Selected Strategies for the Delivery of siRNA In Vitro and In Vivo

RNA-based therapeutic strategies are considered as a highly promising alternative to conventional drug development. Among the different classes of oligonucleotide-derived prospective drugs, small interfering RNAs (siRNAs) are of particular interest. However, cellular uptake and subsequent intracellular trafficking to the effector complex (RNA-induced silencing complex; RISC) represent major technical hurdles for the efficacy of these macromolecular drugs. Thus, the development of appropriate delivery systems is an essential requirement to turn these molecules into medicine. In this review, we will focus on two particular auspicious aspects in this context, the phosphorothioate-stimulated uptake of naked siRNA and the use of cell-penetrating peptides as shuttles for a controlled cellular uptake. Moreover, we will present some of the most promising recent approaches for siRNA delivery in vivo, which may help to pave the road to drugs of the future.