New Tumor Suppressor Destroys Key Link In Cancer Chain

A tumor-suppressing protein snatches up an important cancer-promoting enzyme and tags it with molecules that condemn it to destruction, a research team led by scientists at The University of Texas M. D. Anderson Cancer Center reports this week in the journal Molecular Cell.

"KEAP1 is a recently discovered tumor suppressor, but how it works has not been known. IKKß is a known oncoprotein that promotes cancer in at least two different ways, but we did not know how it was regulated. We think we've answered both questions with this research," said senior author Mien-Chie Hung, Ph.D., chair and professor of M. D. Anderson's Department of Molecular and Cellular Oncology.

The researchers showed that KEAP1, short for the tongue-twisting Kelch-like ECH-associated protein 1, binds to IKKß and attaches molecules known as ubiquitins to the oncoprotein, which targets it for dissolution by the cell's proteasome complex.

They also showed that underexpression of KEAP1 is associated with poor survival among breast cancer patients, and that it's mutated and inactivated in some breast, liver, lung and colon tumors.

"KEAP1 underexpression or inactivation is involved in multiple cancers, so we are working now to identify its activation mechanism, which could lead to development of new anti-cancer drugs," Hung said. He and his colleagues also want to know whether KEAP1 works on other known oncoproteins.

Blocking overexpression of IKKß, short for IkB kinase ß, is crucial for at least two reasons. Hung and colleagues have shown that the protein inhibits at least two other important tumor suppressors. More importantly, IKKß activates the NF?B (nuclear factor ?b) signaling pathway, which regulates expression of genes involved in the immune response, cellular proliferation, growth of new blood vessels, cell survival, tumor invasion, and the lethal spreading of cancer known as metastasis.

Hung and colleagues first demonstrated that the presence of KEAP1 inhibits the NF?B signaling pathway and then conducted a series of experiments to find out how that happens. They found that depletion of KEAP1 leads to the accumulation of IKKß, and then discovered that the tumor suppressor binds to a specific site on IKKß, capturing it to feed it to the proteasome.

Hung likens this snatching of IKKß to plucking stuffed animals with a mechanical claw out of an arcade game, imagery that wound up on the cover of Molecular Cell.

KEAP1 is a ubiquitin ligase that attaches to the target protein and works in a complex with another protein, CUL3, that connects the ubiquitins to the bound protein.

The team analyzed both KEAP1 and CUL3 expression in the tumors of 119 breast cancer patients and correlated the findings to overall survival. They found that underexpression of KEAP1 alone was associated with poor survival. Patients with strong expression of both KEAP1 and CUL3 had an 80 percent survival rate at five years while those with little expression of either had a 43 percent 5-year survival rate.

Next, they sequenced KEAP1's genes in 26 cancer lines (18 breast, four liver, four lung) and in 119 primary tumors (17 breast, 78 liver, 13 lung, 11 colon) and found two functional genetic mutations that shut down the protein's ability regulate IKKß. The mutations affected the portion of the protein that binds to IKKß.

The research in this paper was funded by grants from the National Cancer Institute, including M. D. Anderson's Specialized Program in Research Excellence (SPORE) grants in breast, pancreatic and ovarian cancers, the Breast Cancer Research Foundation, Kadoorie Charitable Foundations, Patel Memorial Breast Cancer Endowment Fund, the National Breast Cancer Foundation, and by the Taiwan National Science Council.

Hung noted that first author Dung-Fang Lee, Ph.D., led his lab's research on IKKß as a doctoral candidate in The University of Texas Graduate School of Biomedical Sciences at Houston, a joint program of M. D. Anderson and The University of Texas Health Science Center at Houston. Lee received the GSBS Alfred Knudson Jr. Outstanding Dissertation Award when he graduated last year. Lee is now a postdoctoral fellow at Mount Sinai School of Medicine in New York.

Co-authors with Lee and Hung are Hsu-Ping Kuo, Ph.D., Mo Liu, Chao-Kai Chou, Ph.D., Weiya Xia, M.D., Yi Du, Jia Shen, Chun Te Chen, Longfei Huo, Ph.D., Ming-Chuan Hsu, Ph.D., Chia-Wei Li, Ph.D., and Qing-Qing Ding, all of M. D. Anderson's Department of Molecular and Cellular Oncology; Kuo, Liu, Chou, Du, Shen, and Chen are also students in the GSBS. Also, Tsai-Lien Liao, Ann-Chi Lin, Ya-Hui Chang, Shih Feng Tsai, M.D., Ph.D., all of the Division of Molecular and Genomic Science, National Health Research Institutes, Taiwan; Chien-Chen Lai, Ph.D., Division of Molecular and Genomic Medicine, National Health Research Institutes, and the Graduate Institute of Chinese Medical Science, China Medical University, both in Taiwan; and Long-Yuan Li., Ph.D.,Center for Molecular Medicine and Graduate Institute of Cancer Biology, China Medical University and Hospital, and Asia University, both in Taiwan.

