Trans-lesion synthesis and mismatch repair pathway crosstalk defines chemoresistance and hypermutation mechanisms in glioblastoma

Almost all Glioblastoma (GBM) are either intrinsically resistant to the chemotherapeutical drug temozolomide (TMZ) or acquire therapy-induced mutations that cause chemoresistance and recurrence. The genome maintenance mechanisms responsible for GBM chemoresistance and hypermutation are unknown. We show that the E3 ubiquitin ligase RAD18 (a proximal regulator of TLS) is activated in a Mismatch repair (MMR)-dependent manner in TMZ-treated GBM cells, promoting post-replicative gap-filling and survival. An unbiased CRISPR screen provides an aerial map of RAD18-interacting DNA damage response (DDR) pathways deployed by GBM to tolerate TMZ genotoxicity. Analysis of mutation signatures from TMZ-treated GBM reveals a role for RAD18 in error-free bypass of O6mG (the most toxic TMZ-induced lesion), and error-prone bypass of other TMZ-induced lesions. Our analyses of recurrent GBM patient samples establishes a correlation between low RAD18 expression and hypermutation. Taken together we define molecular underpinnings for the hallmark tumorigenic phenotypes of TMZ-treated GBM.

Breaking the feed forward inflammatory cytokine loop in the tumor microenvironment of PDGFB-driven glioblastomas

Glioblastoma (GBM) tumor-associated macrophages (TAMs) provide a major immune cell population contributing to growth and immunosuppression via the production of proinflammatory factors, including IL-1. In this issue of the JCI, Chen, Giotti, and colleagues investigated loss of ll1b in the immune tumor microenvironment (TME) in GBM models driven by PDGFB expression and Nf1 knockdown. Survival was only improved in PDGFB-driven GBM models, suggesting that tumor cell genotype influenced the immune TME. IL-1β in the TME increased PDGFB-driven GBM growth by increasing tumor-derived NF-κB, expression of monocyte chemoattractants, and increased infiltration of bone marrow-derived myeloid cells (BMDMs). In contrast, no requirement for IL-1β was evident in Nf1-silenced tumors due to high basal levels of NF-κB and monocyte chemoattractants and increased infiltration of BMDM and TAMs. Notably, treatment of mice bearing PDGFB-driven GBM with anti-IL-1β or an IL1R1 antagonist extended survival. These findings suggest that effective clinical immunotherapy may require differential targeting strategies.

Spatially Resolved Whole Transcriptome Analysis of Histologically-Characterized Tissue Microarray of Patient-Matched Primary and Recurrent Glioblastomas to Identify Underlying Mechanisms of Treatment Resistance

PURPOSE/OBJECTIVE(S)

Glioblastoma multiforme (GBM) is a lethal CNS malignancy. Radiation therapy increases overall survival, but tumors often recur in high-radiation dose regions. Additionally, recent investigations have underscored the importance of intra-tumoral heterogeneity as a driver of GBM biology. The purpose of this investigation is to characterize transcriptome differences in primary and recurrent GBM patient clinical samples using a digital spatial profiling approach to better appreciate treatment resistance mechanisms.

MATERIALS/METHODS

To address the lack of understanding of molecular mechanisms of resistance in GBM, patient-matched primary and recurrent GBM pathological specimens were identified within the brain tissue biorepository and tissue cores were selected for generation of a tissue microarray (TMA). Hematoxylin and eosin staining with histomorphological (cellular tumor, pseudopalisading necrosis, invasive edge, and perivascular inflammation) scoring were performed in a blinded fashion for every core. This array was then molecularly characterized using digital spatial profiling of the transcriptome. Quality assurance including filtering of lowly expressed genes followed by downstream analyses of the data were performed using the manufacturer's recommended methods within their Bioconductor library. Gene Set Enrichment Analysis (GSEA) was then performed on the ranked gene lists.

RESULTS

After recommended filtering, 6171 genes and 248 regions of interest remained for downstream analysis representing 22 unique patients across four different tumor histomorphological types. Significance testing revealed 679 genes that were differentially expressed between primary and recurrent tumor samples (at FDR<1%). On GSEA analysis, the chromosomal positional locus that contains genes most strongly up-regulated is 12q14, a locus that was previously identified as genomically amplified in multiple patient-derived xenograft lines after radiation selection. Additionally, recurrent tumors display a transcriptional profile more similar to the mesenchymal subtype, whereas primary tumors have a more classical transcriptional phenotype. The epithelial-to-mesenchymal transition pathway is particularly strongly up-regulated in recurrent tumors.

CONCLUSION

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.

Glioma Stem Cells Are Sensitized to BCL-2 Family Inhibition by Compromising Histone Deacetylases

Glioblastoma (GBM) remains an incurable disease with an extremely high five-year recurrence rate. We studied apoptosis in glioma stem cells (GSCs) in response to HDAC inhibition (HDACi) combined with MEK1/2 inhibition (MEKi) or BCL-2 family inhibitors. MEKi effectively combined with HDACi to suppress growth, induce cell cycle defects, and apoptosis, as well as to rescue the expression of the pro-apoptotic BH3-only proteins BIM and BMF. A RNAseq analysis of GSCs revealed that HDACi repressed the pro-survival BCL-2 family genes MCL1 and BCL-XL. We therefore replaced MEKi with BCL-2 family inhibitors and observed enhanced apoptosis. Conversely, a ligand for the cancer stem cell receptor CD44 led to reductions in BMF, BIM, and apoptosis. Our data strongly support further testing of HDACi in combination with MEKi or BCL-2 family inhibitors in glioma.

Haploinsufficiency of NFKBIA reshapes the epigenome antipodal to the IDH mutation and imparts disease fate in diffuse gliomas

Genetic alterations help predict the clinical behavior of diffuse gliomas, but some variability remains uncorrelated. Here, we demonstrate that haploinsufficient deletions of chromatin-bound tumor suppressor NFKB inhibitor alpha (NFKBIA) display distinct patterns of occurrence in relation to other genetic markers and are disproportionately present at recurrence. NFKBIA haploinsufficiency is associated with unfavorable patient outcomes, independent of genetic and clinicopathologic predictors. NFKBIA deletions reshape the DNA and histone methylome antipodal to the IDH mutation and induce a transcriptome landscape partly reminiscent of H3K27M mutant pediatric gliomas. In IDH mutant gliomas, NFKBIA deletions are common in tumors with a clinical course similar to that of IDH wild-type tumors. An externally validated nomogram model for estimating individual patient survival in IDH mutant gliomas confirms that NFKBIA deletions predict comparatively brief survival. Thus, NFKBIA haploinsufficiency aligns with distinct epigenome changes, portends a poor prognosis, and should be incorporated into models predicting the disease fate of diffuse gliomas.

Relationships between gene expression and behavior in mice in response to systemic modulation of the O-GlcNAcylation pathway

Enhancing protein O-GlcNAcylation by pharmacological inhibition of the enzyme O-GlcNAcase (OGA), which removes the O-GlcNAc modification from proteins, has been explored in mouse models of amyloid-beta and tau pathology. However, the O-GlcNAcylation-dependent link between gene expression and neurological behavior remains to be explored. Using chronic administration of Thiamet G (TG, an OGA inhibitor) in vivo, we used a protocol designed to relate behavior with the transcriptome and selected biochemical parameters from the cortex of individual animals. TG-treated mice showed improved working memory as measured using a Y-maze test. RNA sequencing analysis revealed 151 top differentially expressed genes with a Log2fold change >0.33 and adjusted p-value <0.05. Top TG-dependent upregulated genes were related to learning, cognition and behavior, while top downregulated genes were related to IL-17 signaling, inflammatory response and chemotaxis. Additional pathway analysis uncovered 3 pathways, involving gene expression including 14 cytochrome c oxidase subunits/regulatory components, chaperones or assembly factors, and 5 mTOR (mechanistic target of rapamycin) signaling factors. Multivariate Kendall correlation analyses of behavioral tests and the top TG-dependent differentially expressed genes revealed 91 statistically significant correlations in saline-treated mice and 70 statistically significant correlations in TG-treated mice. These analyses provide a network regulation landscape that is important in relating the transcriptome to behavior and the potential impact of the O-GlcNAC pathway.

