C O M M U N I C A T I O N S
Figure 1. (a) HPLC analysis was used to monitor the drug release process
from chlorambucil-grafted CD-MSN material under 420 nm light irradiation
(10 mW/cm2). Inset is the partial progress for the release of chlorambucil
from CD-MSN material under bright and dark conditions. “ON” indicates
the beginning of light irradiation; “OFF” indicates the ending of light
irradiation. (b) As time elapsed, HPLC determined the profiles of released
chlorambucil under two-photon NIR excitation at 800 nm.
pH (SI, Table S4). The high remaining rate (94.5%) in culture media
suggested that this DDS was quite stable and suitable for the
following biological study in Vitro. The time courses of the drug
release under photolysis at both 420 nm visible light (a xenon lamp)
(Figure 1a) and two-photon 800 nm NIR light (Figure 1b) were
monitored by HPLC. Both photolytic processes progressed ef-
fectively; the release controlled by two-photon NIR irradiation
reached 40% after 2 h with a ∼1 mm diameter beam spot (SI, Figure
S9). The maximum release in Figure 1a had reached 97% after 3 h
of irradiation (10 mW/cm2), and the enhancement of the light
intensity by using visible light (λ > 400 nm, 120 mW/cm2) could
complete the release process within 15 min, suggesting that external
light intensity could regulate the drug release. In addition, there
were no detectable side products in the photolysis for the CD-MSN
based DDS. This was an outstanding result compared to the small
molecular prodrug system11 and MSN-based systems with pore-
blocking caged caps,1c,6 because the generation of side products
might have a potential negative effect for the therapy. Precise
control of the photolytic release was demonstrated by monitoring
the progress of chlorambucil release after periods of exposure to
light and dark conditions, as shown in the inset of Figure 1a. The
distinctive “stepped” profile revealed that the drug release only
proceeded under light conditions, thus realizing “light-regulated
precise release”. All the results indicated that the CD-MSN based
DDS could precisely control drug release by manipulating external
light intensity, irradiation wavelength, and time. These results hint
that it is possible to precisely release anticancer drugs containing
-COOH, -NH2, -OH, -SH groups et al.10 both in Vitro and in
ViVo.
Surface-functionalized MSNs can be efficiently endocytosed by
mammalian cells.9b,12 For the CD-MSN materials, the effective
endocytosis was confirmed by both confocal images (Figure 2a-c)
and two-photon laser scanning microscopy (SI, Figure S10). ICP-
OES determined that the internalized silicon concentration was
3-13 pg/cell after the cells were cultured with 20 µg/mL MSN
materials for 6 h (SI, Table S5). Cell viability was quantified by
an MTT assay using both HeLa (Figure 2d) and MCF-7 cells (SI,
Figure S11). An IC50 value of 20 µg/mL (chlorambucil payload 2
µM) was observed upon irradiation of CD-MSN, which was much
lower than that for CD-MSN treated with light first and then
incubated with cells in the dark (IC50 > 160 µg/mL). And as shown
in Figure 2e, there was no significant cell death observed when the
cells were treated with light in the case of AP-MSN and C-MSN,
respectively. The cytotoxicity was likely caused by the released
drug, chlorambucil, upon irradiation. Upon comparison with the
same amount of chlorambucil as shown in Figure 2d, the CD-MSN
upon irradiation showed a higher cytotoxicity to cancer cells, which
Figure 2. Confocal fluorescence and brightfield images of HeLa cells
incubated with 20 µg/mL CD-MSN for 3 h: (a) brightfield; (b) fluorescence
(λex ) 405 nm); (c) the overlay image of a and b. (d) Cytotoxicity to HeLa
cells is plotted against the concentrations of chlorambucil and CD-MSN
under control conditions and 15 min light exposure. (e) Effect of different
conditions on the viability of HeLa cells: the concentration of MSN materials
is 20 µg/mL and the corresponding concentration of free chlorambucil is 2
µM, and the light exposure time is 15 min. (f) Cell viability with different
durations of light exposure: the concentration of CD-MSN used is 5 µg/
mL. Visible light (λ > 400 nm) intensity used in cell cytotoxicity tests was
120 mW/cm2.
could be explained by the effective cell endocytosis of CD-MSN
resulting in a higher accumulation of chlorambucil inside the cells.13
Here, CD-MSN serves as both a drug carrier and a photocage for
the release of the anticancer drug. Furthermore, to validate our
ability to externally regulate drug release, the HeLa cells incubated
with CD-MSN were exposed to visible light for 0, 3, 10, and 15
min. These results show that the drug release can be regulated by
the duration of the applied light (Figure 2f).
In summary, we have successfully prepared an excellent MSN-
based DDS for regulated release under the irradiation of two-photon
NIR excitation. In this system, CD-MSN serves as both a carrier
and photocage for the drug whose release can be regulated precisely
by controlling the irradiation wavelength, intensity, and time of
the external light. We envision that good biocompatibility, cellar
uptake property, and efficient photoregulated drug release will be
of great benefit to future controlled release for in ViVo biomedical
applications.
Acknowledgment. We thank Shanghai Sci. Tech. Comm.
(08pj1403100), Innovation Program of Shanghai Municipal Educa-
tionCommission(092259),NSFC(20903039),andMOE(wk0913002)
for financial support. We also thank Dr. B. Li for two-photon
photolysis study and helpful discussions.
Supporting Information Available: Preparation, photolysis mech-
anism, cellular studies, and other experimental details. This material is
9
10646 J. AM. CHEM. SOC. VOL. 132, NO. 31, 2010