The role of moxifloxacin in tuberculosis therapy

Fluoroquinolones and Biofilm: A Narrative Review

Background: Biofilm-associated infections frequently span multiple body sites and represent a significant clinical challenge, often requiring a multidisciplinary approach involving surgery and antimicrobial therapy. These infections are commonly healthcare-associated and frequently related to internal or external medical devices. The formation of biofilms complicates treatment, as they create environments that are difficult for most antimicrobial agents to penetrate. Fluoroquinolones play a critical role in the eradication of biofilm-related infections. Numerous studies have investigated the synergistic potential of combining fluoroquinolones with other chemical agents to augment their efficacy while minimizing potential toxicity. Comparative research suggests that the antibiofilm activity of fluoroquinolones is superior to that of beta-lactams and glycopeptides. However, their activity remains less effective than that of minocycline and fosfomycin. Noteworthy combinations include fluoroquinolones with fosfomycin and aminoglycosides for enhanced activity against Gram-negative organisms and fluoroquinolones with minocycline and rifampin for more effective treatment of Gram-positive infections. Despite the limitations of fluoroquinolones due to the intrinsic characteristics of this antibiotic, they remain fundamental in this setting thanks to their bioavailability and synergisms with other drugs. Methods: A comprehensive literature search was conducted using online databases (PubMed/MEDLINE/Google Scholar) and books written by experts in microbiology and infectious diseases to identify relevant studies on fluoroquinolones and biofilm. Results: This review critically assesses the role of fluoroquinolones in managing biofilm-associated infections in various clinical settings while also exploring the potential benefits of combination therapy with these antibiotics. Conclusions: The literature predominantly consists of in vitro studies, with limited in vivo investigations. Although real world data are scarce, they are in accordance with fluoroquinolones' effectiveness in managing early biofilm-associated infections. Also, future perspectives of newer treatment options to be placed alongside fluoroquinolones are discussed. This review underscores the role of fluoroquinolones in the setting of biofilm-associated infections, providing a comprehensive guide for physicians regarding the best use of this class of antibiotics while highlighting the existing critical issues.

Role of DNA Double-Strand Break Formation in Gyrase Inhibitor-Mediated Killing of Nonreplicating Persistent Mycobacterium tuberculosis in Caseum

Tuberculosis is the leading cause of mortality by infectious agents worldwide. The necrotic debris, known as caseum, which accumulates in the center of pulmonary lesions and cavities is home to nonreplicating drug-tolerant Mycobacterium tuberculosis that presents a significant hurdle to achieving a fast and durable cure. Fluoroquinolones such as moxifloxacin are highly effective at killing this nonreplicating persistent bacterial population and boosting TB lesion sterilization. Fluoroquinolones target bacterial DNA gyrase, which catalyzes the negative supercoiling of DNA and relaxes supercoils ahead of replication forks. In this study, we investigated the potency of several other classes of gyrase inhibitors against M. tuberculosis in different states of replication. In contrast to fluoroquinolones, many other gyrase inhibitors kill only replicating bacterial cultures but produce negligible cidal activity against M. tuberculosis in ex vivo rabbit caseum. We demonstrate that while these inhibitors are capable of inhibiting M. tuberculosis gyrase DNA supercoiling activity, fluoroquinolones are unique in their ability to cleave double-stranded DNA at low micromolar concentrations. We hypothesize that double-strand break formation is an important driver of gyrase inhibitor-mediated bactericidal potency against nonreplicating persistent M. tuberculosis populations in the host. This study provides general insight into the lesion sterilization potential of different gyrase inhibitor classes and informs the development of more effective chemotherapeutic options against persistent mycobacterial infections.

Recent efforts in the development of glycoconjugate vaccine and available treatment for tuberculosis

Tuberculosis (TB) continues to pose a grave threat to global health, despite relentless eradication efforts. In 1882, Robert Koch discovered that Mycobacterium tuberculosis (Mtb) is the bacterium responsible for causing tuberculosis. It is a fact that tuberculosis has claimed the lives of more than one billion people in the last few decades. It is imperative that we must take immediate and effective action to increase resources for TB research and treatment. Effective TB treatments demand an extensive investment of both time and finances, often requiring 6-9 months of rigorous antibiotic therapy. The most efficient way to control tuberculosis is by receiving a childhood Bacillus Calmette-Guérin (BCG) vaccination. Despite years of research on vaccine development, we still do not have any new approved vaccine for tuberculosis, except BCG, which is partially effective in young children. This review discusses briefly the available treatment for tuberculosis and remarkable advancements in glycoconjugate-based TB vaccine developments in recent years (2013-2024) and offers valuable direction for future research priorities.

Determination of moxifloxacin in milk using a ratiometric fluorescent sensor based on Ag-MOF@curcumin

Moxifloxacin (MFX) has attracted increasing public concern recently, and the development of a simple and effective analysis method has become a research focus. In this work, a simple, sensitive and ratiometric fluorescent sensor based on Ag-MOF@curcumin was designed and investigated. Ag-MOF@curcumin displays emission at 410 nm and 475 nm under excitation at 330 nm. When MFX is added, a new emission peak appears at 500 nm, and the F500/F410 ratio has a linear relationship with the MFX concentration in the range 0-35 μmol L-1 with a low LOD (0.179 μmol L-1). Finally, the developed sensor was used for the determination of MFX in milk. This work provides an excellent fluorescent sensor for highly selective and rapid detection of MFX residues.

Gyrase and Topoisomerase IV: Recycling Old Targets for New Antibacterials to Combat Fluoroquinolone Resistance

Beyond their requisite functions in many critical DNA processes, the bacterial type II topoisomerases, gyrase and topoisomerase IV, are the targets of fluoroquinolone antibacterials. These drugs act by stabilizing gyrase/topoisomerase IV-generated DNA strand breaks and by robbing the cell of the catalytic activities of these essential enzymes. Since their clinical approval in the mid-1980s, fluoroquinolones have been used to treat a broad spectrum of infectious diseases and are listed among the five "highest priority" critically important antimicrobial classes by the World Health Organization. Unfortunately, the widespread use of fluoroquinolones has been accompanied by a rise in target-mediated resistance caused by specific mutations in gyrase and topoisomerase IV, which has curtailed the medical efficacy of this drug class. As a result, efforts are underway to identify novel antibacterials that target the bacterial type II topoisomerases. Several new classes of gyrase/topoisomerase IV-targeted antibacterials have emerged, including novel bacterial topoisomerase inhibitors, Mycobacterium tuberculosis gyrase inhibitors, triazaacenaphthylenes, spiropyrimidinetriones, and thiophenes. Phase III clinical trials that utilized two members of these classes, gepotidacin (triazaacenaphthylene) and zoliflodacin (spiropyrimidinetrione), have been completed with positive outcomes, underscoring the potential of these compounds to become the first new classes of antibacterials introduced into the clinic in decades. Because gyrase and topoisomerase IV are validated targets for established and emerging antibacterials, this review will describe the catalytic mechanism and cellular activities of the bacterial type II topoisomerases, their interactions with fluoroquinolones, the mechanism of target-mediated fluoroquinolone resistance, and the actions of novel antibacterials against wild-type and fluoroquinolone-resistant gyrase and topoisomerase IV.

