Targeted pulmonary delivery of inducers of host macrophage autophagy as a potential host-directed chemotherapy of tuberculosis

Xenophagy receptors Optn and p62 and autophagy modulator Dram1 independently promote the zebrafish host defense against Mycobacterium marinum

Anti-bacterial autophagy, also known as xenophagy, is a crucial innate immune process that helps maintain cellular homeostasis by targeting invading microbes. This defense pathway is widely studied in the context of infections with mycobacteria, the causative agents of human tuberculosis and tuberculosis-like disease in animal models. Our previous work in a zebrafish tuberculosis model showed that host defense against Mycobacterium marinum (Mm) is impaired by deficiencies in xenophagy receptors, optineurin (Optn) or sequestome 1 (p62), and Damage-regulated autophagy modulator 1 (Dram1). However, the interdependency of these receptors and their interaction with Dram1 remained unknown. In the present study, we used single and double knockout zebrafish lines in combination with overexpression experiments. We show that Optn and p62 can compensate for the loss of each other's function, as their overexpression restores the infection susceptibility of the mutant phenotypes. Similarly, Dram1 can compensate for deficiencies in Optn and p62, and, vice versa, Optn and p62 compensate for the loss of Dram1, indicating that these xenophagy receptors and Dram1 do not rely on each other for host defense against Mm. In agreement, Dram1 overexpression in optn/p62 double mutants restored the interaction of autophagosome marker Lc3 with Mm. Finally, optn/p62 double mutants displayed more severe infection susceptibility than the single mutants. Taken together, these results suggest that Optn and p62 do not function downstream of each other in the anti-mycobacterial xenophagy pathway, and that the Dram1-mediated defense against Mm infection does not rely on specific xenophagy receptors.

Advancements in Chitosan-Based Nanoparticles for Pulmonary Drug Delivery

The evolution of respiratory diseases represents a considerable public health challenge, as they are among the leading causes of death worldwide. In this sense, in addition to the high prevalence of diseases such as asthma, chronic obstructive pulmonary disease, pneumonia, cystic fibrosis, and lung cancer, emerging respiratory diseases, particularly those caused by members of the coronavirus family, have contributed to a significant number of deaths on a global scale over the last two decades. Therefore, several studies have been conducted to optimize the efficacy of treatments against these diseases, focusing on pulmonary drug delivery using nanomedicine. Thus, the development of nanocarriers has emerged as a promising alternative to overcome the limitations of conventional therapy, by increasing drug bioavailability at the target site and reducing unwanted side effects. In this context, nanoparticles composed of chitosan (CS) show advantages over other nanocarriers because chitosan possesses intrinsic biological properties, such as anti-inflammatory, antimicrobial, and mucoadhesive capacity. Moreover, CS nanoparticles have the potential to enhance drug stability, prolong the duration of action, improve drug targeting, control drug release, optimize dissolution of poorly soluble drugs, and increase cell membrane permeability of hydrophobic drugs. These properties could optimize the performance of the drug after its pulmonary administration. Therefore, this review aims to discuss the potential of chitosan nanoparticles for pulmonary drug delivery, highlighting how their biological properties can improve the treatment of pulmonary diseases, including their synergistic action with the encapsulated drug.

A roadmap to pulmonary delivery strategies for the treatment of infectious lung diseases

Pulmonary drug delivery is a highly attractive topic for the treatment of infectious lung diseases. Drug delivery via the pulmonary route offers unique advantages of no first-pass effect and high bioavailability, which provides an important means to deliver therapeutics directly to lung lesions. Starting from the structural characteristics of the lungs and the biological barriers for achieving efficient delivery, we aim to review literatures in the past decade regarding the pulmonary delivery strategies used to treat infectious lung diseases. Hopefully, this review article offers new insights into the future development of therapeutic strategies against pulmonary infectious diseases from a delivery point of view.

