Organometallic anticancer agents that interfere with cellular energy processes: A subtle approach to inducing cancer cell death

Article abstract of DOI:10.1039/c2dt31936e

Two hybrid compounds comprising an antimetastatic ruthenium-arene fragment tethered to an indazole-3-carboxylic acid derivative that inhibits aerobic glycolysis in cancer cells have been prepared and evaluated in a variety of cancer cell lines, including highly relevant human glioblastoma cells, with an apparent synergistic action between the two components observed.

Full text of DOI:10.1039/c2dt31936e

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Organometallic anticancer agents that interfere with cellular energy
processes: a subtle approach to inducing cancer cell death.
Alexey A. Nazarov*a,b, Daniel Gardinia, Mathurin Baquié a, Lucienne Juillerat-Jeanneretc, Tatiana P.
Serkovad, Elena P. Shevtsovad, Rosario Scopellitia and Paul J. Dyson*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
First published on the web Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
21
the imidazole group.20,
This rather simple approach to
Two hybrid compounds comprising an antimetastatic
ruthenium-arene fragment tethered to an indazole-3-carboxylic
ligand design, i.e. modifying an imidazole with a biologically
55 active organic group, appears to be very effective provided
appropriate bioꢀactive compounds are selected. Related
approaches have been reported by others.22ꢀ27
10 acid derivative that inhibits aerobic glycolysis in cancer cells have
been prepared and evaluated in a variety of cancer cell lines,
including highly relevant human glioblastoma cells, with an
apparent synergistic action between the two components
observed.
15 Metallocenes were evaluated for anticancer activity, following
the introduction of cisplatin into the clinic,1, 2 with titanocene
dichloride being identified as a promising drug candidate.3 It
was subsequently evaluated in numerous in vitro and in vivo
models and even in clinical trials on patients, but finally was
20 not approved for use.4 Jaouen later showed that derivatization
of ferrocene with biologically active tamoxifens affords
compounds that enhance the activity of the organic molecule
leading to a strong cytotoxic effect in hormoneꢀindependent
Fig. 1 The structures of RAPTAꢀC (a), an example of a sugarꢀbased
60 phosphite analogue (b) and an imidazole derivative, termed RuꢀA (c).
In cancer chemotherapy drug combinations are almost always
applied28ꢀ30 and in this sense the organometallic and organic
components can be viewed as a covalently linked drug
combination. In this context, we hypothesized that it may be
65 worthwhile combining the ruthenium(II)ꢀarene dichloride unit
with aerobic glycolysis inhibitors, and for this purpose
lonidamine, [1ꢀ(2,4ꢀdichlorobenzyl)ꢀ1Hꢀindazoleꢀ3ꢀcarboxylic
acid], was selected. Lonidamine inhibits aerobic glycolysis in
cancer cells while simultaneously enhancing aerobic
70 glycolysis in normal cells,31 thus providing a potentially
highly selective ruthenium drug molecule. In this paper we
describe the synthetic strategy adopted to afford the
ruthenium(II)ꢀlonidamine hybrid derivatives together with an
account of their characterization and preliminary biological
75 evaluation in relevant cancer cell lines.
breast
cancer
cells
(MDAꢀMBA231),
where
25 hydroxytamoxifen and ferrocene are inactive.5, 6
Following the early studies by Fish on the aqueous chemistry
of transition metalꢀarene compounds and their reactivity with
nucleobases, nucleosides and nucleotides,7ꢀ9 we became
interested in the application of ruthenium(II)ꢀarene
30 compounds
cymene)(pta)Cl2
in
medicine.
(pta
The
complex
1,3,5ꢀtriazaꢀ7ꢀ
Ru(η6ꢀpꢀ
=
phosphatricyclo[3.3.1.1]decane), termed RAPTAꢀC, is
endowed with and
antitumour,10 antimetastatic11
antiangiogenic12 properties in vivo. These compounds exert
35 their anticancer effect in rather subtle manner; the
a
compounds are not particularly cytotoxic, nor binding
strongly to DNA, but rather interacting with protein targets
with moderate binding constants leading to the interference of
various cellular processes and pathways. A crystal structure of
40 RAPTAꢀC bound to the nucleosome core particle reveals
exclusive binding to the histone protein core via substitution
of both chloride ligands, emphasizing the importance of the
two labile chlorides in the RAPTA structure.13
The pta ligand may be replaced by other ligands including
45 sugarꢀbased phosphites that potentially target tumours14ꢀ16 and
imidazole ligands (Fig. 1).17 The choice of the latter ligand
was inspired by NAMIꢀA, one of the two ruthenium(III)
coordination complexes currently undergoing clinical trials,
19
which contains an imidazole ligand amongst others.18,
50 Moreover, the cytotoxicity of ruthenium(II)ꢀarene complexes
can be increased by covalently linking organic inhibitors of
proteins that are responsible for drug resistance in tumours via
Scheme 1 Synthesis of 1, 2 and 3.
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Table 1 Cytotoxicity of lonidamine, 1 ꢀ 3, RAPTAꢀC and cisplatin towards the ovarian cancer cell lines A2780 and A2780R and the human glioblastoma
cell lines LN18, LN229, LNZ308, HEK and cortex neurons.
. Compound
Cell line, IC50 (72 h) /ꢁM
A2780
A2780R
LN18
LN229
LNZ308
HEK
cortex neuronsa
lonidamine
