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

Toward a Bactericidal Oral Drug Combination for the Treatment of Mycobacterium abscessus Lung Disease

Treatment of Mycobacterium abscessus lung disease relies on underperforming drug combinations and includes parenteral, poorly tolerated, and bacteriostatic antibiotics. We posit that safe, oral, and bactericidal regimens are needed to improve cure rates and shorten treatment. Here, we combined oral representatives of three well-tolerated bactericidal drug classes, the β-lactam tebipenem (together with the β-lactamase inhibitor avibactam), the fluoroquinolone moxifloxacin, and the rifamycin rifabutin, and profiled the combination in vitro and in vivo. The combination potentiated bactericidal activity of its components against replicating M. abscessus and retained bactericidal activity against the nonreplicating, drug-tolerant form of the bacterium residing in surrogate caseum. When combined, the drugs retained the ability to induce lethal secondary effects associated with the β-lactam and fluoroquinolone, including cell wall and DNA damage, increased metabolism, and generation of reactive oxygen species. Thus, the triple-drug combination appears to exert two lethal punches while suppressing bacterial reprogramming to counter the drug-induced stresses, providing a plausible rationale for the enhanced kill effect. Addition of a bacteriostatic agent resulted in drug-specific patterns of interactions with regards to bactericidal activity reflected by the lethal secondary effects. The triple-drug combination also exerted a pronounced postantibiotic effect and reduced emergence of spontaneous resistant mutants. Collectively, this work provides a combination prototype for optimization and a profiling workflow that may be useful for the development of sterilizing regimens.

In vitro, intracellular and in vivo synergy between amoxicillin, imipenem and relebactam against Mycobacterium abscessus

OBJECTIVES

Mycobacterium abscessus is the most frequent of the rapidly growing mycobacteria responsible for lung infections in patients suffering from cystic fibrosis and COPD. Imipenem is currently recommended in the treatment of these infections in spite of β-lactamase production. Since the targets of β-lactams include transpeptidases of both the l,d and d,d specificities, we tested, in vitro, intracellularly and in vivo, a combination of two β-lactams active on these enzymes, amoxicillin and imipenem, alone or in combination with the β-lactamase inhibitor relebactam.

METHODS

Drug combinations were evaluated against M. abscessus CIP 104536T and clinical isolates (n = 35) by determining MICs, FIC indices and time-killing. Drug combinations were also evaluated in macrophages and in mice.

RESULTS

In the presence of relebactam, synergy between amoxicillin and imipenem was observed against both M. abscessus CIP 104536T and the clinical isolates. Against M. abscessus CIP 104536T, the addition of 1 mg/L imipenem and 4 mg/L relebactam led to a decrease in the MIC of amoxicillin from 64 to 1 mg/L. The triple combination was active in vitro and intracellularly (a 4.30 decrease in the log10 cfu/mL and 82% killing, respectively). The triple combination was effective in reducing log10 cfu in mouse organs and mouse spleen weights, and in preventing losses in mouse weights.

CONCLUSIONS

The amoxicillin/imipenem/relebactam combination was synergistic in vitro and effective in vivo against M. abscessus. Since these drugs are clinically available, the triple combination should be considered by clinicians and further evaluated based on the reporting of the patient outcomes.

Antibacterials with Novel Chemical Scaffolds in Clinical Development

The rise of antimicrobial resistance represents a significant global health threat, driven by the diminishing efficacy of existing antibiotics, a lack of novel antibacterials entering the market, and an over- or misuse of existing antibiotics, which accelerates the evolution of resistant bacterial strains. This review focuses on innovative therapies by highlighting 19 novel antibacterials in clinical development as of June 2024. These selected compounds are characterized by new chemical scaffolds, novel molecular targets, and/or unique mechanisms of action, which render their potential to break antimicrobial resistance particularly high. A detailed analysis of the scientific foundations behind each of these compounds is provided, including their pharmacodynamic profiles, current development state, and potential for overcoming existing limitations in antibiotic therapy. By presenting this subset of chemically novel antibacterials, the review highlights the ability to innovate in antibiotic drug development to counteract bacterial resistance and improve treatment outcomes.

