Near infrared light-triggered drug generation and release from gold nanoparticle carriers for photodynamic therapy

Article abstract of DOI:10.1002/smll.201303329

A photoprecursor Pc 227 is covalently bound onto gold nanoparticles (Au NPs) to produce the known photodynamic therapy (PDT) drug Pc 4 upon 660 nm photoirradiation. The photochemical formation of the photoproduct Pc 4 is identified by spectroscopy, chromatography, and mass spectrometry and its PDT efficacy is equal to Pc 4 when administered non-covalently by Au NPs, with the added benefit of improved covalent delivery and targeted NIR-triggered release from the covalent Pc 227-Au NP conjugate, while during transport the attached Pc 227 is quenched by the Au NP and PDT inactivated.

Full text of DOI:10.1002/smll.201303329

Photodynamic Therapy
Near Infrared Light-Triggered Drug Generation
and Release from Gold Nanoparticle Carriers for
Photodynamic Therapy
Yu Cheng, Tennyson L. Doane, Chi-Hung Chuang, Assem Ziady,*
and Clemens Burda*
A photoprecursor Pc 227 is covalently bound onto gold nanoparticles (Au NPs)
to produce the known photodynamic therapy (PDT) drug Pc 4 upon 660 nm
photoirradiation. The photochemical formation of the photoproduct Pc 4 is identified
by spectroscopy, chromatography, and mass spectrometry and its PDT efficacy is
equal to Pc 4 when administered non-covalently by Au NPs, with the added benefit of
improved covalent delivery and targeted NIR-triggered release from the covalent Pc
227-Au NP conjugate, while during transport the attached Pc 227 is quenched by the
Au NP and PDT inactivated.
Controlled delivery of the typically hydrophobic drugs is contrast, the visible-near infrared (Vis-NIR) range of light
one of the major challenges encountered in photodynamic between 620 nm and 850 nm, the so-called “phototherapeutic
therapy (PDT) cancer treatment. PEGylated gold nano- window”, is harmless with maximum tissue penetration.[11,12]
particle (Au NP)-based delivery systems have attracted sig- A Vis-NIR-triggered drug release holds promise for applica-
nificant attention to improve the solubility and selectivity tions in drug delivery and phototherapy.[13,14]
of PDT drugs due to their properties of biocompatibility,
The use of silicon phthalocyanine 4 (Pc 4) as a hydro-
high drug loading capacity, chemically versatile surface, and phobic PDT drug has been developed and is currently FDA-
controlled drug release.[1,2] As an external stimulus, light is approved in clinical trials.[15,16] A PEGylated Au NP based
widely employed for controlled drug release in the treat- delivery system with improved water solubility and stability
ment of diseases.[3–6] However, most of the photo-stimu- has been shown to greatly enhance the efficacy of Pc 4 in
lated drug delivery systems utilize ultraviolet light below vivo through non-covalent drug delivery.[17,18] Although cova-
400 nm to release the drug molecules.[7–10] Unfortunately, lent delivery provides a stable delivery approach, it is a for-
short-wavelength light has poor skin penetration and can midable challenge to control the drug release with a stimulus
cause the damage to DNA which limits their application. In while maintaining the therapeutic and biological properties
of the drug load. In some instances, covalent attachment of
drugs to the vector can alter the delivery mechanism and
even eliminate any PDT efficacy, as was recently observed in
HeLa cells.[17]
Dr. Y. Cheng, Dr. T. L. Doane,
Dr. C.-H. Chuang, Prof. C. Burda
Department of Chemistry
In this communication, we describe an example of a Vis-
NIR-light triggered PDT drug delivery-and-release system
by attaching Pc 227 (a Pc 4 precursor) on a Au NP via a
Au-S bond. Pc 227 is designed with a NIR photosensitive
Si-C bond (Scheme 1, red bond) in order to enable the drug
release through 660 nm Vis-NIR irradiation. It is known that
photolysis of Si-C bonds on axial ligands of silicon porphyrin
complexes undergoes homolysis during visible light irradia-
tion.[20,21] Phthalocyanine-based photosensitizers used herein
Case Western Reserve University
Cleveland, Ohio
Fax: +1 216 368 3006
E-mail: burda@case.edu
Prof. A. Ziady
Department of Pediatrics, Emory University
Atlanta, Georgia
E-mail: assem.ziady@emory.edu
DOI: 10.1002/smll.201303329
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Y. Cheng et al.
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irradiation. 10 seconds post of the irradiation, the Q band
of Pc 227 at 676 nm shifted to 670 nm, which was the same
as Pc 4. The blue shifted of the Q band was completed at
180 sections post of the irradiation. There was no significant
change post 4 minutes and 5 minutes of irradiation. A sim-
ilar blue shift trend in the emission of the photolysis product
was observed in the fluorescence spectra. Compared to the
Pc 227, the maximum emission of the photolysis product
showed a 7 nm blue shift. The fluorescence quantum yield of
Pc 227 was 1% and Pc 4 was 16.9% using methylene blue
as the reference. The increased fluorescence intensity upon
irradiation confirmed the generation of Pc 4. These results
suggest that the photolysis of Pc 227 is efficient and could
generate Pc 4 upon irradiation.
Scheme 1. Schematic of phototriggered PDT drug Pc 4 release from Au
NP-Pc 227. The thiol group in Pc 227 allows for covalent bonding of the
drug precursor to the Au NP surface.
Singlet oxygen 1O2 is the reactive species in PDT and
highly toxic to the biomolecules.[16] It can be generated by
energy transfer from the excited photosensitizer to the molec-
ular oxygen. Silicon phthalocyanine molecules with high sin-
glet oxygen generation yields are excellent photosensitizer for
PDT. After photolysis of Pc 227, the singlet oxygen quantum
yield (ΦΔ%) was measured by the photodecomposition of
have strong absorptions with εmax = 2 × 105 cm−1M−1 in the
660–690 nm wavelength regime.[22] Similar to the published
silicon porphyrin complexes, the axial alkyl ligand on silicon
phthalocyanines is photosensitive and
can photocleave the Si-C bond homolyti-
cally.[21] To the best of our knowledge, this
is the first report of a NIR photo-cleav-
able drug delivery system, which results
in a fully active and FDA-approved PDT
agent (Pc 4) upon release.
Here, we describe the synthesis, char-
acterization, and Vis-NIR light activation
of this novel conjugate, and demonstrate
the PDT efficacy in vitro. The synthesis
of Pc 227 was previously published and
confirmed using both NMR and MS anal-
ysis.[19] Thus it is simple to differentiate
between Pc 227 and Pc 4.[15] On the other
hand, the photophysical properties of Pc
227 are very similar to those of Pc 4 and
generally reflect the main contributions
of the aromatic macrocyclic ring struc-
ture with minor electronic effects from
the axial ligands. From the absorption
(Figure 1A) and fluorescence (Figure 1B)
of Pc 227 and Pc 4, it is apparent that Pc
227 absorbs and emits light at slightly
longer wavelengths compared to Pc 4,
which made it straightforward to follow
the progress of the photolysis reaction
by monitoring the resulting Vis-NIR
spectra. Thus, the conversion of Pc 227 to
the photoactive Pc 4 could be monitored
(Figure 1C) and additionally confirmed
by UV-Vis and fluorescence spectrometry
(Figure 1E and 1F). The photolysis of Pc
Figure 1. Normalized absorbance (A) and fluorescence (B) spectra of Pc 227 and the
resulting photoproduct after irradiation with λ = 660 nm light (∼3.5 mW cm−2). (C) Schematic
of homolytic bond cleavage and subsequent ligand exchange with water onto the central
Si atom to generate the PDT drug Pc 4, as confirmed by MS spectrometry. UV-Vis (D) and
fluorescence (E) spectra of Pc 227 in methanol before and after irradiation at 660 nm with
227 in methanol was monitored over time
at the laser wavelength of 660 nm with
the power of 0.082 mW. Changes in the
absorption and fluorescence spectra were
recorded at different intervals during the the laser power of 0.082 mW.
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Near Infrared Light-Triggered Drug Generation and Release from Gold Nanoparticle Carriers for Photodynamic Therapy
1,3-diphenylisobenzenofuran (DPBF) in methanol. Meth-
ylene blue (ΦΔ = 49%) was the reference compound. The
photolysis products of Pc 227 showed similar singlet oxygen
generation ability as Pc 4 in methanol. 49.0 3.5% quantum
yield of the products was observed.
