Novel drugs against tuberculosis: a clinician's perspective

Isatin-pyrimidine hybrid derivatives as enoyl acyl carrier protein reductase (InhA) inhibitors against Mycobacterium tuberculosis

Tuberculosis is a worldwide problem that impose a burden on the economy due to continuous development of resistant strains. The development of new antitubercular drugs is a need and can be achieved through inhibition of druggable targets. Mycobacterium tuberculosis enoyl acyl carrier protein (ACP) reductase (InhA) is an important enzyme for Mycobacterium tuberculosis survival. In this study, we report the synthesis of isatin derivatives that could treat TB through inhibition of this enzyme. Compound 4l showed IC50 value (0.6 ± 0.94 µM) similar to isoniazid but is also effective against MDR and XDR Mycobacterium tuberculosis strains (MIC of 0.48 and 3.9 µg/mL, respectively). Molecular docking studies suggest that this compound binds through the use of relatively unexplored hydrophobic pocket in the active site. Molecular dynamics was used to investigate and support the stability of 4l complex with the target enzyme. This study paves the way for the design and synthesis of novel antitubercular drugs.

Analytical Methodologies for the Estimation of Oxazolidinone Antibiotics as Key Members of anti-MRSA Arsenal: A Decade in Review

Gram-positive bacterial infections are among the most serious diseases related with high mortality rates and huge healthcare costs especially with the rise of antibiotic-resistant strains that limits treatment options. Thus, development of new antibiotics combating these multi-drug resistant bacteria is crucial. Oxazolidinone antibiotics are the only totally synthetic group of antibiotics that showed activity against multi-drug resistant Gram positive bacteria including MRSA because of their unique mechanism of action in targeting protein synthesis. This group include approved marketed members (tedizolid, linezolid and contezolid) or those under development (delpazlolid, radezolid and sutezolid). Due to the significant impact of this class, larger number of analytical methods were required to meet the needs of both clinical and industrial studies. Analyzing these drugs either alone or with other antimicrobial agents commonly used in ICU, in the presence of pharmaceutical or endogenous biological interferences, or in the presence of matrix impurities as metabolites and degradation products poses a big analytical challenge. This review highlights current analytical approaches published in the last decade (2012-2022) that dealt with the determination of these drugs in different matrices and discusses their advantages and disadvantages. Various techniques have been described for their determination including chromatographic, spectroscopic, capillary electrophoretic and electroanalytical methods. The review comprises six sections (one for each drug) with their related tables that depict critical figures of merit and some experimental conditions for the reviewed methods. Furthermore, future perspectives about the analytical methodologies that can be developed in the near future for determination of these drugs are suggested.

Nanosized Drug Delivery Systems to Fight Tuberculosis

Tuberculosis (TB) is currently the second deadliest infectious disease. Existing antitubercular therapies are long, complex, and have severe side effects that result in low patient compliance. In this context, nanosized drug delivery systems (DDSs) have the potential to optimize the treatment's efficiency while reducing its toxicity. Hundreds of publications illustrate the growing interest in this field. In this review, the main challenges related to the use of drug nanocarriers to fight TB are overviewed. Relevant publications regarding DDSs for the treatment of TB are classified according to the encapsulated drugs, from first-line to second-line drugs. The physicochemical and biological properties of the investigated formulations are listed. DDSs could simultaneously (i) optimize the therapy's antibacterial effects; (ii) reduce the doses; (iii) reduce the posology; (iv) diminish the toxicity; and as a global result, (v) mitigate the emergence of resistant strains. Moreover, we highlight that host-directed therapy using nanoparticles (NPs) is a recent promising trend. Although the research on nanosized DDSs for TB treatment is expanding, clinical applications have yet to be developed. Most studies are only dedicated to the development of new formulations, without the in vivo proof of concept. In the near future, it is expected that NPs prepared by "green" scalable methods, with intrinsic antibacterial properties and capable of co-encapsulating synergistic drugs, may find applications to fight TB.

The Changing Paradigm of Drug-Resistant Tuberculosis Treatment: Successes, Pitfalls, and Future Perspectives

Drug-resistant tuberculosis (DR-TB) remains a global crisis due to the increasing incidence of drug-resistant forms of the disease, gaps in detection and prevention, models of care, and limited treatment options. The DR-TB treatment landscape has evolved over the last 10 years. Recent developments include the remarkable activity demonstrated by the newly approved anti-TB drugs bedaquiline and pretomanid against Mycobacterium tuberculosis. Hence, treatment of DR-TB has drastically evolved with the introduction of the short-course regimen for multidrug-resistant TB (MDR-TB), transitioning to injection-free regimens and the approval of the 6-month short regimens for rifampin-resistant TB and MDR-TB. Moreover, numerous clinical trials are under way with the aim to reduce pill burden and shorten the DR-TB treatment duration. While there have been apparent successes in the field, some challenges remain. These include the ongoing inclusion of high-dose isoniazid in DR-TB regimens despite a lack of evidence for its efficacy and the inclusion of ethambutol and pyrazinamide in the standard short regimen despite known high levels of background resistance to both drugs. Furthermore, antimicrobial heteroresistance, extensive cavitary disease and intracavitary gradients, the emergence of bedaquiline resistance, and the lack of biomarkers to monitor DR-TB treatment response remain serious challenges to the sustained successes. In this review, we outline the impact of the new drugs and regimens on patient treatment outcomes, explore evidence underpinning current practices on regimen selection and duration, reflect on the disappointments and pitfalls in the field, and highlight key areas that require continued efforts toward improving treatment approaches and rapid biomarkers for monitoring treatment response.

