Organoruthenium Complexes with C^N Ligands are Highly Potent Cytotoxic Agents that Act by a New Mechanism of Action

Necrosis inducing tetranuclear Ru(II)-Re(I) metal complex for anticancer therapy

Chemotherapy is one of the most widely used anticancer treatments worldwide. However, despite its clinical effectiveness, most chemotherapeutic agents are associated with severe side effects. To address this limitation, there is an urgent need for the development of novel anticancer agents. Among the promising alternatives, Ruthenium and Rhenium complexes have garnered significant attention in the scientific literature. This study proposes combining these two metal moieties into a single tetranuclear complex, bridged by a 2,2'-bipyrimidine ligand. Cytotoxicity tests revealed broad activity of the novel metal complex against multiple cancer cell lines. Mechanistic studies suggested that the complex induces cell death by necrosis. Further analyses demonstrated its ability to eradicate colon carcinoma tumor spheroids at micromolar concentrations. To the best of our knowledge, this represents the first example of a Ru(II)-Re(I) tetranuclear metal complex as an anticancer agent.

A Novel Substituted Benzo[g]quinoxaline-Based Cyclometalated Ru(II) Complex as a Biocompatible Membrane-Targeted PDT Colon Cancer Stem Cell Agent

Herein, we describe and investigate biological activity of three octahedral ruthenium(II) complexes of the type [Ru(C∧N)(phen)2]+, RuL1-RuL3, containing a π-expansive cyclometalating substituted benzo[g]quinoxaline ligand (C∧N ligand) (phen = 1,10-phenanthroline). Compounds RuL1-RuL3 in cervical, melanoma, and colon human cancer cells exhibit high phototoxicity after irradiation with light (particularly blue), with the phototoxicity index reaching 100 for the complex RuL2 in most sensitive HCT116 cells. RuL2 accumulates in the cellular membranes. If irradiated, it induces lipid peroxidation, likely connected with photoinduced ROS generation. Oxidative damage to the fatty acids leads to the attenuation of the membranes, the activation of caspase 3, and the triggering of the apoptotic pathway, thus implementing membrane-localized photodynamic therapy. RuL2 is the first photoactive ruthenium-based complex capable of killing the hardly treatable colon cancer stem cells, a highly resilient subpopulation within a heterogeneous tumor mass, responsible for tumor recurrence and the metastatic progression of cancer.

Fine-Tuning of the Optical and Electrochemical Properties of Ruthenium(II) Complexes with 2-Arylbenzimidazoles and 4,4'-Dimethoxycarbonyl-2,2'-bipyridine

A series of cyclometalated complexes of ruthenium (II) with four different substituents in the aryl fragment of benzimidazole was synthesized in order to study the effect of substituent donation on the electronic structure of the substances. The resulting complexes were studied using X-ray diffraction, NMR spectroscopy, MALDI mass spectrometry, electron absorption spectroscopy, luminescence spectroscopy, and cyclic voltammetry as well as DFT/TDDFT was also used to interpret the results. All the complexes have intense absorption in the range of up to 700 nm, the triplet nature of the excited state was confirmed by measurement of luminescence decay. With an increase in substituent donation, a red shift of the absorption and emission bands occurs, and the lifetime of the excited state and the redox potential of the complex decrease. The combination of these properties shows that the complexes are excellent dyes and can be used as photosensitizers.

Ruthenium(II)-Tris-pyrazolylmethane Complexes Inhibit Cancer Cell Growth by Disrupting Mitochondrial Calcium Homeostasis

While ruthenium arene complexes have been widely investigated for their medicinal potential, studies on homologous compounds containing a tridentate tris(1-pyrazolyl)methane ligand are almost absent in the literature. Ruthenium(II) complex 1 was obtained by a modified reported procedure; then, the reactions with a series of organic molecules (L) in boiling alcohol afforded novel complexes 2–9 in 77–99% yields. Products 2–9 were fully structurally characterized. They are appreciably soluble in water, where they undergo partial chloride/water exchange. The antiproliferative activity was determined using a panel of human cancer cell lines and a noncancerous one, evidencing promising potency of 1, 7, and 8 and significant selectivity toward cancer cells. The tested compounds effectively accumulate in cancer cells, and mitochondria represent a significant target of biological action. Most notably, data provide convincing evidence that the mechanism of biological action is mediated by the inhibiting of mitochondrial calcium intake.

