A new pyrazolone based ternary Cu(II) complex: Synthesis, characterization, crystal structure, DNA binding, protein binding and anti-cancer activity towards A549 human lung carcinoma cells with a minimum cytotoxicity to non-cancerous cells

Article abstract of DOI:10.1016/j.poly.2013.08.051

With the aim of exploring the anticancer properties of coordination compounds, we report for the first time the synthesis of the new ternary complex [Cu(TMCPMP-TS)(Phen)] (TMCPMP-TS; (Z)-2-((1-(3-chlorophenyl)-3-methyl-5-oxo-4, 5-dihydro-1H-pyrazol-4-yl)(p-tolyl)methylene) hydrazinecarbothioamide and Phen; 1,10-phenanthroline). The complex was characterized by various techniques, including X-ray crystallography which showed that the geometry of the metal centre was between square pyramidal and trigonal bipyramidal. The interaction with calf-thymus DNA showed binding through intercalation. The protein binding ability with bovine serum albumin revealed a stronger binding of complex as compared to the free ligands. The anticancer activity of the complex was investigated by exposing it to the A549 (human lung cancer) cell line, which showed mitochondrial damage via an oxidative mechanism. After 24 h treatment, the complex arrested S and G2/M phases in the cell cycle progression and induced cell death. The results envisaged herein indicate that Cu(TMCPMP-TS)(Phen) holds ample merit to develop it as a therapeutic agent against cancer.

Full text of DOI:10.1016/j.poly.2013.08.051

Accepted Manuscript
A new pyrazolone based ternary Cu(II) complex: Synthesis, characterization,
crystal structure, DNA binding, protein binding and anti-cancer activity towards
A549 human lung carcinoma cells with a minimum cytotoxicity to non-cancer‐
ous cells
Komal M. Vyas, R.N. Jadeja, Dipak Patel, R.V. Devkar, Vivek K. Gupta
PII:
S0277-5387(13)00614-1
DOI:
http://dx.doi.org/10.1016/j.poly.2013.08.051
POLY 10311
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
20 April 2013
6 August 2013
Please cite this article as: K.M. Vyas, R.N. Jadeja, D. Patel, R.V. Devkar, V.K. Gupta, A new pyrazolone based
ternary Cu(II) complex: Synthesis, characterization, crystal structure, DNA binding, protein binding and anti-cancer
activity towards A549 human lung carcinoma cells with a minimum cytotoxicity to non-cancerous cells,
Polyhedron (2013), doi: http://dx.doi.org/10.1016/j.poly.2013.08.051
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A new pyrazolone based ternary Cu(II) complex: Synthesis, characterization,
crystal structure, DNA binding, protein binding and anti-cancer activity towards
A549 human lung carcinoma cells with a minimum cytotoxicity to non-
cancerous cells
a
a*
b
b
c
Komal M. Vyas , R. N. Jadeja , Dipak Patel , R. V. Devkar , Vivek K. Gupta
a
Department of Chemistry, Faculty of Science, The M. S. University of Baroda, Vadodara 390 002, India
b
Division of Phytotherapeutics and Metabolic Endocrinology, Faculty of Science, The M.S. University of
Baroda, Vadodara 390002, Gujarat, India
c
Post-Graduate Department of Physics & Electronics, University of Jammu, Jammu Tawi 180 006, India
*
E-mail- rajendra_jadeja@yahoo.com, Tel: +91-265-2795552 ext 30
Abstract
With the aim of exploring the anticancer properties of coordination compounds, we
report for the first time the synthesis of the new ternary complex [Cu(TMCPMP-TS)(Phen)]
(TMCPMP-TS; (Z)-2-((1-(3-chlorophenyl)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-yl)(p-
tolyl)methylene) hydrazinecarbothioamide and Phen; 1,10-phenanthroline). The complex was
characterized by various techniques, including X-ray crystallography which showed that the
geometry of the metal centre was between square pyramidal and trigonal bipyramidal. The
interaction with calf-thymus DNA showed binding through intercalation. The protein binding
ability with bovine serum albumin revealed a stronger binding of complex as compared to the
free ligands. The anticancer activity of the complex was investigated by exposing it to the
A549 (human lung cancer) cell line, which showed mitochondrial damage via an oxidative
mechanism. After 24 hr treatment, the complex arrested S and G2/M phases in the cell cycle
progression and induced cell death. The results envisaged herein indicate that Cu(TMCPMP-
TS)(Phen) holds ample merit to develop it as a therapeutic agent against cancer.
1

Keywords: pyrazolone based thiosemicarbazone, phenanthroline, ternary Cu(II) complex,
DNA binding, Protein binding, Anti-cancer activity
1
. Introduction
One of the most rapidly developing areas of pharmaceutical research is the discovery
of drugs for cancer therapy. Lung cancer has been recognized as one of the leading causes of
death worldwide. The highly proliferative nature of cancer cells has undoubtedly been
realized and consequently, inhibition of proliferative pathways is considered to be an
effective strategy to fight cancer. Much attention has recently been paid to the discovery and
development of new, more selective anticancer agents. Due to serious side effects and
acquired drug resistance of anticancer drugs, there are considerable attempts being made to
replace these drugs with suitable alternatives and therefore numerous transition metal
complexes have been synthesized and tested for their anticancer activities.
Pyrazolone, as a prominent structural motif, is found in numerous active compounds.
Pyrazolone derivatives have occupied a unique position in drug discovery due to their broad
range of biological activities, such as anti-inflammatory, anti-bacterial, anti-microbial, anti-
cancer, antioxidant and analgesic activities. Due to their easy preparation and rich biological
activity [1-3], pyrazolone and its complexes have received considerable attention in
coordination chemistry and medicinal chemistry. Schiff base ligands of pyrazolone and their
metal complexes have been reported widely. Among these, thiosemicarbazone derivatives
have been paid attention due to their rich biological properties [4-6]. This type of ligand has
been reported widely to show photochromic properties by Dian-zeng Jia and co-workers [7-
9
], whereas the related complexes have not been explored that much [10-13]. Moreover, the
ligands and their metal complexes possess strong biological activity, like DNA binding, DNA
cleavage, anticancer, etc [14,15]. The biological activities of metal complexes differ from
2

