Based on its clinical benefits, Trikafta — the combination of folding correctors VX-661 (tezacaftor), VX-445 (elexacaftor), and the gating potentiator VX-770 (ivacaftor) — was FDA approved for treatment of patients with cystic fibrosis (CF) carrying deletion of phenylalanine at position 508 (F508del) of the CF transmembrane conductance regulator ( CFTR ) on at least 1 allele. Neither the mechanism of action of VX-445 nor the susceptibility of rare CF folding mutants to Trikafta are known. Here, we show that, in human bronchial epithelial cells, VX-445 synergistically restores F508del-CFTR processing in combination with type I or II correctors that target the nucleotide binding domain 1 (NBD1) membrane spanning domains (MSDs) interface and NBD2, respectively, consistent with a type III corrector mechanism. This inference was supported by the VX-445 binding to and unfolding suppression of the isolated F508del-NBD1 of CFTR. The VX-661 plus VX-445 treatment restored F508del-CFTR chloride channel function in the presence of VX-770 to approximately 62% of WT CFTR in homozygous nasal epithelia. Substantial rescue of rare misprocessing mutations (S13F, R31C, G85E, E92K, V520F, M1101K, and N1303K), confined to MSD1, MSD2, NBD1, and NBD2 of CFTR, was also observed in airway epithelia, suggesting an allosteric correction mechanism and the possible application of Trikafta for patients with rare misfolding mutants of CFTR.

A post-antibiotic world is fast becoming a reality, given the rapid emergence of pathogens that are resistant to current drugs. Therefore, there is an urgent need to discover new classes of potent antimicrobial agents with novel modes of action. Cannabis sativa is an herbaceous plant that has been used for millennia for medicinal and recreational purposes. Its bioactivity is largely due to a class of compounds known as cannabinoids. Recently, these natural products and their analogs have been screened for their antimicrobial properties, in the quest to discover new anti-infective agents. This paper seeks to review the research to date on cannabinoids in this context, including an analysis of structure–activity relationships. It is hoped that it will stimulate further interest in this important issue.

Antibiotics have served humankind through their use in modern medicine as effective treatments for otherwise fatal bacterial infections. Teixobactin is a first member of newly discovered natural antibiotics that was recently identified from a hitherto-unculturable soil bacterium, Eleftheria terrae, and recognized as a potent antibacterial agent against various Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci. The most distinctive characteristic of teixobactin as an effective antibiotic is that teixobactin resistance could not be evolved in a laboratory setting. It is purported that teixobactin’s “resistance-resistant” mechanism of action includes binding to the essential bacterial cell wall synthesis building blocks lipid II and lipid III. In the present study, metabolomics was used to investigate the potential metabolic pathways involved in the mechanisms of antibacterial activity of the synthetic teixobactin analogue Leu₁₀-teixobactin against a MRSA strain, S. aureus ATCC 700699. The metabolomes of S. aureus ATCC 700699 cells 1, 3, and 6 h following treatment with Leu₁₀-teixobactin (0.5 μg/ml, i.e., 0.5× MIC) were compared to those of the untreated controls. Leu₁₀-teixobactin significantly perturbed bacterial membrane lipids (glycerophospholipids and fatty acids), peptidoglycan (lipid I and II) metabolism, and cell wall teichoic acid (lipid III) biosynthesis as early as after 1 h of treatment, reflecting an initial activity on the cell envelope. Concordant with its time-dependent antibacterial killing action, Leu₁₀-teixobactin caused more perturbations in the levels of key intermediates in pathways of amino-sugar and nucleotide-sugar metabolism and their downstream peptidoglycan and teichoic acid biosynthesis at 3 and 6 h. Significant perturbations in arginine metabolism and the interrelated tricarboxylic acid cycle, histidine metabolism, pantothenate, and coenzyme A biosynthesis were also observed at 3 and 6 h. To conclude, this is the first study to provide novel metabolomics mechanistic information, which lends support to the development of teixobactin as an antibacterial drug for the treatment of multidrug-resistant Gram-positive infections. IMPORTANCE Antimicrobial resistance is one of the greatest threats to the global health system. It is imperative that new anti-infective therapeutics be developed against problematic “superbugs.” The cyclic depsipeptide teixobactin holds much promise as a new class of antibiotics for highly resistant Gram-positive pathogens (e.g., methicillin-resistant Staphylococcus aureus [MRSA]). Understanding its molecular mechanism(s) of action could lead to the design of new compounds with a broader activity spectrum. Here, we describe the first metabolomics study to investigate the killing mechanism(s) of teixobactin against MRSA. Our findings revealed that teixobactin significantly disorganized the bacterial cell envelope, as reflected by a profound perturbation in the bacterial membrane lipids and cell wall biosynthesis (peptidoglycan and teichoic acid). Importantly, teixobactin significantly suppressed the main intermediate d-alanyl-d-lactate involved in the mechanism of vancomycin resistance in S. aureus. These novel results help explain the unique mechanism of action of teixobactin and its lack of cross-resistance with vancomycin.

