The Brain Tumor Center at Johns Hopkins | Research: stem cells, brain tumors, immune response, new drugs for brain cancers

Research Areas

Stem Cells and Brain Tumors

Finding successful treatments for brain tumors remains an elusive task. The Brain Tumor Team at Johns Hopkins is currently studying the organization and cellular makeup of the stem cells in a particular portion of the human brain called the subventricular zone (SVZ). Our goal is to not only understand the function of these brain stem cells and how they may play a role in the development of brain tumors, but to ultimately genetically engineer these cells to fight brain cancer.

Neural stem cells have been suggested to function as the primary precursors of new neurons. Most of our current knowledge in this area comes from our work with rodents. Because we believe the SVZ of the brain is the most prominent region of neurgenic cells in adulthood, we have focused on understanding the rodent SVZ and comparing it to the human SVZ. In doing so, we have been able to appreciate the intricacies of the human subventricular zone. Our studies have suggested that astrocytes (a star-shaped glial cell) in the rodent’s brains are adult neural stem cells. We now want to use human specimens to study the function of the human brain.

In our attempts to understand the human SVZ and test whether human astrocytes can function as neuronal stem cells, our laboratory is analyzing human brain tissue using special techniques to label proteins that are expressed by neuronal stem cells. We strive to learn whether the neuronal stem cells in the SVZ have oncogenic properties and if they are implicated in the development of human brain tumors. If a positive implication does exist, the hope is to develop new cell replacement approaches to treat those suffering from brain tumors.

This work is supported by grants from the NIH.

Immune Response to Brain Tumors

Together, primary (originating in the brain) and metastatic (spreading from other parts of the body) brain tumors constitute the third leading cause of death in young adults ages 20-39. Among these brain tumors, malignant gliomas are the most common and aggressive. Gliomas account for the majority of deaths due to primary neoplasms. Despite recent advances in treatment by combination surgery, radiotherapy, and chemotherapy, the average life expectancy of patients with gliomas remains low. One of the main factors leading to such poor prognosis is the fact that these tumors are able to grow within the brain without any significant impedance from the immune system. Although the immune system attempts to attack and remove the glioma, the T-cells aren’t able to sufficiently infiltrate the areas of tumor growth. Furthermore, gliomas express a protein, FasL that, when in contact with immune cells, causes them to commit suicide. Recently, the Brain Tumor team at Johns Hopkins has shown that the expression of FasL by tumor cells is actually higher than in normal brain cells. We hope that by inhibiting the expression of the FasL protein in brain tumors, it will be possible for the immune system to produce an adequate defense to eliminate the tumor.

Our lab is currently working towards developing methods to down regulate the expression of FasL in tumor cells and facilitate a more effective immune response towards these highly aggressive tumors. Through the incorporation of molecular techniques and animal cancer models we are developing viral based immuno-therapies that can be delivered directly to the site of tumor growth. By engineering retroviruses to deliver siRNA for FasL, it is possible to target tumor cells while leaving the normal cells of the brain unharmed. siRNA is a new technology that allows the highly specific inhibition of particular genes. This work will allow us to better understand how tumor cells avoid attack by the immune system and also uncover new avenues for tumor vaccine development and improvement. Once established, we are confident that these methods will be applicable to a variety of different cancers types.

History

In our Hunterian Neurosurgical Research Laboratory, our Brain Tumor team seeks out ways to develop local drug delivery techniques that allow direct access to tumors while avoiding the adverse effects of standard systemic drug therapy. Under the direction of Henry Brem, the strategies of local drug delivery devised in the lab have had immediate impact on the care of patients with brain tumors. In fact, in 1995 the FDA approved the use of Gliadel®, a biodegradable polymer loaded with the chemotherapeutic agent BCNU, for the treatment of recurrent gliomas. It was the first product newly approved by the FDA for the treatment of malignant brain tumors in over 23 years. The laboratory experiments which led to clinical trials with GLIADEL®, and ultimately to its approval for commercial use, were all performed in the Hunterian Laboratory.

Where We are Now

In addition to polymer-based delivery systems Johns Hopkins, in cooperation with the Massachusetts Institute of Technology, have been exploring alternative devices to locally deliver multiple drugs in precisely timed regimens. One of our recent developments is a novel microelectromechanical device (microchip) for local drug delivery. This device represents an alternative to our established polymer-based systems and offers the advantage of extremely precise control of drug delivery. Chemotherapeutic agents released from this device demonstrated growth inhibition of implanted rodent tumors. BCNU delivered from the devices was as effective as subcutaneous injections of BCNU at inhibiting tumor growth.

