In Vitro Efficacy of Free and Nanoparticle Formulations of Gallium(III) meso-Tetraphenylporphyrine against Mycobacterium avium and Mycobacterium abscessus and Gallium Biodistribution in Mice

Identification of the Optimal Cultivation Period Required to Isolate Representatives of Mycobacterium abscessus Complex Isolated from Patients with Cystic Fibrosis

BACKGROUND

In patients with cystic fibrosis (CF), representatives of the fast-growing Mycobacterium abscessus complex (MABSc) are often distinguished, but the culture of the material taken from such patients increases the growth time. We analyzed the terms of cultivation of MABSc representatives on dense nutrient media and also evaluated the productivity of a modified nutrient medium based on agar for the isolation of Burkholderia cepacia complex (BCC).

METHODS

Sixty-four strains of MABSc isolated from patients with CF and suspected tuberculosis were analyzed. The material from the patients was cultured on a universal chromogenic medium, 5% blood agar, yolk-salt agar, selective medium for isolation of BCC, and Löwenstein-Jensen medium. The cultures were incubated for 5 days (37°C, aerobic conditions), after for 23 days (28°C, aerobic conditions). The productivity of the developed nutrient medium was evaluated by the number of cells that gave visible growth after culturing 0.1 mL of a bacterial suspension of 103 CFU/mL.

RESULTS

76.8% of the strains grew in a 2-week period, and 23.2% of the strains were obtained at a later date from 18 to 28 days (average: 21.23 days). The modified medium with a concentration of 240 mg of iron (III) polymaltose hydroxide proved to be the most optimal for the isolation of MABSc.

CONCLUSION

When using a chromogenic medium for culture material from patients with CF, it is necessary to extend incubation up to 28 days to increase the probability of MABSc isolation. The modified BCC medium showed a good selectivity result but required further investigation.

Investigating Novel IspE Inhibitors of the MEP Pathway in Mycobacterium

In a recent effort to mitigate harm from human pathogens, many biosynthetic pathways have been extensively evaluated for their ability to inhibit pathogen growth and to determine drug targets. One of the important products/targets of such pathways is isopentenyl diphosphate. Isopentenyl diphosphate is the universal precursor of isoprenoids, which are essential for the normal functioning of microorganisms. In general, two biosynthetic pathways lead to the formation of isopentenyl diphosphate: (1) the mevalonate pathway in animals; and (2) the non-mevalonate or methylerythritol phosphate (MEP) in many bacteria, and some protozoa and plants. Because the MEP pathway is not found in mammalian cells, it is considered an attractive target for the development of antimicrobials against a variety of human pathogens, including Mycobacterium tuberculosis (M.tb). In the MEP pathway, 4-diphosphocytidyl-2-c-methyl-d-erythritol kinase (IspE) phosphorylates 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDPME) to form 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate (CDPME2P). A virtual high-throughput screening against 15 million compounds was carried out by docking IspE protein. We identified an active heterotricyclic compound which showed enzymatic activity; namely, IC50 of 6 µg/mL against M.tb IspE and a MIC of 12 µg/mL against M.tb (H37Rv). Hence, we designed and synthesized similar new heterotricyclic compounds and tested them against mycobacterium, observing a MIC of 5 µg/mL against M. avium. This study will provide the critical insight necessary for developing novel antimicrobials that target the MEP pathways in pathogens.

Deferiprone-gallium-protoporphyrin (IX): A promising treatment modality against Mycobacterium abscessus

Non-Tuberculous Mycobacterial Pulmonary Disease (NTM-PD) caused by Mycobacterium abscessus is a frequent complication in patients with cystic fibrosis (CF) that worsens lung function over time. Currently, there is no cure for NTM-PD, hence new therapies are urgently required. Disrupting bacterial iron uptake pathways using gallium-protoporphyrin (IX) (GaPP), a heme analog, has been proposed as a novel antibacterial approach to tackle multi-drug resistant M. abscessus. However, the antibacterial activity of GaPP has been tested only in iron-deficient media, which cannot accurately mirror the potential activity in vivo. Herein, we investigated the potential synergistic activity between GaPP and the iron-chelating agent deferiprone (Def) in regular media against M. abscessus-infected macrophages. The safety of the treatment was assessed in vitro using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in Nuli-1 and THP-1 cell lines. Def-GaPP had synergistic activity against M. abscessus-infected macrophages where 10 mM-12.5 mg/L of Def-GaPP reduced the viability by up to 0.9 log10. Furthermore, Def-GaPP showed no cytotoxicity to Nuli-1 and THP-1 cell lines at the effective antibacterial concentrations (10 mM-12.5 mg/L) of Def- GaPP. These data encourage future investigation of Def-GaPP as a novel antimicrobial against NTM-PD.

