Strategic Design of an Effective β-Lactamase Inhibitor

Oct. 9, 2009

The rapidly increasing number of antibiotic-resistant Gram-negative microorganisms represents a grave threat to human health. The first-line treatments for such infections are β-lactam antibiotics, and the most common mechanism of resistance to such agents is bacterial production of β-lactamases. Regrettably, Enterobacteriaceae resistant to penicillins and extended-spectrum cephalosporins are continuing to threaten the efficacy of our available β-lactam antibiotics. Of greatest concern is the emerging number of community-acquired E. coli< and Klebsiella spp. that are resistant to these cephalosporins. This latter group presents a very significant future danger to the current use of β-lactam antibiotics to treat common infections in the ambulatory setting.

In an effort to devise strategies for overcoming bacterial β-lactamases we studied LN-1-255, a 6-alkylidene-2'-substituted penicillin sulfone inhibitor. By possessing a catecholic functionality that resembles a natural bacterial siderophore, LN-1-255 is unique among β-lactamase inhibitors. LN-1-255 combined with piperacillin was more potent against E. coli DH10B strains bearing blaSHV extended-spectrum and inhibitor-resistant β-lactamases than an equivalent amount of tazobactam and piperacillin. In addition, LN-1-255 significantly enhanced the activity of ceftazidime and cefpirome against extended-spectrum cephalosporin and Sme-1 containing carbapenem-resistant clinical strains. LN-1-255 inhibited SHV-1 and SHV-2 β-lactamases with nM affinity (KI = 110 ± 10 and 100 ± 10 nM respectively). When LN-1-255 inactivated SHV β-lactamases, a single intermediate at +488 Da was detected by mass spectrometry (Figure 1A). The crystal structure of LN-1-255 in complex with SHV-1 was determined at 1.55Å resolution (Figure 1B). Interestingly, this novel inhibitor forms a bicyclic aromatic intermediate with its carbonyl oxygen pointing out of the oxyanion hole and forming hydrogen bonds with Lys-234 and Ser-130 in the active site. The 2'-substituted penicillin sulfone, LN-1-255, is proving to be an important lead compound for novel β-lactamase inhibitor design.

Figure 1.

(A) Deconvoluted mass spectrum of SHV-1 and LN-1-255-inactivating SHV-1. (B) Interactions of LN-1-255 in active site of SHV-1 β-lactamase.

Results from: Pattanaik, P., Bethel, C., Hujer, A., Hujer, K., Distler, A., Taracila, M., Anderson, V., Fritsche, T., Jones, R. Strategic Design of an Effective beta-Lactamase Inhibitor, J. Biol. Chem., 284, 945-953, 2009.