Epidermal growth factor receptor targeting using cetuximab labeled ultrasound contrast agents — A feasibility study

This paper details the potential of cetuximab (C225) labeled microbubbles (MBs) to improve ultrasound (US) imaging of head and neck squamous cell carcinoma (HNSCC). C225 is a therapeutic monoclonal antibody to the epidermal growth factor receptor (EGFR) and currently approved for the treatment of recurrent HNSCC. Conjugating C225 to the surface of US MBs produces a targeted contrast agent that selectively binds to over expressed EGFR on the tumor endothelium to improve visualization and therapeutic monitoring. Analysis of targeted MB binding in vitro was performed using SCC-1 and normal dermal fibroblasts (NDF) cell lines. Cells were incubated with MBs conjugated to either C225 or IgG isotype control antibodies. Light microscopy was used to quantify MB receptor binding. Attached MB were normalized by cell count and recorded for each group. To evaluate C225-labeled MBs in an animal model, SCC-1 cells were implanted in the flank of nude athymic mice (N 8). MBs labeled with C225 or control antibodies were administered via a bolus tail vein injection and tumors were examined using a MB sensitive harmonic imaging mode. For each tumor, US images from the targeted and control groups were paired and assessed by a blinded reviewer to determine greatest degree of intratumoral contrast enhancement. MBs labeled with C225 exhibited significantly higher SCC-1 cell attachment levels relative to control group measurements (p 0.001). Specifically, the mean number of attached MBs per cell was 3.6 ± 0.7 and 0.7 ± 0.1 for the C225and control antibody-labeled groups, respectively, yielding nearly a 6-fold difference. Given presentation of paired animal data, it was determined that 75% (6 of 8) of the US images from the C225 labeled MB experimental day exhibited increased enhancement compared to the same animals administered control MBs. This study demonstrates feasibility of targeted US imaging of HNSCC using cetuximab-labeled MBs.