Invalidation of dieckol and 1,2,3,4,6-pentagalloylglucose (PGG) as SARS-CoV-2 main protease inhibitors and the discovery of PGG as a papain-like protease inhibitor
Open accessAbstract
The COVID-19 pandemic spurred a broad interest in antiviral drug discovery. The SARS-CoV-2 main protease (M pro) and papain-like protease (PL pro) are attractive antiviral drug targets given their vital roles in viral replication and modulation of host immune response. Structurally disparate compounds were reported as M pro and PL pro inhibitors from either drug repurposing or rational design. Two polyphenols dieckol and 1,2,3,4,6-pentagalloylglucose (PGG) were recently reported as SARS-CoV-2 M pro inhibitors. With our continuous interest in studying the mechanism of inhibition and resistance of M pro inhibitors, we report herein our independent validation/invalidation of these two natural products. Our FRET-based enzymatic assay showed that neither dieckol nor PGG inhibited SARS-CoV-2 M pro (IC 50 > 20 µM), which is in contrary to previous reports. Serendipitously, PGG was found to inhibit the SARS-CoV-2 PL pro with an IC 50 of 3.90 µM. The binding of PGG to PL pro was further confirmed in the thermal shift assay. However, PGG was cytotoxic in 293T-ACE2 cells (CC 50 = 7.7 µM), so its intracellular PL pro inhibitory activity could not be quantified by the cell-based Flip-GFP PL pro assay. In addition, we also invalidated ebselen, disulfiram, carmofur, PX12, and tideglusib as SARS-CoV-2 PL pro inhibitors using the Flip-GFP assay. Overall, our results call for stringent hit validation, and the serendipitous discovery of PGG as a putative PL pro inhibitor might worth further pursuing. Graphical abstract.
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The inhibitory potential of DIS on Mpro and PLpro was contradictory.
“Ultimately, the inhibitory potential of DIS on Mpro and PLpro was contradictory.98,99”
From Off-label and repurposed use of disulfiram beyond alcohol dependence: A systematic review of clinical and preclinical evidence (2026) · cites this paper as [99]
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Cites
Characteristics of SARS-CoV-2 and COVID-19
Hu, B., Guo, H., Zhou, P., & Shi, Z.-L. (2021) · Nature Reviews Microbiology · doi:10.1038/s41579-020-00459-7 · Cited by 5,291 · see citing works
Structure of Mpro from SARS-CoV-2 and discovery of its inhibitors
Jin, Z., Du, X., Xu, Y., Deng, Y., Liu, M., Zhao, Y., Zhang, B., Li, X., Zhang, L., Peng, C., et al. (2020) · Nature · doi:10.1038/s41586-020-2223-y · Cited by 4,432 · see citing works
A SARS-CoV-2 protein interaction map reveals targets for drug repurposing
Gordon, D. E., Jang, G. M., Bouhaddou, M., Xu, J., Obernier, K., White, K. M., O’Meara, M. J., Rezelj, V. V., Guo, J. Z., Swaney, D. L., et al. (2020) · Nature · doi:10.1038/s41586-020-2286-9 · Cited by 4,405 · see citing works
Coronavirus biology and replication: implications for SARS-CoV-2
V’kovski, P., Kratzel, A., Steiner, S., Stalder, H., & Thiel, V. (2020) · Nature Reviews Microbiology · doi:10.1038/s41579-020-00468-6 · Cited by 3,175 · see citing works
Broad-spectrum antiviral GS-5734 inhibits both epidemic and zoonotic coronaviruses
Sheahan, T. P., Sims, A. M., Graham, R. L., Menachery, V. D., Gralinski, L. E., Case, J. B., Leist, S. R., Pyrć, K., Feng, J. Y., Trantcheva, I., et al. (2017) · Science Translational Medicine · doi:10.1126/scitranslmed.aal3653 · Cited by 1,575 · see citing works
