Project Title: Characterization of the Structure-Function Relationship of a Host-Targeted anti-Salmonella Agent
Project Mentor: John Gunn – Microbial Pathogenesis
Background: Typhoid fever, primarily caused by enteric Salmonella enteritica serovar Typhi, remains a major global health problem with approximately 14 million new infections and 136,000 fatalities annually. While there are a few antibiotic options available to treat the disease, the global increase in multidrug resistant strains necessitates alternative therapeutic options. Our previous cell-based screen assay identified 3-(methoxycarbonyl) benzyl 2-hydroxy-4-quinoline carboxylate (KH-2) that inhibits Salmonella growth inside macrophages but does not have direct anti-Salmonella killing in vitro. There is a weak bond ester link between KH-2 carboxylate group and quinoline group raising the possibility that the observed anti-Salmonella phenotype is mediated by carboxylic acid that was released from KH-2 due to intracellular metabolic activities of the infected macrophages.
Methods: In this study, we structurally replaced the weak ester link by a more stable amine linkage between carboxylate group and quinoline group resulting in two KH-2 analogs: MC-1-40 and MC-1-41. Toxicity of these derivatives as well as compound KH-2 on J774.1 macrophages using an LDH assay was examined. In addition, the abilities of these compounds to inhibit the Salmonella growth inside macrophages and their ability to directly kill Salmonella by measuring colony forming units was evaluated. Assessment of compound activity in Salmonella-infected macrophages, compound analogs, as well as direct toxicity of KH-2 and its analogs at variable doses are important to characterize the structure-function relationship of KH-2.
Results: In vitro examination of toxicity showed that MC-1-40 and MC-1-41 displayed a similar non-toxic effect on J774.1 macrophages as their parent compound KH-2. Preliminary data for their anti-Salmonella activity in macrophages indicated that structural modification in MC-1-40 and MC-1-41 does not affect the anti-Salmonella activity of KH-2 as measured by colony forming unit analysis.
Conclusion: Our studies provide insight into the structure-function relationship of KH-2 for the development of a lead compound for host-targeted therapy to control Typhoid fever.