HDAC and PI3K Antagonists Cooperate to Inhibit Growth of MYC-Driven Medulloblastoma

Medulloblastoma (MB) is a highly malignant pediatric brain tumor. Despite aggressive therapy, many patients succumb to the disease, and survivors experience severe side effects from treatment. MYC-driven MB has a particularly poor prognosis and would greatly benefit from more effective therapies. We used an animal model of MYC-driven MB to screen for drugs that decrease viability of tumor cells. Among the most effective compounds were histone deacetylase inhibitors (HDACIs). HDACIs potently inhibit survival of MYC-driven MB cells in vitro, in part by inducing expression of the FOXO1 tumor suppressor gene. HDACIs also synergize with phosphatidylinositol 3-kinase inhibitors to inhibit tumor growth in vivo. These studies identify an effective combination therapy for the most aggressive form of MB.

Prognostic value of medulloblastoma extent of resection after accounting for molecular subgroup: a retrospective integrated clinical and molecular analysis

Background

Incomplete surgical resection of medulloblastoma is controversially considered a marker of high-risk disease; driving aggressive surgical resections, “second-look” surgeries, and/or intensified chemoradiotherapy. All prior publications evaluating the clinical importance of extent of resection (EOR) failed to account for molecular subgroup. We analysed the prognostic value of EOR across 787 medulloblastoma samples in a subgroup-specific manner.

Methods

We retrospectively identified patients from Medulloblastoma Advanced Genomics International Consortium (MAGIC) centres with a histological diagnosis of medulloblastoma and complete extent of resection and survival data. Specimens were collected from 35 international institutions. Medulloblastoma subgroup affiliation was determined using nanoString gene expression profiling on frozen or formalin-fixed paraffin-embedded tissues. Extent of resection (EOR) based on post-operative imaging was classified as gross total (GTR), near total (NTR, <1·5cm²), or subtotal (STR, ≥ 1·5cm²). Overall survival (OS) and progression-free survival (PFS) multivariable analyses including subgroup, age, metastatic status, geographical location of therapy (North America/Australia vs world), and adjuvant therapy regimen were performed. The primary endpoint was the impact of surgical EOR by molecular subgroup and other clinical variables on OS and PFS.

Findings

787 medulloblastoma patients (86 WNT, 242 SHH, 163 Group 3, and 296 Group 4) were included in a multivariable Cox model of PFS and OS. The marked benefit of EOR in the overall cohort was greatly attenuated after including molecular subgroup in the multivariable analysis. There was an observed PFS benefit of GTR over STR (hazard ration [HR] 1·45, 95% CI; 1·07–1·96, p=0·02) but there was no observed PFS or OS benefit of GTR over NTR (HR 1·05, 0·71–1·53, p=0·82 and HR 1·14, 0·75–1·72, p=0.55). There was no statistically significant survival benefit to greater EOR for patients with WNT, SHH, or Group 3 patients (HR 1·03, 0·67–1·58, p=0·9 for STR vs. GTR). There was a PFS benefit for GTR over STR in patients with Group 4 medulloblastoma (HR1·97, 1·22–3·17, p=0·01), particularly those with metastatic disease (HR 2·22, 1–4·93, p=0·05). A nomogram based on this multivariable cox proportional hazards model shows the comparably smaller impact of EOR on relative risk for PFS and OS than subgroup affiliation, metastatic status, radiation dose, and adjuvant chemotherapy.

Interpretation

The prognostic benefit of EOR for patients with medulloblastoma is attenuated after accounting for molecular subgroup affiliation. Although maximal safe surgical resection should remain the standard of care, surgical removal of small residual portions of medulloblastoma is not recommended when the likelihood of neurological morbidity is high as there is no definitive benefit to GTR over NTR. Our results suggest a re-evaluation of the long-term implications of intensified craniospinal irradiation (36 Gy) in children with small residual portions of medulloblastoma.

Funding

Funding Canadian Cancer Society Research Institute, Terry Fox Research Institute, Canadian Institutes of Health Research, National Institutes of Health, Pediatric Brain Tumor Foundation, Garron Family Chair in Childhood Cancer Research.

Effect of intravitreal dexamethasone implant on retinal and choroidal thickness in refractory diabetic macular oedema after multiple anti-VEGF injections

AimsTo investigate the effect of intravitreal dexamethasone implant (IVD) on central foveal thickness (CFT), choroidal thickness (CT) and its correlation with visual acuity in eyes with refractory diabetic macular oedema (DMO).MethodsThis was a retrospective interventional case-series. Thirty-five eyes of 35 patients were treated with a single injection of IVD because of refractory DMO with CFT over 300 μm, and persistent intraretinal and subretinal fluid despite of multiple intravitreal bevacizumab injections. Patients were followed-up for 6 months for the evaluation of CFT and subfoveal CT by spectral-domain optical coherence tomography.ResultsAll eyes (mean age: 59.4±12.35 years; 18 males, 17 females) had been previously treated with multiple bevacizumab injections and showed persistent DMO (mean number of injections 4.08±2.98) The preoperative logMAR BCVA was 0.49±0.24, which gradually improved to 0.46±0.32 at 6 months (P=0.652) and 26% gained two or more lines of Snellen visual acuity. At baseline, the mean CFT was 526.29±123.48 μm, which significantly improved to 316.15±100.09 μm at 3 months (P<0.001). However, CFT deteriorated to 457.07±136.53 μm at 6 months (P=0.051). Similarly, the mean preoperative subfoveal CT was 288.91±36.47 μm and it decreased to 266.85±30.93 μm at 3 months (P<0.01), but increased to 278.63±32.55 μm at 6 months (P=0.137). The reduction of CFT from baseline showed significant correlation with that of subfoveal CT at 3 months (P=0.041) and at 6 months (P=0.008).ConclusionsIn DMO refractory to multiple bevacizumab injections, IVD significantly reduced CFT and subfoveal CT, with BCVA improvement in one-fourth of the patients. The reduction of CFT showed significant correlation with reduction of subfoveal CT.

Comparison of short wrist transverse open and limited open techniques for carpal tunnel release: a randomized controlled trial of two incisions

The purpose of this randomized controlled trial was to compare outcomes of limited open and short wrist transverse techniques in patients with carpal tunnel syndrome. In a single centre randomized controlled trial, 84 patients with idiopathic carpal tunnel syndrome were randomized before surgery to limited open or short wrist transverse open carpal tunnel release. The patients were evaluated at 6 weeks, 3 months, 6 months, and 1 and 2 years after surgery. At every follow-up, the Brigham and Women's Carpal Tunnel Questionnaire scores, scar discomfort, and subjective patient satisfaction were evaluated. Two years after surgery, five patients were lost to follow-up. The groups had similar Brigham and Women's Carpal Tunnel Questionnaire Symptom Severity and Functional Status scores and subjective satisfaction scores. The incidence of scar discomfort was not significantly different between the two groups on serial postoperative follow-up. Short wrist transverse open release surgery showed similar early postoperative symptoms and subjective and functional outcomes to limited open release.

LEVEL OF EVIDENCE

II.

