MST4 Phosphorylation of ATG4B Regulates Autophagic Activity, Tumorigenicity, and Radioresistance in Glioblastoma

ATG4B stimulates autophagy by promoting autophagosome formation through reversible modification of ATG8. We identify ATG4B as a substrate of mammalian sterile20-like kinase (STK) 26/MST4. MST4 phosphorylates ATG4B at serine residue 383, which stimulates ATG4B activity and increases autophagic flux. Inhibition of MST4 or ATG4B activities using genetic approaches or an inhibitor of ATG4B suppresses autophagy and the tumorigenicity of glioblastoma (GBM) cells. Furthermore, radiation induces MST4 expression, ATG4B phosphorylation, and autophagy. Inhibiting ATG4B in combination with radiotherapy in treating mice with intracranial GBM xenograft markedly slows tumor growth and provides a significant survival benefit. Our work describes an MST4-ATG4B signaling axis that influences GBM autophagy and malignancy, and whose therapeutic targeting enhances the anti-tumor effects of radiotherapy.

A relative increase in circulating platelets following chemoradiation predicts for poor survival of patients with glioblastoma

Background

Thrombocytosis is triggered by and promotes tumor growth. The relationship between the change in circulating platelets after chemoradiation therapy (CRT) or adjuvant temozolomide (TMZ) and survival in glioblastoma remains unclear. We hypothesized that an increase in platelets after these treatments would be predictive of a shorter survival.

Methods

We retrospectively reviewed data on 122 patients with newly diagnosed, pathologically proven glioblastoma who had been treated with surgery, followed by CRT and adjuvant TMZ, from 2007 to 2016. The association between the changes in blood count levels and survival was analyzed by the log-rank test. To adjust for confounding, we performed a multivariate analysis using known prognostic co-variates.

Results

Patients were dichotomized on the basis of the relative change in platelets after CRT from the baseline: ≤30% increase, low (n = 101) vs >30% increase, high (n = 12). The median survival for high vs. low platelets were 11 vs 28 months (p = 0.0062). No significant survival differences were observed on the basis of platelet changes during adjuvant TMZ. Similarly, changes in lymphocyte counts were not significantly prognostic. On multivariate analysis, MGMT, performance status, and an increase in platelets after CRT were significantly associated with survival (HR for platelets, 4.5; 95% confidence interval, 1.6-12.6).

Conclusions

Increased platelet counts after CRT are predictive of poor survival in glioblastoma. The effect is platelet specific and does not reflect bone marrow changes, as lymphocyte changes were not significantly prognostic. These results suggest an interaction between platelets and tumor aggressiveness. Thus, platelets serve as a novel, minimally invasive liquid biopsy for predicting outcome.

Glioblastoma stem cells exploit the αvβ8 integrin-TGFβ1 signaling axis to drive tumor initiation and progression

Glioblastoma (GBM) is a primary brain cancer that contains populations of stem-like cancer cells (GSCs) that home to specialized perivascular niches. GSC interactions with their niche influence self-renewal, differentiation and drug resistance, although the pathways underlying these events remain largely unknown. Here, we report that the integrin αvβ8 and its latent transforming growth factor β1 (TGFβ1) protein ligand have central roles in promoting niche co-option and GBM initiation. αvβ8 integrin is highly expressed in GSCs and is essential for self-renewal and lineage commitment in vitro. Fractionation of β8^high cells from freshly resected human GBM samples also reveals a requirement for this integrin in tumorigenesis in vivo. Whole-transcriptome sequencing reveals that αvβ8 integrin regulates tumor development, in part, by driving TGFβ1-induced DNA replication and mitotic checkpoint progression. Collectively, these data identify the αvβ8 integrin-TGFβ1 signaling axis as crucial for exploitation of the perivascular niche and identify potential therapeutic targets for inhibiting tumor growth and progression in patients with GBM.

Tumor Evolution of Glioma-Intrinsic Gene Expression Subtypes Associates with Immunological Changes in the Microenvironment

We leveraged IDH wild-type glioblastomas, derivative neurospheres, and single-cell gene expression profiles to define three tumor-intrinsic transcriptional subtypes designated as proneural, mesenchymal, and classical. Transcriptomic subtype multiplicity correlated with increased intratumoral heterogeneity and presence of tumor microenvironment. In silico cell sorting identified macrophages/microglia, CD4⁺ T lymphocytes, and neutrophils in the glioma microenvironment. NF1 deficiency resulted in increased tumor-associated macrophages/microglia infiltration. Longitudinal transcriptome analysis showed that expression subtype is retained in 55% of cases. Gene signature-based tumor microenvironment inference revealed a decrease in invading monocytes and a subtype-dependent increase in macrophages/microglia cells upon disease recurrence. Hypermutation at diagnosis or at recurrence associated with CD8⁺ T cell enrichment. Frequency of M2 macrophages detection associated with short-term relapse after radiation therapy.

Tumor Evolution of Glioma-Intrinsic Gene Expression Subtypes Associates with Immunological Changes in the Microenvironment

We leveraged IDH wild-type glioblastomas, derivative neurospheres, and single-cell gene expression profiles to define three tumor-intrinsic transcriptional subtypes designated as proneural, mesenchymal, and classical. Transcriptomic subtype multiplicity correlated with increased intratumoral heterogeneity and presence of tumor microenvironment. In silico cell sorting identified macrophages/microglia, CD4⁺ T lymphocytes, and neutrophils in the glioma microenvironment. NF1 deficiency resulted in increased tumor-associated macrophages/microglia infiltration. Longitudinal transcriptome analysis showed that expression subtype is retained in 55% of cases. Gene signature-based tumor microenvironment inference revealed a decrease in invading monocytes and a subtype-dependent increase in macrophages/microglia cells upon disease recurrence. Hypermutation at diagnosis or at recurrence associated with CD8⁺ T cell enrichment. Frequency of M2 macrophages detection associated with short-term relapse after radiation therapy.

Efficacy of Onalespib, a Long-Acting Second-Generation HSP90 Inhibitor, as a Single Agent and in Combination with Temozolomide against Malignant Gliomas

Purpose: HSP90, a highly conserved molecular chaperone that regulates the function of several oncogenic client proteins, is altered in glioblastoma. However, HSP90 inhibitors currently in clinical trials are short-acting, have unacceptable toxicities, or are unable to cross the blood-brain barrier (BBB). We examined the efficacy of onalespib, a potent, long-acting novel HSP90 inhibitor as a single agent and in combination with temozolomide (TMZ) against gliomas in vitro and in vivoExperimental Design: The effect of onalespib on HSP90, its client proteins, and on the biology of glioma cell lines and patient-derived glioma-initiating cells (GSC) was determined. Brain and plasma pharmacokinetics of onalespib and its ability to inhibit HSP90 in vivo were assessed in non-tumor-bearing mice. Its efficacy as a single agent or in combination with TMZ was assessed in vitro and in vivo using zebrafish and patient-derived GSC xenograft mouse glioma models.Results: Onalespib-mediated HSP90 inhibition depleted several survival-promoting client proteins such as EGFR, EGFRvIII, and AKT, disrupted their downstream signaling, and decreased the proliferation, migration, angiogenesis, and survival of glioma cell lines and GSCs. Onalespib effectively crossed the BBB to inhibit HSP90 in vivo and extended survival as a single agent in zebrafish xenografts and in combination with TMZ in both zebrafish and GSC mouse xenografts.Conclusions: Our results demonstrate the long-acting effects of onalespib against gliomas in vitro and in vivo, which combined with its ability to cross the BBB support its development as a potential therapeutic agent in combination with TMZ against gliomas. Clin Cancer Res; 23(20); 6215-26. ©2017 AACR.

Efficacy and safety results of ABT-414 in combination with radiation and temozolomide in newly diagnosed glioblastoma

BACKGROUND

The purpose of this study was to determine the maximum tolerated dose (MTD), recommended phase II dose (RPTD), safety, and pharmacokinetics of ABT-414 plus radiation and temozolomide in newly diagnosed glioblastoma. ABT-414 is a first-in-class, tumor-specific antibody-drug conjugate that preferentially targets tumors expressing overactive epidermal growth factor receptor (EGFR).

METHODS

In this multicenter phase I study, patients received 0.5-3.2 mg/kg ABT-414 every 2 weeks by intravenous infusion. EGFR alterations, O6-methylguanine-DNA methyltransferase (MGMT) promoter hypermethylation, and isocitrate dehydrogenase (IDH1) gene mutations were assessed in patient tumors. Distinct prognostic classes were assigned to patients based on a Molecular Classification Predictor model.

RESULTS

As of January 7, 2016, forty-five patients were enrolled to receive ABT-414 plus radiation and temozolomide. The most common treatment emergent adverse events were ocular: blurred vision, dry eye, keratitis, photophobia, and eye pain. Ocular toxicity at any grade occurred in 40 patients and at grades 3/4 in 12 patients. RPTD and MTD were set at 2 mg/kg and 2.4 mg/kg, respectively. Among 38 patients with pretreatment tumor tested centrally, 39% harbored EGFR amplification, of which 73% had EGFRvIII mutation. Among patients with available tumor tissue (n = 30), 30% showed MGMT promoter methylation and none had IDH1 mutations. ABT-414 demonstrated an approximately dose proportional pharmacokinetic profile. The median duration of progression-free survival was 6.1 months; median overall survival has not been reached.

CONCLUSION

ABT-414 plus chemoradiation demonstrated an acceptable safety and pharmacokinetic profile in newly diagnosed glioblastoma. Randomized studies are ongoing to determine efficacy in newly diagnosed (NCT02573324) and recurrent glioblastoma (NCT02343406).

Abstract 5854: TIE2-mediated epigenetic marks regulate therapeutic resistance of glioblastoma

Glioblastomas (GBs), the most common subtype of primary brain tumors in adults, are resistant to current strategies of surgery, irradiation and chemotherapy with a median survival that ranges from 9 to 15 months. GBs invariably recur after therapy due to the presence of cells exhibiting a multidrug-resistance phenotype in the core of the tumor. There is an urgent need of developing the new therapeutic strategies for brain tumor treatment including the identification of novel molecular pathways regulating this resistant phenotype. One of the key phenomena of GB is that tyrosine kinase receptors (TKRs) are abnormally regulated and related to poor treatment outcomes. We have previously reported the expression of TIE2 in human surgical glioma specimens in relation to malignancy, and the role of TIE2 in endothelial-glioma adhesion, tumor invasion and multi-drug resistance of gliomas. Recently, we have identified that the unexpected membrane-to-nuclear trafficking of TIE2 is related to radioresistance of brain tumor stem cells. Interestingly, TIE2 binds, upon IR stress, to DNA/protein complexes and directly phosphorylates core histones. Specifically we discovered a new histone H4 mark (H4pY51) that is read by ABL1. TIE2/H4pY54/ABL1 complex binds to DNA repair proteins, such as ATM, DNA-PK, and pChk2, activating a NHEJ DNA repair mechanism. In an effort to find the molecular mechanisms underlying TIE2 nuclear translocation, we identified that TIE2 binds and directly phosphorylates caveolin-1 (CAV1) at Tyr14 residue in vitro and in vivo. Importantly, CAV1-pTyr14 is necessary for the translocation of both TIE2 and CAV1 to the nucleus. We also uncovered new TIE2-mediated epigenetic marks. Thus, TIE2 binds and phosphorylates histone H2B at Tyr37 and this modification enhances the recruitment of DNA repair proteins to the DNA damage site. Our results summarize that upon IR stress TIE2 localizes to the nucleus where it is involved in key cellular functions by directly phosphorylating core histones, and recruiting SH2 domain proteins to the DNA damage sites, that are complexing to the DNA repair machinery. Our discovery related to tyrosine modification of core histones might be of high significance to understand the resistance of cancer to DNA-damage inducers, which eventually might result in the design of TIE2-targeting combinational therapies for patients with GBs.

Citation Format: Mohammad Belayat Hossain, Rehnuma Shifat, Jingyi Li, Yisel Rivera-Mokina, Francisco Puerta Martinez, David G. Johnson, Mark T. Bedford, Mien-Chie Hung, Erik P. Sulman, Frederick Lang, Raymond Sawaya, Juan Fueyo, Candelaria Gomez-Manzano. TIE2-mediated epigenetic marks regulate therapeutic resistance of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5854. doi:10.1158/1538-7445.AM2017-5854

Abstract 5606: Fibrinogen-like protein 2 drives malignant tumor progression in glioma

