Influence of the arene ligand, the number and type of metal centers, and the leaving group on the in vitro antitumor activity of polynuclear organometallic compounds

Article abstract of DOI:10.1021/om900715j

Dinuclear ruthenium complexes were shown to exhibit strong antiproliferative properties in human tumor cell lines. In order to extend the structure-activity relationships (SARs), a series of new Ru^II(arene)X complexes (X = Cl, Br, I) linked by

Full text of DOI:10.1021/om900715j

6260 Organometallics 2009, 28, 6260–6265
DOI: 10.1021/om900715j
Influence of the Arene Ligand, the Number and Type of Metal Centers,
and the Leaving Group on the in Vitro Antitumor Activity of Polynuclear
Organometallic Compounds
Maria G. Mendoza-Ferri,† Christian G. Hartinger,*,†,‡ Alexey A. Nazarov,*,†,‡
Rene E. Eichinger,† Michael A. Jakupec,† Kay Severin,‡ and Bernhard K. Keppler†
†
€
Institute of Inorganic Chemistry, University of Vienna, Wahringer Strasse 42, A-1090 Vienna, Austria, and
Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015
‡
ꢀ
ꢀ ꢀ
Lausanne, Switzerland
Received August 13, 2009
Dinuclear ruthenium complexes were shown to exhibit strong antiproliferative properties in
human tumor cell lines. In order to extend the structure-activity relationships (SARs), a series of
new RuII(arene)X complexes (X = Cl, Br, I) linked by pyridinone-based spacers were synthesized
and assayed for their in vitro antineoplastic effect. The SARs were established in terms of the arene
ligand, the leaving group (the halide ligand), and the nature and number of the metal centers. It was
demonstrated that, besides the previously shown effect of the spacer length, the nature of the metal
center has the biggest influence on the in vitro anticancer activity. The halide ligand had no effect on
the cytotoxicity, due to rapid formation of the same aquation product for all evaluated compounds.
Furthermore, nearly identical activity was observed when varying the arene ligand from p-cymene to
biphenyl. However, the number of metal centers was found to be important, with the dinuclear
compound being more active than the analogous mono- and trinuclear species.
Introduction
of such complexes in aqueous solution.12 Furthermore, in
dependence of the electronic properties of the ligands, the
complexes’ properties may be modulated in terms of their
aquation, pKa of the aqua complexes, and nucleobase speci-
ficity (e.g., in [Ru(η6-arene)Cl(ethylenediamine)]PF6,8,9
RAPTA, and analogous complexes6,10,11,13). Furthermore,
(organometallic) analogues with Os and Rh were assayed for
their tumor-inhibiting properties.14-19
Organometallic complexes have recently gained attention
as antitumor agents1-5 and can be tuned to facilitate the
uptake of the complexes into the cells or for selectivity for
reactions with DNA or proteins.6,7 In order to enable
covalent interaction with biological targets, the compounds
are usually equipped with a halide leaving group, most
frequently a chloride.2,3,6,8-11 Replacement of chloride by
other halides or carboxylates may play a role in the behavior
Ruthenium complexes have shown potential as anticancer
agents with high activity in different tumor models. As a
result of tumor selectivity,20 they show low general toxicity,
*To whom correspondence should be addressed. Phone: þ43-1-4277-
52609. Fax: þ43-1-4277-9526. E-mail: christian.hartinger@univie.ac.at;
alex.nazarov@univie.ac.at.
(1) Allardyce, C. S.; Dorcier, A.; Scolaro, C.; Dyson, P. J. Appl.
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(2) Yan, Y. K.; Melchart, M.; Habtemariam, A.; Sadler, P. J. Chem.
Commun. 2005, 4764–4776.
(3) Liu, H.-K.; Berners-Price, S. J.; Wang, F.; Parkinson, J. A.; Xu, J.;
Bella, J.; Sadler, P. J. Angew. Chem., Int. Ed. 2006, 45, 8153–8156.
(4) Hartinger, C. G.; Nazarov, A. A.; Ashraf, S. M.; Dyson, P. J.;
Keppler, B. K. Curr. Med. Chem. 2008, 15, 2574–2591.
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(6) Scolaro, C.; Chaplin, A. B.; Hartinger, C. G.; Bergamo, A.;
Cocchietto, M.; Keppler, B. K.; Sava, G.; Dyson, P. J. Dalton Trans.
2007, 5065–5072.
(12) Ang, W. H.; Daldini, E.; Scolaro, C.; Scopelliti, R.; Juillerat-
Jeannerat, L.; Dyson, P. J. Inorg. Chem. 2006, 45, 9006–9013.
(13) Berger, I.; Hanif, M.; Nazarov, A. A.; Hartinger, C. G.; John, R.;
Kuznetsov, M. L.; Groessl, M.; Schmitt, F.; Zava, O.; Biba, F.; Arion,
V. B.; Galanski, M.; Jakupec, M. A.; Juillerat-Jeanneret, L.; Dyson,
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r
pubs.acs.org/Organometallics
Published on Web 10/15/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 21, 2009 6261
Figure 1. Chemical formulas of the synthesized mono- and polynuclear ruthenium(II)- and osmium(II)-arene complexes.
and two Ru(III) compounds have reached the stage of
clinical evaluation.21,22
features, herein the series of dinuclear complexes is extended
to trinuclear compounds, the ruthenium center has been
replaced by Os(II), and the influence of the arene ligand
and the leaving halide is discussed (Figure 1). The new
compounds were obtained by a synthetic route similar to
that described recently.28,29 For the synthesis of the iodido
and bromido complexes the dimeric precursor [(η6-p-cym-
Polynuclear organometallic Ru compounds have been
rarely studied for their anticancer properties, and if they
were assayed, they exhibited lower activity than their mono-
nuclear analogues,23,24 whereas in the case of platinum
complexes the linkage of metal centers has led to the devel-
opment of compounds overcoming resistance of cancer cells
to cisplatin.25-27 We have recently reported on the develop-
ment of dinuclear organometallic compounds28,29 with high
in vitro anticancer activity, whereas the mononuclear mal-
tolato compound was found to be inactive.18 The activity of
compounds initially appeared to be determined by their
lipophilicity;28 however, DNA and protein interaction stu-
dies revealed high potential for DNA-protein and interdu-
plex cross-linking.30
31
ene)RuCl2]2 was converted into [(η6-p-cymene)RuBr2]2
and [(η6-p-cymene)RuI2]2 by treatment with KBr and KI,
respectively. The new compounds were obtained in good to
moderate yields and were characterized by elemental analy-
sis, NMR spectroscopy, and ESI-MS.
