Glioblastoma (GBM) is the most aggressive primary brain tumor, with a median survival of 12-15 months post-diagnosis, and TP53 mutations are detected in ~30% of sporadic GBM cases. Recent studies suggest that the dysregulation of adhesion G-protein coupled receptors (aGPCRs) may play a role in GBM development. Brain-specific angiogenesis inhibitor 3 (BAI3), a member of the BAI1-3 subfamily of aGPCRs, is highly expressed in neuronal and glial cells. Although BAI3 can regulate synaptic plasticity, dendritic morphogenesis, and apoptotic cell clearance, its role as a tumor suppressor and in GBM pathogenesis has yet to be defined. Analysis of TCGA datasets revealed that BAI3 mRNA and protein expression are significantly downregulated in GBM compared to normal brain tissue. To explore this observed decrease in expression of BAI3 in GBM, we generated constitutive Bai3-/- mice, but tumor formation did not occur. Since TP53 is highly mutated in GBM and BAI3 is involved in regulatory brain functions, we generated a Bai3-/-Trp53f/dNestin-Cre mouse model, combining Bai3-/- mice with Trp53f/dNestin-Cre mice to induce the simultaneous loss of Bai3 and Trp53 in neural and glial progenitor cells, the putative cells of origin of GBM. Trp53f/dNestin-Cre mice developed tumors at a frequency of 26%, while the combined loss of Bai3 and Trp53 increased the incidence of GBM formation to 71%, p = 0.0009. Transcriptomic profiling of the tumors revealed a significant suppression of core metabolic pathways in the Bai3-/-Trp53f/dNestin-Cre GBM. Brain tumor-derived cell lines from both genotypes exhibited high expression of neural stem and glial markers, with low expression of mature neuronal markers. These findings suggest that BAI3 functions as a tumor suppressor in TP53-deficient GBM, by impacting core metabolic GBM pathways, and with its loss of expression, causes tumor incidence to increase by 45%.

Abstract Introduction: In the US, there are racial disparities in PDAC incidence and mortality, higher among blacks than whites. In addition to socioeconomic status, lifestyles, and age, genetics also contributes to these disparities. Thus, we conducted transcriptomic analyses (RNA-seq) of PDAC samples collected from African American (AA) and Caucasian (CA) patients to identify race/ethnicity-specific gene expression profiles and their related pathways to find determinants that contribute to the aggressive phenotypes of PDACs. This study is relevant to the UAB catchment area, since about 30% of patients with PDAC are AAs. Methodology: Histologically confirmed PDACs (n=40) from AA (9 PDAC and 3 matching normal tissues) and CA (31 PDAC and 5 matching normal tissues) were included in this study. FFPE sections of PDACs and their corresponding normal tissues were macro-dissected for RNA isolation. Whole transcriptomic sequencing was performed with a NextSeq 500/550 platform. Trimmed reads were mapped to a human reference genome (hg38) using HISAT, and gene level read count data were obtained using HTSeq. Differential expression analysis was performed using the DESeq2 bioconductor package. ClusterProfiler/DOSE R packages were used for gene ontology and KEGG pathway enrichment analyses. Genes with log 2-fold change of ≥1 and adjusted P-value <0.05 were considered as differentially expressed. Results: Among the top upregulated genes altered in only AA PDACs, compared to their normal tissues, were RNF144B, TESPA1, KLHL17, H2AX, MDGA1, CDK20, PHLDA3, SLC6A16, PARVG, GATD3, NUDT16, RENBP, RTL8C, C1QTNF1, HLA−DRB5, PARP15, PPP1R16B, RASGRP2, and CHST15. Of note, targeting CHST15, by an RNA oligonucleotide, STNM01 in Phase I/IIa trial on unresectable PDAC patients showed improved overall survival. Additionally, inhibition of KLHL17, an upstream activator of Ras/MAPK, could be a candidate target in PDAC. The KEGG pathways altered in AA PDACs, were glycerophospholipid metabolism; bile secretion; retinol metabolism; regulation of lipolysis in adipocytes; and pantothenate and CoA biosynthesis. In CAs, the top upregulated genes in PDACs, compared to their normal tissues, were PPY, UGT1A10, GPR20, SDR16C5, KLK7, MYBPC1, ITLN1, PADI1, CLCA1, UGT1A9, and SERPINB3.The KEGG pathways altered in CA PDACs, were cellular senescence; AGE−RAGE signaling pathway in diabetic complication; PD−L1 and PD−1 checkpoint pathway; and central carbon metabolism. There were 13 genes differentially modulated in AA PDACs as compared to CA PDACs. The 6 down-regulated were USP17L1, C2CD4D, MMP13, DCUN1D5, and 2 genes without annotations (ENSG00000276345 and ENSG00000280966); the 7 up-regulated genes were SEMA4A, LETM2, HMOX1, OTUB2, MEDAG, VEGFD, and HBA1. Immunohistochemical validation of these markers is in progress. Conclusions: Findings of this study showed distinct gene expression profiles and differentially modulated pathways in AA and CA PDAC patients. These results will aid in identifying aggressive phenotypes and new targets for developing race/ethnicity-based therapeutic interventions. Citation Format: Prachi Bajpai, Ravi Paluri, Sameer Al Diffalha, Darshan S. Chandrashekar, Farrukh Afaq, Ryan Bash, C. Ryan Miller, Sooryanarayana Varambally, Moh’d Khushman, Upender Manne. Differential gene expression to delineate racial disparities in the molecular landscape of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A006.

