Clofazimine analogs with efficacy against experimental tuberculosis and reduced potential for accumulation

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Identification of bacterial determinants of tuberculosis infection and treatment outcomes: a phenogenomic analysis of clinical strains

BACKGROUND

Bacterial diversity could contribute to the diversity of tuberculosis infection and treatment outcomes observed clinically, but the biological basis of this association is poorly understood. The aim of this study was to identify associations between phenogenomic variation in Mycobacterium tuberculosis and tuberculosis clinical features.

METHODS

We developed a high-throughput platform to define phenotype-genotype relationships in M tuberculosis clinical isolates, which we tested on a set of 158 drug-sensitive M tuberculosis strains sampled from a large tuberculosis clinical study in Ho Chi Minh City, Viet Nam. We tagged the strains with unique genetic barcodes in multiplicate, allowing us to pool the strains for in-vitro competitive fitness assays across 16 host-relevant antibiotic and metabolic conditions. Relative fitness was quantified by deep sequencing, enumerating output barcode read counts relative to input normalised values. We performed a genome-wide association study to identify phylogenetically linked and monogenic mutations associated with the in-vitro fitness phenotypes. These genetic determinants were further associated with relevant clinical outcomes (cavitary disease and treatment failure) by calculating odds ratios (ORs) with binomial logistic regressions. We also assessed the population-level transmission of strains associated with cavitary disease and treatment failure using terminal branch length analysis of the phylogenetic data.

FINDINGS

M tuberculosis clinical strains had diverse growth characteristics in host-like metabolic and drug conditions. These fitness phenotypes were highly heritable, and we identified monogenic and phylogenetically linked variants associated with the fitness phenotypes. These data enabled us to define two genetic features that were associated with clinical outcomes. First, mutations in Rv1339, a phosphodiesterase, which were associated with slow growth in glycerol, were further associated with treatment failure (OR 5·34, 95% CI 1·21-23·58, p=0·027). Second, we identified a phenotypically distinct slow-growing subclade of lineage 1 strains (L1.1.1.1) that was associated with cavitary disease (OR 2·49, 1·11-5·59, p=0·027) and treatment failure (OR 4·76, 1·53-14·78, p=0·0069), and which had shorter terminal branch lengths on the phylogenetic tree, suggesting increased transmission.

INTERPRETATION

Slow growth under various antibiotic and metabolic conditions served as in-vitro intermediate phenotypes underlying the association between M tuberculosis monogenic and phylogenetically linked mutations and outcomes such as cavitary disease, treatment failure, and transmission potential. These data suggest that M tuberculosis growth regulation is an adaptive advantage for bacterial success in human populations, at least in some circumstances. These data further suggest markers for the underlying bacterial processes that contribute to these clinical outcomes.

FUNDING

National Health and Medical Research Council/A∗STAR, National Institutes of Allergy and Infectious Diseases, National Institute of Child Health and Human Development, and the Wellcome Trust Fellowship in Public Health and Tropical Medicine.

Unveiling the Antimicrobial and Larvicidal Potential of Butyrolactones and Orsellinic Acid Derivatives from the Morus alba-derived Fungus Aspergillus terreus via Integrated In vitro and In silico Approaches

The emergence of multi-drug-resistant microbial strains spurred the search for antimicrobial agents; as a result, two distinct approaches were combined: four in vitro studies and four corresponding molecular docking investigations. Antituberculosis, anti-methicillin-resistant Staphylococcus aureus (anti-MRSA), antifungal, and larvicidal activities of the crude extract, two fractions, and seven isolated compounds from Aspergillus terreus derived from Morus alba roots were explored. The isolated compounds (5 butyrolactones and 2 orsellinic acid derivatives) showed potent to moderate antitubercular activity with MIC values ranging from 1.95 to 62.5 μg/mL (compared to isoniazid, 0.24 μg/mL) and promising anti-MRSA potential with inhibition zone diameters ranging from 8 to 25 mm. Additionally, the in silico study proved that the isolated compounds bind to the two corresponding proteins' active sites with high to moderate -(C-Docker interaction energies) and stable interactions. The isolated compounds displayed antifungal activities against different fungal strains at diverse degrees of activity, among them compound (8"S,9")-dihydroxy-dihydrobutyrolactone I eliciting the best antifungal activity. Meanwhile, all isolated compounds, fractions, and the crude extract demonstrated extremely selective potent to moderate activity against Cryptococcus neoformans. The isolated five butyrolactone derivatives could develop potential mosquito larvicidal agents as a result of promising docking outcomes in the larval enzyme carboxylesterase.

Sudapyridine (WX-081) antibacterial activity against Mycobacterium avium, Mycobacterium abscessus, and Mycobacterium chelonae in vitro and in vivo

Sudapyridine (WX-081) is a structural analog of bedaquiline (BDQ), which shows anti-tuberculosis and non-tuberculous mycobacteria (NTM) activities but, unlike BDQ, did not prolong QT interval in animal model studies. This study evaluated the antibacterial activity of this novel compound against Mycobacterium avium, Mycobacterium abscessus, and Mycobacterium chelonae in vitro and in vivo. The minimum inhibitory concentration (MIC) of WX-081 against three kinds of non-tuberculous mycobacteria (NTM) clinical strains was determined using microplate-based alamarBlue assay (MABA), and the antibacterial activity of WX-081 against NTM in J774A.1 cells and mice was evaluated. MIC ranges of WX-081 against clinical strains of M. avium and M. abscessus were 0.05-0.94 μg/mL, 0.88-7.22 μg/mL (M. abscessus subsp. abscessus), and 0.22-8.67 μg/mL (M. abscessus subsp. massiliense), respectively, which were slightly higher than those of BDQ. For M. avium, M. abscessus, and M. chelonae, WX-081 can reduce the intracellular bacterial load by 0.13-1.18, 0.18-1.50, and 0.17-1.03 log10 colony forming units (CFU)/mL, respectively, in a concentration-dependent manner. WX-081 has bactericidal activity against three NTM species in mice. WX-081 exhibited anti-NTM activity to the same extent as BDQ both in vivo and in vitro. WX-081 is a promising clinical candidate and should be studied further in clinical trials.

IMPORTANCE

Due to the rapidly increased cases globally, non-tuberculous mycobacteria (NTM) disease has become a significant public health problem. NTM accounted for 11.57% of all mycobacterial isolates in China, with a high detection rate of Mycobacterium abscessus, Mycobacterium avium, and Mycobacterium chelonae during 2000-2019. Treatment of NTM infection is often challenging, as natural resistance to most antibiotics is quite common among different NTM species. Hence, identifying highly active anti-NTM agents is a priority for potent regimen establishment. The pursuit of new drugs to treat multidrug-resistant tuberculosis may also identify some agents with strong activity against NTM. Sudapyridine (WX-081) is a structural analog of bedaquiline (BDQ), which was developed to retain the anti-tuberculosis efficacy but eliminates the severe side effects of BDQ. This study initially evaluated the antimicrobial activity of this novel compound against M. avium, M. abscessus, and M. chelonae in vitro, in macrophages and mice, respectively.

