Pipeline of anti-Mycobacterium abscessus small molecules: Repurposable drugs and promising novel chemical entities

Alternative therapies against Mycobacterium abscessus infections

BACKGROUND

Mycobacterium abscessus (Mab) is considered as the most pathogenic rapid-growing mycobacteria in humans, causing pulmonary and extra-pulmonary diseases, especially in patients with cystic fibrosis. Mab shows intrinsic and acquired resistance to many drugs, leaving limited treatment options that lead to a generally poor prognosis. The standard therapeutic regimen last for more than 6 months and consists of a drug cocktail that ideally includes a macrolide and amikacin. Yet, toxicity and efficacy are suboptimal due also to the high toxicity. There is a need to introduce innovative and out-of-the-box approaches to improve treatments.

OBJECTIVES

In this narrative review, we summarize the recent research on the alternative strategies proposed and discuss the importance of using appropriate experimental assays to assess their activity.

SOURCES

Included articles were identified by searching PubMed and MEDLINE until June 2023. The search terms were 'Mycobacterium abscessus', 'antimicrobial', and 'alternative therapies'. Additional relevant references were obtained from articles retrieved from the primary search.

CONTENT

Therapies against Mab including host directed therapies, repurposed drugs, phage therapy, anti-virulence strategies, essential oils, and inhalation therapies.

IMPLICATIONS

Alternative treatments may represent a valid tool to cope the burden of antimicrobial resistance in Mab-caused diseases.

Computational drug repositioning identifies niclosamide and tribromsalan as inhibitors of Mycobacterium tuberculosis and Mycobacterium abscessus

Tuberculosis (TB) is still a major global health challenge, killing over 1.5 million people each year, and hence, there is a need to identify and develop novel treatments for Mycobacterium tuberculosis (M. tuberculosis). The prevalence of infections caused by nontuberculous mycobacteria (NTM) is also increasing and has overtaken TB cases in the United States and much of the developed world. Mycobacterium abscessus (M. abscessus) is one of the most frequently encountered NTM and is difficult to treat. We describe the use of drug-disease association using a semantic knowledge graph approach combined with machine learning models that has enabled the identification of several molecules for testing anti-mycobacterial activity. We established that niclosamide (M. tuberculosis IC90 2.95 μM; M. abscessus IC90 59.1 μM) and tribromsalan (M. tuberculosis IC90 76.92 μM; M. abscessus IC90 147.4 μM) inhibit M. tuberculosis and M. abscessus in vitro. To investigate the mode of action, we determined the transcriptional response of M. tuberculosis and M. abscessus to both compounds in axenic log phase, demonstrating a broad effect on gene expression that differed from known M. tuberculosis inhibitors. Both compounds elicited transcriptional responses indicative of respiratory pathway stress and the dysregulation of fatty acid metabolism.

Therapeutic developments for tuberculosis and nontuberculous mycobacterial lung disease

Tuberculosis (TB) drug discovery and development has undergone nothing short of a revolution over the past 20 years. Successful public-private partnerships and sustained funding have delivered a much-improved understanding of mycobacterial disease biology and pharmacology and a healthy pipeline that can tolerate inevitable attrition. Preclinical and clinical development has evolved from decade-old concepts to adaptive designs that permit rapid evaluation of regimens that might greatly shorten treatment duration over the next decade. But the past 20 years also saw the rise of a fatal and difficult-to-cure lung disease caused by nontuberculous mycobacteria (NTM), for which the drug development pipeline is nearly empty. Here, we discuss the similarities and differences between TB and NTM lung diseases, compare the preclinical and clinical advances, and identify major knowledge gaps and areas of cross-fertilization. We argue that applying paradigms and networks that have proved successful for TB, from basic research to clinical trials, will help to populate the pipeline and accelerate curative regimen development for NTM disease.

