Pipeline of drugs for related diseases: tuberculosis

Unlocking translational machinery for antitubercular drug development

Targeting translational factor proteins (TFPs) presents significant promise for the development of innovative antitubercular drugs. Previous insights from antibiotic binding mechanisms and recently solved 3D crystal structures of Mycobacterium tuberculosis (Mtb) elongation factor thermo unstable-GDP (EF-Tu-GDP), elongation factor thermo stable-EF-Tu (EF-Ts-EF-Tu), and elongation factor G-GDP (EF-G-GDP) have opened up new avenues for the design and development of potent antituberculosis (anti-TB) therapies.

Omadacycline pharmacokinetics/pharmacodynamics and efficacy against multidrug-resistant Mycobacterium tuberculosis in the hollow fiber system model

Seventy-five years ago, first-generation tetracyclines demonstrated limited efficacy in the treatment of tuberculosis but were more toxic than efficacious. We performed a series of pharmacokinetic/pharmacodynamic (PK/PD) experiments with a potentially safer third-generation tetracycline, omadacycline, for the treatment of multidrug-resistant tuberculosis (MDR-TB). Mycobacterium tuberculosis (Mtb) H37Rv and an MDR-TB clinical strain (16D) were used in the minimum inhibitory concentration (MIC) and static concentration-response studies in test tubes, followed by a PK/PD study using the hollow fiber system model of TB (HFS-TB) that examined six human-like omadacycline doses. The inhibitory sigmoid maximal effect (Emax) model and Monte Carlo experiments (MCEs) were used for data analysis and clinical dose-finding, respectively. The omadacycline MIC for both Mtb H37Rv and MDR-TB clinical strain was 16 mg/L but dropped to 4 mg/L with daily drug supplementation to account for omadacycline degradation. The Mycobacteria Growth Indicator Tube MIC was 2 mg/L. In the test tubes, omadacycline killed 4.39 log10 CFU/mL in 7 days. On Day 28 of the HFS-TB study, the Emax was 4.64 log10 CFU/mL, while exposure mediating 50% of Emax (EC50) was an area under the concentration-time curve to MIC (AUC0-24/MIC) ratio of 22.86. This translates to PK/PD optimal exposure or EC80 as AUC0-24/MIC of 26.93. The target attainment probability of the 300-mg daily oral dose was 90% but fell at MIC ≧4 mg/L. Omadacycline demonstrated efficacy and potency against both drug-susceptible and MDR-TB. Further studies are needed to identify the omadacycline effect in combination therapy for the treatment of both drug-susceptible and MDR-TB.

The Mur Enzymes Chink in the Armour of Mycobacterium tuberculosis cell wall

TUBERCULOSIS: (TB) transmitted by Mycobacterium tuberculosis (Mtb) is one of the top 10 causes of death globally. Currently, the widespread occurrence of resistance toward Mtb strains is becoming a significant concern to public health. This scenario exaggerated the need for the discovery of novel targets and their inhibitors. Targeting the "Mtb cell wall peptidoglycan synthesis" is an attractive strategy to overcome drug resistance. Mur enzymes (MurA-MurF) play essential roles in the peptidoglycan synthesis by catalyzing the ligation of key amino acid residues to the stem peptide. These enzymes are unique and confined to the eubacteria and are absent in humans, representing potential targets for anti-tubercular drug discovery. Mtb Mur ligases with the same catalytic mechanism share conserved amino acid regions and structural features that can conceivably exploit for the designing of the inhibitors, which can simultaneously target more than one isoforms (MurC-MurF) of the enzyme. In light of these findings in the current review, we have discussed the recent advances in medicinal chemistry of Mtb Mur enzymes (MurA-MurF) and their inhibitors, offering attractive multi-targeted strategies to combat the problem of drug-resistant in M. tuberculosis.

