Claudia Calcagno1,2, Carlos Perez-Medina1,2, Tina Binderup3, Mark E Lobatto4, Seigo Ishino1,2, Mootaz Eldib1,2, Philip Robson1,2, Sarayu Ramachandran1,2, Thomas Reiner5, Edward Fisher6, Zahi A Fayad1,2, and Willem JM Mulder1,2
1Department of Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 2Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 3University of Copenaghen, Copenaghen, Denmark, 4Academisch Medisch Centrum, Amsterdam, Netherlands, 5Memorial Sloan Kettering Cancer Center, New York, NY, United States, 6New York University School of Medicine, New York, NY, United States
Synopsis
Abundant, active
inflammatory cells are a hallmark of high-risk atherosclerotic plaques.
High-density lipoprotein (HDL) is a natural nanoparticle composed of
phospholipids, cholesterol and apolipoprotein A-I (APOA1), which has been shown
to have atheroprotective properties. .
The recent development of combined PET/MRI scanners and new advances in radio-labeling
technology gives the opportunity to investigate theese properties in vivo. Using a unique
set-up combining PET/CT and PET/MRI, we non-invasively assess the
pharmacokinetics, distribution, metabolism and turnover of 89Zr-HDL’s in a rabbit model of atherosclerosis. PURPOSE
Abundant, active
inflammatory cells are a hallmark of high-risk atherosclerotic plaques
1.
High-density lipoprotein (HDL) is a natural nanoparticle composed of
phospholipids, cholesterol and apolipoprotein A-I (APOA1), which has been shown
to have atheroprotective properties. It
is believed that these properties are mainly mediated by cholesterol efflux
from macrophages in plaques and its transport to the liver for excretion
2.
The recent development of combined PET/MRI scanners and new advances in radiolabeling
technology gives the opportunity to investigate the behavior of HDL
nanoparticles
in vivo. Using a unique
set-up combining PET/CT and PET/MRI, we non-invasively assessed the
pharmacokinetics, distribution, metabolism and turnover of
89Zr-HDL
3-4
in a rabbit model of atherosclerosis.
METHODS
Nanoparticles were prepared by conjugation of DFO-p-NCS
to APOA1, and then radiolabeled with
89Zr
3-4. Atherosclerosis was induced in male New
Zealand White rabbits using a combination of high-fat diet and double balloon
injury of the abdominal aorta (n=13)
5. Non-atherosclerotic rabbits
were used as controls (n=8). Rabbits were injected with
89Zr-HDL and Cy5.5-HDL. For pharmacokinetics, blood was sampled via the ear vein
at 30 min, 24, 48, 72 and 120 h post injection and its radioactivity content
measured on an automatic gamma counter. Rabbits
were imaged on a Siemens mMR 3T PET/MRI
scanner and on a Siemens mCT Biograph PET/CT scanner.
PET/MRI and PET/CT scans were acquired within the first hour and then at
24, 48, 72 and 120 h after
89Zr-HDL administration. For PET/MRI,
after scout scans, the PET scan was initiated and co-acquired with a radial
VIBE MR sequence, used to analyze organ nanoparticle uptake. Time-of-flight
(TOF) non-contrast enhanced angiography was also performed for localization of
arterial anatomical landmarks. Animals were sacrificed after the last imaging
session. For
ex vivo validation, tissue samples were
harvested for radioactivity
counting and imaged using near infrared fluorescence (NIRF) to quantify Cy5.5-HDL uptake. To determine the
distribution of
89Zr-HDL, digital autoradiography was also performed.
Statistical analyses were conducted using non-parametric unpaired Mann-Whitney
tests (p<0.05 considered significant).
RESULTS
Pharmacokinetics. Blood time-activity curves are shown in figure 1A. Radioactivity
clearance was 1.13 and 1.05 days in control and atherosclerotic animals,
respectively. Radioactivity distribution in selected tissues was measured at 5
days post injection (p.i.) (figure 1B). Kidneys showed the highest uptake
values, higher for atherosclerotic animals compared to controls, although these
differences were not statistically significant. Spleen and liver uptakes were
around 0.1 %ID/g.
