Silicon(IV) phthalocyanines substituted axially with different nucleoside moieties. Effects of nucleoside type on the photosensitizing efficiencies and in vitro photodynamic activities

Article abstract of DOI:10.1016/j.jphotobiol.2016.03.055

A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted axially with different nucleoside moieties have been synthesized and evaluated for their singlet oxygen quantum yields (Φ_Δ) and in vitro photodynamic activities. The adenosine-substituted SiPc shows a lower photosensitizing efficiency (Φ_Δ = 0.35) than the uridine- and cytidine-substituted analogs (Φ_Δ = 0.42-0.44), while the guanosine-substituted SiPc exhibits a weakest singlet oxygen generation efficiency with a Φ_Δ value down to 0.03. On the other hand, replacing axial adenosines with chloro-modified adenosines and purines can result in the increase of photogenerating singlet oxygen efficiencies of SiPcs. The formed SiPcs 1 and 2, which contain monochloro-modified adenosines and dichloro-modified purines respectively, appear as efficient photosensitizers with Φ_Δ of 0.42-0.44. Both compounds 1 and 2 present high photocytotoxicities against HepG2 and BGC823 cancer cells with IC₅₀ values ranging from 9 nM to 33 nM. The photocytotoxicities of these two compounds are remarkably higher than the well-known anticancer photosensitizer, chlorin e6 (IC₅₀ = 752 nM against HepG2 cells) in the same condition. As revealed by confocal microscopy, for both cell lines, compound 1 can essentially bind to mitochondria, while compound 2 is just partially localized in mitochondria. In addition, the two compounds induce cell death of HepG2 cells likely through apoptosis.

Full text of DOI:10.1016/j.jphotobiol.2016.03.055

Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology, B: Biology
journal homepage: www.elsevier.com/locate/jphotobiol
Silicon(IV) phthalocyanines substituted axially with different nucleoside
moieties. Effects of nucleoside type on the photosensitizing efficiencies
and in vitro photodynamic activities
Bi-Yuan Zheng, Xiao-Min Shen, Dong-Mei Zhao, Yi-Bin Cai, Mei-Rong Ke, Jian-Dong Huang
College of Chemistry, State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzhou 350108, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted axially with different nucleoside moieties have
been synthesized and evaluated for their singlet oxygen quantum yields (ΦΔ) and in vitro photodynamic activi-
ties. The adenosine-substituted SiPc shows a lower photosensitizing efficiency (ΦΔ = 0.35) than the uridine- and
cytidine-substituted analogs (ΦΔ = 0.42–0.44), while the guanosine-substituted SiPc exhibits a weakest singlet
oxygen generation efficiency with a ΦΔ value down to 0.03. On the other hand, replacing axial adenosines with
chloro-modified adenosines and purines can result in the increase of photogenerating singlet oxygen efficiencies
of SiPcs. The formed SiPcs 1 and 2, which contain monochloro-modified adenosines and dichloro-modified pu-
rines respectively, appear as efficient photosensitizers with ΦΔ of 0.42–0.44. Both compounds 1 and 2 present
high photocytotoxicities against HepG2 and BGC823 cancer cells with IC50 values ranging from 9 nM to 33 nM.
The photocytotoxicities of these two compounds are remarkably higher than the well-known anticancer photo-
sensitizer, chlorin e6 (IC50 = 752 nM against HepG2 cells) in the same condition. As revealed by confocal micros-
copy, for both cell lines, compound 1 can essentially bind to mitochondria, while compound 2 is just partially
localized in mitochondria. In addition, the two compounds induce cell death of HepG2 cells likely through
apoptosis.
Received 10 August 2015
Received in revised form 28 March 2016
Accepted 29 March 2016
Available online 08 April 2016
Keywords:
Silicon(IV) phthalocyanine
Photosensitizer
Photodynamic therapy
Nucleoside
Singlet oxygen quantum yields
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
dark toxicity, and ease of chemical modification, phthalocyanines have
been found to be highly promising as second-generation photosensi-
Photodynamic therapy (PDT) has attracted considerable attention as
a promising minimal-invasive treatment for both neoplastic and non-
neoplastic diseases [1–4]. One of the prominent advantages of PDT lies
in its ability to eradicate malignant tissue without systemic toxicity,
which is a major drawback of traditional therapeutic methods like che-
motherapy and radiotherapy. PDT typically involves the systemic ad-
ministration of a photosensitizer and the tumor-oriented illumination
with a light of specific wavelength to generate reactive oxygen species
(ROS), particularly singlet oxygen, leading to cell and tissue damage.
The overall efficacy of the treatment depends greatly on the behavior
of photosensitizers. As a result, various strategies have been developed
to obtain a favorable photosensitizer [4–11]. Among these approaches,
the conjugation of a photosensitizer with biological ligands (such as an-
tibodies, peptides, carbohydrates, and folic acid), which are capable of
improving the biocompatibility and tumor-targeting of the photosensi-
tizers, has received a great deal of interest [6–13].
tizers for PDT [2–4,12–16]. The introduction of biomolecules on the
axial positions of phthalocyanines has appeared as an efficient and
promising approach to obtain the desirable phthalocyanine-based pho-
tosensitizers [17–22]. Apart from aforementioned improvement of bio-
compatibility and tumor-targeting, the method could effectively
decrease intrinsic aggregated propensity of phthalocyanines, which
will lead to inefficient ROS generation and poor solubility in aqueous
media. Among these biomolecules, we are particularly interested in nu-
cleosides, which are important building blocks of DNA and RNA. More-
over, a number of nucleoside derivatives have been used as antiviral [23,
24] and anticancer [25] drugs. However, the photobiological properties
of phthalocyanines functionalized with nucleoside moieties remain
hardly explored, although the synthesis and characterization of a few
phthalocyanine-nucleoside conjugates have been reported [18,26–31].
Very recently, our group have reported the photodynamic activities
of a series of silicon(IV) phthalocyanines (SiPcs) axially disubstituted
with uridine and cytidine moieties in a preliminary communication
[18]. As an extension of this study, we report herein four new analogs
axially disubstituted with adenosine, purine, and guanosine derivatives,
including their synthesis, spectroscopic properties, singlet oxygen gen-
eration efficiencies, and in vitro photodynamic activities against
Having a number of advantageous characteristics, such as intense
absorption in the “phototherapeutic window” (650–800 nm), low
E-mail address: jdhuang@fzu.edu.cn (J.-D. Huang).
http://dx.doi.org/10.1016/j.jphotobiol.2016.03.055
1011-1344/© 2016 Elsevier B.V. All rights reserved.