Recombinant Human Lactoferrin Reduces Inflammation and Increases Fluoroquinolone Penetration to Primary Granulomas During Mycobacterial Infection of C57Bl/6 Mice

Infection with Mycobacterium tuberculosis (Mtb) results in the primary formation of a densely packed inflammatory foci that limits entry of therapeutic agents into pulmonary sites where organisms reside. No current therapeutic regimens exist that modulate host immune responses to permit increased drug penetration to regions of pathological damage during tuberculosis disease. Lactoferrin is a natural iron-binding protein previously demonstrated to modulate inflammation and granuloma cohesiveness, while maintaining control of pathogenic burden. Studies were designed to examine recombinant human lactoferrin (rHLF) to modulate histological progression of Mtb-induced pathology in a non-necrotic model using C57Bl/6 mice. The rHLF was oral administered at times corresponding to initiation of primary granulomatous response, or during granuloma maintenance. Treatment with rHLF demonstrated significant reduction in size of primary inflammatory foci following Mtb challenge, and permitted penetration of ofloxacin fluoroquinolone therapeutic to sites of pathological disruption where activated (foamy) macrophages reside. Increased drug penetration was accompanied by retention of endothelial cell integrity. Immunohistochemistry revealed altered patterns of M1-like and M2-like phenotypic cell localization post infectious challenge, with increased presence of M2-like markers found evenly distributed throughout regions of pulmonary inflammatory foci in rHLF-treated mice.

Clionamines stimulate autophagy, inhibit Mycobacterium tuberculosis survival in macrophages, and target Pik1

The pathogen Mycobacterium tuberculosis (Mtb) evades the innate immune system by interfering with autophagy and phagosomal maturation in macrophages, and, as a result, small molecule stimulation of autophagy represents a host-directed therapeutics (HDTs) approach for treatment of tuberculosis (TB). Here we show the marine natural product clionamines activate autophagy and inhibit Mtb survival in macrophages. A yeast chemical-genetics approach identified Pik1 as target protein of the clionamines. Biotinylated clionamine B pulled down Pik1 from yeast cell lysates and a clionamine analog inhibited phosphatidyl 4-phosphate (PI4P) production in yeast Golgi membranes. Chemical-genetic profiles of clionamines and cationic amphiphilic drugs (CADs) are closely related, linking the clionamine mode of action to co-localization with PI4P in a vesicular compartment. Small interfering RNA (siRNA) knockdown of PI4KB, a human homolog of Pik1, inhibited the survival of Mtb in macrophages, identifying PI4KB as an unexploited molecular target for efforts to develop HDT drugs for treatment of TB.

The Macrophage Response to Mycobacterium tuberculosis and Opportunities for Autophagy Inducing Nanomedicines for Tuberculosis Therapy

The major causative agent of tuberculosis (TB), i.e., Mycobacterium tuberculosis (Mtb), has developed mechanisms to evade host defense responses and persist within host cells for prolonged periods of time. Mtb is also increasingly resistant to existing anti-TB drugs. There is therefore an urgent need to develop new therapeutics for TB and host directed therapies (HDTs) hold potential as effective therapeutics for TB. There is growing interest in the induction of autophagy in Mtb host cells using autophagy inducing compounds (AICs). Nanoparticles (NPs) can enhance the effect of AICs, thus improving stability, enabling cell targeting and providing opportunities for multimodal therapy. In this review, we focus on the macrophage responses to Mtb infection, in particular, the mechanistic aspects of autophagy and the evasion of autophagy by intracellular Mtb. Due to the overlap between the onset of autophagy and apoptosis; we also focus on the relationship between apoptosis and autophagy. We will also review known AICs in the context of Mtb infection. Finally, we discuss the applications of NPs in inducing autophagy with the intention of sharing insights to encourage further research and development of nanomedicine HDTs for TB therapy.

