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Proteasome inhibitors bortezomib and carfilzomib are FDA-approved anticancer agents that have contributed to significant improvements in treatment outcomes. However, the eventual onset of acquired resistance continues to limit their clinical utility, yet a clear consensus regarding the underlying mechanisms has not been reached. Bortezomib and carfilzomib are known to target both the constitutive proteasome and the immunoproteasome, two conventional proteasome subtypes comprising distinctive sets of catalytic subunits. While it has become increasingly evident that additional, ‘intermediate’ proteasome subtypes, which harbor non-standard mixtures of constitutive proteasome and immunoproteasome catalytic subunits, represent a considerable proportion of the proteasome population in many cell types, less is known regarding their contribution to cellular responses to proteasome inhibitors. Importantly, previous studies in murine models have shown that individual proteasome subtypes differ in sensitivity to specific proteasome inhibitors. Furthermore, research efforts in our laboratory and others have revealed that proteasome catalytic subunit expression levels and activity profiles are altered when human cancer cells acquire resistance to proteasome inhibitors. We therefore hypothesized that changes in the relative abundances of individual proteasome subtypes contribute to the acquired resistance of cancer cells to bortezomib and carfilzomib. A major obstacle in testing our hypothesis was a lack of chemical probes suitable for use in identifying distinct proteasome subtypes. We addressed this by developing a series of bifunctional proteasome probes capable of crosslinking specific pairs of catalytic subunits colocalized within individual proteasome complexes and compatible with immunoblotting-based detection of the crosslinked subunit pairs. We confirmed the utility of these probes in discerning the identities of individual proteasome subtypes in a multiple myeloma cell line that abundantly expresses catalytic subunits of both the constitutive proteasome and immunoproteasome. Our findings indicate that constitutive proteasomes, immunoproteasomes, and intermediate proteasomes co-exist within these cells and support conclusions drawn from previous studies in other cell types. We also established non-small cell lung cancer cell line models of acquired bortezomib and carfilzomib resistance in which to test our hypothesis. Using immunoblotting and proteasome activity assays, we discovered that changes in the expression levels and activities of individual catalytic proteasome subunits were associated with the emergence of acquired resistance to bortezomib or carfilzomib. These changes were inhibitor-dependent and persisted after the selective pressure of the inhibitor was removed. Finally, results obtained using our bifunctional proteasome probes suggest that the altered abundance of an intermediate proteasome subtype is associated with acquired proteasome inhibitor resistance. Collectively, our results provide evidence linking changes proteasome composition with acquired proteasome inhibitor resistance and support the hypothesis that such changes are involved in resistance mechanisms to these inhibitors.

Motivation: Cardiovascular heart disease (CVD) is the leading cause of death worldwide. Risk markers for CVD include, amongst others, the haemostatic factors tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor type 1 (PAI-1), factor VII (FVII) and fibrinogen and more recently, C-reactive protein (CRP), a sensitive marker of inflammation. Epidemiological studies have demonstrated an inverse association between dietary fibre (DF) consumption and risk factors for CVD and CVD prevalence. Some research indicates that this protection may be related to favourable changes in the haemostatic profile and inflammatory markers. This is applicable for the consumption of total DF, as well as soluble and insoluble fibre. However, clinical intervention trials report conflicting data on the effects of DF on t-PA, PAI-1, FVII, fibrinogen and CRP. In addition, available literature is not clear on the mechanisms through which DF may have favourable effects. Objective: The main objective of this study was to review the results of randomised controlled trials systematically on the effects of DF on the above-mentioned selected haemostatic variables and CRP in healthy adults and subjects with hypertriglyceridaemia and the metabolic syndrome. Methods: Human adult intervention trials, at least two weeks in duration, with an increased and measurable consumption of DF were included. Electronic databases were searched from the earliest record to May/July 2006 and supplemented by crosschecking reference lists of relevant publications. From the literature search, two reviewers identified studies that were rated for quality based on the published methodology. No formal statistical analysis was performed due to the large differences in the study designs of the dietary intervention trials. The primary outcome measures were percentage changes between intervention and control groups, or baseline to end comparisons for t-PA, PAI-1, FVII, fibrinogen and CRP. Results t-PA activity increased significantly (14-167%) over the short and long-term following increased fibre intakes. PAI-1 activity decreased significantly between 15-57% over periods ranging from two to six weeks. These favourable changes in t-PA and PAI-1 occurred in healthy, hypertriglyceridaemic and metabolic syndrome subjects following consumption of diets containing ≥3.3 g/MJ DF and ≥4.5 g/MJ DF respectively. Mechanisms through which DF may affect t-PA and PAI-1 include its lowering effect on insulinaemic and glycaemic responses, decreasing triglycerides which are a precursor of very-low-density lipoproteins, fermentation of DF to short-chain fatty acids, which may reduce free fatty acid concentrations, as well as the role of DF in promoting weight loss. High DF intakes did not have a significant effect on fibrinogen concentrations possibly because of relatively little weight loss, too low DF dosages and maintaining a good nutritional status. Inadequate study designs deterred from meaningful conclusions. Significant decreases in FVll coagulant activity (6-16%) were observed with DF intakes of ≥3.3 g/MJ and concomitant decreased saturated fat intakes and weight loss in healthy and hypertriglyceridaemic subjects. Confounding factors include weight loss and a simultaneous decreased intake of saturated fats. The type of fibre seems to play a role as well. Mechanisms through which DF may reduce FVll concentrations include its effects on triglyceride-rich lipoproteins, insulin and weight loss. Increased DF consumption with dosages ranging between 3.3-7.8 g/MJ were followed by significantly lower CRP concentrations (25-54%), however, simultaneous weight loss and altered fatty acid intakes were also present in all the studies. Mechanisms are inconclusive but may involve the effect of DF on weight loss, insulin, glucose, adiponectin, interleukin-6, free fatty acids and triglycerides. Conclusions: Epidemiological evidence indicates an association between DF and the CVD risk factors t-PA, PAI-1, FVII, fibrinogen and CRP. In general, the risk of CVD may improve with high-fibre intakes as indicated by the favourable changes in some of the parameters. However, simultaneous reduced fat intakes and weight loss presented difficulties in separating out the effects of specific components. Furthermore, DF is consumed in a variety of different forms and different dosages that may have different effects. Overall, the study designs used in the intervention trials prevented significant conclusions. DF did, however, play a role in modifying t-PA, PAI-1, FVII and CRP. Potential effects on fibrinogen were not quantifiable. Recommendations: The results from this investigation provide the motivation for additional controlled clinical research to establish the effect and mechanisms of DF on haemostatic variables and CRP. A critical aspect of future studies would be to set up suitable protocols. The amount of subjects, duration of the trials, confounding factors such as weight loss and altered fat intakes and differentiation between types and dosage of DF are important. DF supplemental studies are recommended as they may be the most suitable method to reach meaningful conclusions. / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2007

Iminosugars are polyhydroxylated alkaloids, and can be generally defined as sugar mimetics in which the endocyclic oxygen atom has been replaced with a basic nitrogen. A common affect of this atomic substitution is to bestow these compounds with the ability to inhibit various sugarprocessing enzymes; most significantly the glycosidases (glycoside hydrolases) which areintimately involved in a huge array of biological functions. Compounds which inhibit these enzymes concordantly possess much potential as medicinal agents for the treatment of a variety of diseases. Several iminosugars have already achieved market approval as drugs, and many more are promising candidates in the late stages of clinical development. As such there remains considerable interest in this class of compound, both in terms of the exploration of novel iminosugar structures, as well as the continual development of more efficient general methodology for their synthesis. The densely-packed functionality and stereochemical information present in iminosugars makes them challenging targets for asymmetric chemical synthesis, whereas carbohydrates are clearly very attractive as chiral-pool starting materials for this purpose. Indeed, the majority of the most successful syntheses of iminosugars use the latter approach, and such is the focus of this thesis. Chapter 1 presents a relatively brief introduction to iminosugars, including their types of structure, natural occurrence and biological mode of action. The rationale behind their use as therapeutic agents for the treatment of some significant disease targets is also discussed. Chapter 2 is concerned with the preparation of a number of novel polyhydroxylated azetidines, and their evaluation as glycosidase inhibitors. Such compounds represent an almost entirely neglected class of iminosugars within the literature. An overview of natural and synthetic products incorporating an azetidine motif is given, as well as a brief review of preparative methods and known azetidine iminosugars. A highly efficient and flexible method for the key azetidine ring formation is demonstrated by the cyclisations of 3,5-di-O-triflates of pentoses and hexoses, and of a 2,4-di-O-triflate of glucose, with various primary amines. In this manner, many azetidine triols and tetrols were prepared in good yield. Furthermore, this process is readily adaptable to the installation of added functionality to the azetidine scaffold, as demonstrated by the preparation of 1-acetamido analogues. The initial biological screening of these compounds showed a promising array of glycosidase inhibition, including that of selective inhibition of fungal enzymes. Chapter 3 describes a strategy with which to prepare all sixteen stereoisomers of a known piperidine iminosugar, alpha-homonojirimycin (alpha-HNJ), in a highly divergent manner from just four of the possible thirty-two 6-azidoheptitols using traditional chemical synthesis in tandem with biotechnological transformations. One half of the execution of this strategy is described in this thesis. Two 6-azidoheptitols were prepared from D-mannose, thereby providing access to four 6-azidoketoheptoses through a combination of microbial oxidation and enzymatic epimerisation. Catalytic hydrogenation of these 6-azidoketoheptoses furnished four diastereomeric mixtures of 2,6-iminoheptitols, with varying degrees of stereoselectivity. Purification of these mixtures allowed six 2,6-iminoheptitols to be isolated, two of which have never previously been tested for glycosidase inhibition. Significantly, one of them was found to be a potent and highly selectiveinhibitor of alpha-galactosidases, and may therefore be of interest in the treatment of Fabry disease.

This study examined the relationship between selective serotonin reuptake inhibitor (SSRI) medication and auditory measures in clinically depressed women. Experimental subjects were tested in both a medicated and unmedicated condition. Experimental subjects were compared to a normal control group; additionally intrasubject comparison was made within the experimental group. Test measures included: audiometry, tympanometry, otoacoustic emissions, uncomfortable loudness level, masking level difference, SCAN-A, Synthetic Sentence Identification (SSI), and the low predictability section of the Revised Speech in noise (RSPIN). The unmedicated group scored significantly less favorably than the control group on the following tests; SCAN-A (composite, filtered words, and auditory figure ground), R-SPIN (0MCR condition in both the right and left ears). Additionally, the unmedicated group scored significantly less favorably than the medicated group on the SSI (-20MCR condition right ear only) and of the R-SPIN (0MCR condition right ear only). Other test measures indicated consistent trends but did reach significance.

<p>Trehalose is a non-reducing disaccharide essential for pathogenic fungal survival and virulence. The biosynthesis of trehalose requires the trehalose-6-phosphate synthase, Tps1, and trehalose-6-phosphate phosphatase, Tps2. More importantly, the trehalose biosynthetic pathway is absent in mammals, conferring this pathway as an ideal target for antifungal drug design. However, lack of germane biochemical and structural information hinders antifungal drug design against these targets. </p><p>In this dissertation, macromolecular X-ray crystallography and biochemical assays were employed to understand the structures and functions of proteins involved in the trehalose biosynthetic pathway. I report here the first eukaryotic Tps1 structures from Candida albicans (C. albicans) and Aspergillus fumigatus (A. fumigatus) with substrates or substrate analogs. These structures reveal the key residues involved in substrate binding and catalysis. Subsequent enzymatic assays and cellular assays highlight the significance of these key Tps1 residues in enzyme function and fungal stress response. The Tps1 structure captured in its transition-state with a non-hydrolysable inhibitor demonstrates that Tps1 adopts an “internal return like” mechanism for catalysis. Furthermore, disruption of the trehalose biosynthetic complex formation through abolishing Tps1 dimerization reveals that complex formation has regulatory function in addition to trehalose production, providing additional targets for antifungal drug intervention. </p><p>I also present here the structure of the Tps2 N-terminal domain (Tps2NTD) from C. albicans, which may be involved in the proper formation of the trehalose biosynthetic complex. Deletion of the Tps2NTD results in a temperature sensitive phenotype. Further, I describe in this dissertation the structures of the Tps2 phosphatase domain (Tps2PD) from C. albicans, A. fumigatus and Cryptococcus neoformans (C. neoformans) in multiple conformational states. The structures of the C. albicans Tps2PD -BeF3-trehalose complex and C. neoformans Tps2PD(D24N)-T6P complex reveal extensive interactions between both glucose moieties of the trehalose involving all eight hydroxyl groups and multiple residues of both the cap and core domains of Tps2PD. These structures also reveal that steric hindrance is a key underlying factor for the exquisite substrate specificity of Tps2PD. In addition, the structures of Tps2PD in the open conformation provide direct visualization of the conformational changes of this domain that are effected by substrate binding and product release. </p><p>Last, I present the structure of the C. albicans trehalose synthase regulatory protein (Tps3) pseudo-phosphatase domain (Tps3PPD) structure. Tps3PPD adopts a haloacid dehydrogenase superfamily (HADSF) phosphatase fold with a core Rossmann-fold domain and a α/β fold cap domain. Despite lack of phosphatase activity, the cleft between the Tps3PPD core domain and cap domain presents a binding pocket for a yet uncharacterized ligand. Identification of this ligand could reveal the cellular function of Tps3 and any interconnection of the trehalose biosynthetic pathway with other cellular metabolic pathways. </p><p>Combined, these structures together with significant biochemical analyses advance our understanding of the proteins responsible for trehalose biosynthesis. These structures are ready to be exploited to rationally design or optimize inhibitors of the trehalose biosynthetic pathway enzymes. Hence, the work described in this thesis has laid the groundwork for the design of Tps1 and Tps2 specific inhibitors, which ultimately could lead to novel therapeutics to treat fungal infections.</p> / Dissertation

Acetylcholinesterase (AChE) is an essential enzyme with an evolutionary conserved function: to terminate nerve signaling by rapid hydrolysis of the neurotransmitter acetylcholine. AChE is an important target for insecticides. Vector control by the use of insecticide-based interventions is today the main strategy for controlling mosquito-borne diseases that affect millions of people each year. However, the efficiency of many insecticides is challenged by resistant mosquito populations, lack of selectivity and off-target toxicity of currently used compounds. New selective and resistance-breaking insecticides are needed for an efficient vector control also in the future. In the work presented in this thesis, we have combined structural biology, biochemistry and medicinal chemistry to characterize mosquito AChEs and to develop selective and resistance-breaking inhibitors of this essential enzyme from two disease-transmitting mosquitoes.We have identified small but important structural and functional differences between AChE from mosquitoes and AChE from vertebrates. The significance of these differences was emphasized by a high throughput screening campaign, which made it evident that the evolutionary distant AChEs display significant differences in their molecular recognition. These findings were exploited in the design of new inhibitors. Rationally designed and developed thiourea- and phenoxyacetamide-based non-covalent inhibitors displayed high potency on both wild type and insecticide insensitive AChE from mosquitoes. The best inhibitors showed over 100-fold stronger inhibition of mosquito than human AChE, and proved insecticide potential as they killed both adult and larvae mosquitoes.We show that mosquito and human AChE have different molecular recognition and that non-covalent selective inhibition of AChE from mosquitoes is possible. We also demonstrate that inhibitors can combine selectivity with sub-micromolar potency for insecticide resistant AChE.

This thesis is focused on enzymatic studies of the secreted aspartic proteases (Saps) from Candida albicans as a tool for discovery of anti-candida drugs. C. albicans causes infections in a number of different locations, which differ widely in the protein substrates available and pH. Since C. albicans needs Saps during virulent growth, these enzymes are good targets for drug development. In order to investigate the catalytic characteristics of Saps and their inhibitor affinities, substrate-based kinetic assays were developed. Due to the low sensitivity of these assays, especially at the sub-optimal pH required to mimic the different locations of infections, these assays were not satisfactory. Therefore, a biosensor assay was developed whereby, it was possible to study interaction between Saps and inhibitors without the need to optimise catalytic efficacy. Furthermore, the biosensor assay allowed determination of affinity, as well as the individual association and dissociation rates for inhibitor interactions. Knowledge about substrate specificity, Sap subsite adaptivity, and the pH dependencies of catalytic efficacy has been accumulated. Also, screening of transition-state analogue inhibitors designed for HIV-1 protease has revealed inhibitors with affinity for Saps. Furthermore, the kinetics and pH dependencies of their interaction with Saps have been investigated. One of these inhibitors, BEA-440, displayed a complex interaction with Saps, indicating a conformational change upon binding and a very slow dissociation rate. A time dependent interaction was further supported by inhibition measurements. The structural information obtained affords possibilities for design of new more potent inhibitors that might ultimately become drugs against candidiasis. The strategy to combine substrate specificity studies with inhibitor screening has led to complementary results that generate a framework for further development of potent inhibitors.

Advances in several areas of scientific research is currently hampered by the slow progress in developing a non-viral, high precision technique capable of safely and efficiently injecting targeted single cells with impermeable molecules. To date, one of the most promising techniques employs the laser to temporarily create a pore in the cell membrane to allow the entry of exogenous molecules. This technique has potentially wide applications. In this thesis, I utilised the precision of laser transfection, also known as optoporation, to deliver two histone demethylase inhibitors (8-hydroxyquinoline and FMF1293) of the JmjC-domain protein JMJD3 into vital cells. The enzyme, JMJD3, demethylates histone H3 lysine K27, the methylation state of which has been shown in previous studies to regulate genes in such a way as to play a key role in the formation of tumours and even maintenance of stem cell pluripotency. The research here shows proof of principle that optoporation can be employed to quickly screen and test the efficacy of novel drugs by delivering them into cells at significantly low concentrations while still maintaining inhibition activity. I also used optoporation to deliver relatively large proteins such as bovine serum albumin (BSA), phalloidin and novel synthetic antibodies into living cells without fixatives. This offers the possibility of using reporter systems to monitor living cells over time. Finally, an attempt was made to generate iPS colonies by optoporating plasmid DNA into somatic cells, however, I find that this technique was unable to efficiently transfect and reprogram primary cells. Two automated image-based systems that can be integrated into existing microscopes are presented here. First, an image processing algorithm that can quickly identify stem cell colonies non-invasively was implemented. When tested, the algorithm’s resulting specificity was excellent (95 – 98.5%). Second, because optoporation is a manual and time consuming procedure, an algorithm to automate optoporation by using image processing to locate the position of cells was developed. To my knowledge, this is the first publication of a system which automates optoporation of human fibroblasts in this way.

In the last decade, dynamic combinatorial mass spectrometry (DCMS) with protein targets has emerged as a promising method for the identification of enzyme-inhibitors. 2-Oxoglutarate (2OG) oxygenases are involved in important biological processes related to many diseases; several human 2OG oxygenases are targeted for pharmaceutical intervention. This thesis describes inhibition studies on three 2OG oxygenases using DCMS and structure activity relation (SAR) studies. Disulphide based DCMS was used for the identification of N-oxalyl based lead inhibitors for the 2OG oxygenase AlkB from Escherichia coli. Crystallographic analyses of AlkB with a lead inhibitor assisted in the design of a second generation of inhibitors using N-oxalyl, pyridyl and quinolinyl scaffolds. Crystallographic and kinetic data of three potent and selective AlkB inhibitors validates the DCMS approach for the development of 2OG oxygenase inhibitors. The hypoxia inducible factor hydroxylase, prolyl hydroxylase domain 2 (PHD2), was then used as the model enzyme for the development of a novel DCMS approach employing the reversible reaction of boronic acids with diols to form boronate esters. The ‘boronate’ DCMS method was used to identify pyridyl- substituted lead compounds. Further modification of the pyridine scaffold, based on structural analyses, led to the development of highly potent and selective PHD2 inhibitors. To identify inhibitors for the fat mass and obesity associated protein (FTO), another 2OG oxygenase, an inhibition assay was developed. The inhibition assay was used in conjunction with a differential scanning fluorimetry (DSF) binding assay to identify isoquinolinyl and pyridyl inhibitor scaffolds, related to those used in the DCMS studies. FTO complexed structures of these compounds, and with a natural product anthraquinone, enabled the design and synthesis of new inhibitors that are both co-substrate and substrate competitors of FTO. One such compound proved to be a potent FTO inhibitor with improved selectivity over other 2OG oxygenases. Overall, the work validates the use of DCMS methods for the development of potent and selective inhibitors for 2OG oxygenases, and by implication of other enzyme families.