In Vivo Efficacy of Novel Monobactam LYS228 in Murine Models of Carbapenemase-Producing Klebsiella pneumoniae Infection

LYS228 has potent antibacterial activity against carbapenem-resistant strains of Enterobacteriaceae LYS228 was efficacious in neutropenic thigh models established with Klebsiella pneumoniae producing KPC-2 or NDM-1; pretreatment with uranyl nitrate considerably shifted calculated static doses of LYS228. In murine ascending pyelonephritis, LYS228 reduced bacterial burden in kidney, urine, and bladder. The successful treatment of murine infection models established with carbapenem-resistant K. pneumoniae further supports the clinical development of LYS228.

Impact of Inducible blaDHA-1 on Susceptibility of Klebsiella pneumoniae Clinical Isolates to LYS228 and Identification of Chromosomal mpl and ampD Mutations Mediating Upregulation of Plasmid-Borne blaDHA-1 Expression

Twenty-three Klebsiella pneumoniae (blaDHA-1) clinical isolates exhibited a range of susceptibilities to LYS228, with MICs of ≥8 μg/ml for 9 of these. Mutants with decreased susceptibility to LYS228 and upregulated expression of blaDHA-1 were selected from representative isolates. These had mutations in the chromosomal peptidoglycan recycling gene mpl or ampD Preexisting mpl mutations were also found in some of the clinical isolates examined, and these had strongly upregulated expression of blaDHA-1.

Mode of Action of the Monobactam LYS228 and Mechanisms Decreasing In Vitro Susceptibility in Escherichia coli and Klebsiella pneumoniae

The monobactam scaffold is attractive for the development of new agents to treat infections caused by drug-resistant Gram-negative bacteria because it is stable to metallo-β-lactamases (MBLs). However, the clinically used monobactam aztreonam lacks stability to serine β-lactamases (SBLs) that are often coexpressed with MBLs. LYS228 is stable to MBLs and most SBLs. LYS228 bound purified Escherichia coli penicillin binding protein 3 (PBP3) similarly to aztreonam (derived acylation rate/equilibrium dissociation constant [k2/Kd ] of 367,504 s-1 M-1 and 409,229 s-1 M-1, respectively) according to stopped-flow fluorimetry. A gel-based assay showed that LYS228 bound mainly to E. coli PBP3, with weaker binding to PBP1a and PBP1b. Exposing E. coli cells to LYS228 caused filamentation consistent with impaired cell division. No single-step mutants were selected from 12 Enterobacteriaceae strains expressing different classes of β-lactamases at 8× the MIC of LYS228 (frequency, <2.5 × 10-9). At 4× the MIC, mutants were selected from 2 of 12 strains at frequencies of 1.8 × 10-7 and 4.2 × 10-9 LYS228 MICs were ≤2 μg/ml against all mutants. These frequencies compared favorably to those for meropenem and tigecycline. Mutations decreasing LYS228 susceptibility occurred in ramR and cpxA (Klebsiella pneumoniae) and baeS (E. coli and K. pneumoniae). Susceptibility of E. coli ATCC 25922 to LYS228 decreased 256-fold (MIC, 0.125 to 32 μg/ml) after 20 serial passages. Mutants accumulated mutations in ftsI (encoding the target, PBP3), baeR, acrD, envZ, sucB, and rfaI These results support the continued development of LYS228, which is currently undergoing phase II clinical trials for complicated intraabdominal infection and complicated urinary tract infection (registered at ClinicalTrials.gov under identifiers NCT03377426 and NCT03354754).

In Vitro Activity of LYS228, a Novel Monobactam Antibiotic, against Multidrug-Resistant Enterobacteriaceae

LYS228 is a novel monobactam with potent activity against Enterobacteriaceae LYS228 is stable to metallo-β-lactamases (MBLs) and serine carbapenemases, including Klebsiella pneumoniae carbapenemases (KPCs), resulting in potency against the majority of extended-spectrum β-lactamase (ESBL)-producing and carbapenem-resistant Enterobacteriaceae strains tested. Overall, LYS228 demonstrated potent activity against 271 Enterobacteriaceae strains, including multidrug-resistant isolates. Based on MIC₉₀ values, LYS228 (MIC₉₀, 1 μg/ml) was ≥32-fold more active against those strains than were aztreonam, ceftazidime, ceftazidime-avibactam, cefepime, and meropenem. The tigecycline MIC₉₀ was 4 μg/ml against the strains tested. Against Enterobacteriaceae isolates expressing ESBLs (n = 37) or displaying carbapenem resistance (n = 77), LYS228 had MIC₉₀ values of 1 and 4 μg/ml, respectively. LYS228 exhibited potent bactericidal activity, as indicated by low minimal bactericidal concentration (MBC) to MIC ratios (MBC/MIC ratios of ≤4) against 97.4% of the Enterobacteriaceae strains tested (264/271 strains). In time-kill studies, LYS228 consistently achieved reductions in CFU per milliliter of 3 log₁₀ units (≥99.9% killing) at concentrations ≥4× MIC for Escherichia coli and K. pneumoniae reference strains, as well as isolates encoding TEM-1, SHV-1, CTX-M-14, CTX-M-15, KPC-2, KPC-3, and NDM-1 β-lactamases.