Impact of various lipophilic substituents on ruthenium(II), rhodium(III) and iridium(III) salicylaldimine-based complexes: synthesis, in vitro cytotoxicity studies and DNA interactions

Anticancer activity of Ni(II) and Zn(II) complexes based on new unsymmetrical salophen-type ligands: synthesis, characterization and single-crystal X-ray diffraction

The discovery of new coordination compounds with anticancer properties is an active field of research due to the severe side effects of platinum-based compounds currently used in chemotherapy. In the search for new agents for the treatment of cancer, unsymmetrical N2O2-tetradentate ligand (H2L1 and H2L2) and their Ni(II) and Zn(II) asymmetric complexes (NiII-L1-2 and ZnII-L1-2) have been synthesized and fully characterized. 1H NMR studies revealed that the ligands and complexes were stable in mixtures of DMSO : D2O (9 : 1). Complementary UV-Vis studies confirmed that ZnII derivatives also exhibit high stability in mixtures DMSO : buffer (6 : 4) after 24 h. Single-crystal X-ray diffraction studies confirmed the molecular structures of H2L1, H2L2, NiII-L1, and NiII-L2. At the molecular level, complexes were completely planar without significant distortions of the square-planar geometry according to τ4 parameter. Furthermore, the crystalline structures revealed non-classical intermolecular interactions of the C-H⋯O and the Ni⋯Ni type. The ligands and complexes were screened against the human osteosarcoma (MG-63), human colon cancer (HCT-116), breast cancer (MDA-MB-231) cell lines, and non-cancerous cells (L929). H2L1 and H2L2 ligands not caused cytotoxic effects at a concentration of 100 μM, while NiII-L2, ZnII-L1, and ZnII-L2 complexes induce cytotoxic effects in all cell lines. NiII-L2 was a more active complex against MG-63 (3.9 ± 1.5) and HCT-116 (3.4 ± 1.7) cell lines with IC50 values in the low micromolar range. In addition, this compound was 10-, 5-, and 11-fold more potent than cisplatin in MG-63 (39 ± 1.8), HCT-116 (17.2), and MDA-MB-231 (131 ± 18), respectively. Three complexes exhibited great selectivity for tumoral cells with SI values ranging from 1.6 to 7.4.

Ru(II) CONTAINING PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CRITIQUE ON REPORTING AND AN ATTEMPT TO COMPARE EFFICACY

Ruthenium(II)-based coordination complexes have emerged as photosensitizers (PSs) for photodynamic therapy (PDT) in oncology as well as antimicrobial indications and have great potential. Their modular architectures that integrate multiple ligands can be exploited to tune cellular uptake and subcellular targeting, solubility, light absorption, and other photophysical properties. A wide range of Ru(II) containing compounds have been reported as PSs for PDT or as photochemotherapy (PCT) agents. Many studies employ a common scaffold that is subject to systematic variation in one or two ligands to elucidate the impact of these modifications on the photophysical and photobiological performance. Studies that probe the excited state energies and dynamics within these molecules are of fundamental interest and are used to design next-generation systems. However, a comparison of the PDT efficacy between Ru(II) containing PSs and 1st or 2nd generation PSs, already in clinical use or preclinical/clinical studies, is rare. Even comparisons between Ru(II) containing molecular structures are difficult, given the wide range of excitation wavelengths, power densities, and cell lines utilized. Despite this gap, PDT dose metrics quantifying a PS's efficacy are available to perform qualitative comparisons. Such models are independent of excitation wavelength and are based on common outcome parameters, such as the photon density absorbed by the Ru(II) compound to cause 50% cell kill (LD50) based on the previously established threshold model. In this focused photophysical review, we identified all published studies on Ru(II) containing PSs since 2005 that reported the required photophysical, light treatment, and in vitro outcome data to permit the application of the Photodynamic Threshold Model to quantify their potential efficacy. The resulting LD50 values range from less than 1013 to above 1020 [hν cm-3], indicating a wide range in PDT efficacy and required optical energy density for ultimate clinical translation.

