New model unlocks clues to treating deadly childhood cancer

CIRM-funded research at Sanford Burnham Prebys Medical Discovery Institute in San Diego is identifying compounds that could be used to help children battling a deadly brain cancer.

The cancer is choroid plexus carcinoma (CPC), a rare brain tumor that occurs mainly in children. As it grows the tumor can affect nearby parts of the brain resulting in nausea, vomiting and headaches.

Treatment involves surgery to remove the tumor followed by chemotherapy and radiation. However, many of the children are too young to undergo radiation and only around 40 percent are still alive five years after being diagnosed. Even those who do survive often experience life-long consequences such as developmental disabilities.

One obstacle to developing better therapies has been the lack of a good animal model to enhance our understanding of the disease. That’s where this later research, published in the journal Cancer Research, comes in.

The team at Sanford Burnham developed a new mouse model, by knocking out p53, a gene known to suppress tumor formation, and activating a gene called Myc, which is known to cause cancer.  

Robert Wechsler-Reya

In a news release, Robert Wechsler-Reya, the senior author of the paper, says this new model mirrors the way CPC grows and develops in humans.

“This model is a valuable tool that will increase our understanding of the biology of the cancer and allow us to identify and test novel approaches to therapy. This advance brings us one step closer to a future where every child survives—and thrives—after diagnosis with CPC.”

As proof of that the team tested nearly 8,000 compounds against the mouse tumor cells, to see if they could help stop or slow the progression of the disease. They identified three that showed potential of not just stopping the cancer, but of also not harming healthy surrounding cells.

“These compounds are promising, much-needed leads in the quest for an effective CPC treatment,” says Wechsler-Reya. “Our laboratory plans to evaluate these and additional compounds that can effectively treat this cancer.”

Achilles’ Heel of Brain Cancer Identified in Tumor Stem Cells

Few words strike me with more dread than glioblastoma, the name for a very aggressive, incurable cancer of the brain. Although surgery and chemotherapy can help hold off or reverse a glioblastoma’s growth for a while, almost inevitably the tumor comes back along with a terrible prognosis: an average survival time of 12 to 15 months after diagnosis with a less than 5% survival rate beyond five years.

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MRI scans of glioblastoma in the brain of a 15 year-old boy.
Image: Wikipedia

Brain tumor stem cells (BTSCs) are thought to be the culprits behind the cancer’s reoccurrence because of their stem cell-like ability for limitless self-renewal. So the idea is that even a tiny number of BTSCs left behind after treatment will likely to lead to a tumor regrowth and treatment relapse. If researchers can better understand what makes the BTSCs tick, they could find ways to eliminate them and cure this dreadful disease.

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Brain tumor stem cells (BTSCs).
Image: Takrima Haque / Arezu Jahani-Asl Laboratory

This week researchers largely from The Ottawa Hospital Research Institute report on the identification of a key piece of BTSCs’ molecular machinery that provides a promising target for novel glioblastoma treatments. The study, published in Nature Neuroscience, focuses on the epidermal growth factor (EGF) cell signaling pathway. In normal cells, the EGF protein binds to the EGF receptor (EGFR) on a cell’s surface which triggers a cascade of protein interactions inside the cell that stimulate cell growth among other things.

EGFRvIII: a cancer stem cell gas pedal stuck to the floorboard
Eventually a given EGF signaling event subsides. But many BTSCs found in glioblastoma tissue samples have a mutant form of EGFR, called EGFRvIII, that permanently switches this signaling pathway into the “on position” even in the absence of EGF. It’s like the gas pedal of a car that gets stuck to the floorboard, causing the car to dangerously accelerate even though no one is pressing on the accelerator.

Previous studies had shown this always-on EGFRvIII growth signal causes abnormally high activation of a messenger protein, STAT3, which in turn hyper stimulates a network of genes that leads to cancerous growth of the tumor stem cells. But it wasn’t clear exactly how this protein carries out the uncontrolled cell division. Through a detailed genetic analysis of BTSCs from several glioblastoma patient samples, the team zeroed in on the oncostatin M receptor (OSMR) as a critical player. This analysis revealed that STAT3 was a natural activator of the OSMR gene and that high levels of both proteins in patient samples correlated to a poorer prognosis.

No OSMR = no tumors
To investigate further, human BTSCs genetically engineered to lack OSMR were injected under the skin of mice and showed an 80% reduction in tumor formation. Injection of similar cells directly into the brains of mice found no tumor formation when OSMR was absent. In an interview posted by Genetic Engineering News, senior author Michael Rudnicki recalled his team’s reaction to this finding:

“Being able to stop tumor formation entirely was a dramatic and stunning result. It means that this protein is a key piece of the puzzle, and could be a possible target for future treatments.”

