A physicist and a professor of basic medical sciences at Purdue have unveiled a new method to observe how different cancer drugs affect tumor cells. Holographic Tissue Dynamics Spectroscopy (TDS), as the technique is called, creates a three-dimensional hologram of the internal structure of a tumor up to a millimeter in diameter. Applying various drugs to the tumor provides a unique signature of the mechanical interactions happening within.
Purdue physics professor David D. Nolte, inventor of the technology, explains:
"If a car travels toward you on a sunny day, you cannot see the driver because the glare off the windshield prevents you from seeing inside. The image-bearing light of the driver is actually there; you just can’t see it because your eye is being saturated with the glare," he said. "But put on a pair of polarized sunglasses to take away the glare, and you can see the driver. Our holographic approach gets rid of the light scattered by skin and tissue, and we uncover the image-bearing light that is already there."
The newly developed tissue dynamics spectroscopy used in Nolte’s technology creates an image [see side] similar to a voice print used in voice-recognition security software. This voice print shows changes taking place inside the cells.
"After making the hologram, my colleagues and I use spectroscopy to measure the time-dependent changes in the hologram," Nolte said. "Fluctuation spectroscopy breaks down the changes into different frequencies, and we can tell how a cell’s membranes, mitochondria, nucleus and even cell division respond to drugs. We measure the frequency of the light fluctuations as a function of time after a drug is applied."
The resulting colorful frequency-versus-time spectrogram represents a unique voice-print of the drug used on the cells.
"We’ve discovered that individual drugs have quite different spectrograms, but with similarities within specific classes of drugs," Nolte said. "By looking at how the cell motion is responding to drugs, we can differentiate very fine mechanistic points between them."
Press release: Purdue researcher’s technology ‘listens’ to cancer cells, shows effects of drug therapies
Abstract in Journal of Biomedical Optics: Speckle fluctuation spectroscopy of intracellular motion in living tissue using coherence-domain digital holography