Biodegradable polymeric prodrugs for the delivery of antimalarial combination therapy
| dc.contributor.advisor | Klumperman, Lubertus | en_ZA |
| dc.contributor.advisor | Pfukwa, Rueben | en_ZA |
| dc.contributor.author | Fortuin, Lisa | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. | en_ZA |
| dc.date.accessioned | 2019-10-21T07:10:10Z | en_ZA |
| dc.date.accessioned | 2019-12-11T06:39:12Z | en_ZA |
| dc.date.available | 2022-10-28T03:00:12Z | en_ZA |
| dc.date.issued | 2019-12 | en_ZA |
| dc.description | Thesis (PhD)--Stellenbosch University, 2019. | en_ZA |
| dc.description.abstract | 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. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Die ontwerp en sintese van ‘n nuwe polimeriese pro-middel is bewerkstellig vir die sinergistiese antimalariële middelkombinasie van artemether en lumefantrine. Ten einde hierdie resultaat te bereik is ʼn lumefantrine-gekonjugeerde amfifiliese blokkopolimeer self-saamgestel in miselle met artemether vasgevang binne die hidrofobiese kern van die miselle. Om dit te ontwikkel was verskillende suur-labiele verbindings ondersoek vir hul vermoë om selektief skeiding te ondergaan onder die lae pH-toestande van die parasitoforiese voedselvakuool binne 'n Plasmodium-besmette rooibloedsel (pH 5.0) en stabiel te bly in die pH-toestande van bloedserum (pH 7.4). Die β-tiopropionaat-ester-, amied- en maleimiedverbindings, sowel as die asetale verbinding is bestudeer deur gebruik te maak van ¹H KMR kinetiese analise deur die sintese van sewe model-entmiddelsamestellings, waar die model-entmiddel (aromatiese groep) verbind is tot RAFT gepolimiseerde poli(N-vinielpyrrolidoon) (PVP). Die modelsisteem gebaseer op die asetaalverbinding het 'n t12⁄ van 107 uur teen pH 5.0 gehad en het stabiel gebly by pH 7.4, en het derhalwe die impetus verskaf vir die gebruik daarvan in die sintese van die antimalariële polimeerpro-middel. Die blokkopolimeer van PVP-blok-poli(δ-valerolaktoon) (PVP-b-PVL) is ondersoek en die sintese geoptimiseer om die ontwikkeling van PVP-blok-poli(α-allielvalerolaktoon) (PVP-b-PAVL) te fasiliteer, wat gebruik is as die polimeerdraer in die middel afleweringsisteem. Om dit te bereik is hidroksiefunksionele PVP gebruik as die makro-inisieerder in die ring-openingspolimerisasie van valerolaktoon of die alliel-afgeleide daarvan, waar daar bevind is dat triazabisiklodekeen die doeltreffender organokatalisator is in vergelyking met diazabisikloundekeen en kokatalisator thio-ureum. Die kristalisasie-gedrewe self-samestelling gedrag van PVP-b-PVL is in detail bestudeer en deur middel van TEM analise, is sferiese miselle, staafagtige miselle, silindriese miselle en lamella miselle waargeneem. 'n Nuwe metode om molekulêre morfologiese oorgange te bewerkstellig, is ontwikkel in die vorm van die vries-ontdooiingsproses. Lumefantrine is gekonjugeer met die blokkopolimeer in ‘n ‘kliek’-tipe reaksie via ‘n asetaalverbinding, nadat PVP-b-PAVL gekarboksileer en met EGVE gefunksionaliseer is. Artemether was fisies vasgevang binne die kern van sferiese miselle (114 nm in deursnee van DLS) deur gebruik te maak van die mede-oplosmiddelstegniek met THF as die nie-selektiewe oplosmiddel en water as die selektiewe oplosmiddel vir die hidrofobiese blok, PVL. Die teikenligand, ʼn lae molekulêre gewig peptied met volgorde ‘GSRSKGT’ is verander om tiolgroepe te dra deur gebruik te maak van SPDP verandering (kwantitatief) en dit was biogekonjugeer met die blokkopolimeer miselle deur disulfied-uitruiling (12 ± 3 mol%). Die pro-middel miselle het ‘n middelladingsinhoud van 20.5 gew.%, ʼn kritieke miselkonsentrasie van 2.0 10-3 mg·mL-1 wat termodinamiese stabiliteit aandui, en het tot vier dae binne ʼn gesimuleerde fisiologiese omgewing stabiel gebly. Onbeduidende hemolise vir rooibloedsele en nie-sitotoksisiteit vir HepG2 selle is gevind. Die pro-middel miselle kan geklassifiseer word as synde goeie aktiwiteit te toon teenoor P. falciparum parasiete, alhoewel hulle 'n hoër IC50-waarde van 1021.8 ± 270.9 nM toon in vergelyking met die vrye entmiddel kombinasie. Die onwikkelde middel afleweringsisteem is robuust, verstelbaar en nie-toksies vir gesonde selle, wat daarop dui dat dit potensiaal het vir die toepassing en verdere ontwikkeling in terapeutiese nanosisteme. | af_ZA |
| dc.description.version | Doctorate | en_ZA |
| dc.embargo.terms | 2022-10-20 | en_ZA |
| dc.format.extent | xix, 139, vii pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/106923 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Polymeric drugs | en_ZA |
| dc.subject.lcsh | Block copolymers | en_ZA |
| dc.subject.lcsh | Antimalarials | en_ZA |
| dc.subject.lcsh | Combination therapy | en_ZA |
| dc.title | Biodegradable polymeric prodrugs for the delivery of antimalarial combination therapy | en_ZA |
| dc.type | Thesis | en_ZA |