Manganese(II) complexes of quinoline derivatives: Characterization, catalase activity, interaction with mitochondria and anticancer activity

Article abstract of DOI:10.1007/s11243-014-9876-z

In order to find mitochondria-targeted mimics of catalase that can attenuate the metabolism of oxygen for cancer chemotherapy, two complexes [Mn(QA)Cl₂] and [Mn(QA)(OAc)(H₂O)₂](OAc) (QA = 2-di(picolyl)amine-N-(quinoline-8-yl)acetamide) were synthesized and characterized by spectroscopic methods. In addition, the crystal structure of [Mn(QA)Cl₂] shows that the Mn(II) atom is coordinated by three N atoms (N1, N2,and N3), and one oxygen atom (O1) of the ligand QA, plus two chloride atoms (Cl1 and Cl2), forming a distorted octahedral geometry. The complex [Mn(QA)(OAc)(H₂O)₂](OAc) could disproportionate H₂O₂ in Tris-HCl solution at 37 °C, with K _cat/K _M = 9,226. Furthermore, both Mn(II) complexes were found to be active against the proliferation of HepG-2 cells and could attenuate the swelling of calcium-overloaded mitochondria. These results demonstrate that Mn(II) complexes of quinoline derivatives have potential as attenuators of the absorption of Ca²⁺ in mitochondria and can interfere with the metabolism of O₂ for cancer chemotherapy.

Full text of DOI:10.1007/s11243-014-9876-z

Transition Met Chem (2014) 39:917–924
DOI 10.1007/s11243-014-9876-z
Manganese(II) complexes of quinoline derivatives:
characterization, catalase activity, interaction
with mitochondria and anticancer activity
Zhi-Wei Wang
•
Qiu-Yun Chen Qing-Shan Liu
•
Received: 17 June 2014 / Accepted: 21 August 2014 / Published online: 4 September 2014
Ó Springer International Publishing Switzerland 2014
Abstract In order to find mitochondria-targeted mimics
of catalase that can attenuate the metabolism of oxygen for
Introduction
cancer chemotherapy, two complexes [Mn(QA)Cl ] and
2
The quinoline nucleus is a common substructure of many
biologically active compounds and occupies an important
position in medicinally relevant heterocyclic systems [1–
3]. Tasquinimod, an oral quinolone-3-carboxamide with
antitumor activity that is currently under investigation in
preclinical models of prostate cancer, has been tested in
patients with minimally symptomatic castration-resistant
prostate cancer, showing promising inhibitory effects on
the occurrence of metastasis. Although cisplatin and its
analogs have several major drawbacks, such as cumulative
nephrotoxicity and ototoxicity as well as inherent or
treatment-induced resistance, these drugs have provided
the motivation for developing novel metal complexes as
anticancer agents [4, 5]. Di(picolyl)amine (dpa) has been
used as a neutral, nondeprotonated chelating ligand capable
of complexing Zn(II), Cu(II), Fe(II, III), and Mn(II) atoms
to recognize proteins [6]. Previously, we found that a
[
Mn(QA)(OAc)(H O) ](OAc) (QA = 2-di(picolyl)amine-
2 2
N-(quinoline-8-yl)acetamide) were synthesized and char-
acterized by spectroscopic methods. In addition, the crystal
structure of [Mn(QA)Cl ] shows that the Mn(II) atom is
2
coordinated by three N atoms (N1, N2,and N3), and one
oxygen atom (O1) of the ligand QA, plus two chloride
atoms (Cl1 and Cl2), forming a distorted octahedral
geometry. The complex [Mn(QA)(OAc)(H O) ](OAc)
2
2
could disproportionate H O in Tris–HCl solution at 37 °C,
2
2
with K /KM = 9,226. Furthermore, both Mn(II) com-
cat
plexes were found to be active against the proliferation of
HepG-2 cells and could attenuate the swelling of calcium-
overloaded mitochondria. These results demonstrate that
Mn(II) complexes of quinoline derivatives have potential
2
?
as attenuators of the absorption of Ca in mitochondria
and can interfere with the metabolism of O for cancer
2
chemotherapy.
Mn(II) complex, [Mn(Adpa)(Cl)(H O)] (Adpa = bis(pyri-
2
dylmethyl)amino-2-propionic acid), could both target
mitochondria and inhibit the proliferation of human glioma
cells (U251) with IC50 value of 9.5 lM in vitro [7]. Hence,
there is the possibility that special Mn(II) complexes could
target cancer cells through an ATP-related Ca transporter.
