👤 Madaan Y

The interaction of ruthenium (II) complex [Ru(bpy)2(mal)](2+) (RBM) and [Ru(phen)2(mal)](2+) (RPM) (bpy = 2, 2-bipyridine, phen = 1,10-phenanthroline, mal = malonyl carboxylate) with human serum albumin (HSA) has been investigated by using fluorescence, UV absorption and circular dichroism (CD) spectroscopy approaches. A strong fluorescence quenching reaction of complexes to HSA was observed and the quenching mechanism was suggested as static quenching according to the Stern-Volmer (S-V) equation. The number of binding sites n and observed binding constant Kb was measured by fluorescence quenching method. The thermodynamic parameters ΔH, ΔS, and ΔG at different temperatures were calculated and the results indicate the binding reaction is mainly entropy-driven and Vander Waals force played a major role in the reaction. The result of CD showed that the secondary structure of HSA molecules was changed in the presence of the ruthenium (II) complexes. Furthermore, the cell viability of ruthenium (II) complexes was evaluated by MTT and complex RPM has shown significant higher anticancer potency than RBM against all the cell lines screened. RPM showed a significant antitumor activity through induction of apoptosis in A549 cells. Show less

Mitochondria-targeted compounds represent a promising approach to target tumors selectively and overcome resistance to current anticancer therapies. In this work, three cyclometalated iridium(III) complexes (1-3) containing bis-N-heterocyclic carbene (NHC) ligands have been explored as theranostic and photodynamic agents targeting mitochondria. These complexes display rich photophysical properties, which greatly facilitates the study of their intracellular fate. All three complexes are more cytotoxic than cisplatin against the cancer cells screened. 1-3 can penetrate into human cervical carcinoma (HeLa) cells quickly and efficiently, and they can carry out theranostic functions by simultaneously inducing and monitoring the morphological changes in mitochondria. Mechanism studies show that these complexes exert their anticancer efficacy by initiating a cascade of events related to mitochondrial dysfunction. Additionally, they display up to 3 orders of magnitude higher cytotoxicity upon irradiation at 365 nm, which is so far the highest photocytotoxic responses reported for iridium complexes. Show less

We report herein a systematic study on interactions of organometallic ruthenium(II) anticancer complex [(η(6)-arene)Ru(en)Cl](+) (arene = p-cymene (1) or biphenyl (2), en = ethylenediamine) with human transferrin (hTf) and the effects of the hTf-ligation on the bioavailability of these complexes with cisplatin as a reference. Incubated with a 5-fold excess of complex 1, 2, or cisplatin, 1 mol of diferric hTf (holo-hTf) attached 0.62 mol of 1, 1.01 mol of 2, or 2.14 mol of cisplatin. Mass spectrometry revealed that both ruthenium complexes coordinated to N-donors His242, His273, His578, and His606, whereas cisplatin bound to O donors Tyr136 and Tyr317 and S-donor Met256 in addition to His273 and His578 on the surface of both apo- and holo-hTf. Moreover, cisplatin could bind to Thr457 within the C-lobe iron binding cleft of apo-hTf. Neither ruthenium nor platinum binding interfered with the recognition of holo-hTf by the transferrin receptor (TfR). The ruthenated/platinated holo-hTf complexes could be internalized via TfR-mediated endocytosis at a similar rate to that of holo-hTf itself. Moreover, the binding to holo-hTf well preserved the bioavailability of the ruthenium complexes, and the hTf-bound 1 and 2 showed a similar cytotoxicity toward the human breast cancer cell line MCF-7 to those of the complexes themselves. However, the conjugation with holo-hTf significantly reduced the cellular uptake of cisplatin and the amount of platinated DNA adducts formed intracellularly, leading to dramatic reduction of cisplatin cytotoxicity toward MCF-7. These findings suggest that hTf can serve as a mediator for the targeting delivery of Ru(arene) anticancer complexes while deactivating cisplatin. Show less

d-glucose end-capped polylactide ruthenium cyclopentadienyl complex (RuPMC) was newly synthesized by a straightforward method. RuPMC was tested against human MCF7 and MDAMB231 breast and A2780 ovarian adenocarcinoma revealing IC50 values in the micromolar range. A pH dependent hydrolysis is advanced by preliminary UV-visible spectroscopy. Cellular distribution studies showed that RuPMC is predominantly found in the nucleus and in the membrane. Data suggest potential application of RuPMC as a new drug delivery system for Ru(II)Cp compounds. Show less