Regulatory Mechanisms of Autophagy-Targeted Antimicrobial Therapeutics Against Mycobacterial Infection

Mycobacterium tuberculosis (Mtb) is an intracellular pathogen causing human tuberculosis, an infectious disease that still remains as a global health problem. Autophagy, a lysosomal degradative process, has emerged as a critical pathway to restrict intracellular Mtb growth through enhancement of phagosomal maturation. Indeed, several autophagy-modulating agents show promise as host-directed therapeutics for Mtb infection. In this Review, we discuss recent progress in our understanding the molecular mechanisms underlying the action of autophagy-modulating agents to overcome the immune escape strategies mediated by Mtb. The factors and pathways that govern such mechanisms include adenosine 5'-monophosphate-activated protein kinase, Akt/mammalian TOR kinase, Wnt signaling, transcription factor EB, cathelicidins, inflammation, endoplasmic reticulum stress, and autophagy-related genes. A further understanding of these mechanisms will facilitate the development of host-directed therapies against tuberculosis as well as infections with other intracellular bacteria targeted by autophagic degradation.

Transient Transfection of the Respiratory Epithelium with Gamma Interferon for Host-Directed Therapy in Pulmonary Tuberculosis

Nebulized gamma interferon (IFN-γ) protein has been studied for clinical safety and efficacy against pulmonary tuberculosis (TB). The protein is expensive, requires a cold chain, and is difficult to deploy in limited-resource, high-incidence settings. We generated a preclinical proof of concept (PoC) for a dry powder inhalation (DPI) containing DNA constructs to transiently transfect the lung and airway epithelium of mice with murine IFN-γ. Bacterial colony-forming units (CFU) in the lungs of mice infected with Mycobacterium tuberculosis (Mtb) reduced from about 106/g of tissue to ~104 after four doses given once a week. Nodular inflammatory lesions in the lungs reduced significantly in number. Immunohistochemistry of infected lung sections for LC3-1 and LAMP-1 indicated autophagy induction between 18 and 48 h after inhalation. ELISA on bronchoalveolar lavage (BAL) fluid showed differences in kinetics of IFN-γ concentrations in the epithelial lining fluid of healthy versus infected mice. Uninfected mice receiving DNA constructs expressing a fluorescent protein were live-imaged. The fluorescence signals from the intracellular protein peaked at about 36 h after inhalation and declined by 48 h. These results establish preclinical PoC of the efficacy of a DPI and dosing regimen as a host-directed and transient gene therapy of experimental pulmonary TB in mice, justifying preclinical development.

Xenophagy in innate immunity: A battle between host and pathogen

Autophagy is a fundamental bulk intracellular degradation and recycling process that directly eliminates intracellular microorganisms through "xenophagy" in various types of cells, especially in macrophages. Meanwhile, bacteria have evolved strategies and cellular self-defense mechanisms to prevent autophagosomal degradation and even attack the immune system of host. The lack of knowledge about the roles of autophagy in innate immunity severely limits our understanding of host defensive system and the development of farmed industry consisting of aquaculture. Increasing evidence in recent decades has shown the importance of autophagy. This review focuses on the triggering of xenophagy, targeting of invading pathogens to autophagosomes and elimination in the autophagolysosomes during pathogen infection. How the pathogen can escape from the xenophagy pathway was also discussed. Overall, we aim to reduce diseases and improve industrial production in aquaculture by providing theoretical and technical guidance on xenophagy.

Ornithine-A urea cycle metabolite enhances autophagy and controls Mycobacterium tuberculosis infection

Macrophages are professional phagocytes known to play a vital role in controlling Mycobacterium tuberculosis (Mtb) infection and disease progression. Here we compare Mtb growth in mouse alveolar (AMs), peritoneal (PMs), and liver (Kupffer cells; KCs) macrophages and in bone marrow-derived monocytes (BDMs). KCs restrict Mtb growth more efficiently than all other macrophages and monocytes despite equivalent infections through enhanced autophagy. A metabolomics comparison of Mtb-infected macrophages indicates that ornithine and imidazole are two top-scoring metabolites in Mtb-infected KCs and that acetylcholine is the top-scoring in Mtb-infected AMs. Ornithine, imidazole and atropine (acetylcholine inhibitor) inhibit Mtb growth in AMs. Ornithine enhances AMPK mediated autophagy whereas imidazole directly kills Mtb by reducing cytochrome P450 activity. Intranasal delivery of ornithine or imidazole or the two together restricts Mtb growth. Our study demonstrates that the metabolic differences between Mtb-infected AMs and KCs lead to differences in the restriction of Mtb growth.

