Dual-Emissive Platinum(II) Metallacage with a Sensitive Oxygen Response for Imaging of Hypoxia and Imaging-Guided Chemotherapy

Article abstract of DOI:10.1002/anie.202009442

Imaging of hypoxia in vivo helps with accurate cancer diagnosis and evaluation of therapeutic outcomes. A Pt^II metallacage with oxygen-responsive red phosphorescence and steady fluorescence for in vivo hypoxia imaging and chemotherapy is reported. The therapeutic agent and diagnostic probe were integrated into the metallacage through heteroligation-directed self-assembly. Nanoformulation by encapsulating the metallacage into nanoparticles greatly enhanced its stability the in physiological environment, rendering biomedical applications feasible. Apart from enhanced red phosphorescence upon hypoxia, the ratio between red and blue emissions, which only varies with intracellular oxygen level, provides a more precise standard for hypoxia imaging and detection. Moreover, in vivo explorations demonstrate the promising potential applications of the metallacage-loaded nanoparticles as theranostic agents for tumor hypoxia imaging and chemotherapy.

Full text of DOI:10.1002/anie.202009442

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Dual-Emissive Pt(II) Metallacage with Sensitive Oxygen
Response for Imaging of Hypoxia and Imaging-Guided
Chemotherapy
Authors: Huangtianzhi Zhu, Qi Li, Bingbing Shi, Fujing Ge, Yuezhou
Liu, Zhengwei Mao, Hong Zhu, Sheng Wang, Guocan Yu,
Feihe Huang, and Peter J. Stang
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RESEARCH ARTICLE
Dual-Emissive Pt(II) Metallacage with Sensitive Oxygen Response
for Imaging of Hypoxia and Imaging-Guided Chemotherapy
Huangtianzhi Zhu,[a,b] Qi Li,[a,b] Bingbing Shi,[b] Fujing Ge,[d] Yuezhou Liu,[a] Zhengwei Mao,[e] Hong
Zhu,[d] Sheng Wang,[c,*] Guocan Yu,[a,*] Feihe Huang[a,f,*] and Peter J. Stang[b,*]
[a]
H. Zhu, Q. Li, Y. Liu, Dr. G. Yu, Prof. Dr. F. Huang
State Key Laboratory of Chemical Engineering, Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang
University, Hangzhou 310027, P. R. China.
E-mail: fhuang@zju.edu.cn; guocanyu@zju.edu.cn
[b]
[c]
H. Zhu, Q. Li, Dr. B. Shi, Prof. Dr. P. J. Stang
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States.
E-mail: stang@chem.utah.edu
Prof. Dr. S. Wang
School of Life Sciences, Tianjin University and Tianjin Engineering Center of Micro-Nano Biomaterials and Detection-Treatment Technology, Tianjin
300072, P. R. China.
E-mail: shengwang@tju.edu.cn
[d]
[e]
F. Ge, Prof. Dr. H. Zhu
College of Pharmaceutical Science, Zhejiang University, Hangzhou 310058, P. R. China.
Prof. Dr. Z. Mao
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou
310027, P. R. China.
[f]
Prof. Dr. F. Huang
Green Catalysis Center and College of Chemistry, Zhengzhou University, Zhengzhou 450001, P. R. China.
Supporting information for this article is given via a link at the end of the document.
Abstract: Imaging of hypoxia in vivo helps with accurate cancer
diagnosis and evaluation of therapeutic outcomes. Here we report a
Pt(II) metallacage with oxygen-responsive red phosphorescence and
steady fluorescence for in vivo hypoxia imaging and chemotherapy.
Intriguingly, the therapeutic agent and diagnostic probe are
further applications in reversibly monitoring the intracellular O2
level. The second method employs phosphorescence probes
showing dynamic emission varying with O2 concentration.[5]
Nevertheless, most of the phosphorescent probes are based on
a mono-phosphorescent dye. The mono-emissive intensity is
easily altered by the concentration of the probe and other
biological conditions, with a relative lack of accuracy and
reliability.[6] Consequently, for the demands of cancer diagnosis
and potential treatments, it’s important to develop new hypoxia
probes with multiple emissions and phosphorescence
characteristics.