Mitochondria-targeted cyclometalated iridium (III) complex for H2S-responsive intracellular redox regulation as potent photo-oxidation anticancer agent

Owing to the safety and low toxicity, photodynamic therapy (PDT) for cancer treatment has received extensive attention. However, the excess H₂S in cancer cells reduces the PDT efficiency, because H₂S indirectly depletes the reactive oxygen species (ROS). To improve anticancer efficiency, a mitochondria-targeted iridium(III) complex Ir-MMB has been developed as H₂S consumer and photo-oxidation anticancer agent. On the one hand, complex Ir-MMB can consume H₂S with sensitive phosphorescence turn-on, which has been successfully applied to exogenous and endogenous H₂S response imaging in living cells. On the other hand, Ir-MMB can enhance its anticancer activity and cause photo-oxidation damage via catalyzing the oxidation of reduced form of nicotinamide-adenine dinucleotide (NADH) to NAD⁺ and producing H₂O₂ under light, and ultimately results in cell apoptosis through mitochondrial depolarization and ROS production.

Advancement in specific strand scission of DNA and evaluation of in-vitro biological assessment by pharmacologically significant tetraaza macrocyclic metal complexes constrained by triazole

INTRODUCTION

Recent Advances in Schiff Base Ruthenium Metal Complexes: Synthesis and Applications

This review concentrates on recent developments in ruthenium Schiff bases, whose steric and electronic characteristics can be manipulated easily by selecting suitable condensing aldehydes or ketones and primary amines, and their metal complexes. Ruthenium metal-based complexes and Schiff base ligands are rapidly becoming conventionally considered for biological applications (antioxidant, anticancer, antimicrobial), in catalysis, in functional materials, in sensors, and as pigments for dyes. Ruthenium complexes exhibit a broad variety of activities concerning simple Schiff base ligands. This may be due to the octahedral bonding of both Ru(II) and Ru(III) complexes, which acquire an extended reservoir of a three-dimensional framework, providing the potential for an elevated degree of site selectivity for binding to their biological targets. This review provides an overview of this field, and intends to highlight both ligand design and synthetic methodology development, as well as significant applications of these metal complexes. In this review, we summarize our work on the development of ruthenium complexes, which was performed over the last few years.

Anticancer Half-Sandwich Rhodium(III) Complexes

Platinum-based anticancer drugs are most likely the most successful group of bioinorganic compounds. Their apparent disadvantages have led to the development of anticancer compounds of other noble metals, resulting in several ruthenium-based drugs which have entered clinical trials on oncological patients. Besides ruthenium, numerous rhodium complexes have been recently reported as highly potent antiproliferative agents against various human cancer cells, making them potential alternatives to Pt- and Ru-based metallodrugs. In this review, half-sandwich Rh(III) complexes are overviewed. Many representatives show higher in vitro potency than and different mechanisms of action (MoA) from the conventional anticancer metallodrugs (cisplatin in most cases) or clinically studied Ru drug candidates. Furthermore, some of the reviewed Rh(III) arenyl complexes are also anticancer in vivo. Pioneer anticancer organorhodium compounds as well as the recent advances in the field are discussed properly, and adequate attention is paid to their anticancer activity, solution behaviour and various processes connected with their MoA. In summary, this work summarizes the types of compounds and the most important biological results obtained in the field of anticancer half-sandwich Rh complexes.

