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

Abstract

Multidrug-resistant (MDR) <i>Acinetobacter</i> spp. poses a significant therapeutic challenge in part due to the presence of chromosomally encoded β-lactamases, including class C <i>Acinetobacter</i>-derived cephalosporinases (ADC) and class D oxacillinases (OXA), as well as plasmid-mediated class A β-lactamases. Importantly, OXA-like β-lactamases represent a gap in the spectrum of inhibition by recently approved β-lactamase inhibitors such as avibactam and vaborbactam. ETX2514 is a novel, rationally designed, diazabicyclooctenone inhibitor that effectively targets class A, C, and D β-lactamases. We show that addition of ETX2514 significantly increased the susceptibility of clinical <i>Acinetobacter</i><i>baumannii</i> isolates to sulbactam. AdeB and AdeJ were identified to be key efflux constituents for ETX2514 in <i>A. baumannii</i> The combination of sulbactam and ETX2514 was efficacious against <i>A. baumannii</i> carrying <i>bla</i>_TEM-1, <i>bla</i>_ADC-82, <i>bla</i>_OXA-23, and <i>bla</i>_OXA-66 in a neutropenic murine thigh infection model. We also show that, <i>in vitro</i>, ETX2514 inhibited ADC-7 (<i>k</i>₂/<i>K_i</i> 1.0 ± 0.1 × 10⁶ M^-1 s^-1) and OXA-58 (<i>k</i>₂/<i>K_i</i> 2.5 ± 0.3 × 10⁵ 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 β-lactamases as well as class A and C β-lactamases and is a promising therapeutic candidate for infections caused by MDR <i>Acinetobacter</i> spp.<b>IMPORTANCE</b> The number and diversity of β-lactamases are steadily increasing. The emergence of β-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 β-lactamase inhibitors with class D activity. The sulbactam-ETX2514 combination demonstrates the potential to become a treatment regimen of choice for <i>Acinetobacter</i> spp. producing class D β-lactamases.