Mixed-ligand ruthenium polypyridyl complexes as apoptosis inducers in cancer cells, the cellular translocation and the important role of ROS-mediated signaling

Tracking the cellular uptake and phototoxicity of Ru(ii)-polypyridyl-1,8-naphthalimide Tröger's base conjugates

Ruthenium(ii) complexes are attracting significant research attention as a promising class of photosensitizers (PSs) in photodynamic therapy (PDT). Having previously reported the synthesis of two novel Ru(ii)-polypyridyl-1,8-naphthalimide Tröger's base compounds 1 and 2 with interesting photophysical properties, where the emission from either the Ru(ii) polypyridyl centres or the naphthalimide moieties could be used to monitor binding to nucleic acids, we sought to use these compounds to investigate further and in more detail their biological profiling, which included unravelling their mechanism of cellular uptake, cellular trafficking and cellular responses to photoexcitation. Here we demonstrate that these compounds undergo rapid time dependent uptake in HeLa cells that involved energy dependent, caveolae and lipid raft-dependent mediated endocytosis, as demonstrated by confocal imaging, and transmission and scanning electron microscopy. Following endocytosis, both compounds were shown to localise to mostly lysosomal and Golgi apparatus compartments with some accumulation in mitochondria but no localisation was found to the nucleus. Upon photoactivation, the compounds increased ROS production and induced ROS-dependent apoptotic cell death. The photo-activated compounds subsequently induced DNA damage and altered tubulin, but not actin structures, which was likely to be an indirect effect of ROS production and induced apoptosis. Furthermore, by changing the concentration of the compounds or the laser used to illuminate the cells, the mechanism of cell death could be changed from apoptosis to necrosis. This is the first detailed biological study of Ru(ii)-polypyridyl Tröger's bases and clearly suggests caveolae-dependent endocytosis is responsible for cell uptake - this may also explain the lack of nuclear uptake for these compounds and similar results observed for other Ru(ii)-polypyridyl complexes. These conjugates are potential candidates for further development as PDT agents and may also be useful in mechanistic studies on cell uptake and trafficking.

Recent Advances in Mitochondria-Localized Luminescent Ruthenium(II) Metallodrugs as Anticancer Agents

Presently, the most effective way to transport drugs specifically to mitochondria inside the cells is of pharmacophoric interest, as mitochondria are recognized as one of the most important targets for new drug design in cancer diagnosis. To date, there are many reviews covering the photophysical, photochemical, and anticancer properties of ruthenium(II) based metallodrugs owing to their high interest in biological applications. There are, however, no reviews specifically covering the mitochondria-localized luminescent Ru(II) complexes and their subsequent mitochondria-mediated anticancer activities. Therefore, this review describes the physicochemical basis for the mitochondrial accumulation of ruthenium complexes, their synthetic strategies to localize and monitor the mitochondria in living cells, and their related underlying anticancer results. Finally, we review the related areas from previous works describing the mitochondria-localized ruthenium complexes for the treatment of cancer-related diseases. Along with this, we also deliberate the perspectives and future directions for emerging more bifunctional Ru(II) complexes that can target, image, and kill tumors more efficiently in comparison with the existing mitochondria-targeted cancer therapeutics.

Ruthenium(II)-Dithiocarbazates as Anticancer Agents: Synthesis, Solution Behavior, and Mitochondria-Targeted Apoptotic Cell Death

The reaction of the Ru(PPh₃ )₃ Cl₂ with HL^1-3 -OH (-OH stands for the oxime hydroxyl group; HL¹ -OH=diacetylmonoxime-S-benzyldithiocarbazonate; HL² -OH=diacetylmonoxime-S-(4-methyl)benzyldithiocarbazonate; and HL³ -OH=diacetylmonoxime-S-(4-chloro)benzyl-dithiocarbazonate) gives three new ruthenium complexes [Ru^II (L^1-3 -H)(PPh₃ )₂ Cl] (1-3) (-H stands for imine hydrogen) coordinated with dithiocarbazate imine as the final products. All ruthenium(II) complexes (1-3) have been characterized by elemental (CHNS) analyses, IR, UV-vis, NMR (¹ H, ¹³ C, and ³¹ P) spectroscopy, HR-ESI-MS spectrometry and also, the structure of 1-2 was further confirmed by single crystal X-ray crystallography. The solution/aqueous stability, hydrophobicity, DNA interactions, and cell viability studies of 1-3 against HeLa, HT-29, and NIH-3T3 cell lines were performed. Cell viability results suggested 3 being the most cytotoxic of the series with IC₅₀ 6.9±0.2 μM against HeLa cells. Further, an apoptotic mechanism of cell death was confirmed by cell cycle analysis and Annexin V-FITC/PI double staining techniques. In this regard, the live cell confocal microscopy results revealed that compounds primarily target the mitochondria against HeLa, and HT-29 cell lines. Moreover, these ruthenium complexes elevate the ROS level by inducing mitochondria targeting apoptotic cell death.

Metal complexes of benzimidazole-derived as potential anti-cancer agents: synthesis, characterization, combined experimental and computational studies

In this study, a series of 14 Cu (II), Zn (II), Ni (II) and Ag (I) complexes containing bis-benzimidazole derivatives were successfully designed and synthesized from 2-(1H-benzimidazole-2-yl)-phenol derivatives and corresponding metal salt solutions. The compound structures were identified by FT-IR, ¹H-NMR, powder X-ray diffraction and ESI-MS analyses, and the presence of the metal in the complexes was confirmed by ultraviolet-visible spectroscopy and ICP optical emission spectrometry. Electronic structure calculations were also carried out to describe the detailed structures in addition to the electronic absorption spectra of the ligands. The cytotoxic activity of the complexes was evaluated against three human cancer cell lines: lung (A549), breast (MDA-MB-231) and prostate (PC3) cancer cells. All complexes inhibited anti-proliferative cancer cells better than free ligands, especially Zn (II) and Ag (I) complexes, which are most sensitive to MDA-MB-231 cells. In addition, showing the growth inhibition of three cancer cell lines with IC₅₀ < 10.4 µM, complexes C₁ , C₃ and C₁₄ could be considered potential multi-targeted anti-cancer agents.

Metal complexes of benzimidazole-derived as potential anti-cancer agents: synthesis, characterization, combined experimental and computational studies

In this study, a series of 14 Cu (II), Zn (II), Ni (II) and Ag (I) complexes containing bis-benzimidazole derivatives were successfully designed and synthesized from 2-(1H-benzimidazole-2-yl)-phenol derivatives and corresponding metal salt solutions. The compound structures were identified by FT-IR, ¹H-NMR, powder X-ray diffraction and ESI-MS analyses, and the presence of the metal in the complexes was confirmed by ultraviolet-visible spectroscopy and ICP optical emission spectrometry. Electronic structure calculations were also carried out to describe the detailed structures in addition to the electronic absorption spectra of the ligands. The cytotoxic activity of the complexes was evaluated against three human cancer cell lines: lung (A549), breast (MDA-MB-231) and prostate (PC3) cancer cells. All complexes inhibited anti-proliferative cancer cells better than free ligands, especially Zn (II) and Ag (I) complexes, which are most sensitive to MDA-MB-231 cells. In addition, showing the growth inhibition of three cancer cell lines with IC₅₀ < 10.4 µM, complexes C₁ , C₃ and C₁₄ could be considered potential multi-targeted anti-cancer agents.

Highly Cytotoxic Osmium(II) Compounds and Their Ruthenium(II) Analogues Targeting Ovarian Carcinoma Cell Lines and Evading Cisplatin Resistance Mechanisms

(1) Background: Ruthenium and osmium complexes attract increasing interest as next generation anticancer drugs. Focusing on structure-activity-relationships of this class of compounds, we report on 17 different ruthenium(II) complexes and four promising osmium(II) analogues with cinnamic acid derivatives as O,S bidentate ligands. The aim of this study was to determine the anticancer activity and the ability to evade platin resistance mechanisms for these compounds. (2) Methods: Structural characterizations and stability determinations have been carried out with standard techniques, including NMR spectroscopy and X-ray crystallography. All complexes and single ligands have been tested for cytotoxic activity on two ovarian cancer cell lines (A2780, SKOV3) and their cisplatin-resistant isogenic cell cultures, a lung carcinoma cell line (A549) as well as selected compounds on three non-cancerous cell cultures in vitro. FACS analyses and histone γH2AX staining were carried out for cell cycle distribution and cell death or DNA damage analyses, respectively. (3) Results: IC50 values show promising results, specifically a high cancer selective cytotoxicity and evasion of resistance mechanisms for Ru(II) and Os(II) compounds. Histone γH2AX foci and FACS experiments validated the high cytotoxicity but revealed diminished DNA damage-inducing activity and an absence of cell cycle disturbance thus pointing to another mode of action. (4) Conclusion: Ru(II) and Os(II) compounds with O,S-bidentate ligands show high cytotoxicity without strong effects on DNA damage and cell cycle, and this seems to be the basis to circumvent resistance mechanisms and for the high cancer cell specificity.

A family of amphiphilic dioxidovanadium(V) hydrazone complexes as potent carbonic anhydrase inhibitors along with anti-diabetic and cytotoxic activities

A family of dioxidovanadium(V) complexes (1-4) of the type [Na(H₂O)_x]⁺[V^VO₂(HL^1-4)]^- (x = 4, 4.5 and 7) where HL^2- represents the dianionic form of 2-hydroxybenzoylhydrazone of 2-hydroxyacetophenone (H₂L¹, complex 1), 2-hydroxy-5-methylacetophenone (H₂L², complex 2), 2-hydroxy-5-methoxyacetophenone (H₂L³, complex 3) and 2-hydroxy-5-chloroacetophenone (H₂L⁴, complex 4), have been synthesized and characterized by analytical and spectral methods. These complexes exhibited the potential abilities to suppress the erythrocytes carbonic anhydrase enzymatic activity in type 1 and type 2 diabetic patients (in vitro), promising antidiabetic activity against T2 diabetic mice (in vivo). They also exhibited significant cytotoxic activity against cervical cancer (SiHa) cells (in vitro) as the IC₅₀ value of complexes 1, 2 and 4 is substantially lower than the value found for cisplatin while that of 3 is comparable and follow the order: 4 < 1 < 2 < 3 and can kill the cells by apoptosis via the generation of reactive oxygen species (ROS). The complexes are soluble both in water and octanol media and also non-toxic at working concentrations. The antidiabetic activity of these four complexes follows the order: 4 > 2 > 1 > 3 while both the carbonic anhydrase and cytotoxic activity follow the order: 4 > 1 > 2 > 3 suggesting that complex 4, containing electron withdrawing Cl atom is the most reactive while 3 with electron donating OCH₃ group is the least reactive species. The molecular docking study on hCA-I and hCA-II demonstrates that complexes interact via hydrogen bonding as well as different types of π-stacking.

Metal Complexes or Chelators with ROS Regulation Capacity: Promising Candidates for Cancer Treatment

Reactive oxygen species (ROS) are rapidly eliminated and reproduced in organisms, and they always play important roles in various biological functions and abnormal pathological processes. Evaluated ROS have frequently been observed in various cancers to activate multiple pro-tumorigenic signaling pathways and induce the survival and proliferation of cancer cells. Hydrogen peroxide (H₂O₂) and superoxide anion (O₂^•-) are the most important redox signaling agents in cancer cells, the homeostasis of which is maintained by dozens of growth factors, cytokines, and antioxidant enzymes. Therefore, antioxidant enzymes tend to have higher activity levels to maintain the homeostasis of ROS in cancer cells. Effective intervention in the ROS homeostasis of cancer cells by chelating agents or metal complexes has already developed into an important anti-cancer strategy. We can inhibit the activity of antioxidant enzymes using chelators or metal complexes; on the other hand, we can also use metal complexes to directly regulate the level of ROS in cancer cells via mitochondria. In this review, metal complexes or chelators with ROS regulation capacity and with anti-cancer applications are collectively and comprehensively analyzed, which is beneficial for the development of the next generation of inorganic anti-cancer drugs based on ROS regulation. We expect that this review will provide a new perspective to develop novel inorganic reagents for killing cancer cells and, further, as candidates or clinical drugs.

Cyclometalated Ru(II) β-carboline complexes induce cell cycle arrest and apoptosis in human HeLa cervical cancer cells via suppressing ERK and Akt signaling

Two new cyclometalated Ru(II)-β-carboline complexes, [Ru(dmb)₂(Cl-Ph-βC)](PF₆) (dmb = 4,4'-dimethyl-2,2'-bipyridine; Cl-Ph-βC = Cl-phenyl-9H-pyrido[3,4-b]indole; RuβC-3) and [Ru(bpy)₂(Cl-Ph-βC)](PF₆) (bpy = 2,2'-bipyridine; RuβC-4) were synthesized and characterized. The Ru(II) complexes display high cytotoxicity against HeLa cells, the stabilized human cervical cancer cell, with IC₅₀ values of 3.2 ± 0.4 μM (RuβC-3) and 4.1 ± 0.6 μM (RuβC-4), which were considerably lower than that of non-cyclometalated Ru(II)-β-carboline complex [Ru(bpy)₂(1-Py-βC)] (PF₆)₂ (61.2 ± 3.9 μM) by 19- and 15-folds, respectively. The mechanism studies indicated that both Ru(II) complexes could significantly inhibit HeLa cell migration and invasion, and effectively induce G0/G1 cell cycle arrest. The new Ru(II) complexes could also trigger apoptosis through activating caspase-3 and poly (ADP-ribose) polymerase (PARP), increasing the Bax/Bcl-2 ratio, enhancing reactive oxygen species (ROS) generation, decreasing mitochondrial membrane potential (MMP), and inducing cytochrome c release from mitochondria. Further research revealed that RuβC-3 could deactivate the ERK/Akt signaling pathway thus inhibiting HeLa cell invasion and migration, and inducing apoptosis. In addition, RuβC-3-induced apoptosis in HeLa cells was closely associated with the increase of intracellular ROS levels, which may act as upstream factors to regulate ERK and Akt pathways. More importantly, RuβC-3 exhibited low toxicity on both normal BEAS-2B cells in vitro and zebrafish embryos in vivo. Consequently, the developed Ru(II) complexes have great potential on developing novel low-toxic anticancer drugs.

Binding mode transformation and biological activity on the Ru(II)-DMSO complexes bearing heterocyclic pyrazolyl ligands

Three Ru(II)-DMSO complexes (1-3) containing 2-(3-pyrazolyl)pyridine (PzPy), 2-pyrazol-3-ylfuran (PzO), or 2-pyrazol-3-ylthiophene (PzS) ligand, were synthesized and characterized. The monodentate coordination of the heterocyclic pyrazolyl ligand (Pz^Py) with Ru(II) ion via N atom was confirmed by single crystal X-ray diffraction. Complex 1 could be converted to the known η²-bidentate Pz^Py complex cis(Cl), cis(S)-[RuCl₂(Pz^Py)(DMSO)₂] (4) under reflux conditions. The mechanism underlying binding mode transformation was studied by ¹H NMR spectroscopy and density functional theory (DFT) calculations. The binding abilities of the complexes (1-4) with calf-thymus (CT) DNA and bovine serum albumin (BSA) were investigated using spectroscopic and molecular docking techniques. Among the four Ru(II) complexes, complexes 1 and 3 inhibited the long-term proliferation of human breast cancer cells, whereas complexes 2 and 4 did not inhibit their proliferation to a considerable extent. Interestingly, complexes 1 and 3 did not induce significant cell death but rather attenuated the clonogenicity of breast cancer cells by upregulating reactive oxygen species (ROS), endoplasmic reticulum (ER) and autophagic stress.

Cr(V)-Cr(III) in-situ transition promotes ROS generation to achieve efficient cancer therapy

The development of metal-based anticancer drugs is of considerable interest and significance in inorganic medicine. In contrast to noble metal-based small molecules, the anticancer property of earth abundant metal-based small molecules is much less explored which are usually essential trace element for the human body. Among earth abundant metals, chromium (Cr) in the +3 valent is an essential trace element for the human body to low down the blood lipids and maintain the blood sugar; on the other hand, Cr(VI) are known to be highly toxic due to their oxidation power. To design stable high-valent Cr small molecules to construct Cr(high-valent)-Cr(III) in-situ transition system to achieve low-toxic and highly efficient anti-cancer therapy is a very desirable approach. Herein we report the Cr(V)-Cr(III) in-situ transition system promotes ROS generation to achieve efficient cancer therapy in vivo and in vitro. To the best of our knowledge, these Cr-based small molecules are the first stable Cr(V) compounds with potent anticancer efficacy, especially towards malignant cancers.

