Short-course therapy with daily rifapentine in a murine model of latent tuberculosis infection

Bactericidal and sterilizing activity of sudapyridine-clofazimine-TB47 combined with linezolid or pyrazinamide in a murine model of tuberculosis

As an obligate aerobe, Mycobacterium tuberculosis relies on its branched electron transport chain (ETC) for energy production through oxidative phosphorylation. Regimens targeting ETC exhibit promising potential to enhance bactericidal activity against M. tuberculosis and hold the prospect of shortening treatment duration. Our previous research demonstrated that the bacteriostatic drug candidate TB47 (T) inhibited the growth of M. tuberculosis by targeting the cytochrome bc1 complex and exhibited synergistic activity with clofazimine (C). Here, we found synergistic activities between C and sudapyridine (S), a structural analog of bedaquiline (B). S has shown similar anti-tuberculosis efficacy and may share a mechanism of action with B, which inhibits ATP synthesis and the energy metabolism of bacteria. We evaluated the efficacy of SCT in combination with linezolid (L) or pyrazinamide (Z) using a well-established murine model of tuberculosis. Compared to the BPa(pretomanid)L regimen, SCT and SCTL demonstrated similar bactericidal and sterilizing activities. There was no significant difference in activity between SCT and SCTL. In contrast, SCZ and SCTZ showed much higher activities, with none of the 15 mice experiencing relapse after 2 months of treatment with either SCZ or SCTZ. However, T did not contribute to the activity of the SCZ. Our findings emphasize the efficacy and the potential clinical significance of combination therapy with ETC inhibitors. Additionally, cross-resistance exists not only between S and B but also between S/B and C. This is supported by our findings, as spontaneous S-resistant mutants exhibited mutations in Rv0678, which are associated with cross-resistance to B and C.

Using Dynamic Oral Dosing of Rifapentine and Rifabutin to Simulate Exposure Profiles of Long-Acting Formulations in a Mouse Model of Tuberculosis Preventive Therapy

Administration of tuberculosis preventive therapy (TPT) to individuals with latent tuberculosis infection is an important facet of global tuberculosis control. The use of long-acting injectable (LAI) drug formulations may simplify and shorten regimens for this indication. Rifapentine and rifabutin have antituberculosis activity and physiochemical properties suitable for LAI formulation, but there are limited data available for determining the target exposure profiles required for efficacy in TPT regimens. The objective of this study was to determine exposure-activity profiles of rifapentine and rifabutin to inform development of LAI formulations for TPT. We used a validated paucibacillary mouse model of TPT in combination with dynamic oral dosing of both drugs to simulate and understand exposure-activity relationships to inform posology for future LAI formulations. This work identified several LAI-like exposure profiles of rifapentine and rifabutin that, if achieved by LAI formulations, could be efficacious as TPT regimens and thus can serve as experimentally determined targets for novel LAI formulations of these drugs. We present novel methodology to understand the exposure-response relationship and inform the value proposition for investment in development of LAI formulations that have utility beyond latent tuberculosis infection.

Using dynamic oral dosing of rifapentine and rifabutin to simulate exposure profiles of long-acting formulations in a mouse model of tuberculosis preventive therapy

Administration of tuberculosis preventive therapy (TPT) to individuals with latent tuberculosis infection is an important facet of global tuberculosis control. The use of long-acting injectable (LAI) drug formulations may simplify and shorten regimens for this indication. Rifapentine and rifabutin have anti-tuberculosis activity and physiochemical properties suitable for LAI formulation, but there are limited data available for determining the target exposure profiles required for efficacy in TPT regimens. The objective of this study was to determine exposure-activity profiles of rifapentine and rifabutin to inform development of LAI formulations for TPT. We utilized a validated paucibacillary mouse model of TPT in combination with dynamic oral dosing of both drugs to simulate and understand exposure-activity relationships to inform posology for future LAI formulations. This work identified several LAI-like exposure profiles of rifapentine and rifabutin that, if achieved by LAI formulations, could be efficacious as TPT regimens and thus can serve as experimentally-determined targets for novel LAI formulations of these drugs. We present novel methodology to understand the exposure-response relationship and inform the value proposition for investment in development of LAI formulations that has utility beyond latent tuberculosis infection.

Immunological aspects of host-pathogen crosstalk in the co-pathogenesis of diabetes and latent tuberculosis

Introduction

Diabetes is a potent risk factor for the activation of latent tuberculosis and worsens the tuberculosis (TB) treatment outcome. The major reason for mortality and morbidity in diabetic patients is due to their increased susceptibility to TB. Thus, the study was conducted to understand the crosstalk between M. tuberculosis and its host upon latent tuberculosis infection and under hyperglycemic conditions or diabetes.

Methods

An animal model was employed to study the relationship between latent tuberculosis and diabetes. BCG immunization was done in mice before infection with M. tuberculosis, and latency was confirmed by bacillary load, histopathological changes in the lungs and gene expression of hspX, tgs1, tgs3 and tgs5. Diabetes was then induced by a single high dose of streptozotocin (150 mg/kg body weight). Host factors, like various cytokines and MMPs (Matrix metalloproteinases), which play an important role in the containment of mycobacterial infection were studied in vivo and in vitro.

Results

A murine model of latent TB was developed, which was confirmed by CFU counts (<10⁴ in the lungs and spleen) and granuloma formation in lungs in the latent TB group. Also, the gene expression of hspX, tgs1, and tgs5 was upregulated, and after diabetes induction, blood glucose levels were >200 mg/dl. An in vitro study employing a THP-1 macrophage model of latent and active tuberculosis under normal and high glucose conditions showed that dormant bacilli were better contained in the presence of 5.5 mM glucose concentration as compared with active bacilli. However, the killing and restriction efficiency of macrophages decreased, and CFU counts increased significantly with an increase in glucose concentration.

Discussion

The decreased levels of MCP-1, decreased expression of mmp-9, and increased expression of mmp-1 in the latent group at high glucose concentrations could explain the failure of granuloma formation at high glucose conditions.

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

B21 DNA vaccine expressing ag85b, rv2029c, and rv1738 confers a robust therapeutic effect against latent Mycobacterium tuberculosis infection

Latent tuberculosis infection (LTBI) treatment is known to accelerate the decline in TB incidence, especially in high-risk populations. Mycobacterium tuberculosis (M. tb) expression profiles differ at different growth periods, and vaccines protective and therapeutic effects may increase when they include antigenic compositions from different periods. To develop a post-exposure vaccine that targets LTBI, we constructed four therapeutic DNA vaccines (A39, B37, B31, and B21) using different combinations of antigens from the proliferation phase (Ag85A, Ag85B), PE/PPE family (Rv3425), and latent phase (Rv2029c, Rv1813c, Rv1738). We compared the immunogenicity of the four DNA vaccines in C57BL/6j mice. The B21 vaccine stimulated the strongest cellular immune responses, namely Th1/Th17 and CD8⁺ cytotoxic T lymphocyte responses. It also induced the generation of strengthened effector memory and central memory T cells. In latently infected mice, the B21 vaccine significantly reduced bacterial loads in the spleens and lungs and decreased lung pathology. In conclusion, the B21 DNA vaccine can enhance T cell responses and control the reactivation of LTBI.

Mycobacterium tuberculosis Dormancy: How to Fight a Hidden Danger

Both latent and active TB infections are caused by a heterogeneous population of mycobacteria, which includes actively replicating and dormant bacilli in different proportions. Dormancy substantially affects M. tuberculosis drug tolerance and TB clinical management due to a significant decrease in the metabolic activity of bacilli, which leads to the complexity of both the diagnosis and the eradication of bacilli. Most diagnostic approaches to latent infection deal with a subpopulation of active M. tuberculosis, underestimating the contribution of dormant bacilli and leading to limited success in the fight against latent TB. Moreover, active TB appears not only as a primary form of infection but can also develop from latent TB, when resuscitation from dormancy is followed by bacterial multiplication, leading to disease progression. To win against latent infection, the identification of the Achilles' heel of dormant M. tuberculosis is urgently needed. Regulatory mechanisms and metabolic adaptation to growth arrest should be studied using in vitro and in vivo models that adequately imitate latent TB infection in macroorganisms. Understanding the mechanisms underlying M. tuberculosis dormancy and resuscitation may provide clues to help control latent infection, reduce disease severity in patients, and prevent pathogen transmission in the population.

