Half-Sandwich Iridium(III) and Ruthenium(II) Complexes Containing P^P-Chelating Ligands: A New Class of Potent Anticancer Agents with Unusual Redox Features

Article abstract of DOI:10.1021/acs.inorgchem.7b01959

A series of half-sandwich Ir^III pentamethylcyclopentadienyl and Ru^II arene complexes containing P^P-chelating ligands of the type [(Cp^x/arene)M(P^P)Cl]PF₆, where M = Ir, Cp^x is pentamethylcyclopentadienyl (Cp?), or 1-biphenyl-2,3,4,5-tetramethyl cyclopentadienyl (Cp^xbiPh); M = Ru, arene is 3-phenylpropan-1-ol (bz-PA), 4-phenylbutan-1-ol (bz-BA), or p-cymene (p-cym), and P^P is 2,20-bis(diphenylphosphino)-1,10-binaphthyl (BINAP), have been synthesized and fully characterized, three of them by X-ray crystallography, and their potential as anticancer agents explored. All five complexes showed potent anticancer activity toward HeLa and A549 cancer cells. The introduction of a biphenyl substituent on the Cp? ring for the iridium complexes has no effect on the antiproliferative potency. Ruthenium complex [(η⁶-p-cym)Ru(P^P)Cl]PF₆ (5) displayed the highest potency, about 15 and 7.5 times more active than the clinically used cisplatin against A549 and HeLa cells, respectively. No binding to 9-MeA and 9-EtG nucleobases was observed. Although these types of complexes interact with ctDNA, DNA appears not to be the major target. Compared to iridium complex [(η⁵-Cp?)Ir(P^P)Cl]PF₆ (1), ruthenium complex (5) showed stronger ability to interfere with coenzyme NAD⁺/NADH couple through transfer hydrogenation reactions and to induce ROS in cells, which is consistent with their anticancer activities. The redox properties of the complexes 1, 5, and ligand BINAP were evaluated by cyclic voltammetry. Complexes 1 and 5 arrest cell cycles at the S phase, Sub-G₁ phase and G₁ phase, respectively, and cause cell apoptosis toward A549 cells.

Full text of DOI:10.1021/acs.inorgchem.7b01959

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Half-Sandwich Iridium(III) and Ruthenium(II) Complexes Containing
P^P-Chelating Ligands: A New Class of Potent Anticancer Agents
with Unusual Redox Features
JuanJuan Li, Meng Tian, Zhenzhen Tian, Shumiao Zhang, Chao Yan, Changfang Shao, and Zhe Liu*
Institute of Anticancer Agents Development and Theranostic Application, The Key Laboratory of Life-Organic Analysis and Key
Laboratory of Pharmaceutical Intermediates and Analysis of Natural Medicine, Department of Chemistry and Chemical Engineering,
Qufu Normal University, Qufu 273165, China
S
* Supporting Information
ABSTRACT: A series of half-sandwich IrIII pentamethylcyclopentadienyl and
RuII arene complexes containing P^P-chelating ligands of the type [(Cpx/
arene)M(P^P)Cl]PF6, where M = Ir, Cpx is pentamethylcyclopentadienyl (Cp*),
or 1-biphenyl-2,3,4,5-tetramethyl cyclopentadienyl (CpxbiPh); M = Ru, arene is 3-
phenylpropan-1-ol (bz-PA), 4-phenylbutan-1-ol (bz-BA), or p-cymene (p-cym),
and P^P is 2,20-bis(diphenylphosphino)-1,10-binaphthyl (BINAP), have been
synthesized and fully characterized, three of them by X-ray crystallography, and
their potential as anticancer agents explored. All five complexes showed potent
anticancer activity toward HeLa and A549 cancer cells. The introduction of a
biphenyl substituent on the Cp* ring for the iridium complexes has no effect on
the antiproliferative potency. Ruthenium complex [(η6-p-cym)Ru(P^P)Cl]PF6
(5) displayed the highest potency, about 15 and 7.5 times more active than the
clinically used cisplatin against A549 and HeLa cells, respectively. No binding to
9-MeA and 9-EtG nucleobases was observed. Although these types of complexes
interact with ctDNA, DNA appears not to be the major target. Compared to iridium complex [(η5-Cp*)Ir(P^P)Cl]PF6 (1),
ruthenium complex (5) showed stronger ability to interfere with coenzyme NAD+/NADH couple through transfer
hydrogenation reactions and to induce ROS in cells, which is consistent with their anticancer activities. The redox properties of
the complexes 1, 5, and ligand BINAP were evaluated by cyclic voltammetry. Complexes 1 and 5 arrest cell cycles at the S phase,
Sub-G1 phase and G1 phase, respectively, and cause cell apoptosis toward A549 cells.
reported a series of cytotoxic trichlorido or Cp* IrIII complexes
INTRODUCTION
■
containing N^N-chelating polypyridyl ligands, such as fac-
Cisplatin is one of the earliest and most successful metal based
[Ir(phen)(dmso-kS)Cl3] (phen = 1,10-phenanthroline), which
anticancer drugs in the clinic, which is still used in cancer
treatment after almost five decades since its chance discovery.1
are highly active against MCF-7 human breast cancer cells and
HT-29 human colon cancer cells.26,27 The Sadler group started
In the field of metal based anticancer agents, cisplatin is still the
benchmark for evaluation of antiproliferative activity and
to explore iridium based anticancer agents in 2008. At the start,
a series of IrIII Cp* chlorido complexes containing N^N-,
O^O-, or O^N-chelating ligands, such as [(η5-Cp*)Ir(phen)-
Cl]PF6, were synthesized; however, the antiproliferative activity
test showed that they were inactive (IC50, concentration at
which 50% of the cell growth is inhibited, >100 μM) against
A2780 human ovarian cancer cells.28 However, when a phenyl
or biphenyl ring was introduced onto the Cp* ring, a significant
increase in the anticancer activity against A2780 cells was
comparison of mechanism of action.2,3 However, due to the
disadvantages of cisplatin and other platinum based anticancer
drugs, such as dose-dependent side effects and the development
of resistance of some carcinomas, a wide range of novel
transition metal complexes that might be effective against a
wider range of cancers, with less side effects and different
mechanisms of action, are being screened for their use as
therapeutic agents.4−10
achieved, for example, from [(η5-Cp*)Ir(phen)Cl]PF6 (IC50
100 μM) to [(η5-Cpxbiph)Ir(phen)Cl]PF6 (Cpxbiph
>
Iridium (Ir) is a third-row transition metal, and its
compounds are usually considered to be too inert to possess
high activity. A few early trials seem to confirm this
assumption.11,12 However, very recently, iridium(III) com-
plexes have been shown to possess great potential as novel
anticancer agents, which not only showed high potency toward
a wide range of cancer cells but also displayed completely
different mechanisms of action (MOAs) from the clinically
used platinum based drugs.13−25 Sheldrick and co-workers
=
C5Me4C6H4C6H5) (IC50 = 0.72 μM).28 Furthermore, Cp*
complex [(η5-Cp*)Ir(C^N)Cl]PF6, bearing an anionic C^N-
chelating 2-phenylpyridine ligand, instead of a neutral diimine
type ligand (such as phen and 2,2′-bipyridine), displayed
Received: July 31, 2017
© XXXX American Chemical Society
A
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Inorganic Chemistry
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Chart 1. Organometallic IrIII Cyclopentadienyl [(η5-
Cpx)Ir(P^P)Cl]PF6 and RuII Arene [(η6-
arene)Ru(P^P)Cl]PF6 Complexes Studied in This Work
promising anticancer activity, with IC50 value 10.8 μM against
A2780 cell line.29 Going from [(η5-Cp*)Ir(C^N)Cl]PF6 to
[(η5-Cpxbiph)Ir(C^N)Cl]PF6 (C^N = 2-phenylpyridine), an
order of magnitude increase in potency, from IC50 10.8 to 0.7
μM against A2780 cells, was achieved upon the inclusion of a
biphenyl substituent to the Cp* ring.30
Ruthenium is another valuable metal in the search for
therapeutic agents.2 Ruthenium compounds are attracting
much attention for anticancer drug design since they have a
rich redox chemistry (RuII and RuIII) and exhibit a similar
spectrum of kinetics to platinum(II).31 In general, ruthenium
complexes show less toxicity than their platinum analogues, as
ruthenium is able to mimic iron during its interaction with
proteins, such as transferrin and albumin; thus, more selective
entry into cancer tissues can be achieved as more transferrin
receptors located on the cancer cell surface.2,32,33 A large
number of ruthenium compounds have been designed and
displayed potent anticancer activities. Moreover, two
ruthenium(III) complexes have entered clinical trials.34−36
The RuII ethylenediamine (en) complexes developed by the
Sadler group, [(η6-arene)Ru(en)Cl]+, have been evaluated for
activity both in vitro in A2780 cancer cells and in vivo, showing
potent activity and non-cross-resistance to cisplatin-resistant
cells.37 Dyson et al. reported the high selectivity of an arene
RuII PTA series of compounds (pta = 1,3,5-triaza-7-phospha-
tricyclo-[3.3.1.1]decane) toward the TS/A mouse adenocarci-
noma cancer cells and HBL-100 human mammary normal
cells.38
With regard to half-sandwich IrIII and RuII complexes [(Cpx/
arene)M(L^L′)Z]0/n+, all of the ligands around the metal center
including the cyclopentadienyl/arene, chelating ligand, L^L′,
and leaving group Z can influence the anticancer activity
dramatically.4,15,18,39 RuII arene anticancer complexes, where
arene, for example, is benzene, p-cymene (p-cym), biphenyl,
9,10-dihydroanthracene (DHA), and 5,8,9,10-tetrahydroanthra-
cene (THA), have been widely investigated for the effects of
RESULTS AND DISCUSSION
■
The dinuclear dichloro-bridged complexes [(η5-Cp*)IrCl2]2
(dimer 1) and [(η5-Cpxbiph)IrCl2]2 (dimer 2) were synthesized
by microwave heating of IrCl3 and relative cyclopentadienyl
ligand in absolute methanol.18 Dimeric μ-chloro-bridged
complexes [(η6-bz-PA)RuCl2]2 (dimer 3), [(η6-bz-BA)RuCl2]2
(dimer 4)47 and [(η6-p-cym)RuCl2]2 (dimer 5)48 are readily
formed upon conversion of 3′-(2,5-dihydrophenyl)propanol,
4′-(2,5-dihydrophenyl)butanol,49 and α-terpinene, respectively,
with RuCl3 under refluxing in absolute methanol (Scheme 1).
Complexes 1−5 were synthesized by reactions between the
ligand BINAP and the dinuclear iridium/ruthenium precursors
dimers 1−5 in methanol at ambient temperature. All
complexes are newly synthesized compounds and were
various arenes on the chemical and biological activities.40,41
A
large number of metal complexes based on N^N-chelating
ligands have been evaluated for their medicinal application,
while complexes containing P^P-chelating ligands are much less
investigated.36,42−44 Only a few IrIII complexes with P^S-
chelating ligand show comparable or even higher antiprolifer-
ative activities than cisplatin against 8505C and SW480 cell
lines.45
1
characterized by H NMR, mass spectroscopy, and elemental
Metal complexes of 2,20-bis(diphenylphosphino)-1,10-bi-
naphthyl (BINAP) have recently drawn attention as promising
asymmetric catalyts in many organic reactions.46 However, to
the best of our knowledge, no biological activity of iridium or
ruthenium BINAP complexes has been reported so far. In this
work, a series of half-sandwich IrIII and RuII complexes of the
type [(η5-Cpx)Ir(P^P)Cl]PF6, where Cpx is pentamethylcyclo-
pentadienyl Cp* (1), biphenyl (Cpxbiph) derivatives (2), and
[(η6-arene)Ru(P^P)Cl]PF6, where the arene is 3-phenyl-
propan-1-ol (bz-PA) (3), 4-phenylbutan-1-ol (bz-BA) (4),
and p-cymene (p-cym) (5), with BINAP as P^P-chelating
ligand, were synthesized and characterized (Chart 1). We
report studies of the nucleobase binding, DNA interactions,
BSA interactions, and cell toxicity of the complexes. The work
also explores the MoA of these metal complexes by cell cycle,
ROS, apoptosis, and catalytic hydride transfer analysis. The
results suggest that this series of metal complexes are potential
candidates for development as new therapeutic agents.
−
analysis. All complexes were isolated as PF6 salts.
X-ray Crystal Structures. Single crystals of [(η5-Cp*)Ir-
(P^P)Cl]PF6 (1), [(η6-bz-PA)Ru(P^P)Cl]PF6 (3), and [(η6-p-
cym)Ru(P^P)Cl]PF6 (5) were grown by slow diffusion of
hexane into a saturated dichloromethane solution of these
complexes. The structures and their atom numbering schemes
are shown in Figure 1. Crystallographic data and selected bond
lengths and angles are listed in Tables 1 and 2. Complexes of 1,
3, and 5 are arranged in the triclinic and monoclinic crystal
systems with the P1, P21/n, C2/c space groups, respectively.
̅
Each complex has the expected pseudo-octahedral half-
sandwich piano stool geometry. The distance between the
iridium center and the centroid of η5-cyclopentadienyl ring is
1.913 Å, while the distances between the ruthenium center and
the centroid of η6-arene for complexes 3 and 5 are 1.760 and
1.799 Å, respectively. The three complexes have similar metal−
Cl bond distances for 1, 3, and 5: 2.3922(17), 2.384(3), and
2.391(3) Å, respectively. The Ir−P bond lengths in 1 are similar
B
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Inorganic Chemistry
Article
ranging from 1.4 to 35.0 μM, and against HeLa cells with IC50
values from 1.0 to 23.7 μM. The activities of complexes 1−5 fall
in the following order 5 > 1 > 2 > cisplatin > 4 > 3 toward both
HeLa and A549 cancer cells. Against our expectations,28 the
Cp* complex 1 exhibited an antiproliferative activity 2 times
higher toward both cell lines than its Cpxbiph analogue 2. This
result is contrary to our previous conclusions, which showed
the anticancer activity increased significantly with an increase in
the number of phenyl rings on the Cp* ring.4 The presence of
the extended phenyl rings not only increased the hydro-
phobicity of the complexes, thereby easing their passage
through the cell membrane so that more complex could find
its way into the cells, but also had the potential for intercalation
into DNA base pairs. The result here may be indicating that the
presence of arenes in the chelating ligand BINAP may have
offset the advantages of having the extended arenes on the Cp*.
Complex 1 containing Cp* showed similar activity compare to
[(η5-Cp*)Ir(N^O)Cl]PF6 (N^O = 1,2-naphthoquinone-1-
oximato) against HeLa cells.51 Sheldrick and co-workers
reported a series of cytotoxic Cp* IrIII complexes containing
N,N-chelating polypyridyl ligands. In general, the antiprolifer-
ative effects of this type of N,N-bound polypyridyl IrIII
complexes are governed by the size of the polypyridyl ligands
in the order of bpy < phen, dpq < dppz < dppn.52
Scheme 1. Synthesis of dimers 3−5 and Respective Half-
Sandwich IrIII and RuII Complexes
Ruthenium complex 5 displayed the most potent anti-
proliferative activity against both cell lines: about 15 and 7.5
times more potent than cisplatin toward A549 and HeLa cells,
respectively. Ruthenium complexes 3 and 4 containing the
−OH group are less active, probably due to the hydrophilicity
of −OH, and therefore noneffective in penetrating into the cell
membrane.53 From complex 3 to 4, the antiproliferative activity
improved slightly with the increase of ligand length of the
backbond. Sadler et al. reported that the more hydrophobic the
arene ligand is, the better cancer cell growth inhibitory
activity.37 Kim’s group also reported a similar trend in the in
vitro anticancer activity of Ir(III), Rh(III), and Ru(II)
complexes against the lymphoma cell line.54
For the most potent two complexes 1 and 5, their
antiproliferative activities were further evaluated against two
human bronchial epithelial normal cells 16HBE and BEAS-2B
(Table 3). Unfortunately, no selectivity was observed for the
two complexes between cancer cells versus normal cells. Hence,
more structural modification is necessary to improve the
selectivity in future work.
Partition Coefficients (log P). Lipophilicity is often
consistent with the cellular uptake efficiencies of chemo-
therapeutic agents, and therefore, it has significant effects on
their cytotoxic potency. The log P values for complexes 1 and 5
in octanol/water systems were determined because of their low
IC50 values. NaCl (50 mM) was used to suppress hydrolysis of
the complexes so the log P values tested are for the chlorido
complexes. The values of log P for 1 (2.04) and 5 (1.36) are
varied with the metals and cyclopentadienyl or arene of the
complexes (Table 4). The log P values of new pharmacophores
in the Comprehensive Medicinal Chemistry database range
from −0.4 to 5.6.55 The log P values for complexes 1 and 5 are
within this range. The hydrophobicity and anticancer activity
were not correlated in this study. Complex 5 displays lower
hydrophobicity but the most cytotoxic activity.
to the Ru−P bond lengths in 3 and 5. However, slight
differences between the metal−P1 and metal−P2 distances were
observed in all three complexes (Table 2).
Comparison between the η6-arene in complexes 3 and 5
shows that the functionalized arene in complex 3 is closer to
the RuII center. This could be due to the presence of the
stronger electron-donating group OH in addition to the steric
hindrance effect of the isopropyl group. Due to the relatively
strong trans effect of the P^P-chelating ligand BINAP, the Ir-
centroid bond length 1.913 Å in complex 1 is significantly
longer than the 1.820 and 1.786 Å found in the C^N complex
[(η5-Cp*)Ir(phpy)Cl] and the N^N complex [(η5-Cp*)Ir-
(bpy)Cl]Cl, respectively.28,29,50 The Ir−Cl bond length
2.3922(17) Å in complex 1 is similar to the Ir−Cl bond length
2.3968(7) Å in [(η5-Cp*)Ir(phpy)Cl] and 2.404(2) Å in [(η5-
Cp*)Ir(bpy)Cl]Cl.
Cytotoxicity. The aim of the present study is to investigate
the in vitro viability of HeLa human cervical and A549 human
lung cancer cell lines after treatment with various concen-
trations of complexes 1−5 over 24 h. The potentials of the
synthesized complexes 1−5 on the IC50 values (concentration
at which 50% of the cell growth is inhibited) after 24 h of
exposure to the compounds are listed in Table 3. The HeLa
cells and A549 cells were treated with cisplatin in the same
concentration range and used as a control, and they showed an
IC50 value of 7.5 μM toward HeLa cancer cells and 21.3 μM
toward A549 lung cancer cells, respectively. Excitingly, the
newly synthesized five complexes exhibited potency at least
comparable to cisplatin against A549 cells with IC50 values
Nucleobases Binding. As DNA is usually an important
target for metal based anticancer compounds, the interaction
between nucleobase models 9-ethylguanine (9-EtG) and 9-
methyladenine (9-MeA) and complexes 1−5 was investigated.
C
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Inorganic Chemistry
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Figure 1. X-ray crystal structures for (A) [(η5-Cp*)Ir(P^P)Cl]PF6 (1), (B) [(η6-bz-PA)Ru(P^P)Cl]PF6 (3), and (C) [(η6-p-cym)Ru(P^P)Cl]PF6
−
(5). Hydrogen atoms, solvent CH2Cl2, and counterions PF6 are omitted for clarity.
Table 1. Crystallographic Data for [(η5-Cp*)Ir(P^P)Cl]PF6 (1), [(η6-bz-PA)Ru(P^P)Cl]PF6 (3), and [(η6-p-
cym)Ru(P^P)Cl]PF6 (5)
1
3
5
formula
C54H47ClF6IrP3
1130.48
C53H44ClF6OP3Ru
1040.31
0.20 × 0.12 × 0.08
0.71073
293(2)
C56H50Cl5F6P3Ru
1208.19
MW
Cryst size (mm)
λ (Å)
0.42 × 0.35 × 0.30
0.71073
0.30 × 0.20 × 0.12
0.71073
temp (κ)
cryst syst
space group
a (Å)
298(2)
298(2)
Triclinic
Monoclinic
P21/n
Monoclinic
C2/c
P1
̅
12.2960(11)
12.7308(12)
15.3989(14)
77.0650(10)
86.567(2)
85.275(2)
2339.2(4)
2
16.296(2)
18.704(3)
16.701(2)
90
33.150(3)
15.2970(14)
21.6051(19)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
110.879(3)
90
99.1530(10)
90
vol (Å3)
4756.3(11)
4
10816.4(16)
8
Z
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF
0.0506
0.0948
0.1264
0.1294
0.2319
0.3086
1.043
0.948
1.048
1
9-MeA or 9-EtG (3 mol equiv) was added to a solution of 1−5
(1.0 mM) in 80% DMSO-d6/20% D2O (v/v) at 310 K. No
additional H NMR peaks were detected over 24 h (Figure S1
in the Supporting Information). Also, no adducts formation was
detected by mass spectrometry.
Interaction with GSH. GSH is plentiful in cells and
participates in the detoxification of many anticancer drugs.15
Therefore, we investigated the stability of complexes 1 and 5 in
the absence and presence of GSH due to their high anticancer
potency. H NMR spectra showed that no hydrolysis was
observed for complexes 1 and 5 in 80% DMSO-d6/20% D2O
(v/v) after 24 h at 310 K (Figure S2 in the Supporting
Information). DMSO was used to ensure solubility of metal
complexes in solution. Then GSH (5 mol equiv) was added to
the solution under N2 atmosphere. The resulting solution was
monitored by 1H NMR at 310 K. No adduct of complexes and
GSH was detected after 2 h, suggesting that the iridium/
ruthenium chloride complexes are stable in the absence and
1
D
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a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[(η5-Cp*)Ir(P^P)Cl]PF6 (1), [(η6-bz-PA)Ru(P^P)Cl]PF6
(3), and [(η6-p-cym)Ru(P^P)Cl]PF6 (5)
Table 4. Log P for Complexes 1 and 5
log P
complex
1
Mean
1
3
5
2.04 0.12
1.36 0.07
M−C (cyclopentadienyl)
2.242(7)
2.250(7)
2.259(7)
2.272(7)
2.324(6)
2.182(12)
2.228(12)
2.248(12)
2.249(12)
2.266(12)
2.304(11)
1.760
2.231(15)
2.262(15)
2.265(18)
2.31(2)
5
a
Results are obtained from three independent experiments.
2.330(17)
2.330(17)
1.799
M−C(centroid)
M−P1
M−P2
1.913
2.3272(16)
2.3522(17)
2.3922(17)
91.72(6)
85.59(6)
91.23(6)
2.365(3)
2.338(3)
2.384(3)
91.15(10)
88.31(10)
85.88(10)
2.333(4)
2.391(4)
2.391(3)
90.53(13)
84.70(12)
89.28(13)
M−Cl
P1−M−P2
P1−M−Cl
P2−M−Cl
Figure 2. UV−vis spectra of complexes 4 and 5 (3.33 μM) upon
addition of ctDNA (0−0.3 mM) in 5 mM Tris−HCl/10 mM NaCl
buffer solution (pH = 7.2). The arrows show the direction of change in
absorbance upon increasing the concentration of the complex. Inset:
Plot of A0/(A − A0) vs 1/ [DNA].
presence of GSH, which may avoid deactivation too early
before reaching their targets.
Interaction with ctDNA. The experiment was carried out
keeping the concentration of complexes 1−5 constant (3.33
μM) and increasing the concentration of ctDNA (0−0.3 mM),
and the reaction solution was monitored by UV−vis spectros-
copy (Figure 2, Figure S3 in the Supporting Information, and
Table 5). Addition of increasing amounts of ctDNA results in
hypochromism at 214−220 nm and moderate bathochromic
shift (3−6 nm) for all complexes, indicating a significant
interaction with ctDNA, probably due to noncovalent binding
modes of electrostatic binding and/or intercalations between
base pairs.56,57 Intercalation into DNA by complexes often
causes bathchromism and hypochromism due to strong
stacking interaction between aromatic chromophore and base
pairs of DNA. Compared to the iridium complexes 1 and 2,
ruthenium complexes 3−5 caused more significant hypochrom-
ism.
Table 5. Absorption Spectroscopic Properties of the IrIII/
RuII Complexes on Binding to DNA
Absorption λmax
(nm)
a
Complex
Free
Bound
Δλ Hypochromicity (%)
Kb (M−1
)
1
2
3
4
5
215
214
218
223
219
218
219
224
225
223
3
5
6
2
4
22.0
21.0
44.1
42.5
45.9
6.4 × 104
3.1 × 103
1.6 × 104
4.1 × 103
3.6 × 104
a
[M] = 3.33 μM at [DNA]/[M] = 90.
Interactions of the complexes with ctDNA were fitted to the
Benesi−Hildebrand equation (eq 1) to calculate the binding
As the four complexes have the same P^P-chelating ligand
and overall charge on the complex, the difference between
binding constants is mainly related to the nature of the
cyclopentadienyl/arene ring and the metal ions. In general,
iridium complexes showed higher binding constants Kb than
ruthenium complexes, and Ir Cp* complex 1 displayed the
highest Kb to ctDNA in the four complexes tested. Sadler and
co-workers have previously reported that Cpxbiph complexes
displayed a much higher intercalative ability compared to their
Cp* analogues.28 However, in comparison with 1, substitution
of the methyl group with biphenyl decreases the Kb from 6.4 ×
104 M−1 to 3.1 × 103 M−1 (2 vs 1). The introduction of
functionalized ligand p-cym analogue increases the value of Kb
58
constants Kb
A0
(A − A0)
εf
εf
=
+
(εb − εf)
Kb(εb − εf)[DNA]
(1)
where εb and εf are the extinction coefficients of the complex in
bound and free form, respectively; A0 is the initial absorbance
of free complex, and A is the absorbance of the compound in
the presence of DNA. The plot of A0/(A − A0) versus 1/
[DNA] gives a straight line, and the binding constants (Kb)
were calculated as slope/intercept ratio (Figure 2 inset and
Figure S3 inset in the Supporting Information).
Table 3. In Vitro Anticancer Activity of Complexes 1−5 toward A549 and HeLa Cancer Cells and 16HBE and BEAS-2B Normal
Cells over 24 h
IC50 (μM)
Complex
A549
HeLa
16HBE
BEAS-2B
2.8 0.1
[(η5-Cp*)Ir(P^P)Cl]PF6 (1)
[(η5-Cpxbiph)Ir(P^P)Cl]PF6 (2)
[(η6-bz-PA)Ru(P^P)Cl]PF6 (3)
[(η6-bz-BA)Ru(P^P)Cl]PF6 (4)
[((η6-p-cym)Ru(P^P)Cl]PF6 (5)
Cisplatin
4.6 0.1
8.0 0.1
35.0 1.1
31.1 3.4
1.4 0.1
21.3 1.7
3.4 0.5
6.2 0.3
23.7 1.5
21.4 2.5
1.0 0.1
7.5 0.2
2.4 0.1
1.3 0.1
1.3 0.1
E
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by approximately 2.3 times compared to the 3-phenylpropan-1-
ol (5 vs 3) and about 9 times compared to the 4-phenylbutan-
1-ol.
Supporting Information). As NADH has a UV absorption at
339 nm while its oxidized form NAD+ has not, the turnover
numbers (TONs) of complexes 1 (4.1), 2 (4.1), 3 (5.6), 4
(6.2), and 5 (15.5) were calculated by measuring the intensity
changes at 339 nm (Figure 3B and Figure S6 in the Supporting
Information). Ruthenium complex 5 possesses the highest
TON among the four complexes, which is consistent with the
most potent anticancer activity of 5.
Reaction with NADH. In a wide range of biocatalyzed
processes, coenzyme nicotinamide adenine dinucleotide
NADH and its oxidized form NAD+ play crucial roles. Sadler
and co-workers have reported that aqua IrIII cyclopentadienyl
complexes can catalytically convert NADH to NAD+ and can
produce ROS H2O2 and thus offer an oxidant pathway.15,59
Therefore, reactions between metal complexes 1−5 and NADH
were investigated. First, complexes 1 and 5 were chosen again
because of their low IC50 values and their reactions with NADH
were monitored by 1H NMR. Mixed CD3OD-d4 and D2O (v/v
2:1) was used to enhance the solubility of IrIII/RuII complexes.
When NADH (5 mol equiv) was added to the above solution
of complexes 1 and 5 (1 mM), new peaks at 8.9, 9.3, and 9.5
ppm corresponding to NAD+ were observed, which indicates
NADH was converted into its oxidized form NAD+.
Interestingly, a singlet peak at −12.1 and −0.8 ppm,
corresponding to the Ru−H and Ir−H hydride peaks,
respectively, was observed after 2 h (Figure 3A and Figure S4
We showed that the IrIII cyclopentadienyl and the RuII arene
complexes catalyzed the NAD+/NADH hydride transfer
reactions effectively. RhIII derivative can drive enzymatic
reactions relying on NADH as a cofactor.60 The large downfield
shift of the Ir−H peak in [(η5-Cp*)Ir(P^P)H]+ is notable
compared to −11.1 ppm for [(η5-Cp*)Ir(phen)(H)]+.61 The
TON of complex 5 (15.5) is about 2 times that of the half-
sandwich IrIII C^N-bound phenylpyridine complex and is much
lower than that of the IrIII N^N complex (max. 75).15,18 The
good catalytic performance may offer a pathway to the
induction of ROS and a redox based MoA.
Electrochemical Properties. We performed cyclic voltam-
metry to further investigate the redox properties of the ligand
BINAP and complexes 1 and 5 due to their low IC50 values in
DMSO (Figure 4 and Figure S7 in the Supporting
Figure 4. Cyclic voltammograms of complexes 1 and 5 in anhydrous
DMSO solutions (1 mM), scan rate = 100 mV/s.
Information). All complexes were subject to two consecutive
scans from 2 to −3 V at a scan rate of 100 mV/s. The two
complexes showed similar electrochemical characteristics, and
three irreversible reduction processes arose at reduction wave
potentials of −2.10, −1.32, and 0.15 V for complex 1 and at
−2.00, −1.33, and 0.16 V for complex 5 (Figure 4). The
electrochemical data show that complexes with the same p^p
ligands have similar CV behaviors. Comparison of the cyclic
voltammograms of complexes 1 and 5 and ligand BINAP
indicates that the three irreversible waves of complexes 1 and 5
may be assigned to the reduction of the p^p ligand and that the
ancillary ligand BINAP has a significant effect on the electronic
properties of these complexes.
Apoptosis Assay. The two most promising complexes with
low IC50 values, 1 (iridium) and 5 (ruthenium), are selected to
carry out further investigations in order to shed light on their
mechanism of action. Apoptosis is a means of programmed cell
death. A great deal of metal based anticancer complexes inhibit
cell growth via an apoptosis pathway.62 In this work, we tried to
investigate whether the cytotoxicity of the complexes 1 and 5 is
due to apoptosis. A549 cancer cells were treated by the two
complexes at concentrations of 0.5, 1, 2, and 3 × IC50 for 24 h.
Annexin V and propidium iodide were used as stain agents, and
the treated cells were analyzed by flow cytometry. After 24 h,
complex 1 at a concentration of 0.5 × IC50 caused 9.7% and
15.1% of A549 cells in early apoptosis and late apoptosis,
respectively (Figure 5 and Table S1 in the Supporting
1
Figure 3. (A) H NMR spectra showing reaction of complex 5 (1
mM) in 67% CD3OD-d4 and 33% D2O (v/v) with NADH (5 mol
equiv) at 310 K after 10 min and 2 h. Peaks labeled correspond to
newly formed Ru−H complex. Inset: the generated Ru−H hydride
peak (−12.1 ppm). (B) Left: conversion of NADH (100 μM) to
NAD+ by complex 5 (1 μM) in 50% MeOH/50% H2O (v/v) recorded
by UV−vis at 298 K for 9 h. Right: TONs of complexes 1−5.
in the Supporting Information). Second, we investigated
whether these complexes could catalyticallyl convert NADH
to NAD+. Complexes 1−5 (1 μM) and NADH (100 μM) were
mixed in 50% MeOH/50% H2O (v/v) and monitored by UV−
vis at 298 K (Figure 3B and Figure S6 in the Supporting
Information). To evaluate the actual catalytic activity, we
incubated the 100 μM NADH in a 50% MeOH/50% H2O (v/
v) solution as the control experiments (Figure S5 in the
F
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Figure 5. Apoptosis of A549 cancer cells induced by complexes 1 and 5 (concentrations used: 0.5, 1, 2, and 3 × IC50) after 24 h at 310 K. Control:
cells untreated. (A) Apoptotic cell death examined by flow cytometry. (B) Bar chart showing cell populations in various phases.
Information). At 3 × IC50, cells in an apoptotic phase (early
apoptosis + late apoptosis) increased to 57.9%. Interestingly,
the ruthenium complex 5 displayed a much stronger ability to
induce apoptosis than iridium 1, where 79.1% of A549 cells
were in apoptosis at IC50 and 96.5% at 3 × IC50. This result is
consistent with their antiproliferative performance. The results
suggested that cell death caused by the complexes was induced
mainly through apoptosis.
Cell Cycle Analysis. Next the effect of complexes 1 and 5
on cell cycle was studied by flow cytometry at 0.25 and 0.5 ×
IC50 of 1 and 5 over 24 h (Figure 6, Table S2 in the Supporting
Information). Upon exposure of the A549 cells to 1 at
concentration of 0.5 × IC50, the percentages of cells in the S
and Sub-G1 phase increased 4.5% and 6.7%, respectively,
suggesting cell cycle disturbing at the S and Sub-G1 phase. The
obviously dose-dependent increased subdiploid peak usually
correlated to apoptosis (Figure 6A). For complex 5, the
percentages of cells in the G1 phase of the cell cycle increased
from 52.7% to 64.6% at concentration 0.5 × IC50, suggesting an
obvious cell cycle arrest at the G1 phase. In addition, a slight
apoptosis was observed as reflected by the small subdiploid
peak (Figure 6A) for complex 5 at 0.5 × IC50.
ROS Induction. Excessive generated reactive oxygen species
(ROS) often cause cell damage.15,63 In order to examine the
ROS levels in A549 cancer cells induced by complexes 1 and 5,
flow cytometry analysis was performed (Figure 7, Table S3 in
the Supporting Information). The ROS levels were found to be
significantly increased in cells upon exposure to 1 and 5 for 24
h. Even at 0.25 × IC50, about 68% and 86% of A549 cells were
at high ROS levels after exposure to 1 and 5, respectively
(Figure 7). Ruthenium complex 5 is a stronger ROS inducer
than the iridium complex 1. This result correlates well with
their antiproliferative behavior. These observations are
consistent with the proposed MoA for 1 and 5, which is
based on the disruption of the cellular redox balance.64 The
dramatically increased ROS levels contributed to the killing of
cancer cells.
The increased ROS levels in cells by complexes 1 and 5 may
be related to the catalytic conversion of NADH to NAD+.
Sadler and co-workers have previously reported the possible
chemical mechanisms of induction of ROS induced by iridium
complexes, involving catalytic hydride transfer from NADH to
iridium complexes to form iridium−hydride complexes and
finally to oxygen to produce the ROS H2O2 as a product.15
CONCLUSION
■
This work seems to be the first report of organometallic iridium
and ruthenium anticancer complexes containing BINAP as
P^P-chelating ligand. We have studied here the effects on the
chemical and anticancer activities by varying the Cpx and η6-
arene ligand in [(η5-Cpx)Ir(P^P)Cl]PF6 or [(η6-arene)Ru-
(P^P)Cl]PF6. Three X-ray crystal structures were determined.
Complexes 1−5 displayed from promising to highly potent
antiproliferative activity toward HeLa and A549 cancer cells
(Figure 8). Ruthenium complex 5 is the best candidate and is
15 times more potent than clinically used cisplatin toward A549
cells. The anticancer activity can be fine-tuned by changing
both metals and the cyclopentadienyl/arene ligands, in the
order of Cp* > Cpxbiph and p-cym > bz-BA > bz-PA.
Although interaction with ctDNA was observed, DNA
possibly is not the main target. The complexes are effective
catalysts for the oxidation of NADH to NAD+ using NADH as
the hydride source. This may induce ROS in cells. Indeed,
complexes 1 and 5 increased ROS levels significantly in A549
cells even at low concentration. In addition, the metal
complexes 1 and 5 disturbed the cell cycle at the Sub-G1
G
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Figure 6. A549 cell cycle arrest by complexes 1 and 5 (concentrations used: 0.25 and 0.5 × IC50) after 24 h at 310 K. Cell staining: PI. Control: cells
untreated. (A) Cell cycle analysis examined by flow cytometry. (B) Bar chart showing cell populations in various cell cycles.
Figure S8, complexes 1−5 are shown in Figures S10−S14 in the
Supporting Information.
phase/S phase and G1 phase, respectively. Additionally,
significant apoptosis was induced by complexes 1 and 5 in
A549 cancer cells. Complex 5 is more effective than complex 1
in the induction of ROS and apoptosis in A549 cells. This trend
is consistent with their anticancer activity. Here, we conclude
that the cytotoxicity of the complexes may be associated with
the redox mechanism of action. This type of metal complex is
worth further evaluation as chemotherapeutic agents.
Synthesis of Ligand 3′-(2,5-dihydrophenyl)propanol. A
solution of 3-phenylpropan-1-ol (3.00 g, 22 mmol) in ethanol (10
mL) was slowly added to a stirred, cooled solution of ammonia (250
mL) at −78 °C. Small pieces of sodium were added to the reaction
mixture until the blue colored persisted. During the addition of
sodium, a small amount of ethanol was added to facilitate stirring.
After the addition of sodium over the course of 4 h, the reaction
mixture was left overnight to evaporate ammonia. The reaction was
quenched carefully with ammonium chloride (sat., 100 mL), and
extracted by DCM (3 × 25 mL). The combined organic layer was
dried over magnesium sulfate, filtered and concentrated under reduced
EXPERIMENTAL SECTION
■
Materials. Unless otherwise noted, all manipulations were
performed using standard Schlenk tube techniques under nitrogen
atmosphere. The reagents IrCl3·nH2O (≥99% purity), hydrated
RuCl3·nH2O (≥99% purity), octan-1-ol (≥99%), and NaCl
(>99.999%), Nitric acid (72%), 2,3,4,5-tetramethyl-2-cyclopentenone
(95%), 1,2,3,4,5-pentamethyl-cyclopentadiene (95%), butyllithium
solution (1.6 M in hexane), 2,20-bis(diphenylphosphino)-1,10-
binaphthyl (BINAP) (98%) 4-phenylbutan-1-ol, 3-phenylpropan-1-ol,
α-terpinene were purchased from Sigma-Aldrich. CpxbiphH18 were
prepared as described. For the biological experiments, BSA, ctDNA,
DMEM medium, fetal bovine serum, penicillin/streptomycin mixture,
trypsin/EDTA, and phosphate-buffered saline (PBS) were purchased
from Sangon Biotech. Testing compounds was dissolved in DMSO
and diluted with the tissue culture medium before use.
1
pressure to afford colorless oil (2.80 g, 92% yield). H NMR (500
MHz, DMSO) δ 5.98 (d, J = 5.8 Hz, 1H), 5.74 (dd, J = 10.8, 5.7 Hz,
2H), 4.43 (t, J = 5.2 Hz, 1H), 3.42 (dd, J = 11.8, 6.3 Hz, 4H), 2.47−
2.40 (m, 2H), 1.60 (dd, J = 10.0, 5.5 Hz, 2H), 1.48 (dd, J = 14.7, 6.7
Hz, 2H).
Synthesis of [(η6-bz-PA)RuCl2]2 (dimer 3). The ligand 3′-(2,5-
dihydrophenyl)propanol (1.06 g,7.65 mmol) and RuCl3 (400 mg, 1.53
mmol) was dissolved in methanol (60 mL) in a dry round-bottom
flask equipped with stirrer and nitrogen atmosphere. The reaction
mixture was heated to reflux for 16 h and subsequently cooled to −18
°C. The precipitate was filtered off, washed with cold ethanol and
pentane (each 2 × 5 mL) and the red brown precipitate was dried in
vacuo. Yield: 80% (377.2 mg, 0.61 mmol) 1H NMR (500 MHz,
CDCl3) δ 7.32−7.23 (m, 2H), 7.23−7.08 (m, 3H), 3.64 (d, J = 6.5 Hz,
2H), 2.69 (d, J = 7.9 Hz, 2H), 1.91−1.85 (m, 2H), 1.77 (s, 1H).
Synthesis of Complexes 1−5. General method: The ligand 2,20-
bis(diphenylphosphino)-1,10-binaphthyl (BINAP) (0.10 mmol) and
1
Syntheses. The H NMR (500 MHz, CDCl3) peak integrals of
[(η6-bz-PA)RuCl2]2 (dimer 3) are shown in Figure S9 in the
Supporting Information. The 1H NMR (500 MHz, DMSO) peak
integrals of ligand 3′-(2,5-dihydrophenyl)propanol are shown in
H
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Figure 7. Induction of ROS levels in A549 cells by complexes 1 and 5 (concentrations used: 0.25 × IC50) after 24 h at 310 K. (A) ROS levels
analysis examined by flow cytometry. (B) Bar chart showing cell populations in high/low ROS levels.
1
[(η5-Cp*)Ir(P^P)Cl]PF6 (1). Yield: 61.73 mg, 54.6%. H NMR (500
MHz, DMSO) δ 7.96 (d, J = 9.0 Hz, 1H), 7.89−7.74 (m, 3H), 7.73−
7.62 (m, 7H), 7.51−7.42 (m, 2H), 7.40−7.30 (m, 2H), 7.27−6.97 (m,
11H), 6.96−6.81 (m, 4H), 6.50 (d, J = 8.7 Hz, 1H), 5.93 (d, J = 8.6
Hz, 1H), 1.12 (s, 15H). Anal. Calcd For [(η5-Cp*)Ir(P^P)Cl]PF6
(1130.53): C, 57.37; H, 4.19; P, 8.22; Found: C, 57.45; H, 4.30; P,
8.35. MS: m/z 951.13 [(η5-Cp*)Ir(P^P) + H]+.
[(η5-Cpxbiph)Ir(P^P)Cl]PF6 (2). Yield: 66.23 mg, 52.2%. 1H NMR
(500 MHz, DMSO) δ 7.96 (d, J = 10.0 Hz, 1H), 7.93−7.79 (m, 5H),
7.70 (d, J = 8.3 Hz, 4H), 7.66−7.52 (m, 5H), 7.46 (dd, J = 11.8, 7.7
Hz, 3H), 7.40−7.02 (m, 13H), 6.87 (ddd, J = 32.0, 18.2, 9.4 Hz, 8H),
6.53 (dd, J = 9.6, 3.6 Hz, 2H), 5.94 (d, J = 8.1 Hz, 1H), 1.76−1.58 (m,
6H), 0.97 (s, 3H), 0.79 (s, 3H). Anal. Calcd For [(η5-Cpxbiph)Ir-
(P^P)Cl]PF6 (1268.70): C, 61.54; H, 4.21; P, 7.32; Found: C, 61.65;
H, 4.13; P, 7.41. MS: m/z 1089.30 [(η5-Cpxbiph)Ir(P^P) + H]+.
Figure 8. IC50 values of the complexes studied in this work toward
A549 and HeLa cancer cells after an incubation of 24 h.
1
[(η6-bz-PA)Ru(P^P)Cl]PF6 (3). Yield: 64.71 mg, 62.2%. H NMR
(500 MHz, DMSO) δ 7.86 (d, J = 8.8 Hz, 2H), 7.79 (d, J = 8.2 Hz,
1H), 7.76−7.56 (m, 9H), 7.52−7.13 (m, 12H), 6.99 (dt, J = 25.7, 8.5
Hz, 3H), 6.85 (t, J = 6.7 Hz, 2H), 6.41 (d, J = 8.7 Hz, 1H), 6.16 (d, J =
6.5 Hz, 1H), 5.84 (t, J = 6.1 Hz, 2H), 5.74 (dd, J = 9.6, 5.6 Hz, 1H),
metal dimer [(η5-Cpx)IrCl2]2 or [(η6-arene)RuCl2]2 (0.05 mmol) was
4.86−4.80 (m, 1H), 4.59 (t, J = 6.5 Hz, 2H), 3.43−3.37 (m, 2H), 2.60
(dd, J = 10.4, 5.4 Hz, 1H), 2.36−2.29 (m, 1H), 1.71−1.60 (m, 2H).
Anal. Calcd For [(η6-bz-PA)Ru(P^P)Cl]PF6 (1040.35): C, 61.19; H,
4.26; O, 1.54; P, 8.93; Found: C, 61.06; H, 4.25; O, 1.59; P, 8.84. MS:
m/z 859.95 [(η6-bz-PA)Ru(P^P)]+.
dissolved in methanol in a dry round-bottom flask equipped with
stirrer and nitrogen atmosphere. After constant stirring for 4 h,
NH4PF6 (0.2 mmol) was added at room temperature. The reaction
mixture was stirred for 20 h at room temperature, and the progress of
reaction was monitored by TLC. After complete conversion, methanol
was removed under reduced pressure and product was dissolved in
dichloromethane and filtered through Celite filtration funnel and
recrystallized by slow diffusion of n-hexane in a concentrated solution
of the compound in dichloromethane to obtain the corresponding
complexes (1−5).
1
[(η6-bz-BA) Ru (P^P)Cl]PF6 (4). Yield: 58.20 mg, 55.2%. H NMR
(500 MHz, DMSO) δ 7.92−7.85 (m, 2H), 7.79 (d, J = 8.4 Hz, 1H),
7.69 (dd, J = 22.4, 7.9 Hz, 7H), 7.53−7.12 (m, 12H), 7.04−6.83 (m,
4H), 6.62−6.54 (m, 1H), 6.41 (d, J = 8.4 Hz, 1H), 6.16 (d, J = 6.3 Hz,
1H), 5.85 (dd, J = 10.0, 4.2 Hz, 2H), 5.75−5.68 (m, 1H), 4.85 (t, J =
I
DOI: 10.1021/acs.inorgchem.7b01959
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5.0 Hz, 1H), 4.58 (d, J = 5.9 Hz, 2H), 4.39 (dt, J = 30.6, 5.0 Hz, 2H),
2.60−2.54 (m, 1H), 2.46−2.42 (m, 1H), 2.28 (dt, J = 10.3, 6.7 Hz,
2H), 1.60−1.50 (m, 2H), 1.46−1.37 (m, 2H). Anal. Calcd For [(η6-bz-
BA)Ru(P^P)Cl]PF6 (1054.38): C, 61.51; H, 4.40; O, 1.52; P, 8.81;
Found: C, 61.43; H, 4.36; O,1.58; P, 8.73; MS: m/z 874.98 [(η6-bz-
BA)Ru(P^P) + H]+.
chelated imino-pyridyl ligands that are selectively toxic to cancer cells.
Chem. Commun. 2017, 53, 12810−12813.
(7) Leung, C.-H.; Zhong, H.-J.; Chan, D. S.-H.; Ma, D.-L. Bioactive
iridium and rhodium complexes as therapeutic agents. Coord. Chem.
Rev. 2013, 257, 1764−1776.
(8) Albada, B.; Metzler-Nolte, N. Organometallic−Peptide Bio-
conjugates: Synthetic Strategies and Medicinal Applications. Chem.
Rev. 2016, 116, 11797−11839.
1
[((η6 -p-cym)Ru(P^P)Cl]PF6 (5). Yield: 60.54 mg 58.3%. H NMR
(500 MHz, DMSO) δ 7.96 (s, 2H), 7.79 (d, J = 8.6 Hz, 2H), 7.77−
7.64 (m, 5H), 7.60 (t, J = 9.0 Hz, 2H), 7.48−7.09 (m, 9H), 7.02−6.91
(m, 2H), 6.90−6.85 (m, 1H), 6.84−6.73 (m, 2H), 6.35 (dd, J = 31.6,
7.9 Hz, 4H), 5.83 (d, J = 6.3 Hz, 2H), 5.77 (d, J = 9.1 Hz, 1H), 4.52
(d, J = 7.1 Hz, 2H), 4.32 (d, J = 4.1 Hz, 2H), 2.97−2.92 (m, 1H), 1.76
(s, 3H), 1.31 (d, J = 6.9 Hz, 3H), 0.95 (d, J = 6.7 Hz, 3H). Anal. Calcd
For [((η6-p-cym)Ru(P^P)Cl]PF6 (1038.38): C, 62.46; H, 4.47; P,
8.95; Found: C, 62.45; H, 4.48; P, 8.93. MS: m/z 858.98 [((η6-p-
cym)Ru(P^P) + H]+.
(9) Allardyce, C. S.; Dyson, P. J. Metal-based drugs that break the
rules. Dalton Trans. 2016, 45, 3201−3209.
(10) Prohl, M.; Schubert, U. S.; Weigand, W.; Gottschaldt, M. Metal
̈
complexes of curcumin and curcumin derivatives for molecular
imaging and anticancer therapy. Coord. Chem. Rev. 2016, 307, 32−41.
(11) Sava, G.; Giraldi, T.; Mestroni, G.; Zassinovich, G. Antitumor
effects of rhodium (I), iridium (I) and ruthenium (II) complexes in
comparison with cis-dichlorodiammino platinum (II) in mice bearing
Lewis lung carcinoma. Chem.-Biol. Interact. 1983, 45, 1−6.
ASSOCIATED CONTENT
(12) Messori, L.; Marcon, G.; Orioli, P.; Fontani, M.; Zanello, P.;
Bergamo, A.; Sava, G.; Mura, P. Molecular structure, solution
chemistry and biological properties of the novel [ImH][trans-IrCl4
(Im)(DMSO)],(I) and of the orange form of [(DMSO)2H][trans-
IrCl4(DMSO)2],(II), complexes. J. Inorg. Biochem. 2003, 95, 37−46.
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01959.
́
(13) Hearn, J. M.; Romero-Canelon, I.; Qamar, B.; Liu, Z.; Hands-
Experimental details; Figures S1−S14; and Tables S1−S3
(PDF)
Portman, I.; Sadler, P. J. Organometallic iridium (III) anticancer
complexes with new mechanisms of action: NCI-60 screening,
mitochondrial targeting, and apoptosis. ACS Chem. Biol. 2013, 8,
1335−1343.
Accession Codes
CCDC 1562301−1562303 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(14) Novohradsky, V.; Zerzankova, L.; Stepankova, J.; Kisova, A.;
Kostrhunova, H.; Liu, Z.; Sadler, P. J.; Kasparkova, J.; Brabec, V. A
dual-targeting, apoptosis-inducing organometallic half-sandwich iri-
dium anticancer complex. Metallomics 2014, 6, 1491−1501.
́
(15) Liu, Z.; Romero-Canelon, I.; Qamar, B.; Hearn, J. M.;
Habtemariam, A.; Barry, N. P.; Pizarro, A. M.; Clarkson, G. J.;
Sadler, P. J. The potent oxidant anticancer activity of organoiridium
catalysts. Angew. Chem., Int. Ed. 2014, 53, 3941−3946.
AUTHOR INFORMATION
■
(16) Li, Y.; Tan, C. P.; Zhang, W.; He, L.; Ji, L. N.; Mao, Z. W.
Phosphorescent iridium(III)-bis-N-heterocyclic carbene complexes as
mitochondria-targeted theranostic and photodynamic anticancer
agents. Biomaterials 2015, 39, 95−104.
Corresponding Author
*E-mail: liuzheqd@163.com.
ORCID
(17) Tabrizi, L.; Chiniforoshan, H. Designing new iridium (III) arene
complexes of naphthoquinone derivatives as anticancer agents: a
structure−activity relationship study. Dalton Trans. 2017, 46, 2339−
2349.
Zhe Liu: 0000-0001-5796-4335
Notes
The authors declare no competing financial interest.
(18) Wang, C.; Liu, J.; Tian, Z.; Tian, M.; Tian, L.; Zhao, W.; Liu, Z.
Half-sandwich iridium N-heterocyclic carbene anticancer complexes.
Dalton Trans. 2017, 46, 6870−6883.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(Grant No. 21671118) and the Taishan Scholars Program for
support. We thank Dr Abraha Habtemariam for stimulating
discussions.
(19) He, L.; Tan, C. P.; Ye, R. R.; Zhao, Y. Z.; Liu, Y. H.; Zhao, Q.; Ji,
L. N.; Mao, Z. W. Theranostic Iridium (III) Complexes as One-and
Two-Photon Phosphorescent Trackers to Monitor Autophagic
Lysosomes. Angew. Chem., Int. Ed. 2014, 53, 12137−12141.
(20) Sudding, L. C.; Payne, R.; Govender, P.; Edafe, F.; Clavel, C. M.;
Dyson, P. J.; Therrien, B.; Smith, G. S. Evaluation of the invitro
anticancer activity of cyclometalated half-sandwich rhodium and
iridium complexes coordinated to naphthaldimine-based poly-
(propyleneimine) dendritic scaffolds. J. Organomet. Chem. 2014, 774,
79−85.
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