In vivo imaging of mesenchymal-epithelial transition factor (c-Met) expression using an optical imaging system.
Mesenchymal-epithelial transition factor (c-Met) is a receptor tyrosine kinase that has been shown to be overexpressed and mutated in a variety of malignancies, such as glioma. We have recently found that an (125)I-radiolabeled Gly-Gly-Gly (GGG)- or 8-aminooctanoic acid (AOC)-containing c-Met binding peptide (cMBP) specifically targets c-Met receptor in vivo and in vitro. In this report, cyanine dye 5.5 (Cy5.5)-conjugated GGG- or AOC-containing cMBPs were evaluated in human cancer cell xenografts in order to investigate the possibility of c-Met receptor targeting using an optical imaging system. The receptor binding affinity of Cy5.5-conjugated peptides was tested in 96-well plates coated with a c-Met/Fc chimeric protein. Optical imaging studies were performed in U87MG and Ramos bearing athymic mice. The binding affinities of Cy5.5-conjugated GGG- or AOC-containing cMBPs were determined to be 0.318 and 0.342 microM, respectively. Confocal images show that Cy5.5-conjugated peptides bound mainly to the cell surface and that peptide binding was clearly inhibited by free cMBP. Subcutaneous U87MG tumors were clearly visualized with each of the two fluorescent probes. Of the two, cMBP-AOC-Cy5.5 displayed higher tumor uptake and tumor-to-normal tissue ratios at 10 min to 24 h postinjection in the U87MG tumor model. For the in vivo blocking study, cMBP-AOC-Cy5.5 (4 nmol) was co-injected with cold cMBP (0.13 micromol) into the U87MG xenograft mice. Image-based tumoral uptake decreased up to approximately 35%. These results suggest that Cy5.5-conjugated cMBP could potentially be used to detect c-Met-positive cancers in vivo. However, additional modifications to this optical imaging agent are needed to further improve its efficacy.
Kim
Eun-Mi
EM
Department of Nuclear Medicine, Research Institute of Clinical Medicine, Cyclotron Research Center, Chonbuk National University Medical School and Hospital, Jeonju, Jeonbuk, Republic of Korea.
Park
Eun-Hye
EH
Cheong
Su-Jin
SJ
Lee
Chang-Moon
CM
Jeong
Hwan-Jeong
HJ
Kim
Dong Wook
DW
Lim
Seok Tae
ST
Sohn
Myung-Hee
MH
D000818:Animals; D002210:Caprylates / Q000138:chemical synthesis / Q000737:chemistry; D002232:Carbocyanines / Q000138:chemical synthesis / Q000737:chemistry; D045744:Cell Line, Tumor; D003952:Diagnostic Imaging / Q000379:methods*; D005260:Female; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D018613:Microscopy, Confocal; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000175:diagnosis*; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D019859:Proto-Oncogene Proteins c-met / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics
D002210:Caprylates; D002232:Carbocyanines; D005456:Fluorescent Dyes; D009842:Oligopeptides; D010455:Peptides; D012333:RNA, Messenger; C085321:cyanine dye 5; C046323:omega-aminocaprylic acid; C035647:glycyl-glycyl-glycine; D019859:Proto-Oncogene Proteins c-met