Targeted Delivery of siRNA to Tumor Cells with Designed Ankyrin Repeat Protein Nanocomplexes

Specific delivery to tumors and efficient cellular uptake of nucleic acids are major challenges for gene-targeted cancer therapies. Tumor-targeted delivery using antibody fragments or immunoliposomes have already been demonstrated to enhance cellular uptake of nucleic acids by receptor-mediated endocytosis. Here we report the first use of an epithelial cell adhesion molecule (EpCAM)-specific designed ankyrin repeat protein (DARPin) as a carrier for siRNA. Designed ankyrin repeat proteins are a novel class of non-immunoglobulin binding proteins relying on the modularity of ankyrins. Their short length, high stability, and the lack of intramolecular cysteines facilitate proper folding, result in high-yield expression in E. coli, and allow engineering procedures usually not well tolerated by antibodies. A DARPin binding to EpCAM was derived from a designed protein library using ribosome display.