Scientists develop faster, smarter way to classify tumors using single-cell technology

Dr. Stephen Lin, CIRM Senior Science Officer

By Dr. Stephen Lin

Single-cell.  It is the new buzzword in biology.  Single-cell biology refers to the in-depth characterization of individual cells in an organ or similar microenvironment.  Every organ, like the brain or heart, is composed of thousands to millions of cells.  Single-cell biology breaks those organs down into their individual cell components to study the diversity within those cells.  For example, the heart is composed of cardiomyocytes, but within that bulk population of cardiomyocytes there are specialized cardiomyocytes for the different chambers of the heart and others that control beating, plus others not even known yet.  Single-cell studies characterize cell-to-cell variability in the body down to this level of detail to gain knowledge of tissues in a way that was not possible before.   

The majority of single-cell studies are based on next generation sequencing technologies of genetic material such as DNA or RNA.  The cost of sequencing each base of DNA or RNA has dropped precipitously since the first human genome was published in 2000, often compared to the trend seen with Moore’s Law in computing.  As a result it is now possible to sequence every gene that is expressed in an individual cell, called the transcriptome, for thousands and thousands of cells.   

The explosion of data coming from these technologies requires new approaches to study and analyze the information.  The scale of the genetic sequences that can be generated is so big that it is often not possible anymore for scientists to interpret the data manually as had been traditionally done.  To apply this exciting field to stem cell research and therapies, CIRM funded the Genomics Initiative which created the Centers of Excellence in Stem Cell Genomics (CESCG).  The goal of the CESCG is to create novel genomic information and create new bioinformatics tools (i.e. computer software) specifically for stem cell research, some of which was highlighted in past blogs.  Some of the earliest single-cell gene expression atlases of the human body were created under the CESCG. 

The latest study from CESCG investigators creates both new information and new tools for single-cell genomics.  In work funded by the Genomics Initiative, Stephen Quake and colleagues at Stanford University and the Chan-Zuckerberg Biohub studied tumor formation using single-cell approaches.  Drawing from one of the earliest published single-cell studies, the team had surveyed human brain transcriptome diversity that included samples from the brain cancer, glioblastoma. 

Recognizing that the data coming from these studies would eventually become too large and numerous to classify all of the cell types by hand, they created a new bioinformatics tool called Northstar to apply artificial intelligence to automatically classify cell types generated by single-cell studies.  The cell classifications generated by Northstar were similar to the original classifications created manually several years ago including the identification of specific cancerous cells. 

Some of the features that make Northstar a powerful bioinformatics tool for these studies are that the software is scalable for large numbers of cells, it performs the computations to classify cells very fast, and it requires relatively low computer processing power to go through literally millions of data points. 

The scalability of the tool was demonstrated on the Tabula Muris data collection, a single-cell compendium of 20 mouse organs with over 200,000 cells of data.  Finally, Northstar was used to classify the tumors from new single-cell data generated by the CESCG via samples of 11 patient pancreatic cancer patients obtained from Stanford Hospital.  Northstar correctly found the origins of cancerous cells from the specific diagnoses of pancreatic cancer that the patients had, for example cancerous cells in the endocrine cell lineage from a patient diagnosed with neuroendocrine pancreas cancer.  Furthermore, Northstar identified previously unknown origins of cancerous cell clusters from other patients with pancreatic cancer.  These new computational tools demonstrate how big data from genomic studies can become important contributors to personalized medicine.

The full study was published in Nature.

Charting a new course for stem cell research

What are the latest advances in stem cell research targeting cancer? Can stem cells help people battling COVID-19 or even help develop a vaccine to stop the virus? What are researchers and the scientific community doing to help address the unmet medical needs of underserved communities? Those are just a few of the topics being discussed at the Annual CIRM Alpha Stem Cell Clinic Network Symposium on Thursday, October 8th from 9am to 1.30pm PDT.

Like pretty nearly everything these days the symposium is going to be a virtual event, so you can watch it from the comfort of your own home on a phone or laptop. And it’s free.