Novel approaches for the treatment of infections due to multidrug-resistant bacterial pathogens

Antimicrobial resistance (AMR), which is a major challenge for global healthcare, emerging because of several reasons including overpopulation, increased global migration and selection pressure due to enhanced use of antibiotics. Antibiotics are the widely used therapeutic options to combat infectious diseases; however, unfortunately, inadequate and irregular antibiotic courses are also major contributing factors in the emergence of AMR. Additionally, persistent failure to develop and commercialize new antibiotics has created the scarcity of effective anti-infective drugs. Thus, there is an urgent need for a new class of antimicrobials and other novel approaches to curb the menace of AMR. Besides the conventional approaches, some novel approaches such as the use of antimicrobial peptides, bacteriophages, immunomodulation, host-directed therapy and antibodies have shown really promising potentials.

Pretomanid for tuberculosis treatment: an update for clinical purposes

Coronavirus disease (COVID-19) pandemic determined a 10 years-set back in tuberculosis (TB) control programs. Recent advances in available therapies may help recover the time lost. While Linezolid (LZD) and Bedaquiline (BDQ), previously Group D second line drugs (SLDs) for TB, have been relocated to Group A, other drugs are currently being studied in regimens for drug resistant TB (DR-TB). Among these, Pretomanid (PA), a recently introduced antimycobacterial drug derived from nitroimidazole with both solid bactericidal and bacteriostatic effect, and with an excellent effectiveness and tolerability profile, is in the spotlight. Following promising data obtained from recently published and ongoing randomized controlled trials (RCTs), the World Health Organization (WHO) determined to include PA in its guidelines for the treatment of rifampicin-resistant (RR), multi drug resistant (MDR) and pre-extensively drug resistant TB (pre-XDR-TB) with BDQ, LZD and Moxifloxacine (MFX) in a 6-month regimen. Although further studies on the subject are needed, PA may also represent a treatment option for drug-susceptible TB (DS-TB), latent TB infection (LTBI) and non tuberculous mycobacteria (NTM). This narrative review aims to examine current implementation options and future possibilities for PA in the never-ending fight against TB.

Functionalized Dioxonaphthoimidazoliums: A Redox Cycling Chemotype with Potent Bactericidal Activities against Mycobacterium tuberculosis

Disruption of redox homeostasis in mycobacteria causes irreversible stress induction and cell death. Here, we report the dioxonaphthoimidazolium scaffold as a novel redox cycling antituberculosis chemotype with potent bactericidal activity against growing and nutrient-starved phenotypically drug-resistant nongrowing bacteria. Maximal potency was dependent on the activation of the redox cycling quinone by the positively charged scaffold and accessibility to the mycobacterial cell membrane as directed by the lipophilicity and conformational characteristics of the N-substituted side chains. Evidence from microbiological, biochemical, and genetic investigations implicates a redox-driven mode of action that is reliant on the reduction of the quinone by type II NADH dehydrogenase (NDH2) for the generation of bactericidal levels of the reactive oxygen species (ROS). The bactericidal profile of a potent water-soluble analogue 32 revealed good activity against nutrient-starved organisms in the Loebel model of dormancy, low spontaneous resistance mutation frequency, and synergy with isoniazid in the checkerboard assay.

Current Molecular Therapeutic Agents and Drug Candidates for Mycobacterium abscessus

Mycobacterium abscessus has been recognised as a dreadful respiratory pathogen among the non-tuberculous mycobacteria (NTM) because of misdiagnosis, prolonged therapy with poor treatment outcomes and a high cost. This pathogen also shows extremely high antimicrobial resistance against current antibiotics, including the anti-tuberculosis agents. Therefore, current chemotherapies require a long curative period and the clinical outcomes are not satisfactory. Thus, there is an urgent need for discovering and developing novel, more effective anti-M. abscessus drugs. In this review, we sum the effectiveness of the current anti-M. abscessus drugs and drug candidates. Furthermore, we describe the shortcomings and difficulties associated with M. abscessus drug discovery and development.

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.

The Tuberculosis-Depression Syndemic and Evolution of Pharmaceutical Therapeutics: From Ancient Times to the Future

The interplay between tuberculosis and depression has been problematic since the humoralists. Over the centuries similarities in disease management have transpired. With the advent of isoniazid chemotherapy, transformation of tuberculosis patients from morbidly depressive to euphoric was noted. Isoniazid was thereafter widely prescribed for depression: hepatotoxicity ending its use as an antidepressant in 1961. Isoniazid monotherapy led to the emergence of drug resistant tuberculosis, stimulating new drug development. Vastly increased investment into antidepressants ensued thereafter while investment in new drugs for tuberculosis lagged. In the 21st century, both diseases independently contribute significantly to global disease burdens: renewed convergence and the resultant syndemic is detrimental to both patient groups. Ending the global tuberculosis epidemic and decreasing the burden of depression and will require multidisciplinary, patient-centered approaches that consider this combined co-morbidity. The emerging era of big data for health, digital interventions and novel and repurposed compounds promise new ways to treat both diseases and manage the syndemic, but absence of clinical structures to support these innovations may derail the treatment programs for both. New policies are urgently required optimizing use of the current advances in healthcare available in the digital era, to ensure that patient-centered care takes cognizance of both diseases.

Synthesis and evaluation of thiophene based small molecules as potent inhibitors of Mycobacterium tuberculosis

Herein, we report the synthesis and anti-tubercular studies of novel molecules based on thiophene scaffold. We identified two novel small molecules 4a and 4b, which demonstrated 2-fold higher in vitro activity (MIC₉₉: 0.195 μM) compared to first line TB drug, isoniazid (0.39 μM). The identified leads demonstrated additive effect with front line TB drugs (isoniazid, rifampicin and levofloxacin) and synergistic effect with a recently FDA-approved drug, bedaquiline. Mechanistic studies (i) negated the role of Pks13 and (ii) suggested the involvement of KatG in the anti-tubercular activity of these identified leads.

Pretomanid: A novel therapeutic paradigm for treatment of drug resistant tuberculosis

Tuberculosis is currently an anticipated driver of pandemic diseases. It remains an imminent issue accounting for about 1.4 million deaths annually across the world. Since the evolution of human entity drug susceptible tuberculosis was managed through potent first line therapies. Unfortunately, the emergence of newer multitude strains refractory amongst available drugs in Drug resistant TB has led to an emergence MDR-TB and XDR-TB. Moreover, the increasing incidence of drug susceptible TB in developing countries paved way to development of new guidelines for treating various form of tuberculosis. Furthermore, newer regimens are warranted to combat resistance that preferably cause a reduction in mortality. Until now, various ongoing trials are being carried in order to potentially evaluate the suitable novel drug candidates, repurposed drugs and host directed therapies that will optimistically be safe, easy to tolerate, cost effective and non-toxic that will modify the prospects for treating drug resistant TB and latent TB. In context, the current scenario seems to impose a significant challenge on health care researchers in the field of drug discovery owing to complexities, prolong treatment duration, and is cumbersome. Pretomanid is a novel drug with potent bactericidal properties emerging a key advancement used in combination along with other drug therapies This review details the role of pretomanid in treating tuberculosis and the clinical trials in adultsd.

Outcomes and adverse events of pre- and extensively drug-resistant tuberculosis patients in Kinshasa, Democratique Republic of the Congo: A retrospective cohort study

Background

Extensively drug-resistant tuberculosis (XDR TB) is a very serious form of tuberculosis that is burdened with a heavy mortality toll, especially before the advent of new TB drugs. The Democratic Republic of the Congo (DRC) is among the countries most affected by this new epidemic.

Methods

A retrospective analysis was performed of the records of all patients with pre- and extensively drug-resistant tuberculosis hospitalized from January 1, 2015 to December 31, 2017 and monitored for at least 6 months to one year after the end of their treatment in Kinshasa; an individualized therapeutic regimen with bedaquiline for 20 months was built for each patient. The adverse effects were systematically monitored.

Results

Of the 40 laboratory-confirmed patients, 32 (80%) patients started treatment, including 29 preXRB and 3 XDR TB patients. In the eligible group, 3 patients (9.4%) had HIV-TB coinfections. The therapeutic success rate was 53.2%, and the mortality rate was 46.8% (15/32); there were no relapses, failures or losses to follow-up. All coinfected HIV–TB patients died during treatment. The cumulative patient survival rate was 62.5% at 3 months, 53.1% at 6 months and 53.1% at 20 months. The most common adverse events were vomiting, Skin rash, anemia and peripheral neuropathy.

Conclusion

The new anti-tuberculosis drugs are a real hope for the management of Drug Resistant tuberculosis patient and other new therapeutic combinations may improve favorable outcomes.

