Abstract 1661: Development of a patient-derived glioblastoma model in the transgenic Rag2 Null rat: In vivo imaging, histology, and combination therapy assessment
Authors: Jackson Luke R. , Masi Megan R. , zarrinmayeh Hamideh , Das Sudip K. , Green Mark A. , Snyder Scott E. , Wang Nian , Pollok Karen , Hutchins Gary D. , Butch Elizabeth R. , Veronesi Michael C. 
Published: June 2022

Abstract
An important obstacle to translating promising drug treatments against glioblastoma (GBM) to the clinic is lack of resistant GBM animal models that more accurately parallel the clinical course of GBM drug resistance found in patients.
In this project, a recurrent patient derived intracranial GBM tumor model (GB10) was developed for the first time in the novel Rag2 Null transgenic rat to establish a reproducible preclinical brain tumor model. Histologic characterization confirmed markers of high nuclear proliferation (30% Ki67) and presence of neovascularity (3% Von Willebrand Factor VIII) in all tumors. Serial in vivo imaging was performed to determine a clinically relevant late stage of tumor across all rats before initiation of treatment, accounting for heterogeneity of tumor size and growth rate characteristics. Overall survival was measured following oral administration of control, Temozolomide (TMZ), or combination therapy with TMZ and Idasanutlin.
Eighteen Rag2 Null rats were intracranially implanted with GB10, a well characterized, recurrent cell line from the Mayo Clinic Brain Tumor Patient-Derived Xenograft National Resource. Bi-weekly high resolution, 2-dimensional T2 magnetic resonance imaging (2DT2 MRI) was performed on a Bruker 9.4 tesla scanner until tumor volume reached 30 µL. 14 days later, simultaneous positron emission tomography and magnetic resonance imaging (PET MRI) was performed on each rat with three dimensional T1 post-contrast (3DT1 CE), amino acid-based 18F-Flouroethyltyrosine (18F-FET), and amide proton transfer-chemical exchange saturation transfer (amide-CEST). Measured tumor parameters included volumetry (3DT1 CE), metabolic activity (18F-FET), and mobile phase intracellular protein content (amide-CEST), to confirm late-stage viable tumors of similar size (15.3 mm^2 +/-1.38 based on SEM, N=16) and metabolism (2:1 ratio of activity of tumor relative to contralateral control brain tissue). Two rats were removed: 1 died prematurely of infection and 1 had extra-axial tumor location.
Oral treatment groups were as follows: Control (N= 5), TMZ (N=6) or TMZ + Idasanutlin (N=5). Kaplan Meier survival curves for the TMZ treated group (80.2+/-4.1 days) and combined TMZ + Idasanutlin group (93.8+/-6.2 days) were both significantly increased (P&lt;0.001) compared to control (67.4+/-4.5 days). Survival for the TMZ + Idasanutlin treated group was also significantly increased (P&lt;0.001) relative to TMZ treated group indicating efficacy of combination therapy.
In conclusion, a robust, resistant, patient derived GBM animal model was developed using serial, high field, non-invasive, multimodality, molecular imaging along with histopathologic analysis. Feasibility of assessing treatment response was also demonstrated with both a standard of care and experimental combination therapy, in the late stage of GBM growth.
Citation Format: Luke R. Jackson, Megan R. Masi, Hamideh zarrinmayeh, Sudip K. Das, Mark A. Green, Scott E. Snyder, Nian Wang, Karen Pollok, Gary D. Hutchins, Elizabeth R. Butch, Michael C. Veronesi. Development of a patient-derived glioblastoma model in the transgenic Rag2 Null rat: In vivo imaging, histology, and combination therapy assessment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1661.