rifampin and mycothiol

Actinomycetes, including Mycobacterium species, are Gram-positive bacteria that use the small molecule mycothiol (MSH) as their primary reducing agent and in the detoxification of xenobiotics. Due to these important functions, MSH is a potential target for the development of antibiotics for the treatment of tuberculosis. This review summarizes the progress to date on the viability of enzymes involved in MSH biosynthesis and MSH-dependent detoxification as drug targets, biochemical characterization of target enzymes (structure, mechanism and substrate specificity) and development of MSH biosynthesis and MSH-dependent detoxification enzyme inhibitors. In addition, the ability of MSH to influence the sensitivity of mycobacteria to existing antibiotics and potential of MSH biosynthesis and MSH-dependent detoxification enzyme inhibitors to modulate the activity of existing antibiotics are described.

Topics: Animals; Anti-Bacterial Agents; Antitubercular Agents; Cysteine; Drug Delivery Systems; Drug Synergism; Enzyme Inhibitors; Glycopeptides; Humans; Inositol; Mycobacterium tuberculosis; Rifampin

The mycothiol biosynthesis enzyme MshC catalyzes the ligation of cysteine with the pseudodisaccharide GlcN-Ins and has been identified as an essential enzyme in Mycobacterium tuberculosis. We now report on the development of NTF1836 as a micromolar inhibitor of MshC. Using commercial libraries, we conducted preliminary structure-activity relationship (SAR) studies on NTF1836. Based on this data, NTF1836 and five structurally related compounds showed similar activity towards clinical strains of M. tuberculosis. A gram scale synthesis was developed to provide ample material for biological studies. Using this material, we determined that inhibition of M. tuberculosis growth by NTF1836 was accompanied by a fall in mycothiol and an increase in GlcN-Ins consistent with the targeting of MshC. We also determined that NTF1836 kills non-replicating M. tuberculosis in the carbon starvation model of latency.

Topics: Animals; Bacterial Proteins; Chlorocebus aethiops; Cysteine; Dibenzothiazepines; Drug Evaluation, Preclinical; Enzyme Inhibitors; Glycopeptides; Inositol; Mycobacterium tuberculosis; Structure-Activity Relationship; Vero Cells

Mycothiol, MSH or 1D-myo-inosityl 2-(N-acetyl-L-cysteinyl)amido-2-deoxy-alpha-D-glucopyranoside, is an unusual conjugate of N-acetylcysteine (AcCys) with 1D-myo-inosityl 2-acetamido-2-deoxy-alpha-D-glucopyranoside (GlcN-Ins), and is the major low-molecular-mass thiol in mycobacteria. Mycothiol has antioxidant activity as well as the ability to detoxify a variety of toxic compounds. Because of these activities, MSH is a candidate for protecting Mycobacterium tuberculosis from inactivation by the host during infections as well as for resisting antituberculosis drugs. In order to define the protective role of MSH for M. tuberculosis, we have constructed an M. tuberculosis mutant in Rv1170, one of the candidate MSH biosynthetic genes. During exponential growth, the Rv1170 mutant bacteria produced approximately 20% of wild-type levels of MSH. Levels of the Rv1170 substrate, GlcNAc-Ins, were elevated, whereas those of the product, GlcN-Ins, were reduced. This establishes that the Rv1170 gene encodes for the major GlcNAc-Ins deacetylase activity (termed MshB) in the MSH biosynthetic pathway of M. tuberculosis. The Rv1170 mutant grew poorly on agar media lacking catalase and oleic acid, and had heightened sensitivities to the toxic oxidant cumene hydroperoxide and to the antibiotic rifampin. In addition, the mutant was more resistant to isoniazid, suggesting a role for MSH in activation of this prodrug. These data indicate that MSH contributes to the protection of M. tuberculosis from oxidants and influences resistance to two first-line antituberculosis drugs.

Topics: Amidohydrolases; Anti-Bacterial Agents; Antitubercular Agents; Bacterial Proteins; Benzene Derivatives; Catalase; Cell Division; Culture Media; Cysteine; Disaccharides; Drug Resistance, Multiple, Bacterial; Glycopeptides; Inositol; Isoniazid; Microbial Sensitivity Tests; Mutation; Mycobacterium smegmatis; Mycobacterium tuberculosis; Oleic Acid; Oxidants; Pyrazoles; Rifampin; Sulfhydryl Compounds

Mycothiol (MSH) is the major low molecular weight thiol in mycobacteria. Two chemical mutants with low MSH and one with no MSH (strain 49) were produced in Mycobacterium smegmatis mc2155 to assess the role of MSH in mycobacteria. Strain 49 was shown to not produce 1-d-myo-inosityl-2-amino-2-deoxy-alpha-d-glucopyranoside (GlcN-Ins), an intermediate in MSH biosynthesis. Relative to the parent strain, mutant 49 formed colonies more slowly on solid media and was more sensitive to H2O2 and rifampin, but less sensitive to isoniazid. Complementation of mutant 49 with DNA from M. tuberculosis H37Rv partially restored production of GlcN-Ins and MSH, and resistance to H2O2, but largely restored colony growth rate and sensitivity to rifampin and isoniazid. The results indicate that MSH and GlcN-Ins are not essential for in vitro survival of mycobacteria but may play significant roles in determining the sensitivity of mycobacteria to environmental toxins.

Topics: Culture Media; Cysteine; Disaccharides; Drug Resistance, Microbial; Genetic Complementation Test; Glucosides; Glycopeptides; Hydrogen Peroxide; Inositol; Isoniazid; Mutagenesis; Mycobacterium smegmatis; Pyrazoles; Rifampin; Sulfhydryl Compounds