Abstract A08: IGF1R as a key target in high risk, metastatic medulloblastoma

The risk or presence of metastasis in childhood medulloblastoma represents a substantial cause of morbidity and mortality. Relatively little has been known about the molecular mechanisms of medulloblastoma dissemination throughout the cerebrospinal axis. To determine potential interventions that address both metastasis and tumor growth, we examined the expression of cytokines and growth factors in the CSF of metastatic medulloblastoma patients that were also present in the conditioned media of metastatic, MYC amplified medulloblastoma cell lines and/or cell culture models of the leptomeninges. The presence of IGF1, the IGF-sequestering protein Igfbp3, which can be cleaved by metal metalloproteases (MMP) and the serine protease tPA, and the presence of corresponding protease modulators TIMP1 and SerpinE1/PAI-1, led us to explore the bioactivity of IGF1 in medulloblastoma. IGF1 led not only to receptor phosphorylation but also increased migration and increased relative cell growth. A tumor cell viability screen of 60 clinically-related compounds prioritized IGF1R inhibitors. Our findings support a model whereby medulloblastoma tumor cells actively migrate, rather than arrive passively, to the leptomeningeal cell surface and provide a rationale for exploring IGF1R as a target for therapeutics in future clinical trials.

Citation Format: Matthew N. Svalina, Ken Kikuchi, Jinu Abraham, Sangeet Lal, Monika A. Davare, Jennifer L. Peckham, Yoon-Jae Cho, Melanie Jackson, Daniel J. Guillaume, Nathan R. Selden, Darell D. Bigner, Kellie J. Nazemi, Sarah C. Green, Christopher L. Corless, Sakir Gultekin, Brian P. Rubin, Randall Woltjer, Charles Keller. IGF1R as a key target in high risk, metastatic medulloblastoma. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr A08.

Mitochondrial p32 is upregulated in Myc expressing brain cancers and mediates glutamine addiction

Metabolic reprogramming is a key feature of tumorigenesis that is controlled by oncogenes. Enhanced utilization of glucose and glutamine are the best-established hallmarks of tumor metabolism. The oncogene c-Myc is one of the major players responsible for this metabolic alteration. However, the molecular mechanisms involved in Myc-induced metabolic reprogramming are not well defined. Here we identify p32, a mitochondrial protein known to play a role in the expression of mitochondrial respiratory chain complexes, as a critical player in Myc-induced glutamine addiction. We show that p32 is a direct transcriptional target of Myc and that high level of Myc in malignant brain cancers correlates with high expression of p32. Attenuation of p32 expression reduced growth rate of glioma cells expressing Myc and impaired tumor formation in vivo. Loss of p32 in glutamine addicted glioma cells induced resistance to glutamine deprivation and imparted sensitivity to glucose withdrawal. Finally, we provide evidence that p32 expression contributes to Myc-induced glutamine addiction of cancer cells. Our findings suggest that Myc promotes the expression of p32, which is required to maintain sufficient respiratory capacity to sustain glutamine metabolism in Myc transformed cells.

Comparison of short wrist transverse open and limited open techniques for carpal tunnel release: a randomized controlled trial of two incisions

The purpose of this randomized controlled trial was to compare outcomes of limited open and short wrist transverse techniques in patients with carpal tunnel syndrome. In a single centre randomized controlled trial, 84 patients with idiopathic carpal tunnel syndrome were randomized before surgery to limited open or short wrist transverse open carpal tunnel release. The patients were evaluated at 6 weeks, 3 months, 6 months, and 1 and 2 years after surgery. At every follow-up, the Brigham and Women's Carpal Tunnel Questionnaire scores, scar discomfort, and subjective patient satisfaction were evaluated. Two years after surgery, five patients were lost to follow-up. The groups had similar Brigham and Women's Carpal Tunnel Questionnaire Symptom Severity and Functional Status scores and subjective satisfaction scores. The incidence of scar discomfort was not significantly different between the two groups on serial postoperative follow-up. Short wrist transverse open release surgery showed similar early postoperative symptoms and subjective and functional outcomes to limited open release.

LEVEL OF EVIDENCE

II.

Transarterial embolisation of renal arteriovenous malformation: safety and efficacy in 24 patients with follow-up

AIM

To evaluate the efficacy and safety of renal artery embolisation (RAE) for renal arteriovenous malformation (AVM) as well as its outcomes.

MATERIALS AND METHODS

The technical and clinical success rates, radiological and laboratory findings, and complications of RAE for 31 renal AVMs in 24 patients (M:F=9:15, mean age 46 years) at two separate medical institutions were retrospectively evaluated. Technical success was defined as complete occlusion of feeding arteries with no residual nidus seen on post-treatment angiography. Clinical failure was defined as recurrence of haematuria, presence of AVM on follow-up ultrasound or computed tomography, repeated RAE or surgery for the control of haematuria. Overall clinical success was defined as resolution haematuria or disappearance of AVM on follow-up imaging after single or multiple sessions of RAE.

RESULTS

Types of renal AVM were AVM, arterio-venous fistula (AVF) with intranidal aneurysm, and acquired AVF in 19, 1, and 4 patients, respectively. 18 patients (75%) underwent a single session of RAE, while 6 patients (25%) had two or more sessions of RAE. The level of embolisation was feeder, segmental artery, and main renal artery in 28 (90%), 2 (6%), and 1 (4%) procedures, respectively. Coil, n-butyl 2-cyanoacrylate, and polyvinyl alcohol were the most frequently chosen embolic materials and were used in 19, 14, and 8 procedures, respectively. The clinical success rate after initial RAE was 67% (16/24). Overall clinical success rate, including multisession RAE, was 88% (21/24). The technical success rate of 31 procedures was 65% (20/31). Among 11 technical failures in 10 patients, 4 achieved clinical success without additional RAE, 3 underwent second session RAE to achieve clinical success, and 3 patients underwent nephrectomy due to recurrence.

CONCLUSION

RAE is a safe and effective treatment for renal AVM. Technical failure of RAE does not always lead to clinical failure and multiple embolisation sessions may be effective for recurrent renal AVM.

WNT activation by lithium abrogates TP53 mutation associated radiation resistance in medulloblastoma

TP53 mutations confer subgroup specific poor survival for children with medulloblastoma. We hypothesized that WNT activation which is associated with improved survival for such children abrogates TP53 related radioresistance and can be used to sensitize TP53 mutant tumors for radiation. We examined the subgroup-specific role of TP53 mutations in a cohort of 314 patients treated with radiation. TP53 wild-type or mutant human medulloblastoma cell-lines and normal neural stem cells were used to test radioresistance of TP53 mutations and the radiosensitizing effect of WNT activation on tumors and the developing brain. Children with WNT/TP53 mutant medulloblastoma had higher 5-year survival than those with SHH/TP53 mutant tumours (100% and 36.6% ± 8.7%, respectively (p < 0.001)). Introduction of TP53 mutation into medulloblastoma cells induced radioresistance (survival fractions at 2Gy (SF2) of 89% ± 2% vs. 57.4% ± 1.8% (p < 0.01)). In contrast, β-catenin mutation sensitized TP53 mutant cells to radiation (p < 0.05). Lithium, an activator of the WNT pathway, sensitized TP53 mutant medulloblastoma to radiation (SF2 of 43.5% ± 1.5% in lithium treated cells vs. 56.6 ± 3% (p < 0.01)) accompanied by increased number of γH2AX foci. Normal neural stem cells were protected from lithium induced radiation damage (SF2 of 33% ± 8% for lithium treated cells vs. 27% ± 3% for untreated controls (p = 0.05). Poor survival of patients with TP53 mutant medulloblastoma may be related to radiation resistance. Since constitutive activation of the WNT pathway by lithium sensitizes TP53 mutant medulloblastoma cells and protect normal neural stem cells from radiation, this oral drug may represent an attractive novel therapy for high-risk medulloblastomas.

