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Aim: To evaluate the activity of the 2-aminothiazole UPAR-174 following an unexplored approach: targeting Mycobacterium tuberculosis with lipophilic compounds that present antituberculosis and efflux inhibitory activity., Methods: Antituberculosis activity was assessed against replicating, nonreplicating and intracellular bacilli. Its capacity to inhibit active efflux was determined. ATP quantification and membrane potential analysis were performed. Intracellular activity was studied on human-monocyte-derived macrophages., Results: UPAR-174 is an efflux inhibitor active against replicating, nonreplicating and intracellular M. tuberculosis. It dissipates the membrane potential and causes ATP depletion., Conclusion: Targeting M. tuberculosis with lipophilic efflux inhibitors, exploring their dual activity - dissipation of the proton motive force and efflux inhibition - represents an attractive strategy to fight against drug-resistant tuberculosis.

Tuberculosis remains one of the deadliest infectious diseases in the world, and the increased number of multidrug-resistant and extremely drug-resistant strains is a significant reason for concern. This makes the discovery of novel antitubercular agents a cogent priority. We have previously addressed this need by reporting a series of substituted 2-aminothiazoles capable to inhibit the growth of actively replicating, nonreplicating persistent, and resistant Mycobacterium tuberculosis strains. Clues from the structure-activity relationships lining up the antitubercular activity were exploited for the rational design of improved analogues. Two compounds, namely N-phenyl-5-(2-(p-tolylamino)thiazol-4-yl)isoxazole-3-carboxamide 7a and N-(pyridin-2-yl)-5-(2-(p-tolylamino)thiazol-4-yl)isoxazole-3-carboxamide 8a, were found to show high inhibitory activity toward susceptible M. tuberculosis strains, with an MIC 90 of 0.125-0.25 μg/mL (0.33-0.66 μM) and 0.06-0.125 μg/mL (0.16-0.32 μM), respectively. Moreover, they maintained good activity also toward resistant strains, and they were selective over other bacterial species and eukaryotic cells, metabolically stable, and apparently not susceptible to the action of efflux pumps.

Drug resistance is a major problem in Mycobacterium tuberculosis control, and it is critical to identify novel drug targets and new antimycobacterial compounds. We have previously identified an imidazo[1,2-a]pyridine-4-carbonitrile-based agent, MP-III-71, with strong activity against M. tuberculosis. In this study, we evaluated mechanisms of resistance to MP-III-71. We derived three independent M. tuberculosis mutants resistant to MP-III-71 and conducted whole-genome sequencing of these mutants. Loss-of-function mutations in Rv2887 were common to all three MP-III-71-resistant mutants, and we confirmed the role of Rv2887 as a gene required for MP-III-71 susceptibility using complementation. The Rv2887 protein was previously unannotated, but domain and homology analyses suggested it to be a transcriptional regulator in the MarR (multiple antibiotic resistance repressor) family, a group of proteins first identified in Escherichia coli to negatively regulate efflux pumps and other mechanisms of multidrug resistance. We found that two efflux pump inhibitors, verapamil and chlorpromazine, potentiate the action of MP-III-71 and that mutation of Rv2887 abrogates their activity. We also used transcriptome sequencing (RNA-seq) to identify genes which are differentially expressed in the presence and absence of a functional Rv2887 protein. We found that genes involved in benzoquinone and menaquinone biosynthesis were repressed by functional Rv2887. Thus, inactivating mutations of Rv2887, encoding a putative MarR-like transcriptional regulator, confer resistance to MP-III-71, an effective antimycobacterial compound that shows no cross-resistance to existing antituberculosis drugs. The mechanism of resistance of M. tuberculosis Rv2887 mutants may involve efflux pump upregulation and also drug methylation., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Tuberculosis, caused by Mycobacterium tuberculosis, is still one of the leading infectious diseases globally. Therefore, novel approaches are needed to face this disease. Efflux pumps are known to contribute to the emergence of M. tuberculosis drug resistance. Thioridazine has shown good anti-TB properties both in vitro and in vivo, likely due to its capacity to inhibit efflux mechanisms. Here we report the design and synthesis of a number of putative efflux inhibitors inspired by the structure of thioridazine. Compounds were evaluated for their in vitro and ex vivo activity against M. tuberculosis H37Rv. Compared to the parent molecule, some of the compounds synthesized showed higher efflux inhibitory capacity, less cytotoxicity, and a remarkable synergistic effect with anti-TB drugs both in vitro and in human macrophages, demonstrating their potential to be used as coadjuvants for the treatment of tuberculosis.

