Organometallic Ruthenium(II) Arene Compounds with Antiangiogenic Activity

Beyond transition block metals: exploring the reactivity of phosphine PTA and its oxide [PTA(O)] towards gallium(iii)

The water-soluble cage-like phosphine PTA (1,3,5-triaza-7-phosphaadamantane) and its phosphine oxide derivative [PTA(O)] (1,3,5-triaza-7-phosphaadamantane-7-oxide) were used to explore their reactivity towards two gallium(iii)-halide precursors, namely GaCl3 and GaI3, for the first time. By using various reaction conditions, a series of N-mono-protonated phosphine salts with [GaCl4]- or [I]- as counterions were obtained in all cases, while the formation of coordinated Ga-PTA and Ga-[PTA(O)] complexes was not observed. All compounds were characterized in solution using multinuclear NMR spectroscopy (1H, 13C{1H}, 31P{1H} and 71Ga) and in the solid state using FT-IR spectroscopy and X-ray crystal diffraction. The new Ga-phosphine salts resulted stable and highly soluble in aqueous solution at room temperature. Density functional theory (DFT) calculations were also performed to further rationalize the coordination features of PTA with Ga3+ metal ion, highlighting that the phosphorus-gallium bond is about twice weaker than the phosphorus-metal bond commonly established by PTA with transition metals such as gold. Furthermore, the mono-protonation of PTA (or [PTA(O)]) makes the formation of ionic gallium-PTA coordination complexes thermodynamically unstable, as confirmed experimentally by the formation of Ga-phosphine salts reported herein.

Carbohydrate effect of novel arene Ru(II) phenanthroline-glycoconjugates on metastatic biological processes

Novel water-soluble half-sandwich ruthenium(II) polypyridyl-glycoconjugates [Ru(p-cymene)Cl{N-(1,10-phenanthroline-5-yl)-β-glycopyranosylamine}][Cl] (glycopyranosyl = d-glucopyranosyl (1), D-mannopyranosyl (2), L-rhamnopyranosyl (3) and l-xylopyranosyl (4)) have been synthesized and fully characterized. Their behaviour in water under physiological conditions has been studied by nuclear magnetic resonance spectroscopy, revealing their hydrolytic stability. Interactions of the novel compounds with duplex-deoxiribonucleic acid (dsDNA) were investigated by different techniques and the results indicate that, under physiological pH and saline conditions, the metal glycoconjugates bind DNA in the minor groove and/or through external, electrostatic interactions, and by a non-classical, partial intercalation mechanism in non-saline phosphate buffered solution. Effects of compounds 1-4 on cell viability have been assessed in vitro against two human cell lines (androgen-independent prostate cancer PC-3 and non-tumorigenic prostate RWPE-1), showing moderate cytotoxicities, with IC50 values higher than those found for free ligands [N-(1,10-phenanthroline-5-yl)-β-glycopyranosylamine] (glycopyranosyl = d-glucopyranosyl (a), D-mannopyranosyl (b), L-rhamnopyranosyl (c) and l-xylopyranosyl (d)) or corresponding metal-aglycone. Cell viability was assayed in the presence and absence of the glucose transporters (GLUTs) inhibitor [N4-{1-(4-cyanobenzyl)-5-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl}-7-fluoroquinoline-2,4-dicarboxamide] (BAY-876), and the results point to a negligible impact of the inhibition of GLUTs on the cytotoxicity caused by Ru(II) compounds 1-4. Remarkably, glycoconjugates 1-4 potently affect the migration pattern of PC-3 cells, and the wound healing assay evidence that the presence of the carbohydrate and the Ru(II) center is a requisite for the anti-migratory activity observed in these novel derivatives. In addition, derivatives 1-4 strongly affect the matrix metalloproteinase MMP-9 activities of PC-3 cells, while proMMP-2 and especially proMMP-9 were influenced to a much lesser extent.

Complexing Properties of Synthesized 1,3,5-Triaza-7-Phosphaadamantane Derivatives Towards Some Lanthanides and Transition Metal Cations With Significant Antimicrobial and Antioxidant Activities

The synthesis of new water-soluble N-alkylated derivatives of 1,3,5-triaza-7-phosphaadamantane is presented. Ru(PPh3)2Cl2 has been used to react with 1-(4-nitrobenzyl)-3,5-triaza-1-azonia-7-phosphaadamantane bromide (PTAR). By using elemental analysis, NMR, and IR spectroscopy, the obtained compounds were identified. The UV-visible absorption spectroscopy has been used to monitor the complexation of various transition metal cations. Studies on conductivity have been utilized to validate the complexes' stoichiometries. Using the disc diffusion method, five bacteria strains were used for the study of the antimicrobial activity of compounds 1-3. All tested pathogens, including M luteus LB 141107, were found to have strong biologic activity against the compounds tested in this study. Additionally, DPPH (2,2-diphenyl-1-picrylhydrazyl) has been tested for its ability to scavenge hydrogen peroxide and free radicals. According to our results, these compounds exhibit excellent radical scavenging properties.

Fine-tuning the cytotoxicity of ruthenium(II) arene compounds to enhance selectivity against breast cancers

Ruthenium-based complexes have been suggested as promising anticancer drugs exhibiting reduced general toxicity compared to platinum-based drugs. In particular, Ru(η6-arene)(PTA)Cl2 (PTA = 1,3,5-triaza-7-phosphaadamantane), or RAPTA, complexes have demonstrated efficacy against breast cancer by suppressing metastasis, tumorigenicity, and inhibiting the replication of the human tumor suppressor gene BRCA1. However, RAPTA compounds have limited cytotoxicity, and therefore comparatively high doses are required. This study explores the activity of a series of RAPTA-like ruthenium(II) arene compounds against MCF-7 and MDA-MB-231 breast cancer cell lines and [Ru(η6-toluene)(PPh3)2Cl]+ was identified as a promising candidate. Notably, [Ru(η6-toluene)(PPh3)2Cl]Cl was found to be remarkably stable and highly cytotoxic, and selective to breast cancer cells. The minor groove of DNA was identified as a relevant target.

