Transition metal complexes with 6,7-dichloro-5,8-quinolinedione as mitochondria-targeted anticancer agents

Article abstract of DOI:10.1016/j.poly.2020.114482

Herein, a series of transition metal complexes, [Zn(DQ)₂(CH₃OH)₂] (1), [Zn(DMQ)₂(CH₃OH)₂] (2), [Co(DQ)₂(CH₃OH)₂] (3), [Co(DMQ)₂(CH₃OH)₂] (4), [Ni(DQ)₂(CH₃OH)₂] (5), [Cu(DMQ)₂(CH₃OH)₂] (6), [Mn(DQ)₂(H₂O)₂] (7) and [Mn(DMQ)₂(H₂O)₂] (8), containing 6,7-dichloro-5,8-quinolinedione (DQ) and 6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands have been synthesized and characterized as potential antitumor agents. These complexes 1–8 exhibited evident anti-tumor activity in HeLa (cervical), MCF-7 (breast), Hep-G2 (hepatoma), T-24 (bladder), and SK-OV-3 (ovarian) human cancer cells. Interestingly, complexes 1–8 showed higher cytotoxicity than cisplatin against human cervical HeLa cells, and less cytotoxicity on the HL-7702 nontumorigenic cells. Mechanism studies suggested that complexes 1 and 2 arrested the cell cycle in the G1 phase and induced cancer cell death through mitochondrial dysfunction pathways. The cytotoxicity of 2 was higher than that of 1. The different biological behavior of 1 and 2 may correlate with the presence of a 2-methyl group in 6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligand. In general, our study demonstrated that Zn(II) complex 2 with 6,7-dichloro- 2-methyl-5,8-quinolinedione showed high potential to be developed as a mitochondria-targeted metal antitumor agent.

Full text of DOI:10.1016/j.poly.2020.114482

Journal Pre-proofs
Transition metal complexes with 6,7-dichloro-5,8-quinolinedione as mito‐
chondria-targeted anticancer agents
Bi-Qun Zou, Xiao-Ling Huang, Qi-Pin Qin, Zhen-Feng Wang, Xue-Yu Wu,
Ming-Xiong Tan, Hong Liang
PII:
DOI:
Reference:
S0277-5387(20)30139-X
https://doi.org/10.1016/j.poly.2020.114482
POLY 114482
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
29 July 2019
26 February 2020
28 February 2020
Please cite this article as: B-Q. Zou, X-L. Huang, Q-P. Qin, Z-F. Wang, X-Y. Wu, M-X. Tan, H. Liang,
Transition metal complexes with 6,7-dichloro-5,8-quinolinedione as mitochondria-targeted anticancer agents,
Polyhedron (2020), doi: https://doi.org/10.1016/j.poly.2020.114482
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Elsevier Ltd. All rights reserved.

Transition metal complexes with 6,7-dichloro-5,8-quinolinedione
as mitochondria-targeted anticancer agents
Bi-Qun Zou,a,b,c Xiao-Ling Huang,b Qi-Pin Qin,*b,c Zhen-Feng Wang,b Xue-Yu Wu,b
Ming-Xiong Tan,*b,c Hong Liang*c
a Department of Chemistry, Guilin Normal College, 9 Feihu Road, Gulin 541199, China.
b Guangxi Key Lab of Agricultural Resources Chemistry and Biotechnology, College of Chemistry
and Food Science, Yulin Normal University, 1303 Jiaoyudong Road, Yulin 537000, PR China.
c
State Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources,
School of Chemistry and Pharmacy, Guangxi Normal University, 15 Yucai Road, Guilin 541004,
PR China.
Corresponding author. E-mail: qpqin2018@126.com (Q.-P. Qin), mxtan2018@126.com (M.-X.
Tan), Tel./Fax.: +86-775-2623650; E-mail: hliang00@126.com (H. Liang). Fax
+86-773-2120958.
1

Abstract
Herein, a series of transition metal complexes, [Zn(DQ)2(CH3OH)2] (1),
[Zn(DMQ)2(CH3OH)2] (2), [Co(DQ)2(CH3OH)2] (3), [Co(DMQ)2(CH3OH)2] (4),
[Ni(DQ)2(CH3OH)2] (5), [Cu(DMQ)2(CH3OH)2] (6), [Mn(DQ)2(H2O)2] (7) and
[Mn(DMQ)2(H2O)2] (8), containing 6,7-dichloro-5,8-quinolinedione (DQ) and
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands have been synthesized and
characterized as potential antitumor agents. These complexes 1−8 exhibited evident
anti-tumor activity in HeLa (cervical), MCF-7 (breast), Hep-G2 (hepatoma), T-24
(bladder), and SK-OV-3 (ovarian) human cancer cells. Interestingly, complexes 1−8
showed higher cytotoxicity than cisplatin against human cervical HeLa cells, and less
cytotoxicity on the HL-7702 nontumorigenic cells. Mechanism studies suggested that
complexes 1 and 2 arrested the cell cycle in the G1 phase and induced cancer cell
death through mitochondrial dysfunction pathways. The cytotoxicity of 2 was higher
than that of 1. The different biological behavior of 1 and 2 may correlate with the
presence of a 2-methyl group in 6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ)
ligand. In general, our study demonstrated that Zn(II) complex 2 with 6,7-dichloro-
2-methyl-5,8-quinolinedione showed high potential to be developed as a
mitochondria-targeted metal antitumor agent.
Keywords: 6,7-dichloro-2-methyl-5,8-quinolinedione, Zn(II) complex, cell apoptosis,
mitochondrial dysfunction
2

