Over the past few years, G-quadruplex DNA has been established as a potential target for anti-cancer drugs. The formation of quadruplexes in the promoter region of certain oncogenes (such as c-myc) is thought to play an important role in regulating their expression. Furthermore the stabilisation of quadruplex DNA in the telomeric region is thought to inhibit telomerase, an enzyme overexpressed in cancerous cells and related to cell proliferation. Therefore the development of small molecules with the ability to interact selectively with quadruplex DNA is receiving increasing attention. In particular metal complexes provide a novel approach for targeting quadruplex DNA.
In this thesis a series of mono-, bi- and tri-nuclear metal(II)-terpyridine (with the metal being copper(II), platinum(II) and zinc(II)), and platinum(II)-phenanthroline complexes have been prepared and evaluated as quadruplex DNA (Htelo and c-myc DNA) binders. The metals complexes were designed to have planar geometries to π-π stack atop quadruplex DNA. Side arms were incorporated to provide additional interactions with the loops, grooves and phosphate backboneof DNA.
Once prepared, the ability of the complexes to π-π stack in solid and solution state was probed using X-ray crystallography and 1H NMR and/or UV-Vis spectroscopy respectively. This gave an insight into the propensity of the complexes to π-π stack with quadruplex DNA. Metal complex-quadruplex DNA interactions were studied using a number of well established biophysical techniques. Fluorescence intercalator displacement assays, UV-Vis, fluorescence, 1H NMR and circular dichroism spectroscopic studies were used to probe non-covalent interactions. Several of the compounds were found to bind with high affinity and selectivity to quadruplex DNA (especially c-myc DNA). 1H NMR spectroscopic experiments with guanosine were used to investigate the potential of the complexes to form covalent bonds with DNA.
A selection of the most potent quadruplex DNA binders were studied in cells. The MTS assay was used to determine the toxicity of the complexes towards cancer (U2OS and 293T) and normal (GM0575) cell lines. The IC50 values showed the potential of the metal complexes as anti-cancer drugs. To gain a better understanding of metal complex induced cell death, cellular uptake and DNA-flow cytometric studies were carried out. Additionally, RT q-PCR was used to probe the ability of these metal complexes to regulated c-myc oncogene expression.