Role of cell cycle events and apoptosis in mediating the anti-cancer activity of a silver(I) complex of 4-hydroxy-3-nitro-coumarin-bis(phenanthroline) in human malignant cancer cells.

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of 4-hydroxy-3-nitro-coumarin (hncH), and the mixed-ligand silver (I) complex of 4-oxy-3-nitro-coumarin-bis(phenanthroline), [Ag(hnc)(phen)(2)] using four human-derived model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could decrease the proliferation of all four cell lines including neoplastic renal and hepatic, namely A-498 and HepG(2) cells, respectively, along with two non-neoplastic renal and hepatic cell lines, HK-2 and Chang, respectively. Furthermore, non-neoplastic hepatic cells (Chang) appeared to be less sensitive to the effect of the complex, but this effect was not replicated in the non-neoplastic renal (HK-2) cells. Based on IC(50) values [Ag(hnc)(phen)(2)] was shown to be almost four times more potent than cisplatin, using HepG(2) cells. In addition, the observed anti-proliferative effect was shown to be both dose- and time-dependent. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease anti-proliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein] showed that cell death appeared to result from apoptosis, with the possibility of secondary necrosis. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Ag(hnc)(phen)(2)] has been shown to be a more potent anti-proliferative agent than cisplatin, capable of altering key biochemical events leading to cell death. Additional mechanistic studies are underway to probe more fully its mechanism of action.

Apoptotic cell death: a possible key event in mediating the in vitro anti-proliferative effect of a novel copper(II) complex, [Cu(4-Mecdoa)(phen)(2)] (phen=phenanthroline, 4-Mecdoa=4-methylcoumarin-6,7-dioxactetate), in human malignant cancer cells.

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of the parent ligand, 4-methylcoumarin-6,7-dioxyacyeic acid (4-MecdoaH(2)), and its copper (II) complex, bis(phenanthroline4-methylcoumarin-6,7-dioxacetatocopper(II) ([Cu(4-Mecdoa)(phen)(2)]) using four human model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could alter proliferation of both human neoplastic renal (A-498) and hepatic (HepG2) cells. Furthermore, non-neoplastic hepatic (CHANG) cells appeared to be less sensitive. However, this effect was not duplicated with non-neoplastic renal (HK-2) cells, a profile shared by cisplatin. The observed anti-proliferative effect appeared to be dose-and time-dependent, and could be attributed to the complex, rather than any of the free components i.e. the 1,10-phenanthroline or coumarin ligand, or the simple metal salt. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Based on IC(50) values, [Cu(4-Mecdoa)(phen)(2)] was shown to be almost 12 times more potent than cisplatin. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease anti-proliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein], showed that cell death could switch between apoptosis and necrosis, and this effect appeared to be concentration-dependent. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Cu(4-Mecdoa)(phen)(2)] has been shown to be a more potent anti-proliferative agent than either the ligand or cisplatin, and is capable of altering key biochemical events leading to the execution of apoptotic and/or necrotic cell death, suggesting that it is worthy of further investigation.

Synthesis, characterisation and antimicrobial activity of copper(II) and manganese(II) complexes of coumarin-6,7-dioxyacetic acid (cdoaH2) and 4-methylcoumarin-6,7-dioxyacetic acid (4-MecdoaH2): X-ray crystal structures of [Cu(cdoa)(phen)2].8.8H(2)O and [Cu(4-Mecdoa)(phen)2].13H2O (phen=1,10-phenanthroline).