---

Adapted from materials provided by University of Texas M. D. Anderson Cancer Center.

How Cancers Spread To The Brain

Breast cancer cells (in green) grow only on blood vessels (red) in the brain of a mouse. (Credit: Copyright Shawn Carbonell)
-----------------------------------------------------------------------------------------------------------------------------------------
Research has shown for the first time how cancers that spread to the brain establish themselves and begin to grow.

The Oxford University study, published in the journal PLoS One, has identified the mechanism that metastatic cancer cells use to anchor themselves to blood vessels in the brain. This could allow new drugs to be developed to stop cancers from spreading and growing in the brain.

Metastasis is the process where cancer breaks out from where a tumour has initially grown and spreads to other parts of the body. It is usually the reason why cancer is fatal.

Brain metastases are the most common malignant tumours of the central nervous system, outnumbering by ten times those that originate in the brain. Once such cancers have reached the brain the prognosis is not good: the median survival is 9 months with maximal treatment. Over 20% of all cancer patients will eventually develop metastatic cancer in the central nervous system.

‘Metastasis to the brain is essentially terminal, and very little is known about the process by which it occurs,’ says Dr W Shawn Carbonell, a post-doctoral research scientist at the MRC/CRUK Gray Institute for Radiation Oncology and Biology at the University of Oxford. ‘But by quickly remedying our lack of knowledge, we hope to be able to come up with new and better ways of treating such cancers.’

The Oxford University team, led by Professor Ruth Muschel at the Gray Institute for Radiation Oncology and Biology with funding from Cancer Research UK, the Medical Research Council and the US National Institutes of Health, set out to answer the question: how do tumour cells grow in the brain. They looked at a comprehensive range of cancer cell types from humans and mice – breast cancer cell lines, melanoma cells and a lymphoma cell line – and examined how the cells establish themselves in the brain in laboratory studies.

The researchers found that the metastatic cancer cells start to grow on the walls of blood vessels in the brain in over 95% of cases, and not on the nerve cells. The researchers suggest that by ‘co-opting’ the vascular networks in the brain, the cancer cells can get all the nutrients and oxygen they need to start growing without having to grow new blood vessels of their own first. In addition the cancer cells require the brain blood vessels to invade into the brain for further cancer growth.

The team also discovered that a particular protein called an integrin on the outside surface of the cancer cells is necessary for them to stick to the blood vessels. Removal of the integrin stopped the cancer cells from attaching and starting to grow. This discovery is promising, as it may be possible to develop drugs to target the integrin and stop brain metastasis.

'Our research describes a novel mechanism which explains how tumour cells metastasize to the brain. The dependency of early brain metastases on the host blood vessels might provide a target for new drug therapies,' says Professor Muschel.

Dr Helen George, Cancer Research UK's head of science information, says: ‘This is an important part of the puzzle. Our research shows that cancer cells which spread to the brain latch on to blood vessels, paving the way for new and much-needed treatments to tackle cancers that have spread to the brain, in the future.’

---

Journal reference:

1. W. Shawn Carbonell1, Olaf Ansorge, Nicola Sibson, Ruth Muschel. The Vascular Basement Membrane as %u201CSoil%u201D in Brain Metastasis. PLoS One, 4(6): e5857 DOI: 10.1371/journal.pone.0005857

Adapted from materials provided by University of Oxford.

Crystal Ball For Brain Cancer? New Method Predicts Which Brain Tumors Will Respond To Drug

Left image: Good prognosis. This brain scan shows the wavy borders of a dying tumor in white at right. Dying cells leak fluid, causing swelling and water movement linked to a good response to Avastin therapy. Right image: Poor prognosis. This brain scan shows the white mass of a solid tumor at left. The lack of water movement in the tumor and surrounding tissue suggests that this tumor would not be a good candidate for treatment by Avastin. (Credit: UCLA/Pope lab)
-----------------------------------------------------------------------------------------------------------------------------------------
UCLA researchers have uncovered a new way to scan brain tumors and predict which ones will be shrunk by the drug Avastin -- before the patient ever starts treatment. By linking high water movement in tumors to positive drug response, the UCLA team predicted with 70 percent accuracy which patients' tumors were the least likely to grow six months after therapy.