Update on tuberculosis/HIV coinfections: across the spectrum from latent infection through drug-susceptible and drug-resistant disease

Tuberculosis (TB) remains the leading cause of death among people with HIV, and annual risk of progression from latent TB infection to active disease in this population is 10%. Diagnostic tests for latent and active TB remain suboptimal for people with HIV who have a CD4+ count below 200 cells/μL, and there is an urgent need for assays that predict progression from latent to active disease, monitor treatment response, and test for cure after latent and active TB treatment. Traditional treatment duration for latent infection and active TB disease has been onerous for patients; however, shorter-course regimens are increasingly available across the spectrum of TB, including for drug-resistant TB. Simultaneous treatment of HIV and TB is complicated by drug-drug interactions, although trials are ongoing to better understand the magnitude of these interactions and guide clinicians in how to use short-course regimens, particularly for people with HIV.

Efficacy of Long-Acting Bedaquiline Regimens in a Mouse Model of Tuberculosis Preventive Therapy

RATIONALE

Completion of preventive therapy is a major bottleneck in global tuberculosis control. Long-acting injectable drug formulations would shorten therapy administration and may thereby improve completion rates. Recently, a long-acting formulation of bedaquiline demonstrated anti-tuberculosis activity for up to 12 weeks post-injection in a validated mouse model of preventive therapy.

OBJECTIVES

The objectives of this study were to (i) determine the total duration of activity following an injection of long-acting bedaquiline, and (ii) evaluate the activity of regimens comprised of long-acting bedaquiline plus short (2-4 week) oral companion courses of bedaquiline, with or without rifapentine, using the validated mouse model of tuberculosis preventive therapy.

METHODS

After establishment of a stable Mycobacterium tuberculosis lung infection in BCG-immunized BALB/c mice, treatment was initiated with one of 12 randomly assigned regimens. In addition to positive and negative controls, six regimens included 1 or 2 injections of long-acting bedaquiline (alone or with oral bedaquiline +/- rifapentine), and 4 comparator regimens consisted of oral agents only. Lung bacterial burden was measured monthly for up to 28 weeks.

MEASUREMENTS AND MAIN RESULTS

One injection of long-acting bedaquiline at 160 mg/kg exerted anti-tuberculosis activity for 12 weeks. Compared to the positive control (daily isoniazid-rifapentine for 4 weeks), six regimens had equivalent bactericidal activity (including two all-oral comparator regimens), and two regimens has superior sterilizing activity: one injection with 2 weeks of oral bedaquiline and high-dose rifapentine; and 2 injections with 4 weeks of oral bedaquiline.

CONCLUSION

Long-acting injectable bedaquiline has significant potential for shortening tuberculosis preventive therapy.

Comparative Efficacy of Rifapentine Alone and in Combination with Isoniazid for Latent Tuberculosis Infection: a Translational Pharmacokinetic-Pharmacodynamic Modeling Study

Rifapentine has facilitated treatment shortening for latent tuberculosis infection (LTBI) in combination with isoniazid once weekly for 3 months (3HP) or daily for 1 month (1HP). Our objective was to determine the optimal rifapentine dose for a 6-week monotherapy regimen (6wP) and predict clinical efficacy. Rifapentine and isoniazid pharmacokinetics were simulated in mice and humans. Mouse lung CFU data were used to characterize exposure-response relationships of 1HP, 3HP, and 6wP and translated to predict clinical efficacy. A 600-mg daily dose for 6wP delivered greater cumulative rifapentine exposure than 1HP or 3HP. The maximum regimen effect (E_max) was 0.24 day^-1. The regimen potencies, measured as the concentration at 50% of E_max (EC₅₀), were estimated to be 2.12 mg/liter for 3HP, 3.72 mg/liter for 1HP, and 4.71 mg/liter for 6wP, suggesting that isoniazid contributes little to 1HP efficacy. Clinical translation predicted that 6wP reduces bacterial loads at a higher rate than 3HP and to a greater extent than 3HP and 1HP. 6wP (600 mg daily) is predicted to result in equal or better efficacy than 1HP and 3HP for LTBI treatment without the potential added toxicity of isoniazid. Results from ongoing and future clinical studies will be required to support these findings.

Reactivation of latent tuberculosis through modulation of resuscitation promoting factors by diabetes

The evidence of an association between diabetes and latent tuberculosis infection (LTBI) remains limited and inconsistent. Thus, the study aims to delineate the role of diabetes in activation of latent tuberculosis infection. Murine model of latent tuberculosis and diabetes was developed, bacillary load and gene expression of resuscitation promoting factors (rpfA-E) along with histopathological changes in the lungs and spleen were studied. Treatment for LTBI [Rifampicin (RIF) + Isoniazid (INH)] was also given to latently infected mice with or without diabetes for 4 weeks. Diabetes was found to activate latent tuberculosis as the colony forming unit (CFU) counts were observed to be > 10⁴ in lungs and spleen. The gene expression of hspX was downregulated and that of rpfB and rpfD was observed to be upregulated in latently infected mice with diabetes compared to those without diabetes. However, no significant reduction in the CFU counts was observed after 4 weeks of treatment with RIF and INH. Diabetes helps in the progression of LTBI to active disease mainly through altered expression of resuscitation promoting factors rpfB and rpfD, which can serve as important targets to reduce the shared burden of tuberculosis and diabetes.

A recombinant selective drug-resistant M. bovis BCG enhances the bactericidal activity of a second-line anti-tuberculosis regimen

Drug-resistant tuberculosis (DR-TB) poses a new threat to global health; to improve the treatment outcome, therapeutic vaccines are considered the best chemotherapy adjuvants. Unfortunately, there is no therapeutic vaccine approved against DR-TB. Our study assessed the therapeutic efficacy of a recombinant drug-resistant BCG (RdrBCG) vaccine in DR-TB. We constructed the RdrBCG overexpressing Ag85B and Rv2628 by selecting drug-resistant BCG strains and transformed them with plasmid pEBCG or pIBCG to create RdrBCG-E and RdrBCG-I respectively. Following successful stability testing, we tested the vaccine's safety in severe combined immune deficient (SCID) mice that lack both T and B lymphocytes plus immunoglobulins. Finally, we evaluated the RdrBCG's therapeutic efficacy in BALB/c mice infected with rifampin-resistant M. tuberculosis and treated with a second-line anti-TB regimen. We obtained M. bovis strains which were resistant to several second-line drugs and M. tuberculosis resistant to rifampin. Notably, the exogenously inserted genes were lost in RdrBCG-E but remained stable in the RdrBCG-I both in vitro and in vivo. When administered adjunct to a second-line anti-TB regimen in a murine model of DR-TB, the RdrBCG-I lowered lung M. tuberculosis burden by 1 log10. Furthermore, vaccination with RdrBCG-I adjunct to chemotherapy minimized lung tissue pathology in mice. Most importantly, the RdrBCG-I showed almost the same virulence as its parent BCG Tice strain in SCID mice. Our findings suggested that the RdrBCG-I was stable, safe and effective as a therapeutic vaccine. Hence, the "recombinant" plus "drug-resistant" BCG strategy could be a useful concept for developing therapeutic vaccines against DR-TB.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb's development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound's effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound's development.