those of either the free ligands or metal ions, and increased or decreased activities in relation
to the non-complexed thiosemicarbazones have been reported for several transition metal
complexes [12].
Among the transition metal complexes, Cu(II) complexes are considered the best
alternatives to cisplatin because copper is biocompatible and exhibits many significant roles
in biological systems. Several copper complexes containing pyridyl-type ligands, such as
1
,10-phenanthraline [16], were screened for their anticancer activity [16-19].
Sigman and co-workers [20] have developed the first chemical nuclease, bis-(1,10-
phenanthroline) Cu(I) complex. Recently, there has been a substantial increase in the design
and study of DNA binding and cleavage properties of mixed ligand Cu(II) complexes [21-24]
and the development of new copper-based metallodrugs.
Serum albumins, as the most abundant proteins in the circulatory system, act as a
transporter and disposer of many endogenous and exogenous compounds [25]. Bovine serum
albumin (BSA) is structurally homologous to human serum albumin (HSA) [26]. Studies on
serum albumins can provide information on the structural features that determines the
therapeutic effectiveness of drugs and standardized screens for protein binding in new drug
design and for fixing dose limits [27]. Therefore, the binding of drugs to serum albumin in
vitro, considered as a model in protein chemistry to study the binding behavior of proteins,
has been an interesting research field in chemistry, life sciences and clinical medicine [28].
Because copper complexes containing either thiosemicarbazones or pyridyl-type
ligands showed moderate anticancer activities [14-19], we considered that ternary complexes
containing both types of ligands would be good candidates for the discovery of new novel
anticancer metallodrugs. All of the above facts have stimulated our interest in the present
work. Hence, this report describes the synthesis of a ternary Cu(II) complex derived from a 4-
toluoyl pyrazolone based thiosemicarbazone and 1,10-phenanthroline, using a new synthetic
3

procedure. The crystal structure of this type of ternary complex has been reported for the first
time. The DNA binding, protein binding and anticancer activity against A549 lung cancer
cells of this kind of complex have been reported here for the first time here in detail.
2
2
. Experimental
.1. Materials
The compound 1-(3-chlorophenyl)-3-methyl-1H-pyrazol-5(4H)-one (MCPMP) was
obtained from Nutan Dye Chem., Sachin, Surat, India. Dioxane was obtained from E. Merck
India) Ltd. Calcium hydroxide, copper nitrate trihydrate and 1,10-phenanthroline were
(
obtained from LOBA Chem. Pvt. Ltd., Mumbai and used as supplied. Thiosemicarbazide was
obtained from Sisco Research Lab. Pvt. Ltd., Mumbai, India. Absolute alcohol was obtained
from Baroda Chem. Industry Ltd. and was used after distillation. Methanol was obtained
from Spectrochem., Mumbai, India and was used after distillation. CT-DNA (Calf Thymus
DNA) and BSA (Bovine Serum Albumin) were purchased from Sigma Aldrich. All the
chemicals used were of AR grade. Solvents used in this study were purified following
standard procedures [29]. Dulbeco’s Modified Eagle Medium (DMEM), Trypsin Phosphate
Versene Glucose (TPVG) solution Trypsin and methylthiazolyldiphenyl- tetrazolium bromide
(
MTT) were purchased from HiMedia Laboratories Pvt. Ltd. (Bombay, India). Fetal bovine
serum (FBS) was purchased from Biosera (Ringmer, East Sussex UK) and dimethyl sulfoxide
DMSO) was purchased from the Sisco Research Laboratories Pvt. Ltd. (Mumbai, India).
(
Rhodamine 123, 4',6-diamidino-2-phenylindole (DAPI) and 2’,7’-dichlorofluorescein
diacetate (DCFDA) were purchased from Sigma (Delhi, India).
2
.2. Pharmacology
Human lung carcinoma (A549) cells were obtained from the National Centre for Cell
5
Science, Pune, India and were seeded (1x 10 cells/ T25 flask) and cultured in DMEM
containing 10% FBS and 1% antibiotic-antimycotic solution at 37 °C in a water jacketed CO2
4

incubator (Thermo scientific, forma II). Cells were sub-cultured every third day by
trypsinization with TPVG solution. The reagents used herein were filtered through a 0.22 μ
filter (Laxbro Bio-medical Aids Pvt. Ltd) prior to their use for the experiment. A549 cells
were maintained for a period of 24 h in the absence of Cu(TMCPMP)(Phen) at a cell density
3
5
of 5.0 x 10 cells/well in a 96 well plate for MTT and LDH assay and 1 x 10 cells/well in a 6
well plate for LDH release assay, mitochondrial membrane potential assay, DCFDA and AO-
EB staining, cell cycle analysis and Annexin V-PI staining assays.
2
.3. Characterization techniques
The synthesized compounds were characterized using elemental analyses, FT-IR and
UV-visible spectroscopy, molar conductance, magnetic measurement and X-ray
crystallography. Elemental analyses (C, H, N) of the synthesized compounds were performed
-1
on a model 2400 Perkin-Elmer elemental analyzer. Infrared spectra (4000-400 cm , KBr
discs) of the samples were recorded on a model RX 1 FTIR Perkin-Elmer spectrophotometer.
1
The H NMR spectrum of the ligand was recorded with a Bruker AV 400 MHz spectrometer
using DMSO-d as the solvent and TMS as an internal reference. The mass spectrum of the
6
ligand was recorded on a Trace GC ultra DSQ II. Electronic spectra (in DMF at room
temperature) in the range 400-800 nm were recorded on a model Perkin Elmer Lambda 35
UV-VIS spectrophotometer. Fluorescence spectra were recorded on a model JASCO, FP-
-3
6
300 fluorescence spectrophotometer. The molar conductivity of a 10 M solution of the
complex in DMF was measured at room temperature with a model Elico CM 180 digital
direct reading deluxe digital conductivity meter. The copper content was determined by
EDTA after decomposing the complex with HNO . Magnetic susceptibility measurement of
3
the complex was carried out with a Gouy balance using [HgCo(CN) ] as the calibrant.
4
2
.4. Synthesis
5

