Researchers, inspired by the Labyrinth of Greek mythology, created a new chip etched with fluid channels that send blood samples through a hydrodynamic maze to separate out rare circulating cancer cells into a relatively clean stream for analysis. This chip is currently in use in a breast cancer clinical trial.
Tumor cells isolated from blood samples have the potential to revolutionize cancer treatment by enabling doctors to plan customized treatments, monitor genetic changes, and flag the presence of aggressive cells that are likely to spread cancer. The trouble is circulating cancer cells account for only one in a billion blood cells and there are not good options for accurately capturing cancer stem cells, which are thought to be especially aggressive and drug-resistant.
"You cannot put a box around these cells," said Sunitha Nagrath, University of Michigan associate professor of chemical engineering, who led the development of the chip along with Max Wicha, the Madeline and Sidney Forbes Professor of Oncology at Michigan Medicine.
Cancer stem cells are fluid in gene expression, transitioning from stem-like cells that are good at surviving in the blood to more ordinary cell types that are better at growing and dividing. Conventional cell targets which grab proteins known to be on the cell’s surface do not work well.
"The markers for them are so complex, there is no one marker we could target for all these stages," Nagrath said.
Smaller sorting gets around this problem, but this technique was too imprecise to use on its own until the labyrinth came along. Conventional chips, that have spiral-shaped channels, left each cancer cell contaminated with thousands of other cells, white blood cells in particular.
The labyrinth riffs on the spiral. It sorts the blood’s contents according to the sizes of the cells, with smaller white and red blood cells accumulating in different parts of the fluid channel. There are a few forces at play: on the inside of the curve, eddies push particles away from the wall. The larger cancer cells are pushed a bit harder than the smaller white blood cells. Outside of the curve, smaller particles feel more drawn to the wall.
The innovation of the labyrinth is in its number of corners.
"Bigger cells, like most cancer cells, focus pretty fast due to the curvature. But the smaller the cell is, the longer it takes to get focused," Nagrath said. "The corners produce a mixing action that makes the smaller white blood cells come close to the equilibrium position much faster."
The tortuous route meant that Eric Lin, U-M doctoral student in chemical engineering was able to fit 60 centimeters of the channel on a chip that would only contain 10 centimeters in a spiral layout.
Without the need to wait for cancer cells to bind with traps or markers, the blood flow through the chip was fast. The team can reduce the number of white blood cells contaminating the cancer cell sample by 10 times just by running the captured portion of the blood through a second labyrinth chip. This process only took an extra five minutes.
A thousand white blood cells mixed in with around 9 to 50 tumor cells may seem like a lot, but this level of contamination is manageable in the single cell analysis lab. The team analyzed individual cells to explore which genes were active in the cancer cells.
Through genetic profiling the team could pick out cells that were on their way to and from stem-like states, capturing the spectrum of cancer stem cells. They tested the chip with blood samples from pancreatic and late-stage breast cancer patients.
"We think that this may be a way to monitor patients in clinical trials," Wicha said. "Rather than just counting the cells, by capturing them, we can perform molecular analysis so know what we can target with treatments."
In the clinical trial, the labyrinth chip is isolating cancer cells from the blood of patients with an aggressive form of breast cancer. The trial is investigating whether a treatment blocking an immune signaling molecule called interleukin-6. This helps heal wounds by temporarily activating adult stem cells, and can make progress against cases of breast cancer that don’t respond to standard treatments.
The team suspects that the interleukin-6 is enabling cancer stem cells, so they expect to see the population of stem-like cells in the blood fall during treatment.
A paper on this research was published in Cell Systems.