Development of patient derived xenograft (PDX) animal models
We have developed and characterized primary cell lines and xenografts from surgical biopsies obtained from children with brain tumors. In combination with the pediatric neuro-oncology program at Lurie Children’s Hospital and other collaborative institutions, we are working with 60 cell lines and 25 xenografts including glioblastoma (GBM), high and low-grade glioma, diffuse pontine glioma (DIPG), ependymoma, meduloblastoma, and atypical teratoid rhabdoid tumor (AT/RT). These model systems are excellent tools for studying disease pathogenesis and development of novel therapeutic approaches for pediatric brain tumors.
Targeting histone mutations for the treatment of DIPG
Gliomas located in the brainstem represent approximately 10% of all pediatric central nervous system (CNS) tumors, and 80% are restricted to the ventral pons. These tumors, known as diffuse intrinsic pontine gliomas (DIPGs), primarily affect very young children with peak incidence at 6 years of age and have the highest mortality of all childhood solid tumors. Recent whole-genome sequencing has identified novel, gain-of-functions, somatic histone gene mutations. This results in replacement of lysine 27 by methionine (K27M) in the encoded histone H3 proteins (for as many as 80% of these tumors) and when present is associated with a significantly shorter survival of patients. We recently established tumorigenic DIPG cell lines derived from human biopsy samples and these cells harbor oncogenic histone H3K27M mutations. The orthotopic brainstem xenografts injecting with the human DIPG cells recapitulate the histopathology and genotype of a subset of high-grade gliomas. This model system is an excellent tool for the development of new therapies for pre-clinical testing for DIPGs. We have recently reported that inhibition of the histone H3K27 demethylase JMJD3 acts to restore H3K27 methylation in DIPG cells, while demonstrating potent anti-tumor activity, both in cell culture and in xenograft models of DIPG. The molecular as well as tumor biological consequences of, and therapeutic options for treating K27M DIPG are subjects of intense interest, and our research strategy is intended to advance our understanding of these aspects of this intriguing gene alteration.
Epigenetic targeting therapy for atypical teratoid rhabdoid tumor (ATRT)
AT/RT, is a highly malignant CNS neoplasm that primarily affects young children (more than 90% before 5 years) and has a very poor outcome despite aggressive treatment. Deﬁnitive diagnosis of AT/RT is now based on the detection of deletions and/or biallelically inactivating mutations of the chromosome 22-localized INI1/hSNF5 tumor suppressor gene in tumor tissue, and/or the absence of nuclear immunoreactivity for the INI1/hSNF5 gene product, BAF47 in the tumor cells. The low incidence of ATRT complicates progress 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 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 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 and/or novel agents that show promising activity against this cancer. The development of effective therapies for AT/RTs has been hindered by its relatively low incidence, and a limited understanding of oncogenic pathways that might lead to the identification of new therapeutic targets. INI1/hSNF5 tumor suppressor gene encodes a subunit of ATP-dependent SWI/SNF chromatin remodeling complexes that appear to regulate histone modification and play critical roles in a variety of differentiation pathways. The core subunit SNF5 appears to function as a tumor suppressor by modulating the transcription of a subset of genes that regulate the balance between cell proliferation and differentiation. Our research will be to examine the consequence of the loss of SNF5 function in our AT/RT models.
The infiltrative nature and anatomic location of DIPGs 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 (CNS). 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. The effectiveness of IND can be increased by using special formulations such as liposomes or nanoparticles. 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 treated animals with brainstem tumors.
Rintaro Hashizume, MD/PhD
Assistant Professor in Neurological Surgery and Biochemistry and Molecular Genetics