Predictive Power of In Silico Approach to Evaluate Chemicals against M. tuberculosis: A Systematic Review

Mycobacterium tuberculosis (Mtb) is an endemic bacterium worldwide that causes tuberculosis (TB) and involves long-term treatment that is not always effective. In this context, several studies are trying to develop and evaluate new substances active against Mtb. In silico techniques are often used to predict the effects on some known target. We used a systematic approach to find and evaluate manuscripts that applied an in silico technique to find antimycobacterial molecules and tried to prove its predictive potential by testing them in vitro or in vivo. After searching three different databases and applying exclusion criteria, we were able to retrieve 46 documents. We found that they all follow a similar screening procedure, but few studies exploited equal targets, exploring the interaction of multiple ligands to 29 distinct enzymes. The following in vitro/vivo analysis showed that, although the virtual assays were able to decrease the number of molecules tested, saving time and money, virtual screening procedures still need to develop the correlation to more favorable in vitro outcomes. We find that the in silico approach has a good predictive power for in vitro results, but call for more studies to evaluate its clinical predictive possibilities.

Time to appropriate treatment in patients with multidrug-resistant tuberculosis in South Korea: Are we still in 2010?

Background

This study investigated the time to appropriate treatment and factors affecting late treatment initiation in patients with multidrug-resistant tuberculosis (MDR-TB) in South Korea.

Methods

Data from patients with culture-confirmed pulmonary MDR-TB who received treatment at Pusan National University Hospital (PNUH) between January 2010 and July 2018 were reviewed retrospectively. Patients were divided into two groups according to the first institution they visited [patients who were transferred to PNUH after diagnosis of MDR-TB (Group A) and patients who were initially diagnosed with TB at PNUH (Group B)].

Results

A total of 100 patients were included (53 in Group A and 47 in Group B). The percentage of patients in whom line probe assays (LPAs) for isoniazid and rifampin or Xpert MTB/RIF assays were performed was higher in Group B than in Group A [20.8 vs. 57.4% (P < 0.001) and 17.0 vs. 46.8% (P = 0.001), respectively]. The median time from the first visit to appropriate treatment initiation was longer in Group A (102.0 vs. 77.0 days, P = 0.002). However, a subgroup analysis of patients with pre-extensively or extensively drug-resistant TB (pre-XDR- or XDR-TB) revealed that the time to appropriate treatment did not differ between Groups A and B. Although the time to appropriate treatment decreased during the study period in both Groups A and B, this trend was not evident in patients with pre-XDR- or XDR-TB in Group B. Based on multivariate analyses, performance of LPAs for isoniazid and rifampin, performance of Xpert MTB/RIF assays, and the presence of uncomplicated MDR-TB were protective against delays in appropriate treatment initiation.

Conclusions

The time to appropriate treatment in patients with MDR-TB in South Korea was not acceptable, particularly for patients diagnosed outside of PNUH and for patients with pre-XDR- or XDR-TB. The use of rapid molecular drug susceptibility tests in various healthcare settings and introduction of second-line LPAs are required.

Challenges and recent progress in drug discovery for tropical diseases

Infectious tropical diseases have a huge effect in terms of mortality and morbidity, and impose a heavy economic burden on affected countries. These diseases predominantly affect the world's poorest people. Currently available drugs are inadequate for the majority of these diseases, and there is an urgent need for new treatments. This Review discusses some of the challenges involved in developing new drugs to treat these diseases and highlights recent progress. While there have been notable successes, there is still a long way to go.

Copper-related toxicity in replicating and dormantMycobacterium tuberculosiscaused by 1-hydroxy-5-R-pyridine-2(1H)-thiones

1-Hydroxy-5-R-pyridine-2(1H)-thiones are novel copper-dependentM. tuberculosisinhibitors that provide intracellular accumulation of toxic concentrations of copper.

Performance of the GenoType MTBDRsl assay for the detection second-line anti-tuberculosis drug resistance

The rapid detection of drug-resistant tuberculosis (TB) is important to improve treatment outcomes and prevent disease transmission. The GenoType MTBDRsl assay (MTBDRsl assay) was developed to detect fluoroquinolone (FQ) and second-line injectable drug (SLID) resistance. The aim of this study was to evaluate the performance and clinical utility of MTBDRsl assay. We retrospectively reviewed patient medical records with MTBDRsl assay data between December 2011 and February 2017. MTBDRsl assay results were compared with that of phenotypic drug susceptibility testing. In addition, treatment outcomes were analyzed to evaluate the clinical utility of the MTBDRsl assay. Among 107 clinical isolates (84 cultured isolates and 23 sputum specimens), 85 (79.4%) were multidrug-resistant TB and 9 (8.4%) were extensively drug-resistant TB (XDR-TB). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of MTBDRsl assay for detecting FQ resistance was 87.5%, 94.7%, 87.5%, 94.7%, and 92.5%, respectively. The sensitivity, specificity, PPV, NPV, and accuracy of MTBDRsl assay for detecting SLID resistance was 88.9%, 98.9%, 94.1%, 97.8%, and 97.2%, respectively. Novel drugs such as bedaquiline and linezolid were more commonly used in patients with FQ or SLID resistance detected by the MTBDRsl assay and, probably therefore, the treatment outcome was favorable irrespective of FQ or SLID resistance. The MTBDRsl assay could be used as a rule-in test to detect FQ and SLID resistance. By detecting FQ- and SLID-drug resistance rapidly, novel or repurposed drugs could be initiated earlier, suggesting that better treatment outcomes would be expected in patients with pre-XDR- and XDR-TB.