Dichloro Ru(II)-p-cymene-1,3,5-triaza-7-phosphaadamantane (RAPTA-C): A Case Study

The use of organometallic compounds to treat various phenotypes of cancer has attracted increased interest in recent decades. Organometallic compounds, which are transitional between conventional inorganic and organic materials, have outstanding and one-of-a-kind features that offer fresh insight into the development of inorganic medicinal chemistry. The therapeutic potential of ruthenium(II)-arene RAPTA-type compounds is being thoroughly investigated, specifically owing to the excellent antimetastatic property of the initial candidate RAPTA-C. This review gives a thorough analysis of this complex and its evolution as a potential anticancer drug candidate. The numerous mechanistic investigations of RAPTA-C are discussed, and they are connected to the macroscopic biological characteristics that have been found. The "multitargeted" complex described here target enzymes, peptides, and intracellular proteins in addition to DNA that allow it to specifically target cancer cells. Understanding these may allow researchers to find specific targets and tune a new-generation organometallic complex accordingly.

New Organometallic Ru(II) Compounds with Lonidamine Motif as Antitumor Agents

The combination of one molecule of organic and metal-based fragments that exhibit antitumor activity is a modern approach in the search for new promising drugs. In this work, biologically active ligands based on lonidamine (a selective inhibitor of aerobic glycolysis used in clinical practice) were introduced into the structure of an antitumor organometallic ruthenium scaffold. Resistant to ligand exchange reactions, compounds were prepared by replacing labile ligands with stable ones. Moreover, cationic complexes containing two lonidamine-based ligands were obtained. Antiproliferative activity was studied in vitro by MTT assays. It was shown that the increase in the stability in ligand exchange reactions does not influence cytotoxicity. At the same time, the introduction of the second lonidamine fragment approximately doubles the cytotoxicity of studied complexes. The ability to induce apoptosis and caspase activation in tumour cell MCF7 was studied by employing flow cytometry.

Piano-stool ruthenium(II) complexes with maleimide and phosphine or phosphite ligands: synthesis and activity against normal and cancer cells

In these studies, we designed and investigated cyto- and genotoxic potential of five ruthenium cyclopentadienyl complexes bearing different phosphine and phosphite ligands. All of the complexes were characterized with spectroscopic analysis (NMR, FT-IR, ESI-MS, UV-vis, fluorescence and XRD (for two compounds)). For biological studies, we used three types of cells - normal peripheral blood mononuclear (PBM) cells, leukemic HL-60 cells and doxorubicin-resistance HL-60 cells (HL-60/DR). We compared the results obtained with those obtained for the complex with maleimide ligand CpRu(CO)₂(η¹-N-maleimidato) 1, which we had previously reported. We observed that the complexes CpRu(CO)(PPh₃)(η¹-N-maleimidato) 2a and CpRu(CO)(P(OEt)₃)(η¹-N-maleimidato) 3a were the most cytotoxic for HL-60 cells and non-cytotoxic for normal PBM cells. However, complex 1 was more cytotoxic for HL-60 cells than complexes 2a and 3a (IC₅₀ = 6.39 μM vs. IC₅₀ = 21.48 μM and IC₅₀ = 12.25 μM, respectively). The complex CpRu(CO)(P(OPh)₃)(η¹-N-maleimidato) 3b is the most cytotoxic for HL-60/DR cells (IC₅₀ = 104.35 μM). We found the genotoxic potential of complexes 2a and 3a only in HL-60 cells. These complexes also induced apoptosis in HL-60 cells. Docking studies showed that complexes 2a and CpRu(CO)(P(Fu)₃)(η¹-N-maleimidato) 2b have a small ability to degrade DNA, but they may cause a defect in DNA damage repair mechanisms leading to cell death. This hypothesis is corroborated with the results obtained in the plasmid relaxation assay in which ruthenium complexes bearing phosphine and phosphite ligands induce DNA breaks.

Anticancer evaluation of new organometallic ruthenium(ii) flavone complexes

Targeting multiple malignancy features such as angiogenesis, proliferation and metastasis with one molecule is an effective strategy in developing potent anticancer agents. Ruthenium metal complexation to bioactive scaffolds is reported to enhance their biological activities. Herein, we evaluate the impact of Ru chelation on the pharmacological activities of two bioactive flavones (1 and 2) as anticancer candidates. The novel Ru complexes (1Ru and 2Ru) caused a loss of their parent molecules' antiangiogenic activities in an endothelial cell tube formation assay. 1Ru enhanced the antiproliferative and antimigratory activities of its 4-oxoflavone 1 on MCF-7 breast cancer cells (IC₅₀ = 66.15 ± 5 μM and 50% migration inhibition, p < 0.01 at 1 μM). 2Ru diminished 4-thioflavone's (2) cytotoxic activity on MCF-7 and MDA-MB-231 yet significantly enhanced 2's migration inhibition (p < 0.05) particularly on the MDA-MB-231 cell line. The test derivatives also showed non-intercalative interaction with VEGF and c-myc i-motif DNA sequences.

