Discovery of Novel Vinyl Isocyanide Antibiotics for the Treatment of MRSA

  • Liam Stephens

Student thesis: Doctoral ThesisPhD

Abstract

Antibiotic resistant bacteria are becoming an ever increasing threat to public health. The problems associated with their inexorable rise has been further intensified by the lack of new antibiotics coming through the drug development pipeline. In particular, there has been a dearth of new antibiotic classes to target the multi-drug resistant bacteria that have now developed resistance to last line of defence compounds including vancomycin. It is widely acknowledged that if we fail to act now and develop new antibiotics, then we risk entering a ‘post-antibiotic era’. Not only would this see the return of pandemic bacterial infections, but invasive surgical procedures and treatments such as chemotherapy would not be possible without the inevitable increase in loss of life. This thesis concerns itself with the development of a new class of antibiotic for the treatment of MRSA, which is now the largest contributor to nosocomial and community-acquired bacterial infections worldwide.Firstly, the past, present and future of antibiotic therapy is reviewed, paying particular attention to the methods by which bacteria have evolved resistance to the current arsenal of antibiotic compounds. Compounds currently undergoing clinical trials are also detailed, as well as the alternative approaches to combat antibiotic resistance. These include novel small molecules that inhibit the action of Beta-lactamase enzymes, efflux pump systems and aminoglycoside modifying enzymes. The structure-activity-relationship study based on the vinyl isocyanide natural products, byelyankacin, rhabduscin and 4-phenol vinyl isocyanide is described in chapter 2. The study, using 4-phenol vinyl isocyanide as the core framework, has resulted in the generation of a new class of antibiotic with potent inhibition of MRSA. Each compound synthesised was screened against five clinically relevant bacterial strains, which indicated the S. aureus specificity of the compounds developed in-house. The systemic toxicity of the compounds was also determined using Galleria mellonella and Manduca sexta in vivo models. Importantly, only two of the compounds synthesised showed any signs of toxicity at concentrations below their minimum inhibition concentration (MIC).Having previously determined the potent inhibition of a number of the vinyl isocyanides against planktonic MRSA, the in vitro biofilm prevention and eradication properties of these compounds is detailed in chapter 3. Biofilm studies performed on six compounds showed the excellent anti-biofilm prevention and attenuation properties of the vinyl isocyanides at sub-MIC concentrations. Chapter 4 discusses the biological assays performed on the vinyl isocyanides which helped determine the cell membrane as their target site of action. With the aid of two research collaborations, the vinyl isocyanides were shown to perturb the physical integrity of S. aureus membranes and cause membrane depolarisation. Importantly, cytotoxicity, haemolysis and complement studies suggested the vinyl isocyanides specifically target bacterial cells, with no associated toxicity against eukaryotic cells. The Community for Open Antimicrobial Drug Discovery (CO-ADD) demonstrated that the vinyl isocyanides possess excellent antifungal properties, with nM inhibition of a number of multi-drug resistant fungal strains. Biological assays conducted in-house showed the inability of S. aureus to develop resistance to the vinyl isocyanides. The compounds were also found to be stable in the presence of acid, glutathione and cysteine, further suggesting their potential future application as a new class of antibiotic for treatment against S. aureus.The final chapter in this thesis details the small structure-activity-relationship study on the sugar fragment of the natural products, byelyankacin and rhabduscin. The study revealed that vinyl isocyanide analogues containing Beta-glycosidic linkages had significantly reduced antibiotic activity.
Date of Award21 Mar 2018
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorSteven Bull (Supervisor) & Toby Jenkins (Supervisor)

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