The CIRM Alpha Clinics are a network of leading medical centers here in California. They specialize in delivering stem cell and gene therapies to patients. So, while many conferences look at the promise of stem cell therapies, here we deal with the reality; what’s in the clinic, what’s working, what do we need to do to help get these therapies to patients in need?

It’s a relatively short meeting, with short presentations, but that doesn’t mean it will be short on content. Some of the best stem cell researchers in the U.S. are taking part so you’ll learn an awful lot in a short time.

We’ll hear what’s being done to find therapies for

  • Rare diseases that affect children
  • Type 1 diabetes
  • HIV/AIDS
  • Glioblastoma
  • Multiple myeloma

We’ll discuss how to create a patient navigation system that can address social and economic determinants that impact patient participation? And we’ll look at ways that the Alpha Clinic Network can partner with community care givers around California to increase patient access to the latest therapies.

It’s going to be a fascinating day. And did I mention it’s free!

All you have to do is go to this Eventbrite page to register.

And feel free to share this with your family, friends or anyone you think might be interested.

We look forward to seeing you there.

New CAR-T cell therapy using scorpion venom developed to treat brain tumors

Contributed by Wikimedia Commons (Public Domain)

Glioblastoma (GBM) is an aggressive form of cancer that begins in the brain and results in tumors that can be very difficult to treat. This condition has claimed the lives of Beau Biden, former Vice President Joe Biden’s son, and John McCain, former Senator of Arizona. However, a new approach to combat this condition is being developed at City of Hope and has just received approval from the FDA to conduct clinical trials. The innovative approach involves using a combination of chimeric antigen receptor (CAR)-T cell therapy and specific components of scorpion venom!

Before we dive into how the scorpion venom is being used, what exactly is CAR-T cell therapy?

Diagram of CAR-T Cell Therapy
Image Source: National Cancer Institute

This approach consists of using T cells, which are an immune system cell that can destroy foreign or abnormal cells, and modifying them with a protein called a chimeric antigen receptor (CAR). These newly designed CAR-T cells are able to identify and destroy cancer cells by detecting a specific protein on these cells. What makes CAR-T cell even more promising is that the specific protein detected can be set to virtually anything.

This is where the scorpion venom comes into play. One of the components of this venom is called chlorotoxin (CLTX), which has the ability to specifically bind to brain tumor cells.

Michael Barish, Ph.D. (Left), Christine Brown, Ph.D. (Center), Dongrui Wang (Right)
Photo Credit: Business Wire

For this study, Dr. Christine Brown, Dr. Michael Barish, and a team of researchers at City of Hope designed CAR-T cells using chlorotoxin in order to specifically detect and destory brain tumor cells. Now referred to as CLTX-CAR-T cells, they found that these newly engineered cells were highly effective at selectively killing brain tumor cells in animal models. What’s more remarkable is that the CLTX-CAR-T cells ignored non-tumor cells in the brain and other organs.

In a press release, Dr. Barish describes the CLTX-CAR-T cell approach in more detail.

“Much like a scorpion uses toxin components of its venom to target and kill its prey, we’re using chlorotoxin to direct the T cells to target the tumor cells with the added advantage that the CLTX-CAR T cells are mobile and actively surveilling the brain looking for appropriate target. We are not actually injecting a toxin, but exploiting CLTX’s binding properties in the design of the CAR. The idea was to develop a CAR that would target T cells to a wider variety of GBM tumor cells than the other antibody-based CARs.”

In the same press release, Dr. Brown talks about the promise of this newly developed therapy.

“Our chlorotoxin-incorporating CAR expands the populations of solid tumors potentially targeted by CAR T cell therapy, which is particularly needed for patients with cancers that are difficult to treat such as glioblastoma. This is a completely new targeting strategy for CAR T therapy with CARs incorporating a recognition structure different from other CARs.”

The first-in-human clinical trial using the CLTX-CAR T cells is now screening potential patients.

CIRM has funded a separate clinical trial conducted by Dr. Brown that also involves CAR-T cell therapy for brain tumors.

The full results of this study was published in Science Translational Medicine.

A video talking about this approach can also be found here.