Kupffer cells are more resistant to M. tuberculosis when compared with alveolar macrophages. Here the authors show that this distinction is caused by the presence of ornithine and imidazole in Kupffer cells and that these metabolites can drive autophagy and M. tuberculosis killing in alveolar macrophages when given intranasally to infected mice.

Autophagy-activating strategies to promote innate defense against mycobacteria

Mycobacterium tuberculosis (Mtb) is a major causal pathogen of human tuberculosis (TB), which is a serious health burden worldwide. The demand for the development of an innovative therapeutic strategy to treat TB is high due to drug-resistant forms of TB. Autophagy is a cell-autonomous host defense mechanism by which intracytoplasmic cargos can be delivered and then destroyed in lysosomes. Previous studies have reported that autophagy-activating agents and small molecules may be beneficial in restricting intracellular Mtb infection, even with multidrug-resistant Mtb strains. Recent studies have revealed the essential roles of host nuclear receptors (NRs) in the activation of the host defense through antibacterial autophagy against Mtb infection. In particular, we discuss the function of estrogen-related receptor (ERR) α and peroxisome proliferator-activated receptor (PPAR) α in autophagy regulation to improve host defenses against Mtb infection. Despite promising findings relating to the antitubercular effects of various agents, our understanding of the molecular mechanism by which autophagy-activating agents suppress intracellular Mtb in vitro and in vivo is lacking. An improved understanding of the antibacterial autophagic mechanisms in the innate host defense will eventually lead to the development of new therapeutic strategies for human TB.

Therapies that promote intracellular digestion of microbes could prove a valuable addition to antibiotic weapons against tuberculosis. Mycobacterium tuberculosis (Mtb) establishes itself within immune cells, and employs a variety of tricks to protect itself as it sickens its host. Researchers led by Eun-Kyeong Jo at Chungnam National University, Daejeon, South Korea, have reviewed efforts to defeat this pathogen by jump-starting a cellular ‘recycling’ pathway called autophagy. Autophagy helps cells break down both biomolecules aggregates and potential invaders, but Mtb can elude such digestion. Jo and colleagues highlight antimycobacterial agents that can potentially render Mtb vulnerable to autophagy, as well as promising cellular targets that may allow researchers to access this process. For example, evidence suggests that agents that activate a regulatory protein such as ERRα or PPARα could stimulate cellular degradation of Mtb.

A role for Wnt/β-catenin signalling in suppressing Bacillus Calmette-Guerin-induced macrophage autophagy

Mycobacterium tuberculosis (Mtb)-induced autophagy of alveolar macrophages has been confirmed to play a central role in the pathogenesis of tuberculosis. Growing evidence indicates that excessive or uncontrolled autophagic activity, which results in type II programmed cell death, can be regulated by many factors, including Wnt/β-catenin signalling. Wnt/β-catenin signalling has been demonstrated to be involved in multiple diseases through the regulation of autophagy; however, its exact role in regulating autophagy induced by Mtb remains unclear. Accordingly, this study examined the function of the Wnt/β-catenin signalling pathway in regulating Mycobacterium bovis Bacillus Calmette-Guerin (BCG)-induced autophagy in RAW264.7 macrophage cell line. In the present study, we found that BCG induced the autophagy of RAW264.7 cells in a time- and dose-dependent manner along with an accumulation of LC3 (Microtubule-associated protein 1 light chain 3) protein. Intriguingly, Wnt3a, a Wnt/β-catenin signalling ligand, significantly inhibited autophagy, with decreased autophagy rates and autophagic flux. An immunoblot analysis further revealed that Wnt/β-catenin signalling was capable of inhibiting the expression of the LC3 and autophagy-associated gene (Atg) cascade proteins in BCG-infected cells. Mechanistically, Wnt/β-catenin signalling may inhibit autophagy in BCG-infected macrophages by activating mTOR-dependent pathways. Our findings reveal the mechanisms of Wnt/β-catenin signalling regulates cellular autophagy induced by Mtb and provide novel insights into physiological and immune control of tuberculosis by modulating autophagy processes.

