Receptor-Binding,Biodistribution,and Metabolism Studies of 64 Cu-DOTA-Cetuximab,a PET-Imaging Agent for Epidermal Growth-Factor Receptor-Positive Tumors

Abstract

The epidermal growth-factor receptor (EGFR) and its ligands have been recognized as critical factors in the pathophysiology of tumorigenesis. Overexpression of the EGFR plays a significant role in the tumor progression of a wide variety of solid human cancers. Therefore, the EGFR represents an attractive target for the design of novel diagnostic and therapeutic agents for cancer. Cetuximab (C225, Erbitux ^® ) was the first monoclonal antibody targeted against the ligand-binding site of EGFR approved by the Food and Drug Administration for the treatment of patients with EGFR-expressing, metastatic colorectal carcinoma, although clinical trials showed variability in the response to this treatment. The aim of this study involved using cetuximab to design a positron emission tomography (PET) agent to image the overexpression of EGFR in tumors. Cetuximab was conjugated with the chelator, DOTA, for radiolabeling with the positron-emitter, ⁶⁴Cu (T_1/2 = 12.7 hours). ⁶⁴Cu-DOTA-cetuximab showed high binding affinity to EGFR-positive A431 cells (K_D of 0.28 nM). Both biodistribution and microPET imaging studies with ⁶⁴Cu-DOTA-cetuximab demonstrated greater uptake at 24 hours postinjection in EGFR-positive A431 tumors (18.49% ± 6.50% injected dose per gram [ID/g]), compared to EGFR-negative MDA-MB-435 tumors (2.60% ± 0.35% ID/g). A431 tumor uptake at 24 hours was blocked with unlabeled cetuximab (10.69% ± 2.72% ID/g), suggesting that the tumor uptake was receptor mediated. Metabolism experiments in vivo showed that ⁶⁴Cu-DOTA-cetuximab was relatively stable in the blood of tumor-bearing mice; however, there was significant metabolism in the liver and tumors. ⁶⁴Cu-DOTA-cetuximab is a potential agent for imaging EGFR-positive tumors in humans.