Where in the cell is our cargo? Current methods to study intracellular cytosolic localization

Abstract

The internalization and delivery of active substances into cells is a field of growing interest for chemical biology and therapeutics. As we move from small‐molecule based drugs towards bigger cargos, such as antibodies, enzymes, nucleases or nucleic acids, the development of efficient delivery systems becomes critical for their practical application. Different strategies and synthetic carriers have been developed including cationic lipids, gold nanoparticles, polymers, cell‐penetrating peptides, protein surface modification, etc. However, all these methodologies still present limitations related to the precise targeting of the different intracellular compartments and, in particular, the difficult access to the cellular cytosol. Additionally, the precise quantification of the cellular uptake of a molecule is not enough to demonstrate delivery and/or functional activity. Therefore, methods to determine the cellular distribution of cargos and carriers are of critical importance to identify the barriers that are blocking the activity. In this mini‐review, we survey the different techniques that can be currently used to track and monitor the subcellular localization of the synthetic molecules that we deliver inside cells