Vivid tumor imaging utilizing liposome-carried bimodal radiotracer

Article abstract of DOI:10.1021/ml400513g

By developing a new bimodal radioactive tracer that emits both luminescence and nuclear signals, a trimodal liposome for optical, nuclear, and magnetic resonance imaging is efficiently prepared. Fast clearance of the radiotracer from reticuloendothelial s

Full text of DOI:10.1021/ml400513g

Letter
pubs.acs.org/acsmedchemlett
Vivid Tumor Imaging Utilizing Liposome-Carried Bimodal
Radiotracer
Jonghee Kim,† Darpan N. Pandya,† Woonghee Lee,† Jang Woo Park,‡ Youn Ji Kim,† Wonjung Kwak,†
Yeong Su Ha,† Yongmin Chang,†,‡ Gwang Il An,*,§ and Jeongsoo Yoo*,†
†Department of Molecular Medicine, BK21 Plus KNU Biomedical Convergence Program, Kyungpook National University, Daegu
700-422, South Korea
‡Department of Medical & Biological Engineering, Kyungpook National University, Daegu 700-422, South Korea
§Molecular Imaging Research Center, KIRAMS, Seoul 139-706, South Korea
S
* Supporting Information
ABSTRACT: By developing a new bimodal radioactive tracer
that emits both luminescence and nuclear signals, a trimodal
liposome for optical, nuclear, and magnetic resonance imaging
is efficiently prepared. Fast clearance of the radiotracer from
reticuloendothelial systems enables vivid tumor imaging with
minimum background.
KEYWORDS: Imaging agent, radiopharmaceutical, multimodal imaging, Cerenkov radiation, liposome
t is now well accepted that multimodal imaging is more
many attractive characteristics as a multimodal imaging
platform, including a well-established preparation method,
easy size control, easy surface modification, large loading
capacity, and excellent in vivo stability.13 The only drawback is
that all imaging contrast components should be added into
liposomes to become multimodal imaging probe.5 However, as
the number of different imaging contrast components is
increased, the liposome preparation process becomes compli-
cated, and various issues regarding characterization and
reproducibility are raised. Probably, this is why very few
liposome-based trimodality imaging probes have been reported
so far.14,15
Here we report on a new strategy for preparation of a
trimodal liposome for optical, nuclear, and MR tumor imaging.
By synthesizing a new radioactive tracer emitting luminescent
light, hybrid trimodal liposomes were prepared by supplement-
ing with only two different imaging components instead of
three. The radiotracer excreted fast from RES resulting in vivid
tumor imaging with high tumor-to-background ratio.
1,2
Iefficient and accurate in the diagnosis of various diseases.
Along with the development of multimodal imaging instru-
ments (e.g., PET (positron emission tomography)/CT
(computed tomography), SPECT (single photon emission
computed tomography)/CT, PET/MR (magnetic resonance),
optical/PET, optical/MR scanner),3 a variety of multimodal
imaging probes have been synthesized and tested as new
contrasting agents.4,5 Among several multimodal imaging
platforms, metal-based nanocrystals such as iron oxide,
quantum dots, and gold nanoparticles have been especially
preferred because these nanocrystals can serve as intrinsic MR,
optical, and CT contrasting agents, respectively, and only
additional imaging components are needed.6,7 However, after
systemic injection, many nanocrystal-based imaging agents
showed slow clearance from the reticuloendothelial system
(RES, e.g., liver and spleen), and toxicity and safety issues
remain as a substantial hurdle for further advancement to
clinical applications, especially when radiolabeled for nuclear
imaging.8,9 The radiolabeled imaging agent should be excreted
within certain time period from nontarget organs to minimize
unnecessary radiation exposures. Furthermore, the slow
clearance increases background noise to make accurate tumor
detection difficult in nuclear imaging.
First, we developed a new radioactive tracer capable of
emitting both nuclear and optical imaging signals. Recently,
Cerenkov radiation, which is the light emitted when a charged
particle travels with a velocity greater than that of light in a
given medium, seeks new application in optical molecular
imaging.16,17 We screened Cerenkov luminescence properties
In contrast, liposomes are the more preferred option to
develop multimodal imaging probes for clinical application as it
is made up from biocompatible, nontoxic, and biodegradable
materials.10,11 Many liposomes are already FDA approved for
effective drug delivery carriers.12 Furthermore, liposomes have
Received: December 13, 2013
Accepted: February 4, 2014
Published: February 4, 2014
© 2014 American Chemical Society
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ACS Medicinal Chemistry Letters
Letter
of various radionuclides and found that some radionuclides
commonly used for PET imaging such as 68Ga, 124I, 18F, and
64Cu emit strong Cerenkov light.18,19
radiolabeling and purification steps were finished less than 40
min without any time-consuming HPLC purification.
