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Xu Z, Wang H, Meng Q, Ding Y, Zhu M, Zhou H, Zhang N, Shi L. Otilonium Bromide acts as a selective USP28 inhibitor and exhibits cytotoxic activity against multiple human cancer cell lines. Biochem Pharmacol 2023; 215:115746. [PMID: 37579857 DOI: 10.1016/j.bcp.2023.115746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Accepted: 08/11/2023] [Indexed: 08/16/2023]
Abstract
USP28 contributes to tumorigenesis through modulating the lifespan of oncogenic factors such as c-Myc and ΔNp63, and it has been identified as a potential target for anti-cancer drug development. Currently, although quite a number of USP28 inhibitors have been developed, they all are still in preclinical research stage. Besides, none of them exhibits satisfying inhibition selectivity against USP28 over its closest homologue USP25. Here in this manuscript, a high-throughput screening aiming to discover USP28 inhibitors with novel scaffold and enhanced inhibition selectivity were conducted. After the primary screening and the second round of validation, Otilonium Bromide, an approved drug for treating irritable bowel syndrome, was identified to inhibit USP28's activity with the IC50 value at 6.90 ± 0.90 μM. Besides, the drug exhibits a 3-4 folds inhibition selectivity against USP28 over USP25. According to the enzymatic kinetics analysis data and the hydrogen-deuterium exchange mass spectrometry results, Otilonium Bromide could bind to the allosteric pocket of USP28 and inhibit its activity in a reversible and non-competitive mode. The following performed cell-based assays revealed that the drug could cause cytotoxicity against human colorectal cancer cells and lung squamous carcinoma cells potentially through down-regulating USP28's oncogenic substrates c-Myc and/or ΔNp63. Meanwhile, since Otilonium Bromide has been found to preferentially distribute to gastrointestinal tissues, we then evaluated its potential in the combination treatment of colorectal cancer cells with Regorafenib, which is an approved drug for colorectal cancer therapy. As expected, Otilonium Bromide could significantly enhance the sensitivity of colorectal cancer cells to Regorafenib.
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Affiliation(s)
- Zhuo Xu
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China; University of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
| | - Hui Wang
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China; University of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
| | - Qian Meng
- State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China
| | - Yiluan Ding
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China
| | - Mengying Zhu
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China; University of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
| | - Hu Zhou
- State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China; University of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
| | - Naixia Zhang
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China; University of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China.
| | - Li Shi
- State Key Laboratory of Chemical Biology, Analytical Research Center for Organic and Biological Molecules, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China.
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2
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Zhou L, Qin B, Yassine DM, Luo M, Liu X, Wang F, Wang Y. Structure and function of the highly homologous deubiquitinases ubiquitin specific peptidase 25 and 28: Insights into their pathophysiological and therapeutic roles. Biochem Pharmacol 2023; 213:115624. [PMID: 37245535 DOI: 10.1016/j.bcp.2023.115624] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 05/19/2023] [Accepted: 05/22/2023] [Indexed: 05/30/2023]
Abstract
Deubiquitination is the reverse process of ubiquitination, an important protein post-translational modification. Deubiquitination is assisted by deubiquitinating enzymes (DUBs), which catalyze the hydrolysis and removal of ubiquitin chains from targeted proteins and play an important role in regulating protein stability, cell signaling transduction, and programmed cell death. Ubiquitin-specific peptidases 25 and 28 (USP25 and USP28), important members of the USP subfamily of DUBs, are highly homologous, strictly regulated, and closely associated with various diseases, such as cancer and neurodegenerative diseases. Recently, the development of inhibitors targeting USP25 and USP28 for disease treatment has garnered extreme attention. Several non-selective and selective inhibitors have shown potential inhibitory effects. However, the specificity, potency, and action mechanism of these inhibitors remain to be further improved and clarified. Herein, we summarize the structure, regulation, emerging physiological roles, and target inhibition of USP25 and USP28 to provide a basis for the development of highly potent and specific inhibitors for the treatment of diseases, such as colorectal cancer, breast cancer and so on.
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Affiliation(s)
- Lihui Zhou
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Biying Qin
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Demna Mohamed Yassine
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Maoguo Luo
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Xiaoling Liu
- School of Life Sciences, Beijing University of Chinese Medicine, Beijing, China
| | - Feng Wang
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Yanfeng Wang
- Key Laboratory of Molecular Medicine and Biotherapy, School of Life Science, Beijing Institute of Technology, Beijing 100081, China.
