{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,27]],"date-time":"2026-09-27T14:02:56Z","timestamp":1790517776576,"version":"4.1.0"},"reference-count":43,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2020,2,18]],"date-time":"2020-02-18T00:00:00Z","timestamp":1581984000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>Influenza A viruses (IAV) have been a major public health threat worldwide, and options for antiviral therapy become increasingly limited with the emergence of drug-resisting virus strains. New and effective anti-IAV drugs, especially for highly pathogenic influenza, with different modes of action, are urgently needed. The influenza virus glycoprotein hemagglutinin (HA) plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a potential target for the development of anti-influenza drugs. In this study, we show that OA-10, a newly synthesized triterpene out of 11 oleanane-type derivatives, exhibited significant antiviral activity against four different subtypes of IAV (H1N1, H5N1, H9N2 and H3N2) replications in A549 cell cultures with EC50 ranging from 6.7 to 19.6 \u03bcM and a negligible cytotoxicity (CC50 &gt; 640 \u03bcM). It inhibited acid-induced hemolysis in a dose-dependent manner, with an IC50 of 26 \u00b5M, and had a weak inhibition on the adsorption of H5 HA to chicken erythrocytes at higher concentrations (\u226540 \u00b5M). Surface plasmon resonance (SPR) analysis showed that OA-10 interacted with HA in a dose-dependent manner with the equilibrium dissociation constants (KD) of the interaction of 2.98 \u00d7 10\u221212 M. Computer-aided molecular docking analysis suggested that OA-10 might bind to the cavity in HA stem region which is known to undergo significant rearrangement during membrane fusion. Our results demonstrate that OA-10 inhibits H5N1 IAV replication mainly by blocking the conformational changes of HA2 subunit required for virus fusion with endosomal membrane. These findings suggest that OA-10 could serve as a lead for further development of novel virus entry inhibitors to prevent and treat IAV infections.<\/jats:p>","DOI":"10.3390\/v12020225","type":"journal-article","created":{"date-parts":[[2020,2,19]],"date-time":"2020-02-19T04:06:01Z","timestamp":1582085161000},"page":"225","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["An Oleanolic Acid Derivative Inhibits Hemagglutinin-Mediated Entry of Influenza A Virus"],"prefix":"10.3390","volume":"12","author":[{"given":"Mengdie","family":"Ye","sequence":"first","affiliation":[{"name":"Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, Guangzhou 510642, China"},{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yixian","family":"Liao","sequence":"additional","affiliation":[{"name":"College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Li","family":"Wu","sequence":"additional","affiliation":[{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wenbao","family":"Qi","sequence":"additional","affiliation":[{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Namrta","family":"Choudhry","sequence":"additional","affiliation":[{"name":"Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, Guangzhou 510642, China"},{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yahong","family":"Liu","sequence":"additional","affiliation":[{"name":"Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, Guangzhou 510642, China"},{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5221-9771","authenticated-orcid":false,"given":"Weisan","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gaopeng","family":"Song","sequence":"additional","affiliation":[{"name":"College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jianxin","family":"Chen","sequence":"additional","affiliation":[{"name":"Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, Guangzhou 510642, China"},{"name":"College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,2,18]]},"reference":[{"key":"ref_1","first-page":"3","article-title":"Pandemic influenza as a current threat","volume":"333","author":"Yen","year":"2009","journal-title":"Curr. Top. Microbiol. Immunol."},{"key":"ref_2","unstructured":"World Health Organization (2018, November 13). Influenza (Avian and Other Zoonotic). Available online: https:\/\/www.who.int\/en\/news-room\/fact-sheets\/detail\/influenza-(avian-and-other-zoonotic)."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"115","DOI":"10.1006\/viro.1998.9529","article-title":"Characterization of the surface proteins of influenza A (H5N1) viruses isolated from humans in 1997-1998","volume":"254","author":"Bender","year":"1999","journal-title":"Virology"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"3531","DOI":"10.2174\/138161207782794248","article-title":"Strategies of development of antiviral agents directed against influenza virus replication","volume":"13","author":"Hsieh","year":"2007","journal-title":"Curr. Pharm. Des."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"8445","DOI":"10.1021\/jm500892k","article-title":"Discovery of N-Substituted Oseltamivir Derivatives as Potent and Selective Inhibitors of H5N1 Influenza Neuraminidase","volume":"57","author":"Xie","year":"2014","journal-title":"J. Med. Chem."