Abstract 808: PDGF-A overexpression and p53 depletion in rat neural precursor cells induces large brain tumors that resemble human glioblastoma

One of the major obstacles in developing new therapeutics for glioblastoma is testing these agents in reliable models that recapitulate the tumor biology of human disease. The RCAS/tv-a system enables spatial, temporal, and cell-type specific control of oncogenic transformations in the brain. In this study, we sought to develop a rat RCAS-TVA model of glioblastoma to eventually facilitate translational studies using magnetic resonance imaging (MRI), targeted radiation, focused ultrasound, and local drug delivery strategies. We developed a high copy number nestin-promoter driven tv-a (Ntv-a) transgenic Sprague-Dawley rat line. To initiate tumors, RCAS PDGF-A and p53 shRNA constructs were injected intracranially. The tumors were followed over time using MRI and MR proton spectroscopy. Animal survival was monitored and histopathology and gene expression analyses were performed. All animals (n=8) developed tumors that could be visualized with MRI throughout the tumor formation process. Early stage tumors showed relatively homogenous characteristics with minimal mass effect. Later stage tumors demonstrated large heterogeneous lesions with evidence of necrosis, increased vascularity, and significant mass effect. MR proton spectroscopy revealed increases in choline to creatinine ratio (Cho/Cr) and decreases in NAA, consistent with aggressive tumor progression. Immunohistochemistry revealed pseudopallisading necrosis, brain invasion, and vascular proliferation, all key features of human GBM. Immunohistochemistry confirmed a high proliferative index within the tumor core as well as neovascularization as evidenced by positive Ki67 and Smooth Muscle Actin (SMA) respectively. Gene expression analysis revealed approximately 1000 differentially expressed transcripts between the normal and tumor tissue. In addition to typical markers such as Ki67 and PDGFR-A overexpression, SPP1 and POSTN both of which are linked to glioma and tumor-associated macrophages, were found to be differentially expressed in the tumor. Comparisons between the rat gene expression profile and published human TCGA data indicated that the RCAS/tv-a tumors appear to align with the proneural GBM subtype. In summary, transgenic Ntv-a rats generate reproducible brain tumors following combined PDGF-A and p53 genetic alterations. The tumor progression process from low-grade tumor to high grade malignancy can be visualized with MRI. Histopathological features strongly resemble human GBM, and gene expressio