Abstract Glioblastoma (GBM) is the most common primary malignant brain tumor with an abysmal 15-month median survival. Therefore, novel therapeutic interventions are urgently needed. EGFR is a receptor tyrosine kinase that is mutated in over 50% of GBM and is a logical target for precision oncology approaches. While aberrant EGFR signaling has been successfully targeted in other cancers, early attempts to target EGFR in GBM clinical trials have not been successful. Since these early trials, several studies have revealed that GBM EGFR biology is unique and cannot be generalized from other EGFR-driven neoplasms. To better understand EGFR biology in a GBM-specific context, we have characterized the GBM transcriptome with RNAseq, the epigenome with CUT&RUN, and the kinase proteome with Multiplexed inhibitor beads with Mass Spectrometry (MIB-MS), collectively referred to as ‘multiomics’, after modeling EGFR resistance. An isogenic mouse astrocyte (mAc) model of GBM was genetically engineered to overexpress EGFRvIII (CEv3), the most common EGFR mutation in GBM. Expression of EGFRvIII induces a unique multiomic profile that mediates many hallmark cancer phenotypes including proliferation and stemness. Chronic EGFR resistance was modeled both in vitro and in vivo through continuous exposure to erlotinib or gefitinib, EGFR tyrosine kinase inhibitors (TKI). Additionally, acute EGFR resistance was modeled using a single exposure to EGFR TKI afatinib or neratinib in vitro over a 48-hour time course. Preliminary multiomic characterization of these data has revealed several targets that can be further investigated for therapeutic exploitation. Further investigation into these targets using orthotopic allografts with CEv3 cells shows that combinatorial therapy with neratinib and abemacilib, a CDK inhibitor, significantly (p < 0.001, n= 20 mice per group) extends survival (56 days) compared to neratinib alone (31.5 days). Future integrated multiomic analysis aims to elucidate the synergistic relationship between neratinib and abemacilib.

Recurrent selection at previously identified genomic loci and molecular pathways underscores a possible conserved set of pathways for treatment resistance. This analysis has yielded a set of gene and molecular pathways that will guide future work in our lab targeting treatment resistance using novel therapeutics and radiation techniques in GBM. Future directions include assessing the feasibility of mapping these clinical samples onto our previously generated panel of comprehensively characterized patient-derived xenograft lines.

Glioblastoma (GBM) is a devastating malignant brain tumor with a dismal 15-month median survival. Current treatments have not been successful at preventing recurrence, thus novel therapeutic modalities are urgently needed. EGFR is a tyrosine kinase receptor that is commonly mutated in ~60% of GBM and is an attractive target for GBM precision oncology. Aberrant EGFR signaling drives tumor proliferation and maintenance, thus further study of common EGFR alterations in GBM, including interstitial deletions (EGFRvIII) and missense mutations (EGFRA289), is needed to develop effective EGFR-targeted therapies. This is especially important in the context of a retrospective study that showed EGFRA289 driven GBM was more clinically aggressive. EGFRA289 positive GBM had a unique, invasive radiographic signature on magnetic resonance imaging (MRI) and patients had a significantly shorter median overall survival of 6-months. We hypothesize that the malignant clinical phenotypes of EGFRA289 GBM are driven by unique epigenomic and transcriptomic, collectively referred to as (epi)genomic, programs linked to EGFRA289 signaling. Prior studies using established cell lines show that EGFRvIII overexpression drives malignant (epi)genomic programs mediated by transcription factor (TF) activation. To better understand variant specific EGFR biology in GBM, we have developed novel genetically engineered mouse astrocyte (mAc) models that overexpress wtEGFR (MA-WT), vIII (MA-v3), and EGFRA289V (MA-A289V). Phospho-immunoblots show that these mAc models have differential EGFR ligand dependance, which match published studies. Despite this difference in EGFR signaling, all mAc models have similar sensitivities to EGFR tyrosine kinase inhibitor (TKI) treatment. However, MA-A289V is more proliferative and migratory compared to the other mAc variants. Preliminary RNA-Seq on our mAc models has identified similar and unique TFs differentially expressed (DE) between MA-v3 and MA-A289V when compared to parental MA-C. Integration of RNA-Seq and CUT&RUN followed by mechanistic genetic interrogation will elucidate the relationship between EGFR variant-specific (epi)genomic mechanisms and their unique malignant phenotype.

