Cancer cells are often most threatening when they break off from their original site and start invading other parts of the body, a process called metastasis. To find out if that's happening in a patient, doctors often look for them in a sample of blood.
Current methods often try to filter these cells out of the bloodstream by running a tiny amount of blood through a channel in a microfluidic device. The channel is coated with antibodies that can latch on to specific proteins on a cancer cells' surface. But the antibodies are simply too short -- just a few nanometers in length -- to catch much in the flowing liquid, especially since whole cells can be 10 to 30 micrometers long (a micrometer is 1,000 nanometers).
A study published this week in Proceedings of the National Academy of Sciences looked to nature for a solution to this intractable problem. Senior author Jeffrey Karp, a bioengineer at Brigham and Women's Hospital, and colleagues at the Massachusetts Institute of Technology and Harvard University thought about the way marine animals like jellyfish and sea cucumbers use long tentacles or arms with sticky patches to snag tiny prey out of the water.
Thus inspired, they designed a device with long chains of DNA made out of aptamers -- repeating, "sticky" blocks of DNA -- specially made to latch on to a protein called tyrosine kinase 7, which is found in certain leukemia cells as well as in lung and colon cancers. The researchers also cut the flow surface into a herringbone pattern, causing the flowing blood to swirl around rather than go straight through; that made any cancer cells more likely to get snared by the DNA tentacles.
Karp and his colleagues found they could push fluid through 10 times faster than previous systems allowed. They also showed that their bio-inspired device can catch up to 80 percent of target cells. Scaling the technology up could increase the flow rate 100-fold and make it practical for future use in hospitals.
And since the tentacles can also be severed with enzymes, the captured cancer cells can be freed and recovered in the sample for later analysis, the study pointed out.
Since different aptamers can snag different types of proteins, the technology could prove useful for finding a number of different cancers. It may also be able to capture free-floating fetal cells in a pregnant woman's bloodstream, the researchers said.
Identifying these metastatic cancer cells earlier would help doctors personalize their patients' treatment. And for leukemia patients, it could one day help doctors see whether a treatment is working without resorting to painful bone marrow sampling.
©2012 Los Angeles Times
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