UBC Theses and Dissertations
The development of novel antimicrobial peptides and various strategies to improve their activity and biocompatibility Kumar, Prashant Sandeep
With the advent of antibiotic resistance and crisis, it is crucial to find substitutes to conventional antibiotics. Antimicrobial peptides (AMPs) are considered to be viable alternatives, because they are broad spectrum and bacteria develop little or no resistance towards AMPs. Interestingly, only few AMPs are used as therapeutics, due to problems such as host toxicity, protease cleavage and short half-life. Therefore, there is a need to improve the efficacy of AMPs by the use of D-peptides and/or delivery vehicles. The introduction of the thesis describes the diversity and various mechanisms of action (MOA) of AMPs. The issues and ways to improve the efficacy of AMPs, which forms the foundation of this thesis, are also discussed. Recently, hyperbranched polyglycerol (HPG) has gained attention due to its excellent biocompatibility, multifunctionality and long blood circulation time. The body of the thesis describes a methodology to covalently attach aurein 2.2 and its mutants to HPG and study the influence of the molecular weight on the antimicrobial activity. A peptide array was used to design tryptophan and arginine mutants of aurein 2.2. Mutant peptide 77 had significantly superior antimicrobial and antibiofilm activity compared to aurein 2.2 but was more toxic. We found that HPG can be used as a general scaffold to alleviate the toxicity of the peptides. The conjugates/peptides were tested in an in vivo mice skin infection (abscess) model. Surprisingly, peptide 73 and aurein 2.2 has similar efficacy in vivo indicating both the antimicrobial activity and toxicity, i.e. therapeutic index, are important. The conjugates (HPG-73c) were not active in mice abscess model, whereas 73c and D-73 encapsulated in micelles composed of DSPE-PEG2000 had excellent activity suggesting the release of the peptide from the delivery vehicle is necessary for in vivo activity. Without encapsulation D-73 was too toxic. A bacterial expression system was used to produce isotopically (¹⁵N) labeled aurein 2.2 and its interaction with whole bacterial cells was examined by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) confirming the MOA. Finally, the results presented will be discussed in the broad context of designing AMPs for therapeutics and understanding their MOA.
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