Targeting Oncogene Amplification in Glioblastoma
Abstract
Malignant gliomas originate in astrocytes, or neural progenitor cells, within the brain. These tumors rarely metastasize outside of the brain, and they exert their devastating health effects by damaging this vital organ. Glioblastoma is the most aggressive type of glioma, and unfortunately the most frequent in adults, with an incidence of about 12,000 new cases per year in the United States. Surgery followed by radiation and chemotherapy with a DNA targeting agent temozolomide are able to control the disease temporarily. We have learned from the many failed clinical trials that these tumors have been unexpectedly resistant to therapy directed at what seemed to be promising targets. In over 70% of the cases, proteins that drive glioblastoma growth are overexpressed due to greatly increased gene copy numbers in amplified genomic regions. In this project we are focusing on two oncogenes, CDK4 (cyclin-dependent kinase 4) and MDM2 (mouse double minute 2 homolog), that overrule the two central regulatory pathways of cell proliferation. Novel potent inhibitors targeting these oncogenes are now in clinical trials, enrolling glioblastoma patients. This project involves bringing the clinical challenges to the research laboratory in a tangible way by testing these novel therapies in patient-derived models (neurosphere cells and mouse xenografts), which are as hard to treat as the original tumors, because we have shown they indeed preserve the genomic complexity and oncogene amplifications of glioblastomas. Similar to clinical studies, this project uses genomic information to assign glioblastoma patient-derived models to drugs that, in theory, should be effective. However, unlike the clinical setting, the same “patient” will be assigned to multiple treatment arms simultaneously. In this project we will investigate the pharmacological properties, specificity, and efficacy of the most promising pharmacological inhibitors of MDM2 and CDK4 in treating glioblastoma models with a diverse set of genomic abnormalities. Like most oncogenes in glioblastoma, MDM2 and CDK4 genes are frequently amplified in circular segments of DNA, which are not part of a chromosome and have no centromeres, so they can increase dramatically in number. Furthermore the tumor cells have different amounts of these circular DNA elements, thus variable levels of the drug target within the same tumor. This likely poses a challenge for these new drug treatments. For this reason we are adding another therapeutic strategy to our study. Using novel pharmacological inhibitors in clinical trials, we will target an enzyme that is a core regulator of DNA repair, which is named DNA-dependent protein kinase (DNA-PK). This strategy has a broader application for glioblastoma treatment, because radiation and temozolomide inflict DNA damage, as does the rapid cell proliferation rate. If DNA repair is inhibited, the damage to the DNA becomes toxic and eventually lethal to the cell. However, here we will specifically test if DNA inhibitions affects the propagation of the circular DNA elements carrying oncogenes, as a novel application for DNA-PK inhibitors. First, we will test each of the CDK4 and MDM2 pharmacological inhibitors as monotherapy in the glioblastoma cells and xenografts representing patients with diverse genomic profile. We will quantify their efficacy in selectively inhibiting their targets, determine to what extent they can control glioblastoma growth, and determine their potential to sensitize cells to radiation and temozolomide. If resistance to therapy is observed, we will analyze these tumors in novel and important ways. We will quantify the shifts in the number of the circular DNA elements that carry the oncogenes, along with other molecular changes that will be analyzed in collaboration with Dr. Poisson, a co-investigator in this project and bioinformatics expert. We will then test the efficacy of DNA-PK inhibitors in the same way. It is not feasible to conduct these
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 19, 2019
- Source ID
- W81XWH1910693
Entities
People
- Ana Decarvalho
Organizations
- Henry Ford Health
- United States Army