Abstract A47: Inhibition of histone methyltransferase with novel epipolythiodioxopiperazines (ETP) alkaloids in pediatric high-grade glioma

Pediatric high-grade glioma (HGG), which ranks among the most lethal of cancers among children, contain two recurrent mutations within the histone H3 gene H3F3A (K27M and G34R/V). It is not known whether these mutations directly alter specific epigenetic regulatory mechanisms that may be involved in tumor proliferation and growth, or contribute to their therapeutic resistance and rapid recurrence. Preliminary findings from our lab have identified that Chaetocin (CH), a pan histone methyltransferase (HMT) inhibitor, and two newly synthesized epipolythiodioxopiperazines (ETP) alkaloids that are structurally and functionally distinct HMT inhibitors can effectively kill pediatric HGG (N=7), including three that contain the H3 K27M mutation. In addition, CH and ETPs can also inhibit tumor sphere formation and cell migration at low concentrations (<0.5uM) through in vitro studies. In H3 K27M tumors, these HMTi were shown to reverse hypomethylation of K27me3 transiently (<48 hours). We also found these HMTis to decrease tumor stem cell expression (Sox2, Oct4), and increase tumor-suppressor activity (PTEN, p53) for three pediatric HGG up to 72 hours. These results suggest ETP effectiveness that acts through direct HMT inhibition may also influence other tumorigenic pathways, which may in part contribute to their aggressive nature. Results from this investigation have advanced our understanding of epigenetic regulation of solid brain tumors, and identified drugs that may specifically target pediatric H3 K27M tumor subtypes and could ultimately improve overall survival in pediatric patients with high-grade glioma.

Citation Format: Stephen Dombrowski, Thamara Abou-Antoun, Anthony Mansour, Rewa Arar, Mohammad Movassaghi, Erin Murphy, Shuvojit Banerjee, Xiao-Nan Li, Peter Houghton, Darell Bigner, Angel Montero Carcaboso, Jeremy Rich, Violette Recinos. Inhibition of histone methyltransferase with novel epipolythiodioxopiperazines (ETP) alkaloids in pediatric high-grade glioma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr A47.

Abstract LB-302: Oncolytic poliovirus-mediated inflammation and immunity in breast cancer

Breast cancer is the most common malignancy among women in the United States and the second leading cause of cancer deaths in women. Disease prognosis, local recurrence rates and response to therapy are all related to receptor status of the individual cancer. Triple negative breast cancer (TNBC; ER-, PR-, and HER2-negative) is a subset of breast cancer with poor prognosis and high rate of local recurrence and metastasis with limited therapeutic options.

The oncolytic poliovirus, PVSRIPO, is a recombinant polio:rhinovirus chimera that has been engineered to eliminate neuropathogenicity and has demonstrated promising responses in patients with recurrent glioblastoma. PVSRIPO is oncolytic in tumor cells and enters cells via its receptor CD155, which is overexpressed in solid malignancies, including TNBC. Treatment of primary TNBC tissue with PVSRIPO induces IFN-I and pro-inflammatory cytokines. In a murine immunotherapy model, intratumoral injection of PVSRIPO induces IFN-I, IL12 and IFN-γ and rapid recruitment of neutrophils into the tumor followed by infiltration of DCs, T cells and B cells. Treatment of orthotopic breast tumors with PVSRIPO results in delayed tumor growth and increased survival in an immunocompetent murine immunotherapy model.

We have designed a pilot study to examine the effects of intratumoral injection of PVSRIPO into six women with TNBC with at least 1 cm of residual tumor after chemotherapy. The primary exploratory objective is to describe the changes in the amount of tumor infiltrating immune cells in tumor tissue pre- and post-injection of PVSRIPO. We will also collect blood at different time points during PVSRIPO treatment to evaluate inflammatory and immune signatures. We hypothesize that intratumoral administration of PVSRIPO will cause inflammation thus stimulating innate and adaptive immune activation.

This study is funded by the Department of Defense Breast Cancer Research Program award W81XWH-16-1-0354 (PI, Smita Nair).

Citation Format: Karenia Landa, Eda Holl, Michael Brown, James Herndon, Lars Grimm, Jeremy Force, Darell Bigner, Shelley Hwang, Matthias Gromeier, Smita Nair. Oncolytic poliovirus-mediated inflammation and immunity in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-302.

