Nanoparticles, like this liposome, may be the future of drug delivery. Nanotechnology is the study and manipulation of matter at sizes between 1 and 100 nanometers. Nanomedicine is a burgeoning branch of nanotechnology that focuses on applying the principles of nanotechnology to advancing medicine and health care. Much of the work in nanomedicine has focused on how drug delivery can be enhanced using nanoparticles.

One area that has been the focus of nanomedicine is oncology. Chemotherapy agents used for cancer treatment are capable of destroying cancer cells because they disrupt various processes in the cell, such as cell growth and proliferation. The processes disrupted by chemotherapeutic agents are not unique to diseased cancer cells, however. Normal healthy cells also grow, proliferate and carry out similar functions. Consequently, chemotherapy agents have damaging effects on normal cells, resulting in myriad side effects for patients. Given that nanotechnology allows for more specific mechanisms of drug delivery, recent research has focused on how nanotechnology could enhance the delivery of anti-cancer drugs. One key property of nanoparticles is that they are better retained in cancer tissue. Cancer cells send signals to surrounding tissues and promote the growth of blood vessels, which help nourish them. These blood vessels nourishing cancer cells are more leaky and disorganized in their architecture, making them less capable of retaining traditional uncoated drugs. It has been shown that nanoparticles, because of they are larger than uncoated drugs, can permeate through the lining of these tumor blood vessels and are retained in the interstitial tissue around the cancer cells for longer periods of time. Furthermore, because they are larger, they do not permeate the blood vessels lining healthy tissues, rendering them more selective to cancer tissues. This phenomenon is called the enhanced permeability and retention effect (EPR), which makes nanoparticles an appealing option for cancer treatment.

There are a variety of nanoparticles that have been used for drug delivery to cancer cells. Among these, liposomes and polymeric drug formulations are two examples. Liposomes are small spherical particles that have a membrane made up of a phospholipid bilayer similar to the cell membrane. Cancer drugs can be placed within the liposome and delivered to cancer cells. The sizes of liposomes vary and can be within the range of nanoparticles, in which case they are referred to as nanosomes. One of the advantages of nanosomes is their lipid solubility and their ability to permeate non-water soluble barriers. This is highly advantageous because they serve as vectors that allow water-soluble cancer drugs to permeate through non-water soluble membranes and reach cancer cells. Polymeric drug formulations have also been used to create nanomer-sized chemotherapeutic drug preparations. These polymers have several advantages including their increased solubility, their prolonged retention in cancer tissue, and their selectivity in targeting cancer cells. It has been shown that cancer cells are less likely to become resistant to polymeric formulations of chemotherapy agents than their traditional non-polymeric counterparts.

Sandia National Lab fellow Carlee Ashley prepares a nanoparticle sample as University of New Mexico professor Jeff Brinker watches. Photo: Randy Montoya Another area where the applications of nanotechnology have contributed to medicine is in the development of drugs that traverse the blood-brain barrier. The blood-brain barrier is comprised of a tightly arranged group of endothelial cells (cells that line the wall of blood vessels), which has evolved to protect the brain from exposure to harmful molecules. The blood-brain barrier also makes it more difficult to deliver drug molecules to the central nervous system when treating neurological disorders that affect the brain and spinal cord. Nanoparticles can serve as a vehicle through which therapeutic molecules can be delivered to the brain. Surfactants, molecules that can alter the surface tension of liquids, are used to coat nanoparticles and enhance penetration of the blood-brain barrier. Lipid-based nanoparticles have also been used to deliver drugs to the central nervous system. In fact, recently studies have shown enhanced permeability of lipid-based nanoparticles carrying drugs against HIV to the brain. These findings may have broad implications in the treatment of the neurological manifestations of HIV/AIDS.

Nanotechnology is a burgeoning field of medicine that holds a great deal of promise for enhancing the delivery of drug molecules to target tissues in a selective fashion. Plenty of active research is ongoing in this area. In addition to actually delivering drugs, another interesting application of nanotechnology under investigation is the use of nanoparticles to couple the delivery of drugs with fluorescent dyes that would enable clinicians to visualize where administered therapies are exerting their effects at a molecular level. These investigations and other ongoing research show once again the importance of the interdisciplinary application of various scientific disciplines such as chemistry, pharmacology and material science to solving complex problems.