Structure-Based Design of MptpB Inhibitors That Reduce Multidrug-Resistant Mycobacterium tuberculosis Survival and Infection Burden in Vivo

Coastal natural products: a review applied to antimycobacterial activity

Despite the many advances in drug research, natural products are still being explored as a promising source for discovering new bioactive compounds to treat global diseases such as tuberculosis. However, there is a lack of studies and information about coastal natural products, which thrive in the transitional environment between two different ecosystems and produce unique secondary metabolites. Mangroves, estuaries, and mudflats make up areas for coastal species and have shown promising results in antituberculosis research, some of them are present in hotspot areas. This review focuses on research conducted in coastal environments and explores the reasons why these natural products tend to outperform non-coastal ones against the causative agent of tuberculosis, Mycobacterium tuberculosis.

Exploring rhodanine linked enamine-carbohydrazide derivatives as mycobacterial carbonic anhydrase inhibitors: Design, synthesis, biological evaluation, and molecular docking studies

With the rise of multidrug-resistant tuberculosis, the imperative for an alternative and superior treatment regimen, incorporating novel mechanisms of action, has become crucial. In pursuit of this goal, we have developed and synthesized a new series of rhodanine-linked enamine-carbohydrazide derivatives, exploring their potential as inhibitors of mycobacterial carbonic anhydrase. The findings reveal their efficacy, displaying notable selectivity toward the mycobacterial carbonic anhydrase 2 (mtCA 2) enzyme. While exhibiting moderate activity against human carbonic anhydrase isoforms, this series demonstrates promising selectivity, positioning these compounds as potential antitubercular agents. Compound 6d was the best one from the series with a Ki value of 9.5 µM toward mtCA 2. Most of the compounds displayed moderate to good inhibition against the Mtb H37Rv strain; compound 11k showed a minimum inhibitory concentration of 1 µg/mL. Molecular docking studies revealed that compounds 6d and 11k show metal coordination with the zinc ion, like classical CA inhibitors.

MptpB Inhibitor Improves the Action of Antibiotics against Mycobacterium tuberculosis and Nontuberculous Mycobacterium avium Infections

Treatment of Mycobacterium tuberculosis and Mycobacterium avium infections requires multiple drugs for long time periods. Mycobacterium protein-tyrosine-phosphatase B (MptpB) is a key M. tuberculosis virulence factor that subverts host antimicrobial activity to promote intracellular survival. Inhibition of MptpB reduces the infection burden in vivo and offers new opportunities to improve current treatments. Here, we demonstrate that M. avium produces an MptpB orthologue and that the MptpB inhibitor C13 reduces the M. avium infection burden in macrophages. Combining C13 with the antibiotics rifampicin or bedaquiline showed an additive effect, reducing intracellular infection of both M. tuberculosis and M. avium by 50%, compared to monotreatment with antibiotics alone. This additive effect was not observed with pretomanid. Combining C13 with the minor groove-binding compounds S-MGB-362 and S-MGB-363 also reduced the M. tuberculosis intracellular burden. Similar additive effects of C13 and antibiotics were confirmed in vivo using Galleria mellonella infections. We demonstrate that the reduced mycobacterial burden in macrophages observed with C13 treatments is due to the increased trafficking to lysosomes.

Isoxazole carboxylic acid methyl ester-based urea and thiourea derivatives as promising antitubercular agents

In our continued efforts to find potential chemotherapeutics active against drug-resistant (DR) Mycobacterium tuberculosis (Mtb), causative agent of Tuberculosis (TB) and to curb the current burdensome treatment regimen, herein we describe the synthesis and biological evaluation of urea and thiourea variants of 5-phenyl-3-isoxazolecarboxylic acid methyl esters as promising anti-TB agent. Majority of the tested compounds displayed potent in vitro activity not only against drug-susceptible (DS) Mtb H37Rv but also against drug-resistant (DR) Mtb. Cell viability test against Vero cells deemed these compounds devoid of significant toxicity. 3,4-Dichlorophenyl derivative (MIC 0.25 µg/mL) and 4-chlorophenyl congener (MIC 1 µg/mL) among urea and thiourea libraries respectively exhibited optimum potency. Lead optimization resulted in the identification of 1,4-linked analogue of 3,4-dichlorophenyl urea derivative demonstrating improved selectivity. Further, in silico study complemented with previously proposed prodrug like attributes of isoxazole esters. Taken together, this molecular hybridization approach presents a new chemotype having potential to be translated into an alternate anti-Mtb agent.