Four [Ru(tpy)(N-N)(L)] type complexes: [Ru(tpy)(bpy)(Nh)](2+) (Ru1, tpy = 2,2';6',2″-terpyridine, bpy = 2'2-bipyridine, Nh = Norharman), [Ru(tpy)(phen)(Nh)](2+) (Ru2, phen = 1,10-phenanthroline), [Ru(tpy)(dpa)(Nh)](2+) (Ru3, dpa = 2,2'-dipyridylamine) and [Ru(tpy)(dip)(Nh)](2+) (Ru4, dip = 4,7-diphenyl-1,10-phenanthroline) were presented as anticancer drugs. In vitro cytotoxicity assays indicated that these complexes showed anticancer activity against various cancer cells. Flow cytometry and signaling pathways analysis demonstrated that these complexes induced apoptosis via the mitochondrial pathway, as evidenced by the loss of mitochondrial membrane potential and the release of cytochrome c. The resulting accumulation of p53 proteins from phosphorylation at serine-15 and serine-392 was correlated with an increase in p21 and caspase activation. Taken together, these findings suggested that Ru1-Ru4 may contribute to the future development of improved chemotherapeutics against human cancers. Show less

In the present study, the interaction between GC-rich sequence of bcl-2 gene P1 promoter (Pu39) and two ruthenium (II) polypyridyl complexes, [Ru(bpy)₂(tip)]²⁺ (1) and [Ru(phen)₂(tip)]²⁺ (2), was investigated by UV-Visible, fluorescence spectroscopy, circular dichroism, fluorescence resonance energy transfer melting assay and polymerase chain reaction stop assay. Those experimental results indicated that the two complexes can effectively stabilize the G-quadruplex of Pu39. It was found that the complex 2 exhibited greater cytotoxic activity than 1 against human Hela cells and can enter into Hela cells in a short period of time to effectively induce apoptosis of cells. Further experiments found that complexes 1 and 2 had as potent inhibitory effects on ECV-304 cell migration as suramin. Those noteworthy results provide new insights into the development of anticancer agents for targeting G-quadruplex DNA. Show less

Two ruthenium(II) complexes (Ru-complexes) were synthesized and characterized in this study. The selectivity and ability of the complexes to interact with bcl-2 DNA were investigated here. It turned out that [Ru(ip)3](ClO4)2·2H2O (complex 1, ip = 1H-iminazole [4,5-f][1,10] phenanthroline) could induce and stabilize the formations of G-quadruplexes more effectively than [Ru(pip)3](ClO4)2·2H2O (complex 2, pip = 2-phenylimidazo-[4,5-f][1,10]phenanthroline) did. Considering the important role of the Ru-complex ligand in inducing and stabilizing the formations of G-quadruplex in our previous studies, we speculate that the overlarge ligand of complex 2 may block its binding affinity for G-quadruplexes. Complex 1 also induced cell apoptosis in in vitro assays. In general, this study provided potentially important information for further development of the Ru-complexes as good inducers and stabilizers of bcl-2 G-quadruplex DNA for cancer treatment. Show less

