Activity of MMV Pandemic Response Box compounds against Mycobacterium ulcerans viability and mycolactone production

Mycobacterium ulcerans causes Buruli ulcer (BU), a skin neglected tropical disease, largely through the expression of a potent cytotoxin known as mycolactone. As mycolactone is central for BU pathogenesis, it follows that targeting its production with drugs could be one means of controlling the infection. However, this has not yet been attempted due to the difficulty of applying typical mycolactone-detecting assays, such as mass spectrometry, to routine drug screening to identify suitable drugs for this purpose. In this repurposing study, we screened the Pandemic Response Box, an open-source collection of 400 compounds compiled by the Medicines for Malaria Venture and the Drugs for Neglected Diseases Initiative, using a highly sensitive and specific mycolactone capture ELISA that we have previously developed. By combining this mycolactone-detecting assay with the routinely used resazurin microplate assay, we identified hits (such as pradigastat) that are potential starting points for further development of antivirulence drugs for BU. We also showed the activity of alexidine and fusidic acid against M. ulcerans viability, the first report of this activity to our knowledge. In addition, we reliably reidentified drugs known to be active against M. ulcerans (such as bedaquiline, Q203, clofazimine, sutezolid, and epetraborole), thus validating our screening approach.IMPORTANCEMycolactone is a key requirement in the pathogenesis of Buruli ulcer (BU). Without this unique toxin, Mycobacterium ulcerans only causes a transient infection, as the immune system is able to clear the bacteria when mycolactone is absent. There has, therefore, been a long-standing interest in targeting mycolactone to develop new drugs against BU, but a lack of simple drug screening tools has been a major obstacle to this goal. Here, we used our screening platform, which comprises a simple mycolactone-detecting ELISA combined with a standard resazurin microplate assay, to identify a set of hits from the Medicines for Malaria Venture Pandemic Response Box that could reduce mycolactone expression even without affecting M. ulcerans viability. This screening methodology will contribute to further development of antivirulence drugs for BU.