Three proteins form a vicious cycle toward cancerous growth
Additional experiments testing the interactions between EGFRvIII, STAT3 and OSMR point out where those future treatments should act. Like the screeching audio feedback you hear when a microphone is held too close to a speaker, the team showed these three proteins create a self amplifying signal. In the tumor stem cells, EGFRvIII comes in direct physical contact with OSMR and together these two proteins act as co-receptors to activate STAT3 which, in turn, stimulates the production of OSMR which, in turn, stimulates even more STAT3 production. And so on and so on.

Co-senior author, Azad Bonni, explained how they intend to break up this vicious cycle while also acknowledging these are very early days for developing a treatment:

“The next step is to find small molecules or antibodies that can shut down the protein OSMR or stop it from interacting with EGFR. But any human treatment targeting this protein is years away.”

Watch this video to hear from the study’s first author, Arezu Jahani-Asl, now an assistant professor at McGill university:

 

Scientists use human stem cell models to target deadly brain cancer

Malignant brain cancer is a devastating disease and it’s estimated that more than 16,000 patients will die of it this year. One of the most aggressive forms of brain cancer is gliomas, which originate from the support cells in the brain or spine that keep nerve cells happy and functioning. Unfortunately, there is no cure for gliomas and common treatments involving surgery, radiation and chemotherapy are not effective in fully eradicating these tumors.

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Brain CT scan of human glioma.

In hopes of finding a cure, scientists have turned to animal models and human cell models derived from tumor biopsies or fetal tissue, to gain understanding of how gliomas form and what makes these type of tumors so deadly and resistant to normal cancer treatments.  These models have their limitations, and scientists continue to develop more relevant models in hopes of identifying new potential treatments for brain cancer.

Speaking of which, a CIRM-funded research team from the Salk Institute recently reported a new human stem cell-based model for studying gliomas in Nature Communications. The team figured out how to transform human induced pluripotent stem cells (iPS cells) into glioma tumor-initiating cells (GTICs) that they used to model how gliomas develop and to screen for drugs that specifically target this deadly form of cancer.

Making the Model

One theory for how gliomas form is that neural progenitor cells (brain stem cells) can transform and take on new properties that turn them into glioma tumor-initiating cells or GTICs, which are a subpopulation of cancer stem cells that are really good at staying alive and reproducing themselves into nasty tumors.

The Salk team created a stem cell model for glioma by generating GTICs in a dish from human iPS cells. They genetically manipulated brain progenitor cells (which they called induced neural progenitor cells or iNPCs) derived from human iPS cells to look and behave like GTICs. Building off of previous studies reporting that a majority of human gliomas have genetic mutations in the p53 and Src-family kinase (SFK) genes, they developed different iNPC lines that either turned off expression of p53, a potent tumor suppressor, or that ramped up expression of SFKs, whose abnormal expression are associated with tumor expansion.

The team then compared the transformed iNPC lines to primary GTICs isolated from human glioma tissue. They found that the transformed iNPCs shared many similar characteristics to primary GTICs including the surface markers they expressed, the genes they expressed, and their metabolic profiles.

Their final test of their stem cell model determined whether transformed iNPCs could make gliomas in an animal model. They transplanted normal and transformed iNPC lines into the brains of mice and saw aggressive tumors develop only in mice that received transformed cells. When they dissected the gliomas, they found a mixture of GTICs, more mature brain cells produced from GTICs, and areas of dead cells. This cellular makeup was very similar to that of advanced grade IV primary glioblastomas.

Screening for drugs that target glioma initiating cells

Now comes the applied part of this study. After developing a new and relevant stem cell model for glioma, the team screened their transformed iNPC lines with a panel of 101 FDA-approved anti-cancer drugs to see if any of them were effective at stopping the growth and expansion of GTICs. They identified three compounds that were able to target and kill both transformed iNPCs and primary GTICs in a dish. They also tested these compounds on living brain slices that were injected with GTICs to form tumors and saw that the drugs worked well at reducing tumor size.

The authors concluded that their transformed iNPCs are appropriate for modeling certain features of how GTICs develop into adult gliomas. Their hope is that this model will be useful for developing new targeted therapies for aggressive forms of brain cancer.

“Our results highlight the potential of hiPSCs for studying human tumourigenesis. Similar to conventional disease modeling strategies based on the use of hiPSCs, the establishment of hiPSC cancer models might facilitate the future development of novel therapeutics.”


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Brain’s Own Activity Can Fuel Growth of Deadly Brain Tumors, CIRM-Funded Study Finds

Not all brain tumors are created equal—some are far more deadly than others. Among the most deadly is a type of tumor called high-grade glioma or HGG. Most distressingly, HGG’s are the leading cause of brain tumor death in both children and adults. And despite extraordinary progress in cancer research as a whole, survival rates for those diagnosed with an HGG have yet to improve.

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But recent research from Stanford University scientists could one day help move the needle—and give renewed hope to the patients and their families affected by this devastating disease.

The study, published today in the journal Cell, found that one key driver for HGG’s deadly diagnosis is that the tumor can be stimulated to grow by the brain’s own neural activity—specifically the nerve activity in the brain’s cerebral cortex.

