Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C∧N-Chelated and Pyridine Ligands

Rhodium(iii) complexes with isoquinoline derivatives as potential anticancer agents: in vitro and in vivo activity studies

Two rhodium complexes Rh1 and Rh2 with isoquinoline derivatives were synthesized and characterized.

Mitochondria-targeting cyclometalated iridium(iii) complexes for tumor hypoxic imaging and therapy

The organometallic anthraquinone iridium(iii) complexes display an efficient turn-on phosphorescence response to hypoxia. The complexes can induce cell apoptosis in HeLa cells via mitochondrial dysfunction and caspase-3 activation making them excellent candidates as theranostic agents for hypoxic cancer cells.

Zwitterionic and cationic half-sandwich iridium(iii) ruthenium(ii) complexes bearing sulfonate groups: synthesis, characterization and their different biological activities

This work is the first demonstration of the different biological activity between zwitterionic and cationic complexes.

New half-sandwich ruthenium(ii) complexes as proteosynthesis inhibitors in cancer cells

New Ru(ii) arene anticancer complexes with a non-coordinated CHO group that are able to inhibit the protein synthesis; this is a new mode of action for half-sandwich metal complexes.

Phenoxide chelated Ir(iii) N-heterocyclic carbene complexes: synthesis, characterization, and evaluation of their in vitro anticancer activity

Twelve novel half-sandwich IrIII-NHC complexes [(η5-Cpx)Ir(C^O)Cl] were synthesized and characterized. These complexes showed higher cytotoxic activity toward A549 cells and HeLa cells than cisplatin. An increase in the number of contained phenyl groups was related to better anticancer activity. The reaction of complexes with nucleobases 9-MeA, nucleobases 9-EtG, plasmid DNA and CT-DNA showed no significant effects. These complexes captured hydrogen from NADH and converted it to NAD+, which produced the reactive oxygen species (ROS). ROS led to a decrease in the mitochondrial membrane potential and lysosomal damage, finally inducing apoptosis.

Effect of sulfonamidoethylenediamine substituents in RuII arene anticancer catalysts on transfer hydrogenation of coenzyme NAD+ by formate

A series of neutral pseudo-octahedral RuII sulfonamidoethylenediamine complexes [(η6-p-cym)Ru(N,N')Cl] where N,N' is N-(2-(R1,R2-amino)ethyl)-4-toluenesulfonamide (TsEn(R1,R2)) R1,R2 = Me,H (1); Me,Me (2); Et,H (3); benzyl,H (Bz, 4); 4-fluorobenzyl,H (4-F-Bz, 5) or naphthalen-2-ylmethyl,H (Naph, 6), were synthesised and characterised including the X-ray crystal structure of 3. These complexes catalyse the reduction of NAD+ regioselectively to 1,4-NADH by using formate as the hydride source. The catalytic efficiency depends markedly on the steric and electronic effects of the N-substitutent, with turnover frequencies (TOFs) increasing in the order: 1 < 2 < 3, 6 < 4, 5, achieving a TOF of 7.7 h-1 for 4 with a 95% yield of 1,4-NADH. The reduction rate was highest between pH* (deuterated solvent) 6 and 7.5 and improved with an increase in formate concentration (TOF of 18.8 h-1, 140 mM formate). The calculations suggested initial substitution of an aqua ligand by formate, followed by hydride transfer to RuII and then to NAD+, and indicated specific interactions between the aqua complex and both NAD+ and NADH, the former allowing a preorganisation involving interaction between the aqua ligand, formate anion and the pyridine ring of NAD+. The complexes exhibited antiproliferative activity towards A2780 human ovarian cancer cells with IC50 values ranging from 1 to 31 μM, the most potent complex, [(η6-p-cym)Ru(TsEn(Bz,H))Cl] (4, IC50 = 1.0 ± 0.1 μM), having a potency similar to the anticancer drug cisplatin. Co-administration with sodium formate (2 mM), increased the potency of all complexes towards A2780 cells by 20-36%, with the greatest effect seen for complex 6.

Novel half-sandwich iridium(iii) imino-pyridyl complexes showing remarkable in vitro anticancer activity

Seven novel half-sandwich Ir^III cyclopentadienyl complexes, [(η⁵-Cp^x)Ir(N^N)Cl]PF₆, have been prepared and characterized, where Cp^x is Cp* or the biphenyl derivative Cp^xbiph (C₅Me₄C₆H₄C₆H₅), and the N^N-chelating ligands are imino-pyridyl Schiff-bases. The X-ray crystal structures of complexes 2A, 2B, and 3A have been determined. Excitingly, most of the complexes show potent antiproliferative activity towards A549 and HeLa cancer cells, except for Cp* complex 1A towards HeLa cells. Cp^xbiph complex 2B displayed the highest potency, about 19 and 6 times more active than the clinically used drug cisplatin toward A549 and HeLa cells, respectively. These complexes undergo hydrolysis, and the kinetics data have been calculated. DNA binding has been studied by interaction with nucleobases 9-ethylguanine and 9-methyladenine, cleavage of plasmid DNA, and interaction with ctDNA. Interaction with DNA does not appear to be the major mechanism of action. Protein binding (bovine serum albumin, BSA) has been established by UV-Vis, fluorescence and synchronous spectroscopic studies. The stability of complex 2B in the presence of GSH was evaluated. The complexes catalytically convert coenzyme NADH to NAD⁺via hydride transfer. Cp^xbiph complexes 2B and 4B induce cell apoptosis and arrest cell cycles at the S and G₂/M phases towards A549 cancer cells and increase the reactive oxygen species dramatically, which appear to contribute to the remarkable anticancer activity.

Organometallic Conjugates of the Drug Sulfadoxine for Combatting Antimicrobial Resistance

Fourteen novel arene Ru^II , and cyclopentadienyl (Cp^x ) Rh^III and Ir^III complexes containing an N,N'-chelated pyridylimino- or quinolylimino ligand functionalized with the antimalarial drug sulfadoxine have been synthesized and characterized, including three by X-ray crystallography. The rhodium and iridium complexes exhibited potent antiplasmodial activity with IC₅₀ values of 0.10-2.0 μm in either all, or one of the three Plasmodium falciparum assays (3D7 chloroquine sensitive, Dd2 chloroquine resistant and NF54 sexual late stage gametocytes) but were only moderately active towards Trichomonas vaginalis. They were active in both the asexual blood stage and the sexual late stage gametocyte assays, whereas the clinical parent drug, sulfadoxine, was inactive. Five complexes were moderately active against Mycobacterium tuberculosis (IC₅₀ <6.3 μm), while sulfadoxine showed no antitubercular activity. An increase in the size of both the Cp^x ligand and the aromatic imino substituent increased hydrophobicity, which resulted in an increase in antiplasmodial activity.

Significant effects of counteranions on the anticancer activity of iridium(iii) complexes

The rational design of the ligands around transition metals has achieved success in the development of anticancer complexes.

Electronic effects on reactivity and anticancer activity by half-sandwich N,N-chelated iridium(iii) complexes

This work demonstrated how the chemical reactivity and anticancer activity as well as the selectivity of these half-sandwich N,N-chelated iridium(iii) complexes can be controlled and fine-tuned by the modification of the ligand electronic perturbations.

Anticancer activity of complexes of the third row transition metals, rhenium, osmium, and iridium

A summary of recent developments on the anticancer activity of complexes of rhenium, osmium, and iridium is described.

Cyclometalated iridium(iii) complexes induce mitochondria-derived paraptotic cell death and inhibit tumor growthin vivo

A potent anticancer Ir(iii) complex induces paraptotic cell death by causing mitochondrial dysfunction rapidly and inhibits tumor growth significantlyin vivo.

DNA interactions and in vitro anticancer evaluations of pyridine-benzimidazole-based Cu complexes

Copper is an essential element and has redox potential, thus copper complexes have been developed rapidly with the hope of curing cancer. To further develop anticancer agents and investigate their anticancer mechanisms, two Cu complexes, [Cu(bpbb)_0.5·Cl·SCN]·(CH₃OH) (1) and [Cu₂(bpbb)·Br₃·(OH)] _n (2), were synthesized and characterized using 4,4'-bis((2-(pyridin-2-yl)-1H-benzo[d]imidazol-1-yl)methyl)biphenyl (bpbb), with associated Cu(ii) salts. Complex 1 is a binuclear structure, whereas 2 is a one-dimensional complex. Compared with 2, complex 1 exhibited potent in vitro cytotoxicity toward four cell lines (HCT116, BGC823, HT29, and SMMC7721), and was most effective against HCT116 cells. Therefore, further in-depth investigation was carried out using complex 1. Absorption spectral titration experiments, ethidium bromide displacement assays, and circular dichroism spectroscopic studies suggested that complex 1 binds strongly to DNA by intercalation. Complex 1 exhibited a clear concentration-dependent pBR322 DNA cleavage activity. Inductively coupled plasma mass spectrometry testing implied that complex 1 could enter cells and that DNA was one important target. Cellular level assays suggested that complex 1 activates the generation of intracellular reactive oxygen species, causing DNA damage, promoting cell cycle arrest and mitochondria dysfunction, and inducing cellular apoptosis.