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3
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Ren X, Jiang M, Ding P, Zhang X, Zhou X, Shen J, Liu D, Yan X, Ma Z. Ubiquitin-specific protease 28: the decipherment of its dual roles in cancer development. Exp Hematol Oncol 2023; 12:27. [PMID: 36879346 PMCID: PMC9990303 DOI: 10.1186/s40164-023-00389-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 02/15/2023] [Indexed: 03/08/2023] Open
Abstract
As significant posttranslational modifications, ubiquitination and deubiquitination, whose balance is modulated by ubiquitin-conjugating enzymes and deubiquitinating enzymes (DUBs), can regulate many biological processes, such as controlling cell cycle progression, signal transduction and transcriptional regulation. Belonging to DUBs, ubiquitin-specific protease 28 (USP28) plays an essential role in turning over ubiquitination and then contributing to the stabilization of quantities of substrates, including several cancer-related proteins. In previous studies, USP28 has been demonstrated to participate in the progression of various cancers. Nevertheless, several reports have recently shown that in addition to promoting cancers, USP28 can also play an oncostatic role in some cancers. In this review, we summarize the correlation between USP28 and tumor behaviors. We initially give a brief introduction of the structure and related biological functions of USP28, and we then introduce some concrete substrates of USP28 and the underlying molecular mechanisms. In addition, the regulation of the actions and expression of USP28 is also discussed. Moreover, we concentrate on the impacts of USP28 on diverse hallmarks of cancer and discuss whether USP28 can accelerate or inhibit tumor progression. Furthermore, clinical relevance, including impacting clinical prognosis, influencing therapy resistance and being the therapy target in some cancers, is depicted systematically. Thus, assistance may be given to future experimental designs by the information provided here, and the potential of targeting USP28 for cancer therapy is emphasized.
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Affiliation(s)
- Xiaoya Ren
- Department of Thoracic Surgery, Tangdu Hospital, Air Force Medical University, 1 Xinsi Road, Xi'an, 710038, China.,Department of Medical Oncology, Senior Department of Oncology, Chinese PLA General Hospital, The Fifth Medical Center, 28 Fuxing Road, Beijing, 100853, China
| | - Menglong Jiang
- Department of Thoracic Surgery, 1st Affiliated Hospital of Anhui Medical University, Hefei City, China
| | - Peng Ding
- Department of Thoracic Surgery, Tangdu Hospital, Air Force Medical University, 1 Xinsi Road, Xi'an, 710038, China
| | - Xiaoyan Zhang
- Department of Aerospace Medicine, Air Force Medical University, Xi'an, China
| | - Xin Zhou
- Department of Medical Oncology, Senior Department of Oncology, Chinese PLA General Hospital, The Fifth Medical Center, 28 Fuxing Road, Beijing, 100853, China
| | - Jian Shen
- Senior Department of Cardiology, The Sixth Medical Center, Chinese PLA General Hospital and Chinese PLA Medical School, 28 Fuxing Road, Beijing, 100853, China
| | - Dong Liu
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences, Peking Union Medical College, 167 Beilishi Road, Beijing, 100037, China.
| | - Xiaolong Yan
- Department of Thoracic Surgery, Tangdu Hospital, Air Force Medical University, 1 Xinsi Road, Xi'an, 710038, China.
| | - Zhiqiang Ma
- Department of Medical Oncology, Senior Department of Oncology, Chinese PLA General Hospital, The Fifth Medical Center, 28 Fuxing Road, Beijing, 100853, China.
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4
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Sun X, Cai M, Wu L, Zhen X, Chen Y, Peng J, Han S, Zhang P. USP28 Deubiquitinates TCF7L2 to Govern the Action of Wnt Signaling Pathway in Hepatic Carcinoma. Cancer Sci 2022; 113:3463-3475. [PMID: 35880246 PMCID: PMC9530868 DOI: 10.1111/cas.15509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 07/14/2022] [Accepted: 07/18/2022] [Indexed: 11/29/2022] Open
Abstract
Overexpression of ubiquitin‐specific protease 28 (USP28) is found in hepatic carcinoma. It is unclear whether the deubiquitinase plays a role in hepatocarcinogenesis. Deregulation of the Wnt signaling pathway is frequently associated with liver cancer. Transcription factor 7‐like 2 (TCF7L2) is an important downstream transcription factor of the Wnt/β‐catenin signaling pathway, but the mechanisms by which TCF7L2 itself is regulated have not yet been revealed. Here, we report that USP28 promotes the activity of the Wnt signaling pathway through maintaining the stability of TCF7L2. We further show that FBXW7 is the E3 ubiquitin ligase for TCF7L2. By regulating the levels of TCF7L2, USP28 modulates the Wnt/β‐catenin signaling in liver cancer and USP28 depletion or inhibition by a small molecule inhibitor leads to a halt of growth in liver cancer cells. These results suggest that USP28 could be a potential therapeutic target for liver cancer.