This file contains the differentially expressed genes and enriched pathways lists from the gene expression microarray analyses in Supplemental Table S1, with sample information in S1a. Lists are for the following comparisons: SUM149 Control vs. ABT888 (S1b), MDA-MB-436 Control vs. ABT888 (S1c), SUM149 Control vs. Carboplatin (S1d), MDA-MB-436 Control vs. Carboplatin (S1e), SUM149 Control vs Carboplatin+ABT888 (S1f), MDA-MB-436 Control vs Carboplatin+ABT888 (S1g), SUM149 Carboplatin vs Carboplatin+ABT888 (S1h), MDA-MB-436 Carboplatin vs Carboplatin+ABT888 (S1i). DAVID pathway enrichment analysis results are shown for the significantly up-regulated (S1j) and down-regulated (S1k) genes with Carboplatin treatment for both models.

This file contains the compiled Supplemental Figures S1-S9. Figure S1 is a flowchart describing the process of normalizing the microarray data for the SUM149 model for the different scanners used. Figure S2 depicts the scanner differences in the microarray data for the SUM149 model before and after normalization. Figure S3 is a flowchart depicting the analytical process used to analyze and compare the SUM149 and MDA-MB-436 models microarray results, and Figure S4 shows the difference in scale between models before and after the scaling process for visual comparison of the SUM149 and MDA-MB-436 models. Figure S5 demonstrates the lack of survival benefit of Carboplatin +/- ABT88 in the two BRCA-wt models, MDA-MB-468 and MDA-MB-231BR. Figure S6 contains representative images of IHC cC3 staining for the BRCA-wt model, MDA-MB-468. Figure S7 shows the unsupervised clustering of the BRCA-mut SUM149 and MDA-MB-436 models with treatment. Figure S8 contains the supervised clustering based on carboplatin treatment in these two models. Figure S9 demonstrates the expression levels of the 38 commonly regulated genes in both models with carboplatin treatment.

Abstract Glioblastoma (GBM) is the most common brain tumor and standard therapy only extends survival from 12 to 15 months. The receptor tyrosine kinase EGFR is altered in ~60% of GBM, resulting in aberrant activation of downstream pathways, including PI3K, that potentiate tumorigenesis. Though EGFR targeting has been successful in other cancers, clinical trials with EGFR tyrosine kinase inhibitors (TKI) have failed in GBM, in part due to resistance. Trial results suggested that the most common oncogenic EGFR variant, EGFRvIII (vIII), and negative regulator of PI3K signaling, PTEN, were biomarkers of response. To dissect the role of PTEN in GBM tumorigenesis and EGFR TKI response, we utilized vIII-expressing mouse astrocytes with and without functional Pten. Pten loss potentiated tumorigenesis in vitro and in vivo, as proliferation and stemness were significantly increased, and mouse survival was decreased upon implantation as orthoptic allografts. Both RNA-seq and proteomic analysis using multiplex inhibitor beads with mass spectrometry (MIB-MS) showed significantly altered kinome profiles. Pten deleted cells were 5-fold more sensitive to the EGFR TKI neratinib, a drug that induced Pten-dependent modulation of the kinase transcriptome over 48h. This acute transcriptional adaptation implies alteration of the epigenetic landscape. We hypothesized that disruption of enhancer dynamics via BET bromodomain inhibition would improve EGFR TKI durability. We found that cells expressing Pten were 10-fold more sensitive to multiple BET inhibitors, including JQ1, birabresib, and molibresib, and these inhibitors synergized with neratinib to reduce proliferation only in the Pten wild type model. Ongoing work is focused on defining the role of PTEN in maintenance of differential transcriptional and epigenetic programs. We will explore potential mechanistic roles of both the enzymatic and non-enzymatic functions of Pten and characterize its effect on hallmark cancer phenotypes such as proliferation, stemness/self-renewal, and tumorigenesis in the presence and absence of EGFR ± BET inhibitors.