Effect of Host Cholesterol on the Membrane Dynamics of Outer Membrane Lipids of Mycobacteria

The ability of Mycobacterium tuberculosis to remain dormant after primary infection represents the prime cause of new TB cases throughout the world. Hence, diagnosis and treatment of individuals hosting dormant mycobacterium is one of the crucial strategies to be adopted for the prevention of Tuberculosis. Among many strategies unleashed by the latent bacterium, one of them is scavenging host cholesterol for carbon source. Cholesterol modifies lipid membranes over many scales and here, its effect on mycobacterial membrane biophysics and the subsequent effect on partitioning of antibiotics into cholesterol- enriched mycobacterial membranes was investigated. Our research showed that cholesterol alters the phase state behavior of mycobacterial outer membrane lipids by enhancing the overall membrane order at the headgroup and acyl chain region and is integrated into both ordered and disordered domains/phases, with a preference for the latter. Exogenous cholesterol further alters the drug partitioning behavior of structurally different drugs, pointing to a larger clinical potential of using more hydrophobic medications to target dormant bacteria.

Unlocking therapeutic potential: integration of drug repurposing and immunotherapy for various disease targeting

Drug repurposing, also known as drug repositioning, entails the application of pre-approved or formerly assessed drugs having potentially functional therapeutic amalgams for curing various disorders or disease conditions distinctive from their original remedial indication. It has surfaced as a substitute for the development of drugs for treating cancer, cardiovascular diseases, neurodegenerative disorders, and various infectious diseases like Covid-19. Although the earlier lines of findings in this area were serendipitous, recent advancements are based on patient centered approaches following systematic, translational, drug targeting practices that explore pathophysiological ailment mechanisms. The presence of definite information and numerous records with respect to beneficial properties, harmfulness, and pharmacologic characteristics of repurposed drugs increase the chances of approval in the clinical trial stages. The last few years have showcased the successful emergence of repurposed drug immunotherapy in treating various diseases. In this light, the present review emphasises on incorporation of drug repositioning with Immunotherapy targeted for several disorders.

Moxifloxacin Metal Complexes: Synthesis, Characterisation, Antimicrobial and Antidiabetic Activities with Docking Studies

Six new metal complexes of Fe(III), Cu(II), and Hg(II) were synthesised, i.e., three (2, 4, and 5) with moxifloxacin (mono-ligand) and the other three (1, 3 and 6) with moxifloxacin and hydrazine (biligand). These were characterised through UV-Vis, FT-IR, elemental analysis (CHN), atomic absorption spectroscopy, TGA, scanning electron microscopy (SEM), and powder XRD studies. Further, all of these compounds were screened for their antimicrobial, cytotoxic, and antidiabetic potential. The study revealed that the synthesised metal complexes possess an excellent ability to become antifungal agents compared to moxifloxacin. Additionally, the cytotoxicity of compounds 1, 3, and 4 was in the acceptable range with much better antidiabetic potential as compared to the ligand moxifloxacin. Interestingly, the α-amylase inhibition activity of complexes 1 and 3 was found very close to the standard drug acarbose. Furthermore, the computational studies also authenticate the results of the antidiabetic potential of complexes 1, 3, and 4 by presenting the necessary interactions of these compounds with their respective binding sites. The overall results indicate that the antifungal and antidiabetic ability of moxifloxacin is enhanced significantly by complexation with the given metals and the secondary ligand, thereby making it a suitable lead compound for yet another avenue of an antifungal and antidiabetic agent in the field of drug discovery and development.

In Vitro and In Vivo Activity of Gepotidacin against Drug-Resistant Mycobacterial Infections

Mycobacterial pathogens, including nontuberculous mycobacteria (NTM) and Mycobacterium tuberculosis, are pathogens of significant worldwide interest owing to their inherent drug resistance to a wide variety of FDA-approved drugs as well as causing a broad range of serious infections. Identifying new antibiotics active against mycobacterial pathogens is an urgent unmet need, especially those antibiotics that can bypass existing resistance mechanisms. In this study, we demonstrate that gepotidacin, a first-in-class triazaacenapthylene topoisomerase inhibitor, demonstrates potent activity against M. tuberculosis and M. fortuitum, as well as against other clinically relevant NTM species, including fluoroquinolone-resistant M. abscessus. Furthermore, gepotidacin exhibits concentration-dependent bactericidal activity against various mycobacterial pathogens, synergizes with several drugs utilized for their treatment, and reduces bacterial load in macrophages in intracellular killing assays comparably to amikacin. Additionally, M. fortuitum ATCC 6841 was unable to generate resistance to gepotidacin in vitro. When tested in a murine neutropenic M. fortuitum infection model, gepotidacin caused a significant reduction in bacterial load in various organs at a 10-fold lower concentration than amikacin. Taken together, these findings show that gepotidacin possesses a potentially new mechanism of action that enables it to escape existing resistance mechanisms. Thus, it can be projected as a potent novel lead for the treatment of mycobacterial infections, particularly for NTM, where present therapeutic interventions are extremely limited.

Moxifloxacin Concentration Correlate with QTc Interval in Rifampicin-Resistant Tuberculosis Patients on Shorter Treatment Regimens

Background

Drug-resistant tuberculosis (DR-TB) continues to be a global threat. Moxifloxacin is one of the components of the shorter treatment regimen which is suspected to increase the risk of QT prolongation, although it is also likely to be the most effective against DR-TB. A study to evaluate the correlation between the concentration of moxifloxacin and QTc interval in RR-TB patients who received shorter regimens is needed.

Methods

This was an observational study in 2 groups of RR-TB patients on shorter treatment regimens (intensive phase and continuation phase), contain moxifloxacin with body weight-adjusted dose. Blood samples were collected at 2 h after taking the 48th-hour dose and 1 h before taking the 72nd-hour dose.

Results

Forty-five RR-TB patients were included in this study. At 2 h after taking the 48th-hour dose, the mean of QTc interval in intensive phase and continuation phase was 444.38 ms vs. 467.94 ms, p = 0.026, while mean of moxifloxacin concentration in intensive phase and continuation phase was 4.3 µg/mL vs. 4.61 µg/mL, p = 0.686). At 1 h before taking the 72nd-hour dose, both moxifloxacin concentration and QTc interval in intensive phase and continuation showed no significant difference with p-value of 0.610 and 0.325, respectively. At 2 h after taking the 48th-dose, moxifloxacin concentration did not correlate with QTc interval, both in intensive phase (p = 0.576) and in continuation phase (p = 0.691). At 1 h before taking the 72nd-hour dose, moxifloxacin concentration also did not correlate with QTc interval in intensive phase (p = 0.531) and continuation phase (p = 0.209).

