64Cu-Labeled tetraiodothyroacetic acid-conjugated liposomes for PET imaging of tumor angiogenesis
Introduction
Nanoparticles have been utilized for molecular imaging due to their unique characteristics that allow delivery of bioactive molecules to target tissues by carrying them inside or conjugating them to a large surface area. Nuclear imaging provides highly sensitive and quantitative information on biochemical and physiological changes in vivo. The benefits of combining these properties have led to increased uses for nuclear imaging using radiolabeled nanoparticles including liposomes, metals, quantum dots, carbon nanotubes, dendrimers and others [1], [2].
Liposomes are nanoparticles composed of phospholipids and have long been used for drug delivery. For the last three decades, liposomes have been used in nuclear imaging by encapsulating radioisotopes or labeling radioisotopes on their surfaces [3]. 99mTc, 111In, 67Ga, 18F, and 64Cu-labeled liposomes were used to study pharmacokinetics or to visualize tumors, infection, or cardiovascular abnormalities by SPECT or PET imaging [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. Among them, 111In-loaded or 111In-DTPA-PEG-labeled liposomes showed potential for the in vivo imaging of various human tumors [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17].
Liposomes are also excellent candidates for molecular imaging because of easy modification with various functionalities and, perhaps most importantly, their biocompatibility. It has been reported that liposomes could preferentially penetrate into neovasculature of tumor tissues and retain in the tissues [18], which is termed as an enhanced permeation and retention (EPR) effect. Furthermore, distribution of liposomes to tumor tissues can be enhanced by conjugation with molecules such as antibodies, proteins, peptides, or small ligands with high binding affinities to antigens or receptors which are over-expressed in certain tumors [19], [20], [21], [22], [23], [24]. As such, small anti-angiogenic molecules with high binding affinity to the integrin αVβ3 can be good candidates for the targeted delivery of liposomes to integrin αVβ3-expressing tumor tissues.
Angiogenesis is associated with integrin αVβ3, which mediates adhesion, migration, proliferation, differentiation, and survival of endothelial cells and is found to be over-expressed on tumor endothelial cells [25], [26]. Because of this important role, integrin αVβ3 has been the key molecular imaging target for tumor angiogenesis imaging. Cyclic Arg-Gly-Asp (RGD), an integrin αVβ3 antagonist, has been developed as nuclear imaging probes for monitoring the expression of the integrin αVβ3, and some of them showed promising outcomes in animal models and patients [27], [28]. It was also reported that integrin αVβ3 has a binding site for thyroid hormone (T4), which was supported by the strong binding of T4 to integrin αVβ3 (Kd = 333 pM) as well as T4-induced phosphorylation of MAPK and angiogenesis [29]. The binding of T4 to integrin αVβ3 was inhibited by 3,3′5,5′-tetraiodothyroacetic acid (tetrac), RGD peptide, and αVβ3 antibody, suggesting that the T4 binding site may be located at or near the RGD recognition site [29]. Tetrac, a thyroid hormone derivative, was shown to have anti-angiogenic activity by binding to the cell surface receptor for T4 on integrin αVβ3 [30]. It was also shown that tetrac inhibited tumor growth and tumor angiogenesis in renal cell carcinoma xenografted mice and in human medullary thyroid carcinoma xenografted mice [31], [32]. Moreover, tetrac-conjugated nanoparticles consisting of poly(lactide-co-glycolide) were reported to provide antitumor activity similar to tetrac in animal models [31], [32]. A recent study demonstrated that tetrac-conjugated liposomes inhibited tumor growth and thus increased survival of A375 tumor-bearing mice compared to control liposomes when edelfosine, an alkyl lysophospholipid-based anticancer drug, was loaded into both liposomes [33]. Thus, this previous study supports tetrac's key role in enhancing drug delivery to tumors.
The diagnosis of tumor tissues with the high sensitivity and specificity of PET imaging is crucial for the early and accurate detection of tumors. The PET-based detection of tumor tissues, however, still suffers from the lack of probes that can differentiate tumors from normal tissues. Given that tetrac may serve as a ligand that provides enhanced drug delivery to tumors, we hypothesized that tetrac-conjugated liposomes could be useful for PET imaging of tumors.
In the present study, we prepared 64Cu-labeled tetrac-conjugated liposomes and evaluated them for tumor angiogenesis imaging using PET (Fig. 1).
Section snippets
Materials and equipment
1,4,7,10-Tetraazacyclododecane-N,N′,N″,N′″-tetraacetic acid (DOTA)-NHS ester was purchased from Macrocyclics (Dallas, TX, USA). 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethyleneglycol)-2000] (DSPE-PEG-NH2), DSPE-N[methoxy(polyethylene glycol)-2000] (DSPE-mPEG), egg l-α-phosphatidylcholine (PC), egg l-α-phosphatidyl-dl-glycerol (PG), and cholesterol (Chol) were purchased from Avanti Polar Lipids (Alabaster, AL, USA). 64CuCl2 and U87MG human glioblastoma cells were kindly
Synthesis of tetrac/DOTA- and DOTA-conjugated liposomes
Tetrac-PEG-DSPE and DOTA-PEG-DSPE were synthesized (Fig. 2A and B) and identified by MALDI-TOF mass spectrometry, which showed repeating patterns of molecular ions by 44 mass units, a characteristic mass distribution of PEG (Fig. 2C and D) [35]. The unreacted DSPE-PEG-NH2 (molecular weight: 2772.7711 Da) was not detected based on the mass spectrometric analysis data (Fig. 2C and D). Further HPLC analysis showed that purity of tetrac-PEG-DSPE and DOTA-PEG-DSPE was 87.9% and 89.1%, respectively.
