Light-responsive micelles of spiropyran initiated hyperbranched polyglycerol for smart drug delivery

Article abstract of DOI:10.1021/bm401670t

Light-responsive polymeric micelles have emerged as site-specific and time-controlled systems for advanced drug delivery. Spiropyran (SP), a wellknown photochromic molecule, was used to initiate the ring-opening multibranching polymerization of glycidol to afford a series of hyperbranched polyglycerols (SP-hb-PG). The micelle assembly and disassembly were induced by an external light source owing to the reversible photoisomerization of hydrophobic SP to hydrophilic merocyanine (MC). Transmission electron microscopy, atomic force microscopy, UV/vis spectroscopy, and dynamic light scattering demonstrated the successful assembly and disassembly of SP-hb-PG micelles. In addition, the critical micelle concentration (CMC) was determined through the fluorescence analysis of pyrene to confirm the amphiphilicity of respective SP-hb-PG _n(n = 15, 29, and 36) micelles, with CMC values ranging from 13 to 20 mg/L, which is correlated to the length of the polar polyglycerol backbone. Moreover, the superior biocompatibility of the prepared SP-hb-PG was evaluated using WI-38 cells and HeLa cells, suggesting the prospective applicability of the micelles in smart drug delivery systems.

Full text of DOI:10.1021/bm401670t

Article
pubs.acs.org/Biomac
Light-Responsive Micelles of Spiropyran Initiated Hyperbranched
Polyglycerol for Smart Drug Delivery
Suhyun Son, Eeseul Shin, and Byeong-Su Kim*
Department of Chemistry and Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology
(
UNIST), Ulsan 689-798, Korea
*
S Supporting Information
ABSTRACT: Light-responsive polymeric micelles have emerged as site-specific
and time-controlled systems for advanced drug delivery. Spiropyran (SP), a well-
known photochromic molecule, was used to initiate the ring-opening
multibranching polymerization of glycidol to afford a series of hyperbranched
polyglycerols (SP-hb-PG). The micelle assembly and disassembly were induced
by an external light source owing to the reversible photoisomerization of
hydrophobic SP to hydrophilic merocyanine (MC). Transmission electron
microscopy, atomic force microscopy, UV/vis spectroscopy, and dynamic light
scattering demonstrated the successful assembly and disassembly of SP-hb-PG
micelles. In addition, the critical micelle concentration (CMC) was determined
through the fluorescence analysis of pyrene to confirm the amphiphilicity of
respective SP-hb-PG (n = 15, 29, and 36) micelles, with CMC values ranging
n
from 13 to 20 mg/L, which is correlated to the length of the polar polyglycerol
backbone. Moreover, the superior biocompatibility of the prepared SP-hb-PG
was evaluated using WI-38 cells and HeLa cells, suggesting the prospective applicability of the micelles in smart drug delivery
systems.
INTRODUCTION
active therapeutic release and high controllability over the drug
release profile using a specific wavelength of light. Along the
same line, various light-responsive smart delivery systems have
been reported to date that operate on the principle of
photoisomerization, photoinduced cleavage of the photo-
chromic moiety or junction, and reversible photo-cross-
■
Over the past few decades, drug delivery systems have advanced
to achieve time-controlled and site-specific delivery of
therapeutic agents to enhance the efficacy of drugs while
1
,2
minimizing undesirable side effects. Self-assembled nano-
structures have long been exploited as potential drug delivery
carriers, including liposome, dendrimer, micelle, and artificial
12−15
linking.
3
,4
As an alternative to traditional poly(ethylene glycol) (PEG),
which is the most biocompatible synthetic polymer, its
polyether analogue, hyperbranched polyglycerol (hb-PG), is
actively investigated, owing to its excellent biocompatibility and
advantages over PEG, such as the ease of synthesis, controllable
structure, multi (or hetero)-functional groups, and oxidation
DNA. In particular, self-assembled polymeric micelles have
been highlighted as promising vehicles based on their
distinctive features, such as high loading capacity, and enhanced
solubility and circulation lifetime of active therapeutics, as well
as prioritized accumulation at tumor sites owing to the
5
−7
enhanced permeability and retention (EPR) effect.
