MIC of Delamanid (OPC-67683) against Mycobacterium tuberculosis Clinical Isolates and a Proposed Critical Concentration

Designing molecular diagnostics for current tuberculosis drug regimens

Diagnostic development must occur in parallel with drug development to ensure the longevity of new treatment compounds. Despite an increasing number of novel and repurposed anti-tuberculosis compounds and regimens, there remains a large number of drugs for which no rapid and accurate molecular diagnostic option exists. The lack of rapid drug susceptibility testing for linezolid, bedaquiline, clofazimine, the nitroimidazoles (i.e pretomanid and delamanid) and pyrazinamide at any level of the healthcare system compromises the effectiveness of current tuberculosis and drug-resistant tuberculosis treatment regimens. In the context of current WHO tuberculosis treatment guidelines as well as promising new regimens, we identify the key diagnostic gaps for initial and follow-on tests to diagnose emerging drug resistance and aid in regimen selection. Additionally, we comment on potential gene targets for inclusion in rapid molecular drug susceptibility assays and sequencing assays for novel and repurposed drug compounds currently prioritized in current regimens, and evaluate the feasibility of mutation detection given the design of existing technologies. Based on current knowledge, we also propose design priorities for next generation molecular assays to support triage of tuberculosis patients to appropriate and effective treatment regimens. We encourage assay developers to prioritize development of these key molecular assays and support the continued evolution, uptake, and utility of sequencing to build knowledge of tuberculosis resistance mechanisms and further inform rapid treatment decisions in order to curb resistance to critical drugs in current regimens and achieve End TB targets.Trial registration: ClinicalTrials.gov identifier: NCT05117788..

Revolutionizing control strategies against Mycobacterium tuberculosis infection through selected targeting of lipid metabolism

Lipid species play a critical role in the growth and virulence expression of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). During Mtb infection, foamy macrophages accumulate lipids in granulomas, providing metabolic adaptation and survival strategies for Mtb against multiple stresses. Host-derived lipid species, including triacylglycerol and cholesterol, can also contribute to the development of drug-tolerant Mtb, leading to reduced efficacy of antibiotics targeting the bacterial cell wall or transcription. Transcriptional and metabolic analyses indicate that lipid metabolism-associated factors of Mtb are highly regulated by antibiotics and ultimately affect treatment outcomes. Despite the well-known association between major antibiotics and lipid metabolites in TB treatment, a comprehensive understanding of how altered lipid metabolites in both host and Mtb influence treatment outcomes in a drug-specific manner is necessary to overcome drug tolerance. The current review explores the controversies and correlations between lipids and drug efficacy in various Mtb infection models and proposes novel approaches to enhance the efficacy of anti-TB drugs. Moreover, the review provides insights into the efficacious control of Mtb infection by elucidating the impact of lipids on drug efficacy. This review aims to improve the effectiveness of current anti-TB drugs and facilitate the development of innovative therapeutic strategies against Mtb infection by making reverse use of Mtb-favoring lipid species.

Determining the Delamanid Pharmacokinetics/Pharmacodynamics Susceptibility Breakpoint Using Monte Carlo Experiments

Antimicrobial susceptibility testing, based on clinical breakpoints that incorporate pharmacokinetics/pharmacodynamics (PK/PD) and clinical outcomes, is becoming a new standard in guiding individual patient therapy as well as for drug resistance surveillance. However, for most antituberculosis drugs, breakpoints are instead defined by the epidemiological cutoff values of the MIC of phenotypically wild-type strains irrespective of PK/PD or dose. In this study, we determined the PK/PD breakpoint for delamanid by estimating the probability of target attainment for the approved dose administered at 100 mg twice daily using Monte Carlo experiments. We used the PK/PD targets (0- to 24-h area under the concentration-time curve to MIC) identified in a murine chronic tuberculosis model, hollow fiber system model of tuberculosis, early bactericidal activity studies of patients with drug-susceptible tuberculosis, and population pharmacokinetics in patients with tuberculosis. At the MIC of 0.016 mg/L, determined using Middlebrook 7H11 agar, the probability of target attainment was 100% in the 10,000 simulated subjects. The probability of target attainment fell to 25%, 40%, and 68% for PK/PD targets derived from the mouse model, the hollow fiber system model of tuberculosis, and patients, respectively, at the MIC of 0.031 mg/L. This indicates that an MIC of 0.016 mg/L is the delamanid PK/PD breakpoint for delamanid at 100 mg twice daily. Our study demonstrated that it is feasible to use PK/PD approaches to define a breakpoint for an antituberculosis drug.

New and Repurposed Drugs for the Treatment of Active Tuberculosis: An Update for Clinicians

Although tuberculosis (TB) is preventable and curable, the lengthy treatment (generally 6 months), poor patient adherence, high inter-individual variability in pharmacokinetics (PK), emergence of drug resistance, presence of comorbidities, and adverse drug reactions complicate TB therapy and drive the need for new drugs and/or regimens. Hence, new compounds are being developed, available drugs are repurposed, and the dosing of existing drugs is optimized, resulting in the largest drug development portfolio in TB history. This review highlights a selection of clinically available drug candidates that could be part of future TB regimens, including bedaquiline, delamanid, pretomanid, linezolid, clofazimine, optimized (high dose) rifampicin, rifapentine, and para-aminosalicylic acid. The review covers drug development history, preclinical data, PK, and current clinical development.