Two studies identify a molecule that could be used to block Zika virus and kill cancer cells

Dr. Tariq Rana (left) and Dr. Jeremy Rich (right) both lead independent teams at UC San Diego that identified a molecule, αvβ5 integrin, as the Zika virus’ key to getting into brain stem cells

Zika virus is caused by a virus transmitted by Aedes mosquitoes. People usually develop mild symptoms that include fever, rash, and muscle and joint pain. However, Zika virus infection during pregnancy can lead to much more serious problems. The virus causes infants to be born with microcephaly, a condition in which the brain does not develop properly, resulting in an abnormally small head. In 2015-2016, the rapid spread of the virus was observed in Latin America and the Caribbean, increasing the urgency of understanding how the virus affected brain development.

Working independently, Dr. Tariq Rana and Dr. Jeremy Rich from UC San Diego identified the same molecule, αvβ5 integrin, as the Zika virus’ key to entering brain stem cells. The two studies, with the aid of CIRM funding, discovered how to take advantage of the molecule in order to block the Zika virus from infecting cells. In addition to this, they were able to turn it into something useful: a way to destroy brain cancer stem cells.

In the first study, Dr. Rana and his team used CRISPR gene editing on brain cancer stem cells to delete individual genes, which was done to see which genes are required for the Zika virus to enter the cells. They discovered that the gene responsible for αvβ5 integrin also enabled the Zika virus.

In a press release by UC San Diego, Dr. Rana elaborates on the importance of his findings.

“…we found Zika uses αvβ5, which is unique. When we further examined αvβ5 expression in brain, it made perfect sense because αvβ5 is the only integrin member enriched in neural stem cells, which Zika preferentially infects. Therefore, we believe that αvβ5 is the key contributor to Zika’s ability to infect brain cells.”

In the second study, Dr. Rich and his team use an antibody to block αvβ5 integrin and found that it prevented the virus from infecting brain cancer stem cells and normal brain stem cells. The team then went on to block αvβ5 integrin in a mouse model for glioblastoma, an aggressive type of brain tumor, by using an antibody or deactivating the gene responsible for the molecule. Both approaches blocked Zika virus infection and allowed the treated mice to live longer than untreated mice. 

Dr. Rich then partnered with Dr. Alysson Muotri at UC San Diego to transplant glioblastoma tumors into laboratory “mini-brains” that can be used for drug discovery. The researchers discovered that Zika virus selectively eliminates glioblastoma stem cells from the mini-brains. Additionally, blocking αvβ5 integrin reversed that anti-cancer activity, further demonstrating the molecule’s crucial role in Zika virus’ ability to destroy cells.

In the same UC San Diego press release, Dr. Rich talks about how understanding Zika virus could help in treating glioblastoma.

“While we would likely need to modify the normal Zika virus to make it safer to treat brain tumors, we may also be able to take advantage of the mechanisms the virus uses to destroy cells to improve the way we treat glioblastoma.”

Dr. Rana’s full study was published in Cell Reports and Dr. Rich’s full study was published in Cell Stem Cell.

Drug used to treat multiple sclerosis may improve glioblastoma outcomes

Dr. Jeremy Rich, UC San Diego

Glioblastoma is an aggressive form of cancer that invades brain tissue, making it extremely difficult to treat. Current therapies involving radiation and chemotherapy are effective in destroying the bulk of brain cancer cells, but they are not able to reach the brain cancer stem cells, which have the ability to grow and multiply indefinitely. These cancer stem cells enable the glioblastoma to continuously grow even after treatment, which leads to recurring tumor formation.

Dr. Jeremy Rich and his team at UC San Diego examined glioblastomas further by obtaining glioblastoma tumor samples donated by patients that underwent surgery and implanting these into mice. Dr. Rich and his team tested a combinational treatment that included a targeted cancer therapy alongside a drug named teriflunomide, which is used to treatment patients with multiple sclerosis. The research team found that this approach successfully halted the growth of glioblastoma stem cells, shrank the tumor size, and improved survival in the mice.

In order to continue replicating, glioblastoma stem cells make pyrimidine, one of the compounds that make up DNA. Dr. Rich and his team noticed that higher rates of pyrimidine were associated with poor survival rates in glioblastoma patients. Teriflunomide works by blocking an enzyme that is necessary to make pyrmidine, therefore inhibiting glioblastoma stem cell replication.

In a press release, Dr. Rich talks about the potential these findings hold by stating that,

“We’re excited about these results, especially because we’re talking about a drug that’s already known to be safe in humans.”

However, he comments on the need to evaluate this approach further by saying that,

“This laboratory model isn’t perfect — yes it uses human patient samples, yet it still lacks the context a glioblastoma would have in the human body, such as interaction with the immune system, which we know plays an important role in determining tumor growth and survival. Before this drug could become available to patients with glioblastoma, human clinical trials would be necessary to support its safety and efficacy.”

The full results to this study were published in Science Translational Medicine.

California gets first royalty check from Stem Cell Agency investments

COH image

CIRM recently shared in a little piece of history. The first royalty check, based on CIRM’s investment in stem cell research, was sent to the California State Treasurer’s office from City of Hope. It’s the first of what we hope will be many such checks, helping repay, not just the investment the state made in the field, but also the trust the voters of California showed when they created CIRM.

The check, for $190,345.87, was for a grant we gave City of Hope back in 2012 to develop a therapy for glioblastoma, one of the deadliest forms of brain cancer. That has led to two clinical trials and a number of offshoot inventions that were subsequently licensed to a company called Mustang Bio.

Christine Brown, who is now the principal investigator on the project, is quoted in a front page article in the San Francisco Chronicle, on the significance of the check for California:

“This is an initial payment for the recognition of the potential of this therapy. If it’s ultimately approved by the FDA as a commercial product, this could be a continued revenue source.”

In the same article, John Zaia, Director of the City of Hope Alpha Stem Cell Clinic, says this also reflects the unique nature of CIRM:

“I think this illustrates that a state agency can actually fund research in the private community and get a return on its investment. It’s something that’s not done in general by other funding agencies such as the National Institutes of Health, and this is a proof of concept that it can work.”

Maria Millan, CIRM’s President & CEO, says the amount of the payment is not the most significant part of this milestone – after all CIRM has invested more than $2.5 billion in stem cell research since 2004. She says the fact that we are starting to see a return on the investment is important and reflects some of the many benefits CIRM brings to the state.

“It’s a part of the entire picture of the return to California. In terms of what it means to the health of Californians, and access to these transformative treatments, as well as the fact that we are growing an industry.”

 

Novel approach to slowing deadly brain cancer stem cells may lead to new treatments

Glioblastoma, a form of brain cancer, is one of the most dreaded cancer diagnoses. Standard radiation and chemotherapy treatments for glioblastoma almost always prove ineffective because of the cancer’s ability to grow back. With their unlimited potential to self-renew, cancer stem cells within the brain tumor are thought to be responsible for its aggressive reoccurrence. Not surprisingly, researchers looking to develop more effective therapies are focused on trying to better understand the biology of these cancer stem cells in order to exploit their vulnerabilities.

Glioblastoma_-_MR_coronal_with_contrast

MRI image of high grade glioma brain tumor (white mass on left). Image: Wikipedia

This week, the Dartmouth-Hitchcock Medical Center reports that a research team led by Damian A. Almiron Bonnin has identified a cell signal that the brain cancer stem cells rely on to resist standard treatments and to regrow. They also showed that drugs which interrupt this signal reduced tumor growth in animal studies.

Because if its aggressive growth, the cells within the glioblastoma eventually become starved for oxygen or, in scientific lingo, they become hypoxic. The presence of hypoxia in brain tumors is actually predictive of a poor prognosis in affected patients. A protein called hypoxia-inducible factor (HIF) becomes activated in these low oxygen conditions and helps the cancer stem cells to survive and continue to grow. The research team found that HIF carries out this function by triggering a cascade of cell activity that leads to the secretion of a protein called VEGF out into the microenvironment of the tumor. As secreted VEGF spreads through the tumor, it stimulates new blood vessel growth which is key to the tumor’s survival by nourishing the tumor with oxygen and nutrients.