Optimizing Bedaquiline for cardiotoxicity by structure based virtual screening, DFT analysis and molecular dynamic simulation studies to identify selective MDR-TB inhibitors

Since the last 4 decades, Bedaquiline has been the first drug discovered as a new kind of anti-tubercular agent and received FDA approval in December 2012 to treat pulmonary multi-drug resistance tuberculosis (MDR-TB). It demonstrates excellent efficacy against MDR-TB by effectively inhibiting mycobacterial ATP synthase. In addition to these apparent assets of Bedaquiline, potential disadvantages of Bedaquiline include inhibition of the hERG (human Ether-à-go-related gene; KCNH2), potassium channel (concurrent risk of cardiac toxicity), and risk of phospholipidosis due to its more lipophilic nature. To assist the effective treatment of MDR-TB, highly active Bedaquiline analogs that display a better safety profile are urgently needed. A structure-based virtual screening approach was used to address the toxicity problems associated with Bedaquiline. Among the virtually screened compound, CID 15947587 had significant docking affinity (- 5.636 kcal/mol) and highest binding free energy (ΔG bind - 85.2703 kcal/mol) towards the Mycobacterial ATP synthase enzyme with insignificant cardiotoxicity and lipophilicity. During MD simulation studies (50 ns), the molecule optimizes its conformation to fit better the active receptor site justifying the binding affinity. The obtained results showed that CID15947587 could be a useful template for further optimizing the MDR-TB inhibitor.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-021-00086-x.

Repurposing of FDA-approved drugs to target MurB and MurE enzymes in Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) is one amongst the top 10 causes of death worldwide. The growing rise in antibiotic resistance compounded with slow and expensive drug discovery has further aggravated the situation. 'Drug repurposing' is a promising approach where known drugs are examined for a new indication. In the present study, we have attempted to identify drugs that could target MurB and MurE enzymes involved in the muramic acid synthesis pathway (Mur Pathway) in Mtb. FDA-approved drugs from two repositories i.e. Drug Bank (1932 drugs) and e-LEA3D (1852 drugs) were screened against these proteins. Several criteria were applied to study the protein-drug interactions and the consensus drugs were further studied by molecular dynamics (MD) simulation. Our study found Sulfadoxine (-7.3 kcal/mol) and Pyrimethamine (-7.8 kcal/mol) to show stable interaction with MurB while Lifitegrast (-10.5 kcal/mol) and Sildenafil (-9.1 kcal/mol) showed most reliable interaction with MurE. Furthermore, binding free energy (ΔG_bind), RMSD and RMSF data and the number of hydrogen bonds corroborated the stability of interactions and hence these drugs for repurposing should be explored further.Communicated by Ramaswamy H. Sarma.

Design, synthesis, and bioevaluation of a novel class of (E)-4-oxo-crotonamide derivatives as potent antituberculosis agents

A series of novel (E)-4-oxo-2-crotonamide derivatives were designed and synthesized to find potent antituberculosis agents. All the target compounds were evaluated for their in vitro activity against Mycobacterium tuberculosis H₃₇Rv(MTB). Results reveal that 4-phenyl moiety at part A and short methyl group at part C were found to be favorable. Most of the derivatives displayed promising activity against MTB with MIC ranging from 0.125 to 4 µg/mL. Especially, compound IIIa16 was found to have the best activity with MIC of 0.125 μg/mL against MTB and with MIC in the range of 0.05-0.48 µg/mL against drug-resistant clinical MTB isolates.

Treatment Outcomes for Patients with Extensively Drug-Resistant Tuberculosis, KwaZulu-Natal and Eastern Cape Provinces, South Africa

Results underscore the need for timely and adequate treatment for tuberculosis and HIV/AIDS.

