The sialidases/neuraminidases represent a family of enzymes whose function is important in the pathogenicity of bacteria and the virulence of influenza. Relenza and Tamiflu represent two drugs that were developed using structure-based drug design (SBDD) and computational-assisted drug design (CADD). These drugs target the active site of the influenza neuraminidase A and B (GH-34 family). Sialidases in the GH-33 family could represent novel drug targets for the treatment of bacterial or parasitic infection. SBDD was employed to develop chemical tools of two GH-33 sialidases, NanB and TcTS. NanB is a potential drug target for S. pneumoniae. The chemical tool developed for NanB follows on from work within the Taylor and Westwood research groups, in which a molecule of CHES and a glycerol were found serendipitously bound within a water channel at an allosteric site. Using this information as a basis for SBDD an allosteric inhibitor of NanB, Optactin was developed. Within this work, synthesis of this inhibitor was achieved and optimised. Optactin was then modified to improve potency. This proceeded through an amide analogue and addition of an arene resulting in a mid- micromolar inhibitor (IC50: 55.4±2.5 μM). Addition of polar substituents improved potency further resulting in a low micromolar inhibitor of NanB, Optactamide (IC50: 3.0±1.7 μM). Application of this tool in vitro demonstrated that NanB and NanA have a role in invasion of S. pneumoniae into lung epithelial cells. TcTS is a potential drug target for the treatment of Chagas disease. A CADD approach using a fragment library was unsuccessful at identifying an allosteric inhibitor of TcTS despite structural similarity with NanB. A re-task of the CADD approach towards the active site was successful in identifying an inhibitor of TcTS and a fragment useful for further development. This work sets the groundwork for the development of a chemical tool targeting TcTS.

Cancer cells, unlike normal tissue, frequently rely on glycolysis for the production of energy and the metabolic intermediates required for their growth regardless of cellular oxygenation levels. This metabolic reconfiguration, termed the Warburg effect, provides a potential strategy to preferentially target tumours from a therapeutic perspective. The present study sought to investigate the glycolytic phenotype of breast and ovarian cancer, and assess the possibility of exploiting several glycolytic targets therapeutically. Initially the growth dependency of breast and ovarian cancer cells on the availability of glucose was established. An array of 10 compounds reported to inhibit key enzymes of the glycolytic pathway were investigated and compared against an extended panel of breast and ovarian cancer cell line models. All inhibitors investigated, targeted against multiple points of the pathway, were shown to block the glycolytic pathway as demonstrated by glucose accumulation in the culture media combined with decreased lactate secretion, and attenuated breast and ovarian cancer cell proliferation in a concentration dependent manner. Furthermore their mechanism of action was investigated by flow cytometric analysis and their antiproliferative effect was associated with induction of apoptosis and G0/G1 cell cycle arrest. The glycolytic inhibitors were further assessed in combination strategies with established chemotherapeutic and targeted agents and several synergistic interactions, characterised by low combination index values, were revealed. Among them, 3PO (a novel PFKFB3 inhibitor) enhanced the effect of cisplatin in both platinum sensitive and platinum resistant ovarian cancer cells suggesting a strategy for treatment of platinum resistant disease. Furthermore robust synergy was identified between IOM-1190 (a novel GLUT1 inhibitor) and metformin, an antidiabetic inhibitor of oxidative phosphorylation, resulting in strong inhibition of breast cancer cell growth. This combination is proposed for the treatment of highly aggressive triple negative breast tumours. An additional objective of this research was to investigate the effect of the oxygen level on sensitivity to glycolysis inhibition. Breast cancer cells were found to be more sensitive to glycolysis inhibition in high oxygen conditions. This enhanced resistance at low oxygen levels was associated with upregulation of the targeted glycolytic enzymes as demonstrated at both the mRNA (by gene expression microarray profiling, Illumina BeadArrays) and protein level (by Western blotting). Manipulation of LDHA (Lactate Dehydrogenase A) by siRNA knockdown provided further evidence that downregulation of this target was sufficient to significantly suppress breast cancer cell proliferation. Finally, the expression of selected glycolytic targets was examined in a clinical tissue microarray set of a large cohort of ovarian tumours using quantitative immunofluorescence technology, AQUA. The role of the glycolytic phenotype in ovarian cancer was suggested and interesting associations between the glycolytic profile and clear cell and endometrioid ovarian cancers revealed. Increased PKM2 (Pyruvate kinase isozyme M2) and LDHA expression were demonstrated in clear cell tumours and also low expression of these enzymes was significantly correlated with improved survival of endometrioid ovarian cancer patients. Taken together the findings of this study support the glycolytic pathway as a legitimate target for further investigation in breast and ovarian cancer treatment.

Both of the acute phase reactants, C-reactive protein and fibrinogen, as well as neutrophils have been shown to accumulate at sites of tissue injury or inflammation. The association of C-reactive protein with neutrophils and the concomitant degradation of this ligand by a phorbol 12-myristate 13 acetateactivatable membrane-associated neutral protease has been shown in previous studies. Degradation of C-reactive protein by the neutrophil protease was shown to result in peptides with an ability to modulate various immune functions of the neutrophil. The aim of this study has been to investigate specific characteristics of the protease, with respect to cellular distribution and molecular size. The ability of this neutrophil membrane-associated protease to degrade the acute phase protein, fibrinogen was investigated. The mechanism of degradation of both C-reactive protein and fibrinogen during their association with the neutrophil was also examined. The neutrophil protease, capable of degrading C-reactive protein, was also associated with the cytoskeleton and was proposed to be a submembrane protease localised at sites of attachment of the membrane with the cytoskeleton. The protease was found to have a molecular mass of approximately 600 kDa which, on sodium dodecyl sulphate polyacrylamide gel electrophoresis, separated into four bands which migrated to molecular mass values of 209 kDa, 316 kDa, 398 kDa and 501 kDa. This protease also possessed fibrinogenolytic activity. The fibrinogen degradation products generated by this neutrophil membrane-associated protease were distinct from the products generated by the fibrinogenolytic systems of plasmin, human neutrophil elastase and neutrophil lysosomal enzymes and were unclottable through cleavage of the Aα chain from the N-terminus and the Bβ and γ chains from the C-terminus. N-terminal cleavage of the Aα chain by the neutrophil membrane-associated protease generated the Aα1-21 peptide, previously regarded as a unique consequence of elastase activity. Degradation of C-reactive protein and fibrinogen occurred as a result of their interaction with the neutrophil near to the CD11c integrin receptor. This interaction resulted in the egress of proteolytic activity into the extracellular medium. The fibrinogen products generated outside the cell associated with the neutrophil via the β₂ integrin receptors and the IgG Fc receptor. The interaction of the Creactive protein degradation products with the neutrophil could not be determined. Both C-reactive protein and fibrinogen are degraded by non-stimulated neutrophils but activation with phorbol 12- myristate 13 acetate resulted in maximum degradation This upregulation of activity was achieved through activation of H7 and trifluoperazine inhibitable cellular kinases and changes in microfilament assembly. The generation of non-clottable fibrinogen together with possible modulation of neutrophil receptormediated functions by the fibringen degradation products as well as the knowledge that the neutrophil protease generates C-reactive protein peptides with immunomodulatory activity implicates this neutrophil membrane-associated protease in the modulation of various inflammatory processes.

Therapeutic inefficacy of conventional cancer treatment is a particular dilemma associated with metastatic triple negative breast cancer (TNBC), with patients still facing poor prognosis. The design and development of novel anticancer agents specifically targeted to cancer-associated pathways is of therapeutic interest. The rationale is twofold: firstly, targeted therapy overcomes widespread toxicity and adverse effects of conventional chemotherapy due to the selectivity of the treatment modality. Secondly, synergistic combinations of different classes of highly targeted therapies could hold therapeutic promise to overcome resistance by simultaneously circumventing multiple cancer hallmarks. This study evaluates the in vitro antiproliferative activity of six compounds using breast cancer cell lines as experimental model. Five of these compounds are novel, agents designed in silico to selectively target cancer hallmarks via inhibition of specific cancer-associated proteins. The compounds include an antimitotic (STX1972), three variants of bromodomain 4 (BRD4) inhibitors (Bzt-W41, Bzt-W49 and Bzt-W52), an inhibitor of both sirtuin (SIRT) 1 and 2 (W137) and an inhibitor of janus kinases 1 and 2 (Ruxolitinib). The synergism between paired combinations was also explored. Two breast cancer cell lines, MDA-MB-231 and MCF-7 were used as experimental models. The MDA-MB-231 cell line is oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) negative and is therefore commonly used to model triple negative breast cancer with invasive and metastatic properties. MCF-7 cells are ER and PR positive and represent the hormone-dependent breast cancer model. The endothelial EA.hy926 cell line was used to represent non-cancerous cells. A crystal violet assay was used to determine the half maximal inhibitory concentration (IC50) of the six compounds on the tested cell lines after 48 h exposure. Drug combination studies based on the Chou-Talalay method of paired drug combinations were performed. Effects of treatment on cell morphology was assessed by means of confocal-microscopy. Flow cytometry was used to study the effects on cell cycle progression, apoptosis, autophagy/lysosomal activity, reactive oxygen species (ROS) production, changes in mitochondrial membrane potential (ΔΨm) and the serine 70 phosphorylation status of Bcl-2. Real-time quantitative PCR was used to analyse the effects of the compounds on the mRNA expression levels of p53, c-myc and bcl-2. Quantitative protein expression of c-MYC was analysed by means of enzyme-linked immunosorbent assay. In vitro screening for antiproliferative activity revealed that the compounds showed cancer-selective cytotoxic effects when compared to the EA.hy926 control cell line. The initial screening identified three compounds for further investigative inclusion, namely the antimitotic (STX1972), the BRD4i (Bzt-W41) and the SIRTi (W137). STX1972 was found to inhibit cell growth in the nanomolar concentration range, whilst the rest of the compounds showed growth inhibition in micromolar concentration ranges. Bzt-W41 showed significant preferential selectivity for the TNBC MDA-MB-231 cell line versus the hormone-dependent MCF-7 cell line, while STX1972 and W137 exhibited only slight differential selectivity. Two combinations (STX + Bzt-W41 and Bzt-W41 + W137) exhibited synergism, whilst the STX + W137 combination exhibited antagonistic interaction. Cell cycle and apoptosis analysis revealed that STX1972 and Bzt-W41, alone and in combination, selectively induced cell cycle arrest and apoptosis in cancer cells. However, the W137 +Bzt-W137 combination did not show preferential targeting of breast cancer cell lines, with apoptosis induced equally or even more so in the control EA.hy926 cell line. STX1972 and Bzt-W41, as well as their paired combination, was further probed in aim of deciphering their individual and combined mode of action. STX1972, Bzt-W41 as well as the paired combination proved to selectively inhibit cancer targets resulting in several molecular changes, leading to downstream pathway activation which culminates in both apoptotic and autophagy-related cellular demise. The study contributed towards deducing possible hypotheses regarding the mechanistic behaviours of the individual compounds and elucidated their combined effect during dual treatment. Results warrant future studies to further probe the intricate interaction of pathways involved in the synergistic combination of antimitotics and epigenetic regulators as a novel anticancer therapeutic modality. / Thesis (PhD)--University of Pretoria, 2020. / Physiology / PhD / Unrestricted

This work explores a binary reagent approach to increase the specificity of covalent inhibitors. In this approach, two ligand analogs equipped with inert pre-reactive groups specifically bind a target biopolymer. The binding event brings the pre-reactive groups in proximity with each other. The two groups react, generating active chemical intermediates that covalently modify and inactivate the target. In the present study we compare the new approach with the traditional single-component reagent strategy using DNA polymerase from bacteriophage T4 as a model target biopolymer. We report the design and synthesis of two analogs of deoxythymidine triphosphate, a natural DNA polymerase substrate. Together, the analogs function as a binary nucleotide reagent which is activated by light with wavelengths 365 nm and longer. However, the active analog functions as a traditional single component reagent when activated by light with wavelengths at 300 nm and longer. The traditional single-component reagent efficiently inactivated DNA polymerase. However, in the presence of non-target protein the inactivation efficiency is greatly diminished. Under the same conditions, the binary nucleotide reagent also inactivated DNA polymerase, and the inactivation efficiency is not affected by the presence of the non-target protein. Our results validate that a binary approach can be employed to design highly specific covalent inhibitors. The binary reagent strategy might be useful as a research tool for investigation of ligand-protein interactions in complex biological systems and for drug design

Note:

Call number: LD2668 .T4 1978 C51 / Master of Science

published_or_final_version / abstract / Surgery / Doctoral / Doctor of Philosophy

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

No description available.