More
16−19
stability.
The recent synthetic advancement by the Frey
importantly, the high tunability of their chemical and physical
properties based on the choice of monomer, polymerization
degree, architecture, and other parameters, makes self-
assembled polymeric micelles among the top choices as
group has allowed the development of well-defined and
complex architectures of polyglycerols with relatively low
1
7,20
polydispersity.
These polyglycerols also exhibit flexibility of
8
the physicochemical properties by the protected monomer,
variation of initiators, and combination with other polymer-
prospective carriers.
Despite the advantages of self-assembled polymeric micelles,
the sophisticated delivery of active therapeutics in a time-
specific and stimuli-specific manner continues to be a
challenging endeavor. To meet this objective, smart drug
delivery carriers that encapsulate drugs and release them at a
targeted region in response to external stimuli such as pH, light,
redox, temperature, and biological stimuli have been actively
21−23
ization techniques.
Recently, polyglycerols with varying
architectures have been designed and synthesized for
biomedical applications. Brooks and co-workers have studied
the suitability of hydrophobically functionalized hyperbranched
polyglycerols for use as synthetic albumin substitutes and
9
−11
studied.
For example, Zhao and co-workers have
Received: November 11, 2013
Revised: January 15, 2014
Published: January 16, 2014
extensively investigated the development of light-responsive
micelle systems owing to the feasibility of remote triggering of
©
2014 American Chemical Society
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Scheme 1. Illustration of Light-Responsive Micelle Assembly and Disassembly of Spiropyran-Hyperbranched-Polyglycerol (SP-
a
hb-PG)
a
Micelle structure is not drawn to scale.
2
4
general drug delivery vehicles. In addition, our group has
ToF) measurements were carried out on an Ultraflex III MALDI mass
spectrometer. The laser system consisted of a pulsed UV laser, an
attenuator that allowed the fine adjustment of the laser fluence, a lens
system to focus the laser beam, and a mirror system to direct the beam
recently employed various architectures of the hb-PG in pH-
responsive smart drug delivery systems.
no report in which the hb-PG is utilized in light-responsive drug
delivery systems.
2
5,26
However, there is
into the ion source on the target plate. The standard was a N laser
2
with 337 nm wavelength (pulse energy of 150 μJ) and 3 ns pulse width
for use with matrix components absorbing light of this wavelength
In this article, we present the design of photoresponsive
micelles using spiropyran (SP) initiated hyperbranched
polyglycerols (SP-hb-PG) and investigation of their potential
in light-controlled release of model therapeutics (Scheme 1).
Among the class of synthetic photoresponsive molecules, SP, a
well-known photochromic molecule, was employed owing to its
unique tunability, stability, and fast response time. Specifi-
cally, SP can undergo a reversible transformation from colorless
to pink-colored merocyanine (MC) upon UV irradiation with a
marked increase in the polarity associated with the structural
conversion from neutral to charge-separated zwitterions. This
solubility switching of SP from hydrophobic to hydrophilic can
induce the destabilization of polymeric micelles of SP-hb-PG
into individual chains (Scheme 1). Moreover, this destabiliza-
tion induces controlled release of model hydrophobic
therapeutics by UV irradiation.
(IVB product). α-Cyano-4-hydroxycinnamic acid (CHCA) was used
as a matrix. A 10 g/L solution of the polymer in methanol and a 10 g/
L solution of the matrix solution were prepared separately. The two
solutions were then mixed and a 1 μL aliquot of the mixture was
applied to a target plate, and the solvent was evaporated. The
morphology of the SP-hb-PG micelle was investigated using
transmission electron microscopy (TEM, JEM-2100, JEOL, Japan)
and atomic force microscopy (AFM, Dimension 3100, Veeco, U.S.A.).
