Using Polio Virus to Kill Deadly Brain Tumors


If you spend any time with people in retirement homes, they will sometimes tell you stories about their childhood and the dreaded “summer plague” known as polio. During the summer, children would go to ponds and lakes to swim in order to cool off from the summer heat. In those bodies of water, polio viruses would lurk, waiting to infect their new host. In most cases, infected people would experience a very flu-like disease that never went any further. In other cases, the flu-like disease might be more severe. Even in these people, the virus would be shed from the body by the digestive system and contaminate sewage water.

In rare cases, the central nervous system would be affected, but the aftermath of the disease would vary substantially.  Some  might some numbness for a little while. In a fraction of cases, they might actually experience paralysis that did not go away. The extent of this paralysis could vary tremendously. In some cases, people might retain the ability to walk, but with a limp. In other cases, they might not be able to walk at all. And in more severe cases, they might lose the ability to breathe on their own and require an iron lung to breathe for them. Polio struck young and old, male and female, rich and poor alike and was no respecter of persons.

polio_life_cycle

The polio vaccines made by Jonas Salk (a formalin-killed vaccine) and the live vaccine made by Albert Sabin essentially eradicated polio in many countries and saved untold of millions of lives from suffering. In fact, Albert Sabin gave away the rights to his vaccine even though those rights could have made him a millionaire. Because his live vaccine could be given in a sugar cube, it was extremely easy and inexpensive to administer to large populations.

Albert Sabin
Albert Sabin

Given this history, why would clinicians reinstate a deadly virus to fight cancer? The answer is that polio viruses is a highly lytic virus, but it can be genetically manipulated to specifically attack cancer cells.

First a bit about the molecular biology of polio virus.  Polio virus is a member of a group of RNA viruses called the “picornaviruses.”  The name of this group comes from “pico” meaning small, “RNA” to refer to the type of nucleic acid found in the virus, and the virus to indicate the type of infectious agent that it happens to be.  Viruses are nucleic acid molecules encases in a protein capsid.  When ingested from contaminated water by drinking or simply putting your hands in your mouth, the polio virus binds to a cell surface protein called CD155 found in the intestinal walls.  It enters these cells and uncoats.  The RNA genome of the polio virus is then translated by ribosomes in the cell into a large protein.  This is a key feature of picornaviruses; their viral RNA genomes can serve as messenger RNAs that are directly translated into protein right after emerging from their capsids.

polio molecular biology

This large protein has the ability to process itself.  That processing comes in the form of clipping pieces of the protein into small pieces.  These smaller pieces have specific functions.  The first pieces are creatively called P1, P2 and P3 (you have to love those biochemists and their ability to dream up creative names – yes that was a joke).  Eventually, the viral proteinases (enzymes that clip proteins) 2A and 3C further process these three precursor proteins to form the viral capsid proteins VP1-4 (formed from P1) and the viral replication proteins 2A, 2B, 2C (formed from P2), 3A, 3B, 3C, and 3D (formed from P3). As mentioned before, 2A and 3C are proteinases, 3B is a protein called VPg, and 3D is RNA-dependent RNA polymerase that replicates the viral RNA into copies that are packaged into viral capsids.

The whole infection process is insidiously effective because there is a piece of RNA at the very front of the poliovirus genome called the IRES, which stands for the internal ribosome entry site.  This sequence of 400 to 500 bases directs the viral translation initiation step in a manner independent of whether or not there is a special cap-structure on the front end of the RNA.  It allows poliovirus RNAs to be effectively recognized by the host cell and the cell’s own mRNAs to not be well-recognized because the polio 2A protease degrades elements of the cell’s own translation machinery, which prevents the cell from recognizing its own mRNAs.

As it turns out, if you swap this IRES with IRESs from other types of viruses, you can change the types of cells that polio virus will infect.  In 2000, Eckard Wimmer and his group from the State University of New York at Stony Brook showed that substituting the polio virus IRES for that of the IRES from the common cold virus (Rhinovirus) allowed poliovirus to grow in cultured brain tumor cells (see Gromeier M, et al., Proc Natl Acad Sci U S A. 2000, 97(12): 6803–6808).  Since these tumors expressed CD155, the receptor for poliovirus, they could be infected with it.  Wimmer and his team made attenuated strains of these viruses and used them in non-human primates that had brain tumors.  When injected directly into the tumor, the viruses infected only the tumor cells, and grew poorly, but the immune response against the virus and the infected cells caused the tumors to aggressively shrink.

So Gromeier and his team collaborated with neuro-oncologists to use their engineered polio viruses to treat human patients with glioblastomas.  These are very aggressive cancers that usually end up killing the patient.  in a clinical trial, of 22 people enrolled in the trial, half are doing well, and several are considered to be in remission, which is pretty much unheard of for glioblastomas.

