Trends in the discovery of new drugs for Mycobacterium tuberculosis therapy with a glance at resistance

Bedaquiline: An Insight Into its Clinical Use in Multidrug-Resistant Pulmonary Tuberculosis

Every year, the World Health Organization reports 500,000 new cases of drug-resistant tuberculosis (TB), which poses a serious global danger. The increased number of XDR-TB and MDR-TB cases reported worldwide necessitates the use of new therapeutic approaches. The main issues with the antitubercular medications now in use for the treatment of multidrug-resistant tuberculosis are their poor side effect profile, reduced efficacy, and antimicrobial resistance. One possible remedy for these problems is bedaquiline. The need for better treatment strategies is highlighted by the strong minimum inhibitory concentrations that bedaquiline (BDQ), a novel anti-TB medicine, exhibits against both drug-resistant and drug-susceptible TB. Bedaquiline may be able to help with these problems. Bedaquiline is a medication that is first in its class and has a distinct and particular mode of action. Bedaquiline is an ATP synthase inhibitor that is specifically directed against Mycobacterium tuberculosis and some nontuberculous mycobacteria. It is metabolized by CYP3A4. Bedaquiline preclinical investigations revealed intralesional drug biodistribution. The precise intralesional and multi-compartment pharmacokinetics of bedaquiline were obtained using PET bioimaging and high-resolution autoradiography investigations. Reduced CFU counts were observed in another investigation after a 12-week course of therapy. Meta-analyses and systematic reviews of phase II trials on bedaquiline's efficacy in treating drug-resistant tuberculosis in patients reported higher rates of cure, better culture conversion, and lower death rates when taken in conjunction with a background regimen. Here is a thorough medication profile for bedaquiline to aid medical professionals in treating individuals with tuberculosis.

Phages for the treatment of Mycobacterium species

Highly drug-resistant strains are not uncommon among the Mycobacterium genus, with patients requiring lengthy antibiotic treatment regimens with multiple drugs and harmful side effects. This alarming increase in antibiotic resistance globally has renewed the interest in mycobacteriophage therapy for both Mycobacterium tuberculosis complex and non-tuberculosis mycobacteria. With the increasing number of genetically well-characterized mycobacteriophages and robust engineering tools to convert temperate phages to obligate lytic phages, the phage cache against extensive drug-resistant mycobacteria is constantly expanding. Synergistic effects between phages and TB drugs are also a promising avenue to research, with mycobacteriophages having several additional advantages compared to traditional antibiotics due to their different modes of action. These advantages include less side effects, a narrow host spectrum, biofilm penetration, self-replication at the site of infection and the potential to be manufactured on a large scale. In addition, mycobacteriophage enzymes, not yet in clinical use, warrant further studies with their additional benefits for rupturing host bacteria thereby limiting resistance development as well as showing promise in vitro to act synergistically with TB drugs. Before mycobacteriophage therapy can be envisioned as part of routine care, several obstacles must be overcome to translate in vitro work into clinical practice. Strategies to target intracellular bacteria and selecting phage cocktails to limit cross-resistance remain important avenues to explore. However, insight into pathophysiological host-phage interactions on a molecular level and innovative solutions to transcend mycobacteriophage therapy impediments, offer sufficient encouragement to explore phage therapy. Recently, the first successful clinical studies were performed using a mycobacteriophage-constructed cocktail to treat non-tuberculosis mycobacteria, providing substantial insight into lessons learned and potential pitfalls to avoid in order to ensure favorable outcomes. However, due to mycobacterium strain variation, mycobacteriophage therapy remains personalized, only being utilized in compassionate care cases until there is further regulatory approval. Therefore, identifying the determinants that influence clinical outcomes that can expand the repertoire of mycobacteriophages for therapeutic benefit, remains key for their future application.

Virtual Screening Identifies Novel and Potent Inhibitors of Mycobacterium tuberculosis PknB with Antibacterial Activity