1. Introduction
Cisplatin and its analogues are widely used for the treatment of tumors.[1–24]
However, the clinical success of cisplatin and its derivatives are limited by high
toxicity and significant side effects.[1–25] Researchers are designing new
non-platinum drugs to overcome these drawbacks. [26–36] Many transition metal
complexes, such as Pt(II), Ru(II), Cu(II), Co(II), Zn(II) and Au(III) complexes,
exhibit high cytotoxicity and can inhibit cancer growth by causing cell apoptosis .[26–
36]
Metal ions Zn, Co, Ni, Mn, and Cu are the essential trace elements in a cell, and
they represent the endogenously occurring metal ions. In the past decade, many Zn,
Co, Ni, Mn, and Cu complexes have been explored.[37–65] These transition metal
complexes display significant antitumor activity and potential medicinal value, and
some of them have been demonstrated as promising telomerase- and
G-quadruplex-targeting agents.[37–65]
5,8-Quinolinedione and its derivatives such as lavendamycin and streptonigrin
exhibit antibacterial, anti-tumor, antimalarial and anti-tumor activities.[66–72]
Complexes of Ru(II), Os(II), Ir(III), Pt(II) and Rh(III) with 6,7-dichloro-5,8-
quinolinedione (DQ) are reported as apoptosis inhibitors.[66,73,74] To date,
complexes of transition metal Zn, Co, Ni, Mn, and Cu with
6,7-dichloro-5,8-quinolinedione (DQ) and 6,7-dichloro-2-methyl-5,8-quinolinedione
(DMQ) ligands have yet to be reported, and the biological activities of these transition
metal complexes remain to be explored.
The aim of present work is to synthesize a series of new transition metal
complexes,
[Zn(DQ)2(CH3OH)2]
(1),
[Zn(DMQ)2(CH3OH)2]
(2),
[Co(DQ)2(CH3OH)2] (3), [Co(DMQ)2(CH3OH)2] (4), [Ni(DQ)2(CH3OH)2] (5),
3

[Cu(DMQ)2(CH3OH)2] (6), [Mn(DQ)2(H2O)2] (7) and [Mn(DMQ)2(H2O)2] (8),
containing 6,7-dichloro-5,8-quinolinedione (DQ) and
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands as potential antitumor
agents. The in vitro antiproliferative activity of 1−8 was investigated against HeLa
(cervical), MCF-7 (breast), Hep-G2 (hepatoma), T-24 (bladder), and SK-OV-3
(ovarian) human cancer cells as well as HL-7702 nontumorigenic cells. To elucidate
the possible anti-tumor mechanisms, Zn(II) complexes 1 and 2 were evaluated for
mitochondrial damage (loss of Δψm), effect on cell cycle distribution, ROS (reactive
oxygen species) level, and initiation of mitochondria-associated events that leads to
cancer cell apoptosis.
2. Experimental methods
2.1. Synthesis of DQ and DMQ ligands
The
syntheses
of
6,7-dichloro-5,8-quinolinedione
(DQ)
and
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands were carried out according
to the reported procedures (Scheme 1).[66,73,74]
2.2. Synthesis of 1−8
The
complexes
1−8
were
prepared
by
treating
2.0
mmol
6,7-dichloro-5,8-quinolinedione (DQ) and 6,7-dichloro-2-methyl-5,8-quinolinedione
(DMQ) ligands with Zn(NO3)2·6H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O,
Cu(NO3)2·3H2O and Mn(NO3)2·6H2O (1.0 mmol) in 5.0 mL CH3OH at 80 C for 4.0
h. The brown crystals suitable for X-ray diffraction analysis were harvested.
Data for 1. Yield: 70.2%. Elemental analysis calcd. (%) for C20H14Cl2N2O8Zn: C
43.94, H 2.58, N 5.12; found: C 43.91, H 2.60, N 5.10. IR (KBr): 3394, 3083, 1700,
1
1596, 1523, 1280, 1220, 1121, 1003, 851, 684, 561, 461 cm−1. H NMR (500 MHz,
4

DMSO-d6) δ 8.54 (d, J = 3.6 Hz, 1H), 8.40 (d, J = 7.7 Hz, 1H), 7.84 (dd, J = 7.6, 5.2
Hz, 1H), 3.35 (s, 3H).13C NMR (126 MHz, DMSO-d6) δ 180.02, 170.50, 167.96,
151.26, 148.56, 137.33, 127.96, 127.55, 113.09, 40.55, 40.38, 40.22, 40.05, 39.88,
39.72, 39.55.
Data for 2. Yield: 79.1%. Elemental analysis calcd. (%) for C22H18Cl2N2O8Zn: C
45.98, H 3.16, N 4.87; found: C 45.97, H 3.19, N 4.86. IR (KBr): 3394, 1691, 1527,
1
1375, 1262, 1125, 1022, 864, 695, 674, 504, 433 cm−1. H NMR (500 MHz,
DMSO-d6) δ 8.28 (d, J = 7.9 Hz, 1H), 7.68 (d, J = 7.9 Hz, 1H), 3.35 (s, 3H), 2.70 (s,
3H). 13C NMR (126 MHz, DMSO-d6) δ 180.08, 163.52, 148.77, 137.11, 128.12,
125.23, 113.33, 40.57, 40.40, 40.24, 40.07, 39.90, 39.74, 39.57, 24.06.
Data for 3. Yield: 59.8%. Elemental analysis calcd. (%) for C20H14Cl2CoN2O8: C
44.47, H 2.61, N 5.19; found: C 44.49, H 2.60, N 5.17. IR (KBr): 3470, 3329, 2361,
1693, 1595, 1517, 1396, 1280, 1220, 1121, 1002, 853, 746, 683, 562, 459 cm−1.
Data for 4. Yield: 62.4%. Elemental analysis calcd. (%) for C22H18Cl2CoN2O8: C
46.50, H 3.19, N 4.93; found: C 46.48, H 3.22, N 4.92. IR (KBr): 3355, 2830, 1691,
1523, 1371, 1264, 1126, 1021, 861, 768, 694, 573, 505, 430 cm−1.
Data for 5. Yield: 75.6%. Elemental analysis calcd. (%) for C20H14Cl2N2CoO8: C
44.49, H 2.61, N 5.19; found: C 44.48, H 2.64, N 5.18. IR (KBr): 3324, 1654, 1513,
1348, 1224, 1120, 1017, 862, 675, 478 cm−1.
Data for 6. Yield: 80.1%. Elemental analysis calcd. (%) for C22H18Cl2CuN2O8: C
46.13, H 3.17, N 4.89; found: C 46.10, H 3.20, N 4.87. IR (KBr): 3481, 3065, 2938,
1698, 1620, 1521, 1408, 1253, 1126, 1021, 861, 795, 628, 436 cm−1.
Data for 7. Yield: 59.6%. Elemental analysis calcd. (%) for C18H10Cl2MnN2O8:
C 42.55, H 1.98, N 5.51; found: C 42.53, H 2.00, N 5.50. IR (KBr): 3462, 2292, 1692,
1598, 1518, 1278, 1220, 1114, 1001, 852, 677, 581, 447 cm−1.
5

