Rifampicin is an effective drug for treating tuberculosis (TB) but is not used to treat Mycobacterium abscessus infections due to poor in vitro activity. While rifabutin, another rifamycin, has better anti-M. abscessus activity, its activity is far from the nanomolar potencies of rifamycins against Mycobacterium tuberculosis. Here, we asked (i) why is rifabutin more active against M. abscessus than rifampicin, and (ii) why is rifabutin's anti-M. abscessus activity poorer than its anti-TB activity? Comparative analysis of naphthoquinone- versus naphthohydroquinone-containing rifamycins suggested that the improved activity of rifabutin over rifampicin is linked to its less readily oxidizable naphthoquinone core. Although rifabutin is resistant to bacterial oxidation, metabolite and genetic analyses showed that this rifamycin is metabolized by the ADP-ribosyltransferase ArrMab like rifampicin, preventing it from achieving the nanomolar activity that it displays against M. tuberculosis. Based on the identified dual mechanism of intrinsic rifamycin resistance, we hypothesized that rifamycins more potent than rifabutin should contain the molecule's naphthoquinone core plus a modification that blocks ADP-ribosylation at its C-23. To test these predictions, we performed a blinded screen of a diverse collection of 189 rifamycins and identified two molecules more potent than rifabutin. As predicted, these compounds contained both a more oxidatively resistant naphthoquinone core and C-25 modifications that blocked ADP-ribosylation. Together, this work revealed dual bacterial metabolism as the mechanism of intrinsic resistance of M. abscessus to rifamycins and provides proof of concept for the repositioning of rifamycins for M. abscessus disease by developing derivatives that resist both bacterial oxidation and ADP-ribosylation.
Bibliographical noteFunding Information:
Research reported in this work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under award numbers R01AI132374 (to T.D.) and U19AI142731 (to David S. Perlin; Center for Discovery and Innovation, Hackensack Meridian Health, Nutley, NJ).
We thank Yong-Mo Ahn and Joel Freundlich (New Jersey Medical School, Rutgers University, Newark, New Jersey) for discussion. We are grateful to Wei Chang Huang (Taichung Veterans General Hospital, Taichung, Taiwan) for providing M. abscessus Bamboo. We acknowledge BIO Ventures for Global Health (BVGH) for facilitating a collaboration with Novartis International AG through WIPO Re:Search for the sharing of rifamycin analogues. Research reported in this work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under award numbers R01AI132374 (to T.D.) and U19AI142731 (to David S. Perlin; Center for Discovery and Innovation, Hackensack Meridian Health, Nutley, NJ). U.S.G., Conceptualization, Methodology, Investigation, Writing - Original Draft Preparation, Writing - Review and Editing. T.L., Investigation. P.K., Resources, Data Curation, Project Administration. M.L., Investigation. M.D.Z., Methodology, Investigation. H.H., Investigation. J.P.S., Methodology, Investigation. J.C.E., Investigation. V.D., Conceptualization, Writing - Review and Editing. C.C.A., Conceptualization, Writing - Review and Editing T.D., Conceptualization, Funding Acquisition, Writing - Review and Editing.
© 2021 Ganapathy et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.
- Bacterial cell pharmacokinetics
- Mycobacterium abscessus