Mycobacterium tuberculosis protein kinase B (PknB) is essential to mycobacterial growth and has received considerable attention as an attractive target for novel anti-tuberculosis drug development. Here, virtual screening, validated by biological assays, was applied to select candidate inhibitors of M. tuberculosis PknB from the Specs compound library (www.specs.net). Fifteen compounds were identified as hits and selected for in vitro biological assays, of which three indoles (2, AE-848/42799159; 4, AH-262/34335013; 10, AP-124/40904362) inhibited growth of M. tuberculosis H37Rv with minimal inhibitory concentrations of 6.2, 12.5, and 6.2 μg/mL, respectively. Two compounds, 2 and 10, inhibited M. tuberculosis PknB activity in vitro, with IC₅₀ values of 14.4 and 12.1 μM, respectively, suggesting this to be the likely basis of their anti-tubercular activity. In contrast, compound 4 displayed anti-tuberculosis activity against M. tuberculosis H37Rv but showed no inhibition of PknB activity (IC₅₀ > 128 μM). We hypothesize that hydrolysis of its ethyl ester to a carboxylate moiety generates an active species that inhibits other M. tuberculosis enzymes. Molecular dynamics simulations of modeled complexes of compounds 2, 4, and 10 bound to M. tuberculosis PknB indicated that compound 4 has a lower affinity for M. tuberculosis PknB than compounds 2 and 10, as evidenced by higher calculated binding free energies, consistent with experiment. Compounds 2 and 10 therefore represent candidate inhibitors of M. tuberculosis PknB that provide attractive starting templates for optimization as anti-tubercular agents.

“Upcycling” known molecules and targets for drug-resistant TB

Despite reinvigorated efforts in Tuberculosis (TB) drug discovery over the past 20 years, relatively few new drugs and candidates have emerged with clear utility against drug resistant TB. Over the same period, significant technological advances and learnings around target value have taken place. This has offered opportunities to re-assess the potential for optimization of previously discovered chemical matter against Mycobacterium tuberculosis (M.tb) and for reconsideration of clinically validated targets encumbered by drug resistance. A re-assessment of discarded compounds and programs from the “golden age of antibiotics” has yielded new scaffolds and targets against TB and uncovered classes, for example beta-lactams, with previously unappreciated utility for TB. Leveraging validated classes and targets has also met with success: booster technologies and efforts to thwart efflux have improved the potential of ethionamide and spectinomycin classes. Multiple programs to rescue high value targets while avoiding cross-resistance are making progress. These attempts to make the most of known classes, drugs and targets complement efforts to discover new chemical matter against novel targets, enhancing the chances of success of discovering effective novel regimens against drug-resistant TB.

Investigation of quinolone-tethered aminoguanidine as novel antibacterial agents

A recent study identified quinolone-based thiosemicarbazone with an MIC₉₀ value of 2 µM against Mycobacterium tuberculosis (Mtb). Herein, we report further optimization of the previous hit, which led to the discovery of quinolone-tethered aminoguanidine molecules with generally good antitubercular activity. Compounds 7f and 8e emerged as the hits of the series with submicromolar antitubercular activity, exhibiting MIC₉₀ values of 0.49/0.90 and 0.49/0.60 µM, respectively, in the 7H9 CAS GLU Tx medium. This shows a fivefold increase in antitubercular activity compared to the previous study. Target compounds were also screened against ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens. However, the series generally exhibited poor antibacterial activities, with only compounds 8d and 8e demonstrating >50% growth inhibition of Staphylococcus aureus and Pseudomonas aeruginosa at 32 µg/ml. The compounds displayed selective antitubercular activity as they showed no cytotoxicity effects against two noncancerous human cell lines. In silico studies predict 7f to have good solubility, no inhibitory effect on cytochrome P450 isoenzymes, and to be a non-pan-assay interfering compound.

A review on enzyme complexes of electron transport chain from Mycobacterium tuberculosis as promising drug targets

Energy metabolism is a universal process occurring in all life forms. In Mycobacterium tuberculosis (Mtb), energy production is carried out in two possible ways, oxidative phosphorylation (OxPhos) and substrate-level phosphorylation. Mtb is an obligate aerobic bacterium, making it dependent on OxPhos for ATP synthesis and growth. Mtb inhabits varied micro-niches during the infection cycle, outside and within the host cells, which alters its primary metabolic pathways during the pathogenesis. In this review, we discuss cellular respiration in the context of the mechanism and structural importance of the proteins and enzyme complexes involved. These protein-protein complexes have been proven to be essential for Mtb virulence as they aid the bacteria's survival during aerobic and hypoxic conditions. ATP synthase, a crucial component of the electron transport chain, has been in the limelight, as a prominent drug target against tuberculosis. Likewise, in this review, we have explored other protein-protein complexes of the OxPhos pathway, their functional essentiality, and their mechanism in Mtb's diverse lifecycle. The review summarises crucial target proteins and reported inhibitors of the electron transport chain pathway of Mtb.

Tuberculosis challenges: Resistance, co-infection, diagnosis, and treatment

Early diagnosis of tuberculosis (TB), followed by effective treatment, is the cornerstone of global TB control efforts. An estimated 3 million cases of TB remain undetected each year. Early detection and effective management of TB can prevent severe disease and reduce mortality and transmission. Intrinsic and acquired drug resistance of Mycobacterium tuberculosis (MTB) severely restricted the anti-TB therapeutic options, and public health policies are required to preserve the new medications to treat TB. In addition, TB and HIV frequently accelerate the progression of each other, and one disease can enhance the other effect. Overall, TB-HIV co-infections show an adverse bidirectional interaction. For HIV-infected patients, the risk of developing TB disease is approximately 22 times higher than for persons with a protective immune response. Analysis of the current TB challenges is critical to meet the goals of the end TB strategy and can go a long way in eradicating the disease. It provides opportunities for global TB control and demonstrates the efforts required to accelerate eliminating TB. This review will discuss the main challenges of the TB era, including resistance, co-infection, diagnosis, and treatment.

Protein O-mannosyltransferase Rv1002c contributes to low cell permeability, biofilm formation in vitro, and mycobacterial survival in mice

Mycobacterium tuberculosis (M. tuberculosis) Rv1002c encodes the protein O-mannosyltransferase (PMT), which catalyzes the transfer of mannose to serine or threonine residues of proteins. We explored the function of PMT in vitro and in vivo. Rv1002c protein was heterogeneously overexpressed in nonpathogenic Mycobacterium smegmatis (named as MS_Rv1002c). A series of trials including mass spectrometry, transmission electron microscope, biofilm formation and antibiotics susceptibility were performed to explore the function of PMT on bacterial survival in vitro. Mouse experiments were carried out to evaluate the virulence of PMT in vivo. PMT decreased the cell envelope permeability and promoted microbial biofilm formation. PMT enhanced the mycobacterial survival in vivo and inhibited the release of pro-inflammatory cytokines in serum. The function might be associated with an increased abundance of some mannoproteins in culture filtrate (CF). PMT is likely to be involved in mycobacterial survival both in vivo and in vitro due to increasing the mannoproteins abundance in CF.

Structure-Based Virtual Screening of Benzaldehyde Thiosemicarbazone Derivatives against DNA Gyrase B of Mycobacterium tuberculosis

Emergence of antibiotic-resistant Mycobacterium tuberculosis (M. tuberculosis) restricts the availability of drugs for the treatment of tuberculosis, which leads to the increased morbidity and mortality of the disease worldwide. There are many intrinsic and extrinsic factors that have been reported for the resistance mechanism. To overcome such mechanisms, chemically synthesized benzaldehyde thiosemicarbazone derivatives were screened against M. tuberculosis to find potential inhibitor for tuberculosis. Such filtering process resulted in compound 13, compound 21, and compound 20 as the best binding energy compounds against DNA gyrase B, an important protein in the replication process. The ADMET prediction has shown the oral bioavailability of the novel compounds.

Mechanism of Action, Resistance, Synergism, and Clinical Implications of Delamanid Against Multidrug-Resistant Mycobacterium tuberculosis

Multidrug-resistant (MDR) isolates of Mycobacterium tuberculosis (MTB) remain a primary global threat to the end of tuberculosis (TB) era. Delamanid (DLM) is a nitro-dihydro-imidazooxazole derivative utilized to treat MDR-TB. DLM has distinct mechanism of action, inhibiting methoxy- and keto-mycolic acid (MA) synthesis through the F420 coenzyme mycobacteria system and generating nitrous oxide. While DLM resistance among MTB strains is uncommon, there are increasing reports in Asia and Europe, and such resistance will prolong the treatment courses of patients infected with MDR-TB. In this review, we address the antimycobacterial properties of DLM, report the global prevalence of DLM resistance, discuss the synergism of DLM with other anti-TB drugs, and evaluate the documented clinical trials to provide new insights into the clinical use of this antibiotic.

3D host cell and pathogen-based bioassay development for testing anti-tuberculosis (TB) drug response and modeling immunodeficiency

Tuberculosis (TB) is a global health threat that affects 10 million people worldwide. Human Immunodeficiency Virus (HIV) remains one of the major contributors to the reactivation of asymptomatic latent tuberculosis (LTBI). Over the recent years, there has been a significant focus in developing in-vitro 3D models mimicking early events of Mycobacterium tuberculosis (Mtb) pathogenesis, especially formation of the granuloma. However, these models are low throughput and require extracellular matrix. In this article, we report the generation of a matrix-free 3D model, using THP-1 human monocyte/macrophage cells and mCherry-expressing Mycobacterium bovis BCG (Bacilli Camille Guérin), henceforth referred as 3D spheroids, to study the host cell-bacterial interactions. Using mCherry-intensity-based tracking, we monitored the kinetics of BCG growth in the 3D spheroids. We also demonstrate the application of the 3D spheroids for testing anti-TB compounds such as isoniazid (INH), rifampicin (RIF), as well as a host-directed drug, everolimus (EVR) as single and combinational treatments. We further established a dual infection 3D spheroid model by coinfecting THP-1 macrophages with BCG mCherry and pseudotype HIV. In this HIV-TB co-infection model, we found an increase in BCG mCherry growth within the 3D spheroids infected with HIV pseudotype. The degree of disruption of the granuloma was proportional to the virus titers used for co-infection. In summary, this 3D spheroid assay is an useful tool to screen anti-TB response of potential candidate drugs and can be adopted to model HIV-TB interactions.

Evaluating the Frequency of Resistance to Pyrazinamide Among Drug-resistant Strains of Mycobacterium tuberculosis in Isfahan, Iran

Background: Pyrazinamide is one of the most important first-line medications for the treatment of tuberculosis and an alternative intake for MDR-TB and XDR-TB patients. Objectives: The purpose of this study was to evaluate resistance to pyrazinamide in the isolates resistant to the Mycobacterium tuberculosis drug in patients in the city of Isfahan. Methods: In this study, the drug susceptibility test was performed with pyrazinamide using the proportion method and PZA assay on 47 isolates resistant to Mycobacterium tuberculosis. Then, the mutations of the pncA and rpsA genes of the isolates resistant to pyrazinamide were evaluated by the sequencing method. Results: According to the proportion method, 19 cases were resistant to pyrazinamide, 16 of which had mutations in their pncA and rpsA genes. Besides, five new mutations were recorded, and three isolates lacked mutations in the mentioned genes. Conclusions: Pyrazinamide resistance is high in MDR-TB and INH mono-resistant isolates. Therefore, evaluating the susceptibility to pyrazinamide in patients with MDR-TB before the initiation of treatment with pyrazinamide is considered essential.

Performance of the MeltPro MTB Assays in the Diagnosis of Drug-Resistant Tuberculosis Using Formalin-Fixed, Paraffin-Embedded Tissues

OBJECTIVES

The MeltPro MTB assays for detection of resistance to antituberculosis (TB) drugs perform well in genotypic drug susceptibility testing (DST) of clinical samples, but their effectiveness with formalin-fixed, paraffin-embedded (FFPE) tissues is unknown.

METHODS

FFPE tissues were obtained from 334 patients with TB. Susceptibility to rifampicin (RIF), isoniazid (INH), and fluoroquinolones was examined using the MeltPro MTB assays, with Xpert MTB/RIF (Xpert) and/or phenotypic DST (pDST) results as references. Samples with discordant results were analyzed by multiplex polymerase chain reaction-targeted amplicon sequencing (MTA-seq).

RESULTS

With pDST as the reference, the MeltPro MTB assays sensitivity for RIF, INH, levofloxacin (LVX), and moxifloxacin (MXF) was 95.00%, 96.00%, 100%, and 100%, respectively, and the specificity was 95.15%, 95.92%, 94.69%, and 89.92%, respectively. Concordance was 99.08% between the MeltPro MTB and Xpert (κ = 0.956) for RIF and 95.12% (κ = 0.834), 95.93% (κ = 0.880), 95.12% (κ = 0.744), and 90.24% (κ = 0.367) between the MeltPro MTB and pDST for RIF, INH, LVX, and MXF, respectively. MTA-seq confirmed the discordancy between the MeltPro MTB and pDST for 26 (89.66%) of 29 samples.

CONCLUSIONS

The MeltPro MTB assays rapidly and efficiently predict Mycobacterium tuberculosis resistance to the main first- and second-line anti-TB drugs in FFPE tissues.

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.

Bedaquiline: Current status and future perspectives

The development of drug-resistant tuberculosis (TB) is a major threat worldwide. Based on World Health Organization (WHO) reports, it is estimated that more than 500 000 new cases of drug-resistant TB occur annually. In addition, there are alarming reports of increasing multidrug-resistant TB (MDR-TB) and the emergence of extensively drug-resistant TB (XDR-TB) from different countries of the world. Therefore, new options for TB therapy are required. Bedaquiline (BDQ), a novel anti-TB drug, has significant minimum inhibitory concentrations (MICs) both against drug-susceptible and drug-resistant TB. Moreover, BDQ was recently approved for therapy of MDR-TB. The current narrative review summarises the available data on BDQ resistance, describes its antimicrobial properties, and provides new perspectives on clinical use of this novel anti-TB agent.

