Abstract 1527: BRD3 as a specific vulnerable therapeutic target in neuroblastoma

Abstract

Abstract Introduction: BET inhibitors have raised high expectations for cancer treatment given their anti-proliferative effect by inhibiting BRD4 controlled enhancer activity of highly transcribed genes such as MYC(N). However, current inhibitors also target BRD2 and BRD3 which are functionally nonredundant with BRD4. In neuroblastoma only MYCN amplified tumors respond well to these drugs. Methods: We performed an integrated bioinformatics approach to scrutinize BET family genes as well as further candidate epigenetic regulators as targets for novel therapies in neuroblastoma. Results: First we performed a time-resolved expression data analysis of week 1 and 2 hyperplastic lesions and tumors derived from the TH-MYCN transgenic mouse model and confirmed dynamic regulation during tumor development for established neuroblastoma oncogenes and tumor suppressor genes. Next, we filtered within the highest upregulated genes for Cancer Gene Census (CGC) genes and identified 21 upregulated CGC genes mainly involved in chromatin remodeling and DNA repair. Finally, after further selection based on expression in CCLE and survival in neuroblastoma patients, BRD3 was identified as the top-ranked candidate. BRD3 exhibits drastic upregulation during tumor formation. Elevated BRD3 expression is the highest expressed gene in neuroblastoma cell lines upon analysis of the CCLE panel and associated with very poor prognosis. To explore the nonredundant functions of BRD3 in relation to BRD4, we performed RNA-sequencing after stable knockdown of BRD3 in neuroblastoma cell lines and compared the downstream effects on the transcriptome as well as the impact on cell viability to knockdown of BRD4 and pharmacological treatment with BET-inhibitors (JQ1, OTX015). In addition, we dissected the BRD3 protein complex by means of label-free mass spectrometry analysis to gain further insights into the BRD3 specific functions in relation to control of gene transcription and putative interaction with transcription factors such as MYCN. Current efforts are ongoing to test cooperative interaction of BRD3 versus BRD4 in dbh-MYCN driven neuroblastoma formation in zebrafish as well as BRD3 and BRD4 ChIP-sequencing in neuroblastoma cells. Conclusion: We identified BRD3 as a candidate novel driver gene in neuroblastoma and will present differential transcriptional control and protein interactions of BRD3 versus BRD4. This study can open the way towards developing BRD3 specific inhibitors for neuroblastoma and other BRD3 overexpressing cancers such as T-ALL and small cell lung carcinoma. Citation Format: Kaat Durinck, Jolien Dewyn, Anneleen Beckers, Siebe Loontiens, Suzanne Vanhauwaert, Daniel Carter, Belamy Chueng, Glenn Marshall, Katleen Depreter, Frank Westermann, Frank Speleman. BRD3 as a specific vulnerable therapeutic target in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1527. doi:10.1158/1538-7445.AM2017-1527