Study helps resolve debate about how tumors spread

November 29, 2012

A team of scientists, led by researchers at the University of California, San Diego School of Medicine, has shown for the first time how cancer cells control the ON/OFF switch of a program used by developing embryos to effectively metastasize in vivo, breaking free and spreading to other parts of the body, where they can proliferate and grow into secondary tumors.

The findings are published in the December 11 issue of the journal Cancer Cell.

In 90 percent of cancer deaths, it is the spreading of cancer, known as metastasis, which ultimately kills the patient by impacting ever-more tissues and functions until the body fails. Ten years ago, a French cancer researcher named Jean Paul Thiery hypothesized that tumor cells metastasized by exploiting a developmental process known as epithelial-to-mesenchymal transition or EMT.

EMT is seen in developing embryos whose cells transform from stationary epithelial cells into more mobile mesenchymal cells, the latter able to migrate to new locations and create new types of tissue and organs. Thiery proposed that cancer cells also switch "ON" EMT, temporarily changing attributes so that they can detach from primary tumors, enter the bloodstream and seed new tumors elsewhere. After arriving at a new location, the cancer cells then turn "OFF" the EMT program and grow into carcinoma metastases or tumors.

Thiery's hypothesis was controversial because researchers haven't been able to find supporting evidential proof in vivo. "Although this model was proposed in 2002, there have been no experiments done to attest to it in a spontaneous tumor model," said Jing Yang, PhD, associate professor of pharmacology and pediatrics and senior author of the Cancer Cell paper. "Our new study provides an in vivo demonstration of the reversible EMT in metastasis and helps to resolve the controversy on this leading theory in metastasis."

Using a mouse squamous cell carcinoma model, Jeff Tsai, PhD, a postdoctoral fellow in Yang's lab and first author of the study, with help from collaborators at the Whitehead Institute for Biomedical Research in Cambridge, MA and The Sanford-Burnham Medical Research Institute in La Jolla, showed that activation of an EMT-inducing gene called Twist1 is sufficient to turn "ON" the EMT switch and promote carcinoma cells to disseminate into blood circulation. Equally importantly, the researchers found that turning "OFF" the EMT switch at distant sites is essential for disseminated tumor cells to proliferate and form metastases. Their findings indicate that reversible EMT likely represents a key driving force in human carcinoma metastasis.

"There are many similarities between developmental EMT and EMT in metastasis," Yang said. "Both processes seem to use the same cellular machineries and signaling pathways to activate the EMT program. During embryogenesis, the EMT program tends to be more permanent and epithelial cells commit to a mesenchymal fate. Our study shows that carcinoma cells need a reversible EMT to achieve efficient metastasis. It suggests that EMT reversion could be a critical step to wake up tumor cells from dormancy, a phenomenon in which cancer patients develop metastasis years after the initial primary tumor diagnosis and removal."

It's not entirely known how Twist1 becomes active in primary tumors, though previous studies have pointed to factors like hypoxia and inflammation in the tumor microenvironment. Researchers do not know exactly how Twist1 is "turned off at distant organs." Yang said these are subjects of current experiments.

More broadly, the published findings suggest that more research is needed to determine how to target EMT to combat cancer metastasis. Several pharmaceuticals and research institutes are already pursuing EMT inhibitors as possible cancer treatments.

"Since reversion of EMT promotes colonization and growth of metastases, this study actually cautions that therapies inhibiting EMT could be counterproductive in preventing distant metastases when patients already present circulating tumor cells. Instead, blocking EMT reversion may prevent dormant tumor cells from establishing metastases."
-end-
Co-authors of the paper include Sandra Chau, Department of Pharmacology, UCSD School of Medicine; Joana Liu Donaher, Whitehead Institute for Biomedical Research; and Danielle A. Murphy, The Sanford-Burnham Medical Research Institute.

Funding came, in part, from the American Cancer Society, the National Institutes of Health, the Sidney Kimmel Foundation for Cancer Research, California Breast Cancer Research program, University of California Cancer Research Coordinating Committee, UCSD Cancer Center Training Program in Drug Development and UCSD Cancer Center Specialized Support Grant.

University of California - San Diego

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.