Development of fluorescent assays for biological analysis
Ladyman, Melissa Kate
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The work in this thesis is divided into two parts; the first is the synthesis of a ‘switch-on’ fluorophore to measure cell viability, and the second is the development of a fluorescent detection method for protein−peptide affinity assays applied in the identification of protein-protein inhibitors. Tetrazolium salts are often used in cytotoxicity assays as indicators of cell viability as they are reduced to deeply coloured formazans exclusively in healthy cells. However, measuring the absorbance of the formazan is prone to bias from other coloured species in the cell media, requires solubilisation and can be difficult to quantify. A preferable method of detection is direct fluorescence as it is easily quantified, more sensitive and would ideally remove the need to solubilise the insoluble dye. The aim of this project was to synthesise a tetrazolium salt that could be reduced to a soluble fluorescent formazan in healthy cells as an indicator of cell viability. A number of fluorescent formazans were synthesised by incorporation of a fluorophore. The corresponding tetrazolium salts were non-fluorescent and could be reduced to the formazan in vitro. Several formazans were synthesised to attempt to increase the emission wavelength and intensity to overcome cellular autofluorescence. Protein-protein interactions have been implicated in the pathogenesis of many human diseases but until recently were considered undruggable. However, peptides have emerged as ideal compounds for targeting the large and relatively featureless protein interfaces. Work focussed on the discovery of peptide inhibitors for the E3 ubiquitin ligase stationary-phase kinase associated protein (Skp2). Potential peptide inhibitors were identified using CelluSpot synthesis and array technology to screen peptide libraries. Qualitative analysis of the protein affinity assay results by enhanced chemiluminescent detection was found to be misleading, and so a quantifiable and more sensitive fluorescent detection method was developed.