The expression of vascular endothelial growth factor and Syndecan-4 in cartilage from osteoarthritic knees

Previous studies support the important role of vascular endothelial growth factor (VEGF) and syndecan-4 in the pathogenesis of osteoarthritis (OA). Both VEGF and syndecan-4 are expressed by chondrocytes and both are involved in the regulation of matrix metalloproteinase-3, resulting in the activation of aggrecanase II (ADAMTS-5), which is essential in the pathogenesis of OA. However, the relationship between VEGF and syndecan-4 has not been established. As a pilot study, we assayed the expression of VEGF and syndecan-4 in cartilage samples and cultured chondrocytes from osteoarthritic knee joints and analysed the relationship between these two factors. Specimens were collected from 21 female patients (29 knees) who underwent total knee replacement due to severe medial OA of the knee (Kellgren-Lawrence grade 4). Articular cartilage samples, obtained from bone and cartilage excised during surgery, were analysed and used for chondrocyte culture. We found that the levels of expression of VEGF and syndecan-4 mRNA did not differ significantly between medial femoral cartilage with severe degenerative changes and lateral femoral cartilage that appeared grossly normal (p = 0.443 and 0.622, respectively). Likewise, the levels of expression of VEGF and syndecan-4 mRNA were similar in cultured chondrocytes from medial and lateral femoral cartilage. The levels of expression of VEGF and syndecan-4 mRNAs were significantly and positively correlated in cartilage explant (r = 0.601, p = 0.003) but not in cultured chondrocytes. These results suggest that there is a close relationship between VEGF and syndecan-4 in the cartilage of patients with OA. Further studies are needed to determine the exact pathway by which these two factors interact in the pathogenesis of OA.

A five-gene hedgehog signature developed as a patient preselection tool for hedgehog inhibitor therapy in medulloblastoma

PURPOSE

Distinct molecular subgroups of medulloblastoma, including hedgehog (Hh) pathway-activated disease, have been reported. We identified and clinically validated a five-gene Hh signature assay that can be used to preselect patients with Hh pathway-activated medulloblastoma.

EXPERIMENTAL DESIGN

Gene characteristics of the Hh medulloblastoma subgroup were identified through published bioinformatic analyses. Thirty-two genes shown to be differentially expressed in fresh-frozen and formalin-fixed paraffin-embedded tumor samples and reproducibly analyzed by RT-PCR were measured in matched samples. These data formed the basis for building a multi-gene logistic regression model derived through elastic net methods from which the five-gene Hh signature emerged after multiple iterations. On the basis of signature gene expression levels, the model computed a propensity score to determine Hh activation using a threshold set a priori. The association between Hh activation status and tumor response to the Hh pathway inhibitor sonidegib (LDE225) was analyzed.

RESULTS

Five differentially expressed genes in medulloblastoma (GLI1, SPHK1, SHROOM2, PDLIM3, and OTX2) were found to associate with Hh pathway activation status. In an independent validation study, Hh activation status of 25 medulloblastoma samples showed 100% concordance between the five-gene signature and Affymetrix profiling. Further, in medulloblastoma samples from 50 patients treated with sonidegib, all 6 patients who responded were found to have Hh-activated tumors. Three patients with Hh-activated tumors had stable or progressive disease. No patients with Hh-nonactivated tumors responded.

CONCLUSIONS

This five-gene Hh signature can robustly identify Hh-activated medulloblastoma and may be used to preselect patients who might benefit from sonidegib treatment.

Abstract B6: Epigenetic regulation of Hedgehog pathway transcriptional output by BET bromodomain proteins

Aberrant activation of Hedgehog signaling drives oncogenesis in several types of cancer. As a result, there has been significant interest in developing therapeutic strategies targeting this pathway, most notably through inhibition of Smoothened. Though Smoothened inhibitors have shown efficacy in several cancer clinical trials, the initial enthusiasm for these inhibitors has been tempered by emergence of resistance and a priori resistance, often via mutation of Smoothened itself or through dysregulation of downstream components of the Hedgehog signaling axis. Here we reveal a strategy that overcomes these resistance mechanisms by targeting the far downstream transcriptional mediators of Hedgehog signaling through inhibition of the BET bromodomain protein, BRD4. We show that knockdown of BRD4 or treatment with the BET bromodomain inhibitor, JQ1, dramatically inhibits transcription of GLI1 and other Hedgehog target genes upon ligand-mediated or genetic activation of the Hedgehog pathway. We confirm the inhibitory effect of JQ1 occurs downstream of SMO and SUFU and verify by chromatin immunoprecipitation that Brd4 directly occupies the GLI1 and GLI2 promoters, with a substantial decrease in the engagement of these genomic sites upon treatment with JQ1. We observe a corresponding downregulation of genes associated with medulloblastoma-specific GLI1 binding sites upon exposure to JQ1, confirming the direct regulation of GLI1 by BET bromodomain proteins. Finally, using patient- and GEMM-derived cell lines of Hedgehog-driven cancer (basal cell carcinoma, medulloblastoma and ATRT), we show that JQ1 decreases Hh pathway output and proliferation, even in cell lines resistant to Smoothened inhibitors. These results expand the role of BET bromodomain inhibitors to targeting Hedgehog-driven cancers and highlight a strategy that overcomes the limitation of Hedgehog pathway inhibitors currently in clinical use.

Citation Format: Yujie Tang, Simone Schubert, Jun Qi, Brian Nguyen, Sabran Masoud, Nujsaunusi Vue, Brianna Balansay, Furong Yu, Scott X. Atwood, Ramon J. Whitson, Anitha Ponnuswami, Spencer Chen, Sharareh Gholamin, Woo J. Pamelyn, Michelle Monje-Diesseroth, Sekyung Oh, Alex Lee, Jean Y. Tang, Rob Wechsler-Reya, Anthony E. Oro, James E. Bradner, Yoon-Jae Cho. Epigenetic regulation of Hedgehog pathway transcriptional output by BET bromodomain proteins. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B6.

