Design and mechanism of action of organometallic anticancer complexes

Since the discovery of cisplatin, numerous attempts have been made to emulate its activity while reducing its collateral toxicity. Coordination complexes based on a wide number of transition metals have been developed in the search for improved bioavailability, selectivity and reduced adverse side-effects. Ruthenium(II) complexes have been widely developed in this field as a viable alternative to platinum chemotherapeutics. This thesis is concerned with the synthesis, characterization and biological evaluation of three series of novel half-sandwich complexes of the general formula [RuII(arene)(X)(YZ)]n+. These piano-stool RuII complexes have been designed as to allow the fine-tuning of their chemical and biological properties. In the first two series, the arene unit has been varied between p-cymene, biphenyl and terphenyl to investigate the correlation between hydrophobicity and antiproliferative activity, while the N,N-imino pyridine chelating ligand, YZ, has been modified to include either a higher number of aromatic units that could allow better DNA intercalation or substituent groups that could affect the overall charge distribution in the complex. Finally, the monodentate ligand, X, is either chloride or iodide. These compounds have been fully characterised by NMR, MS and elemental analysis. Their aqueous behaviour has been investigated together with the extent of 9-EtG binding, as an indication of the possible interaction with nucleobases. The antiproliferative activity of these novel RuII complexes was determined, several of them show promising IC50 values, in the low μM range, against ovarian, colon, lung and breast cancer cell lines, in many cases the activities observed are better than cisplatin. The pathways for cellular accumulation were investigated. Complexes with an I as the monodentate ligand, X, exhibit partial energy-independent uptake. Overall results indicate that the novel RuII complexes synthesised in this thesis are most likely to be multi-targeted and that their mechanism of action depends to a great extent on the nature of the monodentate ligand, X. Two particularly active complexes in these series include the impy-NMe2 ligand as YZ chelate. These have been compared to their isostructural azopyridine analogues and also to their OsII equivalents. In this case, experiments were designed to study the activation of landmark events that lead to apoptosis, allowing contrasting the effects of different metal centres (Ru vs Os), isoelectronic ligands (impy-NMe2 vs azpy-NMe2) and monodentate ligands (Cl vs I). Results indicate that the molecular pathway followed by the iodido complexes is p53-independent. In comparison, the chlorido analogues activate the intrinsic apoptotic pathway and their activity relies on the existence of this tumour suppressor. DNA intercalation was also evaluated as a possible mechanism of action. Finally, the third series includes inactive RuII complexes with tetrahydroquinoline derivatives, which were found to enhance the activity of platinum drugs in clinical use. These promising preliminary results in the use of RuII complexes in combination therapy open a world of possibilities for the dose-reduction of platinum-chemotherapeutics

The contrasting activity of iodido versus chlorido ruthenium and osmium arene azo- and imino-pyridine anticancer complexes : control of cell selectivity, cross-resistance, p53 dependence, and apoptosis pathway

Organometallic half-sandwich complexes [M(p-cymene)(azo/imino-pyridine)X]+ where M = RuII or OsII and X ═ Cl or I, exhibit potent antiproliferative activity toward a range of cancer cells. Not only are the iodido complexes more potent than the chlorido analogues, but they are not cross-resistant with the clinical platinum drugs cisplatin and oxaliplatin. They are also more selective for cancer cells versus normal cells (fibroblasts) and show high accumulation in cell membranes. They arrest cell growth in G1 phase in contrast to cisplatin (S phase) with a high incidence of late-stage apoptosis. The iodido complexes retain potency in p53 mutant colon cells. All complexes activate caspase 3. In general, antiproliferative activity is greatly enhanced by low levels of the glutathione synthase inhibitor l-buthionine sulfoxime. The work illustrates how subtle changes to the design of low-spin d6 metal complexes can lead to major changes in cellular metabolism and to potent complexes with novel mechanisms of anticancer activity

Transfer hydrogenation catalysis in cells as a new approach to anticancer drug design

Organometallic complexes are effective hydrogenation catalysts for organic reactions. For example, Noyori-type ruthenium complexes catalyse reduction of ketones by transfer of hydride from ​formate. Here we show that such catalytic reactions can be achieved in cancer cells, offering a new strategy for the design of safe metal-based anticancer drugs. The activity of ruthenium(II) sulfonamido ethyleneamine complexes towards human ovarian cancer cells is enhanced by up to 50 × in the presence of low non-toxic doses of ​formate. The extent of conversion of coenzyme ​NAD+ to ​NADH in cells is dependent on ​formate concentration. This novel reductive stress mechanism of cell death does not involve apoptosis or perturbation of mitochondrial membrane potentials. In contrast, iridium cyclopentadienyl catalysts cause cancer cell death by oxidative stress. Organometallic complexes therefore have an extraordinary ability to modulate the redox status of cancer cells

