K. Karami et al. / European Journal of Medicinal Chemistry 73 (2014) 8e17
15
Table 5
activity of the Pd(II) compound in these three cell lines, as observed
in the screening of other antitumor agents [73,74].
Cytotoxicity data (IC50) of the dppe and N-benzyl ethylamine ligands and their
palladium (II) complexes against human Hela, HT-29, K562 and MCF-7 tumor cell
lines.
3. Conclusion
Compound
IC50
(
m
M) ꢄ SD
HT-29
Hela
K562
MCF-7
Two new cyclopalladated compounds bearing biphosphinic
ligand dppe have been described in this work. The single crystal
X-ray crystallographic study of 1 revealed a slightly tetrahedrally
distorted square planar geometry around the Pd(II) ion. The DNA-
binding properties of the two complexes were explored by
electronic absorption and fluorescence spectroscopy. The results
suggested that both complexes could interact with FS-DNA
through the intercalation mode and both follow the binding af-
finity order of 2 > 1. The reactivity towards BSA revealed that the
quenching of BSA fluorescence by the two complexes are static
quenching, and complex 2 exhibits greater binding affinity than
that of complex 1. The binding distances of 1 and 2 with BSA
were calculated to be 2.92 and 3.91 nm, respectively, on the basis
of the Foster’s theory, which indicates the energy transfer from
BSA to complexes can occur. The cytotoxic studies show that the
complexes exhibit high cytotoxic activity against different cell
lines tested. Also, the results of cytotoxicity revealed that the
metal complexes are more effective than that of the respective
free ligands under identical experimental conditions and the use
of bromide instead of chloride improved the biological activity. It
is interesting that the DNA and protein binding abilities of the
two complexes are consistent with in vitro cytotoxic activity and
follow the order of 2 > 1.
dppe
>100
>100
8.5 ꢄ 0.4
7.5 ꢄ 0.6
53.5 ꢄ 1.4
100 ꢄ 0.02
100 ꢄ 0.09
7.5 ꢄ 0.22
5.3 ꢄ 0.5
100 ꢄ 0.1
100 ꢄ 0.07
3.1 ꢄ 0.02
2.5 ꢄ 0.51
7.6 ꢄ 0.07
>100
N-Benzyl ethylamine
1
2
100 ꢄ 0.06
7.5 ꢄ 0.02
7.5 ꢄ 0.05
5.2 ꢄ 0.04
cisplatin
41.2 ꢄ 0.09
distance between each complex and BSA is less than 8 nm, and
0.5R0 < r < 1.5R0, implying that the energy transfer from BSA to
complexes occurred with high probability. The bigger r value
compared with that of R0 again indicated the presence of static
quenching mechanism in the binding of two complexes to BSA [70].
2.5. Cytotoxic activity against human tumor cell lines
In vitro cytotoxicity of compounds was evaluated by means of
the standard MTT-dye reduction assay which is a widely used
method in biological evaluation. Recently, new metal complexes
were assessed using this method [71,72]. The cytotoxic activity of
the dppe and N-benzyl ethylamine ligands and their Pd(II) com-
plexes were tested against human cervix carcinoma (Hela), colon
cancer (HT-29), leukemia cancer (K562) and human breast carci-
noma (MCF-7) tumor cell lines. The results are reported in Table 5 in
terms of IC50 values (the concentration needed to inhibit 50% of the
cellular proliferation). For comparison purposes, the cytotoxicity of
cisplatin, a standard antitumor drug, was evaluated under the same
conditions. As depicted in Table 5, compounds 1 and 2 exhibit high
4. Experimental
4.1. General
antiproliferative activity with IC50 values in the range 2e9
mM
Starting materials and solvents were purchased from Sigmae
Aldrich or Alfa Aesar and used without further purification. FS-DNA
and BSA were purchased from SigmaeAldrich and were used as
supplied. Cisplatin was gifted from Isfahan University of Medical
Sciences. Infrared spectra were recorded on a FT-IR JASCO 680
spectrophotometer in the spectral range 4000e400 cmꢀ1 using the
KBr pellets technique. NMR spectra were measured on a Bruker
spectrometer at 400.13 MHz (1H) and 161.97 MHz (31P) using
standard pulse sequences at 298 K. Elemental analysis was per-
formed on a Leco, CHNS-932 apparatus. UVeVis spectra were
recorded on a JASCO 7580 UVeViseNIR double-beam spectro-
photometer using a quartz cell with a path length of 10 mm.
Fluorescence spectra were performed on a PerkineElmer LS55
fluorescence spectrofluorometer.
below those of cisplatin in three cell lines, which is a reflection of
their good solubility and lipophilicity. The lipophilicity of the
bridged complexes can be related to the presence of two bulky PPh2
groups from dppe which facilitate transport through the cellular
membranes. In addition, the dppe bridge leads to the more flexi-
bility in the structures and makes more interactions with DNA.
It was also observed that 1 and 2 demonstrated a noticeable
cytotoxicity against all cell lines when compared with the free li-
gands, implying that the biological activity is largely ascribed by the
presence of the Pd(II) metal center. In addition, compound 2
exhibited a slightly higher toxicity than 1 against Hela, HT-29 and
K562 cell lines (Fig. 10). These results suggest that the replacement
of the chloride by the bromide ligand increased the cytotoxic
4.2. Synthesis of [Pd2{(C,N)eC6H4CH2NH(Et)}2(m-dppe)(Cl)2] (1)
To a suspension of the dimer [Pd2{(C,N)eC6H4CH2NH(Et)}2(
m-
Cl)2] (0.077 g, 0.14 mmol) in dichloromethane (15 mL) was added
dppe (0.055 g, 0.14 mmol). The reaction mixture was stirred for 2 h
at room temperature and then filtered through a plug of MgSO4.
The filtrate was concentrated to ca. 2 mL and to this concentrated
solution, n-hexane (15 mL) was added to precipitate a white solid,
which was collected and air-dried. White crystals of 1 were ob-
tained from CH2Cl2ehexane. Yield: 85%. 1H NMR (CDCl3, ppm):
d
¼ 1.29 (t, 3H, CH3), 2.72e2.81 (m, 1H, CHaH), 2.85e3.20 (m, 2H,
CH2), 3.20e3.26 (m, 1H, CHbH), 3.81e3.90 (m, 2H, CH2 (dppe)), 4.68
(br s, 1H, NH), 6.28 (br s, 1H, C6H4), 6.40 (t, 1H, C6H4), 6.80 (t, 1H,
C6H4), 6.98 (d, 1H, C6H4), 7.28e7.95 (m, 10H, Ph); 31P{1H} NMR
(CDCl3, ppm):
55.5; H, 5.08; N, 2.94. Found: C, 55.3; H, 5.02; N, 2.90%.
d
¼ 37.3 (s). Anal. calcd. for C44H48N2P2Cl2Pd2: C,
Fig. 10. In vitro cytotoxic activity of 1 and 2 against different human tumor cell lines.
Karami, Kazem
