Design, synthesis and anticancer activity of diam(m)ine platinum(II) complexes bearing a small-molecular cell apoptosis inducer dichloroacetate

Article abstract of DOI:10.1016/j.jinorgbio.2015.02.002

Four new diam(m)ine platinum complexes containing the dichloroacetate moiety in 3-dichoroacetoxylcyclobutane-1,1-dicarboxylate as the leaving group were synthesized, characterized by elemental analysis as well as by ESI⁺-MS (electrospray ionization mass spectrometry in positive mode), FT-IR, ¹H- and ¹³C-NMR, and evaluated for their in vitro anticancer activity against human lung cancer cell line (A549) and ovarian cancer cell lines (SK-OV-3, SK-OV-3/DDP). Diam(m)ines used in the present study belong to the carriers of six clinically approved platinum drugs. Among the complexes synthesized, complex 2, cis-[Pt(II)(1R,2R-diaminocyclohexane)·(3-dichoroacetoxylcyclobutane-1,1-dicarboxylate)] is the most promising in terms of water solubility and potential of being totally devoid of cross-drug resistance with cisplatin. Therefore, complex 2 was selected for the dichloroacetate release test. The test shows dichloroacetate can be efficiently released from complex 2 under physiological conditions via the hydrolysis of an ester bond bridging the dichloroacetate moiety and platinum pharmacophores together. Our study supports the further evaluation of this complex as a drug candidate.

Full text of DOI:10.1016/j.jinorgbio.2015.02.002

Journal of Inorganic Biochemistry 146 (2015) 14–18
Contents lists available at ScienceDirect
Journal of Inorganic Biochemistry
journal homepage: www.elsevier.com/locate/jinorgbio
Design, synthesis and anticancer activity of diam(m)ine platinum(II)
complexes bearing a small-molecular cell apoptosis inducer dichloroacetate
a
a
b
a
b
a
b,
Weiping Liu , Jing Jiang , Yongping Xu , Shuqian Hou , Liping Sun , Qingsong Ye , Liguang Lou ⁎
a
State Key Laboratory for Platinum Group Metals, Kunming Institute of Precious Metals, 650106 Yunnan, PR China
Shanghai Institute of Materia Medica, Chinese Academy of Science, Shanghai 201203, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new diam(m)ine platinum complexes containing the dichloroacetate moiety in 3-dichoroacetoxylcyclobutane-
Received 10 December 2014
Received in revised form 4 February 2015
Accepted 5 February 2015
+
1
,1-dicarboxylate as the leaving group were synthesized, characterized by elemental analysis as well as by ESI -MS
1
13
(electrospray ionization mass spectrometry in positive mode), FT-IR, H- and C-NMR, and evaluated for their
in vitro anticancer activity against human lung cancer cell line (A549) and ovarian cancer cell lines (SK-OV-3,
SK-OV-3/DDP). Diam(m)ines used in the present study belong to the carriers of six clinically approved
platinum drugs. Among the complexes synthesized, complex 2, cis-[Pt(II)(1R,2R-diaminocyclohexane)·(3-
dichoroacetoxylcyclobutane-1,1-dicarboxylate)] is the most promising in terms of water solubility and potential
of being totally devoid of cross-drug resistance with cisplatin. Therefore, complex 2 was selected for the
dichloroacetate release test. The test shows dichloroacetate can be efficiently released from complex 2 under
physiological conditions via the hydrolysis of an ester bond bridging the dichloroacetate moiety and platinum
pharmacophores together. Our study supports the further evaluation of this complex as a drug candidate.
Available online 12 February 2015
Keywords:
Platinum complexes
Anticancer activity
Drug resistance
Dichloroacetate
©
2015 Elsevier Inc. All rights reserved.
1
. Introduction
platinum complexes, however the outcomes of clinical trials remained
below expectations and none of these compounds has been approved
for clinical application [9].