A trimodal liposome was prepared by one-pot formulation of
phosphatidylcholine, cholesterol, PEGylated lipid, lipophilic
gadolinium complex, and the radiolabeled [124I]HIB (Figure 2).
Among these radionuclides, 124I was chosen as a radioisotope
source because of its attractive physical properties; long half-life
(4.2 d), which allows sufficient time for preparation and for
ease of conducting long follow-up studies after administration,
and the high kinetic energy of positrons emitted during decay
(Eβ+ mean, 819 keV) leading to strong Cerenkov luminescence
light (2.5 and 6 times stronger compared to 18F and 64Cu,
respectively).19
For efficient incorporation into the liposomal bilayer and
high in vivo stability of radio-iodinated compounds, a long alkyl
chain linked with a 4-iodobenzoyl group was designed as a
target compound (Figure 1a). The lipophilic long alkyl chains
Figure 2. Schematic diagram of trimodal liposome and its imaging
components.
A chloroform solution of 1,2-dipalmitoyl-sn-glycero-3-phospho
choline (DPPC), 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1′-
rac-glycerol) (DPPG), cholesterol, 1,2-distearoyl-sn-glycero-3-
phosphoethanolamine-N[methoxy(polyethylene glycol)-2000]
(DSPE-PEG2000), and gadolinium-1,2-dipalmitoyl-sn-glycero-
3-phosphoethanolamine-N-diethylenetriaminepenta acetic acid
(Gd-DTPA-DPPE) at a molar ratio of 8:8:3:1:7 and [124I]HIB
were well mixed and dried to form a thin lipid film, which was
hydrated with saline for 25 min at 50 °C.22,23 The resultant
opaque liposomal solution was sequentially extruded through
membrane filters with a pore size of 1000, 400, 200, and 100
nm. The extruded liposome was further purified using a size
exclusion column (PD-10, GE Healthcare).
The formed liposome was characterized using a dynamic
light scattering (DLS) size analyzer and transmission electron
microscopy (TEM). In DLS measurements, the liposomes
showed good size distribution of mean diameter of 127.8 8.4
nm (Figure 3a). Negative staining TEM images also confirmed
globular liposomal structure of ca. 120 nm (Figure 3b). The
lipid bilayer was clearly identifiable in TEM imaging. The
PEGylated lipid (DSPE-PEG2000) was added as one of the
liposome components in order to reduce the immediate
capture of liposomes by the RES after systemic administration
and to allow longer blood circulation time for higher tumor
accumulation.24 The liposome diameter of ca. 100 nm was
chosen in order to maximize passive tumor targeting due to
enhanced permeability and retention effect.25
Figure 1. Synthesis scheme of standard and precursor for HIB (a),
radiolabeling scheme of [124I]HIB (b), UV chromatogram of HIB (c),
and radio chromatogram of [124I]HIB (d).
were widely used for tight anchor on cell membrane,20 and
iodo-aryl compound was selected to minimize deiodination in
physiological conditions.21 Nonradioactive standard hexadecyl-
4-iodo benzoate (1, HIB) was prepared by esterification of 4-
iodobenzoyl chloride with 1-hexadecanol in the presence of
triethylamine as a base. The crude product was extracted with
dichloromethane and recrystallized to give white crystalline
needles (80% yield). For the preparation of precursor for
radiolabeling, to a solution of hexadecyl-4-iodobenzoate
dissolved in toluene, hexabutylditin and a catalytic amount of
Pd(Ph3)4 were added, refluxed, concentrated, and purified by
column chromatography to afford pure hexadecyl-4-tributyl-
stannylbenzoate (2) in 71% yield.