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1700","DOI":"10.1016\/S0140-6736(15)60074-5","article-title":"Influenza: The rational use of oseltamivir","volume":"385","author":"Kelly","year":"2015","journal-title":"Lancet"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1423","DOI":"10.1056\/NEJMc060077","article-title":"Oseltamivir resistance in influenza A (H5N1) infection","volume":"354","author":"Gupta","year":"2006","journal-title":"New Engl. J. Med."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1108","DOI":"10.1038\/4371108a","article-title":"Avian flu\u2014Isolation of drug-resistant H5N1 virus","volume":"437","author":"Le","year":"2005","journal-title":"Nature"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"953","DOI":"10.1056\/NEJMp0900648","article-title":"Global Transmission of Oseltamivir-Resistant Influenza","volume":"360","author":"Moscona","year":"2009","journal-title":"New Engl. J. Med."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"460","DOI":"10.1016\/j.ejphar.2011.04.013","article-title":"CL-385319 inhibits H5N1 avian influenza A virus infection by blocking viral entry","volume":"660","author":"Liu","year":"2011","journal-title":"Eur. J. Pharmacol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"5480","DOI":"10.1021\/acs.biochem.8b00764","article-title":"The Stabilities of the Soluble Ectodomain and Fusion Peptide Hairpins of the Influenza Virus Hemagglutinin Subunit II Protein Are Positively Correlated with Membrane Fusion","volume":"57","author":"Ranaweera","year":"2018","journal-title":"Biochemistry"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"301","DOI":"10.1002\/med.21289","article-title":"Emerging Antiviral Strategies to Interfere with Influenza Virus Entry","volume":"34","author":"Vanderlinden","year":"2014","journal-title":"Med. Res. Rev."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"10058","DOI":"10.1021\/jm5014067","article-title":"Discovery of pentacyclic triterpenoids as potential entry inhibitors of influenza viruses","volume":"57","author":"Yu","year":"2014","journal-title":"J. Med. Chem."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2967","DOI":"10.1021\/bi00063a007","article-title":"Inhibition of the fusion-inducing conformational change of influenza hemagglutinin by benzoquinones and hydroquinones","volume":"32","author":"Bodian","year":"1993","journal-title":"Biochemistry"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"4062","DOI":"10.1128\/jvi.71.5.4062-4070.1997","article-title":"Molecular mechanism underlying the action of a novel fusion inhibitor of influenza A virus","volume":"71","author":"Luo","year":"1997","journal-title":"J. Virol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"140","DOI":"10.1128\/JVI.73.1.140-151.1999","article-title":"Inhibition of influenza A virus replication by compounds interfering with the fusogenic function of the viral hemagglutinin","volume":"73","author":"Plotch","year":"1999","journal-title":"J. Virol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"865","DOI":"10.1007\/s007050050552","article-title":"Identification of a novel HA conformational change inhibitor of human influenza virus","volume":"144","author":"Yoshimoto","year":"1999","journal-title":"Arch. Virol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"4277","DOI":"10.1128\/JVI.02325-09","article-title":"Novel Inhibitors of Influenza Virus Fusion: Structure-Activity Relationship and Interaction with the Viral Hemagglutinin","volume":"84","author":"Vanderlinden","year":"2010","journal-title":"J. Virol."},{"key":"ref_19","first-page":"1056","article-title":"A small-molecule fusion inhibitor of influenza virus is orally active in mice","volume":"363","author":"Kadam","year":"2019","journal-title":"Science"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"7342","DOI":"10.1021\/jm500763m","article-title":"Conjugation of a Nonspecific Antiviral Sapogenin with a Specific HIV Fusion Inhibitor: A Promising Strategy for Discovering New Antiviral Therapeutics","volume":"57","author":"Wang","year":"2014","journal-title":"J. Med. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"951","DOI":"10.1002\/med.21484","article-title":"Recent progress in the antiviral activity and mechanism study of pentacyclic triterpenoids and their derivatives","volume":"38","author":"Xiao","year":"2018","journal-title":"Med. Res. Rev."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"601","DOI":"10.1016\/j.ejmech.2013.12.058","article-title":"Functionalization, cyclization and antiviral activity of A-secotriterpenoids","volume":"83","author":"Grishko","year":"2014","journal-title":"Eur. J. Med. Chem."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2029","DOI":"10.1021\/jm3016969","article-title":"New Betulinic Acid Derivatives for Bevirimat-Resistant Human Immunodeficiency Virus Type-1","volume":"56","author":"Dang","year":"2013","journal-title":"J. Med. Chem."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"4300","DOI":"10.1021\/jm301910a","article-title":"Development of Oleanane-Type Triterpenes as a New Class of HCV Entry Inhibitors","volume":"56","author":"Yu","year":"2013","journal-title":"J. Med. Chem."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"258","DOI":"10.1016\/j.ejmech.2014.03.017","article-title":"Development of bivalent oleanane-type triterpenes as potent HCV entry inhibitors","volume":"77","author":"Yu","year":"2014","journal-title":"Eur. J. Med. Chem."