4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Biophysical studies of metal chelate binding by HSA: Towards an understanding of metallodrug transport(University of the Witwatersrand, Johannesburg, 2023) Sookai, Sheldon; Munro, OrdeHuman serum albumin (HSA) is the most abundant blood protein, transporting many exogenous compounds including clinically deployed and investigational drugs that are generally organic in nature. HSA may largely influence the pharmacokinetics and pharmacodynamics of these drugs. Therefore, studying their interactions with HSA is vital in progressing drug development. In this thesis we present work on the synthesis and characterisation of five Schiff base bis(pyrrolide-imine) ligands that were metalated with either Au(III) (Chapters 2 and 3) or Pt(II) (Chapters 4 and 5). One of the ligands H2L1 was further metalated with Ni(II) and Pd(II) (Chapter 6). In Chapters 2 and 3 focus on a patented class of anti-cancer bis(pyrrolide-imine) Au(III) Schiff base chelates. Three Au(III) chelates were synthesized in Chapter 2 and underwent National Cancer Institute (NCI)-60 cytotoxic screening. Among them, AuL1 and AuL3 underwent full-five dose testing and recorded GI50 values of 7.3 µM and 11.5 µM, and IC50 values of 15.7 µM and 30.9 µM, respectively. AuL1 was tested further and found to be an interfacial poison of topoisomerase II at 0.5–5 µM and a catalytic inhibitor at 50 µM. In Chapter 3, two chiral tetradentate cyclohexane-1,2-diamine-bridged bis(pyrrole-imine) Au(III) complexes were reported, both of which were found to be cytotoxic in the NCI-60 screen. The chiral Au(III) chelates had a different mode of action compared to AuL1. Hierarchical cluster analysis suggest that their mode of action is similar to that of taxol. All five Au(III) chelates bound to HSA with moderate affinity (104–105 M–1) and minimally perturbed the structure of the protein. This highlights the potential for the Au(III) complexes to be transported by the HSA-mediated pathway. Chapters 4 and 5 focused on the synthesis of novel and previously reported Pt(II) Schiff base chelates to spectroscopically and computationally study their interaction with HSA and elucidate if the chelates could act as theranostic agents. It was found that switching the linking bis(imine) carbon linkage altered the binding affinity of the complex. However, the Pt(II) ion ensured that all three Pt(II) chelates preferred binding to Sudlow’s site II of HSA. The data was corroborated by molecular docking simulations and ONIOM calculations. Only 2 was found to be cytotoxic when irradiated with UV light but was found to act as a photosensitizer rather than a theranostic agent. Chapter 6 investigated the influence of d8 metal ions (Ni(II), Pd(II) and Pt(II) within the same ligand scaffold (H2PrPyrr) binding to HAS, which was investigated by steady state fluorescence quenching. The affinity constants, Ka, ranged from -3.5 -103 M−1 to-1- 106 M–1 at 37 C, following the order Pd(PrPyrr) > Pt(PrPyrr) > Ni(PrPyrr) >H2PrPyrr. The Pd(II) chelate was prone to hydrolysis and had a unique binding mode which we attribute to the unusually high binding affinity. The complexes uptake is enthalpically driven, hinging mainly on London dispersion forces. In summation, twelve metal complexes were successfully synthesized, of which 11 bound to HSA with a moderate binding affinity. The Au(III) chelates preferred Sudlow’s site I, while the Pt(II) chelates preferred Sudlow’s site II. Overall, the metal complexes bound fully intact to HSA.Item Synthesis, characterization and investigation of the mode of action in the anticancer activity of novel platinum complexes(University of the Witwatersrand, Johannesburg, 2024) Peega, Tebogo; Harmse, Leonie; Kotzé, Izak. A.Cancer remains a global health concern, causing approximately 10 million deaths in 2020. Lung cancer, accounting for 18% of cancer-related deaths, and colorectal cancer, contributing 9.4%, are major contributors to this alarming statistic, emphasizing the urgent need for innovative and effective treatment options. Despite the success of platinum-based drugs such as cisplatin, carboplatin, and oxaliplatin, their limitations and severe adverse effects necessitate the exploration of alternative chemotherapeutic agents. This research project focused on synthesizing and characterizing square planar platinum(II) complexes bearing variations of two bidentate coordinating ligands; disubstituted acylthiourea and diimine ligands, each possessing unique physical and chemical properties. A series of cationic [Pt(diimine)(Ln-κO,S)]Cl complexes were successfully synthesized and characterized using nuclear magnetic resonance spectroscopy, infrared spectroscopy, mass spectrometry, and elemental analysis. The anticancer activity of these complexes was evaluated against two lung cancer cell lines, A549 and H1975, and a colorectal cancer cell line, HT-29. In vitro cytotoxicity studies included the determination of IC50 values of active complexes and assessing their cell death mechanisms through multiple biochemical marker assays. These included annexin-V binding, caspase-3/7 and caspase-8 activity, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) and immunofluorescence for the expression of key proteins involved in the DNA damage response and oxidative stress response, such as p21 and haemoxygenase-1 (HO-1). A proteome array was employed to investigate the effects on apoptosis-associated proteins. The results indicated that these platinum complexes were more cytotoxic than cisplatin with IC50 values ranging between 0.68 μM and 2.28 μM. Further investigation showed that the platinum complexes induced cell stress, chromatin condensation, nuclear fragmentation, increased phosphatidylserine (PS) on the outer cell membranes and activated caspase-3/7. Platinum complexes induced intrinsic apoptosis in cancer cells, as evidenced by the loss of mitochondrial membrane potential and the absence of caspase-8 activity. Elevated ROS levels, increased HO-1 expression and increased expression of p21 suggested oxidative stress and DNA damage as the trigger source for intrinsic apoptotic cell death. The active complexes downregulated pro-survival proteins (IGFs) in lung cancer cells and anti-apoptotic proteins (survivin and HSP70) and upregulated pro-apoptotic proteins (p21, TRAIL R2), across the three cancer cell lines, indicating potential dual activation of apoptotic pathways. DNA binding studies indicated groove binding and intercalation as the mode of interaction with DNA. The findings highlight the potential of these platinum complexes as promising candidates for further development as cancer therapeutics.Item Implication of Regulated Cannabis Legalisation on Wellbeing and Economic Growth(University of the Witwatersrand, Johannesburg, 2022) Quarshie, Emmanuel; Alagidede, Imhotep PaulThis is a thesis on the cost benefit analysis of cannabis legalisation, public (mis)perception about cannabis usage and cannabis users, the medical application of cannabinoids and their commercial and industrial potential in the new global political economy. The study shows that, although there are misconceptions about cannabis, there is still much to unpack about its effects on human well-being. Drawing on both qualitative and quantitative cross-country dataset from Ghana and South Africa, the study employed a logit model to address the following questions: (a) What does society know about cannabis and its industrial and medical applications? (b) What is the evidence-based scientific claims of cannabis regarding human well-being? (c) What are the existing gaps between perception and knowledge? Among the contributions, this study clarifies the often-misunderstood position of cannabis in society and illuminates the blind side of the role of cannabis as an economic enabler in the post pandemic world. More importantly, while some schools of thought project cannabis as a gateway drug to the infernal realm, this study provides evidenced based on real-time practical experience from well- informed and educated users. The study provides a model for regulated cannabis legalisation, a proper guide on value-added supply chain mechanism, and guiding principles to ensure the model functions properly, based on lessons and best practices from countries that have legalized cannabis, such as the Netherlands, Canada, Lesotho, Malawi, Zambia, South Africa, and Zimbabwe. This study further establishes empirical and theoretical foundations for the key thematic subjects of cannabis use, as well as a policy direction pertaining to its regulated legalisation, prohibition, or decriminalization in Ghana and South Africa. Given the disconnect between knowledge and perception about cannabis, the study recommended knowledge enhancement and adequate advocacy on the pros and cons of cannabis for society to enhance understanding of the benefits and its side effects to provide evidence-based guidance on the medical application and industrial potentialsItem Management factors contributing to delays in cancer drug registration in South Africa(University of the Witwatersrand, Johannesburg, 2022) Shai, Mmatsela LorraineOne of the leading causes of sickness and early death worldwide is cancer.The cancer mortality is especially high in low and middle-income countries (LMICs). The National Medicines Regulatory Authorities (NMRAs) play an important role to ensure that drugs meet the quality, safety, and efficacy requirements made available to patients. The National regulatory authorities are also accountable for enforcing regulatory demands promptly andensuring that patients have timely access to drugs. Delays in the registration of cancer drugs will have an adverse impact on cancer patients such as poor quality of life and early death. Section 27 of the Constitution of South Africa guarantees the right to have access to health care service. The study aims to determine management factors that contribute to delays in the registration of cancer drugs. As a result, the research contributes to the theoretical body of knowledge. The study took a qualitative approach by sending out an interview schedule to 10 South African pharmaceutical companies for self-completion. Several methods were considered in determining a suitable study strategy, study design, research approach, and self-administered interview questions. These methods were implemented in order to achieve the study’s objectives. This served as a primary source of information. The interview questions were completed and uploaded for analysis using the Qualtrics XM tool. The information that was gathered showed that all of the participants have to deal with the problem of registration delays for cancer drugs. The findings could help to clarify the overall critical factors, their impact, and the relationship between the key factors and stakeholders involved in cancer drug registration. The uniqueness of this research lies in the results provided by different participants from the pharmaceutical industry and in evaluating their perspectives on these delays. The research adds significant value through its evidence based on the responses receivedItem Evaluation of outcomes in patients with pancreatic cancer and Human Immunodeficiency Virus at Chris Hani Baragwanath Academic Hospital and the Donald Gordon Medical Centre, Johannesburg(2024) Wing, Jessica RobertaBackground: Cancers which are not associated with Acquired Immune Deficiency Syndrome (AIDS) are increasing in incidence and mortality in the HIV-positive population. Pancreatic cancer (PC) is projected to be the second most common cause of cancer-related death by 2030. No literature exists on patients with PC and concomitant human immunodeficiency virus (HIV) infection in South Africa (SA), which has the highest number of HIV-positive people in the world. Objectives: To compare the demographics, stage, histological grade of disease, and survival outcomes of HIV-positive compared to HIV-negative patients diagnosed with PC. Methods: Records of patients diagnosed with PC were collected from Chris Hani Baragwanath Academic Hospital (CHBAH) and the Wits Donald Gordon Medical Centre (DGMC) from the 1 st of January 2013 to the 31st of December 2018. A total of 240 patients’ records were obtained. Demographic, clinical, and survival data were collected. Results: There were predominantly black Africans (64.6%) and males (54.6%) in the study. Although overall survival between the HIV-positive and negative patients did not differ (p=0.051), the median time of survival from presentation was significantly shorter in the HIV-positive compared to the HIV-negative patients (2.1 months; IQR 1.2-6.0 vs. 4.7 months; IQR 1.6-13.0; p=0.017). The HIV-positive cohort presented at a significantly younger age compared to the negative cohort (54.6; ±9.6 vs 62.4; ±11.1; p=0.0001) and at a more advanced stage of disease (72.2% vs. 43.1%; p=0.017). No difference was found between the histological grade of PC in both cohorts (p=0.298). The median survival time for HIV-positive patients on therapy at presentation was significantly longer compared to patients who were not (3.0; IQR 1.3-7.8 vs 1.1 months; IQR 0.9-1.9; p=0.037). Overall survival in patients who underwent pancreaticoduodenectomy at Wits DGMC was shown to be higher compared CHBAH V (41.7% vs. 12.5%; p=0.049). The majority of the patients presented with regionally advanced (30.6%) and metastatic (50.3%) disease. Conclusion: This is the first study in SA to provide insight into the clinical disease profile and survival outcomes of HIV-positive patients diagnosed with PC. This study has shown that HIV-infected patients with PC have a specific disease profile. Therefore, testing for HIV infection should be included in the management of all patients with PC, a higher index of suspicion for cancer should be maintained in younger HIV-positive patients and initiation of Antiretroviral treatment (ART) must be timeous.