We analyzed data for a retrospective cohort of patients treated for extensively drug-resistant tuberculosis in 2 provinces in South Africa and compared predictors of treatment outcome in HIV-positive patients who received or had not received antiretroviral drugs with those for HIV-negative patients. Overall, 220 (62.0%) of 355 patients were HIV positive. After 2 years, 34 (10.3%) of 330 patients with a known HIV status and known outcome had a favorable outcome. Multivariate analysis showed that predictors of favorable outcome were negative results for acid-fast bacilli by sputum microscopy at start of treatment and weight >50 kg. HIV-positive patients were more likely to have an unfavorable outcome. The strongest predictor of unfavorable outcome was weight <50 kg. Overall outcomes were poor. HIV status was not a predictor of favorable outcome, but HIV-positive patients were more likely to have an unfavorable outcome. These results underscore the need for timely and adequate treatment for tuberculosis and HIV infection.

Delamanid: a review of its use in patients with multidrug-resistant tuberculosis

Delamanid (Deltyba(®)), a nitroimidazo-oxazole derivative, is a new anti-tuberculosis (TB) drug which exhibits potent in vitro and in vivo antitubercular activity against drug-susceptible and -resistant strains of Mycobacterium tuberculosis. It is approved in several countries, including Japan and those of the EU, for use as part of an appropriate combination regimen in adults with multidrug-resistant tuberculosis (MDR-TB) when an effective treatment regimen cannot otherwise be composed due to resistance or tolerability. In a robust phase II trial in adult patients with MDR-TB, oral delamanid 100 mg twice daily for 2 months plus an optimized background regimen improved sputum culture conversion rates to a significantly greater extent than placebo. In a 6-month extension study, long-term (≤8 months) treatment with delamanid was associated with a higher incidence of favourable outcomes (i.e. cured or completed all treatment) than short-term (≤2 months) treatment, with an accompanying reduction inunfavourable outcomes as defined by the WHO (i.e. pre-specified proportion of TB-positive sputum cultures, death or treatment discontinuation for ≥2 months without medical approval). Delamanid was not associated with clinically relevant drug-drug interactions, including with antiretroviral drugs and those commonly used in treating TB. Delamanid was generally well tolerated in patients with MDR-TB, with gastrointestinal adverse events and insomnia reported most commonly. Although the incidence of QT interval prolongation was higher with delamanid-based therapy, it was not associated with clinical symptoms such as syncope and arrhythmia. In conclusion, delamanid is a useful addition to the treatment options currently available for patients with MDR-TB.

Determination of [11C]rifampin pharmacokinetics within Mycobacterium tuberculosis-infected mice by using dynamic positron emission tomography bioimaging

Information about intralesional pharmacokinetics (PK) and spatial distribution of tuberculosis (TB) drugs is limited and has not been used to optimize dosing recommendations for new or existing drugs. While new techniques can detect drugs and their metabolites within TB granulomas, they are invasive, rely on accurate resection of tissues, and do not capture dynamic drug distribution in the tissues of interest. In this study, we assessed the in situ distribution of (11)C-labeled rifampin in live, Mycobacterium tuberculosis-infected mice that develop necrotic lesions akin to human disease. Dynamic positron emission tomography (PET) imaging was performed over 60 min after injection of [(11)C]rifampin as a microdose, standardized uptake values (SUV) were calculated, and noncompartmental analysis was used to estimate PK parameters in compartments of interest. [(11)C]rifampin was rapidly distributed to all parts of the body and quickly localized to the liver. Areas under the concentration-time curve for the first 60 min (AUC0-60) in infected and uninfected mice were similar for liver, blood, and brain compartments (P > 0.53) and were uniformly low in brain (10 to 20% of blood values). However, lower concentrations were noted in necrotic lung tissues of infected mice than in healthy lungs (P = 0.03). Ex vivo two-dimensional matrix-assisted laser desorption ionization (MALDI) imaging confirmed restricted penetration of rifampin into necrotic lung lesions. Noninvasive bioimaging can be used to assess the distribution of drugs into compartments of interest, with potential applications for TB drug regimen development.