Preclinical murine models for the testing of antimicrobials against Mycobacterium abscessus pulmonary infections: Current practices and recommendations

Mycobacterium abscessus, a rapidly growing nontuberculous mycobacterium, is increasingly recognized as an important pathogen of the human lung, disproportionally affecting people with cystic fibrosis (CF) and other susceptible individuals with non-CF bronchiectasis and compromised immune functions. M. abscessus infections are extremely difficult to treat due to intrinsic resistance to many antibiotics, including most anti-tuberculous drugs. Current standard-of-care chemotherapy is long, includes multiple oral and parenteral repurposed drugs, and is associated with significant toxicity. The development of more effective oral antibiotics to treat M. abscessus infections has thus emerged as a high priority. While murine models have proven instrumental in predicting the efficacy of therapeutic treatments for M. tuberculosis infections, the preclinical evaluation of drugs against M. abscessus infections has proven more challenging due to the difficulty of establishing a progressive, sustained, pulmonary infection with this pathogen in mice. To address this issue, a series of three workshops were hosted in 2023 by the Cystic Fibrosis Foundation (CFF) and the National Institute of Allergy and Infectious Diseases (NIAID) to review the current murine models of M. abscessus infections, discuss current challenges and identify priorities toward establishing validated and globally harmonized preclinical models. This paper summarizes the key points from these workshops. The hope is that the recommendations that emerged from this exercise will facilitate the implementation of informative murine models of therapeutic efficacy testing across laboratories, improve reproducibility from lab-to-lab and accelerate preclinical-to-clinical translation.

An anti-mycobacterial conjugated oligoelectrolyte effective against Mycobacterium abscessus

Infections caused by nontuberculous mycobacteria have increased more than 50% in the past two decades and more than doubled in the elderly population. Mycobacterium abscessus (Mab), one of the most prevalent of these rapidly growing species, is intrinsically resistant to numerous antibiotics. Current standard-of-care treatments are not satisfactory, with high failure rate and notable adverse effects. We report here a potent anti-Mab compound from the flexible molecular framework afforded by conjugated oligoelectrolytes (COEs). A screen of structurally diverse, noncytotoxic COEs identified a lead compound, COE-PNH2, which was bactericidal against replicating, nonreplicating persisters and intracellular Mab.COE-PNH2 had low propensity for resistance development, with a frequency of resistance below 1.25 × 10-9 and showed no detectable resistance upon serial passaging. Mechanism of action studies were in line with COE-PNH2 affecting the physical and functional integrity of the bacterial envelope and disrupting the mycomembrane and associated essential bioenergetic pathways. Moreover, COE-PNH2 was well-tolerated and efficacious in a mouse model of Mab lung infection. This study highlights desirable in vitro and in vivo potency and safety index of this COE structure, which represents a promising anti-mycobacterial to tackle an unmet medical need.

Exploring antibiotic resistance mechanisms in Mycobacterium abscessus for enhanced therapeutic approaches

Mycobacterium abscessus, a leading cause of severe lung infections in immunocompromised individuals, poses significant challenges for current therapeutic strategies due to resistance mechanisms. Therefore, understanding the intrinsic and acquired antibiotic resistance of M. abscessus is crucial for effective treatment. This review highlights the mechanisms employed by M. abscessus to sustain antibiotic resistance, encompassing not only conventional drugs but also newly discovered drug candidates. This comprehensive analysis aims to identify novel entities capable of overcoming the notorious resistance exhibited by M. abscessus, providing insights for the development of more effective therapeutic interventions.

Pharmacological validation of dihydrofolate reductase as a drug target in Mycobacterium abscessus

