Today, malaria remains the biggest killer of the third world, killing over a million people every year, despite intensive research efforts. Carbamoyl phosphate synthetase II (CPSII) is the first and rate-limiting enzyme in pyrimidine biosynthesis of Plasmodium falciparum, the causative agent of malaria. PfCPSII is a unique target for DNAzyme therapy due to the presence of two unique insertion sequences of 700bp and 1800bp that exist within the mature mRNA transcript. Previous studies have demonstrated that exogenous delivery of nucleic acids such as ribozymes and DNAzymes targeting PfCPSII insertion II effectively inhibited the growth of P. falciparum cultures at sub-micromolar levels. The objective of this study was to investigate the insertion sequences within CPSII from rodent malaria species P. berghei, P. chabaudi and P. yoelii in order to further validate the insertions as DNAzyme targets in vivo. In addition, the insertions were isolated from another human malaria parasite, P. vivax. All Plasmodium CPSII genes investigated encoded two highly hydrophilic insertion sequences of similar size and nature, in the precise position seen in PfCPSII. Although these insertions are poorly conserved, border and internal regions of high homology are present. Thirty-one new DNAzymes were designed to target the P. berghei CPSII insertion II region, seventeen of which demonstrated the ability to cleave the target RNA. Of these, four showed significant cleavage activity, with the DNAzyme MD14 cleaving greater than half the target RNA within five minutes. These DNAzymes were then further characterised for kinetic behaviour. Again, MD14 displayed favourable kinetics of cleavage and was chosen as a suitable candidate in an in vivo rodent malaria trial. Analysis of parasitaemia from the MD14 treated mice indicated the administration of MD14 effected a highly statistically significant reduction of parasitaemia, although this reduction was low (6.3%). More efficient DNAzyme delivery methods were investigated in order to improve DNAzyme efficacy and included the novel use of porphyrin conjugated DNAzymes. The porphyrin-conjugated DNAzymes improved uptake into parasitised red blood cells and significantly reduced parasite growth in vitro at nanomolar levels.
| Identifer | oai:union.ndltd.org:ADTP/257277 |
| Date | January 2007 |
| Creators | Katrib, Marilyn, School of Biotechnology & Biomolecular Science, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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