The need to accelerate access to new drugs for multidrug-resistant tuberculosis

Approximately half a million people are thought to develop multidrug-resistant tuberculosis annually. Barely 20% of these people currently receive recommended treatment and only about 10% are successfully treated. Poor access to treatment is probably driving the current epidemic, via ongoing transmission. Treatment scale-up is hampered by current treatment regimens, which are lengthy, expensive, poorly tolerated and difficult to administer in the settings where most patients reside. Although new drugs provide an opportunity to improve treatment regimens, current and planned clinical trials hold little promise for developing regimens that will facilitate prompt treatment scale-up. In this article we argue that clinical trials, while necessary, should be complemented by timely, large-scale, operational research that will provide programmatic data on the use of new drugs and regimens while simultaneously improving access to life-saving treatment. Perceived risks - such as the rapid development of resistance to new drugs - need to be balanced against the high levels of mortality and transmission that will otherwise persist. Doubling access to treatment and increasing treatment success could save approximately a million lives over the next decade.

Complications of tuberculosis

PURPOSE OF REVIEW

Diagnosis and management of tuberculosis (TB) remains challenging and complex because of the heterogeneity of disease presentations. Despite effective treatment, TB disease can lead to significant short-and long-term health consequences. We review potential acute and chronic complications of TB disease and current management approaches.

RECENT FINDINGS

Acute and subacute complications of TB disease are attributable to structural damage or vascular compromise caused by Mycobacterium tuberculosis, as well as metabolic abnormalities and host inflammatory responses. TB-related sepsis is a life-threatening acute complication for which current diagnostic and management approaches are likely inadequate. Therapeutic intensification and usage of immunomodulators are areas of ongoing research. Paradoxical reaction or symptom worsening during TB treatment may benefit from corticosteroids. Despite successful cure of TB, chronic complications can arise from anatomic alterations at disease sites. Examples include mycetomas developing within residual TB cavities, impaired pulmonary function, or focal neurologic deficits from tuberculomas.

SUMMARY

Effective management of TB requires attention to potential structural, metabolic, vascular, and infectious complications. In some instances, individualizing treatment regimens may be necessary. Imunosuppression and other host factors predispose to complications; others occur despite adequate treatment. Public health TB programs and health systems require additional resources to provide comprehensive TB and post-TB care.

Profile of delamanid for the treatment of multidrug-resistant tuberculosis

New approaches to the treatment of multidrug-resistant and extensively drug-resistant tuberculosis (TB) are badly needed. Not only is the success rate of current treatment regimens suboptimal but existing regimens require multiple drugs and lengthy courses and may lead to significant toxicities. The treatment landscape is beginning to shift, however, with the recent approvals of the new TB drugs bedaquiline and delamanid. Delamanid, a dihydro-imidazooxazole, has been shown to have excellent activity against Mycobacterium tuberculosis in both in vitro and in murine TB models. It has also recently been reported to improve rates of sputum culture conversion in patients with multidrug-resistant TB when added to an optimized background regimen. Although generally well tolerated, delamanid has been associated with QT prolongation, which may be of particular clinical concern when paired with other TB drugs that may also have this effect, most notably the fluoroquinolones. Ongoing studies will help to clarify delamanid's role in the treatment of drug-resistant TB.

Mathematical Modelling and Tuberculosis: Advances in Diagnostics and Novel Therapies

As novel diagnostics, therapies, and algorithms are developed to improve case finding, diagnosis, and clinical management of patients with TB, policymakers must make difficult decisions and choose among multiple new technologies while operating under heavy resource constrained settings. Mathematical modelling can provide helpful insight by describing the types of interventions likely to maximize impact on the population level and highlighting those gaps in our current knowledge that are most important for making such assessments. This review discusses the major contributions of TB transmission models in general, namely, the ability to improve our understanding of the epidemiology of TB. We focus particularly on those elements that are important to appropriately understand the role of TB diagnosis and treatment (i.e., what elements of better diagnosis or treatment are likely to have greatest population-level impact) and yet remain poorly understood at present. It is essential for modellers, decision-makers, and epidemiologists alike to recognize these outstanding gaps in knowledge and understand their potential influence on model projections that may guide critical policy choices (e.g., investment and scale-up decisions).

