The discovery that Gram-negative bacteria employ small molecules, namely N-acyl homoserine lactones (AHLs), to globally regulate the production of secondary metabolites and control the expression of virulence determinants has provided a new potential target for anti-infective therapy. Genes regulated through this pathway include exotoxins and other pathogenicity factors, as well as genes for bacterial self-defense such as biofilm formation, which contribute to antibiotic resistance. Interference with this pathway, either by sequestration of the AHLs or cleavage of the lactone bond, has been shown to attenuate pathogenic bacteria and render them harmless. Throughout the realm of Gram-negative bacteria these AHL-signaling molecules differ only in their acyl moiety, leaving the homoserine lactone as the core structure. This feature makes AHLs an attractive target for anti-microbial antibody therapy. Specifically, the aims of this application are (1) the chemical synthesis of AHL-based analogues, including: a) a phosphonate transition state analogue (TSA) of lactone hydrolysis, b) native lactone structures that differ only in the acyl chain substitution pattern; (2) generation of monoclonal antibodies (mAbs) against these AHL-based haptens, with the TSA being designed such that catalytic antibodies will be elicited that are capable of hydrolyzing the lactone bond and thereby inactivate the signaling molecule; (3) the isolation of fully human antibody fragments that bind AHL; (4) characterization and evaluation of these antibodies for their ability to sequester or inactivate AHL molecules and so inhibit the quorum sensing signaling pathway. The work proposed herein represents a novel strategy to combat antibiotic-resistant Gram-negative bacteria using immunotherapy.