Data for 8. Yield: 48.2%. Elemental analysis calcd. (%) for C20H14Cl2MnN2O8:
C 44.80, H 2.63, N 5.22; found: C 44.78, H 2.66, N 5.20. IR (KBr): 3363, 1692, 1526,
1376, 1269, 1119, 1015, 863, 706, 574, 498, 431 cm−1.
2.3. The other methods
The in vitro antitumor activities of 1−8 were performed as reported by Metzler-Nolte
and Lippard et al. [2,75−80] In addition, the experimental steps for
6,7-dichloro-5,8-quinolinedione complexes 1−8 were all provided in Supporting
Information.
3. Results and discussion
3.1. Synthesis
The
syntheses
of
6,7-dichloro-5,8-quinolinedione
(DQ)
and
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands were carried out according
to the reported procedures (Scheme 1).[66,73,74] Treatment of 1.0 mmol
Zn(NO3)2·6H2O,
Co(NO3)2·6H2O,
Ni(NO3)2·6H2O,
Cu(NO3)2·3H2O
and
Mn(NO3)2·6H2O with 2.0 equivalents of 6,7-dichloro-5,8-quinolinedione (DQ) and
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligands, respectively, in 5.0 mL
CH3OH at 80 C for 4.0 h led to the formation of a series of new transition metal
complexes,
[Zn(DQ)2(CH3OH)2]
(1),
[Zn(DMQ)2(CH3OH)2]
(2),
[Co(DQ)2(CH3OH)2] (3), [Co(DMQ)2(CH3OH)2] (4), [Ni(DQ)2(CH3OH)2] (5),
[Cu(DMQ)2(CH3OH)2] (6), [Mn(DQ)2(H2O)2] (7) and [Mn(DMQ)2(H2O)2] (8)
(Scheme 1). Their structures were characterized by single-crystal X-ray diffraction
analysis (Tables S1−S24), elemental analysis, infrared spectroscopy, UV-Vis
spectroscopy and NMR (Figures S1−S31). In addition, we showed that complexes
1−8 (2.0×10-5 mol/L) were stable in Tris-HCl buffer solution for 48 h by UV-Vis
6

spectroscopy (Figure S1).
Scheme 1. Synthetic routes for 6,7-dichloro-5,8-quinolinedione (DQ),
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) and their complexes 1−8. (a)
NaClO3 (5.5 g), HCl (37.0 mL), 5.0 M NaOH solution (269.0 mL), H2O (160.0 mL),
reflux; (b) Zn(NO3)2·6H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O or
Mn(NO3)2·6H2O, CH3OH (5.0 mL), 80 C, 4.0 h.
3.2. Crystal structure
As shown in Fig. 1, the Zn(II) atom is coordinated by O(1), N(1), O(4), and N(2) from
the two DQ ligands, and two O atoms [O(7) and O(8)] from two CH3OH ligands. The
angle of O(1)–Zn(1)–N(1) was 80.04(8) °, while the angle of O(4)–Zn(1)–N(1) was
99.96(8) °. The coordination geometry around the Zn(II) center was octahedral with
different ligating atoms (N and O atoms) from the coordination plane (Fig. 1 and
Tables S1−S3). The Zn–O distances were in the range of 2.058(2)–2.192(3) Å, and
the angle (°) are shown in Tables S1−S4.
Similar to Zn(II) in complex 1, the coordination geometry around the Zn(II),
Co(II), Ni(II), Cu(II) and Mn(II) atoms in complexes 2−8 was also distorted
octahedral, as shown in Figs. 2, S26−S31. The crystallographic data and selected bond
lengths (Å) are shown in Tables S1−S24, respectively.
7

Fig. 1. Molecular structure of 1.
Fig. 2. Molecular structure of 2.
3.3. In vitro cytotoxicity
8

