Ruthenium versus platinum: interactions of anticancer metallodrugs with duplex oligonucleotides characterised by electrospray ionisation mass spectrometry

Preliminary anti-cancer photodynamic therapeutic in vitro studies with mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes

We report the synthesis and characterisation of mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes, which were used as potential photodynamic therapeutic agents for melanoma cell growth inhibition. The novel complexes, [Ru(pbt)2(phen2DTT)](PF6)2·1.5H2O 1 (where phen2DTT = 1,4-bis(1,10-phenanthrolin-5-ylsulfanyl)butane-2,3-diol and pbt = 2-(2'-pyridyl)benzothiazole) and [Ru(pbt)2(tpphz)](PF6)2·3H2O 2 (where tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) were synthesised and characterised. Compound 1 was reacted with [VO(sal-L-tryp)(H2O)] (where sal-L-tryp = N-salicylidene-L-tryptophanate) to produce [Ru(pbt)2(phen2DTT)VO(sal-L-tryp)](PF6)2·5H2O 4; while [VO(sal-L-tryp)(H2O)] was reacted with compound 2 to produce [Ru(pbt)2(tpphz)VO(sal-L-tryp)](PF6)2·6H2O 3. All complexes were characterised by elemental analysis, HRMS, ESI MS, UV-visible absorption, ESR spectroscopy, and cyclic voltammetry, where appropriate. In vitro cell toxicity studies (with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay) via dark and light reaction conditions were carried out with sodium diaqua-4,4',4'',4''' tetrasulfophthalocyaninecobaltate(II) (Na4[Co(tspc)(H2O)2]), [VO(sal-L-tryp)(phen)]·H2O, and the chloride salts of complexes 3 and 4. Such studies involved A431, human epidermoid carcinoma cells; human amelanotic malignant melanoma cells; and HFF, non-cancerous human skin fibroblast cells. Both chloride salts of complexes 3 and 4 were found to be more toxic to melanoma cells than to non-cancerous fibroblast cells, and preferentially led to apoptosis of the melanoma cells over non-cancerous skin cells. The anti-cancer property of the chloride salts of complexes 3 and 4 was further enhanced when treated cells were exposed to light, while no such effect was observed on non-cancerous skin fibroblast cells. ESR and (51)V NMR spectroscopic studies were also used to assess the stability of the chloride salts of complexes 3 and 4 in aqueous media at pH 7.19. This research illustrates the potential for using mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes to fight skin cancer.

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.

Comparison of MS/MS methods for characterization of DNA/cisplatin adducts

The development of activation/dissociation techniques such as ultraviolet photodissociation (UVPD), infrared multiphoton dissociation (IRMPD), and electron transfer dissociation (ETD) as alternatives to collision induced dissociation (CID) has extended the range of strategies for characterizing biologically relevant molecules. Here, we describe a comprehensive comparison of CID, IRMPD, UVPD, ETD, and hybrid processes termed ETcaD and ET-IRMPD (and analogous hybrid methods in the negative mode NETcaD and NET-IRMPD) for generating sequence-specific fragment ions and allowing adduction sites to be pinpointed for DNA/cisplatin adducts. Among the six MS/MS methods, the numerous products generated by the IRMPD and UVPD techniques resulted in the most specific and extensive backbone cleavages. We conclude that IRMPD and UVPD methods generally offer the best characteristics for pinpointing the cisplatin adduction sites in the fragment-rich spectra.

OMA and OPA--software-supported mass spectra analysis of native and modified nucleic acids

The platform-independent software package consisting of the oligonucleotide mass assembler (OMA) and the oligonucleotide peak analyzer (OPA) was created to support the analysis of oligonucleotide mass spectra. It calculates all theoretically possible fragments of a given input sequence and annotates it to an experimental spectrum, thus, saving a large amount of manual processing time. The software performs analysis of precursor and product ion spectra of oligonucleotides and their analogues comprising user-defined modifications of the backbone, the nucleobases, or the sugar moiety, as well as adducts with metal ions or drugs. The ability to expand the library of building blocks and to implement individual structural variations makes it extremely useful for supporting the analysis of therapeutically active compounds. The functionality of the software tool is demonstrated on the examples of a platinated double-stranded oligonucleotide and a modified RNA sequence. Experiments also reveal the unique dissociation behavior of platinated higher-order DNA structures.

