Nanomaterials for Drug Delivery

All drugs face several transport barriers on their tortuous journey from their site of introduction to their molecular site of action. Critical barriers include rapid filtration in the kidney and clearance via the reticulo-endothelial system (RES)—particularly for drugs that spend a lot of time in the bloodstream—as well as transport from the bloodstream to target cells within tissues. At the tissue or cellular target, the drug must cross the plasma membrane, and within the cell, it must escape the harsh acidic environment of endolysosomes, within which biomolecular drugs such as proteins and oligonucleotides may be inactivated or degraded. Other barriers are the nuclear membrane and the multiple drug resistance mechanisms that pathological cells can develop. Recent studies illustrate some particularly promising ways in which nanomaterials as drug or vaccine carriers can assist in navigating these barriers, with a particular focus on administration by injection.