Host-targeted therapy for tuberculosis: Time to revisit the concept

Tuberculosis (TB) is an important cause of morbidity and mortality worldwide. Every year millions of people die due to TB. Drug resistance has been a major factor that has obstructed successful control and treatment of TB. As the rate of spread of drug-resistant TB outpaces the rate of discovery of new anti-tubercular drugs, targeted therapy may provide a new approach to TB cure. In a scenario where drug resistance is spreading rapidly, and existing drugs regimens seem to be dwindling away, this review summarizes the concept of host-targeted therapy which may be the ray of hope for the effective management and control of the rapidly spreading drug-resistant TB (multidrug resistant and extensively drug resistant).

Autophagy: A new strategy for host-directed therapy of tuberculosis

Tuberculosis (TB), which is primarily caused by the major etiologic agent Mycobacterium tuberculosis (Mtb), remains a serious infectious disease worldwide. Recently, much effort has been made to develop novel/improved therapies by modulating host responses to TB (i.e., host-directed therapy). Autophagy is an intracellular catabolic process that helps maintain homeostasis or the removal of invading pathogens via a lysosomal degradation process. The activation of autophagy by diverse drugs or agents may represent a promising treatment strategy against Mtb infection, even to drug-resistant strains. Important mediators of autophagy activation include vitamin D receptor signaling, the AMP-activated protein kinase pathway, sirtuin 1 activation, and nuclear receptors. High-throughput approaches have identified numerous natural and synthetic compounds that enhance antimicrobial defense against Mtb infection through autophagy. In this review, we discuss the current knowledge of, advancements in, and perspectives on new therapeutic strategies targeting autophagy against TB. Understanding the mechanisms and key players involved in modulating antibacterial autophagy will provide innovative improvements in anti-TB therapy via an autophagy-targeting approach.

Abbreviations: TB: Tuberculosis; Mtb: Mycobacterium tuberculosis; HDT: host-directed therapy; MDR: multidrug resistant; XDR: extensively drug resistant; LAP: LC3-associated phagocytosis; ROS: reactive oxygen species; VDR: vitamin D receptor; TFEB: transcription factor EB; ERRα: estrogen-related receptor α; PGC1α: PPARγ coactivator-1 α

The Immune Mechanisms of Lung Parenchymal Damage in Tuberculosis and the Role of Host-Directed Therapy

Impaired lung function is common in people with a history of tuberculosis. Host-directed therapy added to tuberculosis treatment may reduce lung damage and result in improved lung function. An understanding of the pathogenesis of pulmonary damage in TB is fundamental to successfully predicting which interventions could be beneficial. In this review, we describe the different features of TB immunopathology that lead to impaired lung function, namely cavities, bronchiectasis, and fibrosis. We discuss the immunological processes that cause lung damage, focusing on studies performed in humans, and using chest radiograph abnormalities as a marker for pulmonary damage. We highlight the roles of matrix metalloproteinases, neutrophils, eicosanoids and cytokines, like tumor necrosis factor-α and interleukin 1β, as well as the role of HIV co-infection. Finally, we focus on various existing drugs that affect one or more of the immunological mediators of lung damage and could therefore play a role as host-directed therapy.

GABAergic signaling linked to autophagy enhances host protection against intracellular bacterial infections

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the brain; however, the roles of GABA in antimicrobial host defenses are largely unknown. Here we demonstrate that GABAergic activation enhances antimicrobial responses against intracellular bacterial infection. Intracellular bacterial infection decreases GABA levels in vitro in macrophages and in vivo in sera. Treatment of macrophages with GABA or GABAergic drugs promotes autophagy activation, enhances phagosomal maturation and antimicrobial responses against mycobacterial infection. In macrophages, the GABAergic defense is mediated via macrophage type A GABA receptor (GABA_AR), intracellular calcium release, and the GABA type A receptor-associated protein-like 1 (GABARAPL1; an Atg8 homolog). Finally, GABAergic inhibition increases bacterial loads in mice and zebrafish in vivo, suggesting that the GABAergic defense plays an essential function in metazoan host defenses. Our study identified a previously unappreciated role for GABAergic signaling in linking antibacterial autophagy to enhance host innate defense against intracellular bacterial infection.