2?
Mitochondrial Ca loading has profound consequences
for mitochondrial function, such as regulating cellular
respiration and mediating cell death by apoptosis or
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-014-9876-z) contains supplementary
material, which is available to authorized users.
2?
necrosis [8, 9]. The ability of the Ca ion to regulate both
cell death and proliferation offers the possibility of new
drug targets in cancer. In addition to attenuation of the
absorption of calcium in mitochondria, Mn(II) complexes
of di(picolyl)amine derivatives have been reported as
models for nonheme dioxygenase [10]. For example,
Mn(II) complexes of bis(2-pyridylmethyl)benzylamine can
Z.-W. Wang ꢀ Q.-Y. Chen (&) ꢀ Q.-S. Liu
School of Chemistry and Chemical Engineering, Jiangsu
University, Zhenjiang 212013, P.R.China
e-mail: chenqy@ujs.edu.cn
Q.-Y. Chen
State Key Laboratory of Coordination Chemistry, Nanjing
University, Nanjing 210093, P.R.China
123

9
18
Transition Met Chem (2014) 39:917–924
react with H O , resulting in intramolecular aromatic
2
a white solid, which was purified by silica gel column
chromatography using ethyl acetate and petroleum ether
(3:1, v/v) as the eluent to afford the product. Yield 0.75 g
(85 %). Anal. Calc. for C H N OCl: C 59.9 %, H 4.1 %,
2
hydroxylation (pro-oxidant) [11]. The manganese(II)
?
complex [Mn (l-OAc) L ] (L = bis(pyridyl methyl)a-
2
3 2
mine) and aminopyridine manganese(II) complexes were
1
1 9 2
found to disproportionate H O and produce highly valued
2
N 12.7 %. Found: C 59.8 %, H 3.9 %, N 12.6 %.
2
intermediates [12, 13]. Hence, manganese(II) complexes of
bis(2-pyridylmethyl)amine derivatives may disproportion-
ate H O or react with H O to produce an oxidant. Cel-
Synthesis of 2-di(picolyl)amine-N-(quinoline-8-
yl)acetamide
2
2
2 2
lular levels of H O directly or indirectly play a key role in
2
2
malignant transformation and in sensitizing cancer cells to
death. During the overexpression of H O -detoxifying
2-Chloro-N-(quinol-8-yl)-acetamide (0.75 g, 3.5 mmol),
di(picolyl)amine (0.56 g, 3 mmol), Et N (0.3 g, 3 mmol),
3
2
2
enzymes or catalase in vivo, H O concentration was
2
and potassium iodide (20 mg) were dissolved in acetoni-
trile (30 ml), and the mixture was stirred under reflux for
10 h under a nitrogen atmosphere. The mixture was cooled
to room temperature, and the solvent was removed to
obtain a yellow oil, which was purified by silica gel column
2
observed to decrease, and the cancer cells reverted to
normal appearance [14]. Cancer cells are more susceptible
to H O -induced cell death than are normal cells. There-
2
2
fore, manganese(II) complexes of N-substituted di(picol-
yl)amines could act as multifunctional complexes that
inhibit the proliferation of cancer cells by attenuating the
chromatography using ethyl acetate as eluent to afford the
1
product. Yield 0.8 g (70 %). HNMR (400 MHz, CDCl ):
3
2
?
absorption of Ca in mitochondria as well as dispropor-
tionation of H O . The combination of the quinoline group,
d 3.56 (s, 2H), 4.04 (s, 4H), 7.15–7.19 (m, 2H), 7.51–7.55
(m, 3H), 7.66 (d, J = 7.7 Hz, 2H), 8.00 (d, J = 7.9 Hz,
2H), 8.21 (d, J = 5.9 Hz, 1H), 8.54 (d, J = 4.9 Hz, 2H),
2
2
Mn(II) ligand and di(picolyl)amine, could give multifunc-
tional mimics of catalase against cancer cells. Here, we
report the syntheses, characterization, interaction with ct-
DNA and mitochondria, catalase activities, and antitumor
8.77–8.80 (m, 1H), 8.96 (d, J = 5.9 Hz, 1H), 11.62(s, 1H).
