BET Inhibitors Target the SCLC-N subtype of Small Cell Lung Cancer by Blocking NEUROD1 Transactivation

Small cell lung cancer can be divided into several molecular subtypes based on the expression of four master transcription factors (ASCL1, NEUROD1, POU2F3, and YAP1). These master factors have not been directly druggable, and we hypothesized that targeting their transcriptional coactivator(s) could provide an alternative approach. Here, we identify that BET bromodomain proteins physically interact with NEUROD1 and function as transcriptional coactivators. Using CRISPR knockout and ChIP-seq, we demonstrate that NEUROD1 plays a critical role in defining the landscapes of BET bromodomain proteins in the SCLC genome. Targeting BET bromodomain proteins by BET inhibitors leads to broad suppression of the NEUROD1-target genes, especially those associated with superenhancers, and reduces SCLC growth in vitro and in vivo. LSAMP, a membrane protein in the IgLON family, was identified as one of the NEUROD1-target genes mediating BET inhibitor sensitivity in SCLC. Altogether, our study reveals that targeting transcriptional coactivators could be a novel approach to blocking the master transcription factors in SCLC for therapeutic purposes. The purpose of this part of the study was to investigate what genes are affected by BET inhibitor JQ1 in small cell lung cancer cell line COR-L279 (a SCLC-N subtype). Comparative gene expression profiling analysis of RNA-seq data was performed in COR-L279 cells treated with two doses of JQ1 (0.5µM and 1.5µM; 24hours) for 24 hours versus DMSO. Each sample had three biological replicates.