JOHNS HOPKINS (US)—Observing cells in a 3-D environment yields more accurate information about how they move—information that could help develop more effective drugs to prevent cancer’s spread—researchers report in Nature Cell Biology.
“Finding out how cells move and stick to surfaces is critical to our understanding of cancer and other diseases. But most of what we know about these behaviors has been learned in the 2-D environment of Petri dishes,” says Denis Wirtz, principal investigator of the study and a professor of chemical and biomolecular engineering at Johns Hopkins University.
“Our study demonstrates for the first time that the way cells move inside a three-dimensional environment, such as the human body, is fundamentally different from the behavior we’ve seen in conventional flat lab dishes. It’s both qualitatively and quantitatively different.”
One implication of this discovery is that a common high-speed 2-D method of screening drugs to prevent cell migration produces results that are, at best, misleading, says Wirtz. This is important because cell movement spreads cancer, he adds.
“Our study identified possible targets to dramatically slow down cell invasion in a three-dimensional matrix,” he says.
When cells are grown in a flat dish, Wirtz says, certain proteins help to form attachments called focal adhesions on the dish’s surfaces. Under these 2-D conditions, these adhesions can last several seconds to several minutes. The cell also develops a broad, fan-shaped protrusion called a lamella along its leading edges, which helps move it forward.
“In 3-D, the shape is completely different,” Wirtz says. “It is more spindlelike with two pointed protrusions at opposite ends. Focal adhesions, if they exist at all, are so tiny and so short-lived they cannot be resolved with microscopy.”
The study’s lead author, Stephanie Fraley, a Johns Hopkins doctoral student, says that the shape and mode of movement for cells in 2-D are merely an “artifact of their environment,” which could produce misleading results when testing the effect of different drugs.
“It is much more difficult to do 3-D cell culture than it is to do 2-D cell culture,” Fraley says. “Typically, any kind of drug study that you do is conducted in 2-D cell cultures before it is carried over into animal models. Sometimes, drug study results don’t resemble the outcomes of clinical studies. This may be one of the keys to understanding why things don’t always match up.”
To study cells in 3-D, the team coated a glass slide with layers of collagen-enriched gel several millimeters thick. Collagen, the most abundant protein in the body, forms a network in the gel of cross-linked fibers similar to the natural extracellular matrix scaffold upon which cells grow in the body.
The researchers then mixed cells into the gel before it set. Next, they used an inverted confocal microscope to view the cells traveling within the gel matrix. The displacement of tiny beads embedded in the gel was used to show movement of the collagen fibers as the cells extended protrusions in both directions and then pulled inward before releasing one fiber and propelling themselves forward.
Fraley compared the movement of the cells to a person trying to maneuver through an obstacle course crisscrossed with bungee cords. “Cells move by extending one protrusion forward and another backward, contracting inward, and then releasing one of the contacts before releasing the other,” she explains. Ultimately, the cell moves in the direction of the contact released last.
When a cell moves along on a 2-D surface, the underside of the cell is in constant contact with a surface, where it can form many large and long-lasting focal adhesions. Cells moving in 3-D environments, however, only make brief contacts with the network of collagen fibers surrounding them—contacts too small to see and too short-lived to even measure, the researchers observed.
Researchers from Johns Hopkins University and Washington University in St. Louis collaborated on the work, which was funded by the National Cancer Institute.
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