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Identification of Licoflavone C as a cap-dependent endonuclease inhibitor against severe fever with thrombocytopenia syndrome virus

Acta Pharmacologica Sinica volume 46, pages 2482–2495 (2025)Cite this article

Abstract

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus with a high fatality rate. Currently no approved drugs or vaccines are available against it. Sharing a common replication mechanism with negative-stranded, segmented viruses (NSVs), SFTSV utilizes a cap-dependent endonuclease (CEN) domain of the L segment to execute the cap-snatching process upon genome transcription initiation. Given the crucial role of CEN in the life cycle of NSVs, it is considered a promising target for discovery of antiviral agents against SFTSV. In this study, we established a high-throughput FRET-based enzymatic screening system to discover inhibitors of SFTSV CEN from a chemical library containing 3467 natural compounds. Finally, three compounds, i.e., Licoflavone C, 3,4-dicaffeoylquinic acid, and oleanolic acid displayed exceptional antiviral effects and minimal cytotoxicity. Licoflavone C (EC50 = 1.85 μM) was selected for further investigation. Administration of Licoflavone C (20 mg/kg, i.v.) significantly reduced tissue viral loads in SFTSV-challenged mouse model. We demonstrated that Licoflavone C did not directly bind to the active pocket of SFTSV CEN but disrupted its active conformation, resulting in substrate non-competitive inhibition. Licoflavone C also exhibited broad-spectrum inhibition on several NSV CENs (HRTV, GTV, and LCMV) besides SFTSV. Furthermore, 15 analogs of Licoflavone C sharing a typical flavonoid structure were verified for targeting SFTSV CEN and exhibiting antiviral activities. In conclusion, Licoflavone C is a promising inhibitor of SFTSV, offering insights into targeting CEN with flavonoids in drug discovery.

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Fig. 1: Screening of natural products against severe fever with thrombocytopenia syndrome virus (SFTSV) in vitro.
Fig. 2: Antiviral efficacy of 3,4-Dicaffeoylquinic acid, Licoflavone C, and Oleanolic acid against SFTSV in C57BL/6 J mice.
Fig. 3: Evaluation of the antiviral activity of Licoflavone C in vivo.
Fig. 4: Licoflavone C inhibits SFTSV at the post-infection stage.
Fig. 5: Licoflavone C binds to SFTSV CEN in a substrate non-competitive manner.
Fig. 6: Licoflavone C has a broad-spectrum inhibitory activity against negative-strand, segmented RNA viruses.

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Acknowledgements

We are particularly grateful to the Institutional Center for Shared Technologies and Facilities of Wuhan Institute of Virology, CAS, for their technical support. We also thank the National Virus Resource Center, Wuhan Institute of Virology, CAS, for providing important research materials. We acknowledge the National Natural Science Foundation of China (Grant No. 82130101), the Youth Innovation Promotion Association of CAS (Grant No. 2021333), and the Natural Science Foundation of Wuhan (Grant No. 2024040701010067) for financial support.

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  1. These authors contributed equally: Xiao Gao, Xiao-xue He

Authors and Affiliations

  1. State Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430200, China

    Xiao Gao, Xiao-xue He, Xue-rui Zhu, Yan Wu, Jia Lu, Xin-lan Chen, Chen-shu Zhao, Hao-yu Li, Zhong-fa Zhang, Geng-fu Xiao & Xiao-yan Pan

  2. University of Chinese Academy of Sciences, Beijing, 101400, China

    Xiao Gao, Jia Lu, Xin-lan Chen, Hao-yu Li, Geng-fu Xiao & Xiao-yan Pan

  3. School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, 510515, China

    Shu-wen Liu

  4. Guangdong Basic Research Center of Excellence for Integrated Traditional and Western Medicine for Qingzhi Diseases, Guangzhou, 510515, China

    Shu-wen Liu

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Contributions

XG and XXH designed and performed most of the biochemical, cellular, and animal experiments and drafted the manuscript; XRZ helped with the docking analysis; YW, JL, XLC and CSZ assisted with plasmid construction and protein expression and purification; HYL and ZFZ helped with data analysis; SWL and GFX coordinated the project; XYP contributed to the interpretation of the results, revised, and approved the manuscript.

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Correspondence to Xiao-yan Pan.

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Gao, X., He, Xx., Zhu, Xr. et al. Identification of Licoflavone C as a cap-dependent endonuclease inhibitor against severe fever with thrombocytopenia syndrome virus. Acta Pharmacol Sin 46, 2482–2495 (2025). https://doi.org/10.1038/s41401-025-01533-7

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