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March 26, 2003



Dual "Molecular Beacons" Might Eventually Lead to Very Early Cancer Diagnosis

An improved version of a nanoscale gene-detection tool called a "molecular beacon" could eventually help scientists and physicians locate intracellular molecular markers that signal the development of cancer or other diseases. Gang Bao, PhD, an associate professor in the Coulter Department of Biomedical Engineering at Emory University and the Georgia Institute of Technology, has developed "dual-FRET" molecular beacons that form a more sensitive and more effective probe than other gene detectors such as northern blotting developed in the past. Dr. Bao presented his research at the 225th National Meeting of the American Chemical Society in New Orleans on March 26.

A molecular beacon is a new type of biosensor that uses principles of photonics to seek out and illuminate specific target genes. The beacon is a short piece of single-stranded DNA (ssDNA) in the shape of a hairpin loop with a fluorescent dye molecule at one end and a "quencher" molecule at the other end. The ssDNA is synthesized to match a region on a specific mRNA that is unique to the gene or where a mutation is known to occur. The fluorescence of the beacon is quenched, or suppressed, until it seeks out and binds to a complementary target mRNA, which causes the hairpin to open up and the beacon to illuminate. When used for gene detection in living cells, however, the conventional molecular beacon design could cause a lot of false-positive signals.

Dr. Bao’s new "dual-FRET" molecular beacons technology uses a pair of molecular beacons with FRET dyes (fluorescence resonance energy transfer). The FRET signal does not occur until both donor and acceptor beacons are bound to adjacent sites on the same target mRNA, which results in transfer of energy between the two dye molecules. The dual-beacon technology could significantly reduce the false-positive signals of living cell gene detection, says Dr. Bao.

In the laboratory, Dr. Bao is applying his molecular beacon technology to the detection of pancreatic cancer, which is the fourth-leading cause of cancer deaths in the U.S. Pancreatic cancer is extremely difficult to detect in its early stages, and many patients diagnosed with the cancer die within six months. The one-year survival rate is 12 percent. Pancreatic cancer is most commonly detected using x-rays, CT scans, or biopsies, which are only effective after the tumor becomes large and in a very late stage.

"This is a simple and promising tool that we hope can eventually be applied to the detection of many cancer-related genetic markers," Dr. Bao said. He is designing his tiny molecular beacon to detect a specific genetic mutation in the K-ras gene that is present in 80 to100 percent of pancreatic cancers. Working with Dr. Margaret Offermann at Emory University, his lab has started detecting viral infection in cells using molecular beacons. He also hopes his technology will eventually be used clinically to target genetic markers of other diseases with high sensitivity, specificity, and efficiency.

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