The emission enhancement behavior and photocleavage activity of a ruthenium(II) arene complex, [(η(6)-p-cymene)Ru(dppn)(py)](2+) (1) (dppn = 4,5,9,16-tetraaza-dibenzo[a,c]naphthacene, py = pyridine), towards DNA were compared with [(η(6)-p-cymene)Ru(bpy)(py)](2+) (2), [Ru(bpy)2(dppz)](2+) (3) and [Ru(bpy)2(dppn)](2+) (4) (bpy = 2,2'-bipyridine, dppz = dipyrido-[3,2-a:2',3'-c]phenazine). It was found that 1 emits fluorescence from the dppn-based ligand-centered (LC) singlet excited state and generates singlet oxygen ((1)O2) from the dppn-based LC triplet excited state. As a result, 1 displays emission enhancement behavior and photocleavage activity towards DNA simultaneously. In contrast, 3 is the most classical DNA light switch but shows poor DNA photocleavage activity, while 4 is an efficient DNA photocleaver but cannot report DNA binding by luminescence enhancement. An increased cytotoxicity against human lung carcinoma cells A549 by about 10-fold was also observed for 1 upon visible light activation. These intriguing properties result from the unique combination of the Ru(II) arene and dppn subunits. Show less

A ruthenium(II) β-carboline complex [Ru(tpy)(Nh)3](2+) (tpy = 2,2':6',2″-terpyridine, Nh = Norharman, Ru1) has been synthesized and characterized. This complex induced apoptosis against various cancer cell lines and had high selectivity between tumor cells and normal cells. In vivo examination indicated Ru1 decreased mouse MCF-7 and HepG2 tumor growth. Signaling pathways analysis demonstrated that this complex induced apoptosis via the mitochondrial pathway, as evidenced by the loss of mitochondrial membrane potential (MMP, ΔΨm) and the release of cytochrome c. The resulting accumulation of p53 proteins from phosphorylation at Ser-15 and Ser-392 correlated with an increase in p21 and caspase activation. Taken together, these findings suggest that Ru1 exhibits high and selective cytotoxicity induced p53-mediated apoptosis and may contribute to the future development of improved chemotherapeutics against human cancers. Show less

The complexation with organoruthenium fragments confers 4-anilinoquinazoline pharmacophores with higher potential for inducing cellular apoptosis while the highly inhibitory activity of 4-anilinoquinazolines against EGFR and the reactivity of the ruthenium centre to 9-ethylguanine are well preserved. Show less

Five iridium(III) complexes with two N-heterocyclic carbene (NHC) ligands and an ancillary ligand have been designed and successfully synthesized. With multicolor photoluminescence and low toxicity, these carbene complexes were tested, for the first time, as living cell imaging reagents and showed promise for application beyond the OLED (organic light emitting diode) area. Show less

A new ruthenium complex [Ru(phen)(2)(mitatp)](2+) (phen = 1,10-phenanthroline, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) has been synthesized and characterized. The interaction of the complex with DNA has been studied and the results indicate that [Ru(phen)(2)(mitatp)](2+) could efficiently photocleave pBR322 DNA under irradiation at visible light and the singlet oxygen (1)O(2) was proved to be reactive species in the photocleavage process. The cytotoxicity has also been evaluated by MTT method, and [Ru(phen)(2)(mitatp)](2+) shows prominent anticancer activity against various cancer cells. Live cell imaging study and flow cytometric analysis demonstrate that the complex could cross cell membrane accumulating in the nucleus and inducing cell death by induction of G0/G1 cells cycle arrest and apoptosis. Show less

