Nanoparticles Identify, Kill Cancer Cells

The study, published in the April 13, 2005, issue of the journal Nano Letters, reported that current molecular imaging approaches only identify malignancies but do not provide a treatment method. "You can look for a molecular marker that may indicate a significant clinical problem, but you can't do anything about it,” said Rebekah Drezek, Ph.D., a professor of bioengineering at Rice University (Houston, TX, USA). "We don't want to simply find the cancerous cells. We would like to locate the cells, be able to make a rational choice about whether they need to be destroyed, and if so, proceed immediately to treatment.”

To do this, the Rice researchers devised a new imaging and treatment technique based on metal "nanoshells,” miniscule spheres of silica coated with a thin layer of gold. Because these spheres are built on a nanometer scale (one billionth of a meter, the range where molecular interactions occur), they demonstrate distinctive size-dependent behavior, such as tunable optical characteristics. This allows investigators to develop particles that scatter and absorb light at specific wavelengths.

This light scattering characteristic provides the optical signal used to identify cancer cells, which then "light up” when they come into contact with the nanoshells. In this study, the scientists engineered the nanoshells to search for breast cancer biomarkers on the surface of the cancer cells. The method can be easily extended to target other kinds of cancer or disease processes that have known surface markers.

This added capability of the particles to absorb light is utilized to generate heat, which then kills the cancer cells. "Nanoshells are very unique in that we can engineer the particles so that both the optical scattering and absorption peaks occur in the near-infrared [NIR] spectral region where light penetration through tissue is highest,” stated Dr. Drezek. The NIR absorption also makes destruction of the targeted cells less invasive for patients since it uses a light source from outside of the body that passes harmlessly through normal tissue and only heats the tissue containing nanoshells.

This new method has considerable advantages over other alternatives that are being developed, according to Dr. Drezek. For example, optical imaging is much more rapid and less expensive that other medical imaging methods. Gold nanoparticles are also more biocompatible than other kinds of optically active nanoparticles, such as quantum dots.

"There is a prior history of the use of gold inside the body that makes the safety issues somewhat easier to address,” Dr. Drezek stated. Certainly, any new technology needs an extensive safety evaluation before being marketed, but early results from these nanoshell studies are promising. Nanoshells developed for therapeutic applications have already been assessed by Nanospectra Bioscience, Inc. (Houston, TX, USA), with no evident side effects found in their studies. The company is now in the process of marketing the technology.

The Rice scientists have successfully assessed the separate imaging and therapy components of the nanoshells in lab animals, and are now currently assessing the combined imaging/therapy nanoshells in a mouse tumor model, which they expect to be completed by the Fall of 2005.