(507e) Continuous, High Throughput Microfluidic Device to Monitor Circulating Tumor Cells in Cancer Patients

Although tissue biopsies are an excellent diagnostic and prognostic tool, they are highly invasive making them non-ideal for routine monitoring. “Liquid biopsies” are a possible alternative to traditional tissue biopsies and offer the advantages of being less invasive and therefore lower risk to patients. These liquid biopsies detect and allow the analysis of circulating biomarkers such as circulating tumor cells (CTCs). Although prognostically informative, CTCs are extremely rare with only 1-10 CTCs per mL of blood.¹ It is predicted that higher CTC numbers would allow for more informative analysis to be conducted from sampling blood. Current technologies are largely ex vivo and typically process 1-10 mL of blood obtained from a single venipuncture. In this study, we designed an in vivo, ex-dwelling CTC-capture system to isolate CTCs directly from whole blood and return the remaining blood to the patient. This allows us to drastically increase the blood volume processed which will lead to increased cell numbers available for further analysis.

Current CTC detection technologies include CellSearch and the Gilupi Cell Collector. CellSearch is the only FDA approved technology and identifies CTCs from 7.5 mL of blood.² The Gilupi Cell Collector is approved in European and Chinese markets. It is a wire coated with an anti-Epithelial Cell Adhesion Marker (EpCAM) that is inserted in the patients arm for half an hour.³ EpCAM was used to coat the Gilupi Cell Collector because it is a protein found on the surface of epithelial cells that is not found on normal blood cells. CellSearch is limited by the blood volume that can be processed while the Gilupi Cell Collector is limited by its low capture efficiency of 0.0016%.⁴ To overcome these limitations, a microfluidic device was selected for the CTC capture device. Microfluidic devices are small in size and may have increased sensitivity over standard isolation technologies. For this system, the Herringbone Graphene Oxide (^HBGO) device was used. Similarly to the Gilupi Cell Collector, the ^HBGO uses EpCAM to capture the cells of interest on its surface which allows the normal blood cells to be returned to the body. The ^HBGO has a capture efficiency of 80% and can process up to 6 mL of blood an hour.

To be able to process more blood, the ^HBGO was used as the CTC capture device on an ex-dwelling system. The system utilizes a dual lumen catheter to draw and return blood through the same injection site. The blood is pumped through the system using a peristaltic pump. A second pump introduces heparin at the front of the system to prevent the blood from clotting. The blood is flown through the CTC capture device to isolate CTCs based on their EpCAM expression. EpCAM was selected as the capture antibody because it is found on most epithelial cells but not white blood cells. After being flown through the system, all non-captured cells and other blood components are returned to the patient through the dual lumen catheter. A small, lightweight carriage system was designed to hold all the system components such that the system can be worn by the patient; allowing them to have full mobility during the test.⁵

The system was first optimized as a benchtop unit before being placed on investigational canines. All tests were run using fluorescently labeled MCF7 cells, a human breast cancer cell line. To show the ^HBGO device captures the cells as predicted, MCF7s were spiked into canine blood and flown through the device. For the ex vivo experiments, MCF7 cells were injected into a canine and blood was drawn to mimic capturing CTCs ex vivo from a blood draw. Once it was confirmed that the device works in the system, the system was tested on investigational canines. MCF7 cells were injected into the canine then the system captured “CTCs” continuously for a two hour time period. No adverse effects were observed in the canines during the time of the experiment or the following 48 hours.⁵

Because this system has an acceptably high flow rate and high capture efficiency, it has a significantly higher interrogation efficiency, defined as the capture efficiency multiplied by the blood fraction processed, than other systems with available data. A larger interrogation efficiency means that more CTCs will be isolated which increases the number of downstream assays that can be performed as well as the statistical significance of the assays that are currently performed on CTCs.

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2. Circulating Tumor Cell Kit (Epithelial). https://documents.cellsearchctc.com/pdf/e631600001/e631600001_EN.pdf. Accessed April 23, 2018.
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