For radio-iodination, the tributylstannyl group of 2 was
replaced by radioactive iodine-124 (Figure 1b). The precursor 2
was reacted with [124I]NaI (0.5−5 mCi) in the presence of
acetic acid and 3% H2O2. The mixture was shaken for 30 min at
70 °C and dried completely under vacuum. Only radiolabeled
hexadecyl-4-[124I]iodobenzoate ([124I]HIB) was simply ex-
tracted by acetonitrile, concentrated, and reconstituted in
dichloromethane for the following studies. Its radiochemical
yield was over 90%, and the radiochemical purity reached 100%
after the extraction, as determined by radio-TLC and radio-
HPLC analysis [Luna C8 column, 4.6 × 50 mm, 5 μm; 95:5
MeCN/H2O, 1 mL/min flow rate] (Figure 1c,d). All
Each 200 μL fraction of the prepared radioactive liposome
from the size exclusion column was collected and counted using
a gamma counter. Most radiolabeled liposomes were eluted at
an elution volume of around 4 mL (Figure 3c), while the free
[
124I]HIB was stuck to the column because of its extremely low
water solubility (log P = 2.19 0.04). The radio-incorporation
yield of [124I]HIB into liposome was over 75% after column
purification. All eluted fractions were transferred to a 96-well
plate and imaged by luminescence and PET and MR imaging
(Figure 3d). As expected, the optical luminescence imaging
pattern matched well with that of PET imaging because both
optical and nuclear imaging signals originate from the
radioactive [124I]HIB. However, upon close examination, the
optical imaging showed better spatial resolution and higher
sensitivity than nuclear PET imaging.18,26 When considering
much shorter imaging time of optical imaging compared to
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ACS Medicinal Chemistry Letters
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Figure 4. Blood half-life of [124I]HIB (a) and [124I]HIB-Gd-liposome
(b) up to 24 h (n = 2). The insets show a pattern of early blood
clearance (0−20 min).
most vividly imaged with minimum background at 4 h
postinjection (Figure 5a-left). In addition to high uptake in
Figure 3. Size distribution of liposome measured by DLS analyzer (a),
TEM image of liposome (b), size exclusion chromatogram profile of
[
124I]HIB-Gd-containing liposome (c), and optical, PET, and MR
images of SEC elution fractions (d).
nuclear imaging (1 min vs 20 min, respectively), it becomes
more obvious that optical imaging is a better choice for ex vivo
characterization than nuclear imaging. MR imaging of the same
well plate showed a precise outline of each well because of its
excellent spatial resolution. The MR signal intensity of each
well was closely related to the well’s radioactivity (Figure 3d),
indicating that both [124I]HIB and the Gd-DTPA complex were
well incorporated into the liposome and move together.
However, even though a 5 × 104-fold excess of Gd complexes
(2.4 × 10−7 mol in 200 μL well at 4 mL elution point, ICP
measurement) was contained within the same liposome in
comparison to [124I]HIB (4.8 × 10−12 mol, equivalent to 150
μCi), because of its poor sensitivity, fewer wells were
differentiated from the adjacent background wells in MR
imaging compared with optical and PET imaging. An extremely
large loading capacity of liposomes made it possible to
incorporate two different imaging components having such a
big concentration difference into a single probe.
To characterize in vivo stability of the prepared liposomes,
first, the blood half-life of [124I]HIB-assembled liposome was
measured by serial retro-orbital bleeds and compared to that of
Figure 5. Typical optical luminescence, PET and MR image of CT26
tumor-bearing mouse at 4 h postinjection of [124I]HIB-Gd-liposome
(n = 3) (a). Tumor, red arrow; liver, yellow arrow; spleen, white
arrowhead; bladder, green arrowhead. Maximum intensity projection
images of PET at 2, 4, and 24 h (b). Thyroid: white arrow.
Radioactivity uptakes in various organs at 2, 4, and 24 h (n = 3) (c).
Tumor-to-organ uptake ratio at 24 h (d).
[
124I]HIB itself (n = 2 mice per group). Both blood half-life
data of [124I]HIB and [124I]HIB-labeled liposomes fit a two-
phase exponential decay model with the values of 1.3 and 70.8
min, respectively (Figure 4a,b). These huge differences of blood
half-life data clearly indicated that the [124I]HIB-labeled
liposomes move together in the body without immediate
dissociation of [124I]HIB from the liposome.
the tumor, other hot spots were observed around the
abdominal region, which could be attributed to liver even
though precise assignment was not feasible because of the poor
tissue penetration and high scattering characteristics of
Cerenkov light. The precise internal distribution of the
liposome-carried [124I]HIB was confirmed by nuclear PET
imaging thanks to its high tissue penetration feature (Figure 5a-
Then, the purified [124I]HIB-Gd-containing liposomes (150
μCi) were injected into CT26 tumor-bearing BALB/c mice for
in vivo imaging studies. Because of its excellent sensitivity and
short imaging time, the tumor uptake of the injected liposomes
was initially monitored by optical imaging up to 48 h. With the
help of photographic images of mice, the CT26 tumor was
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ACS Medicinal Chemistry Letters
Letter
middle). The abdominal hot spots in optical imaging were
clearly assigned as liver and spleen in tomographic PET images.
