(338c) Microfluidic Cell Isolation Technology for Drug Testing of Single Tumor Cells and Their Clusters

There is a growing interest in conducting drug assays with patient-derived cells such as circulating tumor cells (CTCs) to predict better cancer patient outcomes. Recent advances in separating CTCs and their clusters from blood have opened up new opportunities for downstream assays of rare CTCs for drug discovery and probing drug resistance. However, conducting drug assays with CTCs can be challenging due to potential loss of the rare cells (1- 100 CTCs per mL of blood) while handling. Although ex vivo culture methods are beginning to emerge to culture CTCs for drug assays, the molecular heterogeneity of individual CTCs and clusters is often lost during the bulk expansion process making it difficult to identify drug resistant cells.

In this study, we present a pipette-based microfluidic cell isolation (MCI) technology that is capable of conducting single cell resolution drug assays with a small number of tumor cells or their clusters present in small sample volumes (e.g. 10 â?? 100 cells in 10 mL). A micropipette is used to deliver both the carrier fluid as well as the assay fluid through a microchannel network to nanoliter-sized fluidic traps. The method can digitize the assay fluid producing an array of stationary droplets laden with single cells or their clusters. To establish proof-of-principle of our pipette-based MCI method, we use breast cancer cells (MCF-7) and a chemotherapy drug, doxorubicin. We demonstrate that (i) our method can efficiently isolate single MCF-7 cells without appreciable loss during the pipetting and digitization steps (ii) our method can isolate clustered tumor cells with a distribution of 2-22 cells/cluster (iii) the droplet surrounded by an immiscible carried fluid does not adversely affect the viability of anchorage-dependent breast cancer cells (iv) although individual tumor cells display significant heterogeneity in the kinetics of uptake of doxorubicin, they all undergo apoptosis when a critical amount of drug is accumulated (v) the overall viability of clusters is improved simply due to a greater number of cells per cluster suggesting that a CTC cluster has a better chance of surviving chemotherapy drug treatment than a single CTC. Thus, our microfluidic cell isolation technology has significant potential as a simple yet efficient tool for time-resolved analysis of rare tumor cells and their clusters.