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Publication Abstract from PubMed

beta-Lactamase production is the major beta-lactam resistance mechanism in Gram-negative bacteria. beta-Lactamase inhibitors (BLIs) efficacious against serine beta-lactamase (SBL) producers, especially strains carrying the widely disseminated class A enzymes, are required. Relebactam, a diazabicyclooctane (DBO) BLI is in phase-3 clinical trials in combination with imipenem, for treatment of infections by multi-drug resistant Enterobacteriaceae. We show that relebactam inhibits five clinically-important class A SBLs (despite their differing spectra of activity), representing both chromosomal and plasmid-borne enzymes, i.e. the extended spectrum beta-lactamases L2 (inhibition constant 3 muM) and CTX-M-15 (21 muM); and the carbapenemases, KPC-2, -3 and -4 (1 - 5 muM). Against purified class A SBLs, relebactam is an inferior inhibitor compared to the clinically approved DBO avibactam, (9 to 120-fold differences in IC50). Minimum inhibitory concentration assays indicate relebactam potentiates beta-lactam (imipenem) activity against KPC-producing Klebsiella pneumoniae with similar potency to avibactam (with ceftazidime). Relebactam is less effective than avibactam in combination with aztreonam against Stenotrophomonas maltophilia K279a. X-ray crystal structures of relebactam bound to CTX-M-15, L2, KPC-2, KPC-3 and KPC-4 reveal its C2 linked piperidine ring can sterically clash with Asn104 (CTX-M-15) or His/Trp105 (L2 and KPCs), rationalizing its poorer inhibition activity compared to avibactam, which has a smaller C2 carboxyamide group. Mass spectrometry and crystallographic data show slow, pH-dependent relebactam desulfation by KPC-2, -3 and -4. This comprehensive comparison of relebactam binding across five clinically-important class A SBLs will inform the design of future DBOs with the aim of improving clinical efficacy of BLI:beta-lactam combinations.

Molecular Basis of Class A beta-lactamase Inhibition by Relebactam.,Tooke CL, Hinchliffe P, Lang PA, Mulholland AJ, Brem J, Schofield CJ, Spencer J Antimicrob Agents Chemother. 2019 Aug 5. pii: AAC.00564-19. doi:, 10.1128/AAC.00564-19. PMID:31383664^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.