Focus review 2013: Label free microfluidic technologies for isolation of circulating tumor cells (CTCs)

Label-free isolation of circulating tumor cells in microfluidic devices: Current research and perspectives

This paper is quite comprehensive in covering the many label free approaches to CTC isolation reported so far, including, filters, accoustophoresis, magnetophoresis, etc.

The general recommendation of the paper is towards adoption of these technologies for clinical use.

undoubtedly, there are several advantages to label-free isolation of CTCs, specially filtration techniques, which are simple, inexpensive, fast and easy to use. However, there are some important limitations that need to be considered,  which I was hoping the paper would shed light upon, but didnt.

the general limitations of filtration techniques are listed here.

It was also recently reported that the deformability of tumor initiating cells is less differentiated from normal blood cells. This makes the sized and deformability based techniques vulnerable to missing these important subtypes of CTCs. This is covered here 

Microfluidics separation reveals the stem-cell–like deformability of tumor-initiating cells

Microfluidics separation reveals the stem-cell–like deformability of tumor-initiating cells

Key findings:
Here we report a microfluidics method to enrich physically deformable cells by mechanical manipulation through artificial microbarriers. Driven by hydrodynamic forces, flexible cells or cells with high metastatic propensity change shape to pass through the microbarriers and exit the separation device, whereas stiff cells remain trapped. We demonstrate the separation of (i) a mixture of two breast cancer cell types (MDA-MB-436 and MCF-7) with distinct deformabilities and metastatic potentials, and (ii) a heterogeneous breast cancer cell line (SUM149), into enriched flexible and stiff subpopulations. We show that the flexible phenotype is associated with overexpression of multiple genes involved in cancer cell motility and metastasis, and greater mammosphere formation efficiency. Our observations support the relationship between tumor-initiating capacity and cell deformability, and demonstrate that tumor-initiating cells are less differentiated in terms of cell biomechanics.

Significance: This is a key finding, which raises the following question; are technologies that use size and deformability as a criteria to enrich Circulating Tumor Cells (CTCs) are inherently biased towards missing cells with high metastatic propensity?

Paper Commentary: SSA-MOA: a novel CTC isolation platform using selective size amplification (SSA) and a multi-obstacle architecture (MOA) filter - Lab on a Chip (RSC Publishing)

SSA-MOA: a novel CTC isolation platform using selective size amplification (SSA) and a multi-obstacle architecture (MOA) filter - Lab on a Chip (RSC Publishing)

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Update (10 Feb, 2013): A follow up improvement of this technology has been published here
performance: 95% isolation efficiency, 59% purity from 3 ml of blood (total isolation time ~ 30 mins)
no results from clinical samples were reported.

another recent publication from Samsung in Biomicrofluidics 
an older publication from Samsung advanced Institute of Technology can be found here
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Summary:

This paper presents a novel method of enriching CTCs by combining EpCAM based bead tagging followed by size filtration. The basic premise of this paper is that purely size-based techniques suffer from size overlap between CTCs and WBCs. To overcome this, CTCs are selectively tagged with 3 micron polymer beads to enhance their size, followed by filtration through a lateral filter surface. recoveries of upto 99.1% are reported in spiked cells.

Advantages:

• Results show that the size enhancement seems to work in appropriately discriminating between WBCs and MCF-7 cells

Limitations:

• Fundamentally, this is an antigen dependent technology, hence belongs to positive enrichment family of techniques. Its inherently limited by antigen expression and its variability as well as the efficiency of binding interaction.
• There are other known cancer cell lines which are smaller than the MCF-7 cells, how does this technique work with smaller cancer cells? smaller cells will require larger beads for effective differentiation, however, steric hindrance will become a factor between adjoining binding sites
• silicon manufacturing technology is expensive as it is. it is unclear how expensive is the silicon on glass technology
• throughput is 20ul/min, which is considerably lower than size filtration systems, which have reported as fast as 2 mls in 5 minutes. the overall assay time is also increased due to the need to pre-conjugate beads to cells
• the effect of occupancy of antigen binding sites by microbeads on downstream molecular characterization of tumor cells
• lack of clinical data
• lateral flow filtration is inherently limited by the requirement of scaling for higher throughput versus large area staining and imaging requirement

other considerations:

1. http://www.clearbridgebiomedics.com/ --> has a platform for size and deformability based CTC isolation
2. cell size enhancement product is available here  http://pluriselect.com/home.html, 
3. how is the performance of this paper in comparison to item 2 above, which should be relatively inexpensive and has a higher thorughput