Computational exploration and anti-mycobacterial activity of potential inhibitors of Mycobacterium tuberculosis acetyl coenzyme A carboxylase as anti-tubercular agents

Acetyl Coenzyme A Carboxylase (AccD6) is a homodimeric protein which is involved in the carboxylation of acetyl coenzyme A to produce malonyl coenzyme A, which plays an important role in the biosynthesis of fatty acid chain. However, studies suggest that AccD6 in combination with AccA3 produces malonyl co-A. Certain herbicides are known to inhibit plant ACC. Among these herbicides, haloxyfop was found to inhibit AccD6 at IC50 of 21.1 ± 1 µM. In this study, we have performed molecular docking of the Maybridge database consisting of ~55,000 compounds in the active site of the protein with haloxyfop as a reference molecule, followed by molecular dynamics study and biological activity determination of prioritized compounds. Out of the nine compounds selected for biological evaluation, three compounds - CD07230, HTS08529 and KM08871 - were found to exhibit anti-mycobacterial activity.

Weighted Gene Co-Expression Network Analysis Identifies Key Modules and Hub Genes Associated with Mycobacterial Infection of Human Macrophages

Tuberculosis (TB) is still a leading cause of death worldwide. Treatments remain unsatisfactory due to an incomplete understanding of the underlying host–pathogen interactions during infection. In the present study, weighted gene co-expression network analysis (WGCNA) was conducted to identify key macrophage modules and hub genes associated with mycobacterial infection. WGCNA was performed combining our own transcriptomic results using Mycobacterium aurum-infected human monocytic macrophages (THP1) with publicly accessible datasets obtained from three types of macrophages infected with seven different mycobacterial strains in various one-to-one combinations. A hierarchical clustering tree of 11,533 genes was built from 198 samples, and 47 distinct modules were revealed. We identified a module, consisting of 226 genes, which represented the common response of host macrophages to different mycobacterial infections that showed significant enrichment in innate immune stimulation, bacterial pattern recognition, and leukocyte chemotaxis. Moreover, by network analysis applied to the 74 genes with the best correlation with mycobacteria infection, we identified the top 10 hub-connecting genes: NAMPT, IRAK2, SOCS3, PTGS2, CCL20, IL1B, ZC3H12A, ABTB2, GFPT2, and ELOVL7. Interestingly, apart from the well-known Toll-like receptor and inflammation-associated genes, other genes may serve as novel TB diagnosis markers and potential therapeutic targets.

Mycobacteriophages as Potential Therapeutic Agents against Drug-Resistant Tuberculosis

The current emergence of multi-, extensively-, extremely-, and total-drug resistant strains of Mycobacterium tuberculosis poses a major health, social, and economic threat, and stresses the need to develop new therapeutic strategies. The notion of phage therapy against bacteria has been around for more than a century and, although its implementation was abandoned after the introduction of drugs, it is now making a comeback and gaining renewed interest in Western medicine as an alternative to treat drug-resistant pathogens. Mycobacteriophages are genetically diverse viruses that specifically infect mycobacterial hosts, including members of the M. tuberculosis complex. This review describes general features of mycobacteriophages and their mechanisms of killing M. tuberculosis, as well as their advantages and limitations as therapeutic and prophylactic agents against drug-resistant M. tuberculosis strains. This review also discusses the role of human lung micro-environments in shaping the availability of mycobacteriophage receptors on the M. tuberculosis cell envelope surface, the risk of potential development of bacterial resistance to mycobacteriophages, and the interactions with the mammalian host immune system. Finally, it summarizes the knowledge gaps and defines key questions to be addressed regarding the clinical application of phage therapy for the treatment of drug-resistant tuberculosis.

A Glutamine Insertion at Codon 432 of RpoB Confers Rifampicin Resistance in Mycobacterium tuberculosis

Tuberculosis (TB) is an infectious respiratory disease caused by Mycobacterium tuberculosis and one of the top 10 causes of death worldwide. Treating TB is challenging; successful treatment requires a long course of multiple antibiotics. Rifampicin (RIF) is a first-line drug for treating TB, and the development of RIF-resistant M. tuberculosis makes treatment even more difficult. To determine the mechanism of RIF resistance in these strains, we searched for novel mutations by sequencing. Four isolates, CDC-1, CDC-2, CDC-3, and CDC-4, had high-level RIF resistance and unique mutations encoding RpoB G¹⁵⁸R, RpoB V¹⁶⁸A, RpoB S¹⁸⁸P, and RpoB Q⁴³²insQ, respectively. To evaluate their correlation with RIF resistance, plasmids carrying rpoB genes encoding these mutant proteins were transfected into the H₃₇Rv reference strain. The plasmid complementation of RpoB indicated that G¹⁵⁸R, V¹⁶⁸A, and S¹⁸⁸P did not affect the MIC of RIF. However, the MIC of RIF was increased in H₃₇Rv carrying RpoB Q⁴³²insQ. To confirm the correlation between RIF resistance and Q⁴³²insQ, we cloned an rpoB fragment carrying the insertion (encoding RpoB Q⁴³²insQ) into H₃₇Rv by homologous recombination using a suicide vector. All replacement mutants expressing RpoB Q⁴³²insQ were resistant to RIF (MIC > 1 mg/L). These results indicate that RpoB Q⁴³²insQ causes RIF resistance in M. tuberculosis.