B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
197
Scheme 1. Preparation of SiPcs 1–4.
HepG2 and BGC823 cells. With the goal of understanding the structure–
activity relationship of this intriguing class of novel nucleoside-
containing photosensitizer, the effects of nucleoside type on the photo-
chemical properties and in vitro photodynamic activities have been
discussed.
1H NMR spectra were recorded on Bruker a AVANCE III 400 or 500
spectrometer in DMSO-d6 and CDCl3. Chemical shifts were relative to
internal SiMe4 (δ = 0 ppm). High resolution mass spectra were re-
corded on an Agilent ESI-Q-Tof 6520 mass spectrometer or a Thermo
Fisher Scientific Exactive Plus Orbitrap LC–MS spectrometer. Electronic
absorption spectra were measured on a Shimadzu UV-2450 UV–vis
spectrophotometer. Fluorescence spectra were taken on an Edinburgh
FL900/FS900 spectrofluorometer. ΦF and ΦΔ were determined as de-
scribed in our previous manuscripts [18,32].
2. Experimental Section
2.1. General
The purity of all the new phthalocyanines was determined by HPLC
and was found to be ≥95%. The analytical HPLC experiments were per-
formed on a Kromasir KR100-10C18 column (5 μm, 4.6 mm × 250 mm)
by using a Shimadzu LC-10AT controller with a SPD-M10A diode array
detector. The conditions were set as follows: mobile phase from 5% B
changed to 95% B over 30 min, then maintained 95% B for a further
20 min (solvent A = distilled water; solvent B = DMF). The column
All the reactions were performed under an atmosphere of nitrogen.
Acetone and toluene were distilled from anhydrous calcium sulfate
and sodium, respectively. 2′,3′-o-isopropyl-adenosin (9) and 2′,3′-o-
isopropyl-guanosine (10) were purchased from Acros. Cremophor EL
and ZnPc were obtained from Sigma Aldrich. Ce6 was obtained from
J&K Scientific. Chromatographic purifications were performed on silica
gel columns (100–200 mesh, Qingdao Haiyang Chemical Co., Ltd.,
China) with the indicated eluents. Size exclusion chromatography was
performed on Bio-Rad Bio-Beads S-X3 beads with the indicated eluents.
All other solvents and reagents were of reagent grade and used as
received.
temperature was set at 30 °C. The flow-rate was fixed at 0.5 ml min−1
.
Statistical analyses were performed by using the Student's t-test. P
values of 0.05 were considered as statistically significant.
2.2. Synthesis
Table 1
2′,3′-o-isopropyl-2-chloro-adenosin (7).
A mixture of p-
Photophysical and photochemical data for SiPcs 1–4 and 11–12 in DMF.
toluenesulfonic acid (PTSA) (1.72 g, 10 mmol) and dry acetone
(20 ml) was added dropwise into a stirring mixture of 2-chloro-
adenosin (309 mg, 1 mmol) and dry acetone (20 ml) in ice-water
bath. The mixture was stirred at room temperature for 22 h and then
was poured into ice sodium bicarbonate solution (4% w.t.) with stirring
until the bubble disappeared. The liquid was then extracted with CH2Cl2
for three times. The organic layers were dried over anhydrous MgSO4
and concentrated to afford a faint yellow solid 7 (283 mg, 83%). 1H
NMR (400 MHz, DMSO-d6): δ = 8.37 (s, 1H, imidazole-H), 7.89 (br.,
2H, NH2), 6.06 (d, J = 2.4 Hz, 1H, 1′-H), 5.28–5.30 (m, 1H, 2′-H), 5.10–
5.12 (m, 1H, OH), 4.93–4.95 (m, 1H, 3′-H), 4.21–4.23 (m, 1H, 4′-H),
3.54–3.57 (m, 2H, 5′-H), 1.55 (s, 3H, CH3), 1.33 ppm (s, 3H, CH3);
SiPcs
λ
max (nm)
λ
em (nm)a Stokes shift (nm) ε × 105
(M−1·cm−1
ΦFb ΦΔc
)
1
2
3
4
677
679
677
676
685
687
686
682
687
685
8
8
9
6
9
8
1.77
0.34 0.42
0.25 0.44
0.30 0.35
0.02 0.03
0.37 0.44
0.36 0.42
1.92
1.80
1.80
2.00
2.13
11 [18] 678
12 [18] 677
a
Excited at 610 nm.
Using ZnPc in DMF as the reference (ΦF = 0.28) [33].
b
c
Determined by using DPBF as chemical quencher, and ZnPc in DMF as the reference
(ΦΔ = 0.56) [34].

198
B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
Fig. 1. Structures of silicon(IV) phthalocyanines 11 and 12.
HRMS (ESI) m/z [M + H]+ calcd. for C13H17ClN5O4: 342.0969, found:
342.0968.
in vacuo, the residue was dissolved in CH2Cl2 and then washed with
water. The organic layers were collected, dried over anhydrous
MgSO4, and concentrated to afford crude product, which was further
purified by column chromatography (silica gel) using tetrahydrofuran
(THF) as eluent, followed by size-exclusion chromatography by using
THF as the eluent to give a blue solid 1 (48 mg, 60%). UV–vis (DMF):
2′,3′-o-isopropyl-2,6-dichloropurine riboside (8). According to
the above procedure, a solution of 2,6-dichloropurine riboside
(321 mg, 1 mmol) in dry acetone (20 ml) was treated with PTSA
(1.72 g, 10 mmol) in dry acetone (20 ml) for 16 h and neutralized
with ice sodium bicarbonate solution (4 wt.%) to afford a clear solution,
which was extracted with CH2Cl2 for three times. The organic layers
were dried over anhydrous MgSO4 and concentrated to afford crude
product, which was further purified by column chromatography (silica
gel) with ethyl acetate as eluent. The main component was collected
and concentrated to give a white solid 8 (324 mg, 90%). 1H NMR
(500 MHz, CDCl3): δ = 8.33 (s, 1H, imidazole-H), 6.01 (d, J = 4.5 Hz,
1H, 1′-H), 5.17–5.19 (m, 1H, 2′-H), 5.11–5.13 (m, 1H, 3′-H), 4.54–4.55
(m, 1H, 4′-H), 4.31 (br., 1H, OH), 4.00–4.02 (m, 1H, 5′-H), 3.85–3.88
(m, 1H, 5′-H), 1.66 (s, 3H, CH3), 1.40 (s, 3H, CH3), 1.26 ppm (s, 3H,
CH3); HRMS (ESI) m/z [M + Cl]− calcd. for C13H14Cl3N4O4: 395.0081,
found: 395.0094.