Quinolinate promotes macrophage-induced immune tolerance in glioblastoma through the NMDAR/PPARγ signaling axis

There has been considerable scientific effort dedicated to understanding the biologic consequence and therapeutic implications of aberrant tryptophan metabolism in brain tumors and neurodegenerative diseases. A majority of this work has focused on the upstream metabolism of tryptophan; however, this has resulted in limited clinical application. Using global metabolomic profiling of patient-derived brain tumors, we identify the downstream metabolism of tryptophan and accumulation of quinolinate (QA) as a metabolic node in glioblastoma and demonstrate its critical role in promoting immune tolerance. QA acts as a metabolic checkpoint in glioblastoma by inducing NMDA receptor activation and Foxo1/PPARγ signaling in macrophages, resulting in a tumor supportive phenotype. Using a genetically-engineered mouse model designed to inhibit production of QA, we identify kynureninase as a promising therapeutic target to revert the potent immune suppressive microenvironment in glioblastoma. These findings offer an opportunity to revisit the biologic consequence of this pathway as it relates to oncogenesis and neurodegenerative disease and a framework for developing immune modulatory agents to further clinical gains in these otherwise incurable diseases.

Cooperativity between H3.3K27M and PDGFRA poses multiple therapeutic vulnerabilities in human iPSC-derived diffuse midline glioma avatars

Diffuse midline glioma (DMG) is a leading cause of brain tumor death in children. In addition to hallmark H3.3K27M mutations, significant subsets also harbor alterations of other genes, such as TP53 and PDGFRA. Despite the prevalence of H3.3K27M, the results of clinical trials in DMG have been mixed, possibly due to the lack of models recapitulating its genetic heterogeneity. To address this gap, we developed human iPSC-derived tumor models harboring TP53R248Q with or without heterozygous H3.3K27M and/or PDGFRAD842V overexpression. The combination of H3.3K27M and PDGFRAD842V resulted in more proliferative tumors when gene-edited neural progenitor (NP) cells were implanted into mouse brains compared to NP with either mutation alone. Transcriptomic comparison of tumors and their NP cells of origin identified conserved JAK/STAT pathway activation across genotypes as characteristic of malignant transformation. Conversely, integrated genome-wide epigenomic and transcriptomic analyses, as well as rational pharmacologic inhibition, revealed targetable vulnerabilities unique to the TP53R248Q; H3.3K27M; PDGFRAD842V tumors and related to their aggressive growth phenotype. These include AREG-mediated cell cycle control, altered metabolism, and vulnerability to combination ONC201/trametinib treatment. Taken together, these data suggest that cooperation between H3.3K27M and PDGFRA influences tumor biology, underscoring the need for better molecular stratification in DMG clinical trials.

TB-1 ADDITIONAL GENETIC ALTERATIONS DIFFERENTIALLY ALTER THE TRANSCRIPTOMIC LANDSCAPE OF H3 K27M-MUTANT DIFFUSE MIDLINE GLIOMA

Histone H3 K27M mutation is a hallmark mutation for H3 K27M-mutant diffuse midline glioma (DMG), but targeting this mutation has yet to achieve a significant survival benefit in clinical trials. Recent analyses revealed alterations in several genes, such as NF1 and PDGFRA, are observed in substantial subpopulations of H3 K27M-mutant DMG patients in addition to H3 mutation and recurrent TP53 mutations, indicating patient-to-patient tumor heterogeneity and the potential necessity of tailored target therapy for the treatment of this disease. Here, using our human induced pluripotent stem cells (iPSC)-derived glioma avatar platform, we designed DMG models by introducing TP53R248Q with or without heterozygous H3 K27M mutation in combination with further genetic modifications of either NF1 knockout or PDGFRAD842V overexpression to recapitulate DMG subpopulations. Mice with TP53R248Q; H3F3AK27M (QM) tumors survived significantly longer than those harboring QM;NF1-/- (QMN) tumors and QM; PDGFRAD842Voe (QMP) tumors. RNA-sequencing of those induced DMG (iDMG) neurospheres revealed altered patterns of upregulation of MAPK pathway genes both in QMN and QMP-iDMG neurospheres compared to their H3 wildtype counterparts with the same combinations of genetic alterations, suggesting that those additional mutations modifies the oncogenic signaling associated with H3 K27M mutation. Further, differential expression analysis comparing QMN and QMP-iDMG neurospheres revealed 405 differentially expressed genes. Gene set enrichment analysis showed upregulation of transcriptional programs related to mesenchymal signature in QMN-iDMG neurospheres and proneural signature in QMP-iDMG neurosphere as expected. These data show that NF1 deletion and PDGFRAD842V overexpression significantly alter gene expression in H3 K27M-mutant iDMG tumors, potentially opening up a new therapeutic avenue in these devastating tumors with patient-to-patient heterogeneity. Further work using these models will shed light on the development of tailored therapy based on detailed genetic information on each patient sample, such as combining targeted kinase inhibition with HDAC inhibitors that have shown promise in the clinic.

Inter-pathologist agreement on diagnosis, classification and grading of canine glioma

Histopathological evaluation of tumours is a subjective process, but studies of inter-pathologist agreement are uncommon in veterinary medicine. The Comparative Brain Tumour Consortium (CBTC) recently published diagnostic criteria for canine gliomas. Our objective was to assess the degree of inter-pathologist agreement on intracranial canine gliomas, utilising the CBTC diagnostic criteria in a cohort of eighty-five samples from dogs with an archival diagnosis of intracranial glioma. Five pathologists independently reviewed H&E and immunohistochemistry sections and provided a diagnosis and grade. Percentage agreement and kappa statistics were calculated to measure inter-pathologist agreement between pairs and amongst the entire group. A consensus diagnosis of glioma subtype and grade was achieved for 71/85 (84%) cases. For these cases, percentage agreement on combined diagnosis (subtype and grade), subtype only and grade only were 66%, 80% and 82%, respectively. Kappa statistics for the same were 0.466, 0.542 and 0.516, respectively. Kappa statistics for oligodendroglioma, astrocytoma and undefined glioma were 0.585, 0.566 and 0.280 and were 0.516 for both low-grade and high-grade tumours. Kappa statistics amongst pairs of pathologists for combined diagnosis varied from 0.352 to 0.839. 8 % of archival oligodendrogliomas and 61% of archival astrocytomas were reclassified as another entity after review. Inter-pathologist agreement utilising CBTC guidelines for canine glioma was moderate overall but varied from fair to almost perfect between pairs of pathologists. Agreement was similar for oligodendrogliomas and astrocytomas but lower for undefined gliomas. These results are similar to pathologist agreement in human glioma studies and with other tumour entities in veterinary medicine.

EGFR, the Lazarus target for precision oncology in glioblastoma

The Lazarus effect is a rare condition that happens when someone seemingly dead shows signs of life. The epidermal growth factor receptor (EGFR) represents a target in the fatal neoplasm glioblastoma (GBM) that through a series of negative clinical trials has prompted a vocal subset of the neuro-oncology community to declare this target dead. However, an argument can be made that the core tenets of precision oncology were overlooked in the initial clinical enthusiasm over EGFR as a therapeutic target in GBM. Namely, the wrong drugs were tested on the wrong patients at the wrong time. Furthermore, new insights into the biology of EGFR in GBM vis-à-vis other EGFR-driven neoplasms, such as non-small cell lung cancer, and development of novel GBM-specific EGFR therapeutics resurrects this target for future studies. Here, we will examine the distinct EGFR biology in GBM, how it exacerbates the challenge of treating a CNS neoplasm, how these unique challenges have influenced past and present EGFR-targeted therapeutic design and clinical trials, and what adjustments are needed to therapeutically exploit EGFR in this devastating disease.

