Photoactive platinum(II) β-diketonates as dual action anticancer agents

Article abstract of DOI:10.1039/c6dt02590k

Platinum(ii) complexes, viz. [Pt(L)(cur)] (1), [Pt(L)(py-acac)] (2) and [Pt(L)(an-acac)] (3), where HL is 4,4′-bis-dimethoxyazobenzene, Hcur is curcumin, Hpy-acac and Han-acac are pyrenyl and anthracenyl appended acetylacetone, were prepared, characterized and their anticancer activities were studied. Complex [Pt(L)(acac)] (4) was used as a control. Complex 1 showed an absorption band at 430 nm (? = 8.8 × 10⁴ M^-1 cm^-1). The anthracenyl and pyrenyl complexes displayed bands near 390 nm (? = 3.7 × 10⁴ for 3 and 4.4 × 10⁴ M^-1 cm^-1 for 2). Complex 1 showed an emission band at 525 nm (Φ = 0.017) in 10% DMSO-DPBS (pH, 7.2), while 2 and 3 were blue emissive (λ_em = 440 and 435, Φ = 0.058 and 0.045). There was an enhancement in emission intensity on glutathione (GSH) addition indicating diketonate release. The platinum(ii) species thus formed acted as a transcription inhibitor. The released β-diketonate base showed photo-chemotherapeutic activity. The complexes photocleaved plasmid DNA under blue light of 457 nm forming ～75% nicked circular (NC) DNA with hydroxyl radicals and singlet oxygen as the ROS. Complexes 1-3 were photocytotoxic in skin keratinocyte HaCaT cells giving IC₅₀ of 8-14 μM under visible light (400-700 nm, 10 J cm^-2), while being non-toxic in the dark (IC₅₀: ～60 μM). Complex 4 was inactive. Complexes 1-3 generating cellular ROS caused apoptotic cell death under visible light as evidenced from DCFDA and annexin-V/FITC-PI assays. This work presents a novel way to deliver an active platinum(ii) species and a phototoxic β-diketone species to the cancer cells.

Full text of DOI:10.1039/c6dt02590k

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DOI: 10.1039/C6DT02590K
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Photoactive platinum(II) β-diketonates as dual action anticancer
agents†
Received 00th January 20xx,
Accepted 00th January 20xx
Md Kausar Razaa,#, Koushambi Mitraa,#, Abhijith Shettarb, Uttara Basua, Paturu Kondaiah*,b and
Akhil R. Chakravarty*,a
DOI: 10.1039/x0xx00000x
Platinum(II) complexes, viz. [Pt(L)(cur)] (1), [Pt(L)(py-acac)] (2) and [Pt(L)(an-acac)] (3), where HL is 4,4’-
bis-dimethoxyazobenzene, Hcur is curcumin, Hpy-acac and Han-acac are pyrenyl and anthracenyl appended
acetylacetone, were prepared, characterized and their anticancer activity studied. Complex [Pt(L)(acac)] (4)
was used as a control. Complex 1 showed an absorption band at 430 nm (ε = 8.8 x 104 M–1 cm–1). The
anthracenyl and pyrenyl complexes displayed bands near 390 nm (ε = 3.7 x 104 for 3 and 4.4 x 104 M–1 cm–1
for 2). Complex 1 showed an emission band at 525 nm (Φ = 0.017) in 10% DMSO-DPBS (pH, 7.2), while 2
and 3 were blue emissive (λem = 440 and 435, Φ = 0.058 and 0.045). There was an enhancement in emission
intensity on glutathione (GSH) addition indicating diketonate release. The platinum(II) species thus formed
acted as transcription inhibitor. The released -diketonate base showed photo-chemotherapeutic activity. The
complexes photocleaved plasmid DNA in blue light of 457 nm forming ~75% nicked circular (NC) DNA with
hydroxyl radicals and singlet oxygen as the ROS. Complexes 1-3 were photocytotoxic in skin keratinocyte
HaCaT cells giving IC50 of 8-14 μM in visible light (400-700 nm, 10 J cm-2), while being non-toxic in the dark
(IC50: ~60 μM). Complex 4 was inactive. Complexes 1-3 generating cellular ROS caused apoptotic cell death
in visible light as evidenced from DCFDA and annexin-V/FITC-PI assays. This work presents a novel way to
deliver an active platinum(II) species and a phototoxic -diketone species in the cancer cells.
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to show anticancer activity with transcription inhibition properties
and improved aqueous solubility, hydrolytic stability, and cellular
uptake.11,12 The platinum(II) drugs are extracellular charge neutral
Introduction
Cisplatin, oxaliplatin and carboplatin are the platinum-based
compounds currently used as chemotherapeutic agents for a variety
of cancers. The drug activity is related to the release of the labile
ligands with concomitant generation of active platinum(II) species
that acts as DNA crosslinker with transcription inhibition properties.
1-5 Cisplatin suffers from its reduced activity due to rapid loss of the
chloride ligands in an intracellular medium and thus getting
deactivated.6 The rate of intracellular ligand release is relatively slow
when the chlorides are substituted by a dianionic dicarboxylate in
carboplatin or an oxalate ligand in oxaliplatin.7,8 This leads to an
enhancement of the drug activity. Despite their successful clinical
use, these drugs suffer from several side effects. Photodynamic
therapy (PDT) has emerged as an alternate non-invasive therapeutic
method for treatment of several forms of cancer.9,10 Platinum(II) β-
diketonates with the ligands acting as good leaving group are known
species showing significant nuclear uptake with nuclear DNA being
the primary target of binding. We have recently shown that similar
charge neutral platinum(II) catecholates of 2-(phenylazo)pyridine
(pap) are efficient photocytotoxic agents giving IC50 values of ~5
µM in visible light (400-700 nm) in HaCaT (human skin
keratinocytes) and MCF-7 (human breast cancer) cells with low dark
toxicity (IC50 >40 µM) and significant nuclear uptake.13 The
anticancer activity is due to glutathione (GSH)-triggered release of
the catecholate ligand to generate an active pap-bound platinum(II)
species as a DNA crosslinker. The released photoactive catecholate
acts as a phototoxin. With a follow-up to this work we have
successfully prepared
a cis-diammineplatinum(II) complex of
curcumin (Hcur) and this complex, named as Platicur, showed
photoactivated curcumin release thus forming dual action DNA
crosslinking and photochemotherapeutic agents.14 Unlike the
conventional platinum(II) drugs, [Pt(cur)(NH3)2](NO3) is
a
monocationic species with curcumin in its enolic form as a
monoanionic -diketonate ligand. Interestingly, the complex
displays cytosolic localization in preference to the nuclear uptake.
