Circulating Tumor Cell Isolation and Analysis

Abstract

Isolation and analysis of cancer cells from body fluids have significant implications in diagnosis and therapeutic treatment of cancers. Circulating tumor cells (CTCs) are cancer cells circulating in the peripheral blood or spreading iatrogenically into blood vessels, which is an early step in the cascade of events leading to cancer metastasis. Therefore, CTCs can be used for diagnosing for therapeutic treatment, prognosing a given anticancer intervention, and estimating the risk of metastatic relapse. However, isolation of CTCs is a significant technological challenge due to their rarity and low recovery rate using traditional purification techniques. Recently microfluidic devices represent a promising platform for isolating cancer cells with high efficiency in processing complex cellular fluids, with simplicity, sensitivity, and throughput. This review summarizes recent methods of CTC isolation and analysis, as well as their applications in clinical studies.

Keywords: Biomarkers; Cancer; Circulating tumor cells; Diagnosis; Microfluidics.

Fig. 1

Scheme of capturing cancer cells in a microfluidic device. Avidin is immobilized on the surface of microchannels via physical adsorption, followed by conjugation with biotinylated aptamers through biotin–avidin chemistry. Target cancer cells are then captured via the interaction between the aptamers and the receptors on cell surfaces. W. Sheng, et al., Aptamer-enabled efficient isolation of cancer cells from whole blood using a microfluidic device. Anal. Chem. 84(9) (2012) 4199–4206. Reproduced with a permission of The American Chemical Society.

Fig. 2

(A) Picture of the device. The size of the device is 1 in. ×3 in., the same size of a microscope slide. (B) Image of the geometrically optimized micromixer structures inside microchannels. (C) Scheme of using an ensemble of aptamers and antibodies as capture reagents inside microchannels. W. Sheng, et al., Capture, release and culture of circulating tumor cells from pancreatic cancer patients using an enhanced mixing chip. Lab Chip 14(1) (2014) 89–98; J. Zhang, W. Sheng, Z.H. Fan, An ensemble of aptamers and antibodies for multivalent capture of cancer cells. Chem. Commun. 50(51) (2014) 6722–6725. Reproduced with a permission of The Royal Society of Chemistry.

Fig. 3

Fluorescence microscope images of CTCs captured from patient bloods: (A) a representative image of CTCs, with DAPI+, cytokeratin+, and CD45−; (B) typical image of white blood cells (WBCs), with DAPI+, CK−, and CD45+. Scale bar=10 μm. W. Sheng, et al., Capture, release and culture of circulating tumor cells from pancreatic cancer patients using an enhanced mixing chip. Lab Chip 14(1) (2014) 89–98. Reproduced with a permission of The Royal Society of Chemistry.

Fig. 4

CTC–substrate interaction model. The CTC is modeled as a rigid sphere. Receptors are modeled as strings randomly distributed on the surface of the CTC. Each receptor has a length of r₀, forming a capture zone with a radius of r₀. When ligands, which are modeled as an array of points on the device surface, are located within the capture zone, it is possible that a ligand–receptor is formulated. The ligand–receptor bond is considered as a spring. C.B., Korn, U.S. Schwarz, Dynamic states of cells adhering in shear flow: from slipping to rolling. Phys. Rev. E 77(4) (2008) 041904. Reproduced with a permission of American Physical Society.

Fig. 5

(A–C) The number of CTCs per mL of blood from pancreatic cancer patients at different treatment cycles for three patients: (A) patient #1; (B) patient #2; (C) patient #3. (D and E) CT scan image of patient #3 at (D) the beginning of the treatment (cycle 1); (E) the latter stage of treatment (cycle 11); the red (dark gray in the print version) arrows indicate the regression of the primary pancreatic cancer. Each treatment cycle is 14 days. W. Sheng, et al., Capture, release and culture of circulating tumor cells from pancreatic cancer patients using an enhanced mixing chip. Lab Chip 14(1) (2014) 89–98. Reproduced with a permission of The Royal Society of Chemistry.