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in neuronal systems, but the potential role for such neurotransmitters on the immune system are emerging. Here the authors show GABA signaling is linked to autophagy, enhancing the host response against intracellular bacteria.

Bolstering Immunity through Pattern Recognition Receptors: A Unique Approach to Control Tuberculosis

The global control of tuberculosis (TB) presents a continuous health challenge to mankind. Despite having effective drugs, TB still has a devastating impact on human health. Contributing reasons include the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), the AIDS-pandemic, and the absence of effective vaccines against the disease. Indeed, alternative and effective methods of TB treatment and control are urgently needed. One such approach may be to more effectively engage the immune system; particularly the frontline pattern recognition receptor (PRR) systems of the host, which sense pathogen-associated molecular patterns (PAMPs) of Mtb. It is well known that 95% of individuals infected with Mtb in latent form remain healthy throughout their life. Therefore, we propose that clues can be found to control the remainder by successfully manipulating the innate immune mechanisms, particularly of nasal and mucosal cavities. This article highlights the importance of signaling through PRRs in restricting Mtb entry and subsequently preventing its infection. Furthermore, we discuss whether this unique therapy employing PRRs in combination with drugs can help in reducing the dose and duration of current TB regimen.

Host-directed therapies offer novel opportunities for the fight against tuberculosis

Tuberculosis (TB) remains a leading global health problem that is exacerbated by the emergence of multidrug and extensively drug-resistant Mycobacterium tuberculosis strains. Control of the disease requires novel therapeutic strategies. Modulating host homeostasis appears to be a promising approach, and recent studies have identified novel potential host targets and compounds that could be investigated for host-directed therapies (HDTs). Moreover, the recent development of intracellular high-throughput phenotypic assays makes it possible to screen large libraries of compounds to identify more rapidly new effectors for mycobacterial elimination. Technological advances combined with the novel HDT concept opens an interesting and promising research area that could ultimately deliver personalized TB treatment.

Morphoproteomic-Guided Host-Directed Therapy for Tuberculosis

In an effort to develop more effective therapy for tuberculosis (TB), research efforts are looking toward host-directed therapy, reprograming the body's natural defenses to better control the infection. While significant progress is being made, the efforts are limited by lack of understanding of the pathology and pathogenesis of adult type TB disease. We have recently published evidence that the developing lesions in human lungs are focal endogenous lipid pneumonia that constitutes a region of local susceptibility in a person with strong systemic immunity. Since most such lesions regress spontaneously, the ability to study them directly with immunohistochemistry provides means to investigate why some progress to clinical disease while others asymptomatically regress. Furthermore, this should enable us to develop more effective host-directed therapies. Morphoproteomics has proven to be an effective means of characterizing protein expression that can be used to identify metabolic pathways, which can lead to more effective therapies. The purpose of this perspective will argue that using morphoproteomics on human TB lung tissue is a particularly promising method to direct selection of host-directed therapeutics.

Metformin: Candidate host-directed therapy for tuberculosis in diabetes and non-diabetes patients

Despite major advances in tuberculosis (TB) control, TB continues to be a leading cause of death worldwide. The discovery of new anti-TB treatment drugs and regimens that target drug-sensitive and drug-resistant TB are being complemented with a search for adjunct host-directed therapies that synergize for Mycobacterium tuberculosis (Mtb) elimination. The goal of host-directed therapies is to boost immune mechanisms that diminish excess inflammation to reduce lung tissue damage and limit Mtb growth. Metformin is the most commonly-used medication for type 2 diabetes, and a candidate for host-directed therapy for TB. Preliminary data suggests metformin may be beneficial for TB control by reducing the deleterious inflammation associated with immune pathology and enhancing the anti-mycobacterial activity of immune cells. In this review I summarize current findings, knowledge gaps and the potential benefits as well as points of caution for using metformin as adjunct therapy for TB in patients with and without type 2 diabetes.