Influence of the Metal Center: Ruthenium vs Osmium. In
comparison to numerous Ru(II)-arene complexes, which
were already evaluated for their tumor-inhibiting properties,
only a few Os(II)-arene complexes with anticancer activity
were reported. Recently, Dyson et al. have compared the
effect of replacing Ru by Os in RAPTA-C, a well-explored
drug candidate, and found for Ru and Os only minor dif-
ferences in terms of in vitro anticancer activity, while a struc-
turally related Rh complex was significantly more active.15
A comparison of Os and Ru ethylenediamine complexes
revealed that the Ru compounds are much more active than
their Os analogues,16 whereas in other cases the Os com-
pounds are the more potent agents,32 or both compounds are
equally active as in the case with paullone ligands.33
In order to set up structure-activity relationships for
ruthenium(II)-arene complexes with pyridinonato ligands,
the influence of the type of metal center and of the leaving halide
ligand as well as of the nature of the arene group and the number
of metal centers on the antineoplastic activity was studied.
Results and Discussion
Dinuclear Ru(II)-arene complexes with the metal centers
being linked by coordination to alkyl-bridged pyridinone
ligands were shown to exhibit high in vitro antitumor activ-
ity, and studies on their mode of action were reported
previously.28-30 In order to expand the structure-activity
relationships from the mere spacer length to other structural
When the osmium(II) complexes 1a and 2a are compared to
the analogous Ru(II) complexes 1b and 2b, a first obvious
difference between the Ru and Os complexes is a significantly
lower solubility in water of both osmium complexes. Compar-
1
ison of the aquation by H NMR and UV-vis spectroscopy
revealed similarly rapid exchange of the halogenido by aqua
(21) Rademaker-Lakhai, J. M.; Van Den Bongard, D.; Pluim, D.;
Beijnen, J. H.; Schellens, J. H. M. Clin. Cancer Res. 2004, 10, 3717–3727.
(22) Hartinger, C. G.; Zorbas-Seifried, S.; Jakupec, M. A.; Kynast,
B.; Zorbas, H.; Keppler, B. K. J. Inorg. Biochem. 2006, 100, 891–904.
(23) Huxham, L. A.; Cheu, E. L. S.; Patrick, B. O.; James, B. R. Inorg.
Chim. Acta 2003, 352, 238–246.
(24) Chen, H.; Parkinson, J. A.; Novakova, O.; Bella, J.; Wang, F.;
Dawson, A.; Gould, R.; Parsons, S.; Brabec, V.; Sadler, P. J. Proc. Natl.
Acad. Sci. U.S.A. 2003, 100, 14623–14628.
(25) Farrell, N.; Qu, Y.; Bierbach, U.; Valsecchi, M.; Menta, E.
Structure-activity relationships within di- and trinuclear platinum
phase-I clinical anticancer agents. Cisplatin: Chemistry and Biochemistry
of a Leading Anticancer Drug; Lippert, B., Ed.; Wiley-VCH, Helvetica
Chimica Acta: Weinheim, Zurich, 1999; pp 479-496.
(26) Farrell, N. Polynuclear platinum drugs. In Metal Ions in Biolo-
gical Systems; Sigel, A.; Sigel, H., Eds.; Marcel Dekker: New York, 2004;
Vol. 42, pp 251-296.
1
ligands for both Os and Ru complexes. Accordingly, the H
NMR spectra of the osmium complexes in D2O did not change
over time (followed for 24 h) or after addition of AgNO3 to
induce the release of the chlorido ligands, also suggesting instant
and quantitative aquation. A kinetic study on the stability of 1a
in water by UV-vis spectroscopy (two absorption bands at 322
and 222 nm) indicated only slight changes within 24 h.
Investigations on the in vitro activity of the osmium
complexes 1a and 2a in the human tumor cell line SW480
have shown a SAR parallel to the analogous ruthenium
complexes:28 a correlation between the chain length and
the cytotoxicity was observed, but the Os complexes are
approximately 3-6 times less active than the Ru analogues
1b and 2b (Table 1). The influence of the metal center was
(27) Kloster, M.; Kostrhunova, H.; Zaludova, R.; Malina, J.;
Kasparkova, J.; Brabec, V.; Farrell, N. Biochemistry 2004, 43, 7776–7786.
(28) Mendoza-Ferri, M. G.; Hartinger, C. G.; Eichinger, R. E.;
Stolyarova, N.; Jakupec, M. A.; Nazarov, A. A.; Severin, K.; Keppler,
B. K. Organometallics 2008, 27, 2405–2407.
(31) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74–78.
(32) Peacock, A. F. A.; Parsons, S.; Sadler, P. J. J. Am. Chem. Soc.
2007, 129, 3348–3357.
(33) Schmid, W. F.; John, R. O.; Arion, V. B.; Jakupec, M. A.;
Keppler, B. K. Organometallics 2007, 26, 6643–6652.
(29) Mendoza-Ferri, M. G.; Hartinger, C. G.; Nazarov, A. A.;
Kandioller, W.; Severin, K.; Keppler, B. K. Appl. Organomet. Chem.
2008, 22, 326–332.
ꢀ
ꢀ
(30) Novakova, O.; Nazarov, A. A.; Hartinger, C. G.; Keppler, B. K.;
Brabec, V. Biochem. Pharmacol. 2009, 77, 364–374.

