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The continued spread of drug-resistant tuberculosis is one of the most pressing and complex challenges facing tuberculosis management worldwide. Therefore, developing a new class of drugs is necessary and urgently needed to cope with the increasing threat of drug-resistant tuberculosis. This study aims to discover a potential new class of tuberculosis drug candidates different from existing tuberculosis drugs. By screening a library of compounds, methyl (S)-1-((3-alkoxy-6,7-dimethoxyphenanthren-9-yl)methyl)-5-oxopyrrolidine-2-carboxylate (PP) derivatives with antitubercular activity were discovered. MIC ranges for PP1S, PP2S, and PP3S against clinically isolated drug-resistant Mycobacterium tuberculosis strains were 0.78 to 3.13, 0.19 to 1.56, and 0.78 to 6.25 μg/ml, respectively. PPs demonstrated antitubercular activities in macrophage and tuberculosis mouse models, showing no detectable toxicity in all assays tested. PPs specifically inhibited M. tuberculosis without significantly changing the intestinal microbiome in mice. Mutants selected in vitro suggest that the drug targets the PE-PGRS57, which has been found only in the genomes of the M. tuberculosis complex, highlighting the specificity and safety potency of this compound. As PPs show an excellent safety profile and highly selective toxicity specific to M. tuberculosis, PPs are considered a promising new candidate for the treatment of drug-resistant tuberculosis while maintaining microbiome homeostasis., Competing Interests: The authors have declared that no competing interests exist.

Due to the emergence of multidrug-resistant and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis, new antituberculosis drugs are urgently required to improve the efficacy of current tuberculosis (TB) treatment. To achieve this goal, ca. 1000 chemical compounds were screened for potential antimycobacterial activity, among which methyl 5-(2-diethylaminoethoxy)-7,12-dioxo-7,12 dihydrodinaphtho[1,2-b;2',3'-d]furan-6-carboxylate (DNF-3) showed strong activity against all of the tested drug-susceptible and -resistant M. tuberculosis strains, with 50% minimum inhibitory concentrations (MIC 50 values) of 0.02-0.39 µg/mL both in culture broth and within murine RAW 264.7 macrophage cells. When DNF-3 was used in combination with rifampicin or streptomycin, it exhibited direct synergy against XDR-TB and an additive effect against M. tuberculosis H37Rv. DNF-3 displayed a long post-antibiotic effect (PAE) that was comparable with rifampicin but was superior to isoniazid, streptomycin and ethambutol. Importantly, DNF-3 showed no cytotoxicity to any cell line tested, with a selectivity index (SI) of >32. DNF-3 was also active against 27 nontuberculous mycobacteria (NTM) strains, Staphylococcus spp. and Streptococcus spp. Taken together, these results indicate that DNF-3 is a promising new candidate drug for treating TB. Further studies are warranted to establish the in vivo effect and therapeutic potential of DNF-3., (Copyright © 2019. Published by Elsevier B.V.)

Tuberculosis, one of the world's major health problems, has become more serious due to the emergence of multi-drug resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis (MTB). In this study, we performed three anti-MTB assays to evaluate the anti-mycobacterial activity of naphthofuroquinone derivatives against drug-resistant MTB. Among them, methyl 5-[2-(dimethylamino)ethoxy]-7,12-dioxo-7,12-dihydrodinaphtho[1,2-b:2',3'-d]furan-6-carboxylate (DFC2) exhibited strong anti-mycobacterial activity against MTB H37Ra, H37Rv and four drug-resistant MTB strains. The MIC of DFC2 ranged from 0.19-0.39 μg/ml to 0.78-1.56 μg/ml against all tested MTB strains. Moreover, DFC2 showed low cytotoxicity against fibroblast cells (L929) at concentrations 10-40-fold higher than their MICs. The IC 50 value of DFC2 against L929 cells was 15.218 μg/ml. In addition, DFC2 reduced the number of intracellular M. tuberculosis in macrophages in a dose-dependent manner. Taken together, our results indicate DFC2 to be promising new candidate agents for the treatment of tuberculosis.

DFC-2, a methyl 5-[2-(dimethylamino)ethoxy]-7,12-dioxo-7,12-dihydrodinaphtho[1,2-b:2',3'-d]furan-6-carboxylate, is reported to have antitubercular effects against Mycobacterium tuberculosis . At concentrations ranging from 0.19 to 0.39 μg/ml, DFC-2 inhibited both drug-susceptible and -resistant strains of M. tuberculosis . Microarray analyses were employed to gain insights into the molecular mechanisms of DFC-2's action in M. tuberculosis . The most affected functional gene category was "lipid biosynthesis," which is involved in mycolic acid synthesis. The decrease in transcription of genes related to mycolic acid synthesis was confirmed by RT-PCR. Furthermore, we found that DFC-2 triggered a reduction in mycolic acid levels, showing a similar pattern to that of mycolic acid synthesis inhibitor isoniazid. These results may explain how this compound kills mycobacteria efficiently by inhibiting mycolic acid synthesis.

