Nanoparticles in modern medicine: state of the art and future challenges

Abstract

Nanoparticles are materials with overall dimensions in the nanoscale, ie, under 100 nm. In recent years, these materials have emerged as important players in modem medicine, with clinical applications ranging from contrast agents in imaging to carriers for drug and gene delivery into tumors. Indeed, there are some instances where nanoparticles enable analyses and therapies that simply cannot be performed otherwise. However, nanoparticles also bring with them unique environmental and societal challenges, particularly in regard to toxicity. This review aims to highlight the major contributions of nanoparticles to modem medicine and also discuss environmental and societal aspects of their use.

Figure 1

Quantum dots (QDs) used in tumor imaging. (A) Surface modification of the CdSe/ZnS QD with a capping ligand TOPO which keeps QDs from aggregating in solution; this assembly is enclosed by an amphiphilic polymer whose hydrophobic segments bind to TOPO and whose hydrophilic carboxylic acid groups can bind to affinity ligands (such as a tumor-specific antibody) or PEG. (B) Fluorescence image of a live mouse showing targeted delivery of QDs to a tumor. Adapted from Gao et al (2004) with permission from Macmillian Publishers Ltd: Nature Biotechnology. Copyright © 2004.

Figure 2

Visualization of lymph node metastases in prostate cancer using iron oxide nanoparticles as MRI contrast agents. (A) A conventional MRI image can only vaguely indicate the presence of metastases. (B) Two metastases, indicated by arrows, can be clearly seen when the iron oxide nanoparticles are used. Scale bars = 4 mm (added based on the authors’ description of 2 mm metastases). Adapted from Harisinghani et al (2003) with permission. Copyright © 2003. Massachusetts Medical Society. All rights reserved.

Figure 3

Schematic representations of (A) a polymeric matrix and (B) a liposome, both of which can enclose a drug. Reprinted with permission from Brigger I, Dubernet C, Couvreur P. 2002. Nanoparticles in cancer therapy and diagnosis. Adv Drug Deliv Rev, 54:631–51 (Elsevier) and John AE, Lukacs NW, Berlin AA, et al 2003. Discovery of a potent nanoparticle P-selectin antagonist with anti-inflammatory effects in allergic airway disease. FASEB J, 17:2296–8.

Figure 4

Liposome-based drug delivery to the nervous system. Gold-labeled liposomes (colored black in image) among astrocytes and microglia in rat spinal cord sections indicating penetration of the blood–brain barrier (astrocytes and microglia stained red); scale bar = 100 μm. Adapted from Schmidt et al (2003) by permission of Oxford University Press.

Figure 5

Selective binding of liposomes presenting fucose and sulfate ester groups to activated endothelial cells in mouse lungs following allergen challenge. (A) Negative control (liposomes without fucose and sulfate ester groups). (B) Liposomes with fucose and sulfate ester groups. Scale bars in both images = 30 μm. Adapted with permission from John et al (2003). Abbreviations: alv, alveolar wall; bv, blood vessel; e, endothelium; PLNP, liposomes.