Abstract PR12: Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody

CD47 is an anti-phagocytic cell surface protein mediating cancer cell evasion of phagocytosis by the innate immune system. Preclinical data suggest that CD47 is appears to be an indispensable means by which many cancer cells, including cancer stem cells, overcome intrinsic expression of their pro-phagocytic “eat me” signals. Blockade of CD47 with mAbs enables phagocytosis of cancer cells in vitro and in vivo. We have developed a novel humanized mAb (huCD47-Ab) that specifically binds CD47 and blocks it from interacting with its ligand, signal regulatory protein–α; (SIRPα), on phagocytic cells, resulting in the phagocytosis and elimination of cancer cells through their “eat me” signals. Normal cells generally do not express eat me signals, and are unaffected by CD47 blocking mAb. We observed expression of CD47 on aggressive pediatric tumors, including acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), Ewing's sarcoma, neuroblastoma, and several cancers of the central nervous system (CNS), including atypical tetroid rhabdoid tumor (ATRT), primitive neuroectodermal tumor (PNET), medulloblastoma (MB), and pediatric high-grade glioma (pHGG). In-vitro phagocytosis assays, of primary patient samples shows significant engulfment by human peripheral blood derived macrophages upon incubation with the HuCD47-Ab antibody as compared to control. Furthermore we observe potent anti-tumor efficacy and survival benefit in MB, pHGG, ATRT and PNET orthotopic xenografts models establishing the ability of the huCD47 antibody to across the blood brain barrier by the CD47 blocking antibody. Using a novel human neural stem cell/brain tumor co-engraftment orthotopic xenograft model we show specificity of the HuCD47 antibody to only tumor cells and not normal human cells. We further observe potent anti-tumor efficacy in non-CNS tumor (ALL, AML and Osteosarcoma) xenograft models as well.

Furthermore we demonstrate that HuCD47-Ab can be administered safely to non-human primates at therapeutic serum levels. Pre-IND and IMPD meetings with the FDA in the US and the MHRA in the UK, have been held, and the clinical trials for adult patients with advanced stage malignancies will start in early 2014. After determining safety in these phase I trials, we initiate protocols for adult CNS tumors as part of expansion cohorts, and subsequently extend the trials to pediatric cancer patients, given manageable toxicity and signs of efficacy in the adult patients.

This abstract is also presented as Poster A86.

Citation Format: Siddhartha S. Mitra, Sharareh Gholamin, Jens-Peter Volkmer, Abdullah Feroze, Jie Liu, Achal Achrol, Lijuan Wang, Leanne Sayles, Michael Zhang, Kathleen Sakamoto, Michelle Monje-Deisseroth, Yoon-Jae Cho, Alejandro Sweet-Cordero, Ravi Majeti, Samuel Cheshier, Irving Weissman. Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr PR12.

Abstract 4771: Identification of inhibitors of TWIST1 as a treatment for lung cancer

Although a large fraction of non-small cell lung cancers (NSCLC) are dependent on defined oncogenic driver mutations, little progress has been made in the treatment of patients with the most frequently observed driver mutation, mutant KRAS. Acquired resistance to therapy targeting other driver mutations (EGFR mutant and ALK translocation positive tumors) is all but inevitable. We recently demonstrated that Twist1, a basic helix-loop-helix transcription factor, cooperates with mutant Kras to induce lung adenocarcinoma in mouse models, and that inhibition of Twist1 in murine models and human lung cancer cell lines led to oncogene-induced senescence (OIS) and in some cases, apoptosis. We have also found that TWIST1 is essential for tumor maintenance in human NSCLCs characterized by oncogenic drivers including KRAS mutation, EGFR mutation and c-MET amplification. As TWIST1 is not typically expressed post-natally, therapies directed against TWIST1 may present a more specific and perhaps less toxic therapy. Targeting the TWIST1 pathway represents an exciting and novel therapeutic strategy which may have a significant clinical impact.

We employed a combined bioinformatics-chemical approach to identify pharmacologic inhibitors of TWIST1. We used gene expression profiles from several KRAS mutant human NSCLC cell lines following shRNA-mediated TWIST1 knockdown to perform connectivity map (CMAP) analysis. We found that several of our highly ranked compounds had significant growth inhibitory effects in NSCLC cell lines. Furthermore, several of our candidate agents produced dose-dependent inhibition of TWIST1-induced dissemination in a novel 3D organoid dissemination assay. Interestingly, a family of related harmala alkaloids including harmine ranked highly on the CMAP analysis. We found that harmine could not only inhibit growth in several oncogene driver defined NSCLC cell lines through the induction of apoptosis but could also decrease TWIST1 levels through a post-transcriptional mechanism. The growth inhibitory effects of the harmala alkaloids correlated with the ability to degrade TWIST1. Additionally, independent of our CMAP analysis, we identified another compound, salinomycin, which appears to modulate cancer cell growth and resulted in a decrease in TWIST1 levels through a post-transcriptional mechanism as well. Interestingly, salinomycin treatment induced a mesenchymal-epithelial transition (MET) in NSCLC which could be partially blocked in TWIST1 overexpressing NSCLC cell lines. We are currently examining the in vivo efficacy of these agents. In conclusion, we have identified several compounds that inhibit TWIST1 dependent dissemination and in some cases can lead to TWIST1 degradation. Since TWIST1 is essential for not only KRAS mutant NSCLC but more broadly for oncogene driven NSCLC, these studies could lead to the development of a novel class of inhibitors which could have a significant clinical impact.

Citation Format: Sarah NH Chatley, Jessica Cades, Neil Neumann, Lucia Mazzacurati, Zachary Yochum, Katriana Nugent, Yoon-Jae Cho, Andrew Ewald, Charles Rudin, Phuoc Tran, Timothy F. Burns. Identification of inhibitors of TWIST1 as a treatment for lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4771. doi:10.1158/1538-7445.AM2014-4771

EphrinB1 expression is dysregulated and promotes oncogenic signaling in medulloblastoma

Eph receptors and ephrin ligands are master regulators of oncogenic signaling required for proliferation, migration, and metastasis. Yet, Eph/ephrin expression and activity in medulloblastoma (MB), the most common malignant brain tumor of childhood, remains poorly defined. We hypothesized that Eph/ephrins are differentially expressed by sonic hedgehog (SHH) and non-SHH MB and that specific members contribute to the aggressive phenotype. Affymetrix gene expression profiling of 29 childhood MB, separated into SHH (N = 11) and non-SHH (N = 18), was performed followed by protein validation of selected Eph/ephrins in another 60 MB and two MB cell lines (DAOY, D556). Functional assays were performed using MB cells overexpressing or deleted for selected ephrins. We found EPHB4 and EFNA4 almost exclusively expressed by SHH MB, whereas EPHA2, EPHA8, EFNA1 and EFNA3 are predominantly expressed by non-SHH MB. The remaining family members, except EFNB1, are ubiquitously expressed by over 70-90 % MB, irrespective of subgroup. EFNB1 is the only member differentially expressed by 28 % of SHH and non-SHH MB. Corresponding protein expression for EphB/ephrinB1 and B2 was validated in MB. Only ephrinB2 was also detected in fetal cerebellum, indicating that EphB/ephrinB1 expression is MB-specific. EphrinB1 immunopositivity localizes to tumor cells within MB with the highest proliferative index. EphrinB1 overexpression promotes EphB activation, alters F-actin distribution and morphology, decreases adhesion, and significantly promotes proliferation. Either silencing or overexpression of ephrinB1 impairs migration. These results indicate that EphrinB1 is uniquely dysregulated in MB and promotes oncogenic responses in MB cells, implicating ephrinB1 as a potential target.

Dasatinib suppression of medulloblastoma survival and migration is markedly enhanced by combining treatment with the aurora kinase inhibitor AT9283

Medulloblastoma (MB) expresses Src kinase, while aurora kinase A overexpression correlates with poor survival. We thus investigated novel combination treatment with dasatinib and AT9283, inhibitors of Src and aurora kinase, respectively, on MB growth in vitro and in vivo. Treatment with each drug significantly reduced cell viability and combined treatment markedly potentiated this response. AT9283 induced p53 expression, autophagy, and G2/M cell-cycle arrest, while combined treatment induced S phase arrest. Dasatinib treatment caused tumor regression in vivo. Activated Src was detected in 44% MB analyzed. We conclude that further evaluation of this combination therapy for MB is highly warranted.