In today's world malignant tumors have become one of the most
common and serious diseases, and rank first in human disease-
related lethality. Chemotherapy is a central component in the fight
against malignant tumors, and it is based on different classes of anti-
cancer drugs. Among them, platinum-based drugs represent an im-
portant class characterized by killing cancer cells primarily through
cross-linking DNA and inhibiting transcription [1,2]. Platinum-based
drugs now available for clinical options include cisplatin (DDP,
cis-diamminedichloroplatinum(II)), carboplatin, oxaliplatin, nedaplatin,
heptaplatin and lobaplatin, and they have been successfully used in the
treatment of solid tumors [3–5]. However, like other chemotherapy
agents, the clinical applications of platinum-based drugs are largely
restricted by side-effects as well as by drug resistance [6–8]. Ovarian
cancer is a typical example of drug resistance. Most women with ovarian
cancer respond fully to the initial cisplatin-based chemotherapy, but
as tumors recur, they develop resistance not only to cisplatin but also
to other platinum drugs. Drug resistance leads to the failure of
chemotherapy. As a result, ovarian cancer has the highest mortality
among gynecological cancers, highlighting the need for the development
of new strategies to overcome this drawback. One of the strategies
involves the synthesis and evaluation of non-classical platinum com-
pounds represented by picoplatin, polynuclear complexes, and trans-
Drug resistance can emerge from failure to execute apoptosis
despite initiation of the apoptotic cascade caused by either the predom-
inance of anti-apoptotic factors or defects in downstream effectors. It
has been demonstrated that failure to achieve final cell death after the
formation of platinum-DNA adduct might be an important factor
contributing to the drug resistance mechanisms in platinum-based
chemotherapy [10,11]. One innovative and efficient strategy for com-
bating this drug resistance, as highlighted by Dhara, Xiao and Lippard
[12,13], is to incorporate dichloroacetate groups into the existing
platinum drugs to form a prodrug. Dichloroacetate is a small-molecular
cell apoptosis inducer and can trigger apoptosis through selectively
targeting the mitochondria of cancer cells resistant to the anticancer
drugs [14–16]. The resulting complex molecules contain both the
platinum pharmacophore and dichloroacetate moiety displaying a
dual-functional profile. As a result, the enhanced drug sensitivity and
decreased resistance of tumor cells via a synergistic effect between
the two active components were verified. Furthermore, molecular
hybridization is an important drug discovery strategy which involves
the rational design of new chemical entities by the fusion of two drugs
[17].
Based on the above findings, we previously synthesized two mixed-
NH
3
/amine (amine = cyclopentylamine, cyclohexylamine) platinum(II)
complexes featuring a dichloroacetate moiety tethered to the leaving
group via an ester bond [18]. They exhibited markedly cytotoxicity
⁎
Corresponding author. Tel./fax: +86 21 50806056.
E-mail address: liguanglou1@126.com (L. Lou).
http://dx.doi.org/10.1016/j.jinorgbio.2015.02.002
162-0134/© 2015 Elsevier Inc. All rights reserved.
0

W. Liu et al. / Journal of Inorganic Biochemistry 146 (2015) 14–18
15
toward cancer cells by selectively inducing the apoptosis of cancer cells,
resulting in the decreased resistance of SK-OV-3 cancer cells to cisplatin.
Unfortunately, the two complexes appeared very insoluble in water
photodiode array detector was employed to determine the release
of dichloroacetate from the complexes.