Cyclic Peptide-Polymer Nanotubes as Efficient and Highly Potent Drug Delivery Systems for Organometallic Anticancer Complexes

Functional drug carrier systems have potential for increasing solubility and potency of drugs while reducing side effects. Complex polymeric materials, particularly anisotropic structures, are especially attractive due to their long circulation times. Here, we have conjugated cyclic peptides to the biocompatible polymer poly(2-hydroxypropyl methacrylamide) (pHPMA). The resulting conjugates were functionalized with organoiridium anticancer complexes. Small angle neutron scattering and static light scattering confirmed their self-assembly and elongated cylindrical shape. Drug-loaded nanotubes exhibited more potent antiproliferative activity toward human cancer cells than either free drug or the drug-loaded polymers, while the nanotubes themselves were nontoxic. Cellular accumulation studies revealed that the increased potency of the conjugate appears to be related to a more efficient mode of action rather than a higher cellular accumulation of iridium.

Mitochondria-targeted spin-labelled luminescent iridium anticancer complexes

Mitochondria generate energy but malfunction in many cancer cells, hence targeting mitochondrial metabolism is a promising approach for cancer therapy. Here we have designed cyclometallated iridium(iii) complexes, containing one TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) spin label [C43H43N6O2Ir1·PF6]˙ (Ir-TEMPO1) and two TEMPO spin labels [C52H58N8O4Ir1·PF6]˙ (Ir-TEMPO2). Electron paramagnetic resonance (EPR) spectroscopy revealed spin-spin interactions between the TEMPO units in Ir-TEMPO2. Both Ir-TEMPO1 and Ir-TEMPO2 showed bright luminescence with long lifetimes (ca. 35-160 ns); while Ir-TEMPO1 displayed monoexponential decay kinetics, the biexponential decays measured for Ir-TEMPO2 indicated the presence of more than one energetically-accessible conformation. This observation was further supported by density functional theory (DFT) calculations. The antiproliferative activity of Ir-TEMPO2 towards a range of cancer cells was much greater than that of Ir-TEMPO1, and also the antioxidant activity of Ir-TEMPO2 is much higher against A2780 ovarian cancer cells when compared with Ir-TEMPO1. Most notably Ir-TEMPO2 was particularly potent towards PC3 human prostate cancer cells (IC50 = 0.53 μM), being ca. 8× more active than the clinical drug cisplatin, and ca. 15× more selective towards cancer cells versus normal cells. Confocal microscopy showed that both Ir-TEMPO1 and Ir-TEMPO2 localise in the mitochondria of cancer cells.

Targeting cancer cell mitochondria as a therapeutic approach: recent updates

Mitochondria play a key role in ATP generation, redox homeostasis and regulation of apoptosis. Due to the essential role of mitochondria in metabolism and cell survival, targeting mitochondria in cancer cells is considered as an attractive therapeutic strategy. However, metabolic flexibility in cancer cells may enable the upregulation of compensatory pathways, such as glycolysis to support cancer cell survival when mitochondrial metabolism is inhibited. Thus, compounds capable of both targeting mitochondria and inhibiting glycolysis may be particularly useful to overcome such drug-resistant mechanism. This review provides an update on recent development in the field of targeting mitochondria and novel compounds that impact mitochondria, glycolysis or both. Key challenges in this research area and potential solutions are also discussed.

Side Reactions with an Equilibrium Constraint: Detailed Mechanism of the Substitution Reaction of Tetraplatin with dGMP as a Starting Step of the Platinum(IV) Reduction Process

Two possible pathways of the substitution reaction within the reduction process of the Pt^IV(DACH)Cl₄ by dGMP are compared: associative reaction course and autocatalytic Basolo-Pearson mechanisms. Since two forms: single-protonated and fully deprotonated phosphate group of dGMP are present in equilibrium at neutral and mildly acidic solutions, consideration of a side reactions scheme with acido-basic equilibrium-constraint is a very important model for obtaining reliable results. The examined complexes are optimized at the B3LYP-GD3BJ/6-31G(d) level with the COSMO implicit solvation model and Klamt's radii used for cavity construction. Energy characteristics and thermodynamics for all reaction branches are determined using the B3LYP-GD3BJ/6-311++G(2df,2pd)/IEF-PCM/scaled-UAKS level with Wertz's entropy corrections. Rate constants are estimated for each individual branch according to Eyring's transition state theory (TST), averaged according to equilibrium constraint and compared with available experimental data. The determined reaction barriers of the autocatalytic pathway fairly correspond with experimental values. Furthermore, autocatalytic reaction of tetraplatin and its two analogues complexes [Pt^IV(en)Cl₄ and Pt^IV(NH₃)₂Cl₄] are explored and compared with measured data in order to examined general reaction descriptors.