Conclusions

Our study found that moxifloxacin concentration did not correlate with QTc interval, which indicates the safe use of moxifloxacin on QTc interval. In addition to close monitoring of QTc interval, the clinicians should also consider other variables which potentially increase risk for QTc prolongation in DR-TB patients who received shorter treatment regimens.

Interaction of Host Pattern Recognition Receptors (PRRs) with Mycobacterium Tuberculosis and Ayurvedic Management of Tuberculosis: A Systemic Approach

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (Mtb), infects the lungs' alveolar surfaces through aerosol droplets. At this stage, the disease progression may have many consequences, determined primarily by the reactions of the human immune system. However, one approach will be to more actively integrate the immune system, especially the pattern recognition receptor (PRR) systems of the host, which notices pathogen-associated molecular patterns (PAMPs) of Mtb. Several types of PRRs are involved in the detection of Mtb, including Toll-like receptors (TLRs), C-type lectin receptors (CLRs), Dendritic cell (DC) -specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), Mannose receptor (MR), and NOD-like receptors (NLRs) related to inflammasome activation. In this study, we focus on reviewing the Mtb pathophysiology and interaction of host PPRs with Mtb as well as adverse drug effects of anti-tuberculosis drugs (ATDs) and systematic TB treatment via Ayurvedic medicine.

Intracellular Accumulation of Novel and Clinically Used TB Drugs Potentiates Intracellular Synergy

The therapeutic repertoire for tuberculosis (TB) remains limited despite the existence of many TB drugs that are highly active in in vitro models and possess clinical utility. Underlying the lack of efficacy in vivo is the inability of TB drugs to penetrate microenvironments inhabited by the causative agent, Mycobacterium tuberculosis, including host alveolar macrophages. Here, we determined the ability of the phenoxazine PhX1 previously shown to be active against M. tuberculosis in vitro to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. We also investigated the extent of permeation into uninfected and M. tuberculosis-infected human macrophage-like Tamm-Horsfall protein 1 (THP-1) cells directly and by comparing to results obtained in vitro in synergy assays. Our data indicate that PhX1 (4,750 ± 127.2 ng/ml) penetrates more effectively into THP-1 cells than do the clinically used anti-TB agents, rifampin (3,050 ± 62.9 ng/ml), moxifloxacin (3,374 ± 48.7 ng/ml), bedaquiline (4,410 ± 190.9 ng/ml), and linezolid (770 ± 14.1 ng/ml). Compound efficacy in infected cells correlated with intracellular accumulation, reinforcing the perceived importance of intracellular penetration as a key drug property. Moreover, we detected synergies deriving from redox-stimulatory combinations of PhX1 or clofazimine with the novel prenylated amino-artemisinin WHN296. Finally, we used compound synergies to elucidate the relationship between compound intracellular accumulation and efficacy, with PhX1/WHN296 synergy levels shown to predict drug efficacy. Collectively, our data support the utility of the applied assays in identifying in vitro active compounds with the potential for clinical development. IMPORTANCE This study addresses the development of novel therapeutic compounds for the eventual treatment of drug-resistant tuberculosis. Tuberculosis continues to progress, with cases of Mycobacterium tuberculosis (M. tuberculosis) resistance to first-line medications increasing. We assess new combinations of drugs with both oxidant and redox properties coupled with a third partner drug, with the focus here being on the potentiation of M. tuberculosis-active combinations of compounds in the intracellular macrophage environment. Thus, we determined the ability of the phenoxazine PhX1, previously shown to be active against M. tuberculosis in vitro, to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. In addition, the extent of permeation into human macrophage-like THP-1 cells and H37Rv-infected THP-1 cells was measured via mass spectrometry and compared to in vitro two-dimensional synergy and subsequent intracellular efficacy. Collectively, our data indicate that development of new drugs will be facilitated using the methods described herein.

The Mycobacterial Efflux Pump EfpA Can Induce High Drug Tolerance to Many Antituberculosis Drugs, Including Moxifloxacin, in Mycobacterium smegmatis

Active efflux of drugs across the membrane is a major survival strategy of bacteria against many drugs. In this work, we characterize an efflux pump, EfpA, from the major facilitator superfamily, that is highly conserved among both slow-growing and fast-growing Mycobacterium species and has been found to be upregulated in many clinical isolates of Mycobacterium tuberculosis. The gene encoding EfpA from Mycobacterium smegmatis was overexpressed under the control of both a constitutive and an inducible promoter. The expression of the efpA gene under the control of both promoters resulted in >32-fold-increased drug tolerance of M. smegmatis cells to many first-line (rifampicin, isoniazid, and streptomycin) and second-line (amikacin) antituberculosis drugs. Notably, the drug tolerance of M. smegmatis cells to moxifloxacin increased by more than 180-fold when efpA was overexpressed. The increase in MICs correlated with the decreased uptake of drugs, including norfloxacin, moxifloxacin, and ethidium bromide, and the high MIC could be reversed in the presence of an efflux pump inhibitor. A correlation was observed between the MICs of drugs and the efflux pump expression level, suggesting that the latter could be modulated by varying the expression level of the efflux pump. The expression of high levels of efpA did not impact the fitness of the cells when supplemented with glucose. The efpA gene is conserved across both pathogenic and nonpathogenic mycobacteria. The efpA gene from Mycobacterium bovis BCG/M. tuberculosis, which is 80% identical to efpA from M. smegmatis, also led to decreased antimicrobial efficacy of many drugs, although the fold change was lower. When overexpressed in M. bovis BCG, 8-fold-higher drug tolerance to moxifloxacin was observed. This is the first report of an efflux pump from Mycobacterium species that leads to higher drug tolerance to moxifloxacin, a promising new drug for the treatment of tuberculosis.

In vitro Synergism of Six Antituberculosis Agents Against Drug-Resistant Mycobacterium tuberculosis Isolated from Retreatment Tuberculosis Patients

Background

Retreatment tuberculosis (TB) has become a major source of drug-resistant TB. In contrast to the combination of isoniazid (INH) and rifampicin (RIF), that of pasiniazid (Pa) and rifabutin (RFB) or rifapentine (RFP) appears to have better activity in vitro against drug-resistant Mycobacterium tuberculosis (MTB), especially when combined with moxifloxacin (MXF). However, there has been limited study of potential synergism among Pa, RFB, RFP, and MXF, or simultaneous comparison with the standard INH and RIF combination.