Adding drugs that block a cell’s ability to release proteins, led to a reduction in glioblastoma tumor growth both in petri dishes and in animal studies. With these results, published in Oncogene, Dr. Almiron Bonnin’s team is performing the necessary preclinical studies that could lead to testing this novel strategy in patients. He summed this effort in a press release:

s200_damian.almiron_bonnin

Damian Almiron Bonnin

“Being able to target the cancer stem cells within these tumors, like we did here, could potentially improve response to current chemotherapies and prevent recurrences, which would translate into an increase in patient survival rates.”

 

Stem Cell Stories That Caught Our Eye: Halting Brain Cancer, Parkinson’s disease and Stem Cell Awareness Day

Stopping brain cancer in its tracks.

Experiments by a team of NIH-funded scientists suggests a potential method for halting the expansion of certain brain tumors.Michelle Monje, M.D., Ph.D., Stanford University.

Scientists at Stanford Medicine discovered that you can halt aggressive brain cancers called high-grade gliomas by cutting off their supply of a signaling protein called neuroligin-3. Their research, which was funded by CIRM and the NIH, was published this week in the journal Nature. 

The Stanford team, led by senior author Michelle Monje, had previously discovered that neuroligin-3 dramatically spurred the growth of glioma cells in the brains of mice. In their new study, the team found that removing neuroligin-3 from the brains of mice that were transplanted with human glioma cells prevented the cancer cells from spreading.

Monje explained in a Stanford news release,

“We thought that when we put glioma cells into a mouse brain that was neuroligin-3 deficient, that might decrease tumor growth to some measurable extent. What we found was really startling to us: For several months, these brain tumors simply didn’t grow.”

The team is now exploring whether targeting neuroligin-3 will be an effective therapeutic treatment for gliomas. They tested two inhibitors of neuroligin-3 secretion and saw that both were effective in stunting glioma growth in mice.

Because blocking neuroligin-3 doesn’t kill glioma cells and gliomas eventually find ways to grow even in the absence of neuroligin-3, Monje is now hoping to develop a combination therapy with neuroligin-3 inhibitors that will cure patients of high-grade gliomas.

“We have a really clear path forward for therapy; we are in the process of working with the company that owns the clinically characterized compound in an effort to bring it to a clinical trial for brain tumor patients. We will have to attack these tumors from many different angles to cure them. Any measurable extension of life and improvement of quality of life is a real win for these patients.”

Parkinson’s Institute CIRM Research Featured on KTVU News.

The Bay Area Parkinson’s Institute and Clinical Center located in Sunnyvale, California, was recently featured on the local KTVU news station. The five-minute video below features patients who attend the clinic at the Parkinson’s Institute as well as scientists who are doing cutting edge research into Parkinson’s disease (PD).

Parkinson’s disease in a dish. Dopaminergic neurons made from PD induced pluripotent stem cells. (Image courtesy of Birgitt Schuele).

One of these scientists is Dr. Birgitt Schuele, who recently was awarded a discovery research grant from CIRM to study a new potential therapy for Parkinson’s using human induced pluripotent stem cells (iPSCs) derived from PD patients. Schuele explains that the goal of her team’s research is to “generate a model for Parkinson’s disease in a dish, or making a brain in a dish.”

It’s worth watching the video in its entirety to learn how this unique institute is attempting to find new ways to help the growing number of patients being diagnosed with this degenerative brain disease.

Click on photo to view video.

Mark your calendars for Stem Cell Awareness Day!

Every year on the second Wednesday of October is Stem Cell Awareness Day (SCAD). This is a day that our agency started back in 2009, with a proclamation by former California Mayor Gavin Newsom, to honor the important accomplishments made in the field of stem cell research by scientists, doctors and institutes around the world.