Design of novel water-soluble isoxazole-based antimicrobial agents and evaluation of their cytotoxicity and acute toxicity

Based on the readily available 3-organyl-5-(chloromethyl)isoxazoles, a number of previously unknown water-soluble conjugates of isoxazoles with thiourea, amino acids, some secondary and tertiary amines, and thioglycolic acid were synthesized. The bacteriostatic activity of aforementioned compounds has been studied against Enterococcus durans B-603, Bacillus subtilis B-407, Rhodococcus qingshengii Ac-2784D, and Escherichia coli B-1238 microorganisms (provided by All-Russian Collection of Microorganisms, VKM). The influence of the nature of the substituents in positions 3 and 5 of the isoxazole ring on the antimicrobial activity of the obtained compounds has been determined. It is found that the highest bacteriostatic effect is observed for compounds containing 4-methoxyphenyl or 5-nitrofuran-2-yl substituents in position 3 of the isoxazole ring as well as methylene group in position 5 bearing residues of l-proline or N-Ac-l-cysteine (5a-d, MIC 0.06-2.5 µg/ml). The leading compounds showed low cytotoxicity on normal human skin fibroblast cells (NAF1nor) and low acute toxicity on mice in comparison with the well-known isoxazole-containing antibiotic oxacillin.

Mycobacterium tuberculosis and its secreted tyrosine phosphatases

Tuberculosis is one of the most common infectious diseases and has been a major burden for a long time now. Increasing drug resistance in TB is slowing down the process of disease treatment. Mycobacterium tuberculosis, the causative agent of TB is known to have a cascade of virulence factors to fight with host's immune system. The phosphatases (PTPs) of Mtb plays a critical role as these are secretory in nature and help the survival of bacteria in host. Researchers have been trying to synthesize inhibitors against a lot of virulence factors of Mtb but recently the phosphatases have gained a lot of interest due to their secretory nature. This review gives a concise overview of virulence factors of Mtb with emphasis on mPTPs. Here we discuss the current scenario of drug development against mPTPs.

Design, synthesis and biological evaluation of 3-substituted-2-thioxothiazolidin-4-one (rhodanine) derivatives as antitubercular agents against Mycobacterium tuberculosis protein tyrosine phosphatase B

Mycobacterium tuberculosis infections still pose a serious threat to human health. Combination therapies are effective medical solutions to the problem. Mycobacterium tuberculosis is an intracellular pathogen that mainly depends on a virulence factor (Mycobacterium tuberculosis protein tyrosine phosphatase B, MptpB) for its survival in the host. Therefore, MptpB inhibitors are potential components of tuberculosis combination treatments. Herein, a new series of MptpB inhibitors bearing a rhodanine group were developed using a structure-based strategy based on the virtual screening hit. The new MptpB inhibitors displayed potent MptpB inhibitory activities and great improvements in cell membrane permeability. The optimal compounds reduced the bacterial burden in a dose-dependent manner in a macrophage infection model, especially, a combination of compound 20 and rifampicin led to a bacterial burden reduction of more than 95%, greater than the reductions achieved with compound 20 or rifampicin alone. This research provides new insights into the rational design of new MptpB inhibitors and verifies that the MptpB inhibitor has a promising potential as a component of tuberculosis treatment.