Methods

In vitro synergism of four two-drug combinations (INH and RIF, Pa and RFB, Pa and RFP, MXF and Pa) and two three-drug combinations (MXF and Pa combined with RFB or RFP) was evaluated against 90 drug-resistant MTB strains isolated from retreatment TB patients by the checkerboard method. The fractional inhibitory concentration index (FICI) was calculated for each combination.

Results

The synergistic activity of the combination of Pa with RFB or RFP was higher than that of INH and RIF or MXF and Pa, and the synergistic activity of Pa in combination with RFP was even higher than that of RFB, although RFP yielded an MIC₉₀ of 64 mg/liter, higher than that of RFB of 8 mg/liter against 90 drug-resistant MTB strains. Meanwhile, for three-drug combinations, the synergistic effects of MXF and Pa combined with RFB or RFP were similar. Further stratification analysis showed that, for XDR-MTB strains, the synergistic effect of the Pa and RFP combination was also better than those of other two-drug combinations.

Conclusion

The combination of Pa with RFP shows better in vitro synergism than Pa with RFB and standard INH with RIF combinations, which can provide a reference for new regimens for retreatment TB patients.

ANCA associated glomerulonephritis in tuberculosis: a paradoxical reaction

We present a case of antineutrophil cytoplasmic antibodies (ANCA)-associated rapidly progressive glomerulonephritis in the context of treatment of pulmonary tuberculosis (TB). A 42-year-old woman was treated for drug-susceptible pulmonary TB and represented with paradoxical worsening of symptoms and radiological features. She was HIV negative. A severe acute kidney injury with features of glomerulonephritis was evident on admission. Perinuclear ANCA and antimyeloperoxidase antibodies were present in serum and renal biopsy was consistent with ANCA-associated vasculitis. The patient was successfully treated with both antituberculous therapy and immunosuppression (corticosteroids and mycophenolate mofetil) with subsequent clinical improvement and amelioration of renal function. We propose this is the first case that describes the association between paradoxical reactions during TB treatment and ANCA-associated glomerulonephritis.

Chemical Classes Presenting Novel Antituberculosis Agents Currently in Different Phases of Drug Development: A 2010-2020 Review

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a curable airborne disease currently treated using a drug regimen consisting of four drugs. Global TB control has been a persistent challenge for many decades due to the emergence of drug-resistant Mtb strains. The duration and complexity of TB treatment are the main issues leading to treatment failures. Other challenges faced by currently deployed TB regimens include drug-drug interactions, miss-matched pharmacokinetics parameters of drugs in a regimen, and lack of activity against slow replicating sub-population. These challenges underpin the continuous search for novel TB drugs and treatment regimens. This review summarizes new TB drugs/drug candidates under development with emphasis on their chemical classes, biological targets, mode of resistance generation, and pharmacokinetic properties. As effective TB treatment requires a combination of drugs, the issue of drug-drug interaction is, therefore, of great concern; herein, we have compiled drug-drug interaction reports, as well as efficacy reports for drug combinations studies involving antitubercular agents in clinical development.

In vitro potency of 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione against drug-resistant and non-replicating persisters of Mycobacterium tuberculosis

OBJECTIVES

New antituberculosis agents active against drug-resistant and non-replicating tubercle bacilli are required. We evaluated a previously identified hit, 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione (PAMCHD), against several clinical Mycobacterium tuberculosis isolates, including multidrug-resistant (MDR) strains and non-replicating drug-tolerant persisters of M. tuberculosis H37Rv.

METHODS

PAMCHD's potential against drug-resistant M. tuberculosis was investigated by broth microdilution. CFU enumeration was performed to determine PAMCHD's activity against five types of dormant bacilli.

RESULTS

No significant differences in MICs of PAMCHD were observed against M. tuberculosis H37Rv (2.5-5 µg/mL) and eight drug-susceptible strains (1.25-5 µg/mL) as well as drug-resistant strains including six isoniazid (INH)-resistant (2.5-10 µg/mL), one INH + ethambutol (EMB)-resistant (5 µg/mL), one rifampicin (RIF) + EMB-resistant (5 µg/mL) and three MDR (2.5-10 µg/mL) strains. Thus, PAMCHD maintains activity against all kinds of clinical strains, especially MDR. Regarding drug-tolerant persisters, INH and RIF killed, respectively, 0.5 and 5.0 log10 CFU of non-replicating persisters developed by hypoxia and 1.5 and 2.5 log₁₀ CFU developed by nutrient starvation at 64 × of their respective MIC against actively dividing cultures. In contrast, PAMCHD sterilised persister cultures developed by hypoxia (killed 6.5 log10 CFU) or starvation (killed 7.5 log10 CFU). PAMCHD sterilised RIF-tolerant (tolerance level up to 100 µg/mL of RIF) 100-day-old static persisters at 64 × MIC, while moxifloxacin killed only 1.0 log10 CFU of these persisters at 64 × MIC.

CONCLUSION

PAMCHD offers significant potential against MDR-TB and exhibits notable potency against non-replicating drug-tolerant M. tuberculosis persisters. These findings warrant further studies of PAMCHD for further anti-TB drug development.

The pentapeptide-repeat protein, MfpA, interacts with mycobacterial DNA gyrase as a DNA T-segment mimic

DNA gyrase, a type II topoisomerase, introduces negative supercoils into DNA using ATP hydrolysis. The highly effective gyrase-targeted drugs, fluoroquinolones (FQs), interrupt gyrase by stabilizing a DNA-cleavage complex, a transient intermediate in the supercoiling cycle, leading to double-stranded DNA breaks. MfpA, a pentapeptide-repeat protein in mycobacteria, protects gyrase from FQs, but its molecular mechanism remains unknown. Here, we show that Mycobacterium smegmatis MfpA (MsMfpA) inhibits negative supercoiling by M. smegmatis gyrase (Msgyrase) in the absence of FQs, while in their presence, MsMfpA decreases FQ-induced DNA cleavage, protecting the enzyme from these drugs. MsMfpA stimulates the ATPase activity of Msgyrase by directly interacting with the ATPase domain (MsGyrB47), which was confirmed through X-ray crystallography of the MsMfpA-MsGyrB47 complex, and mutational analysis, demonstrating that MsMfpA mimics a T (transported) DNA segment. These data reveal the molecular mechanism whereby MfpA modulates the activity of gyrase and may provide a general molecular basis for the action of other pentapeptide-repeat proteins.

