Type
Text
Type
Dissertation
Advisor
Tonge, Peter J | Drueckhammer, Dale | London, Erwin | Walker, Stephen.
Date
2015-08-01
Keywords
Chemistry | inhibition, in vivo, kinetics, mechanism, menaquinone, S. aureus
Department
Department of Chemistry.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/77128
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Drug resistance in bacteria has become a global threat to public health care. The emergence of methicillin resistant Staphylococcus aureus (MRSA) exemplifies the eroding clinical efficacy of first-line antibiotics and emphasizes the need for new antibacterial drugs with novel mechanisms of action. The bacterial menaquinone (MK) biosynthesis pathway and fatty acid biosynthesis pathway (FAS-II) represent potential yet relatively underexploited targets for antibiotic development. My research is mainly focused on: 1) activity evaluation and mechanistic exploration of novel inhibitors targeting 1,4-dihydroxynaphthoyl-CoA synthase (MenB) from MRSA; 2) identification of a menaquinone salvage pathway in a defect S. aureus strain; 3) evaluation of a series of enoyl-ACP reductase (FabI) inhibitors against MRSA in animal infection models, investigating the impact of residence time (tR) on in vivo antibacterial efficacy. We first demonstrated that a series of 4-oxo-4-phenylbut-2-enoate compounds were active against MRSA with promising minimum inhibitory concentrations (MIC). Subsequently, we elucidated the mode of action of these compounds. The results support our `prodrug' hypothesis by showing that the butenoyl methyl esters penetrated into bacterial cells where they were hydrolyzed and converted into corresponding CoA adducts. We then confirmed by quantitating menaquinone levels in bacteria before and after drug treatment that the 4-oxo-4-phenylbut-2-enoates acted through a specific effect on menaquinone biosynthesis. Additionally, we evaluated the in vivo efficacy of the most potent compound in a mouse model of MRSA, and demonstrated its potential as a new anti-MRSA candidate. Small colony variants (SCVs) in S. aureus have recently attracted great interest. The aberrant bacteria have been identified to be auxotrophic to exogenous supplements such as menadioine (MD). Here, we discovered that a menaquinone-defect S. aureus strain (menD-) was viable in rich growth media but not in minimal media. We subsequently identified that a series of quinone-based molecules, in addition to menadione, were able to restore the growth of the menD- strain. By showing the recovery of menaquinone biosynthesis in complemented bacteria, we demonstrated that the quinones were converted into a complete set of menaquinone species in S. aureus. We further identified that this conversion was catalyzed by 1,4-dihydroxy-2-naphtoate octaprenyl transferase (MenA). Our lab has developed a library of diphenyl ether-based compounds targeting FabI as novel antibacterial candidates. The kinetics of drug-target interaction, which is described by the parameter of tR, has been extensively studied. In my research, a series of FabI inhibitors that have distinctive tR values were selected, and their antibacterial activity was evaluated in a mouse model of MRSA. The in vivo efficacy of the tested molecules were demonstrated to correlate more directly with tR rather than minimum inhibitory concentration (MIC) or the equilibrium dissociation constant (Ki). This observation supports the concept that the kinetics of drug-target interaction is more important than thermodynamic parameters when predicting drug efficacy in an open system. Imaging techniques, such as positron emission tomography (PET), have been important medical probes that provide a non-invasive approach to perform examination in a living animal or human. Here, we labeled two FabI inhibitors with 11C radionuclide and investigated their biological properties, such as in vitro cell uptake and in vivo drug distribution, using PET. In addition, an initial assay of imaging infections in living animals with FabI inhibitor-based radiotracers was performed. The results provide us important information to modify our PET imaging studies, which will ultimately facilitate infection diagnosis. | 214 pages
Recommended Citation
Lu, Yang, "Activity and Mechanism Studies on Novel Antibacterial Molecules Targeting Menaquinone Biosynthesis and Fatty Acid Biosynthesis in Drug Resistant S. aureus" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2964.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2964