Solubility Enhancement and Inhalation Delivery of Cyclodextrin-Based Inclusion Complex of Delamanid for Pulmonary Tuberculosis Treatment

Tuberculosis (TB) is a contiguous airborne disease caused by Mycobacterium tuberculosis (M.tb), primarily affecting the human lungs. The progression of drug-susceptible TB to drug-resistant strains, MDR-TB and XDR-TB, has become a global challenge toward eradicating TB. Conventional TB treatment involves frequent dosing and prolonged treatment regimens predominantly by an oral or invasive route, leading to treatment-related systemic adverse effects and patient's noncompliance. Pulmonary delivery is an attractive option as we could reduce dose, limit systemic side-effects, and achieve rapid onset of action. Delamanid (DLD), an antituberculosis drug, has poor aqueous solubility, and in this study, we aim to improve its solubility using cyclodextrin complexation. We screened different cyclodextrins and found that HP-β-CD resulted in a 54-fold increase in solubility compared to a 27-fold and 13-fold increase by SBE-β-CD and HP-ɣ-CD, respectively. The stability constant (265 ± 15 M^-1) and complexation efficiency (8.5 × 10^-4) suggest the formation of a stable inclusion complex of DLD and HP-β-CD in a 2:1 ratio. Solid-state characterization studies (DSC, PXRD, and NMR) further confirmed successful complexation of DLD in HP-β-CD. The nebulized DLD-CD complex solution showed a mass median aerodynamic diameter of 4.42 ± 0.62 μm and fine particle fraction of 82.28 ± 2.79%, suggesting deposition in the respiratory airways. In bacterial studies, minimum inhibitory concentration of DLD-CD complex was significantly reduced (four-fold) compared to free DLD in M.tb (H37Ra strain). Furthermore, accelerated stability studies confirmed that the inclusion complex was stable for 4 weeks with 90%w/w drug content. In conclusion, we increased the aqueous solubility of DLD through cyclodextrin complexation and improved its efficacy in vitro.

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.

Delamanid Added to an Optimized Background Regimen in Children with Multidrug-Resistant Tuberculosis: Results of a Phase I/II Clinical Trial

Delamanid has been demonstrated to be safe and effective for treatment of adult multidrug-resistant tuberculosis (MDR-TB) and has been approved by the European Commission for treatment of pediatric MDR-TB patients at least 10 kg in weight, making the drug no longer limited to adults. A 10-day phase I age deescalation study was conducted, followed by a 6-month phase II extension study, to assess the pharmacokinetics, safety, tolerability, and preliminary efficacy of delamanid when combined with optimized background regimen (OBR) in children (birth to 17 years) with MDR-TB. Delamanid administered at 100 mg twice-daily (BID), 50 mg BID, and 25 mg BID resulted in exposures in 12- to 17- (n = 7), 6- to 11- (n = 6), and 3- to 5-year-olds (n = 12), respectively, comparable with those in adults at the approved adult dosage (100 mg BID). Exposures in 0- to 2-year-olds (n = 12) following a weight-based dosing regimen (5 mg once daily [QD] to 10 mg BID) were lower than predicted from pharmacokinetic modeling of the older three age groups and below target exposures in adults. Overall, the safety profile of delamanid in children 0 to 17 years of age was similar to the adult profile. At 24 months after the first delamanid dose, 33/37 children (89.2%) had favorable treatment outcomes, as defined by the World Health Organization (15/37 [40.5%] cured and 18/37 [48.6%] completed treatment). A new pediatric delamanid formulation used in 0- to 2-year-olds and 3- to 5-year-olds was palatable per child/parent and nurse/investigator reports. Data from initial phase I/II studies inform our understanding of delamanid use in children and support its further assessment in the setting of pediatric MDR-TB. (This study has been registered at ClinicalTrials.gov under identifiers NCT01856634 [phase I trial] and NCT01859923 [phase II trial].).

OUP accepted manuscript

Given the low treatment success rates of drug-resistant tuberculosis (TB), novel TB drugs are urgently needed. The landscape of TB treatment has changed considerably over the last decade with the approval of three new compounds: bedaquiline, delamanid and pretomanid. Of these, delamanid and pretomanid belong to the same class of drugs, the nitroimidazoles. In order to close the knowledge gap on how delamanid and pretomanid compare with each other, we summarize the main findings from preclinical research on these two compounds. We discuss the compound identification, mechanism of action, drug resistance, in vitro activity, in vivo pharmacokinetic profiles, and preclinical in vivo activity and efficacy. Although delamanid and pretomanid share many similarities, several differences could be identified. One finding of particular interest is that certain Mycobacterium tuberculosis isolates have been described that are resistant to either delamanid or pretomanid, but with preserved susceptibility to the other compound. This might imply that delamanid and pretomanid could replace one another in certain regimens. Regarding bactericidal activity, based on in vitro and preclinical in vivo activity, delamanid has lower MICs and higher mycobacterial load reductions at lower drug concentrations and doses compared with pretomanid. However, when comparing in vivo preclinical bactericidal activity at dose levels equivalent to currently approved clinical doses based on drug exposure, this difference in activity between the two compounds fades. However, it is important to interpret these comparative results with caution knowing the variability inherent in preclinical in vitro and in vivo models.

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.

Additional Drug Resistance in Patients with Multidrug-resistant Tuberculosis in Korea: a Multicenter Study from 2010 to 2019

BACKGROUND

Drug-resistance surveillance (DRS) data provide key information for building an effective treatment regimen in patients with multidrug-resistant tuberculosis (MDR-TB). This study was conducted to investigate the patterns and trends of additional drug resistance in MDR-TB patients in South Korea.

