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Epigenetic inhibition of adaptive bypass responses to lapatinib by targeting BET Bromodomains.

ABSTRACT: The characterization of kinases as oncogenic drivers has led to more than 30 FDA-approved targeted kinase inhibitors for cancer treatment. Unfortunately, these therapeutics fail to have clinical durability because of adaptive responses from the kinome and transcriptome that bypass inhibition of the targeted pathway. In our recent work, we describe a method to prevent these adaptive responses at an epigenetic level, generating a durable response to kinase inhibition.

SUBMITTER: Stuhlmiller TJ

PROVIDER: S-EPMC4845204 | biostudies-other | 2016 Jan

REPOSITORIES: biostudies-other

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Project description:Bromodomain inhibition comprises a promising therapeutic strategy in cancer, particularly for hematologic malignancies. To date, however, genomic biomarkers to direct clinical translation have been lacking. We conducted a cell-based screen of genetically-defined cancer cell lines using a prototypical inhibitor of BET bromodomains. Integration of genetic features with chemosensitivity data revealed a robust correlation between MYCN amplification and sensitivity to bromodomain inhibition. We characterized the mechanistic and translational significance of this finding in neuroblastoma, a childhood cancer with frequent amplification of MYCN. Genome-wide expression analysis demonstrated downregulation of the MYCN transcriptional program accompanied by suppression of MYCN transcription. Functionally, bromodomain-mediated inhibition of MYCN impaired growth and induced apoptosis in neuroblastoma. BRD4 knock-down phenocopied these effects, establishing BET bromodomains as transcriptional regulators of MYCN. BET inhibition conferred a significant survival advantage in three in vivo neuroblastoma models, providing a compelling rationale for developing BET bromodomain inhibitors in patients with neuroblastoma. Significance: Biomarkers of response to small-molecule inhibitors of BET bromodomains, a new compound class with promising anti-cancer activity, have been lacking. Here, we reveal MYCN amplification as a strong genetic predictor of sensitivity to BET bromodomain inhibitors, demonstrate a mechanistic rationale for this finding, and provide a translational framework for clinical trial development of BET bromodomain inhibitors for pediatric patients with MYCN-amplified neuroblastoma. JQ1 is a novel thieno-triazolo-1,4-diazepine, which displaces BET bromodomains from chromatin by competitively binding to the acetyl lysine recognition pocket. BE(2)-C and Kelly cells were treated in triplicate with 1 ÂµM JQ1 or DMSO for 24 hours. RNA was extracted and a decrease in MYCN transcript was confirmed by real time RT-PCR as described above. The samples were profiled using the Affymetrix PrimeView Human Gene Expression Array (Affymetrix) at Beth Israel Deaconess Medical Center (Boston, MA, USA).

Project description:Triple negative breast cancer (TNBC) is heterogeneous with patients exhibiting at least two molecular subtypes, basal-like (BL) and claudin-low (CL). MEK inhibitor (MEKi) treatment of BL and CL cell lines and mouse model tumors induced subtype-specific alterations in overall kinome activity referred to as protein kinase reprogramming. BL- and CL-specific reprogramming involving increases in receptor tyrosine kinases was also seen in TNBC patients comparing tumor samples before and after a one week treatment with the MEKi, trametinib. Combination of kinase inhibitors targeted to the BL and CL reprogrammed signatures would need to be individually selected due to the heterogeneous resiliency of BL and CL kinomes. To overcome this “reprogramming dilemma” we targeted the transcriptional co-activator BRD4 with BET bromodomain inhibitors, JQI and IBET151; both strongly inhibited kinome reprogramming and onset of MEKi resistance in BL and CL cells. Targeting chromatin modifiers may therapeutically block resistance due to kinome reprogramming.BL and CL TNBC are commonly treated as a single disease despite genomic studies showing they represent distinct molecular subtypes1. Recent Cancer Genome Atlas data demonstrated that the 518 protein kinases in the human genome (the kinome) were infrequently mutated in BL breast cancer; however, EGFR, KRAS and BRAF were amplified in 22, 32 and 31% of BL tumors, respectively. These findings are consistent with frequent activation of the BRAF-MEK-ERK pathway in TNBC2,3 and inhibitors targeting kinases in this pathway are currently in clinical trials for TNBC. As single agents, targeted kinase inhibitors generally fail to sustain durable responses when used to treat a range of human cancers including TNBC4-6. Onset of kinase inhibitor resistance can be due to selection of mutations in the targeted kinase7,8, activating mutations or amplification of RAS or downstream kinases9,10 or kinome reprogramming, a process in which there are system-wide changes in kinase networks11-13. Each of these resistance mechanisms allows the cancer cell to circumvent the targeted inhibition of specific kinases14. We previously developed chemical, proteomic methods that assay the activation state of protein kinases en masse15,16. Our methods utilize ¬Multiplexed Inhibitor Beads (MIBs), mixtures of covalently immobilized, linker adapted, kinase inhibitors. The immobilized inhibitors are primarily type I kinase inhibitors that preferentially bind activated (versus inactive) kinase17. Kinase capture is highly reproducible and is a function of kinase affinity for different immobilized inhibitors as well as the kinase activation state. Activated kinases preferentially bind, inactive kinases do not. By coupling MIB capture with mass spectrometry (MIB/MS), the technique allows quantitative interrogation of hundreds of kinases in a single mass spectrometry run. This also interrogates kinases known by sequence but which have been understudied due to lack of reagents such as specific phospho-antibodies. We report here both in preclinical models and patients that BL and CL TNBC have different baseline kinome activation states and both respond differently to MEKi with subtype-specific tyrosine kinase reprogramming. To avoid treatment strategy that uses multiple kinase inhibitors in individual patients, we discovered a novel pharmacologic strategy to block the initial reprogramming response to MEKi involving inhibition of epigenetic processes.

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Epigenetic inhibition of adaptive bypass responses to lapatinib by targeting BET Bromodomains.

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