Novel treatments in multidrug-resistant tuberculosis

Emergence of antibiotic-specific Mycobacterium tuberculosis phenotypes during prolonged treatment of mice

A major challenge in tuberculosis (TB) therapeutics is that antibiotic exposure leads to changes in the physiology of M. tuberculosis (Mtb), which may enable the pathogen to withstand treatment. While antibiotic-treated Mtb has been evaluated in in vitro experiments, it is unclear if and how long-term in vivo treatment with diverse antibiotics with varying treatment-shortening activity (sterilizing activity) affects Mtb physiologic processes differently. Here, we used SEARCH-TB, a pathogen-targeted RNA-sequencing platform, to characterize the Mtb transcriptome in the BALB/c high-dose aerosol infection mouse model following 4 weeks of treatment with three sterilizing and three non-sterilizing antibiotics. Certain transcriptional changes were shared among most antibiotics, including decreased expression of genes associated with protein synthesis and metabolism and the induction of certain genes associated with stress responses. However, the magnitude of this shared response differed between antibiotics. Sterilizing antibiotics rifampin, pyrazinamide, and bedaquiline generated a more quiescent Mtb state than did non-sterilizing antibiotics isoniazid, ethambutol, and streptomycin, as indicated by the decreased expression of genes associated with translation, transcription, secretion of immunogenic proteins, metabolism, and cell wall synthesis. Additionally, we identified distinguishing transcriptional effects specific to each antibiotic, indicating that different mechanisms of action induce distinct patterns in response to cellular injury. In addition to elucidating the Mtb physiologic changes associated with antibiotic stress, this study demonstrates the value of SEARCH-TB as a highly granular pharmacodynamic assay that reveals antibiotic effects that are not apparent based on culture alone.

Structural toxicity relationship (STR) of linezolid to mitigate myelosuppression and serotonergic toxicity

Tuberculosis (TB) remains a significant global health challenge, with multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains posing severe threats to treatment efficacy. Linezolid, a key component of the BPaL (Bedaquiline, Pretomanid and Linezolid) regimen, has demonstrated substantial efficacy against MDR-TB and XDR-TB. However, its clinical utility is often limited by side effects such as myelosuppression and monoamine oxidase (MAO) inhibition, linked to its mechanism of action. This perspective centres on the structural toxicity relationship (STR) of Linezolid and its analogues, exploring modifications to the C-ring and C-5 position that aim to reduce these toxicities while maintaining or enhancing antibacterial activity. Several promising analogues have been identified that exhibit reduced myelosuppression and MAO inhibition, highlighting the potential for developing safer Linezolid derivatives. The findings underscore the importance of continued research into the structure toxicity relationships of oxazolidinones to improve the therapeutic profiles of these essential drugs in combating drug-resistant TB.

Advancements and challenges in tuberculosis drug discovery: A comprehensive overview

Tuberculosis continues to pose a health challenge causing the loss of millions of lives despite the existence of multiple drugs, for treatment. The emergence of drug-resistant strains has made the situation more complex making it increasingly difficult to fight against this disease. This review outlines the challenges associated with TB drug discovery, the nature of Mycobacterium tuberculosis shedding light on the mechanisms that lead to treatment failure and antibiotic resistance. We explore promising drug targets, encompassing inhibition of mycolyarabinogalactan peptidoglycan (MAGP) assembly, mycolic acid biosynthesis, DNA replication, transcription, translation, protein synthesis, and bioenergetics/metabolism pathways. A comprehensive overview of the global pipeline of anti-tuberculosis drugs at various stages of clinical trials, the diverse strategies being pursued to tackle this complex disease. By gaining an understanding of the mechanisms that contribute to resistance development and identifying suitable targets, we can pave the way for more effective treatments and contribute to global efforts to combat drug-resistant tuberculosis.

