Third-generation device significantly improves capture of circulating tumour cells

System rapidly produces purified solution of tumour cells for pathological, molecular analysis

A new system for isolating rare circulating tumour cells (CTCs) shows significant improvement over previously developed devices and does not require prior identification of tumour-specific target molecules. Developed at the Massachusetts General Hospital (MGH) Centre for Engineering in Medicine and the MGH Cancer Centre, the device rapidly delivers a population of unlabelled tumour cells that can be analysed with both standard clinical diagnostic cytopathology and advanced genetic and molecular technology. The MGH team's report has been published in Science Translational Medicine.

This new technology allows following how cancer cells change through the process of metastasis, according to Mehmet Toner, PhD, director of the BioMicroElectroMechanical Systems Resource Centre in the MGH Centre for Engineering in Medicine and the Benedict Professor of Surgery at Harvard Medical School, the paper's senior author.

Cancer loses many of its tissue characteristics during metastasis

The new device – called the CTC-iChip – is the third microchip-based device for capturing CTCs developed at the MGH Centre for Engineering in Medicine. The first two systems relied on prior knowledge of a tumour-specific surface marker in order to sort CTCs from whole blood and required significant adjustment for each different type of cancer. The systems also required four to five hours to process a single blood sample.

The only USA Food and Drug Administration-cleared, commercially available device for capturing and enumerating CTCs – the CELLSEARCH® system developed by Veridex, LLC – relies on magnetic nanoparticles that bind to the same epithelial protein used in the MGH-developed microchip-based devices and cannot always find CTCs present at very low numbers. In January 2011 the MGH entered into a collaborative agreement with Veridex and its affiliate Janssen Research & Development, LLC, to establish a centre of excellence in research on CTC technologies.

Combining elements of both approaches – magnetic labelling of target cells and microfluidic sorting – the CTC-iChip works by putting a blood sample through three stages. The first removes from the sample, on the basis of cell size, all blood components except for CTCs and white blood cells. The second step uses a microfluidic process developed at the MGH to align the cells in a single file, allowing for extremely precise and rapid sorting. In the third stage, magnetically labelled target cells – either CTCs tagged via the epithelial marker or white blood cells tagged on known blood-cell antigens – are sorted out. Tagging white blood cells instead of CTCs leaves behind a population of unlabelled and unaltered tumour cells and doesn't rely on the presence of the epithelial marker or other known tumour antigens on the cell surface.

The new system was able to process blood samples at the extremely rapid rate of 10 million cells per second, handling a tube of blood in less than an hour. Both the mode of sorting out tagged CTCs, called tumour-antigen-dependent, and the technique that depletes white blood cells, called tumour-antigen-independent, recovered more than 80% of tumour cells from different types of cancer that had been added to blood samples. Comparison of the antigen-dependent-mode CTC-iChip with existing commercial technology for processing blood samples from patients with prostate, breast, pancreatic, colorectal and lung cancer showed the CTC-iChip to be more sensitive at detecting low levels of CTCs.

In the antigen-independent mode, the CTC-iChip successfully identified CTCs from several types of cancers that had lost or never had the epithelial marker, including triple-negative breast cancer and melanoma. CTCs isolated through this mode were put through standard cytopathological analysis, which revealed structural similarities to the original tumour, and detailed molecular genotyping of CTCs from a single patient found significant differences in gene expression patterns among individual CTCs.

According to Ravi Kapur, PhD, of the Centre for Engineering in Medicine, leader of the innovation team within the MGH Circulating Tumour Cell Centre the CTC-iChip provides a first-in-class device for high-efficiency, high-speed tumour cell sorting from a clinically relevant blood volume. The chip is designed for mass manufacturing, and simple automation for clinical translation. The team is working with collaborators at Veridex and Janssen to refine the system for commercial development.

Study co-author Daniel Haber, MD, PhD, director of the MGH Cancer Centre and Isselbacher/Schwartz Professor of Oncology at Harvard Medical School believes this new approach is likely to be a game changer in the field. Support for this work comes from Veridex, a subsidiary of Johnson & Johnson, a "dream team" award from Stand Up to Cancer, and grants from the USA National Institutes of Health and other funders. The MGH has applied for a patent on the CTC-iChip technology

Caption for image: Antigen-independent cell sorting begins by tagging the white cells in a blood sample with magnetic beads. The sample is then passed into the CTC-iChip microfluidic system, which first removes red cells, plasma and free magnetic beads and then sorts out tagged white blood cells, leaving a purified solution of circulating tumour cells.
Credit for image: Emre Ozkumur, Massachusetts General Hospital Centre for Engineering in Medicine