OPC-167832, a Novel Carbostyril Derivative with Potent Antituberculosis Activity as a DprE1 Inhibitor.

There is an urgent need for new, potent antituberculosis (anti-TB) drugs with novel mechanisms of action that can be included in new regimens to shorten the treatment period for TB. After screening a library of carbostyrils, we optimized 3,4-dihydrocarbostyril derivatives and identified OPC-167832 as having potent antituberculosis activity. The MICs of the compound for Mycobacterium tuberculosis ranged from 0.00024 to 0.002 µg/ml. It had bactericidal activity against both growing and intracellular bacilli, and the frequency of spontaneous resistance for M. tuberculosis H37Rv was less than 1.91 × 10-7 It did not show antagonistic effects with other anti-TB agents in an in vitro checkerboard assay. Whole-genome and targeted sequencing of isolates resistant to OPC-167832 identified decaprenylphosphoryl-ß-d-ribose 2'-oxidase (DprE1), an essential enzyme for cell wall biosynthesis, as the target of the compound, and further studies demonstrated inhibition of DprE1 enzymatic activity by OPC-167832. In a mouse model of chronic TB, OPC-167832 showed potent bactericidal activities starting at a dose of 0.625 mg/kg of body weight. Further, it exhibited significant combination effects in 2-drug combinations with delamanid, bedaquiline, or levofloxacin. Finally, 3- or 4-drug regimens comprised of delamanid and OPC-167832 as the core along with bedaquiline, moxifloxacin, or linezolid showed efficacy in reducing the bacterial burden and preventing relapse superior to that of the standard treatment regimen. In summary, these results suggest that OPC-167832 is a novel and potent anti-TB agent, and regimens containing OPC-167832 and new or repurposed anti-TB drugs may have the potential to shorten the duration of treatment for TB.

Synthesis and antituberculosis activity of a novel series of optically active 6-nitro-2,3-dihydroimidazo[2,1-b]oxazoles.

In an effort to develop potent new antituberculosis agents that would be effective against both drug-susceptible and drug-resistant strains of Mycobacterium tuberculosis, we prepared a novel series of optically active 6-nitro-2,3-dihydroimidazo[2,1-b]oxazoles substituted at the 2-position with various phenoxymethyl groups and a methyl group and investigated the in vitro and in vivo activity of these compounds. Several of these derivatives showed potent in vitro and in vivo activity, and compound 19 (OPC-67683) in particular displayed excellent in vitro activity against both drug-susceptible and drug-resistant strains of M. tuberculosis H37Rv (MIC = 0.006 microg/mL) and dose-dependent and significant in vivo efficacy at lower oral doses than rifampicin in mouse models infected with M. tuberculosis Kurono. The synthesis and structure-activity relationships of these new compounds are presented.