Utilizing the Pt-O(cur) bond dissociation on photo-activation, this
complex exemplified a prodrug that leads to facile cellular delivery
of curcumin (Hcur) which is an active ingredient of turmeric with
important medicinal values.15-19
a
Department of Inorganic and Physical Chemistry, Indian Institute of Science,
Bangalore 560012, India
b Department of Molecular Reproduction, Development and Genetics, Indian
Institute of Science, Bangalore 560012, India.
# Authors contributed equally to the manuscript.
†
Electronic Supplementary Information (ESI) available: spectral and
electrochemical plots, DNA binding, cleavage, cellular and DFT data (Scheme S1,
Fig. S1 – S42, Table S1). See DOI: 10.1039/b000000x/
This journal is © The Royal Society of Chemistry 20xx
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The present work stems from our interests to design platinum(II) Result and Discussion
complexes of monoanionic -diketonate ligands like curcumin
(Hcur) and acetylacetone (Hacac) derivatives having photoactive
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DOI: 10.1039/C6DT02590K
Synthesis and characterization
Complexes 1-4 were synthesized in high yields (~80%) from a
general reaction involving a precursor platinum(II) allyl dimeric
complex with 4,4’-bis-dimethoxyazobenzene in chloroform to obtain
an intermediate species of formulation [Pt(L)(µ-Cl)]2 (Scheme S1,
ESI†). This dimeric species was subsequently reacted with the
thallium salt of the β-diketonates (Hcur for 1, Hpy-acac for 2, Han-
acac for 3 and Hacac for 4) in dichloromethane to isolate the desired
products. Melting point measurements of the complexes 1-4 showed
their decomposition at 180, 188, 168 and 145 ºC respectively. The
complexes were characterized from their analytical and
spectroscopic data (Fig. 2, Fig. S1-S24, ESI†). Selected
physicochemical data are given in Table 1. The ESI-MS spectra of 1-
3 in methanol displayed a single peak (respective m/z = 804.18,
722.17 and 698.16) corresponding to the [M+H]+ species (Fig. S1-
S3, ESI†). The isotopic distribution pattern indicated the presence of
platinum in the complexes and the unipositive charge of the
fragments the complexes under applied voltages. The 1H NMR
spectral data were used to characterize the diamagnetic platinum(II)
complexes (Fig. S4-S7, ESI†). The β-diketonate ligands showed
characteristic singlet peak in the range of 5.50-6.20 ppm, which is
assignable to the hydrogen atom of the γ-protons of the methylene
groups. The aromatic hydrogen atom peaks of the curcumin, pyrenyl
or anthracenyl moiety were in the range of 7.0−8.9 ppm, while the
hydrogen atoms of the azo liand gave signals within 6−8 ppm. The
protons corresponding to the methoxy groups of the azo ligand were
within 3.8-4.1 ppm. The NMR peaks observed near 2.0 ppm were
moieties (Hpy-acac, Han-acac) and study their
photochemotherapeutic activity. Organometallic compounds have
recently been found to be promising anticancer drug.20 The choice of
organometallic, a monoanionic C,N-donor azo ligand is to obtain
charge neutral complexes while the presence of monoanionic O,O-
donor -diketonate ligands ensures slow release of the ligand to
generate an active platinum(II) species that could possibly form
covalent linkage to the cellular DNA. The cyclometallated
platinum(II) moiety is expected to have a {PtII(C–,N)}+ core which is
stable in a cellular medium like the well known active platinum(II)
species.21-23 The objective of using curcumin (Hcur) and
pyrenyl/anthracenyl appended acetylacetonates as -diketonates is
to achieve photo-induced and/or glutathione-triggered generation of
two active species, viz. a cisplatin analogue as the cytotoxin and the
released curcumin/acac derivatives as phototoxins. GSH as a non-
protein thiol is the key regulator for various biological processes
involving the platinum-based drugs.24,25 An elevated level of GSH is
found in most cancer cells (~15 mM) and it could act as a potent
tumour target. Recent reports have shown that platinum(II) and half-
sandwich organometallic (6-arene)ruthenium(II) complexes are
highly cytotoxic because of the redox reactions of the metal-
coordinated azo ligands and GSH.13,26-30 As mentioned above, the
GSH triggered release of the platinum(II) bound catecholate ligands assigned to the protons of the methyl groups. The 13C NMR spectra
of the ligands and their metal complexes showed the presence of
C=O (β-diketonate moiety) carbons, giving signals within 190-160
ppm (Fig. S8-S13 ESI†). The carbon atoms of complex 1 bearing the
OH moiety appeared at 142 and 148 ppm. The characteristics γ-
carbon peaks of the β-diketonate moiety for free ligands and in metal
bound form showed signals within 110-90 ppm. The signals around
is shown to enhance the efficacy of the complexes on targeting
different cellular organelles.13,31-33 Herein, we report platinum(II)
complexes [Pt(L)(cur)] (1), [Pt(L)(py-acac)] (2) and [Pt(L)(an-acac)]
(3), where HL is 4,4’-bis-dimethoxyazobenzene, Hcur is curcumin,
Hpy-acac
is
pyrenylacetylacetone
and
Han-acac
is
1
anthracenylacetylacetone (Fig. 1). Complex [Pt(L)(acac)] (4) of
acetylacetone (Hacac) was prepared and used as a control. The
significant results of this work include photocytotoxicity of the
complexes 1-3 in skin keratinocytes HaCaT cells giving IC50 values
of 8-14 μM in visible light (400-700 nm, 10 J cm-2), while being
significantly less toxic in the dark (IC50: ~60 μM).