Gliomas are the most common type of brain tumor in both children and adults. Several low-grade gliomas (LGG) have the ability to progress into more aggressive tumors -high-grade gliomas (HGG) including glioblastoma (GB). Although patients harboring a LGG may survive for years, after the tumor transforms to HGG, life expectancy rapidly declines to 12 to 15 months in adults and 40 months in children. Thus, inhibiting this process of malignant transformation (MT) is an attractive therapeutic strategy because of the more indolent course associated with LGGs. Immune response plays a critical role in surveillance against malignant transformation. Our previous study shows that fibrinogen-like protein 2 (FGL2) is a key hub of tumor-mediated immune suppression. Hence, we investigated the role of FGL2 in promoting tumor progression from LGG to HGG in glioma. Analysis of TCGA expression data showed that increased FGL2 expression is associated with poorer survival in LGG and GB patients. And there is a positive correlation of expression level between FGL2 and mesenchymal glioma marker CD44, and a negative correlation between FGL2 and proneural glioma marker OLIG2. Engineered expression of FGL2 in a PDGFB-dependent mouse model of oligodendroglioma, a common glioma subtype, yielded a significantly higher rate of HGGs (72% vs 29%, p=0.034) and poorer-symptom free survival (63 vs 90 days, p=0.003) than PDGFB expression alone. And HGGs from FGL2 + PDGFB expressing mice exhibited a distinct mesenchymal phenotype validating TCGA data. Further, FGL2 induced high numbers of CD4+FoxP3+ cells from an early time point of tumor formation underscoring its role in tumor progression. And FGL2 overexpression educated M2 skew in the tumors characterized by high expression of Iba1 and Arginase1 in macrophages. Finally, treatment with anti-FGL2 antibody significantly improves survival in mice, shifts the phenotype from mesenchymal HGG to proneural LGG, and rescues M2 macrophage skewing. Our results show that FGL2 is critical for malignant progression of glioma by inducing immunosuppression in tumor microenvironment, and raise the potential of FGL2 to be a promising target to suppress/reverse glioma progression and provide survival benefit in clinical.

Citation Format: Khatri Latha, Jun Yan, Yuhui Yang, Loyola V. Gressot, Lingyuan Kong, Ganiraju Manyam, Ravesanker Ezhilarasan, Qianghu Wang, Erik P. Sulman, Jingda Xu, Richard E. Davis, Suyun Huang, Gregory N. Fuller, Arvind Rao, Amy B. Heimberger, Shulin Li, Ganesh Rao. Fibrinogen-like protein 2 drives malignant tumor progression in glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5606. doi:10.1158/1538-7445.AM2017-5606

Retrospective Analysis of Molecular and Immunohistochemical Characterization of 381 Primary Brain Tumors

The classification of brain tumors has traditionally depended on microscopic examination of hematoxylin and eosin-stained tissue sections. The increased understanding of clinically relevant genetic alterations has led to the incorporation of molecular signatures as part of the diagnosis of brain malignancies. Advances in sequencing technologies have facilitated the use of next-generation sequencing (NGS) assays in clinical laboratories. We performed a retrospective analysis of sequencing results for 381 brain tumors tested by NGS at our institution using a validated, commercially available panel. The results of the NGS assay were analyzed in conjunction with the results of immunohistochemical stains. A genetic alteration was detected in approximately two thirds of the cases. The most commonly mutated genes were TP53 (37.2%), IDH1 (29.4%), PIK3CA (8%), PTEN (8%), and EGFR (7.5%). BRAF mutations were detected in ∼3% of the cases, including 50% of gangliogliomas and ∼20% of gliosarcomas. No mutations were detected in 6 medulloblastomas. PIK3CA and CTNNB1 mutations were detected in 1 rosette-forming glioneuronal tumor and 1 adamantinomatous craniopharyngioma, respectively. Approximately 23% of cases showed amplification of 1 or more of the genes included in the NGS panel. This analysis demonstrates the utility of NGS for detecting genetic alterations in brain tumors in the clinical setting.

Relative thrombocytosis following chemoradiation of patients with glioblastoma to predict survival

e13527

Background: Thrombocytosis is associated with poor survival in several malignancies and is both triggered by and promoting of tumor growth. We hypothesized that an increase in circulating platelets following standard temozolamide (TMZ) CRT and/or adjuvant TMZ would predict for decreased survival in patients with glioblastoma (GBM). Methods: We reviewed data of 122 patients with newly diagnosed, pathological-proven GBM from 2007 to 2016 with documented complete blood counts before the start of CRT, after CRT, before adjuvant TMZ, and after a minimum 2 cycles of adjuvant TMZ. The association between changes in blood count levels and patient survival was analyzed by log-rank test. Multivariate analysis was performed using known prognostic co-variates, including MGMT methylation, patient age, and performance status (PS). Results: The mean change in platelets before and after CRT was -46 k/µl (range -387 to 179 k/µl) and before and after adjuvant TMZ was -25 k/µl (range -408 to 143 k/µl). As a reference, the mean change in lymphocytes was -5.7 k/µl (range -0.7 to 1.3 k/µl) and -0.0 k/µl (range -1.6 to 0.9 k/µl) for CRT and adjuvant TMZ, respectively. Patients were dichotomized based on the relative change in platelets and lymphocytes from baseline (≤30% increase, “low”, n = 101 vs > 30% increase, “high”, n = 12). The median survival of low patients vs. high patients was 30 vs 13 months (p = 0.006). Potential confounders, such as infection or thrombosis, were not associated with the high group. However, no significant survival difference was observed between groups based on platelet changes during adjuvant TMZ. Similarly, changes in lymphocyte counts were not significantly prognostic. In multivariate analysis, extent of resection, MGMT status, PS and the increase in platelets after CRT were significantly associated with survival (HR for platelets 4.0, 95% CI 1.6-10.1). Conclusions: Increased platelet counts after CRT predict for poor survival in patients with GBM. The effect is platelet specific and does not reflect general bone marrow changes, as lymphocyte changes were not significantly prognostic. These results suggest a potential interaction between platelets and tumor aggressiveness.

