Riminophenazine Derivatives as Potential Antituberculosis Agents: Synthesis, Biological, and Electrochemical Evaluations.

A series of novel riminophenazine derivatives, having ionizable alkyl substituents at N-5 and a variety of substituents on the C-3 imino nitrogen, at C-8 and on the pendant aryl group, have been designed and synthesized. Preliminary investigations into the relationship between lipophilicity, redox potential, and antimycobacterial activity were conducted, using the in vitro activity against Mycobacterium tuberculosis H37Rv, mammalian cytotoxicity, and the redox potential of the compounds determined by cyclic voltammetry as measures. Results revealed an activity "cliff" associated with C-8 substitution (10l and 10m) that, along with defined redox activity, point to a new class of riminophenazines as potential anti-tuberculosis agents having reasonable activity (MIC99 ~1 µM).

The evaluation of the anti-cancer drug elesclomol that forms a redox-active copper chelate as a potential anti-tubercular drug.

The observations that the innate immune system employs copper to eliminate bacterial infection and that resistance to copper enhances virulence of Mycobacterium tuberculosis (Mtb) prompted us to examine the effects the anti-cancer agent elesclomol on Mtb. As a bis-thionohydrazide, elesclomol chelates with copper to form a copper complex in situ that via redox cycling of the metal ion greatly enhances oxidative stress in tumour cells. Here, we demonstrate that elesclomol is relatively potent against Mtb H37Rv with minimum inhibitory concentration of 10 µM (4 mg/L) and against multidrug resistant clinical isolates of Mtb, displays additive interactions with known tuberculosis drugs such as isoniazid and ethambutol, and a synergistic interaction with rifampicin. Controlled supplementation of elesclomol with copper in culture medium increased Mtb sensitivity by >65 fold. Overall, the activities of elesclomol in principle indicate the possibility of repurposing elesclomol or designing new thionohydrazides as potential drugs for use against Mtb. © 2019 IUBMB Life, 71(5):532-538, 2019.

Topical Delivery of Artemisone, Clofazimine and Decoquinate Encapsulated in Vesicles and Their In vitro Efficacy Against Mycobacterium tuberculosis.

Vesicles are widely investigated as carrier systems for active pharmaceutical ingredients (APIs). For topical delivery, they are especially effective since they create a "depot-effect" thereby concentrating the APIs in the skin. Artemisone, clofazimine and decoquinate were selected as a combination therapy for the topical treatment of cutaneous tuberculosis. Delivering APIs into the skin presents various challenges. However, utilising niosomes, liposomes and transferosomes as carrier systems may circumvent these challenges. Vesicles containing 1% of each of the three selected APIs were prepared using the thin-film hydration method. Isothermal calorimetry, differential scanning calorimetry and hot-stage microscopy indicated no to minimal incompatibility between the APIs and the vesicle components. Encapsulation efficiency was higher than 85% for all vesicle dispersions. Vesicle stability decreased and size increased with an increase in API concentration; and ultimately, niosomes were found the least stable of the different vesicle types. Skin diffusion studies were subsequently conducted for 12 h on black human female skin utilising vertical Franz diffusion cells. Transferosomes and niosomes delivered the highest average concentrations of clofazimine and decoquinate into the skin, whereas artemisone was not detected and no APIs were present in the receptor phase. Finally, efficacy against tuberculosis was tested against the Mycobacterium tuberculosis H37Rv laboratory strain. All the dispersions depicted some activity, surprisingly even the blank vesicles portrayed activity. However, the highest percentage inhibition (52%) against TB was obtained with niosomes containing 1% clofazimine.

Formulation of Natural Oil Nano-Emulsions for the Topical Delivery of Clofazimine, Artemisone and Decoquinate.

PURPOSE: The aim of this study was to formulate nano-emulsions comprising natural oils and the active pharmaceutical ingredients (APIs) clofazimine (CLF), artemisone (ATM) and decoquinate (DQ) in order to determine effectiveness of the nano-emulsions for topical delivery of the APIs. The APIs alone do not possess suitable physicochemical properties for topical drug delivery. METHODS: Nano-emulsions were formulated with olive and safflower oils encapsulating the APIs. Skin diffusion and tape stripping studies were performed. By using the lactate dehydrogenase (LDH) assay, in vitro toxicity studies were carried out on immortalized human keratinocytes (HaCaT) cell line to determine cytotoxicities due to the APIs and the nano-emulsions incorporating the APIs. RESULTS: The nano-emulsions were effective in delivering the APIs within the stratum corneum-epidermis and the epidermis-dermis, were non-cytotoxic towards HaCaT cell lines (p < 0.05) and inhibited Mycobacterium tuberculosis in vitro. CONCLUSION: Natural oil nano-emulsions successfully deliver CLF, ATM and DQ and in principle could be used as supplementary topical treatment of cutaneous tuberculosis (CTB). Graphical Abstract ᅟ.