Design, synthesis, in vitro and in silico evaluation of novel substituted 1,2,4-triazole analogues as dual human VEGFR-2 and TB-InhA inhibitors

Cancer is a leading cause of death globally and has been associated with Mycobacterium tuberculosis (Mtb). The angiogenesis-related VEGFR-2 is a common target between cancer and Mtb. Here, we aimed to synthesize and validate potent dual human VEGFR-2 inhibitors as anticancer and anti-mycobacterial agents. Two series of 1,2,4-triazole-based compounds (6a-l and 11a-e) were designed and synthesized through a molecular hybridization approach. Activities of all synthesized compounds were evaluated against human VEGFR-2 in addition to drug-sensitive, multidrug-resistant and extensive-drug resistant Mtb. Compounds 6a, 6c, 6e, 6f, 6h, 6l, 11a, 11d and 11e showed promising inhibitory effect on VEGFR-2 (IC50 = 0.15 - 0.39 µM), anti-proliferative activities against cancerous cells and low cytotoxicity against normal cells. The most potent compounds (6e and 11a) increased apoptosis percentage. Additionally, compounds 6h, 6i, 6l and 11c showed the highest activities against all Mtb strains, and thus were evaluated against enoyl-acyl carrier protein reductase (InhA) which is essential for Mtb cell wall synthesis. Interestingly, the compounds showed excellent InhA inhibition activities with IC50 range of 1.3 - 4.7 µM. Docking study revealed high binding affinities toward targeted enzymes; human VEGFR-2 and Mtb InhA. In conclusion, 1,2,4-triazole analogues are suggested as potent anticancer and antimycobacterial agents via inhibition of human VEGFR-2 and Mtb InhA.

Targeting Mycobacterium tuberculosis iron-scavenging tools: a recent update on siderophores inhibitors

Among the various bacterial infections, tuberculosis (TB) remains a life-threatening infectious disease responsible as the most significant cause of mortality and morbidity worldwide. The co-infection of human immunodeficiency virus (HIV) in association with TB burdens the healthcare system substantially. Notably, M.tb possesses defence against most antitubercular antibiotic drugs, and the efficacy of existing frontline anti-TB drugs is waning. Also, new and recurring cases of TB from resistant bacteria such as multidrug-resistant TB (MDR), extensively drug-resistant TB (XDR), and totally drug-resistant TB (TDR) strains are increasing. Hence, TB begs the scientific community to explore the new therapeutic class of compounds with their novel mechanism. M.tb requires iron from host cells to sustain, grow, and carry out several biological processes. M.tb has developed strategic methods of acquiring iron from the surrounding environment. In this communication, we discuss an overview of M.tb iron-scavenging tools. Also, we have summarized recently identified MbtA and MbtI inhibitors, which prevent M.tb from scavenging iron. These iron-scavenging tool inhibitors have the potential to be developed as anti-TB agents/drugs.

Coadministration of bedaquiline and pyrifazimine reduce exposure to toxic metabolite N-desmethyl bedaquiline

Background: A new, effective anti-tuberculosis (TB) regimen containing bedaquiline (BDQ) and pyrifazimine (TBI-166) has been recommended for a phase IIb clinical trial. Preclinical drug-drug interaction (DDI) studies of the combination of BDQ and TBI-166 have been designed to support future clinical trials. In this study, we investigated whether a DDI between BDQ and TBI-166 affects the pharmacokinetics of BDQ. Methods: We performed in vitro quantification of the fractional contributions of the fraction of drug metabolism by individual CYP enzymes (f m) of BDQ and the inhibition potency of key metabolic pathways of TBI-166. Furthermore, we conducted an in vivo steady-state pharmacokinetics study in a murine TB model and healthy BALB/c mice. Results: The in vitro f m value indicated that the CYP3A4 pathway contributed more than 75% to BDQ metabolism to N-desmethyl-bedaquiline (M2), and TBI-166 was a moderate (IC50 2.65 µM) potential CYP3A4 inhibitor. Coadministration of BDQ and TBI-166 greatly reduced exposure to metabolite M2 (AUC0-t 76310 vs 115704 h ng/mL, 66% of BDQ alone), whereas the exposure to BDQ and TBI-166 did not changed. The same trend was observed both in healthy and TB model mice. The plasma concentration of M2 decreased significantly after coadministration of BDQ and TBI-166 and decreased further during treatment in the TB model. Conclusions: In conclusion, our results showed that the combination of BDQ and TBI-166 significantly reduced exposure to the toxic metabolite M2 by inhibiting the activity of the CYP3A4 pathway. The potential safety and efficacy benefits demonstrated by the TB treatment highly suggest that coadministration of BDQ and TBI-166 should be studied further.

Rv1453 is associated with clofazimine resistance in Mycobacterium tuberculosis

Clofazimine (CFZ) has been repurposed for treating tuberculosis (TB), especially multidrug-resistant tuberculosis (MDR-TB). However, the mechanisms of resistance to clofazimine are poorly understood. We previously reported a mutation located in the intergenic region of Rv1453 that was linked to resistance to CFZ and demonstrated that an Rv1453 knockout resulted in an increased minimum inhibitory concentration (MIC) of CFZ. The current study aims to go back and describe in detail how the mutation was identified and further explore its association with CFZ resistance by testing additional 30 isolates. We investigated MICs of clofazimine against 100 clinical strains isolated from MDR-TB patients by microplate alamarBlue assay. Whole-genome sequencing (WGS) was performed on 11 clofazimine-resistant and 7 clofazimine-susceptible strains, including H37Rv. Among the 11 clofazimine-resistant mutants subjected to WGS, the rate of mutation in the intergenic region of the Rv1453 gene was 55% (6/11) in clofazimine-resistant strains. Among another 30 clofazimine-resistant clinical isolates, 27 had mutations in the intergenic region of the Rv1453 gene. A mutation in the Rv1453 gene associated with clofazimine resistance was identified, which shed light on the mechanisms of action and resistance of clofazimine. IMPORTANCE Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis, especially the emergence of multidrug-resistant tuberculosis (MDR-TB) brings great distress to humans. Clofazimine (CFZ) plays an important role in the treatment of MDR-TB. To understand the underlying mechanism of clofazimine resistance better, in this study, we review and detail the findings of the mutation of intergenic region of Rv1453 and find additional evidence that this mutation is related to clofazimine resistance in 30 additional isolates. The significance of our research is to contribute to a comprehensive understanding of clofazimine-resistant mechanisms, which is critical for reducing the emergence of resistance and for anti-TB drug discovery.

Design, synthesis and antitubercular activity of novel N-(amino)piperazinyl benzothiazinones with improved safety

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB) remains a major global health problem and new therapeutic antitubercular agents are urgent needed. Among the novel antituberculosis drugs in the pipeline, Benzothiazinones (BTZs) are among the most potent antituberculosis agents against both drug-susceptible and multidrug-resistant (MDR) tuberculosis. Our group has focused on structural modifications of the side chain at C-2 position of the BTZ core and WAP-2101/2102 with excellent in vitro activity were discovered in our lab. However, the severe in vivo toxicity was observed during subsequent acute toxicity evaluation. Herein, a series of novel N-(amino)piperazinyl benzothiazinone derivatives were designed and synthesized as new anti-TB agents to reduce the in vivo toxicity. Our results show that majority of them exhibit the same potent or comparable activity against both MTB H₃₇Rv and MDR-MTB strains (MIC: 4.00 - <1 ng/mL) as PBTZ169. Especially, compound 2c with low cardiac toxicity, low cell cytotoxicity and acceptable oral pharmacokinetic (PK) profiles have low acute toxicity in mice (LD₅₀ > 500 mg/kg), suggesting it may serve as a promising lead compound for further antitubercular drug discovery.

High-throughput phenogenotyping of Mycobacteria tuberculosis clinical strains reveals bacterial determinants of treatment outcomes

Background

Combatting the tuberculosis (TB) epidemic caused by Mycobacterium tuberculosis ( Mtb ) necessitates a better understanding of the factors contributing to patient clinical outcomes and transmission. While host and environmental factors have been evaluated, the impact of Mtb genetic background and phenotypic diversity is underexplored. Previous work has made associations between Mtb genetic lineages and some clinical and epidemiological features, but the bacterial traits underlying these connections are largely unknown.

Methods

We developed a high-throughput functional genomics platform for defining genotype-phenotype relationships across a panel of Mtb clinical isolates. These phenotypic fitness profiles function as intermediate traits which can be linked to Mtb genetic variants and associated with clinical and epidemiological outcomes. We applied this approach to a collection of 158 Mtb strains from a study of Mtb transmission in Ho Chi Minh City, Vietnam. Mtb strains were genetically tagged in multiplicate, which allowed us to pool the strains and assess in vitro competitive fitness using deep sequencing across a set of 14 host-relevant antibiotic and metabolic conditions. Phylogenetic and monogenic associations with these intermediate traits were identified and then associated with clinical outcomes.