The in vitro cytotoxic activities of DQ, DMQ, complexes 1−8, Zn(NO3)2·6H2O,
Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, cisplatin and Mn(NO3)2·6H2O
were evaluated against HeLa (cervical), MCF-7 (breast), Hep-G2 (hepatoma), T-24
(bladder), and SK-OV-3 (ovarian) human cancer cells as well as HL-7702
nontumorigenic cells as determined by MTT assay. As shown in Table 1, complexes
1−8 showed higher antitumor activity to cancer cell lines than that of DQ, DMQ,
Zn(NO3)2·6H2O,
Co(NO3)2·6H2O,
Ni(NO3)2·6H2O,
Cu(NO3)2·3H2O
and
Mn(NO3)2·6H2O. Notably, complexes 1−8 showed lower IC50 values of 1.08−10.21
μM against HeLa (cervical) cancer cells, and displayed approximately 1.2−11.8 fold
higher cytotoxic activity than cisplatin (12.69 ± 0.29 μM). And their cytotoxic
activities were in the following order: 2 > 1 > 6 > 4 > 3 > 8 > 7 > 5 > cisplatin > DMQ
> DQ > Zn(NO3)2·6H2O ～Co(NO3)2·6H2O ～ Ni(NO3)2·6H2O ～ Cu(NO3)2·3H2O ～
Mn(NO3)2·6H2O. The different biological behavior of 1 and 2 may correlate with the
presence of a 2-methyl group in 6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ)
ligand. Remarkably, complex 2 was the most cytotoxic compound in HeLa cells, with
an IC50 value of 1.08 ± 0.15 μM, which was 1.7−16.5 times more potent than that of
6,7-dichloro-5,8-quinolinedione (DQ) Ru(II), Os(II), Ir(III), Pt(II) and Rh(III)
complexes (IC50 > 1.8 ± 0.7 μM) [66,73,74]. In addition, complexes 1−8 displayed
less cytotoxicity on the HL-7702 nontumorigenic cells (IC50 > 60.0 μM), indicating
the selectivity of complexes 1−8 on HeLa cells.
Table 1. Cytotoxicities (IC50, μM) of DQ, DMQ, complexes 1−8,
Zn(NO3)2·6H2O,
Co(NO3)2·6H2O,
Ni(NO3)2·6H2O,
Cu(NO3)2·3H2O,
Mn(NO3)2·6H2O and cisplatin toward the selected human cell lines for 24 h.
9

HeLa
MCF-7
Hep-G2
SK-OV-3
Compounds
DQ
T-24
HL-7702
40.15 ±
1.96
25.16 ± 1.47
28.12 ± 1.09
40.15 ±
0.77
65.08 ±
1.12
31.04 ± 1.07
30.22 ±
0.64
18.63 ± 0.32
15.03 ± 1.00
30.57 ±
1.05
63.55 ±
0.98
70.15 ±
0.25
72.19 ±
1.09
65.03 ±
0.54
64.17 ±
0.32
69.08 ±
0.99
60.15 ±
0.88
65.03 ±
0.57
DMQ
20.17 ± 0.58
8.45 ± 1.79
5.26 ± 0.52
15.99 ± 1.22
12.97 ± 0.63
30.00 ± 0.46
10.56 ± 0.49
25.87 ± 1.29
20.39 ± 0.31
1
2
3
4
5
6
7
8
3.03 ± 0.28
1.08 ± 0.15
5.08 ± 1.08
4.34 ± 0.81
3.37 ± 0.26
1.59 ± 0.43
6.01 ± 0.89
5.56 ± 1.08
12.37 ± 1.81
4.88 ± 0.57
9.85 ± 0.33
8.93 ± 1.11
6.19 ± 1.49
4.95 ± 0.82
10.41 ± 1.09
8.93 ± 1.02
20.15 ± 1.02
7.58 ± 0.66
15.08 ± 1.64
13.62 ± 1.00
4.26 ± 0.71
2.58 ± 0.33
9.06 ± 2.03
7.89 ± 1.59
10.21 ±
0.44
15.08 ±
0.99
4.01 ± 1.05
9.01 ± 1.84
6.21 ± 0.55
5.99 ± 0.18
13.06 ±
1.14
10.57 ±
0.33
80.71 ±
1.49
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
Zn(NO3)2·6H2O
Co(NO3)2·6H2O
Ni(NO3)2·6H2O
Cu(NO3)2·3H2O
Mn(NO3)2·6H2O
> 100
> 100
> 100
> 100
> 100
12.69 ±
0.29
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
15.59 ±
1.06
> 100
> 100
> 100
> 100
> 100
18.52 ±
0.51
12.56 ± 0.25
13.88 ± 1.03
Cisplatin
15.02 ± 1.96
3.4. Cell cycle analysis
Recent studies suggested that some of the complexes can induce cell cycle arrest, and
thereby induce apoptosis.[38,74–82] After treatment with 1 (3.0 μM) and 2 (1.0 μM)
for 24 h (Fig. 3), the populations of G1 phase were 51.80% and 53.79% in comparison
with the control cells (43.57%), suggesting that 1 (3.0 μM) and 2 (1.0 μM) caused G1
phase arrest.
Fig. 3. Cell cycle distribution of HeLa cells (A) exposure to 1 (3.0 μM) and 2 (1.0
μM) for 24 h.
10