METHODS

Phenotypic drug susceptibility test (DST) results of MDR-TB patients collected from seven hospitals in South Korea from 2010 to 2019 were retrospectively analyzed.

RESULTS

In total, 633 patients with MDR-TB were included in the analysis. Of all patients, 361 (57.0%) were new patients. All patients had additional resistance to a median of three anti-TB drugs. The resistance rates of any fluoroquinolone (FQ), linezolid, and cycloserine were 26.2%, 0.0%, and 6.3%, respectively. The proportions of new patients and resistance rates of most anti-TB drugs did not decrease during the study period. The number of additional resistant drugs was significantly higher in FQ-resistant MDR-TB than in FQ-susceptible MDR-TB (median of 9.0 vs. 2.0). Among 26 patients with results of minimum inhibitory concentrations for bedaquiline (BDQ) and delamanid (DLM), one (3.8%) and three (11.5%) patients were considered resistant to BDQ and DLM with interim critical concentrations, respectively. Based on the DST results, 72.4% and 24.8% of patients were eligible for the World Health Organization's longer and shorter MDR-TB treatment regimen, respectively.

CONCLUSION

The proportions of new patients and rates of additional drug resistance in patients with MDR-TB were high and remain stable in South Korea. A nationwide analysis of DRS data is required to provide effective treatment for MDR-TB patients in South Korea.

Prevalence of Mycobacterium tuberculosis resistant to bedaquiline and delamanid in China

OBJECTIVES

The new antituberculous drugs delamanid and bedaquiline form the last line of defence against drug-resistant tuberculosis (TB). Understanding the background prevalence of resistance to new drugs can help predict the lifetime of these drugs' effectiveness and inform regimen design.

METHODS

Mycobacterium tuberculosis without prior exposure to novel anti-TB drugs were analysed retrospectively. Drug susceptibility testing for bedaquiline, delamanid, linezolid, clofazimine and widely used first- and second-line anti-TB drugs was performed. All TB isolates with resistance to new or repurposed drugs were subjected to whole-genome sequencing to explore the molecular characteristics of resistance and to perform phylogenetic analysis.

RESULTS

Overall, resistance to delamanid, bedaquiline, linezolid and clofazimine was observed in 0.7% (11/1603), 0.4% (6/1603), 0.4% (7/1603) and 0.4% (6/1603) of TB isolates, respectively. Moreover, 1.0% (1/102), 2.9% (3/102), 3.9% (4/102) and 1.0% (1/102) of multidrug-resistant TB (MDR-TB) were resistant to bedaquiline, delamanid, linezolid and clofazimine, respectively. Whereas 22.2% (2/9) of extensively-drug resistant tuberculosis (XDR-TB) isolates were resistant to both delamanid and linezolid, and none was resistant to bedaquiline or clofazimine. Phylogenetic analysis showed that recent transmission occurred in two XDR-TB with additional resistance to delamanid and linezolid. None known gene mutation associated with delamanid resistance was detected. All four isolates with cross-resistance to bedaquiline and clofazimine had a detected gene mutation in Rv0678. Three of five strains with linezolid resistance had a detected gene mutation in rplC.

CONCLUSION

Detection of resistance to new anti-TB drugs emphasises the pressing need for intensive surveillance for such resistance before their wide usage.

Treatment of Multidrug-Resistant and Extensively Drug-Resistant Tuberculosis in Children: The Role of Bedaquiline and Delamanid

Multidrug-resistant (MDR) tuberculosis (TB) has been emerging at an alarming rate over the last few years. It has been estimated that about 3% of all pediatric TB is MDR, meaning about 30,000 cases each year. Although most children with MDR-TB can be successfully treated, up to five years ago effective treatment was associated with a high incidence of severe adverse effects and patients with extensively drug-resistant (XDR) TB had limited treatment options and no standard regimen. The main objective of this manuscript is to discuss our present knowledge of the management of MDR- and XDR-TB in children, focusing on the characteristics and available evidence on the use of two promising new drugs: bedaquiline and delamanid. PubMed was used to search for all of the studies published up to November 2020 using key words such as "bedaquiline" and "delamanid" and "children" and "multidrug-resistant tuberculosis" and "extensively drug-resistant tuberculosis". The search was limited to articles published in English and providing evidence-based data. Although data on pediatric population are limited and more studies are needed to confirm the efficacy and safety of bedaquiline and delamanid, their use in children with MDR-TB/XDR-TB appears to have good tolerability and efficacy. However, more evidence on these new anti-TB drugs is needed to better guide their use in children in order to design effective shorter regimens and reduce adverse effects, drug interactions, and therapeutic failure.

The Role of Nitroreductases in Resistance to Nitroimidazoles

Antimicrobial resistance is a major challenge facing modern medicine, with an estimated 700,000 people dying annually and a global cost in excess of $100 trillion. This has led to an increased need to develop new, effective treatments. This review focuses on nitroimidazoles, which have seen a resurgence in interest due to their broad spectrum of activity against anaerobic Gram-negative and Gram-positive bacteria. The role of nitroreductases is to activate the antimicrobial by reducing the nitro group. A decrease in the activity of nitroreductases is associated with resistance. This review will discuss the resistance mechanisms of different disease organisms, including Mycobacterium tuberculosis, Helicobacter pylori and Staphylococcus aureus, and how these impact the effectiveness of specific nitroimidazoles. Perspectives in the field of nitroimidazole drug development are also summarised.