Nanostructured lipid carriers for incorporation of copper(II) complexes to be used against Mycobacterium tuberculosis

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis. Cessation of treatment before the recommended conclusion may lead to the emergence of multidrug-resistant strains. The aim of this study was to develop nanostructured lipid carriers (NLCs) for use in the treatment of M. tuberculosis. The NLCs comprised the following lipid phase: 2.07% polyoxyethylene 40 stearate, 2.05% caprylic/capric triglyceride, and 0.88% polyoxyl 40 hydrogenated castor oil; the following aqueous phase: 3.50% poloxamer 407 (F1-F6), and 0.50% cetyltrimethylammonium bromide (F7-F12); and incorporated the copper(II) complexes [CuCl₂(INH)₂]·H₂O (1), [Cu(NCS)₂(INH)₂]·5H₂O (2), and [Cu(NCO)₂(INH)₂]·4H₂O (3) to form compounds F11.1, F11.2, and F11.3, respectively. The mean diameter of F11, F11.1, F11.2, and F11.3 ranged from 111.27±21.86 to 134.25±22.72 nm, 90.27±12.97 to 116.46±9.17 nm, 112.4±10.22 to 149.3±15.82 nm, and 78.65±6.00 to 122.00±8.70 nm, respectively. The polydispersity index values for the NLCs ranged from 0.13±0.01 to 0.30±0.09. The NLCs showed significant changes in zeta potential, except for F11.2, with F11, F11.1, F11.2, and F11.3 ranging from 18.87±4.04 to 23.25±1.13 mV, 17.03±1.77 to 21.42±1.87 mV, 20.51±1.88 to 22.60±3.44 mV, and 17.80±1.96 to 25.25±7.78 mV, respectively. Atomic force microscopy confirmed the formation of nanoscale spherical particle dispersions by the NLCs. Differential scanning calorimetry determined the melting points of the constituents of the NLCs. The in vitro activity of copper(II) complex-loaded NLCs against M. tuberculosis H₃₇R_v showed an improvement in the anti-TB activity of 55.4, 27.1, and 41.1 times the activity for complexes 1, 2, and 3, respectively. An in vivo acute toxicity study of complex-loaded NLCs demonstrated their reduced toxicity. The results suggest that NLCs may be a powerful tool to optimize the activity of copper(II) complexes against M. tuberculosis.

Thioridazine: A Non-Antibiotic Drug Highly Effective, in Combination with First Line Anti-Tuberculosis Drugs, against Any Form of Antibiotic Resistance of Mycobacterium tuberculosis Due to Its Multi-Mechanisms of Action

This review presents the evidence that supports the use of thioridazine (TZ) for the therapy of a pulmonary tuberculosis infection regardless of its antibiotic resistance status. The evidence consists of in vitro and ex vivo assays that demonstrate the activity of TZ against all encountered Mycobacterium tuberculosis (Mtb) regardless of its antibiotic resistance phenotype, as well as in vivo as a therapy for mice infected with multi-drug resistant strains of Mtb, or for human subjects infected with extensively drug resistant (XDR) Mtb. The mechanisms of action by which TZ brings about successful therapeutic outcomes are presented in detail.

Effect of common and experimental anti-tuberculosis treatments on Mycobacterium tuberculosis growing as biofilms

Much is known regarding the antibiotic susceptibility of planktonic cultures of Mycobacterium tuberculosis, the bacterium responsible for the lung disease tuberculosis (TB). As planktonically-grown M. tuberculosis are unlikely to be entirely representative of the bacterium during infection, we set out to determine how effective a range of anti-mycobacterial treatments were against M. tuberculosis growing as a biofilm, a bacterial phenotype known to be more resistant to antibiotic treatment. Light levels from bioluminescently-labelled M. tuberculosis H37Rv (strain BSG001) were used as a surrogate for bacterial viability, and were monitored before and after one week of treatment. After treatment, biofilms were disrupted, washed and inoculated into fresh broth and plated onto solid media to rescue any surviving bacteria. We found that in this phenotypic state M. tuberculosis was resistant to the majority of the compounds tested. Minimum inhibitory concentrations (MICs) increased by 20-fold to greater than 1,000-fold, underlying the potential of this phenotype to cause significant problems during treatment.