Insights into the Intramolecular Properties ofη6-Arene-Ru-Based Anticancer Complexes Using Quantum Calculations

The factors that determine the stability and the effects of noncovalent interaction on theη6-arene ruthenium anticancer complexes are determined using DFT method. The intramolecular and intra-atomic properties were computed for two models of these half-sandwich ruthenium anticancer complexes and their respective hydrated forms. The results showed that the stability of these complexes depends largely on the network of hydrogen bonds (HB), strong nature of charge transfer, polarizability, and electrostatic energies that exist within the complexes. The hydrogen bonds strength was found to be related to the reported anticancer activities and the activation of the complexes by hydration. The metal–ligand bonds were found to be closed shell systems that are characterised by high positive Laplacian values of electron density. Two of the complexes are found to be predominantly characterised by LMCT while the other two are predominately characterised by MLCT.

Anticancer metallodrug research analytically painting the "omics" picture--current developments and future trends

Anticancer metallodrug development has for a long time been characterised by the similarity of new drug candidates to cisplatin and DNA as the primary target. Recent advances in bioanalytical techniques with high sensitivity and selectivity have revealed that metal-based drugs can undergo a wide range of biomolecular interactions beyond DNA and have generated interest in proteins as possible targets for metallodrugs. In fact, implementation of metallomics approaches that are able to reveal the fate of the compounds in biological systems can help to move drug development towards more targeted and rational design of novel metallodrugs. Additionally, proteomic screening and gene expression analysis can provide insight into physiological response to drug treatment and identify the reasons for drug resistance. Herein, we review selected applications which led to a better understanding of the mode of action of clinically established metal-based anticancer agents and novel metallodrug candidates.

Altered DNA binding and amplification of human breast cancer suppressor gene BRCA1 induced by a novel antitumor compound, [Ru(η(6)-p-phenylethacrynate)Cl(2)(pta)]

The ruthenium-based complex [Ru(η(6)-p-phenylethacrynate)Cl(2)(pta)] (pta = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane), termed ethaRAPTA, is an interesting antitumor compound. The elucidation of the molecular mechanism of drug activity is central to the drug development program. To this end, we have characterized the ethaRAPTA interaction with DNA, including probing the sequence specific modified DNA structural stability and DNA amplification using the breast cancer suppressor gene 1 (BRCA1) of human breast and colon adenocarcinoma cell lines as models. The preference of ethaRAPTA base binding is in the order A > G > T > C. Once modified, the ethaRAPTA-induced BRCA1 structure has higher thermal stability than the modified equivalents of its related compound, RAPTA-C. EthaRAPTA exhibits a higher efficiency than RAPTA-C in inhibiting BRCA1 amplification. With respect to both compounds, the inhibition of BRCA1 amplification is more effective in an isolated system than in cell lines. These data provide evidence that will help to understand the process of elucidating the pathways involved in the response induced by ethaRAPTA.

Ru binding to RNA following treatment with the antimetastatic prodrug NAMI-A in Saccharomyces cerevisiae and in vitro

[ImH][trans-Ru(III)Cl(4)(DMSO)(Im)] (where DMSO is dimethyl sulfoxide and Im is imidazole) (NAMI-A) is an antimetastatic prodrug currently in phase II clinical trials. The mechanisms of action of this and related Ru-based anticancer agents are not well understood, but several cellular targets have been suggested. Although Ru has been observed to bind to DNA following in vitro NAMI-A exposure, little is known about Ru-DNA interactions in vivo and even less is known about how this or related metallodrugs might influence cellular RNA. In this study, Ru accumulation in cellular RNA was measured following treatment of Saccharomyces cerevisiae with NAMI-A. Drug-dependent growth and cell viability indicate relatively high tolerance, with approximately 40% cell death occurring at 6 h for 450 μM NAMI-A. Significant dose-dependent accumulation of Ru in cellular RNA was observed by inductively coupled plasma mass spectrometry measurements on RNA extracted from yeast treated with NAMI-A. In vitro, binding of Ru species to drug-treated model DNA and RNA oligonucleotides at pH 6.0 and 7.4 was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in the presence and absence of the reductant ascorbate. The extent of Ru-nucleotide interactions increases slightly with lower pH and significantly in the presence of ascorbate, with differences in observed species distribution. Taken together, these studies demonstrate the accumulation of aquated and reduced derivatives of NAMI-A on RNA in vitro and in cellulo, and enhanced binding with nucleic acid targets in a tumorlike acidic, reducing environment. To our knowledge, this is also the first study to characterize NAMI-A treatment of S. cerevisiae, a genetically tractable model organism.

Cellular uptake and subcellular distribution of ruthenium-based metallodrugs under clinical investigation versus cisplatin

The cellular uptake and subcellular distribution including adduct formation with genomic DNA and uptake into mitochondria of two ruthenium(iii)-based drugs in clinical trials, KP1019 and NAMI-A, and cisplatin, was investigated in cisplatin sensitive and resistant A2780 human ovarian carcinoma cells. These data indicate that reduced metal uptake into mitochondria in combination with increased binding towards low molecular weight components involved in detoxification mechanisms is essential for cisplatin resistance. The ruthenium drugs show distinct differences with respect to cisplatin, especially in the cisplatin resistant cells; in comparison to the sensitive cells, KP1019 exhibits higher cytotoxicity and an only slightly changed metabolism of the drug, whereas NAMI-A treatment results in increased intracellular ruthenium levels and a higher number of ruthenium-DNA adducts. In addition, size exclusion-inductively coupled mass spectrometry indicates that adduct formation with high molecular weight components in the particulate and nuclear fractions is crucial for the therapeutic effect of KP1019 in both cisplatin resistant and sensitive cell lines.

Is the reactivity of M(II)-arene complexes of 3-hydroxy-2(1H)-pyridones to biomolecules the anticancer activity determining parameter?

Hydroxypyr(id)ones are versatile ligands for the synthesis of organometallic anticancer agents, equipping them with fine-tunable pharmacological properties. Herein, we report on the preparation, mode of action, and in vitro anticancer activity of Ru(II)- and Os(II)-arene complexes with alkoxycarbonylmethyl-3-hydroxy-2-pyridone ligands. The hydrolysis and binding to amino acids proceed quickly, as characterized by NMR spectroscopy and ESI mass spectrometry. However, the reaction with amino acids causes cleavage of the pyridone ligands from the metal center because the amino acids act as multidentate ligands. A similar behavior was also observed during the reactions with the model proteins ubiquitin and cytochrome c, yielding mainly [protein + M(eta(6)-p-cymene)] adducts (M = Ru, Os). Notably the ligand cleavage of the Os derivative was significantly slower than of its Ru analogue, which could explain its higher activity in in vitro anticancer assays. Furthermore, the reaction of the compounds to 5'-GMP was characterized and coordination to the N7 of the guanine moiety was demonstrated by (1)H NMR spectroscopy and X-ray diffraction analysis. CDK2/Cyclin A protein kinase inhibition studies revealed potent activity of the Ru and Os complexes.

The RING heterodimer BRCA1-BARD1 is a ubiquitin ligase inactivated by the platinum-based anticancer drugs

The breast cancer susceptibility protein 1 (BRCA1) participates in the maintenance of cells genomic integrity through DNA repair, cell cycle checkpoint, protein ubiquitination, and transcriptional regulation. The N-terminus of BRCA1 contains a RING domain that preferentially forms a heterodimeric complex with BARD1. The BRCA1-BARD1 RING complex has an E3 ubiquitin ligase activity that plays an essential role in response to DNA damage. Preclinical and clinical studies have recently revealed that structural changes to the heterodimer result in alterations to the BRCA1-mediated DNA repair pathways in cancer cells, and lead to hypersensitivity to several chemotherapeutic agents. It is of interest to approach the BRCA1 RING domain as a potentially molecular target for platinum-based drugs for cancer therapy. A previous study has shown that the anticancer drug cisplatin formed intramolecular and intermolecular BRCA1 adducts in which His117 was the primary platinum-binding site, and conferred conformational changes and induced thermostability. Here, we have studied the functional consequence of the in vitro platination of the BRCA1 RING domain by a number of platinum complexes. The BRCA1 ubiquitin ligase activity was inhibited by transplatin > cisplatin > oxaliplatin > carboplatin in that order. The consequences of the binding of the platinum complexes on the reactivity of the BRCA1 were also discussed. The data raised the possibility of selectively targeting the BRCA1 DNA repair for cancer therapy.

Proteins as possible targets for cytotoxic trans-platinum(II) complexes with aliphatic amine ligands: Further exceptions to the DNA paradigm

The reactivity of three cytotoxic trans-Pt(II) complexes bearing aliphatic amine ligands, with transferrin and single-stranded oligonucleotides as DNA models, was investigated by ESI-MS and the results obtained are discussed in comparison with cisplatin. Tandem MS studies provided additional information on the preferential Pt binding sites. To determine whether trans-Pt(II) complexes can migrate from a peptide to an oligonucleotide, transfer experiments were also performed using ESI-MS, and competitive binding of the trans-Pt(II) complexes toward a model peptide and different oligonucleotides was also investigated. Significant differences in the reactivity of the trans complexes with respect to cisplatin were observed. In general, adduct formation with the selected peptide is favored for the trans compounds, whereas cisplatin shows a preference for oligonucleotides, especially if adjacent G-G residues are present. The results are discussed in relation to the possible mechanism of action of the trans-Pt(II) complexes.