TU‐G‐134‐04: Multifunctional Molecular Probes for Targeting and Imaging of Epidermal Growth Factor Receptors in Vivo

Abstract

Purpose: To demonstrate the epidermal growth factor receptor (EGFR) targeting specificity in‐vivo of a multifunctional molecular probe by combining receptor‐targeting monoclonal antibody (mAb) with the positive contrast agent Gadolinium (Gd) in dendrimer nanoclusters. Methods: The molecular probe comprised two functional subunits: anti‐EGFR antibodies for tumor targeting and dendrimer nanoclusters (DNCs) loaded with Gd for MRI contrast. DNCs were formed by crosslinking G5 dendrimers using Bis‐N‐succinimidyl‐(pentaethylene glycol) ester and sulfo‐NHS‐LC‐biotin. DiethyleneTriaminePentaacetic Acid (DTPA) anhydride was used to bind Gd to the DNC in alkaline conditions. Biotinylated anti‐EGFR mAb(C225) was mixed with the DNC, followed by the addition of avidin, a cross‐linker that facilitates probe synthesis. The probe was injected through the tail vein into nude mice that were subcutaneously implanted with human head and neck cancer (TU159) xenografts. A 3‐dimensional FLASH‐MRI time course study was performed on a 7T scanner, such that volumetric images were acquired every minute in the first 5 min after the injection, every 5 min in the first hour, and after 4 hours. Region of interest (ROI) analysis was performed using ImageJ. Results: An increase in image contrast was observed in the ROI corresponding to the targeted tumor following the tail vein injection of the probe. The time course study showed that the image contrast (IC) at the target region increased substantially in the first 5 min after probe injection and was stable through the first 240 min. In a control experiment, the IC increase was observed on the mouse with the same injected dose of gadodiamine; however in this case, IC subsided after the first 30 min. Conclusion: The molecular nanoprobe is able to 1) selectively target the EGF receptors in vivo and 2) allow drug uptake to be imaged while using less toxic probe doses.