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Analytical Chemistry

Chip Scales Up Studies Of Cancer Cell Metastasis

Bioanalytics: A high-throughput automated assay mimics cancer cell invasion in three dimensions

by Louisa Dalton
November 3, 2014

UPWARD BOUND
Schematic of 3-D high-throughput cancer cell migration assay.
Credit: J. Am. Chem. Soc.
In a new microassay for analyzing cell migration, researchers first load cells into 200-μm wells (far left) then add collagen gel (pink). Wells are topped with more gel containing a nutrient (red). The nutrient diffuses down, mimicking diffusion from a blood vessel and attracting invasive cancer cells (blue) to migrate upward (far right). Noncancerous cells (orange) stay put.

If scientists could figure out how to prevent cancer from metastasizing, or spreading from one part of the body to another, cancer survival rates would soar. Now, a Texas research group has introduced a tool to pick up the pace of metastasis research: a three-dimensional high-throughput assay that mimics cancer cell invasion, automatically tracking cell movements in 4,000 microwells at a time (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja5072114).

When cancer cells metastasize from a tumor, their first step is to move toward and invade a blood vessel. Many laboratories use 2-D migration assays to study a cancer cell’s inclination to invade. In the body, however, cancer cells don’t slide along a flat petri dish; they move in a 3-D environment. Current 3-D cell invasion assays, which follow the movement of a cancer cell through a porous gel, can replicate the invasion process but are “quite cumbersome and very low throughput,” says Alan Wells of the University of Pittsburgh, who was not involved with the research.

INVASION IN 3-D
[+]Enlarge
Credit: J. Am. Chem. Soc.
A microassay for cancer cell invasion consists of a chip containing 4,000 gel-filled microwells.
Micrograph of gel-filled microwells of a 3-D high-throughput assay for cancer cell invasion.
Credit: J. Am. Chem. Soc.
A microassay for cancer cell invasion consists of a chip containing 4,000 gel-filled microwells.

Lidong Qin of Houston Methodist Research Institute and his group, with their expertise in microfluidics and nanotechnology, set out to streamline the 3-D assay for high-throughput experiments.

To scale up, Qin first miniaturized. He shrunk each well down to nanoliter-size, making it feasible to study even one cell at a time. He manufactured 40 100-well grids on a poly(dimethylsiloxane) plate. After adding cells to the wells, he covered them with collagen gel and then a layer of nutrients. As the nutrients diffused through the gel toward the cells, they created a gradient, mimicking the body’s increasing nutrient concentration close to a blood vessel.

An automated fluorescence microscope took pictures of each well at various depths over time. This captured images of invasive cancer cells as they rose toward the highest nutrient concentration.

Qin and his group tested the assay by comparing the movement of noninvasive breast cancer cells to that of metastatic, or highly invasive, cells. After 48 hours, 20% of the metastatic cells migrated to the top nutrient layer compared with only 5% of the noninvasive cancer cells. Throughout the assay, Qin was able to closely observe how the cells changed shape and moved. Because the shifting form of a traveling cell gives clues about the different biochemical pathways involved, the assay can help discern the mechanisms behind cancer cell movement.

With this high-throughput approach, Wells says, a researcher can test whole libraries of inhibiting molecules, genetic knock-out cell lines, or different cell densities and conditions at once. It opens up the possibility of “going into discovery science mode” and finding novel pathways involved in metastasis.

Wells says the new assay offers a number of benefits for metastasis research, including the ability to do automated tracking of cells, to visualize them at various depths, and to analyze a single cell or groups of cells. “Putting it all together is a nice big step forward,” he says.

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