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Oncology is one field of medicine where NP-mediated drug delivery systems can potentially have a significant impact since issues with solubility and pharmacokinetics have limited the clinical application of many new, potentially effective anticancer drug candidates. There are several classes of promising NP drug delivery systems, including drug nanocrystals, liposomes, micelles, dendrimers, and polymeric NPs (Fig. 171-1).2 Drug nanocrystals are simply pure drugs that have been processed down to nanometer sizes.3 The extremely small particle size increases the surface area of the drug, thereby increasing solubility. In contrast, liposomes are spherical lipid bilayers measuring a few nanometers in diameter.4 When used as a drug delivery vehicle, insoluble drugs can be transported within the hydrophobic environment of the lipid bilayer, whereas soluble drugs are contained within the internal aqueous compartment inside the liposome, thereby altering the pharmacokinetics and biodistribution of the native drug. Like liposomes, micelles are also composed of phospholipids. In aqueous solution, a micelle is formed by spontaneous self-assembly resulting in the exposure of the hydrophilic head regions to the surrounding solvent and aggregation of the hydrophobic tails at the micelle center. The core of the micelle can thereby contain small hydrophobic molecules such as therapeutic drugs, while remaining stable in aqueous solution. Dendrimers are highly branched molecules that can be used to deliver drugs via two different methods. Drugs can either be attached to the outer functional groups of the dendrimer branches, or encapsulated within the dendrimers to form a drug-dendrimer supermolecular assembly. Finally, polymeric NPs, which encapsulate drug within various polymers, tend to be more stable than liposomes and can increase the effective solubility of hydrophobic drugs. In addition, unlike liposomes, several polymeric systems appear to allow programmable, or at least controlled, drug release through the manipulation of the structure and composition of the polymer used to prepare the particles.1,5,6

Figure 171-1

Schematic diagram of different types of nanoparticles used for drug delivery.

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