Simple and sensitive method for the analysis of 14 antituberculosis drugs using liquid chromatography/tandem mass spectrometry in human plasma

Monitoring plasma concentration and adjusting doses of antituberculosis (TB) drugs are beneficial for improving responses to drug treatment and avoiding adverse drug reactions. A simple and sensitive liquid chromatography/tandem mass spectrometry method was developed to measure the plasma concentrations of 14 anti-TB drugs: ethambutol, isoniazid, pyrazinamide, levofloxacin, gatifloxacin, moxifloxacin, prothionamide, linezolid, rifampin, rifapentine, rifabutin, cycloserine, p-aminosalicylic acid, and clofazimine.

METHODS

Human plasma was precipitated by acetonitrile and was subsequently separated by an AQ-C18 column with a gradient elution. Drug concentrations were determined using multiple reaction monitoring in positive ion electrospray ionization mode. According to pharmacokinetic data of patients, the peak concentration ranges and the timing of blood collection were determined.

RESULTS

Intra- and interday precision was < 14.8%. Linearity, accuracy, extraction recovery, and matrix effect were acceptable for each drug. The stability of the method satisfied different storage conditions.

CONCLUSIONS

The method allowed the sensitive and reproducible determination of 14 frequently used anti-TB drugs which has already been of benefit for some TB patients.

Drug-Resistant Tuberculosis 2020: Where We Stand

The control of tuberculosis (TB) is hampered by the emergence of multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb) strains, defined as resistant to at least isoniazid and rifampin, the two bactericidal drugs essential for the treatment of the disease. Due to the worldwide estimate of almost half a million incident cases of MDR/rifampin-resistant TB, it is important to continuously update the knowledge on the mechanisms involved in the development of this phenomenon. Clinical, biological and microbiological reasons account for the generation of resistance, including: (i) nonadherence of patients to their therapy, and/or errors of physicians in therapy management, (ii) complexity and poor vascularization of granulomatous lesions, which obstruct drug distribution to some sites, resulting in resistance development, (iii) intrinsic drug resistance of tubercle bacilli, (iv) formation of non-replicating, drug-tolerant bacilli inside the granulomas, (v) development of mutations in Mtb genes, which are the most important molecular mechanisms of resistance. This review provides a comprehensive overview of these issues, and releases up-dated information on the therapeutic strategies recently endorsed and recommended by the World Health Organization to facilitate the clinical and microbiological management of drug-resistant TB at the global level, with attention also to the most recent diagnostic methods.

Synthesis and antimicrobial evaluation of piperic acid amides and their lower homologues

Seven piperic acid amides along with their lower homologs (12) were synthesized using HATU-DIPEA coupling reagent. All the synthesized derivatives were evaluated for their antibacterial activities against Staphylococcus aureus, Pseudomonas aeruginosa, and vancomycin-resistant P. aeruginosa. They were found to be more active on P. aeruginosa than on S. aureus. However, they did not exhibit potent activity on Vancomycin resistant P. aeruginosa. Among the tested compounds, methylenedioxycinnamic acid amide of anthranilic acid (MDCA-AA, 2a) was found to be most active against S. aureus with MIC of 3.125 μg/ml. The PAS and INH amides of piperic acid were screened against Mycobacterium tuberculosis H37R_a strain. They were found to be most active among all the tested compounds but were found to be less active than the standard drug, isoniazid.

Characterization of Arabinosyl Transfer Reactions in the Biosynthesis of Mycobacterial Cell Envelope (Lipo)Polysaccharides

D-Arabinofuranose is a major glycosyl constituent of mycobacteria found in two essential cell envelope heteropolysaccharides, arabinogalactan and lipoarabinomannan. Seven different arabinosyltransferases at least are required to synthesize the arabinan domain of these two major glycans. Because of their interest from the perspective of drug development, these enzymes have been the object of intense investigations. In this chapter, we describe the protocols used to perform nonradioactive arabinosyltransferase assays with synthetic acceptor and donor substrates and characterize the enzymatic products of the reactions by mass spectrometry.