Reversed isoniazids: Design, synthesis and evaluation against Mycobacterium tuberculosis.

Novel reversed isoniazid (RINH) agents were synthesized by covalently linking isoniazid with various efflux pump inhibitor (EPI) cores and their structural motifs. These RINH agents were then evaluated for anti-mycobacterial activity against sensitive, isoniazid mono-resistant and MDR clinical isolates of M. tuberculosis and a selected number of compounds were also tested ex vivo for intracellular activity as well as in the ethidium bromide (EB) assay for efflux pump inhibition efficacy. The potency of some compounds against various strains of M. tuberculosis (4a-c, 7 and 8; H37Rv-MIC99 ≤1.25 µM, R5401-MIC99 ≤2.5 µM, X_61-MIC99 ≤5 µM) demonstrated the potential of the reversed anti-TB agent strategy towards the development of novel anti-mycobacterial agents to address the rapidly growing issue of resistance. Further, macrophage activity with >90% inhibition by 1a-c and 3b (MIC90 ≤13.42 µM) and inhibition of EB efflux demonstrated by these compounds are encouraging.

Preliminary Evaluation of Artemisinin-Cholesterol Conjugates as Potential Drugs for the Treatment of Intractable Forms of Malaria and Tuberculosis.

To evaluate the feasibility of developing drugs that may be active against both malaria and tuberculosis (TB) by using in part putative cholesterol transporters in the causative pathogens and through enhancement of passive diffusion in granulomatous TB, artemisinin-cholesterol conjugates were synthesized by connecting the component molecules through various linkers. The compounds were screened in vitro against Plasmodium falciparum (Pf) and Mycobacterium tuberculosis (Mtb). Antimalarial activities (IC50 ) against Pf drug-sensitive NF54, and drug-resistant K1 and W2 strains ranged from 0.03-2.6, 0.03-1.9, and 0.02-1.7 µm. Although the compounds are less active than the precursor artemisinin derivatives, the cholesterol moiety renders the compounds relatively insoluble in the culture medium, and variation in solubilities among the different compounds may reflect in the range of efficacies observed. Activities against Mtb H37Rv were assessed using a standardized colony-forming unit (CFU) assay after 24 h pretreatment of cultures with each of the compounds. Percentage inhibition ranged from 3-38 % and 18-52 % at 10 and 80 µm, respectively. Thus, in contrast to the comparator drug artemether, the conjugates display enhanced activities. The immediate aims include the preparation of conjugates with enhanced aqueous solubilities, assays against malaria and TB in vivo, and for TB, assays using an infected macrophage model and assessment of granuloma influx.

Anti-mycobacterium tuberculosis activity of polyherbal medicines used for the treatment of tuberculosis in Eastern Cape, South Africa.

BACKGROUND: The emergence of drug-resistant strains of Mycobacterium tuberculosis has become a global public health problem. Polyherbal medicines offer great hope for developing alternative drugs for the treatment of tuberculosis. OBJECTIVE: To evaluate the anti-tubercular activity of polyherbal medicines used for the treatment of tuberculosis. METHODS: The remedies were screened against Mycobacterium tuberculosis H37Rv using Middlebrook 7H9 media and MGIT BACTEC 960 system. They were liquid preparations from King Williams Town site A (KWTa), King Williams Town site B (KWTb), King Williams Town site C (KWTc), Hogsback first site (HBfs), Hogsback second site (HBss), Hogsback third site (HBts), East London (EL), Alice (AL) and Fort Beaufort (FB). RESULTS: The susceptibility testing revealed that all the remedies contain anti-tubercular activity with KWTa, KWTb, KWTc, HBfs, HBts, AL and FB exhibiting more activity at a concentration below 25 µl/ml. Furthermore, MIC values exhibited inhibitory activity with the most active remedies from KWTa, HBfs and HBts at 1.562 µg/ml. However, isoniazid showed more inhibitory activity against M. tuberculosis at 0.05 µg/ml when compare to the polyherbal remedies. CONCLUSION: This study has indicated that these remedies could be potential sources of new anti-mycobacterial agents against M. tuberculosis. However, the activity of these preparations and their active principles still require in vivo study in order to assess their future as new anti-tuberculosis agents.