The Mycobacterium abscessus drug development pipeline is poorly populated, with particularly few validated target-lead couples to initiate de novo drug discovery. Trimethoprim, an inhibitor of dihydrofolate reductase (DHFR) used for the treatment of a range of bacterial infections, is not active against M. abscessus. Thus, evidence that M. abscessus DHFR is vulnerable to pharmacological intervention with a small molecule inhibitor is lacking. Here, we show that the pyrrolo-quinazoline PQD-1, previously identified as a DHFR inhibitor active against Mycobacterium tuberculosis, exerts whole cell activity against M. abscessus. Enzyme inhibition studies showed that PQD-1, in contrast to trimethoprim, is a potent inhibitor of M. abscessus DHFR and over-expression of DHFR causes resistance to PQD-1, providing biochemical and genetic evidence that DHFR is a vulnerable target and mediates PQD-1's growth inhibitory activity in M. abscessus. As observed in M. tuberculosis, PQD-1 resistant mutations mapped to the folate pathway enzyme thymidylate synthase (TYMS) ThyA. Like trimethoprim in other bacteria, PQD-1 synergizes with the dihydropteroate synthase (DHPS) inhibitor sulfamethoxazole (SMX), offering an opportunity to exploit the successful dual inhibition of the folate pathway and develop similarly potent combinations against M. abscessus. PQD-1 is active against subspecies of M. abscessus and a panel of clinical isolates, providing epidemiological validation of the target-lead couple. Leveraging a series of PQD-1 analogs, we have demonstrated a dynamic structure-activity relationship (SAR). Collectively, the results identify M. abscessus DHFR as an attractive target and PQD-1 as a chemical starting point for the discovery of novel drugs and drug combinations that target the folate pathway in M. abscessus.

A novel chemogenomic discovery platform identifies bioactive hits with rapid bactericidal activity against Mycobacteroides Abscessus

Mycobacteroides abscessus (M. ab) infections are innately resistant to most currently available antibiotics and present a growing, poorly addressed medical need. The existing treatment regimens are lengthy and produce inadequate outcomes for many patients. Importantly, most clinically used drugs and drug candidates against M. ab are either bacteriostatic, or only weakly bactericidal. New strategies exploring a broader chemical space are urgently needed, as innovative agents in development are scarce and hit rates in large unbiased screens against the mycobacterium have been discouragingly low. Here we present a computational chemogenomics-driven approach to discovery of novel antibacterials that effectively reveals drug-like compounds active against M. ab, paired with small sets of predicted molecular targets for the compounds. Several of the bioactive hits identified exhibited rapid bactericidal, including sterilizing, activity against the mycobacterium, indicating that there are currently unexploited chemically tractable molecular mechanisms for rapid sterilization of M. ab. Interestingly, starvation, which typically induces drug tolerance, sensitized M. ab to some of the compounds, resulting in potencies similar to those of drugs in clinical use. The presented drug discovery platform has potential to identify highly differentiated prototype anti-infective molecules and thereby contribute to development of regimens for shorter treatment and improved outcomes for non-tuberculous mycobacterial infections.

Activity of Oral Tebipenem-Avibactam in a Mouse Model of Mycobacterium abscessus Lung Infection

The combination of the β-lactam tebipenem and the β-lactamase inhibitor avibactam shows potent bactericidal activity against Mycobacterium abscessus in vitro. Here, we report that the combination of the respective oral prodrugs tebipenem-pivoxil and avibactam ARX-1796 showed efficacy in a mouse model of M. abscessus lung infection. The results suggest that tebipenem-avibactam presents an attractive oral drug candidate pair for the treatment of M. abscessus pulmonary disease and could inform the design of clinical trials.

Effect of Panax quinquefolius extract on Mycobacterium abscessus biofilm formation

Mycobacterium abscessus (M. abscessus) can exist either as planktonic bacteria or as a biofilm. Biofilm formation is one of the important causes of conversion to resistance to antibiotics of bacteria that were previously sensitive when in their planktonic form, resulting in infections difficult to manage. Panax quinquefolius and its active ingredient ginsenosides have the potential ability in fighting pathogenic infections. In this study, the P. quinquefolius extract (PQE) showed good antibacterial/bactericidal activity against the M. abscessus planktonic cells. The extract reduced the biomass, thickness, and number of M. abscessus in the biofilm and altered its morphological characteristics as well as the spatial distribution of dead/alive bacteria. Moreover, the ginsenoside CK monomer had a similar inhibitory effect on M. abscessus planktonic bacteria and biofilm formation. Therefore, PQE and its monomer CK might be potential novel antimicrobial agents for the clinical prevention and treatment of M. abscessus, including biofilms in chronic infections.