Treatment of latent M. tuberculosis infection and use of antiretroviral therapy to prevent tuberculosis

Even with treatment of HIV with antiretroviral therapy (ART), the risk of tuberculosis (TB) reactivation remains higher in HIV-infected than HIV-uninfected persons. In this issue of the JCI, Ganatra et al. explored TB reactivation in the context of ART using TB and simian immunodeficiency virus-coinfected (TB/SIV-coinfected) nonhuman primates. The authors found that treating rhesus macaques with ART restored CD4+ T cells in whole blood, spleen, and bronchoalveolar lavage (BAL) fluid, but not in the lung interstitium. TB risk was not decreased in the coinfected macaques treated with ART for 14-63 days, suggesting that ART does not decrease the short-term risk of reactivation. Reactivation occurred as CD4+ T cells were increasing, which is consistent with observations made in humans. This study provides a potential model for systematic evaluation of TB/SIV coinfection and different treatment regimens and strategies to prevent TB reactivation.

Are We There Yet? Short-Course Regimens in TB and HIV: From Prevention to Treatment of Latent to XDR TB

PURPOSE OF REVIEW

Despite broad uptake of antiretroviral therapy (ART), tuberculosis (TB) incidence and mortality among people with HIV remain unacceptably high. Short-course regimens for TB, incorporating both novel and established drugs, offer the potential to enhance adherence and completion rates, thereby reducing the global TB burden. This review will outline short-course regimens for TB among patients with HIV.

RECENT FINDINGS

After many years without new agents, there is now active testing of many novel drugs to treat TB, both for latent infection and active disease. Though not all studies have included patients with HIV, many have, and there are ongoing trials to address key implementation challenges such as potent drug-drug interactions with ART. The goal of short-course regimens for TB is to enhance treatment completion without compromising efficacy. Particularly among patients with HIV, studying these shortened regimens and integrating them into clinical care are of urgent importance. There are now multiple short-course regimens for latent infection and active disease that are safe and effective among patients with HIV.

Systematic review on tuberculosis risk in patients with rheumatoid arthritis receiving inhibitors of Janus Kinases

INTRODUCTION

Janus kinases inhibitors (anti-JAKs), including tofacitinib, baricitinib, upadacitinib, and filgotinib, represent a new class of synthetic targeted drugs for the treatment of rheumatoid arthritis (RA). In this review, the risk of active tuberculosis (TB) occurrence in patients receiving anti-JAKs was assessed. The literature on this topic, updated to 29 February 2020 was reviewed. Overall, 40 reports (22 tofacitinib, 10 baricitinib, 5 upadacitinib, 3 filgotinib) were examined. A low frequency, not exceeding 0.25%, of active TB cases in patients were exposed to anti-JAKs. Only 1 of 89 recorded cases in tofactinib and baricitinib exposure occurred in countries at intermediate or high TB risk, and most of the cases probably were due to first mycobacterium tuberculosis (Mtb) exposure. Although no cases were observed in patients receiving upadacitinib and filgotinib, long-term trials and data from real-life are required to more precisely address the TB risk associated with the two drugs.

AREAS COVERED

Discussion on the TB risk associated with anti-JAKs, and on the need for accurate evaluation of host-related risk factors in high risk countries.

EXPERT OPINION

Available data on anti-JAKs suggest a negligible risk of active TB occurrence in low endemic areas.

Activity of a Long-Acting Injectable Bedaquiline Formulation in a Paucibacillary Mouse Model of Latent Tuberculosis Infection

The potent antituberculosis activity and long half-life of bedaquiline make it an attractive candidate for use in long-acting/extended-release formulations for the treatment of latent tuberculosis infection (LTBI). Our objective was to evaluate a long-acting injectable (LAI) bedaquiline formulation in a validated paucibacillary mouse model of LTBI.

The potent antituberculosis activity and long half-life of bedaquiline make it an attractive candidate for use in long-acting/extended-release formulations for the treatment of latent tuberculosis infection (LTBI). Our objective was to evaluate a long-acting injectable (LAI) bedaquiline formulation in a validated paucibacillary mouse model of LTBI. Following immunization with Mycobacterium bovis rBCG30, BALB/c mice were challenged by aerosol infection with M. tuberculosis H37Rv. Treatment began 13 weeks after challenge infection with one of the following regimens: an untreated negative-control regimen; positive-control regimens of daily rifampin (10 mg/kg of body weight), once-weekly rifapentine (15 mg/kg) and isoniazid (50 mg/kg), or daily bedaquiline (25 mg/kg); test regimens of one, two, or three monthly doses of LAI bedaquiline at 160 mg/dose (B_LAI-160); and test regimens of daily bedaquiline at 2.67 mg/kg (B_2.67), 5.33 mg/kg (B_5.33), or 8 mg/kg (B₈) to deliver the same total amount of bedaquiline as one, two, or three doses of B_LAI-160, respectively. All drugs were administered orally, except for B_LAI-160 (intramuscular injection). The primary outcome was the decline in M. tuberculosis lung CFU counts during 12 weeks of treatment. The negative- and positive-control regimens performed as expected. One, two, and three doses of B_LAI-160 resulted in decreases of 2.9, 3.2, and 3.5 log₁₀ CFU/lung, respectively, by week 12. Daily oral dosing with B_2.67, B_5.33, and B₈ decreased lung CFU counts by 1.6, 2.8, and 4.1 log₁₀, respectively. One dose of B_LAI-160 exhibited activity for at least 12 weeks. The sustained activity of B_LAI-160 indicates that it shows promise as a short-course LTBI treatment requiring few patient encounters to ensure treatment completion.

One Month of Rifapentine plus Isoniazid to Prevent HIV-Related Tuberculosis

BACKGROUND

Tuberculosis is the leading killer of patients with human immunodeficiency virus (HIV) infection. Preventive therapy is effective, but current regimens are limited by poor implementation and low completion rates.

METHODS

We conducted a randomized, open-label, phase 3 noninferiority trial comparing the efficacy and safety of a 1-month regimen of daily rifapentine plus isoniazid (1-month group) with 9 months of isoniazid alone (9-month group) in HIV-infected patients who were living in areas of high tuberculosis prevalence or who had evidence of latent tuberculosis infection. The primary end point was the first diagnosis of tuberculosis or death from tuberculosis or an unknown cause. Noninferiority would be shown if the upper limit of the 95% confidence interval for the between-group difference in the number of events per 100 person-years was less than 1.25.

RESULTS

A total of 3000 patients were enrolled and followed for a median of 3.3 years. Of these patients, 54% were women; the median CD4+ count was 470 cells per cubic millimeter, and half the patients were receiving antiretroviral therapy. The primary end point was reported in 32 of 1488 patients (2%) in the 1-month group and in 33 of 1498 (2%) in the 9-month group, for an incidence rate of 0.65 per 100 person-years and 0.67 per 100 person-years, respectively (rate difference in the 1-month group, -0.02 per 100 person-years; upper limit of the 95% confidence interval, 0.30). Serious adverse events occurred in 6% of the patients in the 1-month group and in 7% of those in the 9-month group (P = 0.07). The percentage of treatment completion was significantly higher in the 1-month group than in the 9-month group (97% vs. 90%, P<0.001).

CONCLUSIONS

A 1-month regimen of rifapentine plus isoniazid was noninferior to 9 months of isoniazid alone for preventing tuberculosis in HIV-infected patients. The percentage of patients who completed treatment was significantly higher in the 1-month group. (Funded by the National Institute of Allergy and Infectious Diseases; BRIEF TB/A5279 ClinicalTrials.gov number, NCT01404312.).