Inhalable Particles for "Pincer Therapeutics" Targeting Nitazoxanide as Bactericidal and Host-Directed Agent to Macrophages in a Mouse Model of Tuberculosis

Nitazoxanide (NTZ) has moderate mycobactericidal activity and is also an inducer of autophagy in mammalian cells. High-payload (40-50% w/w) inhalable particles containing NTZ alone or in combination with antituberculosis (TB) agents isoniazid (INH) and rifabutin (RFB) were prepared with high incorporation efficiency of 92%. In vitro drug release was corrected for drug degradation during the course of study and revealed first-order controlled release. Particles were efficiently taken up in vitro by macrophages and maintained intracellular drug concentrations at one order of magnitude higher than NTZ in solution for 6 h. Dose-dependent killing of Mtb and restoration of lung and spleen architecture were observed in experimentally infected mice treated with inhalations containing NTZ. Adjunct NTZ with INH and RFB cleared culturable bacteria from the lung and spleen and markedly healed tissue architecture. NTZ can be used in combination with INH-RFB to kill the pathogen and heal the host.

Dry powder inhalable formulations for anti-tubercular therapy

Tuberculosis (TB) is an intracellular infectious disease caused by the airborne bacterium, Mycobacterium tuberculosis. Despite considerable research efforts, the treatment of TB continues to be a great challenge in part due to the requirement of prolonged therapy with multiple high-dose drugs and associated side effects. The delivery of pharmacological agents directly to the respiratory system, following the natural route of infection, represents a logical therapeutic approach for treatment or vaccination against TB. Pulmonary delivery is non-invasive, avoids first-pass metabolism in the liver and enables targeting of therapeutic agents to the infection site. Inhaled delivery also potentially reduces the dose requirement and the accompanying side effects. Dry powder is a stable formulation of drug that can be stored without refrigeration compared to liquids and suspensions. The dry powder inhalers are easy to use and suitable for high-dose formulations. This review focuses on the current innovations of inhalable dry powder formulations of drug and vaccine delivery for TB, including the powder production method, preclinical and clinical evaluations of inhaled dry powder over the last decade. Finally, the risks associated with pulmonary therapy are addressed. A novel dry powder formulation with high percentages of respirable particles coupled with a cost effective inhaler device is an appealing platform for TB drug delivery.

Preparation and Preclinical Evaluation of Inhalable Particles Containing Rapamycin and Anti-Tuberculosis Agents for Induction of Autophagy

PURPOSE

Mycobacterium tuberculosis (Mtb) inhibits host defense mechanisms, including autophagy. We investigated particles containing rapamycin (RAP) alone or in combination with isoniazid (INH) and rifabutin (RFB) for: targeting lung macrophages on inhalation; inducing autophagy; and killing macrophage-resident Mtb and/or augmenting anti-tuberculosis (TB) drugs.

METHODS

PLGA and drugs were spray-dried. Pharmacokinetics, partial biodistribution (LC-MS/MS) and efficacy (colony forming units, qPCR, acid fast staining, histopathology) in mice following dry powder inhalation were evaluated.

RESULTS

Aerodynamic diameters of formulations were 0.7-4.7 μm. Inhaled particles reached deep lungs and were phagocytosed by alveolar macrophages, yielding AUC0-48 of 102 compared to 0.1 μg/ml × h obtained with equivalent intravenous dose. RAP particles induced more autophagy in Mtb-infected macrophages than solutions. Inhaled particles containing RAP alone in daily, alternate-day and weekly dosing regimens reduced bacterial burden in lungs and spleens, inducing autophagy and phagosome-lysosome fusion. Inhalation of particles containing RAP with INH and RFB cleared the lungs and spleens of culturable bacteria.

CONCLUSIONS

Targeting a potent autophagy-inducing agent to airway and lung macrophages alone is feasible, but not sufficient to eliminate Mtb. Combination of macrophage-targeted inhaled RAP with classical anti-TB drugs contributes to restoring tissue architecture and killing Mtb.