Hop (the Hsp90/Hsp70 organising protein) is a co-chaperone that acts as an adapter between the major molecular chaperones Hsp90 and Hsp70 during the cellular assembly of the Hsp90 complex. The Hsp90 complex regulates the stability and conformational maturation of a range of important cellular proteins, many of which are deregulated in cancer. In this study, we hypothesised that Hop knockdown inhibits proliferation and migration of cancer cells. We characterised the expression of Hop in cell models of different cancerous status, and provided evidence that Hop was upregulated in tumour cells compared to normal cell counterparts. Using an RNA interference approach, a 60-90% knockdown of Hop was achieved for up to 144 hours in the MDA-MB-231 and Hs578T breast cancer cell lines. Hop knockdown resulted in downregulation of the Hsp90 client proteins, Akt and Stat3, as well as a change in the expression of other Hsp90 co-chaperones, p23, Cdc37 and Aha1, while no change in the levels of Hsp90 or Hsp70 was observed. Silencing of Hop impaired cell proliferation in Hs578T cells but an increase in proliferation in MDA-MB-231, suggesting that the role of Hop in cancer cell proliferation was dependent on type of cancer cell. Hop knockdown in Hs578T and MDA-MB- 231 cells did not lead to any significant changes in the half maximal inhibitory concentrations (IC50) of selected small molecule inhibitors (paclitaxel, geldanamycin and novobiocin) in these cell lines after 72 hours. Hop knockdown cells were however, more sensitive than control cells to the Hsp90 inhibitors geldanamycin and novobiocin at earlier time points and in the presence of the drug transporter inhibitor, verapamil. Hop knockdown caused a decrease in cell migration as measured by the wound healing assay in both Hs578T and MDA-MB-231 cells. Hop was present in purified pseudopodia fractions of migrating cells, and immunofluorescence analysis showed that Hop colocalised with actin at the leading edges of pseudopodia, points of adhesion and at intercellular junctions of cells that have been stimulated to migrate with the chemokine stromal derived factor-1. Hop was able to bind to actin in vitro using actin cosedimentation assays, and silencing of Hop dramatically reduced the capacity of Hs578T cells to form pseudopodia. These results establish a correlation between Hop and actin dynamics, pseudopodia formation and migration in the context of Hop silencing, and collectively suggest that Hop plays a role in cancer cell migration. This study presents experimental evidence for a promising alternative to targeting Hsp90 and Hsp70 chaperones, a novel drug target in cancer therapy.

Breast cancer is one of the most common forms of cancer in not only South African women, but women all over the world. The molecular chaperone heat shock protein 90 (HSP90) is upregulated in cancer and is almost exclusively associated with proteins involved in intracellular signal transduction, thus it plays an important role in signalling pathways within the cell. In cancer, there is an aberrant activation of the Wnt signaling pathway, which results in stabilized β-catenin being able to translocate to the nucleus where it can trigger the transcription of oncogenes found to be involved in the self-renewal of cells. The level of β-catenin is usually kept in check by a destruction complex comprising glycogen synthase kinase 3-beta (GSK-3β), axin1, adenomatous polyposis coli (APC) which phosphorylate β-catenin, resulting in its ubiquitination and degradation. HSP90 has been found to be associated with GSK-3β, but whether this association is only transient is debatable. Very little is known about the association of HSP90 with other members of the Wnt pathway in breast cancer. In this study, we have attempted to further identify the direct associations between HSP90 and GSK-3β, β-catenin, p-β-catenin and axin1. Immunofluorescence and confocal microscopy co-localization studies suggested a potential association between HSP90 and these proteins. Treatment with HSP90 inhibitors, 17-AAG and novobiocin resulted in a shift of axin1 to what appeared to be the plasma membrane. The associations of HSP90 with GSK-3β, β-catenin, p-β-catenin and axin1 were confirmed biochemically by co-immunoprecipitation and inhibition using 17-AAG, geldanamycin and novobiocin. We showed, for the first time that HSP90 is associated in a possible complex with β-catenin, p-β-catenin and axin1 therefore is potentially involved in the modulation of p-β-catenin in the Wnt pathway through the stabilization of the destruction complex.