TMET-11. QUINOLINATE PROMOTES ALTERNATIVELY ACTIVATED MACROPHAGE-INDUCED IMMUNE TOLERANCE IN GLIOBLASTOMA THROUGH THE NMDA/PPARG SIGNALING AXIS

There has been considerable interest in understanding the biological consequence and therapeutic implications of aberrant tryptophan metabolism in brain tumors and neurodegenerative diseases. An overwhelming majority of this work has focused on the first-step of tryptophan metabolism (kynurenine); however, this has yet to result in clinical application. Using global metabolomic profiling on &gt;100 patient-derived brain tumors, we identified a 64-fold accumulation of quinolinate (QA), a downstream metabolic intermediate of the tryptophan pathway, in glioblastoma when compared to low-grade glioma. As several metabolites in the tryptophan pathway have been implicated in immune modulation, we sought to determine the impact of QA on the immune microenvironment. We identified the capacity of QA to strongly skew macrophage polarization towards the “pro-tumorigenic” M2-phenotype with suppressive properties, which recent studies suggest play a dominant role in the immune microenvironment in glioblastoma. Intriguingly, QA conferred an “M2-like” phenotype to M1 macrophages and microglia, attenuating their phagocytosis efficiency. We went on to systematically delineate a novel mechanism of macrophage polarization through QA-induced NMDA receptor activation and Foxo1/PPARg signaling. We then determined that tumor cells and host macrophages/microglia work in concert to complete both upstream and downstream metabolism of tryptophan, respectively, resulting in the accumulation of QA. We discovered a very strong positive feedback loop involving the expression of kynureninase (KYNU) in macrophages, an enzyme involved in the downstream metabolism of tryptophan and QA production, making this a lead candidate for targeting this pathway. As this represents a novel target and agents designed to inhibit this enzyme are not commercially available, we generated a Kynu-/- knockout mouse model. Intriguingly, consistent with in vitro data, tumors grown in Kynu-/- mice had a ~50% reduction in M2 macrophages, increased immune activation, decreased growth, and improved overall survival in two orthotopic glioblastoma models, supporting the therapeutic potential of targeting this pathway.

IMMU-05. THE INFLUENCE OF THE KETOGENIC DIET ON THE IMMUNE TOLERANT MICROENVIRONMENT IN GLIOBLASTOMA

Glioblastoma (GBM) represents a particularly aggressive and immune-resistant cancer. Preclinical investigations have identified the anti-tumor activity of a ketogenic diet (KD) in GBM, potentially being used as a tool to target its glycolytic phenotype. Since immune cells in the tumor have a similar reliance upon nutrients to perform their individual functions, we sought to determine if the KD influenced the immune landscape of GBM. Utilizing genetically-engineered murine GBM tumor cells orthotopically implanted in immune-competent mice, we demonstrate that KD improved survival in GBM. Immunophenotyping of tumors identified a novel role KD plays in macrophage polarization, with a paradoxical 50% increase in immune-suppressive M2-macrophages and a decrease in pro-inflammatory M1-macrophages. We recapitulated KD in vitro using a modified cell culture based on comprehensive metabolomic profiling of serum in KD-fed mice. Consistent with in vivo studies, murine macrophages cultured in these conditions skewed polarization towards the M2-phenotype with immune-suppressive properties. We went on to mechanistically link these findings to the activation of transcription factor PPARg. Although anti-tumor activity was observed in mice fed a KD, we hypothesized this parallel increase in M2 macrophage polarization tempered its potential therapeutic benefit. Colony-stimulating factor 1 (CSF-1) plays a central role in macrophage differentiation, and CSF-1R inhibition is actively being investigated as a strategy to skew their polarization towards an M1-phenotype. Therefore, we tested a combination of KD with the brain-penetrant CSF-1R inhibitor BLZ945. Consistent with our hypothesis, this combination demonstrated a striking improvement in survival (p = 0.0004), with 50% of mice achieving long-term survival ( &gt; 50 days). Correlative studies confirmed the capacity of BLZ945 to normalize KD-induced increases in M2s, and the combination induced an increase of anti-tumor iNOS+M1s. Combinatorial strategies using agents designed to modulate macrophage polarization represent a rational approach to improve the anti-tumor activity of KD in GBM.

α2,6 Sialylation mediated by ST6GAL1 promotes glioblastoma growth

One of the least-investigated areas of brain pathology research is glycosylation, which is a critical regulator of cell surface protein structure and function. β-Galactoside α2,6-sialyltransferase (ST6GAL1) is the primary enzyme that α2,6 sialylates N-glycosylated proteins destined for the plasma membrane or secretion, thereby modulating cell signaling and behavior. We demonstrate a potentially novel, protumorigenic role for α2,6 sialylation and ST6GAL1 in the deadly brain tumor glioblastoma (GBM). GBM cells with high α2,6 sialylation exhibited increased in vitro growth and self-renewal capacity and decreased mouse survival when orthotopically injected. α2,6 Sialylation was regulated by ST6GAL1 in GBM, and ST6GAL1 was elevated in brain tumor-initiating cells (BTICs). Knockdown of ST6GAL1 in BTICs decreased in vitro growth, self-renewal capacity, and tumorigenic potential. ST6GAL1 regulates levels of the known BTIC regulators PDGF Receptor β (PDGFRB), Activated Leukocyte Cell Adhesion Molecule, and Neuropilin, which were confirmed to bind to a lectin-recognizing α2,6 sialic acid. Loss of ST6GAL1 was confirmed to decrease PDGFRB α2,6 sialylation, total protein levels, and the induction of phosphorylation by PDGF-BB. Thus, ST6GAL1-mediated α2,6 sialylation of a select subset of cell surface receptors, including PDGFRB, increases GBM growth.

Reciprocal SOX2 regulation by SMAD1-SMAD3 is critical for anoikis resistance and metastasis in cancer

Growth factors in tumor environments are regulators of cell survival and metastasis. Here, we reveal the dichotomy between TGF-β superfamily growth factors BMP and TGF-β/activin and their downstream SMAD effectors. Gene expression profiling uncovers SOX2 as a key contextual signaling node regulated in an opposing manner by BMP2, -4, and -9 and TGF-β and activin A to impact anchorage-independent cell survival. We find that SOX2 is repressed by BMPs, leading to a reduction in intraperitoneal tumor burden and improved survival of tumor-bearing mice. Repression of SOX2 is driven by SMAD1-dependent histone H3K27me3 recruitment and DNA methylation at SOX2's promoter. Conversely, TGF-β, which is elevated in patient ascites, and activin A can promote SOX2 expression and anchorage-independent survival by SMAD3-dependent histone H3K4me3 recruitment. Our findings identify SOX2 as a contextual and contrastingly regulated node downstream of TGF-β members controlling anchorage-independent survival and metastasis in ovarian cancers.

An in vivo model of glioblastoma radiation resistance identifies long non-coding RNAs and targetable kinases

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.

ARID1A-deficient bladder cancer is dependent on PI3K signaling and sensitive to EZH2 and PI3K inhibitors

Metastatic urothelial carcinoma is generally incurable with current systemic therapies. Chromatin modifiers are frequently mutated in bladder cancer, with ARID1A-inactivating mutations present in about 20% of tumors. EZH2, a histone methyltransferase, acts as an oncogene that functionally opposes ARID1A. In addition, PI3K signaling is activated in more than 20% of bladder cancers. Using a combination of in vitro and in vivo data, including patient-derived xenografts, we show that ARID1A-mutant tumors were more sensitive to EZH2 inhibition than ARID1A WT tumors. Mechanistic studies revealed that (a) ARID1A deficiency results in a dependency on PI3K/AKT/mTOR signaling via upregulation of a noncanonical PI3K regulatory subunit, PIK3R3, and downregulation of MAPK signaling and (b) EZH2 inhibitor sensitivity is due to upregulation of PIK3IP1, a protein inhibitor of PI3K signaling. We show that PIK3IP1 inhibited PI3K signaling by inducing proteasomal degradation of PIK3R3. Furthermore, ARID1A-deficient bladder cancer was sensitive to combination therapies with EZH2 and PI3K inhibitors in a synergistic manner. Thus, our studies suggest that bladder cancers with ARID1A mutations can be treated with inhibitors of EZH2 and/or PI3K and revealed mechanistic insights into the role of noncanonical PI3K constituents in bladder cancer biology.

PVT1 is a stress-responsive lncRNA that drives ovarian cancer metastasis and chemoresistance

Metastatic growth of ovarian cancer cells into the peritoneal cavity requires adaptation to various cellular stress factors to facilitate cell survival and growth. Here, we demonstrate the role of PVT1, one such stress induced long non-coding RNA, in ovarian cancer growth and metastasis. PVT1 is an amplified and overexpressed lncRNA in ovarian cancer with strong predictive value for survival and response to targeted therapeutics. We find that expression of PVT1 is regulated by tumor cells in response to cellular stress, particularly loss of cell-cell contacts and changes in matrix rigidity occurring in a YAP1-dependent manner. Induction of PVT1 promotes tumor cell survival, growth, and migration. Conversely, reducing PVT1 levels robustly abrogates metastatic behavior and tumor cell dissemination in cell lines and syngeneic transplantation models in vivo. We find that reducing PVT1 causes widespread changes in the transcriptome leading to alterations in cellular stress response and metabolic pathways including doxorubicin metabolism, which impacts chemosensitivity. Together, these findings implicate PVT1 as a promising therapeutic target to suppress metastasis and chemoresistance in ovarian cancer.