Supramolecular coordination complexes (SCCs), which rely
on the spontaneous self-assembly of metal acceptors and
Lewis-basic organic ligands, have seen attention in order to
mimic and study natural supramolecular assemblies.[7] In the
past few decades, achievements have been made in
coordination-driven self-assembly, from accurate assemblies of
various Pt(II) metallacycles and metallacages, to multiple
applications of these self-assemblies, typically in photophysics
including cell imaging, optoelectronics and sensing.[8] Therefore,
applying Pt(II) SCCs in hypoxia imaging is promising. Moreover,
due to the directional coordination and charges of SCCs, the
aggregation of ligands is prevented, which further promotes the
accuracy of imaging by avoiding possible emission shifts upon
aggregation of dyes.[9]
sophisticatedly
integrated
into
the
metallacage
through
by
heteroligation-directed
self-assembly.
Nanoformulation
encapsulating the metallacage into nanoparticles greatly enhance its
stability in physiological environment, making the biomedical
applications feasible. Apart from the enhanced red phosphorescence
upon hypoxia, the ratio between red and blue emissions, which only
varies with intracellular oxygen level, provides a more precise
standard for hypoxia imaging and detection. Moreover, in vivo
explorations demonstrate the promising potential applications of the
metallacage-loaded nanoparticles as theranostic agents for tumor
hypoxia imaging and chemotherapy.
Introduction
Intracellular oxygen (O2) is essential for aerobic respiration that
provides metabolic energy for living systems. Usually tissues
with fast proliferation and metabolism, such as solid tumors,
vascular diseases and brain abnormalities, can consume more
O2 that causes a hypoxia condition.[1,2] Therefore, detecting and
imaging hypoxia in living cells are not only important for accurate
cancer diagnosis but also very useful for the evaluation of
therapeutic effects.[3] Up to now, many methods have been
developed for sophisticated imaging methods of hypoxia, and
two main approaches are involved. The first approach focuses
on the detection of reductive enzymes including nitroreductase
and azoreductase resulting from an enhanced reductive stress
upon hypoxia by nitro- or azo-containing fluorophores.[4] Albeit
showing selective response and easy preparation, the emission
of the probe is irreversible due to bioreduction, which limits their
Herein, we report a Pt(II) metallacage (1) with dual-emissive
and phosphorescent properties and its application in hypoxia
imaging.
Pt(II)-meso-tetra(4-carboxyphenyl)porphine
was
chosen as a phosphorescent ligand. This compound emits
strong red phosphorescence with a long-lived triplet state in a
deaerated atmosphere and the intensity is highly depended on
O2 concentration, hence a candidate as a sensitive O2 probe.[10]
However, this complex suffers from π-π stacking that weakens
its emission,[11] and thus it’s useful to use the metallacage to
disperse it by taking advantage of the directional coordination
1
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10.1002/anie.202009442
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RESEARCH ARTICLE
self-assembly. To achieve
a
dual-emissive property, the
encapsulate the metallacage to prepare a nanoparticulate
formulation aiming to enhance the stability of the metallacage.
Benefiting from the nanotechnology, the circulation time and
tumor accumulation of the metallacage-loaded nanoparticles are
significantly improved, which facilitate the optimization of the
imaging and therapeutic performances. In vivo experiments
demonstrate that the materials act as brilliant theranostic agents
for tumor hypoxia imaging and chemotherapy, effectively
suppressing the tumor growth with negligible side effects
attributing to the enhanced permeability and retention effect. We
anticipate that the sophisticated theranostic metallacage
sensitive to tumor hypoxia can offer perspectives for enhanced
emission of the other ligand cannot be in the red region, and
Förster resonance energy transfer (FRET) should also be
avoided to sustain a steady fluorescence. Therefore, anthracene
was selected as a blue fluorophore.[12] The combination of two
ligands endows
1
with sensitive O2-responsive red
phosphorescence and steady blue fluorescence. The
metallacage was also applied in hypoxia imaging in vitro and in
vivo. Compared with traditional mono-emissive hypoxia probes,
the metallacage not only shows reversible and sensitive O2-
reponsive phosphorescence but also provides a more reliable
standard for hypoxia imaging and detection by calculating the
ratio between red and blue emissions. For biomedical
applications, an amphiphilic diblock copolymer is employed to
molecular
diagnostics
and
image-guided
therapeutic
applications.