35-25 ppm were assignable to the methyl carbon atoms. The H and
13C NMR spectra of the complexes showed peaks similar to those
observed for the free ligands. Some additional peaks in the aromatic
region were observed in the spectra of the complexes, which are due
to carbon atoms of the azo ligand. The IR spectra of the complexes
showed disappearance of the signal of the O-H stretching frequency
around 3400-3500 cm-1, present in the free ligands, indicating the
loss of hydrogen atom upon binding to the metal ion. Two intense
peaks within 1600-1610 and 1590-1490 cm-1 are due to respective
C=O (β-diketonate moiety) and conjugated C=C of acac derivatives
stretching frequencies. The metal bound azo N=N of the 4,4’-
dimethoxyazobenzene ligand showed sharp characteristic peaks near
1250 cm-1 (Fig. S14-S20, ESI†). The complexes gave molar
conductance values of ~30 S m2 M-1 in DMF at room temperature
suggesting their non-electrolytic nature. Platinum azo complexes are
well known for their redox properties.34 The cyclic voltammograms
of the complexes in DMF-0.1M TBAP (tetrabutylammonium
perchlorate) showed two responses near –1.1 and –0.85 V vs. SCE
(Fig. S21, S22, ESI†). The responses that are quasi-reversible or
irreversible in nature are assignable to two-step azo reductions. The
absorption spectra of the complexes were recorded in 10% DMSO-
DPBS solutions (pH, 7.2) (Fig. 2a). Complexes 1-3 showed an
intense absorption band near 400 nm with high ε values. Complex 4
displayed one weak absorption band near 412 nm. The complexes
displayed a band at ~540 nm that arises from transitions involving
the Pt(II) coordinated azo ligand. The low ε values for 4 indicates the
important role of the photoactive -diketonate moieties. The
curcumin analogue 1 showed an emission band at 525 nm (λex = 430
nm) in DMSO–water (3:1 v/v) at 25 °C with a quantum yield (Φ)
value of 0.017 (Fig. 2b). The pyrenyl and anthracenyl complexes
Fig. 1. Chemical structures of the complexes 1-4.
2 | J. Name., 2012, 00, 1-3
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also exhibited characteristic structured emissive bands at 440 and
435 nm (Φ of 0.058 and 0.045).35 The free ligands mimicked the
emission spectra of respective complexes (Φ within 0.020 to 0.067)
(Table 1, Fig. S23, S24, ESI†). Significant reduction in the emission
intensity and low  value make these complexes unsuitable for
cellular imaging studies.
NMR spectral measurements. The complexes (50 μM Viinew1A0r%ticleDOMnliFne-
DOI: 10.1039/C6DT02590K
DPBS) showed slow degradation at 37 ºC as seen from the loss in
intensity in the absorption bands in the visible region (Fig. S27, S28
ESI†). Curcumin was found to be more stable in the metal bound
1
form in 1 under similar conditions. The time dependent H NMR
spectral study in deuterated dimethyl sulfoxide up to 24 h at 37 ºC
showed that complexes are stable. Complex 1 and 2 were found to
be more stable than 3 showing appearance of free ligand peaks on
longer duration of the experiment (Fig. S29, S30 ESI†). Complexes
1-3 (25 μM) in DMSO-DPBS buffer (3:2 v/v) were treated with
increasing equivalents of glutathione (GSH, 50-650 μM) and
emission spectra recorded are shown in Fig. 4 (Fig. S31, ESI†). A
GSH concentration dependent enhancement in the emission intensity
was observed suggesting possible cleavage of the Pt-O bonds,
thereby releasing the β-diketonate ligands.42,43 The emission intensity
reached a saturation indicating complete release of the ligands. The
samples when diluted with methanol and subjected to mass
spectrometry showed the presence of free ligands with m/z value of
369.13 for HCur in 1, 287.11 for Hpy-acac in 2 and 263.10 for Han-
acac in 3 (Fig. S32-S34, ESI†). An additional peak in the mass
spectra of the GSH treated complexes was observed at m/z of 759.23
(Fig. S32, ESI†). This was assigned to a GSH bound {Pt(L)}
species. Time-dependent 1H NMR studies also corroborated the
leaching out of β-diketonate ligands from the platinum(II)
complexes. The peak observed at 6.1 ppm is assignable to the γ-H
proton of the free ligand. Interestingly, formation of any GSSG was
Fig. 2. (a) Absorption spectra of 1-4 in 10% DMSO-DPBS. (b)
Emission spectra of 1-3 in aq. DMSO (1:3 v/v) (λex: 430 nm, 1;
370 nm, 2; 365 nm, 3).
Theoretical study
Computational studies were carried out using B3LYP/LanL2DZ
level of theory with G09 suites of programs to gain insights into the
photophysical properties of the complexes.36-38 The initial
coordinates for the complexes were directly taken from the reported
crystal structure of 4 and then modified by adding fragments as per
the requirement.39 These coordinates were then utilized for obtaining
energy-minimized structures of 1-3 using density functional theory
(DFT) (Table S1, Fig. S25, ESI†). The frontier orbital diagrams
shown in Fig. 3 reveal that the HOMO in 1-3 mainly resides on the
platinum bound azo moiety having small contributions from the
O,O-donor ligands. For 1, the LUMO has significant contributions
from both curcumin and the azo ligand (Fig. 3b). However, for 2 and
3, the orbital contribution from LUMO is dominated by the platinum
bonded azo moiety (Fig. S26, ESI†). Importantly, these orbitals are
dissociative in nature indicating the possibility of the Pt–O bond
cleavage.40,41
1
not observed in the mass and H NMR spectra postulating that GSH
is not undergoing any redox reaction but merely substituting the
O,O-donor ligand (Fig. S35, ESI†). This is different from what is
reported on the platinum(II) catecholates.13 Thus, we conclude that
the C,N-donor azo ligand behaves differently than its N,N-azo
analogue. This is also supported from the absence of any GSH
accessible redox peak in the complexes near –0.34 V which was
previously observed for the 2-(phenylazo)pyridine (pap) platinum(II)
catecholates.
Fig 4. Change in the emission spectra of the complexes 1 (a) and
2 (b) on addition of GSH (50-650 μM) in DMSO-DPBS buffer
(3:2 v/v).
Fig 3. (a) Frontier molecular orbitals of complex 1 as obtained
by DFT calculations using B3LYP/LanL2DZ level of theory: (a)
HOMO and (b) LUMO. Colour codes: Pt, red; O, blue; N,
green; C, black. Hydrogen atoms are omitted for clarity.
DNA binding and cleavage
Platinum drugs viz. cisplatin and its analogues are known to target
nuclear DNA. Moreover, the complexes under present investigation
showed release of the active Pt(II) species and the O,O-donor
ligands in presence of GSH. The resulting species are capable of
interacting with DNA. We thus explored the calf thymus (ct) DNA
binding properties from absorption titrations and viscosity
measurements. Complexes 1 and 4 did not show any apparent
Solubility and stability
The complexes were moderately soluble in common organic solvents
other than the hydrocarbons. They were stable in both solid and
solution phases. The stability of the complexes was studied in the
dark and in presence of cellular analytes by UV-visible, mass and
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decrease in the absorption intensity upon addition of ct-DNA in agent (H2O2, 5 mM) or a reducing agent (GSH, 5 mM)ViienwdAartrikclefoOrnl1inhe
DOI: 10.1039/C6DT02590K
absence of any intercalating moiety giving moderate DNA binding showed SC DNA as the predominant form indicating no apparent
constant (Kb) values of 1.5(±0.3) x 104 for 1 and 1.2 (±0.4) x 103 M-1 chemical nuclease activity of the complexes (Fig. S37b, ESI†).
for 4 (Fig. 5a, Table 1, Fig. S36, ESI†). Complexes 2 and 3 and
ligands Hpy-acac and Han-acac having planar pyrenyl and
anthracenyl group showed significant hypochromicity when treated
with ct-DNA.44-46 The Kb values of these compounds having planar
moiety are ~5.0 x 105 M-1 indicating their DNA groove and/or
intercalative binding propensity. In contrast, the curcumin and acac
complexes showed only surface binding to DNA.
Fig. 6. Bar diagram showing photo-induced pUC19 DNA (0.2
μg, 30 μM b.p.) cleavage by 1-4 (15 µM) in blue light of 457 nm
(blue bars) and in the dark (black bars) [NC, nicked circular].
Cellular study
Fig. 5. (a) Spectral changes on addition of ct-DNA to complex 2
The antiproliferative properties of the complexes were
investigated in immortalised human skin keratinocytes (HaCaT)
cell lines using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl
tetrazolium bromide (MTT) assay (Fig. 7, Fig. S38, ESI†).49
HaCaT cells were chosen as the therapeutic action of curcumin as
an active ingredient of turmeric is well documented for skin
related disorders. The cells were treated with the complexes or
the ligands for 4 h. The half maximal inhibitory concentrations
(IC50) in both dark and light are listed in Table 2. The light
exposure was done using visible light of 400-700 nm (Luzchem
in DMF-Tris-HCl buffer (pH = 7.2). (b) Effect of addition of 1-4,
ethidium bromide (EB) and Hoechst 33258 on ct-DNA (170 μM)
relative viscosity at 37.0(±0.1) ºC in 5 mM PBS buffer (pH =
6.8).
The DNA binding interactions were additionally examined by
viscometric titrations.47 The DNA contour length is known to get
affected in different ways in the presence of intercalating molecules,
groove and surface binders. This effect is analysed from the
observed increase in the relative specific viscosity of the ct-DNA.
Intercalation results in an increase in the viscosity of DNA as
compared to the groove or surface interactions. The viscosity plots
for 2 and 3 are similar to that of ethidium bromide (EB) indicating
their intercalative mode of binding to ct-DNA (Fig. 5b). The
curcumin and acac complexes 1 and 4 showed only minor changes in
the relative viscosity similar to that of the DNA minor groove binder
Hoechst 33258 dye. The DNA binding data suggest the pyrenyl and
anthracenyl complexes as DNA intercalators, while their curcumin
analogue is a DNA surface binder.
photoreactor, 10 J cm-2). Complexes
1-3 resulted significant
photocytotoxic effect in visible light giving IC50 values in the
range of 8-14 µM. The dark toxicity ranged within IC50 values of
45 and 61 µM. The intracellular interaction of these complexes
with GSH could facilitate release of active platinum(II) species as
transcription inhibitor thus enabling the complexes to show minor
dark toxicity.50,51 Ligands Py-acac/An-acac showed higher IC50
values compared to the complexes in light. The ligands alone are
thus not responsible for the observed cytotoxicity suggesting
important contribution of the metal.The photo-inactive acac
complex
4 showed no apparent photocytotoxic effect.
The DNA photocleavage study was carried out with complexes
1-3 and the free ligands (15 µM) using supercoiled (SC) pUC19
DNA (30 µM, 2686 bp) in Tris-HCl buffer solution (pH = 7.2) to
explore the effect of the photoactive diketonate ligands on the DNA
cleavage activity of the complexes. Irradiation was done with a laser
of 457 nm (50 mW power). The DNA cleavage potential is estimated
from the percentage of nicked-circular (NC) DNA formed from the
agarose gel electrophoresis assay. Complexes 1-3 exhibited efficient
photocleavage of SC DNA giving 50-75% of NC DNA (Fig. 6, Fig.
S37a, ESI†). The acac analogue did not show any photocleavage of
DNA. The photocleavage activity of 1-3 resulted from the activation
of the charge transfer band near 400 nm. The ligands alone showed
reduced DNA photocleavage activity under similar experimental
conditions thus indicating the importance of the platinum(II) centre
for production of the reactive oxygen species (ROS).48 All the
complexes and ligands were inactive in the dark. Complexes 1-3 (20
µM) when incubated with SC DNA in presence of an oxidizing
Fig. 7. Cell viability plots (a) – (d) showing cytotoxicity of the
respective complex 1-4 in HaCaT cells [black symbols in the dark;
green symbols in visible light (400-700 nm, 10 J cm-2)].
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DCFDA (2’,7’-dichlorofluorescein diacetate) assay was
ARTICLE
Annexin V-FITC/PI assay was done to studyVieawnyArticcleelOlunllinaer
DOI: 10.1039/C6DT02590K
performed using flow cytometry to detect any ROS formation. apoptosis on light exposure using HaCaT cells treated with the
The non-fluorescent DCFDA dye on enzymatic reaction forms complexes. Propidium iodide (PI) emits in the red region, while
H2DCF which upon oxidation by ROS generates fluorescent DCF the annexin V-FITC dye shows green fluorescence. This staining
with an emission maximum at 528 nm. The DCF intensity allowed us to quantify the apoptotic cell. From the dot plots
directly correlates to the amount of ROS. Complex
1 (20 μM) shown in Fig. 10 (Fig. S40-S42, ESI†), where lower left is for
showed pronounced generation of ROS on irradiation with visible live cells, lower right is for early apoptotic cells, upper right is for
light (400-700 nm) as indicated by an increase in DCF mean late apoptotic cells and upper left is for dead cells, we can infer
intensity shown in Fig. 8. The complex also showed some ROS that the percentage cell population in the lower right quadrant
production in dark possibly from the reaction of the platinum(II) increased to ~22% (for
1
) and ~5% for
4 when HaCaT cells were
species with GSH.
treated with the complexes and exposed to light (400-700
1-4
nm) than when kept in the dark. This indicates light induced early
apoptotic cell death promoted in presence of the complexes.
Complex
in light.
4 did not show any significant apoptosis in the dark or
Fig. 8. Shift in band positions of complex 1 in HaCaT cells in light
(400-700 nm, 10 J cm-2) with colour code: green, cells only; red,
cells + DCFDA; black, cells + DCFDA + complex in dark; blue,
cells + DCFDA + complex exposed to visible light (400-700 nm).
