Inhibition of the class C β-lactamase from Acinetobacter spp. Insights into effective inhibitor design

Sarah M. Drawz, Maja Babic, Christopher R. Bethel, Magda Taracila, Anne M. Distler, Claudia Ori, Emilia Caselli, Fabio Prati, Robert A. Bonomo

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


The need to develop β-lactamase inhibitors against class C cephalosporinases of Gram-negative pathogens represents an urgent clinical priority. To respond to this challenge, five boronic acid derivatives, including a new cefoperazone analogue, were synthesized and tested against the class C cephalosporinase of Acinetobacter baumannii [Acinetobacter-derived cephalosporinase (ADC)]. The commercially available carbapenem antibiotics were also assayed. In the boronic acid series, a chiral cephalothin analogue with a meta-carboxyphenyl moiety corresponding to the C 3/C 4 carboxylate of β-lactams showed the lowest Ki (11 ± 1 nM). In antimicrobial susceptibility tests, this cephalothin analogue lowered the ceftazidime and cefotaxime minimum inhibitory concentrations (MICs) of Escherichia coli DH10B cells carrying bla ADC from 16 to 4 μg/mL and from 8 to 1 μg/mL, respectively. On the other hand, each carbapenem exhibited a K i of <20 μM, and timed electrospray ionization mass spectrometry (ESI-MS) demonstrated the formation of adducts corresponding to acyl-enzyme intermediates with both intact carbapenem and carbapenem lacking the C 6 hydroxyethyl group. To improve our understanding of the interactions between the β-lactamase and the inhibitors, we constructed models of ADC as an acyl-enzyme intermediate with (i) the meta-carboxyphenyl cephalothin analogue and (ii) the carbapenems, imipenem and meropenem. Our first model suggests that this chiral cephalothin analogue adopts a novel conformation in the β-lactamase active site. Further, the addition of the substituent mimicking the cephalosporin dihydrothiazine ring may significantly improve affinity for the ADCβ-lactamase. In contrast, theADC-carbapenem models offer a novel role for theR 2 side group and also suggest that elimination of the C 6 hydroxyethyl group by retroaldolic reaction leads to a significant conformational change in the acyl-enzyme intermediate. Lessons from the diverse mechanisms and structures of the boronic acid derivatives and carbapenems provide insights for the development of new β-lactamase inhibitors against these critical drug resistance targets.

Original languageEnglish (US)
Pages (from-to)329-340
Number of pages12
Issue number2
StatePublished - Jan 19 2010
Externally publishedYes


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