penetrating peptides for intracellular siRNA delivery

SiRNA is a promising molecule for gene therapy, but its therapeutic administration remains problematic. Among the recently proposed vectors, cell-penetrating peptides show great promise in in vivo trials for siRNA delivery. The human protein DMBT1 is a pattern recognition molecule that interacts with polyanions and recognizes and aggregates bacteria. Taking advantage of these properties, we investigated whether specific synthetic DMBT1-derived peptides could be used to formulate nanoparticles for siRNA administration. Electrophoretic mobility shift assay and UV spectra identified two DMBT1-peptides that could encapsulate the siRNA with a self- and co-assembly mechanism. The complexes were stable for at least 2 hours in the presence of either FBS or RNAse A, with peptide-dependent timespan protection. Ζ potential, circular dichroism, dynamic light scattering and transmission electron microscopy revealed negatively charged nanoparticles with an average diameter of 10 to 800 nm depending on the reaction conditions and a spherical or rice-shaped morphology depending on the peptide and β-helix conformation. We successfully transfected human MCF7 cells with FITC-DMBT1 peptide-Cy3-siRNA complexes. Finally, in MCF7-recombinant cells, DMBT1-peptides encapsulating a siRNA targeting a fluorescent reporter gene showed efficient gene silencing. These results lay the foundations for a new research line to exploit DMBT1-peptide nanocomplexes for the therapeutic siRNA delivery.