NRF2 and Bip Interconnection Mediates Resistance to the Organometallic Ruthenium-Cymene Bisdemethoxycurcumin Complex Cytotoxicity in Colon Cancer Cells

Organometallic ruthenium (Ru)(II)-cymene complexes display promising pharmacological properties and might represent alternative therapeutic agents in medical applications. Polyphenols, such as curcumin and curcuminoids, display beneficial properties in medicine, including chemoprevention. Here we analyzed the anticancer effect of a cationic Ruthenium (Ru)(II)-cymene Bisdemethoxycurcumin (Ru-bdcurc) complex. The experimental data show that Ru-bdcurc induced cell death of colon cancer cells in vitro. In response to treatment, cancer cells activated the endoplasmic reticulum (ER)-resident chaperone GRP78/BiP and NRF2, the master regulators of the unfolded protein response (UPR) and the antioxidant response, respectively. Pharmacologic targeting of either NRF2 or BiP potentiated the cytotoxic effect of Ru-bdcurc. We also found that NRF2 and UPR pathways were interconnected as the inhibition of NRF2 reduced BiP protein levels. Mechanistically, the increased Ru-bdcurc-induced cell death, following NRF2 or BiP inhibition, correlated with the upregulation of the UPR apoptotic marker CHOP and with increased H2AX phosphorylation, a marker of DNA damage. The findings reveal that BiP and NRF2 interconnection was a key regulator of colon cancer cells resistance to Ru-bdcurc cytotoxic effect. Targeting that interconnection overcame the protective mechanism and enhanced the antitumor effect of the Ru-bdcurc compound.

Cyclometalated Ru(II)-NHC complexes with phenanthroline ligands induce apoptosis mediated by mitochondria and endoplasmic reticulum stress in cancer cells

The exploration of ruthenium complexes as anticancer drugs has been the focus of intense investigation. In this study, we synthesized and characterized four C,N-cyclometalated ruthenium(II) complexes (Ru1-Ru4) coordinated with pyridine-functionalized N-heterocyclic carbene (NHC) and auxiliary ligands (e.g., acetonitrile, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline). X-ray diffraction analysis showed that all of the four cycloruthenated complexes are hexa-coordinated in a typical octahedral geometry. In vitro cytotoxic studies revealed that cyclometalated Ru-NHC complexes Ru3 and Ru4 had stronger anticancer activity than their corresponding Ru-NHC precursor Ru1 and the clinically used cisplatin. For HeLa cells, Ru3 and Ru4 exhibited potent cytotoxicity with the IC₅₀ value of 4.31 ± 0.42 μM and 3.14 ± 0.23 μM, respectively, which was approximately three times lower than that of cisplatin. More interestingly, Ru3 and Ru4 not only effectively inhibited the proliferation of HeLa cells, but also exhibited potential anti-migration activity. In the scratch wound healing assay, Ru3 and Ru4 treatment significantly reduced the wound healing rate of HUVEC cells. Mechanistic studies showed that Ru3 and Ru4 caused a dual action mode of mitochondrial membrane depolarization and endoplasmic reticulum stress and finally induced apoptosis of HeLa cells.

RUNAT-BI: A Ruthenium(III) Complex as a Selective Anti-Tumor Drug Candidate against Highly Aggressive Cancer Cell Lines

Ruthenium compounds have demonstrated promising activity in different cancer types, overcoming several limitations of platinum-based drugs, yet their global structure-activity is still under debate. We analyzed the activity of Runat-BI, a racemic Ru(III) compound, and of one of its isomers in eight tumor cell lines of breast, colon and gastric cancer as well as in a non-tumoral control. Runat-BI was prepared with 2,2'-biimidazole and dissolved in polyethylene glycol. We performed assays of time- and dose-dependent viability, migration, proliferation, and expression of pro- and antiapoptotic genes. Moreover, we studied the growth rate and cell doubling time to correlate it with the apoptotic effect of Runat-BI. As a racemic mixture, Runat-BI caused a significant reduction in the viability and migration of three cancer cell lines from colon, gastric and breast cancer, all of which displayed fast proliferation rates. This compound also demonstrated selectivity between tumor and non-tumor lines and increased proapoptotic gene expression. However, the isolated isomer did not show any effect. Racemic Runat-BI is a potential drug candidate for treatment of highly aggressive tumors. Further studies should be addressed at evaluating the role of the other isomer, for a more precise understanding of its antitumoral potential and mechanism of action.

Extracellular vimentin mimics VEGF and is a target for anti-angiogenic immunotherapy

Anti-angiogenic cancer therapies possess immune-stimulatory properties by counteracting pro-angiogenic molecular mechanisms. We report that tumor endothelial cells ubiquitously overexpress and secrete the intermediate filament protein vimentin through type III unconventional secretion mechanisms. Extracellular vimentin is pro-angiogenic and functionally mimics VEGF action, while concomitantly acting as inhibitor of leukocyte-endothelial interactions. Antibody targeting of extracellular vimentin shows inhibition of angiogenesis in vitro and in vivo. Effective and safe inhibition of angiogenesis and tumor growth in several preclinical and clinical studies is demonstrated using a vaccination strategy against extracellular vimentin. Targeting vimentin induces a pro-inflammatory condition in the tumor, exemplified by induction of the endothelial adhesion molecule ICAM1, suppression of PD-L1, and altered immune cell profiles. Our findings show that extracellular vimentin contributes to immune suppression and functions as a vascular immune checkpoint molecule. Targeting of extracellular vimentin presents therefore an anti-angiogenic immunotherapy strategy against cancer.

The pro-tumorigenic effects of vimentin have been attributed to intracellular functions in tumour cells so far. Here, the authors show that tumour endothelial cells can secrete vimentin as a pro-angiogenic factor and that targeting of vimentin can be used as an immunotherapeutic strategy.