Delamanid Resistance: Update and Clinical Management

Delamanid, a-first-in-class bicyclic nitroimidazole, was recently approved for multidrug-resistant tuberculosis treatment. Pitted against the hope for improving treatment outcomes is the threat of the rapid resistance emergence. This review provides information on the mechanisms of action, resistance emergence, and drug susceptibility testing (DST) for delamanid. Delamanid resistance has already been reported in both in vitro experiments and clinical settings. Although mutations conferring delamanid resistance have been identified in fbiA, fbiB, fbiC, ddn, and fgd1 genes of Mycobacterium tuberculosis, knowledge about the molecular resistance mechanisms is limited, and there remains no standardized DST method. The rapid acquisition of delamanid resistance emphasizes the need for optimal use of new drugs, the need for drug resistance surveillance, and a comprehensive understanding of drug resistance mechanisms. Further studies are necessary to investigate genetic and phenotypic changes that determine clinically relevant delamanid resistance to help develop a rapid delamanid DST.

A Review of Clinical Pharmacokinetic and Pharmacodynamic Relationships and Clinical Implications for Drugs Used to Treat Multi-drug Resistant Tuberculosis

Multidrug-resistant tuberculosis (MDR-TB) is becoming a global health crisis. The World Health Organization has released new guidelines for the use of tuberculosis-active drugs for the treatment of patients with MDR-TB. Despite documented activity against tuberculosis isolates, doses and exposure targets are yet to be optimized. Our objective was therefore to review the clinical pharmacokinetic and pharmacodynamic literature pertaining to drugs recommended to treat MDR-TB and to identify target areas for future research. To date, published research is limited but studies were identified that evaluated the pharmacokinetics and pharmacodynamics of these drugs. Exposure targets were assessed and summarized for each drug. Exposure-based targets (e.g., area under the concentration curve/minimum inhibitory concentration) appear to be most commonly associated with predicting drug efficacy. Dose variation studies based on these targets were largely inconclusive. Future research should focus on determining the risks and benefits of dose optimization to meet exposure targets and improve patient outcomes. The role of therapeutic drug monitoring also remains yet to be confirmed, both from a clinical perspective as well as a resource allocation perspective in regions where MDR-TB is active.

Population Pharmacokinetic Analysis of Delamanid in Patients with Pulmonary Multidrug-Resistant Tuberculosis

A population pharmacokinetic (PopPK) model of delamanid in patients with pulmonary multidrug-resistant tuberculosis (MDR-TB) was developed using data from four delamanid clinical trials. The final PopPK data set contained 20,483 plasma samples from 744 patients with MDR-TB receiving an optimized background regimen (OBR). Delamanid PK was adequately described for all observed dosing regimens and subpopulations by a two-compartment model with first-order elimination and absorption, an absorption lag time, and decreased relative bioavailability with increasing dose. Relative bioavailabilities of 200-mg and higher doses (250 and 300 mg) were 76% and 58% of a 100-mg dose, respectively. Relative bioavailability was 26% higher after evening doses than morning doses and 9% higher in outpatient settings than inpatient settings. The rate of absorption was higher, and lag time was shorter, following a morning dose than an evening dose. Relative bioavailabilities in patients in Northeast Asian and Southeast Asian regions were 53% and 40% higher, respectively, than in patients in non-Asian regions. Apparent clearance was higher (to the power of -0.892) in patients with hypoalbuminemia (albumin levels of <3.4 g/dl). Coadministration of efavirenz in patients with HIV increased delamanid clearance by 35%. Delamanid exposure was not affected by age (18 to 64 years), mild or moderate renal impairment, anti-TB antibiotic resistance status, HIV status, or markers of hepatic dysfunction or by concomitant administration of OBR, lamivudine, tenofovir, pyridoxine, CYP3A4 inhibitors and inducers, or antacids. Model evaluation suggested reasonable model fit and predictive power, indicating that the model should prove reliable to derive PK metrics for subsequent PK/PD analyses.

Cumulative Fraction of Response for Once- and Twice-Daily Delamanid in Patients with Pulmonary Multidrug-Resistant Tuberculosis

Pharmacokinetic (PK) and pharmacodynamic (PD) analyses were conducted to determine the cumulative fraction of response (CFR) for 100 mg twice-daily (BID) and 200 mg once-daily (QD) delamanid in patients with multidrug-resistant tuberculosis (MDR-TB), using a pharmacodynamic target (PDT) that achieves 80% of maximum efficacy. First, in the mouse model of chronic TB, the PK/PD index for delamanid efficacy was determined to be area under the drug concentration-time curve over 24 h divided by MIC (AUC_0–24/MIC), with a PDT of 252.

Pharmacokinetic (PK) and pharmacodynamic (PD) analyses were conducted to determine the cumulative fraction of response (CFR) for 100 mg twice-daily (BID) and 200 mg once-daily (QD) delamanid in patients with multidrug-resistant tuberculosis (MDR-TB), using a pharmacodynamic target (PDT) that achieves 80% of maximum efficacy. First, in the mouse model of chronic TB, the PK/PD index for delamanid efficacy was determined to be area under the drug concentration-time curve over 24 h divided by MIC (AUC_0–24/MIC), with a PDT of 252. Second, in the hollow-fiber system model of tuberculosis, plasma-equivalent PDTs were identified as an AUC_0–24/MIC of 195 in log-phase bacteria and 201 in pH 5.8 cultures. Third, delamanid plasma AUC_0–24/MIC and sputum bacterial decline data from two early bactericidal activity trials identified a clinical PDT of AUC_0–24/MIC of 171. Finally, the CFRs for the currently approved 100-mg BID dose were determined to be above 95% in two MDR-TB clinical trials. The CFR for the 200-mg QD dose, evaluated in a trial in which delamanid was administered as 100 mg BID for 8 weeks plus 200 mg QD for 18 weeks, was 89.3% based on the mouse PDT and >90% on the other PDTs. QTcF (QTc interval corrected for heart rate by Fridericia’s formula) prolongation was approximately 50% lower for the 200 mg QD dose than the 100 mg BID dose. In conclusion, while CFRs of 100 mg BID and 200 mg QD delamanid were close to or above 90% in patients with MDR-TB, more-convenient once-daily dosing of delamanid is feasible and likely to have less effect on QTcF prolongation.

