Short-course treatment regimen to identify potential antituberculous agents in a murine model of tuberculosis

Preparation and Antitubercular Activities of Palindromic Hydrazinecarbothioamides and Carbonothioic Dihydrazides

Background:

With approximately one-third of the world’s population infected, tuberculosis continues to be a global public health crisis. The rise of strains that are unusually virulent or highly resistant to current drugs is a cause of special concern, prompting research into new classes of compounds, as well as the re-evaluation of known chemotherapeutic agents.

Objectives:

The antimycobacterial activities associated with some recently-reported thiocarbonyl compounds kindled our interest in the synthesis of substituted hydrazinecarbothioamides (3) and carbonothioic dihydrazides (4), with the aim of investigating their potential in antitubercular drug design and discovery.

Methods:

In the present study, the title compounds 3 and 4 were prepared by the condensation of hydrazines with isothiocyanates in reactions readily controlled by stoichiometry, temperature and solvent. The compounds were assessed against Mycobacterium bovis BCG in Kirby-Bauer disc diffusion, and minimum inhibitory concentrations were determined against the virulent strain M. tuberculosis Erdman.

Results:

The chemical structures of these thermally stable compounds were determined by IR, 1HNMR, 13C-NMR, high-resolution mass spectrometry and elemental analysis. In the Kirby-Bauer disc diffusion assay, some of the compounds showed substantial diameters of inhibition against BCG. In some cases, the zones of inhibition were so large that no growth at all was observed on the assay plates. Against M. tuberculosis Erdman, several of the compounds showed significant activities. Compound 3h was the most active, demonstrating a minimum inhibitory concentration of 0.5 µg/mL.

Conclusion:

We found that the title compounds may be prepared conveniently in excellent purity and good yields. They are readily identified on the basis of their characteristic spectra. Some members of this class showed significant activities against mycobacteria. We conclude that further work will be warranted in exploring the antitubercular properties of these compounds.

2-N-Arylthiazole inhibitors of Mycobacterium tuberculosis

To develop agents for the treatment of infections caused by Mycobacterium tuberculosis, a novel phenotypic screen was undertaken that identified a series of 2-N-aryl thiazole-based inhibitors of intracellular Mycobacterium tuberculosis. Analogs were optimized to improve potency against an attenuated BSL2 H37Ra laboratory strain cultivated in human macrophage cells in vitro. The insertion of a carboxylic acid functionality resulted in compounds that retained potency and greatly improved microsomal stability. However, the strong potency trends we observed in the attenuated H37Ra strain were inconsistent with the potency observed for virulent strains in vitro and in vivo.

In-Vivo Gene Signatures of Mycobacterium tuberculosis in C3HeB/FeJ Mice

Despite considerable progress in understanding the pathogenesis of Mycobacterium tuberculosis (Mtb), development of new therapeutics and vaccines against it has proven difficult. This is at least in part due to the use of less than optimal models of in-vivo Mtb infection, which has precluded a study of the physiology of the pathogen in niches where it actually persists. C3HeB/FeJ (Kramnik) mice develop human-like lesions when experimentally infected with Mtb and thus make available, a faithful and highly tractable system to study the physiology of the pathogen in-vivo. We compared the transcriptomics of Mtb and various mutants in the DosR (DevR) regulon derived from Kramnik mouse granulomas to those cultured in-vitro. We recently showed that mutant ΔdosS is attenuated in C3HeB/FeJ mice. Aerosol exposure of mice with the mutant mycobacteria resulted in a substantially different and a relatively weaker transcriptional response (< = 20 genes were induced) for the functional category ‘Information Pathways’ in Mtb:ΔdosR; ‘Lipid Metabolism’ in Mtb:ΔdosT; ‘Virulence, Detoxification, Adaptation’ in both Mtb:ΔdosR and Mtb:ΔdosT; and ‘PE/PPE’ family in all mutant strains compare to wild-type Mtb H37Rv, suggesting that the inability to induce DosR functions to different levels can modulate the interaction of the pathogen with the host. The Mtb genes expressed during growth in C3HeB/FeJ mice appear to reflect adaptation to differential nutrient utilization for survival in mouse lungs. The genes such as glnB, Rv0744c, Rv3281, sdhD/B, mce4A, dctA etc. downregulated in mutant ΔdosS indicate their requirement for bacterial growth and flow of carbon/energy source from host cells. We conclude that genes expressed in Mtb during in-vivo chronic phase of infection in Kramnik mice mainly contribute to growth, cell wall processes, lipid metabolism, and virulence.

