Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene

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dc.contributor.advisorHunter, Rogeren_ZA
dc.contributor.advisorKaschula, Catherine Harten_ZA
dc.contributor.authorKusza, Daniel Andreasen_ZA
dc.date.accessioned2017-01-24T09:13:48Z
dc.date.available2017-01-24T09:13:48Z
dc.date.issued2016en_ZA
dc.description.abstractAjoene, 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.en_ZA
dc.identifier.apacitationKusza, D. A. (2016). <i>Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Chemistry. Retrieved from http://hdl.handle.net/11427/22989en_ZA
dc.identifier.chicagocitationKusza, Daniel Andreas. <i>"Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Chemistry, 2016. http://hdl.handle.net/11427/22989en_ZA
dc.identifier.citationKusza, D. 2016. Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Kusza, Daniel Andreas AB - 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. DA - 2016 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2016 T1 - Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene TI - Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene UR - http://hdl.handle.net/11427/22989 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/22989
dc.identifier.vancouvercitationKusza DA. Mechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoene. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Chemistry, 2016 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/22989en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Chemistryen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherChemistryen_ZA
dc.titleMechanistic insights into the cancer cell cytotoxicity and blood stability of the garlic compound ajoeneen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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