Scheme 1. Chemical structures and cartoon representations of (a) the preparation of 1, (b) the formation of nanoparticles, and (c) the oxygen-responsive
emission.
ascribed to the loss of OTf– counterions (m/z = 1437.57 for [M –
5OTf]5+ and m/z = 1471.96 for [M – 4OTf + Na]5+). Three more
peaks were also isotopically resolved and the results were
consistent with their calculated distributions (Figure S5). All
Results and Discussion
these data support the successful preparation of the
metallacage.
The metallacage 1 was prepared by a multicomponent self-
assembly approach by stirring 9,10-di(pyridin-4-yl)anthracene
(2), Pt(II) meso-tetra(4-carboxyphenyl)porphine sodium salt (3)
and 90o Pt(II) acceptor (4) in a 2:1:4 ratio in a mixture of
acetone/water (v/v = 4:1) at 70 oC for 8 h (Scheme 1).
Metallacage
1
was identified by 1H and 31P{1H} NMR
spectroscopies (Figure 1a-d). In the 1H NMR spectra, the peaks
related to the protons on pyridyl groups of 2 shifted downfield
after the cage formation, which agreed with the coordination of
nitrogen atoms to the Pt(II) centers. The protons belonging to 3
matched the pre-designed ratio. The 31P{1H} NMR spectrum of
1 exhibited two doublet peaks with concomitant 195Pt satellites,
indicating two distinct phosphorus environments as required by
a
heteroligated coordination motif. These NMR results
demonstrated the formation of a discrete and single-component
structure with high asymmetry. The stoichiometry of 1 was
examined by electrospray ionization time-of-flight mass
spectrometry (ESI-TOF-MS, Figure 1e), whose results showed
two peaks assigned to an intact moiety with 5+ charge states
2
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red phosphorescence and a nearly steady blue fluorescence. A
similar change of the red phosphorescence was also found with
the excitation wavelength at 510 nm (Figure 2c), and the
promoted red phosphorescence was clearly seen by the naked
eye (Figure 2d). Moreover, the red phosphorescence was
reversible by exposure to O2 (see the supplementary video). To
further validate the phosphorescence property, a lifetime
measurement of the emission at 660 nm was carried out and it
was determined to be 30.1 μs (Figure S8), and this long lifetime
proved the phosphorescence.[14]
Figure 2. (a) Normalized UV-vis spectra of 1, 2 and 3. Fluorescence spectra
of 1 with the excitations of (b) 390 nm and (c) 510 nm when purged with
nitrogen bubbles. (d) Photos of the emissions of an acetone solution of 1 in a
quartz cuvette in a fluorescence spectrometer with the excitations of 510 nm
before and after purging. The concentration for each test was 1.00 mg/mL in
acetone.
Figure 1. Partial 1H NMR (500 MHz, acetone-d6, 298 K) spectra of (a) 2, (b) 1
and (c) 3. (d) 31P{1H} NMR (121 MHz, acetone-d6, 298 K) spectrum of 1. (e)
Calculated (red) and experimental (black) ESI-TOF-MS spectra of 1 (left: [M
– 5OTf]5+ charge state; right: [M – 4OTf + Na]5+ charge state).