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Affiliation(s)
- Xiao Sun
- Department of Oncology, The First Affiliated Hospital, Xi'an Jiaotong University Medical College, Xi'an, China.,Zhejiang Provincial Key Laboratory of Pancreatic Disease, The First Affiliated Hospital of Zhejiang University, Hangzhou, Zhejiang, China
| | - Mengjiao Cai
- Department of Oncology, The First Affiliated Hospital, Xi'an Jiaotong University Medical College, Xi'an, China
| | - Lingzhi Wu
- Zhejiang Provincial Key Laboratory of Pancreatic Disease, The First Affiliated Hospital of Zhejiang University, Hangzhou, Zhejiang, China
| | - Xinghua Zhen
- Zhejiang Provincial Key Laboratory of Pancreatic Disease, The First Affiliated Hospital of Zhejiang University, Hangzhou, Zhejiang, China
| | - Yuetong Chen
- Department of Oncology, The First Affiliated Hospital, Xi'an Jiaotong University Medical College, Xi'an, China
| | - Jin Peng
- Zhejiang Provincial Key Laboratory of Pancreatic Disease, The First Affiliated Hospital of Zhejiang University, Hangzhou, Zhejiang, China
| | - Suxia Han
- Department of Oncology, The First Affiliated Hospital, Xi'an Jiaotong University Medical College, Xi'an, China
| | - Pumin Zhang
- Zhejiang Provincial Key Laboratory of Pancreatic Disease, The First Affiliated Hospital of Zhejiang University, Hangzhou, Zhejiang, China.,Institute of Translational Medicine, Zhejiang University Medical School, Hangzhou, Zhejiang, China.,Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
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5
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Domain interactions reveal auto-inhibition of the deubiquitinating enzyme USP19 and its activation by HSP90 in the modulation of huntingtin aggregation. Biochem J 2020; 477:4295-4312. [PMID: 33094816 DOI: 10.1042/bcj20200536] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Revised: 10/20/2020] [Accepted: 10/23/2020] [Indexed: 01/25/2023]
Abstract
Ubiquitin-specific protease 19 (USP19) is a member of the deubiquitinating (DUB) enzymes that catalyze removing the ubiquitin signals from target proteins. Our previous research has demonstrated that USP19 up-regulates the protein level and aggregation of polyQ-expanded huntingtin through the involvement of heat shock protein 90 (HSP90). Here, we present solution structures of the CS1, CS2 and UbL domains of USP19 and structural insights into their domain interactions. We found that the tandem CS domains fold back to interact with the C-terminal USP domain (USPD) intra-molecularly that leads to inhibition of the catalytic core of USP19, especially CS1 interacts with the embedded UbL domain and CS2 does with the CH2 catalytic core. Moreover, CS2 specifically interacts with the NBD domain of HSP90, which can activate the DUB enzyme. A mechanism of auto-inhibition of USP19 and activation by HSP90 is proposed, on which USP19 modulates the protein level of polyQ-expanded huntingtin in cells. This study provides structural and mechanistic insights into the modulation of protein level and aggregation by USP19 with the assistance of HSP90.
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Wang H, Meng Q, Ding Y, Xiong M, Zhu M, Yang Y, Su H, Gu L, Xu Y, Shi L, Zhou H, Zhang N. USP28 and USP25 are downregulated by Vismodegib in vitro and in colorectal cancer cell lines. FEBS J 2020; 288:1325-1342. [PMID: 32578360 DOI: 10.1111/febs.15461] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 05/23/2020] [Accepted: 06/16/2020] [Indexed: 12/19/2022]
Abstract
Deubiquitinase USP28 plays a crucial role in tumorigenesis by enhancing the stabilities of multiple cancer-related proteins including c-Myc, Notch1, and LSD1, and has become an attractive target for anticancer drug development. However, to date, only a few of USP28-targeted active compounds have been developed, and the active compound-binding pocket in USP28 has not been experimentally revealed yet. In this study, bioassay-based high-throughput screening was applied to discover USP28-targeted inhibitors from the commercially available drug library. Vismodegib, an inhibitor of Hedgehog signaling pathway and FDA-approved drug for the treatment of basal cell carcinoma, was found to exhibit inhibition activity against USP28 (IC50 : 4.41 ± 1.08 μm). Multiple biophysical and biochemical techniques including NMR, ITC, thermal shift assay, HDX-MS, and site-directed mutagenesis analysis were then used to characterize the interaction between Vismodegib and USP28. The binding pocket in USP28 for Vismodegib, which is mainly composed of two helical structures spanning D255-N278 and N286-Y293, was revealed. According to the possible binding pose generated by HDX-MS data-defined molecular docking, the binding cavity occupied by Vismodegib in USP28 aligns well with one of the reported-binding pockets in USP7 for its inhibitors. Furthermore, cellular assays were conducted to confirm that Vismodegib could interact with the evolutionarily related deubiquitinases USP28 and USP25 and downregulate the levels of the two enzymes' substrate proteins c-Myc, Notch1, and Tankyrase-1/2.