Epigenetic targeting of Hedgehog pathway transcriptional output through BET bromodomain inhibition

Hedgehog signaling drives oncogenesis in several cancers and strategies targeting this pathway have been developed, most notably through inhibition of Smoothened. However, resistance to Smoothened inhibitors occurs via genetic changes of Smoothened or other downstream Hedgehog components. Here, we overcome these resistance mechanisms by modulating GLI transcription via inhibition of BET bromodomain proteins. We show the BET bromodomain protein, BRD4, regulates GLI transcription downstream of SMO and SUFU and chromatin immunoprecipitation studies reveal BRD4 directly occupies GLI1 and GLI2 promoters, with a substantial decrease in engagement of these sites upon treatment with JQ1, a small molecule inhibitor targeting BRD4. Globally, genes associated with medulloblastoma-specific GLI1 binding sites are downregulated in response to JQ1 treatment, supporting direct regulation of GLI activity by BRD4. Notably, patient- and GEMM-derived Hedgehog-driven tumors (basal cell carcinoma, medulloblastoma and atypical teratoid/rhabdoid tumor) respond to JQ1 even when harboring genetic lesions rendering them resistant to Smoothened antagonists.

MRI surrogates for molecular subgroups of medulloblastoma

BACKGROUND AND PURPOSE

Recently identified molecular subgroups of medulloblastoma have shown potential for improved risk stratification. We hypothesized that distinct MR imaging features can predict these subgroups.

MATERIALS AND METHODS

All patients with a diagnosis of medulloblastoma at one institution, with both pretherapy MR imaging and surgical tissue, served as the discovery cohort (n = 47). MR imaging features were assessed by 3 blinded neuroradiologists. NanoString-based assay of tumor tissues was conducted to classify the tumors into the 4 established molecular subgroups (wingless, sonic hedgehog, group 3, and group 4). A second pediatric medulloblastoma cohort (n = 52) from an independent institution was used for validation of the MR imaging features predictive of the molecular subtypes.

RESULTS

Logistic regression analysis within the discovery cohort revealed tumor location (P < .001) and enhancement pattern (P = .001) to be significant predictors of medulloblastoma subgroups. Stereospecific computational analyses confirmed that group 3 and 4 tumors predominated within the midline fourth ventricle (100%, P = .007), wingless tumors were localized to the cerebellar peduncle/cerebellopontine angle cistern with a positive predictive value of 100% (95% CI, 30%-100%), and sonic hedgehog tumors arose in the cerebellar hemispheres with a positive predictive value of 100% (95% CI, 59%-100%). Midline group 4 tumors presented with minimal/no enhancement with a positive predictive value of 91% (95% CI, 59%-98%). When we used the MR imaging feature-based regression model, 66% of medulloblastomas were correctly predicted in the discovery cohort, and 65%, in the validation cohort.

CONCLUSIONS

Tumor location and enhancement pattern were predictive of molecular subgroups of pediatric medulloblastoma and may potentially serve as a surrogate for genomic testing.

Pathogen inactivation efficacy of Mirasol PRT System and Intercept Blood System for non-leucoreduced platelet-rich plasma-derived platelets suspended in plasma

BACKGROUND AND OBJECTIVES

This study was conducted to evaluate the efficacy of pathogen inactivation (PI) in non-leucoreduced platelet-rich plasma-derived platelets suspended in plasma using the Mirasol PRT System and the Intercept Blood System.

METHODS

Platelets were pooled using the Acrodose PL system and separated into two aliquots for Mirasol and Intercept treatment. Four replicates of each viral strain were used for the evaluation. For bacteria, both low-titre (45-152 CFU/unit) inoculation and high-titre (7·34-10·18 log CFU/unit) inoculation with two replicates for each bacterial strain were used. Platelets with non-detectable bacterial growth and platelets inoculated with a low titre were stored for 5 days, and culture was performed with the BacT/ALERT system.

RESULTS

The inactivation efficacy expressed as log reduction for Mirasol and Intercept systems for viruses was as follows: human immunodeficiency virus 1, ≥4·19 vs. ≥4·23; bovine viral diarrhoea virus, 1·83 vs. ≥6·03; pseudorabies virus, 2·73 vs. ≥5·20; hepatitis A virus, 0·62 vs. 0·76; and porcine parvovirus, 0·28 vs. 0·38. The inactivation efficacy for bacteria was as follows: Escherichia coli, 5·45 vs. ≥9·22; Staphylococcus aureus, 4·26 vs. ≥10·11; and Bacillus subtilis, 5·09 vs. ≥7·74. Postinactivation bacterial growth in platelets inoculated with a low titre of S. aureus or B. subtilis was detected only with Mirasol.

CONCLUSION

Pathogen inactivation efficacy of Intercept for enveloped viruses was found to be satisfactory. Mirasol showed satisfactory inactivation efficacy for HIV-1 only. The two selected non-enveloped viruses were not inactivated by both systems. Inactivation efficacy of Intercept was more robust for all bacteria tested at high or low titres.

α5-GABAA receptors negatively regulate MYC-amplified medulloblastoma growth

Neural tumors often express neurotransmitter receptors as markers of their developmental lineage. Although these receptors have been well characterized in electrophysiological, developmental and pharmacological settings, their importance in the maintenance and progression of brain tumors and, importantly, the effect of their targeting in brain cancers remains obscure. Here, we demonstrate high levels of GABRA5, which encodes the α5-subunit of the GABAA receptor complex, in aggressive MYC-driven, "Group 3" medulloblastomas. We hypothesized that modulation of α5-GABAA receptors alters medulloblastoma cell survival and monitored biological and electrophysiological responses of GABRA5-expressing medulloblastoma cells upon pharmacological targeting of the GABAA receptor. While antagonists, inverse agonists and non-specific positive allosteric modulators had limited effects on medulloblastoma cells, a highly specific and potent α5-GABAA receptor agonist, QHii066, resulted in marked membrane depolarization and a significant decrease in cell survival. This effect was GABRA5 dependent and mediated through the induction of apoptosis as well as accumulation of cells in S and G2 phases of the cell cycle. Chemical genomic profiling of QHii066-treated medulloblastoma cells confirmed inhibition of MYC-related transcriptional activity and revealed an enrichment of HOXA5 target gene expression. siRNA-mediated knockdown of HOXA5 markedly blunted the response of medulloblastoma cells to QHii066. Furthermore, QHii066 sensitized GABRA5 positive medulloblastoma cells to radiation and chemotherapy consistent with the role of HOXA5 in directly regulating p53 expression and inducing apoptosis. Thus, our results provide novel insights into the synthetic lethal nature of α5-GABAA receptor activation in MYC-driven/Group 3 medulloblastomas and propose its targeting as a novel strategy for the management of this highly aggressive tumor.

Patients' beliefs and behaviors related to treatment adherence in patients with asthma requiring maintenance treatment in Asia

Objectives

To identify patients’ beliefs or behaviors related to treatment adherence and to assess association between asthma control and adherence in Asian patients with asthma.

