This dissertation, "Anti-cancer N-heterocyclic Carbene Complexes of Gold(III), Gold(I) and Platinum(II): Thiol "switch-on" Fluorescent Probes, Thioredoxin Reductase Inhibitors and Endoplasmic Reticulum Targeting Agents" by Taotao, Zou, 邹滔滔, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "Anti-Cancer N-Heterocyclic Carbene Complexes of Gold(III), Gold(I) and Platinum(II): Thiol "Switch-on" Fluorescent Probes, Thioredoxin Reductase Inhibitors and Endoplasmic Reticulum Targeting Agents" Submitted by ZOU TAOTAO for the degree of Doctor of Philosophy at The University of Hong Kong in Feb 2015 Despite the success of cisplatin in combating various cancers, the problems of resistance and side effects have limited its wide application in cancer treatment. Gold complexes have recently emerged as promising candidates for cancer treatment. Unlike cisplatin, gold complexes do not favor DNA binding, but instead preferentially bind SH/SeH-containing proteins/enzymes in cancer cells, giving hope that these compounds may overcome cisplatin's resistance problems. Since the side effects of cisplatin are, at least partially, caused by instability-associated, off-target binding interactions, the incorporation of N-heterocyclic carbene (NHC) ligands may be a useful strategy to improve the stability of metal-based chemotherapeutics due to the strong  donating ability of NHC to form strong M-C(NHC) bonds. Meanwhile, the ease of modification and steric effects of NHC ligands provide favorable lipophilicity, reactivity and binding specificity of metal complexes. Indeed, some Pt(II)-NHC complexes have been reported to specifically target proteins/organelles rather than DNA. 3+ + The reduction of 4-coordinated Au to 2-coordinated Au by thiols has been 3+ demonstrated. Meanwhile, owing to the low energy d 2 2 orbital of Au, most gold(III) x -y complexes are non-emissive in solutions. In Chapter 3, by taking advantage of these unique properties, the synthesis of a class of non-emissive Au(III) complexes containing highly fluorescent N DEGREESN DEGREESN ligands and NHC ligands is described. In these compounds, the NHC ligand prevented further reduction of Au(III) to Au(0) and increased the III + solubility of the Au(III) complexes. The [Au (N DEGREESN DEGREESN)(NHC)] complex was readily reduced by GSH to form [Au (NHC)(GS)], accompanied by the release of the fluorescent H N DEGREESN DEGREESN ligand, therefore acting as a fluorescent "switch-on" probe for thiols. In addition, the anti-cancer activity of Au(I) is owed to its ability to inhibit thiol-enzymes; thus, the Au(III) complexes could also serve as precursors/prodrugs, activated by metal reduction, to deliver anti-cancer active Au(I) species. The major problem of most Au(I) anti-cancer agents is the lack of in vivo anti-tumor activity due to their high thiol-reactivity which leads to many off-target binding interactions with blood thiols. In Chapter 4, the synthesis of a dinuclear gold(I) complex bearing a mixed diphosphine and bis(NHC) ligand is described. This dinuclear Au(I) complex displayed a favorable stability that conveys potent thioredoxin reductase inhibition without being attacked by blood thiols. This complex significantly inhibited tumor growth in two independent mouse models with no observable side effects. The dinuclear Au(I) complex also exhibited anti-angiogenesis activity in a tumor model and inhibited sphere formation of cancer stem cells in vitro. In toxicology studies, neither systemic anaphylaxis in guinea pigs nor localized irritation in rabbits was observed