Half-sandwich organorhodium(III) complexes and their trichloridorhodium(III) counterparts are potent anticancer agents that enhance the formation of reactive oxygen species and invoke a strong induction of apoptosis in leukemia cells. The antiproliferative activity towards human MCF-7 and HT-29 adenocarcinoma cells of novel nonintercalating complexes containing the 5-substituted phenanthroline ligands 5,6-dimethylphenanthroline, 5-chlorophenanthroline, and 5-nitrophenanthroline (phen*) increases dramatically in the order [(η(5)-C(5)Me(5))IrCl(phen*)](CF(3)SO(3)) < [(η(5)-C(5)Me(5))RhCl(phen*)](CF(3)SO(3)) < mer-[RhCl(3)(DMSO)(phen*)] (DMSO is dimethyl sulfoxide). Improved activity was also achieved by attaching a cell-penetrating peptide to the dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligand of an organorhodium(III) complex. Whereas 5-substitution led to significant improvements in the activity of the organoiridium(III) and trichloridorhodium(III) compounds in comparison with the parent phenanthroline complex, the IC(50) values of their organorhodium(III) counterparts remained effectively invariable. The high activities of the trichloridorhodium(III) complexes (IC(50) = 0.06-0.13 μM) were accompanied by pronounced selectivity towards human cancer cells in comparison with immortalized HEK-293 cells. In contrast, [(η(5)-C(5)Me(5))RhCl(5,6-Me(2)phen)](CF(3)SO(3)) (phen is phenanthroline) was markedly more active towards BJAB lymphoma cells than ex vivo healthy leukocytes and caused an immediate decrease in cellular adhesion possibly associated with interactions with membrane proteins. Its dppz analogue invoked an initial increase in glycolysis to compensate for reduced respiration before inducing a delayed onset of cell death. Strong antimitochondrial activity with respiration impairment and release of cytochrome c was established for both complexes. Show less

The cytostatic properties and cellular effects of novel diene-ruthenium(II) complexes of the types OC-6-13-[RuCl(2)(pp)(cod)] 1-5 (pp=2,2'-bipyridyl (bpy), phen=1,10-phenanthroline (phen), 5,6-dimethylphenanthroline (5,6-Me2phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), ethylenediamine (en)) and OC-6-24-[RuCl{(Me(2)N)(2)CS}(pp)(cod)](CF(3)SO(3)) 6-8 (pp=phen, 5,6-Me(2)phen, dpq) have been studied for the human cancer cell lines MCF-7 and HT-29 and for Jurkat leukemia cells. CD spectra indicate that 7 causes a massive distortion of the CT DNA B double helix toward the A form. Whereas the neutral complexes 1, 2 and 5 exhibit only modest antiproliferative activity toward MCF-7 and HT-29 cells, the monocationic complexes are significantly more active, in particular the DNA-distorting complex 7 with its IC(50) values of 0.73 and 0.42 μM, respectively. As established by online monitoring with a cell-based sensor chip, this potent 5,6-Me(2)phen complex invokes dose-dependent decreases in MCF-7 cellular respiration and extracellular acidification rates and causes a time-delayed decrease in the impedance of the cell layers, that can be ascribed to cell death. Treatment of Jurkat cells with 7 leads to high concentrations of reactive oxygen species and the induction of apoptosis. The pronounced dose-dependent inhibition of oxygen consumption by isolated mice mitochondria indicates the involvement of an intrinsic mitochondrial pathway in the programmed cell death process. Show less

Three novel Ru(II) complexes of the general formula [Ru(N-N)(2)(Norharman)(2)](SO(3)CF(3))(2), where N-N = 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), 4,7-diphenyl-1,10-phenanthroline (DIP, 3) and Norharman (9H-pyrido[3,4-b]indole) is a naturally occurring β-carboline alkaloid, have been synthesized and characterized. The molecular structures of 1 and 2 have been determined by X-ray diffraction analysis. The cellular uptake efficiencies, in vitro cytotoxicities and apoptosis-inducing properties of these complexes have been extensively explored. Notably, 1-3 exhibit potent antiproliferative activities against a panel of human cancer cell lines with IC(50) values lower than those of cisplatin. Further studies show that 1-3 can cause cell cycle arrest in the G0/G1 phase and induce apoptosis through mitochondrial dysfunction and reactive oxygen species (ROS) generation. In vitro DNA binding studies have also been conducted to provide information about the possible mechanism of action. Show less

