Drug delivery to intracellular compartment is gaining importance as a field of investigation. Many important drugs for various diseases have intracellular organelle as site of action. The anticancer drug doxorubicin acts in the nucleus. Hence it is necessary to design delivery strategies such that the drug will reach its targeted site of action, which often times is located inside the cell. However, there are many challenges to design therapeutic strategies for successful intracellular delivery. Factors such as lysosomal degradation and size restriction to organelle entry are some of the issues that need to be addressed. Design of nanostructures and targeting ligands are few of the effective strategies adopted to meet those challenges. However, to design a better therapeutic platform it is necessary to monitor the pathway undertaken by these nanostructures once they cross the plasma membrane. The technology that allows such monitoring has been discussed in this review. It is also necessary to know the endosomal pathway undertaken by these nanostructures after they enter the intracellular environment. These pathways and their role in drug delivery platforms such as nanoparticles and other nanostructures have been explored in this review.