PET/CT imaging reveals a therapeutic response to oxazolidinones in macaques and humans with tuberculosis

Oxazolidinone antibiotics such as linezolid have shown significant therapeutic effects in patients with extensively drug-resistant (XDR) tuberculosis (TB) despite modest effects in rodents and no demonstrable early bactericidal activity in human phase 2 trials. We show that monotherapy with either linezolid or AZD5847, a second-generation oxazolidinone, reduced bacterial load at necropsy in Mycobacterium tuberculosis-infected cynomolgus macaques with active TB. This effect coincided with a decline in 2-deoxy-2-[(18)F]-fluoro-d-glucose positron emission tomography (FDG PET) imaging avidity in the lungs of these animals and with reductions in pulmonary pathology measured by serial computed tomography (CT) scans over 2 months of monotherapy. In a parallel phase 2 clinical study of linezolid in patients infected with XDR-TB, we also collected PET/CT imaging data from subjects receiving linezolid that had been added to their failing treatment regimens. Quantitative comparisons of PET/CT imaging changes in these human subjects were similar in magnitude to those observed in macaques, demonstrating that the therapeutic effect of these oxazolidinones can be reproduced in this model of experimental chemotherapy. PET/CT imaging may be useful as an early quantitative measure of drug efficacy against TB in human patients.

Computational pharmacology of rifampin in mice: an application to dose optimization with conflicting objectives in tuberculosis treatment

Dose selection for rifampin in the treatment of active pulmonary tuberculosis (TB) illustrates some of the challenges for dose optimization within multidrug therapies. Rifampin-based anti-TB regimens are often combined with antiretroviral therapies to treat human immunodeficiency virus (HIV) coinfection. The potent cytochrome P450 (CYP) enzyme inducing properties of rifampin give rise to significant drug-drug interactions, the minimization of which by limiting the dose, conflicts with the maximization of bacterial killing by increasing the dose. Such multiple and conflicting objectives lead to a set of trade-off optimal solutions for dose optimization rather than a single best solution. Here, we combine pharmacokinetic/pharmacodynamic (PK/PD) modeling with multiobjective optimization to quantitatively explore trade-offs between therapeutic and adverse effects of optimal dosing for the example of rifampin in TB-infected mice. The PK/PD model describes rifampin concentrations in plasma and liver following oral administration together with hepatic CYP enzyme induction and bacterial killing kinetics. We include optimization objectives descriptive of antimicrobial efficacy, CYP-mediated drug-drug interactions, and drug exposure-dependent toxicity. Results show non-conventional dosing scenarios that allow for increased efficacy relative to uniform dosing without increasing drug-drug interactions. Additionally, we find currently employed dosages for rifampin to be nearly optimal with respect to trade-offs between efficacy and toxicity. While limited by the accuracy and applicability of the PK/PD model, these results provide an avenue for experimental investigation of complex dose optimization problems. This method can be extended to include additional drugs and optimization objectives, and may provide a useful tool for individualized medicine.

Drivers and trajectories of resistance to new first-line drug regimens for tuberculosis

Background

 New first-line drug regimens for treatment of tuberculosis (TB) are in clinical trials: emergence of resistance is a key concern. Because population-level data on resistance cannot be collected in advance, epidemiological models are important tools for understanding the drivers and dynamics of resistance before novel drug regimens are launched.

Methods

 We developed a transmission model of TB after launch of a new drug regimen, defining drug-resistant TB (DR-TB) as resistance to the new regimen. The model is characterized by (1) the probability of acquiring resistance during treatment, (2) the transmission fitness of DR-TB relative to drug-susceptible TB (DS-TB), and (3) the probability of treatment success for DR-TB versus DS-TB. We evaluate the effect of each factor on future DR-TB prevalence, defined as the proportion of incident TB that is drug-resistant.