Therapeutic efficacy of the small molecule GS-5734 against Ebola virus in rhesus monkeys
Warren, T. K., Jordan, R., Lo, M. K., Ray, A. S., Mackman, R. L., Soloveva, V., Siegel, D. S., Perron, M. J., Bannister, R. M., Hui, H. C., et al. (2016) · Nature · doi:10.1038/nature17180 · Cited by 1,561 · see citing works
Eastman, R. T., Roth, J. S., Brimacombe, K. R., Simeonov, A. M., Shen, M., Patnaik, S., & Hall, M. D. (2020) · ACS Central Science · doi:10.1021/acscentsci.0c00489 · Cited by 951 · see citing works
Ma, C., Sacco, M. D., Hurst, B., Townsend, J. A., Hu, Y., Szeto, T., Zhang, X., Tarbet, B., Marty, M. T., Chen, Y., et al. (2020) · Cell Research · doi:10.1038/s41422-020-0356-z · Cited by 880 · see citing works
Self-citationBoth Boceprevir and GC376 efficaciously inhibit SARS-CoV-2 by targeting its main protease
Fu, L., Ye, F., Feng, Y., Yu, F., Wang, Q., Wu, Y., Zhao, C., Sun, H., Huang, B., Niu, P., et al. (2020) · Nature Communications · doi:10.1038/s41467-020-18233-x · Cited by 544 · see citing works
Structure of papain-like protease from SARS-CoV-2 and its complexes with non-covalent inhibitors
Osipiuk, J., Azizi, S., Dvorkin, S., Endres, M. J., Jedrzejczak, R. P., Jones, K. A., Kang, S., Kathayat, R. S., Kim, Y., Lisnyak, V. G., et al. (2021) · Nature Communications · doi:10.1038/s41467-021-21060-3 · Cited by 471 · see citing works
Feline coronavirus drug inhibits the main protease of SARS-CoV-2 and blocks virus replication
Vuong, W., Khan, M. B., Fischer, C., Arutyunova, E. I., Lamer, T., Shields, J. A., Saffran, H. A., McKay, R. T., van Belkum, M. J., Joyce, M., et al. (2020) · Nature Communications · doi:10.1038/s41467-020-18096-2 · Cited by 455 · see citing works
Sacco, M. D., Ma, C., Lagarias, P. I., Gao, A., Townsend, J. A., Meng, X., Dube, P. H., Zhang, X., Hu, Y., Kitamura, N., et al. (2020) · Science Advances · doi:10.1126/sciadv.abe0751 · Cited by 401 · see citing works
Self-citationCox, R. M., Wolf, J. D., & Plemper, R. K. (2020) · Nature Microbiology · doi:10.1038/s41564-020-00835-2 · Cited by 391 · see citing works
Toots, M., Yoon, J.-J., Cox, R. M., Hart, M., Sticher, Z. M., Makhsous, N., Plesker, R., Barrena, A. H., Reddy, P. G., Mitchell, D. G., et al. (2019) · Science Translational Medicine · doi:10.1126/scitranslmed.aax5866 · Cited by 316 · see citing works
Drug Development and Medicinal Chemistry Efforts toward SARS‐Coronavirus and Covid‐19 Therapeutics
Ghosh, A. K., Brindisi, M., Shahabi, D., Chapman, M. E., & Mesecar, A. D. (2020) · ChemMedChem · doi:10.1002/cmdc.202000223 · Cited by 306 · see citing works
Masitinib is a broad coronavirus 3CL inhibitor that blocks replication of SARS-CoV-2
Drayman, N., DeMarco, J. K., Jones, K. A., Azizi, S., Froggatt, H. M., Tan, K., Maltseva, N., Chen, S., Nicolaescu, V. I., Dvorkin, S., et al. (2021) · Science · doi:10.1126/science.abg5827 · Cited by 285 · see citing works
Ma, C., Hu, Y., Townsend, J. A., Lagarias, P. I., Marty, M. T., Kolocouris, A., & Wang, J. (2020) · ACS Pharmacology & Translational Science · doi:10.1021/acsptsci.0c00130 · Cited by 273 · see citing works
Self-citationInhibition mechanism of SARS-CoV-2 main protease by ebselen and its derivatives
Amporndanai, K., Meng, X., Shang, W., Jin, Z., Rogers, M., Zhao, Y., Rao, Z., Liu, Z., Yang, H., Zhang, L., et al. (2021) · Nature Communications · doi:10.1038/s41467-021-23313-7 · Cited by 257 · see citing works