Zn(ii), Cd(ii) and Hg(ii) saccharinate complexes with 2,6-bis(2-benzimidazolyl)pyridine as promising anticancer agents in breast and lung cancer cell lines via ROS-induced apoptosis

New Zn(ii), Cd(ii) and Hg(ii) complexes of saccharinate (sac) and 2,6-bis(2-benzimidazolyl)pyridine (bzimpy), [Zn(bzimpy)2](sac)2·2H2O (Zn), [Cd(sac)2(bzimpy)] (Cd) and [Hg(sac)2(bzimpy)] (Hg), were prepared and fully characterized by spectroscopic methods and X-ray crystallography. In vitro anticancer screening in A549 (lung), MCF-7 (breast) and HT29 (colon) cell lines showed that Zn was highly cytotoxic against A549 and MCF-7 cells with IC50 values of 1.74 ± 0.06 and 3.15 ± 0.10 μM, respectively, and Hg demonstrated potent cytotoxic activity in MCF-7 cells (8.61 ± 0.98 μM), while Cd and bzimpy exhibited moderate growth inhibitory activities in all of the cell lines. In addition, they showed significantly lower toxicity towards normal human breast epithelial MCF10A cells. Moreover, the complexes exhibited significantly high nuclease activity towards plasmid DNA and their interactions with DNA were assessed by gel electrophoresis and DNA docking. Zn and Hg induced G0/G1 cell arrest and apoptotic cell death detected via typical DNA condensation/fragmentation, annexin V staining and caspase 3/7 activity in A549 and MCF-7 cells. These complexes further caused depolarization of mitochondria and oxidative damage of genomic DNA following excessive production of reactive oxygen species (ROS).

Potent half-sandwich Ru(Ⅱ) N^N (aryl-BIAN) complexes: Lysosome-mediated apoptosis, in vitro and in vivo anticancer activities

Herein a new series of organometallic half-sandwich Ru(Ⅱ) complexes bearing aryl-BIAN chelating ligands with various electron-withdrawing and electron-donating substituents have been developed as theranostic agents. All the complexes display much higher anti-proliferative potency than the clinical chemotherapeutic drug cisplatin towards seven cancer cell lines. The anti-proliferative efficacy of these complexes is correlated to their electron-withdrawing ability. Interestingly, complex Ru1 also potently suppresses cancer cell migration in vitro and effectively inhibit tumor growth in vivo in a CT26 colon cancer mouse xenograft model. Mechanisms of action studies display that Ru1 can favorably accumulate in lysosome and exerts anti-cancer potency by inducing a series of events related to lysosomal dysfunction in CT26 cells. Interestingly, inhibition of lysosomal enzymes leads to suppression of cytotoxicity and apoptosis induced by Ru1. Our results elucidate that complex Ru1 can elicit cytotoxicity through lysosome-mediated apoptosis in vitro and suppress tumor growth in vivo.

Ru(II) Complexes Bearing O, O-Chelated Ligands Induced Apoptosis in A549 Cells through the Mitochondrial Apoptotic Pathway

Two new Ru(II) complexes containing O, O-chelated ligands, Ru(dip)₂(SA) (Ru-1) and Ru(dmp)₂(SA) (Ru-2) (dip = 4,7-diphenyl-1,10-phenanthroline; dmp = 2,9-dimethyl-1,10-phenanthroline; SA = salicylate) were synthesized to evaluate their cytotoxicity in vitro. These complexes were found to exhibit moderate antitumor activity to different types of human cancers, including A549 (human lung carcinoma), MCF-7 (breast cancer), HeLa (human cervical cancer), and HepG2 (human hepatocellular carcinoma) cell lines, but displayed low toxicity to human normal cell lines BEAS-2B (immortalized human bronchial epithelial cells) when compared with that of cisplatin. Further studies revealed that these complexes could induce apoptosis in A549 cells, including activating caspase family proteins and poly (ADP-ribose) polymerase (PARP), reducing Bcl-2/Bax and Bcl-xl/Bad ratio, enhancing cellular reactive oxygen species (ROS) accumulation, triggering DNA damage, decreasing mitochondrial membrane potential (MMP), and leading cytochrome c release from mitochondria. Notably, complex Ru-1 showed low toxicity to developing zebrafish embryos. The obtained results suggest that these new synthetic complexes have the potential to be developed as low-toxicity agents for lung cancer treatment.

Anti-adhesive action of novel ruthenium(II) chlorophenyl terpyridine complexes with a high affinity for double-stranded DNA: in vitro and in silico

Interactions of three Ru(II) chlorophenyl terpyridine complexes: [Ru(Cl-Ph-tpy)(en)Cl]Cl (1), [Ru(Cl-Ph-tpy)(dach)Cl]Cl (2) and [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) (Cl-Ph-tpy = 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, en = 1,2-diaminoethane, dach = 1,2-diaminocyclohexane, bpy = 2,2'-bipyridine) with human serum albumin (HSA), calf thymus DNA and a double-helical oligonucleotide d(CGCGAATTCGCG)₂ (1BNA) were examined. Fluorescence emission studies were used to assess the interactions of complexes with HSA, which were of moderate strength for 1 and 2. Molecular docking allowed us to predict mostly π-π stacking and van der Waals interactions between the complexes and the protein. We suggest that the complexes bind to a novel site on HSA, which is different from its druggable sites I, II or III. We suggest a partial intercalation of complexes through the minor groove as a possible mode of interaction with double-helical DNA. Finally, when applied to normal extravillous cell line HTR8/SVneo and JAr choriocarcinoma cell line, complexes 1 and 2 exerted anti-adhesive properties at very low doses, whereas complex 3 had a negligible effect. The obtained results are completion of our studies of Ru(II) terpyridyl complexes that carry N-N ancillary ligands. We suggest a new research direction towards studying the cellular effects of Ru(II) polypyridyl compounds.