(≈0.034 mg/ml), a physico-chemical character unfavorable as a drug
candidate. In the continuation of our interest to develop more effective
platinum anticancer drugs, a series of new platinum complexes, as
shown in Fig. 1, were designed based on the same strategy, synthesized
and biologically evaluated in the present studies. Four diam(m)ines
of clinically approved platinum drugs were used as the carriers
and dichloroacetate-containing 3-dichoroacetoxylcyclobutane-
2.2. General procedures for the synthesis of complexes 1–4
The synthetic procedures were carried out in light protected envi-
ronment when platinum complexes were involved. K [PtCl ] (10 g,
2 4
28 mmol) was dissolved in water (100 ml) and treated with KI (20.9 g,
126 mmol). After standing for 40 min at room temperature, a solution
1
,1-dicarboxylate as the leaving group, with the intention of optimizing
of NH
was added dropwise while stirring, yielding the corresponding interme-
diate cis-[PtA ] (A = 2NH or diamine) and the intermediate was
filtered off, washed with water and ethanol and dried in vacuo at 55 °C.
To a suspension of cis-[PtA ] (6.00 mmol) in 40 ml distilled water,
.039 g (12.00 mol) AgNO in 10 ml distilled water was added, and the
reaction mixture was stirred for 24 h at 35 °C. After the precipitated AgI
3
(34 mmol in 50 ml water) or diamine (28 mmol in 50 ml water)
the structures and improving the solubility of the resulting complexes.
I
2 2
2
3
2
. Experimental section
2 2
I
2
3
2
.1. Materials and instrument
2
+
2 2 2
was filtrated off, the resulting filtrate containing cis-[PtA (H O) ]
Potassium tetrachloroplatinate(II) and 1R,2R-diaminocyclohexane were
species was cooled down to 10 °C and then mixed with a freshly pre-
pared aqueous solution of potassium 3-dichoroacetoxylcyclobutane-1,1-
dicarboxylate (6.6 mmol). A white product precipitated. It was collected
immediately by filtration, washed with distilled icy water and ethanol,
dried under vacuum at 45 °C. Yield: 45% for complex 1, 60% for complex
2, 64% for complex 3, 55% for complex 4. The solubility of the resulting
complexes in different solvents was determined by AAS (atomic absorp-
tion spectroscopy).
purchased from Alfa Aesar, and trans-1.2-bis(methylamine)cyclobutane
was kindly provided by Hainan Changan International Pharmaceutical
Co., Ltd., China. 3-Dichoroacetoxylcyclobutane-1,1-dicarboxylic acid
and (4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1,3-dioxolane were
prepared as previously described [18,19]. All other chemicals obtain-
ed from commercial suppliers were of analytical grade and used as
received. Water was distilled prior to use. Composition analyses for
C, H and N were performed with a Carlo-Ebra instrument, whereas
the content of platinum was analyzed according to the method in
EP6.5. FT-IR spectra were measured in KBr pellets with a Perkin
Complex 1 found (% calculated for C
8 12 2 6 2
H N O Cl Pt): Pt 38.9 (39.2), C
+
19.1 (19.3), H 2.45 (2.40) and N 5.57 (5.62). MS-ESI m/z: 521
+
−1
([M + Na] , 19%). IR (KBr, cm ): 3430 (s, vO–H), 3281 (s, vN–H), 2953,
2857 (w, vC–H), 1749 (s, vC = O), 1631 (vs, vas(COO)), 1383 (vs, va(COO)),
1
13
Elmer 880 spectrometer. H and C NMR spectra were recorded in
DMSO on Brucker AV-400 MHz relative to TMS (tetramethylsilane)
as an external standard. Electrospray ionization mass spectra (ESI-
MS) were recorded on Agilent G6230 TOF MS equipped with an
electrospray ion source. A Waters Associates system equipped
with a 1525 pump, a 717 automated injector, and a Model 2998
1
1175 (m), 1023 (m), 894 (m), 819 (s) and 672 (m). H NMR (dmso, δ):
2.10, 2.22 (≈4H, 2CH
5.57 (≈6H, 2NH
2
, C-2, cyclobutane), 4.65 (≈1H, CH, cyclobutane),
13
3
2
), and 6.84 (≈1H, COCHCl ). C NMR (dmso, δ): 42.1
(C-2, cyclobutane), 48.1 (C-1, cyclobutane), 60.5 (C-4, dichloroacetoxyl),
−
71.0(C-3, cyclobutane), 164.8 (C = O), 177.3 and 177.6 (2COO ).