Combination Therapy with Gallium Protoporphyrin and Gallium Nitrate Exhibits Enhanced Antimicrobial Activity In Vitro and In Vivo against Methicillin-Resistant Staphylococcus aureus

There is a major need for the development of new therapeutics to combat antibiotic-resistant Staphylococcus aureus. Recently, gallium (Ga)-based complexes have shown promising antimicrobial effects against various bacteria, including multidrug-resistant organisms, by targeting multiple heme/iron-dependent metabolic pathways. Among these, Ga protoporphyrin (GaPP) inhibits bacterial growth by targeting heme pathways, including aerobic respiration. Ga(NO3)3, an iron mimetic, disrupts elemental iron pathways. Here, we demonstrate the enhanced antimicrobial activity of the combination of GaPP and Ga(NO3)3 against methicillin-resistant S. aureus (MRSA) under iron-limited conditions, including small colony variants (SCV). This therapy demonstrated significant antimicrobial activity without inducing slow-growing SCV. We also observed that the combination of GaPP and Ga(NO3)3 inhibited the MRSA catalase but not above that seen with Ga(NO3)3 alone. Neither GaPP nor Ga(NO3)3 alone or their combination inhibited the dominant superoxide dismutase expressed (SodA) under the iron-limited conditions examined. Intranasal administration of the combination of the two compounds improved drug biodistribution in the lungs compared to intraperitoneal administration. In a murine MRSA lung infection model, we observed a significant increase in survival and decrease in MRSA lung CFUs in mice that received combination therapy with intranasal GaPP and Ga(NO3)3 compared to untreated control or mice receiving GaPP or Ga(NO3)3 alone. No drug-related toxicity was observed as assessed histologically in the spleen, lung, nasal cavity, and kidney for both single and repeated doses of 10 mg Ga /Kg of mice over 13 days. Our results strongly suggest that GaPP and Ga(NO3)3 in combination have excellent synergism and potential to be developed as a novel therapy for infections with S. aureus.

Mycobacterium abscessus Infections in Cystic Fibrosis Individuals: A Review on Therapeutic Options

Mycobacterium abscessus is an opportunistic pathogen that mainly colonizes and infects cystic fibrosis patients' lungs. M. abscessus is naturally resistant to many antibiotics such as rifamycin, tetracyclines and β-lactams. The current therapeutic regimens are not very effective and are mostly based on repurposed drugs used against Mycobacterium tuberculosis infections. Thus, new approaches and novel strategies are urgently needed. This review aims to provide an overview of the latest ongoing findings to fight M. abscessus infections by analyzing emerging and alternative treatments, novel drug delivery strategies, and innovative molecules.

Combining Gallium Protoporphyrin and Gallium Nitrate Enhances In Vitro and In Vivo Efficacy against Pseudomonas aeruginosa: Role of Inhibition of Bacterial Antioxidant Enzymes and Resultant Increase in Cytotoxic Reactive Oxygen Species

Pseudomonas aeruginosa is a highly antibiotic-resistant opportunistic pathogenic bacteria that is responsible for thousands of deaths each year. Infections with P. aeruginosa disproportionately impact individuals with compromised immune systems as well as cystic fibrosis patients, where P. aeruginosa lung infection is a leading cause of morbidity and mortality. In previous work, we showed that a combination of gallium (Ga) nitrate and Ga protoporphyrin worked well in several bacterial infection models but its mechanism of action (MOA) is unknown. In the current work, we have investigated the MOA of Ga combination therapy in P. aeruginosa and its analysis in the in vivo model. In P. aeruginosa treated with Ga combination therapy, we saw a decrease in catalase and superoxide dismutase (SOD) activity, key antioxidant enzymes, which could correlate with a higher potential for oxidative stress. Consistent with this hypothesis, we found that, following combination therapy, P. aeruginosa demonstrated higher levels of reactive oxygen species, as measured using the redox-sensitive fluorescent probe, H2DCFDA. We also saw that the Ga combination therapy killed phagocytosed bacteria inside macrophages in vitro. The therapy with low dose was able to fully prevent mortality in a murine model of P. aeruginosa lung infection and also significantly reduced lung damage. These results support our previous data that Ga combination therapy acts synergistically to kill P. aeruginosa, and we now show that this may occur through increasing the organism's susceptibility to oxidative stress. Ga combination therapy also showed itself to be effective at treating infection in a murine pulmonary-infection model.