Comprehensive molecular and immune profiling of non-small cell lung cancer and matched distant metastases to suggest distinct molecular mechanisms underlying metastasis

8541

Background: Despite complete resection, many non-small cell lung cancer (NSCLC) patients still develop and succumb to distant metastases. Previous studies suggested distant metastasis may be due to genomic evolution and/or suppressed immune surveillance. However, the relationship between specific genomic alterations and immune surveillance has not been systemically studied. Methods: We performed whole exome sequencing, RNA-Seq, methylation microarray, immunohistochemistry using multiple immune markers, and T cell receptor sequencing on 7 pairs of NSCLC primary tumors and matched metastases including 6 metachronous brain and 1 synchronous liver metastases. Results: On average, 84% of all somatic mutations (54% to 97%) and all 28 canonical cancer gene mutations were shared between primary tumors and paired distant metastases. Metastases also resembled paired primary tumors closely in regard to somatic copy number aberration profiles, methylation profiles. Subclonal analysis showed almost identical clonal architectures in 4 of 7 pairs of primary tumor and metastasis comparable to the similarity observed between different regions within the same tumors. The other 3 pairs, however, displayed clear evidence of clonal evolution. We validated these findings in a published dataset consisting of 38 pairs of primary NSCLC tumors and matched distant metastases. The RNA-Seq data showed that 25 of the top 35 significantly down-regulated signaling pathways in metastases relative to primary tumors were related to immune activation, which was validated in an independent cohort of 41 primary NSCLC tumors and distant metastases using NanoString’s PanCancer Immune Profiling Panel. Conclusions: Our data suggest that molecular mechanisms underlying postsurgical distant metastasis may be variable among NSCLC patients. While genomic evolution may play a role in development of metastasis in some patients, distant metastasis may be early event during carcinogenesis without further genomic evolution in a substantial proportion of NSCLC patients. Furthermore, immune suppression may be a characteristic of cancer cells of metastatic capacity.

m6A Demethylase ALKBH5 Maintains Tumorigenicity of Glioblastoma Stem-like Cells by Sustaining FOXM1 Expression and Cell Proliferation Program

The dynamic and reversible N⁶-methyladenosine (m⁶A) RNA modification installed and erased by N⁶-methyltransferases and demethylases regulates gene expression and cell fate. We show that the m⁶A demethylase ALKBH5 is highly expressed in glioblastoma stem-like cells (GSCs). Silencing ALKBH5 suppresses the proliferation of patient-derived GSCs. Integrated transcriptome and m⁶A-seq analyses revealed altered expression of certain ALKBH5 target genes, including the transcription factor FOXM1. ALKBH5 demethylates FOXM1 nascent transcripts, leading to enhanced FOXM1 expression. Furthermore, a long non-coding RNA antisense to FOXM1 (FOXM1-AS) promotes the interaction of ALKBH5 with FOXM1 nascent transcripts. Depleting ALKBH5 and FOXM1-AS disrupted GSC tumorigenesis through the FOXM1 axis. Our work uncovers a critical function for ALKBH5 and provides insight into critical roles of m⁶A methylation in glioblastoma.

Epigenetic Activation of WNT5A Drives Glioblastoma Stem Cell Differentiation and Invasive Growth

Glioblastoma stem cells (GSCs) are implicated in tumor neovascularization, invasiveness, and therapeutic resistance. To illuminate mechanisms governing these hallmark features, we developed a de novo glioblastoma multiforme (GBM) model derived from immortalized human neural stem/progenitor cells (hNSCs) to enable precise system-level comparisons of pre-malignant and oncogene-induced malignant states of NSCs. Integrated transcriptomic and epigenomic analyses uncovered a PAX6/DLX5 transcriptional program driving WNT5A-mediated GSC differentiation into endothelial-like cells (GdECs). GdECs recruit existing endothelial cells to promote peritumoral satellite lesions, which serve as a niche supporting the growth of invasive glioma cells away from the primary tumor. Clinical data reveal higher WNT5A and GdECs expression in peritumoral and recurrent GBMs relative to matched intratumoral and primary GBMs, respectively, supporting WNT5A-mediated GSC differentiation and invasive growth in disease recurrence. Thus, the PAX6/DLX5-WNT5A axis governs the diffuse spread of glioma cells throughout the brain parenchyma, contributing to the lethality of GBM.