λ
max, nm (ε, M−1·cm−1) 677 (177,000). 1H NMR (500 MHz, CDCl3):
δ = 9.62–9.63 (m, 8H, Pc-Hα), 8.39–8.41 (m, 8H, Pc-Hβ), 6.43 (s, 4H,
NH2), 5.39 (s, 2H, imidazole-H), 4.58 (d, J = 3.0 Hz, 2H, 1′-H), 2.18–
2.19 (m, 2H, 2′-H), 1.80 (s, 2H, 3′-H), 0.92 (s, 6H, CH3), 0.89–0.91 (m,
2H, 4′-H), 0.76 (s, 6H, CH3), −1.28 (dd, J = 12.0, 2.5 Hz, 2H, 5′-H),
−2.29 ppm (dd, J = 12.0, 3.5 Hz, 2H, 5′-H); HRMS (ESI) m/z
[M
1243.2788.
Silicon phthalocyanine 2. According to the procedure described for
+
Na]+ calcd. for C58H46Cl2N18NaO8Si: 1243.2790; found:
SiPc 1, SiPcCl2 (40 mg, 0.065 mmol) was treated with dichloropurine
riboside 8 (187 mg, 0.52 mmol), and NaH (0.42 mmol) in toluene
(20 ml) to give 2 as a blue solid (53 mg, 65%). UV–vis (DMF): λmax
,
Silicon phthalocyanine 1.
A
mixture of SiPcCl2 (40 mg,
nm (ε, M−1·cm−1) 679 (192,000). 1H NMR (500 MHz, CDCl3): δ =
9.56–9.58 (m, 8H, Pc-Hα), 8.44–8.46 (m, 8H, Pc-Hβ), 5.45 (s, 2H,
imidazole-H), 4.50 (d, J = 2.5 Hz, 2H, 1′-H), 1.98 (s, 2H, 2′-H), 1.92–
0.065 mmol), adenosin 7 (177 mg, 0.52 mmol), and NaH (0.42 mmol)
were refluxed in toluene (20 ml) for 24 h. After evaporating the solvent
Fig. 2. (a) UV–vis absorption spectra of SiPcs 1 and 2 (4 μM), formulated with 0.05% Cremophor EL, in RPMI 1640 cellular culture medium. The inset plots the Q-band absorbance versus the
concentration of 1. (b) Fluorescence spectra of SiPcs 1 and 2 in RPMI 1640 cellular culture medium (formulated with 0.05% Cremophor EL) (both at 4 μM, λex = 610 nm). (For
interpretation of the references to color in this figure, the reader is referred to the web version of this article.)

B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
199
Fig. 3. Comparison of the cytotoxic effects of SiPcs (a) 1 and (b) 2 on HepG2 and BGC823 cells in the absence and presence of light (λ N 610 nm) at a dose of 27 J·cm−2. Values represent
mean standard deviation of three separate experiments.
1.94 (m, 2H, 3′-H), 0.94 (s, 6H, CH3), 0.85 (s, 6H, CH3), 0.73–0.74 (m, 2H,
4′-H), −1.19 (dd, J = 12.0, 2.0 Hz, 2H, 5′-H), −2.45 ppm (dd, J = 12.0,
3.0 Hz, 2H, 5′-H); HRMS (ESI) m/z [M]− calcd. for C58H42Cl4N16O8Si:
1260.1865; found: 1260.1877.
100 ml of water), and further diluted with the cellular culture medium
to appropriate concentrations.
In vitro photocytotoxicity. The photocytotoxicity assay is the same
as the procedure described previously [18]. Briefly, About 2 × 104 cells
per well were seeded in 96-well plate and incubated overnight for cell
adherence and growth. The cells were then incubated with 100 μl of
the above phthalocyanine solutions for 2 h under the same conditions.
After that, the cells were rinsed with PBS and re-fed with 100 μl of the
culture medium before irradiated with 27 J/cm2 of a red light
(λ N 610 nm, 15 mW/cm2 for 30 min).
Cell viability was determined by the colorimetric 3-(4,5-dimethyl-2-
thiazolyl) -2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. After il-
lumination, the cells were incubated at 37 °C under 5% CO2 overnight.
An MTT (Sigma) solution in PBS (20 μl, 5 mg/ml) was added to each
well followed by incubation for 4 h under the same environment. A
200 μl of DMSO was then added to each well. The 96-well plate was ag-
itated on a Thermo-Labsystems microplate reader (Multishan MK3) at
ambient temperature for 20 s before the absorbance at 490 nm at
each well was taken. The average absorbance of the blank wells,
which did not contain the cells, was subtracted from the readings of
the other wells. The cell viability was then determined by the equation:
Cell Viability (%) = [Σ(Ai / Ācontrol × 100)] / n, where Ai is the absorbance
of the ith data (i = 1, 2, …, n), Ācontrol is the average absorbance of the
control wells, in which the phthalocyanine was absent, and n (≥3) is
the number of the data points.
Silicon phthalocyanine 3. According to the procedure described for
SiPc 1, SiPcCl2 (40 mg, 0.065 mmol) was treated with adenosin 9
(160 mg, 0.52 mmol), and NaH (0.42 mmol) in toluene (20 ml) to
give 3 as a blue solid (42 mg, 56%). UV–vis (DMF): λmax, nm (ε,
M
−1·cm−1) 677 (180,000). 1H NMR (400 MHz, CDCl3): δ = 9.55–
9.57 (m, 8H, Pc-Hα), 8.36–8.38 (m, 8H, Pc-Hβ), 8.02 (s, 2H,
pyrimidine-H), 5.65 (s, 4H, NH2), 5.37 (s, 2H, imidazole-H), 4.50 (d,
J = 5.4 Hz, 2H, 1′-H), 2.13 (s, 2H, 2′-H), 0.91 (s, 6H, CH3), 0.78 (s, 6H,
CH3), 0.69–0.71 (d, J = 6.0 Hz, 2H, 3′-H), 0.07 (s, 2H, 4′-H), −1.37–
−1.35 (m, 2H, 5′-H), −2.37–−2.33 (m, 2H, 5′-H). HRMS (ESI) m/z
[M + Na]+ calcd. for C58H48N18 NaO8Si: 1175.3569; found: 1175.3550.