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"7368","DOI":"10.1021\/jm900275m","article-title":"Discovery of the First Series of Small Molecule H5N1 Entry Inhibitors","volume":"52","author":"Song","year":"2009","journal-title":"J. Med. Chem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1016\/j.ejmech.2016.04.061","article-title":"Structure-activity relationships of 3-O-beta-chacotriosyl oleanane-type triterpenoids as potential H5N1 entry inhibitors","volume":"119","author":"Song","year":"2016","journal-title":"Eur. J. Med. Chem."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Luo, L., Han, W., Du, J., Yang, X., Duan, M., Xu, C., Zeng, Z., Chen, W., and Chen, J. (2018). Chenodeoxycholic Acid from Bile Inhibits Influenza A Virus Replication via Blocking Nuclear Export of Viral Ribonucleoprotein Complexes. Molecules, 23.","DOI":"10.3390\/molecules23123315"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"45","DOI":"10.1016\/j.jviromet.2017.05.018","article-title":"Measuring influenza RNA quantity after prolonged storage or multiple freeze\/thaw cycles","volume":"247","author":"Granados","year":"2017","journal-title":"J. Virol. Methods"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"82","DOI":"10.1016\/j.antiviral.2015.03.008","article-title":"14-Deoxy-11,12-dehydroandrographolide exerts anti-influenza A virus activity and inhibits replication of H5N1 virus by restraining nuclear export of viral ribonucleoprotein complexes","volume":"118","author":"Cai","year":"2015","journal-title":"Antivir. Res."},{"key":"ref_31","first-page":"71","article-title":"An improvement of the 2^(-delta delta CT) method for quantitative real-time polymerase chain reaction data analysis","volume":"3","author":"Rao","year":"2013","journal-title":"Biostat. Bioinform. Biomath."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1101","DOI":"10.1038\/nprot.2008.73","article-title":"Analyzing real-time PCR data by the comparative C-T method","volume":"3","author":"Schmittgen","year":"2008","journal-title":"Nat. Protoc."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1447","DOI":"10.1128\/JVI.01225-13","article-title":"New Small Molecule Entry Inhibitors Targeting Hemagglutinin-Mediated Influenza A Virus Fusion","volume":"88","author":"Basu","year":"2014","journal-title":"J. Virol."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"578","DOI":"10.1016\/j.antiviral.2013.09.021","article-title":"Germacrone inhibits early stages of influenza virus infection","volume":"100","author":"Liao","year":"2013","journal-title":"Antivir. Res."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"425","DOI":"10.2307\/1592241","article-title":"Survey of the hemagglutinin (HA) cleavage site sequence of H5 and H7 avian influenza viruses: Amino acid sequence at the HA cleveage site as a marker of pathogenicity potential","volume":"40","author":"Senne","year":"1996","journal-title":"Avian Dis."},{"key":"ref_36","unstructured":"Ye, M., and College of Veterinary Medicine, South China Agricultural University, Guangzhou, China Personal Communication."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"206","DOI":"10.1073\/pnas.1617020114","article-title":"Structural basis of influenza virus fusion inhibition by the antiviral drug Arbidol","volume":"114","author":"Kadam","year":"2017","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1099\/vir.0.059477-0","article-title":"Entry of influenza A virus: Host factors and antiviral targets","volume":"95","author":"Edinger","year":"2014","journal-title":"J. Gen. Virol."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1016\/j.bcp.2017.07.023","article-title":"Potent influenza A virus entry inhibitors targeting a conserved region of hemagglutinin","volume":"144","author":"Lin","year":"2017","journal-title":"Biochem. Pharmacol."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"17736","DOI":"10.1073\/pnas.0807142105","article-title":"Structure of influenza hemagglutinin in complex with an inhibitor of membrane fusion","volume":"105","author":"Russell","year":"2008","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1126\/science.1171491","article-title":"Antibody Recognition of a Highly Conserved Influenza Virus Epitope","volume":"324","author":"Ekiert","year":"2009","journal-title":"Science"},{"key":"ref_42","doi-asserted-by":"crossref","unstructured":"Throsby, M., van den Brink, E., Jongeneelen, M., Poon, L.L.M., Alard, P., Cornelissen, L., Bakker, A., Cox, F., van Deventer, E., and Guan, Y. (2008). Heterosubtypic Neutralizing Monoclonal Antibodies Cross-Protective against H5N1 and H1N1 Recovered from Human IgM(+) Memory B Cells. PLoS ONE, 3.","DOI":"10.1371\/journal.pone.0003942"},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"Si, L., Meng, K., Tian, Z., Sun, J., Li, H., Zhang, Z., Soloveva, V., Li, H., Fu, G., and Xia, Q. (2018). Triterpenoids manipulate a broad range of virus-host fusion via wrapping the HR2 domain prevalent in viral envelopes. Sci. Adv., 4.","DOI":"10.1126\/sciadv.aau8408"}],"container-title":["Viruses"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1999-4915\/12\/2\/225\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T08:58:38Z","timestamp":1760173118000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1999-4915\/12\/2\/225"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,2,18]]},"references-count":43,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2020,2]]}},"alternative-id":["v12020225"],"URL":"https:\/\/doi.org\/10.3390\/v12020225","relation":{},"ISSN":["1999-4915"],"issn-type":[{"value":"1999-4915","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,2,18]]}}}