Animal Model for Pre-clinical Therapeutics
My research interests are in understanding of the molecular mechanisms that affect the aggressive/infiltrative biological behavior of brain cancers and would accordingly reveal potential therapeutic targets, and in developing a novel targeted therapies utilizing disease-specific animal model systems. The animal model system should enhance the testing of new therapeutic agents being considered for clinical trials and new strategies to deliver the therapeutic agents bypassing the blood-brain-barrier, such as convection enhanced delivery or intranasal delivery. We have developed animal models of pediatric atypical teratoid rhabdoid tumors (AT/RTs), diffuse intrinsic pontine gliomas (DIPGs), medulloblastoma, meningioma, as well as glioblastoma. Using the animal model systems, we have evaluated new therapeutic agents including small molecule inhibitors and liposomal chemotherapeutics, which have then been translated to clinical trials for adults and children with brain tumors.
Current Research Projects
The low incidence of AT/RT complicates progress that can be made in its treatment through clinical trial activity: a high throughput animal model test system would greatly expedite the discovery of more effective therapies for improved treatment of children with ATRT. We have recently developed an orthotopic AT/RT xenograft model from a primary surgical AT/RT specimen, and established AT/RT cell lines modiﬁed with a luciferase reporter for bioluminescence imaging (BLI) in immunocompromised rodent hosts. The AT/RT xenografts grow rapidly with dissemination patterns and cellular compositions recapitulating those observed in AT/RT patients. Our model system provides an excellent tool for pre-clinical testing, in order to identify clinically approved or novel agents that show promising activity against this cancer.
Pre-clinical Evaluation of CDK4/6 Inhibitor for AT/RT
The development of effective therapies for AT/RTs has been hindered by the relatively low incidence of these tumors and a limited understanding of activated signaling pathways that might lead to the identification of new therapeutic targets. INI1/hSNF5 is a tumor suppressor gene biallelically inactivated in AT/RT. Mechanisms of INI1/hSNF5-mediated tumor suppression include induction of G1 arrest through repression of cyclin D1-CDK4/6 complex, and activation of cyclin-dependent kinase inhibitor p16INK4a, as well as the Rb tumor suppressor. It is a logical assumption that the cyclin D1-CDK4/6-p16INK4a-Rb growth regulatory axis is a critical downstream target of INI1/hSNF5, and may represent a promising molecular target for the treatment of AT/RTs. We recently investigated the efficacy of a specific CDK4/6 inhibitor, PD-0332991, as a single agent and found anti-tumor activity and survival benefit in AT/RT xenografts. The results of our studies will provide pre-clinical data in support for the use of testing PD-0332991 in clinical trials for AT/RT patients.
Diffuse intrinsic pontine gliomas (DIPGs) are malignant tumors that arise almost exclusively in children. A fundamental limitation in the development of new therapies for DIPGs is that the diagnosis is usually confirmed by imaging studies and surgical biopsy is rarely performed. The lack of DIPG tissue samples means that the underlying oncogenic steps contributing to the development of this tumor type remain virtually unknown. We recently established tumorigenic DIPG cell lines derived from human biopsy samples. The orthotopic brainstem xenografts injected with the human DIPG cells recapitulate the histopathology and genotype of a subset of high-grade pediatric astrocytomas. This model system is an excellent tool for the development of new therapies for pre-clinical testing for DIPGs.
PDGFRA amplification occurs in 29-36% of DIPGs. Upregulation of PDGFR signaling in Nestin+ cells of the IVth ventricle subventricular zone, or cells of the dorsolateral pons, results in formation of glioma in mouse models. Preliminary data from our lab reveal that primary human DIPG cells have elevated PDGFRα and Rb, but lack expression of the tumor suppressor p16INK4a, and brainstem tumor xenografts expressed Nestin and Olig2. In the normal human brainstem, a population of Nestin/Olig2 positive cells proliferates during middle childhood, peaking around the age of six years, which corresponds with the peak incidence of DIPGs. This cell population could represent a pool of pontine progenitor cells and may be important for brainstem gliomagenesis. Furthermore, mouse ventral pontine Olig2+ progenitor cells appear to give rise to a dividing oligodendrocyte precursor cell type that expresses PDGFRα. The Hashizume lab is examining the consequences of these specific genetic alterations in rodents.
The infiltrative nature and anatomic location of diffuse intrinsic pontine gliomas in an eloquent area of the brain preclude surgical resection, and the blood-brain barrier (BBB) reduces the availability of systemically administered agents. Intranasal delivery (IND), a practical and noninvasive method of bypassing the BBB, relies upon anatomic connections of the olfactory and trigeminal nerves from the nasal mucosa to the central nervous system. Advantages of IND are the avoidance of hepatic first-pass elimination, thereby reducing systemic side effects, and convenient self-administration for patients. It is an alternative to systemic (intravenous) and/or direct invasive (intraparechymal) drug delivery. We previously showed that IND with GRN163, an oligonucleotide-based telomerase inhibitor, doubled the survival of rats with brain tumors. Using special formulations such as liposomes or nanoparticles can increase the effectiveness of IND. We are currently investigating the hypothesis that IND with liposomal drugs results in improved intratumoral drug uptake, inhibition of tumor growth, and a prolonged lifespan for animals with brainstem tumors.