To achieve the light sensitive Au NP-Pc 227 conjugate,
dodecylamine coated Au NPs were synthesized using the
Brust-Schiffrin method and coated with MeO-PEG-SH (MW
= 5000) in order to achieve solubility in water.[18] In order
to achieve a stable conjugate in water, Pc 227 with the thiol
group on the axial ligand was conjugated on the Au NP and
the final Pc 227 molecules per NP was controlled to be 40
Figure 2. TEM images of dodecylamine coated Au NPs (A) and Au NP-Pc
: 1 quantified via UV-Vis spectrometry. Transmission elec-
tron microscopy (TEM) revealed that the core size of the
Au NP-Pc 227 conjugates were ∼ 5.5 nm, which was slightly
smaller when compared to the dodecylamine coated Au NPs
(Figure 2), indicating the etching via the thiol molecules.
These conjugates were protected by the PEG with neural
charge, which made them fairly stable in aqueous solutions
for at least one year stored in dark. Successful incorporation
227 conjugates (B). Scale bars: 50 nm.
of the caged Pc 4 into the amphiphilic polyethylene glycol
corona of the Au NPs (Au NP-Pc 227) was tested by assessing
the photophysical properties of the NP conjugates in water.
It is clear from the absorbance spectra in water (Figure 3A )
that the drug was successfully conjugated to the NP. The Au
Figure 3. Absorbance (A) and fluorescence (B) spectra of Au NP-Pc 227 conjugates in aqueous media, with overlapping spectra of both the NP
(surface plasmon at 520 nm) and Pc 227 (690 nm absorbance) but with nearly complete quenching of fluorescence. NIR irradiation of Pc 227 in
water (C & D) and chloroform (E & F) was determined through the new absorption band at ∼671 nm and fluorescence at 680 nm.
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Y. Cheng et al.
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NP surface plasmon band was at 520 nm, suggesting the Au
NPs were well dispersed in water. In addition, the attached
Pc 227 showed the distinct band at 690 nm. However, the
fluorescence of Pc 227 was largely quenched in aqueous
media (Figure 3B). When the conjugates are photolyzed with
660 nm light, the Q band at 690 nm blue-shifted, indicating
successful photoloysis (Figure 3C). As can be expected, there
is no significant formation of Pc 4 fl uorescence in aqueous
solution due to the lack of solubility in water (Figure 3D). It
is observed that in aqueous media the hydrophobic Pc 4 does
not diffuse away from the Au NP surface and thus remains
quenched by the Au NP and its aqueous environment. This
conclusion was further confirmed when the same experi-
ment was conducted in organic media. In chloroform, the
Pc 4 absorption band at 673 nm increases with photolysis
time while the original Pc 227 peak at 690 nm decreases
(Figure 3E).
Similar to free Pc 227, the photolysis products on the
NPs show an increase in fluorescence intensity at 677 nm
(Figure 3F). The Au NP-Pc 227 behaves quite differently in
aqueous versus lipophilic solvents. Although in both solvent
environments drug conversion was observed (Figure 3C & E),
only weak fluorescence of the photoproduct was observable
in aqueous media (Figure 3D) when compared to the same
experiment in organic solvent (Figure 3F), which is due to the
hydrophobicity of Pc 4. The drug Pc 4 can only be released
from the NP in apolar environments (cell walls and organic
solvents). On the other hand, in highly polar environments
(blood stream and other aqueous media) the drug is hydro-
phobically forced into the Au NP interior where the photoex-
cited state and its fluorescence are effectively quenched.
Importantly, Pc 227 is similarly photolabile on the sur-
face of Au NPs as the free molecule in solution. Upon irra-
diation, the Si-C bond of Pc 227 is cleaved and generates a
free valency on the central silicon. In aqueous solution, the
unsaturated valence of the central silicon in the phthalo-
cyanine ring reacts with H2O and produces Pc 4 (Figure 4)
as a reaction product. The ESI-MS of Au NP-Pc 227 conju-
gates after irradiation identified the generation of Pc 4 at 717
m/z (Figure 4B). In addition, the major peaks at 701.9 m/z,
674.1 m/z, 577.6 m/z in Figure 4A were identified with the
corresponding ion after the loss of a methyl group, the amine
functionality and the whole upper axial ligand, respectively.
The peak at 288.3 m/z was identified as an impurity from
purging with just solvent (methanol). In keeping with pre-
vious reports of Au NP mediated Pc 4 drug delivery,[18] the
low water solubility of the phthalocyanine ring requires a
non-polar media to mediate drug release. The use of the pho-
tolabile Si-C linker allows for Vis-NIR light triggered drug
release from the Au NP surface.
Figure 4. ESI-MS Spectra of the Au NP-Pc 227 photoproduct after
irradiation in water (A) and the corresponding m/z m/z ESI-MS Spectra
of the Pc 227-Au NP photoproduct at 718 m/z (B).
stains those dead cells only. As shown in Figure 5A, most of
the cells in the images are not stained by trypan blue, which
indicates minimal toxicity of the Au NP-Pc 227 at the per-
formed incubation conditions in the dark. This was further
confirmed with MTT assays (Figure 5B) to determine the
cell survival after 24 hours incubation with the Au NP-Pc 227
conjugates.
No toxicity was observed in the dark with a Pc 227 con-
centration of 1µM when compared to the control samples.
The photolysis product of Pc 227 was Pc 4 as confirmed
through mass spectrometry measurements (Figure 4) and
showed accordingly an equal singlet oxygen generation yield
of 49.0 3.5%, suggesting the efficient cytotoxicity could be
induced via the irradiation.Although the effective release and
generation of a Pc 4 PDT agent from the Au NP-Pc 227 con-
jugates was demonstrated in pure solvents, cell studies were
required to determine whether the PDT efficacy of the pho-
totriggered drug delivery system was preserved and could be
used as an alternative to previously reported phthalocyanine
PDT systems.[17,18] Clearly, the PDT effect of the conjugates
in HeLa cell cultures was observed based on the change of
PEGylated Au NPs as used in this study show little cel-
lular uptake (∼1%) and minimal toxicity to the cancer
cells.[17,18] As shown in previous studies, the 24-hour incu-
bation time is the optimal condition to reach the maximum
intracellular drug concentration for PDT.[17,18] Therefore, the
cancer cells were incubated with the Au NP-Pc 227 conju-
gates for 24 hours and the cytotoxicity were evaluated by
trypan blue exclusion staining and MTT assays, respectively.
Trypan blue can penetrate the membrane of dead cells and
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Near Infrared Light-Triggered Drug Generation and Release from Gold Nanoparticle Carriers for Photodynamic Therapy
concentration and 1 µJ light, and most of the dead cells were
detached from the surface of the Petri dish after staining. To
obtain a relative efficacy data, MTT assays were conducted
to compare covalently attached Au NP-Pc 227 conjugates to
free Pc 4 and Pc 227 (Figure 5B). After light exposure, over
80% of the HeLa cells were killed when incubated with Au
NP-Pc 227 conjugates, which is close to the free Pc 4 in DMF
solution. In addition, cell studies showed that Pc 227 alone
was the least efficient reagent for PDT treatment compared
to Pc 4 and the Au NP-Pc 227 conjugates, due to the fact that
it first photolyzes.
We have previously shown that neutral Au NP conju-
gates have moderate interaction with the cell membranes,
with subsequent release of the non-covalent drug through
cell membrane diffusion.[17] Here, the photolysis of the
covalent Pc 227-Au NP bond leads to release of the PDT
agent near the cell surface, which is sufficiently close for cell
uptake and effective PDT. As the active PDT drug Pc 4 can
be photogenerated from the attached Pc 227, the same cell
uptake and PDT mechanism of the photoproduct Pc 4 as
previously reported are observed.[17,18] Pc 4 can be taken up
by membrane-mediated diffusion, and irradiated at 670 nm
for PDT treatment. The triplet state energy transfer and gen-
erate singlet oxygen with occur with ∼ 50% yield.[17]
In summary, a novel covalent NIR phototriggered Au
NP-PDT drug delivery system has been designed for effi-
cient delivery and controlled release. The Pc 4 drug genera-
tion and release is based on the photolysis of the axial Si-C
bond on the Pc 227 molecule. Release is only possible into
a lipophilic environment such as apoloar solvents or in cell
membranes. No dark toxicity of the Au NP-Pc 227 conjugates
was observed in HeLa cell cultures. However, upon Vis-NIR
irradiation, efficient PDT mediated cell death was observed.
