Mechanisms of resistance against NITD-916, a direct inhibitor of Mycobacterium tuberculosis InhA

Abstract

Summary Isoniazid inhibits Mycobacterium tuberculosis InhA and is a key component of drug regimens that treat tuberculosis. However, the high rate of resistance against isoniazid is a contributing factor to the emergence of multi-drug resistance strains of M. tuberculosis. The 4-hydroxy-2-pyridine NITD-916 is a direct inhibitor of M. tuberculosis InhA that has comparable efficacy to isoniazid in mouse models of TB infection but a lower frequency of resistance. To characterize resistance mechanisms against NITD-916 we isolated resistant mutants in H37Rv (Euro-American lineage) and HN878 (East-Asian lineage) strains of M. tuberculosis. The resistance frequency was similar in both strains. Mutations were identified in residues within or near to the active of InhA or in the fabG1inhA promoter region. All mutants were resistant to NITD-916 but were not cross resistant to isoniazid, despite homology to SNPs identified in isoniazid resistant clinical isolates.

Discovery of a cofactor-independent inhibitor ofMycobacterium tuberculosisInhA

“…AN12855-resistant isolates retained the WT sensitivity to INH ( Table 2 ). To further investigate InhA as the target of AN12855, we tested the activity of AN12855 against M. tuberculosis strains with mutations in inhA , the fabG1inhA promoter region, or both ( Table 3 ) ( McNeil et al, 2017 ). All of these strains are resistant to the direct InhA inhibitor NITD-916 ( McNeil et al, 2017 ).…”

“…To further investigate InhA as the target of AN12855, we tested the activity of AN12855 against M. tuberculosis strains with mutations in inhA , the fabG1inhA promoter region, or both ( Table 3 ) ( McNeil et al, 2017 ). All of these strains are resistant to the direct InhA inhibitor NITD-916 ( McNeil et al, 2017 ). AN12855 was active against most of the strains with mutations in inhA , including mutations in I21 and S94 that are observed in INH-resistant clinical isolates ( Table 3 ) ( Seifert et al, 2015 ).…”

“…This demonstrates that increased expression of a mutant allele of InhA further increases resistance against AN12855. None of the mutants demonstrated cross-resistance to triclosan ( McNeil et al, 2017 ). Combined, these results support the hypothesis that AN12855 is a direct InhA inhibitor but with a unique binding mode.…”

“… b Liquid IC 90 values WT results are presented as μM, whereas RM IC90 are presented as the fold change compared with WT. c INH values are from McNeil et al (2017) . …”

Construction of an overexpression library for Mycobacterium tuberculosis

“…Additional methods for target identification will therefore increase the potential to identify relevant targets or metabolic pathways, enhancing drug development. Target overexpression conferring resistance to antimycobacterial compounds has been used as a diagnostic or confirmatory assay once the target has been identified; in these cases, the target was previously predicted by other methods and overexpression was used to confirm the target [ 12 , 17–22 ].…”