6262 Organometallics, Vol. 28, No. 21, 2009
Mendoza-Ferri et al.
Table 1. Water Solubility and IC50 Values of Ru(II)-Arene
Complexes in Human SW480 and A2780 Cells
IC50/μM
compound
solubility/mM
SW480
A2780
1a
1ba
2a
2b
3a
3b
4
1.6
3.9
0.2
2.2
0.6
0.1
0.6
88 ( 4
26 ( 8
30 ( 6
29 ( 13
5.7 ( 0.5
52 ( 15
36 ( 2
15 ( 5
2.5 ( 0.2
54 ( 4
33 ( 4
25.7 ( 0.3
42 ( 1
59 ( 18
>100
43 ( 1
5
10.3
7.4
>25
88 ( 12
80 ( 7
>100
6
7b
a From ref 28. b From ref 18.
Figure 2. 1H NMR spectra of (a) 1b in CDCl3, (b) 3a in CDCl3,
(c) 1b and 3a in CDCl3, and (d) 1b and 3a in D2O.
confirmed in a separate panel of human tumor cell lines
(LCLC-103H, A-427, RT-4, MCF-7, DAN-G, 5637). 1a
exhibited IC50 values > 20 μM in all cell lines, whereas 1b
has IC50 values < 20 μM in A-427 and MCF-7 cells.34
The higher activity of the compounds with longer spacers
may be explained by the higher lipophilicity, as indicated by
the lower water solubility,28,34 but also by different extents of
interaction with DNA and proteins.30 The Os complexes are
significantly more lipophilic than the Ru compounds, and
therefore it is assumed that the generally more inert nature of
third-row transition metal ions might play an important role
for antineoplastic efficacy. Since hydroxido complexes do
not react as readily as aqua complexes with biomolecules, the
increased propensity of Os complexes to form hydroxido
species at physiological pH might lower the reactivity toward
biological targets and alter the cellular uptake.18
(see Table 1). This is likely the effect of rapid aquation, which
leads to the formation of the same products.
Influence of the Arene Group: p-Cymene vs Biphenyl. The
arene ligand is another structural feature that was found to play
an important role in the mode of action and the tumor-growth
inhibition of Ru(II) complexes.35,36 In order to extend the
π-electron ring system of the arene ligand and to enable hydro-
phobic π-πstacking interactions with DNA bases, the p-cymene
of ligand of 1b was replaced by biphenyl, leading to the more
lipophilic complex 4. Compound 4 is ca. 6 times less soluble
than 1b, but surprisingly exhibits a similar biological activity
(see Table 1). This result is another indication that the lipophi-
licity does not exclusively determine the antitumor activity of the
compound class. For clarification of SARs, a larger set of
compounds might be required.10,11,35,36 However, for the biphe-
nyl/p-cymene system in [Ru(arene)(en)Cl]þ complexes similar
ratios of IC50 values were reported.35,36
Influence of the Number of Ruthenium Centers: Mono- vs
Di- vs Trinuclear. The in vitro anticancer activity of 1b, its
closest mononuclear analogue 5, and the trinuclear complex 6
(Figure 1) was compared. In both SW480 and A2780 cells, 1b
was identified as the most active species, while there is no
meaningful difference between the mono- and the trinuclear
complex (see Table 1). Comparing the lipophilicity of the three
compounds, reflected by their solubility in water, shows that
the mononuclear complex 5 is the most soluble, followed by 6
and 1b (Table 1). The good solubility of 6 is surprising and
might be explained by the presence of a protonable tertiary
amine. The dinuclear compound 1b represents a good com-
promise between solubility and lipophilicity necessary for
cellular uptake. The modification of the compound to link a
higher number of ruthenium moieties improved the water
solubility but decreased the biological effect.
Influence of the Halide: Chloride vs Bromide vs Iodide. In an
attempt to alter the aquation kinetics and thereby the anti-
cancer activity of dinuclear Ru(II)-arene complexes, the
bromido and iodido compounds 3a and 3b were prepared
and compared to their chlorido analogue 1b. The kinetic
studies on the stability of the bromido and iodido complexes
3a and 3b, respectively, in water by UV-vis spectroscopy
have shown no spectral changes over 24 h. This is similar to
the behavior of 1b, since aquation of the ruthenium com-
1
plexes was observed within minutes.34 Comparing the H
NMR spectra of the chlorido complex 1b and the bromido
complex 3a in CDCl3 (Figure 2) shows for 1b four doublets
for the protons of the p-cymene rings, indicating that the
epimerization of the chiral metal center, leading to none-
quivalent aromatic protons, is sufficiently slow to be ob-
served, whereas the spectrum of 3a contained only two
doublets. In addition, the chemical shift of the aromatic
protons is slightly different. Mixing both CDCl3 solutions
and addition of a small amount of D2O induced a change in
the multiplicity of the aromatic proton signals. This suggests
that the fast aquation results in the formation of a single
product that is identical for both compounds, i.e., {[Ru(p-
cymene)(H2O)]2L}þ2, which was also confirmed by UV-vis
spectroscopy, with both aquation products showing the
same absorption maximum. A cytotoxicity assay involving
the halide complexes revealed mostly small differences of the
in vitro activity of 1b, 3a, and 3b in SW480 and A2780 cells
Furthermore, the comparison of the mononuclear pyridi-
nonato compound 5 with the maltolato analogue chlorido-
(maltolato-κO4)(η6-p-cymene)ruthenium(II), 7,18 reveals a
drastically higher in vitro activity for 5 (Table 1).
Conclusions
The influence of modifying the structure of dinuclear Ru-
(II)-arene complexes linked by chelating pyridinone-based
(34) Mendoza-Ferri, M. G.; Hartinger, C. G.; Mendoza, M. A.;
Groessl, M.; Egger, A. E.; 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. J. Med. Chem. 2009, 52,
916–925.