Alternatives to Antibiotics against Mycobacterium abscessus

Mycobacterium abscessus complex is extremely difficult to treat. Intrinsic and acquired bacterial resistance makes this species one of the most challenging pathogens and treatments last from months to years, associated with potential risky antibiotic toxicity and a high number of failures. Nonantibiotic antimicrobial agents against this microorganism have recently been studied so as to offer an alternative to current drugs. This review summarizes recent research on different strategies such as host modulation using stem cells, photodynamic therapy, antibiofilm therapy, phage therapy, nanoparticles, vaccines and antimicrobial peptides against M. abscessus both in vitro and in vivo.

Beyond antibiotics: recent developments in the diagnosis and management of nontuberculous mycobacterial infection

Nontuberculous mycobacteria (NTM) pulmonary disease represents a significant clinical challenge with suboptimal therapy and increasing prevalence globally. Although clinical practice guidelines seek to standardise the approach to diagnosis and treatment of NTM disease, a lack of robust evidence limits their utility and significant variability exists in clinical practice. Here we walk through some novel approaches in diagnosis and therapy that are under development to tackle a disease where traditional strategies are failing.

Prevalence of NTM disease is rising globally, yet current diagnostic and therapeutic strategies are lacking. This review describes some burgeoning diagnostic and therapeutic approaches, but it is clear that real progress will need more focused attention.https://bit.ly/3O0K2SP

Synthesis and in vitro analysis of novel gallium tetrakis(4-methoxyphenyl)porphyrin and its long-acting nanoparticle as a potent antimycobacterial agent

Bacterial heme uptake pathways offer a novel target for antimicrobial drug discovery. Recently, gallium (Ga) porphyrin complexes were found to be effective against mycobacterial heme uptake pathways. The goal of the current study is to build on this foundation and develop a new Ga(III) porphyrin and its nanoparticles, formulated by a single emulsion-evaporation technique to inhibit the growth of Mycobacterium avium complex (MAC) with enhanced properties. Gallium 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin chloride (GaMeOTP) was synthesized from 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin and GaCl₃. GaMeOTP showed enhanced antimicrobial activity against MAC104 and some clinical M. avium isolates. The synthesized Ga(III) porphyrin antimicrobial activity resulted in the overproduction of reactive oxygen species. Our study also demonstrated that F127 nanoparticles encapsulating GaMeOTP exhibited a smaller size than GaTP nanoparticles and a better duration of activity in MAC-infected macrophages compared to the free GaMeOTP. The nanoparticles were trafficked to endosomal compartments within MAC-infected macrophages, likely contributing to the antimicrobial activity of the drug.

The key factors contributing to the risk, diagnosis and treatment of non-tuberculous mycobacterial opportunistic infections

The incidence and prevalence of diseases caused by non-tuberculous mycobacteria (NTM) have been steadily increasing worldwide. NTM are environmental saprophytic organisms; however, a few strains are known to produce diseases in humans affecting pulmonary and extra-pulmonary sites. Although the environment is a major source of NTM infection, recent studies have shown that person-to-person dissemination could be an important transmission route for these microorganisms. Structural and functional lung defects and immunodeficiency are major risk factors for acquiring NTM infections. Diagnosis of NTM diseases is very complex owing to the necessity of distinguishing between a true pathogen and an environmental contaminant. Identification at the species level is critical due to differences in the antibiotic susceptibility patterns of various NTM strains. Such identification is mainly achieved by molecular methods; additionally, mass spectrometry (e.g., MALDI-TOF) is useful for NTM species determination. Natural resistance of NTM species to a wide spectrum of antibiotics makes prescribing treatment for NTM diseases very difficult. NTM therapy usually takes more than one year and requires multi-drug regimens, yet the outcome often remains poor. Therefore, alternatives to antibiotic therapy treatment methods is an area under active exploration. NTM infections are an active global health problem imposing the necessity for better diagnostic tools and more effective treatment methods.