Polyphosphate kinase 1 is involved in formation, the morphology and ultramicrostructure of biofilm of Mycobacterium smegmatis and its survivability in macrophage

The most unique characteristic of Mycobacterium tuberculosis is persistence in the human host, and the biofilm formation is related to the persistance. Polyphosphate (polyP) kinase 1 (PPK1) is conserved in Mycobacteria and is responsible for polyP synthesis. polyP is a chain molecule linked by high-energy phosphate bonds, which is considered to play a very important role in bacterial persistence. However, the relationship of PPK1 and mycobacterial biofilm formation is still adequately unclear. In current study, ppk1-deficient mutant (MT), ppk1-complemented (CT) and wild-type strains of M. smegmatis mc² 155 were used to investigate the formation, morphology and ultramicrostructure of the biofilm and to analyze the lipid levels and susceptibility to vancomycin antibiotic. And then WT, MT and CT strains were used to infect macrophages and to analyze the expression levels of various inflammatory factors, respectively. We found that PPK1 was required for M. smegmatis polyP production in vivo and polyP deficiency not only attenuated the biofilm formation, but also altered the phenotype and ultramicrostructure of the biofilm and reduced the cell lipid composition (except for C16.1 and C17.1, most of the fatty acid components from C8-C24). Moreover, the ppk1-deficient mutant was also significantly more sensitive to vancomycin which targets the cell wall, and its ability to survive in macrophages was decreased, which was related to the change of the expression level of inflammatory factors in macrophage. This study demonstrates that the PPK1 can affect the biofilm structure through affecting the content of short chain fatty acid and promote intracellular survival of M. smegmatis by altering the expression of inflammatory factors. These findings establish a basis for investigating the role of PPK1 in the persistence of M. tuberculosis, and provide clues for treating latent infection of M. tuberculosis with PPK1 as a potential drug target.

Targeting protein phosphatases in cancer immunotherapy and autoimmune disorders

Protein phosphatases act as key regulators of multiple important cellular processes and are attractive therapeutic targets for various diseases. Although extensive effort has been dedicated to phosphatase-targeted drug discovery, early expeditions for competitive phosphatase inhibitors were plagued by druggability issues, leading to the stigmatization of phosphatases as difficult targets. Despite challenges, persistent efforts have led to the identification of several drug-like, non-competitive modulators of some of these enzymes - including SH2 domain-containing protein tyrosine phosphatase 2, protein tyrosine phosphatase 1B, vascular endothelial protein tyrosine phosphatase and protein phosphatase 1 - reigniting interest in therapeutic targeting of phosphatases. Here, we discuss recent progress in phosphatase drug discovery, with emphasis on the development of selective modulators that exhibit biological activity. The roles and regulation of protein phosphatases in immune cells and their potential as powerful targets for immuno-oncology and autoimmunity indications are assessed.

Discovery of biphenyls bearing thiobarbiturate fragment by structure-based strategy as Mycobacterium tuberculosis protein tyrosine phosphatase B inhibitors

Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB) is an important virulence factor that blocks the host immune response and facilitates M. tuberculosis growth in host cells. MptpB inhibitors are potential components of tuberculosis combination treatment. Herein, we present the development of new biphenyls MptpB inhibitors with greatly improved MptpB inhibition based on our reported thiobarbiturate lead 6 by rational design with the structure-based strategy. The eight biphenyls bearing thiobarbiturate fragment target compounds showed more potent MptpB inhibition (IC₅₀: 1.18-14.13 μM) than the lead compound 6. Further molecular docking studies showed that compounds 13, 26, 27 and 28 had multiple interactions with active sites. Among them, compound 13 exhibited dose-dependent increased antituberculosis activity in mouse macrophages. The results displayed that the strategy of modification utilizing biphenyl scaffold was efficient. Our study identifies biphenyls bearing thiobarbiturate fragment as new MptpB inhibitors and verifies the therapeutic potential of antimycobacterial agent targeting MptpB.

Exploration of Isoxazole-Carboxylic Acid Methyl Ester Based 2-Substituted Quinoline Derivatives as Promising Antitubercular Agents

