Abstract 5304: A genetically engineered mouse model for GBM wherein Akt kinase activity can be monitored non-invasively in real-time

Approximately 30-40% of human gliomas exhibit mutations in the tumor suppressor gene PTEN resulting in deregulation of the phosphoinositide 3-kinase/Akt survival signaling pathway. In a significant number of GBMs tumor initiation is additionally driven by an oncogenic signal stemming from the gene locus amplification of the Platelet derived growth factor receptor (PDGFR), also leading to Akt and mammalian target of rapamycin (mTOR) activation. Phosphorylated, active Akt controls a plethora of cellular responses by regulating a large number of substrates, such as GSK-3, BAD, Forkhead transcription factors (FOXO), and MDM2. Elevated Akt activity increases tumor cell growth, survival and impairs apoptosis. Thus blocking Akt phosphorylation to treat cancer in particular gliomas has therapeutic potential. Here we demonstrate the pre-clinical use of a bioluminescent molecular reporter to evaluate Akt kinase inhibition in real time in a genetically engineered PDGF-driven PTEN-deficient mouse model of GBM. Glial cell specific delivery of the bioluminescent reporter was achieved by RCAS-TVA technology. In brief, we utilized genetically engineered PTEN loxP/loxP, Ink4a-Arf -/-, nestin-TVA transgenic animals and delivered the Akt reporter along with Cre recombinase and PDGF by intracranial implantation of chicken cells expressing avian virus containing the specific cargo. PTEN deletion in nestin positive cells resulted in increased Akt kinase phosphorylation as demonstrated by western blotting. Tumor growth was monitored by MRI and Bioluminescence imaging (BLI) technology. The design of the previously described Akt reporter allows for detectable bioluminescence only in the absence of Akt kinase activity due to the reconstitution of the wt luciferase enzyme. To evaluate the therapeutic potential of PI3-kinase- and Akt inhibitors in this pre-clinical GBM model, tumors were treated with either perifosine or API-2. Increased bioluminescence activity was observed in gliomas in a time- and dose-dependent manner with both inhibitors. These findings demonstrate that the Akt reporter provided a quantitative surrogate for Akt activity in PTEN-deficient gliomas. In conclusion we have provided a novel approach of pairing molecular imaging with a murine GBM model to investigate targeted agents. This may aid the future identification of most efficacious drug combinations impinging on PI3-kinase/Akt signaling in gliomas. 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 5304. doi:10.1158/1538-7445.AM2011-5304