3.5. ROS level
HeLa cancer cells were incubated with 1 (3.0 μM) and 2 (1.0 μM) for 24 h to
determine the effect of 1 (3.0 μM) and 2 (1.0 μM) on intracellular ROS generation. As
shown in Fig. 4, 1 (3.0 μM) and 2 (1.0 μM), especially 2 (1.0 μM) can enhance the
ROS levels.
Fig. 4. Intracellular ROS was detected in HeLa cells (a) exposure to 1 (3.0 μM, b) and
2 (1.0 μM, c) for 24 h.
3.6. Mitochondrial membrane potential (MMP) loss
The ROS level is an important factor affecting the MMP expression. [77–85] Thus, to
study the mechanism of 1 (3.0 μM) and 2 (1.0 μM) caused HeLa cell apoptosis, we
measured the MMP by examining the fluorescence intensity of JC-1 staining. Fig. 5
revealed that 1 (3.0 μM) and 2 (1.0 μM) can induce a decrease of MMP and, thereby
cause HeLa cell apoptosis. [77–85]
Fig. 5. The MMP level in HeLa cells (a) exposure to 1 (3.0 μM) and 2 (1.0 μM) for 24
11

h.
3.7. Expression of apoptosis proteins
After treatment of HeLa cells with 1 (3.0 μM) and 2 (1.0 μM) for 24 h (Figs. 6–8), the
levels of cytochrome c (cyt c), apaf-1 and caspase-3/9 proteins were obviously
up-regulated following the order of 2 > 1, suggesting that 1 (3.0 μM) and 2 (1.0 μM)
induced apoptosis of HeLa cells via an ROS-mediated mitochondrial dysfunction.[77–
86]
Fig. 6. The imaging (A) and expression (B) of apoptosis proteins in HeLa cells
induced by 1 (3.0 μM) and 2 (1.0 μM) for 24 h.
Fig. 7 The level of caspase-3 in HeLa cells (a) induced by 1 (b) and 2 (c) for 24 h.
12

Fig. 8. The level of caspase-9 in HeLa cells (a) induced by 1 (b) and 2 (c) for 24 h.
3.8. 1 and 2 promote cell apoptosis
The ability of 1 (3.0 μM) and 2 (1.0 μM) to promote apoptosis was measured by flow
cytometry. As shown in Fig. 9, the percentages (Q2 cells+Q4 cells) of the cells where
1 (3.0 μM) and 2 (1.0 μM) promoted cell apoptosis were 9.75% and 15.07%,
respectively, compared with the control. Our results suggested that the intrinsic
mitochondrial signal pathway was involved in 1 (3.0 μM) and 2 (1.0 μM) induced
apoptosis.[87–92]
Fig. 9. The apoptosis analysis of the HeLa cells (a) treated with 1 (b) and 2 (c) for 24
h.
4. Conclusions
In conclusion, we designed and prepared eight transition metal complexes 1–8 with
13

6,7-dichloro-5,8-quinolinedione (DQ) and 6,7-dichloro-2-methyl-5,8-quinolinedione
(DMQ) ligands. Remarkably, complexes 1−8 showed higher cytotoxicity than
cisplatin against HeLa cells, and less cytotoxicity on the HL-7702 cells. In vitro
mechanism studies indicated that 1 and 2 induced a series of events related to
mitochondrial dysfunction in HeLa cells including ROS production, loss of MMP,
cell cycle arrest at G1 phase, and apoptosis in the order of 2 > 1. The biological
behavior of 1 and 2 may correlate with the presence of a 2-methyl group in
6,7-dichloro-2-methyl-5,8-quinolinedione (DMQ) ligand. Taken together, 2 is a
promising candidate as a mitochondria-targeted anti-cancer agent.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (Nos.
21867017 and 21761033), the Natural Science Foundation of Guangxi (No.
2018GXNSFBA138021, 2018GXNSFBA281188 and 2016GXNSFAA380300), the
basic skills improvement project for the young and middle-aged teachers in Guangxi
colleges and universities (No. 2019KY1163), Guangxi New Century Ten, Hundred and
Thousand Talents Project ([2017]42) as well as the Innovative Team & Outstanding
Talent Program of Colleges and Universities in Guangxi (2014-49 and 2017-38).
Appendix A. Supplementary material
The CCDC contains the supplementary crystallographic data for the complexes 1−8
were 1935961, 1935962, 1935963, 1935964, 1935965, 1936175, 1935966 and
1935967.
These
data
can
be
obtained
or
free
from
of
the
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html,
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
14

1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
[1] A. Gandioso, E. Shaili, A. Massaguer, G. Artigas, A. González-Cantó, J. A.
Woods, P. J. Sadler, V. Marchán, Chem. Commun. 51 (2015) 9169.
[2] Y. Gothe, T. Marzo, L. Messori, N. Metzler-Nolte, Chem. Eur. J. 22 (2016)
12487.
[3] Y.-R. Zheng, K. Suntharalingam, T. C. Johnstone, S. J. Lippard, Chem. Sci. 6
(2015) 1189.
[4] D. Y. Q. Wong, J. Y. Lau, W. H. Ang, Dalton Trans. 41 (2012) 6104.
[5] J. Noh, B. Kwon, E. Han, M. Park, W. Yang, W. Cho, W. Yoo, G. Khang, D. Lee,
Nat. Commun. 6 (2015) 6907.
[6] Q.-P. Qin, S.-L. Wang, M.-X. Tan, Y.-C. Liu, T. Meng, B.-Q. Zou, H. Liang, Eur.
J. Med. Chem. 161 (2019) 334.
[7] Q.-P. Qin, Z.-F. Wang, S.-L. Wang, D.-M. Luo, B.-Q. Zou, P.-F. Yao, M.-X. Tan,
H. Liang, Eur. J. Med. Chem. 170 (2019) 195.
[8] L. H. Hurley, Nat. Rev. Cancer 2 (2002) 188.
[9] O. Pinato, C. Musetti, C. Sissi, Metallomics 6 (2014) 380.
[10] H. Kostrhunova, J. Florian, O. Novakova, A. F. A. Peacock, P. J. Sadler, V.
Brabec, J. Med. Chem. 51 (2008) 3635.
[11] Z. Liu, A. Habtemariam, A. M. Pizarro, S. A. Fletcher, A. Kisova, O. Vrana, L.
Salassa, P. C. A. Bruijnincx, G. J. Clarkson, V. Brabec, P. J. Sadler, J. Med.
Chem. 54 (2011) 3011.
[12] V. Milacic, D. Chen, L. Ronconi, K. R. Landis-Piwowar, D. Fregona, Q. P. Dou,
15

