Designing Ruthenium Anticancer Drugs: What Have We Learnt from the Key Drug Candidates?

Ruthenium(iii) complexes containing thiazole-based ligands that modulate amyloid-β aggregation

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder where one of the commonly observed pathological hallmarks is extracellular deposits of the peptide amyloid-β (Aβ). These deposits contain a high concentration of metals and initially presented a promising target for therapy; however it has become increasingly evident that the soluble form of the peptide is neurotoxic, not the amyloidogenic species. Metal-based therapeutics are uniquely suited to target soluble Aβ and have shown considerable promise to prevent the aggregation and induced cytotoxicity of the peptide in vitro. Herein, we have prepared a small series of derivatives of two promising Ru(iii) complexes NAMI-A (imidazolium [trans-RuCl₄(1H-imidazole)(dimethyl sulfoxide-S)]) and PMRU20 (2-aminothiazolium [trans-RuCl₄(2-aminothiazole)₂]), to determine structure-activity relationships (SAR) for Ru(iii) therapeutics for AD. Using the three complementary methods of Thioflavin T fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM), it was determined that the symmetry around the metal center did not significantly impact the activity of the complexes, but rather the attached thiazole ligand(s) mitigated Aβ aggregation. Across both families of Ru(iii) complexes the determined SAR for the functional groups on the thiazole ligands to modulate Aβ aggregation were NH₂ > CH₃ > H. These results highlight the importance of secondary interactions between the metallotherapeutic and the Aβ peptide where hydrogen-bonding has the greatest impact on modulating Aβ aggregation.

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.

Nanoencapsulation of a ruthenium(ii) complex with triazolopyrimidine in liposomes as a tool for improving its anticancer activity against melanoma cell lines

Two types of ruthenium(ii) complexes containing 1,2,4-triazolo[1,5-a]pyrimidines of the general formulas [RuCl₂(dmso)₃(L)] ((1)-(3)) and [RuCl₂(dmso)₂(L)₂] ((4)-(6)), where L represents 1,2,4-triazolo[1,5-a]pyrimidine (tp for (1)), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp for (2)), 7-isobutyl-5-methyl-1,2,4-trizolo[1,5-a]pyrimidine (ibmtp for (3)), 5,7-diethyl-1,2,4-triazolo[1,5-a]pyrimidine (detp for (4)), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp for (5)) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp for (6)), have been synthesized and characterized by elemental analysis, infrared, multinuclear magnetic resonance spectroscopic techniques (¹H, ¹³C, and ¹⁵N), and X-ray (for (3), (4), and (5)). All these complexes have been thoroughly screened for their in vitro cytotoxicity against melanoma cell lines A375 and Hs294T, indicating cis,cis,cis-[RuCl₂(dbtp)₂(dmso)₂] (5) as the most active representative, in addition to being non-toxic to normal human fibroblasts (NHDF) and not inducing hemolysis of human erythrocytes. In order to develop an intravenous formulation for (5), liposomes composed of soybean phosphatidylcholine (SPC), cholesterol (Chol) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀) were prepared and subsequently characterized. (5)-Loaded liposomes, with spherical morphology, assessed by transmission electron microscope (TEM), exhibited satisfactory encapsulation efficiency and stability. In in vitro experiments, PEG-modified (5)-loaded liposomes were more effective (10-fold) than free (5) for growth inhibition of both human melanoma cell lines. Furthermore, such an approach resulted in the reduction of cancer cell viability that was even 10-fold greater than that observed for free cisplatin.

Copper(ii) complexes containing enoxacin and heterocyclic ligands: synthesis, crystal structures and their biological perspectives

Two copper-based complexes with a distorted square pyramidal geometry show excellent binding and cleavage affinity towards DNA and proteins. Also, these complexes have potential cytotoxicity against MCF-7 cancer cells.

Iron and copper complexes with antioxidant activity as inhibitors of the metastatic potential of glioma cells

Iron and copper complexes with antioxidant activity able to inhibit tumor metastasis by inhibiting epithelial-mesenchymal transition in glioma cells.

Cytotoxic effect, generation of reactive oxygen/nitrogen species and electrochemical properties of Cu(ii) complexes in comparison to half-sandwich complexes of Ru(ii) with aminochromone derivatives