Findings

Mtb clinical strains have a broad range of growth and drug response dynamics that can be clustered by their phylogenetic relationships. We identified novel monogenic associations with Mtb fitness in various metabolic and antibiotic conditions. Among these, we find that mutations in Rv1339 , a phosphodiesterase, which were identified through their association with slow growth in glycerol, are further associated with treatment failure. We also identify a previously uncharacterized subclade of Lineage 1 strains (L1.1.1.1) that is phenotypically distinguished by slow growth under most antibiotic and metabolic stress conditions in vitro . This clade is associated with cavitary disease, treatment failure, and demonstrates increased transmission potential.

Interpretation

High-throughput phenogenotyping of Mtb clinical strains enabled bacterial intermediate trait identification that can provide a mechanistic link between Mtb genetic variation and patient clinical outcomes. Mtb strains associated with cavitary disease, treatment failure, and transmission potential display intermediate phenotypes distinguished by slow growth under various antibiotic and metabolic conditions. These data suggest that Mtb growth regulation is an adaptive advantage for host bacterial success in human populations, in at least some circumstances. These data further suggest markers for the underlying bacterial processes that govern these clinical outcomes.

Funding

National Institutes of Allergy and Infectious Diseases: P01 AI132130 (SS, SMF); P01 AI143575 (XW, SMF); U19 AI142793 (QL, SMF); 5T32AI132120-03 (SS); 5T32AI132120-04 (SS); 5T32AI049928-17 (SS) Wellcome Trust Fellowship in Public Health and Tropical Medicine: 097124/Z/11/Z (NTTT) National Health and Medical Research Council (NHMRC)/A*STAR joint call: APP1056689 (SJD) The funding sources had no involvement in study methodology, data collection, analysis, and interpretation nor in the writing or submission of the manuscript.

Research in context

Evidence before this study: We used different combinations of the words mycobacterium tuberculosis, tuberculosis, clinical strains, intermediate phenotypes, genetic barcoding, phenogenomics, cavitary disease, treatment failure, and transmission to search the PubMed database for all studies published up until January 20 th , 2022. We only considered English language publications, which biases our search. Previous work linking Mtb determinants to clinical or epidemiological data has made associations between bacterial lineage, or less frequently, genetic polymorphisms to in vitro or in vivo models of pathogenesis, transmission, and clinical outcomes such as cavitary disease, treatment failure, delayed culture conversion, and severity. Many of these studies focus on the global pandemic Lineage 2 and Lineage 4 Mtb strains due in part to a deletion in a polyketide synthase implicated in host-pathogen interactions. There are a number of Mtb GWAS studies that have led to novel genetic determinants of in vitro drug resistance and tolerance. Previous Mtb GWAS analyses with clinical outcomes did not experimentally test any predicted phenotypes of the clinical strains. Published laboratory-based studies of Mtb clinical strains involve relatively small numbers of strains, do not identify the genetic basis of relevant phenotypes, or link findings to the corresponding clinical outcomes. There are two recent studies of other pathogens that describe phenogenomic analyses. One study of 331 M. abscessus clinical strains performed one-by-one phenotyping to identify bacterial features associated with clearance of infection and another details a competition experiment utilizing three barcoded Plasmodium falciparum clinical isolates to assay antimalarial fitness and resistance. Added value of this study: We developed a functional genomics platform to perform high-throughput phenotyping of Mtb clinical strains. We then used these phenotypes as intermediate traits to identify novel bacterial genetic features associated with clinical outcomes. We leveraged this platform with a sample of 158 Mtb clinical strains from a cross sectional study of Mtb transmission in Ho Chi Minh City, Vietnam. To enable high-throughput phenotyping of large numbers of Mtb clinical isolates, we applied a DNA barcoding approach that has not been previously utilized for the high-throughput analysis of Mtb clinical strains. This approach allowed us to perform pooled competitive fitness assays, tracking strain fitness using deep sequencing. We measured the replicative fitness of the clinical strains in multiplicate under 14 metabolic and antibiotic stress condition. To our knowledge, this is the largest phenotypic screen of Mtb clinical isolates to date. We performed bacterial GWAS to delineate the Mtb genetic variants associated with each fitness phenotype, identifying monogenic associations with several conditions. We then defined Mtb phenotypic and genetic features associated with clinical outcomes. We find that a subclade of Mtb strains, defined by variants largely involved in fatty acid metabolic pathways, share a universal slow growth phenotype that is associated with cavitary disease, treatment failure and increased transmission potential in Vietnam. We also find that mutations in Rv1339 , a poorly characterized phosphodiesterase, also associate with slow growth in vitro and with treatment failure in patients. Implications of all the available evidence: Phenogenomic profiling demonstrates that Mtb strains exhibit distinct growth characteristics under metabolic and antibiotic stress conditions. These fitness profiles can serve as intermediate traits for GWAS and association with clinical outcomes. Intermediate phenotyping allows us to examine potential processes by which bacterial strain differences contribute to clinical outcomes. Our study identifies clinical strains with slow growth phenotypes under in vitro models of antibiotic and host-like metabolic conditions that are associated with adverse clinical outcomes. It is possible that the bacterial intermediate phenotypes we identified are directly related to the mechanisms of these outcomes, or they may serve as markers for the causal yet unidentified bacterial determinants. Via the intermediate phenotyping, we also discovered a surprising diversity in Mtb responses to the new anti-mycobacterial drugs that target central metabolic processes, which will be important in considering roll-out of these new agents. Our study and others that have identified Mtb determinants of TB clinical and epidemiological phenotypes should inform efforts to improve diagnostics and drug regimen design.

One-pot green synthesis of chitosan biguanidine nanoparticles for targeting M. tuberculosis

Tuberculosis (TB) is considered as one of the most fatal infectious diseases nowadays. Several traditional anti-tuberculosis drugs like isoniazid have been largely applied; however, they are associated with toxicity and poor anti-TB treatment. So, the fabrication of new alternative anti-TB drugs containing natural biopolymers for TB treatment has attracted great attention in recent years because of their remarkable features: biodegradability, biocompatibility and non-toxicity. Therefore, their medicine is very effective with low side effects compared with synthetic drugs. Our current work intends to engineer chitosan biguanidine (ChBG) nanoparticles as a new safe and high-efficient anti-TB drug using one-pot, green, cost-effective ionic gelation method. The chemical structure of as-formed materials was chemically confirmed using various analysis techniques: H-NMR, FTIR, SEM, and TEM. TEM results have proved the formation of uniformly well-distributed ChBG nanoparticles with a small particle size of ~38 nm. The inhibitory activity of these prepared nanoparticles was investigated against the growth of three different M. tuberculosis pathogens such as sensitive, MDR, and XDR, and in a comparison with the isoniazid drug as a standard anti-tuberculosis drug. The antituberculosis assay results showed that ChBG NPs attained MIC values of 0.48, 3.9, 7.81 μg/mL for inhibiting the growth of sensitive, MDR, and XDR M. tuberculosis pathogens compared to bare Ch NPs (15.63, 62.5 > 125 μg/mL) and the isoniazid drug (0.24, 0, 0 μg/mL), respectively. Moreover, cytotoxicity of the ChBG NPs was examined against normal lung cell lines (Wi38) and was found to have cell viability of 100 % with the concentration range of 0.48-7.81 μg/mL.