Cancer Res. 66 (2006) 10478.
[13] Q.-P. Qin, S.-L. Wang, M.-X. Tan, D.-M. Luo, Z.-F. Wang, Q.-M. Wei, X.-Y.
Wu, B.-Q. Zou, Y.-C. Liu, Polyhedron 157 (2019) 219.
[14] A. Zamora, S. A. P erez, M. Rothemund, V. Rodríguez, R. Schobert, C. Janiak, J.
Ruiz, Chem. Eur. J. 23 (2017) 5614.
[15] I. Eryazici, C.N. Moorefield, G. R. Newkome, Chem. Rev. 108 (2008) 1834.
[16] D. Ćoćić, S. Jovanović, S. Radisavljević, J. Korzekwa, A. Scheurer, R. Puchta,
D. Baskić, D. Todorović, S. Popović, S. Matić, B. Petrović, J. Inorg. Biochem.
189 (2018) 91.
[17] S. Gama, I. Rodrigues, F. Mendes, I. C. Santos, E. Gabano, B. Klejevskaja, J.
Gonzalez-Garcia, M. Ravera, R. Vilar, A. Paulo, J. Inorg. Biochem. 160 (2016)
275.
[18] P. Shi, Q. Jiang, Y. Zhao, Y. Zhang, J. Lin, L. Lin, J. Ding, Z. Guo, J. Biol.
Inorg. Chem. 11 (2006) 745.
[19] G. Sava, A. Bergamo, P. J. Dyson, Dalton Trans. 40 (2011) 9069.
[20] Q. Jiang, J. Zhu, Y. Zhang, N. Xiao, Z. Guo, Biometals 22 (2009) 297.
[21] L. Messori, F. Abbate, G. Marcon, P. Orioli, M. Fontani, E. Mini, T. Mazzei, S.
Carotti, T. O′Connell, P. Zanello, J. Med. Chem. 43 (2000) 3541.
[22] K. K.-W. Lo, M.-W. Louie, K. Y. Zhang, Coordin. Chem. Rev. 254 (2010) 2603.
[23] V. M. Manikandamathavan, V. Rajapandian, A. J. Freddy, T. Weyhermüller, V.
Subramanian, B. U. Nair, Eur. J. Med. Chem. 57 (2012) 449.
[24] D. Lazić, A. Arsenijević, R. Puchta, Ž. D. Bugarčić, A. Rilak, Dalton Trans. 45
(2016) 4633.
[25] K. Zheng, F. Liu, X.-M. Xu, Y.-T. Li, Z.-Y. Wu, C.-W. Yan, New J. Chem. 38
(2014) 2964.
16

[26] S. A. Galal, K. H. Hegab, A. M. Hashem, N. S. Youssef, Eur. J. Med. Chem.
2010, 45 (2010) 5685.
[27] T. Meng, Q.-P. Qin, Z.-L. Chen, H.-H. Zou, K. Wang, F.-P. Liang, Eur. J. Med.
Chem. 169 (2019) 103.
[28] Q.-P. Qin, Z.-F. Wang, X.-L. Huang, M.-X. Tan, B.-B. Shi, H. Liang, ACS Med.
Chem. Lett. 10 (2019) 936.
[29] I. Kostova, Curr. Med. Chem. 13 (2006) 1085.
[30] X. Chen, L. Tang, P. Sun, Y. Qiu, G. Liang, J. Inorg. Biochem. 104 (2010) 379.
[31] I. Ott, B. Kircher, P. Schumacher, K. Schmidt, R. Gust, J. Med. Chem. 48 (2005)
622.
[32] M. A. Yakupec, Dalton Trans. (2008) 183.
[33] P. Pigeon, S. Top, A. Vessiéres, M. Huché, E. A. Hillard, E. Salomon, G. Jaouen,
J. Med. Chem. 48 (2005) 2814.
[34] A. Vessiéres, S. Top, W. Beck, E. Hillard, G. Jaouen, Dalton Trans. (2006) 529.
[35] W. H. Ang, P. J. Dyson, Eur. J. Inorg. Chem. (2006) 4003.
[36] X.-D. Song, X. Kong, S.-F. He, J.-X. Chen, J. Sun, B.-B. Chen, J.-W. Zhao,
Z.-W. Mao, Eur. J. Med. Chem. 138 (2017) 246.
[37] Q.-P. Qin, T. Meng, Z.-Z. Wei, C.-H. Zhang, Y.-C. Liu, H. Liang, Z.-F. Chen,
Eur. J. Inorg. Chem. (2017) 1824.
[38] Q.-P. Qin, J.-L. Qin, T. Meng, W.-H. Lin, C.-H. Zhang, Z.-Z. Wei, J.-N. Chen,
Y.-C. Liu, H. Liang, Z.-F. Chen, Eur. J. Med. Chem. 124 (2016) 380.
[39] K. Györyová, E. Szunyogová, J. Kovářová, D. Hudecová, D. Mudroňová, E.
Juhászová, J. Therm. Anal. Calorim. 72 (2003) 587.
[40] S. Emami, S. J. Hosseinimehr, S. M. Taghdisi, S. Akhlaghpoor, Bioorg. Med.
Chem. Lett. 17 (2007) 45.
17