e15597 Background: In the US, colorectal cancer (CRC) is the third most common cancer. Patients receiving regorafenib, a multiple-kinase inhibitor, recommended to manage metastatic CRCs (mCRCs), has a modest improvement in median overall survival but it is associated with several toxicities. Our present study addresses regorafenib-induced toxicity concerns by combining regorafenib with a novel dual JAK-HDAC inhibitor (JAK-HDACi). The rationale for the dual inhibitor drug selection is due to the facts that the JAK/STAT/SOCS pathway is modulated in CRCs, and concurrent inhibition of JAK sensitizes solid tumors to HDACi. This study focused on evaluating the efficacy and reducing regorafenib-induced toxicity with this novel therapeutic combination in CRC preclinical models. Methods: We evaluated the toxicity of the JAK-HDACi, regorafenib, and their combination in normal colonic cells (CRL-1807) and their efficacy in CRC cell lines (HCT116, RKO, HT29, and SW480) exhibiting various statuses of p53, KRAS, BRAF, EGFR, and microsatellite instability, by conducting colony formation, cell proliferation, and cell cycle arrest assays. Kinome profiling and whole transcriptomic analysis were performed. Their efficacy was assessed in vivo in a CRC patient-derived xenograft (PDX) model, and experimental metastasis was evaluated in NSG mice using luciferase-tagged HT29 cells. Non-invasive, whole-body bioluminescence imaging was performed. Tumor tissues were harvested and stored at −80°C or prepared formalin-fixed paraffin-embedded blocks for Hematoxylin and Eosin (H&E) and immunostaining. Serum analysis was performed to evaluate liver and kidney functions to assess the toxicity. Results: At 500 nM concentrations, there was no pronounced death of CRL-1807 cells, but reduced number of colonies in CRC cells. Drug treatments decreased phosphorylation of STAT3 and ERK1/2 and cell viability, wherein the reduction was robust in the combination. The combination reduced activity of various kinases, as evident through kinome profiling. In SW480 cells, the combination caused G0-G1 cell arrest and decreased the S phase. RNA-seq results revealed modulation of key pathways: apoptosis, ECM-receptor interaction, and focal adhesion. The PDX model showed that the combination treatment reduced tumor growth, as evidenced in H&E staining with higher necrosis and reduced Ki67 staining. Experimental metastasis, bioluminescence imaging, and histological examination showed pronounced reduction in metastasis in mice treated with the combination. Serum chemistry profiles showed that the treatments did not cause systemic toxicity to mice used in either model. Conclusions: The combination therapy with the JAK-HDACi and regorafenib was more effective than the single agents with no evident toxicity. These findings lend credence to a clinical trial to assess this combination for treatment of patients with advanced CRC.

Purpose/Objective(s) To molecularly characterize radiation-selected and control GBM patient-derived xenografts using targeted exome sequencing and RNA-seq for gene expression profiling to identify mechanisms of radiation resistance. Materials/Methods GBM is a devastating CNS malignancy, which in spite of chemotherapy and radiation, often recurs causing significant morbidity and mortality. While there exists numerous hypotheses concerning the treatment resistance of these tumors, the molecular nature of their resistance to therapy has not been fully characterized. To address this shortcoming, eight pairs of PDXs were created, with one of each pair being selected for radiation resistance and the other passaged in heterotopic mouse model as a control. Each tumor was molecularly characterized using targeted exome sequencing and RNA-seq for gene expression profiling. Previously validated bioinformatics tools (e.g., PatternCNV, bowtie2, SAMTools, wANNOVAR) in addition to custom scripts were used for analysis. Results At the genomic level, a recurrent locus of copy-number change in RT-selected pairs was identified at chromosome 12q, suggesting one possible mechanism of treatment resistance. At the tumor transcriptome level, the vast majority of genes that significantly change within one PDX pair are not conserved in all other pairs suggesting a diversity in adaptive response. Underlying patterns emerge, though, with genes involved in glycolysis, hypoxia response, and WNT pathway signaling being up-regulated in response to RT-selection. At the level of the tumor microenvironment, genes on the mitochondrial chromosome are disproportionately under-expressed in the mouse tissue with tumors that were RT-selected. Conclusion Our PDX lines generally maintain their classic genomic changes (e.g., EGFR mutation and structural alteration, and mutational profiles) after radiation selection, a finding qualitatively similar to previous studies in human primary and recurrent GBMs. A recurrent locus of amplification (chr12q) occurred suggesting importance in treatment resistance. The RNA-seq findings suggest that there are multiple pathways that undergo dysregulation in response to radiation. However, there is coherence in adaptation both within the tumor and in the tumor microenvironment. Additionally, the difference identified in the mouse transcriptome of the tumor-associated cells further underscores the importance of the tumor microenvironment and tumors' ability to selectively alter its composition. Future extensions of this work will include targeting the identified pathways with drugs known to cross the blood brain barrier.