Bioactivity and Development of Small Non-Platinum Metal-Based Chemotherapeutics

Countless expectations converge in the multidisciplinary endeavour for the search and development of effective and safe drugs in fighting cancer. Although they still embody a minority of the pharmacological agents currently in clinical use, metal-based complexes have great yet unexplored potential, which probably hides forthcoming anticancer drugs. Following the historical success of cisplatin and congeners, but also taking advantage of conventional chemotherapy limitations that emerged with applications in the clinic, the design and development of non-platinum metal-based chemotherapeutics, either as drugs or prodrugs, represents a rapidly evolving field wherein candidate compounds can be fine-tuned to access interactions with druggable biological targets. Moving in this direction, over the last few decades platinum family metals, e.g., ruthenium and palladium, have been largely proposed. Indeed, transition metals and molecular platforms where they originate are endowed with unique chemical and biological features based on, but not limited to, redox activity and coordination geometries, as well as ligand selection (including their inherent reactivity and bioactivity). Herein, current applications and progress in metal-based chemoth are reviewed. Converging on the recent literature, new attractive chemotherapeutics based on transition metals other than platinum—and their bioactivity and mechanisms of action—are examined and discussed. A special focus is committed to anticancer agents based on ruthenium, palladium, rhodium, and iridium, but also to gold derivatives, for which more experimental data are nowadays available. Next to platinum-based agents, ruthenium-based candidate drugs were the first to reach the stage of clinical evaluation in humans, opening new scenarios for the development of alternative chemotherapeutic options to treat cancer.

Ruthenium(ii)-arene complexes as anti-metastatic agents, and related techniques

With the discovery of cisplatin, a vast area of applications of metallodrugs in cancer treatment was opened but due to the side effects caused by the cisplatin complexes, researchers began to look for alternatives with similar anticancer properties but fewer side effects. Ruthenium was found to be a promising candidate, considering its significant anticancer properties and low side effects. Several ruthenium complexes, viz. NAMI-A, KP1019, KP1339, and TLD1433, have entered clinical trials. Some other arene ruthenium complexes such as RM175 and RAPTA-C have also entered clinical trials but very few of them have shown anti-metastatic properties. Herein, we provide information and probable mechanistic pathways for ruthenium(ii)-arene complexes that have been studied, so far, for their anti-metastatic activities. Also, we discuss the techniques and their significance for determining the anti-metastatic effects of the complexes.

The Chicken Embryo Chorioallantoic Membrane as an In Vivo Model for Photodynamic Therapy

For many decades the chicken embryo chorioallantoic membrane (CAM) has been used for research as an in vivo model in a large number of different fields, including toxicology, bioengineering, and cancer research. More specifically, the CAM is also a suitable and convenient model system in the field of photodynamic therapy (PDT), mainly due to the easy access of its membrane and the possibility of grafting or growing tumors on the membrane and, interestingly, to study the PDT effects on its dense vascular network. In addition, the CAM is simple to handle and cheap. Since the CAM is not innervated until later stages of the embryo development, its use in research is simplified compared to other in vivo models as far as ethical and regulatory issues are concerned. In this review different incubation and drug administration protocols of relevance for PDT are presented. Moreover, data regarding the propagation of light at different wavelengths and CAM development stages are provided. Finally, the effects induced by photobiomodulation on the CAM angiogenesis and its impact on PDT treatment outcome are discussed.

The Significant Influence of a Second Metal on the Antiproliferative Properties of the Complex [Ru(η6 -C10 H14 )(Cl2 )(dmoPTA)]

Complexes [Ru(η⁶−C₁₀H₁₄)(Cl₂)(HdmoPTA)](OSO₂CF₃) (1), [Ru(η⁶−C₁₀H₁₄)(Cl₂)(dmoPTA)] (2) and [Ru(η⁶−C₁₀H₁₄)(Cl₂)‐μ‐dmoPTA‐1κP:2κ²N,N’‐MCl₂] (M=Zn (3), Co (4), Ni (5), dmoPTA=3,7‐dimethyl‐1,3,7‐triaza‐5‐phosphabicyclo[3.3.1]nonane) have been synthesized and characterized by elemental analysis and spectroscopic techniques. The crystal structures of 1, 3 and 5 were obtained by single‐crystal X‐ray diffraction. The antiproliferative activity of the complexes was evaluated against colon cancer cell line Caco‐2/TC7 by using the MTT protocol. The monometallic ruthenium complexes 1 and 2 were found to be inactive, but the bimetallic complexes 3, 4 and 5 display an increased activity (IC₅₀3: 9.07±0.27, 4: 5.40±0.19, 5: 7.15±0.30 μM) compared to cisplatin (IC₅₀=45.6±8.08 μM). Importantly, no reduction in normal cell viability was observed in the presence of the complexes. Experiments targeted to obtain information on the possible action mechanism of the complexes, such as cell cycle, ROS and gene expression studies, were performed. The results showed that the complexes display different properties and action mechanism depending on the nature of metal, M, bonded to the CH₃N_dmoPTA atoms.

Investigation of the Effects and Mechanisms of Anticancer Action of a Ru(II)-Arene Iminophosphorane Compound in Triple Negative Breast Cancer Cells

Triple negative breast cancer (TNBC) is one of the breast cancers with poorer prognosis and survival rates. TNBC has a disproportionally high incidence and mortality in women of African descent. We report on the evaluation of Ru-IM (1), a water-soluble organometallic ruthenium compound, in TNBC cell lines derived from patients of European (MDA-MB-231) and African (HCC-1806) ancestry (including IC50 values, cellular and organelle uptake, cell death pathways, cell cycle, effects on migration, invasion, and angiogenesis, a preliminary proteomic analysis, and an NCI 60 cell-line panel screen). 1 was previously found highly efficacious in MDA-MB-231 cells and xenografts, with little systemic toxicity and preferential accumulation in the tumor. We observe a similar profile for this compound in the two cell lines studied, which includes high cytotoxicity, apoptotic behavior and potential antimetastatic and antiangiogenic properties. Cytokine M-CSF, involved in the PI3/AKT pathway, shows protein expression inhibition with exposure to 1. We also demonstrate a p53 independent mechanism of action.