Abstract 632: The immune consequences of a ketogenic diet in GBM and its therapeutic implications

Glioblastoma (GBM) is one of the most complex, deadly, and immune-resistant cancers. Recent investigations have identified a ketogenic diet (KD) as a nutritional intervention in GBM. KD is a high-fat diet with a low carbohydrate intake. It is postulated that a KD dramatically shifts nutritional bioavailability in both tumors and its microenvironment. Since immune cells also rely upon similar nutrients for performing their functions, we hypothesized that a KD might also influence their anti-tumor activity. Consistent with previous publications, utilizing genetically engineered murine GBM tumor cells orthotopically implanted in immune-competent mice, we demonstrated improved survival in mice fed a KD when compared to mice fed a standard diet (p=0.043). To begin to understand the immune consequences of a KD in GBM, we immunophenotyped these tumors. Of the immune cells analyzed, we discovered that KD played an important role in influencing macrophage polarization, which recent investigations suggest play a critical role in inducing a potent immune suppression in GBM. Specifically, anti-tumor activity was observed in mice fed a KD, there was a paradoxical 50% increase in immune suppressive M2 macrophages (CD45+CD11b+F4/80+CD206+) coupled with a decrease in pro-inflammatory M1 macrophages (CD45+CD11b+F4/80+CD80hi). To extend these findings, we recapitulated KD in vitro using a modified cell culture media. Consistent with in vivo studies, murine macrophages cultured in these conditions skewed polarization towards the M2 phenotype with immune suppressive properties and we went on to mechanistically link these findings to activation of transcription factor PPARγ. Although anti-tumor activity was observed in mice fed a KD, we hypothesized this parallel increase in M2 macrophage polarization tempered its potential therapeutic benefit. Colony-stimulating factor 1 (CSF-1) plays a central role in macrophage differentiation and CSF-1 receptor inhibition is actively being investigated as a strategy to skew their polarization towards an M1 anti-tumor phenotype. To test this hypothesis, we performed investigations combining KD with the brain penetrant, clinically relevant CSF-1R inhibitor BLZ945. Consistent with our hypothesis, this combination demonstrated a striking improvement in survival in comparison to KD or BLZ945 alone (p=0.0004) with 50% of mice achieving long term survival (&gt;50 days). Correlative studies confirmed the capacity of BLZ945 to normalize KD-induced increases in M2s and the combination induced an increase of iNOS+ M1s, which are responsible for performing pro-inflammatory functions in tumors. Collectively, although anti-tumor activity was observed with a KD, parallel increases in M2 macrophage tempered its therapeutic benefit. Combinatorial strategies using agents designed to modulate macrophage polarization represent a rational approach to improve the anti-tumor activity of a KD in GBM.

Citation Format: Pravin Kesarwani, Shiva Kant, Yi Zhao, C. Ryan Miller, Prakash Chinnaiyan. The immune consequences of a ketogenic diet in GBM and its therapeutic implications [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 632.

Number needed to screen for TB in clinical, structural or occupational risk groups

BACKGROUND: Screening for active TB using active case-finding (ACF) may reduce TB incidence, prevalence, and mortality; however, yield of ACF interventions varies substantially across populations. We systematically reviewed studies reporting on ACF to calculate the number needed to screen (NNS) for groups at high risk for TB.METHODS: We conducted a literature search for studies reporting ACF for adults published between November 2010 and February 2020. We determined active TB prevalence detected through various screening strategies and calculated crude NNS for - TB confirmed using culture or Xpert^® MTB/RIF, and weighted mean NNS stratified by screening strategy, risk group, and country-level TB incidence.RESULTS: We screened 27,223 abstracts; 90 studies were included (41 in low/moderate and 49 in medium/high TB incidence settings). High-risk groups included inpatients, outpatients, people living with diabetes (PLWD), migrants, prison inmates, persons experiencing homelessness (PEH), healthcare workers, and miners. Screening strategies included symptom-based screening, chest X-ray and Xpert testing. NNS varied widely across and within incidence settings based on risk groups and screening methods. Screening tools with higher sensitivity (e.g., Xpert, CXR) were associated with lower NNS estimates.CONCLUSIONS: NNS for ACF strategies varies substantially between adult risk groups. Specific interventions should be tailored based on local epidemiology and costs.

Reducing regorafenib toxicity by combining with dual JAK-HDAC inhibitor in colorectal cancer

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.

A systematic review of the number needed to screen for active TB among people living with HIV

BACKGROUND: Systematic screening for active TB is recommended for all people living with HIV (PLWH); however, case detection remains poor globally. We investigated the yield of active case finding (ACF) by calculating the number needed to screen (NNS) to detect a case of active TB among PLWH.METHODS: We identified studies reporting ACF for TB among PLWH published from November 2010 to February 2020. We calculated crude NNS for Xpert- or culture-confirmed TB and weighted mean NNS stratified by screening approach, population/risk group, and country TB burden.RESULTS: Of the 27,221 abstracts screened, we identified 58 studies eligible for inclusion, including 5 in low/moderate TB incidence settings and 53 in medium/high incidence settings. Populations screened for TB included inpatients, outpatients not receiving antiretroviral therapy (ART), outpatients receiving ART, those with CD4 < 200 cells/µL, children aged ≤15 years, pregnant PLWH, and PLWH in prisons. Screening tools included symptom-based screening, chest X-ray, C-reactive protein levels, and Xpert. The weighted mean NNS varied across groups but was consistently low, ranging from 4 among inpatients in moderate/high TB burden settings to 137 among pregnant PLWH in moderate/high TB burden settings.CONCLUSIONS: ACF is a high yield intervention among PLWH. Approaches to screening should be tailored to local epidemiological and health-system contexts, and sensitive screening tools such as Xpert should be implemented where feasible.

High-throughput human primary cell-based airway model for evaluating influenza, coronavirus, or other respiratory viruses in vitro

Influenza and other respiratory viruses present a significant threat to public health, national security, and the world economy, and can lead to the emergence of global pandemics such as from COVID-19. A barrier to the development of effective therapeutics is the absence of a robust and predictive preclinical model, with most studies relying on a combination of in vitro screening with immortalized cell lines and low-throughput animal models. Here, we integrate human primary airway epithelial cells into a custom-engineered 96-device platform (PREDICT96-ALI) in which tissues are cultured in an array of microchannel-based culture chambers at an air-liquid interface, in a configuration compatible with high resolution in-situ imaging and real-time sensing. We apply this platform to influenza A virus and coronavirus infections, evaluating viral infection kinetics and antiviral agent dosing across multiple strains and donor populations of human primary cells. Human coronaviruses HCoV-NL63 and SARS-CoV-2 enter host cells via ACE2 and utilize the protease TMPRSS2 for spike protein priming, and we confirm their expression, demonstrate infection across a range of multiplicities of infection, and evaluate the efficacy of camostat mesylate, a known inhibitor of HCoV-NL63 infection. This new capability can be used to address a major gap in the rapid assessment of therapeutic efficacy of small molecules and antiviral agents against influenza and other respiratory viruses including coronaviruses.

Immunohistochemical evaluation of immune cell infiltration in canine gliomas

Evasion of the immune response is an integral part of the pathogenesis of glioma. In humans, important mechanisms of immune evasion include recruitment of regulatory T cells (Tregs) and polarization of macrophages toward an M2 phenotype. Canine glioma has a robust immune cell infiltrate that has not been extensively characterized. The purpose of this study was to determine the distribution of immune cells infiltrating spontaneous intracranial canine gliomas. Seventy-three formalin-fixed, paraffin-embedded tumor samples were evaluated using immunohistochemistry for CD3, forkhead box 3 (FOXP3), CD20, Iba1, calprotectin (Mac387), CD163, and indoleamine 2,3-dioxygenase (IDO). Immune cell infiltration was present in all tumors. Low-grade and high-grade gliomas significantly differed in the numbers of FoxP3+ cells, Mac387+ cells, and CD163+ cells (P = .006, .01, and .01, respectively). Considering all tumors, there was a significant increase in tumor area fraction of CD163 compared to Mac387 (P < .0001), and this ratio was greater in high-grade tumors than in low-grade tumors (P = .005). These data warrant further exploration into the roles of macrophage repolarization or Treg interference therapy in canine glioma.

