Microbiological Characterization of VNRX-5236, a Broad-Spectrum beta-Lactamase Inhibitor for Rescue of the Orally Bioavailable Cephalosporin Ceftibuten as a Carbapenem-Sparing Agent against Strains of Enterobacterales Expressing Extended-Spectrum beta-Lactamases and Serine Carbapenemases

There is an urgent need for oral agents to combat resistant Gram-negative pathogens. Here, we describe the characterization of VNRX-5236, a broad-spectrum boronic acid beta-lactamase inhibitor (BLI), and its orally bioavailable etzadroxil prodrug, VNRX-7145. VNRX-7145 is being developed in combination with ceftibuten, an oral cephalosporin, to combat strains of Enterobacterales expressing extended-spectrum beta-lactamases (ESBLs) and serine carbapenemases. VNRX-5236 is a reversible covalent inhibitor of serine beta-lactamases, with inactivation efficiencies on the order of 10(4) M-1 . sec(-1), and prolonged active site residence times (t(1/2), 5 to 46 min). The spectrum of inhibition includes Ambler class A ESBLs, class C cephalosporinases, and class A and D carbapenemases (KPC and OXA-48, respectively). Rescue of ceftibuten by VNRX-5236 (fixed at 4 mu g/ml) in isogenic strains of Escherichia coli expressing class A, C, or D beta-lactamases demonstrated an expanded spectrum of activity relative to oral comparators, including investigational penems, sulopenem, and tebipenem. VNRX-5236 rescued ceftibuten activity in clinical isolates of Enterobacterales expressing ESBLs (MIC90, 0.25 mu g/ml), KPCs (MIC90, 1 mu g/ml), class C cephalosporinases (MIC90, 1 mu g/ml), and OXA-48-type carbapenemases (MIC90, 1 mu g/ml). Frequency of resistance studies demonstrated a low propensity for recovery of resistant variants at 4x the MIC of the ceftibuten/VNRX-5236 combination. In vivo, whereas ceftibuten alone was ineffective (50% effective dose [ED50], >128 mg/kg), ceftibuten/VNRX-7145 administered orally protected mice from lethal septicemia caused by Klebsiella pneumoniae producing KPC carbapenemase (ED50, 12.9mg/kg). The data demonstrate potent, broad-spectrum rescue of ceftibuten activity by VNRX-5236 in clinical isolates of cephalosporin-resistant and carbapenem-resistant Enterobacterales.