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Exiqon Presents Data Supporting Use of PCR-Based miRNA Assay as Blood-Based Colon Cancer Dx

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By Ben Butkus

Danish life science research and diagnostic firm Exiqon yesterday presented data at a cancer research conference highlighting the potential of its PCR-based microRNA screening technology as a blood-based diagnostic test for early-stage colorectal cancer.

The findings, unveiled at the American Association for Cancer Research's International Conference on Molecular Diagnostics in Cancer Therapeutic Development in Denver, suggest that it is feasible to use Exiqon's test to distinguish early-stage colorectal cancer patients from healthy subjects using a single plasma sample comprising less than 1 mL of blood.

In addition, Exiqon said that it is now starting a large, prospective clinical trial in symptomatic individuals undergoing colonoscopy to validate its test and gather data to support a regulatory filing in Europe and the US. The company hopes that the test can eventually be administered to patients at risk of developing the disease to alert them as to whether they should subsequently undergo a colonoscopy.

Exiqon's test, the miRCURY LNA Universal RT microRNA PCR screening platform, profiles microRNA expression by combining Exiqon's locked nucleic acid technology system with a universal reverse transcription step, the company said.

The use of two LNA-enhanced PCR primers enables quantitation of very low microRNA levels and discrimination between closely related microRNA sequences, according to Exiqon. The universal RT step also greatly reduces sample input requirements and technical variation, the company said.

Exiqon has been pursuing a dual commercialization strategy for its technology. Its microRNA qPCR product line, which it sells to research labs, includes ready-to-use qPCR panels for expression profiling of human, mouse, and rat microRNAs. Each of the more than 1,000 validated primer sets are also available as individual microRNA assays, the company said.

"We have a very robust system that works on very challenging samples such as serum and laser-captured [formalin-fixed, paraffin-embedded tissues," President and CEO Lars Kongsbak told PCR Insider this week.

Kongsbak added that the technology can be used to profile more than 700 miRNAs using as few as 10 cells, although the company prefers to use around 80 cells. This level of sensitivity is what lends promise to the technology as a blood-based diagnostic, according to Exiqon.

Exiqon initially launched its colorectal cancer test for research use only in early 2009. In the meantime, the company launched a CLIA-certified lab in order to conduct various preclinical miRNA profiling studies to distinguish normal tissue from colon cancer tissue.

Exiqon's platform uses a single RT reaction to profile more than 700 human miRNAs from two predefined 384-well plates, and allows high-throughput profiling of miRNAs from clinical sources without the need for pre-amplification.

For the study presented at the AACR meeting, Exiqon, along with collaborators at Aarhus University Hospital, Hvidore Hospital, and the University of Copenhagen, examined blood plasma samples from 50 patients with stage II CRC and 50 matched healthy controls.

Kongsbak said that the company performed this particular study using a Roche Lightcycler PCR system; but added that Exiqon's platform also works on systems from companies such as Life Technologies and Bio-Rad.

Exiqon's test was able to distinguish most of the patients who had been diagnosed with colorectal cancer from healthy subjects, although Kongsbak conceded that it is too early to provide meaningful specificity and sensitivity figures.

"The findings need to be validated in an independent cohort before a specificity or sensitivity profile can be assigned to the test," Kongsbak said.

To that end, Exiqon is now beginning a large, prospective clinical trial that will enroll 3,000 to 5,000 symptomatic patients undergoing colonoscopy at Danish hospitals, Kongsbak said. All patients will donate a blood sample, which will be used in the validation of the finalized test, he added.

In addition, Exiqon has initiated a second large validation study with a Danish hospital. That study will investigate 600 samples from stage II colon cancer patients using an in situ hybridization-based microRNA test to predict recurrence.

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