?
ESI–MS (in CH OH): m/z 384.31 [QA ? H] . IR (KBr,
3
-
1
cm ): 3,310 (m), 3,069 (m), 2,926 (m), 2,858 (m), 1,670
(s), 1,591 (s), 1,541 (m), 1,474 (m), 1,432 (m), 760 (s). UV–
activities of [Mn(QA)Cl ] (1) and [Mn(QA)(OAc)(H2-
2
4
3
-1
-1
O) ](OAc) (2) (QA = 2-di(picolyl)amine- N-(quinoline-8-
2
vis (EtOH/nm) (e 9 10 /dm mol cm ): 208 (5.6), 240
(6.6), 260 (2.3), 316 (1.2).
yl)acetamide).
Synthesis of complex 1
Experimental
To a stirred solution of QA (380 mg, 1 mmol) in ethanol
Materials and measurements
(5 ml), a solution of MnCl ꢀ4H O (198 mg, 1 mmol) in
2
2
ethanol (5 ml) was added dropwise. The mixture was
stirred at 80 °C for 2 h and then cooled to room tempera-
ture. After the solution was diffused with ethyl ether, a
yellow solid was obtained. Yield 0.40 g (80 %). Anal.
Calc. for C H Cl MnN O: C 54.2 %. H 4.1 %, N
All chemicals and solvents used for syntheses were of
reagent grade and used without further purification.
Tris(hydroxymethyl) aminomethane (tris) was obtained
from Sigma. Water was purified with a Millipore Milli-Q
system. The C, H, and N microanalyses were performed on
a Vario EL elemental analyzer. Electronic absorption
spectra were recorded in the 900–190-nm region using a
Varian cary 50-BIO UV–VIS spectrophotometer. Infrared
spectra were recorded on a Nicolet-470 spectrophotometer
2
3
21
2
5
13.7 %. Found: C 54.3 %, H 4.0 %, N 14.0 %. IR (KBr,
-
1
cm ): 3,298 (m), 3,069 (m), 2,908 (m), 1,660 (s), 1,591
(s), 1,542 (m), 1,474 (m), 1,430 (m), 764 (s). UV–vis
4
3
-1
-1
(EtOH/nm) (e 9 10 /dm mol cm ): 209 (4.2), 240
(3.5), 258 (2.7), 316 (0.8).
-
1
in the wavenumber range of 4,000–400 cm using KBr
pellets.
Synthesis of complex 2
Synthesis of 2-chloro-N-(quinol-8-yl)-acetamide
To a stirred solution of QA (380 mg, 1 mmol) in ethanol
(
5 ml), a solution of MnOAc ꢀ4H O (250 mg, 1 mmol) in
2
2
A solution of 2-chloroacetyl chloride (0.54 g, 4.8 mmol)
was dissolved in CH Cl (10 ml) and then added dropwise
ethanol (5 ml) was added dropwise. The mixture was
stirred at 80 °C for 2 h and then cooled to room tempera-
ture. After the solution was diffused with ethyl ether, a
brown solid was obtained and dried. Yield 0.44 g (75 %).
Anal. Calc. for C H MnN O : C 54.7 %. H 5.2 %, N
2
2
to a cooled stirred solution of 8-aminoquinoline (0.58 g,
mmol) and Et N (0.4 g, 4 mmol) in CH Cl (20 ml)
4
3
2
2
within 1 h. After being stirred for 2 h at room temperature,
the mixture was removed under reduced pressure to obtain
2
7
31
5 7
11.8 %. Found: C 53.2 %, H 5.1 %, N 12.3 %. IR (KBr,
1
23

Transition Met Chem (2014) 39:917–924
919
-
1
cm ): 3,424 (m), 3,060 (m), 2,908 (m), 1,558 (s), 1,423
s), 768 (s). ESI–MS (in CH OH): m/z 437.18 [Mn(QA-
Catalase-like activity
(
3
?
H)] (38 %), 468.22 [Mn(QA-H)(CH OH)] (100 %).
?
All of the reactions between the complexes and dihydrogen
peroxide were performed in buffered (Tris/Tris–HCl,
0.1 M, NaCl, 0.1 M, and pH = 7.4) or water solutions at 0
or 37 °C. The reactivity of the complexes with H O was
3
4
3
-1
-1
UV–vis (EtOH/nm) (e 9 10 /dm mol cm ): 210 (2.3),
57 (2.0), 358 (0.4).
