Studying Cell Behaviour in 3-D Identifies New Cancer Targets

"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 behaviour we've seen in conventional flat lab dishes. It's both qualitatively and quantitatively different."

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One implication of this discovery is that the results produced by a common high-speed method of screening drugs to prevent cell migration on flat substrates are, at best, misleading, said Wirtz.

This is important because cell movement is related to the spread of cancer, Wirtz said.

He said: "Our study identified possible targets to dramatically slow down cell invasion in a three-dimensional matrix."

When cells are grown in two dimensions, Wirtz said, certain proteins help to form long-lived attachments called focal adhesions on 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.

Wirtz said: "In 3-D, the shape is completely different. 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 in Chemical and Biomolecular Engineering, said 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.

She said: "It is much more difficult to do 3-D cell culture than it is to do 2-D cell culture. Typically, any kind of drug study that you do is conducted in 2D 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."

Fraley's faculty supervisor, Wirtz, suggested that part of the reason for the disconnect could be that even in studies that are called 3-D, the top of the cells are still located above the matrix. e said: "Most of the work has been for cells only partially embedded in a matrix, which we call 2.5-D. Our paper shows the fundamental difference between 3-D and 2.5-D: Focal adhesions disappear, and the role of focal adhesion proteins in regulating cell motility becomes different."

Wirtz added that "because loss of adhesion and enhanced cell movement are hallmarks of cancer," his team's findings should radically alter the way cells are cultured for drug studies.

For example, the team found that in a 3-D environment, cells possessing the protein zyxin would move in a random way, exploring their local environment. But when the gene for zyxin was disabled, the cells travelled in a rapid and persistent, almost one-dimensional pathway far from their place of origin.

Fraley said such cells might even travel back down the same pathways they had already explored. "It turns out that zyxin is misregulated in many cancers," Fraley said. Therefore, she added, an understanding of the function of proteins like zyxin in a 3-D cell culture is critical to understanding how cancer spreads, or metastasizes. "Of course tumour growth is important, but what kills most cancer patients is metastasis," she said.

Cells moving in 3-D environments, however, only make brief contacts with the network of collagen fibres surrounding them-contacts too small to see and too short-lived to even measure, the researchers observed.

Wirtz said: "We think the same focal adhesion proteins identified in 2-D situations play a role in 3-D motility, but their role in 3-D is completely different and unknown. There is more we need to discover."

Source: ANI