PET imaging also revealed another hot spot in the bladder,
which was not observed in optical image at all, presumably
because of the deep location of bladder from the imaging
surface in supine position. The high activity in urine could be
explained by the renal excretion of catabolized [124I]HIB
molecules in the liver.27 Neither liposomes of >100 nm size nor
lipophilic compounds favor renal excretion.28,29 MR imaging
provided excellent anatomical information, especially regarding
soft tissues, which was missing from both optical and nuclear
imaging (Figure 5a-right). The tumor showed slightly enhanced
contrast due to the Gd(III) complexes incorporated into the
liposome (see Supporting Information). Rapid increase of
contrast-to-noise ratio (CNR) was observed up to 30 min and
slowly increased to maximum value at 3 h in both liver and
tumor. However, the CNR values in liver and tumor were
gradually decreased afterward. However, because of low
sensitivity of MR imaging, the MR contrasting effect was
weaker compared to optical and nuclear PET imaging.30
Whole body distribution and clearance pattern of the
liposome-carried [124I]HIB was serially monitored by PET
imaging (n = 3) (Figure 5b). Most activities were accumulated
in RES (liver and spleen) organs and tumor within 2 h.
However, liver and spleen activities continued to decrease,
while the substantial amount of activity remained in tumor up
to 24 h. Interestingly, high activities were found in bladder,
indicating that lipophilic [124I]HIB seemed to be catabolized in
liver and the hydrophilic components, presumably free
AUTHOR INFORMATION
■
Corresponding Authors
*(J.Y.) Fax: (+82) 53-426-4944. E-mail: yooj@knu.ac.kr.
*(G.I.A.) Fax: (+82) 2-970-2409. E-mail: gwangil@kirams.re.
kr.
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Funding
This research was supported by Kyungpook National
University Research Fund, 2011.
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) Swierczewska, M.; Lee, S.; Chen, X. Inorganic nanoparticles for
multimodal molecular imaging. Mol. Imaging 2011, 10, 3−16.
(2) Huang, W.-Y.; Davis, J. J. Multimodality and nanoparticles in
medical imaging. Dalton Trans. 2011, 40, 6087−6103.
(3) Cherry, S. R.; Semin. Multimodality imaging: beyond PET/CT
and SPECT/CT. Semin. Nucl. Med. 2009, 39, 348−353.
(4) Louie, A. Multimodality Imaging Probes: Design and Challenges.
Chem. Rev. 2010, 110, 3146−3195.
(5) Jarzyna, P. A.; Gianella, A.; Skajaa, T.; Knudsen, G.; Deddens, L.
H.; Cormode, D. P.; Fayad, Z. A.; Mulder, W. J. M. Multifunctional
imaging nanoprobes. Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol.
2010, 2, 138−150.
(6) Xie, J.; Liu, G.; Eden, H. S.; Ai, H.; Chen, X. Surface-engineered
magnetic nanoparticle platforms for cancer imaging and therapy. Acc.
Chem. Res. 2011, 44, 883−892.
[
124I]iodide ions and others, were cleared out by renal
excretion. This hypothesis was further supported by the focal
uptake of free [124I]iodide in thyroid at 24 h.21
(7) Gao, J.; Gu, H.; Xu, B. Multifunctional magnetic nanoparticles:
Design, synthesis, and biomedical applications. Acc. Chem. Res. 2009,
42, 1097−1107.
The radioactivities in the liver, spleen, tumor, and muscle
were quantified based on PET imaging (n = 3) (Figure 5c).
The highest uptake was observed in liver at 2 h, followed by
tumor and spleen (7.5 3.1, 4.6 1.6, and 4.7 0.7 %ID/g,
respectively). Activities in liver and spleen continued to
decrease up to 24 h, and less than 10% of 2 h activities were
(8) Krug, H. F.; Wick, P. Nanotoxicology: An interdisciplinary
challenge. Angew. Chem., Int. Ed. 2011, 50, 1260−1278.