Silicon phthalocyanine 4. According to the procedure described for
SiPc 1, SiPcCl2 (40 mg, 0.065 mmol) was treated with guanosine 10
(168 mg, 0.52 mmol), and NaH (0.42 mmol) in toluene (20 ml) to
give 4 as a blue solid (10 mg, 13%). UV–vis (DMF): λmax, nm (ε,
M
−1·cm−1) 676 (180,000). 1H NMR (400 MHz, d6-DMSO): δ =
10.42–10.43 (d, J = 4.0 Hz, 2H, imidazole-NH), 9.62–9.64 (m, 8H, Pc-
Hα), 8.49–8.51 (m, 8H, Pc-Hβ), 7.95–7.96 (d, J = 4.0 Hz, 2H,
imidazole-NH), 5.73–6.12 (m, 4H, NH2), 4.46–4.47 (d, J = 4.0 Hz, 2H,
1′-H), 2.89–2.90 (d, J = 4.0 Hz, 2H, 2′-H), 2.73–2.75 (d, J = 8.0 Hz, 2H,
3′-H), 1.32–1.35 (d, 2H, J = 8.0 Hz, 4′-H), 0.75 (s, 6H, CH3), 0.62 (s,
6H, CH3), −1.62–−1.58 (m, J = 4.0 Hz, 2H, 5′-H), −2.20–−2.16 (m,
J = 4.0 Hz, 2H, 5′-H). HRMS (ESI) m/z [M + 2H]2+ calcd. for
C58H50N18O10Si: 593.1864; found: 593.1877.
Intracellular fluorescence studies. About 6 × 104 HepG2 cells in
RPMI 1640 culture medium (0.5 ml) were seeded on a confocal dish
and incubated overnight at 37 °C under 5% CO2. After removing the me-
dium, the cells were incubated with SiPcs 1, 2, or Ce6 (all at 2 μM) in the
dark for 2 h, followed by being rinsed with PBS and viewed with a LEICA
TCS SPE confocal microscope. Upon being excited at 635 nm under the
same light intensity, the fluorescence signals of photosensitizers were
monitored at 645–750 nm. The images were then digitized and ana-
lyzed by using the LEICA TCS SPE ROI Fluorescence Statistics. The intra-
cellular fluorescence intensities (a total of 20 cells for each sample)
were also determined.
2.3. In Vitro Studies
The HepG2 human hepatocarcinoma cells and BGC823 human gas-
tric cancer cells (from ATCC) were maintained in RPMI 1640 medium
(Hyclone) supplemented with 10% fetal bovine serum, penicillin
(50 units/ml), and streptomycin (50 μg/ml) at 37 °C in a humidified
5% CO2 atmosphere.
Stock solutions of the studied SiPcs and Ce6 (all at 1 mM) were pre-
pared in DMF and stored at 4 °C in the dark. The solution was then di-
luted to 80 μM with an aqueous solution of Cremophor (1%, 1 g in
Cellular uptake. About 6 × 105 HepG2 cells in RPMI 1640 culture
medium (0.5 ml) were seeded on a confocal dish and incubated over-
night at 37 °C under 5% CO2. After removing the medium, the cells
were incubated with SiPcs 1, 2, or Ce6 (all at 2 μM) in the dark for 2 h,
followed by being rinsed with PBS, and then harvested by trypsin
(0.25%) treatment. The trypsin was then quenched with the medium
(0.5 ml). The solution was transferred to centrifuge tubes (1.5 ml) and
centrifuged at 1000 rpm for 3 min. The pellet was then washed with
PBS (1 ml) and the suspension was centrifuged again. After removing
the PBS, the cells were lyzed with DMF (1.2 ml). The mixture was soni-
cated for 5 min and then centrifuged again. The supernatants were
transferred for UV/Vis spectroscopic measurements. The absorbance at
Table 2
Comparison of the IC50 values of SiPcs 1, 2 and Ce6 against HepG2 and BGC823 cells.
SiPcs
IC50 (nM)
HepG2
BGC823
1
2
Ce6
9
14
750
23
33
–

200
B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
Fig. 4. (a) The bright field and intracellular fluorescence images of SiPcs 1, 2, and Ce6 (all at 2 μM) in HepG2 cells after incubation for 2 h. (b) Comparison of the corresponding intracellular
fluorescence intensities of these photosensitizers. Data are expressed as the mean standard deviation (number of cells = 20). (c) Percentage cellular uptake for 1, 2 and Ce6 determined
by an extraction method. Data are expressed as mean value standard deviation of three independent experiments.
677 nm (1), 679 nm (2) or 663 nm (Ce6) was compared with the re-
spective calibration curves to give the uptake concentrations.
0.5 ml of binding buffer containing Annexin V-FITC (5 μl) and propidium
iodium (PI) (5 μl), and further incubation at 37 °C for 10 min in the dark.
The cells were then viewed using a LEICA TCS SPE fluorescence confocal
microscope. Annexin V-FITC was excited at 488 nm and monitored at
499–529 nm, while PI was excited at 532 nm and monitored at 545–
617 nm. The cell populations at different phase of cell death, namely vi-
able (annexin V-FITC−/PI−), early apoptotic (annexin V-FITC+/PI−),
and necrotic or late-stage apoptotic (annexin V-FITC+/PI+), were deter-
mined by digitally merging fluorescence images and phase contrast
images.
