The bisbenzimide compound ridinilazole has antiviral activity against vaccinia and mpox viruses

Mpox remains a significant global public health threat, highlighting the need for new antiviral therapies. Ridinilazole is a symmetric bisbenzimide developed for the treatment of Clostridium difficile infection that has recently been shown to inhibit human cytomegalovirus. Here, we investigated its antiviral activity against orthopoxviruses (OPXV). Ridinilazole potently inhibited vaccinia virus replication in primary human foreskin fibroblasts, with an IC 50 of 21 nM and minimal cytotoxicity. Importantly, ridinilazole also reduced infectious monkeypox virus (the causative agent of mpox) yields in primary fibroblasts by more than 150-fold. Mechanistic studies demonstrated that ridinilazole did not affect early viral gene expression or viral DNA replication, but significantly reduced the expression of late viral genes at both transcript and protein levels. These findings identify ridinilazole as an effective inhibitor of OPXV replication and support its potential repurposing as a novel therapeutic for mpox.