HGG-12. HUMAN IPSC-DERIVED H3.3K27M NEUROSPHERES: A NOVEL MODEL FOR INVESTIGATING DIPG PATHOGENESIS AND DRUG RESPONSE

Diffuse intrinsic pontine glioma (DIPG) is a subset of high-grade glioma that occurs predominantly in children and has no cure. Up to 80% of DIPG harbor a heterozygous point mutation that results in a lysine 27 to methionine substitution in histone variant H3.3 (H3.3K27M). Existing DIPG models have provided insight into the role of H3.3K27M but have limitations: genetically engineered murine models often rely on overexpression of the mutant histone to form tumors; patient-derived xenografts (PDX) are more genetically faithful but preclude examination of the effect of individual mutations on pathogenesis. To address these shortcomings and better recapitulate the genetics of human tumors, we designed a novel DIPG model based on human induced pluripotent stem cells (iPSC) edited via CRISPR to express heterozygous H3.3K27M. Edited iPSC were chemically differentiated into neural progenitor cells, which upon implantation into the brainstems of immunodeficient mice formed diffusely invasive tumors that were histologically consistent with high-grade glioma. Further, neurospheres cultured from primary tumors formed secondary tumors upon reimplantation with more diffuse invasion, suggesting in vivo evolution. To validate this model’s relevance to DIPG transcriptionally, we performed RNA-sequencing on a cohort of primary and secondary tumor neurospheres (termed primary and secondary iDIPG) and compared them to published RNA-seq data from pediatric PDX and patient tumor samples. Hierarchical clustering and principal component analysis on differentially expressed genes (P<0.05) showed that H3.3K27M iDIPG cluster with H3.3K27M PDX and patient tumors. Further, ssGSEA showed that H3.3K27M iDIPG are enriched for astrocytic and mesenchymal signature genes, a defining feature of H3.3K27M DIPG. Finally, we found that primary H3.3K27M iDIPG neurospheres are sensitive to panobinostat, an HDAC inhibitor shown to be effective against H3.3K27M DIPG cells in vitro. Overall, these data suggest that H3.3K27M iDIPG are a promising tool for investigating DIPG biology and new therapeutic strategies.

Inhibition of Colony-Stimulating Factor-1 Receptor Enhances the Efficacy of Radiotherapy and Reduces Immune Suppression in Glioblastoma

AIM

To use inhibition of colony-stimulating factor-1 receptor (CSF-1R) to target tumor-associated macrophages (TAMs) and improve the efficacy of radiotherapy in glioblastoma (GBM).

MATERIALS AND METHODS

The CSF-1R inhibitor BLZ-945 was used to examine the impact of CSF-1R inhibition on M2 polarization in vitro. Using an orthotopic, immunocompetent GBM model, mice were treated with vehicle, RT, BLZ-945, or RT plus BLZ-945.

RESULTS

BLZ-945 reduced M2 polarization in vitro. BLZ-945 alone did not improve median overall survival (mOS=29 days) compared to control mice (mOS=27 days). RT improved survival (mOS=45 days; p=0.02), while RT plus BLZ-945 led to the longest survival (mOS=not reached; p=0.005). Resected tumors had a relatively large population of M2 TAMs in GBM at baseline, which was increased in response to RT. BLZ-945 reduced RT-induced M2 infiltration.

CONCLUSION

Inhibition of CSF-1R improved response to RT in the treatment of GBM and may represent a promising strategy to improve RT-induced antitumor immune responses.

DDRE-24. ACQUIRED RESISTANCE TO TARGETED INHIBITORS IN EGFR-DRIVEN GLIOBLASTOMA: IDENTIFICATION OF DUAL KINASE TARGETS

Glioblastoma (GBM) is a devastating primary brain tumor with 5-year survival &lt; 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&lt; 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.

CSIG-10. GENOTYPE – KINOME GUIDED DEVELOPMENT OF PRECISION EGFR-TARGETED THERAPEUTICS FOR GLIOBLASTOMA

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.

EXTH-11. PATIENT DERIVED INDUCED NEURAL STEM CELLS FOR TREATMENT OF GLIOBLASTOMA

Induced neural stem-cells (iNSCs) represent a new opportunity in the emerging field of cellular immunotherapy. Patient-derived iNSCs modified to produce anti-tumoral compounds could lead to less rejection and safer outcomes than an off-the-shelf therapy. In this study, we established fibroblast lines (PFs) from skin-biopsies of patients being treated for glioblastoma (GBM) and transdifferentiated those fibroblasts into iNSC lines that produce anti-tumor compounds. We designed a combination of genomic and functional testing to assess iNSC line efficacy. Functional testing revealed differences in rate of transdifferentiation, therapeutic agent production, and tumor-homing amongst cell lines all of which varied among patients. RNAseq profiles of individual cells lines revealed biomarker signatures that differed in tumor-homing-pathways. There was no observed neuronal differentiation in the iNSCs from the transcriptomic profiles, indicating stability after transdifferentiation amongst PFs. Anti-tumor activity of patient-derived iNSCs was measured in vivo by surgical-resection mouse models with invasive CD133+ GBM cells. Patient-derived iNSCs showed variable tumoricidal effectiveness; more highly effective iNSC cells lines reduced tumor burden and increased survival post-resection from 28 to 45 days, whereas less effective cells lines could increase post-resection survival with increased iNSC dosage. PF origination and transcriptomic profile accounted for the differences amongst the iNSC lines. Identification of differentially expressed genes could indicate the cellular pathways that are most important for guaranteeing high, anti-tumoral activity. Further, the cellular profile of the patient-derived fibroblast influences the resulting cellular profile of the iNSC; potentially, correlation of fibroblast gene expression profile could predict tumoricidal efficacy of derived iNSCs.

EPID-14. RACIAL DIFFERENCES AND DISPARITIES IN PATIENTS WITH GLIOMAS: A SINGLE COMPREHENSIVE CANCER CENTER EXPERIENCE FROM 2008–2020

BACKGROUND

Disparities in healthcare delivery in the United States based on race and socioeconomic status are well-documented. Our study examined these disparities along with demographic differences in patients with gliomas.

METHODS

Data was collected retrospectively from an NCI Comprehensive Cancer Center between 2008–2020; 163 African-American patients and 1207 non-Hispanic white patients were included. Demographic variables were entered as predictors of tumor grade and type in an ANOVA model and multinomial logistic regression, respectively. A MANOVA model was used to assess differences in treatments received. Predictors of outcome were determined using cox regression.

RESULTS

Significant differences (p&lt; 0.05) were found between African-American and non-Hispanic white patient groups in; age at diagnosis (48.68 vs 56.12 years, respectively), male/female gender ratio (0.75 vs 1.22), annual household income ($29,442 vs $40,028), insurance type (53.1% private and 42% public vs 63.4% private and 33.6% public) and marital status (43% married vs 74.1%). When controlling for these, there were no significant differences in tumor grade, type, MGMT methylation or IDH1 alteration statuses. Race alone did not predict treatment received, however, two-way interactions between race and other variables did. While gender differences in resection were small for non-Hispanic white controls, resection took place more often in African-American females than males (F = 4.779, p = 0.029). The deleterious effect of increased age on overall survival was diminished in African-Americans (B = -0.033, p &lt; 0.001), while the effect of tumor grade was more pronounced (B = 0.595, p &lt; 0.001).

DISCUSSION

This study suggests that disparities in outcomes are identified when race is considered within the context of other demographic, socioeconomic, and clinical factors. Moreover, these observations demonstrate the need for further studies into intersectional effects on treatment access and clinical outcomes, along with aggressive countermeasures to ensure equity of care.