Detection of transrenal DNA for the diagnosis of pulmonary tuberculosis and treatment monitoring

PURPOSE

Molecular diagnostics of patients with MTB tuberculosis from urine samples.

METHODS

We developed a new molecular assay based on the detection of M. tuberculosis-specific transrenal DNA (trDNA) and tested it for the diagnosis of active tuberculosis at the initiation of anti-tuberculosis therapy and during treatment follow-up.

RESULTS

The overall sensitivity of trDNA was 96 and 100% when smear-microscopy and trDNA was combined. In a subset of TB treatment naïve patients (n = 11) sensitivity and specificity of trDNA was 64 and 100%, respectively. For this subset of patients the sensitivity was 91% when smear-microscopy and trDNA diagnosis were combined. After treatment initiation, trDNA showed a significant reduction in concentration over time reaching undetectable trDNA values at week 12 in 9 of 11 accessible patients (82%). Kinetics in treatment-naïve patients showed low base-line trDNA levels, which increased to maximal trDNA levels within one week indicating bactericidal activity of anti-tuberculosis drugs after the initiation of effective therapy. Maximal trDNA levels correlated positively with a radiological score, suggesting that the process of DNA excretion may reflect the extent of pulmonary disease. Matched samples showed an inverse correlation between the time to positivity of solid culture with maximum trDNA levels as well as the expected positive correlation between smear grade and maximum trDNA values.

CONCLUSION

The detection of M. tuberculosis trDNA from urine specimen is a promising method for the diagnosis tuberculosis. The assay may be a candidate diagnostic tool for patients with paucibacillary and extrapulmonary disease, as method to assess treatment responses and could be helpful to diagnose tuberculosis in children.

Screening of anti-mycobacterial compounds in a naturally infected zebrafish larvae model

OBJECTIVES

Mycobacterium tuberculosis is a deadly human pathogen that causes the lung disease TB. M. tuberculosis latently infects a third of the world's population, resulting in ∼1.5 million deaths per year. Due to the difficulties and expense of carrying out animal drug trials using M. tuberculosis and rodents, infections of the zebrafish Danio rerio with Mycobacterium marinum have become a useful surrogate. However, the infection methods described to date require specialized equipment and a high level of operator expertise.

METHODS

We investigated whether zebrafish larvae could be naturally infected with bioluminescently labelled M. marinum by immersion, and whether infected larvae could be used for rapid screening of anti-mycobacterial compounds using bioluminescence. We used rifampicin and a variety of nitroimidazole-based next-generation and experimental anti-mycobacterial drugs, selected for their wide range of potencies against M. tuberculosis, to validate this model for anti-mycobacterial drug discovery.

RESULTS

We observed that five of the six treatments (rifampicin, pretomanid, delamanid, SN30488 and SN30527) significantly reduced the bioluminescent signal from M. marinum within naturally infected zebrafish larvae. Importantly, these same five treatments also retarded the growth of M. tuberculosis in vitro. In contrast, only three of the six treatments tested (rifampicin, delamanid and SN30527) retarded the growth of M. marinum in vitro.

CONCLUSIONS

We have demonstrated that zebrafish larvae naturally infected with bioluminescent M. marinum M can be used for the rapid screening of anti-mycobacterial compounds with readily available equipment and limited expertise. The result is an assay that can be carried out by a wide variety of laboratories for minimal cost and without high levels of zebrafish expertise.

Tradeoffs in Introduction Policies for the Anti-Tuberculosis Drug Bedaquiline: A Model-Based Analysis

BACKGROUND

New drugs for the treatment of tuberculosis (TB) are becoming available for the first time in over 40 y. Optimal strategies for introducing these drugs have not yet been established. The objective of this study was to compare different strategies for introducing the new TB drug bedaquiline based on patients' resistance patterns.

METHODS AND FINDINGS

We created a Markov decision model to follow a hypothetical cohort of multidrug-resistant (MDR) TB patients under different bedaquiline use strategies. The explored strategies included making bedaquiline available to all patients with MDR TB, restricting bedaquiline usage to patients with MDR plus additional resistance and withholding bedaquiline introduction completely. We compared these strategies according to life expectancy, risks of acquired resistance, and the expected number and health outcomes of secondary cases. For our simulated cohort, the mean (2.5th, 97.5th percentile) life expectancy from time of initiation of MDR TB treatment at age 30 was 36.0 y (33.5, 38.7) assuming all patients with MDR TB received bedaquiline, 35.1 y (34.4, 35.8) assuming patients with pre-extensively drug-resistant (PreXDR) and extensively drug-resistant (XDR) TB received bedaquiline, and 34.9 y (34.6, 35.2) assuming only patients with XDR TB received bedaquiline. Although providing bedaquiline to all MDR patients resulted in the highest life expectancy for our initial cohort averaged across all parameter sets, for parameter sets in which bedaquiline conferred high risks of added mortality and only small reductions in median time to culture conversion, the optimal strategy would be to withhold use even from patients with the most extensive resistance. Across all parameter sets, the most liberal bedaquiline use strategies consistently increased the risk of bedaquiline resistance but decreased the risk of resistance to other MDR drugs. In almost all cases, more liberal bedaquiline use strategies reduced the expected number of secondary cases and resulting life years lost. The generalizability of our results is limited by the lack of available data about drug effects among individuals with HIV co-infection, drug interactions, and other sources of heterogeneity, as well as changing recommendations for MDR TB treatment.

