Structure-Based Optimization of a Non-β-lactam Lead Results in Inhibitors That Do Not Up-Regulate β-Lactamase Expression in Cell Culture

Bacterial expression of β-lactamases is the most widespread resistance mechanism to β -lactam antibiotics. There is a pressing need for novel, non-β-lactam inhibitors of these enzymes. Our lead, compound 1, is chemically dissimilar to β -lactams and is a noncovalent, competitive inhibitor of the enzyme. However, at 26 μM its activity is modest (Figure 1). Using the X-ray structure of the AmpC/1 complex as a template, 14 analogues were designed and synthesized. Among these, compound 10, had a Ki of 1 μM, 26-fold better than the lead. The structures of AmpC in complex with compound 10 and an analogue, compound 11, were determined by X-ray crystallography to 1.97 and 1.96 Å, respectively. Compound 10 was active in cell culture, reversing resistance to the third generation cephalosporin ceftazidime in bacterial pathogens expressing AmpC. In contrast to β-lactam-based inhibitors compound 10 did not up-regulate β-lactamase expression in cell culture but simply inhibited the enzyme expressed by the resistant bacteria. Its escape from this resistance mechanism derives from its dissimilarity to β -lactam antibiotics.