Current Molecular Therapeutic Agents and Drug Candidates for Mycobacterium abscessus

Mycobacterium abscessus has been recognised as a dreadful respiratory pathogen among the non-tuberculous mycobacteria (NTM) because of misdiagnosis, prolonged therapy with poor treatment outcomes and a high cost. This pathogen also shows extremely high antimicrobial resistance against current antibiotics, including the anti-tuberculosis agents. Therefore, current chemotherapies require a long curative period and the clinical outcomes are not satisfactory. Thus, there is an urgent need for discovering and developing novel, more effective anti-M. abscessus drugs. In this review, we sum the effectiveness of the current anti-M. abscessus drugs and drug candidates. Furthermore, we describe the shortcomings and difficulties associated with M. abscessus drug discovery and development.

Photo-damage promoted by tetra-cationic palladium(II) porphyrins in rapidly growing mycobacteria

Antimicrobial photodynamic therapy (aPDT) has gained prominence in microbiology, especially in treating non-invasive infections. Diseases such as mycobacteriosis, which causes localized infections and has a slow treatment, tend to be future targets for this type of technology. Therefore, this study aimed to explore the action of two isomeric Pd(II)-porphyrins on fast-growing mycobacterial strains (RGM). Tetra-cationic porphyrins (4-PdTPyP and 3-PdTPyP) were synthesized and applied against standard strains of Mycobacteroides abscessus subsp. abscessus (ATCC 19977), Mycolicibacterium fortuitum (ATCC 6841), Mycolicibacterium smegmatis (ATCC 700084), and Mycobacteroides abscessus subsp. massiliense (ATCC 48898). Reactive oxygen species (ROS) scavengers were used in an attempt to determine possible ROS produced by the photosensitizers (PS) under study. Moreover, the impact of porphyrin on the mycobacterial surface was further evaluated by atomic force microscopy (AFM), and we observed significant damage on cells walls and altered nanomechanical and electrostatic adhesion properties. The results presented herein show that the positively charged porphyrin at the meta position (3-PdTPyP) was the most efficient PS against the RGM strains, and its bactericidal activity was proven in two irradiation sessions, with singlet oxygen species being the main ROS involved in this process. This study demonstrated the therapeutic potential of porphyrins, especially the 3-PdTPyP derivative.

Nanoparticulate β-Cyclodextrin with Gallium Tetraphenylporphyrin Demonstrates in Vitro and in Vivo Antimicrobial Efficacy against Mycobacteroides abscessus and Mycobacterium avium

The emergence of drug-resistant pathogens causes the greatest challenge for drug development research. Recently, gallium(III)-based compounds have received great attention as novel antimicrobial agents against drug-resistant pathogens. Here, we synthesized a new β-cyclodextrin Ga nanoparticle (CDGaTP) using Ga tetraphenylporphyrin (GaTP, a hemin analogue) and β-cyclodextrin. The newly synthesized nanoparticle was nontoxic and efficient at a single dose, showing sustained drug release for 15 days in vitro. CDGaTP's activity with transferrin or lactoferrin was tested, and synergism in activity was observed against nontuberculosis mycobacteria (NTM), Mycobacterium avium (M. avium), and Mycobacteroides abscessus. Human serum albumin (HSA) decreased the efficacy of both GaTP and CDGaTP in a concentration-dependent manner. The NTMs incubated with GaTP or CDGaTP significantly produced reactive oxygen species (ROS), indicating potential inhibition of antioxidant enzymes, such as catalase. The single-dose CDGaTP displayed a prolonged intracellular inhibitory activity in an in vitro macrophage infection model against both NTMs. In addition, CDGaTP, not GaTP, was effective in a murine lung M. avium infection model when delivered via intranasal administration. These results suggest that CDGaTP provides new opportunities for the development of gallium-porphyrin based antibiotics.