Mutations in fbiD (Rv2983) as a Novel Determinant of Resistance to Pretomanid and Delamanid in Mycobacterium tuberculosis

The nitroimidazole prodrugs delamanid and pretomanid comprise one of only two new antimicrobial classes approved to treat tuberculosis (TB) in 50 years. Prior in vitro studies suggest a relatively low barrier to nitroimidazole resistance in Mycobacterium tuberculosis, but clinical evidence is limited to date. We selected pretomanid-resistant M. tuberculosis mutants in two mouse models of TB using a range of pretomanid doses. The frequency of spontaneous resistance was approximately 10^-5 CFU. Whole-genome sequencing of 161 resistant isolates from 47 mice revealed 99 unique mutations, of which 91% occurred in 1 of 5 genes previously associated with nitroimidazole activation and resistance, namely, fbiC (56%), fbiA (15%), ddn (12%), fgd (4%), and fbiB (4%). Nearly all mutations were unique to a single mouse and not previously identified. The remaining 9% of resistant mutants harbored mutations in Rv2983 (fbiD), a gene not previously associated with nitroimidazole resistance but recently shown to be a guanylyltransferase necessary for cofactor F₄₂₀ synthesis. Most mutants exhibited high-level resistance to pretomanid and delamanid, although Rv2983 and fbiB mutants exhibited high-level pretomanid resistance but relatively small changes in delamanid susceptibility. Complementing an Rv2983 mutant with wild-type Rv2983 restored susceptibility to pretomanid and delamanid. By quantifying intracellular F₄₂₀ and its precursor Fo in overexpressing and loss-of-function mutants, we provide further evidence that Rv2983 is necessary for F₄₂₀ biosynthesis. Finally, Rv2983 mutants and other F₄₂₀H₂-deficient mutants displayed hypersusceptibility to some antibiotics and to concentrations of malachite green found in solid media used to isolate and propagate mycobacteria from clinical samples.

Clinical Outcomes Among Patients With Drug-resistant Tuberculosis Receiving Bedaquiline- or Delamanid-Containing Regimens

BACKGROUND

Bedaquiline and delamanid are newly available drugs for treating multidrug-resistant tuberculosis (MDR-TB); however, there are limited data guiding their use and no comparison studies.

METHODS

We conducted a prospective, observational study among patients with MDR-TB in Georgia who were receiving a bedaquiline- or delamanid-based treatment regimen. Monthly sputum cultures, minimal inhibitory concentration testing, and adverse event monitoring were performed. Primary outcomes were culture conversion rates and clinical outcomes. Targeted maximum likelihood estimation and super learning were utilized to produce a covariate-adjusted proportion of outcomes for each regimen.

RESULTS

Among 156 patients with MDR-TB, 100 were enrolled and 95 were receiving a bedaquiline-based (n = 64) or delamanid-based (n = 31) regimen. Most were male (82%) and the median age was 38 years. Rates of previous treatment (56%) and cavitary disease (61%) were high. The most common companion drugs included linezolid, clofazimine, cycloserine, and a fluoroquinolone. The median numbers of effective drugs received among patients on bedaquiline-based (4; interquartile range [IQR], 4-4) and delamanid-based (4; IQR, 3.5-5) regimens were similar. Rates of acquired drug resistance were significantly higher among patients receiving delamanid versus bedaquiline (36% vs 10%, respectively; P < .01). Adjusted rates of sputum culture conversion at 2 months (67% vs 47%, respectively; P = .10) and 6 months (95% vs 74%, respectively; P < .01), as well as more favorable clinical outcomes (96% vs 72%, respectively; P < .01), were higher among patients receiving bedaquiline versus delamanid.

CONCLUSIONS

Among patients with MDR-TB, bedaquiline-based regimens were associated with higher rates of sputum culture conversion, more favorable outcomes, and a lower rate of acquired drug resistance versus delamanid-based regimens.

Natural Polymorphisms in Mycobacterium tuberculosis Conferring Resistance to Delamanid in Drug-Naive Patients

Mutations in the genes of the F420 signaling pathway of Mycobacterium tuberculosis complex, including dnn, fgd1, fbiA, fbiB, fbiC, and fbiD, can lead to delamanid resistance. We searched for such mutations among 129 M. tuberculosis strains from Asia, South America, and Africa using whole-genome sequencing; 70 (54%) strains had at least one mutation in one of the genes. For 10 strains with mutations, we determined the MIC of delamanid. We found one strain from a delamanid-naive patient carrying the natural polymorphism Tyr29del (ddn) that was associated with a critical delamanid MIC.

