Chemical biology approaches to identify novel anti-pseudomonas aeruginosa agents

• Main Author: Fong, July
• Other Authors: Wu Bin
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Science::Biological sciences::Microbiology::Drug Resistance
• Online Access: https://hdl.handle.net/10356/100420; http://hdl.handle.net/10220/49961
• Institution: Nanyang Technological University

The emergence of multidrug-resistance pathogens has called for alternative therapies to treat bacterial infections. Pseudomonas aeruginosa is an opportunistic pathogen that often causes persistent infections associated with highly antibiotic-resistance and biofilms formation. In this study, various chemical biology approaches were utilized to interfere with bacterial cell-to-cell communication, termed quorum sensing (QS), to address drug resistance problems currently observed worldwide. Many bacteria employ QS to govern the production of virulence factors as well as the formation of biofilms. Instead of targeting components essential for growth and stimulate the development of resistant traits, chemical attenuation of QS could preferentially block QS-regulated cascades of bacterial gene expression, thus leading to attenuation of virulence. In many cases, bacteria employ multiple QS systems, which pose a challenge to develop novel inhibitors. In the first study, two different classes of QS interfering agents, such as quorum sensing inhibitor (QSI) and quorum quenching enzyme (QQE), were studied to suppress multiple pathways of QS of P. aeruginosa. The two QS interfering agents have been studied independently and work in different ways. Using mathematical modeling and biochemical assays, the results from this study suggested a novel approach of utilizing combination therapy of QSI and QQE, and also the importance to develop inhibitors that could suppress all QS systems simultaneously and block pathogenesis. In the second study, a drug repurposing approach was utilized to identify novel functions of FDA-approved drugs as QSI against P. aeruginosa. Given the slow pace of the new antibiotics discovery, repurposing of old drugs has been seen as an attractive strategy to recognize the new function of drugs outside their scope of original medical application, with the advantages of safer toxicity profiles, well-published clinical data, and lower cost and time. Five drugs with excellent QSI activities, namely benzbromarone (uricosuric agent), 8-quinolinol sulfate monohydrate (antineurodegenerative, anticancer, and antidiabetic agent), cetylpyridium chloride (antiseptic agent), zinc pyrithione (antidandruff and antifungal agent), and carbimazole (hyperthyroidism drug) were successfully identified. The application of the compounds in vivo using peritoneal silicone implant models on mice study was also demonstrated. Overall, this study represents how drug repurposing approach could be used to identify repurposable compounds as novel QS-interfering compounds to attenuate the virulence of P. aeruginosa. In the last chapter, a small chemical library based on zinc pyrithione was constructed as part of Structure-Activity Relationship (SAR) study. Novel metal-containing compounds were successfully synthesized and characterized as QSI of P. aeruginosa. SAR study yielded analogs that could reduce the production of QS-regulated virulence factors, as well as successfully eradicate colistin-resistant cells in P. aeruginosa biofilms when used together with the antibiotic. Transcriptomic profiling using RNA sequencing as well as experimental adaptive evolution study reveal the working mechanism of the compounds. As ionophore, the compounds could deliver metal ions through lipid membrane, and once inside the cells, the released metal ions interact with several targets simultaneously and also affect metal homeostasis. Both fur and zur pathways are affected upon treatment with compounds. The findings presented in this study show potentials of chemical attenuation for treating P. aeruginosa infections.