The Chemical Approach to the Control of Tuberculosis

Fox, H. Herbert

doi:10.1126/science.116.3006.129

Cited by 120 publications

(59 citation statements)

References 20 publications

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“…Despite its seemingly simple structure and the discovery over 50 years ago that INH is highly active against Mycobacterium tuberculosis (1,2), the elucidation of its precise mode of action has been difficult. Middlebrook (3) was the first to carefully quantify the bactericidal activity of INH.…”

Section: Isoniazid (Inh)mentioning

confidence: 99%

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Kremer

Dover

Morbidoni

et al. 2003

Journal of Biological Chemistry

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(6) further demonstrated that the inhibition of mycolic acid biosynthesis mediated by INH leads to the accumulation of a saturated C 26 fatty acid within 1 h of INH treatment. By using scanning electron microscopy, it was established that M. tuberculosis treated with INH undergoes a defined order of molecular events that leads to lysis 24 h after initiation of treatment, thus after approximately one cell generation (7). The events that lead from the inhibition of mycolic acid biosynthesis and the accumulation of a saturated C 26 fatty acid to cell lysis are still poorly understood. Moreover, there exists controversy as to which enzymes of the mycolic acid biosynthetic pathway are the actual targets of INH.The mode of action of INH appears to be rather complex and requires activation by the mycobacterial catalase-peroxidase KatG (8,9). Activation of the pro-drug leads to reactive radicals that exert a toxic effect on the tubercle bacillus (9 -11). Presumably activated INH inhibits one or more targets of the mycolic acid biosynthetic pathway which eventually leads to cell death. At least two enzymes have been identified as potential targets of activated INH, the enoyl-ACP reductase InhA (12) and the ␤-ketoacyl-ACP synthase KasA (13). The inhA gene was first identified by conferring co-resistance to INH and ethionamide (ETH) after overexpression in mycobacteria (12). In addition, mutations in inhA confer resistance to both INH and ETH in drug-resistant M. tuberculosis isolates (14 -17).

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Section: Isoniazid (Inh)mentioning

confidence: 99%

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Kremer

Dover

Morbidoni

et al. 2003

Journal of Biological Chemistry

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“…INH is a front-line drug which has been most widely used for the treatment of active TB and latent infection since its discovery in 1952 (5,9). The drug enters the mycobacterial cells by passive diffusion (3).…”

mentioning

confidence: 99%

Precise Null Deletion Mutations of the Mycothiol Synthesis Genes Reveal Their Role in Isoniazid and Ethionamide Resistance in Mycobacterium smegmatis

Vilchèze

Av‐Gay

et al. 2011

Antimicrob Agents Chemother

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Mycothiol (MSH; AcCys-GlcN-Ins) is the glutathione analogue for mycobacteria. Mutations in MSH biosynthetic genes have been associated with resistance to isoniazid (INH) and ethionamide (ETH) in mycobacteria, but rigorous genetic studies are lacking, and those that have been conducted have yielded different results. In this study, we constructed independent null deletion mutants for all four genes involved in the MSH biosynthesis pathway (mshA, mshB, mshC, and mshD) in Mycobacterium smegmatis and made complementing constructs in integrating plasmids. The resulting set of strains was analyzed for levels of MSH, INH resistance, and ETH resistance. The mshA and mshC single deletion mutants were devoid of MSH production and resistant to INH, whereas the mshB deletion mutant produced decreased levels of MSH yet was sensitive to INH, suggesting that MSH biosynthesis is essential for INH susceptibility in M. smegmatis. Further evidence supporting this conclusion was generated by deleting the gene encoding the MSH S-conjugate amidase (mca) from the ⌬mshB null mutant. This double mutant, ⌬mshB ⌬mca, completely abolished MSH production and was resistant to INH. The mshA, mshC, and mshB single deletion mutants were also resistant to ETH, indicating that ETH resistance is modulated by the level of MSH in M. smegmatis. Surprisingly, the mshD deletion mutant lacked MSH production but was sensitive to both INH and ETH. The drug sensitivity was likely mediated by the compensated synthesis of N-formyl-Cys-GlcN-Ins, previously demonstrated to substitute for MSH in an mshD mutant of M. smegmatis. We conclude that MSH or N-formyl-Cys-GlcN-Ins is required for susceptibility to INH or ETH in M. smegmatis.