Size distribution analysis of the SP-hb-PG micelles was performed
using dynamic light scattering (DLS, BI-APD, Brookhaven Instrument,
New York, U.S.A.). UV/vis spectrophotometer (UV-2550, Shimadzu)
was used to measure absorbance of SP-hb-PG. UV irradiation was
conducted using a UV lamp (B-100AP high-intensity UV lamp, 100
W).
27
28
Synthesis of a Spiropyran Derivative. 2-(3′,3′-Dimethyl-6-
nitro-3′H-spiro[chromene-2,2′-indol]-l′-yl)-ethanol (spiropyran) was
29
prepared according to the method reported in the literature.
EXPERIMENTAL SECTION
Materials. All reagents and solvents were purchased from Sigma
Aldrich and Acros unless otherwise stated. Dry solvents purchased
from Sigma-Aldrich were stored over molecular sieves. Deuterated
Polymerization of SP-hb-PG. SP (1 mmol) and cesium
hydroxide monohydrate (0.8 mmol, 0.8 equiv) were placed in a
Schlenk flask, benzene (20 wt %) was added, and the mixture was
stirred for 2 h at 60 °C under a nitrogen atmosphere to produce
cesium alkoxide. The initiator was dried in a vacuum oven for 2 h at 90
■
DMSO-d was purchased from Cambridge Isotope Laboratory, dried,
6
°
C. After the initiator became powdery, dry diglyme (ca. 20 wt %) was
and stored over molecular sieves.
1
added under a nitrogen atmosphere. Glycidol (30 mmol) diluted with
dry diglyme (20 wt %) was then added over 12 h at 90 °C using a
syringe pump. The reaction was terminated by addition of excess
methanol and acidic cation exchange resin. After dissolving the
polymer in methanol, the homogeneous polymer solution was
precipitated and filtered into excess cold diethyl ether. The resulting
material was dried under vacuum at 60 °C for 2 days.
Preparation of SP-hb-PG Micelle. A 1.0 mg sample of SP-hb-PG
was dissolved in 1 mL of DMF, after which 4 mL of water was added
dropwise over 1 h via a syringe pump to form micelles. Subsequently,
Measurements. H NMR spectra were acquired using a 400-MR
DD2 spectrometer operating at 400 MHz, using DMSO-d6 as a
solvent. Gel permeation chromatography (GPC) was performed on a
Tosoh HLC-8120 GPC equipped with a consecutive polystyrene gel
column (TSK-GEL GMHHR-M and GMHHR-N) at 40 °C, using N-
methylpyrrolidone containing 0.01 mol/L lithium bromide as an
eluent at a flow rate of 1.0 mL/min; standard polystyrene samples
were used for calibration in order to measure the number- and weight-
averaged molecular weight (Mn and M ). Matrix-assisted laser
desorption and ionization time-of-flight mass spectrometry (MALDI-
w
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Scheme 2. Synthetic Approach for Preparation of (a) Spiropyran Derivative Containing Hydroxyl Group and (b) SP-hb-PG
Polymers
29
the polymer solution was dialyzed against DI water for 2 days to
(Figure 2a). The prepared SP exhibited a clear color
transition from colorless to pink upon excitation with UV
light at 365 nm, displaying the desired UV-responsive character.
The amphiphilic polymer SP-hb-PG was synthesized via anionic
ring-opening polymerization using the SP initiator generated by
treatment with cesium alkoxide, followed by the slow addition
of a glycidol monomer (Scheme 2b). Three different
hyperbranched SP-hb-PG polymers varying in terms of the
molecular weight of the hb-PG segment, which ranged from
1500 to 3000, were successfully prepared (Table 1). Initially,
exchange the residual DMF. The solution was then filtered through a
0
.22 μm syringe filter before DLS, TEM, and AFM analysis.
