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Schrump, D. S.

Publications and source records attributed to Schrump, D. S..

2 recordsLinked to original sources
bioRxiv2021

mTOR Inhibition Overcomes RSK3-mediated Resistance to BET Inhibitors in Small Cell Lung Cancer

PurposeSCLC is a recalcitrant malignancy with limited treatment options. BET inhibitors have shown promising preclinical activity in SCLC, but their broad sensitivity spectrum limits their clinical prospects in this malignancy. Drug combination could be a solution. Experimental designWe performed high-throughput drug combination screens in SCLC cell lines to identify potential therapeutics synergizing with BET inhibitors. Validation was performed in SCLC cell lines and patient-derived xenograft models. Genome-wide RNA sequencing of xenograft tumors was performed to determine the mechanism underlying the synergy of the drug combination. ResultsInhibitors of the PI-3K-AKT-mTOR pathway were the top candidates from the screens. Among the therapeutics targeting this pathway, mTOR inhibitors showed the highest degree of synergy with BET inhibitors in vitro. Furthermore, the combination of these two classes of drugs showed superior antitumor efficacy and tolerability in vivo. Using both in vitro and in vivo SCLC models, we demonstrate that BET inhibitors activate the intrinsic apoptotic cascade, and mTOR inhibitors further enhance these apoptotic effects. Mechanistically, BET inhibitors activate the TSC2-mTOR-p70S6K1 signaling cascade by upregulating RSK3, an upstream kinase of TSC2. Activation of p70S6K1 leads to BAD phosphorylation and cell survival. mTOR inhibition blocks this survival signaling cascade and potentiates the antitumor effects of BET inhibitors. ConclusionsOur results demonstrate that RSK3 upregulation is a novel resistance mechanism of BET inhibitors in SCLC, and mTOR inhibition can overcome this resistance and enhance apoptosis. These findings provide a rationale to evaluate the combination of mTOR and BET inhibitors in patients with SCLC.

cancer biology↗
bioRxiv2021

BET Bromodomain Inhibitors Target the NEUROD1-subtype SCLC by Blocking NEUROD1 Transactivation

Small cell lung cancer (SCLC) is a recalcitrant malignancy that urgently needs new therapies. Four master transcription factors (ASCL1, NEUROD1, POU2F3, and YAP1) are identified in SCLC, and each defines the transcriptome landscape of one molecular subtype. These master factors have not been directly druggable, and targeting their transcriptional coactivator(s) could provide an alternative approach. Here, we identify that BET bromodomain proteins physically interact with NEUROD1 and function as its 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. SignificanceSmall cell lung cancer (SCLC) is the most aggressive form of lung malignancies, and little progress has been made to improve its outcome in the past two decades. It is now recognized that SCLC is not a single disease but has at least four molecular subtypes, and each subtype features the expression of one master transcription factor. Unfortunately, these master transcription factors are not directly druggable. Here, we identified BET bromodomain proteins as the transcriptional coactivators of NEUROD1, one of the master transcription factors in SCLC. Blocking BET bromodomain proteins with inhibitors suppresses NEUROD1-target genes and reduces tumor growth. Our results demonstrate that blocking transcriptional coactivators could be an alternative approach to targeting the master transcription factors in SCLC.

cancer biology↗