Anti-angiogenic vanadium pentoxide nanoparticles for the treatment of melanoma and their in vivo toxicity study

In recent days, vanadium complexes and nanoparticles have received sustainable attention owing to their vast applications in different fields. In the present study, we report a facile approach for the synthesis of irregular dumbbell shaped vanadium pentoxide nanoparticles (V₂O₅ NPs: 30-60 nm) via the polyol-induced microwave irradiation process along with calcination. The as-synthesized nanoparticles were characterized using various physico-chemical techniques (e.g. XRD, TEM, FT-IR, DLS and XPS). The cell viability assay showed that V₂O₅ NPs could efficiently inhibit the proliferation of different cancer cells (B16F10, A549, and PANC1), depicting their anti-proliferative activity. However, V₂O₅ NPs did not exert significant cytotoxicity to the normal cells (CHO, HEK-293 and NRK-49F), suggesting their biocompatible nature. Interestingly, these nanoparticles inhibited the proliferation and migration of the endothelial cells (HUVECs and EA.hy926) and disrupted the blood vasculature in a chick embryo model, indicating their anti-angiogenic properties. The mechanistic study revealed that the effective internalization of V₂O₅ NPs generated intracellular reactive oxygen species (ROS) which in turn up-regulated p53 protein and down-regulated survivin protein in cancer cells, leading to the apoptosis process. Furthermore, the administration of V₂O₅ NPs to melanoma bearing C57BL6/J mice significantly increased their survivability as compared to the control untreated tumor bearing mice, exhibiting the therapeutic potential of the nanoparticles against melanoma. Additionally, the in vivo toxicity study demonstrated no toxic effect in mice upon sub-chronic exposure to V₂O₅ NPs. Altogether, we strongly believe that V₂O₅ NPs could intrinsically provide a new direction for alternative therapeutic treatment strategies for melanoma and other cancers by employing their anti-angiogenic properties in the future.

Combination of Ruthenium Complex and Doxorubicin Synergistically Inhibits Cancer Cell Growth by Down-Regulating PI3K/AKT Signaling Pathway

Combinational use of drugs has been a common strategy in cancer treatment because of synergistic advantages in reducing dose and toxicity, minimizing or delaying drug resistance. To improve the efficacy of chemotherapy, various potential combinations have been investigated. Ruthenium complex is considered a potential alternative of the platinum-based drugs due to its significant efficacy and safety. Previously, we reported that ruthenium(II) complex (Δ-Ru1) has great anticancer potential and minor toxicity toward normal tissues. However, the therapeutic efficacy and mechanism of action of ruthenium(II) complex combined with other anticancer drugs is still unknown. Here, we investigated the combinational effect of Δ-Ru1 and doxorubicin in different cancer cells. The data assessed by Chou-Talalay method showed significant synergism in MCF-7 cells. Furthermore, the results in antiproliferation efficacy indicated that the combination showed strong cytotoxicity and increasing apoptosis of MCF-7 cells in 2D and 3D multicellular tumor spheroids (MCTSs). Significant inhibition of MCF-7 cells accompanied with increased ROS generation was observed. Furthermore, the expression of PI3K/AKT was significantly down-regulated, while the expression of PTEN was strongly up-regulated in cells treated with combination of Δ-Ru1 and doxorubicin. The expression of NF-κB and XIAP decreased while the expression of P53 increased and associated with apoptosis. These findings suggest that the combination of ruthenium complex and doxorubicin has a significant synergistic effect by down-regulating the PI3K/AKT signaling pathway in MCF-7 cells. This study may trigger more research in ruthenium complex and combination therapy that will be able to provide opportunities for developing better therapeutics for cancer treatment.

Novel cyclometalated iridium(iii) phosphine-imine (P^N) complexes: highly efficient anticancer and anti-lung metastasis agents in vivo

Iridium(iii)-based complexes with phosphine-imine (P^N) ligands are synthesized and authenticated. The combined treatment with Ir(iii) and BIX01294 potently inhibited tumour growth and lung metastasis in vitro and in vivo.

MOF nanoparticles with encapsulated dihydroartemisinin as a controlled drug delivery system for enhanced cancer therapy and mechanism analysis

Schematic illustration of (a) the preparation of DHA@ZIF-8 NPs and (b) their application for cancer therapy.

Triphenylamine/carbazole-modified ruthenium(ii) Schiff base compounds: synthesis, biological activity and organelle targeting

N-phenylcarbazole/triphenylamine modified Schiff base half-sandwich ruthenium(ii) compounds showed potential anticancer activity against A549 and HeLa cells.

Functionalization and cancer-targeting design of ruthenium complexes for precise cancer therapy

The successful clinical application of the three generation platinum anticancer drugs, cisplatin, carboplatin and oxaliplatin, has promoted research interest in metallodrugs; however, the problems of drug resistance and adverse effects have hindered their further application and effects. Thus, scientists are searching for new anticancer metallodrugs with lower toxicity and higher efficacy. The ruthenium complexes have emerged as the most promising alternatives to platinum-based anticancer agents because of their unique multifunctional biochemical properties. In this review, we first focus on the anticancer applications of various ruthenium complexes in different signaling pathways, including the mitochondria-mediated pathway, the DNA damage-mediated pathway, and the death receptor-mediated pathway. We then discuss the functionalization and cancer-targeting designs of different ruthenium complexes in conjunction with other therapies such as photodynamic therapy, photothermal therapy, radiosensitization, targeted therapy and nanotechnology for precise cancer therapy. This review will help in designing and accelerating the research progress regarding new anticancer ruthenium complexes.

Iron (II) Polypyridyl Complexes as Antiglioblastoma Agents to Overcome the Blood-Brain Barrier and Inhibit Cell Proliferation by Regulating p53 and 4E-BP1 Pathways

Background and Purpose: It is urgently required to develop promising candidates to permeate across blood-brain barrier (BBB) efficiently with simultaneous disrupting vasculogenic mimicry capability of gliomas. Previously, a series of iron (II) complexes were synthesized through a modified method. Hence, the aim of this study was to evaluate anticancer activity of Fe(PIP)₃SO₄ against glioma cancer cells. Methods: Cytotoxic effects were determined via MTT assay, and IC₅₀ values were utilized to evaluate the cytotoxicity. Cellular uptake of Fe(PIP)₃SO₄ between U87 and HEB cells was conducted by subtracting content of the complex remaining in the cell culture supernatants. Propidium Iodide (PI)-flow cytometric analysis was used to analyze cell cycle proportion of U87 cells treated with Fe(PIP)₃SO₄. The reactive oxygen species levels induced by Fe(PIP)₃SO₄ were measured by 2'-deoxycoformycin (DCF) probe; ABTS assay was utilized to examine the radical scavenge capacity of Fe(PIP)₃SO₄. To study the bind efficiency to thioredoxin reductase (TrxR), Fe(PIP)₃SO₄ was introduced into solution containing TrxR. To verify if Fe(PIP)₃SO₄ could penetrate BBB, HBMEC/U87 coculture as BBB model was established, and penetrating capability of Fe(PIP)₃SO₄ was tested. In vitro U87 tumor spheroids were formed to test the permeating ability of Fe(PIP)₃SO₄. Acute toxicity and biodistribution of Fe(PIP)₃SO₄ were tested on mice for 72 h. Protein profiles associated with U87 cells treated with Fe(PIP)₃SO₄ were determined by Western blotting analysis. Results: Results showed that Fe(PIP)₃SO₄ could suppress cell proliferation by inducing G2/M phase cycle retardation and apoptotic pathways, which was related with expression of p53 and initiation factor 4E binding protein 1. In addition, Fe complex could suppress cell proliferation by downregulating reactive oxygen species levels via scavenging free radicals and interaction with TrxR. Furthermore, Fe(PIP)₃SO₄ could permeate across BBB and simultaneously inhibited the vasculogenic mimicry-channel of U87 cells, suggesting favorable antiglioblastoma efficacy. Acute toxicity manifested lower degree of the complex compared with cisplatin and temozolomide. Conclusion: Fe(PIP)₃SO₄ exhibited favorable anticancer activity against glioma cells associated with p53 and 4E binding protein 1, accompanied with negligible toxic effects on normal tissues. Herein, Fe(PIP)₃SO₄ could be developed as a promising metal-based chemotherapeutic agent to overcome BBB and antagonize glioblastomas.

Synthesis and Characterization of FITC Labelled Ruthenium Dendrimer as a Prospective Anticancer Drug

Metallodendrimers-dendrimers with included metals-are widely investigated as biocompatible equivalents to metal nanoparticles. Applications can be expected in the fields of catalysis, as chemical sensors in molecular recognition and as anticancer drugs. Metallodendrimers can also mimic certain biomolecules, for example, haemoprotein in the case of using a dendrimer with a porphyrin core. In previous papers, we showed the promising anticancer effects of carbosilane ruthenium dendrimers. The present paper is devoted to studying biocompatibility and the cytotoxic effect on normal and cancer cells of carbosilane ruthenium dendrimers labelled with fluorescent probe fluorescein isothiocyanate (FITC). The addition of fluorescent probe allowed tracking the metallodendrimer in both normal and cancer cells. It was found that carbosilane ruthenium dendrimer labelled with FITC in concentration up to 10 µmol/L was more cytotoxic for cancer cells than for normal cells. Thus, FITC labelled carbosilane ruthenium dendrimer is a good candidate for diagnostic imaging and studying anticancer effects of metallodendrimers in cancer therapy.

Ruthenium Complexes Containing Heterocyclic Thioamidates Trigger Caspase-Mediated Apoptosis Through MAPK Signaling in Human Hepatocellular Carcinoma Cells

Herein, ruthenium complexes containing heterocyclic thioamidates [Ru(mmi)(bipy)(dppb)]PF₆ (1), [Ru(tzdt)(bipy)(dppb)]PF₆ (2), [Ru(dmp)(bipy)(dppb)]PF₆ (3) and [Ru(mpca)(bipy)(dppb)]PF₆ (4) were investigated for their cellular and molecular effects in cancer cell lines. Complexes 1 and 2 were the most potent of the four compounds against a panel of different cancer cell lines in monolayer cultures and showed potent cytotoxicity in a 3D model of multicellular spheroids that formed from human hepatocellular carcinoma HepG2 cells. In addition, both complexes were able to bind to DNA in a calf thymus DNA model. Compared to the controls, a reduction in cell proliferation, phosphatidylserine externalization, internucleosomal DNA fragmentation, and the loss of the mitochondrial transmembrane potential were observed in HepG2 cells that were treated with these complexes. Additionally, coincubation with a pan-caspase inhibitor (Z-VAD(OMe)-FMK) reduced the levels of apoptosis that were induced by these compounds compared to those in the negative controls, indicating that cell death through apoptosis occurred via a caspase-dependent pathway. Moreover, these complexes also induced the phosphorylation of ERK1/2, and coincubation with an MEK inhibitor (U0126), which is known to inhibit the activation of ERK1/2, but not JNK/SAPK and p38 MAPK inhibitors, reduced the complexes-induced apoptosis compared to that in the negative controls, indicating that the induction of apoptotic cell death occurred through ERK1/2 signaling in HepG2 cells. On the other hand, no increase in oxidative stress was observed in HepG2 cells treated with the complexes, and the complexes-induced apoptosis was not reduced with coincubation with the antioxidant N-acetylcysteine or a p53 inhibitor compared to that in the negative controls, indicating that apoptosis occurred via oxidative stress- and p53-independent pathways. Finally, these complexes also reduced the growth of HepG2 cells that were engrafted in C.B-17 SCID mice compared to that in the negative controls. These results indicated that these complexes are novel anticancer drug candidates for liver cancer treatment.

Ruthenium dendrimers against acute promyelocytic leukemia: in vitro studies on HL-60 cells

Coordination of ruthenium arene fragments on carbosilane dendrimers' surface greatly increases their antitumor properties. Newly synthetized ruthenium dendrimers are water-soluble, monodisperse and stable. Since carbosilane dendrimers are good carriers of drugs and genes, the presence of ruthenium in their structure makes them promising candidates for new drug delivery systems with improved antitumor potential. Carbosilane ruthenium dendrimers are more toxic to cancer cells than normal cells. Results of several in vitro studies applied here indicate that carbosilane ruthenium dendrimers induce apoptosis in promyelocytic leukemia HL-60 cells.