Cyclometallated Ruthenium Complex with 3,3',5,5'-Tetramethyl-1,1'-biphenyl-4,4'-bipyrazole and 2,2'-Dicarboxybipyridine: Synthesis, Optical Properties, and Quantum Chemical Modeling

Abstract

New complex [RuL(Dmdcbp)2]PF6 (I) is synthesized by the consecutive reactions of [Ru-p-cymene]2Cl4 with 3,3',5,5'-tetramethyl-1,1'-biphenyl-4,4'-bipyrazole (L) and 4,4'-dicarboxy-2,2'-bipyridine in a methanol–chloroform medium. The composition of complex I is confirmed by NMR and elemental analysis, and the optical and luminescence properties of the complex are studied. Ligand L is characterized for the first time by X-ray diffraction (CIF file CCDC no. 2118676). Quantum chemical calculations in terms of the density functional theory are performed for the interpretation of the absorption and emission spectra. Complex I is promising for using as a photosensitizer.

Novel cis-Pt(II) Complexes with Alkylpyrazole Ligands: Synthesis, Characterization, and Unusual Mode of Anticancer Action

One concept of improving anticancer effects of conventional platinum-based antitumor drugs consists of conjugating these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, physicochemical characterization, biological effects, and mechanisms of action of four new analogs of conventional cisplatin, namely, cis-Pt(II) complexes containing either methyl or ethyl pyrazole N-donor ligands and chlorido or iodido ligands. It is noteworthy that while chlorido complexes display activity in a variety of cancer cell lines comparable to cisplatin, iodido complexes are considerably more potent due to their enhanced hydrophobicity and consequently enhanced cellular accumulation. Moreover, all of the studied Pt(II) alkylpyrazole complexes display a higher selectivity for tumor cells and effectively overcome the acquired resistance to cisplatin. Further results focused on the mechanism of action of the studied complexes and showed that in contrast to cisplatin and several platinum-based antitumor drugs, DNA damage by the investigated Pt(II)-alkylpyrazole complexes does not play a major role in their mechanism of action. Our findings demonstrate that inhibition of the tubulin kinesin Eg5, which is essential for forming a functional mitotic spindle, plays an important role in their mechanism of antiproliferative action.

Pt(ii) complex containing the 1R,2R enantiomer of trans-1,2-diamino-4-cyclohexene ligand effectively and selectively inhibits the viability of aggressive pancreatic adenocarcinoma cells and alters their lipid metabolism

New compounds structurally derived from oxaliplatin exhibit high potency in malignant pancreatic adenocarcinoma cells. Their mechanism of antiproliferative action in pancreatic cancer cells involves inhibition of de novo lipid synthesis.

Ru(ii), Ir(iii), Re(i) and Rh(iii) based complexes as next generation anticancer metallopharmaceuticals

Several anticancer drugs such as cisplatin, and its analogues, epirubicin, and doxorubicin are well known for their anticancer activity but the therapeutic value of these drugs comes with certain side effects and they cannot distinguish between normal and cancer cells. Thus, a major challenge for researchers around the world is to develop an anticancer drug with the least toxicity and more target specificity. With the successful reporting of NAMI-A and KP1019, a new path has emerged in the anticancer field. Recently, several Ru(ii) complexes have been reported for their anticancer activity due to their enhanced cellular uptake and selectivity towards cancer cells. Apart from the Ru(ii) complexes, a large amount of research has been carried out with Ir(iii), Re(i), and Rh(iii) based complexes, which exhibited promising anticancer activity. The present review reports various Ru(ii), Ir(iii), Re(i), and Rh(iii) based complexes for their anticancer activity based on their cytotoxicity profiles, biological targets and mechanism of action.

DNA binding and evaluation of anticancer activity in vitro and in vivo of iridium(III) polypyridyl complexes

In this report, we synthesized three new iridium(III) complexes: [Ir(piq)₂(apip)]PF₆ (Ir1, piq = 1-phenylisoquinoline, apip = 2-aminophenyl-1H-imidazo[4,5-f][1,10]phenanthroline), [Ir(piq)₂(maip)]PF₆ (Ir2, maip = 3-aminophenyl-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ir(piq)₂(paip)]PF₆ (Ir3, paip = 4-aminophenyl-1H-imidazo[4,5-f][1,10]phenanthroline). The DNA binding was investigated. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method was used to detect the cytotoxic activity of Ir1, Ir2 and Ir3, the complexes show highly active against B16 cells with IC₅₀ values of 0.3 ± 0.2 μM, 3.7 ± 0.2 μM and 4.6 ± 1.1 μM, respectively. Subsequently, cellular uptake suggested that the cytotoxicity of the complexes is attributed to their differences in cellular uptake levels. In addition, complexes Ir1, Ir2 and Ir3 induce cell cycle arrest at the G0/G1 phase and regulate the cell cycle mediators such as cyclin D1, CDK6 (cyclin-dependent kinase 6), CDK4 and p21, leading to the inhibition of B16 cells proliferation. The autophagy was investigated by monodansylcadaverine (MDC) staining. The complexes can promote the change from LC3-I to LC3-II, up-regulate levels of Beclin-1 and down-regulate expression of p62. The complexes induced apoptosis by regulating the expression levels of related indicators such as PARP (poly ADP-ribose polymerase), PI3K (phosphoinositide-3 kinase), AKT (protein kinase B), Caspase, Bcl-2 (B-cell lymphoma-2), Bad (Bcl2 associated death promoter), Bax (Bcl2-associated X) and Cyto C (cytochrome C). Additionally, Ir1 exerted significant antitumor activity in the suppression of malignant melanoma proliferation in vivo. As indicated in the above results, these complexes were highly effective for malignant melanoma treatment through the intrinsic pathway and provided much insight into anticancer drugs for tumor therapy.

