Quantification of CD44v6 and EGFR expression in head and neck squamous cell carcinomas using a single-dose radioimmunoassay

Background: In the growing field of tumor targeting, there is an urgent need to profile suitable molecular targets. In this study, CD44v6 and EGFR expression was quantified in samples of patients with head and neck squamous cell carcinoma (HNSCC) using a single-dose (SD) radioimmunoassay. Methods: The SD radioimmunoassay using ¹²⁵I-chimeric monoclonal antibody (cMAb) U36 and ¹²⁵I-cMAb cetuximab was first validated and then applied to quantify the expression of their target antigen molecules, CD44v6 and EGFR, in patient samples. Results were compared to immunohistochemical staining. Results: The SD assay provided sensitive quantitative values of the molecular targets studied, generally agreeing with the immunohistochemistry (IHC) results. The results indicated that expression of CD44v6 (0.2-20 nmol/μg membrane) was generally higher than that of EGFR (0.6-2.3 nmol/μg membrane) in the tumor samples analyzed, which corresponded to an average of 700,000 and 90,000 antigen molecules per cell, respectively. Conclusions: The SD radioimmunoassay is simple, reliable, and can be performed on a small amount (50 mg) of tissue. This assay could be a useful tool in the growing field of personalized cancer therapy, and can be used as a complement to IHC. In the tumors studied, CD44v6 was generally expressed at a higher level than EGFR, which might suggest that it could be more readily targeted by MAbs.