Development of a self-microemulsifying drug delivery system to deliver delamanid via a pressurized metered dose inhaler for treatment of multi-drug resistant pulmonary tuberculosis

Tuberculosis (TB) is a serious health issue that contributes to millions of deaths throughout the world and increases the threat of serious pulmonary infections in patients with respiratory illness. Delamanid is a novel drug approved in 2014 to deal with multi-drug resistant TB (MDR-TB). Despite its high efficiency in TB treatment, delamanid poses delivery challenges due to poor water solubility leading to inadequate absorption upon oral administration. This study involves the development of novel formulation-based pressurized metered dose inhalers (pMDIs) containing self-microemulsifying mixtures of delamanid for efficient delivery to the lungs. To identify the appropriate self-microemulsifying formulations, ternary diagrams were plotted using different combinations of surfactant to co-surfactant ratios (1:1, 2:1, and 3:1). The combinations used Cremophor RH40, Poly Ethylene Glycol 400 (PEG 400), and peppermint oil, and those that showed the maximum microemulsion region and rapid and stable emulsification were selected for further characterization. The diluted self-microemulsifying mixtures underwent evaluation of dose uniformity, droplet size, zeta potential, and transmission electron microscopy. The selected formulations exhibited uniform delivery of the dose throughout the canister life, along with droplet sizes and zeta potentials that ranged from 24.74 to 88.99 nm and - 19.27 to - 10.00 mV, respectively. The aerosol performance of each self-microemulsifying drug delivery system (SMEDDS)-pMDI was assessed using the Next Generation Impactor, which indicated their capability to deliver the drug to the deeper areas of the lungs. In vitro cytotoxicity testing on A549 and NCI-H358 cells revealed no significant signs of toxicity up to a concentration of 1.56 µg/mL. The antimycobacterial activity of the formulations was evaluated against Mycobacterium bovis using flow cytometry analysis, which showed complete inhibition by day 5 with a minimum bactericidal concentration of 0.313 µg/mL. Moreover, the cellular uptake studies showed efficient delivery of the formulations inside macrophage cells, which indicated the potential for intracellular antimycobacterial activity. These findings demonstrated the potential of the Delamanid-SMEDDS-pMDI for efficient pulmonary delivery of delamanid to improve its effectiveness in the treatment of multi-drug resistant pulmonary TB.

Acceleration of infectious disease drug discovery and development using a humanized model of drug metabolism

A key step in drug discovery, common to many disease areas, is preclinical demonstration of efficacy in a mouse model of disease. However, this demonstration and its translation to the clinic can be impeded by mouse-specific pathways of drug metabolism. Here, we show that a mouse line extensively humanized for the cytochrome P450 gene superfamily ("8HUM") can circumvent these problems. The pharmacokinetics, metabolite profiles, and magnitude of drug-drug interactions of a test set of approved medicines were in much closer alignment with clinical observations than in wild-type mice. Infection with Mycobacterium tuberculosis, Leishmania donovani, and Trypanosoma cruzi was well tolerated in 8HUM, permitting efficacy assessment. During such assessments, mouse-specific metabolic liabilities were bypassed while the impact of clinically relevant active metabolites and DDI on efficacy were well captured. Removal of species differences in metabolism by replacement of wild-type mice with 8HUM therefore reduces compound attrition while improving clinical translation, accelerating drug discovery.

In Vitro, In Vivo and In Silico Assessment of the Antimicrobial and Immunomodulatory Effects of a Water Buffalo Cathelicidin (WBCATH) in Experimental Pulmonary Tuberculosis

Tuberculosis (TB) is considered the oldest pandemic in human history. The emergence of multidrug-resistant (MDR) strains is currently considered a serious global health problem. As components of the innate immune response, antimicrobial peptides (AMPs) such as cathelicidins have been proposed to have efficacious antimicrobial activity against Mycobacterium tuberculosis (Mtb). In this work, we assessed a cathelicidin from water buffalo, Bubalus bubalis, (WBCATH), determining in vitro its antitubercular activity (MIC), cytotoxicity and the peptide effect on bacillary loads and cytokines production in infected alveolar macrophages. Our results showed that WBCATH has microbicidal activity against drug-sensitive and MDR Mtb, induces structural mycobacterial damage demonstrated by electron microscopy, improves Mtb killing and induces the production of protective cytokines by murine macrophages. Furthermore, in vivo WBCATH showed decreased bacterial loads in a model of progressive pulmonary TB in BALB/c mice infected with drug-sensitive or MDR mycobacteria. In addition, a synergistic therapeutic effect was observed when first-line antibiotics were administered with WBCATH. These results were supported by computational modeling of the potential effects of WBCATH on the cellular membrane of Mtb. Thus, this water buffalo-derived cathelicidin could be a promising adjuvant therapy for current anti-TB drugs by enhancing a protective immune response and potentially reducing antibiotic treatment duration.