Pyrene Fluorescence Measurement and CMC Study. A total
of 1.0 mg SP-hb-PG polymer was dissolved in 1.0 mL of DMF. A 10
μL solution of pyrene (5.2 mg/L in DMF) was added to the SP-hb-PG
solution and the mixture was stirred for 30 min at room temperature.
A total of 5 mL of DI water was then added to the solution at a rate of
0.5 mL/min using a syringe pump. The fluorescence of each pyrene-
containing polymer micelle solution (with different concentrations)
was measured at an emission wavelength of 372 nm using a
fluorometer. The critical micelle concentration (CMC) values were
determined by calculating the ratio of the fluorescence intensities at
wavelengths of 339.06 and 332.04 nm.
Cytotoxicity Assay. Human epithelial carcinoma cells (HeLa) and
human diploid cells (WI-38) were purchased from the Korean Cell
Line Bank (Seoul, Korea). Cytotoxicity assay was performed using the
Table 1. Characterization of Spiropyran Initiated
Hyperbranched Polyglycerol
M (g/mol)
n
CMC
(mg/L)
traditional MTT assay. Cells were seeded in 96-well plates at a density
a
b
b
c
no. composition calcd NMR
GPC
M /Mn
DB
4
w
of 1 × 10 cells per well and incubated for 24 h in 5% CO at 37 °C.
2
1
2
3
SP-hb-PG15
1500
2500
2210
1690
3100
3870
1.77
1.79
0.53
0.54
0.53
13
19
20
HeLa cells were cultured with Dulbecco’s Modified Eagle’s Medium,
(
1
DMEM, Life Technologies) with 10% fetal bovine serum (FBS) and
% penicillin-streptomycin. WI-38 cells were incubated in Roswell
Park Memorial Institute (RPMI) 1640 media (Life Technologies) with
0% FBS, 25 mM sodium bicarbonate, and 1% penicillin-streptomycin.
SP-hb-PG29
2600
2930
SP-hb-PG36
3000
1.92
a
1
b
M determined via H NMR spectroscopy. M and M measured
n
n
w
1
c
using GPC-RI in NMP with polystyrene standard. Degree of
branching (DB) is determined from inverse gated C NMR
After removing the culture medium, the wells were washed with PBS.
Each well was then refilled with 90 μL of fresh Dulbecco’s Modified
13
spectroscopy and calculated according to Frey’s equation (DB =
Eagle’s Medium (DMEM) and 10 μL of SP-hb-PG polymeric micelle
n
2
D/2D + L; see Supporting Information for details).
solution. After an additional 24 h of incubation, thiazolyl blue
tetrazolium bromide (MTT, Sigma-Aldrich) was added to each well of
the cells (final conc. 0.5 mg/mL) and incubation was performed for 4
h. A solution of 100 μL of DMSO was replaced with SP-hb-PG
solution to solubilize the MTT-formazan product, and the sample was
incubated for a further 15 min at room temperature. The absorbance
of the solution was read at a wavelength of 540 nm.
the molecular weight was determined from 1H NMR by
integrating the signals of the aromatic groups of the SP initiator
at 8.3 ppm and those of the polyether backbone of hb-PGs in
the range of 3.3 to 4.0 ppm (see Supporting Information,
Figure S1). These values were consistent with the theoretical
target molecular weights, as shown in Table 1. In addition, the
M and the polydispersity index (M /M ) of the prepared SP-
RESULTS AND DISCUSSION
■
n
w
n
Synthesis and Characterization of Spiropyran Ini-
tiated Hyperbranched Polyglycerol. SP was initially
prepared according to a method described in the literature
hb-PG samples were determined via GPC-RI, which showed a
n
relatively monomodal molecular weight distribution with
reasonable PDI values for all hyperbranched polymers. Notably,
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the discrepancy between the M values from GPC and NMR
irradiation with UV light (365 nm) for 30 min, a new
absorption band appeared at 550 nm, corresponding to the
absorption of MC, which reflects the isomerization of SP to
generate the MC form (see Supporting Information, Figure
S3). The solution color also changed from colorless to light
pink upon UV irradiation. In contrast, the new peak
disappeared under illumination with visible light (620 nm),
which suggests the isomerization of MC to the SP form in the
SP-hb-PG polymer. Interestingly, we found that this reversible
isomerization could be repeated several times without any
changes in the spectrum of SP-hb-PG (see Supporting
Information, Figure S3).