Subcellular localization studies. About 6 × 104 HepG2 or BGC823
cells in the culture medium were seeded on a confocal dish. After re-
moving the medium, the cells were incubated with the solutions of 1
or 2 in the medium (both at 2 μM, 0.5 ml) for 0.5 h under the same con-
dition, and then Lyso Tracker Red (5 μM, 20 μl) was added for further
60 min co-incubation, followed by Mito Tracker Green (5 μM, 20 μl)
for further 30 min co-incubation, leading to a total incubation time of
2 h for the photosensitizers, 1.5 h for Lyso Tracker Red, and 0.5 h for
Mito Tracker Green. The cells were then rinsed with PBS and viewed
with a LEICA TCS SPE confocal microscope equipped with 488 nm,
532 nm, and 635 nm solid-state lasers. MitoTracker Green and Lyso
Tracker Red were excited at 488 nm and 532 nm monitored at 499–
529 nm and 552–617 nm, respectively, while compounds 1 and 2
were excited at 635 nm and monitored at 645–750 nm. The subcellular
localization of 1 and 2 were revealed by comparing the intracellular
fluorescence images caused by MitoTracker Green, Lyso Tracker Red,
and these phthalocyanines.
3. Results and Discussion
3.1. Synthesis
Apart from the SiPcs axially di-substituted with isopropylidene-
protected adenosines or guanosines (compounds 3 and 4), we also pre-
pared two analogs substituted with chloro-modified adenosines (1) and
chloro-modified purines (2), on which one and two chlorine atom
(s) have been introduced on the pyrimidine ring, respectively, in order
to explore the effects of heavy atoms on the photosensitizing efficiency
[20]. Scheme 1 shows the synthetic route of these SiPcs. Firstly, the
isopropylidene-protected chloro-adenosine moieties 7 and dichloro-
purine moieties 8 were prepared through a classical ketalation of the
2′,3′-hydroxyls of nucleoside derivatives 5 and 6 with acetone, respec-
tively, using p-toluenesulfonic acid (PTSA) as a catalyst. On the other
hand, the isopropylidene-protected adenosine 9 and guanosine 10 are
commercially available. The compounds 7–10 were further treated
with silicon(IV) phthalocyanine dichloride (SiPcCl2), respectively, in
the presence of NaH in toluene, leading to axial substitution, to give
Apoptosis. About 1 × 105 HepG2 cells in the culture medium
(0.5 ml) were seeded on a confocal dish (three dishes for each com-
pound) and incubated overnight at 37 °C under 5% CO2. After removing
the medium, the cells were incubated with the solution of 1 or 2 in the
medium (2 μM, 0.4 ml) for 2 h under the same conditions. The cells were
then rinsed with PBS and refilled with 0.4 ml of the culture medium.
Subsequently, two dishes of the cells were illuminated using a red
light (λ N 610 nm, 15 mW/cm2, 27 J/cm2), and the third one was still
kept in the dark for another 24 h as a control. After that, the illuminated
cells were further incubated in the dark for 6 h and 24 h, respectively. At
the set time, the cells were rinsed with PBS, followed by addition of

B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
201
the corresponding products 1–4. The four final products are highly sol-
uble in common organic solvents and could be readily purified by col-
umn chromatography.
close to the phthalocyanine ring spatially, producing a stronger
quenching because of PET effect, and leading to the very weak fluores-
cence emission and singlet oxygen generation efficiencies.
On the other hand, replacing axial adenosines with chloro-modified
adenosines can result in the increase of photogenerating singlet oxygen
efficiencies of SiPcs. The formed SiPc 1 which contains monochloro-
modified adenosines, appears as more efficient photosensitizers with
3.2. Photophysical and Photochemical Properties
The spectroscopic properties of these compounds were measured in
N,N-dimethylformamide (DMF), and the singlet oxygen quantum yields
(ΦΔ) of the four compounds 1–4 were also measured in DMF using 1,3-
diphenylisobenzofuran (DPBF) as the scavenger [18]. The data are sum-
marized in Table 1. For comparison, the data of analogs substituted with
uridines and cytidines (compounds 10–11, see Fig. 1) [18] are also
added in Table 1.
The absorption spectra of the compounds 1–4 in DMF are similar
with those of analogs 10–11, showing an intense and sharp Q-band at
676–679 nm, as shown in Fig. S1. Their Q-bands strictly follow the Lam-
bert–Beer law, indicating that these SiPcs are essentially free from ag-
gregation in DMF. Upon excitation at 610 nm, the compounds 1–3
show a fluorescence emission at 685–687 nm with a fluorescence quan-
tum yield (ΦF) of 0.25–0.34 relative to unsubstituted zinc(II) phthalocy-
anine (ZnPc) (ΦF = 0.28) [33]. However, the guanosine-containing
compound 4 exhibits an extremely weak fluorescence emission
(ΦF = 0.02) (Table 1).
Moreover, the adenosine-substituted SiPc 3 presents a lower singlet
oxygen generation efficiency (ΦΔ = 0.35) than the uridine- and
cytidine-substituted analogs 10–11 (ΦΔ = 0.42–0.44), while the
guanosine-substituted SiPc 4 exhibits a weakest photosensitizing effi-
ciency with a ΦΔ value down to 0.03. In other word, the introduction
of adenosine and guanosine on the axial position of phthalocyanine re-
sulted in the decrease of fluorescence and singlet oxygen quantum
yields, when compared with introduction of uridine and cytidine. The
reason for this observation is elusive at present, and we speculate that
more nitrogen atoms on the bases of adenosine and guanosine probably
results in relatively strong photoinduced electron transfer (PET) effect
[21,35,36], thereby reducing the photosensitizing efficiency. For com-
pound 4, the primary amino group of the guanosine may be more
ΦΔ of 0.42, when compared with SiPc 3 containing adenosines. What
is unexpected is its ΦF value also increased from 0.30 to 0.34. This result
could not be ascribed to heavy atom effect [20], but may be due to the
electron-withdrawing effects of chlorine atom, which can decrease the
PET effects of amine groups [36].
The electronic absorption spectra of 1 and 2 were further recorded in
the Roswell Park Memorial Institute (RPMI) 1640 medium (formulated
with 0.05% of Cremophor EL, wt.) to examine their aggregation behavior
in a biological environment. As shown in Fig. 2a, the Q-bands of both
compounds show slightly red-shift (2–3 nm) in the medium compared
with that in DMF. For compound 1, the Q-band (679 nm) remains very
sharp and intense in the medium. As shown in the inset, the Q-band also
strictly follows the Lambert–Beer law, suggesting compound 1 is essen-
tially non-aggregated in the culture medium. But compound 2 presents
relative broad Q-band (682 nm) with a slight decrease in intensity in
contrast to compound 1. It means that compound 2 shows a tiny ten-
dency of aggregation in the aqueous condition. Their fluorescence spec-
tra were also compared in RPMI medium. As shown in Fig. 2b, the
fluorescence intensity of 2 in RPMI medium is obviously lower than 1.