Novel therapeutic approaches are urgently needed to combat nosocomial infections caused by extremely drug-resistant (XDR) “superbugs.” This study aimed to investigate the synergistic antibacterial activity of polymyxin B in combination with selective estrogen receptor modulators (SERMs) against problematic Gram-negative pathogens. In vitro synergistic antibacterial activity of polymyxin B and the SERMs tamoxifen, raloxifene, and toremifene was assessed using the microdilution checkerboard and static time–kill assays against a panel of Gram-negative isolates. Polymyxin B and the SERMs were ineffective when used as monotherapy against polymyxin-resistant minimum inhibitory concentration ([MIC] ≥8 mg/L) Pseudomonas aeruginosa, Klebsiella pneumoniae , and Acinetobacter baumannii . However, when used in combination, clinically relevant concentrations of polymyxin B and SERMs displayed synergistic killing against the polymyxin-resistant P. aeruginosa, K. pneumoniae , and A. baumannii isolates as demonstrated by a ≥2–3 log10 decrease in bacterial count (CFU/ml) after 24 hours. The combination of polymyxin B with toremifene demonstrated very potent antibacterial activity against P. aeruginosa biofilms in an artificial sputum media assay. Moreover, polymyxin B combined with toremifene synergistically induced cytosolic green fluorescence protein release, cytoplasmic membrane depolarization, permeabilizing activity in a nitrocefin assay, and an increase of cellular reactive oxygen species from P. aeruginosa cells. In addition, scanning and transmission electron micrographs showed that polymyxin B in combination with toremifene causes distinctive damage to the outer membrane of P. aeruginosa cells, compared with treatments with each compound per se . In conclusion, the combination of polymyxin B and SERMs illustrated a synergistic activity against XDR Gram-negative pathogens, including highly polymyxin-resistant P. aeruginosa isolates, and represents a novel combination therapy strategy for the treatment of infections because of problematic XDR Gram-negative pathogens.

In the present study, we employed untargeted metabolomics to investigate the synergistic killing mechanism of polymyxin B in combination with an aminoglycoside, amikacin, against a polymyxin-susceptible isolate of Pseudomonas aeruginosa , FADDI-PA111 (MIC = 2 mg/liter for both polymyxin B and amikacin), and a polymyxin-resistant Liverpool epidemic strain (LES), LESB58 (the corresponding MIC for both polymyxin B and amikacin is 16 mg/liter).

Multidrug-resistant (MDR) Gram-negative pathogens remain an unmet public health threat. In recent times, increased rates of resistance have been reported not only to commonly used antibiotics, but also to the last-resort antibiotics, such as polymyxins. More worryingly, despite the current trends in resistance, there is a lack of new antibiotics in the drug-discovery pipeline. Hence, it is imperative that new strategies are developed to preserve the clinical efficacy of the current antibiotics, particularly the last-line agents. Combining conventional antibiotics such as polymyxins with non-antibiotics (or adjuvants), has emerged as a novel and effective strategy against otherwise untreatable MDR pathogens. This review explores the available literature detailing the latest polymyxin/non-antibiotic combinations, their mechanisms of action, and potential avenues to advance their clinical application.