SQ31f is a potent non-tuberculous mycobacteria antibiotic by specifically targeting the mycobacterial F-ATP synthase

BACKGROUND

Non-tuberculous mycobacteria (NTM) infection presents a growing global health problem and requires new antibiotics targeting enzymes that are essential for the pathogens under various metabolic conditions, with high target specificity, good solubility and with attractive combinatory potency.

METHODS

SQ31f was synthesized by a simplified synthesis protocol, and its effect on growth inhibition of fast- and slow-growing NTM and clinical isolates, whole-cell ATP depletion, ex vivo macrophages and its potency in combination with other antibiotics were evaluated. Molecular docking studies were employed to assess SQ31f's binding mode.

RESULTS

We present- squaramide SQ31f as a novel anti-NTM inhibitor targeting the NTM F1FO-ATP synthase, essential for ATP formation, regulation of ATP homeostasis and proton motive force under multiple growth conditions. The potency of SQ31f in growth inhibition of fast- and slow-growing NTM and clinical isolates correlates with whole-cell ATP depletion, which is not caused by altered oxygen consumption. SQ31f's high aqueous solubility enables binding to the waterfilled cytosolic proton half channel in the subunits a-c interface of the FO domain. As presented for the fast-growing Mycobacterium abscessus, the compound is active against intracellular-residing M. abscessus. Importantly, SQ31f shows an additive effect of the anti-M. abscessus drugs clofazimine, rifabutin or amikacin, and an attractive potentiation of linezolid, clarithromycin, or the oral pair tebipenem and avibactam.

CONCLUSIONS

SQ31f represents an attractive inhibitor to tackle the issues associated with NTM drug tolerance and toxicity. Its combinatory potency with anti-M. abscessus drugs holds potential for overcoming resistance, while also reducing intensive compound synthesis and associated costs.

In vitro effects of the new oral β-lactamase inhibitor xeruborbactam in combination with oral β-lactams against clinical Mycobacterium abscessus isolates

Non-tuberculosis mycobacteria (NTM), particularly Mycobacterium abscessus subsp. abscessus (M. abscessus), are increasingly being recognized as etiological agents of NTM pulmonary disease. However, treatment options for M. abscessus are limited owing to their natural resistance to most antibiotics, including β-lactams. M. abscessus produces a class A β-lactamase, whose activity is inhibited by cyclic boronic acid β-lactamase inhibitors. We aimed to evaluate the in vitro effects of xeruborbactam, a cyclic boronic acid β-lactamase inhibitor, against M. abscessus when combined with five β-lactams (amoxicillin, tebipenem, cefdinir, cefuroxime, and cefoxitin). The drug susceptibilities of 43 M. abscessus clinical isolates obtained from 43 patients between August 2005 and May 2014 were tested. The MIC results for each β-lactam with or without 4 µg/mL xeruborbactam were examined. Xeruborbactam lowered the MIC90 values of tebipenem, amoxicillin, cefuroxime, and cefdinir by 5, ≥4, 3, and 3 dilutions, respectively. The MIC90 values of cefoxitin without xeruborbactam were 32 µg/mL and did not change upon the addition of xeruborbactam. The lowest MIC90 value was obtained for tebipenem with xeruborbactam. Almost all isolates had an MIC of 4 µg/mL; one isolate had an MIC of 2 µg/mL. With respect to the susceptibility to the same family drug, the number of susceptible isolates increased from 1/43 (2%) to 43/43 (100%) for tebipenem with xeruborbactam. Combining tebipenem and xeruborbactam could be considered an effective all-oral regimen that benefits outpatient treatment of M. abscessus pulmonary disease.

