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BCL6 confers KRAS-mutant non-small-cell lung cancer resistance to BET inhibitors.

ABSTRACT: The bromodomain and extra-terminal domain (BET) proteins are promising therapeutic targets to treat refractory solid tumors; however, inherent resistance remains a major challenge in the clinic. Recently, the emerging role of the oncoprotein B cell lymphoma 6 (BCL6) in tumorigenesis and stress response has been unveiled. Here, we demonstrate that BCL6 was upregulated upon BET inhibition in KRAS-mutant cancers, including non-small-cell lung cancer (NSCLC). We further found that BRD3, not BRD2 or BRD4, directly interacted with BCL6 and maintained the negative autoregulatory circuit of BCL6. Disrupting this negative autoregulation by BET inhibitors (BETi) resulted in a striking increase in BCL6 transcription, which further activated the mTOR signaling pathway through repression of the tumor suppressor death-associated protein kinase 2. Importantly, pharmacological inhibition of either BCL6 or mTOR improved the tumor response and enhanced the sensitivity of KRAS-mutant NSCLC to BETi in both in vitro and in vivo settings. Overall, our findings identify a mechanism of BRD3-mediated BCL6 autoregulation and further develop an effective combinatorial strategy to circumvent BETi resistance in KRAS-driven NSCLC.

SUBMITTER: Guo J

PROVIDER: S-EPMC7773368 | biostudies-literature |

REPOSITORIES: biostudies-literature

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BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors

Project description:We report that OTX015 upregulates BCL6 in KRAS-mutant NSCLC cells. Considering that both BCL6 and BET proteins regulate target genes by affecting transcription, we performed an RNA-seq experiment to identify downstream genes which response to OTX015. Retinal mRNA profiles of A549 cells treated with DMSO (0.1% for 6 hr) and OTX015 (1 μM for 6 hr) were generated by deep sequencing, in triplicate, using the SOLiD v4 sequencing platform. The sequence reads that passed quality filters were analyzed at the transcript isoform level with two methods: Burrows-Wheeler Aligner (BWA) followed by ANOVA (ANOVA) and TopHat followed by Cufflinks. qRT-PCR validation was performed using TaqMan and SYBR Green assays.

2019-08-15 | GSE118645 | GEO

BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors [ChIP-Seq]

Project description:We report that BCL6 interacts with BRD3 and that BRD3 inhibition upregulates BCL6. By obtaining sequence from chromatin immunoprecipitated DNA of A549 cells, we generated genome-wide binding gene spectrums of BCL6 and BRD3. By locating -3000 to +200 bps around TSS, we find that BRD3 binds to the promoters of 2470 genes and that BCL6 binds to the promoters of 694 genes, with 82 genes shared by BRD3 and BCL6. Interestingly, BCL6 itself is one of these 82 shared genes, implying that BCL6 mediated self-repression may require the participation of BRD3. Other shared genes includes SGK2, IDH2, HOXB6, SIRT1, SOCS3 and ZFNs, demonstrating the widely involvement of BRD3 in the regulatory role of BCL6. To examine the dependency of BCL6 on BRD3, we also compared BCL6-binding spectrums with or without a BET inhibitor, OTX015. The ChIP-seq data with BCL6 antibody exhibited a diverse BCL-binding spectrum composed of 731 genes in OTX015 treatment, with only 117 genes overlapped with that of DMSO treatment. These data demonstrates that BET inhibition is sufficient to change BCL6-binding spectrum. This study provides a new insight of BCL6 regulatory roles in KRAS-mutant NSCLCs, where BRD3 is recruited by BCL6 and affect BCL6 binding preference as a cofactor.

2018-09-13 | GSE119863 | GEO

BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors

Project description:BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors

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BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors [ChIP-Seq]

Project description:BCL6 confers KRAS-mutant NSCLCs resistance to BET inhibitors [ChIP-Seq]

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Palbociclib resistance confers dependence on an FGFR-MAP kinase-mTOR-driven pathway in KRAS-mutant non-small cell lung cancer.

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Atorvastatin overcomes gefitinib resistance in KRAS mutant human non-small cell lung carcinoma cells.

