siRNA and RNAi optimization

The discovery and examination of the posttranscriptional gene regulatory mechanism known as RNA interference (RNAi) contributed to the identification of small interfering RNA (siRNA) and the comprehension of its enormous potential for clinical purposes. Theoretically, the ability of specific target gene downregulation makes the RNAi pathway an appealing solution for several diseases. Despite numerous hurdles resulting from the inherent properties of siRNA molecule and proper delivery to the target tissue, more than 50 RNA-based drugs are currently under clinical testing. In this work, we analyze the recent literature in the optimization of siRNA molecules. In detail, we focused on describing the most recent advances of siRNA field aimed at optimize siRNA pharmacokinetic properties. Special attention has been given in describing the impact of RNA modifications in the potential off-target effects (OTEs) such as saturation of the RNAi machinery, passenger strand-mediated silencing, immunostimulation, and miRNA-like OTEs as well as to recent developments on the delivery issue. The novel delivery systems and modified siRNA provide significant steps toward the development of reliable siRNA molecules for therapeutic use. © 2016 Wiley Periodicals, Inc.The work is supported by grants of the European Commission (NMP4-LA-2011-262943, MULTIFUN), the Spanish Ministry of Economy (CTQ2014-52588-R, RTC-2014-2038-1), Generalitat de Catalunya (2014/SGR/624) and the Instituto de Salud Carlos III (CB06_01_0019) with assistance from the European Regional Development Fund.Peer reviewe