Intra-tracheal administration increases gallium availability in lung: implications for antibacterial chemotherapy

The emergence of pan-resistant strains in nosocomial settings underscores the urgent need of novel therapies targeting vital bacterial functions. Bacterial iron metabolism is a fascinating target for new antimicrobials. Iron mimetic metal Ga(III) has been repurposed as an antimicrobial drug, in pre-clinical studies and recent clinical studies have raised the possibility of using Ga(III) for the treatment of P. aeruginosa pulmonary infection. Ga(III) has been approved by FDA for the treatment of cancer, autoimmune and bone resorption disorders. However, some critical issues affect the therapeutic schedule of Ga(III), principally the intra-venous (i.v.) administration, and the nephrotoxicity caused by prolonged administration. Ga(III) aerosolization could represent a viable alternative for treatment of lung infections, since delivery of antimicrobial agents to the airways maximizes drug concentration at the site of infection, improves the therapeutic efficacy, and alleviates systemic toxic effects. We demonstrate the advantage of inhaled vs i.v. administered Ga(III), in terms of bio-distribution and lung acute toxicity, by using a rat model. In vivo results support the use of Ga(III) for inhalation since intra-tracheal Ga(III) delivery improved its persistence in the lung, while the i.v. administration caused rapid clearance and did not allow to attain a significant Ga(III) concentration in this organ. Moreover, local and systemic acute toxicity following intra-tracheal administration was not observed, since no significant signs of inflammation were found. At this stage of evidence, the direct administration of Ga(III) to the lung appears feasible and safe, boosting the development of Ga(III)-based drugs for inhalation therapy.

Simultaneous Delivery of Multiple Antimicrobial Agents by Biphasic Scaffolds for Effective Treatment of Wound Biofilms

Biofilms pose a major challenge to control wound-associated infections. Due to biofilm impenetrability, traditional antimicrobial agents are often ineffective in combating biofilms. Herein, a biphasic scaffold is reported as an antimicrobial delivery system by integrating nanofiber mats with dissolvable microneedle arrays for the effective treatment of bacterial biofilms. Different combinations of antimicrobial agents, including AgNO3 , Ga(NO3 )3 , and vancomycin, are incorporated into nanofiber mats by coaxial electrospinning, which enables sustained delivery of these drugs. The antimicrobial agents-incorporated dissolvable microneedle arrays allow direct penetration of drugs into biofilms. By optimizing the administration strategies, drug combinations, and microneedle densities, biphasic scaffolds are able to eradicate both methicillin-resistant Staphylococcus aureus (MRSA) and MRSA/Pseudomonas aeruginosa blend biofilms in an ex vivo human skin wound infection model without necessitating surgical debridement. Taken together, the combinatorial system comprises of nanofiber mats and microneedle arrays can provide an efficacious delivery of multiple antimicrobial agents for the treatment of bacterial biofilms in wounds.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Competition between abiogenic and biogenic metal cations in biological systems: Mechanisms of gallium's anticancer and antibacterial effect

Metal cations are key players in a plethora of essential biological processes. Over the course of evolution specific biological functions have been bestowed upon two dozen of (biogenic) metal species, some of the most frequently found being sodium, potassium, magnesium, calcium, zinc, manganese, iron, and copper. On the other hand, there is a group of less studied abiogenic metals like lithium, strontium and gallium that possess not known functions in living organisms, but, by mimicking the native ions and/or competing with them for binding to key metalloenzymes, may exert beneficial effect on humans in particular medical conditions. This review summarizes and critically examines the mechanisms of gallium's therapeutic action in anticancer and antibacterial therapies by exploiting the tools of molecular modeling and experimental biochemistry. These approaches allow for identifying key factors for Ga³⁺ beneficial effect such as the electrostatic interactions with the protein ligands, substrates or bacterial siderophores, intramolecular hydrogen bond formation, and pH and dielectric properties of the medium. Several intriguing questions concerning the gallium competition with the native ferric ion have found their answers.