This study explores the antitubercular activity of α-viniferin, a bioactive phytochemical compound obtained from Carex humilis. α-Viniferin was active against both drug-susceptible and -resistant strains of Mycobacterium tuberculosis at MIC 50 s of 4.6 μM in culture broth medium and MIC 50 s of 2.3-4.6 μM inside macrophages and pneumocytes. In combination with streptomycin and ethambutol, α-viniferin exhibited an additive effect and partial synergy, respectively, against M. tuberculosis H37Rv. α-Viniferin also did not show cytotoxicity in any of the cell lines tested up to a concentration of 147 μM, which gives this compound a selectivity index of >32. Moreover, α-viniferin was active against 3 Staphylococcus species, including methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and methicillin-resistant Staphylococcus epidermidis (MRSE)., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: Human tuberculosis, which is caused by the pathogen Mycobacterium tuberculosis, remains a major public health concern. Increasing drug resistance poses a threat of disease resurgence and continues to cause considerable mortality worldwide, which necessitates the development of new drugs with improved efficacy. Thymoquinone (TQ), an essential compound of Nigella sativa, was previously reported as an active anti-tuberculosis agent., Methods: In this study, the effects of TQ on intracellular mycobacterial replication are examined in macrophages. In addition, its effect on mycobacteria-induced NO production and pro-inflammatory responses were investigated in Mycobacterium tuberculosis (MTB)-infected Type II human alveolar and human myeloid cell lines., Results: TQ at concentrations ranging from 12.5 to 25 μg/mL and 6.25 to 12.5 μg/mL reduced intracellular M. tuberculosis H37Rv and extensively drug-resistant tuberculosis (XDR-TB) 72 h post-infection in RAW 264.7 cells. TQ treatment also produced a concentration-dependent reduction in nitric oxide production in both H37Rv and XDR-TB infected RAW 264.7 cells. Furthermore, TQ reduced the expression of inducible nitric oxide synthase (iNOS) and pro-inflammatory molecules such as tumor necrosis factor-alpha (TNF-α) and interlukin-6 (IL-6) in H37Rv-infected cells and eventually reduced pathogen-derived stress in host cells., Conclusions: TQ inhibits intracellular H37Rv and XDR-TB replication and MTB-induced production of NO and pro-inflammatory molecules. Therefore, along with its anti-inflammatory effects, TQ represents a prospective treatment option to combat Mycobacterium tuberculosis infection.

Background: The increasing incidence of multidrug-resistant tuberculosis (MDR-TB) infections has created a need for new effective drugs that also target extensively drug-resistant tuberculosis (XDR-TB) and/or augment the activities of existing drugs against tuberculosis., Aim: This study searched natural products for a new lead compound that targets MDR/XDR-TB., Methods: An active compound was purified from the roots of Cynanchum atratum Bunge (Asclepiadaceae) after screening 1640 plant extracts, and its inhibitory effects against MDR/XDR strains and synergistic effects with existing anti-TB drugs were assessed using the resazurin, MGIT, and checkboard assays., Results: (-)-Deoxypergularinine, purified from the roots of C. atratum, inhibited not only M. tuberculosis but also MDR/XDR strains. The minimum inhibitory concentrations (MICs) of (-)-deoxypergularinine for H37Ra, H37Rv, MDR, and XDR strains were all about 12.5 µg/ml. Moreover, combinations of (-)-deoxypergularinine with the first-line standard drugs rifampicin or isoniazid afforded six- and eight-fold reductions in drug MIC values, respectively, against strain H37Ra., Conclusions: (-)-Deoxypergularinine exerts anti-tubercular activities not only against normal tuberculosis strains but also MDR/XDR strains, and synergic effects with rifampicin and isoniazid for the H37Ra strain. The alkaloid may be valuable for targeting M/XDR M. tuberculosis., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Objective: In order to protect against Mycobacterium tuberculosis (MTB) infection, novel drugs and new targets should be screened from the vast source of plants. We investigated the potentiality of the herbal plant of Artemisia capillaris extract (AC) against Mycobacterium tuberculosis., Design: In this study, we isolated ursolic acid and hydroquinone by bio-activity guided fractionation from the methanol extracts of AC, and tested the inhibitory effects against several strains of MTB. Anti-mycobacterial evaluation of these compounds was carried out using the MGIT™ 960 and resazurin assay. Mycobacterial morphological changes due to the treatment of these compounds were further evaluated by Transmission electron microscopy (TEM)., Results: Ursolic acid (UA) and hydroquinone (HQ) inhibited the growth of both susceptible and resistant strains of M. tuberculosis. The MIC (minimum inhibitory concentration) values of both UA and HQ were 12.5 μg/ml against the susceptible strains of M. tuberculosis. Also both UA and HQ showed 12.5-25 μg/ml of MIC values against MDR/XDR MTB strains. However, against clinical strains of MTB, UA was found sensitive against those strains that are sensitive against both INH and RFP but resistant against those strains that are resistant to INH. On the other hand HQ was sensitive against all clinical strains. TEM image-analysis of the strain H37Ra after treatment with UA revealed cell wall lysis, whereas HQ-treated cells showed deformed cytoplasmic morphology., Conclusion: All these results indicate that AC extracts containing UA and HQ possess promising chemotherapeutic potency against MTB for future use., (Copyright © 2015 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)