(9) Landsiedel, R.; Ma-Hock, L.; Kroll, A.; Hahn, D.;
Schnekenburger, J.; Wiench, K.; Wohlleben, W. Testing metal-oxide
nanomaterials for human safety. Adv. Mater. 2010, 22, 2601−2627.
(10) Kluza, E.; Jacobs, I.; Hectors, S. J. C. G.; Mayo, K. H.; Griffioen,
A. W; Strijkers, G. J.; Nicolay, K. Dual-targeting of αvβ3 and galectin-1
improves the specificity of paramagnetic/fluorescent liposomes to
tumor endothelium in vivo. J. Controlled Release 2012, 158, 207−214.
(11) Chow, T.-H.; Lin, Y.-Y.; Hwang, J.-J.; Wang, H.-E.; Tseng, Y.-L.;
Pang, V. F.; Liu, R.-S.; Lin, W.-J.; Yang, C.-S.; Ting, G. Therapeutic
efficacy evaluation of 111In-labeled PEGylated liposomal vinorelbine in
murine colon carcinoma with multimodalities of molecular imaging. J.
Nucl. Med. 2009, 50, 2073−2081.
found at 24 h (0.45
0.04 and 0.47
0.3 %ID/g,
respectively). However, tumor showed a much slower clearance
pattern. More than 40% activity of the 2 h time point was still
observed in tumor at 24 h (1.9 0.29%ID/g). At 24 h, the
tumor-to-muscle, tumor-to-liver, and tumor-to-spleen ratios
were 16.1, 4.1, and 4.0, respectively (Figure 5d). Only tumor
was clearly visualized with minimum background at 24 h. The
muscle activity at 24 h is as low as 0.12 0.11 %ID/g.
In conclusion, here we reported a facile method for
preparation of a trimodal tumor imaging agent using liposome
platform. By the development of a radiotracer that emits strong
Cerenkov luminescence light, optical and nuclear images were
obtained from the single imaging component. Tumors were
detected by all optical, nuclear, and MR imaging modalities.
The liposome-carried radiotracer showed longer retention in
tumor but cleared quickly from RES organs, resulting in vivid
tumor imaging with minimum background.
(12) Torchilin, V. P. Recent advances with liposomes as
pharmaceutical carriers. Nat. Rev. Drug Discovery 2005, 4, 145−160.
(13) Mulder, W. J. M.; Strijkers, G. J.; van, T. G. A. F.; Cormode, D.
P.; Fayad, Z. A.; Nicolay, K. Nanoparticulate assemblies of amphiphiles
and diagnostically active materials for multimodality imaging. Acc.
Chem. Res. 2009, 42, 904−914.
(14) Li, S.; Goins, B.; Zhang, L.; Bao, A. Novel multifunctional
theranostic liposome drug delivery system: Construction, character-
ization, and multimodality MR, near-infrared fluorescent, and nuclear
imaging. Bioconjugate Chem. 2012, 23, 1322−1332.
(15) Mitchell, N.; Kalber, T. L.; Cooper, M. S.; Sunassee, K.; Chalker,
S. L; Shaw, K. P.; Ordidge, K. L.; Badar, A.; Janes, S. M.; Blower, P. J.;
Lythgoe, M. F.; Hailes, H. C.; Tabor, A. B. Incorporation of
paramagnetic, fluorescent and PET/SPECT contrast agents into
liposomes for multimodal imaging. Biomaterials 2013, 34, 1179−1192.
(16) Robertson, R.; Germanos, M. S.; Li, C.; Mitchell, G. S.; Cherry,
S. R.; Silva, M. D. Optical imaging of Cerenkov light generation from
positron-emitting radiotracers. Phys. Med. Biol. 2009, 54, N355−N365.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis of HIB standard and precursor, radiolabeling,
liposome preparation, in vitro and in vivo imaging studies,
blood half-life measurement, and MR image analyses. This
material is available free of charge via the Internet at http://
pubs.acs.org.
393
dx.doi.org/10.1021/ml400513g | ACS Med. Chem. Lett. 2014, 5, 390−394

ACS Medicinal Chemistry Letters
Letter
(17) Ruggiero, A.; Holland, J. P.; Lewis, J. S.; Grimm, J. Cerenkov
luminescence imaging of medical isotopes. J. Nucl. Med. 2010, 51,
1123−1130.
(18) Park, J. C.; Yu, M. K.; An, G. I.; Park, S. I.; Oh, J.; Kim, H. J.;
Kim, J. H.; Wang, E. K.; Hong, I. H.; Ha, Y. S.; Choi, T. H.; Jeong, K.
