Influence of Hydrogen-Bonding Substituents on the Cytotoxicity of RAPTA Compounds

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.

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.

Antitumor Activity of Pt(II), Ru(III) and Cu(II) Complexes

Metal complexes are currently potential therapeutic compounds. The acquisition of resistance by cancer cells or the effective elimination of cancer-affected cells necessitates a constant search for chemical compounds with specific biological activities. One alternative option is the transition metal complexes having potential as antitumor agents. Here, we present the current knowledge about the application of transition metal complexes bearing nickel(II), cobalt(II), copper(II), ruthenium(III), and ruthenium(IV). The cytotoxic properties of the above complexes causing apoptosis, autophagy, DNA damage, and cell cycle inhibition are described in this review.

A review on 1,1-bis(diphenylphosphino)methane bridged homo- and heterobimetallic complexes for anticancer applications: Synthesis, structure, and cytotoxicity

Herein, we review developments in synthesis, structure, and biological (anti-cancer) activities of 1,1-bis(diphenylphosphino)methane (dppm) bridged homo- and heterobimetallic systems of the type L_mM(μ₂-dppm)M'L_n (M and M' are transition metals which may be different or the same and L_n,m are co-ligands) since the first such reported bimetallic system in 1987 until the present time (2020). As the simplest diphosphine, dppm enables facile formation of bimetallic complexes, where, given the short spacer between the PPh₂ groups, close spatial proximity of the metal centres is ensured. We concentrate on complexes bearing no M-M interaction and contrast biological activities of these complexes with mononuclear counterparts and positive control agents such as cisplatin, in an attempt to elucidate patterns in the biological activities of these complexes.

Selective binding of an organoruthenium complex to G-rich human telomeric sequence by tandem mass spectrometry

RATIONALE

Human telomeric DNA is reported to be a potential target for anticancer organometallic ruthenium(II) complexes, however, the interaction sites were not clearly discriminated and identified.

METHODS

In the current study, tandem mass spectrometry (MS/MS) using collision-induced dissociation (CID) was firstly introduced to identify the interaction sites of an organometallic ruthenium(II) complex [(η⁶ -biphenyl)Ru(en)Cl][PF₆ ] (1; en = ethylenediamine) with 5'-T₁ T₂ A₃ G₄ G₅ G₆ -3' (I), the repeating unit of human telomeric DNA, in both positive- and negative-ion mode at a low reaction molar ratio (1/I = 0.2) which was applied to preserve the site selectivity.

RESULTS

Mass spectrometric results showed that mono-ruthenated I was the main product under the conditions. In positive-ion mode, MS/MS results indicated that ruthenium complex 1 binds to T₂ or G₆ in strand I. However, in negative-ion mode, no efficient information was obtained for exact identification of ruthenation sites which may be attributed to losses of fragment ions due to charge neutralization by the coordination of the positively charged ruthenium complex to the short MS/MS fragments.

CONCLUSIONS

This is the first report of using top-down MS to characterize the interactions of organometallic ruthenium(II) complexes and human telomeric DNA. Thymine can be thermodynamically competitive with guanine for binding to ruthenium complexes even at low reaction molar ratio, which inspired us to explore in greater depth the significance of thymine binding.

Anticancer activity of Ru- and Os(arene) compounds of a maleimide-functionalized bioactive pyridinecarbothioamide ligand

With the aim of increasing the accumulation of Ru anticancer agents in the tumor, a targeted delivery strategy based on a maleimide anchor for the biological vector human serum albumin (HSA) was developed. A group of piano stool Ru- and Os(η⁶-arene) complexes carrying a maleimide-functionalized N-phenyl-2-pyridinecarbothioamide (PCA) ligand was designed allowing for covalent conjugation to biological thiols. The complexes were characterized by NMR spectroscopy, ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The compounds were shown to undergo halido/aqua ligand exchange reactions in aqueous solution, depending mainly on the metal center and the nature of the halide. In vitro cytotoxicity studies revealed low potency which is explained by the observed high reactivity of the maleimide to the thiol of l-cysteine (Cys), while the metal center itself shows little affinity to amino acids of the model protein lysozyme.

