Wednesday, April 28, 2004

Cancer Treatment on a Chip
Scientists have developed what they say could become the world's smallest medical kit: a computer, made of DNA, that can diagnose disease and automatically dispense medicine to treat it.

The computer, so small that one trillion would fit into a drop of water, now works only in a test tube, and it could be decades before something like it is ready for practical use. But it offers an intriguing glimpse of a future in which molecular machines operate inside people, spotting diseases and treating them before noticeable symptoms even appear.

'Eventually we have this vision of a doctor in a cell,' said Dr. Ehud Shapiro of the Weizmann Institute of Science, in Rehovot, Israel, who led the work, published online yesterday by the journal Nature.

DNA's role is to store and process information, the genetic code. So it is not surprising that it can be used for other computing tasks as well, and scientists have in fact used it to solve various mathematical problems. But the Israeli scientists said theirs was the first DNA computer that could have a medical use.

The computer, a liquid solution of DNA and enzymes, was programmed to detect the kind of RNA (a DNA cousin) that would be present if particular genes associated with a disease were active.

In one example, the computer determined that two particular genes were active and two others inactive, and therefore made the diagnosis of prostate cancer. A piece of DNA, designed to act as a drug by interfering with the action of a different gene, was then automatically released from the end of the computer.

Experts called the work ingenious but pointed out that it had been done in a test tube, to which the RNA corresponding to the disease genes was added. It is not clear, they said, whether such a computer could work inside cells, where there would be many pieces of DNA, RNA and chemicals that could interfere.

'I think it's very elegant -it's almost like a beautiful mathematical proof," said Dr. George Church, professor of genetics at Harvard Medical School. "But it's not working in human cells yet."
Elegant to be sure although I don't know about the whole mathematical proof analogy. As near as I can tell the "enzymes" are probably specific nucleases (RNase H being one) that will destroy DNA:RNA hybrids. So let's say we know that a disease/cancer produces (requires) a particular protein to be made and we know the DNA sequence of the transcript (gene) for that protein. The 'computer' would have this DNA sequence and in a person with the cancer/disease the RNA would be made and it would bind to the DNA in the computer and trigger release of the enzyme (or more likely production of the enzyme) that would destroy the bound RNA molecule and thus inhibit disease/cancer progression. It's a great idea but the intracellular environment is very different from a test tube and the necessary reactions could be competing with similar natural reactons in a cell or be inhibited in other ways as well, so its use is still a long ways off -but intriguing nonetheless.


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