2
2
2
X-ray crystallography
first investigated in water via UV–vis spectroscopy titration
at 37 °C. After a solution (10 ml) of the complex (0.1 M)
was stirred at 0 and 37 °C for 30 min, 0.5 ml of H
Crystallographic data for [(QA)MnCl ] (1) are listed in
2
O
2 2
Table 1. A colorless prism crystal of the complex was
selected for lattice parameter determination and collection
of intensity at 298 K on a Rigaku Mercury2 CCD Area
Detector with monochromatized Mo Ka radiation
aqueous solution (30 %) was added, and the spectra were
recorded at 2 min intervals at 37 °C. Volumetric mea-
surements of the evolved dioxygen produced during the
reaction of the complexes with H
O were taken in tripli-
2 2
(
k = 0.0710747 nm). A total of 6,893 reflections were
cate as follows: a 10-ml round-bottom flask containing the
-
3
collected, of which 4,449 reflections were observed with
I [ 2r(I). The structure was solved using direct methods
with the SHELXS-97 program [15], and the nonhydrogen
atoms were located from the trial structure and then refined
anisotropically with SHELXTL using full-matrix least-
required complex (1.0 9 10 M, 3.0 ml) in MeCN sol-
vent (or a buffered system) was placed in an ice
(273.0 ± 0.1 K) bath. The flask was closed with a rubber
septum, and a cannula was used to connect it to an inverted
graduated buret, filled with water. While the solution
containing the complex was being stirred, an aliquot of
2
squares procedures based on F values. The hydrogen atom
positions were fixed geometrically at calculated distances
and allowed to ride on the parent atoms. All calculations
were performed using the SHELX-97 programs.
0.5 ml of H O aqueous solution was added through the
2 2
septum using a microsyringe. The volume of oxygen pro-
duced was measured in the buret. The kinetics measure-
ments for both complexes were taken in MeCN solution at
3
7 °C. Different concentrations of H O were prepared by
2
2
Table 1 Crystal data and structural refinements of complex 1
diluting a 30 % H O aqueous solution with acetonitrile or
2
2
Tris–HCl buffer solution. The optimum reaction order of
the substrate with respect to the complexes was determined
by reacting different concentrations of each complex with a
constant concentration of substrate. Similarly, the optimum
reaction order of the complexes with respect to the sub-
strate was determined by reacting different concentrations
of substrate with a constant concentration of the complex.
Empirical formula
23 2 5
C H21Cl MnN O
Color/shape
Colorless/prism
509.29
Formula weight
Temperature/K
293(2)
Wavelength/nm
0.71073
Crystal system/space group
Orthorhombic/P 21 21 21
7.5725(15)
9.0909(18)
32.768(7)
90.00
a/nm
b/nm
Cytotoxicity assays
c/nm
a(°)
b(°)
c(°)
The cytotoxicity assays were carried using HepG-2 cell
lines. HepG-2 cells were cultured in DMEM medium
90.00
90.00
(
(
dulbecco’s minimum essential medium) containing 10 %
v/v) heat-inactivated fetal bovine serum, antibiotics (100
Final R indices [I [ 2r(I)]
1 2
R = 0.0426; wR = 0.0812
3
Volume/nm
2,255.8(8)
4
-
1
-1
U ml penicillin and 100 U ml streptomycin). All cells
Z
were grown at 37 °C in a humidified atmosphere in the
-
3
Density (calculated)/(gꢀcm
Absorption coefficient/mm
F(000)
)
1.500
0.848
1,044
presence of 5 % CO . Cells were seeded at a density of
2
-
1
4
9 10 cells/ml into 96-sterile-well plates and grown in
4
5
% CO at 37 °C. The test complexes were dissolved in
2
Crystal size/mm
0.32 9 0.3 9 0.28
DMSO and diluted with culture media. After 24 h, the
required complex was added, and the samples were kept for
h range for data collection/(°)
Index ranges
3.27 to 26.02
-6 B h B 9, - 9Bk B 11,
26 B l B 40
48 h. Cell viability was determined by the 3-[4,5-dimeth-
-
ylthiazol-2-yl]-2,5- diphenpyltetrazolium bromide (MTT)
assay by measuring the absorbance at 570 nm with an
ELISA reader. IC50 was calculated using software provided
by Nanjing University. Each test was performed in tripli-
cate. Comparisons were made by one-way analysis of
Reflections collected
6,893
4,449
1.051
Observed reflections [I [ 2r(I)]
2
Goodness of fit on F
R indices (all data)
1 2
R = 0.0498; wR = 0.0886
123

9
20
Transition Met Chem (2014) 39:917–924
variance. Differences were considered to be significant
when p\0.05. All experiments were repeated at least three
times.