Two novel coumarin-based ligands, coumarin-6,7-dioxyacetic acid (1) (cdoaH(2)) and 4-methylcoumarin-6,7-dioxyacetic acid (2) (4-MecdoaH(2)), were reacted with copper(II) and manganese(II) salts to give [Cu(cdoa)(H(2)O)(2)].1.5H(2)O (3), [Cu(4-Mecdoa)(H(2)O)(2)] (4), [Mn(cdoa)(H(2)O)(2)] (5) and [Mn(4-Mecdoa)(H(2)O)(2)].0.5H(2)O (6). The metal complexes, 3-6, were characterised by elemental analysis, IR and UV-Vis spectroscopy, and magnetic susceptibility measurements and were assigned a polymeric structure. 1 and 2 react with Cu(II) in the presence of excess 1,10-phenanthroline (phen) giving [Cu(cdoa)(phen)(2)].8.8H(2)O (7) and [Cu(4-Mecdoa)(phen)(2)].13H(2)O (8), respectively. The X-ray crystal structures of 7 and 8 confirmed trigonal bipyramidal geometries, with the metals bonded to the four nitrogen atoms of the two chelating phen molecules and to a single carboxylate oxygen of the dicarboxylate ligand. The complexes were screened for their antimicrobial activity against a number of microbial species, including methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Candida albicans. The metal-free ligands 1 and 2 were active against all of the microbes. Complexes 3-6 demonstrated no significant activity whilst the phen adducts 7 and 8 were active against MRSA (MIC(80)=12.1microM), E. coli (MIC(80)=14.9microM) and Patonea agglumerans (MIC(80)=12.6microM). Complex 7 also demonstrated anti-Candida activity (MIC(80)=22microM) comparable to that of the commercially available antifungal agent ketoconazole (MIC(80)=25microM).

An in vitro investigation of the induction of apoptosis and modulation of cell cycle events in human cancer cells by bisphenanthroline-coumarin-6,7-dioxacetatocopper(II) complex.

The central objective of the current study was to investigate the potential in vitro anti-proliferative properties of the parent ligand, coumarin-dioxy-acetic acid (cdoaH(2)), and its copper complex, copper-coumarin-dioxyacetic acetate-phenathroline ([Cu(cdoa)(phen)(2)]) using four human-derived model cell lines, two neoplastic and two non-neoplastic. In addition, selected mechanistic studies were carried out using one of the neoplastic-derived model cell lines, Hep-G2. Results obtained show that the complex, rather than the ligand, could alter the proliferation of both human neoplastic renal (A-498) and hepatic (Hep-G2) cells. Furthermore, hepatic non-neoplastic cells (Chang) appeared to be less sensitive. However, this effect was not mirrored in non-neoplastic renal (HK-2) cells, a profile shared with cisplatin. The observed anti-proliferative effect appeared to be concentration- and time-dependant, and could be attributed to the complex, rather than any of the component parts, i.e. 1,10-phenanthroline, the coumarin ligand, or the simple metal salt. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Based on IC(50) values, [Cu(cdoa)(phen)(2)] was shown to be almost six times more potent than cisplatin. Moreover, there was no evidence to show that P-glycoprotein (P-gp)-mediated multi-drug resistance (MDR) was likely to play a role in decreasing the anti-proliferative activity of the complex. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein], suggested that cell death could switch between apoptosis and necrosis, and this effect appeared to be concentration-dependent. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Cu(cdoa)(phen)(2)] has been shown to be a more potent anti-proliferative agent than either the ligand or cisplatin, and is capable of altering key biochemical events leading to the execution of apoptotic and/or necrotic cell death, suggesting that it is worthy of further investigation.

Mechanism of action of coumarin and silver(I)-coumarin complexes against the pathogenic yeast Candida albicans.

The anti-fungal activity and mode of action of a range of silver(I)-coumarin complexes was examined. The most potent silver(I)-coumarin complexes, namely 7-hydroxycoumarin-3-carboxylatosilver(I), 6-hydroxycoumarin-3-carboxylatosilver(I) and 4-oxy-3-nitrocoumarinbis(1,10-phenanthroline)silver(I), had MIC80 values of between 69.1 and 4.6 microM against the pathogenic yeast Candida albicans. These compounds also reduced respiration, lowered the ergosterol content of cells and increased the trans-membrane leakage of amino acids. A number of the complexes disrupted cytochrome synthesis in the cell and induced the appearance of morphological features consistent with cell death by apoptosis. These compounds appear to act by disrupting the synthesis of cytochromes which directly affects the cell's ability to respire. A reduction in respiration leads to a depletion in ergosterol biosynthesis and a consequent disruption of the integrity of the cell membrane. Disruption of cytochrome biosynthesis may induce the onset of apoptosis which has been shown previously to be triggered by alteration in the location of cytochrome c. Silver(I)-coumarin complexes demonstrate good anti-fungal activity and manifest a mode of action distinct to that of the conventional azole and polyene drugs thus raising the possibility of their use when resistance to conventional drug has emerged or in combination with such drugs.