Glioblastoma (GBM) is the most common malignant brain tumor in adults with a dismal 15-month median survival. Standard therapy consisting of surgical resection, radiation, and temozolomide has been unsuccessful in meaningfully extending survival and preventing recurrence; thus, novel therapeutics are urgently needed. One proposed targeted treatment strategy for GBM involves using small molecule inhibitors against common genetic mutations. Epidermal growth factor receptor (EGFR) is the most commonly overexpressed oncogene in GBM (~56%). While EGFR tyrosine kinase inhibitors (TKI) have shown promise in other cancers, GBM clinical trials with EGFR TKI have failed. One reason for this failure is the development of adaptive therapeutic resistance. Understanding the mechanisms behind drug resistance is essential for the development of novel, effective therapeutics for GBM. To better understand adaptive resistance in GBM, we utilized two genetically engineered mouse astrocyte lines harboring common GBM mutations: Cdkn2a-/-, EGFRvIII (CEv3) and Cdkn2a-/-, Pten-/-, EGFRvIII (CEV3P). CDKN2A and PTEN are commonly deleted or otherwise inactivated tumor suppressor genes in GBM while the vIII variant of EGFR is the single most common oncogene mutation, making it an attractive therapeutic target. Cell lines CEv3 and CEv3P are both sensitive to neratinib, an irreversible second-generation EGFR TKI, at IC50 of 0.24μM and 0.13µM, respectively. To better understand adaptive response to neratinib treatment, we profiled the transcriptome with RNA sequencing at 0, 4, 24, and 48 hours. Our data shows that kinome rewiring is detectable after just 4 hours of treatment and sustained through 48 hours, with differential expression of 70% or more of the expressed kinome. We propose that differentially expressed kinases in response to neratinib can potentially activate alternative signaling pathways that bypass EGFR inhibition, which ultimately confers resistance to EGFR targeted therapy. Furthermore, we hypothesize that the epigenome is directly responsible for this adaptive kinome response through BRD4 dependent enhancer remodeling. Because dual therapy against EGFR and BRD4 has shown promising results in other cancers, targeting the epigenome through BRD4 represents a potential combination therapy with EGFR TKI in GBM. To profile BRD4-associated epigenomic changes, we used Cleavage Under Targets and Release Using Nuclease (CUT&RUN) to interrogate several regulatory marks (H3K4me1, K3K4me3, H3K27ac) in addition to BRD4. We seek to integrate RNA sequencing and CUT&RUN data to determine if kinases differentially expressed following neratinib treatment correlate with epigenetic marks for their respective enhancer(s). This work will provide insight into the adaptive resistance mechanism of EGFR driven GBM. Citation Format: Benjamin Lin, Julia Ziebro, Kasey R. Skinner, Abigail Shelton, Erin Smithberger, Ryan Bash, Frank B. Furnari, Ryan Miller. Elucidating the transcriptomic response to EGFR-targeted therapy in EGFR-driven glioblastoma [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 1125.