TB, caused by Mycobacterium tuberculosis, is one of the deadliest infections worldwide. The co-infection with HIV and the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) strains have further increased the burden for this disease. In the attempt to respond to the constant need of novel therapeutic options, we herein report the discovery of 2,4-diphenyl-1H-imidazoles as effective antitubercular agents, with MIC in the low micromolar range against actively replicating and persistent M. tuberculosis strains. The good activity, along with the lack of toxicity and the feasible synthesis, underscore their value as novel scaffolds for the development of new anti-TB drugs., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

New drugs and shorter regimens are needed to fight resistant forms of tuberculosis. Screening of chemical libraries for mining hit compounds is the common approach to find new antituberculars. A new medicinal chemistry and biology directed research rational has recently been successfully described by Lee and coworkers in Nature Medicine., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Tuberculosis (TB) is one of the deadliest infectious diseases of all times, and its recent resurgence is a supreme matter of concern. Co-infection with HIV and, in particular, the continuous isolation of new resistant strains, makes the discovery of novel anti-TB agents a strategic priority. The research of novel agents should be driven by the accessibility of the synthetic procedure and, in particular, by the lack of cross-resistance with the drugs already marketed. Moreover, in order to shorten the duration of the therapy, and therefore decrease the rate of resistance, these molecules should be active also against the nonreplicating persistent form (NRP-TB) of the infection. The availability of an in-house small library of compounds prompted us to investigate their anti-TB activity. Two compounds, embodying a 2-aminothiazole scaffold, were found to possess a certain inhibitory activity toward Mycobacterium tuberculosis H37Rv, and therefore a medicinal chemistry campaign was initiated in order to increase the activity of the hit compounds and, especially, construct a plausible body of structure-activity relationships. The potency of the hit compound was successfully improved, and, much more importantly, some of the molecules synthesized were found to be active toward the persistent phenotype, and, also, toward a panel of resistant strains. These findings encourage further investigations around this interesting antitubercular chemotype., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Tuberculosis (TB) remains one of the leading causes of mortality and morbidity worldwide, with approximately one-third of the world's population infected with latent TB. This is further aggravated by HIV coinfection and the emergence of multidrug- and extensively drug-resistant (MDR and XDR, respectively) TB; hence the quest for highly effective antitubercular drugs with novel modes of action is imperative. We report herein the discovery of an indole-2-carboxamide analogue, 3, as a highly potent antitubercular agent, and the subsequent chemical modifications aimed at establishing a preliminary body of structure-activity relationships (SARs). These efforts led to the identification of three molecules (12-14) possessing an exceptional activity in the low nanomolar range against actively replicating Mycobacterium tuberculosis , with minimum inhibitory concentration (MIC) values lower than those of the most prominent antitubercular agents currently in use. These compounds were also devoid of apparent toxicity to Vero cells. Importantly, compound 12 was found to be active against the tested XDR-TB strains and orally active in the serum inhibition titration assay.

Responsible for nearly two million deaths each year, the infectious disease tuberculosis remains a serious global health challenge. The emergence of multidrug- and extensively drug-resistant strains of Mycobacterium tuberculosis confounds control efforts, and new drugs with novel molecular targets are desperately needed. Here we describe lead compounds, the indoleamides, with potent activity against both drug-susceptible and drug-resistant strains of M. tuberculosis by targeting the mycolic acid transporter MmpL3. We identify a single mutation in mmpL3, which confers high resistance to the indoleamide class while remaining susceptible to currently used first- and second-line tuberculosis drugs, indicating a lack of cross-resistance. Importantly, an indoleamide derivative exhibits dose-dependent antimycobacterial activity when orally administered to M. tuberculosis-infected mice. The bioavailability of the indoleamides, combined with their ability to kill tubercle bacilli, indicates great potential for translational developments of this structure class for the treatment of drug-resistant tuberculosis.