Mycobacterium tuberculosis DprE1 Inhibitor OPC-167832 Is Active against Mycobacterium abscessus In Vitro

The antituberculosis candidate OPC-167832, an inhibitor of DprE1, was active against Mycobacterium abscessus. Resistance mapped to M. abscessus dprE1, suggesting target retention. OPC-167832 was bactericidal and did not antagonize activity of clinical anti-M. abscessus antibiotics. Due to its moderate potency compared to that against Mycobacterium tuberculosis, the compound lacked efficacy in a mouse model and is thus not a repurposing candidate. These results identify OPC-167832-DprE1 as a lead-target couple for a M. abscessus-specific optimization program.

Antimicrobial susceptibility and minimum inhibitory concentration distribution of common clinically relevant non-tuberculous mycobacterial isolates from the respiratory tract

Objective: To determine the minimum inhibitory concentration (MIC) distribution of antibacterial drugs and the susceptibility of non-tuberculous mycobacterial (NTM) isolates to provide a reference basis for the clinical selection of an effective starting regimen.Methods: The common clinical isolates of NTM in the respiratory tract, which met the standards of the American Thoracic Society for NTM lung disease, were collected. The MICs of 81 isolates were determined using the microbroth dilution method (Thermo Fisher Scientific, USA), as recommended by the Clinical and Laboratory Standards Institute, USA.Results: Included were 43 Mycobacterium avium complex (MAC) strains, 24 M. abscessus complex (MAB) strains, and 14 M. kansasii strains. The sensitivity rates of MAC to clarithromycin and amikacin were 81.4% and 79.1%, respectively, while the sensitivity rates to linezolid and moxifloxacin were only 20.9% and 9.3%; the MIC of rifabutin was the lowest (MIC50% was just 2 μg/mL). After incubation for 3-5 days, the sensitivity rate of MAB to clarithromycin was 87.5%; this decreased to 50% after 14 days' incubation. Most of them were susceptible to amikacin (91.6%), and most were resistant to moxifloxacin (95.8%), ciprofloxacin (95.8%), imipenem (95.8%), amoxicillin/clavulanate (95.8%), tobramycin (79.1%), doxycycline (95.8%) and trimethoprim/sulfamethoxazole (95.8%). intermediate (83.3%) and resistant (16.7%) to cefoxitin. The susceptibility to linezolid was only 33.3%. The sensitivity and resistance breakpoints of tigecycline were set to ≤0.5 and ≥8 μg/mL, respectively, and the sensitivity and resistance rates were 50% and 0%, respectively. M. kansasii was susceptible to clarithromycin, amikacin, linezolid, moxifloxacin, rifampicin and rifabutin (100%).Discussion: In Wenzhou, clarithromycin, amikacin and rifabutin have good antibacterial activity against MAC, while linezolid and moxifloxacin have high resistance. Amikacin and tigecycline have strong antibacterial activity against MAB, while most other antibacterial drugs are resistant to varying degrees. Most antibacterial drugs are susceptible to M. kansasii and have good antibacterial activity.Conclusion: The identification of NTM species and the detection of their MICs have certain guiding values for the treatment of NTM lung disease.Key MessageThe three most common respiratory non-tuberculous mycobacterial (NTM) isolates with clinical significance in the Wenzhou area were tested for drug susceptibility. The broth microdilution method was used to determine the minimum inhibitory concentration distribution of antibacterial drugs and the susceptibility of NTM isolates to provide a reference basis for the clinical selection of an effective starting regimen.