Green engineering of TMC-CMS nanoparticles decorated graphene sheets for targeting M. tuberculosis

Our current work intends to primarily engineer a new type of antibacterial composite by preparing a highly biocompatible graphene sheet decorated with TMC-CMS IPNs nanoparticles utilizing one-pot, green, cost-effective ultrasonication approach. The microstructure of as-formed materials was chemically confirmed using various analytical techniques such as ¹H-NMR, FTIR, UV/vis, SEM, and TEM. TEM data has proved the formation of uniformly distributed TCNPs on graphene surfaces with a small particle size of ~22 nm compared with that of pure nanoparticles (~30 nm). The inhibitory activity of these developed materials was examined against the growth of three different M. tuberculosis pathogens and in a comparison with the isoniazid drug as a standard anti-tuberculosis drug. The TCNPs@GRP composite attained MIC values of 0.98, 3.9, and 7.81 μg/mL for inhibiting the growth of sensitive, MDR, and XDR M. tuberculosis pathogens compared to the bare TCNPs (7.81, 31.25, >125 μg/mL) and the isoniazid drug (0.24, 0, 0 μg/mL), respectively. This reveals a considerable synergism in the antituberculosis activity between TCNPs and graphene nanosheets. Cytotoxicity of the TCNPs@GRP was examined against normal lung cell lines (WI38) and was found to have cell viability of 100% with the concentration range of 0.98-7.81 μg/mL.

Targeting mycobacterial membranes and membrane proteins: Progress and limitations

Among the various bacterial infections, tuberculosis continues to hold center stage. Its causative agent, Mycobacterium tuberculosis, possesses robust defense mechanisms against most front-line antibiotic drugs and host responses due to their complex cell membranes with unique lipid molecules. It is now well-established that bacteria change their membrane composition to optimize their environment to survive and elude drug action. Thus targeting membrane or membrane components is a promising avenue for exploiting the chemical space focussed on developing novel membrane-centric anti-bacterial small molecules. These approaches are more effective, non-toxic, and can attenuate resistance phenotype. We present the relevance of targeting the mycobacterial membrane as a practical therapeutic approach. The review highlights the direct and indirect targeting of membrane structure and function. Direct membrane targeting agents cause perturbation in the membrane potential and can cause leakage of the cytoplasmic contents. In contrast, indirect membrane targeting agents disrupt the function of membrane-associated proteins involved in cell wall biosynthesis or energy production. We discuss the chronological chemical improvements in various scaffolds targeting specific membrane-associated protein targets, their clinical evaluation, and up-to-date account of their ''mechanisms of action, potency, selectivity'' and limitations. The sources of anti-TB drugs/inhibitors discussed in this work have emerged from target-based identification, cell-based phenotypic screening, drug repurposing, and natural products. We believe this review will inspire the exploration of uncharted chemical space for informing the development of new scaffolds that can inhibit novel mycobacterial membrane targets.

Clofazimine for the treatment of tuberculosis

Shorter (6-9 months), fully oral regimens containing new and repurposed drugs are now the first-choice option for the treatment of drug-resistant tuberculosis (DR-TB). Clofazimine, long used in the treatment of leprosy, is one such repurposed drug that has become a cornerstone of DR-TB treatment and ongoing trials are exploring novel, shorter clofazimine-containing regimens for drug-resistant as well as drug-susceptible tuberculosis. Clofazimine's repurposing was informed by evidence of potent activity against DR-TB strains in vitro and in mice and a treatment-shortening effect in DR-TB patients as part of a multidrug regimen. Clofazimine entered clinical use in the 1950s without the rigorous safety and pharmacokinetic evaluation which is part of modern drug development and current dosing is not evidence-based. Recent studies have begun to characterize clofazimine's exposure-response relationship for safety and efficacy in populations with TB. Despite being better tolerated than some other second-line TB drugs, the extent and impact of adverse effects including skin discolouration and cardiotoxicity are not well understood and together with emergent resistance, may undermine clofazimine use in DR-TB programmes. Furthermore, clofazimine's precise mechanism of action is not well established, as is the genetic basis of clofazimine resistance. In this narrative review, we present an overview of the evidence base underpinning the use and limitations of clofazimine as an antituberculosis drug and discuss advances in the understanding of clofazimine pharmacokinetics, toxicity, and resistance. The unusual pharmacokinetic properties of clofazimine and how these relate to its putative mechanism of action, antituberculosis activity, dosing considerations and adverse effects are highlighted. Finally, we discuss the development of novel riminophenazine analogues as antituberculosis drugs.

Solubility-driven optimization of benzothiopyranone salts leading to a preclinical candidate with improved pharmacokinetic properties and activity against Mycobacterium tuberculosis

Solubility-driven optimization of the salts of nitro benzothiopyranone 1, which targets DprE1, led to an antimycobacterial preclinical candidate 2. Five pharmaceutically acceptable salts, including the maleate (2), fumarate (3), citrate (4, 5), and l-malate (6) of compound 1, were prepared via the salt formation reaction and evaluated for their physicochemical and pharmacokinetic properties. Compared with 1, all the target salts exhibited greatly increased aqueous solubility and improved oral bioavailability in mice. Maleate salt 2, which displayed higher chemical stability and lower log P, showed substantially improved bioavailability in rats and a much better in vivo effect compared with free base 1 at the same dose. The X-ray crystal structure of 2 revealed that the exposed hydrophilic piperazine-maleate moiety in the crystal structure cell may be critical in increasing the solubility of 2. Thus, this maleate salt 2 overcame the poor druggability of benzothiopyranone derivatives and was identified as a promising preclinical candidate for treating tuberculosis.

The anti-aging, anti-tuberculosis and antioxidant potential benefits of Saudi Arabia Olea-Europaea Leaves extracts

The olive leaf extract and olive leaf indicated a high potential for application in food additives and foodstuffs. It could be these bio-products useful and important in condition therapy related with oxidative stress and can use it to develop functional foods and to improve the food's shelf life. The olive leaf chemical composition of Oleaeuropaea L. grown from eljouf in Saudi Arabia, using solvents of increasing polarity cyclohexane, dichloromethane, chloroform, ethyl acetate, methanol and ethanol was determined using by GC/MS. Furthermore, the antioxidant activity (diphenylpicrylhydrazyl (DPPH), anti-aging, and anti-tuberculosis of olive leaf extracts were evaluated. The results indicated that extract of Oleaeuropaea L. has a considerable contains in polyphenols (hydroxytyrosol, oleuropein and their derivatives) regarding its antioxidant effects, the major components were detected by GC/MS in Olea dichloromethane extract are Hexadecanoic acid (15.82%), 7(4Dimethylaminophenyl)3,3,12trimethyl3,12dihydro6 Hpyrano[2,3c]acridin 6 one (11.21%), and in Olea chloroform extract are Hexatriacontane (12.68%), nTetratr iacontane (10.95%). The results concluded that the plant extract of chloroform showed no anti-aging activities and the lower anti-aging activities for cyclohexane extract, while, the Olea dichloromethane extract was the most active extract. The obtained data confirmed that the most active extract of anti-tubercolisis was for chloroform and ethyl acetate extract, while, anti-tubercolisis activity of ethanolic extract was the lower. The extract amount as well as the solvent polarity influence the inhibitory activity. A favorable connection was demonstrated inter alia the leaf extracts antioxidant activity and the content of total phenol.

