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      Targeting BET Proteins With a PROTAC Molecule Elicits Potent Anticancer Activity in HCC Cells

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          Abstract

          Background and Aim: Bromodomain and extraterminal domain (BET) family proteins are epigenetic regulators involved in human malignances. Targeting BET proteins for degradation using proteolysis-targeting chimera (PROTAC) recently has drawn increasing attention in the field of cancer therapeutics. BET proteins have been found to be overexpressed in HCC cells and tumor tissues. However, the biological activity of BET-PROTACs in hepatocellular carcinoma (HCC) remains unclear. In this study, we investigated anti-HCC activity of BETd-260, a BET-PROTAC molecule using in vitro and in vivo models.

          Methods: BETd-260-mediated anti-HCC activity was investigated by cell viability, apoptosis assays. Efficacy was examined with a cell lines-derived HCC xenograft model in mice. Anticancer mechanism was investigated by RT-PCR, western blotting and immunohistochemical staining.

          Results: BETd-260 potently suppressed cell viability and robustly induced apoptosis in HCC cells. BETd-260 reciprocally modulated the expression of several apoptotic genes in HCC cells, i.e., suppressing the expression of anti-apoptotic Mcl-1, Bcl-2, c-Myc, and X-linked inhibitor of apoptosis (XIAP), whereas increasing the expression of pro-apoptotic Bad. BETd-260 treatment led to disruption of mitochondrial membrane integrity, and triggered apoptosis via intrinsic signaling in HCC cells. BETd-260 triggered apoptosis in HCC xenograft tissue and profoundly inhibited the growth of HCC xenograft tumors in mice.

          Conclusion: Our data suggest that pharmacological targeting of BET for degradation may be a novel therapeutic strategy for the treatment of HCC.

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          Most cited references 33

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          Selective inhibition of BET bromodomains

          Epigenetic proteins are intently pursued targets in ligand discovery. To date, successful efforts have been limited to chromatin modifying enzymes, or so-called epigenetic “writers” and “erasers”. Potent inhibitors of histone binding modules have not yet been described. Here we report a cell-permeable small molecule (JQ1) which binds competitively to acetyl-lysine recognition motifs, or bromodomains. High potency and specificity toward a subset of human bromodomains is explained by co-crystal structures with BRD4, revealing excellent shape complementarity with the acetyl-lysine binding cavity. Recurrent translocation of BRD4 is observed in a genetically-defined, incurable subtype of human squamous carcinoma. Competitive binding by JQ1 displaces the BRD4 fusion oncoprotein from chromatin, prompting squamous differentiation and specific anti-proliferative effects in BRD4-dependent cell lines and patient-derived xenograft models. These data establish proof of concept for targeting protein-protein interactions of epigenetic “readers” and provide a versatile chemical scaffold for the development of chemical probes more broadly throughout the bromodomain family.
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            Selective inhibition of tumor oncogenes by disruption of super-enhancers.

            Chromatin regulators have become attractive targets for cancer therapy, but it is unclear why inhibition of these ubiquitous regulators should have gene-specific effects in tumor cells. Here, we investigate how inhibition of the widely expressed transcriptional coactivator BRD4 leads to selective inhibition of the MYC oncogene in multiple myeloma (MM). BRD4 and Mediator were found to co-occupy thousands of enhancers associated with active genes. They also co-occupied a small set of exceptionally large super-enhancers associated with genes that feature prominently in MM biology, including the MYC oncogene. Treatment of MM tumor cells with the BET-bromodomain inhibitor JQ1 led to preferential loss of BRD4 at super-enhancers and consequent transcription elongation defects that preferentially impacted genes with super-enhancers, including MYC. Super-enhancers were found at key oncogenic drivers in many other tumor cells. These observations have implications for the discovery of cancer therapeutics directed at components of super-enhancers in diverse tumor types. Copyright © 2013 Elsevier Inc. All rights reserved.
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              Regorafenib for patients with hepatocellular carcinoma who progressed on sorafenib treatment (RESORCE): a randomised, double-blind, placebo-controlled, phase 3 trial.

              There are no systemic treatments for patients with hepatocellular carcinoma (HCC) whose disease progresses during sorafenib treatment. We aimed to assess the efficacy and safety of regorafenib in patients with HCC who have progressed during sorafenib treatment.
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                Author and article information

                Contributors
                Journal
                Front Oncol
                Front Oncol
                Front. Oncol.
                Frontiers in Oncology
                Frontiers Media S.A.
                2234-943X
                14 January 2020
                2019
                : 9
                Affiliations
                1Department of Hepatobiliary and Pancreatic Surgery, The First Affiliated Hospital of Zhengzhou University , Zhengzhou, China
                2Open and Key Laboratory of Hepatobiliary & Pancreatic Surgery and Digestive Organ Transplantation at Henan Universities, The First Affiliated Hospital of Zhengzhou University , Zhengzhou, China
                3Zhengzhou Key Laboratory of Hepatobiliary & Pancreatic Diseases and Organ Transplantation , Zhengzhou, China
                4Henan Key Laboratory of Digestive Organ Transplantation , Zhengzhou, China
                5Department of Orthopaedic Surgery, The First Affiliated Hospital of Zhengzhou University , Zhengzhou, China
                Author notes

                Edited by: Qingxin Mu, University of Washington, United States

                Reviewed by: Sida Liao, TScan Therapeutics, Inc., United States; Ning Wei, University of Pittsburgh, United States

                *Correspondence: Shuijun Zhang zhangshuijun@ 123456zzu.edu.cn

                This article was submitted to Cancer Molecular Targets and Therapeutics, a section of the journal Frontiers in Oncology

                †These authors have contributed equally to this work

                Article
                10.3389/fonc.2019.01471
                6971110
                Copyright © 2020 Zhang, Li, Zhang, Shi, Yan, Tang, Chen, Zhang, Wen, Wang, Pang, Li, Guo and Zhang.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 6, Tables: 0, Equations: 0, References: 33, Pages: 11, Words: 6322
                Funding
                Funded by: Natural Science Foundation of Henan Province 10.13039/501100006407
                Funded by: Key Scientific Research Project of Colleges and Universities in Henan Province 10.13039/501100013066
                Categories
                Oncology
                Original Research

                Oncology & Radiotherapy

                apoptosis, bet, hcc, protein degradation, protac

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