Abstract 2161: Characterization of a panel of orthotopic glioblastoma multiforme (GBM) patient-derived xenograft (PDX) mouse models and efficacy evaluation of temozolomide and external radiation therapy

Background Glioblastoma multiforme (GBM) is an aggressive cancer type with poor prognosis. The lack of effective treatment may be due to the complex molecular composition and the heterogeneity of the tumors. Standard of care treatment is surgery, external radiation therapy (XRT) and chemotherapy with temozolomide (TMZ); however, the response rate varies widely. Subcutaneous patient-derived xenograft (PDX) models are increasingly used during drug development. Implantation of GBM PDX tumors orthotopically in the brain displays an advantage as the tumors develop in a microenvironment that resembles that of the original patient tumor. In addition, the impact of the blood brain barrier (BBB) in terms of reduced drug bioavailability is also represented in the orthotopic GBM models. The aim of this study was to develop and characterize a panel of orthotopic GBM PDX models. The models were then used to study the efficacy of TMZ and XRT. Methods A panel of 14 PDX GBM models was characterized for EGFR, EGFRvIII, MGMT and mGluR3 expression. Selected PDX GBM models were furthermore characterized for GBM stem cell markers by flow cytometry. Low passage subcutaneous tumors from seven PDX GBM models (ST108, ST112, ST146, ST545, ST610, ST1388 and ST2473) were used for assessment of XRT sensitivity. Mice were randomized to receive XRT (2 Gy/day for 5 days) or sham. Furthermore, subcutaneous tumors were enzymatically digested and used for intracranial stereotactic injection in nude mice. Tumor take and growth rate was determined by T2-weighted magnetic resonance imaging (MRI) and 18F-fluoro-ethyl-L-tyrosine (18F-FET) PET imaging. At confirmed tumor take, mice were treated with TMZ (20 mg/mg 5 days on/2 days off x3 or 100mg/kg/day for 5 days) or whole brain XRT (2 Gy/day for 5 days). Control groups received vehicle or sham XRT. Final endpoint was survival by humane endpoints and tumors were fixed in formalin for histologic evaluation. Results A wide variation in expression levels of EGFR, EGFRvIII, MGMT and mGluR3 was observed in the PDX GBM panel. Three models had EGFRvIII mutation and all models had variable expression levels of EGFR. XRT showed a variable efficacy outcome on both tumor volume and survival in the PDX GBM models in the subcutaneous and orthotopic setting. TMZ showed efficacy in ST610 and ST2473 whereas ST146 and ST112 were resistant towards TMZ. Histologic evaluation showed typical characteristics of GBM tumors. Conclusion A panel of GBM PDX models was char