Discussion
Recent studies showed that radiolabeled liposomes containing tumor-targeting molecules provide superior tumor uptake compared to control liposomes, indicating an important role of the tumor-targeting molecules in liposomes. 111In-labeled 2C5 antibody-PEG-liposomes had faster and higher tumor uptake than control PEG-liposomes or IgG-PEG-liposomes in 4T1 and LLC tumor-bearing mice, with higher tumor to non-target uptake ratios (tumor/muscle = 16.3 vs. 6.8–7.4; tumor/liver = 0.45 vs. 0.24–0.26) [8].
Conclusion
This study showed that tetrac/64Cu-DOTA-liposomes had higher uptake by HAECs, clear in vivo visualization of tumors in microPET images, and significantly enhanced tumor uptake in tissue distribution, compared to 64Cu-DOTA-liposomes. Moreover, the in vitro endothelial cell binding result was consistent with the in vivo microPET imaging and tissue distribution data of U87MG tumor-bearing mice. Although tumor uptake of tetrac/64Cu-DOTA-liposomes is comparable to that of [18F]galacto-RGD, the most
Acknowledgments
We thank Mr. Hunnyun Kim for operating the microPET imaging system. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF-2011-0030164).
References (45)
- et al.
Radiolabeled liposomes for scintigraphic imaging
Prog Lipid Res
(2000) - et al.
Development of a liposome-encapsulated radionuclide with preferential tumor accumulation – the choice of radionuclide and chelating ligand. Int J Radiat Appl Instrum Part B
Nucl Med Biol
(1992) - et al.
Long-circulating liposomes radiolabeled with [18F]fluorodipalmitin ([18F]FDP)
Nucl Med Biol
(2007) - et al.
PET imaging of brain cancer with positron emitter-labeled liposomes
Int J Pharmaceut
(2011) - et al.
Positron emission tomography imaging of the stability of Cu-64 labeled dipalmitoyl and distearoyl lipids in liposomes
J Control Release
(2011) - et al.
64Cu loaded liposomes as positron emission tomography imaging agents
Biomaterials
(2011) - et al.
Synthesis and evaluation of a novel lipid–peptide conjugate for functionalized liposome
Bioorg Med Chem Lett
(2007) - et al.
Targeted delivery of doxorubicin using stealth liposomes modified with transferrin
Int J Pharmaceut
(2009) - et al.
Delivery of zoledronic acid encapsulated in folate-targeted liposome results in potent in vitro cytotoxic activity on tumor cells
J Control Release
(2010) - et al.
Tetraiodothyroacetic acid-tagged liposomes for enhanced delivery of anticancer drug to tumor tissue via integrin receptor
J Control Release
(2012)
Cholesterol, phospholipids, and fatty acids of normal immature neutrophils: comparison with acute myeloblastic leukemia cells and normal neutrophils
J Lipid Res
Targeted delivery of doxorubicin using stealth liposomes modified with transferrin
Int J Pharm
A multifunctional envelope type nano device (MEND) for gene delivery to tumours based on the EPR effect: a strategy for overcoming the PEG dilemma
Adv Drug Deliv Rev
Intracellular targeting delivery of liposomal drugs to solid tumors based on EPR effects
Adv Drug Deliv Rev
Targeted drug delivery to tumors: myths, reality and possibility
J Control Release
The advantages of nanoparticles for PET
J Nucl Med
Nanoplatforms for targeted molecular imaging in living subjects
Small
Labeling of preformed liposomes with Ga-67 and Tc-99m by chelation
J Nucl Med
Possible application of phospholipid vesicles (liposomes) in diagnostic radiology
J Nucl Med Allied Sci
Tumor uptake of 67Ga-carrying liposomes
Eur J Nucl Med
Enhanced accumulation of long-circulating liposomes modified with the nucleosome-specific monoclonal antibody 2C5 in various tumours in mice: gamma-imaging studies
Eur J Nucl Med Mol Imaging
Biodistribution of immunoliposome labeled with Tc-99m in tumor xenografted mice
Ann Nucl Med
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2020, Journal of Pharmaceutical SciencesCitation Excerpt :Targeted drug delivery using nanoparticles, such as polymeric micelles,1 liposomes,2 and dendrimers,3 are required to enhance therapeutic effects and reduce systemic side effects in the treatment of various diseases. To evaluate the kinetic properties of nanoparticles, various imaging methods, such as positron emission tomography (PET), single-photon emission computed tomography (SPECT), X-ray computed tomography (CT), and fluorescence imaging, are used.4-7 Although PET, SPECT, and X-ray CT facilitate non-invasive live imaging because of the high tissue penetration of radiation, microscale observation is difficult owing to their low resolution.8