Watching how the cells behave as they divide and invade surrounding tissue will help physicians better understand how human cancers act in the body. The new technique also provides a way to quickly and cheaply test anti-cancer drugs without requiring laboratory animals.
"Studies of this type, which used to take months in animal models, can now occur on a time scale of days," said Paul Khavari, MD, PhD, the Carl J. Herzog Professor and chair of dermatology at Stanford. The researchers focused on epithelial cells, which line the surfaces and cavities of the body. Cancers of epithelial cells make up approximately 90 percent of all human cancers.
The study of three-dimensional tumors also avoids the use of cancer cell lines, which are typically grown in single layers and may have accumulated genetic changes that don't accurately reflect what happens in humans.
Khavari, who is also a member of the Stanford Cancer Center and serves as dermatology service chief at the Veterans Affairs Palo Alto Health Care System, is the senior author of the research, which will be published online Nov. 21 in Nature Medicine. Todd Ridky, MD, PhD, a former postdoctoral scholar in Khavari's laboratory, is the first author. Ridky is now an assistant professor at the University of Pennsylvania.
The researchers worked with normal human epithelial cells gathered from surgical samples from skin, cervix, esophagus and throat. Unlike cancer cell lines, some of which have been grown in laboratories around the world for years, these primary cells were minimally cultured.
To make these normal cells cancerous, the researchers used viruses to tweak just two genetic pathways known to be involved in uncontrolled growth. One drives cells forward in the cell cycle while the other disables an internal checkpoint that normally blocks abnormal proliferation. Many naturally occurring human cancers display identical genetic changes, and the researchers found that simultaneously altering the two pathways is highly effective at transforming normal cells.
Khavari and Ridky then added the altered, pre-cancerous epithelial cells to a tissue culture dish containing other components of human skin. Epithelial cells normally sit on a thin partition called the basement membrane that separates them from a lower layer of skin called the stroma. They found that at first the cells nestled down on the basement membrane and formed what looked like a normal, three-dimensional cross-section of skin. But within about six days, the cells started to behave more ominously — punching through the membrane and invading the stromal tissue below.
"This reflects what we see happening in spontaneous human tumors," said Khavari. "Cells go from a pre-malignant state to invasive cancers, often over the course of years. Only in this intact, human-tissue model it occurs much more quickly." In contrast, unaltered cells remained obediently on their side of the basement membrane.
When the researchers examined the patterns of gene expression in the newly cancerous cells, they found that the patterns closely matched the genetic profiles of spontaneously occurring human cancers. But when the cells were grown in a single layer, without the basement membrane, stroma and normal three-dimensional tissue structure, their gene expression profiles were markedly different.
"This tells us that conclusions drawn from studying cells grown in two-dimensional culture need to be correlated with other findings to help ensure clinical relevance," said Khavari.
The researchers took advantage of their new "tumor-in-a-dish" model to test 20 new experimental anti-cancer drugs. Many of these drugs cannot be easily tested in animals because they are difficult to administer and may be toxic in their current form. But Khavari and Ridky were able to quickly home in on three promising candidates that stopped the altered epithelial cells from invading through the membrane. While the drugs will still have to be optimized for testing in animals, this type of pre-screening allows researchers to narrow down the possibilities.
The three-dimensional culture system also indicated that the stromal cells themselves somehow encourage the invasion of the altered epithelial cells, and that the cells don't need to be dividing wildly in order to be able to invade.
"These things had never been directly tested before in human tissue," said Khavari, who pointed out that the new model still doesn't incorporate many other biological players, such as the immune system and an active metabolism. And yet "now that we can create human tumors from multiple different human tissues, we have a new way to assess what might be going on in spontaneous human tumors."
In addition to Ridky and Khavari, other Stanford researchers involved in the work include research assistant Jennifer Chow and postdoctoral scholar David Wong, MD, PhD. The research was funded by the U.S. Veterans Affairs Department of Research and Development, and the National Institutes of Health.
Information about the Department of Dermatology, which also supported the research, is available at http://derm.stanford.edu.
The Stanford University School of Medicine consistently ranks among the nation's top medical schools, integrating research, medical education, patient care and community service. For more news about the school, please visit http://mednews.stanford.edu. The medical school is part of Stanford Medicine, which includes Stanford Hospital & Clinics and Lucile Packard Children's Hospital. For information about all three, please visit http://stanfordmedicine.org/about/news.html.
Krista Conger | EurekAlert!
Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory
How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy