Ethnobotanical fieldwork was carried out in New Guinea. An antibacterial field assay kit was developed using freeze-dried strains of <i>S. epidermidis </i>and <i>E. coli</i> which allowed plants used in traditional medicines to be screened in situ without having to take them back to a laboratory. This approach identified <i>Lunasia amara </i>(Blanco) as a candidate species; the use of its bark by tribes of the Whitman Range to treat tropical ulcers, supported by clear zones of inhibition with <i>S. aureus.</i> Samples of the bark were collected for analysis and through activity-guided fractionation, the anti- <i>S. aureus </i>activity of the bark extract was pinned down to a single well resolved HPLC peak (MIC <i>S. aureus </i>NCTC 6571 64μg/ml) which subsequent NMR analysis revealed to be the quinoline alkaloid lunacridine; 2’-<i>O</i>-trifluoroacetyl lunacridine was found to be a more stable derivative however. Lunacridine’s planar cationic structure suggested it might act as a DNA intercalator; 220μM giving 50% binding in an ethidium bromide displacement assay. This in turn suggested DNA topoisomerase II as a likely target for the compound which was confirmed with a kDNA decatenation assay revealing complete inhibition of the enzyme at 5μM. Cell viability assays with MRC-5, H226 and HELA cells showed the compound to be cytotoxic in a time dependent manner producing non-linear dose response curves indicative of a topoisomerase poison mode of action. Activation of the apoptosis pathway enzymes caspase 3/7 was also detected, reaching maximal activity between 24 and 48 hours for the H226 cell line. Thus, lunacridine does not represent a selective antibiotic but with the right structural modifications could be developed as an antineoplastic agent.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660747 |
| Date | January 2005 |
| Creators | Prescott, T. A. K. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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