Fig. 10. Annexin V-FITC/PI assay using FACS in HaCaT cells with 4 h
incubation of complex 1 (20 μM) in the dark (a) and in light (b) (400-
700 nm, 1h). The % cell population is shown in respective quadrants
[lower left: live cells, lower right: early apoptotic cells, upper right: late
apoptotic cells, upper left, dead cells].
The changes in chromatin organization after light irradiation
in HaCaT cells were determined microscopically after treatment
with the complexes 1-3 by acridine orange and ethidium bromide
(AO/EB) dual staining method. The experiment is based on the
discrimination of live cells from the dead ones on the basis of
membrane integrity. AO stains the DNA of live cells and shows
green fluorescence. EB is excluded from the cells having intact
plasma membrane and stains the DNA of dead cells showings
Platinum uptake
The cellular uptake was evaluated in terms of platinum content of
the cell and expressed as ng platinum per 106 cells. HaCaT cells
were incubated for 4h in the dark with the complexes 1-4 (20
orange fluorescence. HaCaT cells treated with 1-3 (20 μM) for 4
h and kept in the dark showed green fluorescence corresponding
to the emission of AO. However, when the experiment was
performed after visible light exposure, the intensity of red
emission increased significantly indicating photo-induced cell
death (Fig. 9, Fig. S39, ESI†).
µM) and the platinum content of the cell lysates dissolved in 2%
HNO3 was estimated using ICP-MS method along with the
untreated cells and standard platinum solutions. The cellular
uptake values (ng Pt/ 106 cells) of
respectively (Table 2). Complex
1
4
-
4
are 2510, 110, 120, and 60,
showed poor lower cellular
uptake than the complexes 1-3 due to lipophilicity of the
complexes. The presence of curcumin in metal-bound form could
be responsible for the significantly higher platinum uptake of
complex 1.
Conclusions
The C,N-donor azo organometallic platinum(II) complexes of β-
diketonates 1-3 are remarkably PDT active giving IC50 values of
~10 µM in visible light (400-700 nm) while being less toxic in
the dark (IC50: ~60 µM). The complexes could be photo-activated
using their intense absorption band near 400 nm. The complexes
are susceptible to Pt-O bond cleavage on photo-activation. The
photoactive β-diketonate base acts as a phototoxin. Complexes
2
and having planar extended aromatic pyrenyl and anthracenyl
3
Fig. 9. Ethidium bromide (EB)/acridine orange (AO) dual
staining images of complexes 1 and 2 in light and in the dark
as shown in the figure. Scale bar = 10 µm.
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Journal Name
pendant moieties are excellent DNA binders showing using Bruker Avance 400 (400 MHz) NMR spectrometer. The
View Article Online
DOI: 10.1039/C6DT02590K
intercalative binding properties. The complexes showed apoptotic platinum content was obtained by ICP-MS method using Thermo
cell death via generation of light mediated ROS. The DNA X series II instrument.
photocleavage studies reveal the nature of ROS as the hydroxyl
Synthesis
radicals. The present complexes exemplify organometallic
platinum(II) complexes as anticancer agents suitable for selective
Complexes 1-4 were prepared by following a general procedure.
The precursor complex [(L)Pt(µ-Cl)]2 (226 mg, 0.24 mmol) was
delivery of photoactive
curcumin, an active ingredient of turmeric.
-diketonato bases that includes
treated with [Tl(
mg, 0.48 mmol for
mmol for ) in dichloromethane (15 ml) and stirred for 6 h at 30
C. The reaction mixture was filtered off and the solution was

-diketonate)] (274 mg, 0.48 mmol for
1; 235
2
; 223 mg, 0.48 mmol for and 146 mg, 0.48
3
4
Experimental Section
Materials

evaporated under reduced pressure in a rotavac. The solid was
isolated from methanol solution on slow evaporation and dried
The chemicals were procured from commercial sources and used
as received (s. d. Fine Chemicals, India; Aldrich, USA).
Potassium tetrachloroplatinate was obtained from Arora Matthey,
India. Solvents were purified by known procedures.52 Supercoiled
(SC) pUC19 DNA (cesium chloride purified) was from
Bangalore Genie (India). Tris-(hydroxymethyl)aminomethane-
HCl (Tris-HCl) buffer solution was prepared using deionized and
sonicated triple distilled water. Calf thymus (ct) DNA, agarose
(molecular biology grade), ethidium bromide (EB), 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
and 2’,7’-dichlorofluorescein diacetate (H2DCFDA) were
purchased from Sigma Aldrich (USA). Tetrabutylammonium
under vacuum. The product was isolated as a solid (red for
and brown for ).
1-3
4
Complex 1: yield 84% (163 mg). Anal. Calcd for C35H32N2O8Pt
(Mol wt = 803.71 g mol-1): C, 52.30; H, 4.01; N, 3.49. Found: C,
52.13; H, 4.06; N, 3.67. ESI-MS in MeOH: m/z observed,
804.1826; calculated, 804.1885 [M+H]+. IR data/cm-1: 3384 w,
3068w, 1605, 1585 s, 1510vs, 1433 w, 1315 m, 1245 vs, 1166 m,
1022 s, 980 m, 834 m, 786 s, 598 w, 532 m (vs, very strong; s,
strong; m, medium; w, weak). 1H NMR (400 MHz, DMSO-d6) [δ
(ppm)]: 7.90 (d, J = 8.9 Hz, 2H), 7.76 (d, J = 9.2 Hz, 2H), 7.58-
7.41 (m, 6H), 7.31 (s, 1H), 7.22-7.03 (m, 5H), 6.92 (s, 1H), 5.94
(s, 1H), 4.03(s, 6H), 3.87(s, 3H), 3.831 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ 178.10, 176.26, 165.03, 161.12, 158.51,
149.97, 148.28, 145.10, 141.37, 140.29, 133.83, 130.77, 127.79,
123.47, 119.92, 116.82, 114.39, 113.65, 111.80, 97.08, 56.75,
49.51.
perchlorate
(TBAP)
was
prepared
by
reacting
tetrabutylammonium bromide with perchloric acid (Caution!