In pursuit of potent anti-TB agents active against drug resistant tuberculosis (DR-TB), herein we report synthesis and bio-evaluation of a new series of isoxazole-carboxylic acid methyl ester based 2-substituted quinoline derivatives. Preliminary evaluation indicated selectivity towards Mtb H37Rv, with no inhibition of non-tubercular mycobacterial (NTM) & bacterial pathogen panel. Out of 36 synthesized compounds, majority exhibited substantial inhibition of Mtb H37Rv (MIC 0.5-8 μg/mL). Cell viability test against Vero cells revealed no significant cytotoxicity. Further, screening against drug resistant strains (DR-Mtb) found hit compound displaying promising potency (MIC 1-4 μg/mL). Structure optimization of the hit led to the identification of lead compound demonstrating potent inhibition of both drug-susceptible Mtb (MIC 0.12 μg/mL) and drug-resistant Mtb (MIC 0.25-0.5 μg/mL) along with a high selectivity index (SI) >80. Taken together, with appreciable selectivity and potent activity, these chemotypes show prospect to be turned into a potential anti-TB candidate.

Tuberculosis Drug Discovery: Challenges and New Horizons

Over the past 2000 years, tuberculosis (TB) has claimed more lives than any other infectious disease. In 2020 alone, TB was responsible for 1.5 million deaths worldwide, comparable to the 1.8 million deaths caused by COVID-19. The World Health Organization has stated that new TB drugs must be developed to end this pandemic. After decades of neglect in this field, a renaissance era of TB drug discovery has arrived, in which many novel candidates have entered clinical trials. However, while hundreds of molecules are reported annually as promising anti-TB agents, very few successfully progress to clinical development. In this Perspective, we critically review those anti-TB compounds published in the last 6 years that demonstrate good in vivo efficacy against Mycobacterium tuberculosis. Additionally, we highlight the main challenges and strategies for developing new TB drugs and the current global pipeline of drug candidates in clinical studies to foment fresh research perspectives.

Targeting protein tyrosine phosphatases for the development of antivirulence agents: Yersinia spp. and Mycobacterium tuberculosis as prototypes

Protein phosphorylation mediated by protein kinases and phosphatases has a central regulatory function in many cellular processes in eukaryotes and prokaryotes. As a result, several diseases caused by imbalance in phosphorylation levels are known, especially due to protein tyrosine phosphatases (PTPs) activity, an important family of signaling enzymes. Furthermore, over the last decades several studies have shown the main role of PTPs in pathogenic bacteria: they are associated with growth, cell division, cell wall biosynthesis, biofilm formation, metabolic processes, as well as virulence factor. In this way, PTPs have ascended as targets for antibacterial drug design, particularly in view of the antibiotic resistance in pathogenic bacteria, which demands novel therapeutics strategies. Targeting secreted PTPs is an antivirulence strategy to combat the emergence of antimicrobial resistance (AMR). This review focuses on the recent advances in understanding the role of PTPs and the approaches to target them, with an emphasis in Yersinia spp. and Mycobacterium tuberculosis pathogenesis.

Stereoselective synthesis of tri-substituted tetrahydrothiophenes and their in silico binding against mycobacterial protein tyrosine phosphatase B

A facile approach to tri-substituted tetrahydrothiophenes via thia-Michael/aldol has been developed. The cascade reaction was carried out in the presence of 5 mol% of DABCO in ethyl acetate to afford diversely functionalized tetrahydrothiophenes (THTs) with excellent diastereoselectivity. The present methodology has broad substrate tolerance. Gram-scale reaction proceeds with equal efficiency. Functional group transformations further highlight the synthetic potential of the THTs. An asymmetric version of the cascade reaction has also been investigated and a maximum of 72% ee was observed with cinchonidine derived squaramide. Moreover, in silico based molecular docking followed by deep learning based affinity prediction and molecular dynamics simulation analysis indicate the synthesized THT derivatives can act as potent competitive inhibitors of MptpB at low micromolar to nanomolar concentrations. In silico ADME analysis further suggests the plausibility of these compounds to act as future anti-mycobacterial therapeutic leads.

Biginelli Reaction Mediated Synthesis of Antimicrobial Pyrimidine Derivatives and Their Therapeutic Properties

Antimicrobial resistance was one of the top priorities for global public health before the start of the 2019 coronavirus pandemic (COVID-19). Moreover, in this changing medical landscape due to COVID-19, finding new organic structures with antimicrobial and antiviral properties is a priority in current research. The Biginelli synthesis that mediates the production of pyrimidine compounds has been intensively studied in recent decades, especially due to the therapeutic properties of the resulting compounds, such as calcium channel blockers, anticancer, antiviral, antimicrobial, anti-inflammatory or antioxidant compounds. In this review we aim to review the Biginelli syntheses reported recently in the literature that mediates the synthesis of antimicrobial compounds, the spectrum of their medicinal properties, and the structure-activity relationship in the studied compounds.