Ionizing radiation augments glioma tropism of mesenchymal stem cells

OBJECTIVE Mesenchymal stem cells (MSCs) have been shown to localize to gliomas after intravascular delivery. Because these cells home to areas of tissue injury, the authors hypothesized that the administration of ionizing radiation (IR) to tumor would enhance the tropism of MSCs to gliomas. Additionally, they sought to identify which radiation-induced factors might attract MSCs. METHODS To assess the effect of IR on MSC migration in vitro, transwell assays using conditioned medium (CM) from an irradiated commercially available glioma cell line (U87) and from irradiated patient-derived glioma stem-like cells (GSCs; GSC7-2 and GSC11) were employed. For in vivo testing, green fluorescent protein (GFP)-labeled MSCs were injected into the carotid artery of nude mice harboring orthotopic U87, GSC7-2, or GSC17 xenografts that were treated with either 0 or 10 Gy of IR, and brain sections were quantitatively analyzed by immunofluorescence for GFP-positive cells. These GSCs were used because GSC7-2 is a weak attractor of MSCs at baseline, whereas GSC17 is a strong attractor. To determine the factors implicated in IR-induced tropism, CM from irradiated GSC7-2 and from GSC11 was assayed with a cytokine array and quantitative ELISA. RESULTS Transwell migration assays revealed statistically significant enhanced MSC migration to CM from irradiated U87, GSC7-2, and GSC11 compared with nonirradiated controls and in a dose-dependent manner. After their intravascular delivery into nude mice harboring orthotopic gliomas, MSCs engrafted more successfully in irradiated U87 (p = 0.036), compared with nonirradiated controls. IR also significantly increased the tropism of MSCs to GSC7-2 xenografts (p = 0.043), which are known to attract MSCs only poorly at baseline (weak-attractor GSCs). Ionizing radiation also increased the engraftment of MSCs in strong-attractor GSC17 xenografts, but these increases did not reach statistical significance. The chemokine CCL2 was released by GSC7-2 and GSC11 after irradiation in a dose-dependent manner and mediated in vitro transwell migration of MSCs. Immunohistochemistry revealed increased CCL2 in irradiated GSC7-2 gliomas near the site of MSC engraftment. CONCLUSIONS Administering IR to gliomas enhances MSC localization, particularly in GSCs that attract MSCs poorly at baseline. The chemokine CCL2 appears to play a crucial role in the IR-induced tropism of MSCs to gliomas.

Global epigenetic profiling identifies methylation subgroups associated with recurrence-free survival in meningioma

Meningioma is the most common primary brain tumor and carries a substantial risk of local recurrence. Methylation profiles of meningioma and their clinical implications are not well understood. We hypothesized that aggressive meningiomas have unique DNA methylation patterns that could be used to better stratify patient management. Samples (n = 140) were profiled using the Illumina HumanMethylation450BeadChip. Unsupervised modeling on a training set (n = 89) identified 2 molecular methylation subgroups of meningioma (MM) with significantly different recurrence-free survival (RFS) times between the groups: a prognostically unfavorable subgroup (MM-UNFAV) and a prognostically favorable subgroup (MM-FAV). This finding was validated in the remaining 51 samples and led to a baseline meningioma methylation classifier (bMMC) defined by 283 CpG loci (283-bMMC). To further optimize a recurrence predictor, probes subsumed within the baseline classifier were subject to additional modeling using a similar training/validation approach, leading to a 64-CpG loci meningioma methylation predictor (64-MMP). After adjustment for relevant clinical variables [WHO grade, mitotic index, Simpson grade, sex, location, and copy number aberrations (CNAs)] multivariable analyses for RFS showed that the baseline methylation classifier was not significant (p = 0.0793). The methylation predictor, however, was significantly associated with tumor recurrence (p < 0.0001). CNAs were extracted from the 450k intensity profiles. Tumor samples in the MM-UNFAV subgroup showed an overall higher proportion of CNAs compared to the MM-FAV subgroup tumors and the CNAs were complex in nature. CNAs in the MM-UNFAV subgroup included recurrent losses of 1p, 6q, 14q and 18q, and gain of 1q, all of which were previously identified as indicators of poor outcome. In conclusion, our analyses demonstrate robust DNA methylation signatures in meningioma that correlate with CNAs and stratify patients by recurrence risk.