This paper describes the synthesis of new 6-aminoflavone (6AFl (3)) and 6-aminochromone (6AC (4)) complexes with Cu(ii) and Ru(ii) ions ([Cu(6AC)₂Cl₂] (3a), [Cu(6AFl)₂Cl₂] (4a), [Ru(p-cymene)(6AC)Cl₂] (4b)) and comparison of their properties with the previously described 7-aminoflavone (7AFl (1)) and 7-amino-2-methylchromone (7A2MC (2)) analogues. The cytotoxic effect of all these complexes against two human leukaemia cell lines (HL-60 and NALM-6), melanoma WM-115 cells and COLO205 cells, is determined. The cytotoxicity of copper(ii) complexes, especially [Cu(6AFl)₂Cl₂] (3a) was higher than ruthenium(ii) complexes with the same ligands. Their cytotoxic potency was also stronger in comparison to the referential agents like cisplatin. The pro-oxidative properties were determined for the most active complexes and their ability to generate ROS (reactive oxygen species)/RNS (reactive nitrogen species) in cancer cells was confirmed. The type of ligand and the chemical structure of the tested complexes had an influence on the level of ROS/RNS generated in cancer cells. The redox properties of the copper complex compounds were evaluated by cyclic voltammetry, and compared with the data for Ru(ii) complexes. The reduction and oxidation processes of Ru(iii)/Ru(ii) and Cu(ii)/Cu(i) were described as quasi-reversible.

New Cu(ii)/Ru(ii) complexes with 6-aminoflavone/chromone derivatives as ligands were synthesized and characterized. Their cytotoxicity, pro-oxidative and redox properties were investigated.

Anticancer Ruthenium(III) Complexes and Ru(III)-Containing Nanoformulations: An Update on the Mechanism of Action and Biological Activity

The great advances in the studies on metal complexes for the treatment of different cancer forms, starting from the pioneering works on platinum derivatives, have fostered an increasingly growing interest in their properties and biomedical applications. Among the various metal-containing drugs investigated thus far, ruthenium(III) complexes have emerged for their selective cytotoxic activity in vitro and promising anticancer properties in vivo, also leading to a few candidates in advanced clinical trials. Aiming at addressing the solubility, stability and cellular uptake issues of low molecular weight Ru(III)-based compounds, some research groups have proposed the development of suitable drug delivery systems (e.g., taking advantage of nanoparticles, liposomes, etc.) able to enhance their activity compared to the naked drugs. This review highlights the unique role of Ru(III) complexes in the current panorama of anticancer agents, with particular emphasis on Ru-containing nanoformulations based on the incorporation of the Ru(III) complexes into suitable nanocarriers in order to enhance their bioavailability and pharmacokinetic properties. Preclinical evaluation of these nanoaggregates is discussed with a special focus on the investigation of their mechanism of action at a molecular level, highlighting their pharmacological potential in tumour disease models and value for biomedical applications.

Ruthenium(II) Complexes as Potential Apoptosis Inducers in Cancer Therapy

The compound cis-diamminedichloroplatinum(II) (cisplatin) is the most widely used anticancer drug, but due to its serious side effects (including gastrointestinal symptoms, renal tubular injury, neuromuscular complications, and ototoxicity), clinical applications of cisplatin are limited. Therefore, these limitations have provided an encouragement for further research into other transition metal complexes, with an aim to overcome the disadvantages related with cisplatin therapy. In the search for effective complexes that can be targeted against tumor cells, many research groups synthesized various ruthenium( II) complexes with different ligands. Also, newly synthesized ruthenium(II) complexes showed selective anticancer activity against different types of cancer cells. Activity of ruthenium(II) complexes in some cases was even higher than that of cisplatin against the same cells. Precise mechanism of action of ruthenium(II) complexes is not fully understood. The different examples mentioned in this review showed that ruthenium(II) complexes decreased viability of cancer cells by induction of apoptosis and/or by cell cycle arrest which implies their different mechanism of action against different types of cancer cells.

Unconventional Anticancer Metallodrugs and Strategies to Improve Their Pharmacological Profile

For the past 41 years, metal-based drugs have been widely used for the treatment of cancer [...]

NAMI-A and KP1019/1339, Two Iconic Ruthenium Anticancer Drug Candidates Face-to-Face: A Case Story in Medicinal Inorganic Chemistry

NAMI-A ((ImH)[trans-RuCl₄(dmso-S)(Im)], Im = imidazole) and KP1019/1339 (KP1019 = (IndH)[trans-RuCl₄(Ind)₂], Ind = indazole; KP1339 = Na[trans-RuCl₄(Ind)₂]) are two structurally related ruthenium(III) coordination compounds that have attracted a lot of attention in the medicinal inorganic chemistry scientific community as promising anticancer drug candidates. This has led to a considerable amount of studies on their respective chemico-biological features and to the eventual admission of both to clinical trials. The encouraging pharmacological performances qualified KP1019 mainly as a cytotoxic agent for the treatment of platinum-resistant colorectal cancers, whereas the non-cytotoxic NAMI-A has gained the reputation of being a very effective antimetastatic drug. A critical and strictly comparative analysis of the studies conducted so far on NAMI-A and KP1019 allows us to define the state of the art of these experimental ruthenium drugs in terms of the respective pharmacological profiles and potential clinical applications, and to gain some insight into the inherent molecular mechanisms. Despite their evident structural relatedness, deeply distinct biological and pharmacological profiles do emerge. Overall, these two iconic ruthenium complexes form an exemplary and unique case in the field of medicinal inorganic chemistry.