Browsing by Author "Mbizana, Siyasanga"

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    Coordinated autophagy modulation overcomes glioblastoma chemoresistance through disruption of mitochondrial bioenergetics
    (Nature Research, 2018-07-09) Kriel, Jurgen; Muller-Nedebock, Kristian; Maarman, Gerald; Mbizana, Siyasanga; Ojuka, Edward; Klumperman, Bert; Loos, Ben
    Glioblastoma Multiforme (GBM) is known to be one of the most malignant and aggressive forms of brain cancer due to its resistance to chemotherapy. Recently, GBM was found to not only utilise both oxidative phosphorylation (OXPHOS) and aerobic glycolysis, but also depend on the bulk protein degradation system known as macroautophagy to uphold proliferation. Although autophagy modulators hold great potential as adjuvants to chemotherapy, the degree of upregulation or inhibition necessary to achieve cell death sensitisation remains unknown. Therefore, this study aimed to determine the degree of autophagy modulation necessary to impair mitochondrial bioenergetics to the extent of promoting cell death onset. It was shown that coordinated upregulation of autophagy followed by its inhibition prior to chemotherapy decreased electron transfer system (ETS) and oxidative phosphorylation (OXPHOS) capacity, impaired mitochondrial fission and fusion dynamics and enhanced apoptotic cell death onset in terms of cleaved caspase 3 and cleaved PARP expression. Therefore, coordinated autophagy modulation may present a favourable avenue for improved chemotherapeutic intervention in the future.
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    Poly(N-vinylpyrrolidone)-polypeptide based antitumor nanocarrier and cell viable ʟ-arginine, ʟ-aspartic acid and glycine terpolymer
    (Stellenbosch : Stellenbosch University, 2018, 2018-12) Mbizana, Siyasanga; Klumperman, Bert; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Currently, there are few pH responsive nanocarriers based on polypeptide hybrid copolymers, in which the bioactive molecule is conjugated through a degradable linker on the carrier. The first objective of the study, was to prepare a pH responsive nanocarrier based on poly[N-vinylpyrrolidone-b-poly(cysteine-co-glycine)] (PVP-PP) copolymer. The PVP-PP copolymer will be used to deliver an antitumor drug to pathological areas. The dual functional PVP macroinitiators, i.e. acetal-PVP-NH2 (ac-PVP-NH2) and PVP-NH2 were prepared through RAFT mediated polymerization with a phthalimide functionalized RAFT agent. To improve control over polymerization, semi-batch assisted polymerization was chosen followed by subsequent post-polymerization modification reactions to achieve the macroinitiators. Prior to PVP initiated copolymerizations of glycine N-carboxyanhydride NCA (Gly NCA) and S-benzyl-ʟ-cysteine NCA (Bz-Cys NCA), n-butylamine initiated copolymerization kinetics of the two NCAs were investigated to understand their reactivity towards a propagating primary amine end-capped chain. Subsequently PVP-PP block copolymers, with different block ratios and varying the overall copolymer length were prepared. The Bz protecting groups were removed from Cys pendant groups in the PP chain with HBr catalysed acidolysis, followed by conjugation of hydroxychloroquine drug to the free thiols via an acid labile linker. The PVP-PP/drug conjugates self-assembled to spherical micelles in aqueous solutions, the micelles were characterized with TEM and DLS techniques. In addition, drug release studies were carried out and the polymer-drug conjugates were evaluated for cell viability studies, where the released drug decreased cell viability of the Glioma cell lines. The second objective of the study was to prepare arginine (R)-glycine (G)-aspartic acid (D) RGD containing terpolypeptides via ring opening terpolymerizations of β-Bz-ʟ-aspartic acid NCA (Bz-Asp NCA), Gly NCA and Nδ-carbobenzyloxy-ʟ-ornithine (R′) NCA (Z-Orn NCA) (DGR′). The DGR′ sequence is the precursor to RGD sequence which is found in glycoproteins and promotes cell adhesion and proliferations. In the terpolymers, the natural RGD sequence is referred as DGR, due to the mechanism of ROP of NCAs adapted in the study, which proceeds from C- to N- terminus whilst peptide sequences are listed from N- to C- terminus. Binary copolymerizations of the three NCAs were investigated in order to understand their copolymerization kinetics and 6 reactivity ratios were obtained. The reactivity ratios were used to model terpolymerization of the NCAs and were found to define the terpolymerization of these NCAs. Hence, they were used in conjunction with statistical equations to maximize the probability of occurrence of the DGR′ sequence in terpolymers. Subsequently, the ornithine (R′) units in the terpolymers were converted to arginine units and terpolymers with high probability of DGR sequences displayed improved cell proliferation and process formation when compared to natural polymers with the RGD tripeptide sequence.