Why do normal cells grown in a petri dish

The difference has been so dramatic to Wirtz that when he talks about it, he becomes an evangelist for cell biology in three dimensions. To figure out metastasis, he says, scientists must work in 3-D. And it would be a good idea to take hundreds of drugs that were deemed failures after testing them on cells in a dish and test them again in three dimensions.

Wirtz thinks pharmaceutical companies may have missed medicines that will work because of their reliance on Herr Petri's invention. In journal articles, cancer researchers refer to "the metastatic cascade. At the disease's point of origin, cancer cells proliferate and clump, creating the primary tumor and forming blood vessels to nourish themselves in a process called vascularization. Before long, malignant cells begin to detach from the original tumor and move through the surrounding tissue until they run into a blood vessel.

Able to deform themselves, they squeeze between the endothelial cells that form the blood vessel's wall and enter the bloodstream this is known as intravasation. As the heart pumps the blood, it pumps the cancer cells as well to other parts of the body. The cells tumble and bump into the blood vessel's walls, and when that happens some of them adhere and push between the endothelial cells once again and exit the bloodstream extravasation. Now they are inside a lung, or the liver, or some other organ.

Malignancies constantly shed cells by the millions, and almost all of them die before they can do more harm. But enough survive the rough ride through the blood to lodge somewhere new and begin the explosive proliferation characteristic of cancer.

Crucial to understanding this process is figuring out cell motility—how cells move. For many years now, researchers have studied motility usually by growing cancer cells in a Petri dish and observing how they move about. When cultured on a substrate in a dish, cancer cells typically flatten and move in a slow, seemingly random fashion by pulling themselves along by their leading edges.

They also form strong attachments, called focal adhesions, to the floor of the dish. These adhesions consist of proteins that aggregate on the bottom of the cell. Up to a few years ago, that was the picture scientists had of how cancer cells move.

In , Stephanie Fraley, then a doctoral student in Wirtz's lab, was studying motility, but not in a Petri dish. She had become curious about the possibly distorting effects of the planar environment of the dish. What would happen if she placed cancer cells in something that more resembled human tissue?

From a fibrosarcoma cell line called HT, she took cells and inserted them in a gel prepared from collagen I, the protein that forms most connective tissue in the human body. The gel, formed in a cylindrical well, was only a few millimeters thick, but that was enough to constitute a three-dimensional environment for something as tiny as a cancer cell.

Then Fraley watched what happened. What she saw was startling. For one thing, the cells were no longer flat. They were more spherical, with long protrusions at each end that had not been observed in a dish. The proteins that correlate with the metastatic potential of cancer cells and, in a dish, were located mostly on the bottom of the cell, now were diffuse throughout the cell.

Focal adhesions barely existed. The cells did not crawl along in the laborious, erratic fashion observed in two dimensions, but moved rapidly through the 3-D environment by first extending protrusions fore and aft and anchoring them in the collagen matrix, then contracting like springs and releasing one protrusion to snap the cell in the opposite direction.

Fraley's work suggested that much of how cells behaved in a Petri dish was an artifact of the 2-D environment. The cells moved as they did not because that's how motility works in cancer cells but because the cells were in a dish. Put them in a 3-D environment and everything changed. To Wirtz, the implications were staggering. If cells in a 3-D matrix similar to cancer's actual environment behave so differently from cells grown in a dish, then much of what scientists thought they knew about motility, which is central to metastasis, had to be reconsidered.

For decades, various cell biologists had been thinking about experiments using various extracellular matrices, or ECMs, because cancer cells move through the human body's connective tissue, which is an ECM. As far back as , a paper by three UCSF Medical Center researchers in the journal Cell noted that tumor cells "are more likely to resemble their in vivo counterparts when maintained on an extracellular matrix than on plastic.

Wirtz, too, had been pondering the implications of working in three dimensions. Fraley's results convinced him that 3-D was going to be transformative for cancer research.

You forget that in research sometimes the reason you are doing things [a certain way] is for convenience, not because it faithfully reproduces what we already know from studying cancer in vivo.

Scientists know how to work in a dish. Electron microscopy and other important research tools work well only in a dish. Vital sources of research dollars, like the National Institutes of Health, fund studies of cells in a dish. Pharmaceutical companies have developed sophisticated automated processes that screen cancer drugs by testing them on malignant cells—in a dish.