Methods

We conducted a cross-sectional observational study of adult patients with asthma from specialist clinics in six Asian countries. Patients who were deemed by their treating physicians to require a maintenance treatment with an inhaler for at least 1 year were recruited. Patients completed a 12-item questionnaire related to health beliefs and behaviors, the 8-item Morisky Medication Adherence Scale (MMAS-8), the Asthma Control Test (ACT™), and the Standardized Asthma Quality of Life Questionnaire (AQLQ-S).

Results

Of the 1054 patients recruited, 99% were current users of inhaled corticosteroids. The mean ACT score was 20.0 ± 4.5 and 64% had well-controlled asthma. The mean MMAS-8 score was 5.5 ± 2.0 and 53% were adherent. Adherence was significantly associated with patients’ understanding of the disease and inhaler techniques, and with patients’ acceptance of inhaler medicines in terms of benefits, safety, convenience, and cost (p < 0.01 for all). In multivariate analysis, three questions related to patients’ acceptance of inhaler medicines remained significantly associated with poor adherence, after adjusting for potential confounders: “I am not sure inhaler type medicines work well” (p = 0.001), “Taking medicines more than once a day is inconvenient” (p = 0.002), and “Sometimes I skip my inhaler to use it over a longer period” (p < 0.001).

Conclusions

Our study showed that patients’ acceptance of the benefits, convenience and cost of inhaler medications have a significant impact on treatment adherence in the participating Asian countries.

Genome sequencing of SHH medulloblastoma predicts genotype-related response to smoothened inhibition

Smoothened (SMO) inhibitors recently entered clinical trials for sonic-hedgehog-driven medulloblastoma (SHH-MB). Clinical response is highly variable. To understand the mechanism(s) of primary resistance and identify pathways cooperating with aberrant SHH signaling, we sequenced and profiled a large cohort of SHH-MBs (n = 133). SHH pathway mutations involved PTCH1 (across all age groups), SUFU (infants, including germline), and SMO (adults). Children >3 years old harbored an excess of downstream MYCN and GLI2 amplifications and frequent TP53 mutations, often in the germline, all of which were rare in infants and adults. Functional assays in different SHH-MB xenograft models demonstrated that SHH-MBs harboring a PTCH1 mutation were responsive to SMO inhibition, whereas tumors harboring an SUFU mutation or MYCN amplification were primarily resistant.

BET bromodomain inhibition of MYC-amplified medulloblastoma

PURPOSE

MYC-amplified medulloblastomas are highly lethal tumors. Bromodomain and extraterminal (BET) bromodomain inhibition has recently been shown to suppress MYC-associated transcriptional activity in other cancers. The compound JQ1 inhibits BET bromodomain-containing proteins, including BRD4. Here, we investigate BET bromodomain targeting for the treatment of MYC-amplified medulloblastoma.

EXPERIMENTAL DESIGN

We evaluated the effects of genetic and pharmacologic inhibition of BET bromodomains on proliferation, cell cycle, and apoptosis in established and newly generated patient- and genetically engineered mouse model (GEMM)-derived medulloblastoma cell lines and xenografts that harbored amplifications of MYC or MYCN. We also assessed the effect of JQ1 on MYC expression and global MYC-associated transcriptional activity. We assessed the in vivo efficacy of JQ1 in orthotopic xenografts established in immunocompromised mice.

RESULTS

Treatment of MYC-amplified medulloblastoma cells with JQ1 decreased cell viability associated with arrest at G1 and apoptosis. We observed downregulation of MYC expression and confirmed the inhibition of MYC-associated transcriptional targets. The exogenous expression of MYC from a retroviral promoter reduced the effect of JQ1 on cell viability, suggesting that attenuated levels of MYC contribute to the functional effects of JQ1. JQ1 significantly prolonged the survival of orthotopic xenograft models of MYC-amplified medulloblastoma (P < 0.001). Xenografts harvested from mice after five doses of JQ1 had reduced the expression of MYC mRNA and a reduced proliferative index.

CONCLUSION

JQ1 suppresses MYC expression and MYC-associated transcriptional activity in medulloblastomas, resulting in an overall decrease in medulloblastoma cell viability. These preclinical findings highlight the promise of BET bromodomain inhibitors as novel agents for MYC-amplified medulloblastoma.

Cytogenetic prognostication within medulloblastoma subgroups

PURPOSE

Medulloblastoma comprises four distinct molecular subgroups: WNT, SHH, Group 3, and Group 4. Current medulloblastoma protocols stratify patients based on clinical features: patient age, metastatic stage, extent of resection, and histologic variant. Stark prognostic and genetic differences among the four subgroups suggest that subgroup-specific molecular biomarkers could improve patient prognostication.

PATIENTS AND METHODS

Molecular biomarkers were identified from a discovery set of 673 medulloblastomas from 43 cities around the world. Combined risk stratification models were designed based on clinical and cytogenetic biomarkers identified by multivariable Cox proportional hazards analyses. Identified biomarkers were tested using fluorescent in situ hybridization (FISH) on a nonoverlapping medulloblastoma tissue microarray (n = 453), with subsequent validation of the risk stratification models.

RESULTS

Subgroup information improves the predictive accuracy of a multivariable survival model compared with clinical biomarkers alone. Most previously published cytogenetic biomarkers are only prognostic within a single medulloblastoma subgroup. Profiling six FISH biomarkers (GLI2, MYC, chromosome 11 [chr11], chr14, 17p, and 17q) on formalin-fixed paraffin-embedded tissues, we can reliably and reproducibly identify very low-risk and very high-risk patients within SHH, Group 3, and Group 4 medulloblastomas.

CONCLUSION

Combining subgroup and cytogenetic biomarkers with established clinical biomarkers substantially improves patient prognostication, even in the context of heterogeneous clinical therapies. The prognostic significance of most molecular biomarkers is restricted to a specific subgroup. We have identified a small panel of cytogenetic biomarkers that reliably identifies very high-risk and very low-risk groups of patients, making it an excellent tool for selecting patients for therapy intensification and therapy de-escalation in future clinical trials.

TERT promoter mutations are highly recurrent in SHH subgroup medulloblastoma

Telomerase reverse transcriptase (TERT) promoter mutations were recently shown to drive telomerase activity in various cancer types, including medulloblastoma. However, the clinical and biological implications of TERT mutations in medulloblastoma have not been described. Hence, we sought to describe these mutations and their impact in a subgroup-specific manner. We analyzed the TERT promoter by direct sequencing and genotyping in 466 medulloblastomas. The mutational distributions were determined according to subgroup affiliation, demographics, and clinical, prognostic, and molecular features. Integrated genomics approaches were used to identify specific somatic copy number alterations in TERT promoter-mutated and wild-type tumors. Overall, TERT promoter mutations were identified in 21 % of medulloblastomas. Strikingly, the highest frequencies of TERT mutations were observed in SHH (83 %; 55/66) and WNT (31 %; 4/13) medulloblastomas derived from adult patients. Group 3 and Group 4 harbored this alteration in <5 % of cases and showed no association with increased patient age. The prognostic implications of these mutations were highly subgroup-specific. TERT mutations identified a subset with good and poor prognosis in SHH and Group 4 tumors, respectively. Monosomy 6 was mostly restricted to WNT tumors without TERT mutations. Hallmark SHH focal copy number aberrations and chromosome 10q deletion were mutually exclusive with TERT mutations within SHH tumors. TERT promoter mutations are the most common recurrent somatic point mutation in medulloblastoma, and are very highly enriched in adult SHH and WNT tumors. TERT mutations define a subset of SHH medulloblastoma with distinct demographics, cytogenetics, and outcomes.

