An optimized background regimen for treatment of active tuberculosis with the next-generation benzothiazinone Macozinone (PBTZ169) [Susceptibility]

The efficacy of the standardized four-drug regimen (comprising isoniazid, rifampicin, pyrazinamide and ethambutol) for the treatment of tuberculosis (TB) is menaced by the emergence of multidrug (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis. Intensive efforts have been made to develop new antibiotics or to repurpose old drugs and several of these are currently being evaluated in clinical trials for their anti-tubercular activity. Among the new candidate drugs is macozinone (MCZ), the piperazine-containing benzothiazinone, PBTZ169, which is currently being evaluated in phase I/II clinical trials.

Here, we determined the in vitro and in vivo activity of MCZ in combination with a range of anti-TB drugs in order to design a new regimen against active TB. Two-drug combinations with MCZ were tested against M. tuberculosis using checkerboard and CFU enumeration after drug exposure assays. MCZ was observed to have no interactions with all first- and second-line anti-TB drugs. At the MIC of each drug, MCZ with either bedaquiline (BDQ), clofazimine (CLO), delamanid (DMD) or sutezolid (STZ) reduced the bacterial burden by two logs compared to the drugs alone, indicating synergism. MCZ also displays synergism with clomiphene (CLM), a potential inhibitor of the undecaprenyl pyrophosphate synthase (UppS) in mycobacteria. For all the other drugs tested in combination with MCZ, no synergistic activity was observed. Neither antagonism nor increased cytotoxicity were found for most combinations, suggesting that MCZ could be added to different TB regimens without any significant adverse effects.

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