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  • Photoacoustic device hunts melanoma

Mar 2012
Ashley N. Paddock,

COLUMBIA, Mo. — A new photoacoustic device will aid the fight against metastatic melanoma by detecting single melanoma cells in blood samples at a fraction of the cost of current cancer tests.

Melanoma, an aggressive cancer, is characterized by skin growths that in and of themselves aren't seriously dangerous but that can become a quick killer: After metastasis, patients often live less than a year, and fewer than 20 percent live five years, which is why early detection is critical.

But finding metastatic melanoma as it spreads through the body has proved difficult. Detection with MRI or CT imaging equipment requires tumors that are at least a few millimeters in diameter (similar to a grain of rice); at that size, they already consist of millions of cells.

With the new test, scientists can look in the blood system for single melanoma cells propagating through the body, said John Viator of the Bond Life Sciences Center at the University of Missouri.

John Viator, associate professor of biomedical engineering and dermatology, demonstrates a new photoacoustic method with a tabletop device that scans a lymph node biopsy with laser pulses. This method could help doctors identify the stage of melanoma with more accuracy. Courtesy of University of Missouri.

"This is much more effective, because you're looking for a cancer sooner than you could ever detect it with an imaging test," he said. "That's good for the patient, and it's good for the clinician, because if you can find cancer when it's just at the cellular level, then you're fighting a small number of cells versus trying to fight a tumor the size of a softball that's growing around your kidney."

The prototype, when refined into a commercial product, should be about the size of a small copy machine. Clinicians would put blood samples into the device, which would then provide a readout of the samples' results in about 10 minutes. Compared to current techniques for testing, this new machine has the advantages of being inexpensive, fast, compact and easy to use, along with offering earlier detection.

At its center is a photoacoustic technology called laser-induced ultrasound. Viator uses this tool in conjunction with the properties of density, light, heat and color to cause cancer cells to react in a manner that makes them detectable and distinguishable from surrounding cells.

A first step in the testing process is using a centrifuge to separate a patient's blood into white and red blood cells. Melanoma cells are about the same density as white blood cells but less dense than red ones, so melanoma cells are naturally thrown in with white blood cells as the blood separates. The resulting batch of white blood cells (plus any cancer cells present) is then pumped through narrow tubing that contains a tiny glass box where the cells are hit with a short pulse of high-intensity laser light as they pass by. Because white objects reflect light, the white blood cells are not affected, but any cell with pigment will absorb the light. The intense laser beam heats such a cell rapidly, causing thermoelastic expansion, which in turn causes the expanding cell to emit a measurable pressure wave. Detection equipment senses this photo-acoustic wave and thus locates the cancer cell.

Using this method, pigmented melanoma cells stand out and can be separated from the healthy white blood cells, which then are individually tested using biomolecular assays or imaging.

"Not all melanoma cells are the same," Viator said. "You can do some molecular tests and find out [details such as] do they have this genetic type? Or do they have these cell surface markers? We know that such-and-such a cell responds really well to this type of drug, so you could personalize your cancer therapy, potentially, by capturing the cells you've detected in the blood sample and understanding the disease better."

Current treatment tools for melanoma include surgery and a drug, interferon, which is only about 20 percent effective, Viator said. But two new melanoma drugs have been approved this year, and a dozen more are in Phase III trials.

"The availability of melanoma therapies is going to explode," Viator said. "The more therapies there are, the more valuable this [photoacoustic technology] will be, because it can track response to disease."

Initially, the tool will detect and monitor only metastatic melanoma. But Viator's lab is continuing research, with the goal of using photoacoustic methods to detect other cancers such as breast and prostate.

Viator recently signed royalty and licensing agreements with the university to clear the way for his new company, Viator Technologies Inc., to develop a commercial prototype.

Due to the machine's comparatively low cost, he is confident that early cancer diagnosis will become more accessible because it could be available in places where medical facilities can't justify purchasing a much higher-priced MRI machine.

Unfortunately for cancer patients, the new device may not be available for a few more years, as it has not passed FDA tests for safety and effectiveness. Viator is confident, however, that these required tests will demonstrate that it is highly reliable. The machine can grab and save any suspect cell; therefore, the cells can be examined microscopically or genetically to confirm their identity.

The machine does not need FDA clearance before it is used for research. Scientists in academia or industry could use the device for cancer studies as soon as it is produced. Thus, companies testing new cancer drugs could use it to assess their drugs' effectiveness.

The desktop device should be available to researchers by the end of next year; after two or three more years, it may be commercially available for clinical use, Viator said.

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