Abstract 2664: Next generation PET imaging agents: The development of radiolabeled c-Met specific Anticalin 89Zr-PRS-110 with diagnostic and therapeutic drug monitoring applications.
Authors: Terwisscha van Scheltinga Anton G.T. , de Vries Elisabeth G.E. , Hinner Marlon , Verheijen Remy B. , Allesdorfer Andrea , Audoly Laurent , Nagengast Wouter B. , Schröder Carolien P. , Hülsmeyer Martin , Kosterink Jos G.W. , Lub-de Hooge Marjolijn N. , Olwill Shane A. 
Published: August 2014

Abstract
The oncogene c-Met is a clinically validated target having been shown to be involved in tumorigenesis. Imaging agents capable of quantifying c-Met expression in human tumors would be a valuable tool for aiding diagnosis, drug scheduling and monitoring the response to targeted therapies. Anticalins are a novel class of biopharmaceuticals based on the human lipocalin scaffold with many properties which make them desirable imaging agents including their smaller size and ease of manufacturing when compared to antibodies. PRS-110 is a c-Met specific anticalin which is being developed as a therapeutic and imaging modality. The aim of this study was to evaluate the utility of the c-Met anticalin as a positron emission tomography (PET) imaging agent and analyze its biodistribution in human tumor bearing mice.
Methods: A zirconium-89 (89Zr) labeled version of PRS-110 was generated and biodistribution studies were performed 96 h after single dose injection of the tracer (10 to 500 μg) into Balb/c mice bearing subcutaneous c-Met expressing human H441 non-small cell lung cancer tumors. PET imaging was executed at 6, 24, 48 and 96 h after injection of 50 μg 89Zr-PRS-110 to mice bearing H441 (c-Met ++), primary glioblastoma U87-MG (c-Met +) or ovarian cancer A2780 (c-Met -) xenografts. After the final scan, biodistribution analysis was performed. The excised tumors were analyzed for c-Met expression by immunohistochemistry and fluorescent PRS-110-800CW distribution by fluorescence microscopy.
Results: Biodistribution analyses showed a PRS-110 dose-dependent 89Zr-PRS-110 H441-tumor uptake, with the highest tumor uptake at 10 μg PRS-110 resulting in 7.5 %ID/g at 96 h after tracer injection. MicroPET imaging revealed specific tumor uptake of 89Zr-PRS-110 in the c-Met expressing H441 and U87 tumors while imaging of the c-Met negative A2780 tumor model showed background level similar to a non-specific anticalin control. Biodistribution data supported the microPET findings, showing ex vivo tumor uptake of 89Zr-PRS-110 of 5.9, 1.8 and 1.7 %ID/g in H441, U87 and A2780 xenografts respectively, which correlated with c-Met expression levels. Tumor : blood ratios of 89Zr-PRS-110 compared to 89Zr-Tlc-PEG confirmed these finding. Ex vivo fluorescence revealed intracellular presence of PRS-110 96 h after tracer injection.
Conclusion: 89Zr-PRS-110 specifically accumulates in c-Met expressing tumors. PET imaging with this tracer provides real-time non-invasive information about PRS-110 distribution and tumor accumulation. This makes 89Zr-PRS-110, which is ready for clinical evaluation, of interest for the clinical development of PRS-110.
Citation Format: Anton G.T. Terwisscha van Scheltinga, Elisabeth G.E. de Vries, Marlon Hinner, Remy B. Verheijen, Andrea Allesdorfer, Laurent Audoly, Wouter B. Nagengast, Carolien P. Schröder, Martin Hülsmeyer, Jos G.W. Kosterink, Marjolijn N. Lub-de Hooge, Shane A. Olwill. Next generation PET imaging agents: The development of radiolabeled c-Met specific Anticalin 89Zr-PRS-110 with diagnostic and therapeutic drug monitoring applications. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2664. doi:10.1158/1538-7445.AM2013-2664