Studies of anticancer activity in vivo and in vitro behaviors of liposomes encapsulated iridium(III) complex

Iridium(III) complexes have gained great attention in cancer treatment in recent years. In this paper, we designed and synthesized a new iridium(III) complex [Ir(piq)₂(DQTT)](PF₆) Ir1 (piq = 1-phenylisoquinoline, DQTT = 12-(1,4-dihydroquinoxalin-6-yl)-4,5,9,14-tetraazabenzo[b]triphenylene). The Ir1-loaded PEGylated liposomes (Lipo-Ir1) were prepared using the ethanol injection method. The anticancer activity of the complex and Lipo-Ir1 against SGC-7901 (human gastric adenocarcinoma), A549 (human lung carcinoma), HeLa (human cervical carcinoma), HepG2 (human hepatocellular carcinoma), BEL-7402 (human hepatocellular carcinoma), and normal NIH3T3 (mouse embryonic fibroblasts) was tested by the MTT method. The complex Ir1 shows moderate or low cytotoxicity against the selected cancer cells, whereas the Lipo-Ir1 exhibits high anticancer activity toward the same cancer cells. The apoptosis induced by Lipo-Ir1 was assayed by flow cytometry and Lipo-Ir1 induced apoptosis through increasing intracellular reactive-oxygen species levels, decreasing mitochondrial membrane potential, further promoting cytochrome c release and causing the increase of level of intracellular Ca²⁺. Western blot was used to detect the changes in Bcl-2 family protein and PI3K/AKT pathway proteins. The cloning experiments demonstrated that the Lipo-Ir1 can effectively inhibit cell proliferation. In vivo experiments, Lipo-Ir1 inhibited tumor growth in xenograft nude mice, and the percentage of tumor growth inhibition in vivo was 75.70%. Overall, the liposomes Lipo-Ir1 exhibits higher anticancer activity than Ir1 under the same conditions. These results indicated that Lipo-Ir1 may be a valuable resource for cancer therapy.

Crystal structure, Hirshfeld surface analysis and DFT studies of 4-methyl-2-({[4-(tri-fluoro-meth-yl)phen-yl]imino}-meth-yl)phenol

The title compound, C15H12F3NO, crystallizes with one mol-ecule in the asymmetric unit. The configuration of the C=N bond is E and there is an intra-molecular O-H⋯N hydrogen bond present, forming an S(6) ring motif. The dihedral angle between the mean planes of the phenol and the 4-tri-fluoro-methyl-phenyl rings is 44.77 (3)°. In the crystal, mol-ecules are linked by C-H⋯O inter-actions, forming polymeric chains extending along the a-axis direction. The Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from C⋯H/H⋯C (29.2%), H⋯H (28.6%), F⋯H/H⋯F (25.6%), O⋯H/H⋯O (5.7%) and F⋯F (4.6%) inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap. The crystal studied was refined as an inversion twin.

Differences in Stability, Cytotoxicity, and Mechanism of Action of Ru(II) and Pt(II) Complexes of a Bidentate N,O Donor Ligand

We report [Ru^II(L)(η⁶-p-cym)Cl] (1 and 2) and [Pt^II(L)(DMSO)Cl] (3 and 4) complexes, where L is a chelate imine ligand derived from chloroethylamine and salicylaldehyde (HL1) or o-vanillin (HL2). The complexes were characterized by single-crystal X-ray diffraction and other analytical techniques. The ¹H nuclear magnetic resonance data show that both the Ru(II) and Pt(II) complexes start forming the aquated complex within an hour. The aquated complexes are stable at least up to 24 h. The complexes bind to the N⁷ of the model nucleobase 9-ethylguanine (9-EtG). Interaction with calf thymus (CT) DNA shows moderate binding interactions with binding constants, K_b (3.7 ± 1.2) × 10³ M^-1 and (4.3 ± 1.9) × 10³ M^-1 for 1 and 3, respectively. The complexes exhibit significant antiproliferative activity against human pancreas ductal adenocarcinoma (Mia PaCa-2), triple negative metastatic breast adenocarcinoma (MDA-MB-231), hepatocellular carcinoma (Hep G2), and colorectal adenocarcinoma (HT-29) cell lines. The studies show that with the same ligand the Pt(II) complexes are more potent than the Ru(II) complexes. The in vitro potencies of all the complexes toward pancreatic cancer cell line MIA PaCa-2 are more than cisplatin (CDDP). The Pt(II) and Ru(II) complexes show similar binding constants with CT-DNA, but the reactivity of the Pt(II) complex 3 with 9-EtG is faster and their overall cell killing pathways are different. This is evident from the arrest of the cell cycle by the Ru(II) complex 1 in the G2/M phase in contrast to the SubG1 phase arrest by the Pt(II) complex 3. The immunoblot study shows that 3 increases cyclin D and Bcl-2 expression in MDA-MB-231 due to the SubG1 phase arrest where these proteins express in greater quantities. However, both 1 and 3 kill in the apoptotic pathway via dose-dependent activation of caspase 3. Complex 3 depolarizes the mitochondria more efficiently than 1, suggesting its higher preference for the intrinsic pathway of apoptosis. Our work reveals that the same bidentate ligand with a change of the metal center, viz, Pt(II) or Ru(II), imparts significant variation in cytotoxic dosage and pathway of action due to specific intrinsic properties of a metal center (viz, coordination geometry, solution stability) manifested in a complex.