(35) Morris, R. E.; Aird, R. E.; Murdoch, P. d. S.; Chen, H.;
Cummings, J.; Hughes, N. D.; Parsons, S.; Parkin, A.; Boyd, G.; Jodrell,
D. I.; Sadler, P. J. J. Med. Chem. 2001, 44, 3616–3621.
(36) Chen, H.; Parkinson, J. A.; Parsons, S.; Coxall, R. A.; Gould,
R. O.; Sadler, P. J. J. Am. Chem. Soc. 2002, 124, 3064–3082.

Article
Organometallics, Vol. 28, No. 21, 2009 6263
spacers was investigated with regard to tumor-inhibiting
activity in vitro. Taking water solubility as a measure for
lipophilicity, an increase of the latter by extending the spacer
length results in a higher antineoplastic potency in both Os
and Ru compounds. Changing the nuclearity causes a less
pronounced effect on in vitro activity than changing the metal
center from Ru to Os or modifying the spacer length.
Although the trinuclear complex is more water-soluble than
the mononuclear compound, both were found to exhibit
similar antitumor activity. Modifying the leaving group or
changing the arene ligand to a more extended π-electron
system has only minor effects on the in vitro activity. Notably,
replacing the cymene by a biphenyl group causes a significant
change in lipophilicity but does not alter the activity against
cancer cells to a meaningful extent. This shows that factors
other than lipophilicity relevant for the capability of hitting
biomolecular targets, as observed for other non-platinum as
well as for platinum compounds,6,20,37-41 might play an
important role in the mode of action.
Purity of >95% for all compounds was confirmed via elemental
analysis (see Supporting Information).
Syntheses. Bis[dibromido(η6-p-cymene)ruthenium(II)], 10. A
solutionofpotassium bromide (3.00g, 25mmol) inwater (20mL)
was added to a solution of bis[dichlorido(η6-p-isopropyltoluol)-
ruthenium(II)] (0.50 g, 0.82 mmol) in chloroform (20 mL), and
the mixture was stirred vigorously for 2 days. The phases were
separated, and a red solid was obtained after evaporation of
chloroform and dried under vacuum.
Yield: 0.51 g (80%), mp 228-230 °C. 1H NMR in d4-MeOH:
3
δ 1.32 [d, 12H, (CH3)2CH, J = 6.8 Hz], 2.25 [s, 6H, CH3],
3
2.80-2.89 [m, 2H, CH(CH3)2], 5.66 [d, 4H, CHarom, J = 6.3
Hz], 5.88 [d, 4H, CHarom, 3J = 6.3 Hz]. 13C NMR in d4-MeOH:
δ 18.4 [CH3], 21.4 [(CH3)2CH], 31.7 [CH(CH3)2], 78.8 [CH], 79.1
[CH], 90.1 [Carom], 102.6 [Carom].
Bis[diiodido(η6-p-cymene)ruthenium(II)], 100. A solution of
potassium iodide (3.25 g, 19.6 mmol) in water (20 mL) was
added to a solution of bis[dichlorido(η6-p-isopropyltoluol)-
ruthenium(II)] (0.60 g, 0.98 mmol) in chloroform (20 mL), and
the mixture was stirred vigorously for 2 days. The phases were
separated, and a dark violet solid was obtained after evapora-
tion of chloroform and dried under vacuum.
Yield: 0.87 g (91%), mp 240-245 °C. 1H NMR in d4-MeOH:
Experimental Section
3
δ 1.31 [d, 12H, (CH3)2CH, J = 6.8 Hz], 2.35 [s, 6H, CH3],
3
2.85-2.92 [m, 2H, CH(CH3)2], 5.64 [d, 4H, CHarom, J = 6.1
All the chemicals purchased were used without further purifi-
cations. All reactions were carried out in dry solvents and under
argon atmosphere. Bis[dichlorido(η6-biphenyl)ruthenium(II)],42
Hz], 5.86 [d, 4H, CHarom, 3J = 6.1 Hz]. 13C NMR in d4-MeOH:
δ 19.4 [CH3], 21.8 [(CH3)2CH], 32.1 [CH(CH3)2], 79.3 [CH], 80.1
[CH], 90.1 [Carom], 102.4 [Carom].
bis[dichlorido(η6-p-cymene)ruthenium(II)],31
3-benzyloxy-2-
2,20,200-Tris[3-benzyloxy-2-methyl-4(1H)-pyridinon-1-yl]triethyl-
amine (6a). Sodium hydroxide (1.40 g, 35.0 mmol) was added to a
solution of 3-benzyloxy-2-methyl-4-pyrone (10.0 g, 46.2 mmol) and
tris(2-aminoethyl)amine (1.5 g, 10.3 mmol) in a methanol/water
mixture (2:1, 210 mL). The reaction mixture was refluxed for 48 h
and then allowed to cool to room temperature. The product was
extracted with dichloromethane (3ꢀ 50 mL), and the solvents were
removed under vacuum, yielding a brown oil. The beige product
was obtained by silica gel chromatography with pure methanol.
Yield: 3.05 g (40%), mp 199-200 °C. MS (ESIþ): m/z 742
methyl-4-pyrone, 1,6-bis[3-hydroxy-2-ethyl-4(1H)-pyridinon-1-
yl]hexane and 1,8-bis[3-hydroxy-2-ethyl-4(1H)-pyridinon-1-
yl]octane,43 bis[dichlorido(η6-p-cymene)osmium(II)],44 and
chlorido[2-methyl-3-(oxo-κO)-1-propyl-4(1H)-pyridinonato-κO4]-
(η6-p-cymene)ruthenium(II) (5)45 were prepared according to lit-
erature procedures. The dimeric precursor bis[dichlorido(η6-p-
cymene)ruthenium(II)] was converted into bis[dibromido(η6-p-
cymene)ruthenium(II)] and bis[diiodido(η6-p-cymene)ruthenium-
(II)].46 Silica gel (Fluka-60, 70-230 mesh) and silica gel plates
(Polygram SIL G/UV254) were used for preparative and thin-
layer chromatography, respectively.