CONCLUSIONS

If mortality benefits can be empirically verified, our results provide support for expanding bedaquiline access to all patients with MDR TB. Such expansion could improve patients' health, protect background MDR TB drugs, and decrease transmission, but would likely result in greater resistance to bedaquiline.

Effects of Lipid-Lowering Drugs on Vancomycin Susceptibility of Mycobacteria

Tuberculosis is still a cause of major concern, partly due to the emergence of multidrug-resistant strains. New drugs are therefore needed. Vancomycin can target mycobacteria with cell envelope deficiency. In this study, we used a vancomycin susceptibility assay to detect drugs hampering lipid synthesis in Mycobacterium bovis BCG and in Mycobacterium tuberculosis We tested three drugs already used to treat human obesity: tetrahydrolipstatin (THL), simvastatin, and fenofibrate. Only vancomycin and THL were able to synergize on M. bovis BCG and on M. tuberculosis, although mycobacteria could also be inhibited by simvastatin alone. Lipid analysis allowed us to identify several lipid modifications in M. tuberculosis H37Rv treated with those drugs. THL treatment mainly reduced the phthiocerol dimycocerosate (PDIM) content in the mycobacterial cell wall, providing an explanation for the synergy, since PDIM deficiency has been related to vancomycin susceptibility. Proteomic analysis suggested that bacteria treated with THL, in contrast to bacteria treated with simvastatin, tried to recover, inducing, among other reactions, lipid synthesis. The combination of THL and vancomycin should be considered a promising solution in developing new strategies to treat multidrug-resistant tuberculosis.

Delivery of RNAi Therapeutics to the Airways-From Bench to Bedside

RNA interference (RNAi) is a potent and specific post-transcriptional gene silencing process. Since its discovery, tremendous efforts have been made to translate RNAi technology into therapeutic applications for the treatment of different human diseases including respiratory diseases, by manipulating the expression of disease-associated gene(s). Similar to other nucleic acid-based therapeutics, the major hurdle of RNAi therapy is delivery. Pulmonary delivery is a promising approach of delivering RNAi therapeutics directly to the airways for treating local conditions and minimizing systemic side effects. It is a non-invasive route of administration that is generally well accepted by patients. However, pulmonary drug delivery is a challenge as the lungs pose a series of anatomical, physiological and immunological barriers to drug delivery. Understanding these barriers is essential for the development an effective RNA delivery system. In this review, the different barriers to pulmonary drug delivery are introduced. The potential of RNAi molecules as new class of therapeutics, and the latest preclinical and clinical studies of using RNAi therapeutics in different respiratory conditions are discussed in details. We hope this review can provide some useful insights for moving inhaled RNAi therapeutics from bench to bedside.

Emerging strategies for the treatment of pulmonary tuberculosis: promise and limitations?

A worsening scenario of drug-resistant tuberculosis has increased the need for new treatment strategies to tackle this worldwide emergency. There is a pressing need to simplify and shorten the current 6-month treatment regimen for drug-susceptible tuberculosis. Rifamycins and fluoroquinolones, as well as several new drugs, are potential candidates under evaluation. At the same time, treatment outcomes of patients with drug-resistant tuberculosis should be improved through optimizing the use of fluoroquinolones, repurposed agents and newly developed drugs. In this context, the safety and tolerance of new therapeutic approaches must be addressed.

Synthetic investigational new drugs for the treatment of tuberculosis

INTRODUCTION

Tuberculosis (TB) is a major global health concern. And while there are treatments already on the market, there is a demand for new drugs that are effective and safe against Mycobacterium tuberculosis, which reduce the number of drugs and the duration of treatment in both drug-susceptible TB and multidrug-resistant TB (MDR-TB).

AREA COVERED

This review covers promising novel investigational TB drugs that are currently under development. Specifically, the authors review the efficacy of novel agents for the treatment of TB in preclinical, phase I and phase II clinical trials. The authors also review the safety and tolerability profiles of these drugs.

EXPERT OPINION

Bedaquiline and delamanid are the most promising novel drugs for the treatment of MDR-TB, each having high efficacy and tolerability. However, the best regimen for achieving better outcomes and reducing adverse drug reactions remains to be determined, with safety concerns regarding cardiac events due to QT prolongation still to be addressed. Pretomanid is a novel drug that potentially shortens the duration of treatment in both drug-susceptible and drug-resistant TB in combination with moxifloxacin and pyrazinamide. Linezolid shows marked efficacy in the treatment of MDR-TB and extensively drug-resistant TB (XDR-TB), but the drug is known to cause significant adverse drug reactions, including peripheral neuropathy, optic neuropathy and myelosuppression. These adverse reactions must be considered prior to prescribing long-term usage of this drug.