Ursolic acid (3-β-3-hydroxy-urs-12-ene-28-oic-acid; UA) is a triterpenoid carboxylic acid with various pharmaceutical properties. It is commonly found in apples, basil, berries, rosemary, peppermint, lavender, oregano, thyme, hawthorn and prunes. In the present study, the activities of UA against the Mycobacterium tuberculosis H37Rv‑induced release of a panel of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 from RAW 264.7 murine macrophages, A549 alveolar epithelial cells and in concanavalin A (Con A)-stimulated rat splenocytes were investigated. In addition, the present study examined the ability of UA to reduce the expression levels of the inflammatory mediators, cyclooxygenase‑2 (COX‑2) and inducible nitric oxide synthase (iNOS) in the stimulated cells. The reduction of nitric oxide (NO) release by UA was also examined in the stimulated cells. UA significantly inhibited the mRNA expression levels of TNF‑α, IL‑1β and IL‑6 in the stimulated cells. The expression levels of COX‑2 and iNOS were also suppressed by UA, as was the release of NO at a significant level. The data indicated the potency of UA on different cell types, which may assist in the development of anti‑inflammatory drugs. In the case of adjunct host‑directed immune therapy for tuberculosis, UA may be used, in addition to established antibiotic therapies, to improve treatment efficacy and outcome due to their anti‑inflammatory potential. Further detailed investigations are required to establish its use as an anti-inflammatory.

Diterpenoids from the Vietnamese medicinal plant Croton tonkinensis are rich in ent-kaurane, kaurane and the grayanane class and are valuable intermediate plant metabolites with different bioactivities. In this study, we report the antituberculosis activity of these diterpenoids against both susceptible and resistant strains of M. tuberculosis for the first time. All of the ent-kaurane, kaurane and grayanane diterpenoids showed high to moderate activity against Mycobacterium. The highest antituberculosis activity was observed for ent-1β,7α,14β-triacetoxykaur-16-en-15-one (cpp604), with MIC values of 0.78, 1.56 and 3.12-12.5 µg/ml against H37Ra, H37Rv and all other resistant strains of Mycobacterium tuberculosis examined. In addition, other ent-kaurane-type diterpenoids also showed very high activities against mycobacterium, including cpp609 (1.56 µg/ml), cpp610 (1.56 µg/ml), cpp601 (3.12-6.25 µg/ml), cpp602 (3.12-6.25 µg/ml), cpp607 (3.12-6.25 µg/ml) and cpp608 (3.12-6.25 µg/ml). From the structure-activity relationship, functional groups R3 and R5 of the ent-kaurane skeleton were found to modulate the antimycobacterial activity.