Fig. 1. Chemical structures of the designed platinum complexes.

16
W. Liu et al. / Journal of Inorganic Biochemistry 146 (2015) 14–18
Complex 2 found (% calculated for C14
H
20
N
2
O
6
Cl
2
Pt): Pt 33.4 (33.8),
A solution of complex 2 was prepared by simply dissolving 10 mg
complex 2 in 10 ml mixture solvent of water and methanol (50:50, v:v),
and kept in dark place at 22 °C or 37 °C. A 10 μL solution was taken at dif-
ferent time points for HPLC measurement. Comparing the peak area of the
degradation product from complex 2 to that of the reference at a known
concentration would offer the amount of complex 5. Based on the degra-
dation equation, the amount of complex 5 formed in the solution is equal
to the amount of dichloroactetate released from complex 2. The release
percentage of dichloroacetate was calculated from the degree of forma-
tion of complex 5.
+
C 29.4 (29.0), H 3.50 (3.46) and N 4.87 (4.84). MS-ESI m/z: 601
+
−1
(
2
(
[M + Na] , 100%). IR (KBr, cm ): 3441 (s, vO–H), 3246 (s, vN–H),
940, 2863 (w, vC–H), 1748 (s, vC = O), 1628 (vs, vas(COO)), 1378
vs, va(COO)), 1299 (m), 1176 (m), 1031 (m), 902 (w) and 819 (w). H
1
NMR (dmso, δ): 0.98, 1.18 (≈4H, 2CH
2
, C-c, cyclohexane), 1.43, 1.79
, C-b, cyclohexane), 1.97, 2.03 (≈4H, 2CH , C-2, cyclobutane),
.61, 2.65 (≈2H, 2CHNH , cyclohexane), 4.85 (≈1H, CH, cyclobutane),
2
.92, 5.20 (≈4H, 2CH NH ), and 6.87 (≈1H, COCHCl ). C NMR
(
2
5
(
3
≈4H, 2CH
2
2
2
13
2
2
dmso, δ): 24.0, 24.1 (C-c, cyclohexane), 31.4, 31.5 (C-b, cyclohexane),
7.7, 37.8 (C-2, cyclobutane), 48.9 (C-1, cyclobutane), 62.0, 62.2 (C-a,
cyclohexane), 64.8 (C-4, dichloroacetoxyl), 67.3 (C-3, cyclobutane),
2.4. In vitro anticancer activity
−
1
63.9 (C = O), 175.8 and 176.1 (2COO ).
Complex 3 found (% calculated for C16
H
24
N
2
O
8
Cl
2
Pt): Pt 30.8 (30.6),
Human cancer cell lines A549, SK-OV-3 were purchased from the
American Type Culture Collection (Manassas, VA, USA), and SGC-7901
was obtained from the Cell Bank of the Shanghai Institute for Biological
Sciences, Chinese Academy of Science (Shanghai, China), whereas
cisplatin-resistant SK-OV-3 cell line (SK-OV-3/DDP) was kindly provided
by Chinese Academy of Medical Sciences (Beijing, China). Cells
were grown in DMEM or RPMI-1640 medium containing 10% fetal
bovine serum and supplemented with 100 units/mL of penicillin and
100 μg/mL of streptomycin. Cells were maintained at 37 °C in a humid-
+
C 29.7 (30.1), H 3.77 (3.76) and N 4.35 (4.39). MS-ESI m/z: 639
+
(
[M + H] , 10%), and 368 ([M + H-leaving group]+, 70%). IR (KBr,
−
1
cm ): 3445 (s, vO–H), 3227 (s, vN–H), 2967, 2878 (w, vC–H), 1758
(
1
1
(
s, vC = O), 1631 (vs, vas(COO)), 1359 (vs, va(COO)), 1301 (m), 1169 (m),
1
095 (s), 1009 (m) and 819 (m). H NMR (dmso, δ): 0.89 (6H, 2CH
3
),
