Abstract IA21: Enumeration of circulating tumor cells for studying cancer drug sensitivity
Authors: Fan Z. Hugh , Sheng Weian , George Thomas , Liu Chen 
Published: May 2015

More than 90% of cancer deaths result from metastasis, hence understanding of metastasis and detection of cancer before spreading are extremely important. During metastasis, some cancer cells escape from the primary tumor and enter the bloodstream, becoming circulating tumor cells (CTCs). Some of these CTCs acquire the capability to colonize secondary sites to form tumors at other organs. As a result, the number of CTCs could be an indicator of cancer drug sensitivity because an effective therapy would shrink the tumor size and reduce the CTC count.

Enumerating CTCs is technically challenging because CTCs are extremely rare in the bloodstream, typically a few in billions of normal blood cells. To address this, we have developed microfluidic devices that are able to isolate tumor cells efficiently from peripheral blood. The fundamental advantage of a microdevice over a vial or tube is a much shorter diffusion distance before interacting with the capture agents. The reduction in the dimension from millimeters to microns theoretically increases the interaction opportunities by orders of magnitude.

The devices are in the size of a microscope slide. Each device consists of a number of microfabricated hair-thin channels and tens of thousands micropillars, which enhance the probability of their interactions with target cancer cells. Mcromixers have also been integrated in the devices to increase the capture efficiency. We also incorporated gold nanoparticles to enhance the density of capture agents for more interactions with CTCs.

Both aptamers and antibodies have been studied for various cancer cells. We immobilized aptamers onto the surfaces of microchannels and micropillars for isolating leukemia cells. The device geometry and the flow rate have been investigated and optimized by studying their effects on the isolation sensitivity and specificity. The capture efficiency of &gt;95% was obtained at the optimum flow rate. In addition, we have applied the devices for isolating CTCs from peripheral bloods of pancreatic cancer patients while CTCs were verified according to the FDA-approved definition, namely EpCAM+ (epithelial cell adhesion molecule), cytokeratin+, DAPI+ (4,6-diamidino-2- phenylindole), and CD45-. CTCs were found in 94% of clinical samples, and none in the healthy control samples. We also compared the aptamers and antibodies in terms of their capture efficiency, and we studied combining them together for cancer cell isolation.

We investigated the correlation between the CTC number and the clinical result of pancreatic adenocarcinoma patients who went through a clinic trial, in which a colorectal cancer drug cocktail, FOLFOX (5-fluorouracil, leucovorin, oxaliplatin), was combined with a leukemia/prostate cancer drug dasatinib as chemotherapy treatment. For those patients showing the reduction in the tumor size measured by computed tomograms (CT scans) during the course of anti-cancer treatment, we also observed the decrease in the number of CTCs in their peripheral blood samples. The double-blinded experiments show the strong correlation between the CTC number and cancer drug sensitivity.

Citation Format: Z. Hugh Fan, Weian Sheng, Thomas George, Chen Liu. Enumeration of circulating tumor cells for studying cancer drug sensitivity. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr IA21.