As a result of structural isomerization of neutral SP to
zwitterionic MC, the amphiphilic SP-hb-PG is converted to the
all-hydrophilic MC-hb-PG, which eventually drives the
disassembly of the polymeric micelles, as illustrated in Scheme
1. This reversible micelle assembly and disassembly was
monitored by using dynamic light scattering (DLS; Figure 3).
The average diameter of the SP-hb-PG micelles measured by
DLS was 33.2 ± 11.8 nm, which is similar to that determined
from TEM and AFM measurement (Figure 2). Interestingly,
the average diameter of the SP-hb-PG polymer decreased
significantly to about 0.1 nm upon irradiation with UV light at
n
became slightly higher as the molecular weight of the polymer
increased, which could be attributed to the use of a linear
polystyrene standard in measuring the molecular weight of the
hb-PG.
Moreover, the hyperbranched nature of the SP-hb-PG was
further confirmed by measuring the degree of branching (DB)
13
via C NMR and calculation using Frey’s equation (DB = 2D/
L13 + L14 + 2D; L13:1,3 linear portion, L14:1,4 linear portion,
and D: dendritic portion; see Supporting Information, Figure
S2). This equation indicates the ratio of the branched dendritic
segment within the PG backbones that are composed of both
linear and branched segments. The DBs of all polymers were
determined to be about 0.53, which is in good agreement with
17
that of other hyperbranched systems.
The presence of each segment of SP and polyglycerol was
also identified from the MALDI-ToF spectrum (Figure 1). As
3
65 nm for 30 min, suggesting complete disassembly of the
micelles into individual polymeric chains. This solution was
again treated with visible light at 620 nm, at which point the
average diameter returned to about 30 nm, similar to that of the
initial micelles. The reversible nature of the micelle systems was
confirmed from repeated DLS measurements. Light responsive
deconstruction of micelle structures is important because after
the delivery of a drug to a site using the micelles of SP-hb-PG,
the structures can potentially disassemble into all-hydrophilic
polymers of MC-hb-PG, which can be readily cleared and
biodegraded.
Furthermore, we evaluated the potential of the SP-hb-PG
polymer micelles in carrying a model hydrophobic therapeutic,
pyrene. First, to estimate the amphiphilicity of SP-hb-PG, the
critical micelle concentrations (CMCs) of all SP-hb-PG
polymers were determined via an established CMC measure-
Figure 1. MALDI-ToF spectrum of SP-hb-PG15 (Entry 1 of Table 1),
confirming each segment of SP-hb-PG.
shown in Figure 1, the main molecular weight distribution at
3
0,31
1
077.72 corresponds to the molecular weight of SP-hb-PG with
ment method using pyrene.
A higher concentration of
cesium as a counterion (SP(352) + PG(74.09) × 8 +
polymer solution induced greater encapsulation of pyrene,
which resulted in a red-shift of the excitation band at 334 nm
and an increase in the intensity of the excitation band (see
Supporting Information, Figure S4). To measure the shift of
the excitation band, the ratio of the fluorescence intensity at
339 and 332 nm (I339/I332) was plotted as a function of the
concentration of SP-hb-PG, in which a clear crossover point
was observed in the low concentration range of 10 to 20 mg/L,
corresponding to the CMC value. As summarized in Table 1,
the CMC values of all of the polymers show that increasing the
mass of the hydrophilic segment of SP-hb-PG from 1500 to
3000 effectively increased the CMC values from 13 to 20 mg/L
(Table 1). This observation can be attributed to the decreased
hydrophobicity that efficiently reduced the segregation of the
polymer blocks to accommodate the model hydrophobic
therapeutics. This result is also consistent with our previous
report. Because a longer glycerol segment reduces the
amphiphilicity of the SP-hb-PG polymer, it is reasonable that
the micelle formation of the amphiphilic polymer is generated
at a higher concentration.