Multi-drug resistant tuberculosis with simultaneously acquired-drug resistance to bedaquiline and delamanid

This study is the first to report a clinical case of simultaneously acquired resistance to bedaquiline (BDQ) and delamanid (DLM). Whole genome sequencing revealed two nucleotide insertions (Rv0678 and fbiC) in the Mycobacterium tuberculosis isolate. The minimum inhibitory concentrations for BDQ and DLM were 0.25 µg/ml and >2.0 µg/ml, respectively.

Bedaquiline and delamanid for drug-resistant tuberculosis: a clinician's perspective

Drug-resistant tuberculosis (TB) represents a substantial threat to the global efforts to control this disease. After decades of stagnation, the treatment of drug-resistant TB is undergoing major changes: two drugs with a new mechanism of action, bedaquiline and delamanid, have been approved by stringent regulatory authorities and are recommended by the WHO. This narrative review summarizes the evidence, originating from both observational studies and clinical trials, which is available to support the use of these drugs, with a focus on special populations. Areas of uncertainty, including the use of the two drugs together or for prolonged duration, are discussed. Ongoing clinical trials are aiming to optimize the use of bedaquiline and delamanid to shorten the treatment of drug-resistant TB.

Molecule Property Analyses of Active Compounds for Mycobacterium tuberculosis

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

Delamanid Central Nervous System Pharmacokinetics in Tuberculous Meningitis in Rabbits and Humans

Central nervous system tuberculosis (TB) is devastating and affects vulnerable populations. Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculous meningitis (TBM) specifically are nearly uniformly fatal, with little information being available to guide the treatment of these patients. Delamanid (DLM), a nitro-dihydro-imidazooxazole, is a new, well-tolerated anti-TB drug with a low MIC (1 to 12 ng/ml) against Mycobacterium tuberculosis It is used for the treatment of pulmonary MDR-TB, but pharmacokinetic (PK) data for DLM in the central nervous system (CNS) of patients with TBM are not available. In the present study, we measured DLM concentrations in the brain and cerebrospinal fluid (CSF) of six rabbits with and without experimentally induced TBM receiving single-dose DLM. We report the steady-state CSF concentrations from three patients receiving DLM as part of multidrug treatment who underwent therapeutic drug monitoring. Drug was quantified using liquid chromatography-tandem mass spectrometry. In rabbits and humans, mean concentrations in CSF (in rabbits, 1.26 ng/ml at 9 h and 0.47 ng/ml at 24 h; in humans, 48 ng/ml at 4 h) were significantly lower than those in plasma (in rabbits, 124 ng/ml at 9 h and 14.5 ng/ml at 24 h; in humans, 726 ng/ml at 4 h), but the estimated free CSF/plasma ratios were generally >1. In rabbits, DLM concentrations in the brain were 5-fold higher than those in plasma (means, 518 ng/ml at 9 h and 74.0 ng/ml at 24 h). All patients with XDR-TBM receiving DLM experienced clinical improvement and survival. Collectively, these results suggest that DLM achieves adequate concentrations in brain tissue. Despite relatively low total CSF drug levels, free drug may be sufficient and DLM may have a role in treating TBM. More studies are needed to develop a fuller understanding of its distribution over time with treatment and clinical effectiveness.

Finding New Ways to Combat Multidrug-Resistant Tuberculosis

Tuberculosis (TB) is a major issue in global health and affects millions of people each year. Multidrug-resistant tuberculosis (MDR-TB) annually causes many deaths worldwide. Development of a way to diagnose and treat patients with MDR-TB can potentially reduce the incidence of the disease. The current study reviews the risk factors, pattern of progression, mechanism of resistance, and interaction between bacteria and the host immune system, which disrupts the immune response. It also targets the components of Mycobacterium tuberculosis (Mtb) and diagnosis and treatment options that could be available for clinical use in the near future. Mutations play an important role in development of MDR-TB and the selection of appropriate mutations can help to understand the type of resistance in patients to anti-TB drugs. In this way, they can be initially treated with proper and effective therapeutic choices, which can accelerate the course of treatment and improve patient health. Targeting the components and enzymes of Mtb is necessary for understanding bacterial survival and finding a way to destroy the pathogen and allow patients to recover faster and prevent the spread of disease, especially resistant strains.

Dual-targeting GroEL/ES chaperonin and protein tyrosine phosphatase B (PtpB) inhibitors: A polypharmacology strategy for treating Mycobacterium tuberculosis infections

Current treatments for Mycobacterium tuberculosis infections require long and complicated regimens that can lead to patient non-compliance, increasing incidences of antibiotic-resistant strains, and lack of efficacy against latent stages of disease. Thus, new therapeutics are needed to improve tuberculosis standard of care. One strategy is to target protein homeostasis pathways by inhibiting molecular chaperones such as GroEL/ES (HSP60/10) chaperonin systems. M. tuberculosis has two GroEL homologs: GroEL1 is not essential but is important for cytokine-dependent granuloma formation, while GroEL2 is essential for survival and likely functions as the canonical housekeeping chaperonin for folding proteins. Another strategy is to target the protein tyrosine phosphatase B (PtpB) virulence factor that M. tuberculosis secretes into host cells to help evade immune responses. In the present study, we have identified a series of GroEL/ES inhibitors that inhibit M. tuberculosis growth in liquid culture and biochemical function of PtpB in vitro. With further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis - actively replicating bacteria, bacteria evading host cell immune responses, and granuloma formation in latent disease - which would be a significant advance to augment current therapeutics that primarily target actively replicating bacteria.

