Circulating tumor cells (CTCs) is a high interest topic. Several methods have been proposed for capturing CTCs, including field flow fractionation and high-performance capillary electrophoresis (HPCE). Zhang is the lead author reporting a simple chip that selectively captures CTCs from whole blood.1
A nitrocellulose membrane is mounted on a slightly larger poly(methyl methacrylate) (PMMA) wafer for manipulation. An antibody solution is added to the nitrocellulose pad and is then washed and dried. The Fc portion binds to the nitrocellulose. Whole blood from the patient is added to the nitrocellulose pad and incubated. Thirty minutes for capture appears to be optimum. The cells are imaged with conventional brightfield microscopy. In one example, the cancer cells were nonsmall-cell lung cancer NCI-H1650. The antibody was EpCAM CD326.
The capture efficiency was evaluated by spiking cells into 1 mL of whole blood and looking for percent capture. At 20 cells, the capture efficiency was about 30%, but at 400 cells, the efficiency increased to 60%.
This protocol may not seem adequate for diagnostic purposes, but the criteria for serious concern are very low: Five cells per milliliter indicates metastasis. At 7 to 10 cells, the prognosis is bad. Still, CTC assays are superior to biopsy, since they are noninvasive, and elevated CTCs indicate that the tumor is metastasizing.
The choice of epithelial cell adhesion molecule (EpCAM) as the capture antibody is also problematic, since there are CTCs that are not captured by EpCAM. The avidity may be too low to cause association, or interferences may have higher avidity. This would displace the CTC from forming a complex. However, many other antibodies exist. It seems likely that selecting and mixing antibodies could increase retention of other cells.
Reference
- Zhang, P.; Changlong, S. et al. A novel and facile microchip based on nitrocellulose membrane toward efficient capture of circulating tumor cells. Chin. J. Chromatogr.2013, 31(6), 518–21.
Robert L. Stevenson, Ph.D., is a Consultant and Editor of Separation Science for American Laboratory/Labcompare; e-mail: [email protected].