Anti-metastatic effects of RAPTA-C conjugated polymeric micelles on two-dimensional (2D) breast tumor cells and three-dimensional (3D) multicellular tumor spheroids

Macromolecular ruthenium (Ru) complexes are a promising avenue to better, and more selective, chemotherapeutics to treat metastatic cancers. In our previous research, amphiphilic block copolymeric micelles carrying RAPTA-C (RuCl2(p-cymene)(PTA)) were demonstrated to improve the cellular uptake and cytotoxicity of RAPTA-C (Blunden et al., 2013). However, the anti-metastatic effect of RAPTA-C conjugated polymeric micelles is yet to be established. In this work, we investigated the anti-metastatic effects of RAPTA-C conjugated micelles in both 2D and 3D in vitro breast tumor cell models in comparison with free RAPTA-C. RAPTA-C conjugated micelles showed an improved anti-metastatic effect compared with RAPTA-C for 2D cultured breast tumor cells. RAPTA-C micelles selectively targeted the metastatic tumor cells over the nontumorigenic CHO cells. 3D MCTS assays showed that RAPTA-C conjugated micelles showed a cell growth inhibition similar to that of ten times of the free drug. Further improvement of the RAPTA-C delivery vehicle may provide useful tools to harness ruthenium compounds for metastatic cancer therapy.

STATEMENT OF SIGNIFICANCE

The interest in ruthenium drugs stem from their anti-metastatic effect. In contrast to other metal-based drugs that inhibit the growth of tumor cells, ruthenium drugs seem less toxic, but have a pronounce effect on the migration of cancer cells. The ruthenium drug chosen here, RAPTA-C, is capable of inhibiting migration as shown in various assays here. In this publication, we could show for the first time that this effect is enhanced when the drug is delivered using micelles. Important in particular is that the effect is more pronounced in cancerous breast cancer cells while RAPTA-C delivered in micelles does not seem to show any effect on healthy cells. We believe that the presented micelles are suitable carriers for this anti-metastatic drug. The design of the micelle would also allow the encapsulation of other drugs in future studies creating a potentially powerful bullet.

Target profiling of an antimetastatic RAPTA agent by chemical proteomics: relevance to the mode of action

The RAPTA pharmacophore was linked to beads to identify its biomolecular targets in cancer cells.

The clinical development of anticancer metallodrugs is often hindered by the elusive nature of their molecular targets. To identify the molecular targets of an antimetastatic ruthenium organometallic complex based on 1,3,5-triaza-7-phosphaadamantane (RAPTA), we employed a chemical proteomic approach. The approach combines the design of an affinity probe featuring the pharmacophore with mass-spectrometry-based analysis of interacting proteins found in cancer cell lysates. The comparison of data sets obtained for cell lysates from cancer cells before and after treatment with a competitive binder suggests that RAPTA interacts with a number of cancer-related proteins, which may be responsible for the antiangiogenic and antimetastatic activity of RAPTA complexes. Notably, the proteins identified include the cytokines midkine, pleiotrophin and fibroblast growth factor-binding protein 3. We also detected guanine nucleotide-binding protein-like 3 and FAM32A, which is in line with the hypothesis that the antiproliferative activity of RAPTA compounds is due to induction of a G₂/M arrest and histone proteins identified earlier as potential targets.

