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      Identification of a Novel c-Myc Inhibitor 7594-0037 by Structure-Based Virtual Screening and Investigation of Its Anti-Cancer Effect on Multiple Myeloma

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          Abstract

          Introduction

          Multiple myeloma (MM) is an extremely malignant and incurable hematological cancer. Increased expression of the c-Myc oncoprotein is closely associated with shorter overall survival of MM patients, implying that c-Myc is a potential therapeutic target.

          Main Methods

          We identified a potential c-Myc inhibitor 7594–0037 by structure-based virtual screening from the ChemDiv database. CCK8 assay and flow cytometry were used to detect MM cell viability, cell cycle and apoptosis. Q-PCR and Western blot were used to measure corresponding mRNA and protein expression levels. Protein stability assay measured the stability of c-Myc.

          Results

          Compound 7594–0037 exhibited stronger anti-proliferative activity against MM cells, and induced MM cell cycle G2 phase arrest and apoptosis. More importantly, compound 7594–0037 overcame myeloma resistance to bortezomib and exhibited a synergistic effect with bortezomib, resulting in increased MM cell death. The mechanism consists of compound 7594–0037 facilitating c-Myc protein degradation via decreasing the c-Myc S62 phosphorylation levels mediated by PIM1 kinase. Molecular dynamics simulation with the c-Myc/7594-0037 complex showed that compound 7594–0037 bound tightly to the N-terminus of c-Myc, and blocked the binding interaction of the two termini of c-Myc, which resulted in c-Myc entering into an unstable state.

          Conclusion

          Overall, our study provides preliminary data for compound 7594–0037, which can be used as a novel c-Myc inhibitor and is a potential candidate therapeutic drug for multiple myeloma.

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          Most cited references 30

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          Low molecular weight inhibitors of Myc-Max interaction and function.

          c-Myc is helix-loop-helix-leucine zipper (HLH-ZIP) oncoprotein that is frequently deregulated in human cancers. In order to bind DNA, regulate target gene expression, and function in a biological context, c-Myc must dimerize with another HLH-ZIP protein, Max. A large number of c-Myc target genes have been identified, and many of the encoded proteins are transforming. Such functional redundancy, however, complicates therapeutic strategies aimed at inhibiting any single target gene product. Given this consideration, we have instead attempted to identify ways by which c-Myc itself could be effectively disabled. We have used a yeast two-hybrid approach to identify low-molecular-weight compounds that inhibit c-Myc-Max association. All of the compounds prevented transactivation by c-Myc-Max heterodimers, inhibited cell cycle progression, and prevented the in vitro growth of fibroblasts in a c-Myc-dependent manner. Several of the compounds also inhibited tumor growth in vivo. These results show that the yeast two-hybrid screen is useful for identifying compounds that can be exploited in mammalian cells. More specifically, they provide a means by which structural analogs, based upon these first-generation Myc-Max inhibitors, can be developed to enhance antitumor efficacy.
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            Phosphorylation by glycogen synthase kinase-3 controls c-myc proteolysis and subnuclear localization.

            The c-Myc protein is a transcription factor that is a central regulator of cell growth and proliferation. Thr-58 is a major phosphorylation site in c-Myc and is a mutational hotspot in Burkitt's and other aggressive human lymphomas, indicating that Thr-58 phosphorylation restricts the oncogenic potential of c-Myc. Mutation of Thr-58 is also associated with increased c-Myc protein stability. Here we show that inhibition of glycogen synthase kinase-3 (GSK-3) activity with lithium increases c-Myc stability and inhibits phosphorylation of c-Myc specifically at Thr-58 in vivo. Conversely, overexpression of GSK-3 alpha or GSK-3 beta enhances Thr-58 phosphorylation and ubiquitination of c-Myc. Together, these observations suggest that phosphorylation of Thr-58 mediated by GSK-3 facilitates c-Myc rapid proteolysis by the ubiquitin pathway. Furthermore, we demonstrate that GSK-3 binds c-Myc in vivo and in vitro and that GSK-3 colocalizes with c-Myc in the nucleus, strongly arguing that GSK-3 is the c-Myc Thr-58 kinase. We found that c-MycS, which lacks the N-terminal 100 amino acids of c-Myc, is unable to bind GSK-3; however, mutation of Ser-62, the priming phosphorylation site necessary for Thr-58 phosphorylation, does not disrupt GSK-3 binding. Finally, we show that Thr-58 phosphorylation alters the subnuclear localization of c-Myc, enhancing its localization to discrete nuclear bodies together with GSK-3.
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              Clinical and Biological Implications of MYC Activation: A common difference between MGUS and newly diagnosed multiple myeloma

               WJ Chng,  GF Huang,  TH Chung (2011)
              Events mediating transformation from the pre-malignant monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) are unknown. We analyzed a gene expression datasets generated on the Affymetrix U133 platform from 22 MGUS and 101 MM patients using gene-set enrichment analysis. Genes over-expressed in MM were enriched for cell cycle, proliferation and MYC activation gene-sets. Upon dissecting the relationship between MYC and cell cycle genesets, we identified and validated a MYC activation signature dissociated from proliferation. Applying this signature, MYC is activated in 67% of myeloma, but not in MGUS. This was further confirmed by immunohistochemistry using membrane CD138 and nuclear MYC double staining. We also showed that almost all tumors with RAS mutations expressed the MYC activation signature, and multiple mechanisms may be involved in activating MYC. MYC activation, whether assessed by gene expression signature or immunohistochemistry is associated with hyperdiploid MM, and shorter survival even in tumors that are not proliferative. Bortezomib treatment is able to overcome the survival disadvantage in patients with MYC activation.
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                Author and article information

                Journal
                Drug Des Devel Ther
                dddt
                dddt
                Drug Design, Development and Therapy
                Dove
                1177-8881
                28 September 2020
                2020
                : 14
                : 3983-3993
                Affiliations
                [1 ]Blood Diseases Institute, Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China
                [2 ]Department of Hematology, The Affiliated Hospital of Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China
                [3 ]College of Medical Imaging, Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China
                [4 ]Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China
                Author notes
                Correspondence: Kailin Xu Blood Diseases Institute, Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China Email lihmd@163.com
                Jian GaoJiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University , Xuzhou, Jiangsu, People’s Republic of China Email 18626042662@163.com
                Article
                264077
                10.2147/DDDT.S264077
                7532311
                © 2020 Yao et al.

                This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 7, References: 36, Pages: 11
                Categories
                Original Research

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