free QA shows two pyridyl ring bands at approximately
-
1,591 and 1,541 cm ; strong peaks at 3,310 and
1
-
1
1,670 cm
were assigned to the m(N–H) and m(C=O)
stretching vibration frequencies, respectively. The out-of-
Mitochondrial swelling
plane deformation vibration of the pyridyl ring in the free
-
ligand occurred at 760 cm and is shifted to 764 and
1
-
1
Liver mitochondria were isolated by conventional differ-
ential centrifugation from adult rats [16]. The livers were
homogenized in 250-mM sucrose, 1-mM EGTA (ethyl-
enebis(oxyethylenenitrilo)tetraacetic acid), and 10-mM
768 cm in complexes 1 and 2, respectively (Fig. S2).
These shifts indicate that the pyridyl nitrogen atoms are
coordinated to the metal in both complexes [17, 18]. The
shift toward lower frequencies for the m(C=O) vibration
-
1
-1
HEPES
(4-(2-hydroxyethyl)piperazine-1-ethanesulfonic
from 1,670 cm
in the free ligand to 1,660 cm
in
acid) buffer (pH 7.4). The mitochondrial suspension was
washed twice with the same medium containing 0.1-mM
EGTA, and the pellet was resuspended in 250-mM sucrose
to a final protein concentration of 80–100 mg/ml. Mito-
chondria (0.4 mg of protein) were incubated in 1.5 ml of a
medium containing 125-mM sucrose, 65-mM KCl, 10-mM
HEPES–KOH, pH 7.4, and 5-mM potassium succinate
complex 1 indicates that the oxygen atom also coordinates
to the metal, which is consistent with the crystal structure. A
-
strong peak at 3,400 cm for complex 2 is assigned to
1
m(O–H) asymmetric stretching frequencies, showing the
-
presence of water molecules. Complex 2 shows m (OAc )
as
-
1
-
-1
at 1,558 cm and m (OAc ) at 1,423 cm , indicating the
as
presence of carboxylate. Thermal analysis (TG) curves of
complex 2 in the range 0–1,000 °C are shown in Fig. S3.
The thermal decomposition of the [Mn(QA)(OAc)(H2-
(
?2.5 lM rotenone) at 25 °C. Each test complex was
dissolved in H O and diluted with culture media. Various
2
concentrations of the tested complexes (1–100 lM) were
added to the assay mixture. Swelling was initiated by the
O) ](OAc) (2) proceeds in two distinguishable steps. The
2
first falls in the range of 25–210 °C, which is assigned to the
addition of 50-lM CaCl to the sample cuvette at 25 °C.
loss of two H O ligands with a weight loss 6.20 % (calcd.
2
2
Ciclosporin A (5 lM) was used as a positive reference.
Mitochondrial swelling was estimated from the decrease in
absorbance at 540 nm measured with a Hitachi U-2000
spectrophotometer. The extent of mitochondrial swelling
was assayed by measuring the decrease in absorbance
6.08 %). A further 52.62 % weight loss in the range of
-
210–440 °C corresponds to two CH COO and di(pyri-
3
dylmethyl)amine groups from the ligand (calcd 53.37 %).
The thermal decomposition data are consistent with the
proposed structure of complex 2. In the mass spectrum of
[Mn(QA)(OAc)(H O) ](OAc) (2), the main peak at m/
(
A) at 540 nm, and the inhibitory rate of mitochondrial
2
2
swelling was calculated as follows: (DAcontrol-DAdrug)/
DAcontrol 9 100 %, DA = DA0min-A.
z = 468.22 (100 %) corresponds to species [Mn(QA-
?
H)(CH OH)] , while a peak at m/z = 437.18 (38 %) is
3
?
assigned to species [Mn(QA-H)] (Fig. S4). ES-MS data
indicate that complex 2 is a mononuclear manganese(II)
species.