TMOD-07. HUMAN DIFFUSE MIDLINE GLIOMA AVATARS AS A PLATFORM TO SEARCH FOR NOVEL THERAPEUTIC TARGETS

Diffuse midline glioma is the leading cause of brain tumor death among the pediatric population. Drugs that show notable promise in preclinical models inevitably fail to demonstrate efficacy in clinical trials, likely due to the inadequacy of preclinical models. We have recently proposed glioblastoma models derived from human induced pluripotent stem cells (hiPSCs) genetically engineered with different combinations of glioblastoma-associated genetic alterations as a platform to search for therapeutic targets. These glioblastoma avatars authentically recapitulated the different pathobiology of glioblastoma subtypes, depending on what genetic alterations to be introduced. To investigate the biology and to develop novel therapeutics for diffuse midline glioma with H3K27M mutation, we have established a novel model by introducing H3.3 K27M mutation together with one of the most common concurrent genetic alterations, TP53 R248Q mutation, into hiPSCs through CRISPR/Cas9 genome engineering. Orthotopic engraftment of the neural progenitor cells derived from these edited hiPSCs formed diffusely invasive brainstem tumors with histological features of the diffuse midline glioma. These tumor avatars presented a global reduction in H3K27me3 accompanied by the expression of H3K27M. Transcriptome analyses of these models revealed that these avatars with H3K27M cluster apart from the pediatric glioma samples without this particular mutation, and that they present signatures of oligodendroglial progenitor differentiation as discovered in patient samples with this mutation. Using these models faithfully recapitulating histology and pathobiology of the patient tumors, we have performed drug screening and confirmed that their sensitivity to known drugs, including an EZH2 inhibitor and histone deacetylase inhibitors. On these faithful human avatars of diffuse midline glioma with H3K27M, we have applied bioinformatics algorithms of drug sensitivity prediction aiming at developing novel therapeutics for this devastating pediatric glioma.

Abstract 3681: Selective vulnerability of GBM PDX to a panel of EGFR tyrosine kinase inhibitors

Glioblastoma (GBM), a particularly aggressive form of primary brain tumor, has poor survival due to a lack of effective treatments and high recurrence. Epidermal growth factor receptor (EGFR) (mapped to 7p 11.2), is frequently amplified and mutated (&gt;50%) in GBM, and is suggested as a potential therapeutic target. To correlate chemo-vulnerability with genomic aberrations and further determine biomarkers for targeted therapies, a panel of seven EGFR tyrosine kinase inhibitors were tested in a selected nine human GBM patient-derived xenograft (PDX) panel; these preclinical models harbor different mutation combinations of CDKN2A deletion (C), PTEN deletion (P), wild-type EGFR (E) and/or EGFRvIII (Ev3) overexpression. A single agent drug dose response assay (DDR) was performed on GBM PDX neurospheres using drug concentrations ranging from 100uM to 0.5nM with a 12-point serial 3-fold dilution scheme. The cytotoxic efficacy of EGFR inhibition was dependent on both the PDX line and the EFGR inhibitor applied. GBM59 and GBM76 – both triple CEv3P mutants – were the most responsive to EGFR inhibition relative to the other GBM models tested. For GBM59, the IC50 values of afatinib, canertinib and neratinib, were sub-micromolar, and low micromolar (&lt;3uM) for erlotinib, gefitinib and lapatinib. GBM76 had IC50 values of 1-8uM with all seven EGFR inhibitors including AZD3759. However, GBM155 and GBM126 with CEv3 but wildtype PTEN only responded to afatinib, canertinib and neratinib at low micromolar IC50 values (&lt;3uM) but not to erlotinib, gefitinib and lapatinib. A deletion in PTEN may sensitize GBM cells with CEv3 mutations to erlotinib, gefitinib and lapatinib in vitro. The other group of GBM PDX lines (C only) represented by GBM122, GBM150 and GBM182 responded well to afatinib, canertinib and neratinib with IC50 values of 2- 9uM. GBM156 with CE had a similar profile to the group of C only or CEv3. GBM56 with CP showed the most resistance with mild responses to afatinib, canertinib and neratinib, as observed in its high micromolar IC50 values (6-9uM). Overall, neratinib is the most effective compound among the tested EGFR inhibitors based on IC50 values. Canertinib, the triple tyrosine kinase inhibitor against EGFR/HER2/ErbB-4, is the second most effective agent. Afatinib has similar drug efficacy to canertinib. All three compounds moderately inhibit all GBM PDX lines. The drug response mechanism and its correlation with the mutation status of CDKN2A, EGFR, and PTEN will be further investigated cross a broad array of GBM PDX models. Supported by NIH NCI R01 CA204136

Citation Format: Nanyun Tang, George Reid, C Ryan Miller, Michael E. Berens. Selective vulnerability of GBM PDX to a panel of EGFR tyrosine kinase inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3681.

Recent developments and future directions in adult lower-grade gliomas: Society for Neuro-Oncology (SNO) and European Association of Neuro-Oncology (EANO) consensus

The finding that most grades II and III gliomas harbor isocitrate dehydrogenase (IDH) mutations conveying a relatively favorable and fairly similar prognosis in both tumor grades highlights that these tumors represent a fundamentally different entity from IDH wild-type gliomas exemplified in most glioblastoma. Herein we review the most recent developments in molecular neuropathology leading to reclassification of these tumors based upon IDH and 1p/19q status, as well as the potential roles of methylation profiling and deletional analysis of cyclin-dependent kinase inhibitor 2A and 2B. We discuss the epidemiology, clinical manifestations, benefit of surgical resection, and neuroimaging features of lower-grade gliomas as they relate to molecular subtype, including advanced imaging techniques such as 2-hydroxyglutarate magnetic resonance spectroscopy and amino acid PET scanning. Recent, ongoing, and planned studies of radiation therapy and both cytotoxic and targeted chemotherapies are summarized, including both small molecule and immunotherapy approaches specifically targeting the mutant IDH protein.

ScreenTB: a tool for prioritising risk groups and selecting algorithms for screening for active tuberculosis

SETTING AND OBJECTIVES: There is an urgent need to improve tuberculosis (TB) case detection globally. This would require greater focus on the implementation of TB screening programs. However, to be productive, cost-effective, and ethical, TB screening efforts should be tailored to their local context, targeted to the populations most likely to benefit and utilizing diagnostic tools with sufficient accuracy.DESIGN AND RESULTS: We have developed an online tool, ScreenTB to help National TB Programmes (NTPs) and their partners plan TB screening activities by modeling the potential outcomes of screening programs, including yield of TB cases diagnosed (true- and false-positives), costs, and cost-effectiveness, specific to the populations screened and the diagnostic algorithms used. In Myanmar, ScreenTB was used to assist the NTP in prioritizing risk groups for screening efforts and selecting appropriate screening algorithms to maximize case detection and minimize false-positive diagnoses.CONCLUSION: The ScreenTB tool can help facilitate the prioritization of risk groups for screening and the selection of appropriate screening algorithms. This is useful when used as part of a larger planning process that considers feasibility of screening, vulnerability of risk groups, potential impact of screening on TB transmission, human rights implications of screening and equity in health care access.

Comparative Molecular Life History of Spontaneous Canine and Human Gliomas

Sporadic gliomas in companion dogs provide a window on the interaction between tumorigenic mechanisms and host environment. We compared the molecular profiles of canine gliomas with those of human pediatric and adult gliomas to characterize evolutionarily conserved mammalian mutational processes in gliomagenesis. Employing whole-genome, exome, transcriptome, and methylation sequencing of 83 canine gliomas, we found alterations shared between canine and human gliomas such as the receptor tyrosine kinases, TP53 and cell-cycle pathways, and IDH1 R132. Canine gliomas showed high similarity with human pediatric gliomas per robust aneuploidy, mutational rates, relative timing of mutations, and DNA-methylation patterns. Our cross-species comparative genomic analysis provides unique insights into glioma etiology and the chronology of glioma-causing somatic alterations.

DRES-13. DUAL KINASE INHIBITION TO COMBAT EGFR-INHIBITOR RESISTANCE IN GLIOBLASTOMA

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.