Reduced H3K27me3 and DNA hypomethylation are major drivers of gene expression in K27M mutant pediatric high-grade gliomas

Two recurrent mutations, K27M and G34R/V, within histone variant H3.3 were recently identified in ∼50% of pHGGs. Both mutations define clinically and biologically distinct subgroups of pHGGs. Here, we provide further insight about the dominant-negative effect of K27M mutant H3.3, leading to a global reduction of the repressive histone mark H3K27me3. We demonstrate that this is caused by aberrant recruitment of the PRC2 complex to K27M mutant H3.3 and enzymatic inhibition of the H3K27me3-establishing methyltransferase EZH2. By performing chromatin immunoprecipitation followed by next-generation sequencing and whole-genome bisulfite sequencing in primary pHGGs, we show that reduced H3K27me3 levels and DNA hypomethylation act in concert to activate gene expression in K27M mutant pHGGs.

Recurrence patterns across medulloblastoma subgroups: an integrated clinical and molecular analysis

BACKGROUND

Recurrent medulloblastoma is a therapeutic challenge because it is almost always fatal. Studies have confirmed that medulloblastoma consists of at least four distinct subgroups. We sought to delineate subgroup-specific differences in medulloblastoma recurrence patterns.

METHODS

We retrospectively identified a discovery cohort of all recurrent medulloblastomas at the Hospital for Sick Children (Toronto, ON, Canada) from 1994 to 2012 (cohort 1), and established molecular subgroups using a nanoString-based assay on formalin-fixed paraffin-embedded tissues or frozen tissue. The anatomical site of recurrence (local tumour bed or leptomeningeal metastasis), time to recurrence, and survival after recurrence were assessed in a subgroup-specific manner. Two independent, non-overlapping cohorts (cohort 2: samples from patients with recurrent medulloblastomas from 13 centres worldwide, obtained between 1991 and 2012; cohort 3: samples from patients with recurrent medulloblastoma obtained at the NN Burdenko Neurosurgical Institute [Moscow, Russia] between 1994 and 2011) were analysed to confirm and validate observations. When possible, molecular subgrouping was done on tissue obtained from both the initial surgery and at recurrence.

RESULTS

Cohort 1 consisted of 30 patients with recurrent medulloblastomas; nine with local recurrences, and 21 with metastatic recurrences. Cohort 2 consisted of 77 patients and cohort 3 of 96 patients with recurrent medulloblastoma. Subgroup affiliation remained stable at recurrence in all 34 cases with available matched primary and recurrent pairs (five pairs from cohort 1 and 29 pairs from cohort 2 [15 SHH, five group 3, 14 group 4]). This finding was validated in 17 pairs from cohort 3. When analysed in a subgroup-specific manner, local recurrences in cohort 1 were more frequent in SHH tumours (eight of nine [89%]) and metastatic recurrences were more common in group 3 and group 4 tumours (17 of 20 [85%] with one WNT, p=0·0014, local vs metastatic recurrence, SHH vs group 3 vs group 4). The subgroup-specific location of recurrence was confirmed in cohort 2 (p=0·0013 for local vs metastatic recurrence, SHH vs group 3 vs group 4,), and cohort 3 (p<0·0001). Treatment with craniospinal irradiation at diagnosis was not significantly associated with the anatomical pattern of recurrence. Survival after recurrence was significantly longer in patients with group 4 tumours in cohort 1 (p=0·013) than with other subgroups, which was confirmed in cohort 2 (p=0·0075), but not cohort 3 (p=0·70).

INTERPRETATION

Medulloblastoma does not change subgroup at the time of recurrence, reinforcing the stability of the four main medulloblastoma subgroups. Significant differences in the location and timing of recurrence across medulloblastoma subgroups have potential treatment ramifications. Specifically, intensified local (posterior fossa) therapy should be tested in the initial treatment of patients with SHH tumours. Refinement of therapy for patients with group 3 or group 4 tumours should focus on metastases.

Subgroup-specific prognostic implications of TP53 mutation in medulloblastoma

PURPOSE

Reports detailing the prognostic impact of TP53 mutations in medulloblastoma offer conflicting conclusions. We resolve this issue through the inclusion of molecular subgroup profiles.

PATIENTS AND METHODS

We determined subgroup affiliation, TP53 mutation status, and clinical outcome in a discovery cohort of 397 medulloblastomas. We subsequently validated our results on an independent cohort of 156 medulloblastomas.

RESULTS

TP53 mutations are enriched in wingless (WNT; 16%) and sonic hedgehog (SHH; 21%) medulloblastomas and are virtually absent in subgroups 3 and 4 tumors (P < .001). Patients with SHH/TP53 mutant tumors are almost exclusively between ages 5 and 18 years, dramatically different from the general SHH distribution (P < .001). Children with SHH/TP53 mutant tumors harbor 56% germline TP53 mutations, which are not observed in children with WNT/TP53 mutant tumors. Five-year overall survival (OS; ± SE) was 41% ± 9% and 81% ± 5% for patients with SHH medulloblastomas with and without TP53 mutations, respectively (P < .001). Furthermore, TP53 mutations accounted for 72% of deaths in children older than 5 years with SHH medulloblastomas. In contrast, 5-year OS rates were 90% ± 9% and 97% ± 3% for patients with WNT tumors with and without TP53 mutations (P = .21). Multivariate analysis revealed that TP53 status was the most important risk factor for SHH medulloblastoma. Survival rates in the validation cohort mimicked the discovery results, revealing that poor survival of TP53 mutations is restricted to patients with SHH medulloblastomas (P = .012) and not WNT tumors.

CONCLUSION

Subgroup-specific analysis reconciles prior conflicting publications and confirms that TP53 mutations are enriched among SHH medulloblastomas, in which they portend poor outcome and account for a large proportion of treatment failures in these patients.

Abstract PR08: mSWI/SNF (BAF) complexes facilitate decatentation of DNA by topoisomerase IIα

Recent exon sequencing studies of human tumors have revealed frequent mutations in subunits of BAF (mSWI/SNF) complexes. Here we find a novel function for BAF complexes in decatenating newly replicated sister chromatids, which is necessary for proper chromosome segregation during mitosis. We find that deletion of Brg1 leads to anaphase bridge formation and stalling in G2/M phase. In addition, we find that Brg1 point mutants identified from medulloblastoma and Burkitt's lymphoma patients have compromised ATPase function and that their expression similarly results in G2/M arrest and anaphase bridge formation. The G2/M arrest is rescued by caffeine, a known inhibitor of ATM/ATR, key regulators of the decatenation checkpoint, and also by expression of the TopoIIα point mutant, S1524A, which fails to initiate the decatenation checkpoint. Endogenous BAF complexes directly interact with endogenous TopoIIα and are required for TopoIIα binding to about 12,000 sites over the genome. Similarly, cells expressing the oncogenic Brg1 point mutants have compromised TopoIIα binding at Brg1-dependent TopoIIα binding sites. These studies indicate that the ability of TopoIIα to prevent DNA entanglement at mitosis requires BAF complexes and suggest that this activity contributes to the role of Brg1 as a tumor suppressor.