Disulfiram can inhibit MERS and SARS coronavirus papain-like proteases via different modes
Lin, M.-H., Moses, D. C., Hsieh, C.-H., Cheng, S.-C., Chen, Y., Sun, C., & Chou, C. (2017) · Antiviral Research · doi:10.1016/j.antiviral.2017.12.015 · Cited by 251 · see citing works
Ma, C., Sacco, M. D., Xia, Z., Lambrinidis, G., Townsend, J. A., Hu, Y., Meng, X., Szeto, T., Ba, M., Zhang, X., et al. (2021) · ACS Central Science · doi:10.1021/acscentsci.1c00519 · Cited by 201 · see citing works
Self-citationDieckol, a SARS-CoV 3CLpro inhibitor, isolated from the edible brown algae Ecklonia cava
Park, J. Y., Kim, J. H., Kwon, J. M., Kwon, H., Jeong, H. J., Kim, Y. M., Kim, D., Lee, W. S., & Ryu, Y. B. (2013) · Bioorganic & Medicinal Chemistry · doi:10.1016/j.bmc.2013.04.026 · Cited by 188 · see citing works
Ma, C., Xia, Z., Sacco, M. D., Hu, Y., Townsend, J. A., Meng, X., Choza, J. I., Tan, H., Jang, J., Gongora, M. V., et al. (2021) · Journal of the American Chemical Society · doi:10.1021/jacs.1c08060 · Cited by 177 · see citing works
Self-citationHigh-throughput screening identifies established drugs as SARS-CoV-2 PLpro inhibitors
Zhao, Y., Du, X., Duan, Y., Pan, X., Sun, Y., You, T., Han, L., Jin, Z., Shang, W., Yu, J., et al. (2021) · Protein & Cell · doi:10.1007/s13238-021-00836-9 · Cited by 155 · see citing works
Self-citationWęglarz‐Tomczak, E., Tomczak, J. M., Talma, M., Burda‐Grabowska, M., Giurg, M., & Brul, S. (2021) · Scientific Reports · doi:10.1038/s41598-021-83229-6 · Cited by 127 · see citing works
Sargsyan, K., Lin, C.-C., Chen, T., Grauffel, C., Chen, Y.-P., Yang, W., Yuan, H. S., & Lim, C. (2020) · Chemical Science · doi:10.1039/d0sc02646h · Cited by 104 · see citing works
Development of a Fluorescence-Based, High-Throughput SARS-CoV-2 3CL pro Reporter Assay
Froggatt, H. M., Heaton, B. E., & Heaton, N. S. (2020) · Journal of Virology · doi:10.1128/jvi.01265-20 · Cited by 101 · see citing works
Ma, C., Tan, H., Choza, J., Wang, Y., & Wang, J. (2022) · Acta Pharmaceutica Sinica B · doi:10.1016/j.apsb.2021.10.026 · Cited by 86 · see citing works
Self-citationA review on potential of natural products in the management of COVID-19
Chakravarti, R., Singh, R., Ghosh, A., Dey, D., Sharma, P., Ravichandiran, V., Roy, S., & Ghosh, D. (2021) · RSC Advances · doi:10.1039/d1ra00644d · Cited by 80 · see citing works
6-Thioguanine blocks SARS-CoV-2 replication by inhibition of PLpro
Swaim, C. D., Dwivedi, V., Perng, Y.-C., Zhao, X. M., Canadeo, L. A., Harastani, H., Darling, T. L., Boon, A. C. M., Lenschow, D. J., Kulkarni, V., et al. (2021) · iScience · doi:10.1016/j.isci.2021.103213 · Cited by 71 · see citing works
Natural Products with Potential to Treat RNA Virus Pathogens Including SARS-CoV-2
Christy, M. P., Uekusa, Y., Gerwick, L. G., & Gerwick, W. H. (2020) · Journal of Natural Products · doi:10.1021/acs.jnatprod.0c00968 · Cited by 64 · see citing works
The inhibitory effects of PGG and EGCG against the SARS-CoV-2 3C-like protease
Chiou, W.-C., Chen, J., Chen, Y., Yang, J., Hwang, L., Lyu, Y.-S., Yang, H.-Y., & Huang, C. (2021) · Biochemical and Biophysical Research Communications · doi:10.1016/j.bbrc.2020.12.106 · Cited by 61 · see citing works
Validation and Invalidation of SARS-CoV-2 Papain-like Protease Inhibitors
Ma, C., & Wang, J. (2022) · ACS Pharmacology & Translational Science · doi:10.1021/acsptsci.1c00240 · Cited by 56 · see citing works