In vitro anti-tumour and cyto-selective effects of coumarin-3-carboxylic acid and three of its hydroxylated derivatives, along with their silver-based complexes, using human epithelial carcinoma cell lines.

The chemotherapeutic potential of coumarin-3-carboxylic acid (C-3-COOH) and a series of three hydroxylated coumarin-3-carboxylic acid ligands, namely 6-hydroxy-coumarin-3-carboxylic acid (6-OH-C-3-COOH), 7-hydroxy-coumarin-3-carboxylic acid (7-OH-C-3-COOH) and 8-hydroxy-coumarin-3-carboxylic acid (8-OH-C-3-COOH), along with their corresponding silver-based complexes, namely 6-hydroxycoumarin-3-carboxylatosilver (6-OH-C-COO-Ag), 7-hydroxycoumarin-3-carboxylatosilver (7-OH-C-COO-Ag) and 8-hydroxycoumarin-3-carboxylatosilver (8-OH-C-COO-Ag), was determined using two human-derived carcinoma (A-498 and Hep-G2), along with two non-carcinoma human-derived cell lines (CHANG and HK-2). All of the ligands and their silver complexes induced a concentration-dependent cytotoxic effect. Furthermore, hydroxylation of C-3-COOH and its subsequent complexation with silver led to the production of a series of compounds with dramatically enhanced cytotoxicity, with 6-OH-C-3-COO-Ag having the greatest activity. Additionally, all of the metal-based complexes were selectively cytotoxic to both carcinoma-derived cell lines, relative to normal renal and hepatic cells. In comparative studies with cisplatin, and based on the IC(50) values obtained with Hep-G2 cells, it appeared that the coumarin-silver complexes were between 2 and 5.5 times more cytotoxic than cisplatin. All of the coumarin-silver complexes inhibited DNA synthesis, which did not appear to be mediated through intercalation. Furthermore, results obtained from Ames tests showed that all of the test agents and their phase I metabolites were non-mutagenic. Taken together, these findings suggest that both hydroxylation particularly in the 6th position and complexation with silver, served to significantly augment the cytotoxic properties of C-3-COOH, to yield a compound which acts as a cyto-selective agent, as it is a significant killer of cancer, relative to normal cells. We suggest that this group of compounds may have a therapeutic role to play in the successful treatment and management of cancer in man.

A study of the role of apoptotic cell death and cell cycle events mediating the mechanism of action of 6-hydroxycoumarin-3-carboxylatosilver in human malignant hepatic cells.

Previously our research group has studied the anti-proliferative effects of a series of hydroxylated derivatives and silver (I) complexes of coumarin-3-carboxylic acid (C-3-COOH) using two human-derived carcinoma cell lines (A-498 and Hep-G2). Results obtained suggested that both hydroxylation and complexation with silver served to significantly augment the cytotoxic properties of C-3-COOH, to yield a compound, namely 6-hydroxycoumarin-3-carboxylatosilver (6-OH-C-COO-Ag) which could act as a potent and cyto-selective agent, capable of killing cancer cells, and with limited toxicity to cells derived from normal tissue. Here we seek to expand on these findings by probing the molecular mechanism underlying this effect. Results from cytological staining clearly illustrated cellular changes consistent with the induction of apoptotic cell death and which occurred 24 h post-drug-treatment. Additionally, electrophoretic analysis of genomic DNA showed the presence of a ladder pattern, characteristic of apoptotic cell death. This result was subsequently confirmed using a selection of biochemical assays, where increased activity of pro-apoptotic caspases 3 and 9, and increased cleavage of poly(ADP-ribose)-polymerase protein (PARP) were observed. This result was further underpinned by the appearance of a sub-G(1) peak, representing hypo-diploid cells, using flow cytometric analysis. Furthermore, 6-OH-C-COO-Ag was seen to function through an alteration in the percentage of cells entering the G(0)/G(1) phase of cell cycle. Consequently, 6-OH-C-COO-Ag has been shown to a more potent and selective anti-cancer agent than cisplatin, capable of altering key biochemical events leading to the execution of apoptotic cell death as early as 24 h post-treatment, suggesting that it may represent a novel therapeutic agent for the safe and effective treatment of cancer in man.