Chipping Away at the Secrets of Cancer Metastasis

Liam Davenport

May 21, 2015

A novel microfluid chip that can capture clusters of circulating tumor cells (CTCs), rather than single cells, potentially offers important insights into the metastatic process, which in turn could lead to faster, more accurate diagnosis of aggressive disease.

CTCs, which are thought to be instrumental in cancer metastasis, typically constitute fewer than one in one billion blood cells, and CTC clusters are even rarer. Their role in the spread of cancer is consequently not well understood.

The new device, termed the Cluster-Chip, was developed by a team from Massachusetts General Hospital (MGH), in Boston. It has identified clusters in more than a third of metastatic cancer patients, revealing that many contain tumor proliferation markers and immune cells.

"The ability to isolate intact clusters will enable us to investigate carefully their role in the metastatic process, and understanding metastasis really is the 'Holy Grail' of cancer research," said senior author Mehmet Toner, PhD, professor of surgery (biomedical engineering) at MGH, in a press release.

The Cluster-Chip device. (Source: BioMEMS Resource Center, Massachusetts General Hospital.)

Dr Toner hopes that the findings will kick-start further interest in studying CTC clusters. "It's like poking a sleeping bear," he added. "It could really awaken the field to go after clusters and to develop even better technologies to understand their biology in cancer metastasis."

The research was published online May 18 in Nature Methods.

The device contains the third generation of microchips that have been developed by MGH to capture CTCs while preserving their molecular information. The first two relied on cell-surface antigens to capture the cells; however, these markers may be lost during the metastatic process.

The current version, which was developed in 2013 and was initially tested in mice, contains a chip that uses an antigen-independent method of capturing the cell clusters.

To do so, it slowly pushes whole-blood samples through rows of microscopic triangle-shaped posts that are arranged so that the blood is funneled between two posts toward the tip of a third.

At the tip, single cells slide on either side and continue to the next tip. CTC clusters, however, remain at the tip, balanced between the forces pulling the cluster on either side.

On initial testing with fluorescent tagged clusters of between two and 30 cells, the team found that 99% of the clusters were composed of at least four cells, 70% were composed of three-cell clusters, and 41% were composed of two-cell clusters, at a flow rate of 2.5 ml/hr.

Crucially, microscopic examination of the clusters revealed that the chip did not affect the integrity of the clusters.

The researchers next compared the efficacy of the two methods currently used to capture cell clusters: a pore-based filter designed to allow only single cells through; and an antibody-based system that attaches to the surface of tumor cells.

The results showed that the novel chip was significantly more effective than both systems. It was 40% to 50% better than the antibody-based system at finding cell clusters that expressed target markers, and 1000% better at capturing those without such markers.

The team then turned their attention to refining the release of the clusters from the current chip. They found that lowering the temperature of the device to 4° C (39° F) allowed the release of 80% of clusters and improved the purity of the material by reducing the capture of white blood cells.

Tests in Metastatic Cancer Patients

Testing the chip in blood samples from 27 breast cancer patients, 20 melanoma patients, and 13 prostate cancer patients, all of whom had metastatic cancer, the team found that 30% to 40% of patients had cell clusters ranging from two to 19 cells in size.

Specifically, clusters were captured in 41% of breast cancer patients, 30% of melanoma patients, and 31% of prostate cancer patients. This suggests that CTC clusters are far more common than previously suspected, and indicates that they may play an important role in cancer metastasis.

Finally, the team characterized the clusters in one breast cancer patient, finding that 53% were positive for the tumor proliferation marker ki67. Tissue-derived macrophages were also identified within the clusters.

Looking ahead, Dr Toner commented: "We now are looking at ways to improve further the release of captured clusters, but we are only at the beginning of our quest to understand the role and biology of CTC clusters."

"Eventually we could develop ways to target clusters therapeutically, as well as use them as a source of diagnostic information," he added.

Could Be Utilized at Point of Care

Roderic I. Pettigrew, PhD, MD, director of the National Institute of Biomedical Imaging and Bioengineering, in Bethesda, Maryland, which funded the study, described the findings as "good news."

Speaking to Medscape Medical News, he said that he believes the chip could be used on a widespread basis, because information gained is very "rich" and because it is sufficiently simple, small, and inexpensive to be widely deployable.

He added: "I think it could be something that's utilized at the point of care and throughout doctors' offices throughout the country."

"It's not at the stage where it can go virtually any place, like low-resource settings, but I think that in the developed world, it could be widely deployed."

Dr Pettigrew noted that the biopharmaceutical company Johnson & Johnson has licensed the technology and is developing it for commercialization. He expects that the chip will soon be seen in clinical trials for the purposes of US Food and Drug Administration approval.

With regard to the identification of immune cells within the clusters, Dr Pettigrew said that the finding was "intriguing," adding: "That raises the question, what role do these immune cells play?"

"Did they get trapped while trying to defend us against the tumors? Or are they participants in the process and facilitators of the spread and aggressiveness process?"

He continued: "There are emerging data that suggest the latter, that they are in some way enabling this process."

Dr Pettigrew concluded: "Capturing these cluster cells gives us an opportunity to study these biologically and figure out what the heck is going on here, what role they play, and how might we intervene."

He asked: "Is there an opportunity to reprogram the immune cells that are a part of this, so as to stimulate them to be more defensive, as opposed to enablers of the tumor virulence and the tumor lethality?"

The work was funded by the National Institute of Biomedical Imaging and Bioengineering, part of the National Institutes of Health. A. Fatih Sarioglu, PhD, and Dr Toner are inventors on a patent Massachusetts General Hospital filed to protect the Cluster-Chip technology.

Nat Methods. Published online May 18, 2015. Abstract

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