Mycobacterium tuberculosis multistage antigens confer comprehensive protection against pre- and post-exposure infections by driving Th1-type T cell immunity

There is an urgent need for a vaccine against tuberculosis (TB) that is more effective than the current sole licensed option. However, target antigens of Mycobacterium tuberculosis with the vaccine potential remain elusive. Five immunodominant antigens with characteristic expressions at the stages of primary infection (Ag85A), the regulation of nutrition and metabolism when transferring from rapid growth to latency (PhoY2 and Rv3407), latency (Rv2626c), and reactivation (RpfB) were selected to construct the fusion polyprotein WH121, which has better immunogenicity and protection than each multistage antigen. DMT adjuvanted WH121 vaccinated C57BL/6 mice could confer persistent and significant protection against the respiratory challenge with 80 CFU of virulent M. tuberculosis H37Rv at 9 and 18 weeks after immunization, as the BCG vaccine did. Moreover, WH121/DMT could boost the BCG primed mice against post-exposure infection, and more significantly inhibit the growth of M. tuberculosis in the spleen than BCG repeat vaccination. The protection elicited by WH121/DMT is attributed to the WH121-specific Th1-type biased immune responses, characterized by increased antigen-specific IgG2a/IgG1 ratio and high levels of IFN-γ secreted by the splenocytes of vaccinated mice. In particular, high levels of IFN-γ⁺ T_EM cells in the spleen are an effective biomarker for the vaccine-induced early protection, and the persistent protection mainly depends on the increasing IL-2⁺IFN-γ⁺CD4⁺ and CD8⁺ T cells, especially IL-2⁺ T_CM cells. These findings demonstrate that multistage-specific antigens might be promising targets for the next generation TB vaccine, and a combination of these antigens such as WH121/DMT is required for further preclinical evaluation.

Treatment of Latent Tuberculosis Infection and Its Clinical Efficacy

The role of the treatment for latent tuberculosis infection (LTBI) has been underscored in the intermediate tuberculosis (TB) burden countries like South Korea. LTBI treatment is recommended only for patients at risk for progression to active TB-those with frequent exposure to active TB cases, and those with clinical risk factors (e.g., immunocompromised patients). Recently revised National Institute for Health and Care Excellence (NICE) guideline recommended that close contacts of individuals with active pulmonary or laryngeal TB, aged between 18 and 65 years, should undergo LTBI treatment. Various regimens for LTBI treatment were recommended in NICE, World Health Organization (WHO), and Centers for Disease Control and Prevention guidelines, and superiority of one recommended regimen over another was not yet established. Traditional 6 to 9 months of isoniazid (6H or 9H) regimen has an advantage of the most abundant evidence for clinical efficacy-60%-90% of estimated protective effect. However, 6H or 9H regimen is related with hepatotoxicity and low compliance. Four months of rifampin regimen is characterized by less hepatotoxicity and better compliance than 9H, but has few evidence of clinical efficacy. Three months of isoniazid plus rifampin was proved equivalence with 6H or 9H regimen in terms of efficacy and safety, which was recommended in NICE and WHO guidelines. The clinical efficacy of isoniazid plus rifapentine once-weekly regimen for 3 months was demonstrated recently, which is not yet introduced into South Korea.

A Multistage Subunit Vaccine Effectively Protects Mice Against Primary Progressive Tuberculosis, Latency and Reactivation

Adult tuberculosis (TB) is the main cause of TB epidemic and death. The infection results mainly by endogenous reactivation of latent TB infection and secondarily transmitted by exogenous infection. There is no vaccine for adult TB. To this end, we first chose antigens from a potential antigenic reservoir. The antigens strongly recognized T cells from latent and active TB infections that responded to antigens expressed by Mycobacterium tuberculosis cultured under different metabolic states. Fusions of single-stage polyprotein CTT3H, two-stage polyprotein A1D4, and multistage CMFO were constructed. C57BL/6 mice vaccinated with DMT adjuvant ed CMFO (CMFO-DMT) were protected more significantly than by CTT3H-DMT, and efficacy was similar to that of the only licensed vaccine, Bacillus Calmette–Guérin (BCG) and A1D4-DMT in the M. tuberculosis primary infection model. In the setting of BCG priming and latent TB infection, M. tuberculosis in the lung and spleen was eliminated more effectively in mice boosted with CMFO-DMT rather than with BCG, A1D4-DMT, or CTT3H-DMT. In particular, sterile immunity was only conferred by CMFO-DMT, which was associated with expedited homing of interferon-gamma⁺ CD4⁺ T_EM and interleukin-2⁺ T_CM cells from the spleen to the infected lung. CMFO-DMT represents a promising candidate to prevent the occurrence of adult TB through both prophylactic and therapeutic methods, and warrants assessment in preclinical and clinical trials.

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CMFO-DMT provides the comparable protection against primary infection with M. tuberculosis as BCG vaccine does.

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CMFO-DMT boosts an effective protection of BCG primed mice to eliminate latent infection and thwart reactivation.

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CMFO-DMT is a promising vaccine candidate for the prevention of adult TB disease.

Adult pulmonary TB is the main clinical form of the disease and the main component of TB epidemics. There is no effective vaccine to protect adults from primary and secondary TB. Vaccine candidates were constructed using combinations of one-, two- or multi-stage antigens of M. tuberculosis representing different stages of the infection. The antigen combinations directed at different stages of TB may help control adult TB.

Preclinical Efficacy Testing of New Drug Candidates

This is a review of the preclinical efficacy testing of new antituberculosis drug candidates. It describes existing dynamic in vitro and in vivo models of antituberculosis chemotherapy and their utility in preclinical evaluations of promising new drugs and combination regimens, with an effort to highlight recent developments. Emphasis is given to the integration of quantitative pharmacokinetic/pharmacodynamic analyses and the impact of lesion pathology on drug efficacy. Discussion also includes in vivo models of chemotherapy of latent tuberculosis infection.

Animal Models for Tuberculosis in Translational and Precision Medicine

Tuberculosis (TB) is a health threat to the global population. Anti-TB drugs and vaccines are key approaches for TB prevention and control. TB animal models are basic tools for developing biomarkers of diagnosis, drugs for therapy, vaccines for prevention and researching pathogenic mechanisms for identification of targets; thus, they serve as the cornerstone of comparative medicine, translational medicine, and precision medicine. In this review, we discuss the current use of TB animal models and their problems, as well as offering perspectives on the future of these models.

Treatment of Latent Tuberculosis Infection

There are approximately 56 million people who harbor Mycobacterium tuberculosis that may progress to active tuberculosis (TB) at some point in their lives. Modeling studies suggest that if only 8% of these individuals with latent TB infection (LTBI) were treated annually, overall global incidence would be 14-fold lower by 2050 compared to incidence in 2013, even in the absence of additional TB control measures. This highlights the importance of identifying and treating latently infected individuals, and that this intervention must be scaled up to achieve the goals of the Global End TB Strategy. The efficacy of LTBI treatment is well established, and the most commonly used regimen is 9 months of daily self-administered isoniazid. However, its use has been hindered by limited provider awareness of the benefits, concern about potential side effects such as hepatotoxicity, and low rates of treatment completion. There is increasing evidence that shorter rifamycin-based regimens are as effective, better tolerated, and more likely to be completed compared to isoniazid. Such regimens include four months of daily self-administered rifampin monotherapy, three months of once weekly directly observed isoniazid-rifapentine, and three months of daily self-administered isoniazid-rifampin. The success of LTBI treatment to prevent additional TB disease relies upon choosing an appropriate regimen individualized to the patient, monitoring for potential adverse clinical events, and utilizing strategies to promote adherence. Safer, more cost-effective, and more easily completed regimens are needed and should be combined with interventions to better identify, engage, and retain high-risk individuals across the cascade from diagnosis through treatment completion of LTBI.

Rifapentine for the treatment of latent tuberculosis

INTRODUCTION

The goal of this article is to review the use of rifapentine in the treatment of latent tuberculosis infection (LTBI). Controlling LTBI is an important part of the global strategy to end the spread of tuberculosis. Rifapentine's potent sterilizing effect against Mycobacterium tuberculosis combined with its long half-life make it an attractive LTBI treatment option. Areas covered: A systematic literature search of Pubmed using the terms 'rifapentine' and 'tuberculosis' was performed. Articles identified were cross-referenced for other relevant publications. The mechanisms of action and resistance, pharmacokinetic and pharmacodynamics, potential drug interactions and side effects are discussed. Expert commentary: Rifapentine in combination with isoniazid for twelve weeks is the best available option for treating latent TB in the majority of patients in the United States due to its favorable safety profile and the increased likelihood of completing therapy. Currently, rifapentine is not registered or available in other countries.

