Key strategies for circulating tumor cell (CTC) detection and selection

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In the last few years, we have a seen a number of publications showing the great potential that circulating tumor cells (CTCs) have with cancer therapy – and how their use may help benefit cancer patients. The biggest apparent challenge, however, is which technology will be the best one to use for detecting and isolating these highly prized cells. In this blog post, we will introduce the three main strategies used for CTC enrichment.

The first CTC enrichment method that is frequently used for CTC isolation is the immunoaffinity-based strategy. There are two types of approaches within the immunoaffinity-based strategy: 1) positive enrichment, and 2) negative enrichment. Positive enrichment targets tumor-associated antigens, and negative enrichment depletes the hematopoietic cells by targeting CD45.

Both approaches have great advantages. Positive enrichment offers a high level of purity in isolated cells; negative enrichment eliminates bias in the subpopulation isolated since it does not rely on antibody selection.

The second CTC enrichment method uses biophysical properties. This method relies on the physical characteristics of the cell – including size, form and density of the cells. Technologies such as centrifugation or microfiltration have been around for more than 50 years. Even though these technologies are considered to be inexpensive and easy to use, their biggest disadvantage is the relatively low purity levels of the cells isolated. Purity levels can vary anywhere between 1-10%, making these technologies less than ideal when used alone – but more acceptable when used as an initial enrichment step.

And last, but not least, of CTC enrichment methods is direct imaging. Direct imaging may use preenrichment that combines flow cytometry with fluorescence, resulting in improved speed. ImageStream, for example, can analyze 5000 cells/sec – a speed that is five times faster than the speed in previous instruments. Other methods, such as FASTcell, are enrichment-free. FASTcell scans use optical fibers and come with the great advantage of reducing exposure time due to the use of a laser light source and a photomultiplier detector. The disadvantage of these scans, however, is the potential for the high speed imaging to reduce resolution. Lower resolution can worsen accuracy, necessitating the confirmation of cells by microscopy.

Recent advances in the CTC field have seen an explosion of different technologies that help researchers isolate and study important and rare cells. However, only few technologies have used clinical samples to validate their system – highlighting the importance of developing performance metrics to align and compare these different technologies.

 

References

1. Ferreira, M.M., Ramani, V.C. and Jeffrey, S.S. (2016) Circulating tumor cell technologies. Science direct 10, 374–394. (Link)

Myriam Benbrahim joined QIAGEN in 2012 and currently works as a Senior Global Market Manager in Discovery Sciences. She received her Master's degree in cell and molecular biology from Pierre et Marie Curie, Paris 6, and another Master's degree in biotechnology from Paris XI in 2009. Before joining QIAGEN, Myriam worked as an R&D scientist in the pharmaceutical industry and academia, focusing on immunology and infectious disease and as a software specialist for next-generation sequencing in London and Cambridge. Currently, she is involved in managing QIAGEN's assay technology portfolio, specializing in PCR technologies.

Steingrimur Stefansson

Hi Myriam, is QIAGEN looking at other cancer associated cells, such as multinucleated giant cells (Adams et al. PNAS 111.9 (2014): 3514).
And examining the mitotic status of isolated CTCs ( Adams et al. “Mitosis in circulating tumor cells stratifies highly aggressive breast carcinomas.” Breast Cancer Research 18.1 (2016).

Reply
Christine Davis

Hi Steingrimur,

Thanks for the comment! Currently, QIAGEN has not looked into multinucleated giant cells or examined the mitotic status of isolated CTCs. However, this presents an interesting opportunity to investigate in the future. Many recent studies using the AdnaTest have looked at the presence of CTCs throughout treatments, investigated the mutational analysis of CTCs, examined gene expression and considered CTCs as potential biomarkers. You can find a number of publications that look at CTCs here: CTC References.

Best,
Christine Davis

Reply
Steingrimur Stefansson

Hi Christine,
Can you give a link to a QIAGEN instruction manual on how the AdnaTest is to be done from collecting patient samples to PCR analysis.

Reply
Christine Davis

Hi Steingrimur,

No problem, you can find the protocols for sample processing, CTC selection and PCR analysis with the AdnaTest here: http://www.adnagen.com/cfscripts/main_products_englisch.cfm?auswahl=01.20.

For the AdnaTest product information on the QIAGEN site, check out this link: https://www.qiagen.com/us/shop/sample-technologies/tumor-cells-and-exosomes/.

Please let me know if you have any additional questions, and thanks for reading our blog!

Best,
Christine Davis

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