Abstract 4322: A preclinical orthotopic mouse model for human GBM: Recapitulation of features of GEM model of origin and potency of PI3K inhibitors

Abstract

Abstract Glioblastoma (GBM; grade IV) is the most frequent and aggressive brain tumor for which no effective therapy is currently available. It has been shown that PI3 kinase, involving both PI3 kinase – Ras activation and PTEN inhibition, and RB signaling are commonly altered in human GBM. We utilized a GEM model expressing GFAP-T121, KrasG12D and heterozygous mutant in PTEN +/- (TRP+/-) to develop an orthotopic mouse model for the preclinical evaluation of potential therapeutics for GBM treatment. The TRP+/- GEM model recapitulates features of human GBM including tissue invasion, pseudopalisading necrosis and dense vascularisation, however the latency to tumorigenesis (4-6 months) makes its use as a preclinical model for drug screening challenging. Therefore we isolated primary tumor cells from induced TRP+/- GEMs with Grade III or Grade IV astrocytoma and injected cells intracranially (IC) into syngeneic mouse brains. Primary cells induced grade IV tumors and recapitulated TRP+/- GEM tumor histopathology. Highly proliferative, invasive, and vascular, the orthotopic grade IV tumors presented linear foci of necrosis with peudopalisading by neoplastic cells that is characteristic of human GBM. Immunohistochemistry characterization of TRP+/- orthotopic tumors revealed similar T121, GFAP and PTEN expression profile to TRP+/- GEM grade IV tumors. Other cellular markers known to be expressed in neuronal progenitors, glial cells or found to be associated with human GBM aggressiveness were assessed in the orthotopic mouse model GBM tumors in comparison with the TRP+/- GEM model. By adjusting the number of primary cells IC injected, the time period of tumor growth and assessment by MRI was increased from 3 weeks to 6 weeks allowing reasonable time for tumor growth assessment, before potential drug efficacy testing. We used primary cells of grade IV tumor origin from TRP+/- GEM to evaluate the effect of PI3 kinase pathway inhibition on cell proliferation. BEZ235, PI103 and PIK75, compounds that target the PI3 kinase pathway, are effective inhibitors of primary tumor cell proliferation with an EC50 in the 10-100 nM range. MK2206, an Akt inhibitor, was found to be a potential inhibitor of tumor cell proliferation. Although MAPK pathway activation through RB inactivation has been found to be key in triggering cell proliferation in TRP+/- GEM model, MEK inhibitors, namely AZD6244, PD0325901 and UO126 did not have a strong effect on cell proliferation. In vitro inhibition of cell proliferation assays and target validation in TRP+/- GEM primary cells are useful tools to choose compounds for orthotopic mouse efficacy studies. Preliminary in vivo mouse pharmacokinetic studies are underway to insure potential drug distribution in the brain tissue. Using the orthotopic model, we found that PI3 kinase inhibitors may be effective against brain tumors in the mouse orthotopic model for human GBM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4322. doi:10.1158/1538-7445.AM2011-4322