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Apr 1, 2008 (Vol. 28, No. 7)

Cancer Biomarkers Expedite Detection

But Validation Must Be Improved to Obtain Truly Accurate Diagnostic Tools

  • It is widely acknowledged that early detection is the key to successful cancer treatment, yet such aggressive intervention requires accurate screening tools. Traditional diagnostic tests for cancer have a number of drawbacks including poor sensitivity, lack of specificity, and costly and invasive protocols. Now, finally, a variety of new biomarkers offers a wealth of possibilities. At CHI’s recent “PepTalk 2008” meeting the results of studies on markers for lung, pancreatic, and various malignancies were scrutinized.


    Telomerase

    The need for early diagnosis is a powerful driver in the search for new cancer biomarkers. Edouard Nice, Ph.D., and his colleagues at the Ludwig Institute for Cancer Research, recounted their efforts to develop early detection tools for malignancies. “Our strategy was to employ multidimensional, high-performance liquid chromatography to trace enrich low-level components such as growth factors in tumor material prior to the mass spectrometry analysis,” he said.

    Dr. Nice’s studies have focused on a number of putative cancer biomarkers, but much of his discussion concerned telomerase, an enzyme long known to maintain the telomeres, or chromosomal ends, during cycles of cell replication. The decline of telomerase activity with age is thought to be responsible for chromosomal instability, resulting in aging and senescence.

    There is a strong relationship between telomerase and tumor development; telomerase is expressed in more than 85% of cancers. In the Ludwig Institute’s work, the enzyme is measured by using magnetic beads conjugated to the telomere recognition site, a group of repeated TTAGGG nucleotides. The cells are lysed and telomerase activity is detected by the incorporation of multiple biotinylated nucleotides into the growing DNA strands, which are then reacted with streptavidin-conjugated horseradish peroxidase. Dr. Nice and his colleagues validated this assay procedure using a luminescent tag and then examined cells voided in the urine of bladder cancer patients and in the feces of colon cancer patients.

    The gold standard for diagnosis and monitoring of bladder cancer has been cystoscopy combined with urinary cytology. This procedure has many drawbacks, including invasiveness, attendant morbidity, and high cost. Since the vast majority of bladder cancers arise from the urothelium, analysis of the voided cells in the urine provides a potential source of cancer-specific markers.

    The magnetic bead telomerase procedure is exquisitely sensitive, detecting as few as 10 cancer cells, and its accuracy was confirmed by an independent pathological review panel, according to Dr. Nice. Samples from normal healthy volunteers were all telomerase negative. In the future, the assay could be configured for high throughput and automation and is a prime candidate for a first-line assay for detection and monitoring of colon and bladder cancer, he added.

    To this end, Dr. Nice and his colleagues are working with Sienna Cancer Diagnostics to move the technology forward. Sienna recently announced a licensing agreement with Geron for worldwide exclusive rights to develop telomerase for the in vitro diagnostic market.


    Liquid Chromatography & Mass Spec

    The combination of the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry is alive and well as a powerful diagnostic tool, reported Nigel Clarke, Ph.D., director of endocrinology at Quest Diagnostics Nichols Institute.



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