The Role of Metallic Nanoparticles in Inhibition of Mycobacterium Tuberculosis and Enhances Phagosome Maturation into the Infected Macrophage

This review focuses on the role of gallium (Ga) nanoparticles (NPs) to enhance phagosome maturation into the Mycobacterium tuberculosis-infected macrophage and the role of magnetic iron NPs as nanocarriers of antituberculosis drugs. The literature shows that silver (Ag) and zinc oxide (ZnO) NPs with dimensions less than 10 nm can penetrate directly through the macrophage bilayer membrane. Ag NPs increase the permeability membrane by motiving the aggregation of proteins in the periplasmic space and forming nano-sized pores. ZnO NPs can interact with the membrane of M. tuberculosis, which leads to the formation of surface pores and the release of intracellular nucleotides. The colloidal Ag:ZnO mixture NPs with 1:1 ratio can eliminate M. tuberculosis and shows the lowest cytotoxicity effects on MCF-7 and THP-1 cell lines. Ag/ZnO nanocrystals are not able to kill M. tuberculosis alone ex-vivo. Hence, bimetallic gold (Au)/Ag NPs possessed high efficiency to inhibit M. tuberculosis in an ex-vivo THP-1 infection model. Co-delivery of mixed MeNPs into a polymeric carrier collaborated to selective uptake by macrophages through passive targeting, initial burst release of ions from the encapsulated metallic (Me) NPs, and eventually, reduction of MeNPs toxicity, and plays a pivotal role in increasing the antitubercular activity compared to use alone. In addition, Ga NPs can import drugs to the macrophage, inhibit M. tuberculosis growth, and reduce the inhibition of phagosome maturation. Magnetic encapsulated NPs exhibited good drug release properties and might be suitable as carriers of antituberculosis drugs.

Gallium Porphyrin and Gallium Nitrate Synergistically Inhibit Mycobacterial Species by Targeting Different Aspects of Iron/Heme Metabolism

There is an urgent need for new effective and safe antibiotics active against pathogenic mycobacterial species. Gallium (Ga) nitrate (Ga(NO₃)₃) and Ga porphyrin (GaPP) have each been shown to inhibit the growth of a variety of mycobacterial species. The Ga(III) ion derived from Ga(NO₃)₃ has the potential to disrupt the mycobacterial Fe(III) uptake mechanisms and utilization, including replacing iron (Fe) in the active site of enzymes, resulting in the disruption of function. Similarly, noniron metalloporphyrins such as heme mimetics, which can be transported across the bacterial membrane via heme-uptake pathways, would potentially block the acquisition of iron-containing heme and bind to heme-utilizing proteins, making them nonfunctional. Given that they likely act on different aspects of mycobacterial Fe metabolism, the efficacy of combining Ga(NO₃)₃ and GaPP was studied in vitro against Mycobacterium avium, Mycobacterium abscessus, and Mycobacterium tuberculosis (M. tb). The combination was then assessed in vivo in a murine pulmonary infection model of M. abscessus. We observed that Ga(NO₃)₃ in combination with GaPP exhibited synergistic inhibitory activity against the growth of M. avium, M. tb, and M. abscessus, being most active against M. abscessus. Activity assays indicated that Ga(NO₃)₃ and GaPP inhibited both catalase and aconitase at high concentrations. However, the combination showed a synergistic effect on the aconitase activity of M. abscessus. The Ga(NO₃)₃/GaPP combination via intranasal administration showed significant antimicrobial activity in mice infected with M. abscessus. M. abscessus CFU from the lungs of the Ga(NO₃)₃/GaPP-treated mice was significantly less compared to that of nontreated or single Ga(III)-treated mice. These findings suggest that combinations of different Ga(III) compounds can synergistically target multiple iron/heme-utilizing mycobacterial enzymes. The results support the potential of combination Ga therapy for development against mycobacterial pathogens.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Treatment of Virulent Mycobacterium tuberculosis and HIV Coinfected Macrophages with Gallium Nanoparticles Inhibits Pathogen Growth and Modulates Macrophage Cytokine Production

GaNP interrupts iron-mediated enzymatic reactions, leading to growth inhibition of virulent HIV-M. tuberculosis coinfection in macrophages, and also modulates release of cytokines that may contribute to HIV-TB pathogenesis. Macrophage-targeting GaNP are a promising therapeutic approach to provide sustained antimicrobial activity against HIV-M. tuberculosis coinfection.