The Prospect of Repurposing Immunomodulatory Drugs for Adjunctive Chemotherapy against Tuberculosis: A Critical Review

Tuberculosis (TB) remains a global health emergency, with an estimated 2 billion people infected across the world, and 1.4 million people dying to this disease every year. Many aspects of the causative agent, Mycobacterium tuberculosis, make this disease difficult for healthcare and laboratory researchers to fight against, such as unique pathophysiology, latent infection and long and complex treatment regimens, thus causing patient non-compliance with the treatment. Development of new drugs is critical for tackling these problems. Repurposing drugs is a promising strategy for generating an effective drug treatment whilst circumventing many of the challenges of conventional drug development. In this regard, the incorporation of immunomodulatory drugs into the standard regimen to potentiate frontline drugs is found to be highly appealing. Drugs of diverse chemical classes and drug categories are increasingly being evidenced to possess antitubercular activity, both in vitro and in vivo. This article explores and discusses the molecular entities that have shown promise in being repurposed for use in anti-TB adjunctive therapy and aims to provide the most up-to-date picture of their progress.

Pulmonary Targeting of Inhalable Moxifloxacin Microspheres for Effective Management of Tuberculosis

In the present study, the objective was to attain a localized lung delivery of an anti-tubercular fluoroquinolone, moxifloxacin (MXF), targeting the alveolar macrophages through a non-invasive pulmonary route using inhalable microspheres as a dry powder inhaler approach. MXF-loaded poly (lactic-co-glycolic acid) (PLGA) microspheres (MXF-PLGA-MSs) were fabricated by solvent evaporation technique and optimized by using a central composite statistical design. The morphology and particle size, as well as the flowability of the optimized microspheres, were characterized. In addition, the aerosolization performance of the optimized formula was inspected using an Andersen cascade impactor. Furthermore, in vivo fate following intrapulmonary administration of the optimized formula was evaluated. The optimized MXF-PLGA-MSs were spherical in shape with a particle size of 3.16 µm, drug loading of 21.98% and entrapment efficiency of 78.0%. The optimized formula showed a mass median aerodynamic diameter (MMAD) of 2.85 ± 1.04 µm with a favorable fine particle fraction of 72.77 ± 1.73%, suggesting that the powders were suitable for inhalation. Most importantly, in vivo studies revealed that optimized MXF-PLGA-MSs preferentially accumulated in lung tissue as manifested by a two-fold increase in the area under the curve AUC_0–24h, compared to plain drug. In addition, optimized MXF-PLGA-MS sustained drug residence in the lung for up to 24 h following inhalation, compared to plain drug. In conclusion, inhalable microspheres of MXF could be a promising therapeutic approach that might aid in the effective eradiation of tuberculosis along with improving patient adherence to the treatment.

Measurement of the Intracellular Mycobacterium tuberculosis Drug Effect and Prediction of the Clinical Dose-Response Relationship Using Intracellular Pharmacodynamic Modeling (PDi)

The human disease tuberculosis (TB) is the leading cause of death from a single infectious agent. A quarter of the world's population is estimated to be latently infected. Drug development and screening is slow and costly. We have developed a physiologically relevant assay to screen drugs against TB when inside immune cells. This chapter will describe a newly developed preclinical drug screening assay for TB, using high-content imaging and pharmacokinetic/pharmacodynamic modeling.

Modelling the effects of environmental heterogeneity within the lung on the tuberculosis life-cycle

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In silico model of TB in the lung incorporating environmental heterogeneity.

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Preferential conditions at the apex of lung localise post-primary disease there.

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Analysis of the key influences driving disease at different regions of the lung.

Progress in shortening the duration of tuberculosis (TB) treatment is hampered by the lack of a predictive model that accurately reflects the diverse environment within the lung. This is important as TB has been shown to produce distinct localisations to different areas of the lung during different disease stages, with the environmental heterogeneity within the lung of factors such as air ventilation, blood perfusion and oxygen tension believed to contribute to the apical localisation witnessed during the post-primary form of the disease.

Building upon our previous model of environmental lung heterogeneity, we present a networked metapopulation model that simulates TB across the whole lung, incorporating these notions of environmental heterogeneity across the whole TB life-cycle to show how different stages of the disease are influenced by different environmental and immunological factors. The alveolar tissue in the lung is divided into distinct patches, with each patch representing a portion of the total tissue and containing environmental attributes that reflect the internal conditions at that location. We include populations of bacteria and immune cells in various states, and events are included which determine how the members of the model interact with each other and the environment. By allowing some of these events to be dependent on environmental attributes, we create a set of heterogeneous dynamics, whereby the location of the tissue within the lung determines the disease pathological events that occur there.

Our results show that the environmental heterogeneity within the lung is a plausible driving force behind the apical localisation during post-primary disease. After initial infection, bacterial levels will grow in the initial infection location at the base of the lung until an adaptive immune response is initiated. During this period, bacteria are able to disseminate and create new lesions throughout the lung. During the latent stage, the lesions that are situated towards the apex are the largest in size, and once a post-primary immune-suppressing event occurs, it is the uppermost lesions that reach the highest levels of bacterial proliferation. Our sensitivity analysis also shows that it is the differential in blood perfusion, causing reduced immune activity towards the apex, which has the biggest influence of disease outputs.

Quinolones: Mechanism, Lethality and Their Contributions to Antibiotic Resistance

Fluoroquinolones (FQs) are arguably among the most successful antibiotics of recent times. They have enjoyed over 30 years of clinical usage and become essential tools in the armoury of clinical treatments. FQs target the bacterial enzymes DNA gyrase and DNA topoisomerase IV, where they stabilise a covalent enzyme-DNA complex in which the DNA is cleaved in both strands. This leads to cell death and turns out to be a very effective way of killing bacteria. However, resistance to FQs is increasingly problematic, and alternative compounds are urgently needed. Here, we review the mechanisms of action of FQs and discuss the potential pathways leading to cell death. We also discuss quinolone resistance and how quinolone treatment can lead to resistance to non-quinolone antibiotics.

A review of recent advances in anti-tubercular drug development

Tuberculosis is a global threat but in particular affects people from developing countries. It is thought that nearly a third of the population of the world live with its causative bacteria in a dormant form. Although tuberculosis is a curable disease, the chances of cure become slim as the disease becomes multidrug-resistant and the situation gets even worse as the disease becomes extensively drug-resistant. After approximately 5 decades without any new TB drug in the pipeline, there has been some good news in the recent years with the discovery of new drugs such as bedaquiline and delamanid as well as the discovery of new classes of anti-tubercular drugs. Some old drugs such as clofazimine, linezolid and many others which were not previously indicated for tuberculosis have been also repurposed for tuberculosis and they are performing well.

Structural and mechanistic analysis of ATPase inhibitors targeting mycobacterial DNA gyrase

OBJECTIVES

To evaluate the efficacy of two novel compounds against mycobacteria and determine the molecular basis of their action on DNA gyrase using structural and mechanistic approaches.

METHODS

Redx03863 and Redx04739 were tested in antibacterial assays, and also against their target, DNA gyrase, using DNA supercoiling and ATPase assays. X-ray crystallography was used to determine the structure of the gyrase B protein ATPase sub-domain from Mycobacterium smegmatis complexed with the aminocoumarin drug novobiocin, and structures of the same domain from Mycobacterium thermoresistibile complexed with novobiocin, and also with Redx03863.