1
[M þ H]þ. H NMR in d4-MeOH: δ 2.20 [s, 9H, CH3], 2.76
3
[t, 6H, CH2CH2-N, J = 6.8 Hz], 3.81 [t, 6H, CH2-N, J =
3
€
Melting points were determined with a Buchi B-540 apparatus
3
6.8 Hz ], 5.13 [s, 6H, CH2--Ph], 6.46 [d, 3H, CH-CdO, J =
and are uncorrected. Elemental analyses were carried out with a
Perkin-Elmer 2400 CHN elemental analyzer at the Microana-
lytical Laboratory of the University of Vienna. NMR spectra
were recorded on a Bruker Avance DPX400 spectrometer
(Ultrashield Magnet) at 400.13 (1H) and 100.63 MHz
(13C{1H}) at 25 °C in d4-MeOH or in d6-DMSO. Electrospray
ionization (ESI) mass spectra were recorded on a Bruker
Esquire3000 instrument (Bruker Daltonics, Bremen, Germany).
Theoretical and experimental isotope distributions were com-
pared. Ultraviolet-visible (UV-vis) spectra were recorded
on a Perkin-Elmer Lambda 650 instrument from 500 to 200 nm.
7.0 Hz], 7.25-7.42 [m, 15H, CHarom], 7.49 [d, 3H, CH, 3J = 7.5
Hz]. 13C NMR in d4-MeOH: δ 12.0 [CH3], 52.0 [CH2CH2-N],
54.2 [CH2-N], 73.3 [CH2-Ph], 116.3 [CH-CdO], 128.4 [CH],
128.4 [CH], 129.3 [CH], 137.5 [Carom], 140.6 [CH], 143.5 [C-
CH3], 146.1 [C-O], 173.9 [CdO].
2,20,200-Tris[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]triethyl-
amine (6b). Hydrogen was passed through a suspension of 6a (0.50g,
0.67 mmol) and palladium on activated carbon (0.10 g) in 100%
acetic acid (40 mL). The conversion was monitored by means of
TLC, and the reaction was terminated as soon as the spot of the
starting compound had disappeared. The catalyst was filtered off,
the solvent was removed, and the product was dried under vacuum.
Yield: 0.20 g (63%), mp 200-210 °C (dec). MS (ESIþ): m/z
471 [M þ H]þ. 1H NMR in d6-DMSO: δ 2.27 [s, 9H, CH3], 2.79
(37) Reedijk, J. Chem. Rev. 1999, 99, 2499–2510.
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G.; Koellensperger, G. J. Anal. At. Spectrom. 2005, 20, 856–863.
(39) Groessl, M.; Reisner, E.; Hartinger, C. G.; Eichinger, R.;
Semenova, O.; Timerbaev, A. R.; Jakupec, M. A.; Arion, V. B.; Keppler,
B. K. J. Med. Chem. 2007, 50, 2185–2193.
(40) Hartinger, C. G.; Ang, W. H.; Casini, A.; Messori, L.; Keppler,
B. K.; Dyson, P. J. J. Anal. At. Spectrom. 2007, 22, 960–967.
(41) Casini, A.; Hartinger, C. G.; Gabbiani, C.; Mini, E.; Dyson, P. J.;
Keppler, B. K.; Messori, L. J. Inorg. Biochem. 2008, 102, 564–575.
(42) Morris, R. E.; Sadler, P. J.; Chen, H.; Jodrell, D. Half-sandwich
ruthenium(II) compounds comprising nitrogen containing ligands for
treatment of cancer. 2000-GB4144, 2001.
(43) Harris, R. L. N. Aust. J. Chem. 1976, 29, 1329–1334.
(44) Kiel, W. A.; Ball, R. G.; Graham, W. A. G. J. Organomet. Chem.
1990, 383, 481–496.
(45) Lang, R.; Polborn, K.; Severin, T.; Severin, K. Inorg. Chim. Acta
1999, 294, 62–67.
3
3
[t, 6H, CH2CH2-N, J = 6.6 Hz], 3.85 [t, 6H, CH2-N, J =
6.6 Hz], 6.09 [d, 3H, CH-CdO, 3J = 7.3 Hz], 7.37 [d, 3H, CH,
3J = 7.3 Hz]. 13C NMR in d6-DMSO: δ 12.3 [CH3], 51.5
[CH2CH2-N], 54.6 [CH2-N], 111.3 [CH-CdO], 129.2 [C-CH3],
139.0 [CH], 146.3 [C-O], 169.8 [CdO].
General Procedure for the Synthesis of the Complexes. A
solution of bis[dichlorido(η6-p-cymene)metal(II)] (metal = os-
mium, ruthenium) in methanol was added to a suspension of
pyridinone ligand and sodium methoxide in methanol. The
reaction mixture was stirred at room temperature for 2-4 days.
The excess of ligand was removed by filtration, and the solvent
was evaporated under vacuum.
1,6-Bis{chlorido[3-(oxo-KO)-2-methyl-4-(1H)-pyridinonato-KO4]-
(η6-p-cymene)osmium(II)}hexane (1a). Bis[dichlorido(η6-p-
cymene)osmium(II)] (202 mg, 0.26 mmol) in methanol (30 mL),
(46) da Silva, A. C.; Piotrowski, H.; Mayer, P.; Polborn, K.; Severin,
K. Dalton 2000, 2960–2963.

6264 Organometallics, Vol. 28, No. 21, 2009
Mendoza-Ferri et al.
1,6-bis[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]hexane (100 mg,
0.30 mmol), and sodium methoxide (36 mg, 0.66 mmol) in
methanol (30 mL) were used. The complex was extracted with a
dichloromethane/diethyl ether mixture (2:1, 45 mL), the solvent
was removed, and the yellow compound was dried under vacuum.