A detailed investigation of the relevant photophysics and
photochemistry for this system is currently in progress. For
in vivo application, the covalent attachment in a controlled
manner is a favourable approach in drug delivery, which
could minimize the non-specific drug accumulation and
enhance the selectivity to the target. Pc 227, the “caged” Pc 4,
is responsive to the near infrared light to release the active
Pc 4. It can be covalently attached on the Au NPs via the
Au-S bond and is physically more stable when compared to
the Pc 4 on the Au NPs. The in vivo efficacy of Au NP-Pc 227
conjugates is currently under investigation. These results hold
promise for the development of highly selective drug release
through NIR induced photolytic bond cleavage.
Figure 5. Assessment of toxicity and PDT efficacy in HeLa cells via
light microscopy, trypan blue staining (A), and MTT assays (B) after
1 µJ irradiation with > 600 nm light. Cells incubated with Au NP-Pc 227
conjugates at 0.5 and 1 µM concentration after 24 hours remained
healthy as indicated by cellular shape and trypan blue staining (A,
top panel). Dramatic differences in cell morphology were observed by
comparing optical images at 20X magnification before and after PDT
treatment (A, middle panels).These results were further confirmed using
trypan blue staining (A, bottom panel) and successfully quantified via
MTT assays (B), with comparable efficacy to free Pc 4 and improvement
over free Pc 227. Scale bars: 100 µm.
Experimental Section
PEGylated Au NPs were synthesized through the modified Brust-
Schiffrin method followed by ligand exchange with MeO-PEG-SH
(MW5000).[18] The purified Au NPs were dissolved in chloroform
and a 40 fold excess silicon phthalocyanine Pc 227 (Pc 227)
was added into the solution. After 48 hours mixing at room tem-
perature, the solvent was removed under vacuum. The Au NP-Pc
227 conjugates were suspended in aqueous solution and puri-
fied by centrifugation and 200 nm pore filters. The conjugates
were characterized by UV-vis and fluorescence spectrometry.
cell morphology (Figure 5A). Before the PDT treatment, the
cells were slightly elongated and dense monolayers could
be observed after incubation with the Au NP-Pc 227 con-
jugates. After irradiation, the Au NP-Pc 227 treated HeLa
cells changed to a round shape and showed shrinkage in
size, indicating cell death. Additionally, the cells were stained
with trypan blue after PDT treatment, and we could further
confirm that the conjugates were effective PDT systems
(Figure 5A). No cell was found alive at 1 µM Au NP-Pc 227
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[1] J. Kost, R. Langer, Adv. Drug Deliv. Rev. 2001, 46, 125–148.
The average core size of Au NPs was identified by transmission
electron microscopy. The singlet oxygen quantum yield of pho-
tolysis product of Pc 227 was determined by decomposition of
1,3-diphenylisobenzofuran (DPBF) in methanol.[17] The irradia-
tion wavelength for photolysis was 660 nm with a Clark MXR CPA
laser to pump an optical parametric amplifier (OPA, Light Con-
version). The Pc 227 and photolysis samples were analysed by
ESI-MS on a Thermo FINNIGAN LCQ DECA with the ion transfer
capillary temperature at 200 °C.[23,24] The m/z 200 to m/z 800
was monitored.
Cell experiments were carried out with a cervical epithelium
cancer cell line originally derived from Henrietta Lacks (HeLa).
Cells were cultured in the growth medium consisted of the fol-
lowing (final concentrations): Dulbecco's Modified Eagle Medium
(DMEM), 10% fetal bovine serum (FBS) and 1% penicillin/strep-
tomycin.[25] Quantification of cell viability in the dark and after
PDT was determined by MTT assays. 3 × 104 HeLa cells/well were
seeded into two 96-well plates and incubated in the cell culture
growth media for 24 hours. The Pc 4, Pc 227 and Au NP-Pc 227
conjugates in aqueous solution with the specified concentra-
tions were added into the plates and incubated for another 24
hours. The following day, the cells were replaced with fresh growth
media. One plate was kept in dark and the other was exposed
to light (>600 nm) at 1 J cm−2 with the irradiation period of 12
min. The plates were returned for 24 hours in the incubator (37
°C, 5% CO2). 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazo-
lium bromide (MTT) reagent was then added into each well. After
4 hours incubation, the purple formazan crystals were formed
by metabolic active cells. 100 µL of the solubilization solution
(10% sodium dodecyl sulfate in 0.01 M HCl) per well was added
to dissolve the cells and placed into the incubator overnight. The
absorbance at 550 nm (the formazan salt) and 690 nm as the ref-
erence wavelength was measured by a microplate reader. 8 repli-
[2] A. S. Hoffman, J. Controlled Release 2008, 132, 153–16.