A novel inhibitor of gyrase B is a potent drug candidate for treatment of tuberculosis and nontuberculosis mycobacterial infections

New drugs to treat drug-resistant tuberculosis are urgently needed. Extensively drug-resistant and probably the totally drug-resistant tuberculosis strains are resistant to fluoroquinolones like moxifloxacin, which target gyrase A, and most people infected with these strains die within a year. In this study, we found that a novel aminobenzimidazole, VXc-486, which targets gyrase B, potently inhibits multiple drug-sensitive isolates and drug-resistant isolates of Mycobacterium tuberculosis in vitro (MICs of 0.03 to 0.30 μg/ml and 0.08 to 5.48 μg/ml, respectively) and reduces mycobacterial burdens in lungs of infected mice in vivo. VXc-486 is active against drug-resistant isolates, has bactericidal activity, and kills intracellular and dormant M. tuberculosis bacteria in a low-oxygen environment. Furthermore, we found that VXc-486 inhibits the growth of multiple strains of Mycobacterium abscessus, Mycobacterium avium complex, and Mycobacterium kansasii (MICs of 0.1 to 2.0 μg/ml), as well as that of several strains of Nocardia spp. (MICs of 0.1 to 1.0 μg/ml). We made a direct comparison of the parent compound VXc-486 and a phosphate prodrug of VXc-486 and showed that the prodrug of VXc-486 had more potent killing of M. tuberculosis than did VXc-486 in vivo. In combination with other antimycobacterial drugs, the prodrug of VXc-486 sterilized M. tuberculosis infection when combined with rifapentine-pyrazinamide and bedaquiline-pyrazinamide in a relapse infection study in mice. Furthermore, the prodrug of VXc-486 appeared to perform at least as well as the gyrase A inhibitor moxifloxacin. These findings warrant further development of the prodrug of VXc-486 for the treatment of tuberculosis and nontuberculosis mycobacterial infections.

Mycobacterium tuberculosis RNA Expression Patterns in Sputum Bacteria Indicate Secreted Esx Factors Contributing to Growth are Highly Expressed in Active Disease

To identify factors contributing to the ability of tubercle bacilli to grow in the lung during active infection, we analyzed RNA expression patterns in bacteria present in patient sputum. Prominent among bacterial transcripts identified were those encoding secreted peptides of the Esat-6 subfamily that includes EsxK and EsxL (Rv1197 and Rv1198). H37Rv esxKL and esxJI transcripts were differentially expressed under different growth conditions, and disruption of these genes altered growth phase kinetics in typical laboratory batch broth cultures. These growth defects, including the reduced intracellular growth of an ΔesxKL mutant in primary human macrophages, were reversed by either low multiplicity co-infection or co-culture with wild-type bacteria, demonstrating the ability of the secreted factors to rescue isogenic mutants. Complementing either only esxL or esxI alone (Rv1198 or Rv1037c) also reduced observed growth defects, indicating these genes encode factors capable of contributing to growth. Our studies indicate that the Mycobacterium tuberculosis Mtb9.9 family secreted factors EsxL and EsxI can act in trans to modulate growth of intracellular bacteria, and are highly expressed during active human lung infection.

A short-term model for preliminary screening of potential anti-tubercular compounds

Screening of new agents for anti-tubercular activity is a challenging task due to the virulent and slow growing nature of mycobacteria. In this study, we explored the use of Mycobacterium smegmatis as an alternate model to virulent strains. We observed that the effect of standard anti-tubercular drugs was similar in mice infected with M. smegmatis and Mycobacterium tuberculosis. The total duration of the experiment, including incubation time, was 10 days in the M. smegmatis-infected mice model compared with 2 months in M. tuberculosis-infected mice. This model of anti-tubercular screening is a simple, easy to carry out, less time-consuming, safer and economical alternative for preliminary in vivo screening of potential anti-tubercular agents.

Preparation and antitubercular activities in vitro and in vivo of novel Schiff bases of isoniazid

Structural modification of the frontline antitubercular isonicotinic acid hydrazide (INH) provides lipophilic adaptations (3-46) of the drug in which the hydrazine moiety of the parent compound has been chemically blocked from the deactivating process of N(2)-acetylation by N-arylaminoacetyl transferases. As a class, these compounds show high levels of activity against Mycobacterium tuberculosis in vitro and in tuberculosis-infected macrophages. They provide strong protection in tuberculosis-infected mice and have low toxicity. With some representatives of this class achieving early peak plasma concentrations approximately three orders of magnitude above minimum inhibitory concentration, they may serve as tools for improving our understanding of INH-based treatment modalities, particularly for those patients chronically underdosed in conventional INH therapy.

Glycine betaine uptake by the ProXVWZ ABC transporter contributes to the ability of Mycobacterium tuberculosis to initiate growth in human macrophages

Mycobacterium tuberculosis maintains a large genetic capacity necessary for growth in different environments during infection and survival upon aerosol transmission to new hosts. Screening for bacterial RNAs produced in response to host interactions produced candidate lists where we noted proXVWZ, annotated as encoding a putative glycine betaine or proline transporter. As high surface-to-volume ratios make bacterial cells particularly vulnerable to changes in water availability, we investigated the contributions of this transporter to the ability of M. tuberculosis to colonize macrophages. An H37Rv proXVWZ mutant was impaired for initial survival and intracellular growth and exhibited reduced growth at elevated medium osmolarity. This defect could be complemented by restoring proXVWZ and was attributable to a failure to accumulate the compatible solute glycine betaine. We then demonstrated that ProXVWZ allows M. tuberculosis to obtain betaine from host macrophages and thereby contributes to early steps in colonizing this niche.