Functional interrogation and therapeutic targeting of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) counteract the enzymatic activity of protein tyrosine kinases to modulate levels of both normal and disease-associated protein tyrosine phosphorylation. Aberrant activity of PTPs has been linked to the progression of many disease states, yet no PTP inhibitors are currently clinically available. PTPs are without a doubt a difficult drug target. Despite this, many selective, potent, and bioavailable PTP inhibitors have been described, suggesting PTPs should once again be looked at as viable therapeutic targets. Herein, we summarize recently discovered PTP inhibitors and their use in the functional interrogation of PTPs in disease states. In addition, an overview of the therapeutic targeting of PTPs is described using SHP2 as a representative target.

Synthesis and structure-activity relationship of new chalcone linked 5-phenyl-3-isoxazolecarboxylic acid methyl esters potentially active against drug resistant Mycobacterium tuberculosis

In search of novel therapeutic agents active against emerging drug-resistant Mycobacterium tuberculosis and to counter the long treatment protocol of existing drugs, herein we present synthesis and biological evaluation of a new series of 5-phenyl-3-isoxazolecarboxylic acid methyl ester-chalcone hybrids. Among 35 synthesized compounds, 32 analogues displayed potent in-vitro activity against Mycobacterium tuberculosis H37Rv with MIC 0.12-16 μg/mL. Cell viability test against Vero cells indicated 29 compounds to be non-cytotoxic (CC₅₀ > 20 μg/mL & SI > 10). Most potent compounds with MIC 0.12 μg/mL (7 b, 7j, 7 ab) exhibited selectivity index (SI) in excess of 320. Further studies on activity against drug-resistant Mycobacterium tuberculosis revealed 7j as the most potent compound with MIC 0.03-0.5 μg/mL. Time-kill kinetic study suggested compound 7j displaying concentration-dependent bactericidal killing activity with relatively comparable potency to that of current first-line anti-TB drugs. Taken together, 7j presents a novel hit with potential to be translated into a potent antimycobacterial.

Biosynthetic versatility of marine-derived fungi on the delivery of novel antibacterial agents against priority pathogens

Despite the increasing number of novel marine natural products being reported from fungi in the last three decades, to date only the broad-spectrum cephalosporin C can be tracked back as marine fungal-derived drug. Cephalosporins were isolated in the early 1940s from a strain of Acremonium chrysogenum obtained in a sample collected in sewage water in the Sardinian coast, preliminary findings allowing the discovery of cephalosporin C. Since then, bioprospection of marine fungi has been enabling the identification of several metabolites with antibacterial effects, many of which proving to be active against multi-drug resistant strains, available data suggesting also that some might fuel the pharmaceutical firepower towards some of the bacterial pathogens classified as a priority by the World Health Organization. Considering the success of their terrestrial counterparts on the discovery and development of several antibiotics that are nowadays used in the clinical setting, marine fungi obviously come into mind as producers of new prototypes to counteract antibiotic-resistant bacteria that are no longer responding to available treatments. We mainly aim to provide a snapshot on those metabolites that are likely to proceed to advanced preclinical development, not only based on their antibacterial potency, but also considering their targets and modes of action, and activity against priority pathogens.