Radiation Therapy for Glioblastoma: American Society of Clinical Oncology Clinical Practice Guideline Endorsement of the American Society for Radiation Oncology Guideline

Purpose The American Society for Radiation Oncology (ASTRO) produced an evidence-based guideline on radiation therapy for glioblastoma. Because of its relevance to the ASCO membership, ASCO reviewed the guideline and applied a set of procedures and policies used to critically examine guidelines developed by other organizations. Methods The ASTRO guideline on radiation therapy for glioblastoma was reviewed for developmental rigor by methodologists. An ASCO endorsement panel updated the literature search and reviewed the content and recommendations. Results The ASCO endorsement panel determined that the recommendations from the ASTRO guideline, published in 2016, are clear, thorough, and based on current scientific evidence. ASCO endorsed the ASTRO guideline on radiation therapy for glioblastoma and added qualifying statements. Recommendations Partial-brain fractionated radiotherapy with concurrent and adjuvant temozolomide is the standard of care after biopsy or resection of newly diagnosed glioblastoma in patients up to 70 years of age. Hypofractionated radiotherapy for elderly patients with fair to good performance status is appropriate. The addition of concurrent and adjuvant temozolomide to hypofractionated radiotherapy seems to be safe and efficacious without impairing quality of life for elderly patients with good performance status. Reasonable options for patients with poor performance status include hypofractionated radiotherapy alone, temozolomide alone, or best supportive care. Focal reirradiation represents an option for select patients with recurrent glioblastoma, although this is not supported by prospective randomized evidence. Additional information is available at www.asco.org/glioblastoma-radiotherapy-endorsement and www.asco.org/guidelineswiki .

A regulatory circuit of miR-125b/miR-20b and Wnt signalling controls glioblastoma phenotypes through FZD6-modulated pathways

Molecularly defined subclassification is associated with phenotypic malignancy of glioblastoma (GBM). However, current understanding of the molecular basis of subclass conversion that is often involved in GBM recurrence remain rudimentary at best. Here we report that canonical Wnt signalling that is active in proneural (PN) but inactive in mesenchymal (MES) GBM, along with miR-125b and miR-20b that are expressed at high levels in PN compared with MES GBM, comprise a regulatory circuit involving TCF4-miR-125b/miR-20b-FZD6. FZD6 acts as a negative regulator of this circuit by activating CaMKII–TAK1–NLK signalling, which, in turn, attenuates Wnt pathway activity while promoting STAT3 and NF-κB signalling that are important regulators of the MES-associated phenotype. These findings are confirmed by targeting differentially enriched pathways in PN versus MES GBM that results in inhibition of distinct GBM subtypes. Correlative expressions of the components of this circuit are prognostic relevant for clinical GBM. Our findings provide insights for understanding GBM pathogenesis and for improving treatment of GBM.

Glioblastoma (GBM) is classified as proneural (PN), neural, mesenchymal (MES) and classical GBM. Here the authors show that Wnt signalling, miR-125b and miR-20b establish a regulatory circuitry including FZD6 which distinguishes PN from the MES subtype.

Aberrant mesenchymal differentiation of glioma stem-like cells: implications for therapeutic targeting

Differentiation has been proposed as a therapeutic strategy for glioblastoma (GBM) in part due to observations of stem-like cells in GBM that have been shown to undergo terminal differentiation in response to growth factor withdrawal and BMP activation. However, the effects of long term exposure to serum culture conditions on glioma sphere cultures/glioma stem-like cells (GSCs) have not been examined. Here we show that GSCs retained both neurosphere formation and tumor initiation abilities after short or long term serum exposure. Under these conditions, GSCs expressed both neural lineage and stem cell markers, highlighting the aberrant pseudo-differentiation state. GSCs maintained under adherent serum cultured conditions continued to proliferate and initiate tumor formation with efficiencies similar to GSCs maintained under proliferating (neurosphere) conditions. Proneural (PN) GSCs under serum exposure showed an induction of mesenchymal (MES) gene expression signatures. Our data indicate that exposure to serum containing media result in aberrant differentiation (e.g. toward MES lineage) and activation of alternative oncogenic pathways in GSCs.

