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  • br Azacoccone E inhibits cancer cell growth by targeting pho

    2020-08-18


    Azacoccone E inhibits cancer cell growth by targeting 3-phosphoglycerate T dehydrogenase
    a Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China b Wuya College of Innovation, Key Laboratory of Structure-Based Drug Design & Discovery, Ministry of Education, Shenyang Pharmaceutical University, Shenyang 110016, China
    Keywords:
    Azacoccone E
    PHGDH inhibitor
    Natural product
    Cancer 
    Serine plays critically important roles in tumorigenesis. Homo sapiens 3-phosphoglycerate dehydrogenase (PHGDH) catalyzes the first committed step for the synthesis of glucose-derived serine via the phosphoserine pathway and has been associated with a wide variety of cancers, including breast cancer, melanoma, colon cancer, glioma, nasopharyngeal carcinoma, cervical adenocarcinoma, etc. Azacoccone E, an aza-epicoccone derivative from the culture of GW 4869 Aspergillus flavipes, exhibited effective inhibitory activity against PHGDH in vitro. The microscale thermophoresis (MST) method and the cellular thermal shift assay (CETSA) confirmed that azacoccone E directly bound to PHGDH. And the cell-based experiments showed that this compound was se-lectively toxic to PHGDH-dependent cancer cells and could cause apoptosis. Further biochemical assays revealed that it was a noncompetitive inhibitor with respect to the substrate of 3-PG and exhibited a time-dependent inhibition. Furthermore, molecular docking demonstrated that azacoccone E coordinated in an allosteric site of PHGDH with low binding energy. Therefore, azacoccone E can be considered as a possible drug candidate targeting at PHGDH for treatment of cancers.
    1. Introduction
    Serine, one of the so-called non-essential amino acids, supports a number of anabolic processes [1]. It is an essential component of pro-teins and provides the precursors for the synthesis of lipids, such as sphingolipids and phosphatidylserine (PS) [2]. Moreover, serine is the major source of “one-carbon” units carried by tetrahydrofolate and incorporated into nucleotides [3]. Thus, serine plays multiple important roles in cellular metabolism.
    It has long been recognized that serine can not only be obtained exogenously via amino GW 4869 transporters, but also be synthesized from glucose via the phosphoserine pathway in cells [4], in which the NAD+-dependent enzyme 3-phosphoglycerate dehydrogenase (PHGDH) cata-lyzes the first and also the rate-limiting step converting glycolytic in-termediate 3-phosphoglycerate (3-PG) to serine via three sequential enzymatic reactions [5]. An analysis of human cancers showed that PHGDH is in a genomic region of recurrent copy number gain most commonly found in breast cancer and melanoma [6]. Suppression of PHGDH in cell lines with high PHGDH expression level causes the
    reduction of serine synthesis and strong inhibition of cell proliferation, which has triggered great interest in understanding serine synthesis and downstream metabolism including one-carbon unit and alpha-ketoglu-tarate [7]. Thus, PHGDH inhibitors as a targeted cancer therapy re-present an exciting clinical opportunity.
    Natural products (NPs) are considered as a rich source of bioactive molecules for drug discovery, and approximately 60% of the small-molecule anti-cancer drugs approved were either NPs or derivatives of NPs from the 1930s to 2014. In NPs, secondary metabolites of en-dophytic fungi are considered to be rich natural product resources with unique structure and biological activity [8,9]. This study herein is fo-cusing on the identification of small molecule inhibitors of PHGDH. We screened in-house database of NPs which contained more than 600 compounds using the enzymatic assay, and azacoccones C and E, two aza-epicoccone derivatives obtained from Aspergillus flavipes were identified as promising candidates (see Fig. 1), showed significant PHGDH inhibitory activity compared with the positive compound CBR-5884 and had almost no effect on other NAD(P)+-dependent enzymes like isocitrate dehydrogenase (IDH1). Meanwhile, azacoccones C and E
    Corresponding authors.
    1 These authors contributed equally to this work.
    Available online 23 February 2019
    Fig. 1. Biological activity of PHGDH and chemical structures of azacoccones C and E.
    treatment selectively inhibited PHGDH-dependent cancer cell pro-liferation and induced apoptosis. The microscale thermophoresis (MST) method and cellular thermal shift assay (CETSA) showed that aza-coccone E was directly binding to PHGDH. Mechanistically, azacoccone E was found to be a noncompetitive inhibitor in a time-dependent manner. Molecular docking demonstrated that azacoccone E co-ordinated at the allosteric site of PHGDH, which is vital for decreasing the enzyme activity.