Ru(II)(arene)-flavonoids with high in vitro antitumour activity were synthesised. These compounds are capable of inhibiting human topoisomerase IIα and binding covalently to DNA.

The ruthenium compound KP1019 has demonstrated promising anticancer activity in a pilot clinical trial. This study aims to evaluate the intracellular uptake/binding patterns of KP1019 and its sodium salt KP1339, which is currently in a phase I-IIa study. Although KP1339 tended to be moderately less cytotoxic than KP1019, IC(50) values in several cancer cell models revealed significant correlation of the cytotoxicity profiles, suggesting similar targets for the two drugs. Accordingly, both drugs activated apoptosis, indicated by caspase activation via comparable pathways. Drug uptake determined by inductively coupled plasma mass spectrometry (ICP-MS) was completed after 1 h, corresponding to full cytotoxicity as early as after 3 h of drug exposure. Surprisingly, the total cellular drug uptake did not correlate with cytotoxicity. However, distinct differences in intracellular distribution patterns suggested that the major targets for the two ruthenium drugs are cytosolic rather than nuclear. Consequently, drug-protein binding in cytosolic fractions of drug-treated cells was analyzed by native size-exclusion chromatography (SEC) coupled online with ICP-MS. Ruthenium-protein binding of KP1019- and KP1339-treated cells distinctly differed from the platinum binding pattern observed after cisplatin treatment. An adapted SEC-SEC-ICP-MS system identified large protein complexes/aggregates above 700 kDa as initial major binding partners in the cytosol, followed by ruthenium redistribution to the soluble protein weight fraction below 40 kDa. Taken together, our data indicate that KP1019 and KP1339 rapidly enter tumor cells, followed by binding to larger protein complexes/organelles. The different protein binding patterns as compared with those for cisplatin suggest specific protein targets and consequently a unique mode of action for the ruthenium drugs investigated.

Organometallic ruthenium-arene compounds bearing a maltol ligand have been shown to be nearly inactive in in vitro anticancer assays, presumably due to the formation of dimeric Ru(II) species in aqueous solutions. In an attempt to stabilize such complexes, [Ru(eta(6)-p-cymene)(XY)Cl] (XY=pyrones or thiopyrones) complexes with different substitution pattern of the (thio)pyrone ligands have been synthesized, their structures characterized spectroscopically, and their aquation behavior investigated as well as their tumor-inhibiting potency. The aquation behavior of pyrone systems with electron-donating substituents and of thiopyrone complexes was found to be significantly different from that of the maltol-type complex reported previously. However, the formation of the dimer can be excluded as the primary reason for the inactivity of the complex because some of the stable compounds are not active in cancer cell lines either. In contrast, studies of their reactivity towards amino acids demonstrate different reactivities of the pyrone and thiopyrone complexes, and the higher stability of the latter probably renders them active against human tumor cells.

RuII(arene) complexes have been shown to be promising anticancer agents, capable of overcoming major drawbacks of currently used chemotherapeutics. We have synthesized RuII(η6-arene) compounds carrying bioactive flavonol ligands with the aim to obtain multitargeted anticancer agents. To validate this concept, studies on the mode of action of the complexes were conducted which indicated that they form covalent bonds to DNA, have only minor impact on the cell cycle, but inhibit CDK2 and topoisomerase IIα in vitro. The cytotoxic activity was determined in human cancer cell lines, resulting in very low IC50 values as compared to other RuII(arene) complexes and showing a structure-activity relationship dependent on the substitution pattern of the flavonol ligand. Furthermore, the inhibition of cell growth correlates well with the topoisomerase inhibitory activity. Compared to the flavonol ligands, the RuII(η6-p-cymene) complexes are more potent antiproliferative agents, which can be explained by potential multitargeted properties.

Ru(II)-arene complexes with pyrone-derived ligands are rendered active against cancer cells by replacement of the coordinated O,O donor with an S,O donor. The different stabilities of these systems may explain the observed influence of the donor atoms on the anticancer activity in vitro.Metal complexes are playing an important role in the treatment of cancer, and many promising compounds have been developed in recent years. 1-4 Ruthenium complexes have been shown to be among the most promising candidates for new metal-based anticancer drugs. Two of them, KP1019 and NAMI-A, are currently undergoing clinical trials. 2,5 Their low general toxicity might be explained by their modes of action, including protein binding and activation by reduction. [5][6][7] More recently, bioorganometallic chemistry has emerged as a new source of anticancer metallodrugs, with titanocene dichloride being the prototype agent of this compound class. 4,8,9 Furthermore, organometallic Ru(II) compounds that are stabilized in their þ2 oxidation state by coordination of an arene ligand have been investigated for their anticancer properties. These piano-stool complexes have been pioneered by the Dyson and Sadler groups, 10,11 who developed compounds with pta (1,3,5-triaza-7-phoshatricyclo[3.3.1.1]-decane) and en (ethylenediamine) ligands, respectively. 10 For the [(η 6 -arene)Ru II (X)(Y)] complexes, DNA base selectivity strongly depends on the character of the chelating ligand Yexchange of the neutral ethylenediamine by anionic acetylacetonate shifts the affinity from guanine to adenine. 12 In addition to en and pta complexes, maltol-derived mono-and polynuclear ruthenium and osmium complexes have been developed. [13][14][15] The linking of two pyridone moieties opened up new possibilities for tuning the in vitro anticancer activity and lipophilicity, and compounds with interduplex cross-linking capacity were obtained. 14,16-18 In the case of the mononuclear Ru(II) complexes, an increase in cytotoxic activity was achieved by derivatization of the pyrone ring with lipophilic aromatic substituents. 13 In order to study the Ru-ligand interaction and its effect on the in vitro anticancer activity, Ru(II)-cymene complexes (Scheme 1) with pyrones and their corresponding, more lipophilic thiopyrones as chelating agents were prepared. 15,19 Such (thio)pyrone systems have already found application in Scheme 1. Synthesis of the Complexes 2a-d Jakupec, M. A.; Kynast, B.; Zorbas, H.; Keppler, B. K. J. Inorg. Biochem. 2006, 100, 891-904. (6) Groessl, M.; Reisner, E.; Hartinger, C. G.; Eichinger, R.; Semenova, O.; Timerbaev, A. R.; Jakupec, M. A.; Arion, V. B.; Keppler, B. K. Melchart, M.; Habtemariam, A.; Sadler, P. J. Chem. Commun. 2005, 4764-4776. (12) Fernandez, R.; Melchart, M.; Habtemariam, A.; Parsons, S.; Sadler, P. J. Chem. Eur. J. 2004, 10, 5173-5179.(13) Peacock, A. F. A.; Melchart, M.; Deeth, R. J.; Habtemariam, A.; Parsons, S.; Sadler, P. J. Chem. Eur. J. 2007, 13, 2601-2613. (14) Mendoza-Ferri, M. G.; Hartinger, C. G.; Eichinger, R. E.; Stoly...