Abstract 1646: A glioblastoma methylation assay (GaMA) developedfrom genomic analysis of glioma spheroid cultures predicts response toradiation therapy in patients with glioblastoma

Radiation therapy (RT) remains one of the most effective treatments for patients with GBM and has been repeatedly demonstrated to improve survival; yet response to RT is variable. We explored the relationship between methylation status and radiation response to develop a predictor of RT response using the epigenetic data of glioma sphere-forming cells (GSCs). The DNA methylomes of 42 GSCs were profiled using Illumina Infinium 450K methylation bead arrays. 15 GSCs were irradiated with 2-, 4-, and 6-Gy RT and response determined using clonogenic assays. We discovered 168 CpG probes capable of distinguishing sensitive from resistant GSCs. To validate, we analyzed 362 TCGA GBM samples, 272 that received standard 60Gy RT and 90 treated with low or no RT. Using the glioblastoma methylation assay (GaMA) signature, we classified the samples as either RT sensitive or resistant. Survival was significantly different between the predicted sensitive vs resistant patients for those treated with standard RT (median 21.0m vs 14.7m, p&lt;0.005). GaMA did not predict a survival difference among patients receiving no/low-dose RT, suggesting a predictive, but not prognostic, role for the signature. Using the ENCODE ChIP-Seq Significance Tool, we observed that the transcription factor EZH2 was significantly associated with the radiation resistant promoters in the GaMA signature. Among the hypermethylated genes with EZH2 binding sites, the NR2F2 promoter had the greatest number of hypermethylated CpG sites correlated to RT resistance. NR2F2 has previously been identified as negatively associated with activation of the wnt/β-catenin, a pathway associated with RT resistance of mammary progenitor cells. Expression of WNT1 in TCGA GBM cohort was negatively associated with NR2F2 expression. Our GSC RT response-based methylome analysis corroborates this association and provides a rationale for the methylation signature as a predictive biomarker of radiation response.

Citation Format: Qianghu Wang, Ravesanker Ezhilarasan, Eskil Eskilsson, Joy Gumin, Jie Yang, Mona Jaffari, Ming Tang, Kenneth D. Aldape, Frederick F. Lang, Roel G.W. Verhaak, Erik P. Sulman. A glioblastoma methylation assay (GaMA) developedfrom genomic analysis of glioma spheroid cultures predicts response toradiation therapy in patients with glioblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1646.

Abstract 4217: First pre-clinical validation of radiogenomics in glioblastoma

A plethora of Magnetic Resonance Imaging (MRI) features have been correlated to cancer genomics to date, however, none have established causality. Here, we present an in vivo xenograft RNA interference validated, potentially clinically applicable test method termed “Magnetic Resonance Radiomic Sequencing” (MRRS) for the noninvasive detection of cancer genomics in Glioblastoma. MRRS comprehensively assesses the entire tumor mass using imaging texture-based algorithms that generate thousands of variables (features) inherent to the tumor. Two independent glioblastoma stem cells (GSC1 and GSC3) harboring doxycycline inducible short hairpin RNA against Periostin (POSTN), a gene previously identified in our radiogenomic screen, were implanted at orthotopic location in nude mouse brain. In vivo knockdown of &gt;90% and ∼40% POSTN gene was achieved in GSC3 and GSC1 respectively. The T2 and T1 post MRI texture features, in edema and contrast enhancement phenotype features were compared between doxycycline (POSTN knockdown) and sucrose (control) group of mice using T test statistics. The significant features were included in a Stepwise Forward Logistic Regression analysis to build the final predictive model. The accuracy of the model was tested using ROC cure analysis. Among 3600 features in GSC3 mice cohort, 117 features were significantly (p value&lt;0.05) different between the two groups. The significant features were included in a Stepwise Forward Logistic Regression analysis, 2 textures features (feature 234 of edema T1 and feature 251 of edema T2) were selected to be included in the final predictive model. The AUC of the model with leave one out cross validation method was 100%. The similar analyses were done in the GSC1 mice. The final predictive model in the GSC1 group was statistically insignificant (p value = 0.15) with AUC (95% CI) = 73% (46%-98%), suggesting that MRRS is reflective of underlying gene expression levels. Our results therefore describe the ‘first mouse model derived MRRS signature to describe a causal link of gene alteration to MRRS. This novel test method may open an avenue for human-mouse matched co-clinical trials and noninvasive Radiogenomic diagnostics.

Citation Format: Pascal Zinn, Sanjay Singh, Markus M. Luedi, Faramak Zandi, Aikaterini Kotrotsou, Masumeh Hatami, Ginu Thomas, Ahmed Elakkad, Joy Gumin, Erik P. Sulman, Frederick Lang, David Piwnica-Worms, Rivka R. Colen. First pre-clinical validation of radiogenomics in glioblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4217.