Safety and Efficacy Evaluation In Vivo of a Cationic Nucleolipid Nanosystem for the Nanodelivery of a Ruthenium(III) Complex with Superior Anticancer Bioactivity

Simple Summary

The availability of selective, effective, and safe anticancer agents is a major challenge in the field of cancer research. As part of a multidisciplinary research project, in recent years our group has proposed an original class of nanomaterials for the delivery of new anticancer drugs based on ruthenium(III) complexes. In cellular models, these nanosystems have been shown to be effective in counteracting growth and proliferation of human breast cancer cells. Compared to conventional metallochemotherapeutics such as platinum-based agents whose clinical practice is associated with serious undesirable effects, ruthenium complexes share improved biochemical profiles making them more selective towards cancer cells and less cytotoxic to healthy cells. Their combination with biocompatible nanocarriers further enhances these promising features, as here showcased by our research carried out in an animal model which underscores the efficacy and safety in vivo of one of our most promising ruthenium-based nanosystems.

Abstract

Selectivity and efficacy towards target cancer cells, as well as biocompatibility, are current challenges of advanced chemotherapy powering the discovery of unconventional metal-based drugs and the search for novel therapeutic approaches. Among second-generation metal-based chemotherapeutics, ruthenium complexes have demonstrated promising anticancer activity coupled to minimal toxicity profiles and peculiar biochemical features. In this context, our research group has recently focused on a bioactive Ru(III) complex—named AziRu—incorporated into a suite of ad hoc designed nucleolipid nanosystems to ensure its chemical stability and delivery. Indeed, we proved that the structure and properties of decorated nucleolipids can have a major impact on the anticancer activity of the ruthenium core. Moving in this direction, here we describe a preclinical study performed by a mouse xenograft model of human breast cancer to establish safety and efficacy in vivo of a cationic Ru(III)-based nucleolipid formulation, named HoThyRu/DOTAP, endowed with superior antiproliferative activity. The results show a remarkable reduction in tumour with no evidence of animal suffering. Blood diagnostics, as well as biochemical analysis in both acute and chronic treated animal groups, demonstrate a good tolerability profile at the therapeutic regimen, with 100% of mice survival and no indication of toxicity. In addition, ruthenium plasma concentration analysis and tissue bioaccumulation were determined via appropriate sampling and ICP-MS analysis. Overall, this study supports both the efficacy of our Ru-containing nanosystem versus a human breast cancer model and its safety in vivo through well-tolerated animal biological responses, envisaging a possible forthcoming use in clinical trials.

Drug Repurposing to Identify a Synergistic High-Order Drug Combination to Treat Sunitinib-Resistant Renal Cell Carcinoma

Simple Summary

In this study, drug combination screening was used to design a multidrug combination consisting of repurposed drugs to treat sunitinib-resistant clear cell renal cell carcinoma. In the frame of this project, the multidrug combination has been optimized and validated and an insight into the mechanism of action is given. The multidrug combinations significantly altered the transcription of genes related to apoptosis and metabolic pathways. Further analysis of the metabolism revealed strong upregulation of the presence of sphingolipids after multidrug combination treatment. Final evaluation for translation of the multidrug combination in ex vivo organoid-like cultures demonstrated significant anti-cancer efficacy.

Abstract

Repurposed drugs have been evaluated for the management of clear cell renal cell carcinoma (ccRCC), but only a few have influenced the overall survival of patients with advanced disease. To combine repurposed non-oncology with oncological drugs, we applied our validated phenotypic method, which consisted of a reduced experimental part and data modeling. A synergistic optimized multidrug combination (ODC) was identified to significantly reduce the energy levels in cancer remaining inactive in non-cancerous cells. The ODC consisted of Rapta-C, erlotinib, metformin and parthenolide and low doses. Molecular and functional analysis of ODC revealed a loss of adhesiveness and induction of apoptosis. Gene-expression network analysis displayed significant alterations in the cellular metabolism, confirmed by LC-MS based metabolomic analysis, highlighting significant changes in the lipid classes. We used heterotypic in vitro 3D co-cultures and ex vivo organoids to validate the activity of the ODC, maintaining an efficacy of over 70%. Our results show that repurposed drugs can be combined to target cancer cells selectively with prominent activity. The strong impact on cell adherence and metabolism indicates a favorable mechanism of action of the ODC to treat ccRCC.

Metal- and metalloid-based compounds to target and reverse cancer multidrug resistance

Drug resistance remains the major cause of cancer treatment failure especially at the late stage of the disease. However, based on their versatile chemistry, metal and metalloid compounds offer the possibility to design fine-tuned drugs to circumvent and even specifically target drug-resistant cancer cells. Based on the paramount importance of platinum drugs in the clinics, two main areas of drug resistance reversal strategies exist: overcoming resistance to platinum drugs as well as multidrug resistance based on ABC efflux pumps. The current review provides an overview of both aspects of drug design and discusses the open questions in the field. The areas of drug resistance covered in this article involve: 1) Altered expression of proteins involved in metal uptake, efflux or intracellular distribution, 2) Enhanced drug efflux via ABC transporters, 3) Altered metabolism in drug-resistant cancer cells, 4) Altered thiol or redox homeostasis, 5) Altered DNA damage recognition and enhanced DNA damage repair, 6) Impaired induction of apoptosis and 7) Altered interaction with the immune system. This review represents the first collection of metal (including platinum, ruthenium, iridium, gold, and copper) and metalloid drugs (e.g. arsenic and selenium) which demonstrated drug resistance reversal activity. A special focus is on compounds characterized by collateral sensitivity of ABC transporter-overexpressing cancer cells. Through this approach, we wish to draw the attention to open research questions in the field. Future investigations are warranted to obtain more insights into the mechanisms of action of the most potent compounds which target specific modalities of drug resistance.

