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J Nucl Med. 2014 Apr;55(4):665-71. doi: 10.2967/jnumed.113.124941. Epub 2014 Mar 10.

In vivo visualization of MET tumor expression and anticalin biodistribution with the MET-specific anticalin 89Zr-PRS-110 PET tracer.

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Department of Medical Oncology, University of Groningen, University Medical Center Groningen, The Netherlands.


Anticalins are a novel class of biopharmaceuticals, displaying highly desirable attributes as imaging agents. The anticalin PRS-110 was rationally engineered to target the oncogene MET with high affinity and specificity. The aim of this study was to visualize MET expression and analyze biodistribution of (89)Zr-labeled PRS-110 in human tumor-bearing mice.


(89)Zr-PRS-110 was generated. For biodistribution studies (96 h after injection of tracer) 10 μg of (89)Zr-PRS-110 (with 0-490 μg of unlabeled PRS-110) were injected into BALB/c mice bearing high MET-expressing H441 non-small cell lung cancer xenografts. Further characterization with PET imaging was performed at 6, 24, 48, and 96 h after injection of 50 μg of (89)Zr-PRS-110 into mice bearing H441, primary glioblastoma U87-MG (intermediate MET), or ovarian cancer A2780 (low MET) xenografts. Drug distribution was also analyzed ex vivo using fluorescently labeled PRS-110.


Biodistribution analyses showed a dose-dependent tumor uptake of (89)Zr-PRS-110, with the highest fractional tumor uptake at 10 μg of (89)Zr-PRS-110, with no unlabeled PRS-110. Small-animal PET imaging supported by biodistribution data revealed specific tumor uptake of (89)Zr-PRS-110 in the MET-expressing H441 and U87-MG tumors whereas the MET-negative A2780 tumor model showed a lower uptake similar to a non-MET binder anticalin control. Tumor uptake increased up to 24 h after tracer injection and remained high, whereas uptake in other organs decreased over time. Ex vivo fluorescence revealed intracellular presence of PRS-110.


(89)Zr-PRS-110 specifically accumulates in MET-expressing tumors in a receptor density-dependent manner. PET imaging provides real-time noninvasive information about PRS-110 distribution and tumor accumulation in preclinical models.


89Zr; MET; PET; anticalins

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