Intracellular Drug Delivery: Mechanisms for Cell Entry

Over the last half century, the delivery of pharmacologically active substances, such as synthetic drugs, natural compounds, gene material and many other pharmaceutical products, has been widely studied. Understanding the interactions of drug carriers with cells and how these interactions influence the cellular uptake is of paramount importance, since targets for many therapeutic agents against several disorders are localized in the subcellular compartments. Besides, the route of drug carrier entry (direct or via endocytosis) often defines the efficiency, kinetics and final destination of the drug itself. Although classical endocytic pathways such as phagocytosis, macropinocytosis, clathrin-mediated and caveola-dependent pathways are well characterized, their control for pharmaceutical drug delivery applications is still a challenging issue. Also, better knowledge of non-classical endocytic pathways may help optimize targeted drug delivery systems for intracellular delivery. Therefore, this review focuses on mechanisms of intracellular delivery, including direct internalization and endocytosis, as well as factors such as targeting moiety, target receptor, and size, shape, and surface properties of the drug carrier that can influence uptake process. Keywords: Drug delivery systems, intracellular drug delivery, endocytic mechanisms, active targeting, receptor-mediated endocytosis, internalization.