Ruthenium(II) methylimidazole complexes, with the general formula [Ru(MeIm)(4)(N⌢N)](2+) (N⌢N = tip (RMC1), iip (RMC2), dppz (RMC3), dpq (RMC4); MeIm = 1-methylimidazole, tip = 2-(thiophene-2-yl)-1H-imidazo [4,5-f] [1,10]phenanthroline, iip = 2-(1H-imidazol-4-yl)-1H-imidazo [4,5-f] [1,10]phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine, dpq = pyrazino [2,3-f] [1,10]phenanthroline), were synthesized and characterized. As determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, these complexes displayed potent anti-proliferation activity against various cancer cells. RMC1 inhibited the growth of A549 (human lung adenocarcinoma) lung cells through induction of apoptotic cell death, as evidenced by the accumulation of cell population in sub-G1 phase. RMC1 also induced the depletion of mitochondrial membrane potential in A549 cells by regulating the expression of pro-survival and pro-apoptotic Bcl-2 family members. Another experiment showed that Bid protein was also activated by RMC1, which implied that RMC1 could existed two pathways crosstalk, namely, have exogenous death receptor signaling pathway. These results demonstrated that RMC1 induced cancer cell death by acting on both mitochondrial and death receptor apoptotic pathways, suggesting that RMC1 could be a candidate for further evaluation as a chemotherapeutic agent against human cancers. Show less

In this study, two isomeric ruthenium(II) complexes [Ru(bpy)(2)(p-mopip)](2+) (1) and [Ru(bpy)(2)(o-mopip)](2+) (2) (bpy = 2, 2-bipyridine; L: p-mopip = 2-(4-methoxylphenyl) imidazo [4,5-f][1,10]phenanthroline, o-mopip = 2-(2-methoxylphenyl) imidazo[4,5-f][1,10] phenan-throline) contained -OCH(3) at different positions on the phenyl ring and their enantiomers Λ-1, -2 and Δ-1, -2 displayed different properties. The cell viability of these ruthenium(II) complexes was evaluated by MTT, and complex Λ-1 has shown significant higher anticancer potency than Δ-1 against all the cell lines screened. Fluorescence microscopy and flow cytometric analyses demonstrated that complex Λ-1 was able to induce apoptosis. The interactions of complexes Λ-1, 1, and Δ-1 with bovine serum albumin (BSA) were investigated by fluorescence and circular dichroism (CD) measurements. The fluorescence quenching mechanism of BSA by complexes Λ-1, 1, and Δ-1 was determined to be a static process, and the apparent binding constant K(a) values is as follows: Λ-1 >1 > Δ-1. The number of binding sites n for all these complexes was 1. The result of CD showed that the secondary structure of BSA molecules was changed in the presence of the ruthenium(II) complex. Show less

A nonemissive cyclometalated iridium(III) solvent complex, without conjugation with a cell-penetrating molecular transporter, [Ir(ppy)(2)(DMSO)(2)](+)PF(6)(-) (LIr1), has been developed as a first reaction-based fluorescence-turn-on agent for the nuclei of living cells. LIr1 can rapidly and selectively light-up the nuclei of living cells over fixed cells, giving rise to a significant luminescence enhancement (200-fold), and shows very low cytotoxicity at the imaging concentration (incubation time <10 min, LIr1 concentration 10 μM). More importantly, in contrast to the reported nuclear stains that are based on luminescence enhancement through interaction with nucleic acids, complex LIr1 as a nuclear stain has a reaction-based mode of action, which relies on its rapid reaction with histidine/histidine-containing proteins. Cellular uptake of LIr1 has been investigated in detail under different conditions, such as at various temperatures, with hypertonic treatment, and in the presence of metabolic and endocytic inhibitors. The results have indicated that LIr1 permeates the outer and nuclear membranes of living cells through an energy-dependent entry pathway within a few minutes. As determined by an inductively coupled plasma atomic emission spectroscopy (ICP-AEC), LIr1 is accumulated in the nuclei of living cells and converted into an intensely emissive adduct. Such novel reaction-based nuclear staining for visualizing exclusively the nuclei of living cells with a significant luminescence enhancement may extend the arsenal of currently available fluorescent stains for specific staining of cellular compartments. Show less

