Imaging of urokinase-type plasminogen activator receptor expression using a 64Cu-labeled linear peptide antagonist by microPET.
OBJECTIVE
Malignant tumors are capable of degrading the surrounding extracellular matrix, resulting in local invasion or metastasis. Urokinase-type plasminogen activator (uPA) and its cell surface receptor (uPAR) are central molecules in one of the major protease systems involved in extracellular matrix degradation. Noninvasive imaging of this receptor in vivo with radiolabeled peptides that specifically target uPAR may therefore be useful to decipher the potential invasiveness of malignant lesions.


METHODS
In this study, we developed a (64)Cu-labeled uPAR-binding peptide for positron emission tomography (PET) imaging. A linear, high-affinity uPAR-binding peptide antagonist AE105 was conjugated with 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA) and labeled with (64)Cu for microPET imaging of mice bearing U87MG human glioblastoma (uPAR positive) and MDA-MB-435 human breast cancer (uPAR negative).


RESULTS
Surface plasmon resonance measurements show that AE105 with DOTA conjugated at the alpha-amino group (DOTA-AE105) has high affinity toward uPAR. microPET imaging reveals a rapid and high accumulation of (64)Cu-DOTA-AE105 in uPAR-positive U87MG tumors (10.8 +/- 1.5%ID/g at 4.5 hours, n = 3) but not in uPAR-negative MDA-MB-435 tumors (1.2 +/- 0.6%ID/g at 4.5 hours, n = 3). Specificity of this peptide-based imaging of uPAR was validated by further control experiments. First, a nonbinding variant of AE105 carrying a single amino acid replacement (Trp-->Glu) does not target U87MG tumors in vivo. Second, targeting of U87MG tumors by (64)Cu-DOTA-AE105 is specifically inhibited by a nonlabeled antagonist.


CONCLUSIONS
The successful demonstration of the ability of a (64)Cu labeled uPAR-specific probe to visualize uPAR expression in vivo may allow clinical translation of this class of radiopharmaceuticals for uPAR-positive cancer detection and patient stratification for uPA/uPAR system-based cancer therapy.
Li
Zi-Bo
ZB
Molecular Imaging Program at Stanford, Department of Radiology and Bio-X Program, Stanford University School of Medicine, Stanford, California 94305-5484, USA.
Niu
Gang
G
Wang
Hui
H
He
Lina
L
Yang
Lily
L
Ploug
Michael
M
Chen
Xiaoyuan
X
D000818:Animals; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes / Q000737:chemistry; D005260:Female; D006573:Heterocyclic Compounds, 1-Ring / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010455:Peptides / Q000737:chemistry; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D011956:Receptors, Cell Surface / Q000096:biosynthesis*; D055293:Receptors, Urokinase Plasminogen Activator; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020349:Surface Plasmon Resonance
D003301:Copper Radioisotopes; D006573:Heterocyclic Compounds, 1-Ring; C524898:PLAUR protein, human; D010455:Peptides; C524899:Plaur protein, mouse; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid