Browsing by Author "Fortuin, Lisa"

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    Biodegradable polymeric prodrugs for the delivery of antimalarial combination therapy
    (Stellenbosch : Stellenbosch University, 2019-12) Fortuin, Lisa; Klumperman, Lubertus; Pfukwa, Rueben; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: The design and synthesis of a novel polymeric prodrug was achieved for the synergistic antimalarial drug combination of artemether and lumefantrine. To this end, a lumefantrine-conjugated amphiphilic block copolymer (BCP) was self-assembled into micelles with artemether entrapped within the hydrophobic core of the micelles. To develop this, different acid-labile linkages were investigated for their ability to selectively cleave under the low pH conditions of the parasitophorous food vacuole within a Plasmodium-infected red blood cell and remain stable in the neutral pH conditions of serum. The β-thiopropionate ester, amide and maleimide linkages as well as the acetal linkage were studied using 1H NMR spectroscopy-based kinetic analysis, by synthesising seven model drug compounds, where the model drug (aromatic group) was linked to RAFT-made poly(N-vinylpyrrolidone) (PVP). The model system based on the acetal linkage had a t12⁄ of 107 h at pH 5.0, and remained stable at pH 7.4, providing the impetus for its use in the synthesis of the antimalarial polymeric prodrug. The parent BCP of PVP-block-poly(δ-valerolactone) (PVP-b-PVL) was explored and the synthesis optimised to aid in the development of PVP-block-poly(α-allylvalerolactone) (PVP-b-PAVL), used as the polymer carrier in the drug delivery system. To achieve this, hydroxy-functional PVP was applied as the macroinitiator in the ring-opening polymerisation of δ-valerolactone or its allylated derivative, where triazabicyclodecene was found to be the more effective organocatalyst compared with diazabicycloundecene and cocatalyst thiourea. The crystallisation-driven self-assembly (CDSA) behaviour of PVP-b-PVL was studied in detail where spherical micelles, cylindrical micelles and lamellar micelles were observed using TEM analysis. A novel method to induce micellar morphological transitions was developed in the form of the freeze-thaw process. Lumefantrine was conjugated to the BCP in a ‘click’-type reaction via an acetal linkage, after PVP-b-PAVL was carboxylated and functionalised with EGVE. Artemether was physically entrapped within the core of spherical micelles (114 nm in diameter from DLS) using the cosolvent technique with THF as the non-selective solvent and water as the selective solvent for the hydrophilic block, PVP. The targeting ligand, a low molecular weight peptide with sequence ‘GSRSKGT’ was modified to bear thiol groups using succinimidyl 3-(2-pyridyldithio)propionate (SPDP) modification (quantitative) and it was bioconjugated to the BCP prodrug micelles using disulfide exchange (12 ± 3 mol%). The prodrug micelles had a drug loading content of 20.5 wt.%, a critical micelle concentration of 2.0  10-3 mg·mL-1 indicating thermodynamic stability, and remained stable in a simulated physiological environment for up to four days. Negligible haemolysis to RBCs and non-cytotoxicity to HepG2 cells were found. The prodrug micelles can be classified as having good activity towards P. falciparum parasites; however, they exhibit a higher IC50 value of 1021.8 ± 270.9 nM compared with the free drug combination. The developed drug delivery system is robust, tuneable and non-toxic to healthy cells, indicating that it holds potential for its application and further development in therapeutic nanosystems.
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    Facile route to targeted, biodegradable polymeric prodrugs for the delivery of combination therapy for Malaria
    (American Chemical Society, 2020-06) Fortuin, Lisa; Leshabane, Meta; Pfukwa, Rueben; Coertzen, Dina; Birkholtz, Lyn-Marie; Klumperman, Bert
    A facile synthetic methodology has been developed to prepare multifaceted polymeric prodrugs that are targeted, biodegradable, and nontoxic, and used for the delivery of combination therapy. This is the first instance of the delivery of the WHO recommended antimalarial combination of lumefantrine (LUM, drug 1) and artemether (AM, drug 2) via a polymeric prodrug. To achieve this, reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization of N-vinylpyrrolidone (NVP) was conducted using a hydroxy-functional RAFT agent, and the resulting polymer was used as the macroinitiator in the ring-opening polymerization (ROP) of α-allylvalerolactone (AVL) to synthesize the biodegradable block copolymer of poly(N-vinylpyrrolidone) and poly(α-allylvalerolactone) (PVP-b-PAVL). The ω-end thiol group of PVP was protected using 2,2′-pyridyldisulfide prior to the ROP, and was conveniently used to bioconjugate a peptidic targeting ligand. To attach LUM, the allyl groups of PVP-b-PAVL underwent oxidation to introduce carboxylic acid groups, which were then esterified with ethylene glycol vinyl ether. Finally, LUM was conjugated to the block copolymer via an acid-labile acetal linkage in a “click”-type reaction, and AM was entrapped within the hydrophobic core of the self-assembled aggregates to render biodegradable multidrug-loaded micelles with targeting ability for combination therapy.
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    Modified chitosan nano-substrates for mycobacterial capture
    (Stellenbosch : Stellenbosch University, 2015-12) Fortuin, Lisa; Cronje, Lizl; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Tuberculosis (TB) is one of the world’s deadliest diseases, with one third of the population being infected by it. The diagnosis of active tuberculosis entails finding and identifying Mycobacterium tuberculosis (Mtb), the causative pathogen in a specimen of bodily fluid from the patient. Multiple samples will improve the diagnostic yield and specimen volumes should therefore be as large as possible, which is often challenging for patients and especially younger children. Alternatively, a smaller volume could be required if there was a manner in which to concentrate the bacteria within a specimen, through use of a substrate which has an affinity for the pathogenic species. Polymers having intrinsic cellular activity are of interest as such substrates, one such being the natural polysaccharide, chitosan. In this thesis, a variety of modified chitosan derivatives were prepared as potential Mtb-capturing substrates. This was achieved by modifying chitosan with a variety of moieties, selected based on possible interactions with the Mtb cell wall, to render various quaternary ammonium salts of the polymer chitosan. The quaternized chitosan derivatives were then used to synthesize nano-substrates having an affinity for Mtb. Polymer coated superparamagnetic magnetite nanoparticles (SPMNs) were synthesized via an in situ co-precipitation technique, in which modified chitosan is able to chelate with the metal core. Polymer nanofibers were also electrospun via the electrospinning technique. The prepared derivative, N-trimethylammonium chitosan chloride (TMC), was electrospun into nanofibers by blending with suitable non-ionogenic polymers, namely polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyvinyl pyrrolidone (PVP) and polyacrylamide (PAM), required to facilitate nanofiber formation. Affinity studies were conducted between the modified chitosan nano-substrates and the bacillus Calmette-Guérin (BCG) strain of Mycobacterium bovis, the attenuated Mtb-mimic bacteria, for evaluation as mycobacterium capturing substrates. The successful capture of BCG onto the surfaces of the various modified chitosan nanofibers and modified chitosan coated superparamagnetic nanoparticles was confirmed by fluorescence microscopy (FM), light microscopy (LM), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). Analysis of the FM, TEM and FE-SEM images indicated that the chitosan coated nanoparticles functionalized with a C12 aliphatic quaternary ammonium moiety (CS-qC12), captured the most BCG through a combination of ionic and hydrophobic interaction. TMC blended with PVA, to produce nanofibers crosslinked with genipin, were found to have the strongest interaction with BCG of the nanofibrous mats tested. These findings were corroborated by water contact angle measurements, which established that PVA was the least hydrophilic of the non-ionogenic polymers and had hydrogen bond donating groups only, factors influencing the cellular adhesive properties of affinity substrates.