The ΦF values of 2 was calculated to be 0.17, which is also lower than
that of 1 (ΦF = 0.26 for 1). These observations suggest that compound
2 presented more aggregation trend than 1 in RPMI medium.
3.3. In Vitro Studies
3.3.1. Photocytotoxicities Against HepG2 and BGC823 Cells
In view of the higher singlet oxygen generation efficiency, the com-
pounds 1 and 2 were chosen to evaluate their photodynamic activities
against two different cell lines, namely, HepG2 human hepatocarcinoma
Fig. 5. Visualization of the intracellular fluorescence of HepG2 cells by using filter sets specific for (a) Bright field image, (b) Mito Tracker Green (in green), (c) Lyso Tracker Red (in blue),
(d) SiPc 1 (in red), and the corresponding superimposed image of (e) SiPc-Mito Tracker Green and (f) SiPc-Lyso Tracker Red. Scale bar: 25 μm. (For interpretation of the references to color
in this figure legend, the reader is referred to the web version of this article.)

202
B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
Fig. 6. Visualization of the intracellular fluorescence of HepG2 cells by using filter sets specific for (a) Bright field image, (b) Mito Tracker Green (in green), (c) Lyso Tracker Red (in blue),
(d) SiPc 2 (in red), and the corresponding superimposed image of (e) SiPc-Mito Tracker Green and (f) SiPc-Lyso Tracker Red. Scale bar: 25 μm. (For interpretation of the references to color
in this figure legend, the reader is referred to the web version of this article.)
cells and BGC823 human gastric cancer cells. Fig. 3 shows the cytotoxic-
ity of 1 and 2 toward both cell lines in the presence or absence of light. It
can be seen that these compounds are essentially non-cytotoxic in the
dark, but exhibit high photocytotoxicity toward both cell lines with
the IC50 values ranging from 9 nM to 33 nM (Table 2). For the two cell
lines, HepG2 cells are more susceptive to the photosensitizers. By com-
parison, compound 1 substituted with monochloro-adenosine deriva-
tive is slightly more potent than the analog with dichloro-modified
nucleoside derivative (compound 2). Moreover, the photocytotoxicity
of compound 1 against HepG2 cells is comparable with the most potent
uridine-substituted analog 11 (IC50 = 6 nM) among these nucleoside-
substituted SiPcs [18]. On the other hand, both compounds (1 and 2)
show significantly higher photocytotoxicity than a positive control,
chlorin e6 (Ce6), a well-known anticancer photosensitizer [4], with an
IC50 value of 752 nM against HepG2 cells in the same experimental con-
dition (Fig. S2).
quantified by measuring their Q band absorbance. As shown in Fig. 4c,
the uptakes of these compounds follow the trend: 1 N 2 N Ce6. This result
is in accord with intracellular fluorescence intensity analysis previously,
which should be one of the reasons for their large difference in
photocytotoxicities.
3.3.3. Subcellular Localization
Since mitochondrion is an important target of the initiation of apo-
ptosis [37–39], we are interested in whether the photosensitizer has
an affinity to the mitochondria. Therefore, the subcellular localization
of SiPcs 1 and 2 in HepG2 and BGC823 cells were investigated by
CLSM. After incubation with the photosensitizers, the cells were stained
with MitoTracker Green, which is a specific fluorescence probes for mi-
tochondria. As shown in Fig. 5, the fluorescence of compound 1 in
HepG2 cells is essentially overlapped with that of MitoTracker Green
and partially superimposed with Lyso Tracker Red, demonstrating that
1 accumulates mainly into mitochondria of HepG2 cells. But the fluores-
cence of compound 2 compared to MitoTracker Green and Lyso Tracker
Red both just partially superimposed, indicating compound 2 is partly
localized in mitochondria and lysosomes of HepG2 cells (Fig. 6). For
BGC823 cells, similar results could be observed according to the fluores-
cence images of 1, 2, and MitoTracker Green (Fig. S4 in ESI†).
3.3.2. Cellular Uptake
The cellular uptake of these SiPcs 1–2 and Ce6 by HepG2 cells was
also examined by confocal laser scanning microscopy (CLSM) analysis.
Fig. 4 shows the bright fields, fluorescence images and the intracellular
fluorescence intensities. It can be seen that compound 1 exhibits a
slightly stronger fluorescence intensity in the cells than that of 2. The
trend is consistent with the results of photocytotoxicity. On the other
hand, the intracellular fluorescence of both SiPcs 1 and 2 is greatly
stronger than that of Ce6 (about 39–62 folds in intensity) in the same
experimental conditions. Taking the different fluorescence generation
efficiency of the SiPcs 1–2 and Ce6 into account, the fluorescence spec-
tra of 1 and Ce6 were further measured in DMF (Fig. S3). The fluores-
cence intensity of compound 1 is about 3-fold higher than that of Ce6.
Thus, it can be concluded that the significantly stronger intracellular
fluorescence intensity of the SiPcs in contrast to Ce6 is mainly due to
the higher cellular uptake. To confirm this viewpoint, we further
employed an extraction method to quantify the cellular uptake. After in-
cubation with these photosensitizers for 2 h, DMF was used to lyze the
cells and extract the dyes. The dye concentrations inside the cells were
3.3.4. Apoptosis
The mode of cell death induced by PDT of compounds 1 and 2 was
also investigated by using a cell apoptosis/death staining kit, annexin
V-fluorescein isothiocyanate (FITC) and propidium iodide (PI), which
are the fluorescence probes to distinguish viable cells from dead ones
of different stages. The dual fluorescence of annexin V-FITC and PI in
HepG2 cells was examined by fluorescence confocal microscopy at 6 h
and 24 h after PDT treatment, respectively. As shown in Fig. 7a, after
PDT treatment with compound 1 for 6 h, the fluorescence of annexin
V-FITC could be observed in more than half of the cells, while there
was nearly no PI signal detectable. However, after 24 h, the fluorescence
of both annexin V-FITC and PI could be obviously observed in most of
HepG2 cells. These observations indicate that there were viable and

B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
203
Fig. 7. The intracellular fluorescence images of Annexin V-FITC (in green) and PI (in red) in HepG2 cells after PDT treatment with (a) 1 or (b) 2 (both at 20 nM) for 6 h and 24 h. The bright
field and merged images are given in column 1 and 4, respectively. Scale bar: 75 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the web
version of this article.)
