Light Spots Cellular Suicide

Bioengineers now are using scattered light to help determine whether cancer cells are responding to chemotherapy.

The new technology, developed by bioengineers at Duke University, is helping clinicians more precisely detect within a matter of hours whether specific cancer drugs are working.

Most chemotherapy drugs work by forcing cancer cells to commit cellular suicide, a process known as apoptosis. As cells undergo this process, bodies within the cell, such as the nucleus or mitochondria, go through structural changes. Using the new approach, researchers can analyze the light scattered by these bodies to detect the apoptotic changes in real time.

Cells treated with chemotherapeutic agents exhibit their changes after treatment as a grainier texture. Slides (a) and (b) show the nucleus before and after treatment; slides (c) and (d) show mitochondria before and after treatment. Images courtesy of Adam Wax, Duke University.

“The new technology allowed us to detect the tell-tale signs of apoptosis in human breast cancer cells in as little as 90 minutes,” said Adam Wax, associate professor of biomedical engineering and senior member of the research team. “Currently, it can take between six and eight weeks to detect these changes clinically. It appears that this approach has the potential to be helpful in both clinical and laboratory settings.”

The light-scattering technology is known as angle-resolved low coherence interferometry (a/LCI). In this process, light is shone into a cell sample, and sensors capture and analyze the light as it is scattered back. The technique can provide representations of subcellular structure without disrupting the cells and can be used to scan a large number of cells in a short time.

“Now, oncologists typically judge if a chemotherapeutic agent is working by looking for shrinkage in the tumor using imaging techniques, such as MRI or PET, or pathological response at time of surgery,” said Julie Ostrander, Duke molecular cancer biologist. She and Duke bioengineer Kevin Chalut were the paper’s first authors.

“If we had a way to detect early on in the apoptotic process whether or not a drug was working, patients would not have to wait weeks to months to find out,” Ostrander said. “The idea that you could shine a light at a tumor and use the light-scattering pattern to measure the success of drugs is a big step forward.”

For its experiments, the Duke team studied a well-known cell culture line of human breast cancer. The cells were exposed to two common chemotherapy drugs, doxorubicin and paclitaxel. Using the a/LCI technology, the researchers looked for specific patterns indicating that structural changes had occurred.

They found that, when compared with control cells, the paclitaxel-treated cells began showing within 90 minutes significant increases in a pattern called fractal dimension. Doxorubicin-treated cells exhibited the same increases within three hours. Interestingly, the fractal dimensions began decreasing at six hours, only to increase again within 12 hours of treatment.

“The fact that the changes in structure appear over two distinct time scales suggests that multiple mechanisms are involved in these early events in apoptosis,” Wax said. “Further analysis showed the early changes we observed were taking place in the mitochondria, while the changes in the structure of the nucleus were responsible for the later ones.”

Ostrander said that this technology will help laboratory investigators determine how cancer cells become resistant to apoptosis and, therefore, are resistant to drugs. Before this technique can be employed for human breast cancer, further studies will be carried out in animals.

Wax and colleagues at the University of North Carolina at Chapel Hill are conducting a pilot clinical trial in humans using a similar technology for early detection of precancerous cells in the epithelial lining of the esophagus, a condition known as Barrett’s esophagus.

The Duke research was supported by the National Science Foundation, National Institutes of Health and the US Department of Defense.

The results of the Duke team’s experiments were published in the February issue of Cancer Research.

For more information, visit: www.duke.edu