Knockdown of a G protein-coupled receptor through efficient peptide-mediated siRNA delivery

In recent years, therapeutic applications of siRNAs have come into the focus of pharmaceutical research owing to their potential to specifically regulate gene expression. However, oligonucleotides have to overcome a series of extracellular and intracellular barriers which is why delivery systems helping to overcome these barriers are desperately needed. A promising approach to transport nucleic acids beyond cellular membranes is the use of cell-penetrating peptides (CPPs), which are able to autonomously cross the plasma membrane. Recently, we synthesized branched derivatives of truncated human calcitonin (hCT) and identified them as efficient vehicles for non-covalent gene delivery. Here we describe two novel branched hCT-derivatives that are optimized for efficient intracellular delivery of siRNA by conjugation with either a fatty acid or an endosomolytic peptide sequence. As target we chose the human NPY Y₁ receptor (NPY1R), which belongs to the family of G protein-coupled receptors and thus constitutes a model for complex therapeutic targets related to various disorders. For instance, knockdown of Y₁ receptor expression offers a potential therapy for osteoporosis. We present a read-out system that allows for the quantitation of the induced knockdown of receptor expression on the protein as well as on the mRNA level. As a result of this study, we could show that the herein presented cell-penetrating peptides effectively transport siRNA into HEK-293 cells without inducing cytotoxicity and that the knockdown rates are comparable to those obtained by lipofection.