The news show 60 Minutes even did a piece on this treatment and interviewed two patients with aggressive glioblastomas were treated by this polio virus.  Their tumors have essentially disappeared.  In fact, the first person who was ever treated with this treatment is now cancer free.

While this is a small study, it was supposed to be a Phase I study that only determined safe dosages and safety parameters.  you do not expect patients to improve much in Phase I studies because you are still tweaking the treatment.  These results are astonishing.  Also, because it uses the patient’s own immune response against the infected cells it does not depend on massive alterations of the patient’s physiology.

This is a remarkable finding.  I hope it can be developed into something mainstream that turns out to be safe and effective.

Preclinical Study Results Pave the Way for Newly Opened Clinical Trial of Immune Cells Engineered to Attack Protein Found on Tumors in 30 Percent of Patients with Glioblastoma


Scientists from the University of Pennsylvania have engineered immune cells to seek out and attack a type of deadly brain cancer. In an important preclinical study, these souped-up immune cells were shown to be both safe and effective at controlling tumor growth in mice treated with these modified cells. This work is the result of collaboration between a team from the Perelman School of Medicine at the University of Pennsylvania and the Novartis Institutes for BioMedical Research. These results will hopefully be the impetus for a newly opened clinical trial for glioblastoma patients at Penn.

Marcela Maus, assistant professor of Hematology/Oncology at the Penn Abramson Cancer Center, said: “A series of trials that began in 2010 have found that engineered T cells have an effect in treating some blood cancers, but expanding this approach into solid tumors has posed challenges. A challenging aspect of applying engineered T cell technology is finding the best targets that are found on tumors but not normal tissues. This is the key to making this kind of T cell therapy both effective and safe.”

This new preclinical study, which was conducted with Hideho Okada and his colleagues at the University of Pittsburgh, makes use of T cells engineered to express a chimeric antigen receptor (CAR) that specifically binds to a mutant epidermal growth factor receptor protein called EGFRvIII. EGFRvIII is found on the cell surfaces of approximately 30 percent of glioblastoma tumors. Over 22,000 Americans are diagnosed with glioblastoma each year, and those patients whose glioblastomas express the EGFRvIII mutation tend to be more aggressive and are less likely to respond favorably to standard therapies and more likely to recur after treatment.

“Patients with this type of brain cancer have a very poor prognosis. Many survive less than 18 months following their diagnosis,” said M. Sean Grady, who is the Charles Harrison Frazier Professor and chair of the department of Neurosurgery. “We’ve brought together experts in an array of fields to develop an innovative personalized immunotherapy for certain brain cancers.”

This new trial is being led by Donald O’Rourke, associate professor of Neurosurgery, who heads an interdisciplinary collaboration of neurosurgeons, neuro-oncologists, neuropathologists, immunologists, and transfusion medicine experts.

In order to bring this experiment to fruition, Maus and her colleagues had to characterize the EGFRvIII CAR T cell. They had to develop and tested multiple antibodies that bind to cells expressing EGFRvIII on their surface. The single-chain variable fragments or scFvs that recognized the mutant EGFRvIII protein were then extensively tested in order to confirm that they do not also bind to those normal, EGFR proteins that are widely expressed on cells in the human body.

Maus and her group then generated a panel of humanized scFvs and tested their specificity and function in CAR modified T cells. The humanized scFvs have distinct amino acid sequences that more closely resemble human antibodies. From this huge panel of humanized scFvs, they selected one scFv to explore further based on its binding selectivity for EGFRvIII over normal non-mutated EGFR. They also evaluated the EGFRvIII CAR T cells by testing them against normal EGFR-expressing skin cells in mice grafted with human skin. This test showed that the engineered EGFRvIII CAR T cells did not attack cells with normal EGFR, at least under these conditions.

In order to test the selected scFv for its anti-cancer efficacy, Maus and others used human tumor cells that expressed EGFRvIII and showed that the EGFRvIII CAR T cells could multiply and secrete cytokines in response such to tumor cells. When used inside living animals, it was clear that the EGFRvIII CAR T cells ably controlled tumor growth in several mouse models of glioblastoma. The tumors were measured with magnetic resonance imaging (MRI) and the EGFRvIII CAR T cells caused tumor shrinkage, and were also effective with used in combination with the anticancer drug temozolomide, which is normally used to treat patients with glioblastoma.

On the strength of these preclinical successes, this team designed a phase 1 clinical study of CAR T cells transduced with humanized scFv directed to EGFRvIII for both newly diagnosed and recurrent glioblastoma patients who carry the EGFRvIII mutation. “There are unique aspects about the immune system that we’re now able to utilize to study a completely new type of therapy,” said O’Rourke.

For these glioblastoma patients, their T cells were removed by means of apheresis (a process similar to dialysis), and then the T cells were genetically engineered using a viral vector that programs them to find EGFRvIII-expressing cancer cells. The patient’s own engineered cells are infused back into their body, and when the T cells find the EGFRvIII-expressing cells, a signaling domain built into the CAR promotes proliferation of these “hunter” T-cells. This procedure is distinct from other T cell-based therapies that also target some healthy cells, since EGFRvIII seems to only be found on tumor tissue, which the study’s leaders hope will minimize side effects.

This new phase I clinical trial will enroll 12 adult patients whose tumors express EGFRvIII, in two groups: One arm of 6 patients whose cancers have returned after receiving other therapies, and one arm of 6 patients who are newly diagnosed with the disease and still have 1 cm or more of tumor tissue remaining after undergoing surgery to remove it.

The clinical trial is sponsored by the biotech company Novartis. In 2012, the University of Pennsylvania and Novartis announced an exclusive global research and licensing agreement to further study and commercialize novel cellular immunotherapies using CAR technologies. This STM study is the first pre-clinical paper developed within the Penn-Novartis alliance, with Penn and Novartis scientists working collaboratively. Ongoing clinical trials evaluating a different type of Penn-developed CAR therapy known as CTL019 have yielded promising results among some patients with certain blood cancers. In July 2014, the FDA granted CTL019 its Breakthrough Therapy designation for the treatment of relapsed and refractory acute lymphoblastic leukemia in both children and adults.

Using Fat Stem Cells to Treat a Deadly Cancer


Johns Hopkins University researchers have reported the successful use of stem cells derived from human body fat to deliver biological treatments directly to the brains of mice suffering from the most common and aggressive form of brain tumor. Such treatments significantly extended the lives of these cancer-stricken animals.

These experiments offer proof-of-principle that such a technique would work in human patients after surgical removal of brain cancers called glioblastomas. This technique provides a way to find and destroy any remaining cancer cells in those areas of the brain that are difficult to reach. Glioblastoma cells represent a challenge for cancer treatments, since they are quite sprightly, and can migrate across the entire brain, hide out and establish new tumors. Consequently, the cure rates for glioblastoma are notoriously low.

In the mouse experiments conducted by the Johns Hopkins group, investigators used mesenchymal stromal cells (MSCs) from fat tissue. Fat-based MSCs have a mysterious ability to sniff out cancer and other damaged cells. After genetically modifying the MSCs so that they secreted a protein called bone morphogenetic protein 4 (BMP4), these MSCs were injected into the brains of mice that suffered from glioblastomas. BMP-4 is a small, secreted protein that plays essential regulatory roles in embryonic development, but also has a demonstrated tumor suppression function.

Study leader Alfredo Quinones-Hinojosa, M.D., a professor of neurosurgery, oncology and neuroscience at the Johns Hopkins University School of Medicine and his colleagues published the results of this experiment in the journal Clinical Cancer Research. According to their results, those mice that were treated with the BMP-4-secreting fat-based MSCs had significantly less tumor growth and spread. In general the cancers in these animals were less aggressive and had fewer migratory cancer cells compared to mice that didn’t get the treatment. Also, the stem cell-treated mice survived significantly longer (an average of 76 days, compared to 52 days in the untreated mice).

“These modified mesenchymal stem cells are like a Trojan horse, in that they successfully make it to the tumor without being detected and then release their therapeutic contents to attack the cancer cells.”

Standard treatments for glioblastoma include chemotherapy, radiation and surgery. Unfortunately, even a combination of all three rarely leads to more than 18 months of survival after diagnosis. Discovering new ways to seek and destroy straggling glioblastoma cells that other treatments can’t get is a long-sought goal, says Quinones-Hinojosa. However, he also cautions that years of additional studies are needed before human trials of fat-derived MSC therapies could begin.

Quinones-Hinojosa also treated brain cancer patients at Johns Hopkins Kimmel Cancer Center, and he and his co-workers were greatly encouraged that the genetically-engineered stem cells let loose into the brain in his experiments did not transform themselves into new tumors.

These latest findings build on research published in March 2013 by Quinones-Hinojosa and his team, which demonstrated that harvesting MSCs from fat was much less invasive and less expensive than getting them from bone marrow (PLoS One, March 2013).

Ideally, he says, if MSCs work as a cancer treatment, a patient with a glioblastoma would have some adipose tissue (fat) removed from any number of locations in the body a short time before surgery. Afterwards, these fat-derived MSCs would be isolated and manipulated in the laboratory so that they would secrete BMP4. Then, after surgeons removed whatever parts of the brain tumor they could get to, they would deposit these BMP-secreting cells into the brain in the hopes that they would seek out and destroy the left-over cancer cells.