Carbapenemase-producing bacteria now threaten to undermine the efficacy of the carbapenems, long considered to be the most potent and reliable of the -lactam antibiotics. In Gram-negative microorganisms, in particular, the ability to produce class A serine carbapenemases, such as the plasmid-mediated KPC enzymes, or class B metallo-carbapenemases, such as the NDM-1 enzyme, can be combined with other resistance determinants, such as porin deletions and upregulated efflux systems to generate a microorganism that is resistant to virtually all known antibiotic agents. In general, carbapenemases have extremely broad substrate specificity, hydrolyzing penicillins, cephalosporins, carbapenems, and often even monobactams. This project will systematically investigate structural alterations to the carbapenem scaffold that are predicted to improve stability to both serine and metallo-carbapenemases and also to improve antibacterial efficacy. A number of atypical structural modifications are proposed. If successful, these modifications might also be incorporated into other classes of bicyclic -lactam antibiotic to improve -lactamase stability. The biological evaluation of these newly modified carbapenems will involve tests of both inherent antibacterial efficacy as well as carbapenemase stability against a well-characterized series of both carbapenem-susceptible as well as carbapenem-resistant strains, including Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii isolates. In addition, novel carbapenems possessing good antibacterial activity will be profiled for PBP binding potency and susceptibility to renal dehydropeptidases along with an in vitro DMPK investigation of metabolic stability.
Public Health Relevance: Carbapenems are generally regarded as the most potent and dependable of the antibiotics. In order not to promote bacterial resistance, these agents are often reserved for the most serious and resistant bacterial infections. Despite this, however, some strains of bacteria have evolved carbapenem resistance, mainly by producing carbapenemases, which hydrolytically inactivate the antibiotics. This project is focused on the design of new carbapenems that will be carbapenemase resistant. These new agents would then be used to treat infections caused by highly resistant pathogens.