Results and discussion
Synthesis and characterization of the complexes
Crystal structure of complex 1
2
-Di(picolyl)amine-N-(quinoline-8-yl)acetamide (QA) was
synthesized by conjugating dpa (di(picolyl)amine) and
-chloro-N-(quinol-8-yl)acetamide, which was prepared
The crystal structure of complex 1 with the atomic labeling
scheme is shown in Fig. 1, and selected bond lengths and
angles are listed in Table 2. QA acts as a tetradentate ligand
toward the Mn(II) atom, which is coordinated by three N
atoms (N1, N2, and N3), one oxygen atom (O1) of QA and
two chloride ligands (Cl1, Cl2), resulting in a six coordinate
mononuclear Mn(II) complex. Complex 1 shows a distorted
octahedral geometry similar to a previous reported dinuclear
manganese(II) complex [Mn(Aldpa)Cl(l-Cl)]2 (Ald-
pa = N-allyl di(picolyl)amine) [19]. Atoms Cl2, N3, N1,
and N2 form the equatorial tetragonal plane (mean deviation
2
from 8-aminoquinoline and 2-chloroacetyl chloride. Com-
plexes 1 and 2 were synthesized by treating QA with
MnCl ꢀ4H O and MnOAc ꢀ4H O, respectively, in 1:1
2
2
2
2
molar ratio in ethanol solution. Both complexes show a
typical absorption band at 260 nm due to a p ? p* tran-
sition involving the pyridine groups of the ligand. Two
obvious strong bands at 240 nm and 316 nm are attributed
to the p ? p* and n ? p* transitions, respectively, of the
ligands. The typical absorption of the quinoline ring in
complex 2 is shifted to 358 nm compared to the free ligand
and complex 1 with a absorption at 316 nm. This suggests
that the quinoline nitrogen may be coordinated with man-
ganese in complex 2 (Fig. S1). The FTIR spectrum of the
˚
0.0327 A), while Cl1 and O1 occupy the apical positions.
˚
The Mn(II) atom is shifted by 0.3993 A out of the equatorial
plane toward Cl1. The Mn(1)–Cl(1) and Mn(1)–O(1) bond
˚
distances are 2.4496 (9) A and 2.294 (2) A, respectively, and
˚
the Cl(1)–Mn(1)–O(1) angle is 166.17 (6)°.
1
23

Transition Met Chem (2014) 39:917–924
921
Fig. 1 Crystal structure of
complex 1. Thermal ellipsoids
are drawn at 30 % probability;
hydrogen atoms are omitted
Table 2 Selected bond lengths (nm) and bond angles (°) for complex
1
Mn(1)–N(3)
2.278(2)
2.294(2)
2.298(2)
2.3819(9)
2.379(2)
2.4496(9)
84.45(8)
143.66(9)
94.84(7)
94.31(7)
93.37(6)
O(1)–Mn(1)–N(2)
N(3)–Mn(1)–Cl(2)
O(1)–Mn(1)–Cl(2)
N(2)–Mn(1)–Cl(2)
N(3)–Mn(1)–N(1)
O(1)–Mn(1)–N(1)
N(2)–Mn(1)–N(1)
Cl(2)–Mn(1)–N(1)
O(1)–Mn(1)–Cl(1)
Cl(2)–Mn(1)–Cl(1)
78.58(8)
103.25(7)
92.34(6)
109.29(7)
71.95(8)
73.25(8)
72.46(9)
165.02(6)
166.17(6)
101.24(3)
Mn(1)–O(1)
Mn(1)–N(2)
Mn(1)–Cl(2)
Mn(1)–N(1)
Mn(1)–Cl(1)
N(3)–Mn(1)–O(1)
N(3)–Mn(1)–N(2)
N(3)–Mn(1)–Cl(1)
N(2)–Mn(1)–Cl(1)
N(1)–Mn(1)–Cl(1)
Catalase-like activity
A kinetic study of H O disproportionation was carried out
Fig. 2 Rates of the O
[
2
evolution of the complexes at 37 °C in MeCN,
2 2
complex] = 1 mM, 0.5 mL of 30 % H O aqueous solution,
2
2
V
MeCN = 5 mL. Complex 2 (triangle), complex 1 (cross)
by measuring the volume of O evolved in the presence of
2
these complexes. The H O disproportionation promoted
2
2
The parameter Kcat was calculated with the Eq. (2) [17,
by complexes 1 and 2 was carried out in MeCN at 37 °C
Fig. 2). Less O evolution was observed when complex 1
was incubated with H O compared to complex 2, due to
1
8]. The maximum O evolution rates were about 23.4 and
2
(
2
-
1
1
0.3 mM s for complex 2 at 37 °C in MeCN and in Tris–
2
2
-
HCl solution, respectively, which is larger than the previously
the presence of a bridging l-Cl ligand in complex 1 [20–
-
1
reported [Mn (Adpa) (OAc)(H O) ](OAc) (5.4 mM s
at
7 °C in Tris–HCl solution) [23]. The Hill constants obtained
for complex 2 both in MeCN and in buffered solutions were
.6 ± 0.58 and 1.8 ± 0.34, respectively, showing that com-
2
2]. Complex 2 in MeCN and buffered solution at 37 °C
2
2
2
2
3
was a better catalyst for O evolution (Fig. 3). The plot of
2
the initial rate versus the concentration of the H O was
2
2
3
fitted using the Hill Eq. (1) (Fig. S5, Fig. S6).
