id7b00153_si_001.pdf (432.71 kB)
Inhibition of Acinetobacter-Derived Cephalosporinase: Exploring the Carboxylate Recognition Site Using Novel β‑Lactamase Inhibitors
journal contribution
posted on 2017-11-16, 00:00 authored by Emilia Caselli, Chiara Romagnoli, Rachel A. Powers, Magdalena A. Taracila, Alexandra A. Bouza, Hollister C. Swanson, Kali A. Smolen, Francesco Fini, Bradley J. Wallar, Robert A. Bonomo, Fabio PratiBoronic
acids are attracting a lot of attention as β-lactamase inhibitors,
and in particular, compound S02030 (Ki = 44 nM) proved to be a good lead compound against ADC-7
(Acinetobacter-derived cephalosporinase), one of
the most significant resistance determinants in A. baumannii. The atomic structure of the ADC-7/S02030 complex highlighted
the importance of critical structural determinants for recognition
of the boronic acids. Herein, to elucidate the role in recognition
of the R2-carboxylate, which mimics the C3/C4 found in β-lactams, we designed, synthesized, and characterized
six derivatives of S02030 (3a). Out of the
six compounds, the best inhibitors proved to be those with an explicit
negative charge (compounds 3a–c, 3h, and 3j, Ki =
44–115 nM), which is in contrast to the derivatives where the
negative charge is omitted, such as the amide derivative 3d (Ki = 224 nM) and the hydroxyamide derivative 3e (Ki = 155 nM). To develop a
structural characterization of inhibitor binding in the active site,
the X-ray crystal structures of ADC-7 in a complex with compounds 3c, SM23, and EC04 were determined.
All three compounds share the same structural features as in S02030 but only differ in the carboxy-R2 side chain, thereby
providing the opportunity of exploring the distinct binding mode of
the negatively charged R2 side chain. This cephalosporinase demonstrates
a high degree of versatility in recognition, employing different residues
to directly interact with the carboxylate, thus suggesting the existence
of a “carboxylate binding region” rather than a binding
site in ADC enzymes. Furthermore, this class of compounds was tested
against resistant clinical strains of A. baumannii and are effective at inhibiting bacterial growth in conjunction
with a β-lactam antibiotic.