Grant: Collaborative Health Research Projects (NSERC partnered)

Circulating tumor cells (CTCs) are malignant cells shed by a primary tumor. They circulate in the bloodstream and have the potential to establish metastases in anatomically distant tissues. The capture and enumeration of CTCs has gathered considerable attention because of the potential to use the number and status of these cells (1) as a prognostic marker for tailoring systemic therapies to the needs of individual cancer patients, (2) as a rapid surrogate for evaluating the clinical benefit of new drugs, and (3) as a fluid biopsy of a particularly invasive subpopulation of the original solid tumor. The key challenge in working with CTCs has been their extreme rarity. Existing technologies overcome this problem by first enriching the concentration of CTCs by using the cell surface maker, EpCAM to select for cells with epithelial characteristics. The effectiveness of this selection technique has come into question since one of the key steps of invasion and metastasis is epithelial-to-mesenchymal transition where tumor cells initiate a phenotype switch that is accompanied by a loss of epithelial antigens (e.g. EpCAM). As a result, the aggressively metastatic CTCs are actually the most likely group to evade capture by current methods. We propose to develop a new method for enumerating CTCs by initially depleting leukocytes from a blood sample using CD45 magnetic beads and then developing a microfluidics device to separate CTCs from the remaining CD45-negative leukocytes based on their morphological differences. Since CTCs originate in the primary tumor, they are mechanically distinct from normal hematological cells. Our microfluidics device is designed to separate cells based on differences in cell size and cell rigidity with a high degree of specificity. Our hypothesis is that after these two leukocyte-depletion steps, the concentration of CTCs in the sample is sufficiently enriched to be identified by staining and manual selection. The key advantage of the proposed approach over existing methods is the preservation of relevant CTCs that may have lost their expression for EpCAM due to epithelial-to-mesenchymal transition.