Results

 Probability of acquired resistance was the strongest predictor of the DR-TB proportion in the first 5 years after the launch of a new drug regimen. Over a longer term, however, the DR-TB proportion was driven by the resistant population's transmission fitness and treatment success rates. Regardless of uncertainty in acquisition probability and transmission fitness, high levels (>10%) of drug resistance were unlikely to emerge within 50 years if, among all cases of TB that were detected, 85% of those with DR-TB could be appropriately diagnosed as such and then successfully treated.

Conclusions

 Short-term surveillance cannot predict long-term drug resistance trends after launch of novel first-line TB regimens. Ensuring high treatment success of drug-resistant TB through early diagnosis and appropriate second-line therapy can mitigate many epidemiological uncertainties and may substantially slow the emergence of drug-resistant TB.

Preferential adherence to antiretroviral therapy over tuberculosis treatment: a qualitative study of drug-resistant TB/HIV co-infected patients in South Africa

Adherence to antiretroviral therapy (ART) and second-line antituberculosis medications is essential to achieve successful outcomes among individuals co-infected with HIV and multi or extensively drug-resistant TB (M/XDR-TB). In 2012-2013, we designed a qualitative study to explore barriers to adherence in KwaZulu-Natal, South Africa. We conducted six focus groups comprising 23 adults receiving treatment for either MDR-TB (n = 2) or XDR-TB (n = 21); 17 were on concurrent ART. Participants expressed a preference for ART over M/XDR-TB treatment as a result of greater tolerability, lower pill burden and a commitment to ART. Treatment outcomes and the social morbidity associated with M/XDR-TB, characterised by public notification, stigma and social isolation, were perceived to be worse than with HIV. Poor communication, low patient involvement and provider supervision of treatment exacerbated participants' negative experiences with TB care. To improve adherence, it is critical that new regimens for drug-resistant TB be developed with better efficacy, lower pill burden and fewer adverse effects. For the first time, such improved regimens are on the horizon. In parallel and equally important is the implementation of a cohesive approach that promotes patient involvement, empowerment and treatment literacy for HIV and for TB.

Transforming the fight against tuberculosis: targeting catalysts of transmission

The global tuberculosis control community has committed itself to ambitious 10-year targets. To meet these targets, biomedical advances alone will be insufficient; a more targeted public health tuberculosis strategy is also needed. We highlight the role of "tuberculosis transmission catalysts," defined as variabilities in human behavior, bacillary properties, and host physiology that fuel the propagation of active tuberculosis at the local level. These catalysts can be categorized as factors that increase contact rates, infectiousness, or host susceptibility. Different catalysts predominate in different epidemiological and sociopolitical settings, and public health approaches are likely to succeed only if they are tailored to target the major catalysts driving transmission in the corresponding community. We argue that global tuberculosis policy should move from a country-level focus to a strategy that prioritizes collection of data on key transmission catalysts at the local level followed by deployment of "catalyst-targeted" interventions, supported by strengthened health systems.

Antitubercular therapy in patients with cirrhosis: Challenges and options

Tuberculosis (TB) has been a human disease for centuries. Its frequency is increased manyfold in patients with liver cirrhosis. The gold standard of TB management is a 6-mo course of isoniazid, rifampicin, pyrazinamide and ethambutol. Although good results are seen with this treatment in general, the management of patients with underlying cirrhosis is a challenge. The underlying depressed immune response results in alterations in many diagnostic tests. The tests used for latent TB have many flaws in this group of patients. Three of four first-line antitubercular drugs are hepatotoxic and baseline liver function is often disrupted in patients with underlying cirrhosis. Frequency of hepatotoxicity is increased in patients with liver cirrhosis, frequently leading to severe liver failure. There are no established guidelines for the treatment of TB in relation to the severity of liver disease. There is no consensus on the frequency of liver function tests required or the cut-off used to define hepatotoxicity. No specific treatment exists for prevention or treatment of hepatotoxicity, making monitoring even more important. A high risk of multidrug-resistant TB is another major worry due to prolonged and interrupted treatment.