Yield: 176 mg (66%), mp 248-254 °C (dec). MS (ESIþ): m/z
490 [M - 2Cl]2þ. 1H NMR in d4-MeOH: δ 1.29-1.32 [m, 16H,
CH2(CH2)2-N, (CH3)2CH], 1.74 [brs, 4H, CH2CH2-N], 2.31 [s,
6H, CH3], 2.48 [s, 6H, CH3], 2.64-2.73 [m, 2H, CH(CH3)2], 4.09
[t, 4H, CH2-N, 3J = 7.5 Hz ], 5.87 [d, 4H, CHarom, 3J = 5.6 Hz],
6.10 [d, 4H, CHarom, 3J = 5.6 Hz], 6.55 [d, 2H, CH-CdO, 3J =
6.8 Hz], 7.44 [d, 2H, CH, 3J = 6.8 Hz]. 13C NMR in d4-MeOH:
δ 10.9 [CH3], 18.0 [CH3], 22.0 [(CH3)2CH], 25.8 [CH2(CH2)2-N],
30.4 [CH2CH2N], 32.1 [CH(CH3)2], 54.8 [CH2-N], 68.1 [CH],
70.5 [CH], 85.8 [Carom], 86.6 [Carom], 109.0 [CH-CdO], 134.2
[CH], 134.3 [C-CH3], 167.7 [C-O], 175.7 [CdO].
1,8-Bis{chlorido[3-(oxo-KO)-2-methyl-4-(1H)-pyridinonato-KO4]-
(η6-p-cymene)osmium(II)}octane (2a). Bis[dichlorido(η6-p-
cymene)osmium(II)] (199 mg, 0.25 mmol) in methanol (20 mL),
1,8-bis[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]octane (130 mg,
0.36 mmol), and sodium methoxide (43 mg, 0.79 mmol) in
methanol (20 mL) were used. The complex was extracted with a
dichloromethane/diethyl ether mixture (2:1, 60 mL), and the
solvent was removed. The compound was dissolved in dichloro-
methane, and a yellow precipitate was obtained by addition of
n-hexane, which was filtered off and dried under vacuum.
Yield: 255 mg (77%), mp 128-130 °C. MS (ESIþ): m/z 401
[M - 2I]2þ 1H NMR in d4-MeOH: δ 1.32-1.34 [m, 16H,
.
CH2(CH2)2-N, (CH3)2CH], 1.70 [brs, 4H, CH2CH2-N], 2.32 [s,
6H, CH3], 2.43 [s, 6H, CH3], 2.88-2.95 [m, 2H, CH(CH3)2], 4.04
[t, 4H, CH2-N, 3J = 6.8 Hz], 5.42 [d, 4H, CHarom, 3J = 6.1 Hz],
5.62 [d, 4H, CHarom, 3J = 6.1 Hz], 6.44 [d, 2H, CH-CdO, 3J =
6.8 Hz], 7.40 [d, 2H, CH, 3J = 6.8 Hz]. 13C NMR in d4-MeOH:
δ 10.9 [CH3], 18.3 [CH3], 21.8 [(CH3)2CH], 25.7 [CH2(CH2)2-N],
30.4 [CH2CH2N], 31.6 [CH(CH3)2], 54.7 [CH2-N], 78.7 [CH],
79.6 [CH], 84.9 [Carom], 95.3 [Carom], 109.2 [CH-CdO], 133.5
[CH], 133.9 [C-CH3], 167.7 [C-O], 188.4 [CdO].
1,6-Bis{chlorido[3-(oxo-KO)-2-methyl-4-(1H)-pyridinonato-KO4]-
(η6-biphenyl)ruthenium(II)}hexane (4). Bis[dichlorido(η6-
biphenyl)ruthenium(II)] (147 mg, 0.23 mmol) in dichloromethane
(25 mL), 1,6-bis[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]hexane
(100 mg, 0.30 mmol), and sodium methoxide (36 mg, 0.66 mmol) in
dichloromethane (25 mL) were used. The complex was extracted
with a dichloromethane/diethyl ether mixture (2:1, 65 mL), and the
solvent was removed. The compound was dissolved in dichloro-
methane, precipitated by addition of n-hexane, filtered off, and
dried under vacuum.
Yield: 95 mg (46%), mp 188-190 °C. MS (ESIþ): m/z 421
[M - 2Cl]2þ 1H NMR in d4-MeOH: δ 1.30 [brs, 4H, CH2-
.
(CH2)2-N], 1.67 [brs, 4H, CH2CH2-N], 2.40 [s, 6H, CH3], 4.03
[t, 4H, CH2-N, 3J = 7.5 Hz], 5.91-5.94 [m, 6H, CHarom], 6.10
[d, 4H, CHarom, 3J = 5.6 Hz], 6.46 [d, 2H, CH-CdO, 3J = 6.8
Hz], 7.37 [d, 2H, CH, 3J = 6.8 Hz], 7.46-7.48 [m, 6H, CHarom],
7.83 [m, 4H, CHarom]. 13C NMR in d4-MeOH: δ 10.8 [CH3], 25.7
[CH2(CH2)2-N], 30.4 [CH2CH2N], 54.7 [CH2-N], 78.8 [CH],
80.7 [CH], 80.9 [CH], 94.4 [Carom], 109.4 [CH-CdO], 128.9
[CH], 129.6 [CH], 132.1 [Carom], 133.8 [CH], 134.4 [C-CH3],
159.4 [C-O], 173.8 [CdO].