Novel organo-osmium(ii) proteosynthesis inhibitors active against human ovarian cancer cells reduce gonad tumor growth inCaenorhabditis elegans

Novel Os(ii) arene complexes with a deprotonated ppy or ppy-CHO C^N ligand have been synthesized to selectively act on cancer cells as proteosynthesis inhibitorsin vitroand exert antitumor activityin vivoinC. elegansmodels.

Amino-Functionalized Mesoporous Silica Nanoparticle-Encapsulated Octahedral Organoruthenium Complex as an Efficient Platform for Combatting Cancer

In the process of synthesis of a new drug, as important as the drug itself is the formulation used, because the same compound can present a very different efficacy depending on how it is administered. In this work, we demonstrate how the antitumor capacity of a new octahedral organoruthenium complex, [Ru(ppy-CHO)(phen)₂][PF₆] is affected by its encapsulation in different types of mesoporous silica nanoparticles. The interactions between the Ru complex and the silica matrix and how these interactions are affected at two different pHs (7.4 and 5.4, mimicking physiological and endolysosomal acidic conditions, respectively) have been studied. The encapsulation has also been shown to affect the induction of apoptosis and necrosis and progression of the cell cycle compared to the free drug. The encapsulation of the Ru complex in nanoparticles functionalized with amino groups produced very high anticancer activity in cancer cells in vitro, especially against U87 glioblastoma cells, favoring cellular internalization and significantly increasing the anticancer capacity of the initial non-encapsulated Ru complex.

Ru(ii) photosensitizers competent for hypoxic cancers via green light activation

Ru(ii) complexes exhibit phototherapeutic indexes higher than 750 in cancer HeLa cells with low nanomolar IC₅₀ values under low doses of non-harmful green light and are active in normoxia and hypoxia conditions.

Discovery of selective, antimetastatic and anti-cancer stem cell metallohelices via post-assembly modification

Helicates and related metallofoldamers, synthesised by dynamic self-assembly, represent an area of chemical space inaccessible by traditional organic synthesis, and yet with potential for discovery of new classes of drug. Here we report that water-soluble, optically pure Fe(ii)- and even Zn(ii)-based triplex metallohelices are an excellent platform for post-assembly click reactions. By these means, the in vitro anticancer activity and most importantly the selectivity of a triplex metallohelix Fe(ii) system are dramatically improved. For one compound, a remarkable array of mechanistic and pharmacological behaviours is discovered: inhibition of Na+/K+ ATPase with potency comparable to the drug ouabain, antimetastatic properties (including inhibition of cell migration, re-adhesion and invasion), cancer stem cell targeting, and finally colonosphere inhibition competitive with the drug salinomycin.

Hemilabile bonding of 1-oxa-4,7-dithiacyclononane in cyclometallated palladium(ii) complexes

