In chemotherapy, cancer cells may show resistance to a wide range of anticancer drugs, a phenomenon called multidrug resistance (MDR). A well-established cause of MDR in cancer cells involves transporter proteins, such as permeability-glycoprotein (P-gp), multidrug resistance associated protein-1 (MRP1) and breast cancer resistance protein (BCRP). These proteins usually cause efflux of anticancer drugs such as daunorubicin (DNR) and paclitaxel (PTX) from cells, leading to a reduction in cellular drug accumulation. Blocking the activity of transporter proteins using MDR inhibitors is an important approach to overcome drug efflux, a method called MDR reversal. The overall goal of this research was to develop microfluidic chips and methods to enhance intracellular drug accumulation in MDR cells or reverse MDR. To investigate MDR inhibition, a microfluidic method called same-single-cell analysis was used to trap and measure single cells. In this method, drug accumulation was first measured in the trapped cell treated with anticancer drug only (control experiment). Then, enhancement of drug accumulation was measured in the same single cell treated with the drug in the presence of a MDR inhibitor. Cancer cells are usually heterogeneous. This single-cell method allowed us to conduct same cell analysis that overcame the issue of cell heterogeneity. Our method also successfully demonstrated the enhancement of drug accumulation measured in the single cells from cryopreserved patient cells. In addition, the real-time measurement in single cells provided time-dependent kinetic information that correlated with the fold-increase of drug accumulation enhancement by MDR inhibitors. Most importantly, a new integrated microfluidic chip was developed to select and measure rare cancer cells among many blood cells as a model of circulating tumor cells (CTCs). Our label-free microchip was used to separate single prostate cancer cells and measure the drug accumulation enhancement by using MDR inhibitors. A method of capturing a prostate cancer cell among blood cells was developed with an ultimate goal to find the appropriate MDR inhibitors to enhance cellular accumulation of anticancer drugs, leading to more effective chemotherapy.
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