Bronnie McNabb, 57, considers himself lucky. When his aggressive brain cancer returned after chemotherapy and radiation, his UCLA doctor prescribed the off-label use of Avastin, a drug shown to quell cancers in the breast, colon and lung.

One month later, McNabb's tumors had shrunk by 95 percent. Subsequent brain scans show no trace of his cancer at all. The former marathon runner, ordained minister and father of two says he hasn't felt this good since his diagnosis last winter.

In welcome news for patients like McNabb, the U.S. Food and Drug Administration approved the use of Avastin last month for the treatment of brain cancer. The powerful drug shrinks tumors by choking off their blood supply. Half of patients don't respond to the therapy, though, exposing them to unnecessary side effects and medication costing up to $10,000 per month.

Now UCLA scientists have uncovered a new way to image tumors and forecast which patients, like McNabb, are most likely to benefit from Avastin before starting a single dose of treatment. The findings are published in this month's issue of the journal Radiology.

"Avastin is an expensive drug, yet only 50 percent of patients with recurring brain cancers respond to it," said lead author Dr. Whitney Pope, assistant professor of radiological sciences at the David Geffen School of Medicine at UCLA. "Until now, there has been no good way to identify these patients in advance. Our work is the first to suggest that we can predict which tumors will respond before the patient ever starts therapy."

Pope and his colleagues focused on glioblastoma, the most common and deadly form of adult brain tumor, striking 12,000 Americans a year. Despite therapy with surgery, radiation and chemotherapy, the average glioblastoma patient lives only 12 to 15 months after diagnosis.

Survival rates drop even lower if the tumor returns. Conventional therapies produce little benefit; only 8 to 15 percent of patients survive without tumor growth six months after treatment.

The UCLA team studied 82 patients who had undergone surgery and radiation therapy to remove glioblastoma. Half of the patients received infusions of Avastin every two weeks. All underwent monthly brain scans by magnetic resonance imaging (MRI) to monitor change.

The researchers analyzed the MRI scans of the patients whose tumors returned. Explaining what the team saw requires an understanding of how the tumor creates an independent blood supply.

Cancer cells secrete a growth factor called VEGF that spurs the growth of new blood vessels to supply the tumor with oxygen and nutrients. Avastin blocks VEGF, essentially starving the tumor to death.

This process launches a chain of events that is detectable by MRI. Oxygen-starved cells produce more VEGF, which causes blood vessels to leak fluids into the tumor and surrounding tissue. This results in swelling, which boosts water's ability to move freely in the tumor and brain tissue. As cells disintegrate, they no longer pose a physical barrier to water movement.

"We theorized that tumors with more water motion would also have higher VEGF levels," explained Pope. "Because Avastin targets VEGF, it made sense that the drug would work better in tumors with high levels of the growth factor."

By measuring the amount of water motion within the tumor, the researchers were able to predict with 70 percent accuracy which patients' tumors would progress within six months and which would not. They detected greater water movement in the tumors of those persons who later responded best to Avastin.

"When we realized that high levels of VEGF are linked to greater cell death and increased water movement, we were able to predict the patients' response to Avastin before they began treatment," explained Pope. "We were correct 70 percent of the time. Previously, identifying which patients would respond was like flipping a coin. This is a huge improvement."

The research finding presents clear clinical benefits to the patient, says Pope. "Knowing this information ahead of time will help doctors personalize therapy for each patient and decrease exposure to side effects," he noted.

Pope and his colleagues plan to confirm their findings in a larger study. The team will also test the new method's ability to identify responsive patients prior to surgical removal of their tumor.

Pope's coauthors included Dr. Timothy Cloughesy, Hyun Kim, Jing Huo, Jeffry Alger, Matthew Brown, David Gjerson, Dr. Victor Sai, Jonathan Young, Leena Tekchandani, Dr. Paul Mischel, Dr. Albert Lai, Dr. Phioanh Nghiemphu, Dr. Syed Rahmanuddin and Dr. Jonathan Goldin. All authors are affiliated with UCLA, which funded the research.

---

Adapted from materials provided by University of California - Los Angeles, via EurekAlert!, a service of AAAS.