Synthesis of 4-toluoyl pyrazolone [TMCPMP]
The toluoylation reaction of pyrazolone, MCPMP (1-(3-chlorophenyl)-3-methyl-1H-
pyrazol-5(4H)-one), was carried out by following the standard method reported in our
previous articles [15].
2
.4.1. (Z)-2-((1-(3-chlorophenyl)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-yl)(p-
tolyl)methylene) hydrazinecarbothioamide [TMCPMP-TS]
-(3-Chloro-phenyl)-5-methyl-4-(4-methyl-benzoyl)-2,4-dihydro-pyrazol-3-one
TMCPMP, 0.326 g, 1 mmol) and thiosemicarbazide (0.091 g, 1 mmol) in ethanol (50 mL)
2
(
were refluxed for 6 h in round bottom flask. During the reflux a microcrystalline yellow
compound [TMCPMP-TS] separated out, which was isolated by filtration, dried in air and
finally crystallized in the appropriate solvent [15(a)].
TMCPMP-TS consists of light yellow crystals. Yield 85.33 %. M.p. 198 ºC Anal.
calc. for C H ClN OS (M.W.: 399.90): C, 57.07; H, 4.54; N, 17.51; S, 8.02; found: C,
1
9
18
5
1
5
2
7
7.01; H, 4.43; N, 17.44; S, 7.95%; H NMR (DMSO-d ) δ ppm: 1.79 (s, 3H, PZ C–CH ),
6 3
.34 (s, 3H, N-TL C-CH ), 7.68 (s, 2H, NH ), 10.19 (s, 1H, -OH), 7.20-7.36 (m, 4H, Ph),
3
2
-1
.43-7.55 (m, 4H, TL), 8.34 (s, 1H, N-CH), 9.83 (s, 1H, NH-tsc); IR (KBr) υ (cm ): 3274(b)
(
NH ), 3163(b) (NH-tsc), 839(m) (C=S), 1625(m) (C=N, cyclic), 1230 (C=N, azomethane),
2
1
3
1
270(m) (PZ-C-CH ), 935(s) (N-N), 1476(m) (Ph-C-C), 2965(b) (Ph-C-H); C NMR
3
(
DMSO-d ) δ ppm: 15.97-21.40 (methyl groups), 117.68-133.78 (substituted benzene ring);
6
+
+
+
MS: m/z = 398.76 [C H ClN OS, MIP] , 364 [C H N OS] , 334 [C H N OS] , 289
19
18
5
19 18
5
17 12
5
+
+
+
+
+
[
C H N OS] , 261 [C H N OS] , 186 [C H N OS] , 156 [C H N O] , 214 [C H N O] ,
1
3
14
5
11 11
5
5
9
5
9
5
2
12 12
3
+
+
1
2
87 [C H N O] , 91 [C H , Base peak] .
10 9 3 7 7
.4.2. Title complex [Cu(TMCPMP-TS)(Phen)]:
6

To a solution of Cu(NO ) ·3H O (0.241 g, 1mmol) in methanol (5 mL), a solution of
3
2
2
TMCPMP-TS (0.399 g, 1 mmol) in methanol (10 mL) was added while stirring. To this, a
solution of 1,10-phenanthroline (0.198 g, 1 mmol) in methanol (5 mL) was added in warm
methanol (5 mL). The pH of the reaction mixture was maintained at around 7.5 by adding a
1
0% methanolic solution of ammonia. The resultant mixture was refluxed for 3 h. The solid
green crystalline product obtained was filtered off, washed with methanol and dried. The
solid product was dissolved in hot DMSO and was allowed to crystallize at RT. Green
crystals of single crystal X-ray diffraction quality were obtained in 10-15 days. The synthesis
of the complex can be summarized by Scheme 1.
(
Scheme 1)
Cu(TMCPMP-TS)(Phen)]: Green crystals; yield 78.88%. M.p > 250 ºC. Anal. Calc.
for C H ClCuN OS (M.W.: 641.63): C, 58.03; H, 3.77; N, 15.28; Cu, 9.90; found: C, 58.10;
[
3
1
24
7
−
1
H, 3.76; N, 15.15; Cu, 9.78%. IR (KBr, cm ): 3169(b) (NH-tsc), 1192 (C=N, azomethane),
9
6
4
2
38(s) (N-N), 1499(m) (Ph-C-C), 1582(s) (C=N, cyclic), 1192(m) (N-N), 3280(b) (NH2),
41(s) (C–S), 1614(m) (C=N, cyclic), 2919(b) (Ph–C–H), 492(s) (Cu–N), 457(s) (Cu–O),
2
-1
21(s) (Cu–S); Λ /S m M (in DMF, r.t.): 18.
M
.5. Crystallography
Crystals having good morphology were chosen for three-dimensional intensity data
collection. X-ray intensity data of the compounds was collected at room temperature on a
Bruker CCD area-detector diffractometer equipped with graphite monochromated MoKα
radiation (λ = 0.71073 Å). The crystals used for data collection were of suitable dimensions,
0
.30 x 0.20 x 0.10 mm. The unit cell parameters were determined by least-squares refinement
of 16728 reflections. Multi-scan absorption corrections were applied, which also corrected
Lorentz and polarization effects [30]. The structure was solved by direct methods using
SHELXS97 [31]. All non-hydrogen atoms of the molecule were located in the best E-map.
7

