Sputum lipoarabinomannan (LAM) as a biomarker to determine sputum mycobacterial load: exploratory and model-based analyses of integrated data from four cohorts

Safety, pharmacokinetics, and early bactericidal activity of quabodepistat in combination with delamanid, bedaquiline, or both in adults with pulmonary tuberculosis: a randomised, active-controlled, open-label trial

BACKGROUND

Quabodepistat (formerly OPC-167832) showed potent activity in preclinical studies and in the first stage of an early bactericidal activity study in adults with smear-positive, drug-susceptible pulmonary tuberculosis. Stage 2 of this study was designed to evaluate the safety, tolerability, pharmacokinetics, and early bactericidal activity of quabodepistat in combination with delamanid, bedaquiline, or both versus rifampicin, isoniazid, ethambutol, and pyrazinamide combination therapy for 14 days.

METHODS

Stage 2 of this open-label, active-controlled, randomised, parallel-group study was conducted at two research sites in South Africa in adults (aged 18-64 years) with drug-susceptible pulmonary tuberculosis. Eligible participants had a BMI of 16-32 kg/m2 and the ability to produce an adequate volume of sputum (≥10 mL overnight) and were excluded if they had drug-resistant tuberculosis or previous treatment for Mycobacterium tuberculosis within the past 3 years. Participants were centrally randomly assigned via interactive web response technology system, with no stratification, into four treatment groups in a ratio of 14:14:14:4 (quabodepistat 30 mg plus delamanid 300 mg, quabodepistat 30 mg plus bedaquiline 400 mg, or quabodepistat 30 mg plus delamanid 300 mg plus bedaquiline 400 mg orally once daily for 14 days, or rifampicin, isoniazid, ethambutol, and pyrazinamide combination therapy [control] according to local standard of care for 20 days). The primary outcomes were safety and tolerability during and after 14 days of treatment in all participants who received any study medication and pharmacokinetics at day 1 and day 14 in participants in the quabodepistat groups with adequate data for deriving pharmacokinetics parameters. The main secondary outcome was bactericidal activity from baseline to day 14 in all eligible participants who were quantitatively culture-positive at baseline. The study was not powered for formal statistical hypothesis testing; therefore, data were summarised by treatment group with descriptive statistics. This study is registered with ClinicalTrials.gov (NCT03678688) and is closed to new participants.

FINDINGS

98 participants were screened for entry into stage 2 of the trial between Feb 1, 2021, and Jan 27, 2022, of whom 46 were randomly assigned (14 to each quabodepistat group, 4 to the control group) and 44 received at least one dose of study medication (one patient excluded from the quabodepistat plus delamanid and quabodepistat plus bedaquiline groups). 32 (73%) of 44 participants had at least one treatment-emergent adverse event. Most events (30/32 [94%]) were mild or moderate; the most common treatment-emergent adverse events (≥2 participants; not related to study drugs) were headache (4/44 [9%]), dizziness (3/44 [7%]), abdominal pain (2/44 [5%]), pruritus (2/44 [5%]), and nausea (2/44 [5%]). Two serious adverse events were reported in two participants in the quabodepistat and bedaquiline cohort (anal abscess [n=1], pneumothorax [n=1]); both were deemed not related to study drug. Quabodepistat exposure was minimally affected by coadministration of delamanid or bedaquiline, with lower exposure in the quabodepistat and bedaquiline cohorts (maximum plasma concentration for quabodepistat plus delamanid 208 ng/mL [SD 61; n=11]; quabodepistat plus bedaquiline 175 ng/mL [31; n=10]; quabodepistat plus delamanid plus bedaquiline 183 ng/mL [52; n=11]). Maximum quabodepistat concentrations were achieved approximately 3 h after administration in all combinations. Mean elimination half-life was shorter in combinations with bedaquiline than without bedaquiline (12·3-14·5 h vs 15·2 h). Mean changes from baseline to day 14 of sputum log10 colony-forming units per mL were -2·73 (SD 1·51) for quabodepistat plus delamanid plus bedaquiline (n=12) and -2·71 (SD 0·92) for control (n=19); mean change was -2·17 (SD 1·83) in the quabodepistat plus delamanid cohort (n=11) and -1·97 (SD 1·29) in the quabodepistat plus bedaquiline cohort (n=11).

