Circulating Tumor Cells (CTCs)

- Detection and isolation technologies

- During the progression of metastasis, cancer cells detach from the solid primary tumor, enter the blood stream, and travel to different tissues of the body. Breakaway cancer cells in the peripheral blood: Circulating tumor cells (CTCs).

- Extremely rare, comprising as few as one cell per 109 hematologic cells in the blood of patients with metastatic cancer. Tremendous technical challenge.

- A real-time “liquid biopsy” in cancer patients.

Circulating Tumor Cells

Probability of CTC survival

Danila et al. (2007) Clin Cancer Res

Longitudinal correlation of CTCs with disease course

Why study CTCs?

Noninvasive sampling

- Continuous monitoring of patients

- Improving patient compliance

Early detection of cancer

- Metastatic cancer, vascular invasion

Biological insights for cancer

- Understanding of cancer metastasis

Current Methods for CTCs Isolation

Pantel et al., (2010) Trends in Molecular Med

CD45: protein tyrosine phosphatase (PTP) located in hematopoietic cells except ethrocytes and platelets. Leukocyte antigen

Size exclusion methods of CTCs isolation

Zheng et al., (2007) J Chromatography A

- Isolation by size of Epithelial Tumor cells (ISET by ScreenCell):direct enrichment of epithelial cells using filtration and size exclusion, thereby releasing the dependence for detection on the expression of a selected epithelial marker(s) potential to uncover CTC heterogeneity.

- Principles: the majority of leukocytes are the smallest cells in the body and that most flow through the pores whereas larger tumor cells are captured on the membrane or particular channels.

Erythrocyte : 3-5 ㎛Leukocyte : 6-8 ㎛Platelet : 2-3 ㎛Epithelial tumor cells: 10-15 ㎛

Size exclusion methods of CTCs isolation

Mohamed et al., (2009) J Chromatography A

Density gradient isolation of CTCs

- Ficoll (Amersham, Upsala, Sweden), Lymphoprep (Nycomed, Oslo, Norway) or other similar density gradient liquids.

- Whole blood is directly layered on the density gradient. After centrifugation, from bottom to top are found: erythrocytes, neutrophils, mononuclear cells (lymphocytes, monocytes, epithelial cells, tumor cells), and plasma which is the upper layer. Tumor cells can also migrate in the plasma fraction.

Immunomagnetic isolation

CTC

Magnetic particles

(approx. 200nm)

Anti-EpCAM

- The CellSearchTM technology (FDA approved for prognosis in breast, prostate and colorectal cancer) : Ferrofluid consisting of nanoparticles with a magnetic core surrounded by a polymeric layer coated with antibodies targeting epithelial cell adhesion molecule (EpCAM)

- After immunomagnetic capture and enrichment, cells are fixed, permeabilized and labeled with fluorescent probes to identify and enumerate CTCs.

- The standard probe set is comprised of anti-Cytokeratin, (characteristic of epithelial cells), and anti-CD45, allowing negative selection of leukocytes.

Microfluidic isolation: micropost

Shyamala et al 2008, NEJM Nagrath et al 2007, Nature

- The CTC-chip : an array of microposts that are made chemically functional with anti-EpCAM Ab

Microfluidic isolation: herringbone chip

- (C) Herringbone-Chip, and (D) a traditional flat-walled microfluidic device. Flow visualization studies using two paired streams of the same viscosity (one stream is green, the other clear) demonstrate (E) the chaotic microvortices generated by the herringbone grooves, and the lack of mixing in (F) traditional flat-walled devices.

- The HB-Chip design : passive mixing of blood cells through the generation of microvortices significantly increase the interactions between target CTCs and the Ab-coated chip surface.

Scott et al., (2010) PNAS

Nanopillar (fly paper) approach

Wang et al., (2009) Angew. Chem. Int. Ed.

- The use of 3D nanostructured substrates specifically, a silicon-nanopillar (SiNP) array which allows for enhanced local topographic interactions

Micromachine approach

Balasubramanian et al., (2011) Angew. Chem. Int. Ed.

- Microrockets for capture and isolation of cancer cells. - Upon encountering the cells, the anti-CEA mAb-modified microrockets recognize the CEA surface

antigens on the target cancer cells, allowing their selective pickup and transport. - The top-right and bottom-left insets illustrate the preparation of the Ab-modified microrockets

and their functionalization, respectively.

Mei et al., (2008) Advanced Materials

Solovev et al., (2009) Small

Identification of CTCs

- After immunomagnetic capture and enrichment, cells are fixed, permeabilized and labeled with fluorescent probes to identify and enumerate CTCs. The standard probe set is comprised of anti-Cytokeratin, (characteristic of epithelial cells), and anti-CD45 allowing negative selection of leukocytes.

Cancer cell

White blood cell

DAPI Cytoketatin CD45

Analysis of CTCs

Yu et al. (2011) J Cell Biol