IMPORTANCE

Mycobacterium abscessus subsp. abscessus (M. abscessus) disease is treated in two phases; injectable drugs for initial followed by others for continuation. There is a need to develop all-oral treatment methods for M. abscessus infection, especially in the continuation phase. However, treatment options for M. abscessus are limited owing to their natural resistance to most antibiotics. This is the first report to evaluate the in vitro effects of xeruborbactam, a cyclic boronic acid β-lactamase inhibitor capable of inhibiting the class A β-lactamase produced by M. abscessus, against 43 M. abscessus clinical isolates when combined with five β-lactam antibiotics. Xeruborbactam lowered the MIC90 values of tebipenem by five dilutions, and the number of susceptible isolates increased from 1/43 (2%) to 43/43 (100%). We showed that the tebipenem-xeruborbactam combination might be of interest to explore further as a potentially effective oral regimen for outpatient treatment of M. abscessus pulmonary 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.

Dual β-lactam therapy to improve treatment outcome in Mycobacterium abscessus disease

BACKGROUND

Antibiotic treatment of Mycobacterium abscessus disease is toxic and poorly effective and lacks a firm evidence base. Dual β-lactam and β-lactam/β-lactamase inhibitor combinations may be interesting leads to improve treatment outcomes.

OBJECTIVES

To summarize the current preclinical studies on dual β-lactam and β-lactam/β-lactamase inhibitor combinations against M. abscessus.

SOURCES

We performed a literature search using the National Center for Biotechnology Information's PubMed interface with additional snowball sampling.

CONTENT

Select combinations of β-lactam antibiotics, as well as β-lactam/β-lactamase inhibitor combinations show promising in vitro activity and synergy against M. abscessus. β-Lactam antibiotics differ in their ability to reach and interfere with their targets and their resistance to the M. abscessus β-lactamase. The synergy is typically observed for combinations of β-lactam antibiotics or a β-lactam antibiotic with a β-lactamase inhibitor. No additional killing capacity was demonstrated in three-drug combinations of synergistic β-lactam antibiotics and a β-lactamase inhibitor. The efficacy of select dual β-lactam antibiotics and β-lactam/β-lactamase inhibitor combinations is retained in intracellular infection assays and mouse models, but no combination has a complete preclinical portfolio.

IMPLICATIONS

Future clinical strategies should entail either dual β-lactam or β-lactam/β-lactamase inhibitor combinations. Imipenem-ceftaroline and an all-oral tebipenem-avibactam combination are promising leads but still require a complete preclinical portfolio, target product profiles as well as clinical trial confirmation.

Tackling Nontuberculous Mycobacteria by Repurposable Drugs and Potential Leads from Natural Products

Nontuberculous Mycobacteria (NTM) refer to bacteria other than all Mycobacterium species that do not cause tuberculosis or leprosy, excluding the species of the Mycobacterium tuberculosis complex, M. leprae and M. lepromatosis. NTM are ubiquitous and present in soils and natural waters. NTM can survive in a wide range of environmental conditions. The direct inoculum of the NTM from water or other materials is most likely a source of infections. NTMs are responsible for several illnesses, including pulmonary alveolar proteinosis, cystic fibrosis, bronchiectasis, chronic obstructive pneumoconiosis, and pulmonary disease. Recent reports suggest that NTM species have become insensitive to sterilizing agents, antiseptics, and disinfectants. The efficacy of existing anti-NTM regimens is diminishing and has been compromised due to drug resistance. New and recurring cases of multidrug-resistant NTM strains are increasing. Thus, there is an urgent need for ant-NTM regimens with novel modes of action. This review sheds light on the mode of antimicrobial resistance in the NTM species. Then, we discussed the repurposable drugs (antibiotics) that have shown new indications (activity against NTM strains) that could be developed for treating NTM infections. Also, we have summarised recently identified natural leads acting against NTM, which have the potential for treating NTM-associated infections.

The in vitro effect of new combinations of carbapenem-β-lactamase inhibitors for Mycobacterium abscessus

As new treatment alternatives for Mycobacterium abscessus complex (MABC) are urgently needed, we determined the minimum inhibitory concentrations (MICs) for novel carbapenem combinations, including imipenem-relebactam and tebipenem-avibactam against 98 MABC isolates by broth microdilution. The MIC50 was reduced from 16 to 8 mg/L by adding relebactam to imipenem, while the addition of avibactam to tebipenem showed a more pronounced reduction from 256 to 16 mg/L, representing a promising non-toxic, oral treatment option for further exploration.