BET Inhibition Silences Expression of MYCN and BCL2 and Induces Cytotoxicity in Neuroblastoma Tumor Models

Abstract

BET family proteins are epigenetic regulators known to control expression of genes involved in cell growth and oncogenesis. Selective inhibitors of BET proteins exhibit potent anti-proliferative activity in a number of hematologic cancer models, in part through suppression of the MYC oncogene and downstream Myc-driven pathways. However, little is currently known about the activity of BET inhibitors in solid tumor models, and whether down-regulation of MYC family genes contributes to sensitivity. Here we provide evidence for potent BET inhibitor activity in neuroblastoma, a pediatric solid tumor associated with a high frequency of MYCN amplifications. We treated a panel of neuroblastoma cell lines with a novel small molecule inhibitor of BET proteins, GSK1324726A (I-BET726), and observed potent growth inhibition and cytotoxicity in most cell lines irrespective of MYCN copy number or expression level. Gene expression analyses in neuroblastoma cell lines suggest a role of BET inhibition in apoptosis, signaling, and N-Myc-driven pathways, including the direct suppression of BCL2 and MYCN. Reversal of MYCN or BCL2 suppression reduces the potency of I-BET726-induced cytotoxicity in a cell line-specific manner; however, neither factor fully accounts for I-BET726 sensitivity. Oral administration of I-BET726 to mouse xenograft models of human neuroblastoma results in tumor growth inhibition and down-regulation MYCN and BCL2 expression, suggesting a potential role for these genes in tumor growth. Taken together, our data highlight the potential of BET inhibitors as novel therapeutics for neuroblastoma, and suggest that sensitivity is driven by pleiotropic effects on cell growth and apoptotic pathways in a context-specific manner.

An in-tumor genetic screen reveals that the BET bromodomain protein, BRD4, is a potential therapeutic target in ovarian carcinoma

“…We found that, on JQ1 treatment, there was selective downregulation of the predominant MYC isoform in JQ1-sensitive DFs, consistent with the well-established role of BRD4 in promoting MYCN and c-MYC transcription (21)(22)(23)35). Consistently, selectivity of gene down-regulation following BRD4 inhibition has been ascribed to the presence of superenhancer regions, occupied by BRD4, and associated with the transcriptional regulation of key lineage-specific oncogenes and survival genes (36).…”

CRISPR-Cas9 screen reveals a MYCN-amplified neuroblastoma dependency on EZH2

“…Previous studies of MYCN-amplified neuroblastoma have focused on the role of MYCN in transcriptional activation and the superenhancer machinery to drive a neuroblastoma oncogenic program (20,43,56,57). The role of MYCN in repressing tumor suppressor programs in neuroblastoma has not been as well explored.…”

Dual-activity PI3K–BRD4 inhibitor for the orthogonal inhibition of MYC to block tumor growth and metastasis

“…Recent reports have shown that JQ1 suppresses growth of neuroblastoma in a set of in vivo models, including orthotopic transplantation of patient-derived xenografts and the TH-MYC mouse model (19,31). To determine the therapeutic effects of the TP-scaffold inhibitors in aggressive neuroblastoma, we established an s.c. xenograft model of MYCN-amplified neuroblastoma in immunocompromised mice using the SKNBE2 cell line.…”