Comparison of in vitro activity of the nitroimidazoles delamanid and pretomanid against multidrug-resistant and extensively drug-resistant tuberculosis

Delamanid exhibited greater in vitro potency than pretomanid against multidrug-resistant (MDR-) and extensively drug-resistant tuberculosis (XDR-TB) isolates. The pretomanid minimum inhibitory concentration (MIC) values of four MDR-TB isolates were found to be resistant to delamanid ranging from 0.031 to 0.063 mg/L. A novel nonsynonymous mutation within the fbiA gene (Glu249Lys) may be contributing to high-level resistance to delamanid and pretomanid in Mycobacterium tuberculosis.

Delamanid, Bedaquiline, and Linezolid Minimum Inhibitory Concentration Distributions and Resistance-related Gene Mutations in Multidrug-resistant and Extensively Drug-resistant Tuberculosis in Korea

Background

Delamanid, bedaquiline, and linezolid have recently been approved for the treatment of multidrug- and extensively drug-resistant (MDR and XDR, respectively) tuberculosis (TB). To use these drugs effectively, drug susceptibility tests, including rapid molecular techniques, are required for accurate diagnosis and treatment. Furthermore, mutation analyses are needed to assess the potential for resistance. We evaluated the minimum inhibitory concentrations (MICs) of these three anti-TB drugs for Korean MDR and XDR clinical strains and mutations in genes related to resistance to these drugs.

Methods

MICs were determined for delamanid, bedaquiline, and linezolid using a microdilution method. The PCR products of drug resistance-related genes from 420 clinical Mycobacterium tuberculosis strains were sequenced and aligned to those of M. tuberculosis H37Rv.

Results

The overall MICs for delamanid, bedaquiline, and linezolid ranged from ≤0.025 to >1.6 mg/L, ≤0.0312 to >4 mg/L, and ≤0.125 to 1 mg/L, respectively. Numerous mutations were found in drug-susceptible and -resistant strains. We did not detect specific mutations associated with resistance to bedaquiline and linezolid. However, the Gly81Ser and Gly81Asp mutations were associated with resistance to delamanid.

Conclusions

We determined the MICs of three anti-TB drugs for Korean MDR and XDR strains and identified various mutations in resistance-related genes. Further studies are needed to determine the genetic mechanisms underlying resistance to these drugs.

Genetics and roadblocks of drug resistant tuberculosis

Considering the extensive evolutionary history of Mycobacterium tuberculosis, anti-Tuberculosis (TB) drug therapy exerts a recent selective pressure. However, in a microorganism devoid of horizontal gene transfer and with a strictly clonal populational structure such as M. tuberculosis the usual, but not sole, path to overcome drug susceptibility is through de novo mutations on a relatively strict set of genes. The possible allelic diversity that can be associated with drug resistance through several mechanisms such as target alteration or target overexpression, will dictate how these genes can become associated with drug resistance. The success demonstrated by this pathogenic microbe in this latter process and its ability to spread is currently one of the major obstacles to an effective TB elimination. This article reviews the action mechanism of the more important anti-TB drugs, including bedaquiline and delamanid, along with new findings on specific resistance mechanisms. With the development, validation and endorsement of new in vitro molecular tests for drug resistance, knowledge on these resistance mechanisms and microevolutionary dynamics leading to the emergence and fixation of drug resistance mutations within the host is highly important. Additionally, the fitness toll imposed by resistance development is also herein discussed together with known compensatory mechanisms. By elucidating the possible mechanisms that enable one strain to reacquire the original fitness levels, it will be theoretically possible to make more informed decisions and develop novel strategies that can force M. tuberculosis microevolutionary trajectory down through a path of decreasing fitness levels.

Modeling and Simulation of Pretomanid Pharmacokinetics in Pulmonary Tuberculosis Patients

Pretomanid is a nitroimidazole antibiotic in late-phase clinical testing as a component of several novel antituberculosis (anti-TB) regimens. A population pharmacokinetic model for pretomanid was constructed using a Bayesian analysis of data from two phase 2 studies, PA-824-CL-007 and PA-824-CL-010, conducted with adult (median age, 27 years) patients in Cape Town, South Africa, with newly diagnosed pulmonary TB. Combined, these studies included 63 males and 59 females administered once-daily oral pretomanid doses of 50, 100, 150, 200, 600, 1,000, or 1,200 mg for 14 days. The observed pretomanid plasma concentration-time profiles for all tested doses were described by a one-compartment model with first-order absorption and elimination and a sigmoidal bioavailability dependent on dose, time, and the predose fed state. Allometric scaling with body weight (normalized to 70 kg) was used for volume of distribution and clearance, with the scaling exponents equal to 1 and 3/4, respectively. The posterior population geometric means for the clearance and volume of distribution allometric constants were 4.8 ± 0.2 liters/h and 130 ± 5 liters, respectively, and the posterior population geometric mean for the half-maximum-effect dose for the reduction of bioavailability was 450 ± 50 mg. Interindividual variability, described by the percent coefficient of variation, was 32% ± 3% for clearance, 17% ± 4% for the volume of distribution, and 74% ± 9% for the half-maximum-effect dose. This model provides a dose-exposure relationship for pretomanid in adult TB patients with potential applications to dose selection in individuals and to further clinical testing of novel pretomanid-containing anti-TB regimens.