INTERPRETATION

In this 14-day trial, quabodepistat plus delamanid plus bedaquiline, a novel three-drug combination, appeared to be safe, well tolerated, and provided robust early bactericidal activity in adults with drug-susceptible pulmonary tuberculosis. Further evaluation is warranted.

FUNDING

Otsuka Pharmaceutical Development & Commercialization and the Bill & Melinda Gates Foundation.

Update on the diagnosis of tuberculosis

BACKGROUND

Tuberculosis (TB) remains a global public health threat, and the development of rapid and precise diagnostic tools is the key to enabling the early start of treatment, monitoring response to treatment, and preventing the spread of the disease.

OBJECTIVES

An overview of recent progress in host- and pathogen-based TB diagnostics.

SOURCES

We conducted a PubMed search of recent relevant articles and guidelines on TB screening and diagnosis.

CONTENT

An overview of currently used methods and perspectives in the following areas of TB diagnostics is provided: immune-based diagnostics, X-ray, clinical symptoms and scores, cough detection, culture of Mycobacterium tuberculosis and identifying its resistance profile using phenotypic and genotypic methods, including next-generation sequencing, sputum- and non-sputum-based molecular diagnosis of TB and monitoring of response to treatment.

IMPLICATIONS

A brief overview of the most relevant advances and changes in international guidelines regarding screening and diagnosing TB is provided in this review. It aims at reviewing all relevant areas of diagnostics, including both pathogen- and host-based methods.

Development and preliminary evaluation toward a new tuberculosis treatment monitoring tool: the PATHFAST TB LAM Ag assay

The PATHFAST TB LAM Ag assay is based on a chemiluminescent enzyme immunoassay to quantify lipoarabinomannan (LAM) in sputum within 1 h, and was developed as an alternative to conventional culture methods for monitoring tuberculosis (TB) treatment. This study aimed to evaluate the analytical performance and initial clinical feasibility of using five Mycobacterium tuberculosis variants, 178 non-tuberculous mycobacteria (NTM), 34 upper respiratory and oral cavity microorganisms, 100 sputum specimens from untreated patients, and potential interfering substances, including 27 drugs. The results reveled a single-site repeatability coefficient of variation (CV) of 5.2%-7.0%, and a multi-site reproducibility CV of 7.1%-8.4%. The limit of blank, limit of detection, and limit of quantification were 3.03 pg/mL, 6.67 pg/mL, and 7.44 pg/mL, respectively. Linearity was observed over the analytical measurement range (10.0 pg/mL-50,000 pg/mL), and no hook effect was observed. The assay tended to cross-react with slow-growing NTMs, but not with common upper respiratory and oral cavity microorganisms, except Nocardia asteroides, Nocardia farcinica, and Tsukamurella paurometabola. No interference was observed in the presence of mucin, blood, or major anti-TB, anti-HIV, and anti-pneumonia drugs. Regarding clinical performance, the assay had a sensitivity of 88.8% (95% CI: 80.0%-94.0%) and specificity of 100.0% (95% CI: 83.9%-100.0%) using mycobacterial culture as the reference standard, and a correlation (Spearman's r = -0.770) was observed between LAM concentration and time to detection of culture. These findings show, for the first time, that the PATHFAST TB LAM Ag assay has potential value for monitoring TB treatment.

A Systematic Review of Potential Biomarkers for Bacterial Burden and Treatment Efficacy Assessment in Tuberculosis Platform-Based Clinical Trials

Adaptive platform trials can be more efficient than classic trials for developing new treatments. Moving from culture-based to simpler- or faster-to-measure biomarkers as efficacy surrogates may enhance this advantage. We performed a systematic review of treatment efficacy biomarkers in adults with tuberculosis. Platform trials can span different development phases. We grouped biomarkers as: α, bacterial load estimates used in phase 2a trials; β, early and end-of treatment end points, phase 2b-c trials; γ, posttreatment or trial-level estimates, phase 2c-3 trials. We considered as analysis unit (biomarker entry) each combination of biomarker, predicted outcome, and their respective measurement times or intervals. Performance metrics included: sensitivity, specificity, area under the receiver-operator curve (AUC), and correlation measures, and classified as poor, promising, or good. Eighty-six studies included 22 864 participants. From 1356 biomarker entries, 318 were reported with the performance metrics of interest, with 103 promising and 41 good predictors. Group results were: α, mycobacterial RNA and lipoarabinomannan (LAM) in sputum, and host metabolites in urine; β, mycobacterial RNA and host transcriptomic or cytokine signatures for early treatment response; and γ, host transcriptomics for recurrence. A combination of biomarkers from different categories could help in designing more efficient platform trials. Efforts to develop efficacy surrogates should be better coordinated.