Why Matter Matters: Fast-Tracking Mycobacterium abscessus Drug Discovery

Unlike Tuberculosis (TB), Mycobacterium abscessus lung disease is a highly drug-resistant bacterial infection with no reliable treatment options. De novo M. abscessus drug discovery is urgently needed but is hampered by the bacterium's extreme drug resistance profile, leaving the current drug pipeline underpopulated. One proposed strategy to accelerate de novo M. abscessus drug discovery is to prioritize screening of advanced TB-active compounds for anti-M. abscessus activity. This approach would take advantage of the greater chance of homologous drug targets between mycobacterial species, increasing hit rates. Furthermore, the screening of compound series with established structure-activity-relationship, pharmacokinetic, and tolerability properties should fast-track the development of in vitro anti-M. abscessus hits into lead compounds with in vivo efficacy. In this review, we evaluated the effectiveness of this strategy by examining the literature. We found several examples where the screening of advanced TB chemical matter resulted in the identification of anti-M. abscessus compounds with in vivo proof-of-concept, effectively populating the M. abscessus drug pipeline with promising new candidates. These reports validate the screening of advanced TB chemical matter as an effective means of fast-tracking M. abscessus drug discovery.

A New Discovery of Unique 13-(Benzimidazolylmethyl)berberines as Promising Broad-Spectrum Antibacterial Agents

A new hybridization of berberine and benzimidazoles was performed to produce 13-(benzimidazolylmethyl)berberines (BMB) as potentially broad-spectrum antibacterial agents with the hope of confronting multidrug-resistant bacterial infections in the livestock industry. Some of the newly prepared hybrids showed obvious antibacterial effects against tested strains. Particularly, 13-((1-octyl-benzimidazolyl)methyl)berberine 6f (OBMB-6f) was found to be the most promising compound that not only exerted a strong activity (MIC = 0.25-2 μg/mL) and low cytotoxicity but also possessed a fast bactericidal capacity and low propensity to develop resistance toward Staphylococcus aureus and Escherichia coli even after 26 serial passages. Moreover, OBMB-6f displayed the ability to prevent bacterial biofilm formation at low and high temperatures. The mechanistic exploration revealed that OBMB-6f could significantly disintegrate bacterial membranes, markedly facilitate intracellular ROS generation, and efficiently intercalate into DNA. These results provided a profound insight into BMB against multidrug-resistant bacterial infections in the livestock industry.

Strongly Bactericidal All-Oral β-Lactam Combinations for the Treatment of Mycobacterium abscessus Lung Disease

Bioactive forms of oral β-lactams were screened in vitro against Mycobacterium abscessus with and without the bioactive form of the oral β-lactamase inhibitor avibactam ARX1796. Sulopenem was equally active without avibactam, while tebipenem, cefuroxime, and amoxicillin required avibactam for optimal activity. Systematic pairwise combination of the four β-lactams revealed strong bactericidal synergy for each of sulopenem, tebipenem, and cefuroxime combined with amoxicillin in the presence of avibactam. These all-oral β-lactam combinations warrant clinical evaluation.

Activity of Tricyclic Pyrrolopyrimidine Gyrase B Inhibitor against Mycobacterium abscessus

Tricyclic pyrrolopyrimidines (TPPs) are a new class of antibacterials inhibiting the ATPase of DNA gyrase. TPP8, a representative of this class, is active against Mycobacterium abscessus in vitro. Spontaneous TPP8 resistance mutations mapped to the ATPase domain of M. abscessus DNA gyrase, and the compound inhibited DNA supercoiling activity of recombinant M. abscessus enzyme. Further profiling of TPP8 in macrophage and mouse infection studies demonstrated proof-of-concept activity against M. abscessus ex vivo and in vivo.

Drug development challenges in nontuberculous mycobacterial lung disease: TB to the rescue

Nontuberculous mycobacterial pulmonary disease (NTM-PD) is treated with multiple repurposed drugs. Chemotherapy is long and often toxic, includes parenteral drugs, and suffers from poor cure rates. There is an urgent need for more efficacious, tolerated, and oral antibiotics optimized towards the treatment of NTM-PD, adapted to the spectrum of disease. In contrast to the empty NTM pipeline, drug development for the related tuberculosis lung disease has experienced a renaissance. Here, we argue that applying lessons learned from tuberculosis will facilitate the discovery of curative oral regimens for NTM-PD.