206.58±9.44
10.72±1.59
20.81±6.16
19.34±4.08
>250
197.87±20.77
11.56±2.41
24.12± 7.10
17.9±4.04
>250
>50
9.4±2.8
>50
6.4±0.9
>50
12.5±3.5
350.76±39.60
20.63±5.81
30.12±6.97
20.50±6.12
89.4±6.0
21.9±5.4
31.3±11.8
20.2±5.1
1
2
3
6.4±2.1
8.3±2.4
5.7±0.9
RAPTAꢀC
RuꢀA21
cisplatin32
>100
9.5 ± 2.4
>100
31.5 ± 3.4
a % from control after incubation for 72 h with 30.0 ꢁM drug
The lonidamineꢀmodified imidazole ligand, 1, was prepared
via reaction between the acidꢀchloride of lonidamine,
shown in Fig. 2 and key bond parameters are listed in the
caption. The geometry around the ruthenium(II) ion in both
5
prepared in situ, and Nꢀ(aminopropyl)imidazole (see Scheme 25 compounds are similar, with the expected 'pianoꢀstool'
1 and Supporting Information for full details). Subsequent
structure composed from the arene ligand, lonidamineꢀ
derivatized imidazole and two chloride ligands. The structures
show that the lonidamine moiety is attached to the imidazole
group in the expected fashion, and moreover, the lonidamine
30 structure is unperturbed relative to that of the free molecule.33
reaction of 1 with the ruthenium(II) arene dimers, [Ru(η6ꢀ
The cytotoxicity of lonidamine, 1-3 were evaluated against the
A2780 and A2780cisR ovarian cancer cell lines, the latter
having acquired resistance to cisplatin (Table 1). These two
35 cell lines have been extensively used to evaluate the in vitro
anticancer activity of rutheniumꢀbased compounds and
therefore allows comparisons to other classes of compounds to
be made. Complexes 2 and 3 are markedly more cytotoxic
than lonidamine and RAPTAꢀC or RuꢀA ndicating that the
40 two units operate together in
a
concerted fashion.
Nevertheless, compared to cisplatin the complexes are less
cytotoxic. However, their IC50 values in these cell lines are
comparable to those of other promising rutheniumꢀbased
therapeutics.34, 35
45 Since the pꢀcymene derivative, 3, is slightly more cytotoxic
than 2, and displays superior stability, this compound was
evaluated further together with that of 1 in three human
glioblastoma cell lines (Table 1) of direct relevance to
lonidamine that is being clinically evaluated against brain
50 cancers.36
arene)Cl2]2
(arene
=
C6H5CH3
toluene
and
pꢀ
Compared to lonidamine which showed essentially no activity
(> 50 ꢂM) towards the human glioblastoma cells 1 and 3
display excellent cytotoxicity, particularly for 3. It is
interesting to note that incorporation of the propylꢀimidazole
55 group to the lonidamine structure results in a superior
cytotoxic effect, further enhanced in some cell lines by
coordination to the ruthenium(II)ꢀarene fragment. It has
previously been shown the cytotoxicity of compounds can be
enhanced when coordinated to the ruthenium(II)ꢀarene unit as
60 the broad therapeutic action of the organometallic unit, that
can covalently (coordinate) bind to a range of biological
targets operates more effectively when
10 C6H4CH3CH(CH3)2 pꢀcymene), affords complexes 2 and 3.
Fig. 2 Structures of (top) 2 and (bottom) 3 (one of 3 independent
molecules in the asymmetric unit). Key bond lengths (Å) and angles
(deg.) for 2: Ruꢀarene centroid 1.658(4) , RuꢀCl1 2.4298(7), RuꢀCl2
2.4257(7), RuꢀN1 2.108(2), Cl1ꢀRuꢀCl 2 88.98(2), Cl1ꢀRuꢀN1 84.61(6),
15 Cl2ꢀRuꢀN187.62(6) . For 3 (for structure on the figure): Ruꢀarene centroid
1.663(7), RuꢀCl1 2.4404(13), RuꢀCl2 2.4356(13), RuꢀN1 2.118(4), Cl1ꢀ
RuꢀCl2 89.24(4), Cl1ꢀRuꢀN1 85.05(12), Cl2ꢀRuꢀN1 85.21(11).
1
The H and 13C{1H} NMR spectra and other data confirm the
formation of the expected products. The structures of 2 and 3
20 were determined in the solid state on crystals grown from
CH2Cl2/Et2O mixtures. Crystallographic details are provided
in the Supporting Information. The structures of 2 and 3 are
combined with an organic inhibitor that has a very specific
function.20, 21
cerebral cortex from Wistar rats (Table 1). A moderate
preference towards the malignant cells, which is more
65 To obtain more information on the cancer cell selectivity of 1 70 pronounced for the relevant human glioblastoma cell lines, is
– 3 the compounds were evaluated on immortalised nonꢀ
observed.
tumorigenic HEK cells and primary neuronal cultures of the
2
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ruthenium(II)ꢀpꢀcymene unit via an imidazole group displays
highly relevant cytotoxicites in human glioblastoma cell lines
for which better chemotherapeutics are urgently required. This
compound also exhibits a degree of selectivity towards these
cells relative to primary neuronal cultures of the cerebral
cortex. Lonidamine has been used in the treatment of brain
tumours in combination with radiotherapy and temozolomide
10 resulting in the inhibition of tumour growth, with lonidamine
reducing the dose of temozolomide required for
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a Institute of Chemical Sciences and Engineering, Swiss Federal Institute
of Technology (EPFL), 1015, Lausanne, Switzerland. Fax: +41-21-
6939780; Tel: +41-21-6939854; E-mail: paul.dyson@epfl.ch
b Moscow State University, Department of Chemistry, Leninskie gory,
20 119991, Moscow, Russia; E-mail: alexey.nazarov@me.com
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culture and inhibition of cell growth ]. See DOI: 10.1039/b000000x/
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