Redox Cycling Dioxonaphthoimidazoliums Disrupt Iron Homeostasis in Mycobacterium bovis Bacillus Calmette-Guérin

The dioxonaphthoimidazolium scaffold is a novel, highly bactericidal redox cycling antituberculosis chemotype that is reliant on the respiratory enzyme Type II NADH dehydrogenase (NDH2) for the generation of reactive oxygen species (ROS). Here, we employed Mycobacterium bovis Bacillus Calmette-Guérin (M. bovis BCG) reporter strains to show that ROS generated by the redox cycler SA23 simulated an iron deficient state in the bacteria, which led to a compensatory increase in the expression of the iron acquisition mbtB gene while collaterally reducing the expression of the iron storage bfrB gene. Exacerbating the iron deficiency via the inclusion of an iron chelator or aggravating oxidative stress by deploying a catalase (KatG) loss-of-function mutant strain enhanced the activity of SA23, whereas a combined approach of treating the katG mutant strain with an iron chelator led to even greater gains in activity. Our results support the notion that the activity of SA23 pivots on a vicious cycle of events that involve the derailment of iron homeostasis toward greater acquisition of the metal, overwhelmed oxidative stress defenses due to enhanced Fenton reactivity, and, ultimately, self-inflicted death. Hence, we posit that redox cyclers that concurrently perturb the iron equilibrium and cellular respiration are well-positioned to be potent next-generation anti-tubercular drugs. IMPORTANCE Cellular respiration in mycobacteria is a potentially rich target space for the discovery of novel drug entities. Here, we show that a redox cycling bactericidal small molecule that selectively activates a respiratory complex in mycobacteria has the surprising effect of disrupting iron homeostasis. Our results support the notion that the disruption of cellular respiration is a potent driver of reactive oxygen species (ROS) generation by the redox cycling molecule. Mycobacteria respond by acquiring iron to restore the levels depleted by the prevailing oxidizing conditions, which inadvertently trigger the compensatory acquisition of the metal. This leads to overwhelmed oxidative stress defenses and yet more iron depletion. For organisms that are unable to break out of this pernicious cycle of events, cell death is the inevitable outcome. Hence, aberrant ROS production by a redox cycling bactericidal agent inflicts a plethora of damaging effects on mycobacteria, including the derailment of iron homeostasis.

The Struggle to End a Millennia-Long Pandemic: Novel Candidate and Repurposed Drugs for the Treatment of Tuberculosis

This article provides an encompassing review of the current pipeline of putative and developed treatments for tuberculosis, including multidrug-resistant strains. The review has organized each compound according to its site of activity. To provide context, mention of drugs within current recommended treatment regimens is made, thereafter followed by discussion on recently developed and upcoming molecules at established and novel targets. The review is designed to provide a clinically applicable understanding of the compounds that are deemed most currently relevant, including those already under clinical study and those that have shown promising pre-clinical results. An extensive review of the efficacy and safety data for key contemporary drugs already incorporated into treatment regimens, such as bedaquiline, pretomanid, and linezolid, is provided. The three levels of the bacterial cell wall (mycolic acid, arabinogalactan, and peptidoglycan layers) are highlighted and important compounds designed to target each layer are delineated. Amongst others, the highly optimistic and potent anti-mycobacterial activity of agents such as BTZ-043, PBTZ 169, and OPC-167832 are emphasized. The evolving spectrum of oxazolidinones, such as sutezolid, delpazolid, and TBI-223, all aiming to exceed the efficacy achieved with linezolid yet offer a safer alternative to the potential toxicity, are reviewed. New and exciting prospective agents with novel mechanisms of impact against TB, including 3-aminomethyl benzoxaboroles and telacebec, are underscored. We describe new diaryloquinolines in development, striving to build on the immense success of bedaquiline. Finally, we discuss some of these compounds that have shown encouraging additive or synergistic benefit when used in combination, providing some promise for the future in treating this ancient scourge.

Superior Efficacy of a TBI-166, Bedaquiline, and Pyrazinamide Combination Regimen in a Murine Model of Tuberculosis

TBI-166, derived from riminophenazine analogues, shows more potent anti-TB activity than clofazimine and is being assessed against tuberculosis (TB) in a phase IIa clinical trial in China. Preclinical regimen studies containing TBI-166 will support the phase IIb clinical trials of TBI-166. In the present study, we compared the efficacy in three murine TB models of an all-oral drug-resistant TB drug regimen of TBI-166 with bedaquiline (BDQ) and pyrazinamide (PZA) with the first-line regimen of isoniazid (INH) with rifampin (RFP) and PZA (HRZ regimen), the most effective reported TBI-166-containing regimen of TBI-166 with BDQ and linezolid (LZD), and the Nix-TB clinical trial regimen of BDQ with pretomanid and LZD (BPaL regimen). In the C3HeB/FeJ murine TB model, for the TBI-166+BDQ+PZA regimen, the lungs of mice were culture negative at 4 weeks, and there were no relapses at 8 weeks of treatment. The reduction in bacterial burden and relapse rate were greater than those of the HRZ regimen and the TBI-166+BDQ+LZD regimen. Compared with the BPaL regimen, the TBI-166+BDQ+PZA regimen had similar or stronger early bactericidal activity, bactericidal activity, and sterilizing activity in the BALB/c murine TB model. The bacterial burden in the TBI-166+BDQ+PZA regimen group decreased significantly more than that in the BPaL regimen group and was almost or totally relapse free (<13.33% after 8 weeks). In conclusion, oral short-course three-drug regimens, including TBI-166 with high efficacy, were identified. The TBI-166+BDQ+PZA regimen is recommended for further study in a TBI-166 phase IIb clinical trial.

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.

Design, Synthesis, and Biological Evaluation of Pyrrole-2-carboxamide Derivatives as Mycobacterial Membrane Protein Large 3 Inhibitors for Treating Drug-Resistant Tuberculosis

In this work, pyrrole-2-carboxamides were designed with a structure-guided strategy based on the crystal structure of MmpL3 and a pharmacophore model. The structure-activity relationship studies revealed that attaching phenyl and pyridyl groups with electron-withdrawing substituents to the pyrrole ring and attaching bulky substituents to the carboxamide greatly improved anti-TB activity. Most compounds showed potent anti-TB activity (MIC < 0.016 μg/mL) and low cytotoxicity (IC50 > 64 μg/mL). Compound 32 displayed excellent activity against drug-resistant tuberculosis, good microsomal stability, almost no inhibition of the hERG K+ channel, and good in vivo efficacy. Furthermore, the target of the pyrrole-2-carboxamides was identified by measuring their potency against M. smegmatis expressing wild-type and mutated variants of the mmpL3 gene from M. tuberculosis (mmpL3tb) and determining their effect on mycolic acid biosynthesis using a [14C] acetate metabolic labeling assay. The present study provides new MmpL3 inhibitors that are promising anti-TB agents.

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.

Identification of thiophene-benzenesulfonamide derivatives for the treatment of multidrug-resistant tuberculosis

A series of thiophene-benzenesulfonamide derivatives was designed and synthesized by exploring the structure-activity relationship of lead compounds 2,3-disubstituted thiophenes 25a and 297F as antituberculosis agents, which displayed potent antimycobacterial activity against drug-susceptible and clinically isolated drug-resistant tuberculosis. In particular, compound 17b, which had improved activity (minimum inhibitory concentration of 0.023 μg/mL) compared with the lead compounds, displayed good intracellular antimycobacterial activity in macrophages with a reduction of 1.29 log10 CFU. A druggability evaluation indicated that compound 17b had favorable hepatocyte stability, low cytotoxicity, and low hERG channel inhibition. Moreover, compound 17b exhibited modest in vivo efficacy in an acute mouse model of tuberculosis. In addition, the molecular docking study elucidated the binding mode of compound 17b in the active site of DprE1. Therefore, compound 17b may be a promising antituberculosis lead for further research.

