Antiviral activity of anisomycin against chikungunya virus

Chikungunya virus (CHIKV) is a globally prevalent arbovirus transmitted by Aedes mosquitoes, which causes acute fever accompanied by debilitating joint pain that can persist for extended periods. Despite the significant public health impact and an increasing incidence worldwide, antiviral treatment targeting CHIKV has not been clinically approved. In this study, we screened compounds using a newly developed In-Cell ELISA-based assay and CHIKV Indian Ocean Lineage (IOL) and found that an antibiotic derived from Streptomyces bacteria, anisomycin, potentially inhibited CHIKV. The selectivity index of anisomycin was favorable for anti-CHIKV activity, with 50% effective concentration (EC50) of 200 pM and 50% cytotoxic concentration (CC50) of 390 nM in Vero cells. This robust inhibitory activity against CHIKV was confirmed in a human cell line and against a CHIKV East/Central/South African (ECSA) lineage. These effects of anisomycin were apparently independent of its functions as a translation inhibitor and mitogen-activated protein kinase (MAPK) pathway stimulator. These findings, together with the finding that anisomycin suppressed the production of infectious CHIKV virions, suggested that anisomycin inhibits CHIKV via a distinct mechanism. Further mechanistic insights were gained through genetic analyses of anisomycin-resistant mutants, which revealed that a single amino acid substitution (G117R) in the macrodomain of CHIKV nsP3 confers resistance to anisomycin. Importantly, anisomycin reduced footpad swelling and viremia in mice during the early days of CHIKV infection, indicating its therapeutic potential. Given its inhibitory activity against other arboviruses, our study positions anisomycin as a promising lead inhibitor for the future development of broad-spectrum antiviral drugs, including CHIKV. Author summaryChikungunya fever (CHIKF) is a mosquito-borne disease caused by the chikungunya virus (CHIKV) and is characterized by fever, rash, and arthralgia. Although most persons infected with CHIKV recover within days, joint pain and severe complications can persist. However, the management of CHIKF is limited to symptom relief, and specific antiviral treatments are not available. Our study focused on identifying potential inhibitors of CHIKV infection. We found that the natural alkaloid, anisomycin, inhibited CHIKV replication in cultured cells in vitro using a novel screening assay and a chemical compound library. Interestingly, the mechanism by which anisomycin blocks CHIKV infection likely differs from its currently known effects, suggesting a distinct mode of inhibition. We also identified an amino acid change in a nonstructural protein that conferred resistance to anisomycin, providing insights into a viral target of anisomycin. Importantly, anisomycin reduced disease symptoms and viremia in mouse models of CHIKV in vivo. Because anisomycin inhibits other mosquito-borne viruses, our findings suggest that it could serve as a basis for developing broad-acting antiviral drugs.