Yield: 82 mg (30%), mp 248-250 °C (dec). MS (ESIþ): m/z
504 [M - 2Cl]2þ. 1H NMR in d4-MeOH: δ 1.30-1.32 [m, 20H,
CH2(CH2)3-N, CH2(CH2)2-N,(CH3)2CH], 1.73-1.76 [m, 4H,
CH2CH2-N], 2.32 [s, 6H, CH3)], 2.49 [s, 6H, CH3], 2.67-2.74 [m,
2H, CH(CH3)2], 4.11 [t, 4H, CH2-N, 3J = 7.8 Hz], 5.90 [d, 4H,
CHarom, 3J = 5.6 Hz], 6.12 [d, 4H, CHarom, 3J = 5.3 Hz], 6.58 [d,
2H, CH-CdO, 3J = 6.8 Hz], 7.47 [d, 2H, CH, 3J = 6.8 Hz]. 13
C
2,20,200-Tris[chlorido[3-(oxo-KO)-2-methyl-4(1H)-pyridinonato-
KO4](η6-p-cymene)ruthenium(II)]triethylamine (6c). Bis[dichlo-
rido(η6-p-cymene)ruthenium(II)] (166 mg, 0.27 mmol) in metha-
nol (20 mL), pyridinone 6b (100 mg, 0.21 mmol), and sodium
methoxide (38mg, 0.7 mmol) in methanol (20 mL) were used. The
complex was extracted with a dichloromethane/diethyl ether
mixture (2:1, 65 mL), and the solvent was removed. The com-
pound was dissolved in dichloromethane, precipitated by addi-
tion of n-hexane, filtered off, and dried under vacuum.
NMR in d4-MeOH: δ 10.9 [CH3], 18.1 [CH3], 22.1 [(CH3)2CH],
26.1 [CH2(CH2)3-N], 28.9 [CH2(CH2)2-N], 30.6 [CH2CH2-N],
32.1 [CH(CH3)2], 55.0 [CH2-N], 68.2 [CH], 70.6 [CH], 84.9
[Carom], 86.5 [Carom], 108.9 [CH-CdO], 134.2 [CH], 134.3 [C-
CH3], 161.8 [C-O], 175.7 [CdO].
1,6-Bis{bromido[3-(oxo-KO)-2-methyl-4-(1H)-pyridinonato-KO4]-
(η6-p-cymene)ruthenium(II)}hexane (3a). Bis[dibromido(η6-p-
cymene)ruthenium(II)] (184 mg, 0.23 mmol) in methanol (20 mL),
1,6-bis[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]hexane (103 mg,
0.31 mmol), and sodium methoxide (37 mg, 0.68 mmol) in
methanol (20 mL) were used. The complex was extracted with
a dichloromethane/diethyl ether mixture (2:1, 45 mL), and the
solvent was removed. The compound was dissolved in dichloro-
methane, precipitated by addition of n-hexane, filtered off, and
dried under vacuum.
Yield: 150 mg (55%), mp 258-260 °C (dec). MS (ESIþ): m/z
1245 [M - Cl]þ, 604 [M - 2Cl]2þ, 392 [M - 3Cl]3þ. 1H NMR in
d4-MeOH: δ 1.31 [d, 18H, (CH3)2CH, 3J = 6.8 Hz], 2.25 [s, 9H,
CH3], 2.41 [s, 9H, CH3], 2.74 [brs, 6H, CH2CH2-N], 2.80-
2.87 [m, 3H, CH(CH3)2,], 3.78 [brs, 6H, CH2-N], 5.39 [d, 6H,
CHarom, 3J = 4.8 Hz], 5.62 [d, 6H, CHarom, 3J = 5.0 Hz], 6.38
[d, 3H, CH-CdO, 3J = 4.3 Hz], 6.85 [d, 3H, CH, 3J = 5.3 Hz].
13C NMR in d4-MeOH: δ 11.1 [CH3], 17.6 [CH3], 21.6
[(CH3)2CH], 31.4 [CH(CH3)2], 52.8 [CH2CH2-N], 54.4 [CH2-
N], 78.0 [CH], 79.7 [CH], 95.9 [Carom], 99.1 [Carom], 109.3 [CH-
CdO], 133.3 [C-CH3], 134.5 [CH], 159.8 [C-O], 174.5 [CdO].
Yield: 85 mg (38%), mp 130-135 °C. MS (ESIþ): m/z 401
[M - 2Br]2þ 1H NMR in d4-MeOH: δ 1.31-1.34 [m, 16H,
.
CH2(CH2)2-N, (CH3)2CH], 1.70 [brs, 4H, CH2CH2-N], 2.29
[s, 6H, CH3], 2.46 [s, 6H, CH3], 2.82-2.90 [m, 2H, CH(CH3)2],
4.04 [t, 4H, CH2-N, 3J = 7.5 Hz], 5.43 [d, 4H, CHarom, 3J = 5.8
Hz], 5.64 [d, 4H, CHarom, 3J = 5.8 Hz], 6.48 [d, 2H, CH-CdO,
3J = 6.8 Hz], 7.38 [d, 2H, CH, 3J = 6.8 Hz]. 13C NMR in d4-
MeOH: δ 10.8 [CH3], 17.7 [CH3], 21.6 [(CH3)2CH], 25.8
[CH2(CH2)2-N], 30.4 [CH2CH2N], 31.4 [CH(CH3)2], 54.8
[CH2-N], 78.1 [CH], 79.5 [CH], 95.8 [Carom], 99.1 [Carom],
109.3 [CH-CdO], 133.6 [CH], 134.1 [C-CH3], 162.5 [C-O],
174.1 [CdO].
1
Aquation. The aquation was studied using UV-vis and H
NMR spectroscopy. The UV-vis spectrawererecorded from 200
to 500 nm at concentrations of 0.5 mM complex, and the process
was followed for 24
h using a Perkin-Elmer Lambda
650 instrument. For NMR spectroscopy, samples were dissolved
in H2O/D2O (9:1) at 25 °C, and 1H NMR spectra were recorded.
Experimental Protocolfor CellCultureStudies. CellLines and
Cell Culture Conditions. Human SW480 (colon adenocarcinoma)
and A2780 (ovarian carcinoma) cells were kindly provided by
BrigitteMarian(Institute ofCancer Research, MedicalUniversity
of Vienna, Austria) and Evelyn Dittrich (General Hospital, Med-
ical University of Vienna, Austria), respectively. Cells were grown
in 75 cm2 culture flasks (Iwaki/Asahi Technoglass, Gyouda,
Japan) as adherent monolayer cultures in complete culture med-
ium, i.e., minimal essential medium (MEM) supplemented with
10% heat-inactivated fetal bovine serum, 1 mM sodium pyru-
vate, 4 mM L-glutamine, and 1% nonessential amino acids
(100ꢀ) (all purchased from Gibco/Invitrogen, Paisley, UK)
1,6-Bis{iodido[3-(oxo-KO)-2-methyl-4-(1H)-pyridinonato-KO4]-
(η6-p-cymene)ruthenium(II)}hexane (3b). Bis[diiodido(η6-p-
cymene)ruthenium(II)] (309 mg, 0.32 mmol) in methanol (25 mL),
1,6-bis[3-hydroxy-2-methyl-4(1H)-pyridinon-1-yl]hexane (150 mg,
0.45 mmol), and sodium methoxide (54 mg, 0.99 mmol) in methanol
(25 mL) were used. The complex was extracted with a dichloro-
methane/diethyl ether mixture (2:1, 65 mL), and the solvent was
removed. The compound was dissolved in dichloromethane, pre-
cipitated by addition of n-hexane, filtered off, and dried under
vacuum.

Article
Organometallics, Vol. 28, No. 21, 2009 6265
without antibiotics. The cell lines 5637 and RT-4 (bladder cancer),
LCLC-103H and A-427 (lung cancer), DAN-G (pancreatic
cancer), and MCF-7 (breast cancer) were obtained from the
German Collection of Microorganisms and Cell Culture
(DSMZ, Braunschweig, FRG). The three oxoplatin-resistant cell
lines were established at the University of Greifswald through
weekly exposure of cells to increasing concentrations of oxoplatin
over a period of several months. These cells were grown in culture
flasks (Sarstedt, Germany) as adherent monolayer cultures in 90%
RPMI medium supplemented with 10% heat-inactivated fetal
bovine serum and the antibiotics benzylpenicillin and strepto-
mycin. To the medium for the MCF-7 cells were added 1 mM
sodium pyruvate and 1% nonessential amino acids. All cultures
were maintained at 37 °C in a humidified atmosphere containing
5% CO2.
MTT Assay Conditions. Cytotoxicitywas determined by means
of a colorimetric microculture assay [MTT assay, MTT = 3-(4,5-
dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide]. For
this purpose, SW480 and A2780 cells were harvested from culture
flasks by trypsinization and seeded into 96-well microculture
plates (Iwaki/Asahi Technoglass, Gyouda, Japan) in densities of
2.5 ꢀ 103 and 5.0 ꢀ 103 cells/well, respectively, in order to ensure
exponential growth throughout drug exposure. Cells were allowed
to settle in drug-free complete culture medium for 24 h, followed
by the addition of dilutions of the test compounds in 100 μL/well
complete culture medium and incubation for 96 h. Compounds
with low water solubility were stored in DMSO stock solutions,
which were diluted with medium such that the effective DMSO
content did not exceed 1%. At the end of exposure, drug solutions
were replaced by 100 μL/well RPMI 1640 culture medium
(supplemented with 10% heat-inactivated fetal bovine serum
and 2 mM L-glutamine) and 20 μL/well MTT solution in phos-
phate-buffered saline (5 mg/mL). After incubation for 4 h, the
medium/MTT mixtures were removed, and the formazan crystals
formed by vital cells were dissolved in 150 μL of DMSO per well.
Optical densities at 550 nm were measured with a microplate
reader (Tecan Spectra Classic) using a reference wavelength of
690 nm to correct for unspecific absorption. Quantities of vital cells
were expressed in terms of T/C values by comparison to untreated
controls, and 50% inhibitory concentrations (IC50) were calcu-
lated from concentration-effect curves by interpolation. Evalua-
tion is based on means from at least three independent experi-
ments, each comprising six replicates per concentration level.
Crystal Violet Assay Conditions. This assay has been described
in detail elsewhere.47 Culture conditions were the same as used in
the MTT assay. Briefly, cells were seeded into 96-well micro-
culture plates (Sarstedt, FRG) in cell densities of 1.0 ꢀ 103 cells/
well, except for LCLC-103H, which was seeded at 250 cells/well.
After a 24 h preincubation, cells were treated with the test
substance for 96 h. Stock solutions of test substance were
prepared to 20 mM in DMF and diluted 1000-fold in RPMI
1640culture medium containing 10% fetal calfserum. Substances
that showed a g50% growth inhibition at 20 μM were tested at
5 serial dilutions in 4 wells/concentration to determine the IC50
values as described.47 Staining of cells was done for 30 min with a
0.02%crystal violet solutioninwater followed bywashing outthe
excess dye. Cell-bound dye was redissolved in 70% ethanol/water
solution, and the optical densities at λ = 570 nm were measured
with a microplate reader (Anthos 2010).
Acknowledgment. We thank the University of Vienna,
€
the Hochschuljubilaumsstiftung Vienna (H-1826/2008),
the Theodor-Korner-Fonds, the Austrian Council for
€
Research and Technology Development, the FFG-Aus-
trian Research Promotion Agency (Project FA 526003),
€
the FWF-Austrian Science Fund (Schrodinger Fellow-
ship J2613-N19 [C.G.H.]), the EPFL, and COST D39 for
financial support. This research was supported by a
Marie Curie Intra European Fellowship within the 7th
European Community Framework Programme projects
220890-SuRuCo (A.A.N.). We gratefully acknowledge
Prof. Markus Galanski for recording the NMR spectra,
and Prof. Patrick J. Bednarski and Magdalena Maruszak
(University of Greifswald) for contribution to the in vitro
activity data.
Supporting Information Available: Elemental analysis data;
UV/vis data on the hydrolysis of 1a. This material is available
free of charge via the Internet at http://pubs.acs.org.
€
(47) Bracht, K.; Boubakari; Grunert, R.; Bednarski, P. J. Anti-
Cancer Drugs 2006, 17, 41–51.