[41] Q.-M. Huang, Z.-Q. Pan, P. Wang, Z.-P. Chen, X.-L. Zhang, H.-S. Xu, Bioorg.
Med. Chem. Lett. 16 (2006) 3030.
[42] A. Nakayama, M. Hiromura, Y. Adachi, H. Sakurai, J. Biol. Inorg. Chem. 13
(2008) 675.
[43] H. Sakura, Y. Yoshikawa, H. Yasui, Chem. Soc. Rev. 37 (2008) 2383.
[44] M. B. Ferrari, F. Bisceglie, G. Pelosi, P. Tarasconi, R. Albertini, S. Pinelli, J.
Inorg. Biochem. 87 (2001) 137.
[45] C. Bazzicalupi, A. Bencini, A. Bianchi, T. Biver, A. Boggioni, S. Bonacchi, A.
Danesi, C. Giorgi, P. Gratteri, A. M. Ingrain, F. Secco, C. Sissi, B. Valtancoli,
M. Venturini, Chem. Eur. J. 14 (2008) 184.
[46] P. F. Liguori, A. Valentini, M. Palma, A. Bellusci, S. Bernardini, M. Ghedini, M.
L. Panno, C. Pettinari, F. Marchetti, A. Crispini, D. Pucci, Dalton Trans. 39
(2010) 4205.
[47] C. T. Liu, A. A. Neverov, R. S. Brown, J. Am. Chem. Soc. 130 (2008) 13870.
[48] T. S. B. Baul, S. Kundu, A. Linden, N. Raviprakash, S. K. Manna, M. F. C. G. da
Silva, Dalton Trans. 43 (2014) 1191.
[49] S. Mandal, A. K. Rout, A. Ghosh, G. Pilet, D. Bandyopadhyay, Polyhedron 28
(2009) 3858.
[50] D. P. Singh, K. Kumar, C. Sharma, Eur. J. Med. Chem. 45 (2010) 1230.
[51] M.-X. Li, C.-L. Chen, D. Zhang, J.-Y. Niu, B.-S. Ji, Eur. J. Med. Chem. 45
(2010) 3169.
[52] M.-X. Li, L.-Z. Zhang, D. Zhang, B.-S. Ji, J.-W. Zhao, Eur. J. Med. Chem. 46
(2011) 4383.
[53] D. S. Kalinowski, P. C. Sharpe, P. V. Bernhardt, D. R. Richardson, J. Med.
Chem. 50 (2007) 6212.
18

[54] D. R. Richardson, P. C. Sharpe, D. B. Lovejoy, D. Senaratne, D. S. Kalinowski,
M. Islam, P. V. Bernhardt, J. Med. Chem. 49 (2006) 6510.
[55] R. Gust, I. Ott, D. Posselt, K. Sommer, J. Med. Chem. 47 (2004) 5837.
[56] I. Ott, K. Schmidt, B. Kircher, P. Schumacher, T. Wiglenda, R. Gust, J. Med.
Chem. 48 (2005) 622.
[57] M. Belicchi-Ferrari, F. Bisceglie, C. Casoli, S. Durot, I. Morgenstern-Badarau,
G. Pleosi, E. Piltti, S. Pinelli, P. Tarasconi, J. Med. Chem. 48 (2005) 1671.
[58] N. Yamamoto, A. K. Renfrew, B. J. Kim, N. S. Bryce, T. W. Hambley, J. Med.
Chem. 55 (2012) 11013.
[59] B. J. Kim, T. W. Hambley, N. S. Bryce, Chem. Sci. 2 (2012) 2135.
[60] A. K. Renfrew, N. S. Bryce, T. W. Hambley, Chem. Sci. 3 (2013) 3731.
[61] J. Y.-C. Chang, G.-L. Lu, R.J. Stevenson, P. J. Brothers, G. R. Clark, K. J.
Botting, D. M. Ferry, M. Tercel, W. Wilson, W. A. Denny, D. C. Ware, Inorg.
Chem. 52 (2013) 7688.
[62] V. Thamilarasan, A. Jayamani, N. Sengottuvelan, Eur. J. Med. Chem. 89 (2015)
266.
[63] S. N. Georgiades, N. H. A. Karim, K. Suntharalingam, R. Vilar, Angew. Chem.
Int. Ed. 2010, 49 (2010) 4020.
[64] C. Wang, Y. Li, G. Jia, Y. Liu, S. Lu, C. Li, Chem. Commun. 48 (2012) 6232.
[65] S.-T. Von, H.-L. Seng, H.-B. Lee, S.-W. Ng, Y. Kitamura, M. Chikira, C.-H. Ng,
J. Biol. Inorg. Chem. 17 (2012) 57.
[66] M. Kubanik, N. Y. S. Lam, H. U. Holtkamp, T. Sohnel, R. F. Anderson, S. M. F.
Jamieson, C. G. Hartinger, Chem. Commun. 54 (2018) 992.
[67] C.-K. Ryu, H.-J. Kim, Arch. Pharmacal Res., 1994, 17, 139–144.
[68] A. N. Pearce, E. W. Chia, M. V. Berridge, G. R. Clark, J. L. Harper, L. Larsen,
19