We report the synthesis and characterisation of 32 half sandwich phenylazopyridine Os(II) arene complexes [Os(η(6)-arene)(phenylazopyridine)X](+) in which X is chloride or iodide, the arene is p-cymene or biphenyl and the pyridine and phenyl rings contain a variety of substituents (F, Cl, Br, I, CF(3), OH or NO(2)). Ten X-ray crystal structures have been determined. Cytotoxicity towards A2780 human ovarian cancer cells ranges from high potency at nanomolar concentrations to inactivity. In general the introduction of an electron-withdrawing group (e.g. F, Cl, Br or I) at specific positions on the pyridine ring significantly increases cytotoxic activity and aqueous solubility. Changing the arene from p-cymene to biphenyl and the monodentate ligand X from chloride to iodide also increases the activity significantly. Activation by hydrolysis and DNA binding appears not to be the major mechanism of action since both the highly active complex [Os(η(6)-bip)(2-F-azpy)I]PF(6) (9) and the moderately active complex [Os(η(6)-bip)(3-Cl-azpy)I]PF(6) (23) are very stable and inert towards aquation. Studies of octanol-water partition coefficients (log P) and subcellular distributions of osmium in A2780 human ovarian cancer cells suggested that cell uptake and targeting to cellular organelles play important roles in determining activity. Although complex 9 induced the production of reactive oxygen species (ROS) in A2780 cells, the ROS level did not appear to play a role in the mechanism of anticancer activity. This class of organometallic osmium complexes has new and unusual features worthy of further exploration for the design of novel anticancer drugs. Show less

The antiproliferative properties and cellular impact of novel substitutionally inert rhodium(III) complexes of the types [Rh{(CH₃)₂ NCS₂}₂(pp)]Cl 3-5 (pp=5,6-Me₂phen, dpq, dppz) and OC-6-23-[Rh(2-S-py)₂(pp)]Cl 6 and 7 (2-S-py=pyridine-2-thiolate; pp=dpq, dppz) have been investigated for the adherent human cancer cell lines MCF-7 and HT-29 and for non-adherent Jurkat cells. Whereas CD and viscosity measurements indicate that the polypyridyl ligands of 4 and 5 intercalate into CT DNA, this is not the case for the analogous pyridine-2-thiolate complexes 6 and 7. Complexes 3-7 all exhibit a high antiproliferative activity towards MCF-7 and HT-29 cells, with IC(50) values in the range 0.055-0.285 μM. As established by online monitoring with a cell-based sensor chip, the highly cytostatic complex 6 (IC(50)=0.059 and 0.078 μM) invokes an immediate concentration-dependent reduction of MCF-7 cell respiration and a time-delayed decrease in cellular impedance, which can be ascribed to the induction of cell death. Annexin V/PI assays demonstrated that 6 also has a pronounced antiproliferative activity towards Jurkat cells and that it invokes extensive apoptosis and high concentrations of reactive oxygen species in these leukemia cells. The observation of a dose-dependent inhibition of the oxygen consumption of isolated mice mitochondria indicates the involvement of an intrinsic mitochondrial pathway in this process. Show less

The antiproliferative properties and biological impact of octahedral iridium(III) complexes of the type fac-[IrCl3 (DMSO)(pp)] containing pp=phenanthroline (1) and its 4- and 5-methyl (2, 3) and 4,7- and 5,6-dimethyl derivatives (4, 5) were investigated for both adherent and non-adherent cells. A series of similar rhodium(III) complexes were studied for comparison purposes. The antiproliferative activity toward MCF-7 cancer cells increases eightfold from IC50=4.6 for 1 to IC50=0.60 μM for 5, and an even more pronounced 18-fold improvement was established for the analogous rhodium complexes 6 and 8, the respective IC50 values for which are 1.1 and 0.06 μM. Annexin V/propidium iodide assays demonstrated that the 5,6-dimethylphenanthroline complexes 5 and 8 both cause significant inhibition of Jurkat leukemia cell proliferation and invoke extensive apoptosis but negligible necrosis. The percentages of Jurkat cells exhibiting high levels of reactive oxygen species correlate with the percentages of cells undergoing apoptosis. The antiproliferative activity of 5 and 8 is strongly selective toward MCF-7 and HT-29 cancer cells over normal HFF-1 and immortalized HEK-293 cells. Complex 5 also exhibits high selectivity toward BJAB lymphoma cells relative to healthy leukocytes. Both 5 and 8 invoke permanent decreases in the adhesion and respiration of MCF-7 cells. Show less

