No description available.

No description available.

No description available.

No description available.

Poly(ADP-ribose) polymerase (PADPRP) is a nuclear enzyme with a well documented role in DNA repair. Inhibitors of PADPRP, (e.g. 3' substituted benzamides) potentiate the cytotoxicity of a wide range of antitumour drugs. The results presented in this thesis represent, to the best of my knowledge, the first comprehensive and quantitative assessment of the ability of a range of P ADPRP inhibitors to modulate the cellular responses to damaging agents. Two novel PADPRP inhibitors, 8-hydroxy-2-methyl quinazolin-4(3H)-one (NU1025) and 3,4 dihydro-5-methoxyisoquinolin-1-(2H)-one (PD 128763) were compared with two "classical" PADPRP inhibitors, 3-aminobenzamide (3AB) and benzamide (BZ). The relative potencies for 3AB, BZ, NU1025 and PD 128763 as PADPRP inhibitors in vitro were 1.0, ~1.0, ~43 and ~53 respectively. All compounds potentiated the growth inhibition and cytotoxicity of the monofunctional alkylating agent temozolomide (TM) in L1210 cells. For example, 10/-lM NUI025 and PD 128763 gave dose enhancement factors (DEF) of ~2 at 100/0 survival, whereas ImM 3AB and 0.5mM BZ where required to give similar DEF values. Cellular NADl- levels were depleted up to 50% by 1-2mM TM and this depletion was completely prevented by coincubation with 50-100µM PD 128763 and 1-3mM 3AB. TM induced DNA single strand break levels were increased in a concentration dependent manner by the P ADPRP inhibitors. Overall, the relative potencies for ability of the compounds to potentiate TM induced growth inhibition, cytotoxicity and DNA single strand breaks showed good correlation with those determined in an in vitro inhibition study, with both NU1025 and PD 128763 exhibiting ~60 fold increased inhibitory activity as compared to 3AB. The PADPRP inhibitors per se did not effect the growth or survival of the L 121 0 cells, nor increase DNA strand breakage. NAD+ is the substrate for PADPRP. A L1210 cell line made resistant to tiazofurin (TZ) utilising a step wise selection protocol was shown to be deficient in nicotinamide mononucleotide adenyl transferase (NMNAT) , the final enzyme required for NAD+ biosynthesis. The consequences of a reduced NMNAT activity (<3% of the parental line ) and an ~40% reduction in intracellular NAD+ levels were determined. The resistant cells showed an ~3 fold increased sensitivity to TM as compared to the parental cells. Upon coincubation with increasing concentrations of NU1025 in the presence of a fixed concentration of TM, growth inhibition was potentiated ~70 fold in the resistant cells but only ~10 fold in the parental cell line, demonstrating the reduced level of competition between NAD+ and NUI025 for PADPRP. However, DNA single strand breaks were increased in the resistant compared to the parental cell line only when NU1025 was coincubated with TM. In contrast, in the presence of the PADPRP inhibitors alone, equivalent growth inhibitory effects were observed in each of the cell lines, suggesting inhibition of PADPRP was not the cytotoxic effector. The ~40% NAD+ depletion observed could therefore suggest, that NAD+ levels in the resistant cells were reduced to, or near to the KmNAD+ for PADPRP.

This thesis reports voltammetric and quartz crystal microgravimetric studies of the binding of metal complexes to nucleic acids in solution and immobilised on metal surfaces. Cyclic voltam iet y and steady-state microelectrode voltammetsy were applied to the solution phase interactions between metal complexes and nucleic acids. The binding constants were obtained by the analysis of bound and free metal complex concentrations. The binding of N, N, N-1-propylthyminedimethylaminomethylferrocene (Fc-Th), N, N, Ntrimethylaminomethylferrocene (Fc-NMe3), bis(hexamethybenzene)iron(II), hexamuiiineruthenium( III), tris(1,10-phenantlu-oline)iron(II) and tris-(bipyridyl)iron(II) to DNA and RNA was observed. The application of microelectrode voltammetry for metal complexnucleic acid binding studies has not been reported before and this thesis demonstrates the advantages of the method due to increased signal-to noise ratio and better discrimination between free and nucleic acid-bound metal complex. These voltammetric results showed the binding of Fc-Th to DNA is stronger than the binding of Fc-NMe3 to DNA, indicating that even a single nucleobase can influence the binding. The binding of singly charged feirocenyl derivatives to DNA or RNA is mainly electrostatic plus some non-electrostatic contribution from interaction of the thymine with DNA. Fe(bz)22 binds to DNA electrostatically and the binding is senstive to ionic strength. Ru(NH3)63+ binds more strongly to DNA due to its higher charge. The binding of Fe(phen)32+, a known intercalator, is stronger than the binding of Fe(bipy)32+ to DNA and the measured binding constants were in agreement with previous reports, however more precise data could be obtained using the microelectrode technique devised in this thesis. This thesis also describes a novel modification of gold and platinum surfaces by the adsorption of 4-mercaptopyridine and subsequent methylation with methyliodide to produce a positively charged suface at which DNA adsorbs strongly. Cyclic voltammetry was applied to quantify the binding of Fc-Th, Fc-NMe3 , hexammineruthenium(II), and tris(1,10-phenanthroline) iron(II) to DNA or RNA immobilised on a gold electrode. A detectable binding of Fc-Th, Ru(NH3)63+ to DNA was observed, while no bound. FcNMe3 and Fe(phen)32 were detected using cyclic voltammetry. The difference in binding to immobilised DNA compared to dissolved DNA could be rationalised by the effect of the electrostatic interactions of the metal complexes with the charged pyridinium monolayer. Quartz crystal microfravimetry was used to estimate the surface coverage of DNA, Fc-Th, Ru(NH3)63+ and Fe(phen); '+on gold and platinum crystals modified as above. Crystal admittance measurements showed no significant change on DNA adsorption indicating approximate rigid-layer behaviour. In agreement with the CV studies no binding of Fc- NMe3 was detected. Some binding of Fe(phen)32 was observed and the negative result of the CV experiment may be due to instability of the monolayer at the high potentials required to oxidise Fe(phen)32+. In general, the QCM results showed higher surface coverages than detected by CV. Two factors may be important, the absence of solution phase metal complex in the CV experiment leads to some desorption and the QCM measurements are complicated by the unknown extent of solvation of the metal complexes.