Full-matrix least-squares refinement was carried out using SHELXL97 [31]. Hydrogen atoms
were placed at geometrically fixed positions and allowed to ride on the corresponding non-H
atoms with C-H = 0.93-0.96 Å, and U = 1.5 U of the attached C atom for methyl H atoms
iso
eq
and 1.2 U for other H atoms. Atomic scattering factors were taken from the International
eq
Tables for X-ray Crystallography (1992, Vol. C, Tables 4.2.6.8 and 6.1.1.4). An ORTEP [32]
view of the ligand and its complex, with the atomic labelling, are shown in Figs. S1 and 1,
respectively. The packing diagram of the ligand is shown in Fig. S2. The geometries of the
molecules have been calculated using the software PLATON [33] and PARST. [34] The
crystallographic data for the complex and ligand are summarized in Tables 1 and S1,
respectively. Important bond lengths and bond angles of the ligand are listed in Table S2.
2
.6. DNA binding
All of the experiments involving the binding of complex with CT-DNA were carried
out in double distilled water with trisodium citrate (Tris, 15 mM) and sodium chloride (150
mM) and adjusted to pH 7.05 with hydrochloric acid. A DMF solution of the complex was
used throughout the study. The concentration of CT-DNA per nucleotide was estimated from
-1
-1
its known extinction coefficient at 260 nm (6600 M cm ) [35]. Solutions of CT-DNA in tris
buffer gave a ratio of UV absorbance at 260 and 280 nm (A /A ) of 1.8-1.9, indicating
2
60 280
that the DNA was sufficiently free of protein. Absorption titration experiments were
performed by maintaining a constant metal complex concentration (20 μM), while gradually
increasing the concentration of DNA (5-100 μM). While measuring the absorption spectra, an
equal amount of DNA was added to both the test solution and the reference solution to
eliminate the absorbance of DNA itself.
The data were then fitted to eq 1 [36] to obtain the intrinsic binding constant Kb.
…
… (1)
8

where [DNA] is the concentration of DNA in base pairs, ε is the extinction
a
coefficient observed for the MLCT absorption band at the given DNA concentration, ε is the
f
extinction coefficient of the free complex in solution and ε is the extinction coefficient of the
b
complex when fully bound to DNA. A plot of [DNA]/[ε -ε ] versus [DNA] gave a slope of
a
f
1
/[ε -ε ] and Y intercept equal to (1/K )[ε -ε ]. The intrinsic binding constant K is the ratio of
a f b b f b
the slope to the intercept [36].
Competitive studies of the compound with ethidium bromide (EB) have been
investigated by fluorescence spectroscopy in order to examine whether the compound can
displace EB from its CT DNA−EB complex. The CT DNA−EB complex was prepared by
adding 3.3 μM EB and 4.2 μM CT-DNA in buffer (150 mM NaCl and 15 mM trisodium
citrate at pH 7.05). The intercalating effect of the compound with the DNA−EB complex was
studied by adding a certain amount of a solution of the compound step by step (0-30 µM) into
the solution of the DNA−EB complex. The influence of the addition of each compound to the
DNA-EB complex solution has been obtained by recording the variation of fluorescence
emission spectra. The emission spectra were monitored by keeping the excitation of the test
compound at 546 nm and the emission was monitored in the range of 550-750 nm. The
emission was observed at 610 nm.
Commonly, fluorescence quenching can be described by the following Stern-Volmer
equation (eq 2) [37].
…
… (2)
where F and F are the steady-state fluorescence intensities in the absence and
0
presence of quencher, respectively, K is the Stern-Volmer quenching constant, obtained
sv
from the slope of the plot of F /F versus [Complex], [Q] is the total concentration of
0
9

quencher, k is the bimolecular quenching constant and τ is the average lifetime of protein in
q
0
−
8
the absence of quencher, and its value is 10 s.
The apparent DNA binding constant (K ) values of the complex were obtained from
app
the fluorescence spectral measurement. The Kapp values were obtained from the equation:
…
… (3)
where Kapp is the apparent binding constant of the complex studied, [complex] is the
50
concentration of the complex at 50% quenching of DNA-bound ethidium bromide emission
7
-1
intensity, KEB is the binding constant of ethidium bromide (KEB = 1.0×10 M ), and [EB] is
the concentration of ethidium bromide (3.3 μM) [38].
2
.7. Tryptophan Quenching Studies
A similar experimental procedure was followed for the tryptophan quenching study as
used for the DNA binding studies. Quenching of tryptophan residues of BSA was performed
using the complex as a quencher. To solutions of BSA in buffer, increments of the quencher
were added, and the emission signals at 343 nm (excitation wavelength at 296 nm) were
recorded after each addition of the quencher [36].
The data were fitted with the Stern-Volmer eq 2. The Stern-Volmer constant was
obtained from the slope of the plot of F /F versus [Compound].
0
2
.8. Anti-cancer study
2
.8.1. Cell viability (MTT) assay
3
A549 cells (7 x 10 cells/well) were maintain in 96-well culture plates (Tarson India
Pvt. Ltd.) for 24 h in the absence and presence of Cu(TMCPMP)(Phen). At the end of the
incubation period 10μl of 3-(4, 5-dimethylthiazol- 2-yl)-2, 5-diphenyl-tetrazolium bromide
(MTT, 5 mg/ml) was added to the wells and the plates were incubated at 37 °C for 4 h. Later,
culture media were discarded and the wells were washed with Phosphate Buffer Saline (Hi-
1
0

media, India, Pvt. Ltd.), followed by addition of 150 μl of DMSO and subsequent incubation
for 30 min. The absorbance was then read at 540 nm in an ELX800 Universal Microplate
Reader [39].
2
.8.2. Cellular integrity (LDH release) assay
A549 cells were maintained in 96 well plates for 24 h as mentioned above. Later the
supernatant from each well was collected and activity levels of LDH were assayed with a
commercially available kit (Reckon diagnostics Ltd., Mumbai, India) using a Merck microlab
L 300 semi-auto-analyzer and the percentage cytotoxicity was calculated [39].
2
.8.3. Intracellular ROS generation (DCFDA staining)
After 18 h of treatment with Cu(TMCPMP-TS)(Phen), cells were incubated with 7.5
μM 2,7-dichlorodihydrofluoroscein diacetate (CM-H -DCFDA) at 37 °C for 30 min. The
2
cells were observed with a Leica DMRB fluorescent microscope [40].
2
.8.4. Mitochondrial Membrane Potential
The changes in mitochondrial membrane potential were measured using the
fluorescent cationic dye Rhodamine 123 (RHO 123). After 24 h treatment with
Cu(TMCPMP)(Phen), the cells were incubated with 1 μM RHO 123 for 10 min at 37 °C.
The fluorescence was determined at excitation and emission wavelengths of 485 and 530 nm,
respectively using a spectroflurometer (Jasco FP-6300, Japan) and expressed as fluorescence
intensity units (FIU) [41].
2
.8.5. Nuclear morphology assay (DAPI staining)
4
Cells (5 × 10 cells/well) were plated into a 6-well plate. After 80% confluence, the
cells were treated with or without different concentrations of Cu(TMCPMP-TS)(Phen) at 37
C for 24 h. Single-cell suspensions of treated cells were washed with PBS and fixed with
0% ethanol for 20 min at room temperature. Cells were washed again with PBS and stained
with DAPI (0.6 μg/mL in PBS) incubated for 5 min. The nuclear morphology of apoptotic
°
7
1
1

cells with condensed/fragmented nuclei was examined under a fluorescent microscope (Leica
DMRB fluorescence microscope).
2
2
.8.6. Assessment of apoptosis
.8.6.1. AO/EB staining
5
A549 cells (1 x 10 cells/well) were maintained in 6 well plates as described earlier
for 24 h. At the end of the experimental period, the cells were collected using TPVG solution.
One microliter of dye mixture (1 mg/ml AO and 1mg/ml EB in PBS) was mixed with 9 μl of
6
cell suspension (0.5 x 10 cells/ml) on a clean microscope slide, examined and photographed
under a Leica DMRB fluorescence microscope. A minimum of 300 cells were counted in
every sample to calculate the percentage cell death.
2
.8.6.2. Cell cycle analysis
6
Cells (1 × 10 cells/well) were cultured as mentioned earlier for 24 h. After
incubation, the cells were washed once in ice-cold PBS and subjected to cell cycle analysis
5
[
61]. Briefly, 1 × 10 cells were fixed in 4.5 ml of 70% (v/v) cold ethanol for 30 min,
centrifuged at 400 g for 5 min. The supernatant was removed and cells were washed with 5
ml of PBS. Cells were then re-suspended in 0.5 ml of PBS and 0.5 ml of DNA extraction
buffer (Mix 192 ml of 0.2 M Na HPO with 8 ml of 0.1% Triton X-100 v/v) was added. The
2
4
pH was adjusted to 7.8. The cells were incubated at room temperature for 5 min and then
centrifuged at 400 g for 5 min. The supernatant was discarded and the cells were re-
suspended in 1 ml of DNA staining solution (200 mg of PI in 10 ml of PBS + 2 mg of DNase
free RNase). Te cells were then incubated for at least 30 min at room temperature in the dark
and the cell cycle distribution was then analyzed on a flow cytometer (BD FACS Aria III,
USA) using FlowJo (Oregon, USA).
2
.8.6.3. FITC Annexin-V/PI Staining
1
2

Annexin-V FITC/ Propidium iodide double staining assay was used to quantify
apoptosis, according to the manufacturer’s protocol (Invitrogen, UK). After incubation, the
cells were harvested using TPVG solution and washed with ice-cold PBS and suspended in
1
00 μl of 1 × binding buffer (10 mM HEPES, 140 mM NaCl and 2.5 mM CaCl2, pH 7.4). To
this mixture, 5 μl of annexin V-FITC conjugate and 1 μl of propidium iodide solution were
added to each cell suspension, followed by incubation for 15 min at room temperature in the
dark. Later, the samples were analyzed on a flow cytometer (BD FACSAria III, USA) using
FlowJo (Oregon, USA). Double staining of cells with FITC Annexin-V and PI enabled the
-
-
+
-
+
+
discrimination of live cells (FITC PI ), early apoptotic (FITC PI ), late apoptotic (FITC PI )
-
+
or necrotic cells (FITC PI ).
2
.8.6.4. Statistical analysis
The data were analyzed for statistical significance using one way analysis of variance
(ANOVA) followed by Bonferroni’s multiple comparison test and the results were expressed
as mean ± SEM using Graph Pad Prism version 3.0 for Windows, Graph Pad Software, San
Diego, California, USA.
3
3
. Results and discussion
.1. Synthesis
The present work stems from our interest in designing new symmetrical and
unsymmetrical heterocyclic ligands and their mononuclear Cu(II) complexes. The ligand as
well as its ternary Cu(II) complex have been synthesized in a very facile and essentially
identical way. Both compounds are intensively colored, air and moisture free crystalline
solids. They are soluble in common organic solvents, such as DMF, DMSO, MeCN, etc. The
elemental analyses match well with the empirical formula of the ligand and the complex. The
1
3

analytical and spectroscopic data of both the compounds are presented in the experimental
section.
3
.2. Characterization
The ligand has been determined using elemental analysis, FT-IR, H NMR and mass
1
spectroscopies, and by single crystal X-ray diffraction analysis, and the results are consistent
1
with the proposed formula. The FT-IR, H NMR and mass spectra of the ligand are shown in
Figs. S3, S4 and S5, respectively. Detailed characterization of a similar type of ligand system
has been reported by us recently. However, to know the coordination behavior of the ligand,
we have synthesized complexes containing this type of ligand and on the basis of this, it can
act as a binegative tridentate ligand.
The ternary complex has been characterized by elemental analysis, FT-IR and UV-
visible spectroscopy, molar conductance, magnetic measurements and single crystal X-ray
−
3
diffraction analysis. The lesser molar conductance value of the complex in DMF (10
M
solution at 25 °C) indicates that the complex is non-electrolytic in nature [42]. The elemental
analyses data concur well with the planned formulae for the complex and recognize the
[
Cu(TMCPMP-TS)(Phen)] composition.
.3. IR spectroscopy
On comparison of the IR spectrum of the ligand with that of the Cu(II) complex, the
3
-1
IR spectrum of the complex showed a major shift to lower wavenumbers by 20-30 cm for
the azomethane v(C-N) band, suggesting involvement of the azomethane-N with the Cu(II)
ion in the complexation. These overall data suggest that the azomethane-N, enol-O and thiol-
S groups are involved in coordination with the Cu(II) ion during complexation. In the low
frequency region, the spectrum of the complex exhibits new bands which are not present in
-1
the spectrum of the ligand. These bands are at 492, 457 and 421 cm and are assigned to
1
4

