Abstract B24: Therapeutic response to bevacicumab, irinotecan, and temozolomide of PDX from human glioma cannot be correlated to common mutations as routinely identified by panel sequencing
Authors: Orthmann Andrea , Hoffmann Annika , Zeisig Reiner , EL-Heliebi Amin , Ernst Christina , Haybäck Johannes , Jödicke Andreas , Kuhn Susanne , Linnebacher Michael , Hoffmann Jens , Fichtner Iduna 
Published: May 2016

Abstract
The most common malignant brain tumor in adults is glioblastoma multiforme (GBM) showing a very heterogeneous, diffuse infiltrative and aggressive growth. The mean survival is between 8 and 18 months. The standard therapy for glioma consists of neurosurgery, radiation, and chemotherapy with temozolomide (SOC), but frequently resistance to temozolomide or irradiation will be developed. Translational research is focusing on the molecular mechanisms of glioma formation and development of resistance to identify new therapeutic targets.
We have transplanted more than 50 glioma tissue samples to immunodeficient mice and were able to establish 13 new PDX models (engraftment rate 25%). Identical morphology of the s.c. growing PDX (pleomorphic cells with marked anisocytosis/ anisonucleosis; solid, picket similar growth, atypical mitoses) compared with the original glioma was proven by histological and immunohistochemical staining. Heterogeneity of the tumor cells in their size, shape and nuclear irregularities were observed.
Glioma PDX models with stable growth were screened for sensitivity towards several targeted and cytotoxic drugs (everolimus, sorafenib, bevacicumab, irinotecan, salinomycin, temozolomide). Strong initial response to the treatment with bevacicumab, irinotecan, or temozolomide was observed. From our panel, (10/13) PDX were sensitive to temozolomide-treatment, (9/13) to irinotecan, and (7/13) to bevacicumab. The glioma PDX were resistant to most of the other targeted drugs, however in some single models sensitivity was observed. The frequency of common “onco-mutations” was analyzed using the Illumina TrueSeq Cancer panel sequencing. Although some frequent mutations were detected, i.e. in KDR, FGFR3, PIK3CA, PTEN, P53 and NOTCH1, no correlation with drug sensitivity have be identified. Extended correlation between drug sensitivity, gene expression profiles, and further mutations are still under analysis.
The available data demonstrate, that our glioma PDX model panel has retained the original tumor biology and reflect the heterogeneity of the disease, ensuring a high similarity to the clinical situation. Our approach can not only be used for testing of established and new drugs, but also offers an individualized treatment of patients.
For large scale screening the s.c. transplantation of glioma PDX is still the method of choice. However, for some drugs it may become important to implement a functional blood-brain barrier (BBB) in the model system. We have established a technology for orthotopic transplantation of glioma cells using the cell lines U373 and U87. Cells are transplanted into the left hemisphere of immunodeficient mice (NMRI nu/nu). Both cell lines showed good take rates and thus can be used for evaluation of systemic therapy approaches where an intact BBB is required. This technology has been further developed for orthotopic transplantation of glioma PDX and as surrogate models for brain metastases from breast and lung cancer (Ref: Hoffmann et al., Neurooncology, 2009).
Summary: Our new clinically relevant glioma models enable a better understanding of tumor biology, allow correlations between biomarkers, growth and drug sensitivity and have an essential role to improve individual glioma therapy.
Citation Format: Andrea Orthmann, Annika Hoffmann, Reiner Zeisig, Amin EL-Heliebi, Christina Ernst, Johannes Haybäck, Andreas Jödicke, Susanne Kuhn, Michael Linnebacher, Jens Hoffmann, Iduna Fichtner. Therapeutic response to bevacicumab, irinotecan, and temozolomide of PDX from human glioma cannot be correlated to common mutations as routinely identified by panel sequencing. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B24.