In silico-based high-throughput screen for discovery of novel combinations for tuberculosis treatment

There are currently 18 drug classes for the treatment of tuberculosis, including those in the development pipeline. An in silico simulation enabled combing the innumerably large search space to derive multidrug combinations. Through the use of ordinary differential equations (ODE), we constructed an in silico kinetic platform in which the major metabolic pathways in Mycobacterium tuberculosis and the mechanisms of the antituberculosis drugs were integrated into a virtual proteome. The optimized model was used to evaluate 816 triplets from the set of 18 drugs. The experimentally derived cumulative fractional inhibitory concentration (∑FIC) value was within twofold of the model prediction. Bacterial enumeration revealed that a significant number of combinations that were synergistic for growth inhibition were also synergistic for bactericidal effect. The in silico-based screen provided new starting points for testing in a mouse model of tuberculosis, in which two novel triplets and five novel quartets were significantly superior to the reference drug triplet of isoniazid, rifampin, and ethambutol (HRE) or the quartet of HRE plus pyrazinamide (HREZ).

Disulfiram and Copper Ions Kill Mycobacterium tuberculosis in a Synergistic Manner

Tuberculosis is a severe disease affecting millions worldwide. Unfortunately, treatment strategies are hampered both by the prohibitively long treatment regimen and the rise of drug-resistant strains. Significant effort has been expended in the search for new treatments, but few options have successfully emerged, and new treatment modalities are desperately needed. Recently, there has been growing interest in the synergistic antibacterial effects of copper ions (Cu(II/I)) in combination with certain small molecular compounds, and we have previously reported development of a drug screening strategy to harness the intrinsic bactericidal properties of Cu(II/I). Here, we describe the copper-dependent antimycobacterial properties of disulfiram, an FDA-approved and well-tolerated sobriety aid. Disulfiram was inhibitory to mycobacteria only in the presence of Cu(II/I) and exerted its bactericidal activity well below the active concentration of Cu(II/I) or disulfiram alone. No other physiologically relevant bivalent transition metals (e.g., Fe(II), Ni(II), Mn(II), and Co(II)) exhibited this effect. We demonstrate that the movement of the disulfiram-copper complex across the cell envelope is porin independent and can inhibit intracellular protein functions. Additionally, the complex is able to synergistically induce intracellular copper stress responses significantly more than Cu(II/I) alone. Our data suggest that by complexing with disulfiram, Cu(II/I) is likely allowed unfettered access to vulnerable intracellular components, bypassing the normally sufficient copper homeostatic machinery. Overall, the synergistic antibacterial activity of Cu(II/I) and disulfiram reveals the susceptibility of the copper homeostasis system of Mycobacterium tuberculosis to chemical attacks and establishes compounds that act in concert with copper as a new class of bacterial inhibitors.

Disulfiram and Copper Ions Kill Mycobacterium tuberculosis in a Synergistic Manner

Tuberculosis is a severe disease affecting millions worldwide. Unfortunately, treatment strategies are hampered both by the prohibitively long treatment regimen and the rise of drug-resistant strains. Significant effort has been expended in the search for new treatments, but few options have successfully emerged, and new treatment modalities are desperately needed. Recently, there has been growing interest in the synergistic antibacterial effects of copper ions (Cu(II/I)) in combination with certain small molecular compounds, and we have previously reported development of a drug screening strategy to harness the intrinsic bactericidal properties of Cu(II/I). Here, we describe the copper-dependent antimycobacterial properties of disulfiram, an FDA-approved and well-tolerated sobriety aid. Disulfiram was inhibitory to mycobacteria only in the presence of Cu(II/I) and exerted its bactericidal activity well below the active concentration of Cu(II/I) or disulfiram alone. No other physiologically relevant bivalent transition metals (e.g., Fe(II), Ni(II), Mn(II), and Co(II)) exhibited this effect. We demonstrate that the movement of the disulfiram-copper complex across the cell envelope is porin independent and can inhibit intracellular protein functions. Additionally, the complex is able to synergistically induce intracellular copper stress responses significantly more than Cu(II/I) alone. Our data suggest that by complexing with disulfiram, Cu(II/I) is likely allowed unfettered access to vulnerable intracellular components, bypassing the normally sufficient copper homeostatic machinery. Overall, the synergistic antibacterial activity of Cu(II/I) and disulfiram reveals the susceptibility of the copper homeostasis system of Mycobacterium tuberculosis to chemical attacks and establishes compounds that act in concert with copper as a new class of bacterial inhibitors.