A nucleolin-targeted multimodal nanoparticle imaging probe for tracking cancer cells using an aptamer.
The recent advances in molecular imaging techniques, using cancer-targeting nanoparticle probes, provide noninvasive tracking information on cancer cells in living subjects. Here, we report a multimodal cancer-targeted imaging system capable of concurrent fluorescence imaging, radionuclide imaging, and MRI in vivo.


METHODS
A cobalt-ferrite nanoparticle surrounded by fluorescent rhodamine (designated MF) within a silica shell matrix was synthesized with the AS1411 aptamer (MF-AS1411) that targets nucleolin (a cellular membrane protein highly expressed in cancer) using N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC). This purified MF-AS1411 particle was bound with 2-(p-isothio-cyanatobenzyl)-1,4,7-triazacyclonane-1,4,7-triacetic acid (p-SCN-bn-NOTA) chelating agent and further labeled with (67)Ga-citrate (MFR-AS1411). The shape and size distribution of MFR-AS1411 were characterized by transmission electron microscope (TEM). The cellular distribution of the nucleolin protein using the MFR-AS1411 nanoparticle was detected by fluorescence confocal microscopy. Phantom MR images were obtained as the concentration of MFR-AS1411 increased, using a 1.5-T MRI scanner. In vivo (67)Ga radionuclide imaging and MRI were performed using a gamma-camera and a 1.5-T MR imager, respectively.


RESULTS
TEM imaging revealed MF and MFR-AS1411 to be spheric and well dispersed. The purified MFR-AS1411 nanoparticle showed specific fluorescence signals in nucleolin-expressing C6 cells, compared with MFR-AS1411 mutant (MFR-AS1411mt)-treated C6 cells. The rhodamine fluorescence intensity and (67)Ga activity of MFR-AS1411 were enhanced in a dose-dependent manner as the concentration of MFR-AS1411 was increased. The (67)Ga radionuclide was detected in both thighs of the mice injected with MFR-AS1411, whereas the MFR-AS1411 mutant (MFR-AS1411mt) administration revealed rapid clearance via the bloodstream, demonstrating that MFR-AS1411 specifically targeted cancer cells. Bioluminescence images in the C6 cells, stably expressing the luciferase gene, illustrated the in vivo distribution. T2-weighted MR images of the same mice injected with MFR-AS1411 showed dark T2 signals inside the tumor region, compared with the MRI signal of the tumor region injected with MFR-AS1411mt particles.


CONCLUSIONS
We developed a nanoparticle-based cancer-specific imaging probe using the AS1411 aptamer in vivo and in vitro. This multimodal targeting imaging strategy, using a cancer-specific AS1411 aptamer, can be used as a versatile imaging tool for specific cancer diagnosis.
Hwang
Do Won
DW
Program in Neuroscience, Seoul National University, Seoul, Korea.
Ko
Hae Young
HY
Lee
Jung Hwan
JH
Kang
Hyungu
H
Ryu
Sung Ho
SH
Song
In Chan
IC
Lee
Dong Soo
DS
Kim
Soonhag
S
D000818:Animals; D052157:Aptamers, Nucleotide; D045744:Cell Line, Tumor; D002951:Citrates; D015195:Drug Design; D005456:Fluorescent Dyes; D005708:Gallium; D005910:Glioma / Q000000981:diagnostic imaging / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D051379:Mice; D008819:Mice, Nude; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D009369:Neoplasms / Q000000981:diagnostic imaging*; D009838:Oligodeoxyribonucleotides; D019047:Phantoms, Imaging; D010750:Phosphoproteins / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D051381:Rats; D012235:Rhodamines; D000097796:Nucleolin
D052157:Aptamers, Nucleotide; D002951:Citrates; D005456:Fluorescent Dyes; D005708:Gallium; D009838:Oligodeoxyribonucleotides; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D019275:Radiopharmaceuticals; D012235:Rhodamines; D000097796:Nucleolin; C513936:AGRO 100; C103850:gallium citrate