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.

New organometallic ruthenium(ii) complexes with purine analogs - a wide perspective on their biological application

Three half-sandwich organometallic ruthenium(ii) complexes containing purine analogs such as triazolopyrimidines of general formula [(η6-p-cym)Ru(L)Cl2], where p-cym represents p-cymene and L is 5,6,7-trimethyl-1,2,4-triazolo[1,5-a]pyrimidine (tmtp for 1), 5,7-diethyl-1,2,4-triazolo[1,5-a]pyrimidine (detp for 2) and 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO for 3), have been synthesized and characterized by elemental analysis, infrared, multinuclear magnetic resonance spectroscopic techniques (1H, 13C, 15N), and single-crystal X-ray diffraction (for 1 and 2). All these complexes have been thoroughly screened for their in vitro cytotoxicity against MCF-7 and HeLa cell lines as well as L929 murine fibroblast cells, indicating [(η6-p-cym)Ru(HmtpO)Cl2] (3) as the most active representative against the HeLa cell line and simultaneously being 64-fold less toxic to normal L929 murine fibroblast cells than cisplatin. At the same time, 3 has shown antimetastatic activity comparable to NAMI-A against HeLa cells both after 24 and 48 h of treatment in a wound healing assay. In order to better understand the mechanism of anticancer action and differences in the cytotoxic activity of 1-3, the studies were expanded to determining their lipophilicity, the kinetic stability at pH 6.5-8, the effect on reactive oxygen species (ROS) production in HeLa cells and interactions with significant biomolecules (DNA and albumin) by using molecular docking and circular dichroism (CD) experiments. Furthermore, antiparasitic studies against L. braziliensis, L. infantum and T. cruzi reveal that the newly synthesized complexes 1-3 are very promising candidates which can compete with commercial antiparasitic drugs. Complex 3 in particular, on top of exhibiting a high antiparasitic effect (IC50 < 1 μM against two strains), reaches a selectivity index >1000.

Fluorinated-NHC Transition Metal Complexes: Leading Characters as Potential Anticancer Metallodrugs

In the last 20 years, N-Heterocyclic Carbene (NHC) ligands have been ubiquitous in biological and medicinal chemistry. Part of their success lies in the tremendous number of topologies that can be synthesized and thus finely tuned that have been described so far. This is particularly true in the case of those derivatives, including fluorine or fluorinated fragments on their NHC moieties, gaining much attention due to their enhanced biological properties and turning them into excellent candidates for the development of novel metallodrugs. Thus, this review summarizes the development that fluorinated-NHC transition metal complexes have had and their impact on cancer treatment.

Automatic evaluation of cyclooxygenase 2 inhibition induced by metal-based anticancer compounds

An automatic methodology based on micro sequential injection analysis coupled to a lab-on-valve system (termed μSIA-LOV) was developed and used to determine the ability of metal-based anticancer compounds to inhibit cyclooxygenase 2 (COX-2) activity. COX-2 may be involved in pathogenesis of cancer and it is overexpressed in several types of solid tumors. Since platinum-based compounds are extensively used in the treatment of cancer, and ruthenium compounds are considered as promising candidates for next generation of non-targeted anticancer drugs, it is interesting to establish whether COX-2 inhibition is relevant to their mode of action. The μSIA-LOV system was optimized and the IC₅₀ values of each compound were calculated. All the results present RSD values less than 2.5%. IC₅₀ values of 9.7 ± 0.6 μM to 207 ± 3 μM were obtained, with the most active inhibitor for COX-2 being rofecoxib with the metal compounds exhibiting IC₅₀ values in the range 13.7 ± 1.6 to 207 ± 3. The results obtained in this work provide significant information about the mechanism of the studied compounds, mostly ruthenium-based compounds, and the role of COX-2 in their mode of action. Moreover, this work confirmed the potential of the μSIA-LOV system as a simple, versatile, robust, and rapid analytical tool for automating the determination of IC₅₀ values of metal-based compounds.

Disruption of the Microtubule Network and Inhibition of VEGFR2 Phosphorylation by Cytotoxic N,O-Coordinated Pt(II) and Ru(II) Complexes of Trimethoxy Aniline-Based Schiff Bases

Platinum-based complexes are one of the most successful chemotherapeutic agents having a significant ground in cancer chemotherapy despite their side effects. During the past few decades, Ru(II) complexes have been emerging as efficient alternatives owing to their promising activities against platinum-resistant cancer. The pathway of action, lipophilicity, and cytotoxicity of a Pt or Ru complex may be tuned by varying the attached ligands, the coordination mode, and the leaving group. In this work, we report a family of Pt(II) and Ru(II) complexes (1-5) of three N,O and N,N donor-based trimethoxyanilines containing Schiff bases with the general formula [Pt^II(L)(DMSO)Cl], [Ru^II(L)(p-cymene)Cl], [Ru^II(L)(p-cymene)Cl]⁺, and [Pt^II(L)Cl₂]. All of the complexes are characterized by different analytical techniques. ¹H NMR and electrospray ionization mass spectrometry (ESI-MS) data suggest that the N,O-coordinated Pt(II) complexes undergo slower aquation compared to the Ru(II) analogues. The change of the coordination mode to N,N causes the Ru complexes to be more inert to aquation. The N,O-coordinating complexes show superiority over N,N-coordinating complexes by displaying excellent in vitro antiproliferative activity against different aggressive cancer cells, viz., triple-negative human metastatic breast adenocarcinoma MDA-MB-231, human pancreatic carcinoma MIA PaCa-2, and hepatocellular carcinoma Hep G2. In vitro cytotoxicity studies suggest that Pt(II) complexes are more effective than their corresponding Ru(II) analogues, and the most cytotoxic complex 3 is 10-15 times more toxic than the clinical drugs cisplatin and oxaliplatin against MDA-MB-231 cells. Cellular studies show that all of the N,O-coordinated complexes (1-3) initiate disruption of the microtubule network in MDA-MB-231 cells in a dose-dependent manner within 6 h of incubation and finally lead to the arrest of the cell cycle in the G2/M phase and render apoptotic cell death. The disruption of the microtubule network affects the agility of the cytoskeleton rendering inhibition of tyrosine phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2), a key step in angiogenesis. Complexes 1 and 2 inhibit VEGFR2 phosphorylation in a dose-dependent fashion. Among the Pt(II) and Ru(II) complexes, the former displays higher cytotoxicity, a stronger effect on the cytoskeleton, better VEGFR2 inhibition, and strong interaction with the model nucleobase 9-ethylguanine (9-EtG).