Fluorinated cyclometalated iridium(iii) complexes as mitochondria-targeted theranostic anticancer agents

Cyclometalated iridium(iii) complexes bearing different numbers of fluorine atoms were developed to induce apoptosis via mitochondrial pathways and demonstrated much better anticancer activities than the widely used clinical chemotherapeutic agent cisplatin.

Half-sandwich iridium N-heterocyclic carbene anticancer complexes

Half-sandwich iridium N-heterocyclic carbene complexes display potent anticancer activities and are attractive for development as new anticancer agents.

Design of hybrid heterocyclic systems with a furoxanylpyridine core via tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans

Synthetic strategy for the synthesis of hybrid heterocyclic systems with the furoxanylpyridine core based on the tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans with enamine and norbornadiene has been developed.

A novel 4-fluorobenzenetelluronic trimethyltin ester: synthesis, characterization and in vitro cytotoxicity assessment

A novel 4-fluorobenzenetelluronic trimethyltin ester (Me₃Sn)₄[p-F-PhTe(μ-O)(OH)O₂]₂ (1) has been prepared and structurally characterized, and apoptotic cytotoxicity assessments for A549 cells are made.

Half-sandwich iridiumIII complexes with pyrazole-substituted heterocyclic frameworks and their biological applications

Enhancement in the biological function, i.e., DNA binding, molecular docking, antiproliferative activity and DNA cleavage, of metal complexes as compared to free ligands is observed.

Organometallic rhodium(III) and iridium(III) cyclopentadienyl complexes with curcumin and bisdemethoxycurcumin co-ligands

A series of half-sandwich cyclopentadienyl rhodium(III) and iridium(III) complexes of the type [Cp*M(curc/bdcurc)Cl] and [Cp*M(curc/bdcurc)(PTA)][SO3CF3], in which Cp* = pentamethylcyclopentadienyl, curcH = curcumin and bdcurcH = bisdemethoxycurcumin as O^O-chelating ligands, and PTA = 1,3,5-triaza-7-phosphaadamantane, is described. The X-ray crystal structures of three of the complexes, i.e. [Cp*Rh(curc)(PTA)][SO3CF3] (5), [Cp*Rh(bdcurc)(PTA)][SO3CF3] (6) and [Cp*Ir(bdcurc)(PTA)][SO3CF3] (8), confirm the expected "piano-stool" geometry. With the exception of 5, the complexes are stable under pseudo-physiological conditions and are moderately cytotoxic to human ovarian carcinoma (A2780 and A2780cisR) cells and also to non-tumorigenic human embryonic kidney (HEK293) cells, but lack the cancer cell selectivity observed for related arene ruthenium(II) complexes.

DFT Investigation of the Mechanism of Action of Organoiridium(III) Complexes As Anticancer Agents

The potential use of synthetic metal complexes able to catalyze chemical transformations in living organisms is currently attracting a great deal of attention. Recently, organometallic ruthenium and iridium complexes have revealed an unexpected ability to modulate the redox status of cancer cells. In particular, half-sandwich organoiridium(III) cyclopentadienyl complexes of general formula [(η(5)-Cp(x))Ir(III)(X(∧)Y)Z](0/+), where Cp(x) = Cp*, Cp(xph) (tetramethyl-(phenyl)cyclopentadienyl) or Cp(xbiph) (tetramethyl(biphenyl)-cyclopentadienyl), X(∧)Y = bidentate ligand with nitrogen, oxygen, and/or carbon donor atoms, and Z = Cl, H2O, or pyridine (py) have shown promising antiproliferative activity toward cancer cells, higher potency than cisplatin, and a different mechanism of action due to the increase of the oxidative stress in cells. As such, complexes can belong to the class of DNA interacting compounds and attack on DNA can represent a secondary mechanism of action. We have explored here by means of density functional calculations (M06-L) and with the support of experimental observations for both [(η(5)-Cp(xbiph))Ir-(phpy) (Cl)], 1-Cl, and [(η(5)-Cp(xbiph))Ir-(phpy) (py)], 1-py, complexes the mechanistic aspects of the hydrolysis reaction, H2O2 ROS production by assisted hydride transfer from NADH to molecular oxygen, interaction with purine nucleobases adenine and guanine as well as gluthatione, that is highly abundant in cells, alongside the reaction mechanism for the oxidation of the formed sulfur-coordinated thiolate to the corresponding sulfenato complex. The comparison between kinetic and thermodynamic parameters calculated for all the involved processes shows that, according to the hypothesis based on experimental findings, the interaction with the tripeptide glutathione causes deactivation of 1-Cl, whereas 1-py, in both its aquated and nonaquated form, can induce cell apoptosis in a dual manner: DNA damage and H2O2 ROS production to increase oxidative stress.