Testing a Human Antimicrobial RNase Chimera Against Bacterial Resistance

The emergence of bacterial resistance to the most commonly used antibiotics encourages the design of novel antimicrobial drugs. Antimicrobial proteins and peptides (AMPs) are the key players in host innate immunity. They exert a rapid and multifaceted action that reduces the development of bacterial adaptation mechanisms. Human antimicrobial RNases belonging to the vertebrate specific RNase A superfamily participate in the maintenance of tissue and body fluid sterility. Among the eight human canonical RNases, RNase 3 stands out as the most cationic and effective bactericidal protein against Gram-negative species. Its enhanced ability to disrupt the bacterial cell wall has evolved in detriment of its catalytic activity. Based on structure-functional studies we have designed an RNase 3/1 hybrid construct that combines the high catalytic activity of RNase 1 with RNase 3 bactericidal properties. Next, we have explored the ability of this hybrid RNase to target the development of bacterial resistance on an Acinetobacter baumannii cell culture. Synergy assays were performed in combination with colistin, a standard antimicrobial peptide used as an antibiotic to treat severe infections. Positive synergism was observed between colistin and the RNase 3/1 hybrid protein. Subsequently, using an in vitro experimental evolution assay, by exposure of a bacterial culture to colistin at incremental doses, we demonstrated the ability of the RNase 3/1 construct to reduce the emergence of bacterial antimicrobial resistance. The results advance the potential applicability of RNase-based drugs as antibiotic adjuvants.

New Quinolone-Based Thiosemicarbazones Showing Activity Against Plasmodium falciparum and Mycobacterium tuberculosis

Co-infection of malaria and tuberculosis, although not thoroughly investigated, has been noted. With the increasing prevalence of tuberculosis in the African region, wherein malaria is endemic, it is intuitive to suggest that the probability of co-infection with these diseases is likely to increase. To avoid the issue of drug-drug interactions when managing co-infections, it is imperative to investigate new molecules with dual activities against the causal agents of these diseases. To this effect, a small library of quinolone-thiosemicarbazones was synthesised and evaluated in vitro against Plasmodium falciparum and Mycobacterium tuberculosis, the causal agents of malaria and tuberculosis, respectively. The compounds were also evaluated against HeLa cells for overt cytotoxicity. Most compounds in this series exhibited activities against both organisms, with compound 10, emerging as the hit; with an MIC₉₀ of 2 µM against H37Rv strain of M. tuberculosis and an IC₅₀ of 1 µM against the 3D7 strain of P. falciparum. This study highlights quinolone-thiosemicarabazones as a class of compounds that can be exploited further in search of novel, safe agents with potent activities against both the causal agents of malaria and tuberculosis.

Pyrazinamide drug resistance in RpsA mutant (∆438A) of Mycobacterium tuberculosis: Dynamics of essential motions and free-energy landscape analysis

Pyrazinamide is an essential first-line antitubercular drug which plays pivotal role in tuberculosis treatment. It is a prodrug that requires amide hydrolysis by mycobacterial pyrazinamidase enzyme for conversion into pyrazinoic acid (POA). POA is known to target ribosomal protein S1 (RpsA), aspartate decarboxylase (PanD), and some other mycobacterial proteins. Spontaneous chromosomal mutations in RpsA have been reported for phenotypic resistance against pyrazinamide. We have constructed and validated 3D models of the native and Δ438A mutant form of RpsA protein. RpsA protein variants were then docked to POA and long range molecular dynamics simulations were carried out. Per residue binding free-energy calculations, free-energy landscape analysis, and essential dynamics analysis were performed to outline the mechanism underlying the high-level PZA resistance conferred by the most frequently occurring deletion mutant of RpsA. Our study revealed the conformational modulation of POA binding site due to the disruptive collective modes of motions and increased conformational flexibility in the mutant than the native form. Residue wise MMPBSA decomposition and protein-drug interaction pattern revealed the difference of energetically favorable binding site in the wild-type (WT) protein in comparison with the mutant. Analysis of size and shape of minimal energy landscape area delineated higher stability of the WT complex than the mutant form. Our study provides mechanistic insights into pyrazinamide resistance in Δ438A RpsA mutant, and the results arising out of this study will pave way for design of novel and effective inhibitors targeting the resistant strains of Mycobacterium tuberculosis.