Tuberculosis (TB), caused by Mycobacterium tuberculosis, remains a global threat. The course of TB is negatively impacted by coexistent infection with human immunodeficiency virus type 1 (HIV). Macrophage infection with these pathogens modulates their production of pro- and anti-inflammatory cytokines, which could play a crucial role in pathogenesis. Despite the important role of macrophages in containing infection by a variety of microbes, both HIV and M. tuberculosis infect and replicate within these cells during the course of HIV-M. tuberculosis coinfection. Both M. tuberculosis and HIV require iron for growth and replication. We have previously shown that gallium encapsulated in nanoparticles, which interferes with cellular iron acquisition and utilization, inhibited the growth of HIV and an attenuated strain of M. tuberculosis within human monocyte-derived macrophages (MDMs) in vitro. Whether this was true for a fully virulent strain of M. tuberculosis and whether gallium treatment modulates cytokine production by HIV- and/or M. tuberculosis-infected macrophages have not been previously addressed. Therefore, coinfection of MDMs with HIV and a virulent M. tuberculosis strain (H37Rv) was studied in the presence of different gallium nanoparticles (GaNP). All GaNP were readily internalized by the MDMs, which provided sustained drug (gallium) release for 15 days. This led to significant growth inhibition of both HIV and M. tuberculosis within MDMs for up to 15 days after loading of the cells with all GaNP tested in our study. Cytokine analysis showed that HIV-M. tuberculosis coinfected macrophages secreted large amounts of interleukin 6 (IL-6) and IL-8 and smaller amounts of IL-1β, IL-4, and tumor necrosis factor alpha (TNF-α) cytokines. However, all GaNP were able to regulate the release of cytokines significantly. GaNP interrupts iron-mediated enzymatic reactions, leading to growth inhibition of HIV-M. tuberculosis coinfection in macrophages, and also modulates release of cytokines that may contribute to HIV-TB pathogenesis.

IMPORTANCE GaNP interrupts iron-mediated enzymatic reactions, leading to growth inhibition of virulent HIV-M. tuberculosis coinfection in macrophages, and also modulates release of cytokines that may contribute to HIV-TB pathogenesis. Macrophage-targeting GaNP are a promising therapeutic approach to provide sustained antimicrobial activity against HIV-M. tuberculosis coinfection.

Iron/Heme Metabolism-Targeted Gallium(III) Nanoparticles Are Active against Extracellular and Intracellular Pseudomonas aeruginosa and Acinetobacter baumannii

Iron/heme acquisition systems are critical for microorganisms to acquire iron from the human host, where iron sources are limited due to the nutritional immune system and insolubility of the ferric form of iron. Prior work has shown that a variety of gallium compounds can interfere with bacterial iron acquisition. This study explored the intra- and extracellular antimicrobial activities of gallium protoporphyrin (GaPP), gallium mesoporphyrin (GaMP), and nanoparticles encapsulating GaPP or GaMP against the Gram-negative pathogens Pseudomonas aeruginosa and Acinetobacter baumannii, including clinical isolates. All P. aeruginosa and A. baumannii isolates were susceptible to GaPP and GaMP, with MICs ranging from 0.5 to ∼32 μg/ml in iron-depleted medium. Significant intra- and extracellular growth inhibition was observed against P. aeruginosa cultured in macrophages at a gallium concentration of 3.3 μg/ml (5 μM) of all Ga(III) compounds, including nanoparticles. Nanoparticle formulations showed prolonged activity against both P. aeruginosa and A. baumannii in previously infected macrophages. When the macrophages were loaded with the nanoparticles 3 days prior to infection, there was a 5-fold decrease in growth of P. aeruginosa in the presence of single emulsion F127 copolymer nanoparticles encapsulating GaMP (eFGaMP). In addition, all Ga(III) porphyrins and nanoparticles showed significant intracellular and antibiofilm activity against both pathogens, with the nanoparticles exhibiting intracellular activity for 3 days. Ga nanoparticles also increased the survival rate of Caenorhabditis elegans nematodes infected by P. aeruginosa and A. baumannii Our results demonstrate that Ga nanoparticles have prolonged in vitro and in vivo activities against both P. aeruginosa and A. baumannii, including disruption of their biofilms.