Michelle Monje, senior author of the study that was funded in part by two grants from CIRM, was initially surprised by these results, as they run counter to how most types of tumors grow. As she explained in today’s press release:

“We don’t think about bile production promoting liver cancer growth, or breathing promoting the growth of lung cancer. But we’ve shown that brain function is driving these brain cancers.”
 


By analyzing tumor cells extracted from HGG patients, and engrafting it onto mouse models in the lab, the researchers were able to pinpoint how the brain’s own activity was driving tumor growth.

The culprit: a protein called neuroligin-3 that appeared to be calling the shots. There are four distinct types of HGGs that affect the brain in vastly different ways—and have vastly different molecular and genetic characteristics. Interestingly, says Monje, neuroligin-3 played the same role in all of them.

What was so disturbing to the research team, says Monje, is that neuroligin-3 is an essential protein for overall brain development. Specifically, it helps maintain healthy growth and repair of brain tissue over time. In order to grow, HGG tumors hijack this critical protein.

The research team came to this conclusion after a series of experiments that delved deep into the molecular mechanisms that guide both brain activity and brain tumor development. They first employed a technique called optogenetics, whereby scientists use genetic manipulation to insert light-sensitive proteins into the brain cells, or neurons, of interest. This allowed scientists to activate these neurons—or deactivate them—at the ‘flick of a switch.’

When applying this technique to the tumor-engrafted mouse models, the team could then see that tumors grew significantly better when the neurons were switched on. The next step was to narrow it down to why. Additional biochemical analyses and testing on the mouse models confirmed that neuroligin-3 was being hijacked by the tumor to spur growth.

And when they dug deeper into the connection between neuroligin-3 and cancer, they found something even more disturbing. A detailed look at the Cancer Genome Atlas (a large public database of the genetics of human cancers), they found that HGG patients with higher levels of neuroligin-3 in their brain had shorter survival rates than those with lower levels of the same protein.

These results, while highlighting the particularly nefarious nature of this class of brain tumors, also presents enormous opportunity for researchers. Specifically, Monje hopes her team and others can find a way to block or nullify the presence of neuroligin-3 in the regions surrounding the tumor, creating a kind of barrier that can keep the size of the tumor in check. 


Scientists Develop Stem Cell ‘Special Forces’ in order to Target, Destroy Brain Tumors

Curing someone of cancer is, in theory, a piece of cake: all you have to do is kill the cancer cells while leaving the healthy cells intact.

But in practice, this solution is far more difficult. In fact, it remains one of the great unsolved problems in modern oncology: how do you find, target and destroy each individual cancer cell in the body—while minimizing damage to the surrounding cells.

Encapsulated toxin-producing stem cells (in blue) help kill brain tumor cells in the tumor resection cavity (in green). [Credit: Khalid Shah, MS, PhD]

Encapsulated toxin-producing stem cells (in blue) help kill brain tumor cells in the tumor resection cavity (in green). [Credit: Khalid Shah, MS, PhD]

But luckily, Harvard Stem Cell Institute scientists at Massachusetts General Hospital may have finally struck gold: they have designed special, toxin-secreting stem cells that can target and destroy brain tumors. Their findings, which were performed in laboratory mice and which appear in the latest issue of the journal STEM CELLS, offer up an entirely unique method for eradicating deadly cancers.

Harvard Neuroscientist Khalid Shah, who led the study, explained in last Friday’s news release that the idea of engineering stem cells to kill cancer cells is not new—but there was a key difference in scientists’ ability to target individual cells vs. difficult-to-reach tumors, which is often the case with brain cancer:

“Cancer-killing toxins have been used with great success in a variety of blood cancers, but they don’t work as well in solid tumors because the cancers aren’t as accessible and the toxins have a short half-life.”

The solution, Shah and his team argued, was stem cells. Previously, Shah and his team discovered that stem cells could be used to circumvent these problems. The fact that stem cells continuously renew meant that they could also be used to continually deliver toxins to brain tumors.

“But first, we needed to genetically engineer stem cells that could resist being killed themselves by the toxins,” said Shah.

In this study, the research team introduced a small genetic change, or mutation, into the stem cells so that they become impervious to the toxin’s harmful effects. They then introduced a second mutation that allowed the stem cells to maintain and produce and secrete toxins throughout the cells’ lifetime—effectively giving it an unlimited supply of ammunition to use once it encountered the brain tumor.

They then employed a common technique whereby the toxins were tagged so that they only sought out and infected cancer cells—leaving healthy cells unscathed.

“We tested these stem cells in a clinically relevant mouse model of brain cancer,” Shah described. “After doing all of the molecular analysis and imaging to track the inhibition of protein synthesis within brain tumors, we do see the toxins kill the cancer cells and eventually prolonging the survival in animal models.”

While preliminary, these results are encouraging. As the team continues to refine their method of development and delivery, they are optimistic that they can bring their methods to clinical trial within the next five years.