Sudapyridine (WX-081), a Novel Compound against Mycobacterium tuberculosis

Bedaquiline (BDQ) was historically listed by the World Health Organization (WHO) in 2018 as the preferred option for rifampin-resistant tuberculosis (RR-TB) and multidrug-resistant tuberculosis (MDR-TB). However, when there is no other effective regimen, the side effects and weaknesses of BDQ limit its use of MDR-TB. There is a black box warning in the package insert of BDQ to warn patients and health care professionals that this drug may increase the risk of unexplained mortality and QT prolongation, which may lead to abnormal and potentially fatal cardiac rhythm. In addition, the phenomenon of elevated liver enzymes in clinical trials of BDQ is a potential sign of hepatotoxicity. Therefore, it is still a medical need to develop new compounds with better safety profiles, patient compliance, affordability, and the ability to retain the efficacy of BDQ. After extensive lead generation and optimization, a new analog, sudapyridine (WX-081), was selected as a potential new antituberculosis candidate to move into clinical trials. Here, we evaluated WX-081's overall preclinical profile, including efficacy, pharmacokinetics, and toxicology. The in vitro activity of WX-081 against drug-sensitive and drug-resistant tuberculosis was comparable to that of BDQ, and there was comparable efficacy between WX-081 and BDQ in both acute and chronic mouse tuberculosis models using low-dose aerosol infection. Moreover, WX-081 improved pharmacokinetic parameters and, more importantly, had no adverse effects on blood pressure, heart rate, or qualitative ECG parameters from nonclinical toxicology studies. WX-081 is under investigation in a phase 2 study in patients. IMPORTANCE This study is aimed at chemotherapy for multidrug-resistant tuberculosis (MDR-TB), mainly to develop new anti-TB drugs to kill Mycobacterium tuberculosis, a microorganism with strong drug resistance. In this study, the structure of a potent antituberculosis compound, bedaquiline (BDQ), was optimized to generate a new compound, sudapyridine (WX-081). This experiment showed that its efficacy was similar to that of BDQ, its cardiotoxicity was lower, and it had good kinetic characteristics. This compound will certainly achieve significant results in the control and treatment of tuberculosis in the future.

Design, synthesis and biological evaluation of nitrofuran-1,3,4-oxadiazole hybrids as new antitubercular agents

Three series of novel nitrofuran-1,3,4-oxadiazole hybrids were designed and synthesized as new anti-TB agents. The structure activity relationship study indicated that the linkers and the substituents on the oxadiazole moiety greatly influence the activity, and the substituted benzenes are more favoured than the cycloalkyl or heterocyclic groups. Besides, the optimal compound in series 2 was active against both MTB H₃₇Rv strain and MDR-MTB 16883 clinical isolate and also displayed low cytotoxicity, low inhibition of hERG and good oral PK, indicating its promising potential to be a lead for further structural modifications.

Targeting the cytochrome bc1 complex for drug development in M. tuberculosis: review

The terminal oxidases of the oxidative phosphorylation pathway play a significant role in the survival and growth of M. tuberculosis, targeting these components lead to inhibition of M. tuberculosis. Many drug candidates targeting various components of the electron transport chain in M. tuberculosis have recently been discovered. The cytochrome bc₁-aa₃ supercomplex is one of the most important components of the electron transport chain in M. tuberculosis, and it has emerged as the novel target for several promising candidates. There are two cryo-electron microscopy structures (PDB IDs: 6ADQ and 6HWH) of the cytochrome bc₁-aa₃ supercomplex that aid in the development of effective and potent inhibitors for M. tuberculosis. In recent years, a number of potential candidates targeting the QcrB subunit of the cytochrome bc₁ complex have been developed. In this review, we describe the recently identified inhibitors that target the electron transport chain's terminal oxidase enzyme in M. tuberculosis, specifically the QcrB subunit of the cytochrome bc₁ complex.

In vitro and in vivo activity of oxazolidinone candidate OTB-658 against Mycobacterium tuberculosis

In this work, we assess anti-tuberculosis activity of OTB-658 in vitro and in vivo. In vitro, OTB-658 showed bacteriostatic effectiveness with a lower minimum inhibitory concentration than linezolid against Mycobacterium tuberculosis. The minimal bactericidal concentrations and time-kill curves for OTB-658 indicated similar inhibition activity to that of linezolid. OTB-658 entered macrophages to inhibit of M. tuberculosis growth. OTB-658 had a low mutant frequency (10^-8), which would prevent drug-resistant mutations from emerging in combination regimens. In vivo, OTB-658 reduced colony-forming unit counts in the lungs and slightly inhibited bacterial growth in the spleen in the early stage and steady state in acute and chronic murine TB models. These results support the preclinical evaluation of OTB-658 and further clinical trials in China.

In Vitro Profiling of Antitubercular Compounds by Rapid, Efficient, and Nondestructive Assays Using Autoluminescent Mycobacterium tuberculosis

Anti-infective drug discovery is greatly facilitated by the availability of in vitro assays that are more proficient at predicting the preclinical success of screening hits. Tuberculosis (TB) drug discovery is hindered by the relatively slow growth rate of Mycobacterium tuberculosis and the use of whole-cell-based in vitro assays that are inherently time-consuming, and for these reasons, rapid, noninvasive bioluminescence-based assays have been widely used in anti-TB drug discovery and development. In this study, in vitro assays that employ autoluminescent M. tuberculosis were optimized to determine MIC, minimum bactericidal concentration (MBC), time-kill curves, activity against macrophage internalized M. tuberculosis (90% effective concentration [EC₉₀]), and postantibiotic effect (PAE) to provide rapid and dynamic biological information. Standardization of the luminescence-based MIC, MBC, time-kill, EC_90, and PAE assays was accomplished by comparing results of established TB drugs and two ClpC1-targeting TB leads, ecumicin and rufomycin, to those obtained from conventional assays and/or to previous studies. Cumulatively, the use of the various streamlined luminescence-based in vitro assays has reduced the time for comprehensive in vitro profiling (MIC, MBC, time-kill, EC_90, and PAE) by 2 months. The luminescence-based in vitro MBC and EC₉₀ assays yield time and concentration-dependent kill information that can be used for pharmacokinetic-pharmacodynamic (PK-PD) modeling. The MBC and EC₉₀ time-kill graphs revealed a significantly more rapid bactericidal activity for ecumicin than rufomycin. The PAEs of both ecumicin and rufomycin were comparable to that of the first-line TB drug rifampin. The optimization of several nondestructive, luminescence-based TB assays facilitates the in vitro profiling of TB drug leads in an efficient manner.

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).

Clofazimine as a Treatment for Multidrug-Resistant Tuberculosis: A Review

Multidrug-resistant tuberculosis (MDR-TB) is an infectious disease caused by Mycobacterium tuberculosis which is resistant to at least isoniazid and rifampicin. This disease is a worldwide threat and complicates the control of tuberculosis (TB). Long treatment duration, a combination of several drugs, and the adverse effects of these drugs are the factors that play a role in the poor outcomes of MDR-TB patients. There have been many studies with repurposed drugs to improve MDR-TB outcomes, including clofazimine. Clofazimine recently moved from group 5 to group B of drugs that are used to treat MDR-TB. This drug belongs to the riminophenazine class, which has lipophilic characteristics and was previously discovered to treat TB and approved for leprosy. This review discusses the role of clofazimine as a treatment component in patients with MDR-TB, and the drug’s properties. In addition, we discuss the efficacy, safety, and tolerability of clofazimine for treating MDR-TB. This study concludes that the clofazimine-containing regimen has better efficacy compared with the standard one and is also well-tolerated. Clofazimine has the potential to shorten the duration of MDR-TB treatment.

Chemical Classes Presenting Novel Antituberculosis Agents Currently in Different Phases of Drug Development: A 2010-2020 Review

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a curable airborne disease currently treated using a drug regimen consisting of four drugs. Global TB control has been a persistent challenge for many decades due to the emergence of drug-resistant Mtb strains. The duration and complexity of TB treatment are the main issues leading to treatment failures. Other challenges faced by currently deployed TB regimens include drug-drug interactions, miss-matched pharmacokinetics parameters of drugs in a regimen, and lack of activity against slow replicating sub-population. These challenges underpin the continuous search for novel TB drugs and treatment regimens. This review summarizes new TB drugs/drug candidates under development with emphasis on their chemical classes, biological targets, mode of resistance generation, and pharmacokinetic properties. As effective TB treatment requires a combination of drugs, the issue of drug-drug interaction is, therefore, of great concern; herein, we have compiled drug-drug interaction reports, as well as efficacy reports for drug combinations studies involving antitubercular agents in clinical development.

