Dr. Chen’s group is now faced with a large collection of biomarker candidates. In order to prioritize them she has developed a list of criteria including degree of overexpression, role of the protein, availability of ELISA technology, whether the protein is extracellular or membrane bound, correlation with other analyses such as RNA and DNA detection, and the specificity of the protein as an authentic pancreatic cancer marker.
“Using this approach, we have identified several potential biomarker candidates that really work well on the cancer tissues. To be clinically useful for screening the general population, these tissue biomarkers need to be developed into blood assays and further validated in serum/plasma,” Dr. Chen stated.
Discovery to Clinical Validation
There is an active field of cancer biomarker study that focuses on proteins that have been recognized as being associated with states of malignancy. Philip Hemkin, Ph.D., principle scientist, cancer diagnostics R&D, Abbott Laboratories, discussed his group’s investigations of the tissue inhibitor of metalloproteinases-1 (TIMP-1).
Over the last decade a number of cancer researchers have observed elevated levels of TIMP-1 in the plasma of cancer patients, while healthy individuals maintain lower levels within a narrow range. These studies suggested to Dr. Hemkin and his colleagues that TIMP-1 might serve as an early detection signal for colon cancer.
The Abbott group developed an automated, two-step, double-mouse monoclonal sandwich assay in which an antibody against TIMP-1 is attached to a magnetic microparticle. A second antibody labeled with acridium will generate a light signal.
The group optimized the assay procedure, which has a large dynamic range, extending from zero to 2,500 ng/mL. The kit shows great precision and stability, he reported.
With a robust assay available, Dr. Hemkin and his colleagues are well positioned to continue obtaining a detailed clinical evaluation of the efficacy of TIMP-1 as an early marker for colon and other cancers.
DNA immunization, first introduced in 1999, is a technique for rapid generation of antibodies that until recently had not reached it full potential. Strategic Diagnostics adopted this technology for the purpose of producing large numbers of antibodies to putative cancer biomarkers. The approach involves the introduction of genes for target proteins (usually a sequence coding for a representative peptide of about 100 amino acids) into the animal to be used for the immunization procedure.
This results in a savings of time and resources since purification of a protein to a state satisfactory for use as an immunogen can be extremely challenging. With DNA immunization, a precise sequence is inserted into the carrier plasmid and there is no possibility of the inadvertent introduction of contaminating proteins.