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Chen, R. H., Yang, L., Hamdoun, S., Chung, S. K., Lam, C. W.-K., Zhang, K. X., Guo, X., Xia, C., Law, B. Y. K., & Wong, V. K. W. (2021) · Frontiers in Pharmacology · doi:10.3389/fphar.2021.634176 · Cited by 54 · see citing works
Ma, C., & Wang, J. (2021) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.2024420118 · Cited by 54 · see citing works
Self-citationYan, G., Li, D., Lin, Y., Fu, Z., Qi, H., Liu, X., Zhang, J., Si, S., & Chen, Y. (2021) · Cell & Bioscience · doi:10.1186/s13578-021-00720-3 · Cited by 46 · see citing works
Drug Repurposing for the SARS‐CoV‐2 Papain‐Like Protease
Cho, C.-C. D., Li, S. G., Lalonde, T. J., Yang, K. S., Yu, G., Qiao, Y., Xu, S., & Liu, W. R. (2021) · ChemMedChem · doi:10.1002/cmdc.202100455 · Cited by 45 · see citing works
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Li, X., Lidsky, P. V., Xiao, Y., Wu, C.-T., Garcia-Knight, M., Yang, J., Nakayama, T., Nayak, J. V., Jackson, P. K., Andino, R., et al. (2021) · PLoS Pathogens · doi:10.1371/journal.ppat.1009898 · Cited by 42 · see citing works
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Żmudziński, M., Rut, W., Olech, K., Granda, J. M., Giurg, M., Burda‐Grabowska, M., Kaleta, R., Zgarbová, M., Kasprzyk, R., Zhang, L., et al. (2023) · Scientific Reports · doi:10.1038/s41598-023-35907-w · Cited by 82 · see citing works
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Jadhav, P., Huang, B., Osipiuk, J., Zhang, X., Tan, H., Tesar, C., Endres, M. J., Jedrzejczak, R. P., Tan, B., Deng, X., et al. (2023) · European Journal of Medicinal Chemistry · doi:10.1016/j.ejmech.2023.116011 · Cited by 29 · see citing works
Self-citationWang, Z., Song, X.-Q., Xu, W., Lei, S., Zhang, H., & Yang, L. (2023) · Nutrients · doi:10.3390/nu15183885 · Cited by 20 · see citing works
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BindingDB Entry 50021419: Structure-based design of SARS-CoV-2 papain-like protease inhibitors.
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- Authors
- Tan, H., Ma, C., & Wang, J.
- Affiliations
- Rutgers, The State University of New Jersey (US)
- University of Arizona (US)
- Corresponding author
- Wang, Jun
- Venue
- Medicinal Chemistry Research
- Published
- 2022-05-12
- Volume
- 31
- Issue
- 7
- Pages
- 1147-1153
- ISSN
- 1054-2523 (ISSN-L)
- 1554-8120
- PMC
- PMC9095416
- OpenAlex
- W4280488476
- Cited by
- 21
- References
- 37
- Citations by year
- 2026: 2 · 2025: 4 · 2024: 5 · 2023: 10
- FWCI
- 2.32
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Medicinal Chemistry Research (publishedVersion)
- Research Square (acceptedVersion, cc-by)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- PubMed Central (submittedVersion, cc-by)
- Funders
- National Institute of Allergy and Infectious Diseases (AI147325, AI157046, AI158775)
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Physical Sciences › Computer Science › Computational Theory and Mathematics › Computational Drug Discovery Methods
- Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
- Keywords
- dieckol, main protease, papain-like protease, PLpro inhibitors, Mpro inhibitors, antiviral drug repurposing, polyphenols, hit validation, cytotoxicity, ebselen, disulfiram, carmofur, tideglusib, thermal shift assay
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