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Electronics zero in on cancer cells

Posted: 03 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:cancel cell? electroporation? electrical pulses?

Curing cancer is usually the domain of medical doctors, but biomedical engineers at Virginia Tech and the University of California at Berkeley have now invented a promising electronic therapy. Using short electrical pulses that target only cancer cells, together with real-time monitoring via electrical impedance tomography, the procedure has already been shown to cure cancer in lab rats.

"We have invented an inexpensive, minimally invasive surgical technique that makes use of irreversible electroporation, essentially killing cancer cells with short electrical pulses while leaving neighboring healthy cells unharmed," said bioengineering professor Rafael Davalos of Virginia Tech's School of Biomedical Engineering and Science. "We are also using electrical-impedance tomography to monitor progress and make sure all the cancer cells get treated."

Work has progressed from cell cultures to rats to mice, with human trials on prostate cancer slated for next year. If those trials are successful, curing other types of cancer will be tried in humans.

Opening pores
Engineers have been using electroporation since the mid-1960s to take electronic control of the pores in a living cell's outer membrane. For instance, genetic engineers routinely use electroporation to load DNA sequences into cells. By using 2,500V electrical pulses that are 100?s long, pores can be opened in any cell membrane, allowing liquids to flow in and out. Other cancer researchers use electroporation to temporarily make tumor cells more permeable to cancer-killing drugs than to the surrounding healthy tissue.

Davalos and UC-Berkeley collaborator Boris Rubinsky, however, use extended sessions with the electrical pulses to electrocute the cancer cells, permanently opening pores that kill the cell as its contents drain out.

"We use needle electrodes to surround the cancerous area, then we use external electrodes to monitor our progress with electrical-impedance tomography," said Davalos. "When the pores stick open on a cell, it lowers the bulk resistance of that tissue, which we can image with submillimeter cell-scale resolution."

By treating an area while watching their progress using tomography, then moving the needles and repeating as necessary, the engineers have been able to treat different types of cancerous tissue in laboratory animals. The treatment takes about 1min. per affected area. "The pulses are so short that the cells don't heat up," added Davalos.

Freezing cancer
Another technique can claim the same thing: Cryoablation freezes cancer cells. The downside is that killing the cancer cells with cold sometimes damages nearby healthy cells, just as heat can.

"Our procedure doesn't affect neighboring cells," said Davalos. "Our treatment is also tissue-independentall cells just behave in this way. All we have to be able to do is get the needles to the targeted area, and in just one treatment you are rid of the cancer."

A key problem with traditional cancer treatments, the researchers said, is that oncologists cannot tell if the cancer cells are dead until a week or so after treatment. Consequently, if oncologists are not aggressive enough during the treatment, they can miss some cancer cells, and if they are too aggressive, they can damage surrounding healthy tissue.

"With other procedures, you don't get immediate feedback. With ours, you can see how successful the treatment is as you go along," said Davalos.

- R. Colin Johnson
EE Times

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