Synthesis and antiproliferative activity of benzimidazole-based, trinuclear neutral cyclometallated and cationic, N^N-chelated ruthenium(ii) complexes

A series of 2-phenyl and 2-pyridyl tris-benzimidazole ligands was reacted with the [Ru(p-cymene)Cl₂]₂ dimer to yield the corresponding neutral cyclometallated and cationic trinuclear organoruthenium(ii) complexes.

Recent progress in the development of organometallics for the treatment of cancer

From their early successes in medicine, organometallic compounds continue to attract interest as potential chemotherapeutics to treat a range of diseases. Here, we show from recent literature selected largely from the last two years that organometallics offer unique opportunities in medicine and, increasingly, a mechanistic-based approach is applied to their development, which has not always been the case.

Binding mechanisms of half-sandwich Rh(III) and Ru(II) arene complexes on human serum albumin: a comparative study

Abstract

Various half-sandwich ruthenium(II) arene complexes and rhodium(III) arene complexes have been intensively investigated due to their prominent anticancer activity. The interaction of the organometallic complexes of Ru(η⁶-p-cymene) and Rh(η⁵-C₅Me₅) with human serum albumin (HSA) was studied in detail by a combination of various methods such as ultrafiltration, capillary electrophoresis, ¹H NMR spectroscopy, fluorometry and UV–visible spectrophotometry in the presence of 100 mM chloride ions. Binding characteristics of the organometallic ions and their complexes with deferiprone, 2-picolinic acid, maltol, 6-methyl-2-picolinic acid and 2-quinaldic acid were evaluated. Kinetic aspects and reversibility of the albumin binding are also discussed. The effect of low-molecular-mass blood components on the protein binding was studied in addition to the interaction of organorhodium complexes with cell culture medium components. The organometallic ions were found to bind to HSA to a high extent via a coordination bond. Release of the bound metal ions was kinetically hindered and could not be induced by the denaturation of the protein. Binding of the Ru(η⁶-p-cymene) triaqua cation was much slower (ca. 24 h) compared to the rhodium congener (few min), while their complexes interacted with the protein relatively fast (1–2 h). The studied complexes were bound to HSA coordinatively. The highly stable and kinetically inert 2-picolinate Ru(η⁶-p-cymene) complex bound in an associative manner preserving its original entity, while lower stability complexes decomposed partly or completely upon binding to HSA. Fast, non-specific and high-affinity binding of the complexes on HSA highlights their coordinative interaction with various types of proteins possibly decreasing effective drug concentration.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s00775-019-01683-0) contains supplementary material, which is available to authorized users.

