Grant: Collaborative Health Research Projects

Circulating tumor cells (CTCs) are malignant cells shed by a primary tumor. They circulate in the bloodstreamand have the potential to establish metastases in anatomically distant tissues. The capture and enumeration ofCTCs 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 arapid surrogate for evaluating the clinical benefit of new drugs, and (3) as a fluid biopsy of a particularlyinvasive subpopulation of the original solid tumor. The key challenge in working with CTCs has been theirextreme rarity. Existing technologies overcome this problem by first enriching the concentration of CTCs byusing the cell surface maker, EpCAM to select for cells with epithelial characteristics. The effectiveness of thisselection technique has come into question since one of the key steps of invasion and metastasis isepithelial-to-mesenchymal transition where tumor cells initiate a phenotype switch that is accompanied by aloss of epithelial antigens (e.g. EpCAM). As a result, the aggressively metastatic CTCs are actually the mostlikely group to evade capture by current methods. We propose to develop a new method for enumerating CTCsby initially depleting leukocytes from a blood sample using CD45 magnetic beads and then developing amicrofluidics device to separate CTCs from the remaining CD45-negative leukocytes based on theirmorphological differences. Since CTCs originate in the primary tumor, they are mechanically distinct fromnormal hematological cells. Our microfluidics device is designed to separate cells based on differences in cellsize and cell rigidity with a high degree of specificity. Our hypothesis is that after these twoleukocyte-depletion steps, the concentration of CTCs in the sample is sufficiently enriched to be identified bystaining and manual selection. The key advantage of the proposed approach over existing methods is thepreservation of relevant CTCs that may have lost their expression for EpCAM due toepithelial-to-mesenchymal transition.