After understanding the dual-emissive and phosphorescent
properties, we applied this metallacage in hypoxia imaging for
probing the intracellular O2 level. To improve the solubility and
integrity
of
1,
an
amphiphilic
polymer
The photophysical properties of the metallacage 1 were
explored. As shown in the UV-vis spectra, the overlap (Figure
2a) between absorptions of the ligands allowed exciting both
dyes simultaneously. Moreover, after the formation of the
metallacage, the bathochromic shift of the Soret band and the
hypsochromic of the Q band were both found for 3 (Figure S7),
indicating the prevented π-π stacking.[11,13] In the design
principle, FRET was avoided, and this was verified by the
negligible overlap between the fluorescent emission of 2
(maximum at 460 nm)12 and the UV absorbance of 3 (maximum
at 396 nm). The dual-emission property of 1 in a deaerated
atmosphere was evaluated in fluorescence experiments. An
acetone solution of the metallacage showed strong blue (420-
480 nm) and very weak red (630-740 nm) emissions with 390
nm excitation. Upon purging with nitrogen, the red emission
increased, which was a typical feature of phosphorescence,
and thus led to a dual-emissive system (Figure 2b). The
enhancement of the red emission was calculated to be more
than 48 times in a nitrogen atmosphere, while the blue
fluorescence only exhibited 0.30 times of an enhancement,
illustrating that is a useful and sensitive O2 probe with a tunable
methylpoly(ethyleneglycol)-block-poly(γ-benzyl-L-glutamate)
(mPEG-b-PBLG, Scheme 1) was used to encapsulate 1.[15]
mPEG-b-PBLG was prepared via ring-opening-polymerization
(Scheme S3 and Figure S9). By using a co-precipitation
method, 1 was encapsulated inside the self-assembled mPEG-
b-PBLG to form metallacage-loaded nanoparticles (MNPs) with
a loading efficiency of 65%. The morphology of MNPs were
studied. As shown in Figure 3a, spherical MNPs were found
with
a diameter of ~150 nm on transmission electron
microscope (TEM), which was in line with the result of dynamic
light scattering (DLS, 134 ± 13.7 nm, Figure 3b). The zeta
potential of the MNPs was also determined, revealing the
neutral nature of MNPs benefiting from the PEGylation (Figure
S10). These data indicate that the MNPs are favorable for
cellular endocytosis.[16]
3
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10.1002/anie.202009442
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the amount of intracellular platinum increased along with the
incubation time and 182 ng platinum per million cells was
achieved after 8 h incubation, indicating that MNPs were
capable of intracellular accumulation (Figure 4a). For
comparison, the endocytosis of cisplatin was also tested.
According to the results of ICP-MS, MNPs exhibited slightly
lower but sufficient uptake at every incubation time point
compared with those of cisplatin likely arising from the fast
diffusion of the small molecular weight compound. The
biocompatibility of the polymeric carrier was evaluated by a 3-
(4,5-dimethylthiazol-2-yl)-2,5-diphenyl
tetrazolium
bromide
Figure 3. (a) TEM image of MNPs. The scale bar is 0.5 μm. (b) DLS result of
MNPs.
(MTT) assay. The relative cell viability of 4T1 cells after 48 h of
incubation with different samples illustrated that the amphiphilic
polymer mPEG-b-PBLG showed low cytotoxicity even at 200
μM (more than 87% of cells survived). The half-maximal
inhibitory concentration (IC50) value of MNPs, 1 and cisplatin
were 8.58 ± 1.36, 4.50 ± 1.44 and 7.43 ± 1.34 μM, respectively
(Figure 4b). The cytotoxicity of MNPs was attributed to the
platinum-based ligand 4, indicating that its anticancer efficacy
was maintained by the formation of a metallacage.[17] Similar
results were found when A549 (Figure 4c), HeLa and U87 cells
(Figure S11) were employed.