The limitations of cisplatin-based chemotherapy, including high toxicity, undesirable side effects, and drug resistance, have motivated extensive investigations into alternative metal-based cancer therapies. Ruthenium (Ru) possesses several favorable properties suited to rational anticancer drug design and biological applications. In the present study, we synthesized a series of ruthenium polypyridyl complexes containing N,N-chelating ligands, examined their anticancer activities, and elucidated the molecular mechanisms through which they caused the cancer cell death. The results demonstrated that [Ru(phen)(2)-p-MOPIP](PF(6))(2).2H(2)O (RuPOP), a complex with potent antiproliferative activity, is able to induce mitochondria-mediated and caspase-dependent apoptosis in human cancer cells. On the basis of these results, we suggest that RuPOP may be a candidate for further evaluation as a chemopreventive and chemotherapeutic agent for human cancers, especially for melanoma. Show less

The role of autophagy in cancer development and response to cancer therapy has been a subject of debate. Here we demonstrate that a series of ruthenium(II) complexes containing a β-carboline alkaloid as ligand can simultaneously induce autophagy and apoptosis in tumor cells. These Ru(II) complexes are nuclear permeable and highly active against a panel of human cancer cell lines, with complex 3 displaying activities greater than those of cisplatin. The antiproliferative potentialities of 1-3 are in accordance with their relative lipophilicities, cell membrane penetration abilities, and in vitro DNA binding affinities. Complexes 1-3 trigger release of reactive oxygen species (ROS) and attenuation of ROS by scavengers reduced the sub-G1 population, suggesting ROS-dependent apoptosis. Inhibition of ROS generation also reduces autophagy, indicating that ROS triggers autophagy. Further studies show that suppression of autophagy using pharmacological inhibitors (3-methyladenine and chloroquine) enhances apoptotic cell death. Show less

Iodido osmium(II) complexes [Os(η(6)-arene)(XY)I](+) (XY = p-hydroxy or p-dimethylaminophenylazopyridine, arene = p-cymene or biphenyl) are potently cytotoxic at nanomolar concentrations toward a panel of human cancer cell lines; e.g., IC(50) = 140 nM for [Os(η(6)-bip)(azpy-NMe(2))I](+) toward A2780 ovarian cancer cells. They exhibit low toxicity and negligible deleterious effects in a colon cancer xenograft model, giving rise to the possibility of a broad therapeutic window. The most active complexes are stable and inert toward aquation. Their cytotoxic activity appears to involve redox mechanisms. Show less

Three Ru(II) polypyridyl complexes with potential high DNA-binding ability have been designed and synthesized by extending the conjugated plane of the intercalative ligand and introducing electropositive pendants to the ancillary ligand. Spectral titration, DNA thermal denaturation, viscosity experiments, and quantum chemistry calculations were performed, and the complexes were found to intercalate into DNA base pairs with very high affinity even at high salt concentrations. Benefiting from their high DNA-binding ability, the complexes can effectively inhibit the DNA transcription activity by blocking the binding of T7 RNA polymerase to the template DNA. As efficient transcription inhibitors, the complexes demonstrated high in vitro antitumor activity against four selected tumor cell lines. Show less