This year, SCAD is on October 11th. Our Agency will be celebrating this day with a special patient advocate event on Tuesday October 10th at the UC Davis MIND Institute in Sacramento California. CIRM grantees Dr. Jan Nolta, the Director of UC Davis Institute for Regenerative Cures, and Dr. Diana Farmer, Chair of the UC Davis Department of Surgery, will be talking about their CIRM-funded research developing stem cell models and potential therapies for Huntington’s disease and spina bifida (a birth defect where the spinal cord fails to fully develop). You’ll also hear an update on  CIRM’s progress from our President and CEO (Interim), Maria Millan, MD, and Chairman of the Board, Jonathan Thomas, PhD, JD. If you’re interested in attending this event, you can RSVP on our Eventbrite Page.

Be sure to check out a list of other Stem Cell Awareness Day events during the month of October on our website. You can also follow the hashtag #StemCellAwarenessDay on Twitter to join in on the celebration!

One last thing. October is an especially fun month because we also get to celebrate Pluripotency Day on October 4th. OCT4 is an important gene that maintains stem cell pluripotency – the ability of a stem cell to become any cell type in the body – in embryonic and induced pluripotent stem cells. Because not all stem cells are pluripotent (there are adult stem cells in your tissues and organs) it makes sense to celebrate these days separately. And who doesn’t love having more reasons to celebrate science?

Taming the Zika virus to kill cancer stem cells that drive lethal brain tumor

An out of control flame can be very dangerous, even life-threatening. But when harnessed, that same flame sustains life in the form of warm air, a source of light, and a means to cook.

A similar duality holds true for viruses. Once it infects the body, a virus can replicate like wildfire and cause serious illness and sometimes death. But in the lab, researchers can manipulate viruses to provide an efficient, harmless method to deliver genetic material into cells, as well as to prime the immune system to protect against future infections.

In a Journal of Experimental Medicine study published this week, researchers from the University of Washington, St. Louis and UC San Diego also show evidence that a virus, in this case the Zika virus, could even be a possible therapy for a hard-to-treat brain cancer called glioblastoma.

Brain cancer stem cells (left) are killed by Zika virus infection (image at right shows cells after Zika treatment). Image: Zhe Zhu, Washington U., St. Louis.

Recent outbreaks of the Zika virus have caused microcephaly during fetal development. Babies born with microcephaly have a much smaller than average head size due to a lack of proper brain development. Children born with this condition suffer a wide range of devastating symptoms like seizures, difficulty learning, and movement problems just to name a few. In the race to understand the outbreak, scientists have learned that the Zika virus induces microcephaly by infecting and killing brain stem cells, called neural progenitors, that are critical for the growth of the developing fetal brain.

Now, glioblastoma tumors contain a small population of cells called glioblastoma stem cells (GSCs) that, like neural progenitors, can lay dormant but also make unlimited copies of themselves.  It’s these properties of glioblastoma stem cells that are thought to allow the glioblastoma tumor to evade treatment and grow back. The research team in this study wondered if the Zika virus, which causes so much damage to neural progenitors in developing babies, could be used for good by infecting and killing cancer stem cells in glioblastoma tumors in adult patients.

To test this idea, the scientists infected glioblastoma brain tumor samples with Zika and showed that the virus spreads through the cells but primarily kills off the glioblastoma stem cells, leaving other cells in the tumor unscathed. Since radiation and chemotherapy are effective at killing most of the tumor but not the cancer stem cells, a combination of Zika and standard cancer therapies could provide a knockout punch to this aggressive brain cancer.

Even though Zika virus is much more destructive to the developing fetal brain than to adult brains, it’s hard to imagine the US Food and Drug Administration ever approving the injection of a dangerous virus into the site of a glioblastoma tumor. So, the scientists genetically modified the Zika virus to make it more sensitive to the immune system’s first line of defense called the innate immunity. With just the right balance of genetic alterations, it might be possible to retain the Zika virus’ ability to kill off cancer stem cells without causing a serious infection.

The results were encouraging though not a closed and shut case: when glioblastoma cancer stem cells were infected with these modified Zika virus strains, the virus’ cancer-killing abilities were weaker than the original Zika strains but still intact. Based on these results, co-senior author and WashU professor, Dr. Michael S. Diamond, plans to make more tweaks to the virus to harness it’s potential to treat the cancer without infecting the entire brain in the process.

