Data from Targeting MYCN-Driven Transcription By BET-Bromodomain Inhibition

Abstract

<div>Abstract<p><b>Purpose:</b> Targeting BET proteins was previously shown to have specific antitumoral efficacy against <i>MYCN</i>-amplified neuroblastoma. We here assess the therapeutic efficacy of the BET inhibitor, OTX015, in preclinical neuroblastoma models and extend the knowledge on the role of BRD4 in MYCN-driven neuroblastoma.</p><p><b>Experimental Design:</b> The efficacy of OTX015 was assessed in <i>in vitro</i> and <i>in vivo</i> models of human and murine MYCN-driven neuroblastoma. To study the effects of BET inhibition in the context of high MYCN levels, <i>MYCN</i> was ectopically expressed in human and murine cells. The effect of OTX015 on BRD4-regulated transcriptional pause release was analyzed using BRD4 and H3K27Ac chromatin immunoprecipitation coupled with DNA sequencing (ChIP-Seq) and gene expression analysis in neuroblastoma cells treated with OTX015 compared with vehicle control.</p><p><b>Results:</b> OTX015 showed therapeutic efficacy against preclinical MYCN-driven neuroblastoma models. Similar to previously described BET inhibitors, concurrent MYCN repression was observed in OTX015-treated samples. Ectopic <i>MYCN</i> expression, however, did not abrogate effects of OTX015, indicating that MYCN repression is not the only target of BET proteins in neuroblastoma. When <i>MYCN</i> was ectopically expressed, BET inhibition still disrupted MYCN target gene transcription without affecting MYCN expression. We found that BRD4 binds to super-enhancers and MYCN target genes, and that OTX015 specifically disrupts BRD4 binding and transcription of these genes.</p><p><b>Conclusions:</b> We show that OTX015 is effective against mouse and human MYCN-driven tumor models and that BRD4 not only targets MYCN, but specifically occupies MYCN target gene enhancers as well as other genes associated with super-enhancers. <i>Clin Cancer Res; 22(10); 2470–81. ©2015 AACR</i>.</p></div>