Canine Primary Intracranial Cancer: A Clinicopathologic and Comparative Review of Glioma, Meningioma, and Choroid Plexus Tumors

In the dog, primary intracranial neoplasia represents ~2-5% of all cancers and is especially common in certain breeds including English and French bulldogs and Boxers. The most common types of primary intracranial cancer in the dog are meningioma, glioma, and choroid plexus tumors, generally occurring in middle aged to older dogs. Much work has recently been done to understand the characteristic imaging and clinicopathologic features of these tumors. The gross and histologic landscape of these tumors in the dog compare favorably to their human counterparts with many similarities noted in histologic patterns, subtype, and grades. Data informing the underlying molecular abnormalities in the canine tumors have only begun to be unraveled, but reveal similar pathways are mutated between canine and human primary intracranial neoplasia. This review will provide an overview of the clinicopathologic features of the three most common forms of primary intracranial cancer in the dog, delve into the comparative aspects between the dog and human neoplasms, and provide an introduction to current standard of care while also highlighting novel, experimental treatments that may help bridge the gap between canine and human cancer therapies.

A Revised Diagnostic Classification of Canine Glioma: Towards Validation of the Canine Glioma Patient as a Naturally Occurring Preclinical Model for Human Glioma

The National Cancer Institute-led multidisciplinary Comparative Brain Tumor Consortium (CBTC) convened a glioma pathology board, comprising both veterinarian and physician neuropathologists, and conducted a comprehensive review of 193 cases of canine glioma. The immediate goal was to improve existing glioma classification methods through creation of a histologic atlas of features, thus yielding greater harmonization of phenotypic characterization. The long-term goal was to support future incorporation of clinical outcomes and genomic data into proposed simplified diagnostic schema, so as to further bridge the worlds of veterinary and physician neuropathology and strengthen validity of the dog as a naturally occurring, translationally relevant animal model of human glioma. All cases were morphologically reclassified according to a new schema devised by the entire board, yielding a majority opinion diagnosis of astrocytoma (43, 22.3%), 19 of which were low-grade and 24 high-grade, and oligodendroglioma (134, 69.4%), 35 of which were low-grade and 99 were high-grade. Sixteen cases (8.3%) could not be classified as oligodendroglioma or astrocytoma based on morphology alone and were designated as undefined gliomas. The simplified classification scheme proposed herein provides a tractable means for future addition of molecular data, and also serves to highlight histologic similarities and differences between human and canine glioma.

Abstract 2745: Tumor microenvironment and host genetics impact glioma progression in a Collaborative Cross-based orthotopic allograft model

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&lt;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&lt;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&lt;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.

Abstract 3019: Dynamic kinome profiling of EGFRvIII-driven murine astrocyte models of glioblastoma reveals targets for dual kinase inhibitor therapy

Glioblastoma (GBM) is an aggressive brain tumor with few effective treatments. Epidermal growth factor receptor (EGFR) is frequently amplified and mutated in GBM, leading to trials of several EGFR tyrosine kinase inhibitors, but none have proven successful. One potential reason for failure is acquired resistance, particularly acute, adaptive responses in the kinome. To study this adaptive resistance mechanism, we used RNA-seq and multiplex inhibitor bead/mass spectrometry (MIB-MS) to analyze transcriptomes and kinomes of genetically-engineered murine astrocytes with genotypes commonly seen in human GBM. We previously showed that 38% (86 of 228) of the expressed kinome varied among a panel of genetically diverse murine astrocytes harboring Cdkn2a deletion (C) plus Pten deletion (CP), wild-type human EGFR (CE) or EGFRvIII (CEv3) overexpression, or both overexpressed EGFRvIII and Pten deletion (CEv3P). Pairwise genotype comparisons revealed multiple differentially activated kinases, including Pdgfrb, Fgfr2, Lyn, Ddr1, and several Ephrin family members. We further investigated these potential targets for dual therapy with EGFR TKI by examining the transcriptional response of cultured astrocytes at 4, 24, and 48 hours after 3 μM afatinib. Afatinib induced no kinome changes in C and only 3 kinases (Fn3k, Prkg2, and Syk) were altered in CP astrocytes. Despite similar baseline gene expression profiles, CE astrocytes overexpressing wild-type EGFR responded significantly differently than C astrocytes without. Five kinases (Dclk1, Epha3, Epha7, Fgfr3, and Prkg1) were induced, while 14 were repressed. Six were similarly repressed in CEv3 (Bub1, Nek2, Pask, Plk4, Prkcb, and Vrk1). Whereas the kinase transcriptome response was blunted in C, CP, and CE astrocytes, afatinib induced altered expression of significantly more kinases in CEv3 (82) and CEv3P cells (49). One particularly attractive target in CEv3 astrocytes was Epha4, which afatinib induced &gt;40-fold. Dual inhibition of EGFRvIII and Epha4 kinases may thus provide an opportunity for more effective targeted therapy.

Citation Format: Erin Smithberger, Abigail K. Shelton, Madison K. Butler, Alex R. Flores, Ryan E. Bash, Steven P. Angus, Noah Sciaky, Harshil D. Dhruv, Gary L. Johnson, Michael E. Berens, Frank B. Furnari, C. Ryan Miller. Dynamic kinome profiling of EGFRvIII-driven murine astrocyte models of glioblastoma reveals targets for dual kinase inhibitor therapy [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 3019.

Abstract 331: Dynamic kinome targeting reveals kinases involved in acquired resistance to tyrosine kinase inhibitors in EGFR-driven glioblastomas

Glioblastoma (GBM) is a devastating primary brain tumor with limited treatment options. Extensive molecular characterization has revealed two particularly frequent mutations: CDKN2A deletion (50-60%) and EGFR (40-50%). EGFRvIII (~35%) is a constitutively active truncation mutant with exons 2-7 deleted. EGFR is a particularly attractive therapeutic target due to frequent activating mutations, such as EGFRvIII, and ready availability of multiple targeted inhibitors. Several EGFR tyrosine kinase inhibitors (TKI) have failed clinically, due in part to acquired resistance. To mechanistically examine this type of resistance, we used genetically-engineered mouse astrocytes harboring homozygous deletions of Cdkn2a, as well as EGFRvIII (CEv3). CEv3 astrocytes were made intrinsically resistant to the EGFR TKI gefitinib or erlotinib via long-term exposure, both in vitro and in vivo. We found that long-term gefitinib or erlotinib exposure conferred variable levels of cross resistance to a panel of second- and third-generation EGFR TKI (ΔIC50 1.12-36.1-fold), relative to non-resistant parent lines. We have previously shown that dynamic kinome reprogramming may be responsible for TKI resistance in glioblastoma. Therefore, we used a chemical proteomics method, multiplexed inhibitor beads and mass spectrometry (MIB-MS), to examine changes in the expressed and functional kinome, in both the presence or absence of one of several EGFR TKI known to penetrate the blood-brain barrier. Additionally, we performed RNA sequencing (RNA-seq) to inspect transcriptomic alterations in response to these drugs. RNA-seq showed that resistant CEv3 mouse astrocytes clustered separately from their non-resistant in vitro and in vivo counterparts. Acquired resistance also induced transcriptome alterations governing cellular metabolism, including upregulation of metabolic pathways and downregulation of RNA processing genes. Importantly, the kinase transcriptome was rewired, as 67 kinases were differentially expressed across parental and resistant cell lines (Q&lt;0.001). Probing the dynamic kinome response to afatinib, an EGFR TKI, using RNA-seq identified two potential kinases involved in acute, adaptive resistance to afatinib, Bmx and Ntrk3. Integrated kinome profiling using RNA-seq and MIB-MS in murine models of GBM with defined mutational profiles provides a powerful framework to define novel therapeutic targets that could significantly alter current treatment paradigms.

Citation Format: Abby Shelton, Erin Smithberger, Madison Butler, Alex Flores, Ryan Bash, Steve Angus, Noah Sciaky, Harshil Dhruv, Gary L. Johnson, Michael E. Berens, Frank Furnari, C. Ryan Miller. Dynamic kinome targeting reveals kinases involved in acquired resistance to tyrosine kinase inhibitors in EGFR-driven glioblastomas [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 331.

MerTK as a therapeutic target in glioblastoma

Background

Glioma-associated macrophages and microglia (GAMs) are components of the glioblastoma (GBM) microenvironment that express MerTK, a receptor tyrosine kinase that triggers efferocytosis and can suppress innate immune responses. The aim of the study was to define MerTK as a therapeutic target using an orally bioavailable inhibitor, UNC2025.

