Widespread hypertranscription in aggressive human cancers

Cancers are often defined by the dysregulation of specific transcriptional programs; however, the importance of global transcriptional changes is less understood. Hypertranscription is the genome-wide increase in RNA output. Hypertranscription's prevalence, underlying drivers, and prognostic significance are undefined in primary human cancer. This is due, in part, to limitations of expression profiling methods, which assume equal RNA output between samples. Here, we developed a computational method to directly measure hypertranscription in 7494 human tumors, spanning 31 cancer types. Hypertranscription is ubiquitous across cancer, especially in aggressive disease. It defines patient subgroups with worse survival, even within well-established subtypes. Our data suggest that loss of transcriptional suppression underpins the hypertranscriptional phenotype. Single-cell analysis reveals hypertranscriptional clones, which dominate transcript production regardless of their size. Last, patients with hypertranscribed mutations have improved response to immune checkpoint therapy. Our results provide fundamental insights into gene dysregulation across human cancers and may prove useful in identifying patients who would benefit from novel therapies.

Abstract LB177: Widespread hypertranscription in aggressive human cancer

Cancers are often defined by the dysregulation of specific transcriptional programs; however, the importance of global transcriptional changes is less understood. Hypertranscription is the genome-wide increase in RNA output. Hypertranscription’s prevalence, underlying drivers and prognostic significance are undefined in primary human cancer. This is due in part to limitations of expression profiling methods, which assume equal RNA output between samples. Here, we developed a computational method to directly measure hypertranscription in 7,494 human tumors, spanning 31 cancer types. Hypertranscription is ubiquitous across cancer, especially in aggressive disease. It defines patient subgroups with worse survival, even within well-established subtypes. Our data suggest that loss of transcriptional suppression underpins the hypertranscriptional phenotype. Single-cell analysis reveals hypertranscriptional clones, which dominate transcript production regardless of their size. Finally, patients with hypertranscribed mutations have improved response to immune checkpoint therapy. Our results provide fundamental insights into gene dysregulation across human cancers and may prove useful in identifying patients that would benefit from novel therapies.

Citation Format: Matthew Zatzman, Fabio Fuligni, Ryan Ripsman, Tannu Suwal, Lisa-Monique Edward, Rob Denroche, Gun Ho Jang, Faiyaz Notta, Steven Gallinger, Saravana P. Selvanathan, Jeffrey Toretsky, Matthew D. Hellmann, Uri Tabori, Annie Huang, Adam Shlien. Widespread hypertranscription in aggressive human cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB177.

Clinical phenotypes and prognostic features of embryonal tumours with multi-layered rosettes: a Rare Brain Tumor Registry study

BACKGROUND

Embryonal tumours with multi-layered rosettes (ETMRs) are a newly recognised, rare paediatric brain tumour with alterations of the C19MC microRNA locus. Due to varied diagnostic practices and scarce clinical data, disease features and determinants of outcomes for these tumours are poorly defined. We did an integrated clinicopathological and molecular analysis of primary ETMRs to define clinical phenotypes, and to identify prognostic factors of survival and key treatment modalities for this orphan disease.

METHODS

Paediatric patients with primary ETMRs and tissue available for analyses were identified from the Rare Brain Tumor Consortium global registry. The institutional histopathological diagnoses were centrally re-reviewed as per the current WHO CNS tumour guidelines, using histopathological and molecular assays. Only patients with complete clinical, treatment, and survival data on Nov 30, 2019, were included in clinicopathological analyses. Among patients who received primary multi-modal curative regimens, event-free survival and overall survival were determined using Cox proportional hazard and log-rank analyses. Univariate and multivariable Cox proportional hazard regression was used to estimate hazard ratios (HRs) with 95% CIs for clinical, molecular, or treatment-related prognostic factors.

FINDINGS

159 patients had a confirmed molecular diagnosis of primary ETMRs (median age at diagnosis 26 months, IQR 18-36) and were included in our clinicopathological analysis. ETMRs were predominantly non-metastatic (94 [73%] of 128 patients), arising from multiple sites; 84 (55%) of 154 were cerebral tumours and 70 (45%) of 154 arose at sites characteristic of other brain tumours. Hallmark C19MC alterations were seen in 144 (91%) of 159 patients; 15 (9%) were ETMR not otherwise specified. In patients treated with curative intent, event-free survival was 57% (95% CI 47-68) at 6 months and 31% (21-42) at 2 years; overall survival was 29% (20-38) at 2 years and 27% (18-37) at 4 years. Overall survival was associated with non-metastatic disease (HR 0·48, 95% CI 0·28-0·80; p=0·0057) and non-brainstem location (0·42 [0·22-0·81]; p=0·013) on univariate analysis, as well as with gross total resection (0·30, 0·16-0·58; p=0·0014), high-dose chemotherapy (0·35, 0·19-0·67; p=0·0020), and radiotherapy (0·21, 0·10-0·41; p<0·0001) on multivariable analysis. 2-year event-free and overall survival was 0% at 2 years in patients treated with conventional chemotherapy without radiotherapy (regardless of surgery extent), and 21% (95% CI 1-41) and 30% (6-54), respectively, in patients treated with high-dose chemotherapy, and gross total resection without radiotherapy. 2-year event-free survival in patients treated with high-dose chemotherapy and radiotherapy was 66% (95% CI 39-93) for patients with gross total resection and 44% (7-81) for patients with sub-total resection. 2-5-year overall survival was 66% (95% CI 33-99, p=0·038) for patients with gross total resection and 67% (36-98, p=0·0020) for patients with sub-total resection.

