6‑Halopyridylmethylidene Penicillin-Based Sulfones Efficiently Inactivate the Natural Resistance of Pseudomonas aeruginosa to β‑Lactam Antibiotics

Pseudomonas aeruginosa, a major
cause of nosocomial infections, is considered a paradigm of antimicrobial
resistance, largely due to hyperproduction of chromosomal cephalosporinase
AmpC. Here, we explore the ability of 6-pyridylmethylidene penicillin-based
sulfones 1–3 to inactivate the AmpC β-lactamase
and thus rescue the activity of the antipseudomonal ceftazidime. These
compounds increased the susceptibility to ceftazidime in a collection
of clinical isolates and PAO1 mutant strains with different ampC expression levels and also improved the inhibition
kinetics relative to avibactam, displaying a slow deacylation rate
and involving the formation of an indolizine adduct. Bromide 2 was the inhibitor with the lowest KI (15.6 nM) and the highest inhibitory efficiency (kinact/KI). Computational
studies using diverse AmpC enzymes revealed that the aromatic moiety
in 1–3 targets a tunnel-like site adjacent to
the catalytic serine and induces the folding of the H10 helix, indicating
the potential value of this not-always-evident pocket in drug design.