-1
v(Cu-N), v(Cu-O) and v(Cu-S). Bands at ca 1,518, 1,425 and 721 cm in the mixed phen
complex, assigned to v(C=N), v(C=C) and out-of-plane -CH stretching vibrations of 1,10-
phenanthroline, confirm the presence of the phen ligand in the coordination sphere of the
complex.
3
.4. UV-visible spectroscopy
The visible spectrum for the complex under investigation was measured in DMF. In
DMF, the complex displayed absorbance maxima in the 670–690 nm range. For five-
coordinate Cu(II) complexes, this spectral feature is typical for SP or distorted SP geometries,
2 2
x -y
which generally exhibit a band in the 550–660 nm range (d , d → d
). In contrast, TBP
xz
yz
2 2
x -y
2
Cu(II) complexes usually show a maximum at λ > 800 nm (d , d
→ d ) with a higher
xz
z
energy shoulder. Thus, in DMF, the geometry about the Cu(II) centre in the complex is closer
to SP. These data are consistent with the reported literature for distorted square pyramidal
Cu(II) complexes [43].
3
.5. Magnetic measurement studies
The magnetic data provide a great deal of information complementary to that
available from the electronic spectrum. The room temperature magnetic moment of the
complex is 1.78 BM, which is close to one electron paramagnetism of a mononuclear Cu(II)
ion.
3
.6. Crystal structure description of the title complex
The molecular structure and the atom labelling scheme is shown in Fig. 1. The
crystallographic data of the complex are listed in Table 1. The main bond distances and
angles are listed in Table 2. The packing diagram of the complex is shown in Fig. 2.
(
Fig.1)
Fig.2)
(
1
5

As shown in Fig. 1, the Cu(II) ion is pentacoordinated by three nitrogen atoms
azomethane N21 and pyridine N26, N37), one oxygen donor (enol O1) and one sulfur donor
thiol S25). The Cu-Nphen distances observed [Cu1-N26, 2.033(3) Å; Cu1-N37, 2.261(4) Å]
(
(
fall within the range for Cu-Nimine distances observed for other diimine complexes already
reported [44]. In the complex, the copper atom occupies a distorted square pyramidal
environment (SP), where the basal plane is formed by three atoms (N21, S25, O1) supplied
by the thosemicarbazone ligand and one atom (N26) supplied by the phen ligand. The arm of
the phen ligand completes the fifth coordination site, in the apical position (N37). The Cu–
N/O/S distances of the basal plane are Cu(1)-O(1)=1.932(3), Cu(1)-N(21)=1.972(3), Cu(1)-
S(25)=2.2624(11) and Cu(1)-N(26)=2.033(3) Å, and the Cu(1)–N(37) distance is 2.261(4) Å.
The complex shows intermolecular interactions, which are highly relevant to binding studies.
The geometry of N-H…N hydrogen bonds is listed in Table 3.
To obtain the quantitative degree of distortion of the copper polyhedron, the ratio
between the two basal angles, defined as τ = [(θ-φ) /60] × 100, that represents the percentage
of trigonal distortion from square pyramidal geometry [45], was used. For an ideal SP τ is 0,
while for an ideal TBP τ is 100. Thus, for title complex (see Fig. 2 for labelling) the relevant
angles, θ =172.21 and φ = 152.38° (Table 2) yield a τ value of 33%, which indicates a
geometry close to SP.
Complex formation can be proven also by comparing the X-ray data of the ligand and
the title complex. It is clearly seen that there are some changes in the bond distances in the
ligand on complexation. The changes are listed in Table 4. The N22-C23 bond was present as
a single bond in the ligand, but its length decreased after complexation, indicating an increase
in the double bond character in this bond. Also, C3-O3 was present as a double bond in the
ligand, and its bond length increased after complexation, indicating an increased single bond
character of this bond after complexation. Actually, the bond lengths of both these bonds are
1
6

between the single and double bonds, indicating the involvement of these bonds in resonance
forms in the chelate ring after complexation.
3
.7. DNA binding studies
It is a well-known fact that DNA is the primary pharmacological target of many
antitumor compounds, and hence the interaction between DNA and metal complexes is of
paramount importance in understanding the mechanism. Thus, the mode and propensity for
binding of the complex to CT-DNA were studied with the aid of different techniques.
Monitoring the changes in the absorption spectra of metal complexes upon addition of
increasing amounts of DNA is one of the most widely used methods for determining the
overall binding constants. The absorption spectra of the complex in the absence and presence
of CT-DNA (at a constant concentration of complex, 10 µM) is shown in Fig. 3. In the UV
spectrum of the complex, the intense absorption band observed is attributed to the intraligand
transition of the characteristic groups of the coordinated ligand. Any interaction between the
complex and DNA could perturb the intraligand-centered spectral transitions, as observed in
the UV spectra of a 10 µM solution of the complex upon addition of DNA at different
concentrations. In the UV region, the complex exhibited an intense absorption band at 270
nm, which was assigned to the π → π* transition of the aromatic chromophore. With
increasing amounts of CT-DNA (5-100 µM), the absorption bands of complex are affected,
exhibiting hyperchromism for the π → π* transition of the complex. The strong
hyperchromic effect for the π → π* transition suggests that this complex possesses a high
propensity for DNA binding.
(Fig.3)
The results derived from the UV titration experiments suggest that the complex can
bind to CT-DNA [46]. The hyperchromism observed may be a first evidence of possible
external binding to CT-DNA, while the existence of planar ligands may suggest stabilization
1
7