Ruthenium arene complexes in the treatment of 3D models of head and neck squamous cell carcinomas

Current chemotherapy for head and neck squamous cell carcinomas (HNSCCs) are based on cisplatin, which is usually associated to severe side effects. In general, the exploration for metal-based alternatives to cisplatin has resulted in the development of a series of ruthenium complexes that are able to produce a safe therapeutic action against some neoplasms, among which are lung and ovarian cancers. Here, we evaluate the efficacy of well defined, easily available and robust ruthenium(II) η⁶-arene compounds on 3D models of HNSCCs with or without human papillomavirus (HPV) infection and compare their effects to the state-of-the-art RAPTA-C, a promising ruthenium compound with known anti-cancer activity. One of the compounds induces a significant therapeutic action especially on HPV negative carcinoma. Besides viability and repopulation evaluations, we performed quantitative analysis of the internalized Ru compounds to further validate our findings and elucidate the possible mechanisms of action. These results show that Ru arene compounds represent a promising alternative for the treatment of HNSCCs and pave the way for the composition of innovative (co)therapies.

Frontiers of metal-coordinating drug design

Introduction: The occurrence of metal ions in biomolecules is required to exert vital cellular functions. Metal-containing biomolecules can be modulated by small-molecule inhibitors targeting their metal-moiety. As well, the discovery of cisplatin ushered the rational discovery of metal-containing-drugs. The use of both drug types exploiting metal-ligand interactions is well established to treat distinct pathologies. Therefore, characterizing and leveraging metal-coordinating drugs is a pivotal, yet challenging, part of medicinal chemistry.Area covered: Atomic-level simulations are increasingly employed to overcome the challenges met by traditional drug-discovery approaches and to complement wet-lab experiments in elucidating the mechanisms of drugs' action. Multiscale simulations, allow deciphering the mechanism of metal-binding inhibitors and metallo-containing-drugs, enabling a reliable description of metal-complexes in their biological environment. In this compendium, the authors review selected applications exploiting the metal-ligand interactions by focusing on understanding the mechanism and design of (i) inhibitors targeting iron and zinc-enzymes, and (ii) ruthenium and gold-based anticancer agents targeting the nucleosome and aquaporin protein, respectively.Expert opinion: The showcased applications exemplify the current role and the potential of atomic-level simulations and reveal how their synergic use with experiments can contribute to uncover fundamental mechanistic facets and exploit metal-ligand interactions in medicinal chemistry.

A Multitarget Gold(I) Complex Induces Cytotoxicity Related to Aneuploidy in HCT-116 Colorectal Carcinoma Cells

A novel alkynyl phosphane gold(I) complex (trimethylphosphane)(3-(1,3-dimethylxanthine-7-yl)prop-1-yn-1-yl)gold(I) 1 displayed mutiple biological activites including selective proliferation inhibitory, anti-metastatic, and anti-angiogenic effects. The complex also induced effects related to aneuploidy in HCT-116 colon carcinoma cells, which might be mainly ascribed to the dysfunction of mitochondrial bioenergetics and downregulation of glycolysis. Induction of aneuploidy beyond a critical level can provide an effective strategy to target cancer, in particular colorectal tumours with a low tolerance of aneuploidy, and could be of relevance for 1 and other metallodrugs.

Novel NHC-coordinated ruthenium(II) arene complexes achieve synergistic efficacy as safe and effective anticancer therapeutics

There is an urgent need for more effective, less toxic cancer therapy agents. Motivated by this need, we synthesized a small panel of N-heterocyclic carbene (NHC)-coordinated ruthenium(II) arene complexes Ru1-Ru6 with the formula [Ru(p-cymene)(L)Cl]PF₆ (L = NHC ligand with varying substituents). Cell-based in vitro studies revealed that despite the structural similarity, Ru1-Ru6 exhibited distinct cytotoxic activities against cancer cells. In particular, Ru4 and Ru6, which bear n-octyl and pentamethylbenzyl motifs, respectively, were the most active at inducing apoptosis. In human ovarian A2780 cancer cells, Ru4 and Ru6 showed the highest cytotoxicities with IC₅₀ values of 2.74 ± 0.15 μM and 1.98 ± 0.10 μM, respectively, and they were approximately 2-fold more potent than cisplatin (IC₅₀ = 5.55 ± 0.37 μM). In addition to the cell killing capacity, inhibition of cell migration was validated by using these two optimized complexes. Mechanistic studies revealed that Ru4 and Ru6 complexes induced apoptosis in a caspase-dependent manner, primarily through intracellular reactive oxygen species (ROS) overproduction and cell cycle arrest at G1 phase. Furthermore, in a preclinical metastatic model of A2780 tumor xenograft, administration of Ru4 and Ru6 (20 μmol/kg) resulted in a marked inhibition of tumor progression and metastasis. Finally, a substantially alleviated systemic toxicity was observed for both complexes in comparison with cisplatin in animals. Overall, this study greatly increases our understanding of NHC-coordinated Ru(II) arene metallodrugs, aiding further investigation of their therapeutic potential in the treatment of metastatic cancers.