Quinolone-isoniazid hybrids: synthesis and preliminary in vitro cytotoxicity and anti-tuberculosis evaluation

Herein, we propose novel quinolones incorporating an INH moiety as potential drug templates against TB. The quinolone-based compounds bearing an INH moiety attached via a hydrazide-hydrazone bond were synthesised and evaluated against Mycobacterium tuberculosis H37Rv (MTB). The compounds were also evaluated for cytotoxicity against HeLa cell lines. These compounds showed significant activity (MIC₉₀) against MTB in the range of 0.2-8 μM without any cytotoxic effects. Compounds 10 (MIC₉₀; 0.9 μM), 11 (MIC₉₀; 0.2 μM), 12 (MIC₉₀; 0.8 μM) and compound 15 (MIC₉₀; 0.8 μM), the most active compounds in this series, demonstrate activities on par with INH and superior to those reported for the fluoroquinolones. The SAR analysis suggests that the nature of substituents at positions -1 and -3 of the quinolone nucleus influences anti-MTB activity. Aqueous solubility evaluation and in vitro metabolic stability of compound 12 highlights favourable drug-like properties for this compound class.

Molecular detection of rifampin, isoniazid, and ofloxacin resistance in Iranian isolates of Mycobacterium tuberculosis by high-resolution melting analysis

Background

The emergence of drug resistance among Mycobacterium tuberculosis (MTB) strains is a serious health concern worldwide. The development of rapid molecular diagnostic methods in recent years has a significant impact on the early detection of resistance to major anti-TB drugs in MTB isolates, which helps in employing appropriate treatment regimen and prevents the spread of drug-resistant strains. This study was designed to evaluate the efficacy of real-time PCR and high-resolution melting (HRM) curve analysis for the determination of resistance to rifampin (RIF), isoniazid (INH), and ofloxacin (OFX) in MTB isolates and to investigate their resistance-related mutations.

Methods

HRM analysis was performed to screen 52 (32 drug-resistant and 20 fully susceptible) MTB clinical isolates for mutations in rpoB, katG, mab-inhA, and gyrA genes. The HRM results were then confirmed by DNA sequencing.

Results

In total, 32 phenotypically resistant isolates, comprising 18 RIF-, 16 INH-, and five OFX- resistant strains, were investigated. HRM analysis successfully identified 15 out of 18 mutations in rpoB, 14 out of 16 mutations in katG and mab-inhA, and four out of five mutations in gyrA conferring resistance to RIF, INH, and OFX, respectively. The obtained sensitivity and specificity, respectively, for HRM in comparison with phenotypic susceptibility testing were found to be 83.3% and 100% for RIF, 87.5% and 100% for INH, and 80% and 100% for OFX. In five resistant strains (12.8%), no mutation was detected by using HRM and DNA sequencing.

Conclusion

HRM assay is a rapid, accurate, and cost-effective method possessing high sensitivity and specificity for the determination of antibiotic resistance among MTB clinical isolates and screening of their associated mutations. This method can generate results in a shorter period of time than taken by the phenotypic susceptibility testing and also allows for timely treatment and prevention of the emergence of possible MDR strains.

The potential use of rifabutin for treatment of patients diagnosed with rifampicin-resistant tuberculosis

Background

Use of the Xpert MTB/RIF assay has increased the number of people diagnosed with rifampicin-resistant tuberculosis (RR-TB), especially in South Africa where Xpert is now the initial diagnostic for individuals with TB symptoms. We hypothesized that a proportion of RR-TB patients determined by Xpert can be treated with a rifabutin-containing regimen.

Methods

Rifabutin susceptibility by rpoB mutation was assessed in 349 individuals from South Africa and 172 from Belgium. rpoB polymorphisms were identified by Sanger sequencing. Rifampicin and rifabutin susceptibility was assessed phenotypically. A systematic review was performed to comprehensively collate information on rifabutin susceptibility by rpoB polymorphism. Rifabutin susceptibility was assigned to rpoB polymorphisms based on their positive likelihood ratios and ORs.

Results

One hundred and twelve rpoB polymorphisms (67.9% from literature) were identified from all 2045 RR-TB patients, of which 17 polymorphisms could be classified as susceptible/resistant to rifabutin. Eleven polymorphisms were associated with rifabutin susceptibility. The 516GTC mutation was the most common, representing 70% (South Africa) and 76% (Belgium) of all rifabutin-susceptible isolates. At a population level, the 11 polymorphisms associated with rifabutin susceptibility occurred in 33.2% and 16.6% of all South African and Belgian patients diagnosed with RR-TB, respectively.

Conclusions

Identification of the exact rpoB polymorphism leading to the diagnosis of RR-TB has the potential to allow inclusion of rifabutin in the treatment regimen of a substantial proportion of RR-TB patients. A randomized controlled trial evaluating the efficacy of a rifabutin-containing TB treatment regimen in these selected patients is needed to provide the evidence required for a change in policy.