INTERPRETATION

Prompt molecular diagnosis and post-surgical treatment with intensive multi-modal therapy tailored to patient-specific risk features could improve ETMR survival.

FUNDING

Canadian Institute of Health Research, Canada Research Chair Awards, Australian Lions Childhood Cancer Research Foundation, Spanish Society of Pediatrics, Consejería de Salud y Familias de la Junta de Andalucía, Miracle Marnie, Phoebe Rose Rocks, Tali's Funds, Garron Cancer Centre, Grace's Walk, Meagan's Hug, Brainchild, Nelina's Hope, and Jean Martel Foundation.

ETMR-22. TITLE: DEFINING THE CLINICAL AND PROGNOSTIC LANDSCAPE OF EMBRYONAL TUMORS WITH MULTI-LAYERED ROSETTES (ETMRs), A RARE BRAIN TUMOR REGISTRY (RBTC) STUDY

ETMR, an aggressive disease characterised by C19MC alterations, were previously categorised as various histologic diagnoses. The clinical spectrum and impact of conventional multi-modal therapy on this new WHO diagnostic category remains poorly understood as a majority of ~200 cases reported to date lack molecular confirmation. We undertook comprehensive clinico-pathologic studies of a large molecularly confirmed cohort to improve disease recognition and treatment approaches. Amongst 623 CNS-PNETs patients enrolled in the RBTC registry, 159 primary ETMRs were confirmed based on a combination of FISH (125), methylation analysis (88), SNP and RNAseq (32) analyses; 91% had C19MC amplification/gains/fusions, 9% lacked C19MC alterations but had global methylation features of ETMR NOS. ETMRs arose in young patients (median age 26 months) predominantly as localized disease (M0-72%, M2-3 -18%) at multiple locations including cerebrum (60%) cerebellum (18%), midline structures (6%); notably 10% were brainstem primaries mimicking DIPG. Uni-and multivariate analyses of clinical and treatment details of curative regimens available for 110 patients identified metastatic disease (p=0.002), brainstem locations(p=0.005), extent of surgery, receipt of multi-modal therapy including high dose chemotherapy and radiation (P<0.001) as significant treatment prognosticators, while C19MC status, age and gender were non-significant risk factors. Analyses of events in all patients showed respective EFS at 3 and 12 months of 84%(95%CI:77–91) and 37%(95%CI:20–41) and 4yr OS of 27%(95%CI:18–37) indicating despite intensified therapies ETMR is a rapidly progressive and fatal disease. Our comprehensive data on the largest cohort of molecularly-confirmed ETMRs provides a critical framework to guide current clinical management and development of clinical trials.

ETMR-19. SINGLE CELL ANALYSES OF ETMRs REVEAL THAT C19MC+ POPULATION DRIVES CELL CYCLE PROGRESSION AND STEM CELL MAINTENANCE

Embryonal tumors with multilayered rosettes (ETMRs) are highly fatal diseases characterized by recurrent amplification of C19MC, an oncogenic miRNA cluster. While C19MC was discovered as a major driver of ETMRs, its direct role in ETMRs remains unknown. As ETMRs exhibit significant heterogeneity in C19MC expression, we employed single cell transcriptomics to investigate features of C19MC+ population. We conducted single-nuclei RNAseq of 23,269 cells from 6 primary and 2 matched recurrent ETMRs. We also conducted single-cell RNAseq of human neural stem cells (hNSC-5miR) and ETMR cell line (A664-5miR) with stable expression of 5 C19MC miRNAs. Bulk RNAseq (n=27), H3K27Ac ChiP-seq (n=5) and ATAC-seq (n=5) corroborated scRNAseq data and identified core transcription factors (TFs) of C19MC+ population. C19MC+ population (24%) mapped to neuro-epithelial cells and exhibited signatures of cell cycle and stem cell maintenance, consistent with bulk-RNAseq data. The C19MC+ population overlaps with MKI67+ cycling (57%) and PROM1+ stem cell population (56%). Interestingly, interrogation of hNSC-5mir and A664-5miR showed a larger MKI67+/PROM1+ population compared to controls. Likewise, hNSC-5miR/A664-5miR in vitro and in vivo experiments showed increased proliferation/stemness. C19MC+ population is characterized by SHH, WNT, mTOR, Hippo and IGF-signalling and driven by MEIS1, SOX11, ZNF521, RFX4 and NR2F2 TFs. Recurrent ETMRs exhibit a persistent but smaller C19MC+ population. Intriguingly, recurrent tumors were more quiescent with a smaller proliferative population. C19MC is directly involved in driving cell cycle and stemness in ETMRs. Cellular and molecular features of primary and recurrent ETMRs were remarkably different, suggesting that C19MC plays a different role upon recurrence.