“We’re going to introduce additional mutations to sensitize the virus even more to the innate immune response and prevent the infection from spreading,” said Diamond in a press release. “Once we add a few more changes, I think it’s going to be impossible for the virus to overcome them and cause disease.”

 

Brain stem cells unintentionally talk with brain tumors, allowing their spread

A stem cell’s capacity to lay quiet and, when needed, to self-renew plays a key role in restoring and maintaining the health of our organs. Unfortunately, cancer stem cells possess that same property allowing them to evade radiation and chemotherapy treatments which leads to tumor regrowth. And a CIRM-funded study published today in Cell shows the deviousness of these cancer cells goes even further. The Stanford research team behind the study found evidence that brain stem cells, which normally guide brain development and maintenance, unintentionally communicate with brain cancer cells in deadly tumors, called gliomas, providing them a means to invade other parts of the brain. But the silver lining to this scary insight is that it may lead to new treatment options for patients.

High grade gliomas do not end well
The most aggressive forms of glioma are called high grade gliomas and they carry devastating prognoses. For instance, the most common form of these tumors in children has a median survival of just 9 months with a 5-year survival of less than 1%. Surgery or anti-cancer therapies may help for a while but the tumor inevitably grows back.

MRI image of high grade glioma brain tumor (white mass on left). Image: Wikipedia

Researchers have observed that gliomas typically originate in the brain stem and very often invade a brain stem cell-rich area, called the subventrical zone (SVZ), that provides a space for the therapy-resistant cancer stem cells to hole up. This path of tumor spread is associated with a shorter time to relapse and poorer survival but the exact mechanism wasn’t known. The Stanford team hypothesized that SVZ brain stem cells release some factor that attracts the gliomas to preferentially invade that part of the brain.

To test this chemo-attraction idea, they mimicked cancer cell invasion in a specialized, dual compartment petri dish called a Boyden chamber. In the bottom compartment, they placed the liquid food, or media, that SVZ brain stem cells had been grown in. On the upper compartment, they placed the cancerous glioma cells. A porous, gelatin membrane between the two compartments acts as a barrier but allows the cells to receive signals from the lower compartment and migrate down into the media if a chemoattractant is present. And that’s what they saw: a significant glioma cell migration through the gelatin toward the brain stem cell media.

Boyden chamber assay. Image: Integr. Biol., 2009,1, 170-181

Pleiotrophin: an unintentional communicator with brain cancer cells
Something or somethings in the SVZ brain stem cell media had to be attracting the glioma cells. So, the Stanford team analyzed the composition of the media and identified four proteins that, when physically complexed together, had the same chemo-attraction ability as the media. They were pleased to find that one of the four proteins is pleiotrophin which is known to not only play a role in normal brain development and regeneration but also to increase glioma cell migration. And in this study, they showed that higher levels of pleiotrophin are present in the SVZ brain stem cell area compared to other regions of the brain. They went on to show that blocking the production of pleiotrophin in mice reduced the invasion of glioma cells into the SVZ region. This result suggests that blocking the release of pleiotrophin by brain stem cells in the SVZ could help prevent or slow down the spread of glioma in patients’ brains without the need of irradiating this important part of the brain.

The silver lining: hsp90 inhibitors have therapeutic promise

Michelle Monje, MD, PhD

To further explore this potential therapeutic approach, the team examined hsp90, one of the other three proteins complexed with pleiotrophin. Though it doesn’t have chemoattractant properties, it still is a necessary component and may act to stabilize pleiotrophin. It also turns out that inhibitors for hsp90 have already been developed in the clinic for treating various cancers. When the researchers in this study blocked hsp90 production in the SVZ region of mice, they observed a reduced invasion of glioma cells. Though clinical grade hsp90 inhibitors exist, team lead  Michelle Monje, MD, PhD – assistant professor of neurology, Stanford University – tells me that some tweaking of these drugs will be necessary to reach gliomas:

“Our challenge is to find an hsp90 inhibitor that penetrates the brain at effective concentrations.”

Once they find that inhibitor, it could provide new options, and hope, for people diagnosed with this dreadful cancer.