Interactions of the Diazabicyclooctane Serine β-Lactamase Inhibitor ETX1317 with Target Enzymes.

ETX0282 is an orally bioavailable prodrug of the diazabicyclooctane serine β-lactamase inhibitor ETX1317. The combination of ETX0282 with cefpodoxime proxetil is in clinical trials as an oral therapy for complicated urinary tract infections caused by Enterobacterales. Earlier diazabicyclooctane β-lactamase inhibitors, such as avibactam and durlobactam, contain a sulfate moiety as the essential anionic group and are administered intravenously. In contrast, ETX1317 contains a fluoroacetate moiety, which is esterified with an isopropyl group in ETX0282 to provide high oral bioavailability. Previous studies of avibactam and durlobactam showed that covalent inhibition of certain β-lactamases is reversible due to the ability of the ring-opened inhibitors to recyclize and dissociate in their original form. We investigated the interaction of ETX1317 with several β-lactamases commonly found in relevant bacterial pathogens, including CTX-M-15, KPC-2, SHV-5, and TEM-1 from Ambler Class A; Pseudomonas aeruginosa AmpC and Enterobacter cloacae P99 from Class C, and OXA-48 from Class D. The second-order rate constants for inhibition (kinact/Ki) of these enzymes show that ETX1317 is intermediate in potency between durlobactam and avibactam. The partition ratios were all approximately 1, indicating that the inhibitor is not also a substrate of these enzymes. The rate constants for dissociation of the covalent complex (koff) were similar to those for durlobactam and avibactam. Acylation exchange experiments demonstrated that ETX1317 dissociated in its original form. No loss of mass from the inhibitor was observed in the covalent inhibitor-enzyme complexes.