A prime target for a serum-based early detection test is ovarian cancer. Survival rates are quite high when the disease is confined to the ovary, yet early detection is challenging since symptoms are easily confused with many other illnesses. Often by the time the condition clearly manifests itself it is too late. Indeed, only 29% of cases are detected early enough to take remedial action.
Dr. Tainsky and his colleagues use microarrays to which phage displaying different peptides from tumor cDNA libraries are bound. The phage are put through a number of rounds of selection and enrichment in order to produce highly tumor-specific clones, and the end products are robotically spotted to build the microarrays. Using this approach, the Tainsky team was able to isolate 65 antigen-producing phage clones positive for ovarian cancer samples, yet with low binding to sera from women with benign gynecological conditions.
The question of why these biomarker proteins stimulate an immune response in the patients goes to the origins of the cancerous state. According to Dr. Tainsky, the proteins are either normal proteins that are overexpressed so much so that the autoimmune-protective mechanisms of the individual break down, or they are part of the normal repertoire, mutated to a state in which they appear foreign to the host.
The autoantibodies revealed through this technology can be used to detect ovarian cancer, and immunohistochemical studies have determined that some of the epitopes can serve as tissue biomarkers. They also offer the prospect of developing patient-specific cancer vaccines that could be individualized for the patient, Dr. Tainsky said.
High-Density Antibody Arrays
Designing a new generation of biomarker detection platforms requires reducing background to the lowest level possible. Bryce P. Nelson, Ph.D., research and development vp at Gentel Biosciences, discussed progress in building antibody arrays for research use.
In order to lower background, Gentel employs a nonporous, optically clear, ultrathin nitrocellulose film that is attached to a 1 x 3 inch glass slide. The completed unit can be subdivided into 16 wells for multiplex assays containing more than 45 analytes per well.
The company has developed a single capture assay in which antibodies are bound to the surface. The sample to be tested is labeled with fluorescein and serum proteins are specifically captured. The sample is then reacted with a detector antibody (antifluorescein) labeled with a fluorescent dye, which can then be measured using a standard fluorescence scanner.