Antibiotic-Derived Radiotracers for Positron Emission Tomography: Nuclear or "Unclear" Infection Imaging?

The excellent features of non-invasive molecular imaging, its progressive technology (real-time, whole-body imaging and quantification), and global impact by a growing infrastructure for positron emission tomography (PET) scanners are encouraging prospects to investigate new concepts, which could transform clinical care of complex infectious diseases. Researchers are aiming towards the extension beyond the routinely available radiopharmaceuticals and are looking for more effective tools that interact directly with causative pathogens. We reviewed and critically evaluated (challenges or pitfalls) antibiotic-derived PET radiopharmaceutical development efforts aimed at infection imaging. We considered both radiotracer development for infection imaging and radio-antibiotic PET imaging supplementing other tools for pharmacologic drug characterization; overall, a total of 20 original PET radiotracers derived from eleven approved antibiotics.

Novel In Silico Insights into Rv1417 and Rv2617c as Potential Protein Targets: The Importance of the Medium on the Structural Interactions with Exported Repetitive Protein (Erp) of Mycobacterium tuberculosis

Nowadays, tuberculosis is the second leading cause of death from a monopathogenic transmitted disease, only ahead of COVID-19. The role of exported repetitive protein (Erp) in the virulence of Mycobacterium tuberculosis has been extensively demonstrated. In vitro and in vivo assays have identified that Erp interacts with Rv1417 and Rv2617c proteins, forming putative transient molecular complexes prior to localization to the cell envelope. Although new insights into the interactions and functions of Erp have emerged over the years, knowledge about its structure and protein–protein interactions at the atomistic level has not been sufficiently explored. In this work, we have combined several in silico methodologies to gain new insights into the structural relationship between these proteins. Two system conditions were evaluated by MD simulations: Rv1417 and Rv2617c embedded in a lipid membrane and another with a semi-polar solvent to mimic the electrostatic conditions on the membrane surface. The Erp protein was simulated as an unanchored structure. Stabilized structures were docked, and complexes were evaluated to recognize the main residues involved in protein–protein interactions. Our results show the influence of the medium on the structural conformation of proteins. Globular conformations were favored under high polarity conditions and showed a higher energetic affinity in complex formation. Meanwhile, disordered conformations were favored under semi-polar conditions and an increase in the number of contacts between residues was observed. In addition, the electrostatic potential analysis showed remarkable changes in protein interactions due to the polarity of the medium, demonstrating the relevance of Erp protein in heterodimer formation. On the other hand, contact analysis showed that several C-terminal residues of Erp were involved in the protein interactions, which seems to contradict experimental observations; however, these complexes could be transient forms. The findings presented in this work are intended to open new perspectives in the studies of Erp protein molecular interactions and to improve the knowledge about its function and role in the virulence of Mycobacterium tuberculosis.

Discovery of new riminophenazine analogues as antimycobacterial agents against drug-resistant Mycobacterium tuberculosis

Twenty-three new riminophenazine and pyrido[3,2-b]quinoxaline derivatives were prepared and examined for their antimycobacterial activities against Mycobacterium marinum and Mycobacterium tuberculosis H37Rv, taking clofazimine (1) as the lead. Structure-activity relationship (SAR) analysis revealed that the introduction of a heterocycle or diethylamine substituted benzene moiety on the N-5 atom might be beneficial for activity. The most potent compound 7m also displayed enhanced activity against wild-type as well as multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB clinical isolates, with the MICs ranging from 0.08 to 1.25 μg/mL, especially effective toward strain M20A507, resistant to 1. Further mechanism study indicated that its anti-TB activity was independent of cell membrane disruption, but related to NDH-2 reduction and the resulting high ROS production. Our study provides instructive guidance for the further development of clofazimine derivatives into promising antimicrobial agents against MDR and XDR TB.