Antiviral activity of HSP90 inhibitors against Mumps virus and related paramyxoviruses

Abstract Mumps virus (MuV), a member of the family Paramyxoviridae , continues to cause recurrent outbreaks worldwide despite widespread vaccination. Currently, however, no antiviral drugs have been approved for MuV or other paramyxoviruses. In this study, we screened approximately 1,000 small-molecule compounds using a recombinant MuV expressing green fluorescent protein and identified six compounds that significantly suppressed viral replication without detectable cytotoxicity. These compounds were known inhibitors of heat shock protein 90 (HSP90), a host chaperone involved in the assembly and function of viral polymerase complexes. These HSP90 inhibitors exhibited potent antiviral activity with submicromolar EC₅₀ values and high selectivity indices. Moreover, their antiviral efficacy extended to other paramyxoviruses, including measles virus (MeV), canine distemper virus (CDV), and Sendai virus (SeV). Time-of-addition assays demonstrated that these compounds act at a post-entry stage, primarily during viral RNA synthesis. Consistently, minigenome assays of MuV and Nipah virus (NiV) confirmed robust suppression of viral RNA synthesis without direct inhibition of reporter enzyme activity, indicating target specificity. Collectively, our findings highlight the potential of HSP90 inhibitors as host-directed antiviral agents against paramyxoviruses and support their further development for the treatment of emerging and re-emerging paramyxovirus infections.