early apoptotic cells after PDT treatment with 1 for 6 h, and the cells
were almost at necrotic or late apoptotic stage after 24 h. For the cells
PDT-treated with compound 2, similar result could be seen after 6 h,
but after 24 h, apart from the necrotic or late-stage apoptotic cells,
there were still a few early apoptotic ones (Fig. 7b). Therefore, it can
be concluded that HepG2 cells underwent an apoptotic process when
PDT-treated with both 1 and 2.
well-known photosensitizer Ce6 (IC50 = 752 nM against HepG2 cells).
For both cell lines, compound 1 can essentially bind to mitochondria,
while compound 2 is just partially localized in mitochondria. The two
compounds can induce cell death of HepG2 cells likely through
apoptosis.
Acknowledgments
4. Conclusions
This work was supported by the Natural Science Foundation of China
(Grant Nos. 21172037, 21301031, 21473033), the Public Science and
Technology Research Funds Projects of Ocean, China (Grant No.
201305015-2), and Scientific Research Fund of the National Board of
Health and Family Planning (the Joint Research Project of Health and
Education of Fujian), China (Grant No. WKJ-FJ-32).
A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted
axially with different nucleoside moieties have been synthesized and
evaluated for their spectroscopic properties, singlet oxygen quantum
yields (ΦΔ) and in vitro photodynamic activities. The adenosine-
substituted SiPc shows a lower photosensitizing efficiency (ΦΔ
=
0.35) than the uridine- and cytidine-substituted analogs (ΦΔ = 0.42–
0.44), while the guanosine-substituted SiPc exhibits a weakest singlet
oxygen generation efficiency with a ΦΔ value down to 0.03. Moreover,
when replacing axial adenosines with monochloro-modified adeno-
sines, the corresponding SiPc 1 gives higher singlet oxygen generation
efficiency due to the electron-withdrawing effects of chlorine atom,
which decrease the PET effects of amine groups. In view of the high sin-
glet oxygen quantum yields (ΦΔ = 0.42–0.44), in vitro photodynamic
activities of 1 and 2 were further evaluated. They are both highly cyto-
toxic toward HepG2 and BGC823 cells upon illumination with IC50
values ranging from 9 nM to 33 nM. Moreover, the photocytotoxities
of both compounds 1 and 2 are significantly higher than that of the
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.jphotobiol.2016.03.055.
References
[1] C. Robertson, D.H. Evans, H. Abrahamse, Photodynamic therapy (PDT): A short re-
view on cellular mechanisms and cancer research applications for PDT, J.
Photochem. Photobiol. B Biol. 96 (2009) 1–8.
[2] D.E. Dolmans, D. Fukumura, R.K. Jain, Photodynamic therapy for cancer, Nat. Rev.
Cancer 3 (2003) 380–387.

204
B.-Y. Zheng et al. / Journal of Photochemistry & Photobiology, B: Biology 159 (2016) 196–204
[3] S.B. Brown, E.A. Brown, I. Walker, The present and future role of photodynamic ther-
[22] G. Zheng, J. Chen, H. Li, J.D. Glickson, Rerouting lipoprotein nanoparticles to selected
alternate receptors for the targeted delivery of cancer diagnostic and therapeutic
agents, Proc. Natl. Acad. Sci. U. S. A. 102 (2005) 17757–17762.
[23] L. Alexandrova, 4′-C-nucleoside derivatives: synthesis and antiviral properties, Rus.
J. Bioorg. Chem. 37 (2011) 651–671.
[24] N. Tzioumaki, E. Tsoukala, S. Manta, G. Agelis, J. Balzarini, D. Komiotis, Synthesis, an-
tiviral and cytostatic evaluation of unsaturated exomethylene and keto D-
lyxopyranonucleoside analogues, Arch. Pharm. Chem. Life Sci. 342 (2009) 353–360.
[25] A. Matsuda, T. Sasaki, Antitumor activity of sugar-modified cytosine nucleosides,
Cancer Sci. 95 (2004) 105–111.
[26] P. Patel, H.H. Patel, E. Borland, S.M. Gorun, D. Sabatino, Chemically robust fluoroalkyl
phthalocyanine–oligonucleotide bioconjugates and their GRP78 oncogene
photocleavage activity, Chem. Commun. 50 (2014) 6309–6311.
apy in cancer treatment, Lancet Oncol. 5 (2004) 497–508.
[4] M.R. Detty, S.L. Gibson, S.J. Wagner, Current clinical and preclinical photosensitizers
for use in photodynamic therapy, J. Med. Chem. 47 (2004) 3897–3915.
[5] D. Samaroo, E. Perez, A. Aggarwal, A. Wills, N. O'Connor, Strategies for delivering
porphyrinoid-based photosensitizers in therapeutic applications, Ther. Deliv. 5
(2014) 859–872.
[6] F. Schmitt, L. Juillerat-Jeanneret, Drug targeting strategies for photodynamic ther-
apy, Anti Cancer Agents Med. Chem. 12 (2012) 500–525.
[7] N. Shirasu, S.O. Nam, M. Kuroki, Tumor-targeted photodynamic therapy, Anticancer
Res. 33 (2013) 2823–2831.
[8] A.M. Bugaj, Targeted photodynamic therapy—a promising strategy of tumor treat-
ment, Photochem. Photobiol. Sci. 10 (2011) 1097–1109.
[9] J.-P. Taquet, C. Frochot, V. Manneville, M. Barberi-Heyob, Phthalocyanines covalently
bound to biomolecules for a targeted photodynamic therapy, Curr. Med. Chem. 14
(2007) 1673–1687.
[10] W.M. Sharman, J.E. van Lier, C.M. Allen, Targeted photodynamic therapy via receptor
mediated delivery systems, Adv. Drug Deliv. Rev. 56 (2004) 53–76.