TBAP being a perchlorate salt should be handled with care). The
ligands, viz., 4,4-bismethoxyazobenzene, Hpy-acac and Han-acac
were prepared following literature reports.53,54 Complex [(η3-
C4H7)Pt(µ-Cl)]2 and complex
4 were prepared by a modified
literature procedure.39 For the precursor complex having
monoanionic bidentate L, [(η3-C4H7)Pt(µ-Cl)]2 (143 mg, 0.25
mmol) and HL (121 mg, 0.50 mmol) in chloroform (25 ml) were
mixed and refluxed for 30 h, cooled and filtered. A red solid thus
obtained was dried in vacuum. [Tl(acac)] was prepared in
quantitative yield by reacting acetylacetone (0.11 mol) in 50 ml
petroleum ether with thallium(I) ethoxide (0.10 mol) and the
mixture was stirred for ~5 min, chilled and filtered.55 The
thallium salts of Hcur, Hpy-acac and Han-acac were prepared in
a similar way.
Complex 2: yield 81% (141 mg). Anal. Calcd for C34H27N2O8Pt
(Mol wt = 721.68 g mol-1): C, 56.51; H, 3.77; N, 3.88. Found: C,
56.83; H, 3.86; N, 3.69. ESI-MS in MeOH: m/z observed,
722.1741; calculated, 722.1619 [M+H]+. IR data/cm-1: 3384 w,
3068w, 1602, 1587 s, 1509 vs, 1433 w, 1315 m, 1245 vs, 1166
1
m, 1022 s, 980 m, 834 m, 786 s, 598 w 532 m. H NMR (400
MHz, CDCl3): δ (ppm) 8.76 (d, J = 7.2 Hz, 2H), 8.36-7.88 (m,
9H), 7.82 (d, J = 8.4 Hz, 2H), 7.62 (d, J = 8.0 Hz, 2H), 7.51 (d, J
= 7.9 Hz, 2H), 6.20 (s, 1H), 3.99 (s, 3H), 3.50 (s, 3H), 2.27 (s,
3H). 13C NMR (100 MHz, CDCl3): δ 187.42, 176.03, 165.41,
142.18, 132.49, 131.90, 130.25, 129.48, 128.98, 127.02, 126.80,
125.72, 124.83, 113.04, 42.82, 24.37.
Measurements
The elemental analysis was performed using a Thermo Finnigan
FLASH EA 1112 CHNS analyzer. The IR and UV-visible spectra
were recorded on Perkin Elmer Lambda 35 and Perkin Elmer
spectrum one 55 spectrometer, respectively. Cyclic
voltammograms were recorded on an EG&G PAR model 253
VersaStat potentiostat/galvanostat with electrochemical analysis
software 270 using a three electrode setup consisting of a glassy
carbon working, platinum wire auxiliary and a saturated calomel
reference electrode (SCE) in DMF and using TBAP (0.1 M) as a
supporting electrolyte. For molar conductivity measurements, a
Control Dynamics (India) conductivity meter was used.
Electrospray ionization (ESI) mass spectral measurements were
made using Agilent 6538 Ultra High Definition QTOF (LC-
HRMS) mass spectrometer. The NMR spectra were recorded
Complex 3: yield 79% (134 mg); Anal. Calcd for C32H26N2O4Pt
(Mol wt = 697.45 g mol-1): C, 55.09; H, 3.76; N, 4.02. Found: C,
54.82; H, 3.84; N, 4.16. ESI-MS in MeOH: m/z observed,
698.1620: calculated, 698.1619 [M+H]+. IR data/cm-1: 3054 w,
1598 s, 1501 vs, 1430 w, 1383 m, 1315 m, 1246 vs, 1154 m,
1110 m, 1022 s, 946 w, 834 s, 792 m, 730 s, 668 m, 598 m, 526 s.
1H NMR (400 MHz, CDCl3): δ (ppm) 8.56 (s, 1H), 8.03 (d J =
6.8 Hz, 4H), 7.91 (d, J = 7.2 Hz, 2H), 7.88 (d, J = 8.3 Hz, 2H),
7.52 (d, J = 3.4 Hz, 2H), 7.01 (d, J = 8.2 Hz, 4H), 6.97 (s, 1H),
5.97 (s, 1H), 4.01 (s, 3H), 3.88 (s, 3H), 2.20 (s, 3H). 13C NMR
(100 MHz, CDCl3): δ 187.12, 180.11, 163.45, 142.31, 131.52,
129.43, 128.81, 127.10, 126.64, 125.73, 113.75, 105.76, 58.19,
26.38.
6 | J. Name., 2012, 00, 1-3
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Complex
ARTICLE
4
: yield 82% (103 mg); Anal. Calcd for C19H20N2O4Pt (1:1, 10 μM) for 15 min, and observed with a confocal laser
View Article Online
(Mol wt = 535.45 g mol-1): C, 42.62; H, 3.76; N, 5.23. Found: C, scanning microscope (Zeiss LSM 510 apochromat).
DOI: 10.1039/C6DT02590K
42.32; H, 3.84; N, 4.86. IR data/cm-1: 3064 w, 1612 s, 1502 vs,
Annexin V-FITC/PI assay: HaCaT cells (3 x 105) were plated in
1453 m, 1321 w, 1251 vs, 1168 m, 1126 m, 1022 s, 960 w, 828 s,
6 well plates and grown for 24 h. Cells were incubated with the
764 w, 612 w, 528 s. 1H NMR (CDCl3): δ (ppm) 7.91 (d, J = 9.1
Hz, 2H), 7.10 (d, J = 8.6 Hz, 2H), 6.97 (d, J = 2.8 Hz, 1H), 6.76
(d, J = 9.1 Hz, 1H), 6.74 (s, 1H), 5.51 (s, 1H), 3.94 (s, 3H), 3.88
(s, 3H), 2.07 (s, 3H), 1.98 (s, 3H).
complexes 1-4 and cisplatin (20 µM) for 4 h. The medium was
removed and the samples were irradiated for 1 h (400-700 nm, 10
J cm-2) in DPBS. After treatment, cells were allowed to grow for
10 h, washed twice in DPBS and trypsinized. These cells were re-
suspended in 400 µL of 1X binding buffer. Later 1 µL of annexin
V-FITC and 0.5 µL of PI were added to each cell suspension.
These were incubated at room temperature for 10 min and
protected from light. The fluorescence of the cells was
determined immediately with a flow cytometer. Cells in the early
apoptosis showed high annexin V-FITC staining, while the ones
in late apoptotic stage showed high PI and annexin V-FITC
staining. Live cells showed no staining by either PI or annexin V-
FITC and dead cells were stained only by PI.