Use of multiple pharmacodynamic measures to deconstruct the Nix-TB regimen in a short-course murine model of tuberculosis

A major challenge for tuberculosis (TB) drug development is to prioritize promising combination regimens from a large and growing number of possibilities. This includes demonstrating individual drug contributions to the activity of higher-order combinations. A BALB/c mouse TB infection model was used to evaluate the contributions of each drug and pairwise combination in the clinically relevant Nix-TB regimen [bedaquiline-pretomanid-linezolid (BPaL)] during the first 3 weeks of treatment at human equivalent doses. The rRNA synthesis (RS) ratio, an exploratory pharmacodynamic (PD) marker of ongoing Mycobacterium tuberculosis rRNA synthesis, together with solid culture CFU counts and liquid culture time to positivity (TTP) were used as PD markers of treatment response in lung tissue; and their time-course profiles were mathematically modeled using rate equations with pharmacologically interpretable parameters. Antimicrobial interactions were quantified using Bliss independence and Isserlis formulas. Subadditive (or antagonistic) and additive effects on bacillary load, assessed by CFU and TTP, were found for bedaquiline-pretomanid and linezolid-containing pairs, respectively. In contrast, subadditive and additive effects on rRNA synthesis were found for pretomanid-linezolid and bedaquiline-containing pairs, respectively. Additionally, accurate predictions of the response to BPaL for all three PD markers were made using only the single-drug and pairwise effects together with an assumption of negligible three-way drug interactions. The results represent an experimental and PD modeling approach aimed at reducing combinatorial complexity and improving the cost-effectiveness of in vivo systems for preclinical TB regimen development.

Therapeutic developments for tuberculosis and nontuberculous mycobacterial lung disease

Tuberculosis (TB) drug discovery and development has undergone nothing short of a revolution over the past 20 years. Successful public-private partnerships and sustained funding have delivered a much-improved understanding of mycobacterial disease biology and pharmacology and a healthy pipeline that can tolerate inevitable attrition. Preclinical and clinical development has evolved from decade-old concepts to adaptive designs that permit rapid evaluation of regimens that might greatly shorten treatment duration over the next decade. But the past 20 years also saw the rise of a fatal and difficult-to-cure lung disease caused by nontuberculous mycobacteria (NTM), for which the drug development pipeline is nearly empty. Here, we discuss the similarities and differences between TB and NTM lung diseases, compare the preclinical and clinical advances, and identify major knowledge gaps and areas of cross-fertilization. We argue that applying paradigms and networks that have proved successful for TB, from basic research to clinical trials, will help to populate the pipeline and accelerate curative regimen development for NTM disease.

Does PET-CT Have a Role in the Evaluation of Tuberculosis Treatment in Phase 2 Clinical Trials?

Positron emission tomography-computed tomography (PET-CT) has the potential to revolutionize research in infectious diseases, as it has done with cancer. There is growing interest in it as a biomarker in the setting of early-phase tuberculosis clinical trials, particularly given the limitations of current biomarkers as adequate predictors of sterilizing cure for tuberculosis. PET-CT is a real-time tool that provides a 3-dimensional view of the spatial distribution of tuberculosis within the lung parenchyma and the nature of lesions with uptake (ie, whether nodular, consolidative, or cavitary). Its ability to provide functional data on changes in metabolism, drug penetration, and immune control of tuberculous lesions has the potential to facilitate drug development and regimen selection for advancement to phase 3 trials in tuberculosis. In this narrative review, we discuss the role that PET-CT may have in evaluating responses to drug therapy in active tuberculosis treatment and the challenges in taking PET-CT forward as predictive biomarker of relapse-free cure in the setting of phase 2 clinical trials.