, cyclobutane), 4.20, 4.37
), 4.47 (2H, 2CH, 1,3-dioxolane), 4.78 (≈1H, CH,
cyclobutane), 5.27, 5.53 (≈4H, 2NH ), 5.88 (1H, CH, 1,3-dioxolane),
). C NMR (dmso, δ): 16.4, 16.5 (2CH
isopropyl), 31.3 (C-d, isopropyl), 37.9 (C-2, cyclobutane), 48.0 (C-1,
cyclobutane), 64.8 (C-4, dichloroacetoxyl), 67.1, 68.3 (2CH NH ), 70.7
C-3, cyclobutane), 79.5, 77.9 (C-b, 1,3-dioxolane), 106.9 (C-c, 1,3-
.73 (1H, CH, isopropyl), 2.54, 2.62 (4H, 2CH
NH
2
4H, 2CH
2
2
2
1
3
and 6.84 (≈1H, COCHCl
2
3
,
ified incubator with an atmosphere of 5% CO
2
.
In vitro anticancer activity was determined by MTT [3-(4,5-dimethyl-
2-thiazolyl)-2,5 diphenyl-2-H-tetrazolium bromide] assay. A 100 μL of
cell suspension was seeded in 96-well cell culture plates and allowed to
adhere overnight. The tested compounds were dissolved in DMSO just
before the incubation with cancer cells, and diluted in culture media at
the indicated concentrations. The cells were incubated with drugs for
72 h, and then a 20 μL of CellTiter 96® AQueous One Solution Reagent
(Promega, Madison, USA) was added and the cells were further incubated
at 37 °C for 1–2 h. Cell viability was measured by reading the absorbance
at the wavelength of 490 nm. Concentrations of 50% inhibition of growth
(IC50) were calculated on the basis of the relative survival curve.
2
2
(
−
dioxolane), 163.8 (C = O), 175.9 and 176.2 (2COO ).
Complex 4 found (% calculated for C14 Cl Pt): Pt 33.7 (33.8),
C 28.6 (29.0), H 3.49 (3.46) and N 4.81 (4.84). MS-ESI m/z: 601
H
20
N
2
O
6
2
+
+
−1
(
[M + Na] , 50%). IR (KBr, cm ): 3431 (s, vO–H), 3228(s, vN–H), 2944,
2
1
1
4
2
873 (w, vC–H), 1746 (s, vC = O), 1626 (vs, vas(COO)), 1357 (vs, va(COO)),
276 (s), 1212 (s), 1022 (m), 899 (m) and 817 (m). H NMR (dmso, δ):
1
.61, 1.85 (4H, 2CH
.31, 4.57 (4H, 2CH
2
NH ), and 6.87 (≈1H, COCHCl ). C NMR (dmso, δ): 22.3 (C-c), 37.7
2
), 2.29 (2H, 2CH), 2.51, 2.67 (4H, 2CH
2
, cyclobutane),
2
NH ), 4.85 (≈1H, CH, cyclobutane), 5.01, 5.30 (4H,
2
13
2
(
7
C-2), 49.0, 50.0 (C-b), 50.4 (C-1), 64.9 (C-a), 67.2 (C-4, dichloroacetoxyl),
1.0 (C-3), 163.9 (C = O), 176.5 and 177.5 (2COO ).
3. Results and discussion
−
3.1. Synthesis and characterization
2
.3. In vitro release studies of dichloroacetate from complex 2
Four designed complexes 1–4 containing a dichloroacetate moiety in
3
the leaving group and with 2NH or diamines as the carriers were
A HPLC (high performance liquid chromatography) was established to
determine the degradation of complex 2 or formation of cis-[Pt(II)(1R,2R-
diaminocyclohexane)·(3-hydroxylcyclobutane-1,1-dicarboxylate)]
namely complex 5 in Fig. 2). It was prepared according to the reported
synthesized as white precipitates in aqueous solution by the general
procedures (see Scheme 1) owing to their low water solubility.