Physiologically Based Pharmacokinetic Model of Rifapentine and 25-Desacetyl Rifapentine Disposition in Humans

Rifapentine (RPT) is a rifamycin antimycobacterial and, as part of a combination therapy, is indicated for the treatment of pulmonary tuberculosis (TB) caused by Mycobacterium tuberculosis Although the results from a number of studies indicate that rifapentine has the potential to shorten treatment duration and enhance completion rates compared to other rifamycin agents utilized in antituberculosis drug regimens (i.e., regimens 1 to 4), its optimal dose and exposure in humans are unknown. To help inform such an optimization, a physiologically based pharmacokinetic (PBPK) model was developed to predict time course, tissue-specific concentrations of RPT and its active metabolite, 25-desacetyl rifapentine (dRPT), in humans after specified administration schedules for RPT. Starting with the development and verification of a PBPK model for rats, the model was extrapolated and then tested using human pharmacokinetic data. Testing and verification of the models included comparisons of predictions to experimental data in several rat tissues and time course RPT and dRPT plasma concentrations in humans from several single- and repeated-dosing studies. Finally, the model was used to predict RPT concentrations in the lung during the intensive and continuation phases of a current recommended TB treatment regimen. Based on these results, it is anticipated that the PBPK model developed in this study will be useful in evaluating dosing regimens for RPT and for characterizing tissue-level doses that could be predictors of problems related to efficacy or safety.

Controlling the seedbeds of tuberculosis: diagnosis and treatment of tuberculosis infection

The billions of people with latent tuberculosis infection serve as the seedbeds for future cases of active tuberculosis. Virtually all episodes of tuberculosis disease are preceded by a period of asymptomatic Mycobacterium tuberculosis infection; therefore, identifying infected individuals most likely to progress to disease and treating such subclinical infections to prevent future disease provides a crucial opportunity to interrupt tuberculosis transmission and reduce the global burden of tuberculosis disease. Programmes focusing on single strategies rather than comprehensive programmes that deliver an integrated arsenal for tuberculosis control might continue to struggle. Tuberculosis preventive therapy is a poorly used method that is essential for controlling the reservoirs of disease that drive the epidemic. Comprehensive control strategies that combine preventive therapy for the most high-risk populations and communities with improved case-finding and treatment, control of transmission, and health systems strengthening could ultimately lead to worldwide tuberculosis elimination. In this Series paper we outline challenges to implementation of preventive therapy and provide pragmatic suggestions for overcoming them. We further advocate for tuberculosis preventive therapy as the core of a renewed worldwide focus to implement a comprehensive epidemic control strategy that would reduce new tuberculosis cases to elimination targets. This strategy would be underpinned by accelerated research to further understand the biology of subclinical tuberculosis infections, develop novel diagnostics and drug regimens specifically for subclinical tuberculosis infection, strengthen health systems and community engagement, and enhance sustainable large scale implementation of preventive therapy programmes.

Rifamycins (rifampicin, rifabutin and rifapentine) compared to isoniazid for preventing tuberculosis in HIV-negative people at risk of active TB

BACKGROUND

Preventing active tuberculosis (TB) from developing in people with latent tuberculosis infection (LTBI) is important for global TB control. Isoniazid (INH) for six to nine months has 60% to 90% protective efficacy, but the treatment period is long, liver toxicity is a problem, and completion rates outside trials are only around 50%. Rifampicin or rifamycin-combination treatments are shorter and may result in higher completion rates.

OBJECTIVES

To compare the effects of rifampicin monotherapy or rifamycin-combination therapy versus INH monotherapy for preventing active TB in HIV-negative people at risk of developing active TB.

SEARCH METHODS

We searched the Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; clinical trials registries; regional databases; conference proceedings; and references, without language restrictions to December 2012; and contacted experts for relevant published, unpublished and ongoing trials.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of HIV-negative adults and children at risk of active TB treated with rifampicin, or rifamycin-combination therapy with or without INH (any dose or duration), compared with INH for six to nine months.

DATA COLLECTION AND ANALYSIS

At least two authors independently screened and selected trials, assessed risk of bias, and extracted data. We sought clarifications from trial authors. We pooled relative risks (RRs) with their 95% confidence intervals (CIs), using a random-effects model if heterogeneity was significant. We assessed overall evidence quality using the GRADE approach.

MAIN RESULTS

Ten trials are included, enrolling 10,717 adults and children, mostly HIV-negative (2% HIV-positive), with a follow-up period ranging from two to five years. Rifampicin (three/four months) vs. INH (six months) Five trials published between 1992 to 2012 compared these regimens, and one small 1992 trial in adults with silicosis did not detect a difference in the occurrence of TB over five years of follow up (one trial, 312 participants; very low quality evidence). However, more people in these trials completed the shorter course (RR 1.19, 95% CI 1.01 to 1.30; five trials, 1768 participants; moderate quality evidence). Treatment-limiting adverse events were not significantly different (four trials, 1674 participants; very low quality evidence), but rifampicin caused less hepatotoxicity (RR 0.12, 95% CI 0.05 to 0.30; four trials, 1674 participants; moderate quality evidence). Rifampicin plus INH (three months) vs. INH (six months) The 1992 silicosis trial did not detect a difference between people receiving rifampicin plus INH compared to INH alone for occurrence of active TB (one trial, 328 participants; very low quality evidence). Adherence was similar in this and a 1998 trial in people without silicosis (two trials, 524 participants; high quality evidence). No difference was detected for treatment-limiting adverse events (two trials, 536 participants; low quality evidence), or hepatotoxicity (two trials, 536 participants; low quality evidence). Rifampicin plus pyrazinamide (two months) vs. INH (six months) Three small trials published in 1994, 2003, and 2005 compared these two regimens, and two reported a low occurrence of active TB, with no statistically significant differences between treatment regimens (two trials, 176 participants; very low quality evidence) though, apart from one child from the 1994 trial, these data on active TB were from the 2003 trial in adults with silicosis. Adherence with both regimens was low with no statistically significant differences (four trials, 700 participants; very low quality evidence). However, people receiving rifampicin plus pyrazinamide had more treatment-limiting adverse events (RR 3.61, 95% CI 1.82 to 7.19; two trials, 368 participants; high quality evidence), and hepatotoxicity (RR 4.59, 95% 2.14 to 9.85; three trials, 540 participants; moderate quality evidence). Weekly, directly-observed rifapentine plus INH (three months) vs. daily, self-administered INH (nine months) A large trial conducted from 2001 to 2008 among close contacts of TB in the USA, Canada, Brazil and Spain found directly observed weekly treatment to be non-inferior to nine months self-administered INH for the incidence of active TB (0.2% vs 0.4%, RR 0.44, 95% CI 0.18 to 1.07, one trial, 7731 participants; moderate quality evidence). The directly-observed, shorter regimen had higher treatment completion (82% vs 69%, RR 1.19, 95% CI 1.16 to 1.22, moderate quality evidence), and less hepatotoxicity (0.4% versus 2.4%; RR 0.16, 95% CI 0.10 to 0.27; high quality evidence), though treatment-limiting adverse events were more frequent (4.9% versus 3.7%; RR 1.32, 95% CI 1.07 to 1.64 moderate quality evidence)

AUTHORS' CONCLUSIONS

Trials to date of shortened prophylactic regimens using rifampicin alone have not demonstrated higher rates of active TB when compared to longer regimens with INH. Treatment completion is probably higher and adverse events may be fewer with shorter rifampicin regimens. Shortened regimens of rifampicin with INH may offer no advantage over longer INH regimens. Rifampicin combined with pyrazinamide is associated with more adverse events. A weekly regimen of rifapentine plus INH has higher completion rates, and less liver toxicity, though treatment discontinuation due to adverse events is probably more likely than with INH.