Discovery of Novel Thiophene-arylamide Derivatives as DprE1 Inhibitors with Potent Antimycobacterial Activities

In this study, we report the design and synthesis of a series of novel thiophene-arylamide compounds derived from the noncovalent decaprenylphosphoryl-β-d-ribose 2'-epimerase (DprE1) inhibitor TCA1 through a structure-based scaffold hopping strategy. Systematic optimization of the two side chains flanking the thiophene core led to new lead compounds bearing a thiophene-arylamide scaffold with potent antimycobacterial activity and low cytotoxicity. Compounds 23j, 24f, 25a, and 25b exhibited potent in vitro activity against both drug-susceptible (minimum inhibitory concentration (MIC) = 0.02-0.12 μg/mL) and drug-resistant (MIC = 0.031-0.24 μg/mL) tuberculosis strains while retaining potent DprE1 inhibition (half maximal inhibitory concentration (IC₅₀) = 0.2-0.9 μg/mL) and good intracellular antimycobacterial activity. In addition, these compounds showed good hepatocyte stability and low inhibition of the human ether-à-go-go related gene (hERG) channel. The representative compound 25a with acceptable pharmacokinetic property demonstrated significant bactericidal activity in an acute mouse model of tuberculosis. Moreover, the molecular docking study of template compound 23j provides new insight into the discovery of novel antitubercular agents targeting DprE1.

Design, synthesis and biological activity of N-(amino)piperazine-containing benzothiazinones against Mycobacterium tuberculosis

A series of novel benzothiazinone derivatives containing a N-(amino)piperazine moiety, based on the structure of WAP-1902 discovered in our lab, were designed and synthesized as new anti-TB agents. Many of the compounds exhibited excellent in vitro activity against both drug-sensitive MTB strain H37Rv and multidrug-resistant clinical isolates (MIC: < 0.016 μg/mL), and good safety index (CC₅₀: >64 μg/mL). Especially compound 1o displayed low hERG cardiac toxicity and acceptable oral pharmacokinetic profiles, indicating its promising potential to be a lead compound for future antitubercular drug discovery.

Activity of Clofazimine and TBI-166 against Mycobacterium tuberculosis in Different Administration Intervals in Mouse Tuberculosis Models

Clofazimine (CLO) and TBI-166 belong to the riminophenazine class of antimicrobial agent. TBI-166 exhibited promising antituberculosis activity in vitro and in animal models and is currently under phase I clinical development for the treatment of tuberculosis in China. To identify an optimal dosing regimen to support further clinical development of TBI-166, the efficacies of CLO and TBI-166 were evaluated in two aerosol infection models utilizing BALB/c and C3HeB/FeJNju mice. TBI-166 and CLO were dosed at 20 mg/kg daily for 2 weeks, followed by QD (once daily), TIW (thrice weekly), and BIW (twice weekly) for an additional 10 weeks at the same dose level. The bactericidal activities of TBI-166 and clofazimine via QD, TIW, and BIW dosing regimens were determined after treatment. Once-daily administration of CLO and TBI-166 appeared to be more efficacious than the two intermittent dosing regimens. Once-daily administration of TBI-166 increased the bactericidal activity by approximately 1 log₁₀ CFU in the lung and spleen compared with TIW or BIW dosing after 12 weeks of treatment, while once-daily administration of CLO increased the bactericidal activity by 1.27 to 1.90 log₁₀ CFU/lung and by 1.61 to 2.22 log₁₀ CFU/spleen in the BALB/c mouse model compared to the intermittent therapies. The differences between QD and TIW and between QD and BIW were significant (P < 0.05). The data suggest that accumulated total doses correlate with the log₁₀ CFU reductions. Therefore, intermittent administration of TBI-166 and CLO should be further evaluated at the same accumulated total doses in preclinical and clinical studies.

Clofazimine: A Promising Inhibitor of Rabies Virus

With an almost 100% mortality rate, rabies virus (RABV) infection is a global concern. Limited post-exposure prophylaxis and lack of an effective treatment necessitate novel antiviral therapies against RABV. Here, using a high-throughput screening (HTS) method developed in our lab, 11 candidates with anti-RABV activity were identified from a library of 767 clinical drugs. Clofazimine (CFZ), an anti-leprosy drug, displayed an EC₅₀ of 2.28 μM, and SI over 967 against RABV. Investigations into the underlying mechanisms revealed that CFZ targeted viral membrane fusion at the early stages of virus replication. Moreover, CFZ and Clofazimine salicylates (CFZS) exhibited elevated survival rates in vivo, compared with the positive control T-705. Thus, this study revealed CFZ as a promising drug against RABV infection.

Bioenergetic Inhibitors: Antibiotic Efficacy and Mechanisms of Action in Mycobacterium tuberculosis

Development of novel anti-tuberculosis combination regimens that increase efficacy and reduce treatment timelines will improve patient compliance, limit side-effects, reduce costs, and enhance cure rates. Such advancements would significantly improve the global TB burden and reduce drug resistance acquisition. Bioenergetics has received considerable attention in recent years as a fertile area for anti-tuberculosis drug discovery. Targeting the electron transport chain (ETC) and oxidative phosphorylation machinery promises not only to kill growing cells but also metabolically dormant bacilli that are inherently more drug tolerant. Over the last two decades, a broad array of drugs targeting various ETC components have been developed. Here, we provide a focused review of the current state of art of bioenergetic inhibitors of Mtb with an in-depth analysis of the metabolic and bioenergetic disruptions caused by specific target inhibition as well as their synergistic and antagonistic interactions with other drugs. This foundation is then used to explore the reigning theories on the mechanisms of antibiotic-induced cell death and we discuss how bioenergetic inhibitors in particular fail to be adequately described by these models. These discussions lead us to develop a clear roadmap for new lines of investigation to better understand the mechanisms of action of these drugs with complex mechanisms as well as how to leverage that knowledge for the development of novel, rationally-designed combination therapies to cure TB.

Activity of Riminophenazines against Mycobacterium tuberculosis: A Review of Studies that Might be Contenders for Use as Antituberculosis Agents

Tuberculosis is one of the leading cause of death in the world, mainly due to the increasing number of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) strains. Factors such as the HIV pandemic contribute further. Also, the ineffectiveness of the chemotherapy in current use increases the mortality rate. Therefore, new and repurposed antituberculosis drugs are urgently needed for the treatment of MDR-TB, and riminophenazines are among those drugs that are being reinvestigated for their potential in the treatment of TB. This review delivers a brief historical account of riminophenazines, their general synthesis, mechanisms of action, and their physicochemical properties. The discussion is limited to those studies that investigated the activity of these compounds as antituberculosis agents. Given their unique properties, this review will be of great significance in giving direction towards the design and development of new riminophenazine analogues.

Handling the Hurdles on the Way to Anti-tuberculosis Drug Development

The global epidemic of tuberculosis (TB) imposes a sustained epidemiologic vigilance and investments in research by governments. Mycobacterium tuberculosis, the main causative agent of TB in human beings, is a very successful pathogen, being the main cause of death in the population among infectious agents. In 2018, ~10 million individuals were contaminated with this bacillus and became ill with TB, and about 1.2 million succumbed to the disease. Most of the success of the M. tuberculosis to linger in the population comes from its ability to persist in an asymptomatic latent state into the host and, in fact, the majority of the individuals are unaware of being contaminated. Even though TB is a treatable disease and is curable in most cases, the treatment is lengthy and laborious. In addition, the rise of resistance to first-line anti-TB drugs elicits a response from TB research groups to discover new chemical entities, preferably with novel mechanisms of action. The pathway to find a new TB drug, however, is arduous and has many barriers that are difficult to overcome. Fortunately, several approaches are available today to be pursued by scientists interested in anti-TB drug development, which goes from massively testing chemical compounds against mycobacteria, to discovering new molecular targets by genetic manipulation. This review presents some difficulties found along the TB drug development process and illustrates different approaches that might be used to try to identify new molecules or targets that are able to impair M. tuberculosis survival.

