Therapeutic Effect and Mechanisms of the Novel Monosulfactam 0073.

This study aimed to evaluate the antimicrobial activity of the novel monosulfactam 0073 against multidrug-resistant Gram-negative bacteria in vitro and in vivo and to characterize the mechanisms underlying 0073 activity. The in vitro activities of 0073, aztreonam, and the combination with avibactam were assessed by MIC and time-kill assays. The safety of 0073 was evaluated using 3-(4,5-dimethylthizol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and acute toxicity assays. Murine thigh infection and pneumonia models were employed to define in vivo efficacy. A penicillin-binding protein (PBP) competition assay and confocal microscopy were conducted. The inhibitory action of 0073 against ß-lactamases was evaluated by the half-maximal inhibitory concentration (IC50), and resistance development was evaluated via serial passage. The monosulfactam 0073 showed promising antimicrobial activity against Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii isolates producing metallo-ß-lactamases (MBLs) and serine ß-lactamases. In preliminary experiments, compound 0073 exhibited safety both in vitro and in vivo In the murine thigh infection model and the pneumonia models in which infection was induced by P. aeruginosa and Klebsiella pneumoniae, 0073 significantly reduced the bacterial burden. Compound 0073 targeted several PBPs and exerted inhibitory effects against some serine ß-lactamases. Finally, 0073 showed a reduced propensity for resistance selection compared with that of aztreonam. The novel monosulfactam 0073 exhibited increased activity against ß-lactamase-producing Gram-negative organisms compared with the activity of aztreonam and showed good safety profiles both in vitro and in vivo The underlying mechanisms may be attributed to the affinity of 0073 for several PBPs and its inhibitory activity against some serine ß-lactamases. These data indicate that 0073 represents a potential treatment for infections caused by ß-lactamase-producing multidrug-resistant bacteria.

A kinetic analysis of the inhibition of FOX-4 ß-lactamase, a plasmid-mediated AmpC cephalosporinase, by monocyclic ß-lactams and carbapenems.

OBJECTIVES: Class C ß-lactamases are prevalent among Enterobacteriaceae; however, these enzymes are resistant to inactivation by commercially available ß-lactamase inhibitors. In order to find novel scaffolds to inhibit class C ß-lactamases, the comparative efficacy of monocyclic ß-lactam antibiotics (aztreonam and the siderophore monosulfactam BAL30072), the bridged monobactam ß-lactamase inhibitor BAL29880, and carbapenems (imipenem, meropenem, doripenem and ertapenem) were tested in kinetic assays against FOX-4, a plasmid-mediated class C ß-lactamase (pmAmpC). METHODS: The FOX-4 ß-lactamase was purified. Steady-state kinetics, electrospray ionization mass spectrometry (ESI-MS) and ultraviolet difference (UVD) spectroscopy were conducted using the ß-lactam scaffolds described. RESULTS: The K(i) values for the monocyclic ß-lactams against FOX-4 ß-lactamase were 0.04 ± 0.01 µM (aztreonam) and 0.66 ± 0.03 µM (BAL30072), and the Ki value for the bridged monobactam BAL29880 was 8.9 ± 0.5 µM. For carbapenems, the Ki values ranged from 0.27 ± 0.05 µM (ertapenem) to 2.3 ± 0.3 µM (imipenem). ESI-MS demonstrated the formation of stable covalent adducts when the monocyclic ß-lactams and carbapenems were reacted with FOX-4 ß-lactamase. UVD spectroscopy suggested the appearance of different chromophoric intermediates. CONCLUSIONS: Monocyclic ß-lactam and carbapenem antibiotics are effective mechanism-based inhibitors of FOX-4 ß-lactamase, a clinically important pmAmpC, and provide stimulus for the development of new inhibitors to inactivate plasmidic and chromosomal class C ß-lactamases.

Activity of BAL30072 alone or combined with ß-lactamase inhibitors or with meropenem against carbapenem-resistant Enterobacteriaceae and non-fermenters.

OBJECTIVES: We investigated the activity of BAL30072, a dihydroxypyridone monosulfactam, against carbapenem-resistant Enterobacteriaceae and non-fermenters (i) alone, (ii) combined with BAL29880 (to inhibit AmpC) and/or clavulanate [to inhibit extended-spectrum ß-lactamases (ESBLs)] and (iii) combined 1:1 with meropenem. METHODS: Isolates were from multiple UK hospitals. MICs were determined by CLSI agar dilution. Carbapenemases were identified by PCR and sequencing. RESULTS: BAL30072 inhibited 69% of the carbapenem-resistant Enterobacteriaceae at ≤4 mg/L, including 60%-87% with OXA-48, IMP, NDM and VIM enzymes or combinations of impermeability with AmpC or ESBL, and 40% with KPC enzymes. The proportions susceptible exceeded 90% for BAL30072+BAL29880+clavulanate, except for isolates with KPC carbapenemases, where members of the international sequence type (ST) 258 Klebsiella pneumoniae clone remained resistant. At 4 mg/L, BAL30072 was active against all OprD-deficient Pseudomonas aeruginosa, against 8/12 with efflux-type ß-lactam resistance and 19/25 with metallo-carbapenemases; these proportions were little increased if inhibitors were added. Most Acinetobacter baumannii with OXA or NDM carbapenemases were susceptible to BAL30072 alone at ≤4 mg/L, but those with OXA-58 were resistant, probably for reasons other than their ß-lactamase. Addition of meropenem to BAL30072 increased activity against some individual isolates, but with little clear relationship to the resistance mechanism, except for consistent potentiation against OprD-deficient P. aeruginosa. CONCLUSIONS: BAL30072 had good activity against many diverse carbapenem resistance types. Adding clavulanate and/or BAL29880 extended activity against carbapenem-resistant Enterobacteriaceae, but not non-fermenters. Adding meropenem resulted in small increases in activity against individual isolates. Resistance remained common in the K. pneumoniae ST258 KPC clone, even with both inhibitors or meropenem added.