Independent of the DLS measurement, the reversible nature
of the micelle assembly and disassembly with pyrene can be
characterized. As shown in Figure 4, the intensity of the
+
Cs (133)) and the other molecular weight subdistribution at
1
093.90 corresponds to the molecular weight of SP-hb-PG with
+
+
H as a counterion (SP(352) + PG(74.09) × 10 + H (1)). In
addition, the spacing between the main- and the subdistribution
matches well with the molecular weight of the glycidol
monomer, 74.09 g/mol, which indicates the successful
polymerization of SP-hb-PG.
Micelle Formulation and Reversible Micelle System.
As explained in the Experimental Section, the micelles were
prepared from the amphiphilic SP-hb-PG29 polymers by initial
dissolution in DMF followed by the slow addition of excess
amounts of DI water with subsequent dialysis. After preparation
of the micelles, their morphology was investigated using
transmission electron microscopy (TEM) and atomic force
microscopy (AFM; Figure 2). Based on the TEM and AFM
images, the micelles possessed a spherical structure with a
relatively narrow size distribution. The diameter of the micelles
based on each measurement was similar, with values of 31.3 ±
26
8
.1 nm (TEM) and 38.2 ± 9.4 nm (AFM), respectively.
The UV-responsive nature of the SP-hb-PG polymers was
evaluated by means of UV/vis spectroscopy, where isomer-
ization of the SP segment was induced by irradiation. Under
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Figure 2. (a) TEM and (b) height-mode AFM images of SP-hb-PG29 micelles. (c, d) Corresponding size distributions determined by TEM and AFM
showing an average diameter of 31.3 and 38.2 nm, respectively. Inset in (a) shows spherical morphology of micelles.
intensity is only about 40% of the initial intensity. This result
implies that some portion of the released pyrene is not
completely reloaded into the SP-hb-PG micelle core (Figure
4
a). It should be noted that 254 nm UV irradiation was
employed in this case because of the enhanced release kinetics
of pyrene from the micelle core compared to 365 nm
irradiation (see Supporting Information, Figure S5). On the
other hand, it should be also considered that the irradiation at
2
54 nm may induce the cell toxicity during the micelle
disassembly (about 88.2% cell viability for HeLa cells after 30
min irradiation). We found that the cell viability varied
depending on the wavelength and duration of the UV
irradiation as similarly observed in other report (see Supporting
3
2
Information, Figure S6). Therefore, the current UV
irradiation approach needs a better control to enhance the
kinetics of demicellization while minimizing the cell toxicity
induced by the irradiation, which will be the subject of our
ongoing research.
Figure 3. Size distribution of polymeric micelle (under irradiation with
20 nm visible light, purple column) and polymer chain (under 365
6
Finally, we evaluated the cytotoxicity of SP-hb-PGs to
investigate their potential as a drug delivery carrier. The in vitro
cytotoxicity of SP-hb-PGs was assessed by MTT assay using
WI-38 cells and HeLa cells as respective models of normal and
cancer cells (Figure 5). As a representative example, the
viability of both cells after treating the SP-hb-PG36 micelle
solution with varying concentrations was nearly 100%, even at a
high concentration of 1000 μg/mL. These results indicate that
the SP-hb-PGs are highly biocompatible and nontoxic to both
cell lines. We cannot exclude the fact that the uptake efficiency
of the SP-hb-PG micelles is relatively low; however, our
previous report of doxorubicin-conjugated polyglycerol micelles
are readily internalized into the HeLa cells as proved by the
nm UV light, blue column) of SP-hb-PG29 determined by DLS. Inset
graph shows the diameter of SP-hb-PG29 polymeric micelles and
polymeric chain under repetitive irradiation cycles using UV and
visible light.
