Carbocyanine labeled LDL for optical imaging of tumors.
OBJECTIVE
The purpose of this study was to define and characterize carbocyanine labeled low-density lipoprotein (LDL) to be used in the optical imaging of LDL receptor (LDLr)-overexpressing tumor models.


METHODS
1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used to label LDL (DiI-LDL). Scatchard plots were generated to determine the maximum binding capacity B(max) and dissociation constants K(D) of DiI-LDL in B16 melanoma (B16) and hepatoblastoma G(2) (HepG(2)) cell lines. Selective uptake of DiI-LDL into both tumor cells and corresponding subcutaneous tumors in mice were demonstrated by confocal microscopy and three-dimensional Cryo-imaging, respectively.


RESULTS
The labeling efficiency of DiI-LDL was 61 ng DiI/microg LDL protein (34 mol DiI/mol LDL protein). B(max) and K(D) for B16 cells were 6.311 ng LDL/mg cell protein and 60.38 microg protein/mL (117 nM), respectively. B(max) and K(D) were 7.573 ng LDL/mg cell protein and 26.79 microg protein/mL (52 nM) for HepG(2) cells, respectively. Confocal microscopic images showed specific uptake of DiI-LDL throughout the cytoplasm in the B16/HepG(2) cells. Cryo-imaging demonstrated preferential accumulations of DiI-LDL in the viable tumor regions of both B16 and HepG(2) tumors compared with their adjacent normal tissues and corresponding necrotic tumor regions. In addition, uptake of DiI-LDL by the HepG(2) tumor was much higher than that of the B16 tumor, consistent with the fact that the probe binding affinity for LDLrs of HepG(2) cells is 2.3 times that of B16 cells.


CONCLUSIONS
This study suggested that carbocyanine labeled LDL could be used for optical imaging of tumors overexpressing LDLr.
Li
Hui
H
Department of Radiology, University of Pennsylvania Medical School, Chemistry 1958 Wing, Room 284, Box 66, 250 South 33rd Street, Philadelphia, PA 19104 USA.
Zhang
Zhihong
Z
Blessington
Dana
D
Nelson
David S
DS
Zhou
Rong
R
Lund-Katz
Sissel
S
Chance
Britton
B
Glickson
Jerry D
JD
Zheng
Gang
G
D000818:Animals; D002232:Carbocyanines; D006801:Humans; D008077:Lipoproteins, LDL; D008114:Liver Neoplasms, Experimental / Q000473:pathology; D008546:Melanoma, Experimental / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D018613:Microscopy, Confocal; D009369:Neoplasms / Q000473:pathology*; D011973:Receptors, LDL / Q000032:analysis; D014407:Tumor Cells, Cultured
D002232:Carbocyanines; D008077:Lipoproteins, LDL; D011973:Receptors, LDL