Abstract B17: A C19MC-LIN28A-MYCN oncogenic circuit driven by hijacked super-enhancers is a distinct therapeutic vulnerability in ETMRs—a lethal brain tumor

Embryonal tumors with multilayered rosettes (ETMRs) are distinctly challenging brain tumors of infants and very young children, with characteristic rapid progression and only 10-20% overall survival. ETMRs have characteristic amplification of Chr19q13.41 miRNA cluster (C19MC) and enrichment of pluripotency factor LIN28A. Since the discovery of C19MC, an embryonic stem cell-enriched, primate specific miRNA cluster, as a disease marker of ETMR, there has been limited progress in biologic and therapeutic understanding of this disease. In prior studies we demonstrated single C19MC oncomiRs promotes oncogenesis and inhibit neural differentiation, yet the specific mechanisms of C19MC remains unclear. Here we show expression of 5-C19MC oncomiRs cooperatively inhibits multiple cell cycle checkpoint tumor suppressors to drive cellular proliferation. We further show that C19MC oncomiRs activate a potent oncogenic circuit by upregulating MYCN and LIN28A via downregulation of RNA binding protein, Tristetraprolin. Using RNA-IP analyses, we uncovered epigenetic regulators as major targets of LIN28A and showed that LIN28A directly regulates expression of embryonic-neural DNMT3A2 and DNMT3B6 isoforms. Deep epigenetic mapping on primary tumors revealed high DNA-DNA interactions and enhancer hijacking focused on MYCN. We also discovered tumors with TTYH1-C19MC gene fusions harbored a novel hybrid super-enhancer. Lastly, super-enhancer analysis revealed MYCN/MAZ as major transcriptional regulators and that treatment with a potent MYCN and bromodomain inhibitor JQ-1 inhibited proliferation of primary cells. Collectively, our data reveal that tumor-specific genomic and epigenomic alterations of C19MC entrap and drive multiple feed-forward loops to fuel a potent C19MC-LIN28A-MYCN oncogenic circuit, that can be powerfully abrogated by bromodomain inhibitors. Our findings underscore C19MC as a critical oncogene in ETMRs and provide critical therapeutic insights and a framework for developing high-fidelity models for this orphan disease.

Citation Format: Iqra Mumal, Patrick Sin-Chan, Tannu Suwal, Irtisha Singh, Xiao-Nan Li, Charles Lin, Stephen Mack, Jeremy Rich, Annie Huang. A C19MC-LIN28A-MYCN oncogenic circuit driven by hijacked super-enhancers is a distinct therapeutic vulnerability in ETMRs—a lethal brain tumor [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B17.

PDTM-22. A C19MC-LIN28A-MYCN ONCOGENIC CIRCUIT DRIVEN BY HIJACKED SUPER-ENHANCERS IS A DISTINCT THERAPEUTIC VULNERABILITY IN ETMRS – A LETHAL BRAIN TUMOR

Embryonal tumors with multi-layered rosettes (ETMR) are aggressive brain cancers with characteristic C19MC oncomiR amplification and enrichment of pluripotency factor LIN28A. Here we investigated C19MC oncogenic mechanisms and discovered a potent C19MC-LIN28A-MYCN circuitry driven by multiple regulatory loops and super-enhancers resulting from long-range MYCN DNA interactions and C19MC gene fusions. C19MC and LIN28A targets respectively converge on critical cell cycle tumor suppressors and neo-embryonic DNMT3A/B isoforms. We identify a MYCN driven, core transcriptional network, conserved in early neural stem cells, that is potently abrogated by treatment with bromodomain inhibitor JQ1, leading to ETMR cell death. Our collective data suggest C19MC oncomiRs drive a malignant primitive cell state in ETMRs via entrapment of an early neural lineage network, which represents a critical therapeutic vulnerability for this recalcitrant disease.

A C19MC-LIN28A-MYCN Oncogenic Circuit Driven by Hijacked Super-enhancers Is a Distinct Therapeutic Vulnerability in ETMRs: A Lethal Brain Tumor

Embryonal tumors with multilayered rosettes (ETMRs) are highly lethal infant brain cancers with characteristic amplification of Chr19q13.41 miRNA cluster (C19MC) and enrichment of pluripotency factor LIN28A. Here we investigated C19MC oncogenic mechanisms and discovered a C19MC-LIN28A-MYCN circuit fueled by multiple complex regulatory loops including an MYCN core transcriptional network and super-enhancers resulting from long-range MYCN DNA interactions and C19MC gene fusions. Our data show that this powerful oncogenic circuit, which entraps an early neural lineage network, is potently abrogated by bromodomain inhibitor JQ1, leading to ETMR cell death.