Browsing by Author "Kaschula, Catherine Hart"

Now showing 1 - 5 of 5
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    Haematin-Quinoline interactions and structure-activity relationships in the antimalarial chloroquine and related compounds
    (2002) Kaschula, Catherine Hart; Egan, Timothy J; Hunter, Roger
    The nature of the ferriprotoporphyrin IX (Fe(III)PPIX) antimalarial drug target and its interactions with aminoquinolines was investigated spectrophotometrically. The antiquity of malaria, which is caused by protozoan parasites of the genus Plasmodium, is demonstrated by the host specificity of over 100 parasite species found in reptiles, birds and mammals. The four species of plasmodia that infect man are P. vivax, P. malariae, P. ovale and P. falciparum; of which P. falciparum is the most deadly (Bruce-Chwatt 1981 ).
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    An investigation into the anti-cancer mechanism of garlic-related organosulfur compounds
    (2014) Smith, Muneerah; Parker, Iqbal; Kaschula, Catherine Hart
    Crushed garlic contains organosulfur compounds (OSC), which are reported to have cancer chemotherapeutic properties both in vitro and in vivo. A library of 15 organosulfur analogues were obtained as mechanistic probes in WHCO1 oesophageal cancer cells. Structure-activity studies showed a positive correlation between the anti-proliferative-IC50 of disulfides and the relative stability of their anion leaving groups, as assessed through resonance and quantified by predictive pKa-values.
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    Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene
    (2016) Kusza, Daniel Andreas; Hunter, Roger; Kaschula, Catherine Hart
    Ajoene, a garlic-derived natural product and its structural analogues are strongly cytotoxic to cancer cells. These compounds are however known to exhibit low blood stability and erythrocyte toxicity. This thesis reports on the synthesis of eight ajoene analogues designed to probe structure-activity relations into cancer cell cytotoxicity and blood stability. Structural variations included introduction of different solubility enhancing terminal groups (amide and phenol) as well as variations in the sulfoxide / vinyl-disulfide core. The phenol ajoene analogues were found to be more cytotoxic against WHCO1 oesophageal cancer cell proliferation than the corresponding amides. The structureactivity data support a thiolysis mechanism where ajoene forms a mixed disulfide with a reactive cysteine residue on a protein target which leads to both its cytotoxicity and blood instability. This in turn is mediated by the reactivity of the disulfide pharmacophore which is enhanced by the vinyl group. The sulfoxide functional group is perceived as modulating disulphide reactivity by an inductive electron-withdrawal through the aliphatic σ-framework. The dihydroajoenes emerged as attractive candidates for further cancer therapeutic development with improved blood stability with a half-life around 120 minutes and good cancer cell cytotoxicity (IC₅₀ of approximately 20 μM). A spectrophotometric and proteomic binding study demonstrated S-thiolation between ajoene and the cysteine 93 residue in the -subunit of haemoglobin which may explain the observed blood instability. A biotinylated ajoene analogue was designed and synthesised to identify ajoene's protein targets within the cancer cell. This was achieved using a convergent "Click"-strategy, involving azidated ajoene and biotin-alkyne. Both the biotin-ajoene and the azide-ajoene showed strong cytotoxicity against WHCO1 cancer cells. An immunoblotting experiment showed the successful biotinylation of haemoglobin, as a model protein by both whole probe and an in situ "Click"-reaction. This biotinylated probe can be used in future work to identify the ajoene protein targets in cancer cells.
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    Molecular mechanisms involved in the anticancer activity of BISPMB in oesophageal cancer cells
    (2016) Siyo, Vuyolwethu Penelope; Parker, Iqbal; Kaschula, Catherine Hart
    BisPMB (E, Z)-1,8-(Bis-p-methoxyphenyl)-2,3,7-trithiaocta-4-ene 7-oxide) is a synthetic analogue of the garlic compound ajoene. It is 12 times more active at inhibiting the growth of oesophageal squamous cell carcinoma WHCO1 cells and displays selectivity for cancer cells over normal cells. BisPMB is therefore attractive as a potential cancer therapeutic. In this study, bisPMB was found to inhibit WHCO1 cancer cell proliferation in a time and concentration dependent manner with 24 hour IC50's between 6.7 - 8.1 μM against a range of oesophageal cancer cell lines including WHCO1, KYSE30 and WHCO6. The normal oesophageal epithelial cell line, HET1A was found to be five times less responsive to bisPMB. Furthermore, bisPMB was found to induce apoptosis and G2/M cell cycle arrest in WHCO1 cells. Gene expression data obtained from the microarray analysis showed that bisPMB primarily targets the unfolded protein response (UPR) in WHCO1 cells. We also found that bisPMB deregulated the ER stress genes involved in protein processing in the endoplasmic reticulum and also deregulated MAPK pathways in WHCO1 cells. At a protein level, bisPMB was found to induce an increase in protein ubiquitination and in the expression of ER stress and UPR genes ATF4, Grp78 and CHOP in WHCO1 cells. We also observed a decrease in ATF6 90 kDa protein and transient XBP-1 mRNA splicing. The activation of p38, JNK and ERK MAPK pathways in bisPMB treated WHCO1 cells was also observed. Furthermore siRNA mediated knock-down of CHOP abolished the anti-proliferative effect of bisPMB in WHCO1 cells. However, inhibition of JNK and p38 MAPK by chemical inhibitors, SP600125 and SB 203580 respectively, had no effect on bisPMB antiproliferative activity against WHCO1 cells. On the other hand, inhibition of ERK1/2 MAPK by U0126 enhanced the anti-proliferative effect of bisPMB in WHCO1 cells. These results support the hypothesis that ER stress and MAPK signalling pathways are essential for bisPMB induced cytotoxicity in oesophageal cancer cells.
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    A Structure-Activity Relationship Study of Dihydroajoenes as Anti-Cancer Agents
    (2014) Biwi, James Tapiwa; Hunter, Roger; Kaschula, Catherine Hart
    Ajoene (( E-/Z )-4,5,9-trithiadodeca-1,6,11-triene-9-oxide), a constituent of garlic is known to possess in vitro and in vivo anticancer activity based on the presence of a vinyl disulfide as its pharmacophore. This thesis reports on the synthesis of dihydroajoenes, a novel set of ajoene analogues, containing a saturated double bond, in which the intention was to study the influence of removing the double bond on biological activity and metabolic stability, since ajoenes are unstable in blood. A divergent synthetic route to 6 new dihydroajoene analogues has been developed in which a phenolic hydroxyl group at the disulfide end served as a platform for modulating aqueous solubility. The dihydroajoene analogues synthesized retained good in vitro anti-proliferation activity against a WHCO1 oesophageal cancer cell line, with the phenol derivative showing the greatest activity, with an IC 50 of 4.1 μM as about 7-times more active than the parent ajoene. In addition the dihydroajoenes were found to be significantly more stable in the red blood cell fraction of mouse blood, when compared with ajoene analogues retaining the double bond. This opens up the possibility of exploring them as anti-cancer agents in an in vivo setting. This thesis also describes a preliminary study towards the synthesis of an ajoene-drug (fludarabine) conjugate for chemosensitization studies, in which an advanced synthetic intermediate was secured.