Future Directions

Since the biological activity of treatments largely depends on obtaining sufficient concentrations at targeted sites and penetration of the blood-brain barrier requires prohibitively large systemic doses, new agents will be incorporated into controlled local delivery systems and evaluated to establish their safety and efficacy against intracranial models of malignant gliomas. The laboratory will be investigating the efficacy of locally delivered agents, including RNA interference (RNAi) sequences, cytokine-retargeted adenoviruses, inhibitors of glutamate-mediated invasion, and anticancer ribonucleases (RNAase). We will also be investigating the effectiveness of chemotherapy in combination with various agents which have differing and complementary mechanisms of action, such as inhibitors of glutamate-mediated invasion and inhibitors of angiogenesis, resistance-modifiers, immune stimulators, and chemotherapy in combination with a variety of biological agents that intervene in critical pathways of tumorigenesis and tumor growth.

We also plan to continue to build on the laboratory’s successful investigational approach to include technologically advanced drug delivery systems delivering novel and effective chemotherapeutic and biological agents that can best be of benefit to patients if delivered directly to the brain. We will be investigating various polymer types, composition, and geometric configuration, to allow sustained delivery of more effective drug concentrations. A variety of new configurations such as sheets, rods, microspheres, and nanospheres will also be tested and may permit much broader clinical applications and less invasive implantation techniques, such as through stereotactic or endovascular injection.

New Drug Targets For Brain Cancers

The Brain Tumor Team at Johns Hopkins is currently looking to find and use drug targets for the most common malignant brain tumor in children (medulloblastomas) and adults (glioblastomas). In order to accomplish this goal, we have three active projects:

Mutation and amplification detection in tumors
Large-scale expression analysis of brain cancers and brain cancer models
Drug development -- small-molecule screening and development as possible new therapies for brain tumors

Mutation Detection

Our team currently uses two main approaches to fine genomic alterations in these tumors. Once a mutation is found, we test it thoroughly to make sure that it indeed contributes to tumor formation or progression:

High-throughput sequencing of gene --this allows us to look for new mutations. It can take thousands or tens of thousands of reactions to find one mutation. These are typically mutations that are found in the tumor sample, but not in the patient’s DNA from normal tissue. Johns Hopkins has recently further defined the extent to which these mutations occur in glioblastomas.

Digital Karyotyping -- this method was invented at Johns Hopkins. It allows us to look for larger chromosomal changes that occur in cancer. Our team recently used this method to find a gene that is genomically amplified in medulloblastomas. We are analyzing this gene (OTX2) to determine if it is a useful drug target.

Gene Expression Analysis

Our team studies at the messenger RNA level the complex pattern of expression changes that occur during tumor formation. Using Serial Analysis of Gene Expression (SAGE) technology that was developed at Johns Hopkins, we can look at all the expressed genes in a cell at one time. Our lab has developed experimental models to use in conjunction with SAGE in combination with advanced bioinformatics to find the genes with the critical changes that occur during brain tumor progression. This allows us to survey from all the expressed genes only those that have a statistically significant change during key processes of tumor formation.

Johns Hopkins has also produced and expanded a public resource for the National Cancer Institute that helps all researchers find expression based targets for their cancer interests. We have built the largest cancer gene expression database in the world in collaboration with the Cancer Genome Anatomy Project (CGAP).

Our lab has been able to locate genes that are activated in the following processes of brain tumor formation:

Protection against Hypoxia – this core of the tumor is most resistant to current therapies. We have determined some of the genes that protect the hypoxic tumor cell and promote angiogenesis

Tumor Invasion – Invasion of glioblastomas is one of its most malignant features. We have found the genes activated at the mRNA level during cell migration and invasion

Developmental Signaling – Pediatric brain tumors such as medulloblastomas inappropriately use developmental growth signals. We are investigating these new genes as potential targets.

We believe that targeting a combination of these genes will inactivate key processes and ultimately help prevent tumor growth.

Drug Development

Our lab is looking for small molecule inhibitors for gene targets that are altered during glioblastomas or medulloblastomas. This work is funded by the Ludwig Trust and the Children’s Cancer Foundation. We are screening libraries of both synthetic compounds and natural extracts to see what brain cancer cells with specific mutations react to. Our work with natural extracts is in collaboration with the Natural Products Research Lab at Research Triangle International.

So far, we have identified about four compounds that have activity specific for glioblastoma cells with a specific mutation (EGFRv111).