Glioblastoma (GBM) is a malignant brain tumor that has proven difficult to treat, despite expressing promising targets such as EGFRvIII. EGFRvIII, a mutant version of the epidermal growth factor receptor (EGFR), is constitutively active and not present in normal brain cells. The tumor specificity of EGFRvIII and the frequent EGFR amplification seen in GBM make EGFR a potentially attractive therapeutic target; however, clinical studies have shown little to no efficacy for EGFR tyrosine kinase inhibitors (TKI). One reason for this lack of efficacy may be adaptive resistance. We used RNA sequencing and multiplexed inhibitor beads with mass spectrometry (MIB-MS) to study the transcriptomes and kinomes of genetically engineered mouse astrocytes to investigate this resistance and identify potential targets for dual inhibition. Out of 329 kinases detected by MIB-MS, 76 were differentially expressed between cells with Cdkn2a deletion (“C”) and cells that also overexpressed EGFRvIII (“CEv3”). Thirty-four of these kinases were overexpressed in the CEv3 cells relative to the parental C cells (log2 fold change of 5.6, p<1x105). One of these kinases, Cdk6, is also significantly overexpressed in CEv3 cells versus cells that have a further loss of function mutation of Pten (“CEv3P”) (log2 fold change of 5.6, p<1x105). Despite this significant differential expression at the protein level, RNA expression of Cdk6 was similar between cell lines. When these cells were treated with the CDK6 inhibitor abemaciclib, CEv3 cells were found to be significantly more sensitive to inhibition than C and CEv3P cells (IC50 of 0.10 μM vs. 0.18 μM and 0.23 μM, respectively). Similarly, when cells were treated with abemaciclib in combination with the EGFR inhibitor neratinib, there was significantly higher synergy in CEv3 cells than C or CEv3P cells. Genotypically-matched patient-derived xenograft (PDX) cells were assayed for EGFR-CDK6 inhibitor synergy and showed a similar pattern of greater synergy in cells with EGFRvIII overexpression and functional PTEN than cells with EGFRvIII overexpression and PTEN loss. CEv3 and CEv3P cells were orthotopically implanted into mice and treated with neratinib, abemaciclib, or a combination. In CEv3-injected mice, combination treatment led to significantly longer survival than either single agent or control treatment. However, in CEv3P-injected mice, no survival difference was seen between any of the treatment arms. Taken together, these data provide strong evidence that CDK6 is a promising target for combination treatment with EGFR inhibitors in glioblastoma. Citation Format: Erin Smithberger, Abigail K. Shelton, Ryan E. Bash, Madison K. Butler, Alex R. Flores, Allie Stamper, Steven P. Angus, Michael P. East, Gary L. Johnson, Michael E. Berens, Frank B. Furnari, Ryan Miller. Glioblastoma growth is suppressed dual inhibition of EGFR and CDK6 kinases [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 1857.

Key molecular regulators of acquired radiation resistance in recurrent glioblastoma (GBM) are largely unknown, with a dearth of accurate preclinical models. To address this, we generated 8 GBM patient-derived xenograft (PDX) models of acquired radiation therapy-selected (RTS) resistance compared with same-patient, treatment-naive (radiation-sensitive, unselected; RTU) PDXs. These likely unique models mimic the longitudinal evolution of patient recurrent tumors following serial radiation therapy. Indeed, while whole-exome sequencing showed retention of major genomic alterations in the RTS lines, we did detect a chromosome 12q14 amplification that was associated with clinical GBM recurrence in 2 RTS models. A potentially novel bioinformatics pipeline was applied to analyze phenotypic, transcriptomic, and kinomic alterations, which identified long noncoding RNAs (lncRNAs) and targetable, PDX-specific kinases. We observed differential transcriptional enrichment of DNA damage repair pathways in our RTS models, which correlated with several lncRNAs. Global kinomic profiling separated RTU and RTS models, but pairwise analyses indicated that there are multiple molecular routes to acquired radiation resistance. RTS model-specific kinases were identified and targeted with clinically relevant small molecule inhibitors. This cohort of in vivo RTS patient-derived models will enable future preclinical therapeutic testing to help overcome the treatment resistance seen in patients with GBM.

Glioblastoma (GBM) is a devastating primary brain tumor with 5-year survival < 5%. CDKN2A deletion (~60%) and EGFR amplification (55–60%) mutations frequently co-occur in these tumors. EGFR is an attractive therapeutic target due to its mutational frequency and availability of multiple brain-penetrant tyrosine kinase inhibitors (TKI). Several EGFR TKI have failed clinically, due in part to acquired resistance. To mechanistically examine this type of resistance, we used genetically engineered mouse astrocytes harboring Cdkn2a deletion and EGFRvIII, a common (35%) activating mutation. Resistant cells were generated via chronic exposure to gefitinib or erlotinib, either in vitro or in vivo. Resistance to these first-generation EGFR TKI conferred cross resistance (up to 36-fold ΔIC50) to a panel of second- and third-generation TKI relative to sensitive parental lines. Moreover, integrated RNA sequencing (RNA-seq) and chemical proteomics (multiplexed inhibitor beads and mass spectrometry (MIB-MS)) showed that the kinase transcriptome and proteome were rewired in resistant cells: 113 of ~300 detected kinases were differentially expressed (p< 0.05). We then used these techniques to examine acute (≤ 48 h) kinome changes in both sensitive and resistant cells upon treatment with a CNS-penetrant, second-generation EGFR TKI, afatinib. Whereas exposure of treatment-naïve, sensitive cells to afatinib significantly rewired the kinome (120 differentially expressed kinases), the response of resistant cells to drug re-challenge was significantly blunted (13 differentially expressed kinases). A subset of expressed kinases (35 of 263) dynamically responded to afatinib in both sensitive and resistant cells. Overall, upregulated kinases include those implicated in the biology of gliomas (Bmx, Fgfr2) and of other cancers (Pdgfrb, Mapk3/4, Ddr1/2, Pdk2). These kinases thus represent putative druggable targets for dual inhibition therapy. Integrated kinome profiling using MIB-MS and RNA-seq in GBM models with defined mutational profiles provides a powerful framework to identify novel therapeutic targets that could significantly alter current treatment paradigms.