With the reversible and sensitive O2 response established,
we further applied MNPs in hypoxia imaging to monitor the
intracellular O2 level. 4T1 breast cancer cells were chosen for
hypoxia imaging due to their highly aggressive and fast
proliferation characteristics. The endocytosis of MNPs by 4T1
cells was investigated. Inductively coupled plasma mass
spectroscopy (ICP-MS) was chosen to monitor the intracellular
platinum amount upon different incubation times. We found that
Figure 4. (a) ICP-MS results of intracellular Pt amount in 4T1 cells after incubation with MNPs or cisplatin for different times. Relative cell viabilities of (b) 4T1 and
(c) A549 cells after treatment with different administrations. (d) CLSM images of 4T1 cells stained by Syto 9 (green, staining nucleus) and MNPs (blue and red)
under normoxic (top) or hypoxic (bottom) conditions. (e) Quantitively emissive intensities of red phosphorescence and blue fluorescence in 4T1 cells under
normoxic or hypoxic conditions.
After investigating the cytotoxicity of MNPs, hypoxia imaging
experiments were performed. As shown in Figure 4d, the green
and blue emissions were both recorded under the normoxia
condition, whereas the red emission was barely detected. The
blue emission perfused throughout the cells indicated that the
uptake of MNPs was successful. By co-localization with green-
emissive Syto 9, MNPs mainly distributed in the cytoplasm. In
contrast with the images under the normoxia condition, 4T1
cells showed not only green/blue fluorescence but also red
phosphorescence in the hypoxia condition. The increased red
4
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emission under low O2 concentration indicated the
phosphorescence characteristic as well as the success of
hypoxia imaging by the metallacage. Additionally, the merged
image suggested that the blue and red emission are located
identically, showing the dual-emissive property of 1 under the
hypoxia condition. In order to illustrate the uniqueness of the
metallacage, the intensities of blue and red emissions were
quantitatively recorded (Figure 4e). We found that the red
phosphorescence was increased by ~450% after the cells
became hypoxic, while the blue fluorescence remained nearly
stable, so that it could be a potential internal reference to
quantify the intracellular O2 level and detect hypoxia. The ratios
between red phosphorescence and blue fluorescence were
determined to be 0.224 and 0.866 upon normoxia and hypoxia,
respectively. More importantly, the ratio only varies with the O2
level. Compared with mono-emissive probes, which have
different emissive intensities under different concentrations and
endocytosis, the dual-emissive metallacage provides a more
reliable standard for hypoxia detection and imaging.
blood using ICP-MS spectroscopy at different time points after
the injection of MNPs. As shown in Figure 5a, cisplatin was
cleared from the blood quickly and the circulation half-life was
estimated to be about 0.37 h. In contrast, the circulation half-life
of MNPs was prolonged to 2.16 h, about 5.8-fold of cisplatin,
referring to the time-dependent platinum amount in blood.
Besides, the results of MNPs displayed a larger total area
under the curve than that of cisplatin, indicating the improved
circulation behavior of MNPs. The improved circulation time
was ascribed to the stable nanoparticles and their hydrophilic
exteriors that inhibited the protein adsorption. Furthermore, the
biodistribution of MNPs and cisplatin in the tumor and other
organs were determined (Figure 5b and c). According to the
results of ICP-MS, the accumulation of cisplatin in the tumor
was insufficient because of fast clearance, and the highest
concentration of platinum was 2.8 ± 0.5 %ID/g (percent of
dosage per gram organ/tissue). However, the intratumoral
accumulation of MNPs was more feasible and the platinum
concentration located in the tumor increased to 5.8 ± 0.8 %ID/g
gradually after 24 h post injection resulting from the promoted
circulation time of MNPs. Notably, the treatment with MNPs
was able to retain a relatively higher level of intratumoral
platinum amount (4.6 ± 0.7 %ID/g) even at 48 h post-injection.
The extended circulation time and tumor accumulation implied
MNPs were favorable for in vivo hypoxia imaging.