Latent tuberculosis infection: myths, models, and molecular mechanisms

The aim of this review is to present the current state of knowledge on human latent tuberculosis infection (LTBI) based on clinical studies and observations, as well as experimental in vitro and animal models. Several key terms are defined, including "latency," "persistence," "dormancy," and "antibiotic tolerance." Dogmas prevalent in the field are critically examined based on available clinical and experimental data, including the long-held beliefs that infection is either latent or active, that LTBI represents a small population of nonreplicating, "dormant" bacilli, and that caseous granulomas are the haven for LTBI. The role of host factors, such as CD4(+) and CD8(+) T cells, T regulatory cells, tumor necrosis factor alpha (TNF-α), and gamma interferon (IFN-γ), in controlling TB infection is discussed. We also highlight microbial regulatory and metabolic pathways implicated in bacillary growth restriction and antibiotic tolerance under various physiologically relevant conditions. Finally, we pose several clinically important questions, which remain unanswered and will serve to stimulate future research on LTBI.

Engineering more stable, selectable marker-free autoluminescent mycobacteria by one step

In our previous study, we demonstrated that the use of the autoluminescent Mycobacterium tuberculosis as a reporter strain had the potential to drastically reduce the time, effort, animals and costs consumed in evaluation of the activities of drugs and vaccines in live mice. However, the strains were relatively unstable and lost reporter with time without selection. The kanamycin selection marker used wasn’t the best choice as it provides resistance to amino glycosides which are an important class of second line drugs used in tuberculosis treatment. In addition, the marker could limit utility of the strains for screening of new potential drugs or evaluating drug combinations for tuberculosis treatment. Limited selection marker genes for mycobacterial genetic manipulation is a major drawback for such a marker-containing strain in many research fields. Therefore, selectable marker-free, more stable autoluminescent mycobacteria are highly needed. After trying several strategies, we created such mycobacterial strains successfully by using an integrative vector and removing both the resistance maker and integrase genes by Xer site-specific recombination in one step. The corresponding plasmid vectors developed in this study could be very convenient in constructing other selectable marker-free, more stable reporter mycobacteria with diverse applications.

A novel inhibitor of gyrase B is a potent drug candidate for treatment of tuberculosis and nontuberculosis mycobacterial infections

New drugs to treat drug-resistant tuberculosis are urgently needed. Extensively drug-resistant and probably the totally drug-resistant tuberculosis strains are resistant to fluoroquinolones like moxifloxacin, which target gyrase A, and most people infected with these strains die within a year. In this study, we found that a novel aminobenzimidazole, VXc-486, which targets gyrase B, potently inhibits multiple drug-sensitive isolates and drug-resistant isolates of Mycobacterium tuberculosis in vitro (MICs of 0.03 to 0.30 μg/ml and 0.08 to 5.48 μg/ml, respectively) and reduces mycobacterial burdens in lungs of infected mice in vivo. VXc-486 is active against drug-resistant isolates, has bactericidal activity, and kills intracellular and dormant M. tuberculosis bacteria in a low-oxygen environment. Furthermore, we found that VXc-486 inhibits the growth of multiple strains of Mycobacterium abscessus, Mycobacterium avium complex, and Mycobacterium kansasii (MICs of 0.1 to 2.0 μg/ml), as well as that of several strains of Nocardia spp. (MICs of 0.1 to 1.0 μg/ml). We made a direct comparison of the parent compound VXc-486 and a phosphate prodrug of VXc-486 and showed that the prodrug of VXc-486 had more potent killing of M. tuberculosis than did VXc-486 in vivo. In combination with other antimycobacterial drugs, the prodrug of VXc-486 sterilized M. tuberculosis infection when combined with rifapentine-pyrazinamide and bedaquiline-pyrazinamide in a relapse infection study in mice. Furthermore, the prodrug of VXc-486 appeared to perform at least as well as the gyrase A inhibitor moxifloxacin. These findings warrant further development of the prodrug of VXc-486 for the treatment of tuberculosis and nontuberculosis mycobacterial infections.

Thioridazine for treatment of tuberculosis: promises and pitfalls

The articles by De Knegt et al. and Singh et al. in a recent issue of this Journal address one of the current debates regarding the potential role of thioridazine in the treatment of tuberculosis. This commentary presents a summary of the available evidence, and, emphasizing the need for further research, asks the question: "How far can we go in repurposing thioridazine?"

rBCG30-induced immunity and cross-protection against Mycobacterium leprae challenge are enhanced by boosting with the Mycobacterium tuberculosis 30-kilodalton antigen 85B

Leprosy remains a major global health problem and typically occurs in regions in which tuberculosis is endemic. Vaccines are needed that protect against both infections and do so better than the suboptimal Mycobacterium bovis BCG vaccine. Here, we evaluated rBCG30, a vaccine previously demonstrated to induce protection superior to that of BCG against Mycobacterium tuberculosis and Mycobacterium bovis challenge in animal models, for efficacy against Mycobacterium leprae challenge in a murine model of leprosy. rBCG30 overexpresses the M. tuberculosis 30-kDa major secretory protein antigen 85B, which is 85% homologous with the M. leprae homolog (r30ML). Mice were sham immunized or immunized intradermally with BCG or rBCG30 and challenged 2.5 months later by injection of viable M. leprae into each hind footpad. After 7 months, vaccine efficacy was assessed by enumerating the M. leprae bacteria per footpad. Both BCG and rBCG30 induced significant protection against M. leprae challenge. In the one experiment in which a comparison between BCG and rBCG30 was feasible, rBCG30 induced significantly greater protection than did BCG. Immunization of mice with purified M. tuberculosis or M. leprae antigen 85B also induced protection against M. leprae challenge but less so than BCG or rBCG30. Notably, boosting rBCG30 with M. tuberculosis antigen 85B significantly enhanced r30ML-specific immune responses, substantially more so than boosting BCG, and significantly augmented protection against M. leprae challenge. Thus, rBCG30, a vaccine that induces improved protection against M. tuberculosis, induces cross-protection against M. leprae that is comparable or potentially superior to that induced by BCG, and boosting rBCG30 with antigen 85B further enhances immune responses and protective efficacy.

Characterization of a novel necrotic granuloma model of latent tuberculosis infection and reactivation in mice

We sought to develop and characterize a novel paucibacillary model in mice, which develops necrotic lung granulomas after infection with Mycobacterium tuberculosis. Six weeks after aerosol immunization with recombinant Mycobacterium bovis bacillus Calmette-Guerin overexpressing the 30-kDa antigen, C3HeB/FeJ mice were aerosol infected with M. tuberculosis H37Rv. Six weeks later, mice were treated with one of three standard regimens for latent tuberculosis infection or tumor necrosis factor (TNF)-neutralizing antibody. Mouse lungs were analyzed by histological features, positron emission tomography/computed tomography, whole-genome microarrays, and RT-PCR. Lungs and sera were studied by multiplex enzyme-linked immunosorbent assays. Paucibacillary infection was established, recapitulating the sterilizing activities of human latent tuberculosis infection regimens. TNF neutralization led to increased lung bacillary load, disrupted granuloma architecture with expanded necrotic foci and reduced tissue hypoxia, and accelerated animal mortality. TNF-neutralized mouse lungs and sera showed significant up-regulation of interferon γ, IL-1β, IL-6, IL-10, chemokine ligands 2 and 3, and matrix metalloproteinase genes. Clinical and microbiological reactivation of paucibacillary infection by TNF neutralization was associated with reduced hypoxia in lung granulomas and induction of matrix metalloproteinases and proinflammatory cytokines. This model may be useful for screening the sterilizing activity of novel anti-tuberculosis drugs, and identifying mycobacterial regulatory and metabolic pathways required for bacillary growth restriction and reactivation.