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Affiliation(s)
- Hui Wang
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.,University of the Chinese Academy of Sciences, Beijing, China
| | - Qian Meng
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Yiluan Ding
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Muya Xiong
- University of the Chinese Academy of Sciences, Beijing, China.,CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Mengying Zhu
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.,University of the Chinese Academy of Sciences, Beijing, China
| | - Yuanyuan Yang
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.,University of the Chinese Academy of Sciences, Beijing, China
| | - Haixia Su
- University of the Chinese Academy of Sciences, Beijing, China.,CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Lei Gu
- University of the Chinese Academy of Sciences, Beijing, China.,CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Yechun Xu
- University of the Chinese Academy of Sciences, Beijing, China.,CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Li Shi
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Hu Zhou
- University of the Chinese Academy of Sciences, Beijing, China.,CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Naixia Zhang
- Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.,University of the Chinese Academy of Sciences, Beijing, China
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7
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Yang Y, Shi L, Ding Y, Shi Y, Hu HY, Wen Y, Zhang N. Structural and Functional Investigations of the N-Terminal Ubiquitin Binding Region of Usp25. Biophys J 2017; 112:2099-2108. [PMID: 28538147 DOI: 10.1016/j.bpj.2017.04.022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 04/11/2017] [Accepted: 04/18/2017] [Indexed: 10/19/2022] Open
Abstract
Ubiquitin-specific protease 25 (Usp25) is a deubiquitinase that is involved in multiple biological processes. The N-terminal ubiquitin-binding region (UBR) of Usp25 contains one ubiquitin-associated domain, one small ubiquitin-like modifier (SUMO)-interacting motif and two ubiquitin-interacting motifs. Previous studies suggest that the covalent sumoylation in the UBR of Usp25 impairs its enzymatic activity. Here, we raise the hypothesis that non-covalent binding of SUMO, a prerequisite for efficient sumoylation, will impair Usp25's catalytic activity as well. To test our hypothesis and elucidate the underlying molecular mechanism, we investigated the structure and function of the Usp25 N-terminal UBR. The solution structure of Usp251-146 is obtained, and the key residues responsible for recognition of ubiquitin and SUMO2 are identified. Our data suggest inhibition of Usp25's catalytic activity upon the non-covalent binding of SUMO2 to the Usp25 SUMO-interacting motif. We also find that SUMO2 can competitively block the interaction between the Usp25 UBR and its ubiquitin substrates. Based on our findings, we have proposed a working model to depict the regulatory role of the Usp25 UBR in the functional display of the enzyme.
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Affiliation(s)
- Yuanyuan Yang
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China
| | - Li Shi
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China
| | - Yiluan Ding
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Yanhong Shi
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Hong-Yu Hu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Yi Wen
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
| | - Naixia Zhang
- CAS Key Laboratory of Receptor Research, Department of Analytical Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China.
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NMR-based platform for fragment-based lead discovery used in screening BRD4-targeted compounds. Acta Pharmacol Sin 2016; 37:984-93. [PMID: 27238211 DOI: 10.1038/aps.2016.19] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 03/04/2016] [Indexed: 12/13/2022] Open
Abstract
AIM Fragment-based lead discovery (FBLD) is a complementary approach in drug research and development. In this study, we established an NMR-based FBLD platform that was used to screen novel scaffolds targeting human bromodomain of BRD4, and investigated the binding interactions between hit compounds and the target protein. METHODS 1D NMR techniques were primarily used to generate the fragment library and to screen compounds. The inhibitory activity of hits on the first bromodomain of BRD4 [BRD4(I)] was examined using fluorescence anisotropy binding assay. 2D NMR and X-ray crystallography were applied to characterize the binding interactions between hit compounds and the target protein. RESULTS An NMR-based fragment library containing 539 compounds was established, which were clustered into 56 groups (8-10 compounds in each group). Eight hits with new scaffolds were found to inhibit BRD4(I). Four out of the 8 hits (compounds 1, 2, 8 and 9) had IC50 values of 100-260 μmol/L, demonstrating their potential for further BRD4-targeted hit-to-lead optimization. Analysis of the binding interactions revealed that compounds 1 and 2 shared a common quinazolin core structure and bound to BRD4(I) in a non-acetylated lysine mimetic mode. CONCLUSION An NMR-based platform for FBLD was established and used in discovery of BRD4-targeted compounds. Four potential hit-to-lead optimization candidates have been found, two of them bound to BRD4(I) in a non-acetylated lysine mimetic mode, being selective BRD4(I) inhibitors.
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