AJAP1 expression modulates glioma cell motility and correlates with tumor growth and survival

Glioblastoma multiforme (GBM) is one of the most common primary malignant brain tumors. Unraveling the molecular and genetic complexity that determines GBM's pronounced migratory property could provide new options for therapeutic targeting that may significantly complement current surgical and chemoradiation therapy and alter the current poor outcome. In this study, we establish stable AJAP1 overexpressing glioma cells in order to examine in vivo tumor growth. We examine AJAP1 localization by confocal microscopy and AJAP1's functional effect on migration and invasion across surfaces coated with laminin. Finally, analysis of AJAP1 expression in murine xenografts and GBM primary tumors revealed its association with tumor growth and survival. Stable overexpression of AJAP1 promotes adherence, decreases invasion of glioma cells through an extracellular-like matrix, and slows migration in the presence of laminin. These observations are reversed by gene knockdown using multiple siRNAs. Additionally, overexpression of AJAP1 decreases colony formation in glioma cells, and leads to smaller tumor growth with increased survival in glioma xenograft mice. Loss of AJAP1 protein expression predicts worse survival in GBM patients. AJAP1 overexpression decreases cell motility in the presence of laminin and decreases tumor growth in xenografts. Its loss of expression predicts worse survival in patients. This study extends our prior observations and implicates AJAP1 as a potential prognostic marker and a viable target for therapeutic intervention in GBM.

Patient-derived DIPG cells preserve stem-like characteristics and generate orthotopic tumors

Diffuse intrinsic pontine glioma (DIPG) is a devastating brain tumor, with a median survival of less than one year. Due to enormous difficulties in the acquisition of DIPG specimens and the sophisticated technique required to perform brainstem orthotopic injection, only a handful of DIPG pre-clinical models are available. In this study, we successfully established eight patient-derived DIPG cell lines, mostly derived from treatment-naïve surgery or biopsy specimens. These patient-derived cell lines can be stably passaged in serum-free neural stem cell media and displayed distinct morphologies, growth rates and chromosome abnormalities. In addition, these cells retained genomic hallmarks identical to original human DIPG tumors. Notably, expression of several neural stem cell lineage markers was observed in DIPG cell lines. Moreover, three out of eight cell lines can form orthotopic tumors in mouse brainstem by stereotactic injection and these tumors faithfully represented the characteristics of human DIPG by magnetic resonance imaging (MRI) and histopathological staining. Taken together, we established DIPG pre-clinical models resembling human DIPG and they provided a valuable resource for future biological and therapeutic studies.

Long-term Survival in Glioblastoma with Cytomegalovirus pp65-Targeted Vaccination

Purpose: Patients with glioblastoma have less than 15-month median survival despite surgical resection, high-dose radiation, and chemotherapy with temozolomide. We previously demonstrated that targeting cytomegalovirus pp65 using dendritic cells (DC) can extend survival and, in a separate study, that dose-intensified temozolomide (DI-TMZ) and adjuvant granulocyte macrophage colony-stimulating factor (GM-CSF) potentiate tumor-specific immune responses in patients with glioblastoma. Here, we evaluated pp65-specific cellular responses following DI-TMZ with pp65-DCs and determined the effects on long-term progression-free survival (PFS) and overall survival (OS).Experimental Design: Following standard-of-care, 11 patients with newly diagnosed glioblastoma received DI-TMZ (100 mg/m2/d × 21 days per cycle) with at least three vaccines of pp65 lysosome-associated membrane glycoprotein mRNA-pulsed DCs admixed with GM-CSF on day 23 ± 1 of each cycle. Thereafter, monthly DI-TMZ cycles and pp65-DCs were continued if patients had not progressed.Results: Following DI-TMZ cycle 1 and three doses of pp65-DCs, pp65 cellular responses significantly increased. After DI-TMZ, both the proportion and proliferation of regulatory T cells (Tregs) increased and remained elevated with serial DI-TMZ cycles. Median PFS and OS were 25.3 months [95% confidence interval (CI), 11.0-∞] and 41.1 months (95% CI, 21.6-∞), exceeding survival using recursive partitioning analysis and matched historical controls. Four patients remained progression-free at 59 to 64 months from diagnosis. No known prognostic factors [age, Karnofsky performance status (KPS), IDH-1/2 mutation, and MGMT promoter methylation] predicted more favorable outcomes for the patients in this cohort.Conclusions: Despite increased Treg proportions following DI-TMZ, patients receiving pp65-DCs showed long-term PFS and OS, confirming prior studies targeting cytomegalovirus in glioblastoma. Clin Cancer Res; 23(8); 1898-909. ©2017 AACR.

Exomic sequencing of four rare central nervous system tumor types

A heterogeneous population of uncommon neoplasms of the central nervous system (CNS) cause significant morbidity and mortality. To explore their genetic origins, we sequenced the exomes of 12 pleomorphic xanthoastrocytomas (PXA), 17 non-brainstem pediatric glioblastomas (PGBM), 8 intracranial ependymomas (IEP) and 8 spinal cord ependymomas (SCEP). Analysis of the mutational spectra revealed that the predominant single base pair substitution was a C:G>T:A transition in each of the four tumor types. Our data confirm the critical roles of several known driver genes within CNS neoplasms, including TP53 and ATRX in PGBM, and NF2 in SCEPs. Additionally, we show that activating BRAF mutations play a central role in both low and high grade glial tumors. Furthermore, alterations in genes coding for members of the mammalian target of rapamycin (mTOR) pathway were observed in 33% of PXA. Our study supports the hypothesis that pathologically similar tumors arising in different age groups and from different compartments may represent distinct disease processes with varied genetic composition.

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.