Project description:The exact influence of statins on gefitinib resistance in human non-small cell lung cancer (NSCLC) cells with KRAS mutation alone or KRAS/PIK3CA and KRAS/PTEN comutations remains unclear. This work found that transfection of mutant KRAS plasmids significantly suppressed the gefitinib cytotoxicity in Calu3 cells (wild-type KRAS). Gefitinib disrupted the Kras/PI3K and Kras/Raf complexes in Calu3 cells, whereas not in Calu3 KRAS mutant cells. These trends were corresponding to the expression of pAKT and pERK in gefitinib treatment. Atorvastatin (1??M) plus gefitinib treatment inhibited proliferation, promoted cell apoptosis, and reduced the AKT activity in KRAS mutant NSCLC cells compared with gefitinib alone. Atorvastatin (5??M) further enhanced the gefitinib cytotoxicity through concomitant inhibition of AKT and ERK activity. Atorvastatin could interrupt Kras/PI3K and Kras/Raf complexes, leading to suppression of AKT and ERK activity. Similar results were also obtained in comutant KRAS/PTEN or KRAS/PIK3CA NSCLC cells. Furthermore, mevalonate administration reversed the effects of atorvastatin on the Kras/Raf and Kras/PI3K complexes, as well as AKT and ERK activity in both A549 and Calu1 cells. The in vivo results were similar to those obtained in vitro. Therefore, mutant KRAS-mediated gefitinib insensitivity is mainly derived from failure to disrupt the Kras/Raf and Kras/PI3K complexes in KRAS mutant NSCLC cells. Atorvastatin overcomes gefitinib resistance in KRAS mutant NSCLC cells irrespective of PIK3CA and PTEN statuses through inhibition of HMG-CoA reductase-dependent disruption of the Kras/Raf and Kras/PI3K complexes.

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Project description:KRAS mutations are one of the most prevalent oncogenic alterations in cancer. Until recently, drug development targeting KRAS did not convey clinical benefits to patients. Specific KRASG12C inhibitors, such as sotorasib and adagrasib, have been designed to bind to the protein's mutant structure and block KRASG12C in its GDP-bound inactive state. Phase 1/2 trials have shown promising anti-tumor activity, especially in pretreated non-small cell lung cancer patients. As expected, both primary and secondary resistance to KRASG12C inhibitors invariably occurs, and molecular mechanisms have been characterized in pre-clinical models and patients. Several mechanisms such as tyrosine kinase receptors (RTKs) mediated feedback reactivation of ERK-dependent signaling can result in intrinsic resistance to KRAS target therapy. Acquired resistance to KRASG12C inhibitors include novel KRAS mutations such as Y96D/C and other RAS-MAPK effector protein mutations. This review focuses on the intrinsic and acquired mechanisms of resistance to KRASG12C inhibitors in KRASG12C mutant non-small cell lung cancer and the potential clinical strategies to overcome or prevent it.

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Targeting KRAS-mutant non-small cell lung cancer: challenges and opportunities.

Project description:Oncogenic mutations in Kirsten rat sarcoma viral oncogene homolog (KRAS) occur in 15%-30% of non-small cell lung cancer (NSCLC). However, despite decades of intensive research, there is still no direct KRAS inhibitor with clinically proven efficacy. Considering its association with poor treatment response and prognosis of lung cancer, developing an effective inhibitory approach is urgently needed. Here, we review different strategies currently being explored to target KRAS-mutant NSCLC, discuss opportunities and challenges, and also propose some novel methods and concepts with the promise of clinical application.

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BET Bromodomain Inhibition Cooperates with PD-1 Blockade to Facilitate Antitumor Response in Kras-Mutant Non-Small Cell Lung Cancer.

Project description:KRAS mutation is present in approximately 30% of human lung adenocarcinomas. Although recent advances in targeted therapy have shown great promise, effective targeting of KRAS remains elusive, and concurrent alterations in tumor suppressors render KRAS-mutant tumors even more resistant to existing therapies. Contributing to the refractoriness of KRAS-mutant tumors are immunosuppressive mechanisms, such as increased presence of suppressive regulatory T cells (Treg) in tumors and elevated expression of the inhibitory receptor PD-1 on tumor-infiltrating T cells. Treatment with BET bromodomain inhibitors is beneficial for hematologic malignancies, and they have Treg-disruptive effects in a non-small cell lung cancer (NSCLC) model. Targeting PD-1-inhibitory signals through PD-1 antibody blockade also has substantial therapeutic impact in lung cancer, although these outcomes are limited to a minority of patients. We hypothesized that the BET bromodomain inhibitor JQ1 would synergize with PD-1 blockade to promote a robust antitumor response in lung cancer. In the present study, using Kras+/LSL-G12D ; Trp53L/L (KP) mouse models of NSCLC, we identified cooperative effects between JQ1 and PD-1 antibody. The numbers of tumor-infiltrating Tregs were reduced and activation of tumor-infiltrating T cells, which had a T-helper type 1 (Th1) cytokine profile, was enhanced, underlying their improved effector function. Furthermore, lung tumor-bearing mice treated with this combination showed robust and long-lasting antitumor responses compared with either agent alone, culminating in substantial improvement in the overall survival of treated mice. Thus, combining BET bromodomain inhibition with immune checkpoint blockade offers a promising therapeutic approach for solid malignancies such as lung adenocarcinoma. Cancer Immunol Res; 6(10); 1234-45. ©2018 AACR.

| S-EPMC6170698 | biostudies-literature

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