This abstract is also presented as Poster A36.

Citation Format: Emily Dykhuizen, Diana Hargreaves, Erik Miller, Kairong Cui, Andrey Korshunov, Marcel Kool, Stefan Pfister, Yoon-Jae Cho, Keji Zhao, Gerald Crabtree. mSWI/SNF (BAF) complexes facilitate decatentation of DNA by topoisomerase IIα. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr PR08.

Recurrent somatic alterations of FGFR1 and NTRK2 in pilocytic astrocytoma

Pilocytic astrocytoma, the most common childhood brain tumor, is typically associated with mitogen-activated protein kinase (MAPK) pathway alterations. Surgically inaccessible midline tumors are therapeutically challenging, showing sustained tendency for progression and often becoming a chronic disease with substantial morbidities. Here we describe whole-genome sequencing of 96 pilocytic astrocytomas, with matched RNA sequencing (n = 73), conducted by the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. We identified recurrent activating mutations in FGFR1 and PTPN11 and new NTRK2 fusion genes in non-cerebellar tumors. New BRAF-activating changes were also observed. MAPK pathway alterations affected all tumors analyzed, with no other significant mutations identified, indicating that pilocytic astrocytoma is predominantly a single-pathway disease. Notably, we identified the same FGFR1 mutations in a subset of H3F3A-mutated pediatric glioblastoma with additional alterations in the NF1 gene. Our findings thus identify new potential therapeutic targets in distinct subsets of pilocytic astrocytoma and childhood glioblastoma.

Neurologic features of Hutchinson-Gilford progeria syndrome after lonafarnib treatment

OBJECTIVES

The objective of this study was to retrospectively evaluate neurologic status pre- and posttreatment with the oral farnesyltransferase inhibitor lonafarnib in children with Hutchinson-Gilford progeria syndrome (HGPS), a rare, fatal disorder of segmental premature aging that results in early death by myocardial infarction or stroke.

METHODS

The primary outcome measure for intervention with lonafarnib was to assess increase over pretherapy in estimated annual rate of weight gain. In this study, neurologic signs and symptoms were compared pre- and posttreatment with lonafarnib.

RESULTS

Twenty-six participants were treated for a minimum of 2 years. Frequency of clinical strokes, headaches, and seizures was reduced from pretrial rates. Three patients with a history of frequent TIAs and average clinical stroke frequency of 1.75/year during the year before treatment experienced no new events during treatment. One patient with a history of stroke died due to large-vessel hemispheric stroke after 5 months on treatment. Headache prevalence and frequency were reduced. Four patients exhibited pretherapy seizures and no patients experienced recurrent or new-onset seizures.

CONCLUSIONS

This study provides preliminary evidence that lonafarnib therapy may improve neurologic status of children with HGPS. To address this question, we have incorporated prospective neuroimaging and neurologic assessments as measures in subsequent studies involving children with HGPS.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that lonafarnib 115-150 mg/m(2) for 24 to 29 months reduces the prevalence of stroke and TIA and the prevalence and frequency of headache over the treatment period.

BAF complexes facilitate decatenation of DNA by topoisomerase IIα

Recent exon-sequencing studies of human tumours have revealed that subunits of BAF (mammalian SWI/SNF) complexes are mutated in more than 20% of all human malignancies, but the mechanisms involved in tumour suppression are unclear. BAF chromatin-remodelling complexes are polymorphic assemblies that use energy provided by ATP hydrolysis to regulate transcription through the control of chromatin structure and the placement of Polycomb repressive complex 2 (PRC2) across the genome. Several proteins dedicated to this multisubunit complex, including BRG1 (also known as SMARCA4) and BAF250a (also known as ARID1A), are mutated at frequencies similar to those of recognized tumour suppressors. In particular, the core ATPase BRG1 is mutated in 5-10% of childhood medulloblastomas and more than 15% of Burkitt's lymphomas. Here we show a previously unknown function of BAF complexes in decatenating newly replicated sister chromatids, a requirement for proper chromosome segregation during mitosis. We find that deletion of Brg1 in mouse cells, as well as the expression of BRG1 point mutants identified in human tumours, leads to anaphase bridge formation (in which sister chromatids are linked by catenated strands of DNA) and a G2/M-phase block characteristic of the decatenation checkpoint. Endogenous BAF complexes interact directly with endogenous topoisomerase IIα (TOP2A) through BAF250a and are required for the binding of TOP2A to approximately 12,000 sites across the genome. Our results demonstrate that TOP2A chromatin binding is dependent on the ATPase activity of BRG1, which is compromised in oncogenic BRG1 mutants. These studies indicate that the ability of TOP2A to prevent DNA entanglement at mitosis requires BAF complexes and suggest that this activity contributes to the role of BAF subunits as tumour suppressors.

Abstract 5218: Development of Anti-CD47 therapy for pediatric brain tumors

Introduction: Extensive molecular characterization of Brain tumors done in recent years has proven valuable for tumor classification, risk stratification and outcome prediction for current treatment modalities. However the current standard of care has not improved the prognosis and carries an increased risk of cognitive impairments for children with brain tumors. A characteristic feature of tumor progression and recurrence is its ability to evade the immune system. Our hypothesis is that by modulating the innate immune system we can enhance the ability of macrophages to ‘eat and kill’ brain cancer cells. Recent data suggests that the interaction between the cell surface antigen CD47 and its binding partner SIRPα is a mechanism by which non-solid and solid tumors can evade the innate immune system. To see if anti-CD47 therapy is a potential therapy in malignant pediatric brain tumors we first looked at CD47 expression in freshly isolated patient and postmortem samples from 4 different tumor types; Diffused Intrinsic Pontine Glioma, Medulloblastoma, Ependymoma and ATRTs. We tested the hypothesis that blocking CD47- SIRPα interaction induced phagocytosis in an in-vitro phagocytosis assay. We next established orthotopic xenografts models in immune compromised mice and treated them with anti-CD47 humanized antibody, which is currently being developed for clinical trials in hematopoietic and non-CNS malignancies.

Result: CD47 expression was upregulated in all tumor types and was present in &gt;90% of the cells in high grade tumors. Increased CD47 expression was observed in CD15+ and CD133+ putative cancer stem cell population. Blocking the CD47- SIRPα interaction increases tumor phagocytosis by macrophages in-vitro. Systemic treatment with anti-CD47 antibody significantly reduced tumor burden in an orthotopic xenograft setting.

Conclusion: Anti-CD47 therapy is a viable and effective treatment modality for pediatric high grade brain tumors.

Citation Format: Sharareh Gholamin, Siddhartha S. Mitra, Chase Elliott Richard, Achal Achrol, Doosik Kong, Jun Jae Shin, Michelle Monje-Deisseroth, Yoon-Jae Cho, Irving Weissman, Samuel H. Cheshier. Development of Anti-CD47 therapy for pediatric brain tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5218. doi:10.1158/1538-7445.AM2013-5218