In vitro and in vivo antimicrobial activities of a novel piperazine-containing benzothiazinones candidate TZY-5-84 against Mycobacterium tuberculosis

A piperazine-containing benzothiazinones lead compound PBTZ169, served as DprE1 inhibitor, displays nanomolar bactericidal activity against Mycobacteria tuberculosis. Here, we systematically evaluate anti-tuberculosis activity of one of PBTZ169 analogues, TZY-5-84, in vitro and in vivo. The MIC value of TZY-5-84 against M. tuberculosis H37Rv ranged from 0.014 to 0.015 mg/L, lower than those of INH, RFP and BDQ. Five susceptible and thirteen drug-resistant clinical isolates were also susceptive to TZY-5-84. It had anti-tuberculosis activity against intracellular bacilli in infected macrophage model. It exhibited its activity in time-dependent manner and against intracellular bacilli in infected macrophage cells. However, the MIC of TZY-5-84 against three laboratory PBTZ169-induced resistant isolates increased four-fold increment compared to that of H37Rv. No antagonism was observed in any combination between TZY-5-84 and seven commonly used anti-tuberculosis drugs in an in vitro checkerboard assay. In murine infection model, TZY-5-84 at lower dosage (12.5 mg/kg) was found to be comparatively efficacious as PBTZ169 at 25 mg/kg. Our research suggests TZY-5-84 can be a promising preclinical candidate for further study on TB treatment.

Novel Antiviral and Antibacterial Activities of Hibiscus schizopetalus

Hibiscus schizopetalus (Dyer) Hook.f. (Malvaceae) is an ornamental plant. The aim was to investigate its antimicrobial and antioxidant activities. In vitro antiviral, antibacterial, and antioxidant activities of the 70% ethanolic extract (Et-E) of the aerial parts of the plant were determined. The Dichloromethane Fraction (DCM-F) and the n-Butanol Fraction (Bu-F) were assessed using Liquid chromatography-mass spectrometry (LC-MS). The DCM-F showed higher antiviral activities against Coxsackie B4 (CoxB4) viruses (IC₅₀ = 64.13 µg/mL) and adenoviruses (IC₅₀ = 54.88 µg/mL) than acyclovir (IC₅₀ = 72.79 µg/mL for CoxB4 viruses; IC₅₀ = 91.92 µg/mL for adenoviruses). The DCM-F showed higher anti-helicobacter pylori activity (MIC = 3.9 µg/mL) than clarithromycin (MIC = 1.95 µg/mL). The DCM-F inhibited Herpes Simplex Virus (HSV) Type I (IC₅₀ = 29.85 µg/mL) and HSV Type II (IC₅₀ = 74.17 µg/mL). The Bu-F showed higher anti-mycobacterial activity (MIC = 7.81 µg/mL) than isoniazid (MIC = 0.24 µg/mL) and higher antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)(MIC = 7.81 µg/mL) than vancomycin (MIC = 3.9 µg/mL). Antioxidant assays included total antioxidant capacity (TAC), 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), 2,2-diphenyl-1-picryl-hydrazyl (DPPH), and iron reducing power. The Bu-F showed the highest antioxidant activity. Chemical profiles were analyzed using HPLC-HR-ESI-MS to identify the metabolites responsible for these biological activities. We identified more than 60 metabolites that belong to anthocyanins, flavonoids, phenolics, terpenes, sterols, and fatty acids. In conclusion, Hibiscusschizopetalus is endowed with metabolites that could be used against viruses and antibiotic-resistant bacteria. They can also be potent antioxidants.

A review of recent advances in anti-tubercular drug development

Tuberculosis is a global threat but in particular affects people from developing countries. It is thought that nearly a third of the population of the world live with its causative bacteria in a dormant form. Although tuberculosis is a curable disease, the chances of cure become slim as the disease becomes multidrug-resistant and the situation gets even worse as the disease becomes extensively drug-resistant. After approximately 5 decades without any new TB drug in the pipeline, there has been some good news in the recent years with the discovery of new drugs such as bedaquiline and delamanid as well as the discovery of new classes of anti-tubercular drugs. Some old drugs such as clofazimine, linezolid and many others which were not previously indicated for tuberculosis have been also repurposed for tuberculosis and they are performing well.

SAR Analysis of Small Molecules Interfering with Energy-Metabolism in Mycobacterium tuberculosis

Tuberculosis remains the world's top infectious killer: it caused a total of 1.5 million deaths and 10 million people fell ill with TB in 2018. Thanks to TB diagnosis and treatment, mortality has been falling in recent years, with an estimated 58 million saved lives between 2000 and 2018. However, the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains is a major concern that might reverse this progress. Therefore, the development of new drugs acting upon novel mechanisms of action is a high priority in the global health agenda. With the approval of bedaquiline, which targets mycobacterial energy production, and delamanid, which targets cell wall synthesis and energy production, the energy-metabolism in Mtb has received much attention in the last decade as a potential target to investigate and develop new antimycobacterial drugs. In this review, we describe potent anti-mycobacterial agents targeting the energy-metabolism at different steps with a special focus on structure-activity relationship (SAR) studies of the most advanced compound classes.

Validation of in-vitro bioassay methods: Application in herbal drug research

This present review described the validation method of in-vitro bioassay for its application in herbal drug research. Seven sequencing steps that can be taken for performing a valid bioassay include: literature survey, sample stability evaluation, Biosystem performance testing, Sample performance evaluation, determination of 50% effective concentration or cytotoxic concentrations, selective index evaluation, and determination of accurate relative potency of sample. Detailed methods and acceptance criteria for each step are described herein. Method calculations of the relative potency of sample using European Pharmacopeia 10.0, 5.3 (2020) were recommended instead of using United States Pharmacopeia 42 (2019). For having reliable data and conclusions, all methods (chemical and bioassay) need to be first validated before any data collection. Absence of any validation method may results in incorrect conclusions and bias.

Discovery of a Conformationally Constrained Oxazolidinone with Improved Safety and Efficacy Profiles for the Treatment of Multidrug-Resistant Tuberculosis

Tuberculosis (TB) remains a serious public health challenge, and the research and development of new anti-TB drugs is an essential component of the global strategy to eradicate TB. In this work, we discovered a conformationally constrained oxazolidinone 19c with improved anti-TB activity and safety profile through a focused lead optimization effort. Compound 19c displayed superior in vivo efficacy in a mouse TB infection model compared to linezolid and sutezolid. The druggability of compound 19c was demonstrated in a panel of assays including microsomal stability, cytotoxicity, cytochrome P450 enzyme inhibition, and pharmacokinetics in animals. Compound 19c demonstrated an excellent safety profile in a battery of safety assays, including mitochondrial protein synthesis, hERG K⁺, hCav1.2, and Nav1.5 channels, monoamine oxidase, and genotoxicity. In a 4 week repeated dose toxicology study in rats, 19c appeared to have less bone marrow suppression than linezolid, which has been a major liability of the oxazolidinone class.

Design, synthesis and antimycobacterial activity of new benzothiazinones inspired by rifampicin/rifapentine

A series of novel benzothiazinone derivatives containing a N-((methylene)amino)piperazine moiety, inspired by rifampicin/rifapentine, were designed and synthesized. Seven compounds 1a and 1e-j show excellent in vitro activity against both drug-sensitive MTB strain H37Rv and drug-resistant clinical isolates (MIC: <0.029-0.110 μM), and accepted selective index (>1100->4000). Compound 1h displays good safety and pharmacokinetic profiles, suggesting its promising potential to be lead compound for future antitubercular drug discovery.