On the cellular processing of non-viral nanomedicines for nucleic acid delivery: mechanisms and methods

In the field of nanomedicine, ample attention has been paid to the development of nanocarriers for the intracellular delivery of therapeutic cargo, such as nucleic acids for gene therapy. The efficiency with which these non-viral carriers deliver their payload at the required intracellular site of action remains low. Despite extensive research on cellular attachment, endocytosis and intracellular trafficking of nanocarriers, clear-cut rules for the design of effective nanocarriers to improve nucleic acid transfer are still lacking. This is mainly caused by the cell type-dependence of this highly dynamic cellular processing, and to the lack of reliable methods to study these events. For these reasons there is a strong demand for the development and standardization of such methods in order to better understand the intracellular dynamics of nanomedicine processing and validate cellular and intracellular targeting strategies. This review aims at providing an overview of the different processes that are currently known to be involved in the cellular processing of nanomedicines, with a focus on cellular internalization mechanisms, as this has received a great deal of attention in the last couple of years. Furthermore, the intracellular hurdles that need to be overcome to allow efficient NA transfer will be critically discussed. In addition, an overview will be given of various methodologies that have been applied to unravel these cellular processing mechanisms, with a discussion on their strengths and weaknesses.