NEW YORK – Researchers from the University of California, San Diego have developed a microfluidic-based adhesion assay that they hope can be used to risk-stratify breast cancer patients.
Building on nearly a decade of work studying the biology of cell adhesion, the researchers decided to use the assay to determine whether there are differences in adhesion between nonmalignant, nonmetastatic cell lines and malignant and metastatic cell lines, said Adam Engler, a professor of bioengineering at UCSD and one of the test's developers.
The research team discovered that nonmalignant cells "stuck like glue" to their environment and had "very little migration capacity" and "strong adhesion to their extracellular environment," while the metastatic cells did not, Engler said. The researchers' findings were first published in 2017, and a new paper released earlier this month in Cell Reports builds on the earlier work.
In the most recent work, Engler and his colleagues looked at the adhesion of cells in mice and humans and found that in mice, weakly adherent cells form secondary metastases at a "much higher rate" than the strongly adherent cells, Engler said. In addition to the cells' behavior in mice, the researchers also looked at how cells behaved in 16 human patients with normal breast tissue, ductal carcinoma in situ (DCIS), and invasive lobular or ductal carcinoma.
In the mice, adhesion retrospectively predicted metastatic disease with 100 percent specificity, 85 percent sensitivity, and an area under the curve of 0.94, according to the Cell Reports paper.
In human samples, "the overall single-cell population recovered from healthy breast tissue was most strongly adherent, cells from DCIS had intermediate average population adhesion strength, and cells obtained from IDC and ILC tumors were the most weakly adherent across patients," the researchers wrote.
The team's work leverages a microfluidic device with a variable width chamber, or a divergent-wall parallel-plate flow chamber, to analyze cells from resected tumors, Engler said. The device has a wide inlet that tapers inward to the chamber that is coated with adhesive proteins found in breast tissue where the tumor cells are placed and pictures are taken. The team then pumps fluid through the device, causing the cells to detach from the adhesive proteins and allowing the researchers to see whether the cells were classified as weakly adherent or strongly adherent.
The researchers found that there is a correlation between patients that don't have disease and have very sticky cells and patients who have "invasive disease" and have very weakly adherent cells, Engler said.
The microfluidic device the researchers used to determine the adherence of the cells has been patented, and Engler and his colleagues have created a to-be-named startup to license the patent and commercialize the device.
The researchers hope to use the assay for patients with very low-grade tumors whose cells are proliferating but haven't started to disseminate or migrate, because those patients' outcomes can be quite variable, Engler said. "It is hard, given current histological markers … to assess whether a patient with DCIS will eventually develop metastatic disease or not," but hopefully a device like this will give clinicians an additional data point alongside histological analysis to help determine how to best treat their patients, he added.
According to Engler, the test could be used as a screening tool using core needle biopsy samples similar to those that are taken for histological analyses, although clinical use of their technology on human patients could be a ways off.
The team is currently enrolling more DCIS patients to show stronger correlation between patients who have a higher proportion of weakly adherent cells and those who develop metastatic disease. In the Cell Reports paper, the researchers found that DCIS patients have a wide range of adhesion types, so the team plans to follow those patients over the next five years as their disease progresses to determine whether the assay was correct and weakly adherent cells were indicative of metastasis and poorer outcomes.
"When an oncologist orders our test in the future, the outcome of that test could help better decide what the patient's standard of care should be," Engler said. If a patient has DCIS and weakly adherent cells, a clinician may decide to treat the tumor more aggressively.
For now, the utility of the device for detecting cancer in humans is still largely unproven, and additional validation is needed to determine cutoff ranges for what counts as weak adherence versus strong adherence, but the researchers are "hopeful" that additional validation will show clinical utility in humans, Engler said. The startup plans to fund a large clinical trial with hundreds of DCIS patients to more accurately determine the cutoffs and stratify patients by their risk.
The clinical version of the assay would report a number between zero and 1,000 as a result, with the closer a patient is to 1,000 indicating stickier cells. But if a patient has a value near zero, it means the cells aren't adhering to anything and thus won't migrate. There is a "sweet spot" where the most aggressive tumors are located, and the validation trial will help determine the boundaries of that sweet spot, Engler said.
As Engler and his colleagues move toward licensing the patent and commercializing the device, there is still work to be done outside of validation trials. He noted that the device will need to be repackaged into a "more user-friendly interface" so it is easier to use and more automated, although all of the computer coding and microfluidics work for the device has been done.
The device could be applied to more than just breast cancer, Engler added. One of the driving forces behind the original research was the search for a "universal marker" of cancer that was physical in nature rather than biological. The researchers wondered whether "physical markers are going to be universal because the behaviors are universal" in metastatic cancers, he said.
"All of those solid tumors start off as a mass in the host tissue, and then the cells have to disseminate somehow," he noted. "Physical principles could be applied either to the growth of those tumors or to the spread of those tumors."
"As cells migrate out of the tumor, the cells that are leaving the tumor versus the ones that are staying in the tumor have to have some physical difference," Engler added.
The researchers looked at lung and prostate cancer cell lines that were more aggressive to see if they had the same signature as aggressive breast cancer cell lines and found that they did.
"The concept of cell adhesion being really important in the metastatic process at some point" is probably correct "across all solid tumor types," Engler said. One of the graduate students within Engler's laboratory is currently investigating pancreatic cancer cells to determine how universal the concept of cell adhesion and metastases is, he added.