Background Glioblastoma-associated macrophages and microglia (GAMs) are the predominant immune cells in the tumor microenvironment. Activation of MerTK, a receptor tyrosine kinase, polarizes GAMs to an immunosuppressive phenotype, promoting tumor growth. Here, the role of MerTK inhibition in the glioblastoma microenvironment is investigated in vitro and in vivo. Methods Effects of MRX-2843 in glioblastoma microenvironment regulation were determined in vitro by cell viability, cytokine array, in vitro tube formation, Western blotting, and wound healing assays. A syngeneic GL261 orthotopic glioblastoma mouse model was used to evaluate the survival benefit of MRX-2843 treatment. Multiplex fluorescent immunohistochemistry was used to evaluate the expression of CD206, an anti-inflammatory marker on GAMs, and angiogenesis in murine brain tumor tissues. Results MRX-2843 inhibited cell growth and induced apoptosis in human glioblastoma cells and decreased protein expression of phosphorylated MerTK, AKT, and ERK, which are essential for cell survival signaling. Interleukin-8 and C-C motif chemokine ligand 2, the pro-glioma and pro-angiogenic cytokines, were decreased by MRX-2843. Decreased vascular formation and numbers of immunosuppressive (CD206+) GAMs were observed following MRX-2843 treatment in vivo, suggesting that in addition to alleviating immunosuppression, MRX-2843 also inhibits neoangiogenesis in the glioma microenvironment. These results were supported by a prolonged survival in the syngeneic mouse orthotopic GL261 glioblastoma model following MRX-2843 treatment. Conclusion Our findings suggest that MRX-2843 has a therapeutic benefit via promoting GAM polarization away from immunosuppressive condition, inhibiting neoangiogenesis in the glioblastoma microenvironment and inducing tumor cell death.

Glioblastoma (GBM) is an aggressive primary brain tumor with poor survival and limited treatment options. However, it is an attractive candidate for precision therapeutic approaches due to the frequency of amplification and/or activating mutations in the epidermal growth factor receptor (EGFR) gene and the availability of several brain penetrant second- and third-generation EGFR tyrosine kinase inhibitors (TKI). We used comprehensive molecular profiling of a panel of genetically engineered mouse astrocyte models to examine whether mutational profiles, particularly EGFR and PTEN status, could be used to identify kinases upregulated in specific mutational backgrounds. Using RNA-seq and multiplex inhibitor bead/mass spectrometry (MIB-MS) to analyze the kinase transcriptomes and proteomes, respectively, we have identified several potential targets for combination therapy. Overexpression of wild type EGFR in immortalized, Cdkn2a-/- astrocytes resulted in mild rewiring of the GBM kinome. Only 5 kinases aside from EGFR itself were overexpressed on either the transcript or protein levels. One overexpressed kinase, Hck, has been shown to be involved in cell survival, proliferation, adhesion, and migration. In contrast, overexpression of EGFRvIII, a constitutively active, extracellular domain truncation mutant of EGFR, resulted in significant alteration of the GBM kinome – 81 kinases showed differential expression, with 27 upregulated. One potentially attractive target among these was Cdk6, a drug-targetable, prognostically significant cyclin-dependent kinase implicated in proliferation, migration, and invasion. Finally, overexpression of EGFRvIII in cells lacking Pten dysregulated 46 kinases, including 15 upregulated. One particularly interesting target in these cells was Ddr2, a tyrosine kinase involved in migration, invasion, and extracellular matrix remodeling. We conclude that Hck, Cdk6, and Ddr2 represent attractive targets for therapeutic intervention in their relevant genetic contexts. These findings also suggest that molecular diagnostics for EGFR and PTEN status may be useful in guiding development of rational, EGFR TKI-centric drug combinations.

