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The abundant nuclear enzyme poly (ADP-ribose)polymerase (P ARP) catalyses the formation of long homopolymeric chains of ADP-ribose, utilising NAD+ as a substrate, as the immediate cellular response to DNA damage. PARP recognises a damaged section of DNA and initiates polymer synthesis, which is believed to act as a signal to effect the repair of the lesion. A selective, potent PARP inhibitor could block the recognition, and hence repair, of DNA damage induced by cancer chemotherapy. Since increased DNA repair is regarded as a mechanism whereby tumour cells can become resistant to treatment, PARP inhibitors have therapeutic potential as resistance modifying agents. From a study of PARP inhibitors such as 3-hydroxybenzarnide (A), benzimidazole derivatives (B) were proposed as inhibitors of the enzyme, and the synthesis and biological evaluation of a series of such molecules has been achieved. Substituted 2-aryl benzirnidazoles have proved to be highly potent PARP inhibitors (B;R= 4'NO2Ph, IC5o= 59 nM), under a permeabilised cell assay the nitro phenyl derivative (B; R= 4'N02Ph) is the most potent compound reported to date (IC50= 19 nM). 2-Methyl benzirnidazole-4-carboxamide (B; R= Me) has been shown to potentiate the in vitro cytotoxicity of the antitumour agent temozolomide in L1210 cells, and the synthesis of benzimidazole inhibitors suitable for pre-clinical in vivo eluation has also been investigated, This thesis demonstrates that benzimidazole PARP inhibitors have promising potential for clinical development as resistance modifying agents.

Doctor of Philosophy(PhD) / The present study deals with the synthesis, characterization, determination of anticancer activity of three mononuclear trans-planaraminepalladium(II) complexes code named TH5, TH6 and TH7 and three trinuclear complexes code named TH1, TH8 and TH14. The activity of the compounds against human cancer cell lines: A2780, A2780cisR and A2780ZD0473R, cell uptake, DNA-binding and nature of interaction with pBR322 plasmid DNA have been determined. Whereas cisplatin binds with DNA forming mainly intrastrand GG adduct that causes local bending of a DNA strand, TH5, TH6, TH7, TH1 and TH8 bind with DNA forming mainly interstrand GG adducts that causes more of a global change in DNA conformation. Although TH5, TH6 and TH7 each have two substituted pyridine ligands in a trans-geometry (3-hydroxypyridine in TH5, 2-hydroxypyridine in TH6 and 4-hydroxypyridine in TH7), the compounds differ in their activity against ovarian cancer cell lines, indicating that non-covalent interactions involving the hydroxyl group may be playing a significant role in activity of the compounds. Among trinuclear complexes TH1 is found to be significantly more active than cisplatin. It is actually twice as active as cisplatin against the parent cell line A2780, thirteen times as active as cisplatin against the cisplatin-resistant cell line A2780cisR and 11.5 times as active as cisplatin against the cell line A2780ZD0473R. Whereas the resistance factor for cisplatin as applied to the cell lines A2780 and A2780cisR cell lines is 12.9 that for TH1 is 1.98. The results suggest that TH1 has been able to significantly overcome resistance operating in A2780cisR cell line. The compound is soluble in water so that it may be taken orally. Provided it has favourable toxicity profile, TH1 has the potential to be developed into a highly active anticancer drug with a wider spectrum of activity than cisplatin. Although platinum drugs use a shot-gun approach to kill cancerous cells, widespread use in the clinic and increasing volume of their sale indicate that even in the genomic age, there is still need for shot-gun drugs in the clinic.

The main theme of this thesis focuses on the preparation of palladium and platinum phosphine complexes that possess the potential to act as anti-cancer agents. The design of the complexes was based on the known compound, [Au(dppe)2]Cl which was shown to have an anti-mitochondrial mode of action on cancer cells. Major problems were experienced in the synthesis of these novel palladium and platinum compounds as the five phosphine ligands required diverse reaction conditions. Instability was the major hindrance as decomposition occurred during purification. This led to the substitution of the counter-ion (Cl-) with PF6-. The complexes prepared in this study were varied in lipophilicity as the gold complex was found to be non-selective due to high lipophilicity. In total, six compounds were prepared, purified and tested for potency against a panel of cancer cell lines as well as normal cells. The most lipophilic compound, [Au(dppe)2]Cl, was non-selective as it exhibited the highest toxicity to both cancerous and normal cells. In general, in vitro studies showed that palladium complexes were more toxic than the platinum analogues. These novel compounds were also non-toxic to both resting and stimulated lymphocytes signifying high selectivity for cancer cells. Three compounds, Pg 3, Pg 4a and Pg 8 exhibited high toxicity and were hence tested as such on murine cancer cell lines. Pg 8, with intermediate lipophilicity, showed toxicity against a larger number of cancer cell lines and this led to further investigations in an attempt to determine its mode of action. Analysis of the effects of Pg 8 on the mitochodria showed that it did not depolarise the mitochondrial membrane potential. A seven day analysis showed that while it did not have any effect on the mitochondrial membrane potential, it depolarised the plasma membrane potential from day 4. In contrast, [Au(dppe)2]Cl depolarised the mitochondrial membrane potential as expected. Pg 8 was shown to induce apoptosis and necrosis on Jurkat cells after exposure for 48 h. It was also shown to induce cell cycle arrest (after 48 h) as it caused blockade in the S-phase. In contrast, [Au(dppe)2]Cl caused a blockade in the G0/G1 phase. Uptake studies with radiolabelled Pg 8, [103Pd(d2pyrpe)2][PF6]2, showed that it accumulated significantly in Jurkat cells. Biodistribution studies in Wistar rats demonstrated that it was mostly taken up in the spleen followed by the liver. However, it was excreted faster than [198Au(dppe)2]Cl as this latter compound accumulated significantly in the lungs followed by the spleen, small intestine and liver. Acute toxicity studies in Balb/c mice showed that Pg 8 was less toxic than [Au(dppe)2]Cl. The latter compound (at 3 and 6 ìM) caused a significant reduction of total body weight over a 5-day period. Toxicity was evident as it was also shown to cause elevation of liver enzymes (AST and GGT), contrary to the results obtained from the mice treated with Pg 8 (at 3, 6, 12 and 15 ìM). Preparation of a patent for the synthesis as well as anti-cancer properties of the novel compound, [Pd(d2pyrpe)2][PF6]2 (Pg 8) is currently in progress. Copyright / Thesis (PhD)--University of Pretoria, 2009. / Pharmacology / unrestricted

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Yes / Here in, we report the cytotoxicity of both rhodium and iridium functionalised Cp* analogues of the [Cp*MCl2]2 dimers. The functionalised dimers contain a hydroxy tethered arm of differing carbon length. These show promising IC50 values when tested against HT-29, A2780 and cisplatin-resistant A2780cis human cancer cell lines, with the cytotoxicity improving proportionally with an increase in carbon tether length of the Cp* ring. The most promising results are seen for the 14-carbon Cp* tethered rhodium (2d) and iridium (3b) complexes, which show up to a 24-fold increase in IC50 compared to the unfunctionalised [Cp*MCl2]2 dimer. All complexes were potent inhibitors of purified thioredoxin reductase suggesting that disruption of cellular anti-oxidant function is one potential mechanism of action.

No / Several Ru-arene and Ir–Cp* complexes have been prepared incorporating (N,N), (N,O) and (O,O) coordinating bidentate ligands and have been found to be active against both HT-29 and MCF-7 cell lines. By incorporating a biologically active ligand into a metal complex the anti-cancer activity is increased.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.