New antituberculosis (anti-TB) drugs are urgently needed to battle drug-resistant Mycobacterium tuberculosis (Mtb) strains and to shorten the long treatment regimen. A series of isoxazole-based compounds, bearing a carboxy moiety at the C3 position, are highly potent and versatile anti-TB agents. Several members of this compound class exhibit submicromolar in vitro activity against replicating Mtb (R-TB) and thus comparable activity to the current first-line anti-TB drugs. Remarkably, certain compounds also show low micromolar activity in a model for nonreplicating Mtb (NRP-TB) phenotype, which is considered a key to shortening the current long treatment protocol. The series shows excellent selectivity towards Mtb and, in general, shows no cytotoxicity on Vero cells (IC50's > 128 μM). Selected compounds retain their activity against isoniazid (INH), rifampin (RMP), and streptomycin (SM) resistant Mtb strains. The foregoing facts make derivatives of 3- isoxazolecarboxylic acid esters a promising anti-TB chemotype, and as such present attractive lead compounds for TB drug development.

The struggle against tuberculosis (TB) is still far from over. TB, caused by Mycobacterium tuberculosis, is one of the deadliest infections worldwide. Co-infection with human immunodeficiency virus (HIV) and the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) strains have further increased the burden for this disease. Herein, we report the discovery of 2-(4-chlorobenzyl)-3-methyl-1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbonitrile as an effective antitubercular agent and the structural modifications of this molecule that have led to analogues with improved potency and lower toxicity. A number of these derivatives were also active at sub-micromolar concentrations against resistant TB strains and devoid of apparent toxicity to Vero cells, thereby underscoring their value as novel scaffolds for the development of new anti-TB drugs., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

New antituberculosis (anti-TB) drugs are urgently needed to shorten the 6-12 month treatment regimen and especially to battle drug-resistant Mycobacterium tuberculosis (Mtb) strains. In this study, we have continued our efforts to develop isoxazole-based anti-TB compounds by applying rational drug design approach. The biological activity and the structure-activity relationships (SAR) for a designed series of 5-phenyl-3-isoxazolecarboxylic acid ethyl ester derived anti-TB compounds were investigated. Several compounds were found to exhibit nanomolar activity against the replicating bacteria (R-TB) and low micromolar activity against the nonreplicating bacteria (NRP-TB). The series showed excellent selectivity toward Mtb, and in general, no cytotoxicity was observed in Vero cells (IC(50) > 128 muM). Notably, selected compounds also retained their activity against isoniazid (INH), rifampin (RMP), and streptomycin (SM) resistant Mtb strains. Hence, benzyloxy, benzylamino, and phenoxy derivatives of 5-phenyl-3-isoxazolecarboxylic acid ethyl esters represent a highly potent, selective, and versatile series of anti-TB compounds and as such present attractive lead compounds for further TB drug development.

Both in vitro and in vivo metabolism studies suggested that 5-(2,8-bis(trifluoromethyl)quinolin-4-yloxymethyl)isoxazole-3-carboxylic acid ethyl ester (compound 3) with previously reported antituberculosis activity is rapidly converted to two metabolites 3a and 3b. In order to improve the metabolic stability of this series, chemistry efforts were focused on the modification of the oxymethylene linker of compound 3 in the present study. Compound 9d with an alkene linker was found to be both more metabolically stable and more potent than compound 3, with a minimum inhibitory concentration (MIC) of 0.2 microM and 2.6 microM against replicating and nonreplicating Mycobaterium tuberculosis, respectively. These attributes make 9d an interesting lead compound. A number of modifications were made to the structure of 9d, and a series of active compounds were discovered. Although some neurotoxicity was observed at a high dosage, this new series was endowed with both improved in vitro anti-TB activity and metabolic stability in comparison to compound 3.

Tuberculosis (TB), mostly caused by Mycobacterium tuberculosis (Mtb), is one of the leading causes of death from infectious disease worldwide. Its coinfection with HIV and the emergence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) strains have further worsened the TB pandemic. Despite its global impact, TB is considered a neglected disease and no new anti-TB therapeutics have been introduced over the last four decades. The nonreplicating persistent form of TB (NRP-TB) is responsible for the length of the treatment and is the putative cause of treatment failure. Therefore, new anti-TB agents, which are active against both the replicating form of Mtb (R-TB) and NRP-TB, are urgently needed. Herein, we report the synthesis and structure-activity relationships (SAR) of a series of 5-[(E)-2-arylethenyl]-3-isoxazolecarboxylic acid alkyl esters as potent anti-TB agents. Several compounds had submicromolar minimum inhibitory concentrations (MIC) against R-TB and were active against NRP-TB in the low micromolar range, thus representing attractive lead compounds for the possible development of new anti-TB agents.