Glioblastoma (GBM) is an aggressive primary brain tumor with a poor survival rate. One of the most common molecular alterations seen in GBM is amplification and/or mutation of the Epidermal Growth Factor Receptor (EGFR), which has made it an attractive therapeutic target. However, several EGFR tyrosine kinase inhibitors have been tested clinically in GBM with minimal success. One reason for this lack of efficacy could be due to acute, adaptive resistance via alternative pathway activation. To investigate this mechanism of tumor resistance, we used RNA-seq and multiplex inhibitor bead/mass spectrometry (MIB-MS) to analyze the transcriptomes and kinomes of genetically engineered murine astrocytes with common GBM genotypes. We have previously shown that 38% of the expressed kinome varied among a panel of diverse nGEM astrocytes harboring Cdkn2a deletion (C) plus Pten deletion (CP), wild-type human EGFR (CE) or EGFRvIII (CEv3) overexpression or both EGFRvIII overexpression and Pten deletion (CEv3P). Although CE have a similar transcriptional profile to C cells at baseline, when treated with the EGFR inhibitor afatinib, CE respond more similarly to CEv3 cells. When cells containing endogenous murine EGFR (C and CP) are treated with afatinib, fewer than 0.5% of kinases showed differential expression. In cells with EGFR overexpression alone, more than 6% of kinases were differentially expressed upon afatinib treatment, including Ntrk3, Fgfr2 and 3, Lyn, Bmx, Epha2 and 5, Fn3k, a kinase involved in fructosamine processing, and Nrbp2, a kinase involved in regulation of apoptosis. This effect was blunted in cells lacking Pten in addition to having EGFRvIII (CEv3P), resulting in less than 2% of kinases being differentially expressed. The only kinase upregulated in all three EGFR-overexpressing cell types was Coq8a, which is involved in electron transport and response to DNA damage. Given this overlap in response, Coq8a could be a potential dual treatment target for GBM.

Abstract Gliomas are diffusely invasive brain tumors with fatal outcomes and few effective treatments. Precision medicine focuses on targeting the genetics of individual tumors, but not host genetics, despite studies that have linked germline polymorphisms with glioma risk. Accordingly, glioma survival studies in mice utilize genetically variable tumors on identical host genetic backgrounds, which fails to differentiate between cancer cell-autonomous (CCA) and tumor microenvironment (TME) effects on glioma progression and host survival. The Collaborative Cross (CC) is a panel of genetically diverse mouse strains derived from both wild- and traditional inbred laboratory strains that facilitates high-resolution genetic mapping in models of complex disease. Here, we implement a novel platform to discover genetic modifiers of both CCA and TME phenotypes using genetically defined orthotopic murine allograft gliomas and CC hosts. We stereotactically injected Nf1;Trp53-/-oligodendrocyte progenitor-derived mouse tumor cells into syngeneic C57BL/6 control mice and 14 different CC strains. Seven strains survived significantly longer than controls (P<0.05), suggesting slower tumor growth (Gs, growth slow). The remaining 7 strains survived similarly to controls, suggesting fast growth (Gf, growth fast). Variable tumor growth in CC mice suggests that genetic background influences molecular processes in the TME that inhibit or potentiate tumor growth, respectively. To identify candidate genes, we performed RNA sequencing on 36 tumors from 3 Gf strains, 4 Gs strains, and controls. 134 genes were differentially expressed among Gf, Gs, and control tumors (P<0.05). Hierarchical clustering on these genes revealed that Gs strains clustered separately from Gf and controls. Gene ontology analysis using GOrilla showed 30 enriched processes, (FDR q<0.001), all of which were involved in immune responses or extracellular matrix biology. These results suggest that Gs strains activate immune and TME processes that slow tumor growth. Quantitative trait locus (QTL) analyses of host genetics and tumor data are pending and will facilitate identification of genetic variants that influence TME effects on tumor progression. Citation Format: Kasey Skinner, Martin Ferris, Ryan Bash, Abigail Shelton, Erin Smithberger, Steve Angus, Brian Golitz, Noah Sciaky, Jeremy Simon, Jason Stein, Glenn Matsushima, Quinn Ostrom, Lindsay Stetson, Jill Barnholtz-Sloan, Harshil Dhruv, Michael Berens, Fernando Pardo Manuel de Villena, C. Ryan Miller. Tumor microenvironment and host genetics impact glioma progression in a Collaborative Cross-based orthotopic allograft model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2745.