Imaging. Representative PET/CT fusion images of the abdominal
region at three different time points can be seen in figure 1D. Figure 1E shows
representative PET/MRI fusion images of the same animals shown in figure 1D.
PET images obtained with both scanners were almost identical and a strong
correlation was found between the SUVs measured from both systems (figure 1C).
Time-activity curves based on SUVs obtained from PET/CT and PET/MRI images are
shown in figure 2. Initially, within the first hour after intravenous
administration, images were dominated by a strong blood pool signal (figures 1D
and 1E), as well as high signal from liver, spleen and kidneys. At later time
points, images showed very high radioactivity accumulation in kidneys, which
was significantly higher in atherosclerotic animals at all time points
investigated (figure 2). Bone radioactivity was also detected over the five-day
period (SUVs around 5 g/mL). Ex vivo
analysis proved that this was mostly due to bone marrow uptake, as opposed to
mineral bone. Bone marrow uptake was higher in animals with atherosclerosis
(0.17 ± 0.03 vs. 0.13 ± 0.01 %ID/g for controls). PET-measured SUVs were in
good agreement with SUVs determined by ex
vivo gamma counting (R2=0.95). Aortic radioactivity was also
measured at 1, 2, 3 and 5 days. Increased accumulation of activity was found at
day 5 p.i. in atherosclerotic aortas compared to controls by PET/CT imaging
(figure 3A).
Plaque
targeting. Radioactivity
concentration was significantly higher in atherosclerotic aortas (P = 0.03) as determined by gamma
counting at 5 days p.i. (figure 3A). Autoradiography of explanted aortas revealed
a patchy distribution of radioactivity in atherosclerotic aortas, showing
preferential accumulation in lesions (figure 3B). Analysis by NIRF imaging
showed increased accumulation of Cy5.5-HDL in atherosclerotic aortas (figure 3B).
A good correlation was found between total radiant efficiency and radioactivity
concentration (figures 3C).
DISCUSSION/CONCLUSIONS
Here we demonstrated that
it is possible to investigate the in vivo behavior of
89Zr-HDL's by PET/CT
and PET/MRI. This multimodal imaging approach allows the non-invasive
evaluation of HDL’s trafficking, distribution, metabolism and turnover.
Ultimately, this non-invasive imaging tool may be useful to identify patients
amenable to HDL therapy and subsequent treatment monitoring in a theranostic fashion.
Acknowledgements
This work was supported by 5 R01EB009638 11 and 1 R01HL125703 01.References
1. Lusis AJ. Atherosclerosis. Nature 2000;407:233–41.
2. Tardif J-C, Grégoire J, L’Allier PL, et al.
Effects of reconstituted high-density lipoprotein infusions on coronary
atherosclerosis: a randomized controlled trial. JAMA 2007;297:1675–82.
3. Pérez-Medina C, Abdel-Atti D, Zhang Y, et al. A
Modular Labeling Strategy for In Vivo PET and Near-Infrared Fluorescence
Imaging of Nanoparticle Tumor Targeting. J. Nucl. Med. 2014;55:1706–1712.
4. Perez-Medina C, Tang J, Abdel-Atti D, et al. PET
Imaging of Tumor-Associated Macrophages with 89Zr-labeled HDL Nanoparticles. J.
Nucl. Med. 2015.
5. Calcagno C, Cornily JC,
Hyafil F, Rudd JH, Briley-Saebo KC, Mani V, Goldschlager G, Machac J, Fuster V,
Fayad ZA. Detection of neovessels in atherosclerotic plaques of rabbits using
dynamic contrast enhanced MRI and 18F-FDG PET. Arterioscler Thromb Vasc Biol.
2008 Jul;28(7):1311-7