fluorescence excitation band decreases depending on the UV
irradiation time; this change is saturated after about 20 min
with a slight blue-shift, indicating the release of pyrene from the
micelle core. Interestingly, the plot of I339/I332 with respect to
the UV irradiation time shows a trend similar to the CMC
experiment, which suggests degradation of the micelles.
Moreover, the intensity of the fluorescence excitation spectra
increases upon visible light irradiation. This observation is
attributed to the re-encapsulation of released pyrene back into
the micelle core, leading to the enhanced fluorescence band of
the incorporated pyrene. However, this increase of the
excitation intensity is terminated at 120 min and the recovered
25
confocal fluorescence microscopy. In other studies, a good
cellular uptake of rhodamine-labeled hyperbranched PGs
33,34
toward various types of cancer cell lines was demonstrated.
Taken together these evidences in the literature, we postulate
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Figure 4. (a) Illustration of pyrene release upon 254 nm UV irradiation and re-encapsulation upon 620 nm visible irradiation of SP-hb-PG micelles.
b) Changes in excitation spectrum of pyrene encapsulated by SP-hb-PG29 micelle under 254 nm UV irradiation and (c) 620 nm visible irradiation.
Inset shows the plot of I339/I332 vs the exposure time to UV and visible light, respectively.
(
In addition, comparison of the toxicity of SP-hb-PGs toward
normal WI-38 cells shows that an increase of the glycerol
fraction is accompanied by slightly lowered cytotoxicity (Figure
5
b). It is reasonable that SP-hb-PG of higher molecular weight
exhibits greater biocompatibility due to the presence of a large
fraction of highly biocompatible PG.
CONCLUSION
■
A novel light-responsive micelle system was developed using
SP-hb-PG. Because of its considerable amphiphilicity, SP-hb-PG
formed self-assembled polymeric micelles in aqueous medium.
However, upon exposure to UV irradiation, the initially
hydrophobic SP isomerized to zwitterionic MC, leading to
the disassembly of the micelle structures. This structural change
of the micelles was reversible upon exposure to visible light
irradiation. The potential of the SP-hb-PG micelle for use as a
smart drug delivery system was investigated using pyrene as a
model hydrophobic therapeutic. The study suggested successful
loading and release of pyrene upon external UV irradiation. In
addition, the in vitro cytotoxicity of the SP-hb-PG polymers was
evaluated using WI-38 and HeLa cells, demonstrating the
excellent biocompatibility and nontoxicity of the SP-hb-PG
micelles. We anticipate that this light-responsive smart drug
delivery system will provide a new means to sophisticated
delivery of active therapeutics in a time-specific and stimuli-
specific manner.
ASSOCIATED CONTENT
■
*
S
Supporting Information
1
13
Additional H and C NMR spectra, UV/vis spectra, excitation
spectra, and MTT assay. This material is available free of charge
via the Internet at http://pubs.acs.org.
Figure 5. (a) Plot of cell viability of SP-hb-PG36 micelles determined
by MTT assay; (b) WI-38 (normal cell) viability of all SP-hb-PGn
polymers.
AUTHOR INFORMATION
Corresponding Author
*E-mail: bskim19@unist.ac.kr.
that the similarly structured SP-hb-PG would undergo a similar
process to be internalized into the HeLa cells without
exhibiting significant cytotoxicity.
■
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Notes
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ACKNOWLEDGMENTS
1
(
3
(
■
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korean government (No.
2
010-0028684).
(
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dx.doi.org/10.1021/bm401670t | Biomacromolecules 2014, 15, 628−634