Targeting Multidrug-Resistant Acinetobacter spp.: Sulbactam and the Diazabicyclooctenone β-Lactamase Inhibitor ETX2514 as a Novel Therapeutic Agent.

Multidrug-resistant (MDR) Acinetobacter spp. poses a significant therapeutic challenge in part due to the presence of chromosomally encoded beta-lactamases, including class C Acinetobacter-derived cephalosporinases (ADC) and class D oxacillinases (OXA), as well as plasmid-mediated class A beta-lactamases. Importantly, OXA-like beta-lactamases represent a gap in the spectrum of inhibition by recently approved beta-lactamase inhibitors such as avibactam and vaborbactam. ETX2514 is a novel, rationally designed, diazabicyclooctenone inhibitor that effectively targets class A, C, and D beta-lactamases. We show that addition of ETX2514 significantly increased the susceptibility of clinical Acinetobacter baumannii isolates to sulbactam. AdeB and AdeJ were identified to be key efflux constituents for ETX2514 in A. baumannii. The combination of sulbactam and ETX2514 was efficacious against A. baumannii carrying bla(TEM-1), bla(ADC-82), bla(OXA-23), and bla(OXA-66) in a neutropenic murine thigh infection model. We also show that, in vitro, ETX2514 inhibited ADC-7 (k(2)/K-i 1.0 +/- 0.1 x 10(6) M-1 s(-1)) and OXA-58 (k(2)/K-i 2.5 +/- 0.3 x 10(5) M-1 s(-1)). Cocrystallization of ETX2514 with OXA-24/40 revealed hydrogen bonding interactions between ETX2514 and residues R261, S219, and S128 of OXA-24/40 in addition to a chloride ion occupied in the active site. Further, the C3 methyl group of ETX2514 shifts the position of M223. In conclusion, the sulbactam-ETX2514 combination possesses a broadened inhibitory range to include class D beta-lactamases as well as class A and C beta-lactamases and is a promising therapeutic candidate for infections caused by MDR Acinetobacter spp. IMPORTANCE The number and diversity of beta-lactamases are steadily increasing. The emergence of beta-lactamases that hydrolyze carbapenems poses a significant threat to our antibiotic armamentarium. The explosion of OXA enzymes that are carbapenem hydrolyzers is a major challenge (carbapenem-hydrolyzing class D [CHD]). An urgent need exists to discover beta-lactamase inhibitors with class D activity. The sulbactam-ETX2514 combination demonstrates the potential to become a treatment regimen of choice for Acinetobacter spp. producing class D beta-lactamases.