Design, synthesis, and In vitro antituberculosis activity of 2(5H)-Furanone derivatives.

A series of 2(5H)-furanone-based compounds were synthesized from commercially available mucohalic acids. From the first-generation compounds, three showed inhibitory activity (10 µg/mL) of at least 35% against Mycobacterium smegmatis mc(2) 155 growth (Bioscreen C system). In screening the active first-generation compounds for growth inhibition against Mycobacterium tuberculosis H37Rv, the most active compound was identified with a minimum inhibitory concentration (MIC99 ) of 8.07 µg/mL (15.8 µM) using BACTEC 460 system. No cross-resistance was observed with some current first-line anti-TB drugs, since it similarly inhibited the growth of multidrug resistant (MDR) clinical isolates. The compound showed a good selectivity for mycobacteria since it did not inhibit the growth of selected Gram-positive and Gram-negative bacteria. It also showed synergistic activity with rifampicin (RIF) and additive activity with isoniazid (INH) and ethambutol (EMB). Additional time-kill studies showed that the compound is bacteriostatic to mycobacteria, but cytotoxic to the Chinese Hamster Ovarian (CHO) cell line. From a second generation library, two compounds showed improved anti-TB activity against M. tuberculosis H37Rv and decreased CHO cell cytotoxicity. The compounds exhibited MIC values of 2.62 µg/mL (5.6 µM) and 3.07 µg/mL (5.6 µM) respectively. The improved cytotoxicity against CHO cell line of the two compounds ranged from IC50 = 38.24 µg/mL to IC50 = 45.58 µg/mL when compared to the most active first-generation compound (IC50 = 1.82 µg/mL). The two second generation leads with selectivity indices (SI) of 14.64 and 14.85 respectively, warrant further development as anti-TB drug candidates. © 2016 IUBMB Life, 68(8):612-620, 2016.

Synthesis, antimycobacterial evaluation and pharmacophore modeling of analogues of the natural product formononetin.

The synthesis and antimycobacterial activity of formononetin analogues is hereby reported. Formononetin and its analogue 11E showed 88% and 95% growth inhibition, respectively, against the H37Rv strain of Mycobacterium tuberculosis. Pharmacophore modeling studies indicated that the presence of a hydroxyl group in formononetin and its analogues, is crucial for maintaining activity.

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.

Sulfamethoxazole enhances the antimycobacterial activity of rifampicin.

OBJECTIVES: To investigate the effect of trimethoprim/sulfamethoxazole on the survival of Mycobacterium tuberculosis and trimethoprim and sulfamethoxazole individually and combined with the first-line tuberculosis drugs (isoniazid, rifampicin and ethambutol). METHODS: M. tuberculosis strains were exposed to either trimethoprim/sulfamethoxazole combination or sulfamethoxazole and trimethoprim alone at various concentrations. The strains were also exposed to sulfamethoxazole in combination with existing antibiotics to assess the combined effect on the growth of M. tuberculosis in the BACTEC 460TB system. The effect of the drugs was compared with vehicle-treated controls. Drug interactions were interpreted using quotient values obtained from the growth index of cultures treated with a single drug or the combination. RESULTS: Trimethoprim showed a negligible effect on the growth of M. tuberculosis while sulfamethoxazole inhibited 80% of the growth of M. tuberculosis at 4.75 mg/L. There was no synergistic activity between sulfamethoxazole and trimethoprim, although an additive effect was observed. A statistically significant synergistic effect was observed between sulfamethoxazole and rifampicin. Sulfamethoxazole also had an additive effect with ethambutol, but there was no interaction with isoniazid. CONCLUSIONS: Sulfamethoxazole is the main active compound against M. tuberculosis in the combination trimethoprim/sulfamethoxazole and has a synergistic effect with rifampicin. These findings suggest that sulfamethoxazole has potential in the multidrug regimen against M. tuberculosis.