The Petri dish has influenced the fundamental direction of much cancer research, in Wirtz's view. Because the two-dimensional environment of the dish lends itself much more to studying cancer cells' explosive proliferation than motility, that's what scientists have studied. Wirtz argues that the result has been a diversion from the vital study of how cancer cells migrate.

Roger Kamm, another oft-cited researcher and a professor of biological and mechanical engineering at MIT, says, "I agree, and would go a little further. It's not only migration that matters, but all steps in metastasis: epithelial-mesenchymal transition [vital to enabling cancer cell invasion], intravasation, extravasation. And all of these involve studies that cannot be done by standard cell culture techniques. The bottom line is that we now have excellent methods for controlling primary tumors, but have precious little knowledge about how to prevent cancer cells from spreading to remote sites.

Because we can see it! Because then everyone is happy! Pharmaceutical companies are happy, they're selling stuff. The scientists are happy, they're publishing, they're getting funding. The patients are happy, for a while, until it doesn't work. Wirtz adds, "We've obsessed about proliferation. The first statement in any textbook about cancer is that cancer is a disease of high proliferation.

I say this is completely wrong! Completely wrong! We are discovering that often the very cells that successfully metastasize are those that proliferate the least. We're not trained to think about metastasis because it's harder. We have blinders to the point where we don't even think about blinders. Wirtz is slender, boyish in appearance, bespectacled. When he gets excited, his accented English becomes emphatic and he uses his hands a lot. He has formidable instant command of detail when talking about his work, but says he is entirely reliant on his assistant, Tracy Smith, to keep him on schedule and tell him where he needs to go.

His office and lab are in Croft Hall on the Homewood campus, and one day as he walked to a meeting for which he was already late, he had to ask for directions to Gilman Hall. Teased about this, he held up his hands and said, "I've only been here 18 years! How am I to know? He works in cancer cell biology but is not a biologist. His background is in physics, which he studied as an undergraduate at the Free University of Brussels. He says he picked that course of study because he thought physics afforded the best opportunity for graduate study in California, where he wanted to live for a while.

I had no intent to stay in the U. None of it. His PhD adviser, Gerald Fuller, steered him toward study of the long molecules known as polymers. Looking for polymers to investigate, he veered toward biology. I thought, 'Wow, there are polymers everywhere! I'm going to have a fantastic time! He studied physics at Stanford within the chemical engineering department because the university's physics department was more oriented toward classical physics.

When he found a job at Johns Hopkins, it was in chemical and biomolecular engineering. This provided a path into cancer biophysics and connections to Johns Hopkins oncologists, pathologists, and cancer cell biologists who, he says, put him on to the right questions to ask.

To a biologist, there's beauty in complexity; physicists took a different view, Wirtz says. We hate this diversity of cells. I don't, I love it, but most engineers and physicists tend to be kind of pushed away from it. It's too bad because physicists and engineers are the best trained to handle complexity and extract what really matters. Wirtz looks at cancer metastasis as a mechanistic process involving forces that engineers and physicists are well-equipped to study.

For example, the extracellular matrix that cancer cells inhabit subjects them to confinement forces, especially as the cells proliferate and become more densely packed in the tumor. When cancer cells force their way through the walls of blood vessels to enter the bloodstream, that subjects them to more compression forces, as does the reverse process of the cells pushing out of the blood vessels into other organs or tissues.

During their migration through the circulatory and lymph systems, the cells are subject to shear forces. All of that can be studied as physics and engineering.

Wirtz recalls attending meetings of the American Society for Cell Biology 10 or 15 years ago and finding two or three physicists like himself. Now when he attends he finds several hundred, he says, and more and more biologists who are learning physics. Wirtz Lab currently has a dozen doctoral students and seven postdocs; among them are electrical engineers, biophysicists, biologists, and a physician.

Wirtz has turned the focus of the lab entirely toward the study of cancer cells in 3-D, with what he describes as dramatic results. For example, when a tumor grows in a human body, the tissue around it tends to stiffen. Differences in culture techniques matter in biomedicine, according to a growing body of research.

Studies show sometimes dramatic differences in the shape, function and growth patterns of cells cultured in 2-D compared with cells cultured in 3-D.

For example, a recent Brown study found that nerve cells grown in 3-D environments grew faster, had a more realistic shape and deployed hundreds of different genes compared to cells grown in 2-D environments. Brown Technology Partnerships has filed a patent application based on the technology developed in the Morgan lab and is actively pursuing licensing partners.

Napolitano was lead author of the Tissue Engineering article, and Morgan was senior author. Materials provided by Brown University. Note: Content may be edited for style and length.

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