In order to further explore the practical application of the
metallacage in cancer theranostics, in vivo hypoxia imaging
was firstly evaluated on 4T1 tumor-bearing mice. Prior to the
hypoxia imaging studies, we assessed the pharmacokinetic
data and time-dependent tissue distributions of MNPs using
cisplatin as a control. The circulation time of MNPs and
cisplatin were estimated by measuring the platinum amount in
Figure 5. (a) Time-dependent Blood plasma amount of platinum after injecting MNPs and cisplatin. Tissue distributions of (b) cisplatin and (c) MNPs after
injection. Organs: H, heart; Lu, lung; Li, liver; Ki, kidney; Sp, spleen; T, tumor. (d) In vivo fluorescent images of different sized tumor-bearing mice after the
injection of MNPs. The signals were collected in the range of 600-800 nm with the excitation wavelength. (e) Intratumoral platinum amount of difference sized
tumors at 24 h post i.v. injection of MNPs. (f) Immunofluorescence staining of tumor sections of difference sized tumors with an antibody to HIF-1α. Data are
expressed as means ± s.d.
Due to the rapid oxygen consumption, poor vascularization
and insufficient blood supply, the majority of solid tumors will
develop hypoxia as they grow too large in size, which is
responsible for resistances and tumor metastasis. It is reported
that tumors in small size are relatively well vascularized and
commonly display little or no hypoxic condition, while hypoxia
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10.1002/anie.202009442
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reappears in the characteristically perinecrotic distribution
pattern when the tumors grow large.[18] Therefore, we chose
two different sized 4T1 tumors (small tumor I, 100 mm3; large
tumor II, 360 mm3) to illustrate the performance of hypoxia
imaging under different intratumoral oxygen levels because
larger tumors are usually more hypoxic that benefited brighter
phosphorescence. In vivo hypoxia imaging was carried out after
i.v. injection of MNPs, and whole body images were taken after
4 and 24 h post-injection by detecting emission in the range of
600-800 nm. As shown in Figure 5d, bright emissions were
possible to achieve cancer theranostics by MNPs. With the
prolonged circulation time and tumor accumulation in hand, we
subsequently evaluated in vivo antitumor efficiency of MNPs
through 4T1 tumor-bearing mice. When the tumor volume
reached near 90 mm3, the mice were randomly divided into
three groups and treated with (I) PBS, (II) free cisplatin and (III)
MNPs, respectively. According to tumor inhibition curves
(Figure 6a), the average tumor volume of mice injected with
PBS increased rapidly. The mice administrated with cisplatin
showed limited tumor inhibition mainly because of its relatively
poor tumor accumulation and fast clearance. Excitingly, MNPs
performed satisfactory therapeutic outcomes with a tumor
inhibition rate of 79.6 % (Figure S12). The average tumor
weight was calculated to be 1.50, 0.93, and 0.42 g at the end
day of therapy for the mice dosed with PBS, cisplatin and
MNPs, respectively, which was in accordance with the
aforementioned therapeutic results. The excellent antitumor
efficiency of MNPs was also supported by hematoxylin and
eosin (H&E) staining (Figure 6b). Compared with the injections
of PBS and cisplatin, the administration of MNPs led to severe
apoptosis and necrosis in tumor.
Apart from the antitumor efficiency, the systemic toxicity of
MNPs was also investigated. Blood from treated mice was
collected for blood biochemistry tests in order to estimate the
potential long-term systemic toxicity in vivo (Figure 6c-g).
Compared with the blood sample from mice dosed with PBS,
the level of alanine aminotransferase (ALT), aspartate
aminotransferase (AST), blood urea nitrogen (BUN), creatinine
(CREA) and alkaline phosphatase (ALP) all increased in the
blood from mice injected with cisplatin, illustrating severe
nephrotoxicity and hepatotoxicity. However, for the mice
administrated with MNPs, no apparently abnormal parameter
was found within the therapeutic period. Moreover, the
monitoring of body weight changes also provided negligible
weight loss for the MNPs-treated mice during the therapeutic
period, whereas a weight loss appeared when employing
cisplatin, indicating that MNPs had limited systemic toxicity due
to the better tumor-specific distribution. Consequently, the
aforementioned in vivo studies suggest that MNPs can be
applied in theranostics with both hypoxia imaging and antitumor
capabilities.
