Scientists use new technique to identify molecular 'biomarkers' for disease

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Washington, April 1 : Chemists at the University of Florida have made a breakthrough in the fight against serious diseases, by using a new tool to identify their molecular signatures, without any prior knowledge of what these microscopic signatures or "biomarkers" should look like.

The researchers say that the advance could one day lead to earlier detection and improved treatment of some types of cancer as well as other diseases.

"With many diseases, the problem has been that we really don't know what to look for. What we've done is create a technique to identify the biomarkers despite that limitation," said Weihong Tan, a professor of chemistry and the lead author of the paper.

Doctors often diagnose cancer and other diseases based on the appearance of a tumour or a patient's symptoms. While such traditional methods can be effective, they sometimes identify a disease only after it is established.

Because earlier detection typically improves outcomes, doctors would like to spot disease at the molecular level, before it grows or spreads and manifests itself in more obvious and harmful ways. Given that diseased cells' molecular structures differ from those of healthy ones, that approach should be possible, and researchers have had some success finding such "biomarkers" using antibodies, Tan said.

But despite years of research, biomarkers for most diseases remain elusive or unreliable, he said.

In the current study, Tan's group turned to "aptamers," single-strand chains of DNA or RNA that recognize and bind to target protein molecules, as a new tool.

The team reports the first-ever successful use of the aptamers to discover a molecular biomarker - in this case, one for leukemia.

Tan said his group used cell-SELEX, a process his group developed and patented.

Researchers create trillions of different varieties of aptamers in a solution. They then immerse cells known to carry the sought-after disease in the solution. After an incubation period, they rinse the cells.

The vast majority of the aptamers wash away, but those with stronger molecular affinity for the diseased cells remain. The researchers repeat the process several times, eventually shrinking the pool of aptamers to as few as 10 to 25 very strongly attached aptamers - those most closely associated with the diseased cells. Analysis then reveals these aptamers' molecular structure, as well as the molecular structure of the cells' biomarkers they bind to.

"As long as the molecules in question are expressed in a substantially different way on diseased and normal cells, they can be identified," Tan said.

Rebecca Sutphen, associate professor and director of the Genetic Counseling and Testing Service at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, said improved diagnosis might not be the only application of the research.

"The opportunity to identify cancer cell-specific biomarkers and potentially detect small numbers of cancer cells has many potential clinical applications, including disease detection, better imaging of tumors and even potential application for stem cells," she said.

Tan said the research is particularly promising because aptamers are relatively easy and inexpensive to manufacture compared with antibodies.

"This offers the potential for wider application," he said, adding that aptamers could one day be used not only to detect disease, but also to ferry therapeutic agents to diseased cells.

The study is published in the online edition of the Journal of Proteome Research.

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