Cellular experiments
MTT assay: The photocytotoxicity of the complexes was studied
using MTT assay. Approximately, 8000 cells of human skin
keratinocyte (HaCaT) cells were plated separately in 96 wells
culture plate in high glucose Dulbecco’s Modified Eagle Medium
(DMEM) containing 10% FBS. After 24 h of incubation at 37 °C
in a CO2 incubator, various concentrations of the complexes
dissolved in 1% DMSO were added to the cells and incubation
was continued for 4 h in the dark. The media was subsequently
replaced with DPBS and irradiated with a broad band visible light
DNA binding and cleavage
(400-700 nm, 10 J cm-2) using a Luzchem Photoreactor (Model The DNA binding experiments were done using complexes
1-4
LZC-1, Ontario, Canada) fitted with Sylvania make 8 fluorescent and calf thymus (ct)-DNA by UV-visible absorption
white tubes. After photo-exposure, DPBS was removed and spectroscopy and the intrinsic equilibrium binding constant (Kb)
replaced with DMEM-FBS and incubation was continued for a values were obtained by McGhee-von Hippel (MvH) method
further period of 20 h in the dark. After the incubation period, 5 using the expression of Bard and co-workers (vide ESI† for
mg ml-1 of MTT (20 μL) was added to each well and incubated details).42 The viscometric titration experiments were performed
for an additional 3 h. The culture medium was finally discarded to determine the relative specific viscosity of ct-DNA solution
and 200 μL of DMSO was added to dissolve the formazan (130 μM) in 5 mM phosphate buffer in the presence of the
crystals and its absorbance at 540 nm was measured using a complexes 1-4
. Relative specific viscosity of DNA, (η/η0)1/3, was
Molecular Devices Spectra Max M5 plate reader (100-240 V, 3.5 plotted against [complex]/[DNA], where η and η0 are the
A, 50-60 Hz). Cytotoxicitiy of the complex was measured as the viscosity of DNA in the presence and absence of the complexes.
percentage ratio of the absorbance of the treated cells to the The cleavage of supercoiled (SC) pUC19 DNA (0.2 μg, 30 μM,
untreated controls. The IC50 values were determined by nonlinear 2686 base-pairs) was determined by agarose gel electrophoresis
regression analysis (GraphPad Prism 5).
using the complexes in 50 mM Tris–HCl buffer (pH 7.2) and 50
mM NaCl containing 10% DMF. The photo-induced DNA
cleavage reactions were done using Ar-Kr mixed gas ion
monochromatic CW laser (Spectra Physics, power = 50 mW) of
457 nm based on the absorption spectral band at ~428 nm of the
complex and curcumin. The laser power was measured using
Spectra Physics CW Laser Power Meter (Model 407A)). The
observed error in measuring the band intensities was ~5%. The
DNA photocleavage experiments were carried out with the
complexes and the free ligands (15 µM) using supercoiled (SC)
pUC19 DNA (30 µM, 2686 bp) in Tris-HCl buffer solution (pH =
7.2). The DNA cleavage potential was expressed as % of nicked-
circular (NC) DNA as determined from the agarose gel
electrophoresis assay. The chemical nuclease activity
DCFDA assay: 2’,7’-Dichlorofluorescein diacetate was used to
detect the generation of cellular ROS. Cell permeable DCFDA on
oxidation by cellular ROS generates a fluorescent DCF having an
emission maximum at 528 nm. The percentage of cell population
generating ROS was determined by flow cytometry analysis.
HaCaT cells were incubated with
1 (20 μM) for 4 h followed by
photo-irradiation (400-700 nm) for 1 h in DPBS. These cells,
after irradiation, were harvested by trypsinization and a single
cell suspension of 1x106 cells ml-1 was made. The cells were then
treated with 1μM DCFDA solution in DMSO in dark for 15 min
at room temperature. The distribution of DCFDA stained HaCaT
cells was determined by flow cytometry in the FL-1 channel.
EB/AO assay: The changes in chromatin organization after light measurements were done in presence of an oxidizing agent
irradiation in HaCaT cells were determined microscopically after (H2O2, 5 mM) or a reducing agent (GSH, 5 mM) in the dark for
treatment with the complexes 1-3 by dual staining method using 1h.
acridine orange (AO) and ethidium bromide (EB). Briefly, about
2 x 104 cells were allowed to adhere overnight on a cover slip
placed in each well of 12-well plate. The cells were treated with
the complexes (20 μM) for 4 h in the dark, followed by
irradiation with visible light of 400-700 nm (10 J cm-2). Dark
controls were also used. The cells were allowed to recover for 1
h, washed thrice with DPBS, stained with an AO/EB mixture
Experiment on cellular uptake of platinum
To quantify the total platinum uptake, 3 x 105 HaCaT cells were
plated in two 6 well plates. Cells were allowed to grow for 24 h
and later treated with different platinum complexes (1-4) for 8 h.
After the incubation period in both the set of 6 well plates the
medium was aspired and all the wells were washed with PBS.
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Later on one of the set was treated with 0.5 ml of hot (~90 °C)
concentrated nitric acid for 2 h while its similar treatment
counterpart was trypsinized and live cells were counted by using
trypan blue method. Nitric acid treated samples were analyzed
by ICP-MS to determine the total platinum content per well. In
this assay medium alone was taken as a blank and the amount of
platinum per cell was calculated by subtracting the average
amount of platinum found in the blank wells from the average
amount of platinum found in the cell containing wells and
normalizing to the average number of cells per well.
6. L. Liu, Q. Ye, M. Lu, Y.-C. Lo, Y.-H. Hsu, M.-C. Wei, Y.-H.
View Article Online
DOI: 10.1039/C6DT02590K
Chen, S.-C. Lo, S.-J. Wang, D. J. Bain and C. A. Ho, Sci.
Rep., 2015, 5, 10881.
7. M. Patra, T. C. Johnstone, K. Suntharalingam and S. J.
Lippard, Angew. Chem. Int. Ed., 2016, 55, 2550-2554.
8. (a) P. Štarha, I. Popa and Z. Trávníček, Molecules, 2014, 19
,
3832-3847. (b) R. Kitagawa, N. Katsumata, T. Shibata, T.
Kamura, T. Kasamatsu, T. Nakanishi, S. Nishimura, K.
Ushijima, M. Takano, T. Satoh and H. Yoshikawa, J Clin
Oncol., 2015, 33, 2129-2135. (c). W. Liu, J. Su, J. Jiang, X.
Li, Q. Ye, H. Zhou, J. Chen and Y. Li, Sci. Rep., 2013, 3,
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Acknowledgements
9. (a) A. Naik, R. Rubbiani, G. Gasser and B. Spingler, Angew.