Anticancer activity and mechanism of bis-pyrimidine based dimetallic Ru(II)(η6-p-cymene) complex in human non-small cell lung cancer via p53-dependent pathway

Non-small cell lung cancer (NSCLC) is the most common cancer worldwide, which is related with poor prognosis and resistance to chemotherapy. Notably, ruthenium-based complexes have emerged as good alternative to the currently used platinum-based drugs for cancer therapy. In the present study, we synthesized a novel bis-pyrimidine based ligand 1,3-bis(2-methyl-6-(pyridin-2-yl)pyrimidin-4-yl)benzene (L) and used it in the synthesis of a dimetallic Ru(II) cymene complex [(Ru(η⁶-p-cymene)Cl)₂(1,3-bis(2-methyl-6-(pyridin-2-yl)pyrimidin-4-yl)benzene)] (L-Ru). We checked the stability of this complex in solution state in D₂O/DMSO‑d₆ mixture and found it to be highly stable under these conditions. We determined the anticancer activity and mechanism of action of L-Ru in human NSCLC A549 and A427 by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and related biological analyses. These results revealed that L-Ru exerted a strong inhibitory effect on the cells proliferation,G0/G1-arrest, accompanied with upregulation of p53, p21, p15, cleaved Poly (ADP-ribose) polymerase (PARP) protein and downregulation of cell cycle markers. L-Ru inhibited cell migration and invasion. The mitochondria-mediated apoptosis of NSCLC induced by L-Ru was also observed followed by the increase of apoptosis regulator B-cell lymphoma 2 associated X (BAX), and activation of caspase-3/-9. The effects of L-Ru on the cell viability, Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells and Annexin V-positive cells apoptosis induction were remarkably attenuated. This complex induced DNA damage, cell cycle arrest and cell death via caspase-dependent apoptosis involving PARP activation and induction of p53-dependent pathway. These findings suggested that this ruthenium complex might be a potential effective chemotherapeutic agent in NSCLC therapy.

Dimetallic Ru(II) arene complexes appended on bis-salicylaldimine induce cancer cell death and suppress invasion via p53-dependent signaling

A series of bis-salicylaldimine ligands bearing two ON-donor functions were reacted with dichloro(p-cymene)ruthenium(II) dimer in the presence of base (NaOAc) and a series of four dimetallic Ru(II) arene complexes (Ru(p-cymene))₂(bis-salicylaldimine)Cl₂ (C1C4) were prepared. These complexes were obtained in excellent isolated yields and characterized in detail by using different spectroscopic techniques. The structure of C1 was also determined in solid state by single crystal X-ray analysis. These complexes were studied for their cytotoxic effect against three different types of human cancer cells including hepatocellular carcinoma (HepG2), non-small-cell lung cancer (A549) and breast cancer (MCF-7) cells by MTT assay. These complexes showed considerable cytotoxic effect in all the above-mentioned cell lines that was comparable to the effect of cisplatin. C1 and C2 showed moderate anticancer effect while C3 and C4 showed reasonable cytotoxicity. We found the cytotoxicity was increased in series from C1 to C4 representing the effect of ligand modification from small to bulky group at the amine functionality of the salicylaldimine. We selected C3 and C4 for mechanistic anticancer study in MCF-7 cells. The acridine orange/ethidium bromide and DAPI staining assays of MCF-7 cells treated with Ru(II) complexes showed apoptosis in cancer cells. Similarly, these complexes induced p53 protein expression in MCF-7 cells. Further, increased mRNA levels of p63, p73, PUMA, BAX and NOXA genes were observed in response to the treatment with C3 and C4, while cyclinD1, MMP3 and ID1 gene expression was significantly reduced. We found reduced invasion ability in breast cancer cells treated with C3 and C4. Taken together, we demonstrated that bis-salicylaldimine based dimetallic Ru-(p-cymene) complexes exerts anticancer effects by p53 pathway, suggesting the promising chemotherapeutic potentials of these Ru(II) complexes for the treatment of cancer. This study may further pave for their in depth in vitro or in vivo anticancer investigations.