Abstract 2534: Underlying mechanism of response to neddylation inhibition in a subset of glioblastoma
Authors: Ferdosi Shayesteh , Taylor Brett , Lee Matthew , Tang Nanyun , Peng Sen , Bybee Rita , Reid George , Hartman Lauren , Garcia-Mansfield Krystine , Sharma Ritin , Pirrotte Patrick , Furnari Frank , Dhruv Harshil , Berens Michael 
Published: July 2021

Abstract
Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor in adults with a 5-year survival rate of ~3%. The ubiquitin/proteasome system maintains intracellular homeostasis via degradation of unwanted proteins. Bortezomib is a first-in-class, non-specific proteasome inhibitor exploiting this system, although it has poor penetration across the blood brain barrier, and its lack of specificity is accompanied by adverse events. Neddylation is a specific pathway within the ubiquitin/proteasome system that is overactive in glioblastoma (GBM), and whose upregulation has been associated with glioma progression and worse survival. Pevonedistat is a first-in-class small-molecule neddylation inhibitor shown to impact protein degradation, leading to elevated abundance of some tumor suppressor proteins (Wee1, others), which then inhibit growth of GBM cells in culture and orthotopic xenografts. Because the molecular heterogeneity within and across GBM patients obscures therapeutic targets and obfuscates signals of efficacy in clinical trials, we propose the use of molecular “signatures of vulnerability” to targeted agents in subsets of preclinical models. We and others have shown that pevonedistat interferes with the growth of multiple types of cancers, including GBM, but the determinants of vulnerability are not fully understood. Here, we report a selective vulnerability to pevonedistat in a subset of GBM, specifically, instances with mutations or copy number deletions of PTEN are associated with de novo resistance to pevonedistat. Time-course studies of sensitive and non-sensitive GBM cells using transcriptomics and proteomics/phosphoproteomics enable independent discovery and testing for determinants of response to pevonedistat. Our results demonstrate that in GBM, resistance to pevonedistat is driven by reduced PTEN-chromatin binding (loss-of-function or lower expression) that is also independent of PTEN's lipid phosphatase activity (i.e., PI3K/AKT signaling). Across 25 glioma cell lines, we found that PTEN signaling, DNA replication, and chromatin instability pathways are the most significant differentiators between pevonedistat sensitive vs. non-sensitive models. In GBM models with modest to low sensitivity to pevonedistat, TOP2A expression was elevated. Combination treatment with the TOP2A inhibitor, etoposide, proved synergistic with pevonedistat. We report, for the first time, that PTEN status both serves as a novel biomarker for GBM sensitivity to pevonedistat and reveals a synergistic vulnerability of TOP2A inhibitors in combination with pevonedistat. Paired use of GBM PDX models of varying sensitivity with drug development testing allows the advancement of a promising agent as well as a patient-enrollment “signature of vulnerability” likely to increase the likelihood of demonstrating therapeutic efficacy in early clinical trials.
Citation Format: Shayesteh Ferdosi, Brett Taylor, Matthew Lee, Nanyun Tang, Sen Peng, Rita Bybee, George Reid, Lauren Hartman, Krystine Garcia-Mansfield, Ritin Sharma, Patrick Pirrotte, Frank Furnari, Harshil Dhruv, Michael Berens. Underlying mechanism of response to neddylation inhibition in a subset of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2534.