observed in tumor regions after 24
h
post-injection,
demonstrating the capability of in vivo hypoxia imaging for
either small or large tumors. Besides, the emission shown in
the large tumor possessed a better tumor-to-normal-tissue ratio
and a stronger intensity than it in the small tumor, suggesting
that MNPs exhibited a better performance when employed in
large tumors. The stronger emission in large tumor was also
consistent with the enhanced phosphorescence of metallacage
1 under a lower oxygen level in the large tumor. The
intratumoral platinum amount was also measured by ICP-MS
after completing hypoxia imaging in order to exclude the
influence of the MNPs concentration. As shown in Figure 5e,
the results of ICP-MS evidenced that the platinum amount in
large tumors was slightly lower than those in relatively small
tumors possibly caused by the poor vascularization in hypoxic
tumor tissue. These data specified that the stronger emission
was attributed to the more hypoxic condition rather than the
higher MNPs concentration. Evidences for the hypoxic
conditions in these tumors were found by monitoring the
expression of hypoxia inducible factor 1α (HIF-1α). An
immunofluorescence staining with an antibody to HIF-1α of
tumor sections was involved and the results of staining showed
a higher green emission in large tumors, which revealed the
higher expression of the hypoxia-related marker and the more
hypoxic condition in large tumors (Figure 5f). This conclusion
agreed with the stronger emission of MNPs in large tumors that
supported the practical potential of the metallacage in hypoxia
imaging for cancer diagnosis.
cis-Pt(II) moieties are usually employed in antitumor drugs
and the cytotoxicity of MNPs was also pointed out by
aforementioned in vitro experiments. By combining the hypoxia
imaging and antitumor capabilities, we conceived that it was
6
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Figure 6. (a) Tumor volume changes of mice bearing 4T1 tumors with different treatments during therapeutic period. (b) H&E staining of tumor sections from
mice bearing 4T1 tumors with different treatments. Blood biochemistry tests of (c) ALT, (d) AST, (e) BUN, (f) CREA and (g) ALP from mice treated with different
formulations. I, PBS; II, cisplatin; III, MNPs. (h) Body weight changes of mice with different treatments. Data are expressed as means ± s.d.
Conclusion
Acknowledgements
In this work, we prepared a dual-emissive metallacage with
blue fluorescence and red phosphorescence. The structure of
the metallacage was investigated by NMR and MS
spectroscopies. Benefited from the formation of metallacage,
different ligands were able to be combined together by
heteroligated coordinations, endowing the metallacage with the
dual-emissive property. The red phosphorescence of the
metallacage enhanced 48 times in a hypoxic condition, while
the blue fluorescence nearly unchanged upon deaeration. After
encapsulation by an amphiphilic polymer, the self-assembled
nanoparticles showed a capability of hypoxia imaging by the
phosphorescence increase along with the decrease of the
intracellular O2 level. Moreover, a more accurate hypoxia
detection was achieved by using the ratio between red
phosphorescence and steady blue fluorescence, suggested by
in vitro experiments. Additionally, in vivo experiments revealed
MNPs as a potential candidate in practicable theranostics that
comprised both tumor hypoxia imaging and chemotherapy with
improved circulation time and tumor accumulation. The high
sensitivity, reliability and antitumor capability of this metallacage
as a hypoxia probe with chemotherapy has wide future
applications.
F.H. thanks the National Natural Science Foundation of China
(21620102006) and the fundamental research funds for the
central universities for financial support.
Keywords: supramolecular chemistry • self-assembly •
metallacages • hypoxia imaging • theranostics
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Entry for the Table of Contents
Imaging of hypoxia in vivo helps with accurate cancer diagnosis
and evaluation of therapeutic outcomes. Here we report a Pt(II)
metallacage with oxygen-responsive red phosphorescence and
steady fluorescence for in vivo hypoxia imaging and
chemotherapy.
9
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