In Vivo Visualization of MET Tumor Expression and Anticalin Biodistribution with the MET-Specific Anticalin ⁸⁹Zr-PRS-110 PET Tracer

Abstract

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. Methods: 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. Results: 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 METexpressing 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. Conclusion: 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.

c-Met PET Imaging Detects Early-Stage Locoregional Recurrence of Basal-Like Breast Cancer

“…89 Zr-db-/ 76 Brornartuzumab and 89 Zr-PRS-110 were developed and assessed for visualization of c-Met-positive tumors in preclinical models (28,29). Optimal imaging time points were identified to be between 2 and 5 d after tracer administration, thus hampering potential routine clinical use as diagnostic agents.…”

Analysis of progress and challenges for various patterns of c-MET-targeted molecular imaging: a systematic review

“…Terwisscha van Scheltinga et al engineered PRS-110, an anticalin with monovalent specificity for c-MET (binding affinity of 0.6 nmol/L), which is site-specifically conjugated to a branched 40-kDa polyethyleneglycol (PEG) (2 · 20 kDa PEG) moiety for half-life prolongation [73, 74]. A phase I trial in cancer patients supports the use of the anticalin drug platform for broad therapeutic and diagnostic applications [75].…”

Biomarkers in preclinical cancer imaging

“…MET imaging has been pursued using different targeting moieties and different imaging labels. For example, anticalins and antibodies have been used to generate PET tracers for this receptor [137, 138]. Both show activity in vitro and in mouse tumour models.…”