Mycobacterium tuberculosis is a dangerous intracellular pathogen. In order to protect against mycobacterium infection, novel agents with anti-mycobacterial activity should be given emergency priority for evaluation. Ursolic acid (UA), a plant triterpenoid, shows promising bioactivities, including anti-mycobacterial potency. In this study, the action of UA against Mycobacterium tuberculosis H37Ra was evaluated, and the inhibitory concentration was found to range between 10 and 20 μg/ml in a resazurin assay and MGIT 960 instrument. The total mycolic acid in UA-treated H37Ra was detected and compared with INH-treated and non-treated bacterium by LC-MS/MS. Quantitative LC-MS/MS data confirmed that both UA and INH decreased mycolic acid biosynthesis in a dose-dependent manner. Thin-layer chromatogram (TLC) analysis showed that all mycolic acid subtypes were affected by UA treatment in the wild type but not in strains resistant to UA. Electron microscopy images also confirmed that UA treatment affected both H37Ra cell and intracellular content of H37Ra. Altogether, these data confirmed the promise of the inhibitory action of UA in mycolic acid, which might further delineate the mechanistic pathway of mycobacterial inhibition by UA., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Alveolar epithelial cells have been functionally implicated in Mycobacterium tuberculosis infection. This study investigated the role of ursolic acid (UA)-a triterpenoid carboxylic acid with potent antioxidant, anti-tumor, anti-inflammatory, and anti-tuberculosis properties in mycobacterial infection of alveolar epithelial A549 cells. We observed that M. tuberculosis successfully entered A549 cells. Cytotoxi-city was mediated by nitric oxide (NO). A549 toxicity peaked along with NO generation 72 h after infection. The NO generated by mycobacterial infection in A549 cells was insufficient to kill mycobacteria, as made evident by the mycobacteria growth indicator tube time to detect (MGIT TTD) and viable cell count assays. Treatment of mycobacteria-infected cells with UA reduced the expression of inducible nitric oxide synthase, NO generation, and eventually improved cell viability. Moreover, UA was found to quench the translocation of the transcription factor, nuclear factor kappa B (NF-κB), from the cytosol to the nucleus in mycobacteria-infected cells. This study is the first to demonstrate the cytotoxic role of NO in the eradication of mycobacteria and the role of UA in reducing this cytotoxicity in A549 cells.

Recently, it has become a struggle to treat tuberculosis with the current commercial antituberculosis drugs because of the increasing emergence of multidrug-resistant (MDR) tuberculosis and extensively drug-resistant (XDR) tuberculosis. We evaluated here the antimycobacterial activity of tamoxifen, known as a synthetic anti-estrogen, against eight drug-sensitive or resistant strains of Mycobacterium tuberculosis (TB), and the active intracellular killing of tamoxifen on TB in macrophages. The results showed that tamoxifen had antituberculosis activity against drug-sensitive strains (MIC, 3.125-6.25 μg/ml) as well as drug-resistant strains (MIC, 6.25 to 12.5 μg/ml). In addition, tamoxifen profoundly decreased the number of intracellular TB in macrophages in a dose-dependent manner.

Tuberculosis is one of the most threatening infectious diseases to public health all over the world, for which Mycobacterium tuberculosis (MTB) is the etiological agent of pathogenesis. Ursolic acid (UA) has immunomodulatory function and exhibits antimycobacterial activity. However, the intracellular killing effect of UA has yet to be elucidated. The aim of this study was to evaluate the intracellular killing effect of UA during mycobacterial infection. The intracellular killing activity of UA was evaluated in the macrophage cell line THP-1 by the MGIT 960 system as well as by CFU count. The production of reactive oxygen species (ROS) and the level of nitric oxide (NO) were measured using DCF-DA and Griess reagent, respectively. Phagocytosis was observed by a fluorescence-based staining method, and the colony forming units were enumerated on 7H11 agar medium following infection. In addition, MRP8 mRNA expression was measured by qRT-PCR. UA significantly decreased the number of intracellular Mycobacterium through generation of ROS and NO. In addition, it profoundly activated the phagocytosis process of THP-1 cells during MTB-infection. Furthermore, our data demonstrated that UA activated the phagocytosis process in human monocyte cells through MRP8 induction. These data suggest that UA firmly contributes to the intracellular killing effect of macrophages during mycobacterial infection.

Responsible for nearly 1.5 million deaths every year, the infectious disease tuberculosis remains one of the most serious challenges to global health. The emergence of multidrug-resistant tuberculosis and, more recently, extensively drug-resistant tuberculosis poses a significant threat in our effort to control this epidemic. New drugs are urgently needed to combat the growing threat of antimicrobial resistance. To achieve this goal, we screened approximately 500 species of medicinal plant methanol extracts and their solvent partitioned fractions for potential inhibitors of Mycobacterium tuberculosis growth. Using microdilution screening, the ethyl acetate solvent partitioned fraction from the heartwood of Caesalpinia sappan exhibited strong antitubercular activity. We isolated the active compound and identified it as 3-deoxysappanchalcone. The extracted 3-deoxysappanchalcone possessed activity against both drug-susceptible and drug-resistant strains of M. tuberculosis at MIC50 s of 3.125-12.5 μg/mL in culture broth and MIC50 s of 6.25-12.5 μg/mL inside macrophages and pneumocytes. 3-Deoxysappanchalcone was also found to act in partial synergy with streptomycin/ethambutol against M. tuberculosis H37Rv. 3-Deoxysappanchalcone had no cytotoxicity against the A549 cell line up to a concentration of 100 μg/mL (selectivity index > 8-32). Further studies are warranted to establish the in vivo effect and therapeutic potential of 3-deoxysappanchalcone. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]