Bioconjugation Using Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction

Date

2015-12

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Abstract

This dissertation presents different studies aiming at the exploration of copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction in biological systems and conjugating biomolecules. Chapter one introduces the broad field of bioorthogonal reactions with an emphasis on CuAAC reaction. The reaction mechanism, drawbacks and recent development for CuAAC reaction is discussed. The notable applications of CuAAC reaction for conjugation in living systems are reviewed. Copper(I)-mediated oxidation damage is the most prominent drawback undermining the use of CuAAC reaction in bioconjugation. In chapter two, the Cu-catalyst induced peptide and protein oxidation was systematically investigated. The use of OEG-containing tris(triazolylmethyl)amine ligand in CuAAC bioconjugation efficiently protects the biomolecules from oxidation damage. The protection mechanism is through the ligand sacrificial oxidation to intercept the Cu(I)-induced reactive oxygen species (ROS). In Chapter Three, a cell plasma membrane penetrable tris(triazolylmethyl)amine based ligand was designed to extend the use of CuAAC bioconjugation inside living cells. The new CuAAC catalyst exhibits better biocompatibility, enhanced cellular uptake and faster in vitro reaction rate acceleration. However, the higher performance did not result in efficient intracellular bioconjugation. The presence of abundant biothiols in cytoplasm is the major reason to slow down the intracellular CuAAC reaction. The depletion of cellular biothiols significantly improves the CuAAC reaction, but is accompanied by decreased cell viability. Chapter four describes a pioneering study to utilize intracellular CuAAC reaction for more efficient drug delivery. A reported enzyme inhibitor containing an internal triazole motif was used as a model drug formed in-situ inside tumor cells by the internalized azido- and ethynyl- drug fragments. As revealed in LC-MS/MS analyses, a small amount of triazole product was formed inside living cells, but the low concentration limits the potency against tumor cell proliferation. Chapter five presents the localization of antimicrobial peptides (AMPs) on particles and solid support via the optimized CuAAC reaction to enhance the overall antimicrobial activity. Antimicrobial peptide IG-25 was anchored on polymerized liposomes via CuAAC reaction for generating more potent antimicrobial agents. IG-25 peptide was also tethered with a fluorocarbon via CuAAC reaction on commercial contact lens as an antimicrobial coating. Both strategies exhibited enhanced anti-fungal activity.

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Keywords

Bioconjugation, CuAAC

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