Discovery of uncompetitive inhibitors of SapM that compromise intracellular survival of Mycobacterium tuberculosis

SapM is a secreted virulence factor from Mycobacterium tuberculosis critical for pathogen survival and persistence inside the host. Its full potential as a target for tuberculosis treatment has not yet been exploited because of the lack of potent inhibitors available. By screening over 1500 small molecules, we have identified new potent and selective inhibitors of SapM with an uncompetitive mechanism of inhibition. The best inhibitors share a trihydroxy-benzene moiety essential for activity. Importantly, the inhibitors significantly reduce mycobacterial burden in infected human macrophages at 1 µM, and they are selective with respect to other mycobacterial and human phosphatases. The best inhibitor also reduces intracellular burden of Francisella tularensis, which secretes the virulence factor AcpA, a homologue of SapM, with the same mechanism of catalysis and inhibition. Our findings demonstrate that inhibition of SapM with small molecule inhibitors is efficient in reducing intracellular mycobacterial survival in host macrophages and confirm SapM as a potential therapeutic target. These initial compounds have favourable physico-chemical properties and provide a basis for exploration towards the development of new tuberculosis treatments. The efficacy of a SapM inhibitor in reducing Francisella tularensis intracellular burden suggests the potential for developing broad-spectrum antivirulence agents to treat microbial infections.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb's development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound's effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound's development.

Therapeutic Targeting of Protein Tyrosine Phosphatases from Mycobacterium tuberculosis

Tuberculosis (TB) is an airborne infectious disease caused by Mycobacterium tuberculosis (Mtb). According to the World Health Organization, an estimated 10 million people developed TB in 2018. The occurrence of drug-resistant TB demands therapeutic agents with novel mechanisms of action. Antivirulence is an alternative strategy that targets bacterial virulence factors instead of central growth pathways to treat disease. Mycobacterium protein tyrosine phosphatases, mPTPA and mPTPB, are secreted by Mtb into the cytoplasm of macrophages and are required for survival and growth of infection within the host. Here we present recent advances in understanding the roles of mPTPA and mPTPB in the pathogenesis of TB. We also focus on potent, selective, and well-characterized small molecule inhibitors reported in the last decade for mPTPA and mPTPB.

Highly Potent and Selective N-Aryl Oxamic Acid-Based Inhibitors for Mycobacterium tuberculosis Protein Tyrosine Phosphatase B

Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis (Mtb). Mtb protein tyrosine phosphatase B (mPTPB) is a virulence factor required for Mtb survival in host macrophages. Consequently, mPTPB represents an exciting target for tuberculosis treatment. Here, we identified N-phenyl oxamic acid as a highly potent and selective monoacid-based phosphotyrosine mimetic for mPTPB inhibition. SAR studies on the initial hit, compound 4 (IC₅₀ = 257 nM), resulted in several highly potent inhibitors with IC₅₀ values lower than 20 nM for mPTPB. Among them, compound 4t showed a K_i of 2.7 nM for mPTPB with over 4500-fold preference over 25 mammalian PTPs. Kinetic, molecular docking, and site-directed mutagenesis analyses confirmed these compounds as active site-directed reversible inhibitors of mPTPB. These inhibitors can reverse the altered host cell immune responses induced by the bacterial phosphatase. Furthermore, the inhibitors possess molecular weights <400 Da, log D_7.4 < 2.5, topological polar surface area < 75, ligand efficiency > 0.43, and good aqueous solubility and metabolic stability, thus offering excellent starting points for further therapeutic development.

Molecule Property Analyses of Active Compounds for Mycobacterium tuberculosis

Tuberculosis (TB) continues to claim the lives of around 1.7 million people per year. Most concerning are the reports of multidrug drug resistance. Paradoxically, this global health pandemic is demanding new therapies when resources and interest are waning. However, continued tuberculosis drug discovery is critical to address the global health need and burgeoning multidrug resistance. Many diverse classes of antitubercular compounds have been identified with activity in vitro and in vivo. Our analyses of over 100 active leads are representative of thousands of active compounds generated over the past decade, suggests that they come from few chemical classes or natural product sources. We are therefore repeatedly identifying compounds that are similar to those that preceded them. Our molecule-centered cheminformatics analyses point to the need to dramatically increase the diversity of chemical libraries tested and get outside of the historic Mtb property space if we are to generate novel improved antitubercular leads.

