Ruthenium Complexes as Anticancer Agents: A Brief History and Perspectives

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.

Redesigning Nature: Ruthenium Flavonoid Complexes with Antitumour, Antimicrobial and Cardioprotective Activities

Flavonoids are a class of natural polyphenolic compounds sharing a common 2-phenyl-3,4-dihydro-2H-1-benzopyran (flavan) backbone. Typically known for their antioxidant activity, flavonoids are also being investigated regarding antitumour and antimicrobial properties. In this review, we report on the complexation of both natural and synthetic flavonoids with ruthenium as a strategy to modulate the biological activity. The ruthenoflavonoid complexes are divided into three subclasses, according to their most prominent bioactivity: antitumour, antimicrobial, and protection of the cardiovascular system. Whenever possible the activity of the ruthenoflavonoids is compared with that of commercial drugs for a critical assessment of the feasibility of using them in future clinical applications.

Ruthenium Complexes as Promising Candidates against Lung Cancer

Lung cancer is one of the most common malignancies with the highest mortality rate and the second-highest incidence rate after breast cancer, posing a serious threat to human health. The accidental discovery of the antitumor properties of cisplatin in the early 1960s aroused a growing interest in metal-based compounds for cancer treatment. However, the clinical application of cisplatin is limited by serious side effects and drug resistance. Therefore, other transition metal complexes have been developed for the treatment of different malignant cancers. Among them, Ru(II/III)-based complexes have emerged as promising anticancer drug candidates due to their potential anticancer properties and selective cytotoxic activity. In this review, we summarized the latest developments of Ru(II/III) complexes against lung cancer, focusing mainly on the mechanisms of their biological activities, including induction of apoptosis, necroptosis, autophagy, cell cycle arrest, inhibition of cell proliferation, and invasion and metastasis of lung cancer cells.

Ruthenium(II) and Platinum(II) Complexes with Biologically Active Aminoflavone Ligands Exhibit In Vitro Anticancer Activity

Continuing our studies on the mechanisms underlying the cytotoxicity of potential drugs, we have described several aspects of the in vitro anticancer activity of ruthenium(II) and platinum(II) complexes with bioactive, synthetic aminoflavone ligands. We examined the mechanism of proapoptotic activity of cis-dichlorobis(3-imino-2-methoxyflavanone)ruthenium(II), cis-dichlorobis(3-imino-2-ethoxyflavanone)ruthenium(II), and trans-dichlorobis(3-aminoflavone)platinum(II). Cisplatin was used as a reference compound. The cytotoxicity was investigated by MTT assay. The mechanism of proapoptotic activity of the tested compounds was investigated by evaluation of caspase-8 activity, cytometric analysis of annexin-V positive cells, and mitochondrial potential loss measurement. The results showed that ruthenium compounds break partially or completely the cisplatin resistance by activating the caspase 8-dependent apoptosis pathway and loss of mitochondrial membrane potential. Platinum compounds also have a cytostatic effect, but their action requires more exposure time. Potential mechanisms underlying drug resistance in the two pairs of cancer cell lines were investigated: total glutathione content, P-glycoprotein activity, and differences in the activity of DNA repair induced by nucleotide excision. Results showed that cisplatin-resistant cells have elevated glutathione levels relative to sensitive cells. Moreover, they indicated the mechanisms enabling cells to avoid apoptosis caused by DNA damage. Pg-P activity has no effect on the development of cisplatin resistance in the cell lines described.

Gold(III) to Ruthenium(III) Metal Exchange in Dithiocarbamato Complexes Tunes Their Biological Mode of Action for Cytotoxicity in Cancer Cells

Malignant tumors have affected the human being since the pharaoh period, but in the last century the incidence of this disease has increased due to a large number of risk factors, including deleterious lifestyle habits (i.e., smoking) and the higher longevity. Many efforts have been spent in the last decades on achieving an early stage diagnosis of cancer, and more effective cures, leading to a decline in age-standardized cancer mortality rates. In the last years, our research groups have developed new metal-based complexes, with the aim to obtain a better selectivity for cancer cells and less side effects than the clinically established reference drug cisplatin. This work is focused on four novel Au(III) and Ru(III) complexes that share the piperidine dithiocarbamato (pipe-DTC) as the ligand, in a different molar ratio. The compounds [AuCl2(pipeDTC)], [Au(pipeDTC)2]Cl, [Ru(pipeDTC)3] and β-[Ru2(pipeDTC)5] have been synthesized and fully characterized by several chemical analyses. We have then investigated their biological properties in two different cell lines, namely, AGS (gastric adenocarcinoma) and HCT116 (colon carcinomas), showing significant differences among the four compounds. First, the two gold-based compounds and β-[Ru2(pipeDTC)5] display IC50 in the µM range, significantly lower than cisplatin. Second, we showed that [AuCl2(pipeDTC)] and β-[Ru2(pipeDTC)5]Cl drive different molecular mechanisms. The first was able to induce the protein level of the DNA damage response factor p53 and the autophagy protein p62, in contrast to the second that induced the ATF4 protein level, but repressed p62 expression. This study highlights that the biological activity of different complexes bringing the same organic ligand depends on the electronic and structural properties of the metal, which are able to fine tune the biological properties, giving us precious information that can help to design more selective anticancer drugs.

A Novel Ruthenium(II) Complex With Lapachol Induces G2/M Phase Arrest Through Aurora-B Kinase Down-Regulation and ROS-Mediated Apoptosis in Human Prostate Adenocarcinoma Cells

Lapachol is a well-studied natural product that has been receiving great interest due to its anticancer properties that target oxidative stress. In the present work, two novel lapachol-containing ruthenium(II) complexes [Ru(Lap)(dppm)(bipy)]PF6 (1) and [Ru(Lap)(dppm)(phen)]PF6 (2) [Lap = lapachol, dppm = 1,1'-bis(diphosphino)methane, bipy = 2,2'-bipyridine, phen = 1,10-phenantroline] were synthesized, fully characterized, and investigated for their cellular and molecular responses on cancer cell lines. We found that both complexes exhibited a potent cytotoxic effect in a panel of cancer cell lines in monolayer cultures, as well as in a 3D model of multicellular spheroids formed from DU-145 human prostate adenocarcinoma cells. Furthermore, the complex (2) suppressed the colony formation, induced G2/M-phase arrest, and downregulated Aurora-B. The mechanism studies suggest that complex (2) stimulate the overproduction of reactive oxygen species (ROS) and triggers caspase-dependent apoptosis as a result of changes in expression of several genes related to cell proliferation and caspase-3 and -9 activation. Interestingly, we found that N-acetyl-L-cysteine, a ROS scavenger, suppressed the generation of intracellular ROS induced by complex (2), and decreased its cytotoxicity, indicating that ROS-mediated DNA damage leads the DU-145 cells into apoptosis. Overall, we highlighted that coordination of lapachol to phosphinic ruthenium(II) compounds considerably improves the antiproliferative activities of resulting complexes granting attractive selectivity to human prostate adenocarcinoma cells. The DNA damage response to ROS seems to be involved in the induction of caspase-mediated cell death that plays an important role in the complexes' cytotoxicity. Upon further investigations, this novel class of lapachol-containing ruthenium(II) complexes might indicate promising chemotherapeutic agents for prostate cancer therapy.

Synthesis and Structural Characterization of Half-Sandwich Arene–Ruthenium(II) Complexes with Bis(imidazol-1-yl)methane, Imidazole and Benzimidazole

Mono- and binuclear arene–ruthenium(II) complexes with imidazole-containing ligands were prepared by the reaction of the ligands (L1 = bis(imidazole-1-yl)methane; ImH = 1H-Imidazole; BImH = 1H-Benzimidazole) with [(p-cym)Ru(µ-Cl)2]2 dimers. When bis(imidazole-1-yl)methane reacted with [(p-cym)Ru(µ-Cl)2]2 in methanol, a binuclear complex of the type [Ru2(L1)2(p-cym)2Cl2]Cl2 (2) with cyclic structure was synthesized, whereas by using acetonitrile as a solvent under the same reaction conditions, an unexpected C–N bond cleavage was observed, and a complex of formula [Ru(ImH)2(p-cym)Cl]Cl (1) with coordinated imidazole molecules was obtained. Another type of arene–ruthenium complex [Ru(BImH)(p-cym)Cl2] (3) was obtained by the reaction of benzimidazole and [(p-cym)Ru(µ-Cl)2]2. All compounds were characterized by spectral (FT-IR, NMR 1H, 13C) and single-crystal X-ray diffraction methods; their catalytic activity in transfer hydrogenation and the cytotoxicity against MCF-7 and HepG2 cells were evaluated.

Preclinical Pharmacokinetics and Biodistribution of Anticancer Dinuclear Palladium(II)-Spermine Complex (Pd2Spm) in Mice

Palladium-based compounds are regarded as potential analogs to platinum anticancer drugs with improved properties. The present study assessed the pharmacokinetics and biodistribution of a dinuclear palladium(II)-spermine chelate (Pd₂Spm), which has previously been shown to possess promising in vitro activity against several therapy-resistant cancers. Using inductively coupled plasma-mass spectrometry, the kinetic profiles of palladium/platinum in serum, serum ultrafiltrate and tissues (kidney, liver, brain, heart, lungs, ovaries, adipose tissue and mammary glands) were studied in healthy female Balb/c mice after a single intraperitoneal bolus injection of Pd₂Spm (3 mg/kg bw) or cisplatin (3.5 mg/kg bw) between 0.5 and 48 h post-injection. Palladium in serum exhibited biphasic kinetics with a terminal half-life of 20.7 h, while the free palladium in serum ultrafiltrate showed a higher terminal half-life than platinum (35.5 versus 31.5 h). Palladium was distributed throughout most of the tissues except for the brain, with the highest values in the kidney, followed by the liver, lungs, ovaries, adipose tissue and mammary glands. The in vitro cellular accumulation was also evaluated in breast cancer cells, evidencing a passive diffusion as a mechanism of Pd₂Spm’s cellular entry. This study reports, for the first time, the favorable pharmacokinetics and biodistribution of Pd₂Spm, which may become a promising pharmacological agent for cancer treatment.

Taking phototherapeutics from concept to clinical launch

More than four decades have passed since the first example of a light-activated (caged) compound was described. In the intervening years, a large number of light-responsive derivatives have been reported, several of which have found utility under a variety of in vitro conditions using cells and tissues. Light-triggered bioactivity furnishes spatial and temporal control, and offers the possibility of precision dosing and orthogonal communication with different biomolecules. These inherent attributes of light have been advocated as advantageous for the delivery and/or activation of drugs at diseased sites for a variety of indications. However, the tissue penetrance of light is profoundly wavelength-dependent. Only recently have phototherapeutics that are photoresponsive in the optical window of tissue (600-900 nm) been described. This Review highlights these recent discoveries, along with their limitations and clinical opportunities. In addition, we describe preliminary in vivo studies of prospective phototherapeutics, with an emphasis on the path that remains to be navigated in order to translate light-activated drugs into clinically useful therapeutics. Finally, the unique attributes of phototherapeutics is highlighted by discussing several potential disease applications.