Recent research was focused on bioorganometallics with a particular interest in the synthesis of anticancer active mono-, di- and trinuclear compounds with (thio)pyr(id)onato ligands [1]. These complexes were designed for exhibiting their antitumor activity in the tumor tissue (focusing on selective transport into the tumor) or to possess new modes of action (e.g., dinuclear Ru complexes with lower toxicity than Pt compounds and non-common DNA binding modes). We were the first who could demonstrate that the linkage of two Ru centers can result in improved anticancer activity, possibly by crosslinking biological macromolecules [2]. The most active complex was up to 10-fold more active in resistant cancer cell lines than in the respective wild-type cells [3]. These results indicate that the compounds might be an option to tackle the common problem of developed resistance of tumors, frequently occurring during chemotherapy [2,3]. Furthermore, a recent study highlights the potential of Ru(arene) complexes modified with maleimide to react selectively with thiol-containing biomolecules [4].
In our group the development of new drug molecules is complemented by extensive bioanalytical studies to elucidate the mode of action of tumor-inhibiting metal complexes. Biophysical methods (separation methods, online and offline MS) ha
ve been developed and applied for studies e.g. on the 
Ru(III) bisindazole compound KP1019 [5-7]. Those experiments contributed to the selection of KP1019 for clinical development, being currently in clinical phase I/IIa trials in a modified formulation [5,8]. Capillary electrophoresis hyphenated to inductively-coupled plasma mass spectrometry (CE-ICP-MS) was used to show that a Ga-based drug candidate binds in human blood serum preferentially to transferrin, whereas Ru complexes are most often found mainly attached to human serum albumin (HSA) [9]. Application of modern mass spectrometry methods resulted for the first time in the binding site elucidation of a metal-based drug on proteins by employing top-down mass spectrometric approaches. The bioanalytical studies are rounded off by the introduction of new methods, such as the recently reported first-time coupling of microemulsion electrokinetic chromatography (MEEKC) to ICP-MS [10].
References
[1] Kandioller, W.; Kurzwernhart, A.; Hanif, M.; Meier, S. M.; Henke, H.; Keppler, B. K.; Hartinger, C. G. Pyrone derivatives and metals: From natural products to metal-based drugs. J. Organomet. Chem. 2011, 696, 999-1010.
[2] Nováková, O.; Nazarov, A. A.; Hartinger, C. G.; Keppler, B. K.; Brabec, V. DNA interactions of dinuclear RuII arene antitumor complexes in cell-free media. Biochem. Pharmacol. 2009, 77, 364-374.
[3] Mendoza-Ferri, M. G.; Hartinger, C. G.; Mendoza, M. A.; Groessl, M.; Egger, A.; Eichinger, R. E.; Mangrum, J. B.; Farrell, N. P.; Maruszak, M.; Bednarski, P. J.; Klein, F.; Jakupec, M. A.; Nazarov, A. A.; Severin, K.; Keppler, B. K. Transferring the Concept of Multinuclearity to Ruthenium Complexes for Improvement of Anticancer Activity. J. Med. Chem. 2009, 52 916-925.
[4] Hanif, M.; Nazarov, A. A.; Legin, A.; Groessl, M.; Arion, V. B.; Jakupec, M. A.; Tsybin, Y. O.; Dyson, P. J.; Keppler, B. K.; Hartinger, C. G. Maleimide-functionalised organoruthenium anticancer agents and their binding to thiol-containing biomolecules. Chem. Commun. 2012, in press.
[5] Hartinger, C. G.; Zorbas-Seifried, S.; Jakupec, M. A.; Kynast, B.; Zorbas, H.; Keppler, B. K. From bench to bedside – preclinical and early clinical development of the anticancer agent indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019 or FFC14A). J. Inorg. Biochem. 2006, 100, 891-904.
[6] Timerbaev, A. R.; Hartinger, C. G.; Aleksenko, S. S.; Keppler, B. K. Interactions of Antitumor Metallodrugs with Serum Proteins: Advances in Characterization Using Modern Analytical Methodology. Chem. Rev. 2006, 106, 2224-2248.
[7] Groessl, M.; Reisner, E.; Hartinger, C. G.; Eichinger, R.; Semenova, O.; Timerbaev, A. R.; Jakupec, M. A.; Arion, V. B.; Keppler, B. K. Structure-Activity Relationships for NAMI-A-type Complexes – Aquation, Redox Properties, Protein Binding, and Antiproliferative Activity. J. Med. Chem. 2007, 50, 2185-93.
[8] Hartinger, C. G.; Jakupec, M. A.; Zorbas-Seifried, S.; Groessl, M.; Egger, A.; Berger, W.; Zorbas, H.; Dyson, P. J.; Keppler, B. K. KP1019, a new redox-active anticancer agent – preclinical development and results of a clinical phase I study in tumor patients. Chem. Biodiversity 2008, 5, 2140-2155.
[9] Groessl, M.; Bytzek, A.; Hartinger, C. G. The serum protein binding of pharmacologically active gallium(III) compounds assessed by hyphenated CE-MS techniques. Electrophoresis 2009, 30, 2720-2727.
[10] Bytzek, A. K.; Reithofer, M. R.; Galanski, M.; Groessl, M.; Keppler, B. K.; Hartinger, C. G. The first example of MEEKC-ICP-MS coupling and its application for the analysis of anticancer platinum complexes. Electrophoresis 2010, 31, 1144-1150.
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