RESULTS

Both compounds, Redx03863 and Redx04739, were active against selected Gram-positive and Gram-negative species, with Redx03863 being the more potent, and Redx04739 showing selectivity against M. smegmatis. Both compounds were potent inhibitors of the supercoiling and ATPase reactions of DNA gyrase, but did not appreciably affect the ATP-independent relaxation reaction. The structure of Redx03863 bound to the gyrase B protein ATPase sub-domain from M. thermoresistibile shows that it binds at a site adjacent to the ATP- and novobiocin-binding sites. We found that most of the mutations that we made in the Redx03863-binding pocket, based on the structure, rendered gyrase inactive.

CONCLUSIONS

Redx03863 and Redx04739 inhibit gyrase by preventing the binding of ATP. The fact that the Redx03863-binding pocket is distinct from that of novobiocin, coupled with the lack of activity of resistant mutants, suggests that such compounds could have potential to be further exploited as antibiotics.

Two Decades of TB Drug Discovery Efforts—What Have We Learned?

After several years of limited success, an effective regimen for the treatment of both drug-sensitive and multiple-drug-resistant tuberculosis is in place. However, this success is still incomplete, as we need several more novel combinations to treat extensively drug-resistant tuberculosis, as well newer emerging resistance. Additionally, the goal of a shortened therapy continues to evade us. A systematic analysis of the tuberculosis drug discovery approaches employed over the last two decades shows that the lead identification path has been largely influenced by the improved understanding of the biology of the pathogen Mycobacterium tuberculosis. Interestingly, the drug discovery efforts can be grouped into a few defined approaches that predominated over a period of time. This review delineates the key drivers during each of these periods. While doing so, the author’s experiences at AstraZeneca R&D, Bangalore, India, on the discovery of new antimycobacterial candidate drugs are used to exemplify the concept. Finally, the review also discusses the value of validated targets, promiscuous targets, the current anti-TB pipeline, the gaps in it, and the possible way forward.

Preclinical models to optimize treatment of tuberculous meningitis - A systematic review

Tuberculous meningitis (TBM) is the most devastating form of TB, resulting in death or neurological disability in up to 50% of patients affected. Treatment is similar to that of pulmonary TB, despite poor cerebrospinal fluid (CSF) penetration of the cornerstone anti-TB drug rifampicin. Considering TBM pathology, it is critical that optimal drug concentrations are reached in the meninges, brain and/or the surrounding CSF. These type of data are difficult to collect in TBM patients. This review aims to identify and describe a preclinical model representative for human TBM which can provide the indispensable data needed for future pharmacological characterization and prioritization of new TBM regimens in the clinical setting. We reviewed existing literature on treatment of TBM in preclinical models: only eight articles, all animal studies, could be identified. None of the animal models completely recapitulated human disease and in most of the animal studies key pharmacokinetic data were missing, making the comparison with human exposure and CNS distribution, and the study of pharmacokinetic-pharmacodynamic relationships impossible. Another 18 articles were identified using other bacteria to induce meningitis with treatment including anti-TB drugs (predominantly rifampicin, moxifloxacin and levofloxacin). Of these articles the pharmacokinetics, i.e. plasma exposure and CSF:plasma ratios, of TB drugs in meningitis could be evaluated. Exposures (except for levofloxacin) agreed with human exposures and also most CSF:plasma ratios agreed with ratios in humans. Considering the lack of an ideal preclinical pharmacological TBM model, we suggest a combination of 1. basic physicochemical drug data combined with 2. in vitro pharmacokinetic and efficacy data, 3. an animal model with adequate pharmacokinetic sampling, microdialysis or imaging of drug distribution, all as a base for 4. physiologically based pharmacokinetic (PBPK) modelling to predict response to TB drugs in treatment of TBM.

Moxifloxacin interacts with lipid bilayer, causing dramatic changes in its structure and phase transitions

Most drugs besides their intended activity, express undesired side effects, including those with the engagement of cell membrane. Previously, such undesired nonspecific effects on the membrane have been shown for a number of widely used nonsteroidal anti-inflammatory drugs. In this paper, we study the mechanism of interaction between moxifloxacin (Mox), antibacterial drug of broad specificity, with lipid bilayer of the liposomes of various compositions as a model of cell membrane using a combination of spectroscopy methods, including ATR-FTIR spectroscopy, circular dichroism, UV and fluorescence spectroscopy. The fine structure of the moxifloxacin-liposome complex, localization of the drug in bilayer and the main sites of Mox interaction with lipid membrane were determined. Lipid composition of the liposome plays a key role in the interaction with moxifloxacin, drastically affecting the loading efficiency, strength and character of drug binding, lipid phase segregation and phase transition parameters. In case of anionic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and cardiolipin (CL^2-) the electrostatic interaction of negatively charged nitrogen in heterocycle moiety of moxifloxacin with cardiolipin phosphate groups is a crucial factor for stable complex formation. The study of moxifloxacin-liposome complex behavior at phase transition in bilayer by DSC method revealed that in DPPC/CL^2- liposomes system two microphases with different content of CL^2- coexist and Mox interacts with both of these microphases resulting in the formation of two types of complexes with different structure and phase transition temperature. This binding stabilized the gel-state of the lipid bilayer with increasing the phase transition temperature Tm up to 3-5 °C. A different situation is observed for neutral DPPC liposomes: drug interaction with bilayer results in defects formation and a fluidization effect in lipid bilayer, resulted to decrease the Tm value by 2-4 °C. Moxifloxacin is not firmly binding in the membrane of DPPC and drug releases rapidly.

Intracellular Pharmacodynamic Modeling Is Predictive of the Clinical Activity of Fluoroquinolones against Tuberculosis

Clinical studies of new antitubercular drugs are costly and time-consuming. Owing to the extensive tuberculosis (TB) treatment periods, the ability to identify drug candidates based on their predicted clinical efficacy is vital to accelerate the pipeline of new therapies. Recent failures of preclinical models in predicting the activity of fluoroquinolones underline the importance of developing new and more robust predictive tools that will optimize the design of future trials.

Clinical studies of new antitubercular drugs are costly and time-consuming. Owing to the extensive tuberculosis (TB) treatment periods, the ability to identify drug candidates based on their predicted clinical efficacy is vital to accelerate the pipeline of new therapies. Recent failures of preclinical models in predicting the activity of fluoroquinolones underline the importance of developing new and more robust predictive tools that will optimize the design of future trials. Here, we used high-content imaging screening and pharmacodynamic intracellular (PDi) modeling to identify and prioritize fluoroquinolones for TB treatment. In a set of studies designed to validate this approach, we show moxifloxacin to be the most effective fluoroquinolone, and PDi modeling-based Monte Carlo simulations accurately predict negative culture conversion (sputum sterilization) rates compared to eight independent clinical trials. In addition, PDi-based simulations were used to predict the risk of relapse. Our analyses show that the duration of treatment following culture conversion can be used to predict the relapse rate. These data further support that PDi-based modeling offers a much-needed decision-making tool for the TB drug development pipeline.