plex 2 can form a high value intermediate when it reacts with
H O [24]. Complex 2 exhibits high affinity for dihydrogen
peroxide with the Km value of 3.1 mM in Tris–HCl. The
n
n
V0 ¼ Vmax½sꢁ =ðKm þ ½sꢁ Þ
Kcat ¼ Vmax=½Etꢁ
ð1Þ
ð2Þ
2
2
123

9
22
Transition Met Chem (2014) 39:917–924
2
Fig. 4 Inhibition for complexes 1 and 2 on the Ca -induced
mitochondria swelling
?
Fig. 3 Rates of the O
2
evolution of complex 2 at different conditions,
.5 mL of 30 % H O aqueous solution, Vsolvent = 5 mL. [complex
0
2
3
2 2
] = 0.34 mM, 37 °C in MeCN (filled circle), [complex 2] = 1 mM,
7 °C in Tris–HCl (triangle), 0 °C in Tris–HCl (cross)
2
?
generation, which induces the release of Ca from the
endoplasmic reticulum and leads to enhanced uptake of
2?
turnover number Kcat of complex 2 in MeCN and Tris–HCl
-1
solutions is 65 and 28.6 s , respectively, indicating that
Ca by mitochondria. Both complexes can inhibit the
2
swelling of Ca -overloaded mitochondria, indicating that
?
complex 2 is a good catalase mimic. The values of k /K for
M
cat
2
they may interfere with the Ca transport system, which is
?
complex 2 in MeCN and Tris–HCl are 81,250 and 9,226,
respectively, which is higher than most reported Mn(II)
complexes [25–28] (Table 3). The conditions of the reaction
carried out at 37 °C in Tris–HCl solution are close to those
found in cultured cells (37 °C, pH 7.0), suggesting that the
complex 2 might also show good catalase activity in vivo.
similar to the complex [Mn(Adpa)(Cl)(H O)] [7]. Com-
2
paring with manganese(II) complexes of N-substituted
di(picolyl)amines as previously reported [7, 19, 23], it is
found that only mononuclear complexes of dpaMn
(dpa = di(picolyl)amine) can inhibit the swelling of cal-
cium-overloaded mitochondria (Scheme 1), while the
polynuclear Mn(II) complexes with same ligands show no
inhibition on the swelling of calcium-overloaded mito-
chondria [23]. We deduce that the structures of these
Mn(II) complexes may be the key factor for their attenu-
ation of mitochondrial swelling.
Interactions with mitochondria
Mitochondrial swelling is an important method to detect
mitochondrial functions [29]. The interactions of com-
plexes 1 and 2 with mitochondria were studied by mea-
2?
suring the Ca -loaded mitochondrial swelling (Fig. 4).
Complexes 1 and 2 (100 lM) can inhibit the swelling of
calcium-overloaded mitochondria, indicating that an
interaction between the Mn(II) complexes and mitochon-
dria takes place. Mitochondria are involved in the main-
Inhibition of cancer cell proliferation
Complexes 1 and 2 were studied for their antitumor activity
in vitro by determining their inhibition against growth of
cancer cells HepG-2 using the method of MTT reduction.