[3] S. Mizukami, M. Hosoda, T. Satake, S. Okada, Y. Hori, T. Furuta,
K. Kikuchi, J. Am. Chem. Soc. 2010, 132, 9524–9525.
[4] G. C. R. Ellis-Davies, Nature Methods 2007, 4, 619–628.
[5] Y. V. Il’ichev, M. A. Schwörer, J. Wirz, J. Am. Chem. Soc. 2004, 126,
4581–4595.
[6] I. Aujard, C. Benbrahim, M. Gouget, O. Ruel, J.-B. Baudin,
P. Neveu, L. Jullien, Chem. Eur. J. 2006, 12, 6865–6879.
[7] J. L. Vivero-Escoto, I. I. Slowing, C.-W. Wu, V. S.-Y. Lin, J. Am. Chem.
Soc. 2009, 131, 3462–3463.
[8] G. Han, C.-C. You, B.-J. Kim, R. S. Turingan, N. S. Forbes,
C. T. Martin, V. M. Rotello, Angew. Chem. Int. Ed. 2006, 45,
3165–3169.
[9] S. S. Agasti, A. Chompoosor, C.-C. You, P. Ghosh, C. K. Kim,
V. M . R o t e l l o , J. Am. Chem. Soc. 2009, 131, 5728–5729.
[10] L. Paasonen, T. Laaksonen, C. Johans, M. Yliperttula, K. Kontturi,
A. Urtti, J. Controlled Release 2007, 122, 86–93.
[11] K. Szacilowski, W. Macyk, A. Drzewiecka-Matuszek, M. Brindell,
G. Stochel, Chem. Rev. 2005,105, 2647–2694.
[12] S. Stolik, J. A. Delgado, A. Perez, L. Anasagasti, J. Photochem.
Photobiol. B-Biol. 2000, 57, 90–93.
[13] W. Wu, J. Shen, P. Banerjee, S. Zhou, Biomaterials 2011, 32,
598–609.
[14] J. You, G. Zhang, C. Li, ACS Nano 2010, 4, 1033–1041.
[15] N. L. Oleinick, A. R. Antunez, M. E. Clay, B. D. Rihter, M. E. Kenney,
Photochem. Photobiol. 1993, 57, 242–247.
[16] J. D. Miller, E. D. Baron, H. Scull, A. Hsia, J. C. Berlin, T. McConnick,
V. Colussi, M. E. Kenney, K. D. Cooper, N. L. Oleinick, Toxicol. Appl.
Pharmacol. 2007, 224, 290–299.
[17] Y. Cheng, A. C. Samia, J. Li, M. E. Kenney, A. Resnick, C. Burda.
Langmuir 2010, 26, 2248–2255.
[18] Y. Cheng, A. C. Samia, J. D. Meyers, I. Panagopoulos, B. W. Fei,
C . B u r d a , J. Am. Chem. Soc. 2008, 130, 10643–10647.
[19] J. Li, Ph.D. Thesis, Case Western Reserve University Cleveland,
OH, 2008.
[20] J.-Y. Zheng, K. Konishi, T. Aida, J. Am. Chem. Soc. 1998, 120,
9838–9843.
cates were used for each condition. All experiments were repeated [21] S. Ishida, K. Yoshimura, H. Matsumoto, S. Kyushin, Chem. Lett.
2009, 38, 362–363.
3 times.
[22] Y. N. Konan, R. Gurny, E. Allemann, J. Photochem. Photobiol.
B-Biol. 2002, 66, 89–106.
[23] A. G. Ziady, A. Sokolow, S. Shank, D. Corey, R. Myers, S. Plafker,
T. J. Kelley. Am. J. Physiol. Lung Cell Mol. Physiol. 2012. 302,
L1221–1231.
Acknowledgements
[24] A. G. Ziady, M. Kinter, Methods Mol. Biol. 2009, 544, 325–341.
[25] A. G. Ziady, J. Kim, J. Colla, P. B. Davis. Gene Ther. 2004, 11,
1378–1390.
This work was supported by Case Western Reserve University and
National Institute of Biomedical Imaging and Bioengineering
5R01EB012099. We thank Prof. M. Kenney for the donation of the
precursor molecule Pc 227 and for helpful discussions.
Received: October 23, 2013
Revised: December 3, 2013
Published online:
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