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Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

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[18F]Fluorodipalmitin-labeled liposomes

[18F]FDP-liposomes
, PhD
National Center for Biotechnology Information, NLM, NIH, vog.hin.mln.ibcn@dacim

Created: ; Last Update: May 29, 2008.

Chemical name:[18F]Fluorodipalmitin-labeled liposomes
Abbreviated name:[18F]FDP-liposomes
Synonym:3-[18F]fluoro-1,2-dipalmitoyl glycerol-labeled liposomes
Agent Category:Liposome
Target:Non-targeted
Target Category:Blood pool retention
Method of detection:PET
Source of signal/contrasat:18F
Activation:No
Studies:
  • Checkbox In vitro
  • Checkbox Rodents
No structure is currently available in PubChem.

Background

[PubMed]

Liposomes are double-membrane lipid vesicles (1). They have been widely studied as important carriers in controlling the spatial and temporal distribution of drug molecules or other bioactive molecules for targeted therapy; for example, they have been used as universal carriers of tumor chemotherapeutic agents, as antigen carriers to stimulate immune response, as carriers of nucleic acid for gene therapy, and as carriers of antibiotics for infectious disease treatment (2). There are many studies using 18F-, 99mTc-, 67Ga-, and 111In-labeled liposomes for nuclear imaging, which have shown that radiolabeled liposomes exhibit good accumulation characteristics in tumor, infection, and in vivo inflammation (2). However, these radionuclides were either attached with the use of chelators that were covalently bound to the lipids or encapsulated inside the liposome hydrophilic cavity. Marik et al. (3) developed liposomes by incorporation of [18F]fluorodipalmitin ([18F]FDP) into the phospholipid bilayer to minimize internalization and metabolism in cells. Therefore, the images obtained with the use of [18F]FDP-liposomes could be more reflective of the biodistribution of long-circulating liposomes.

Synthesis

[PubMed]

[18F]FDP was synthesized by nucleophilic substitution of the p-toluenesulfonyl moiety of 3-tosyl-1,2-dipalmitoyl glycerol with [18F]F (3). [18F]KF/Kryptofix 2.2.2/K2CO3 and 3-tosyl-1,2-dipalmitoyl glycerol were heated in acetonitrile to 100°C for 20 min with a decay-corrected yield of 43 ± 10% (n = 12). [18F]FDP was purified with chromatography and exhibited a radiochemical purity of 99%, a total synthesis time of 60 min, and a specific activity >111 GBq/mmol (3 Ci/mmol). Long-circulating radiolabeled polyethylene-glycol–coated liposomes were prepared by adding a CH2Cl2 solution of [18F]FDP to a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, cholesterol, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] (61:30:9). After evaporation of the solvent, phosphate-buffered saline (PBS) was added to the residue and sonicated at 50°C for 10 min. The [18F]FDP-liposomes were purified with gel filtration with a decay-corrected yield of 70 ± 8% (n = 4). The specific activity of the [18F]FDP-liposomes was 884 ± 155 MBq (23.9 ± 4.2 mCi)/mg lipid content (n = 4). The total preparation time was ~60 min. The size of the [18F]FDP-liposomes was 45 ± 18 nm and was stable in PBS at room temperature for 24 h.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

No publication is currently available.

Animal Studies

Rodents

[PubMed]

Marik et al. (3) compared positron emission tomography imaging of [18F]FDP with [18F]FDP-liposomes in normal rats (n = 3) for 90 min after injection. [18F]FDP radioactivity accumulated mainly in the liver (5.5% injected dose (ID)/cc maximum at 5 min), spleen (4.2% ID/cc maximum at 5 min), lung (2.5% ID/cc maximum at 1 min), and blood (3% ID/cc maximum at 1 min) with low kidney accumulation (1% ID/cc maximum at 1 min). No accumulation was observed in the bones and heart. Radioactivity levels in the blood and all tissues were cleared within a few minutes. On the other hand, [18F]FDP-liposomes remained in the blood at near-constant levels for at least 90 min, with a maximum of 2.5% ID/cc at 2 min. [18F]FDP-liposomes quickly reached a plateau in the liver (1% ID/cc), spleen (1% ID/cc), kidney (1% ID/cc), and lung (2% ID/cc) in 2–3 min. The carotid vessels, the blood volume in the atria and ventricles, and the brain vasculature were clearly visualized. Minimal radioactivity was detected in the urinary bladder and heart muscle. No activity was detected in the bones and gut.

Other Non-Primate Mammals

[PubMed]

No publication is currently available.

Non-Human Primates

[PubMed]

No publication is currently available.

Human Studies

[PubMed]

No publication is currently available.

NIH Support

R01 CA103828

References

1.
Torchilin V.P. Liposomes as delivery agents for medical imaging. Mol Med Today. 1996;2(6):242–9. [PubMed: 8796897]
2.
Torchilin V.P. Targeted pharmaceutical nanocarriers for cancer therapy and imaging. Aaps J. 2007;9(2):E128–47. [PMC free article: PMC2751402] [PubMed: 17614355]
3.
Marik J., Tartis M.S., Zhang H., Fung J.Y., Kheirolomoom A., Sutcliffe J.L., Ferrara K.W. Long-circulating liposomes radiolabeled with [18F]fluorodipalmitin ([18F]FDP) Nucl Med Biol. 2007;34(2):165–71. [PMC free article: PMC1849971] [PubMed: 17307124]
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