Gold dust could soon help doctors diagnose and treat cancer

by Ann Kushmerick

Photo courtesy of Dr. Ivan El-Sayed Attraction to gold: Gold particles coated with antibodies have attached themselves to these oral cancer cells.

Despite cancer's covert tactics, medical researchers are developing new and better ways to detect the disease while it silently multiplies in an organ or tissue. Cancer can currently be detected by extracting suspect cells and introducing a marker which makes malignant cells visible under a microscope. Some current markers, like quantum dots, work well in laboratory tests, but can be toxic to the tested cells and to humans. In one new method, microscopic gold dust is the tool of choice, and like detectives dusting for fingerprints, researchers are using gold nanoparticles, one-thousandth the width of a human hair, to uncover the mark of cancer. Since the gold nanoparticles are non-toxic, they can potentially be injected into the human body to detect cancer, and even potentially kill it, in a non-invasive manner.

Two of the researchers working on this technique are the father-and-son team of Dr. Mostafa El-Sayed from the Georgia Institute of Technology and Ivan El-Sayed from the University of California at San Francisco Medical Center. "My father has a long history of working with gold due to its novel optical properties," says Ivan El-Sayed. "I bring a medical perspective to the project. It is just a bonus that gold is already used in medicine, that fact gives us hope that it may actually work."

The human body doesn't absorb gold very well so it's not normally toxic. It's been used in humans for the past 50 years, from its use in teeth to implants made of a form of radioactive gold used in cancer treatment. But the gold that the El-Sayeds and their team propose to use is slightly different. Chemically, it's identical to the gold we are familiar with, but when separated into minute quantities it exhibits special properties. Scientists have discovered that nano-sized gold is easy to work with, and as you might imagine, it's also better than other substances at "marking" cancer because it shines much brighter under a microscope.

The researchers conducted their work in a lab, but before they could add the gold to cell samples, they had to link the gold particles with an antibody for epidermal growth factor (EGF). Cancerous cells are very distinct because of the abnormal amount of EGF receptors on their surfaces. These receptors attract epidermal growth factor (EGF), which as its name implies, causes cells to divide excessively. The gold-antibody combo attaches itself easily to the many receptors on the cancerous cells. Similar to the process for detecting fingerprints, where a powder sticks to oils left behind from a human fingertip to reveal a unique outline, the nanoparticles bind to the receptors in the cancer cells to expose those cells as cancerous. Since healthy cells have much fewer EGF receptors, the golden pattern looks very different on the healthy and the cancerous cells. The gold nanoparticles had an attraction to the cancer cells that was 600% greater than their attraction to normal cells.

Photo courtesy of Dr. Ivan El-Sayed Non-cancerous cells don't attract gold as strongly so the particles are scattered over the cell.

Unlike buying gold in visible amounts, using nanoparticles of gold to detect cancer is also very inexpensive, and the process is simple and instantaneous. The only equipment that the researchers needed was a modified student microscope and white light. Because gold scatters light so strongly, the cancer cells sprayed with the gold nanoparticles were immediately visible. This is extremely advantageous for detecting cancer early on and preventing it from spreading.

To perfect the technique for mainstream use, further research is being carried out. "We need to develop appropriate imaging systems, and to determine the best way to deliver the particles to sites of interest," says Ivan El-Sayed. Although the research has been conducted on cells in the laboratory, the researchers are hoping that in the future, the nanoparticles can be injected into the body where they will attach to the cancer cells. Then, low-level lasers can safely kill the gold-coated cancer cells, while leaving the healthy cells unharmed. The researchers also hope that this method could be used to study cellular interactions.

Photo courtesy of Dr. Ivan El-Sayed Dead cancerous cells (blue): They were killed much more easily when coated with gold nanoparticles.

In the meantime, the research team has already started to develop such uses for the gold nanoparticles and is working on using them to actually kill the cancerous cells. "The work with gold as a detection agent is just getting started because there are so many possibilities to explore," Ivan El-Sayed says.

For more info:

Gold Nanoparticles May Simplify Cancer Detection
http://www.gatech.edu/news-room/release.php?id=561

Researchers demonstrate use of gold nanoparticles for cancer detection
http://pub.ucsf.edu/newsservices/releases/200506033/