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“…INH was introduced as an antituberculosis drug in 1952 (4,13) and, soon after, the first INH-resistant (INH r ) M. tuberculosis strains were isolated (35). It is estimated that worldwide up to 28% of the M. tuberculosis strains are INH r , with a median of 6.2% in new TB cases (53).…”

mentioning

confidence: 99%

Altered NADH/NAD ⁺ Ratio Mediates Coresistance to Isoniazid and Ethionamide in Mycobacteria

Vilchèze

Weisbrod

Chen

et al. 2005

Antimicrob Agents Chemother

258

189

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The front-line antituberculosis drug isoniazid (INH) and the related drug ethionamide (ETH) are prodrugs that upon activation inhibit the synthesis of mycolic acids, leading to bactericidal activity. Coresistance to INH and ETH can be mediated by dominant mutations in the target gene inhA, encoding an enoyl-ACP reductase, or by recessive mutations in ndh, encoding a type II NADH dehydrogenase (NdhII). To address the mechanism of resistance mediated by the latter, we have isolated novel ndh mutants of Mycobacterium smegmatis and Mycobacterium bovis BCG. The M. smegmatis ndh mutants were highly resistant to INH and ETH, while the M. bovis BCG mutants had low-level resistance to INH and ETH. All mutants had defects in NdhII activity resulting in an increase in intracellular NADH/NAD ؉ ratios. Increasing NADH levels were shown to protect InhA against inhibition by the INH-NAD adduct formed upon INH activation. We conclude that ndh mutations mediate a novel mechanism of resistance by increasing the NADH cellular concentration, which competitively inhibits the binding of INH-NAD or ETH-NAD adduct to InhA.Despite the declaration by the World Health Organization 10 years ago that tuberculosis (TB) was a global health emergency, the problem has worsened primarily due to the growing human immunodeficiency virus epidemic and the emergence of drug resistance (9, 12). Although TB can be cured by a regimen of several drugs for at least 6 months, the emergence of drug-resistant and multidrug-resistant TB has created new challenges to control and defeat the disease. According to the World Health Organization, drug-resistant Mycobacterium tuberculosis strains are found in at least 72 countries at a rate ranging from 3 to 41% (53). Understanding the mechanisms by which drug resistance occurs is important in order to quickly identify drug-resistant strains to treat the patients adequately. Moreover, knowledge of resistance mechanisms leads to the understanding of the mode of drug action and to the development of strategies to overcome drug resistance.Isoniazid (INH) (17,22,27,41,43,57). The recessive nature of the katG mutations, i.e., the restoration of catalase peroxidase activity and INH susceptibility when replaced or complemented with the wild-type gene, is consistent with the fact that KatG activates INH (20,56,57) to generate a hypothetical isonicotinic acyl radical that reacts with NAD and forms an INH-NAD adduct (45). This adduct binds to and inhibits InhA (29,40,44,45,52), resulting in mycolic acid biosynthesis inhibition (49) and cell death (49, 51). In contrast, overexpressed inhA alleles or alleles causing amino acid substitutions within the structural gene have been shown to confer INH resistance in a dominant fashion, i.e., conferring INH resistance when the mutant alleles replace or complement the wild-type gene (1,26,51). Mutations in INH r clinical isolates of M. tuberculosis have been mapped to the promoter region or the structural gene of inhA (1,2,17,22,27,31,38,41,43). The dominant nature of these mutations w...

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The Chemical Approach to the Control of Tuberculosis

Cited by 120 publications

References 20 publications

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Precise Null Deletion Mutations of the Mycothiol Synthesis Genes Reveal Their Role in Isoniazid and Ethionamide Resistance in Mycobacterium smegmatis

Altered NADH/NAD ⁺ Ratio Mediates Coresistance to Isoniazid and Ethionamide in Mycobacteria

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The Chemical Approach to the Control of Tuberculosis

Cited by 120 publications

References 20 publications

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Inhibition of InhA Activity, but Not KasA Activity, Induces Formation of a KasA-containing Complex in Mycobacteria

Precise Null Deletion Mutations of the Mycothiol Synthesis Genes Reveal Their Role in Isoniazid and Ethionamide Resistance in Mycobacterium smegmatis

Altered NADH/NAD + Ratio Mediates Coresistance to Isoniazid and Ethionamide in Mycobacteria

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Altered NADH/NAD ⁺ Ratio Mediates Coresistance to Isoniazid and Ethionamide in Mycobacteria