Half-sandwich rhodium(III) transfer hydrogenation catalysts : reduction of NAD+ and pyruvate, and antiproliferative activity

Organometallic complexes have the potential to behave as catalytic drugs. We investigate here Rh(III) complexes of general formula [(Cpx)Rh(N,N′)(Cl)], where N,N′ is ethylenediamine (en), 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) or N-(2-aminoethyl)-4-(trifluoromethyl)benzenesulfonamide (TfEn), and Cpx is pentamethylcyclopentadienyl (Cp*), 1-phenyl-2,3,4,5-tetramethylcyclopentadienyl (CpxPh) or 1-biphenyl-2,3,4,5-tetramethyl cyclopentadienyl (CpxPhPh). These complexes can reduce NAD+ to NADH using formate as a hydride source under biologically-relevant conditions. The catalytic activity decreased in the order of N,N-chelated ligand bpy > phen > en with Cp* as the η5-donor. The en complexes (1–3) became more active with extension to the CpX ring, whereas the activity of the phen (7–9) and bpy (4–6) compounds decreased. [Cp*Rh(bpy)Cl]+ (4) showed the highest catalytic activity, with a TOF of 37.4 ± 2 h− 1. Fast hydrolysis of the chlorido complexes 1–10 was observed by 1H NMR (< 10 min at 310 K). The pKa* values for the aqua adducts were determined to be ca. 8–10. Complexes 1–9 also catalysed the reduction of pyruvate to lactate using formate as the hydride donor. The efficiency of the transfer hydrogenation reactions was highly dependent on the nature of the chelating ligand and the Cpx ring. Competition reactions between NAD+ and pyruvate for reduction by formate catalysed by 4 showed a preference for reduction of NAD+. The antiproliferative activity of complex 3 towards A2780 human ovarian cancer cells increased by up to 50% when administered in combination with non-toxic doses of formate, suggesting that transfer hydrogenation can induce reductive stress in cancer cells

A novel dual-functioning ruthenium(II)–arene complex of an anti-microbial ciprofloxacin derivative — anti-proliferative and anti-microbial activity

7-(4-(Decanoyl)piperazin-1-yl)-ciprofloxacin, CipA, (1) which is an analogue of the antibiotic ciprofloxacin, and its ruthenium(II) complex [Ru(η6-p-cymene)(CipA-H)Cl], (2) have been synthesised and the x-ray crystal structures of 1·1.3H2O·0.6CH3OH and 2·CH3OH·0.5H2O determined. The complex adopts a typical pseudo-octahedral ‘piano-stool’ geometry, with Ru(II) π-bonded to the p-cymene ring and σ-bonded to a chloride and two oxygen atoms of the chelated fluoroquinolone ligand. The complex is highly cytotoxic in the low μM range and is as potent as the clinical drug cisplatin against the human cancer cell lines A2780, A549, HCT116, and PC3. It is also highly cytotoxic against cisplatin- and oxaliplatin-resistant cell lines suggesting a different mechanism of action. The complex also retained low μM cytotoxicity against the human colon cancer cell line HCT116p53 in which the tumour suppressor p53 had been knocked out, suggesting that the potent anti-proliferative properties associated with this complex are independent of the status of p53 (in contrast to cisplatin). The complex also retained moderate anti-bacterial activity in two Escherichia coli, a laboratory strain and a clinical isolate resistant to first, second and third generation β-lactam antibiotics

Photoactive platinum(IV) complex conjugated to a cancer-cell-targeting cyclic peptide

A conjugate of cancer-cell targeting cyclic disulphide non a-peptide c(CRWYDENAC) consisting of nine L-amino acids with the photoactive succinate platinum(IV)complex trans, trans-[Pt(N3)2(py)2(OH)(succinate)] (Pt-cP) has been synthesised and characterised. The conjugate was stable in dark, but released succinate–peptide and Pt(II) species upon irradiation with visible light, and formed photoproducts with guanine. Conjugate Pt-cP exhibited higher photocytotoxicity than parent complextrans, trans, trans-[Pt(N3)2(OH)2(py)2] (FM-190) towards cancer cells, including ovarian A2780, lung A549 and prostate PC3 human cancer cells upon irradiation with blue light (465 nm, 17.28 J cm−2) with IC50values of 2.8–22.4μM and the highest potency for A549 cells. Even though the dark cellular accumulation of Pt-cP in A2780 cells was lower than that of parent FM-190, Pt from Pt-cP accumulated in cancer cells upon irradiation to a level >3× higher than that fromFM-190. In addition, the cellular accumulation of Pt from Pt-cPwas enhanced ca. 47× after irradiation