The synthesis and characterization of a series of cyclometallated complexes of Pd(ii) incorporating the mixed donor ligand 1-oxa-4,7-dithiacyclononane ([9]aneS₂O) are presented in this study. Complexes of the form [Pd(C^N)([9]aneS₂O)](PF₆) (C^N = 2-phenylpyridine (ppy) 1b, 4-(2-pyridyl)benzaldehyde (ppyCHO) 2b, 7,8-benzoquinoline (bzq) 3b, 2-benzothienylpyridine (btp) 4b, 2-phenylbenzothiazole (pbt) 5b), were obtained in high-yield from a simple two-step synthetic scheme. All of these complexes were fully characterized by NMR, ESI-MS, IR, combustion analyses, and most (1b, 2b, 4b, 5b) by X-ray crystallography. Solution ¹H and ¹³C NMR studies of [Pd(C^N)([9]aneS₂O)](PF₆) complexes demonstrate complicated [9]aneS₂O behavior at room temperature. Variable temperature NMR reveals dynamic bonding of the [9]aneS₂O ligand consistent with the presence of both endodentate and exodentate bonding modes. This is in stark contrast to the related [9]aneS₃ (1,4,7-trithiacyclononane) cogeners that demonstrate fluxional endodentate bonding only in solution. X-ray structures reveal only exodenate [9]aneS₂O bonding in this series, unlike the related [9]aneS₃ complexes that show endodenate bonding with an axial PdS interaction. DFT calculations performed on endo and exo [9]aneS₂O bonding forms of 4b, as well as a transition state calculation for interconversion, suggest reasonable access to both bonding forms based on the energy barrier. Natural bond order calculations provide further evidence for a weak axial PdO interaction in the endo form of 4b.

A Subset of New Platinum Antitumor Agents Kills Cells by a Multimodal Mechanism of Action Also Involving Changes in the Organization of the Microtubule Cytoskeleton

The substitution inert platinum agent [Pt(1 S,2 S-diaminocyclohexane)(5,6-dimethyl-1,10-phenanthroline)]²⁺ (56MeSS, 5) is a potent cytotoxic metallodrug. In contrast to conventional cisplatin or oxaliplatin, the mechanism of action (MoA) of 5 is fundamentally different. However, details of the mechanism by which the 5,6-dimethyl-1,10-phenanthroline ligand contributes to the cytotoxicity of 5 and its derivatives have not been sufficiently clarified so far. Here, we show that 5 and its Pt(IV) derivatives exhibit an intriguing potency in the triple-negative breast cancer cells MDA-MB-231. Moreover, we show that the Pt(IV) derivatives of 5 act by multimodal MoA resulting in the global biological effects, that is, they damage nuclear DNA, reduce the mitochondrial membrane potential, induce the epigenetic processes, and last but not least, the data provide evidence that changes in the organization of cytoskeleton networks are functionally important for 5 and its derivatives, in contrast to clinically used platinum cytostatics, to kill cancer cells.

Molecular superoxide radical photogeneration in cancer cells by dipyridophenazine iridium(iii) complexes

The switch from Type II to Type I photochemical mechanism by new Ir(iii) complexes for improved PDT of cancer under hypoxia is demonstrated.

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.

A new C,N-cyclometalated osmium(ii) arene anticancer scaffold with a handle for functionalization and antioxidative properties

A series of six osmium(ii) complexes of the type [(η6-p-cymene)Os(C^N)X] (X = chlorido or acetato) containing benzimidazole C^N ligands with an ester group as a handle for further functionalization have been synthesized. They exhibit IC50 values in the low micromolar range in a panel of cisplatin (CDDP)-resistant cancer cells (approximately 10× more cytotoxic than CDDP in MCF-7), decrease the levels of intracellular ROS and reduce the NAD+ coenzyme, and inhibit tubulin polymerization. This discovery could open the door to a new large family of osmium(ii)-based bioconjugates with diverse modes of action.

Imine-N-Heterocyclic Carbenes as Versatile Ligands in Ruthenium(II) p-Cymene Anticancer Complexes: A Structure-Activity Relationship Study

A family of novel imine-N-heterocyclic carbene ruthenium(II) complexes of the general formula [(η⁶ -p-cymene)Ru(C^N)Cl]PF₆ ^- (where C^N is an imine-N-heterocyclic carbene chelating ligand with varying substituents) have been prepared and characterized. In this imine-N-heterocyclic carbene chelating ligand framework, there are three potential sites that can be modified, which distinguishes this class of ligand and provides a body of flexibilities and opportunities to tune the cytotoxicity of these ruthenium(II) complexes. The influence of substituent effects of three tunable domains on the anticancer activity and catalytic ability in converting coenzyme NADH to NAD⁺ is investigated. This family of complexes displays an exceedingly distinct anticancer activity against A549 cancer cells, despite their close structural similarity. Complex 9 shows the highest anticancer activity in this series against A549 cancer cells (IC₅₀ =14.36 μm), with an approximately 1.5-fold better activity than the clinical platinum drug cisplatin (IC₅₀ =21.30 μm) in A549 cancer cells. Mechanistic studies reveal that complex 9 mediates cell death mainly through cell stress, including cell cycle arrest, inducing apoptosis, increasing intracellular reactive oxygen species (ROS) levels, and depolarization of the mitochondrial membrane potential (MMP). Furthermore, lysosomal damage is also detected by confocal microscopy.