upon binding to DNA; in such a case, intercalation due to π → π* stacking interactions
between the base pairs of CT-DNA may not be ruled out [47]. Nevertheless, the exact mode
of binding cannot be merely proposed by UV spectroscopic titration studies. In order to
compare quantitatively the binding strength of the complex with CT-DNA, the intrinsic
binding constant K of the complex was determined by monitoring the changes in absorbance
b
of the π → π* band with increasing concentrations of CT-DNA. The K value was found to
b
4
-1
be 4.3 × 10 M , suggesting that the complex has a strong binding affinity for calf thymus
DNA.
The complex shows no fluorescence either in DMF or in the presence of DNA. So,
the competitive DNA binding of the complex has been studied by monitoring changes in the
emission intensity of ethidium bromide (EtBr) bound to CT-DNA as a function of added
complex concentration to get final proof for the binding of the complex to DNA via
intercalation. Though the emission intensity of EtBr in buffer medium is quenched by the
solvent molecules [47], it is enhanced by its stacking interaction between adjacent DNA base
pairs. When the complex was added to DNA pretreated with EtBr {[DNA]/[EtBr]=1:1}, the
DNA-induced emission intensity of EtBr decreased (Fig. 4 (A)). Addition of a second DNA
binding molecule would quench the EtBr emission by either replacing the DNA-bound EtBr
(if it binds to DNA more strongly than EtBr) or accepting an excited state electron from EtBr.
Because the complex has planar ligands, they efficiently compete with strong intercalators
like EtBr for intercalative binding sites on DNA by replacing EtBr, which is reflected in the
quenching of the emission intensity of DNA-bound EtBr. The titrations were also carried out
for both the ligands (Figs. 4 (B & C)). The emission intensity was decreased in both the
cases, but the effect was much lower as compared to the complex.
(Fig.4)
1
8

Quenching data were analyzed according to the following Stern-Volmer equation for
the complex as well as for the ligands. The plot of F /F versus [Q] is shown in Fig. 5. The
0
5
-1
5
-1
values of the Stern-Volmer constants were found to be 1.3 × 10 M (complex), 0.6 × 10 M
5
-1
(
TMCPMP-TS) and 0.8 × 10 M (1,10-phenanthroline). The values are in good agreement
7
−1
with the constants observed for typical classical intercalators (ethidium–DNA, 1 × 10 M ).
The diminution of the intrinsic binding constants could be explained by the steric constraints
imposed by the ligand framework, thus encouraging a partial intercalation binding mode for
the complex. Further, the apparent binding constant (K ) value was obtained for the
app
6
-1
complex and it was found to be 1.1 × 10 M .
(
Fig.5)
These data suggested that the interaction of the Cu(II) complex with CT-DNA is
stronger than that of the free ligand. Since these changes indicate only one kind of quenching
process, it may be concluded that the compounds bind to CT-DNA via the same mode.
Furthermore, such quenching constants and binding constants of the ligands and Cu(II)
complex suggest that the interactions of all of the compounds with DNA should be
intercalation [48].
3
.8. Protein binding studies
Tryptophan emission quenching experiments were carried out using bovine serum
albumin (BSA) in the presence of the complex and the ligands to investigate their interactions
with proteins. Generally, the fluorescence of BSA is caused by two intrinsic characteristics of
the protein, namely tryptophan and tyrosine. Changes in the emission spectra of tryptophan
are common in response to protein conformational transitions, subunit associations, substrate
binding or denaturation. Therefore, the intrinsic fluorescence of BSA can provide
considerable information on their structure and dynamics and is often utilized in the study of
protein folding and association reactions. The quenching of the emission intensity of BSA
1
9

was observed in the presence of the complex because of the possible changes in the protein
secondary structure, leading to changes in the tryptophan environment of BSA [49].
The interaction of BSA with the complex and the ligands was studied by fluorescence
measurement at room temperature. A solution of BSA (5 μM) was titrated with various
concentrations of the compounds (0-20 μM). The effects of the complex and the ligands on
the fluorescence emission spectrum of BSA are shown in Fig. 6. The addition of the above
compounds to a solution of BSA resulted in a significant decrease in the fluorescence
intensity of BSA at 343 nm, up to 57.37% from the initial fluorescence intensity of BSA.
This result suggests a definite interaction of the compounds with the BSA protein [50].
(Fig.6)
The Stern-Volmer constants were calculated for this system and the values were
5
-1
5
-1
5
-1
found to be 1.7 × 10 M (complex), 1 × 10 M (TMCPMP-TS) and 0.6 × 10 M (1,10-
phenanthroline). These constants were calculated from the slope of the plot F /F versus
0
[
Compound] (Fig. 7). The Ksv values suggest that the complex has a higher binding
propensity than the ligands. The bimolecular constant K was also calculated for the complex
q
1
3
-1 -1
13
-1 -1
and the ligands. The values are 1.7 × 10 M s (complex), 1 × 10 M s (TMCPMP-TS)
1
3
-1 -1
and 0.6 × 10 M s (1,10-phenanthroline).
(Fig.7)
3
.9. Anti-cancer studies
3
.9.1. Cell viability (MTT) and cellular integrity (LDH) release assay
Anticancer activity of Cu(TMCPMP-TS)(Phen) was assessed against A549 lung
carcinoma cells by an MTT assay. Cu(TMCPMP-TS)(Phen) was able to inhibit the growth of
A549 cells in a dose dependent manner (56.86 ±1.01% and 96.85±0.72% at 0.12 μM and
0
.240 μM respectively) (Fig. 8). The cytotoxic nature of Cu(TMCPMP-TS)(Phen) towards
A549 cells was further confirmed by an LDH release assay. LDH enzyme leaches out of dead
2
0

cells and hence quantification of its content in the culture media indirectly reveals the extent
of the cell damage [51,52] Maximum LDH release was recorded (0.240 μM dose) in A549
cells, suggesting extensive damage to the cells following Cu(TMCPMP-TS)(Phen) treatment
(Fig. 9).
(
Fig.8)
Fig.9)
(
3
.9.2. Intracellular ROS generation (DCFDA staining)
Intracellular ROS can trigger apoptosis via initiation of downstream signals in a cell
cycle [53]. The dye (2,7 dichlorodihydrofluorescein - H DCFDA) used in the present study
2
crosses the cell membrane, wherein the intracellular H O converts the non-fluorescent
2
2
H DCFDA to DCF and emits green fluorescence [54,55]. In the present study, A549 cells
2
showed green fluorescence following Cu(TMCPMP-TS)(Phen) treatment, with the most
prominent fluorescence recorded at the 0.240 μM dose (Fig. 10). These results indicate that
Cu(TMCPMP-TS)(Phen) is instrumental in the generation of intracellular ROS in a dose
dependent manner.
(Fig.10)
3
.9.3. Mitochondrial membrane potential
Another dye, RHO 123, accumulates in mitochondria and produces fluorescence. Its
fluorescent intensity is directly proportional to the mitochondrial membrane potential of a
cell, and hence RHO 123 is popularly used to assess the energy state of functional
mitochondria [56]. Treatment of A549 cells with Cu(TMCPMP-TS)(Phen) resulted in a dose
dependent decrement (244.00±4.58 FIU and 69.33±4.48 for 75 FIU and 0.240 μM doses
respectively) as compared to the untreated cells (475.70±7.51) (Fig. 11). These results further
strengthen the claim about the potency of Cu(TMCPMP-TS)(Phen) in induction of
mitochondrial dysfunction of A549 cells in culture following 24 h treatment.
2
1