Metallomics insights into the programmed cell death induced by metal-based anticancer compounds

Since the discovery of cisplatin more than 40 years ago, enormous research efforts have been dedicated to developing metal-based anticancer agents and to elucidating the mechanisms involved in the action of these compounds. Abnormal metabolism and the evasion of apoptosis are important hallmarks of malignant transformation, and the induction of apoptotic cell death has been considered to be a main pathway by which cytotoxic metal complexes combat cancer. However, many cancers have cellular defects involving the apoptotic machinery, which results in an acquired resistance to apoptotic cell death and therefore reduced chemotherapeutic effectiveness. Over the past decade, it has been revealed that a growing number of cell death pathways induced by metal complexes are not dependent on apoptosis. Metal complexes specifically triggering these alternative cell death pathways have been identified and explored as novel cancer treatment options. In this review, we discuss recent examples of metallomics studies on the different types of cell death induced by metal-based anticancer drugs, especially on the three major forms of programmed cell death (PCD) in mammalian cells: apoptosis, autophagy and regulated necrosis, also called necroptosis.

Phenylalanine--a biogenic ligand with flexible η6- and η6:κ1-coordination at ruthenium(II) centres

The reaction of (S)-2,5-dihydrophenylalanine 1 with ruthenium(III) chloride yields the μ-chloro-bridged dimeric η(6)-phenylalanine ethyl ester complex 3, which can be converted into the monomeric analogue, η(6):κ(1)-phenylalanine ethyl ester complex 12, under basic conditions. Studies were carried out to determine the stability and reactivity of complexes bearing η(6)- and η(6):κ(1)-chelating phenylalanine ligands under various conditions. Reaction of 3 with ethylenediamine derivatives N-p-tosylethylenediamine or 1,4-di-N-p-tosylethylenediamine results in the formation of monomeric η(6):κ(1)-phenylalanine ethyl ester complexes 14 and 15, which could be saponified yielding complexes 16 and 17 without changing the inner coordination sphere of the metal centre. The structure of η(6):κ(1)-phenylalanine complex 17 and an N-κ(1)-phenylalanine complex 13 resulting from the reaction of 3 with an excess of pyridine were confirmed by X-ray crystallography.

Oxorhenium complexes bearing the water-soluble tris(pyrazol-1-yl)methanesulfonate, 1,3,5-triaza-7-phosphaadamantane, or related ligands, as catalysts for Baeyer-Villiger oxidation of ketones

New rhenium(VII or III) complexes [ReO3(PTA)2][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4]I (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)2][ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(η(2)-Tpm)(PTA)][ReO4] (4) [Tpm = hydrotris(pyrazol-1-yl)methane, HC(pz)3, pz = pyrazolyl], [ReO3(Hpz)(HMT)][ReO4] (5) (Hpz = pyrazole), [ReO(Tpms)(HMT)] (6) [Tpms = tris(pyrazol-1-yl)methanesulfonate, O3SC(pz)3(-)] and [ReCl2{N2C(O)Ph}(PTA)3] (7) have been prepared from the Re(VII) oxide Re2O7 (1-6) or, in the case of 7, by ligand exchange from the benzoyldiazenido complex [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2], and characterized by IR and NMR spectroscopies, elemental analysis and electrochemical properties. Theoretical calculations at the density functional theory (DFT) level of theory indicated that the coordination of PTA to both Re(III) and Re(VII) centers by the P atom is preferable compared to the coordination by the N atom. This is interpreted in terms of the Re-PTA bond energy and hard-soft acid-base theory. The oxo-rhenium complexes 1-6 act as selective catalysts for the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g., 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone or pinacolone) to the corresponding lactones or esters, in the presence of aqueous H2O2. The effects of a variety of factors are studied toward the optimization of the process.

