Targeted lipid-based systems for siRNA delivery

Gene silencing agents, like small interfering RNA (siRNA), are powerful tools widely used in therapeutic and fundamental studies. However, major limitations to their in vivo and in vitro application have been recognized. Therefore, efficient delivery vehicles are essential for siRNA application in therapeutics. Lipid-based systems, such as liposomes, have been extensively and successfully used as nucleic acid vectors. In this review the major obstacles to siRNA delivery are discussed, as well as the most recent advances regarding the development of nanocarriers designed for such a purpose. Cationic liposomes and targeted stabilized nucleic acid liposomes are described in detail, as they are considered promising tools to mediate intracellular delivery of gene silencing agents. Additionally, the advantages of cellular targeting and long circulation times are discussed. Moreover, combination of drugs and siRNA in the same delivery system is presented as a promising strategy, allowing different molecular targets to be reached within a specific cell population, with a single therapeutic system.