2-Aminoimidazoles Inhibit Mycobacterium abscessus Biofilms in a Zinc-Dependent Manner

Biofilm growth is thought to be a significant obstacle to the successful treatment of Mycobacterium abscessus infections. A search for agents capable of inhibiting M. abscessus biofilms led to our interest in 2-aminoimidazoles and related scaffolds, which have proven to display antibiofilm properties against a number of Gram-negative and Gram-positive bacteria, including Mycobacterium tuberculosis and Mycobacterium smegmatis. The screening of a library of 30 compounds led to the identification of a compound, AB-2-29, which inhibits the formation of M. abscessus biofilms with an IC₅₀ (the concentration required to inhibit 50% of biofilm formation) in the range of 12.5 to 25 μM. Interestingly, AB-2-29 appears to chelate zinc, and its antibiofilm activity is potentiated by the addition of zinc to the culture medium. Preliminary mechanistic studies indicate that AB-2-29 acts through a distinct mechanism from those reported to date for 2-aminoimidazole compounds.

Potential therapeutic targets from Mycobacterium abscessus (Mab): Recently reported efforts towards the discovery of novel antibacterial agents to treat Mab infections

Mycobacterium abscessus (Mab) are rapidly growing mycobacteria that cause severe and persistent infections in both skin and lung tissues. Treatment regimens involve the extended usage of complex combinations of drugs, often leading to severe adverse side effects, particularly in immunocompromised patients. Current macrolide therapies are gradually proving to be less effective, largely due to emergence of antibiotic resistance; there is therefore an increasing need for the discovery of new antibacterials that are active against Mab. This review highlights recent research centred upon a number of potential therapeutic targets from Mab (Ag85C, ClpC1, GyrB, MmpL3 and TrmD), and discusses the various approaches used to discover small molecule inhibitors, in the search for future antibiotics for the treatment of Mab infections.

Recently reported inhibitors developed against targets from Mycobacterium absecessus (Mab).

Mycobacterium abscessus drug discovery using machine learning

The prevalence of infections by nontuberculous mycobacteria is increasing, having surpassed tuberculosis in the United States and much of the developed world. Nontuberculous mycobacteria occur naturally in the environment and are a significant problem for patients with underlying lung diseases such as bronchiectasis, chronic obstructive pulmonary disease, and cystic fibrosis. Current treatment regimens are lengthy, complicated, toxic and they are often unsuccessful as seen by disease recurrence. Mycobacterium abscessus is one of the most commonly encountered organisms in nontuberculous mycobacteria disease and it is the most difficult to eradicate. There is currently no systematically proven regimen that is effective for treating M. abscessus infections. Our approach to drug discovery integrates machine learning, medicinal chemistry and in vitro testing and has been previously applied to Mycobacterium tuberculosis. We have now identified several novel 1-(phenylsulfonyl)-1H-benzimidazol-2-amines that have weak activity on M. abscessus in vitro but may represent a starting point for future further medicinal chemistry optimization. We also address limitations still to be overcome with the machine learning approach for M. abscessus.

Cyclohexyl-griselimycin is active against Mycobacterium abscessus in mice

Cyclohexyl-griselimycin is a preclinical candidate for use against tuberculosis (TB). Here, we show that this oral cyclodepsipeptide is also active against the intrinsically drug-resistant nontuberculous mycobacterium Mycobacterium abscessusin vitro and in a mouse model of infection. This adds a novel advanced lead compound to the M. abscessus drug pipeline and supports a strategy of screening chemical matter generated in TB drug discovery efforts to fast-track the discovery of novel antibiotics against M. abscessus.