Current dogma suggests that the Heat Shock Protein (Hsp) molecular chaperones and associated co-chaperones function primarily within the cell, although growing evidence suggests a role for these proteins on the plasma membrane of cancer cells. Hsp90 does not function independently in vivo, but instead functions with a variety of partner chaperones and co-chaperones, that include Hsp70 and Hsp90/Hsp70 organising protein (Hop), which are thought to regulate ATP hydrolysis and the binding of Hsp90 to its client proteins. Hsp90 on the plasma membrane appears to have distinct roles in pathways leading to cell motility, invasion and metastasis. We hypothesised that Hsp90 on the plasma membrane is present as part of a multi-chaperone complex that participates in the chaperone-assisted folding of client membrane proteins in a manner analogous to the intracellular chaperone complex. This study characterised the membrane expression of Hsp90, Hsp70 and Hop in different cell models of different adhesive and migratory capacity, namely MDA-MB-231 (metastatic adherent breast cancer cell line), MCF-7 (non-metastatic adherent breast cancer cell line), U937 and THP1 (monocytic leukemia suspension cell lines). Membrane expression of the Hsps was analysed using a combination of subcellular fractionation, biotin-streptavidin affinity purification and immunofluorescence. This study provided evidence to suggest that Hsp90, Hsp70 and Hop are membrane associated in MDA-MB-231 and MCF-7 breast cancer cells. Hsp90, Hsp70 and Hop associated with the plasma membrane such that at least part of the protein is located extracellularly. Immunofluorescence analysis showed that Hsp90, Hsp70 and Hop at the leading edge may localize to membrane ruffles in MDA-MB-231 cells, in accordance with the published role of Hsp90 in migration. An increase in this response was seen in cells stimulated to migrate with SDF-1. By immunoprecipitation, we isolated a putative extracellular membrane associated complex containing Hsp90, Hsp70 and Hop. Using soluble Hsp90 and antibodies against membrane associated Hsp90, we suggested roles for soluble extracellular Hsp90 in mediating migration by wound healing assays and inducing actin reorganisation and vinculin-based focal adhesion formation. The effects of extracellular Hsp90 are mediated by signalling through an ERK1/2 dependent pathway. An anti-Hsp90 antibody against an N-terminal epitope in Hsp90 appeared to be able to overcome the death inducing effects of a combination of SDF-1 and AMD3100, while soluble Hsp90 could not overcome this effect. We propose that this study provides preliminary evidence that extracellular Hsp90 functions as part of a multi-chaperone complex that includes Hsp70 and Hop. The extracellular Hsp90 chaperone complex may mediate cell processes such as migration by modulating the conformation of cell surface receptors, leading to downstream signalling.

This thesis is divided into two parts and the rationale of the research conducted is based on the cytotoxicity of the prenylated quinones 1.24-1.29, isolated from the South African nudibranch Leminda millecra, against oesophageal cancer cells. The first part (Chapters 2 and 3) of the thesis initially documents the distribution of cytotoxic and antioxidant prenylated quinones and hydroquinones in the marine environment. We have been able to show, for the first time, that these compounds can be divided into eight structural classes closely related to their phyletic distribution. Secondly, we attempted to synthesize the two marine natural products 1.24 and 1.26 in an effort to contribute to an ongoing collaborative search with the Division of Medical Biochemistry at the University of Cape Town for new compounds with anti-oesophageal cancer activity. Accordingly, we followed the published synthetic procedure for 1.26 and, although we were unable to reproduce the reported results, we have generated five new prenylated quinone analogues 3.53-3.55, 3.63 and 3.71, which are a potentially viable addition to our ongoing structure-activity relationship (SAR) studies. Moreover, we embarked on a 7Li NMR mechanistic study for the synthesis of 3.2 from 3.1 which rewarded us with an improved and reproducible methodology for this crucial reaction that is detailed in Chapter 3. The second part of this thesis (Chapters 4 and 5) is concerned with a synthetic, structural, electrochemical and biological exploration of the 1,4-naphthoquinone nucleus as a primary pharmacophore in our search for new chemical entities which can induce apoptosis in oesophageal cancer cells, thus contributing to our overall ongoing SAR study in this class of compounds. Seven new naphthoquinone derivatves (4.19, 4.30, 4.31, 4.33 and 4.46-4.48) of the natural products 2-deoxylapachol (2.44), lapachol (4.1) and β-lapachone (5.2) were synthesized and 2-(1`-hydroxy-`-phenylmethyl)-1,4-naphthoquinone (4.29) was found to be the most cytotoxic (IC50 1.5 μM) against the oesophageal cancer cell line WHCO1, while 5.2, which is currently in phase II clinical trials as an anticancer drug, was found to be similarly active (IC50 1.6 μM). Electrochemical investigations of the redox properties of the benzylic alcohol derivatives 4.29-4.31 indicated a higher reduction potential compared to their oxidized counterparts 4.45-4.48, and this finding has been correlated to the increased activity of 4.29-4.31 against the WHCO1 cell line. Additionally, 4.29 is synthetically more accessible than either 1.26 or 5.2 and potentially a lead compound in our search for new and more effective chemotherapeutic agents against oesophageal cancer

To date, a significant portion of research has been devoted to understanding the biological role of the molecular chaperone, heat shock protein 90 (Hsp90), in cancer development and metastasis. Studies have alluded to over 300 clients for intracellular Hsp90, many of which are involved in oncogenic signaling pathways, making Hsp90 a bone fide drug target with several inhibitors already in clinical trials. In recent years, a limited number of extracellular Hsp90 clients have been elucidated with roles in cancer cell migration and invasion. Examples of such clients include matrix metalloproteinase-2 (MMP-2), LRP-1/CD91 and HER-2. Inhibition of extracellular Hsp90 using cellimpermeable inhibitors has been shown to reduce cancer cell migration and metastasis by a hitherto undefined mechanism. Using surface biotinylation and an enzyme linked immunosorbent assay, we provided evidence to support that Hsp90 was found extracellularly in cancers of different origin, cell type and malignancy. Next, we isolated extracellular Hsp90-containing complexes from MDA-MB-231 breast cancer cells using a cell impermeable crosslinker followed by immunoprecipitation and identified by mass spectrometry that the extracellular matrix protein, fibronectin, co-precipitated with Hsp90β. This interaction between Hsp90β and fibronectin was confirmed using pull down assays and surface plasmon resonance spectroscopy with the purified proteins. The ability of exogenous Hsp90β to increase the insoluble fibronectin matrix in Hs578T breast cancer cells indicated a role for Hsp90 in fibronectin matrix stability or fibrillogenesis. Hsp90 knockdown by RNA interference or inhibition with the small molecule inhibitor, novobiocin, resulted in a dose and time-dependent reduction of the extracellular fibronectin matrix. Furthermore, novobiocin was shown to cause the internalization of a fluorescently-labeled exogenous fibronectin matrix incorporated into the extracellular matrix by Hs578T cells. This suggested endocytosis as a possible mechanism for fibronectin turnover. This was supported by the colocalization of fibronectin with key vesicular trafficking markers (Rab-5 and LAMP-1) in small, intracellular vesicles. Furthermore, treatment with the vesicular trafficking inhibitor, methyl-β-cyclodextrin, resulted in a dose-dependent recovery in the extracellular fibronectin matrix following treatment with novobiocin. Taken together, these data provided the first evidence to suggest fibronectin as a new client of Hsp90 and that Hsp90 was involved in regulating extracellular fibronectin matrix dynamics.

M.Sc.

Magister Artium (Psychology) - MA(Psych) / The aim of this study is to explore the role of communication between the physician and women with breast cancer, and to examine women’s coping mechanisms from diagnosis through the management of the illness to its resolution. A qualitative methodology was utilised, with purposive sampling of participants from a public hospital in the Western Cape. A semi-structured interview was used to gather the data, after which a thematic analysis was conducted. The findings reveal the information exchange between physician and patient was clear, direct and understandable. Furthermore, the participants coped by accessing and using support from family and friends, by recourse to spirituality and prayer (bargaining with God, questioning of God), and by developing a positive attitude, with hope for recovery and acceptance. There were also emotional and psychological reactions from women in the sample when they received their diagnoses. This study may provide valuable insights into the experiences of women with stages I to III of breast cancer

Small molecules are powerful tools to probe biological systems and cure diseases. In the scope of this dissertation, small molecules were applied to study three distinct disease models: cancer, Sedaghatian-type spondylometaphyseal dysplasia (SSMD), and COVID-19. First, encouraged by the recently reported vulnerability of drug-resistant, metastatic cancers to GPX4 (Glutathione Peroxidase 4) inhibition, we examined the basis for nanomolar potency of proof-of-concept GPX4 inhibitors, which revealed an unexpected allosteric binding site. Through hierarchical screening of a lead-optimized compound library, we identified novel small molecules binding to this allosteric site. Second, a homozygous point mutation in the GPX4 gene was identified in three living patients with SSMD. With a structure-based analysis and cell models of the patient-derived variant, we found that the missense variant significantly changed the protein structure and caused substantial loss of enzymatic function. Proposed proof-of-concept treatments were subsequentially validated in patient fibroblasts. Our further structural investigation into the origin of the reduced enzymatic activity revealed a key residue modulating GPX4 enzymatic function. We also found that the variant alters the degradation of GPX4, unveiling the native degradation mechanism of GPX4 protein. Third, driven by the recent urgent need for COVID-19 antiviral therapeutics, we utilized the conservation of 3CL protease substrate-binding pockets across coronaviruses to identify four structurally divergent lead compounds that inhibit SARS-CoV-2 3CL protease. With structure-based optimization, we ultimately identified drug-like compounds with < 10 nM potency for inhibiting the SARS-CoV-2 3CL protease and blocking SARS-CoV-2 replication in human cells.

Thesis (M. Sc. (Biochemistry)) -- University of Limpopo, 2019 / Cervical cancer is the fourth most common cancer in females, and the seventh of all cancer types in both genders, with an estimated 500,000 new cases each year. As with liver cancer, a large majority (around 85%) of the global burden occurs in the less developed regions, where it accounts for almost 12% of all female cancers. About 90% of cervical cases are associated with human papillomavirus (HPV) as a causative agent and this virus is frequently transmitted through sexual contact involving exchange of fluids (Walboomers et al., 1997). Due to the ineffectiveness, undesirable side effects and costly treatment for the disease the current study was aimed at determining the anti-proliferative effects of extracts of selected medicinal plants for their anticancer activity on HeLa cell line invitro. In order to accomplish the outcome of this research study, medicinal plants (Toona cilliata, Seriphium plumosum and Schkuhria pinnata) from Limpopo Province (South Africa) with history of traditional use on cervical cancer-associated patients were selected. The Toona cilliata plant leaves were collected from Tzaneen, area while Seriphium plumosum and Schkuhria pinnata leaves were collected from Mankweng area. The dried leaves were grounded into powder and extracted using acetone. Thereafter, extracted leaf materials of selected plants were subjected to fingerprint profiling using TLC silicon coated plates immersed in tanks with different mobile phases (TEA, CEF and EMW) of various increasing polarities since. The plates were sprayed with vanillin/H2SO4, dried and visualised under UV light. Scavenging ability of the plant extracts was determined through investigating the presence of antioxidant activities using 0.2% of the 2,2- diphenyl-1- picrylhydrazyl (DPPH) indicator. The quantitative presence of total phenolic and flavonoids contents was also determined using garlic and quercetin as standards, respectively. Quantitative antioxidant scavenging activities were also determined and ascorbic acid was used as a positive control. This was followed by quantitative determination of ferric reducing power and thereafter the EC50 values of the extracts were determined by linear regression. Cell proliferation or viability was determined using the 3[4, 5 dimethylthiazol-2-yl]-2-5 diphenyltetrazolium (MTT) assay with actinomycin as a xv positive control and untreated cells as the negative control. Apoptotic effects of the extracts were determined using the Annexin V Fluos staining kit. This was followed by determining whether apoptosis was calcium dependent or independent using a calorimetric assay. In comparing the acetone extract yield per 10 g leaves of plants, Toona cilliata leaves exhibited the highest yield followed by Seriphium plumosum and with the least yield from Schkuhria pinnata. The finger print profile showed the prominent separation and was achieved from all the plants when using the non-polar TEA solvent. All plants were shown to contain extracts with varying levels of antioxidant activity especially when using CEF and EMW mobile phases. When evaluating the total phenolic and flavonoids contents all plant extracts exhibited presence of phenolic compounds with high presence observed in Seriphium plumosum and Toona cilliata. Extracts from Seriphium plumosum and Toona cilliata showed to have higher concentrations of phytochemicals that may be of a benefit in antioxidant activities as compared to Schkuhria pinnata in relation to the positive control and a similar trend were observed in the ferric reducing power assay. Extracts from Seriphium plumosum were shown to have the best IC50 scavenging values followed by Toona cilliata and Schkuhria pinnata respectively. All the plants exhibited free radical scavenging abilities with Seriphium plumosum shown to possess higher activities in comparison with the positive control. All the plants exhibited a dose-dependent cytotoxicity activity against the HeLa cervical cell line. Evidence of induced apoptotic activity was observed in HeLa cells when using extracts from Seriphium plumosum and Toona cilliata. Induction of apoptosis by plant extracts was shown to be calcium dependent as there was a decrease in calcium concentration with a decrease in the number of viable cells. In conclusion, the leaf extracts from Toona cilliata, Seriphium plumosum and Schkuhria pinnata contain compounds of various polarities with freeradical, antioxidant and anti-cancerous activities that may be beneficial if further studies are conducted to identify chemical compounds that may inhibit anticervical cancer activities.

The goal of our research was to find a cancer treatment that was both effective and cancer specific, sparing immune and normal tissues. We evaluated the efficacy of a combinatorial treatment using the glycolytic inhibitor 3-bromopyruvate and the fatty acid metabolism inhibitor fenofibrate in cancer, immune and normal tissue cells lines. Treatment of the human breast cancer MCF-7 with 3-bromopyruvate and fenofibrate resulted in increased cell death and decreased colony formation. In the immune cells known as peripheral blood mononuclear cells our combinatorial treatment displayed less toxicity than the traditional chemotherapy doxorubicin. Our combinatorial treatment displayed greater toxicity than doxorubicin towards an established breast cell line MCF- 10A, described in the literature as representing normal breast cells. We have shown for the first time a synergistic relationship between 3-bromopyruvate and fenofibrate. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection