Prolonged gene silencing by combining siRNA nanogels and photochemical internalization.

Small interfering RNAs (siRNAs) show potential for the treatment of a wide variety of pathologies with a known genetic origin through sequence-specific gene silencing. However, siRNAs do not have favorable drug-like properties and need to be packaged into nanoscopic carriers that are designed to guide the siRNA to the cytoplasm of the target cell. In this report biodegradable cationic dextran nanogels are used to deliver siRNA across the intracellular barriers. For the majority of non-viral siRNA carriers studied so far, endosomal confinement is identified as the most prominent hurdle, limiting the full gene silencing potential. Thus, there is a major interest in methods that are able to enhance endosomal escape of siRNA to improve its intracellular bioavailability. Photochemical internalization (PCI) is a method that employs amphiphilic photosensitizers to destabilize endosomal vesicles. We show that applying PCI at a later time-point post-transfection significantly prolonged the knockdown of the target protein only in case the siRNA was carried by nanogels and not when a liposomal carrier was used. Combining siRNA nanogels and PCI creates new possibilities to prolong gene silencing by using intracellular vesicles as depots for siRNA and applying PCI at the time when maintaining the RNAi effect becomes critical.