No description available.

Acute and chronic hypoxia exists within the microenvironment of solid tumours and drives therapy resistance, genetic instability and metastasis. Despite its importance in solid tumour progression, very little is known regarding the functional consequences of hypoxia-mediated changes in the expression of DNA repair proteins. I studied the relationship between hypoxia and DNA repair using a prolonged chronic hypoxic gas treatment model in a variety of human tumour cell lines to mimic the dynamic state of proliferation and DNA repair in cells distant from the tumour blood vasculature. I observed decreased expression of homologous recombination (HR) and base excision repair (BER) proteins due to a novel mechanism involving decreased protein synthesis. Error-free HR was suppressed 3-fold under 0.2% O2 as measured by the DR-GFP reporter system and functional BER was impaired as assessed with a functional glycosylase assay. This decrease in protein expression and function resulted in increased sensitivity to the DNA damaging agents MMC, cisplatin, H2O2 and MMS. Additionally, chronically hypoxic cells were relatively radiosensitive (OER = 1.37) when compared to acutely hypoxic or anoxic cells (OER = 1.96 - 2.61). As HR defects are synthetically lethal with poly(ADP-ribose) polymerase 1 (PARP1) inhibition, I evaluated the sensitivity of repair-defective hypoxic cells to PARP inhibition. I observed increased clonogenic killing in HR-deficient hypoxic cells following inhibition or depletion of PARP1. PARP-inhibited hypoxic cells accumulated γH2AX foci consistent with an accumulation of collapsed replication forks. Additionally, tumour xenografts exposed to PARP1 inhibition showed increased γH2AX and cleaved caspase-3 expression in hypoxic subregions with suppressed RAD51 protein expression and decreased ex vivo clonogenic survival. I conclude that persistent down-regulation of DNA repair components by the microenvironment could result in faulty DNA repair with significant implications for therapeutic response and genetic instability in human cancers. Specifically, hypoxic cells may be sensitized to PARP inhibitors and other agents targeting repair pathways down-regulated by hypoxia as a consequence of microenvironment-mediated “contextual synthetic lethality”.

Graphene is a single layer of graphite with many unique mechanical, electrical, and optical properties. In addition, graphene is also known to adsorb wide range of biomolecules including single-stranded DNA. On the other hand, the adsorption of double-stranded DNA was much weaker. To properly disperse in water, graphene oxide (GO) is often used due to its oxygen-containing groups on the surface. Recently, it was discovered that it could efficiently quench the fluorescence of fluorophores that were adsorbed. With these properties, it is possible to prepare DNA-based optical sensors using GO. Majority of the DNA/GO-based fluorescent sensors reported so far were relied on the complete desorption of DNA probes. Even though all these reports demonstrated the sensitivity and selectivity of the system, the fundamentals of binding between DNA and GO were hardly addressed. Understanding and controlling binding between biomolecules and inorganic materials is very important in biosensor development. In this thesis, adsorption and desorption of DNA on the GO surface under different buffer conditions including ionic strength, pH, and temperature were systematically evaluated. For instance, adsorption is favored in a lower pH and a higher ionic strength buffer. It was found that once a DNA was adsorbed on the surface, little desorption occurred even in low salt buffers. Even with high pH or temperature, only small percentage of adsorbed DNA can be desorbed. To completely desorb the DNA, complementary DNA is required. The energies and activation energies associated with DNA adsorption/desorption were measured and molecular pictures of these processes were obtained. With the fundamental understanding of the DNA/GO interaction, we demonstrated that it is possible to achieve sensor regeneration without covalent immobilization. In addition, we also achieved the separation of double-stranded DNAs from single-stranded ones without using gel electrophoresis. We also studied the fluorescence property of DNA near the GO surface using covalently attached DNA probes. It was found that the fluorophore quantum yield and lifetime changed as a function of DNA length. This study is important for rational design of covalently linked DNA sensors. This study confirmed that fluorescence quenching by GO occurs in a distance-dependent manner. Energy transfer occurred between the fluorophore and GO to result in reduced quantum yield, shorter lifetime, and lower fluorescence intensity. Although fluorescent sensors based on covalently attached DNA probes on GO have not yet been reported, the study presented here clearly supported its feasibility.

As the number of drug-resistant malaria parasites continues to grow, pressure is increasing to find an effective, cross-protective, multi-valent malaria vaccine (32). Expression library immunisation is an un-biased screening technique that leads to the identification of novel, protective antigens that can be administered as components of a multivalent DNA vaccine (9, 50, 75, 86, 92). Here, a P. c. adami DS expression library has been evaluated as a malaria vaccine in mice, and several subpools of cross-protective plasmids have been identified. Upon vaccination with these plasmid subpools, mice demonstrate significantly lower mean cumulative parasitemia values than control vaccinated mice, when challenged with avirulent heterologous P. c. adami DK parasites. These cross-protective responses correlate with the induction of opsonizing antibodies against infected red blood cells and the production of IFN-gamma by T-cells. The determination of P. c. adami antigens capable of inducing strain-transcending immunity implies the identification of orthologues in the P. falciparum genome that may be applied as components of a human malaria vaccine.