(Fig.11)
3
.9.4. Nuclear morphology assay (DAPI staining)
DAPI binds to the AT rich regions of DNA and is used to distinguish the compact
chromatin of apoptotic nuclei from that of normal cells. As shown in Fig. 12, exposure of
A549 cells to the complex resulted in the appearance of a greater number of cells with
condensed nuclei as compared to the control cells.
(Fig.12)
3
3
.9.5. Assessment of apoptosis
.9.5.1. AO/EB staining
Acridine Orange stains live cells (green) whereas ethidium bromide stains dead cells
red-to-orange), hence this method of dual staining enables the rapid and easy
(
recognition/differentiation of live-dead cells when visualized under a fluorescence
microscope [57]. The present study showed a dose dependent increment in EtBr positive cells
following Cu(TMCPMP-TS)(Phen) treatment as compared to untreated cells. The highest
dose of 0.240 μM appeared to be the most potent in induction of cell death, as evidenced by a
high number of EtBr positive and a much lower number of AO positive cells (Fig. 10).
3
.9.5.2. Cell cycle analysis
The underlying mechanism involved in the inhibition of growth of A549 cells
exposed to Cu(TMCPMP-TS)(Phen) was examined by assessment of the cell cycle; a method
that is based on evaluation of cellular DNA content. The cell cycle analysis of a control group
showed 93.8 % of cells in the G /G phase and 3.33 % of cells in the sub G /G phase,
0
1
0
1
whereas the Cu(TMCPMP-TS)(Phen) treated group recorded 16.4 % cells in the G /G phase
0
1
and 83.3 % of cells in the sub G /G phase (Fig. 13). As compared to the control group, a
0
1
higher number of cells were recorded in the sub G /G phase, indicating that Cu(TMCPMP-
0
1
TS)(Phen) induced death of A549 cells.
2
2

(Fig.13)
3
.9.5.3. FITC Annexin-V/PI staining
Apoptosis is a process of cell death characterized by various morphological and
biochemical alterations, leading to cell disruption and formation of apoptotic bodies [44].
One of the hallmarks of apoptosis is that membrane phospholipids, such as
phosphatidylserine, rearrange from the inner to the outside surface of the plasma membrane
and get exposed on the cell surface. This can be detected due toa high affinity for annexin V.
A flow cytometric assay with Annexin V/PI double staining of control and Cu(TMCPMP-
TS)(Phen) treated cells showed that the apoptosis rate was increased with
Cu(TMCPMP)(Phen) treatment, wherein the treated cells recorded 20.2 % annexin V positive
(
early apoptotic) and 11.9 % PI positive cells (late apoptotic) (Fig. 14).
Fig.14)
(
A similar cytotoxicity test (MTT assay) was also executed with rat cardiac myocytes
H9C2 cells), wherein the cells were cultured in the presence of Cu(TMCPMP-TS)(Phen).
(
The rationale behind choosing H9C2 cells was to assess the possible cytotoxicity of
Cu(TMCPMP-TS)(Phen) against a normal cell line as sensitive as rat cardiac myocytes. It
was noted that Cu(TMCPMP-TS)(Phen) treated cells revealed no significant cell death, as
evidenced by the fact that the results obtained that were comparable to those of the control
(Fig. 8). The same needs further investigation to probe the underlying mechanism. However,
the anticancer activity of Cu(TMCPMP-TS)(Phen) is possibly attributable to its ability to
bring about conformational changes and cleavage of cellular DNA, and the ability to bind to
the cellular proteins involved in inducing cancer.
4
. Conclusion
This report describes the synthesis and characterization of a ternary Cu(II) complex,
which has been derived from a pyrazolone based thiosemicarbazone and 1,10-phenanthroline.
2
3

The ligand and complex have been characterized by X-ray crystallography. The complex has
a geometry in between SP and TBP, which has been explained on the basis of the trigonality
index. DNA binding and protein binding studies have been investigated using CT-DNA and
bovine serum albumin (BSA), respectively. The binding constants showed that the complex
has a higher binding affinity than the ligand. An anticancer study also revealed a high grade
of cytotoxicity and cell cycle arrest in the sub G /G phase, implying the potency of
0
1
Cu(TMCPMP-TS)(Phen) as an anticancer agent against A549 cells. The results envisaged
herein indicate that Cu(TMCPMP-TS)(Phen) holds ample merit to develop it as a therapeutic
agent against cancer. Presently, we are focusing on understanding the type of interaction
between the copper complex and DNA that is responsible for the cytotoxicity.
The presence of copper, with a daily intake not exceeding 4-7 mg, is safe and can
minimize the above diseases. Therefore, it is appropriate to design anticancer drugs based on
copper, which is anticipated to cause lower toxic effects. In this context, we have started to
develop ternary complexes of Cu(II) that are expected to be less toxic but highly potent in
smaller dosages compared to cisplatin and analogous compounds.
Appendix A. Supplementary data
CCDC 885025 and 815002 contain the supplementary crystallographic data for
[
Cu(TMCPMP-TS)(Phen)] and TMCPMP-TS, respectively. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
3
36-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgement
The authors are thankful to the University Grants Commission, New Delhi for
financial assistance with this work in terms of a major research project to RNJ. They are also
2
4

thankful to the Head, Department of Chemistry and Department of Zoology for providing the
necessary facilities required to carry out this work. The award of a University Research
Fellowship to KMV is also gratefully acknowledged.
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