Population pharmacokinetics of rifapentine and desacetyl rifapentine in healthy volunteers: nonlinearities in clearance and bioavailability

Rifapentine is under active investigation as a potent drug that may help shorten the tuberculosis (TB) treatment duration. A previous rifapentine dose escalation study with daily dosing indicated a possible decrease in bioavailability as the dose increased and an increase in clearance over time for rifapentine and its active metabolite, desacetyl rifapentine. This study aimed to assess the effects of increasing doses on rifapentine absorption and bioavailability and to evaluate the clearance changes over 14 days. A population analysis was performed with nonlinear mixed-effects modeling. Absorption, time-varying clearance, bioavailability, and empirical and semimechanistic autoinduction models were investigated. A one-compartment model linked to a transit compartment absorption model best described the data. The bioavailability of rifapentine decreased linearly by 2.5% for each 100-mg increase in dose. The autoinduction model suggested a dose-independent linear increase in clearance of the parent drug and metabolite over time from 1.2 and 3.1 liters · h(-1), respectively, after a single dose to 2.2 and 5.0 liters · h(-1), respectively, after 14 once-daily doses, with no plateau being reached by day 14. In clinical trial simulations using the final model, rifapentine demonstrated less-than-dose-proportional pharmacokinetics, but there was no plateau in exposures over the dose range tested (450 to 1,800 mg), and divided dosing increased exposures significantly. Thus, the proposed compartmental model incorporating daily dosing of rifapentine over a wide range of doses and time-related changes in bioavailability and clearance provides a useful tool for estimation of drug exposure that can be used to optimize rifapentine dosing for TB treatment. (This study has been registered at ClinicalTrials.gov under registration no. NCT01162486.).

Novel regimens identified in mice for treatment of latent tuberculosis infection in contacts of patients with multidrug-resistant tuberculosis

Preventing the development of tuberculosis (TB) in contacts of patients with multidrug-resistant TB (MDR-TB) by the treatment of latent TB infection (LTBI) is highly desirable. However, few safe, well tolerated, and effective drugs are available to treat MDR-LTBI and the published guidance is limited. Fortunately, six new chemical entities from four classes developed to treat TB have entered clinical trials in the past decade. We tested three of these drugs alone and in combination in an experimental paucibacillary LTBI chemotherapy model using BALB/c and C3HeB/FeJ mice immunized with a recombinant strain of Mycobacterium bovis bacillus Calmette-Guérin (rBCG30) and then challenged with a low-dose aerosol of M. tuberculosis H37Rv. The regimens tested contained bedaquiline (TMC), PA-824 (Pa), sutezolid (PNU), and/or one of two fluoroquinolones. Control mice received rifampin (RIF) or isoniazid (INH). In BALB/c mice, TMC-containing regimens and the Pa-PNU combination were the most active test regimens and were at least as effective as RIF. Pa, PNU, and levofloxacin had activity comparable to that of INH. Virtually identical results were observed in C3HeB/FeJ mice. This study confirms the potent activity of TMC observed previously in BALB/c mice and highlights Pa alone or in combination with either PNU or a fluoroquinolone as a regimen worthy of evaluation in future clinical trials of MDR-LTBI. Given their closer pathological representation of human TB lesions, C3HeB/FeJ mice may become a preferred model for the experimental chemotherapy of LTBI. Future studies should evaluate additional clinically relevant LTBI regimens in this strain including relapse as an endpoint.

An update on the use of rifapentine for tuberculosis therapy

INTRODUCTION

Tuberculosis (TB) remains rampant throughout the world, in large part due to the lengthy treatment times of current therapeutic options. Rifapentine, a rifamycin antibiotic, is currently approved for intermittent dosing in the treatment of TB. Recent animal studies have shown that more frequent administration of rifapentine could shorten treatment times, for both latent and active TB infection. However, these results were not replicated in a subsequent human clinical trial.

AREAS COVERED

This review analyses the evidence for more frequent administration of rifapentine and the reasons for the apparent lack of efficacy in shortening treatment times in human patients. Inhaled delivery is discussed as a potential option to achieve the therapeutic effect of rifapentine by overcoming the barriers associated with oral administration of this drug. Avenues for developing an inhalable form of rifapentine are also presented.

EXPERT OPINION

Rifapentine is a promising active pharmaceutical ingredient with potential to accelerate treatment of TB if delivered by inhaled administration. Progression of current fundamental work on inhaled anti-tubercular therapies to human clinical trials is essential for determining their role in future treatment regimens. While the ultimate goal for global TB control is a vaccine, a short and effective treatment option is equally crucial.

Rifamycins (rifampicin, rifabutin and rifapentine) compared to isoniazid for preventing tuberculosis in HIV-negative people at risk of active TB

BACKGROUND

Preventing active tuberculosis (TB) from developing in people with latent tuberculosis infection (LTBI) is important for global TB control. Isoniazid (INH) for six to nine months has 60% to 90% protective efficacy, but the treatment period is long, liver toxicity is a problem, and completion rates outside trials are only around 50%. Rifampicin or rifamycin-combination treatments are shorter and may result in higher completion rates.

OBJECTIVES

To compare the effects of rifampicin monotherapy or rifamycin-combination therapy versus INH monotherapy for preventing active TB in HIV-negative people at risk of developing active TB.

SEARCH METHODS

We searched the Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; clinical trials registries; regional databases; conference proceedings; and references, without language restrictions to December 2012; and contacted experts for relevant published, unpublished and ongoing trials.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of HIV-negative adults and children at risk of active TB treated with rifampicin, or rifamycin-combination therapy with or without INH (any dose or duration), compared with INH for six to nine months.

DATA COLLECTION AND ANALYSIS

At least two authors independently screened and selected trials, assessed risk of bias, and extracted data. We sought clarifications from trial authors. We pooled relative risks (RRs) with their 95% confidence intervals (CIs), using a random-effects model if heterogeneity was significant. We assessed overall evidence quality using the GRADE approach.

MAIN RESULTS

Ten trials are included, enrolling 10,717 adults and children, mostly HIV-negative (2% HIV-positive), with a follow-up period ranging from two to five years. Rifampicin (three/four months) vs. INH (six months)Five trials published between 1992 to 2012 compared these regimens, and one small 1992 trial in adults with silicosis did not detect a difference in the occurrence of TB over five years of follow up (one trial, 312 participants; very low quality evidence). However, more people in these trials completed the shorter course (RR 1.19, 95% CI 1.01 to 1.30; five trials, 1768 participants; moderate quality evidence). Treatment-limiting adverse events were not significantly different (four trials, 1674 participants; very low quality evidence), but rifampicin caused less hepatotoxicity (RR 0.12, 95% CI 0.05 to 0.30; four trials, 1674 participants; moderate quality evidence). Rifampicin plus INH (three months) vs. INH (six months)The 1992 silicosis trial did not detect a difference between people receiving rifampicin plus INH compared to INH alone for occurrence of active TB (one trial, 328 participants; very low quality evidence). Adherence was similar in this and a 1998 trial in people without silicosis (two trials, 524 participants; high quality evidence). No difference was detected for treatment-limiting adverse events (two trials, 536 participants; low quality evidence), or hepatotoxicity (two trials, 536 participants; low quality evidence). Rifampicin plus pyrazinamide (two months) vs. INH (six months)Three small trials published in 1994, 2003, and 2005 compared these two regimens, and two reported a low occurrence of active TB, with no statistically significant differences between treatment regimens (two trials, 176 participants; very low quality evidence) though, apart from one child from the 1994 trial, these data on active TB were from the 2003 trial in adults with silicosis. Adherence with both regimens was low with no statistically significant differences (four trials, 700 participants; very low quality evidence). However, people receiving rifampicin plus pyrazinamide had more treatment-limiting adverse events (RR 3.61, 95% CI 1.82 to 7.19; two trials, 368 participants; high quality evidence), and hepatotoxicity (RR 4.59, 95% 2.14 to 9.85; three trials, 540 participants; moderate quality evidence). Weekly, directly-observed rifapentine plus INH (three months) vs. daily, self-administered INH (nine months)A large trial conducted from 2001 to 2008 among close contacts of TB in the USA, Canada, Brazil and Spain found directly observed weekly treatment to be non-inferior to nine months self-administered INH for the incidence of active TB (0.2% vs 0.4%, RR 0.44, 95% CI 0.18 to 1.07, one trial, 7731 participants; moderate quality evidence). The directly-observed, shorter regimen had higher treatment completion (82% vs 69%, RR 1.19, 95% CI 1.16 to 1.22, moderate quality evidence), and less hepatotoxicity (0.4% versus 2.4%; RR 0.16, 95% CI 0.10 to 0.27; high quality evidence), though treatment-limiting adverse events were more frequent (4.9% versus 3.7%; RR 1.32, 95% CI 1.07 to 1.64 moderate quality evidence)

AUTHORS' CONCLUSIONS

Trials to date of shortened prophylactic regimens using rifampicin alone have not demonstrated higher rates of active TB when compared to longer regimens with INH. Treatment completion is probably higher and adverse events may be fewer with shorter rifampicin regimens. Shortened regimens of rifampicin with INH may offer no advantage over longer INH regimens. Rifampicin combined with pyrazinamide is associated with more adverse events. A weekly regimen of rifapentine plus INH has higher completion rates, and less liver toxicity, though treatment discontinuation due to adverse events is probably more likely than with INH.