5-Fluorouracil was used as a positive control for
2
?
tenance of intracellular Ca homeostasis. One feature of
tumor cells is their dependence on glycolysis for ATP
Table 3 Catalytic activity of manganese catalase and synthetic catalase mimics
-1
)
-1
-1
)
Complex
K
M
(mM)
kcat (s
k
cat/K
M
(s
M
Hill constant n
Ref
5
4
6
Thermus thermophilus catalase
Thermoleophilum album catalase
83
15
2.6 9 10
2.6 9 10
1,070
250
3.1 9 10
1.7 9 10
34,000
1,000
–
[21]
6
–
[22]
[
[
[
[
Mn (bpia)
2
IV
Mn salpn(l-O)]
2
(l-OAc)
2
](ClO
4
)
2
31.5
–
[23]
2
250
–
[24]
(Adpa)
(Adpa)
2
Mn
Mn
2
(l-OAc)](OAc) (in MeCN)
(l-OAc)](OAc) (in Tris–HCl)
1.44 ± 0.27
1.76 ± 0.32
0.8
6.28
4,361.1
5,615.8
81,250
9,226
3.44 ± 0.58
3.24 ± 0.37
3.6 ± 0.58
1.8 ± 0.34
[19]
2
2
9.88
[19]
Complex 2 (in MeCN)
65
This work
This work
Complex 2 (in Tris–HCl)
3.1
28.6
1
23

Transition Met Chem (2014) 39:917–924
923
Scheme 1 Mn(II) complexes
that can attenuate the swelling
of calcium-overloaded
mitochondria and signal the
apoptosis of cancer cells
Complex (1)
dria, we deduce that the complex 2 could be used as a low
toxicity complex to attenuate the metabolism of oxygen for
cancer recovery chemotherapy in the future.
1
00
8
6
4
2
0
0
0
0
0
Conclusion
The Mn(II) complexes [Mn(QA)Cl2] (1) and
[Mn(QA)(OAc)(H O) ](OAc) (2) are both active against
2
2
HepG-2 cells, with IC50 values of 11.03 lM and 52.24 lM.
Both complexes exhibit good inhibition of the swelling of
calcium-overloaded mitochondria. In particular, the com-
plex 2 is a good mimic of catalase, so that it can be used as
a mitochondria-targeted catalase mimic to attenuate the
5
10
15
20
25
µmol/L
Fig. 5 Concentration-dependent inhibition activities of complex 1 on
HepG-2 cell lines. The samples were kept with the complex for 48 h.
All experiments were repeated at least three times
metabolism of oxygen. Cancer cells use O to generate
2
excessive levels of ROS and H O . The alteration in the
2
2
metabolism of O by catalase mimics plays an important
2
cytotoxicity [30]. Both complexes were active against
HepG-2 cells, giving IC50 values of 11.03 and 52.24 lM,
respectively, for complexes 1 and 2 (Fig. 5, Fig. S7 and
Table S1). Since H O is considered to be a mediator of
role in carcinogenesis. We suggest that the Mn(II) com-
plexes of quinoline derivatives could be developed further
as mitochondrial-related anticancer agents.
2
2
apoptotic cell death, the elimination of the H O is
2
2
important for protection against oxidative stress. The dif-
Supplementary material
ferent IC50 values of complexes 1 and 2 are possibly due to
their H O discriminating ability, which may affect the
2
2
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Cen-
tre, CCDC No. 1008721 for 1. The data can be obtained
free of charge via http://www.ccdc.cam.ac.uk or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB21EZ, UK; fax: (?44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
metabolism of oxygen and the production of ROS signaling
apoptosis in cancer cells. Attenuation of the functions of
the mitochondria, the antioxidant properties of these
manganese(II) complexes, and their catalase activities may
all be important factors in their anticancer activities.
Considering the IC50 values and the effect on mitochon-
123

9
24
Transition Met Chem (2014) 39:917–924
Acknowledgments We thank the financial support from National
Science Foundation of China (21271090).
13. Groni S, Dorlet P, Blain G, Bourcler S, Guillot R, Anxolabehere-
Mallart E (2008) Inorg Chem 47:3166–3172
1
1
4. L o´ pez-L a´ zaro M (2007) Cancer Lett 252:1–8
5. Sheldrick GM (1997) SHELXTL-97, Program for Crystal
Structure Solution and Refinement. University of G o¨ ttingen,
Germany
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