Mycobacterium tuberculosis Metabolism

Mycobacterium tuberculosis is the cause of tuberculosis (TB), a disease which continues to overwhelm health systems in endemic regions despite the existence of effective combination chemotherapy and the widespread use of a neonatal anti-TB vaccine. For a professional pathogen, M. tuberculosis retains a surprisingly large proportion of the metabolic repertoire found in nonpathogenic mycobacteria with very different lifestyles. Moreover, evidence that additional functions were acquired during the early evolution of the M. tuberculosis complex suggests the organism has adapted (and augmented) the metabolic pathways of its environmental ancestor to persistence and propagation within its obligate human host. A better understanding of M. tuberculosis pathogenicity, however, requires the elucidation of metabolic functions under disease-relevant conditions, a challenge complicated by limited knowledge of the microenvironments occupied and nutrients accessed by bacilli during host infection, as well as the reliance in experimental mycobacteriology on a restricted number of experimental models with variable relevance to clinical disease. Here, we consider M. tuberculosis metabolism within the framework of an intimate host-pathogen coevolution. Focusing on recent advances in our understanding of mycobacterial metabolic function, we highlight unusual adaptations or departures from the better-characterized model intracellular pathogens. We also discuss the impact of these mycobacterial "innovations" on the susceptibility of M. tuberculosis to existing and experimental anti-TB drugs, as well as strategies for targeting metabolic pathways. Finally, we offer some perspectives on the key gaps in the current knowledge of fundamental mycobacterial metabolism and the lessons which might be learned from other systems.

Clinical impact of using fluoroquinolone with low antimycobacterial activity on treatment delay in tuberculosis: Hospital-based and population-based cohort study

BACKGROUND/PURPOSE

Little remains known regarding whether newer FQ with less anti-mycobacterial activity (gemifloxacin) would reduce treatment delay.

METHODS

We identified one hospital-based cohort (HBC) and one population-based cohort (PBC) including patients receiving amoxicillin/clavulanate acid (Beta-lactam), gemifloxacin (Gemi), and fluoroquinolones other than gemifloxacin (Non-Gemi FQ) prior to TB treatment.

RESULTS

A total of 201 patients in the HBC and 3544 patients in the PBC were recruited. After 1:1 propensity score matching, TB treatment delay was statistically insignificant between Beta-lactam, Gemi group, and Non-Gemi FQ group in HBC (Beta-lactam vs Gemi: 22.3 ± 21.4 d vs 28.6 ± 27.9 d, p = 0.292; Beta-lactam vs Non-Gemi FQ: 33.3 ± 26.5 d vs 50.3 ± 47.3 d, p = 0.135) and PBC (Beta-lactam vs Gemi: 26.4 ± 29.1 vs 25.0 ± 28.1, p = 0.638; Beta-lactam vs Non-Gemi FQ: 29.4 ± 36.0 d vs 32.7 ± 35.0 d, p = 0.124, Non-Gemi FQ vs Gemi: 28.4 ± 33.0 d vs 25.0 ± 28.1 d, p = 0.29).

CONCLUSION

While limited by relatively low case number, our study showed that use of gemifloxacin neither results in nor reduces delay in TB treatment. The issue of FQ use on TB treatment delay was also not observed in our study. Early survey and maintaining high clinical alertness remains the key to reducing TB treatment delay.

Fluoroquinolone Efficacy against Tuberculosis Is Driven by Penetration into Lesions and Activity against Resident Bacterial Populations

Fluoroquinolones represent the pillar of multidrug-resistant tuberculosis (MDR-TB) treatment, with moxifloxacin, levofloxacin, or gatifloxacin being prescribed to MDR-TB patients. Recently, several clinical trials of “universal” drug regimens, aiming to treat drug-susceptible and drug-resistant TB, have included a fluoroquinolone.

Fluoroquinolones represent the pillar of multidrug-resistant tuberculosis (MDR-TB) treatment, with moxifloxacin, levofloxacin, or gatifloxacin being prescribed to MDR-TB patients. Recently, several clinical trials of “universal” drug regimens, aiming to treat drug-susceptible and drug-resistant TB, have included a fluoroquinolone. In the absence of clinical data comparing their side-by-side efficacies in controlled MDR-TB trials, a pharmacological rationale is needed to guide the selection of the most efficacious fluoroquinolone. The present studies were designed to test the hypothesis that fluoroquinolone concentrations (pharmacokinetics) and activity (pharmacodynamics) at the site of infection are better predictors of efficacy than the plasma concentrations and potency measured in standard growth inhibition assays and are better suited to determinations of whether one of the fluoroquinolones outperforms the others in rabbits with active TB. We first measured the penetration of these fluoroquinolones in lung lesion compartments, and their potency against bacterial populations that reside in each compartment, to compute lesion-centric pharmacokinetic-pharmacodynamic (PK/PD) parameters. PK modeling methods were used to quantify drug penetration from plasma to tissues at human-equivalent doses. On the basis of these metrics, moxifloxacin emerged with a clear advantage, whereas plasma-based PK/PD favored levofloxacin (the ranges of the plasma AUC/MIC ratio [i.e., the area under the concentration-time curve over 24 h in the steady state divided by the MIC] are 46 to 86 for moxifloxacin and 74 to 258 for levofloxacin). A comparative efficacy trial in the rabbit model of active TB demonstrated the superiority of moxifloxacin in reducing bacterial burden at the lesion level and in sterilizing cellular and necrotic lesions. Collectively, these results show that PK/PD data obtained at the site of infection represent an adequate predictor of drug efficacy against TB and constitute the baseline required to explore synergies, antagonism, and drug-drug interactions in fluoroquinolone-containing regimens.

High-resolution mapping of fluoroquinolones in TB rabbit lesions reveals specific distribution in immune cell types

Understanding the distribution patterns of antibiotics at the site of infection is paramount to selecting adequate drug regimens and developing new antibiotics. Tuberculosis (TB) lung lesions are made of various immune cell types, some of which harbor persistent forms of the pathogen, Mycobacterium tuberculosis. By combining high resolution MALDI MSI with histology staining and quantitative image analysis in rabbits with active TB, we have mapped the distribution of a fluoroquinolone at high resolution, and identified the immune-pathological factors driving its heterogeneous penetration within TB lesions, in relation to where bacteria reside. We find that macrophage content, distance from lesion border and extent of necrosis drive the uneven fluoroquinolone penetration. Preferential uptake in macrophages and foamy macrophages, where persistent bacilli reside, compared to other immune cells present in TB granulomas, was recapitulated in vitro using primary human cells. A nonlinear modeling approach was developed to help predict the observed drug behavior in TB lesions. This work constitutes a methodological advance for the co-localization of drugs and infectious agents at high spatial resolution in diseased tissues, which can be applied to other diseases with complex immunopathology.