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.

Characterization and Cytotoxicity of Polyprenol Lipid and Vitamin E-TPGS Hybrid Nanoparticles for Betulinic Acid and Low-Substituted Hydroxyl Fullerenol in MHCC97H and L02 Cells

Background

This study demonstrated an innovative formulation including the polyprenol (GBP) lipid and vitamin E-TPGS hybrid nanoparticles (NPs) which was aimed to control the transfer of betulinic acid (BA) and low-substituted hydroxyl fullerenol (C₆₀(OH)_n). Additionally, it developed BA-C₆₀(OH)n-GBP-TPGS-NPs delivery system and researched the anti-hepatocellular carcinoma (HCC) effects.

Materials and Methods

The NPs were prepared by nanoprecipitation with ultrasonic-assisted emulsification (UAE) method. It was characterized by scanning electronic microscopy (SEM), transmission electron microscopy (TEM), FTIR spectrum, size distribution and zeta potential. Physical and chemical properties were evaluated through measurement of drug release, stability studies, drug loading efficiency (DE) and encapsulation efficiency (EE). Biological activities were evaluated through measurement of MTT assay, lactate dehydrogenase leakage assay (LDH), cell proliferation assays, cell apoptosis analysis, comet assay, wound healing assay, cell invasion and Western blot analysis.

Results and Conclusions

The NPs exhibited clear distribution characteristics, improved solubility and stability. BA and C₆₀(OH)_n for the NPs displayed a biphasic release pattern with sustained drug release properties. The mixture of C₆₀(OH)_n with different hydroxyl groups may have a certain effect on the stability of the NPs system itself. The NPs could effectively inhibit MHCC97H cell proliferation, migration and invasion in vitro. Combined use of C₆₀(OH)_n and BA in GBP lipids may improve the inhibit effect of C₆₀(OH)_n or BA against HCC cells and reduce cytotoxicity and genotoxicity of C₆₀(OH)_n for normal cells. We concluded that one of the important mechanisms of BA-C₆₀(OH)_n-GBP-TPGS-NPs inhibiting MHCC97H cells is achieved by up-regulating the expression of Caspase-3, Caspase-8 and Caspase-9.

Binding Kinetics of Ruthenium Pyrithione Chemotherapeutic Candidates to Human Serum Proteins Studied by HPLC-ICP-MS

The development of ruthenium-based complexes for cancer treatment requires a variety of pharmacological studies, one of them being a drug's binding kinetics to serum proteins. In this work, speciation analysis was used to study kinetics of ruthenium-based drug candidates with human serum proteins. Two ruthenium (Ru) complexes, namely [(η⁶-p-cymene)Ru(1-hydroxypyridine-2(1H)-thionato)Cl] (1) and [(η⁶-p-cymene)Ru(1-hydroxypyridine-2(1H)-thionato)pta]PF₆ (2) (where pta = 1,3,5-triaza-7-phosphaadamantane), were selected. Before a kinetics study, their stability in relevant media was confirmed by nuclear magnetic resonance (NMR). Conjoint liquid chromatography (CLC) monolithic column, assembling convective interaction media (CIM) protein G and diethylamino (DEAE) disks, was used for separation of unbound Ru species from those bound to human serum transferrin (Tf), albumin (HSA) and immunoglobulins G (IgG). Eluted proteins were monitored by UV spectrometry (278 nm), while Ru species were quantified by post-column isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). Binding kinetics of chlorido (1) and pta complex (2) to serum proteins was followed from 5 min up to 48 h after incubation with human serum. Both Ru complexes interacted mainly with HSA. Complex (1) exhibited faster and more extensive interaction with HSA than complex (2). The equilibrium concentration for complex (1) was obtained 6 h after incubation, when about 70% of compound was bound to HSA, 5% was associated with IgG, whereas 25% remained unbound. In contrast, the rate of interaction of complex (2) with HSA was much slower and less extensive and the equilibrium concentration was obtained 24 h after incubation, when about 50% of complex (2) was bound to HSA and 50% remained unbound.

Vascular tone and angiogenesis modulation by catecholamine coordinated to ruthenium

Catecholamines participate in angiogenesis, an important tumor development process. However, the way catecholamines interact with their receptors has not been completely elucidated, and doubts still remain as to whether these interactions occur between catechol and/or amine sites and particular amino acid residues on the catecholamine receptors. To evaluate how catechol and amine groups contribute to angiogenesis, we immobilized the catechol site through ruthenium ion (Ru) coordination, to obtain species with the general formula [Ru(NH₃)₄(catecholamine-R)]Cl. We then assessed the angiogenic activity of the complexes in a chorioallantoic membrane model (CAM) and examined vascular reactivity and calcium mobilization in rat aortas and vascular cells. [Ru(NH₃)₄(catecholamine-R)]Cl acted as partial agonists and/or antagonists of their respective receptors and induced calcium mobilization. [Ru(NH₃)₄(isoproterenol)]⁺ [Ru(NH₃)₄(noradrenaline)]⁺, and [Ru(NH₃)₄(adrenaline)]⁺ behaved as antiangiogenic complexes, whereas [Ru(NH₃)₄(dopamine)]⁺ proved to be a proangiogenic complex. In conclusion, catecholamines and [Ru(NH₃)₄(catecholamine-R)]Cl can modulate angiogenesis, and catechol group availability can modify the way these complexes impact the vascular tone, suggesting that catecholamines and their receptors interact differently after catecholamine coordination to ruthenium.