E. W. Maas, M. J. Page, N. B. Perry, V. L. Webb, B. R. Copp, J. Nat. Prod. 70
(2007) 936.
[69] I. A. Shaikh, F. Johnson, A. P. Grollman, J. Med. Chem. 29 (1986) 1329.
[70] D. Q. Shen, Y. Cheng, L. K. An, X. Z. Bu, Z. S. Huang, L. Q. Gu, Chin. Chem.
Lett. 19 (2008) 533.
[71] Q.-M. Chen, G.-B. Yi, L.-K. An, X.-L. Feng, Acta Crystallogr. Sect. E: Struct.
Rep. Online 67 (2011) o1108.
[72] M. M¸akosza, K. Wojciechowski, Chem. Rev. 104 (2004) 2631.
[73] Z. Li, J. Zhou, Y. Gan, Y. Yin, W. Zhang, J. Yang, Y. Tang, Y. Dai, J. Inorg.
Biochem. 197 (2019) 110701. DOI: 10.1016/j.jinorgbio.2019.110701.
[74] T. Meng, Q.-P. Qin, Z.-L. Chen, H.-H. Zou, K. Wang, F.-P. Liang, Dalton Trans.
48 (2019) 5352.
[75] Z.-F. Chen, Q.-P. Qin, J.-L. Qin, Y.-C. Liu, K.-B. Huang, Y.-L. Li, T. Meng,
G.-H. Zhang, Y. Peng, X.-J. Luo, H. Liang, J. Med. Chem. 58 (2015) 2159.
[76] A. K. P. Taggart, S.-C. Teng, V. A. Zakian, Science 297 (2002) 1023.
[77] C.-C. Zeng, S.-H. Lai, J.-H. Yao, C. Zhang, H. Yin, W. Li, B.-J. Han, Y.-J. Liu,
Eur. J. Med. Chem. 122 (2016) 118.
[78] V. M. Dirsch, D. S. Antlsperger, H. Hentze, A. M. Vollmar, Leukemia 16 (2002)
74.
[79] L. Gamet-Payrastre, P. Li, S. Lumeau, G. Cassar, M. A. Dupont, S. Chevolleau,
N. Gasc, J. Tulliez, F. Terce, Cancer Res. 60 (2000) 1426.
[80] J. Klucar, M. Al-Rubeai, FEBS Lett. 400 (1997) 127.
[81] Q.-P. Qin, S.-L. Wang, M.-X. Tan, Z.-F. Wang, X.-L. Huang, Q.-M. Wei, B.-B.
Shi, B.-Q. Zou, H. Liang, Metallomics 10 (2018) 1160.
[82] Q.-P. Qin, B.-Q. Zou, M.-X. Tan, S.-L. Wang, Y.-C. Liu, H. Liang, New J.
20

Chem. 42 (2018) 15479.
[83] H.-H. Zou, L. Wang, Z.-X. Long, Q.-P. Qin, Z.-K. Song, T. Xie, S.-H. Zhang,
Y.-C. Liu, B. Lin, Z.-F. Chen, Eur. J. Med. Chem. 108 (2016) 1.
[84] J. Qi, K. Qian, L. Tian, Z. Cheng, Y. Wang, New J. Chem. 42 (2018) 10226.
[85] G. Tang, Z. Nikolovska-Coleska, S. Qiu, Yang, Y. C. J. Guo, S. Wang, J. Med.
Chem. 51 (2008) 717.
[86] Q.-P. Qin, Z.-F. Chen, J.-L. Qin, X.-J. He, Y.-L. Li, Y.-C. Liu, K.-B. Huang, H.
Liang, Eur. J. Med. Chem. 92 (2015) 302.
[87] K. Suntharalingam, J. J. Wilson, W. Lin, S. J. Lippard, Metallomics 6 (2014)
437.
[88] J.-Q. Wang, P.-Y. Zhang, L.-N. Ji, H. Chao, J. Inorg. Biochem. 146 (2015) 89.
[89] Q. Cao, Y. Li, E. Freisinger, P. Z. Qin, R. K. O. Sigela, Z.-W. Mao, Inorg. Chem.
Front. 4 (2017) 10.
[90] Q.-P. Qin, Z.-F. Wang, X.-L. Huang, M.-X. Tan, B.-Q. Zou, H. Liang, Eur. J.
Med. Chem. 184 (2019) 111751.
[91] Q.-P. Qin, B.-Q. Zou, Z.-F. Wang, X.-L. Huang, Y. Zhang, M.-X. Tan, S.-L.
Wang, H. Liang, Eur. J. Med. Chem. 183 (2019) 111727.
[92] Q.-P. Qin, Z.-F. Wang, X.-L. Huang, M.-X. Tan, Z.-H. Luo, S.-L. Wang, B.-Q.
Zou, H. Liang, Dalton Trans. 48 (2019) 15247.
Author Contributions Section
Bi-Qun Zou and Xiao-Ling Huang conceived and designed the experiments, Bi-Qun Zou,
Xiao-Ling Huang, Zhen-Feng Wang and Xue-Yu Wu synthesized chemical compounds and
carried out in vitro antitumor activities of complexes 1–8. Qi-Pin Qin, Ming-Xiong Tan and Hong
Liang provided effective directions during the research process. Qi-Pin Qin, Ming-Xiong Tan and
Hong Liang analyzed data, discussed results, wrote and commented on the paper. All authors
reviewed the manuscript.
Declaration of Interest Statement
The authors declared that they have no conflicts of interest to this
21

work.
Graphical abstract
Transition metal complexes with 6,7-dichloro-5,8-quinolinedione
as mitochondria-targeted anticancer agents
22

Bi-Qun Zou,a,b,c Xiao-Ling Huang,b Qi-Pin Qin,*b,c Zhen-Feng Wang,b Xue-Yu Wu,b
Ming-Xiong Tan,*b,c Hong Liang*c
Complexes 1 and 2 arrested the cell cycle in the G1 phase, and inducing cancer cell
death via mitochondrial dysfunction pathways was in the following order of 2 > 1.
Highlights:
• 5,8-quinolinedione transition metal complexes 1−8 have been first reported.
• 1−8 are more selective for HeLa cells versus normal cells (HL-7702).
• 2 also caused mitochondrial dysfunction.
23