Exploring the cytotoxic activity of new phenanthroline salicylaldimine Zn(II) complexes

Zinc(II) complexes bearing N-salicylideneglycinate (Sal-Gly) and 1,10-phenanthroline (phen) or phenanthroline derivatives [NN = 5-chloro-1,10-phenanthroline, 5-amine-1,10-phenanthroline (amphen), 4,7-diphenyl-1,10-phenanthroline (Bphen) and 5,6-epoxy-5,6-dihydro-1,10-phenanthroline] are synthesized. Complexes formulated as [Zn(NN)₂(H₂O)₂]²⁺(NN = phen and amphen), are also prepared. The cytotoxicity of the compounds is evaluated towards a panel of human cancer cells: ovarian (A2780), breast (MCF7) and cervical (HeLa), as well as non-tumoral V79 fibroblasts. All compounds display higher cytotoxicity than cisplatin (IC₅₀ = 22.5 ± 5.0 μM) towards ovarian cells, showing IC₅₀values in the low micromolar range. Overall, all compounds show higher selectivity for the A2780 cells than for the non-tumoral cells and higher selectivity indexes (IC₅₀(V79)/IC₅₀(A2780) than cisplatin. [Zn(Sal-Gly)(NN)(H₂O)] complexes induce caspase-dependent apoptosis in A2780 cells, except [Zn(Sal-Gly)(Bphen)(H₂O)], one of the most cytotoxic of the series. The cellular uptake in the ovarian cells analyzed by Inductively Coupled Plasma mass spectrometry indicates different Zn distribution profiles. Transmission electronic microscopy shows mitochondria alterations and apoptotic features consistent with caspase activation; cells incubated with [Zn(Sal-Gly)(amphen)(H₂O)] present additional nuclear membrane alterations in agreement with significant association with the nucleus. The increase of reactive oxygen species and lipid peroxidation forms could be related to apoptosis induction. [Zn(NN)₂(H₂O)₂]²⁺complexes have high ability to bind DNA through intercalation/groove binding, and circular dichroism data suggests that the main type of species that interact with DNA is [Zn(NN)]²⁺. Studies varying the % of fetal bovine serum (1-15%) in cell media show that albumin binding decreases the complex activity, indicating that distinct speciation of Zn- and phen-containing species in cell media may affect the cytotoxicity.

Ferritin-based anticancer metallodrug delivery: Crystallographic, analytical and cytotoxicity studies

The encapsulation of anticancer metal-based drugs within a protein nanocage represents a valuable strategy to improve the efficacy and selectivity of these compounds towards cancer cells. The preparation, characterization of the in vitro cytotoxicity and X-ray structures of several ferritin-metallodrug nanocomposites (mainly containing platinum-, ruthenium- and gold-based anticancer agents) are here reviewed. The molecular mechanisms of action of these Ft-metallodrug adducts are discussed and future directions in the field are outlined.

Self-Assembly of Copper Polypyridyl Supramolecular Metallopolymers to Achieve Enhanced Anticancer Efficacy

Self‐assembled functional supramolecular metallopolymers have demonstrated application potential in cancer therapy. Herein, a copper polypyridyl complex was found able to self‐assemble into a supramolecular metallopolymer driven by the intermolecular interactions, which could enhance the uptake in cancer cells through endocytosis, and thus effectively inhibiting tumor growth in vivo without damaging to the major organs. This study provides a facile way to achieve enhanced anticancer efficacy by using self‐assembled metallopolymers.

Mitochondria-Targeting Anticancer Metal Complexes

Background:

Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs.

Methods:

Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria.

Results:

This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes.

Conclusion:

Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.

Encapsulation of the Dinuclear Trithiolato-Bridged Arene Ruthenium Complex Diruthenium-1 in an Apoferritin Nanocage: Structure and Cytotoxicity

The effects of encapsulating the cytotoxic dinuclear trithiolato-bridged arene ruthenium complex [(η⁶ -p-MeC₆ H₄ iPr)₂ Ru₂ (μ₂ -S-p-C₆ H₄ tBu)₃ ]Cl (DiRu-1) within the apoferritin (AFt) nanocage were investigated. The DiRu-1-AFt nanocarrier was characterized by UV/Vis spectroscopy, ICP-MS, CD and X-ray crystallography. In contrast to previously reported Au- and Pt-based drug-loaded AFt carriers, we found no evidence of direct interactions between DiRu-1 and AFt. DiRu-1-AFt is cytotoxic toward immortalized murine BALB/c-3T3 fibroblasts transformed with SV40 virus (SVT2) and human epidermoid carcinoma A431 malignant cells, and exhibits moderate selectivity for these cancer cells over normal BALB/c-3T3 cells. DiRu-1-AFt triggers the production of reactive oxygen species, depolarization of mitochondrial membrane potential, and induces cell death via p53-mediated apoptosis. Comparison between our data and previous results suggests that the presence of specific interactions between a metal-based drug and AFt within the protein cage is not essential for drug encapsulation.

Biocompatible ruthenium polypyridyl complexes as efficient radiosensitizers

A biocompatible ruthenium polypyridyl complex has been rationally designed, which could self-assemble into nanoparticles in aqueous solution to enhance the solubility and biocompatibility, and could synergistically realize simultaneous cancer chemo-radiotherapy.

Designing luminescent ruthenium prodrug for precise cancer therapy and rapid clinical diagnosis

The effective design of a targeted drug delivery system could improve the therapeutic efficacy of anticancer drugs by reducing their undesirable adsorption and toxic side effects. Here, an RGD-peptide functionalized and bioresponsive ruthenium prodrug (Ru-RGD) was designed for both cancer therapy and clinical diagnosis. This prodrug can be selectively delivered to cervical tumor sites to enhance theranostic efficacy. The benzimidazole-based ligand of the complex is susceptible to acidic conditions so, after reaching the tumor microenvironment, ligand substitution occurs and the therapeutic drug is released. The deep-red emissions produced by both one-photon and two-photon excitation increases the potential of Ru-RGD for use in the deep tissue imaging of 3D tumor spheroids. The specific accumulation of the Ru prodrug in tumor sites allows for precise tumor diagnosis and therapy in vivo. Luminescence staining of 38 clinical patient specimens shows that Ru-RGD exhibits differences in binding capability between cervical cancer and normal tissue, with a sensitivity of 95% and a specificity of 100%. This study thus provides an approach for the effective design and application of targeted metal complexes in cancer therapy and clinical diagnosis.