S.; Chang, Y.; Welch, M. J.; Jon, S.; Yoo, J. Facile preparation of a
hybrid nanoprobe for triple-modality optical/PET/MR imaging. Small
2010, 6, 2863−2868.
(19) Park, J. C.; An, G. I.; Park, S.-I.; Oh, J.; Kim, H. J.; Ha, Y. S.;
Wang, E. K.; Kim, K. M.; Kim, J. Y.; Lee, J.; Welch, M. J.; Yoo, J.
Luminescence imaging using radionuclides: a potential application in
molecular imaging. Nucl. Med. Biol. 2011, 38, 321−329.
(20) Kawamura, R.; Mishima, M.; Ryu, S.; Arai, Y.; Okose, M.;
Silberberg, Y. R.; Rao, S. R.; Nakamura, C. Controlled cell adhesion
using a biocompatible anchor for membrane-conjugated bovine serum
albumin/bovine serum albumin mixed layer. Langmuir 2013, 29,
6429−6433.
(21) Israel, I.; Brandau, W.; Farmakis, G.; Samnick, S. Improved
synthesis of no-carrier-added p-[124I]iodo-L-phenylalanine and p-
[
131I]iodo-L-phenylalanine for nuclear medicine applications in
malignant gliomas. Appl. Radiat. Isot. 2008, 66, 513−522.
(22) Hadjidemetriou, M.; Pippa, N.; Pispas, S.; Demetzos, C.
Incorporation of dimethoxycurcumin into charged liposomes and the
formation kinetics of fractal aggregates of uncharged vectors. J.
Liposome Res. 2013, 23, 94−100.
(23) Rauchhaus, U.; Schwaiger, F. W.; Panzner, S. Separating
therapeutic efficacy from glucocorticoid side-effects in rodent arthritis
using novel, liposomal delivery of dexamethasone phosphate: long-
term suppression of arthritis facilitates interval treatment. Arthritis Res.
Ther. 2009, 11, R190.
(24) Barreto, J. A.; O’Malley, W.; Kubeil, M.; Graham, B.; Stephan,
H.; Spiccia, L. Nanomaterials: applications in cancer imaging and
therapy. Adv. Mater. 2011, 23, H18−H40.
(25) Liu, D.; Mori, A.; Huang, L. Role of liposome size and RES
blockade in controlling biodistribution and tumor uptake of GM1-
containing liposomes. Acta Biomembr. 1992, 1104, 95−101.
(26) Choi, J.-S.; Park, J. C.; Nah, H.; Woo, S.; Oh, J.; Kim, K. M.;
Cheon, G. J.; Chang, Y.; Yoo, J.; Cheon, J. A hybrid nanoparticle probe
for dual-modality positron emission tomography and magnetic
resonance imaging. Angew. Chem., Int. Ed. 2008, 47, 6259−6262.
(27) Zamboni, W. C.; Eiseman, J. L.; Strychor, S.; Rice, P. M.;
Joseph, E.; Zamboni, B. A.; Donnelly, M. K.; Shurer, J.; Parise, R. A.;
Tonda, M. E.; Yu, N. Y.; Basse, P. H. Tumor disposition of pegylated
liposomal CKD-602 and the reticuloendothelial system in preclinical
tumor models. J. Liposome Res. 2011, 21, 70−80.
(28) Wong, A. W.; Ormsby, E.; Zhang, H.; Seo, J. W.; Mahakian, L.
M.; Caskey, C. F.; Ferrara, K. W. A comparison of image contrast with
(64)Cu-labeled long circulating liposomes and (18)F-FDG in a
murine model of mammary carcinoma. Am. J. Nucl. Med. Mol. Imaging
2013, 3, 32−43.
(29) Yoo, J.; David, E. R.; Kim, J.; Anderson, C. J.; Welch, M. J. A
potential Dubin−Johnson syndrome imaging agent: synthesis,
biodistribution, and microPET imaging. Mol. Imaging 2005, 4, 18−29.
(30) Gore, J. C.; Yankeelov, T. E.; Peterson, T. E.; Avison, M. J.
Molecular imaging without radiopharmaceuticals? J. Nucl. Med. 2009,
50, 999−1007.
394
dx.doi.org/10.1021/ml400513g | ACS Med. Chem. Lett. 2014, 5, 390−394