Host-Directed Therapies and Anti-Virulence Compounds to Address Anti-Microbial Resistant Tuberculosis Infection

Despite global efforts to contain tuberculosis (TB), the disease remains a leading cause of morbidity and mortality worldwide, further exacerbated by the increased resistance to antibiotics displayed by the tubercle bacillus Mycobacterium tuberculosis. In order to treat drug-resistant TB, alternative or complementary approaches to standard anti-TB regimens are being explored. An area of active research is represented by host-directed therapies which aim to modulate the host immune response by mitigating inflammation and by promoting the antimicrobial activity of immune cells. Additionally, compounds that reduce the virulence of M. tuberculosis, for instance by targeting the major virulence factor ESX-1, are being given increased attention by the TB research community. This review article summarizes the current state of the art in the development of these emerging therapies against TB.

Mycobacterium tuberculosis infection of host cells in space and time

Tuberculosis (TB) caused by the bacterial pathogen Mycobacterium tuberculosis (Mtb) remains one of the deadliest infectious diseases with over a billion deaths in the past 200 years (Paulson 2013). TB causes more deaths worldwide than any other single infectious agent, with 10.4 million new cases and close to 1.7 million deaths in 2017. The obstacles that make TB hard to treat and eradicate are intrinsically linked to the intracellular lifestyle of Mtb. Mtb needs to replicate within human cells to disseminate to other individuals and cause disease. However, we still do not completely understand how Mtb manages to survive within eukaryotic cells and why some cells are able to eradicate this lethal pathogen. Here, we summarise the current knowledge of the complex host cell-pathogen interactions in TB and review the cellular mechanisms operating at the interface between Mtb and the human host cell, highlighting the technical and methodological challenges to investigating the cell biology of human host cell-Mtb interactions.

Mechanism of catalysis and inhibition of Mycobacterium tuberculosis SapM, implications for the development of novel antivirulence drugs

Mycobacterium tuberculosis (Mtb) SapM is a secreted virulence factor critical for intracellular survival of the pathogen. The role of SapM in phagosome maturation arrest in host macrophages suggests its potential as a drug target to assist in the clearance of tuberculosis infection. However, the mechanism of action of SapM at the molecular level remains unknown. In this study, we provide new insights into the mechanism of catalysis, substrate specificity and inhibition of SapM, and we identify the critical residues for catalysis and substrate binding. Our findings demonstrate that SapM is an atypical monoester alkaline phosphatase, with a serine-based mechanism of catalysis probably metal-dependent. Particularly relevant to SapM function and pathogenesis, is its activity towards PI(4,5)P₂ and PI3P, two phosphoinositides that function at the early stages of microbial phagocytosis and phagosome formation. This suggests that SapM may have a pleiotropic role with a wider importance on Mtb infection than initially thought. Finally, we have identified two inhibitors of SapM, L-ascorbic acid and 2-phospho-L-ascorbic, which define two different mechanisms by which the catalytic activity of this phosphatase could be regulated. Critically, we demonstrate that 2-phospho-L-ascorbic reduces mycobacterial survival in macrophage infections, hence confirming the potential of SapM as a therapeutic drug target.

An Overview on the Potential Antimycobacterial Agents Targeting Serine/Threonine Protein Kinases from Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), still remains an urgent global health issue, mainly due to the emergence of multi-drug resistant strains. Therefore, there is a pressing need to develop novel and more efficient drugs to control the disease. In this context, targeting the pathogen virulence factors, and particularly signal mechanisms, seems to be a promising approach. An important transmembrane signaling system in Mtb is represented by receptor-type Serine/ Threonine protein kinases (STPKs). Mtb has 11 different STPKs, two of them, PknA and PknB, are essential. By contrast PknG and PknH are involved in Mtb virulence and adaptation, and are fundamental for the pathogen growth in infection models. Therefore, STPKs represent a very interesting group of pharmacological targets in M. tuberculosis. In this work, the principal inhibitors of the mycobacterial STPKs will be presented and discussed. In particular, medicinal chemistry efforts have been focused on discovering new antimycobacterial compounds, targeting three of these kinases, namely PknA, PknB and PknG. Generally, the inhibitory effect on these enzymes do not correlate with a significant antimycobacterial action in whole-cell assays. However, compounds with activity in the low micromolar range have been obtained, demonstrating that targeting Mtb STPKs could be a new promising strategy for the development of drugs to treat TB infections.