Ubiquitous Nature of Fluoroquinolones: The Oscillation between Antibacterial and Anticancer Activities

Fluoroquinolones are synthetic antibacterial agents that stabilize the ternary complex of prokaryotic topoisomerase II enzymes (gyrase and Topo IV), leading to extensive DNA fragmentation and bacteria death. Despite the similar structural folds within the critical regions of prokaryotic and eukaryotic topoisomerases, clinically relevant fluoroquinolones display a remarkable selectivity for prokaryotic topoisomerase II, with excellent safety records in humans. Typical agents that target human topoisomerases (such as etoposide, doxorubicin and mitoxantrone) are associated with significant toxicities and secondary malignancies, whereas clinically relevant fluoroquinolones are not known to exhibit such propensities. Although many fluoroquinolones have been shown to display topoisomerase-independent antiproliferative effects against various human cancer cells, those that are significantly active against eukaryotic topoisomerase show the same DNA damaging properties as other topoisomerase poisons. Empirical models also show that fluoroquinolones mediate some unique immunomodulatory activities of suppressing pro-inflammatory cytokines and super-inducing interleukin-2. This article reviews the extended roles of fluoroquinolones and their prospects as lead for the unmet needs of "small and safe" multimodal-targeting drug scaffolds.

Pharmacokinetics, Tolerability, and Bacteriological Response of Rifampin Administered at 600, 900, and 1,200 Milligrams Daily in Patients with Pulmonary Tuberculosis

In a multiple-dose-ranging trial, we previously evaluated higher doses of rifampin in patients for 2 weeks. The objectives of the current study were to administer higher doses of rifampin for a longer period to compare the pharmacokinetics, safety/tolerability, and bacteriological activity of such regimens. In a double-blind, randomized, placebo-controlled, phase II clinical trial, 150 Tanzanian patients with tuberculosis (TB) were randomized to receive either 600 mg (approximately 10 mg/kg of body weight), 900 mg, or 1,200 mg rifampin combined with standard doses of isoniazid, pyrazinamide, and ethambutol administered daily for 2 months. Intensive pharmacokinetic sampling occurred in 63 patients after 6 weeks of treatment, and safety/tolerability was assessed. The bacteriological response was assessed by culture conversion in liquid and solid media. Geometric mean total exposures (area under the concentration-versus-time curve up to 24 h after the dose) were 24.6, 50.8, and 76.1 mg · h/liter in the 600-mg, 900-mg, and 1,200-mg groups, respectively, reflecting a nonlinear increase in exposure with the dose (P < 0.001). Grade 3 adverse events occurred in only 2 patients in the 600-mg arm, 4 patients in the 900-mg arm, and 5 patients in the 1,200-mg arm. No significant differences in the bacteriological response were observed. Higher daily doses of rifampin (900 and 1,200 mg) resulted in a more than proportional increase in rifampin exposure in plasma and were safe and well tolerated when combined with other first-line anti-TB drugs for 2 months, but they did not result in improved bacteriological responses in patients with pulmonary TB. These findings have warranted evaluation of even higher doses of rifampin in follow-up trials. (This study has been registered at ClinicalTrials.gov under identifier NCT00760149.).

A Review of Moxifloxacin for the Treatment of Drug-Susceptible Tuberculosis

Moxifloxacin, an 8-methoxy quinolone, is an important drug in the treatment of multidrug-resistant tuberculosis and is being investigated in novel drug regimens with pretomanid, bedaquiline, and pyrazinamide, or rifapentine, for the treatment of drug-susceptible tuberculosis. Early results of these studies are promising. Although current evidence does not support the use of moxifloxacin in treatment-shortening regimens for drug-susceptible tuberculosis, it may be recommended in patients unable to tolerate standard first-line drug regimens or for isoniazid monoresistance. Evidence suggests that the standard 400-mg dose of moxifloxacin used in the treatment of tuberculosis may be suboptimal in some patients, leading to worse tuberculosis treatment outcomes and emergence of drug resistance. Furthermore, a drug interaction with the rifamycins results in up to 31% reduced plasma concentrations of moxifloxacin when these are combined for treatment of drug-susceptible tuberculosis, although the clinical relevance of this interaction is unclear. Moxifloxacin exhibits extensive interindividual pharmacokinetic variability. Higher doses of moxifloxacin may be needed to achieve drug exposures required for improved clinical outcomes. Further study is, however, needed to determine the safety of proposed higher doses and clinically validated targets for drug exposure to moxifloxacin associated with improved tuberculosis treatment outcomes. We discuss in this review the evidence for the use of moxifloxacin in drug-susceptible tuberculosis and explore the role of moxifloxacin pharmacokinetics, pharmacodynamics, and drug interactions with rifamycins, on tuberculosis treatment outcomes when used in first-line tuberculosis drug regimens.

Mycobacterium tuberculosis Proteome Response to Antituberculosis Compounds Reveals Metabolic "Escape" Pathways That Prolong Bacterial Survival

Tuberculosis (TB) continues to be one of the most common bacterial infectious diseases and is the leading cause of death in many parts of the world. A major limitation of TB therapy is slow killing of the infecting organism, increasing the risk for the development of a tolerance phenotype and drug resistance. Studies indicate that Mycobacterium tuberculosis takes several days to be killed upon treatment with lethal concentrations of antibiotics both in vitro and in vivo To investigate how metabolic remodeling can enable transient bacterial survival during exposure to bactericidal concentrations of compounds, M. tuberculosis strain H37Rv was exposed to twice the MIC of isoniazid, rifampin, moxifloxacin, mefloquine, or bedaquiline for 24 h, 48 h, 4 days, and 6 days, and the bacterial proteomic response was analyzed using quantitative shotgun mass spectrometry. Numerous sets of de novo bacterial proteins were identified over the 6-day treatment. Network analysis and comparisons between the drug treatment groups revealed several shared sets of predominant proteins and enzymes simultaneously belonging to a number of diverse pathways. Overexpression of some of these proteins in the nonpathogenic Mycobacterium smegmatis extended bacterial survival upon exposure to bactericidal concentrations of antimicrobials, and inactivation of some proteins in M. tuberculosis prevented the pathogen from escaping the fast killing in vitro and in macrophages, as well. Our biology-driven approach identified promising bacterial metabolic pathways and enzymes that might be targeted by novel drugs to reduce the length of tuberculosis therapy.