Abstract 4001: Evaluation of novel therapeutics using the Mayo Clinic GBM Patient-Derived Xenograft (PDX) collection
Authors: Burgenske Danielle M. , Mladek Ann C. , Tian Shulan , Schroeder Mark A. , Hu Zeng , Carlson Brett L. , Decker Paul A. , Eckel-Passow Jeanette E. , Vaubel Rachael , Sarkaria Jann N. 
Published: June 2022

Abstract
The Mayo Clinic collection of patient-derived xenograft (PDXs) has been developed from the direct implantation of glioblastoma (GBM) samples into immunodeficient mice. Over 105 models have been extensively characterized with regards to histology, invasion, flank and orthotopic growth rates, and molecular profiling. Evaluation of orthotopic tumors demonstrated infiltration of tumor cells into the brain parenchymal in 90% of models with contralateral hemisphere involvement in 64%. Extensive molecular profiling confirmed the PDX collection captures the genetic heterogeneity of GBM, with the majority of typical molecular alterations seen at a frequency similar to the TCGA including gain of chromosome 7 and loss of chromosome 10. TERT promoter mutations (86%) and homozygous deletion of CDKN2A (70%) were the most frequent. Additional alterations in the p53 pathway included TP53 mutations (36%) and MDM2/4 amplification (10%/2%). IDH mutations were found in three models while MGMT promoter methylation was observed in 45% of PDXs. The available molecular sequencing results are viewable on cBioPortal. These genetically diverse models are extremely useful for biomarker discovery and efficacy evaluations. Using an innovative 1x1x1 PDX preclinical trial design, we are establishing a workflow to evaluate control and drug treatment in an individual animal across PDX lines in the flank. As our first use of this strategy, a small molecule MDM2 inhibitor was evaluated in 17 PDX lines with variable MDM2 and TP53 statuses. Tumors harboring MDM2 amplification without TP53 mutation (n=5) showed profound response, with 4 PDXs showing a complete response that lasted &gt;150 days. Response in TP53 wild-type tumors lacking MDM2 amplification was variable, with a 1.9 to 4.8 fold longer time to endpoint (mean 3; median 2.7). A more traditionally powered intracranial efficacy study performed with one MDM2 amplified (GBM108) and two non-amplified (GBM14, GBM10) PDX lines confirmed these findings of reduced and more variable response to therapy in MDM2 non-amplified TP53 wild-type tumors. Future studies will aim to examine novel biomarkers indicative of therapeutic response to better understand molecular features associated with MDM2 inhibitor efficacy. With over 20 years of experience, our group has extensive expertise in development of clinically relevant study designs focused on examining efficacy, tolerability, and pharmacokinetic/pharmacodynamic assessments. Our diverse collection of clinically relevant GBM PDX models provides a highly sought-after resource which has been utilized by the pharmaceutical community with 58 working relationships to date (26 contracts, 32 collaborations). Through these collaborations, we aim to expand the use of our highly characterized GBM PDX panel for biomarker discovery using similar strategies.
Citation Format: Danielle M. Burgenske, Ann C. Mladek, Shulan Tian, Mark A. Schroeder, Zeng Hu, Brett L. Carlson, Paul A. Decker, Jeanette E. Eckel-Passow, Rachael Vaubel, Jann N. Sarkaria. Evaluation of novel therapeutics using the Mayo Clinic GBM Patient-Derived Xenograft (PDX) collection [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 4001.