Current management options for latent tuberculosis: a review

Tuberculosis remains the world's second leading infectious cause of death, with nearly one-third of the global population latently infected. Treatment of latent tuberculosis infection is a mainstay of tuberculosis-control efforts in low-to medium-incidence countries. Isoniazid monotherapy has been the standard of care for decades, but its utility is impaired by poor completion rates. However, new, shorter-course regimens using rifamycins improve completion rates and are cost-saving compared with standard isoniazid monotherapy. We review the currently available therapies for latent tuberculosis infection and their toxicities and include a brief economic comparison of the different regimens.

Comprehensive analysis of methods used for the evaluation of compounds against Mycobacterium tuberculosis

In drug development, there are typically a series of preclinical studies that must be completed with new compounds or regimens before use in humans. A sequence of in vitro assays followed by in vivo testing in validated animal models to assess the activity against Mycobacterium tuberculosis, pharmacology and toxicity is generally used for advancing compounds against tuberculosis in a preclinical stage. A plethora of different assay systems and conditions are used to study the effect of drug candidates on the growth of M. tuberculosis, making it difficult to compare data from one laboratory to another. The Bill and Melinda Gates Foundation recognized the scientific gap to delineate the spectrum of variables in experimental protocols, identify which of these are biologically significant, and converge towards a rationally derived standard set of optimized assays for evaluating compounds. The goals of this document are to recommend protocols and hence accelerate the process of TB drug discovery and testing. Data gathered from preclinical in vitro and in vivo assays during personal visits to laboratories and an electronic survey of methodologies sent to investigators is reported. Comments, opinions, experiences as well as final recommendations from those currently engaged in such preclinical studies for TB drug testing are being presented. Certain in vitro assays and mouse efficacy models were re-evaluated in the laboratory as head-to-head experiments and a summary is provided on the results obtained. It is our hope that this information will be a valuable resource for investigators in the field to move forward in an efficient way and that key variables of assays are included to ensure accuracy of results which can then be used for designing human clinical trials. This document then concludes with remaining questions and critical gaps that are in need of further validation and experimentation.

Streptomycin-starved Mycobacterium tuberculosis 18b, a drug discovery tool for latent tuberculosis

Mycobacterium tuberculosis 18b, a streptomycin (STR)-dependent mutant that enters a viable but nonreplicating state in the absence of STR, has been developed as a simple model for drug testing against dormant bacilli. Here, we further evaluated the STR-starved 18b (SS18b) model both in vitro and in vivo by comparing the behavior of 22 approved and experimental tuberculosis drugs. Using the resazurin reduction microplate assay (REMA), rifampin (RIF), rifapentine (RPT), TMC207, clofazimine (CFM), and linezolid (LIN) were found to be active against SS18b in vitro, and their bactericidal activity was confirmed by determining the number of CFU. A latent 18b infection was established in mice, and some of the above-mentioned drugs were used for treatment, either alone or in combination with RIF. RIF, RPT, TMC207, CFM, and pyrazinamide (PZA) were all active in vivo, while cell wall inhibitors were not. A comparative kinetic study of rifamycin efficacy was then undertaken, and the results indicated that RPT clears latent 18b infection in mice faster than RIF. Intrigued by the opposing responses of live and dormant 18b cells to cell wall inhibitors, we conducted a systematic analysis of 14 such inhibitors using REMA. This uncovered an SS18b signature (CWPRED) that accurately predicted the activities of cell wall inhibitors and performed well in a blind study. CWPRED will be useful for establishing the mode of action of compounds with unknown targets, while the SS18b system should facilitate the discovery of drugs for treating latent tuberculosis.

Risk of tuberculosis reactivation with tofacitinib (CP-690550)

Individuals with latent tuberculosis infection (LTBI) live with a risk of reactivation, and several treatments for chronic inflammatory conditions are highly associated with such reactivation. A new Janus kinase inhibitor, tofacitinib (CP-690550), has shown promising results for treatment of inflammatory disorders, thus raising concerns of risk of active tuberculosis. Our goal was to characterize the impact of tofacitinib on LTBI using a mouse model of contained tuberculosis. Our data indicate that tofacitinib reduces host containment of Mycobacterium tuberculosis and promotes bacterial replication in the lungs, suggesting tuberculosis reactivation. Tofacitinib may carry a significant risk for LTBI reactivation in humans.

Autoluminescent Mycobacterium tuberculosis for rapid, real-time, non-invasive assessment of drug and vaccine efficacy

Preclinical efforts to discover and develop new drugs and vaccines for tuberculosis are hampered by the reliance on colony-forming unit (CFU) counts as primary outcomes for in vivo efficacy studies and the slow growth of Mycobacterium tuberculosis. The utility of bioluminescent M. tuberculosis reporter strains for real-time in vitro and ex vivo assessment of drug and vaccine activity has been demonstrated but a simple, non-invasive, real-time surrogate marker to replace CFU counts for real-time evaluation of drug and vaccine efficacy in vivo has not been described. We describe the development of a fully virulent and stable autoluminescent strain of M. tuberculosis and proof-of-concept experiments demonstrating its utility for in vivo bioluminescence imaging to assess the efficacy of new drugs and vaccines for tuberculosis in a mouse model. Relative light unit (RLU) counts paralleled CFU counts during the active phase of bacterial growth, with a lower limit of detection of approximately 10⁶ CFU in live, anesthetized mice. Experiments distinguishing active from inactive anti-tuberculosis drugs and bacteriostatic drug effects from bactericidal effects were completed in less than 5 days. The ability of a recombinant BCG vaccine to limit bacterial growth was demonstrated within 3 weeks. Use of this autoluminescent reporter strain has the potential to drastically reduce the time, effort, animals and costs consumed in the evaluation of drug activity in vitro and the in vivo assessment of drug and vaccine efficacy.

The role of the novel exopolyphosphatase MT0516 in Mycobacterium tuberculosis drug tolerance and persistence

Inorganic polyphosphate (poly P) has been postulated to play a regulatory role in the transition to bacterial persistence. In bacteria, poly P balance in the cell is maintained by the hydrolysis activity of the exopolyphosphatase PPX. However, the Mycobacterium tuberculosis PPX has not been characterized previously. Here we show that recombinant MT0516 hydrolyzes poly P, and an MT0516-deficient M. tuberculosis mutant exhibits elevated intracellular levels of poly P and increased expression of the genes mprB, sigE, and rel relative to the isogenic wild-type strain, indicating poly P-mediated signaling. Deficiency of MT0516 resulted in decelerated growth during logarithmic-phase in axenic cultures, and tolerance to the cell wall-active drug isoniazid. The MT0516-deficient mutant showed a significant survival defect in activated human macrophages and reduced persistence in the lungs of guinea pigs. We conclude that exopolyphosphatase is required for long-term survival of M. tuberculosis in necrotic lung lesions.