AbstractsChemistry

Systemic drug therapies such as chemotherapy are limited by their high toxicity and non-specific targeting of cancerous and non-cancerous cells; leading to characteristic side effects seen in patients undergoing treatment. Localised drug therapies delivered through stimuli responsive self-assembled gels are a potential solution. This Thesis is concerned with gaining an insight into the fundamental interactions between self-assembled gels with living systems, through a systematic exploration of their toxicity, release properties and delivery strategies. To achieve this, three previously reported dipeptide-based gelators (Fmoc-Ala-Ala, Fmoc-Phe-Phe and naphthalene-Phe-Phe) and a novel targeting peptide-based chemotherapeutic were synthesised. Fmoc-Phe-Phe was found to be the most stable gel for cytotoxicity studies. Toxicity was assessed as a function of monomer leaching and exposure times on cancerous and healthy cell lines and also in combination with chemotherapeutics. Two-way ANOVA revealed monomer leachate >72 h and not exposure time was the significant factor affecting cell health. Furthermore, the addition of chemotherapeutics produced synergistic toxic effects as a result of cytotoxic contributions from gelator monomers >72 h. These results were determined with MTT assays, epi-fluorescence and scanning electron microscopy. The chemotherapeutic release properties of these gels were assessed in vitro and in vivo. In vitro studies over 24 h revealed ~76-100% of 5-fluorouracil (5-FU) was gradually released and static release of ~0.03-0.11% of paclitaxel was detected over time. A localised release model utilising Fmoc-Phe-Phe was developed to assess spatiotemporal release of therapeutics and their effects on live cancer cells; toxic contributions from gelator leachate >72 h was negated in this system. Pharmacokinetic studies of 5-FU released from Fmoc-Phe-Phe in rats revealed both compounds were rapidly absorbed (< 2 h) and eliminated from systemic circulation with a bioavailability of ~50% for 5-FU. The development of a targeting chemotherapeutic for localised delivery applications is reported. The first reported synthesis of a 12-mer peptide sequence, VTWTPQAWFQWV with high specificity for U-87 malignant gliomas and subsequent covalent linkage to doxorubicin with HATU coupling in solution is discussed. This derivative was found to be 1.8× more selective for U-87 cells relative to the control, exhibiting a delayed uptake into U-87 MG cells.