Imagine you want to develop a molecular “flag” that binds to cancer cells but not to normal cells. Wouldn’t that be a useful tool for diagnosis? Dr. Weihong Tan and his research group at the University of Florida thought so and set out to “make it happen.” Their novel method exploited the differential binding of DNA fragments to cancer cells versus normal cells, but the real power of their approach involved the Darwinian principle of selection, applied at the molecular level. As reported in the February 1 issue of Analytical Chemistry, Tan’s group took a random mixture of trillions of different DNA sequences and applied them to liver cancer cells, selecting for those that stuck to them. Ones that didn’t stick were discarded. The subset of sequences that stuck was then added to normal (non-cancerous) liver cells. Any of those that stuck to the normal cells were removed and the remaining sequences were amplified by PCR. These remaining DNAs should stick to cancer cells but not stick to normal cells. This process was repeated 15 times to improve the selectivity of sticking. The end product of this work was a set of DNAs that bound only to cancer cells, but not to normal cells. The initial uses of the technology may be to identify cancer cells by tagging the DNAs with a fluorescent dye, thus allowing technicians to easy see cancerous cells in a mixture. Other applications may ultimately come about in therapies based on binding drugs or antibodies to markers placed on the DNAs. Further testing to identify other DNAs for different cancers is underway.
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