Competitive binding sites of a ruthenium arene anticancer complex on oligonucleotides studied by mass spectrometry: ladder-sequencing versus top-down

We report identification of the binding sites for an organometallic ruthenium anticancer complex [(η (6)-biphenyl)Ru(en)Cl][PF6] (1; en = ethylenediamine) on the 15-mer single-stranded oligodeoxynucleotides (ODNs), 5'-CTCTCTX7G8Y9CTTCTC-3' [X = Y = T (I); X = C and Y = A (II); X = A and Y = T (III); X = T and Y = A (IV)] by electrospray ionization mass spectrometry (ESI-MS) in conjunction with enzymatic digestion or tandem mass spectrometry (top-down MS). ESI-MS combined with enzymatic digestion (termed MS-based ladder-sequencing), is effective for identification of the thermodynamically-favored G-binding sites, but not applicable to determine the thermodynamically unstable T-binding sites because the T-bound adducts dissociate during enzymatic digestion. In contrast, top-down MS is efficient for localization of the T binding sites, but not suitable for mapping ruthenated G bases, due to the facile fragmentation of G bases from ODN backbones prior to the dissociation of the phosphodiester bonds. The combination of the two MS approaches reveals that G8 in each ODN is the preferred binding site for 1, and that the T binding sites of 1 are either T7 or T11 on I and IV, and either T6 or T11 on II and III, respectively. These findings not only demonstrate for the first time that T-bases in single-stranded oligonucleotides are kinetically competitive with guanine for such organoruthenium complexes, but also illustrate the relative merits of the combination of ladder-sequencing and top-down MS approaches to elucidate the interactions of metal anticancer complexes with DNA.

Mechanism of interstrand migration of organoruthenium anticancer complexes within a DNA duplex

Organometallic ruthenium(ii) anticancer complexes [(η(6)-arene)Ru(en)Cl][PF(6)] (e.g. arene = biphenyl (bip, 1), indane (ind, 2); en = ethylenediamine) bind to N7 of guanine (G) in DNA selectively. The fragment {(η(6)-bip)Ru(en)}(2+) (1') bound to N7 of one guanine residue at a 14-mer duplex DNA migrates readily to other guanine residues in both the same strand and the complementary strand when the strands are hybridized at elevated temperature. In this work, by applying HPLC coupled to mass spectrometry, the mechanism of such intra- and interstrand migration was investigated using a 15-mer duplex, in which one strand 5'-CTCTCTTG(8)TCTTCTC-3' (I) contained a single guanine (G(8)). The results show that the interstrand migration of complexes 1 and 2 within the duplex involves an SN1 pathway, firstly solvent-assisted dissociation of the initially G(8)-bound adducts I-G(8)-1' and I-G(8)-2' (2' = {(η(6)-ind)Ru(en)}(2+)) as the rate-controlling step, and secondly the coordination of the dissociated 1' and 2' to guanine bases (G(21) for 1', either G(21) or G(18) for 2') on strand II. The high temperature used to anneal the single strands was found to increase the migration rate. The formation of the duplex acts as a key driving force to promote the dissociation of G(8)-bound 1' and 2' due to the competition of cytosine in II with the en-NH(2) groups in 1' and 2' for H-bonding with C6O of guanine. Complex 2 (t(1/2) = 18 h) containing a mono-ringed arene ligand dissociates more readily from the initially binding site G(8) than complex 1 (t(1/2) = 23 h). The extended biphenyl arene ligand which is intercalated into DNA stabilizes the adduct I-G(8)-1'. These results provide new insight into this unusual metal migration, and are of significance for the design and development of more active organometallic ruthenium anticancer complexes.

Transcription Inhibition by Organometallic Ruthenium - Arene Anticancer Complexes in Live Mammalian Cells

Organometallic ruthenium–arene RAPTA complexes, currently being actively pursued as potential anticancer agents, interact with intracellular biological targets to form covalent adducts. Because their mode of action is still unclear, we investigated their binding with DNA and the ability of ruthenated-DNA adducts to elicit cellular responses such as transcription inhibition and repair. To investigate the influence of the spectator arene ligands on RAPTA activity, a novel RAPTA complex containing the bulky 1,3,5-triisopropylbenzene ligand was synthesized and characterized. Transcription experiments carried out in live mammalian cells using ruthenated plasmid probes revealed that increasing steric bulk of the arene ligand did not improve its ability to arrest transcription.