The Antimalarial Mefloquine Shows Activity against Mycobacterium abscessus, Inhibiting Mycolic Acid Metabolism

Some nontuberculous mycobacteria (NTM) are considered opportunistic pathogens. Nevertheless, NTM infections are increasing worldwide, becoming a major public health threat. Furthermore, there is no current specific drugs to treat these infections, and the recommended regimens generally lack efficacy, emphasizing the need for novel antibacterial compounds. In this paper, we focused on the essential mycolic acids transporter MmpL3, which is a well-characterized target of several antimycobacterial agents, to identify new compounds active against Mycobacterium abscessus (Mab). From the crystal structure of MmpL3 in complex with known inhibitors, through an in silico approach, we developed a pharmacophore that was used as a three-dimensional filter to identify new putative MmpL3 ligands within databases of known drugs. Among the prioritized compounds, mefloquine showed appreciable activity against Mab (MIC = 16 μg/mL). The compound was confirmed to interfere with mycolic acids biosynthesis, and proved to also be active against other NTMs, including drug-resistant clinical isolates. Importantly, mefloquine is a well-known antimalarial agent, opening the possibility of repurposing an already approved drug, which is a useful strategy to reduce the time and cost of disclosing novel drug candidates.

Piperidine-4-Carboxamides Target DNA Gyrase in Mycobacterium abscessus

New, more-effective drugs for the treatment of lung disease caused by nontuberculous mycobacteria (NTM) are needed. Among NTM opportunistic pathogens, Mycobacterium abscessus is the most difficult to cure and intrinsically multidrug resistant. In a whole-cell screen of a compound collection active against Mycobacterium tuberculosis, we previously identified the piperidine-4-carboxamide (P4C) MMV688844 (844) as a hit against M. abscessus. Here, we identified a more potent analog of 844 and showed that both the parent and improved analog retain activity against strains representing all three subspecies of the M. abscessus complex. Furthermore, P4Cs showed bactericidal and antibiofilm activity. Spontaneous resistance against the P4Cs emerged at a frequency of 10⁻⁸/CFU and mapped to gyrA and gyrB encoding the subunits of DNA gyrase. Biochemical studies with recombinant M. abscessus DNA gyrase showed that P4Cs inhibit the wild-type enzyme but not the P4C-resistant mutant. P4C-resistant strains showed limited cross-resistance to the fluoroquinolone moxifloxacin, which is in clinical use for the treatment of macrolide-resistant M. abscessus disease, and no cross-resistance to the benzimidazole SPR719, a novel DNA gyrase inhibitor in clinical development for the treatment of mycobacterial diseases. Analyses of P4Cs in recA promoter-based DNA damage reporter strains showed induction of recA promoter activity in the wild type but not in the P4C-resistant mutant background. This indicates that P4Cs, similar to fluoroquinolones, cause DNA gyrase-mediated DNA damage. Together, our results show that P4Cs present a novel class of mycobacterial DNA gyrase inhibitors with attractive antimicrobial activities against the M. abscessus complex.

Activity of Oritavancin and Its Synergy with Other Antibiotics against Mycobacterium abscessus Infection In Vitro and In Vivo

Background: Pulmonary disease caused by Mycobacterium abscessus (M. abscessus) spreads around the world, and this disease is extremely difficult to treat due to intrinsic and acquired resistance of the pathogen to many approved antibiotics. M. abscessus is regarded as one of the most drug-resistant mycobacteria, with very limited therapeutic options. Methods: Whole-cell growth inhibition assays was performed to screen and identify novel inhibitors. The IC₅₀ of the target compounds were tested against THP-1 cells was determined to calculate the selectivity index, and then time–kill kinetics assay was performed against M. abscessus. Subsequently, the synergy of oritavancin with other antibiotics was evaluated by using checkerboard method. Finally, in vivo efficacy was determined in an immunosuppressive murine model simulating M. abscessus infection. Results: We have identified oritavancin as a potential agent against M. abscessus. Oritavancin exhibited time-concentration dependent bactericidal activity against M. abscessus and it also displayed synergy with clarithromycin, tigecycline, cefoxitin, moxifloxacin, and meropenem in vitro. Additionally, oritavancin had bactericidal effect on intracellular M. abscessus. Oritavancin significantly reduced bacterial load in lung when it was used alone or in combination with cefoxitin and meropenem. Conclusions: Our in vitro and in vivo assay results indicated that oritavancin may be a viable treatment option against M. abscessus infection.