[11] G.A.M.S. van Dongen, G.W.M. Visser, M.B. Vrouenraets, Photosensitizer-antibody
conjugates for detection and therapy of cancer, Adv. Drug Deliv. Rev. 56 (2004)
31–52.
[27] T. Torres, A. Gouloumis, D. Sanchez-Garcia, J. Jayawickramarajah, W. Seitz, D.M.
Guldi, J.L. Sessler, Photophysical characterization of a cytidine–guanosine tethered
phthalocyanine–fullerene dyad, Chem. Commun. 3 (2007) 292–294.
[28] R.O. Ogbodu, E.K. Amuhaya, P. Mashazi, T. Nyokong, Photophysical properties of zinc
phthalocyanine–uridine single walled carbon nanotube-conjugates, Spectrochim.
Acta A Mol. Biomol. Spectrosc. 149 (2015) 231–239.
[29] X.-Y. Li, D.K. Ng, Synthesis and spectroscopic properties of the first phthalocyanine–
nucleobase conjugates, Tetrahedron Lett. 42 (2001) 305–309.
[12] R. Schneider, F. Schmitt, C. Frochot, Y. Fort, N. Lourette, F. Guillemin, J.-F. Mullerd, M.
Barberi-Heyob, Design, synthesis, and biological evaluation of folic acid targeted
tetraphenylporphyrin as novel photosensitizers for selective photodynamic therapy,
Bioorg. Med. Chem. 13 (2005) 2799–2808.
[13] M.R. Ke, S.L. Yeung, W.P. Fong, D.K. Ng, P.C. Lo, A phthalocyanine–peptide conjugate
with high in vitro photodynamic activity and enhanced in vivo tumor retention
property, Chem. Eur. J. 18 (2012) 4225–4233.
[14] A.C. Tedesco, J.C.G. Rotta, C.N. Lunardi, Synthesis, photophysical and photochemical
aspects of phthalocyanines for photodynamic therapy, Curr. Org. Chem. 7 (2003)
187–196.
[15] C.M. Allen, W.M. Sharman, J.E. van Lier, Current status of phthalocyanines in the
photodynamic therapy of cancer, J. Porphyrins Phthalocyanines 5 (2001) 161–169.
[16] E.A. Lukyanets, Phthalocyanines as photosensitizers in the photodynamic therapy of
cancer, J. Porphyrins Phthalocyanines 3 (1999) 424–432.
[30] M.R. Reddy, N. Shibata, Y. Kondo, S. Nakamura, T. Toru, Design, synthesis, and spec-
troscopic investigation of zinc dodecakis (trifluoroethoxy) phthalocyanines conju-
gated with deoxyribonucleosides, Angew. Chem. Int. Ed. 45 (2006) 8163–8166.
[31] J.L. Sessler, J. Jayawickramarajah, A. Gouloumis, G. Dan Pantos, T. Torres, D.M. Guldi,
Guanosine and fullerene derived de-aggregation of a new phthalocyanine-linked
cytidine derivative, Tetrahedron 62 (2006) 2123–2131.
[32] X.-M. Shen, X.-J. Jiang, C.-C. Huang, H.-H. Zhang, J.-D. Huang, Highly photostable sil-
icon(IV) phthalocyanines containing adamantane moieties: synthesis, structure,
and properties, Tetrahedron 66 (2010) 9041–9048.
[33] I. Scalise, E.N. Durantini, Synthesis, properties, and photodynamic inactivation of
Escherichia coli using a cationic and a noncharged Zn (II) pyridyloxyphthalocyanine
derivatives, Bioorg. Med. Chem. 13 (2005) 3037–3045.
[34] M.D. Maree, N. Kuznetsova, T. Nyokong, Silicon octaphenoxyphthalocyanines:
photostability and singlet oxygen quantum yields, J. Photochem. Photobiol. A
Chem. 140 (2001) 117–125.
[17] Y.-W. Zheng, S.-F. Chen, B.-Y. Zheng, M.-R. Ke, J.-D. Huang,
A silicon(IV)
phthalocyanine-folate conjugate as an efficient photosensitizer, Chem. Lett. 43
(2014) 1701–1703.
[18] X.M. Shen, B.Y. Zheng, X.R. Huang, L. Wang, J.D. Huang, The first silicon(IV)
phthalocyanine-nucleoside conjugates with high photodynamic activity, Dalton
Trans. 42 (2013) 10398–10403.
[35] X.J. Jiang, P.C. Lo, S.L. Yeung, W.P. Fong, D.K.P. Ng, Phthalocyanine-polyamine conju-
gates as highly efficient photosensitizers for photodynamic therapy, J. Med. Chem.
54 (2011) 320–330.
[36] X.F. Zhang, X. Li, L. Niu, L. Sun, L. Liu, Charge transfer Photophysics of tetra(α-amino)
zinc phthalocyanine, J. Fluoresc. 19 (2009) 947–954.
[19] M. Mitsunaga, M. Ogawa, N. Kosaka, L.T. Rosenblum, P.L. Choyke, H. Kobayashi, Can-
cer cell-selective in vivo near infrared photoimmunotherapy targeting specific
membrane molecules, Nat. Med. 17 (2011) 1685–1691.
[20] P.-C. Lo, C.M. Chan, J.-Y. Liu, W.-P. Fong, D.K. Ng, Highly photocytotoxic glucosylated
silicon (IV) phthalocyanines. Effects of peripheral chloro substitution on the
photophysical and photodynamic properties, J. Med. Chem. 50 (2007) 2100–2107.
[21] T. Nyokong, Effects of substituents on the photochemical and photophysical proper-
ties of main group metal phthalocyanines, Coord. Chem. Rev. 251 (2007)
1707–1722.
[37] J. Morgan, A.R. Oseroff, Mitochondria-based photodynamic anti-cancer therapy,
Adv. Drug Deliv. Rev. 49 (2001) 71–86.
[38] P. Mroz, A. Yaroslavsky, G.B. Kharkwal, M.R. Hamblin, Cell death pathways in photo-
dynamic therapy of cancer, Cancer 3 (2011) 2516–2539.
[39] Y. Ge, X. Weng, T. Tian, F. Ding, R. Huang, L. Yuan, J. Wu, T. Wang, P. Guo, X. Zhou, A
mitochondria-targeted zinc(II) phthalocyanine for photodynamic therapy, RSC Adv.
3 (2013) 12839–12846.