Methods

We examined MerTK expression in tumor cells and macrophages in matched patient GBM samples by double-label immunohistochemistry. UNC2025-induced MerTK inhibition was studied in vitro and in vivo.

Results

MerTK/CD68+ macrophages increased in recurrent tumors while MerTK/glial fibrillary acidic protein-positive tumor cells did not. Pharmacokinetic studies showed high tumor exposures of UNC2025 in a syngeneic orthotopic allograft mouse GBM model. The same model mice were randomized to receive vehicle, daily UNC2025, fractionated external beam radiotherapy (XRT), or UNC2025/XRT. Although median survival (21, 22, 35, and 35 days, respectively) was equivalent with or without UNC2025, bioluminescence imaging (BLI) showed significant growth delay with XRT/UNC2025 treatment and complete responses in 19%. The responders remained alive for 60 days and showed regression to 1%-10% of pretreatment BLI tumor burden; 5 of 6 were tumor free by histology. In contrast, only 2% of 98 GBM mice of the same model treated with XRT survived 50 days and none survived 60 days. UNC2025 also reduced CD206+ macrophages in mouse tumor samples.

Conclusions

These results suggest that MerTK inhibition combined with XRT has a therapeutic effect in a subset of GBM. Further mechanistic studies are warranted.

Phase I/II trial of vorinostat combined with temozolomide and radiation therapy for newly diagnosed glioblastoma: results of Alliance N0874/ABTC 02

Background

Vorinostat, a histone deacetylase (HDAC) inhibitor, has shown radiosensitizing properties in preclinical studies. This open-label, single-arm trial evaluated the maximum tolerated dose (MTD; phase I) and efficacy (phase II) of vorinostat combined with standard chemoradiation in newly diagnosed glioblastoma.

Methods

Patients received oral vorinostat (300 or 400 mg/day) on days 1-5 weekly during temozolomide chemoradiation. Following a 4- to 6-week rest, patients received up to 12 cycles of standard adjuvant temozolomide and vorinostat (400 mg/day) on days 1-7 and 15-21 of each 28-day cycle. Association between vorinostat response signatures and progression-free survival (PFS) and overall survival (OS) was assessed based on RNA sequencing of baseline tumor tissue.

Results

Phase I and phase II enrolled 15 and 107 patients, respectively. The combination therapy MTD was vorinostat 300 mg/day and temozolomide 75 mg/m2/day. Dose-limiting toxicities were grade 4 neutropenia and thrombocytopenia and grade 3 aspartate aminotransferase elevation, hyperglycemia, fatigue, and wound dehiscence. The primary efficacy endpoint in the phase II cohort, OS rate at 15 months, was 55.1% (median OS 16.1 mo), and consequently, the study did not meet its efficacy objective. Most common treatment-related grade 3/4 toxicities in the phase II component were lymphopenia (32.7%), thrombocytopenia (28.0%), and neutropenia (21.5%). RNA expression profiling of baseline tumors (N = 76) demonstrated that vorinostat resistance (sig-79) and sensitivity (sig-139) signatures had a reverse and positive association with OS/PFS, respectively.

Conclusions

Vorinostat combined with standard chemoradiation had acceptable tolerability in newly diagnosed glioblastoma. Although the primary efficacy endpoint was not met, vorinostat sensitivity and resistance signatures could facilitate patient selection in future trials.

Intra-cavity stem cell therapy inhibits tumor progression in a novel murine model of medulloblastoma surgical resection

Background

Cytotoxic neural stem cells (NSCs) have emerged as a promising treatment for Medulloblastoma (MB), the most common malignant primary pediatric brain tumor. The lack of accurate pre-clinical models incorporating surgical resection and tumor recurrence limits advancement in post-surgical MB treatments. Using cell lines from two of the 5 distinct MB molecular sub-groups, in this study, we developed an image-guided mouse model of MB surgical resection and investigate intra-cavity NSC therapy for post-operative MB.

Methods

Using D283 and Daoy human MB cells engineered to express multi-modality optical reporters, we created the first image-guided resection model of orthotopic MB. Brain-derived NSCs and novel induced NSCs (iNSCs) generated from pediatric skin were engineered to express the pro-drug/enzyme therapy thymidine kinase/ganciclovir, seeded into the post-operative cavity, and used to investigate intra-cavity therapy for post-surgical MB.

Results

We found that surgery reduced MB volumes by 92%, and the rate of post-operative MB regrowth increased 3-fold compared to pre-resection growth. Real-time imaging showed NSCs rapidly homed to MB, migrating 1.6-fold faster and 2-fold farther in the presence of tumors, and co-localized with MB present in the contra-lateral hemisphere. Seeding of cytotoxic NSCs into the post-operative surgical cavity decreased MB volumes 15-fold and extended median survival 133%. As an initial step towards novel autologous therapy in human MB patients, we found skin-derived iNSCs homed to MB cells, while intra-cavity iNSC therapy suppressed post-surgical tumor growth and prolonged survival of MB-bearing mice by 123%.

Conclusions

We report a novel image-guided model of MB resection/recurrence and provide new evidence of cytotoxic NSCs/iNSCs delivered into the surgical cavity effectively target residual MB foci.

Genomic profiles of low-grade murine gliomas evolve during progression to glioblastoma

Background

Gliomas are diverse neoplasms with multiple molecular subtypes. How tumor-initiating mutations relate to molecular subtypes as these tumors evolve during malignant progression remains unclear.

Methods

We used genetically engineered mouse models, histopathology, genetic lineage tracing, expression profiling, and copy number analyses to examine how genomic tumor diversity evolves during the course of malignant progression from low- to high-grade disease.

Results

Knockout of all 3 retinoblastoma (Rb) family proteins was required to initiate low-grade tumors in adult mouse astrocytes. Mutations activating mitogen-activated protein kinase signaling, specifically KrasG12D, potentiated Rb-mediated tumorigenesis. Low-grade tumors showed mutant Kras-specific transcriptome profiles but lacked copy number mutations. These tumors stochastically progressed to high-grade, in part through acquisition of copy number mutations. High-grade tumor transcriptomes were heterogeneous and consisted of 3 subtypes that mimicked human mesenchymal, proneural, and neural glioblastomas. Subtypes were confirmed in validation sets of high-grade mouse tumors initiated by different driver mutations as well as human patient-derived xenograft models and glioblastoma tumors.

Conclusion

These results suggest that oncogenic driver mutations influence the genomic profiles of low-grade tumors and that these, as well as progression-acquired mutations, contribute strongly to the genomic heterogeneity across high-grade tumors.

PIK3CA missense mutations promote glioblastoma pathogenesis, but do not enhance targeted PI3K inhibition

Background

Glioblastoma (GBM) is the most common adult primary brain tumor. Multimodal treatment is empiric and prognosis remains poor. Recurrent PIK3CA missense mutations (PIK3CA^mut) in GBM are restricted to three functional domains: adaptor binding (ABD), helical, and kinase. Defining how these mutations influence gliomagenesis and response to kinase inhibitors may aid in the clinical development of novel targeted therapies in biomarker-stratified patients.

Methods

We used normal human astrocytes immortalized via expression of hTERT, E6, and E7 (NHA). We selected two PIK3CA^mut from each of 3 mutated domains and induced their expression in NHA with (NHA^RAS) and without mutant RAS using lentiviral vectors. We then examined the role of PIK3CA^mut in gliomagenesis in vitro and in mice, as well as response to targeted PI3K (PI3Ki) and MEK (MEKi) inhibitors in vitro.

Results

PIK3CA^mut, particularly helical and kinase domain mutations, potentiated proximal PI3K signaling and migration of NHA and NHA^RASin vitro. Only kinase domain mutations promoted NHA colony formation, but both helical and kinase domain mutations promoted NHA^RAS tumorigenesis in vivo. PIK3CA^mut status had minimal effects on PI3Ki and MEKi efficacy. However, PI3Ki/MEKi synergism was pronounced in NHA and NHA^RAS harboring ABD or helical mutations.

Conclusion

PIK3CA^mut promoted differential gliomagenesis based on the mutated domain. While PIK3CA^mut did not influence sensitivity to single agent PI3Ki, they did alter PI3Ki/MEKi synergism. Taken together, our results demonstrate that a subset of PIK3CA^mut promote tumorigenesis and suggest that patients with helical domain mutations may be most sensitive to dual PI3Ki/MEKi treatment.