Mechanisms of resistance to delamanid, a drug for Mycobacterium tuberculosis

Delamanid, a bicyclic nitroimidazooxazole, is effective against M. tuberculosis. Previous studies have shown that resistance to a bicyclic nitroimidazooxazine, PA-824, is caused by mutations in an F₄₂₀-dependent bio-activation pathway. We investigated whether the same mechanisms are responsible for resistance to delamanid. Spontaneous resistance frequencies were determined using M. bovis BCG Tokyo (BCG) and M. tuberculosis H37Rv. F₄₂₀ high-performance liquid chromatography (HPLC) elution patterns of homogenates of delamanid-resistant BCG colonies and two previously identified delamanid-resistant M. tuberculosis clinical isolates were examined, followed by sequencing of genes in the F₄₂₀-dependent bio-activation pathway. Spontaneous resistance frequencies to delamanid were similar to those of isoniazid and PA-824. Four distinct F₄₂₀ HPLC elution patterns were observed, corresponding to colonies with mutations on fgd1, fbiA, fbiB, and fbiC with no change in the ddn mutants from the wildtype. Complementation with the wildtype sequence of the mutated gene restored susceptibility. The two delamanid-resistant clinical isolates had ddn mutations and the wildtype F₄₂₀ HPLC elution pattern. In conclusion, delamanid-resistant bacilli have mutations in one of the 5 genes in the F₄₂₀-dependent bio-activation pathway with distinct F₄₂₀ HPLC elution patterns. Both genetic and phenotypic changes may be considered in the development of a rapid susceptibility test for delamanid.

Discovery of a Potent and Specific M. tuberculosis Leucyl-tRNA Synthetase Inhibitor: (S)-3-(Aminomethyl)-4-chloro-7-(2-hydroxyethoxy)benzo[c][1,2]oxaborol-1(3H)-ol (GSK656)

There is an urgent need to develop new and safer antitubercular agents that possess a novel mode of action. We synthesized and evaluated a novel series of 3-aminomethyl 4-halogen benzoxaboroles as Mycobacterium tuberculosis (Mtb) leucyl-tRNA synthetase (LeuRS) inhibitors. A number of Mtb LeuRS inhibitors were identified that demonstrated good antitubercular activity with high selectivity over human mitochondrial and cytoplasmic LeuRS. Further evaluation of these Mtb LeuRS inhibitors by in vivo pharmacokinetics (PK) and murine tuberculosis (TB) efficacy models led to the discovery of GSK3036656 (abbreviated as GSK656). This molecule shows potent inhibition of Mtb LeuRS (IC₅₀ = 0.20 μM) and in vitro antitubercular activity (Mtb H37Rv MIC = 0.08 μM). Additionally, it is highly selective for the Mtb LeuRS enzyme with IC₅₀ of >300 μM and 132 μM for human mitochondrial LeuRS and human cytoplasmic LeuRS, respectively. In addition, it exhibits remarkable PK profiles and efficacy against Mtb in mouse TB infection models with superior tolerability over initial leads. This compound has been progressed to clinical development for the treatment of tuberculosis.

Delamanid Kills Dormant Mycobacteria In Vitro and in a Guinea Pig Model of Tuberculosis

Tuberculosis (TB) treatment is long and requires multiple drugs, likely due to various phenotypes of TB bacilli with variable drug susceptibilities. Drugs with broad activity are urgently needed. This study aimed to evaluate delamanid's activity against growing or dormant bacilli in vitro as well as in vivo Cultures of Mycobacterium bovis BCG Tokyo under aerobic and anaerobic conditions were used to study the activity of delamanid against growing and dormant bacilli, respectively. Delamanid exhibited significant bactericidal activity against replicating and dormant bacilli at or above concentrations of 0.016 and 0.4 mg/liter, respectively. To evaluate delamanid's antituberculosis activity in vivo, we used a guinea pig model of chronic TB infection in which the lung lesions were similar to those in human TB disease. In the guinea pig TB model, a daily dose of 100 mg delamanid/kg of body weight for 4 or 8 weeks demonstrated strong bactericidal activity against Mycobacterium tuberculosis Importantly, histological examination revealed that delamanid killed TB bacilli within hypoxic lesions of the lung. The combination regimens containing delamanid with rifampin and pyrazinamide or delamanid with levofloxacin, ethionamide, pyrazinamide, and amikacin were more effective than the standard regimen (rifampin, isoniazid, and pyrazinamide). Our data show that delamanid is effective in killing both growing and dormant bacilli in vitro and in the guinea pig TB model. Adding delamanid to current TB regimens may improve treatment outcomes, as demonstrated in recent clinical trials with pulmonary multidrug-resistant (MDR) TB patients. Delamanid may be an important drug for consideration in the construction of new regimens to shorten TB treatment duration.

Nitroimidazoles: Molecular Fireworks That Combat a Broad Spectrum of Infectious Diseases

Infectious diseases claim millions of lives every year, but with the advent of drug resistance, therapeutic options to treat infections are inadequate. There is now an urgent need to develop new and effective treatments. Nitroimidazoles are a class of antimicrobial drugs that have remarkable broad spectrum activity against parasites, mycobacteria, and anaerobic Gram-positive and Gram-negative bacteria. While nitroimidazoles were discovered in the 1950s, there has been renewed interest in their therapeutic potential, particularly for the treatment of parasitic infections and tuberculosis. In this review, we summarize different classes of nitroimidazoles that have been described in the literature in the past five years, from approved drugs and clinical candidates to examples undergoing preclinical or early stage development. The relatively "nonspecific" mode of action and resistance mechanisms of nitromidazoles are discussed, and contemporary strategies to facilitate nitroimidazole drug development are highlighted.