Introduction of a dichloroacetate moiety into cyclobutane-1,1-dicarbox-
ylic acid had been previously described in our report [18]. Shortly,
(
method [20] and used as a reference for HPLC identification. We found
that complex 5 was very stable in water and did not undergo apparent
degradation within 72 h. Therefore it was also applied to HPLC quanti-
tative analysis as the reference in our measurements. The HPLC was
carried out on a Xterra C18 column (4.6 × 250 mm, 5 μm) at 40 °C
K
2
PtCl
4
was first converted to K
2
PtI
4
in situ by the treatment with KI,
followed by addition of 2NH
diam(m)inediiodoplatinum(II) intermediate. The quantitative reac-
tion of the intermediate with silver nitrate in water offered a solution
3
or diamines, forming an insoluble
2 2 2 3 2
of cis-[PtA (H O) ](NO ) which was finally transformed at a low
using a MeOH–H
2
O (29:71) system as the mobile phase. The flow rate
temperature to the target products by mixing with potassium 3-
dichoroacetoxylcyclobutane-1,1-dicarboxylate. The resulting platinum
complexes were characterized by elemental analysis as well as by
was 1.0 ml/min, and the peak was monitoring at λ = 215 nm. Under
these optimized chromatographic conditions, the peaks of two complexes
suitable for quantitative analysis developed, and were effectively sepa-
rated from each other with Rs N 2.5.
ESI -MS, FT-IR, 1H–, and C-NMR (Supplementary Fig. S1–S5),
+
13
and gave satisfactory analytical and spectroscopic data, which are in
Fig. 2. The release reaction of dichloroacetate from complex 2 in water.

W. Liu et al. / Journal of Inorganic Biochemistry 146 (2015) 14–18
17
Scheme 1. Synthetic routes of the target complexes.
accordance with their proposed structures (Fig. 1). The fusion of
dichloroacetate moiety was verified both by the development of a
3.3. In vitro anticancer activity
−
1
strong C = O vibration band approximately at 1750 cm
appearance of a distinct carbon resonance at 164 ppm belonging to
C = O of –OCOCHCl group.
and by
In vitro anticancer activity of the newly synthesized complexes 1–4
was determined by means of MTT assay [21] in the present work against
three human cancer cell lines representing two tumor entities: lung
carcinoma (A549) and ovarian carcinoma (SK-OV-3, SK-OV-3/DDP) in
comparison to cisplatin and carboplatin. Dichloroacetic acid was also
used as a reference. SK-OV-3/DDP is a cell line resistant to cisplatin with
a resistance index of 5-fold. The IC50 values, defined as the concentrations
corresponding to 50% growth inhibition, are presented in Table 1.
Dichloroacetic acid alone had negligible in vitro anticancer activity with
IC50 value up to 200 μM. This value is in accordance with the literature
that dichloroacetic acid needs millimolar doses to elicit cytotoxicity [12,
2
The solubility of four complexes in water was found to be 0.40, 0.48,
0
.083, 0.24 mg/ml at room temperature, respectively for complex 1, 2, 3
and 4, much more soluble than corresponding mixed-NH
3
/amine com-
plexes (0.034 mg/ml). All complexes are fairly soluble in methanol
(
≈5 mg/ml) and DMSO (10 mg/ml), and also have a good solubility
in polyethyleneglycol 400 (N5 mg/ml), a solvent which is frequently
used in the in vivo test. For these complexes no close relationship
could be deducted between the structure and solubility.