Chem. Int. Ed., 2014, 53, 6938-6941. (b) C. Mari, V. Pierroz,
A. Leonidova, S. Ferrari and G. Gasser, Eur. J. Inorg. Chem.,
2015, 3879-3891. (c) A. Frei, R. Rubbiani, S. Tubafard, O.
Blacque, P. Anstaett, A. Felgentrager, T. Maisch, L. Spiccia,
and G. Gasser, J. Med. Chem., 2014, 57, 7280-7292.
10. (a) E. Shaili, Sci. Prog., 2014, 97, 20-40. (b) T. J. Dougherty,
C. J. Gomer, B. W. Henderson, G. Jori, D. Kessel, M.
Korbelik, J. Moan and Q. Peng, J. Natl. Cancer Inst., 1998,
90, 889-905.
We thank the Department of Science and Technology,
Government of India, for financial support (SR/S5/MBD-
02/2015, EMR/2015/000742) and the Alexander von Humboldt
Foundation for donation of an electrochemical system. A.R.C.
thanks the DST for J.C. Bose fellowship. P.K. acknowledges
financial support from DBT-IISc partnership program. K.M. and
A.S. thank respective funding agency for B.M.S. and UGC
Kothari research fellowships. We thank Dr. Ramananda
Chakrabarti, Centre of Earth Sciences CEaS, IISc, for the ICP-
MS facility.
11. J. J. Wilson and S. J. Lippard, J. Med. Chem., 2012, 55, 5326-
5336.
Notes and references
12. (a) A. Muscella, N. Calabriso, F. P. Fanizzi, S. A. De Pascali,
L. Urso, A. Ciccarese, D. Migoni and S. Marsigliante, Br. J.
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aDepartment of Inorganic and Physical Chemistry, Indian
Institute of Science, Bangalore 560012, India.
E-mail:
arc@ipc.iisc.ernet.in;
Tel:
+91-80-22932533
bDepartment of Molecular Reproduction, Development and
Genetics, Indian Institute of Science, Bangalore 560012, India. E-
mail: paturu@mrdg.iisc.ernet.in; Tel: +91-80-22933259
†Electronic Supplementary Information (ESI) available; spectral
and electrochemical plots, DNA binding, cleavage, cellular and
DFT optimization data (Scheme S1, Fig. S1–S31, Table S1). See
DOI: 10.1039/b000000x/
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ARTICLE
Journal Name
View Article Online
Table 1. Selected physicochemical data for the complexes
1
-
4
Table 2. IC50 values of the complexes
related platinum complexes in HaCaT cells
1-4
DOI: 10,.1t0h3e9/lCig6DanTd02s5a9n0dK
Complex
1
2
3
4
Cellular uptake
(ng Pt/106cells)c
Complexes
IC50 (µM)
(Light)a
IC50 (µM)
(Dark)b
1H NMR
5.95
6.20
5.97
5.51
γ(C-H) (ppm)a
2510
1
10.9 ± 0.2 55.6 ± 0.6
8.0 ± 0.3 45.0 ± 0.5
14.2 ± 0.5 61.9 ± 0.8
2
3
110
120
60
IR (in KBr)
1605,
1245
1602,
1255
1598, 1250
27
1612, 1250
30
νC=O, νN=N
,
cm-1
4
95.2 ± 1.1
15.2 ± 0.8
45.2 ± 1.4
7.9± 0.4
>100
>100
ΛM b / S m2
M-1
28
31
Hpy-acac
An-acac
Hcur
>100
430
(8.8),
365
540
(1.2),
381
390 (4.4),
365 (4.4)
524 (1.25),
412 (2.6)
23.2± 1.3
λmax / nm
(10-4 ε / dm3
M-1 cm-1)c
Cisplatin
4.8± 0.7
57.0 ± 1.2
[Pt(pap)(an-cat)]d
5.2 ± 0.1
15 ± 3
6.1
(8.9)
(3.6)
[Pt(cur)(NH3)2](NO3)e
ttt-[Pt(N3)2(OH)2(NH3)(py)]f
>200
>244.3
λem / nmd
440
435
--
--
525
a
The IC50 values correspond to 4 h incubation in dark followed by 1 h
Φ e
0.058
0.045
0.017
photo-exposure to visible light of 400-700 nm (10 J cm-2). b IC50 values
correspond to 4 h incubation in dark. c In HaCaT cells on 4h incubation
-0.89,
-1.24
[80], -
1.50
Ef /V
[ΔEp /mV]f
-0.88,
-1.10
[80]
-0.84,
-1.11
[95]
-0.80, -1.42
d
in dark. Pt content was estimated by ICPMS methods. IC50 value
taken from ref. 13. e IC50 value taken from ref. 14. f IC50 value in UVA
light (365 nm) obtained from ref. 18a (ttt, trans,trans,trans).
Kb g /M-1
7.5(±0.1) x
105
3.2(±0.3) x
105
1.2(±0.4)
x 103
1.5(±0.3)
x 104
a
b
In DMSO-d6/CDCl3 solutions. Molar conductivity in DMF at
c
d
298K. In 10% DMSO-DPBS. Emission spectra in aq. DMSO (1:3
v/v) (λex = 430 nm for , 370 nm for and 365 for
1
2
3
). e Quantum yield
in aq. DMSO (1:3 v/v). Quantum yield measured using quinine
sulphate in 1mM anthracene (Φ = 0.27) or fluorescien (Φ = 0.38) as
standards. Error within ±5%. f Redox couple in DMF-0.1M TBAP.
g
The potentials are vs. SCE. Scan rate = 100 mV s-1. Intrinsic
equilibrium ct-DNA binding constant, Kb from UV-vis absorption
spectral experiments.
10 | J. Name., 2012, 00, 1-3
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Dalton Transactions
Journal Name
ARTICLE
Photoactive platinum(II) β-diketonates as
View Article Online
DOI: 10.1039/C6DT02590K
dual action anticancer agents
Md Kausar Razaa,#, Koushambi Mitraa,#, Abhijith
Shettarb, Uttara Basua, Paturu Kondaiah*,b and Akhil R.
Chakravarty*,a
Keywords: Bioinorganic chemistry, platinum, β-diketonates,
curcumin, photocytotoxicity.
Synopsis (20 words): Cyclometallated platinum(II) -diketonates
show significant photocytotoxicity in skin-keratinocyte HaCaT cells
[IC50: ~10 M (visible light, 400-700 nm), ≥60 M (dark)].
Pictogram:
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