Meridional rhodium(III) polypyridyl complexes of the type mer-[RhX(3)(DMSO)(pp)] (X=Cl, pp=phen 1, dpq 2, dppz 3; X=Br, pp=phen 4) represent a promising class of potent cytostatic agents for the treatment of lymphoma and leukemia. Exposure of their DMSO solutions to light leads to slow isomerization to mixtures of the mer and the generally less active fac isomers. As a result, the IC(50) values of 1 and 2 toward HT-29 cells increase from 0.19 and 0.069 microM on immediate use in the dark to 0.66 and 0.312 microM, respectively, after exposure of their DMSO stock solutions to light for 7 days. In striking contrast, the complexes mer-[IrX(3)(DMSO)(phen)] (X=Cl 7, Br 8) are significantly less cytotoxic than their facial Ir(III) polypyridyl counterparts: IC(50)=20.3 microM for 7 and 4.6 microM for fac-[IrCl(3)(DMSO)(phen)] 5 toward MCF-7 cells. The IC(50) values for the complexes fac-[IrX(3)(L)(pp)] 9-13 decrease in the orders: a) Cl>Br for X and b) H(2)O>DMSO for L. Specific apoptotic cell death by DNA fragmentation was detected for leukemia (NALM-6) and lymphoma (BJAB) cells after incubation with 2, 3, and 11 (X=Br, L=H(2)O, pp=phen) for 72 h. Loss of the mitochondrial membrane potential in lymphoma cells indicates that apoptosis is mediated via the intrinsic mitochondrial pathway. LDH release assays after 1 or 3 h demonstrate that necrotic damage is negligible. Show less

Transcription factor Nrf2 is a major regulator of genes encoding phase 2 detoxifying enzymes and antioxidant stress proteins in response to electrophilic agents and oxidative stress. In the absence of such stimuli, Nrf2 is inactive owing to its cytoplasmic retention by Keap1 and rapid degradation through the proteasome system. We examined the contribution of Keap1 to the rapid turnover of Nrf2 (half-life of less than 20 min) and found that a direct association between Keap1 and Nrf2 is required for Nrf2 degradation. In a series of domain function analyses of Keap1, we found that both the BTB and intervening-region (IVR) domains are crucial for Nrf2 degradation, implying that these two domains act to recruit ubiquitin-proteasome factors. Indeed, Cullin 3 (Cul3), a subunit of the E3 ligase complex, was found to interact specifically with Keap1 in vivo. Keap1 associates with the N-terminal region of Cul3 through the IVR domain and promotes the ubiquitination of Nrf2 in cooperation with the Cul3-Roc1 complex. These results thus provide solid evidence that Keap1 functions as an adaptor of Cul3-based E3 ligase. To our knowledge, Nrf2 and Keap1 are the first reported mammalian substrate and adaptor, respectively, of the Cul3-based E3 ligase system. Show less

Reactive oxygen species (ROS) are thought to be involved in many forms of programmed cell death. The role of ROS in cell death caused by oxidative glutamate toxicity was studied in an immortalized mouse hippocampal cell line (HT22). The causal relationship between ROS production and glutathione (GSH) levels, gene expression, caspase activity, and cytosolic Ca2+ concentration was examined. An initial 5-10-fold increase in ROS after glutamate addition is temporally correlated with GSH depletion. This early increase is followed by an explosive burst of ROS production to 200-400-fold above control values. The source of this burst is the mitochondrial electron transport chain, while only 5-10% of the maximum ROS production is caused by GSH depletion. Macromolecular synthesis inhibitors as well as Ac-YVAD-cmk, an interleukin 1beta-converting enzyme protease inhibitor, block the late burst of ROS production and protect HT22 cells from glutamate toxicity when added early in the death program. Inhibition of intracellular Ca2+ cycling and the influx of extracellular Ca2+ also blocks maximum ROS production and protects the cells. The conclusion is that GSH depletion is not sufficient to cause the maximal mitochondrial ROS production, and that there is an early requirement for protease activation, changes in gene expression, and a late requirement for Ca2+ mobilization. Show less