Exploring the effect of substituent in the hydrazone ligand of a family of μ-oxidodivanadium(v) hydrazone complexes on structure, DNA binding and anticancer activity

The reaction of 2-hydroxybenzoylhydrazine (H₂bh) separately with equimolar amounts of [V^IVO(aa)₂] and [V^IVO(ba)₂] in CHCl₃ afforded the complexes [VO₃(HL¹)₂] (1) and [VO₃(HL²)₂] (2) respectively in good to excellent yield ((HL¹)^2- and (HL²)^2- represent respectively the dianionic form of 2-hydroxybenzoylhydrazones of acetylacetone (H₃L¹) and benzoylacetone (H₃L²) (general abbreviation H₃L)). From X-ray structure analysis, the V^V-O-V^V angle was found to be ∼115° and 180° in 1 and 2 respectively. Upon one-electron reduction selectively at one V centre at an appropriate potential, each of 1 and 2 generated mixed-valence [(HL)V^VO-(μ-O)-OV^IV(HL)]^- species 1A and 2A respectively, which showed valence delocalization at room temperature and localization at 77 K, and the V^IV-O-V^V bond angles were calculated to be 177.5° and 180° respectively. The intercalative mode of binding of the two complexes 1 and 2 with CT DNA has been suggested by UV-visible spectroscopy (K_b = 7.31 × 10⁵ M^-1 and 8.71 × 10⁵ M^-1 respectively for 1 and 2), fluorescence spectroscopy (K_sv = 6.85 × 10⁵ M^-1 and 8.53 × 10⁵ M^-1 respectively for 1 and 2) and circular dichroism spectroscopy. Such intercalative mode of binding of these two complexes with CT DNA and HPV DNA has also been confirmed by molecular docking study. Both complexes 1 and 2 exhibited promising anti-cancer activity against SiHa cervical cancer cells with IC₅₀ values of 28 ± 0.5 μM and 25 ± 0.5 μM respectively for 24 h which is significantly better than that of widely used cisplatin (with IC₅₀ value of 63.5 μM). Nuclear staining experiments reveal that these complexes kill the SiHa cells through apoptotic mode. It is interesting to note that these two complexes are non-toxic to normal T293 cell line. Complex 2 showed higher DNA binding ability with CT DNA and HPV DNA as well as better anti-cancer properties towards SiHa cervical cancer cells in comparison to complex 1, a fact which can be explained by considering the lower energy of LUMO (which favours electron transition from DNA to the metal complex) and also the higher surface area of complex 2 in comparison to complex 1 due to the presence of one extra electron-withdrawing phenyl group in the former.

Kinetic and mechanistic study on the reactions of ruthenium(ii) chlorophenyl terpyridine complexes with nucleobases, oligonucleotides and DNA

In this study, we investigated the ability of Ru(ii) polypyridyl complexes to act as DNA binders. The substitution reactions of three Ru(ii) chlorophenyl terpyridine complexes, i.e. [Ru(Cl-Ph-tpy)(en)Cl]Cl (1), [Ru(Cl-Ph-tpy)(dach)Cl]Cl (2) and [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) (Cl-Ph-tpy = 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, en = 1,2-diaminoethane, dach = 1,2-diaminocyclohexane, bpy = 2,2'-bipyridine), with a mononucleotide guanosine-5'-monophosphate (5'-GMP) and oligonucleotides such as fully complementary 15-mer and 22-mer duplexes with a centrally located GG-binding site for DNA, and fully complementary 13-mer duplexes with a centrally located GG-binding site for RNA were studied quantitatively by UV-Vis spectroscopy. Duplex RNA reacts faster with complexes 1-3 than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. The measured enthalpies and entropies of activation (ΔH^≠ > 0, ΔS^≠ < 0) support an associative mechanism for the substitution process. ¹H NMR spectroscopy studies performed on complex 3 demonstrated that after the hydrolysis of the Cl ligand, it is capable to interact with guanine derivatives (i.e., 9-methylguanine (9MeG) and 5'-GMP) through N7, forming monofunctional adducts. The molecular structure of the cationic compound [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) was determined in the solid state by X-ray crystallography. The interactions of 1-3 with calf thymus (CT) and herring testes (HT) DNA were examined by stopped-flow spectroscopy, in which HT DNA was sensibly more reactive than CT DNA. The reactivity towards the formation of Ru-DNA adducts was also revealed by a gel mobility shift assay, showing that complexes 1 and 2 have a stronger DNA unwinding ability compared to complex 3. Overall, the complexes with bidentate aliphatic diamines proved to be superior to those with bpy in terms of capability to bind to the here studied biomolecules.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Cancer-Targeting Functionalization of Selenium-Containing Ruthenium Conjugate with Tumor Microenvironment-Responsive Property to Enhance Theranostic Effects

A mutifunctional ruthenium-based conjugate Ru-BSe was designed and synthesized. The Ru complex with favorable bioimaging function was covalently linked with a cancer-targeted molecule that could be effectively internalized by the tumor to realize enhanced theranostic effects. The pH-response of the Ru conjugate in tumor acidic microenvironment causes ligand substitution and release of therapeutic complex. This activated complex remains inert to the reducing biomolecule-glutathione and terminally locates in mitochondria, in which it triggers oxidative stress, and activates intrinsic apoptosis. Real-time monitoring reveals that this Ru conjugate could selectively accumulate in tumor tissue in vivo, which significantly suppresses tumor progression and alleviate the damage to normal organs, realizing the precise cancer theranosis.