Coenzyme a biosynthesis and utilization in Plasmodium falciparum : drug targets for antimalarial chemotherapy

Thesis (PhD)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Pantothenate (also known as Vitamin B5) is the sole precursor of the essential enzyme cofactor coenzyme A (CoA) that is required in several metabolic reactions virtually in all living organisms including the human malaria parasite Plasmodium falciparum. While the parasite has the capacity to generate CoA from pantothenate, it cannot produce this nutrient de novo, and as a result depends on external supplies. Processes in the CoA metabolic pathway have been identified as possible targets for drug development and pantothenate analogues as agents that can interfere with those processes to block parasite development. In this dissertation it is shown that the class of pantothenate analogues known as Nsubstituted pantothenamides (PanAms) and N‐substituted pantoyltauramides, inhibit the growth of intraerythrocytic‐stage P. falciparum parasites at sub‐ and low micromolar concentrations respectively. In both cases, the compounds inhibited parasite proliferation through inhibition of pantothenate‐dependent processes. It is also shown that the antiplasmodial potency of PanAms can be strengthened through structural modifications rendering the compounds less susceptible to degradation by enzymes known as pantetheinases, which occur natural and ubiquitously in mammals, particularly in the serum. Finally it is also shown that the antiplasmodial mode of action of PanAms results from the compounds serving as alternative substrates for pantothenate kinase (PanK), the first enzyme intervening in the CoA biosynthesis pathway, thus interfering with the phosphorylation of the natural substrate – pantothenate. In addition, it negatively affects the production of functional CoA and acyl carrier proteins (ACPs) which are required in various cellular metabolic processes.AFRIKAANSE OPSOMMING: Pantotenaat (ook bekend as Vitamien B5) is die enigste voorloper van die noodsaaklike ensiemkofaktor koënsiem A (KoA) wat benodig word in verskeie metaboliese reaksies in feitlik alle lewende organismes, insluitend die malaria parasiet Plasmodium falciparum wat in die mens voorkom. Die parasiet het die kapasiteit om KoA te genereer vanaf pantotenaat, maar kan dié spesifieke voedingstof nie de novo produseer nie en moet gevolglik op eksterne bronne staatmaak. Prosesse in die KoA metaboliese padweg is geïdentifiseer as moontlike teikens vir geneesmiddelontwikkeling en pantotenaatanaloë as middels wat kan inmeng met die prosesse wat parasietontwikkeling blokkeer. In hierdie proefskrif word daar gewys dat die klas van pantotenaat‐analoë bekend as Ngesubstitueerde pantoteenamiede (PanAms) en N‐gesubstitueerde pantoïeltauramiede inhibeer die groei van eritrositiese‐fase P. falciparum by sub‐ en lae mikromolare konsentrasies onderskeidelik. In beide gevalle inhibeer die verbindings die verspreiding van parasiete deur pantotenaat‐afhanklike prosesse te inhibeer. Dit is ook bewys dat die antiplasmodiale werking van PanAms versterk kan word deur middel van strukturele veranderinge wat die verbindings minder vatbaar maak vir afbraak deur ensieme bekend as panteteinases, wat natuurlik en alomteenwoordig in soogdiere voorkom, veral in serum. Ten slotte is dit ook getoon dat die antiplasmodiale werking wat PanAms toon veroorsaak word deur as alternatiewe substrate vir pantotenaatkinase (PanK), die eerste ensiem in die KoA biosintese padweg, op te tree en dus so inmeng met die fosforilering van die natuurlike substraat – pantotenaat. Dit het ook 'n negatiewe invloed op die produksie van funksionele KoA en asieldraer proteïene (ACPs) wat benodig word in verskeie sellulêre metaboliese prosesse