1
3]. In contrast, all the complexes bearing a dichloroacetate moiety
yielded IC50 values in the micro-molar range, displaying greater anti-
cancer activity. Among them, complex 2 is the most active, only less in
SK-OV-3, but greater in A549 and SK-OV-3/DDP than cisplatin. The
overall activity order is complex 2 N cisplatin N 1 N 3 N 4 N carboplatin,
suggesting that both the ligation of dichloroacetate and carriers have
an obvious influence on anticancer activity of the complexes. Complex
1 was established to have greater activity than its direct parent
carboplatin. This enhanced activity is attributed to the ligation of
dichloroacetate. For the four complexes with the same leaving group
(3-dichoroacetoxylcyclobutane-1,1- dicarboxylate) but different
carriers, the activity order is 2 N 1 N 3 N 4. This implies that when
1R,1R-diaminocyclohexane (the carrier of oxaliplatin) is used as a carrier,
it can render platinum drugs the best anticancer potency due to its unique
structure [22]. More significantly, All four complexes had some potential
(b2-fold) to overcome the resistance of SK-OV-3 cells to cisplatin, and
again complex 2 was found to be the most potent one. These results re-
veal that the fusion of dichloroacetate moiety endows platinum drugs
with ability to surmount drug resistance.
3
.2. In vitro release of dichloroacetate
As complex 2 has the greatest water-solubility among the com-
plexes we synthesized, it was selected for in vitro release studies of
dichloroacetate. The ester bond bridging dichloroacetate moiety and
the platinum pharmacophores together is weakened by the inductive
effects of two chlorines, making it relatively easy to be hydrolyzed in
water. The hydrolysis will result in the release of dichloroacetate. The
release percentages from complex 2 in the mixture solvent of water
and methanol (1:1, v:v) was monitored in our studies by an established
HPLC, and complex 5, one of the degradation products, was used as a
reference (Supplementary Fig. S1–S5). The release percentages with
the time at 22 and 37 °C are depicted in Fig. 3. The release profile is
mainly dependent on the temperature. The release was mild at room
temperature (22 °C), but much faster at physiological temperature
(
37 °C) and the release percentage was 100% within 48 h, indicating
that dichloroacetate can be efficiently released from complex 2 under
physiological conditions.
4. Conclusion
In our present study to develop new dichloroacetate moiety-
bearing platinum-based drugs, four diam(m)ine complexes of 3-
dichoroacetoxylcyclobutane-1,1-dicarboxylate as the leaving group
were synthesized. All are more water-soluble than the corresponding
mixed-NH
3
/amine and exhibit some ability to overcome the resistance
of cancer cells to cisplatin. Among them, complex 2, an oxaliplatin-
analogue, is most promising as a drug candidate, supported by its high
Table 1
In vitro anticancer activity of the tested compounds (t = 72 h, n = 3).
Compounds
IC50 (mean ± SD, μM)
Resistance indexa
A549
SK-OV-3
SK-OV-3/DDP
Complex 1
Complex 2
Complex 3
Complex 4
Carboplatin
Cisplatin
6.65 ± 0.52
0.61 ± 0.10
4.46 ± 0.51
7.14 ± 0.80
35.9 ± 2.3
1.76 ± 0.13
N200
7.69 ± 1.03
6.84 ± 0.92
13.5 ± 1.8
15.2 ± 2.0
42.0 ± 3.9
3.61 ± 0.44
N200
16.2 ± 1.9
6.57 ± 0.88
17.9 ± 1.9
22.0 ± 2.8
N100
≈2
≈1
≈1.3
≈1.5
N2.5
≈5
17.4 ± 2.3
N200
Cl
2
CHCOOH
Fig. 3. The release percentage of dichloroacetate from complex 2 (C
aqueous solution of methanol (v:v).
0
= 1.73 mM) in 50%
a
Resistance index is the ratio of IC50 value of resistant cells to that of sensitive cells.

18
W. Liu et al. / Journal of Inorganic Biochemistry 146 (2015) 14–18
[
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