Phase I Single Ascending Dose and Food Effect Study in Healthy Adults and Phase I/IIa Multiple Ascending Dose Study in Patients with Pulmonary Tuberculosis to Assess Pharmacokinetics, Bactericidal Activity, Tolerability, and Safety of OPC-167832

OPC-167832, an inhibitor of decaprenylphosphoryl-β-d-ribose 2'-oxidase, demonstrated potent antituberculosis activity and a favorable safety profile in preclinical studies. This report describes the first two clinical studies of OPC-167832: (i) a phase I single ascending dose (SAD) and food effects study in healthy participants; and (ii) a 14-day phase I/IIa multiple ascending dose (MAD; 3/10/30/90 mg QD) and early bactericidal activity (EBA) trial in participants with drug-susceptible pulmonary tuberculosis (TB). OPC-167832 was well tolerated at single ascending doses (10 to 480 mg) in healthy participants and multiple ascending doses (3 to 90 mg) in participants with TB. In both populations, nearly all treatment-related adverse events were mild and self-limiting, with headache and pruritus being the most common events. Abnormal electrocardiograms results were rare and clinically insignificant. In the MAD study, OPC-167832 plasma exposure increased in a less than dose-proportional manner, with mean accumulation ratios ranging from 1.26 to 1.56 for Cmax and 1.55 to 2.01 for area under the concentration-time curve from 0 to 24 h (AUC0-24h). Mean terminal half-lives ranged from 15.1 to 23.6 h. Pharmacokinetics (PK) characteristics were comparable to healthy participants. In the food effects study, PK exposure increased by less than ~2-fold under fed conditions compared to the fasted state; minimal differences were observed between standard and high-fat meals. Once-daily OPC-167832 showed 14-day bactericidal activity from 3 mg (log10 CFU mean ± standard deviation change from baseline; -1.69 ± 1.15) to 90 mg (-2.08 ± 0.75), while the EBA of Rifafour e-275 was -2.79 ± 0.96. OPC-167832 demonstrated favorable pharmacokinetic and safety profiles, as well as potent EBA in participants with drug-susceptible pulmonary TB.

Standards for model-based early bactericidal activity analysis and sample size determination in tuberculosis drug development

Background: A critical step in tuberculosis (TB) drug development is the Phase 2a early bactericidal activity (EBA) study which informs if a new drug or treatment has short-term activity in humans. The aim of this work was to present a standardized pharmacometric model-based early bactericidal activity analysis workflow and determine sample sizes needed to detect early bactericidal activity or a difference between treatment arms. Methods: Seven different steps were identified and developed for a standardized pharmacometric model-based early bactericidal activity analysis approach. Non-linear mixed effects modeling was applied and different scenarios were explored for the sample size calculations. The sample sizes needed to detect early bactericidal activity given different TTP slopes and associated variability was assessed. In addition, the sample sizes needed to detect effect differences between two treatments given the impact of different TTP slopes, variability in TTP slope and effect differences were evaluated. Results: The presented early bactericidal activity analysis approach incorporates estimate of early bactericidal activity with uncertainty through the model-based estimate of TTP slope, variability in TTP slope, impact of covariates and pharmacokinetics on drug efficacy. Further it allows for treatment comparison or dose optimization in Phase 2a. To detect early bactericidal activity with 80% power and at a 5% significance level, 13 and 8 participants/arm were required for a treatment with a TTP-EBA0-14 as low as 11 h when accounting for variability in pharmacokinetics and when variability in TTP slope was 104% [coefficient of variation (CV)] and 22%, respectively. Higher sample sizes are required for smaller early bactericidal activity and when pharmacokinetics is not accounted for. Based on sample size determinations to detect a difference between two groups, TTP slope, variability in TTP slope and effect difference between two treatment arms needs to be considered. Conclusion: In conclusion, a robust standardized pharmacometric model-based EBA analysis approach was established in close collaboration between microbiologists, clinicians and pharmacometricians. The work illustrates the importance of accounting for covariates and drug exposure in EBA analysis in order to increase the power of detecting early bactericidal activity for a single treatment arm as well as differences in EBA between treatments arms in Phase 2a trials of TB drug development.