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Title: Photoactivatable platinum (IV) anticancer complexes
Author: Shaili, Evyenia
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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In this work, trans-diazido Pt(IV) complexes with general formula [Pt(N3)2(OH)(OCOR)(pyr)2] (where OCOR is a carboxylate axial ligand) and [Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are aromatic N-heterocyclic ligands) have been synthesised and characterised. The chemical and photochemical properties of these complexes, as well as their photobiological behaviour, have been studied in order to check their potential as photoactivatable anticancer drugs. Four trans-diazido Pt(IV) complexes with general formula trans, trans, trans- [Pt(N3)2(OH)(OCOR)(pyr)2] (OCOR= succinate, 4-oxo-4-propoxybutanoate, Nmethylisatoate and succinate-(RGD)f peptide ligands) have been obtained by axial derivatisation of one hydroxido ligand from trans, trans, trans- [Pt(N3)2(OH)2(pyr)2]. The crystal structures of three axially-derivatised complexes have been determined by X-ray diffraction. Photoirradiation studies have shown an improved photoactivity of the carboxylate versus the dihydroxido complexes at the longer wavelengths. Release of the axial ligands was observed in the studied complexes. This fact is especially relevant in the case of the Pt(IV)-(cRGD)f complex, where the RGD was incorporated as a tumour cell targeting moiety. DFT-TDDFT calculations performed on the complex trans, trans, trans- [Pt(N3)2(OH)(Succ)(pyr)2] showed dissociative transitions at longer wavelength, which could explain the photolability observed in these carboxylate derivatives. Studies of photoactivation of the diazido Pt(IV) complexes in the presence of 5’- GMP indicate the formation of a mono-GMP Pt(II) adduct as main photoproduct, therefore DNA could be considered a potential target site for these anticancer compounds. Additionally, EPR studies showed that azidyl radical release was observed when complexes bearing the succinate and 4-oxo-4-propoxybutanoate ligands were irradiated with green light. No such result was obtained for the dihydroxo precursor showing that these complexes could be phototoxic with longer wavelength light activation. Seven trans-diazido Pt(IV) complexes, trans, trans, trans- [Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are pyridine, 2-picoline, 3-picoline, 4- picoline, thiazole or 1-methylimidazole ligands), have been obtained by oxidation of the corresponding trans-[Pt(N3)2(L1)(L2)] precursor. The X-ray crystal structures have been determined for four Pt(IV) diazido complexes from this family of compounds. Photoirradiation studies indicate that the incorporation of a sterically demanding ligand, e.g. trans, trans, trans-[Pt(N3)2(OH)2(2-pic)(pyr)], greatly enhances the photoactivity in these complexes. DFT-TDDFT calculations are in agreement with these results, since higher intensity transitions were observed for such complex at longer wavelength. Phototoxicity studies carried out on A2780, A2780cis and OE19 cell lines with the trans, trans, trans-[Pt(N3)2(OH)2(pyridine)(n-picoline)] family concluded that steric hindrance close to the platinum centre does not favour phototoxicity. Most of the complexes were equally potent in cisplatin resistance against the ovarian cancer cell line (A2780cis), except [Pt(N3)2(OH)2(3-pic)2] and [Pt(N3)2(OH)2(4-pic)2] which exhibited some cross resistance. All of the complexes tested in both OE19 and A2780 cell lines have shown less sensitivity to OE19 than to A2780. Studies in S. pombe yeast strains (WT and ΔRad3) with trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] suggest that DNA is potentially an important target for this type of compounds, although other targets are not excluded. Furthermore, live-cell confocal microscopy was performed on A2780 cells treated with the complex trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] and irradiated with a low dose of blue light. The cell death, monitored by propidium iodide uptake, was captured occurring 2 h 30 min post activation.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC) ; University of Warwick
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH301 Biology ; RC0254 Neoplasms. Tumors. Oncology (including Cancer) ; RS Pharmacy and materia medica