Abstract 279: Small interfering RNA targeting CD44 blocks EGFR signaling in head and neck squamous cell carcinoma (HNSCC)

Abstract

Abstract INTRODUCTION: Head and Neck Squamous Cell Carcinoma (HNSCC) is a disease that accounts for 90% of the 600,000 new diagnoses of head and neck cancers worldwide each year. CD44 is a purported cancer stem cell (CSC) marker, and its colocalization with EGFR has been proposed to activate tyrosine kinase (TK) and mitogen-activated protein kinase (MAPK). Therapies tend to have dismal cure rates. Understanding the interaction between CD44 and EGFR may result in improved therapies for HNSCC. METHODS: To evaluate the effect of CD44 on EGFR, we inhibited CD44 expression in a CD44-overexpressing HNSCC cell line, CAL27, using the siRNA method. The cell line was stably transfected with a DNA plasmid designed to knock down the expression of CD44. We then performed western blots examining CD44 and phosphorylated EGFR (Y1068) in siRNA knockdown clones and in scrambled sequence, followed by implantation of the CD44siRNA clones and scramble controls in nude mice. The mice were sacrificed, and the tumors were embedded in paraffin for IHC analysis. CD44 and EGFR colocalization was examined in 5 HNSCC cases and in CAL 27 xenografts by immunohistochemistry (IHC) and laser scanning confocal microscopy (LSCM). RESULTS: Downregulation of CD44 by siRNA in CAL 27 cells inhibited constitutive EGFR phosphorylation in vitro and in vivo. Knocking down of CD44 by siRNA reduced the tumor growth in mice compared to CAL 27 and scrambled siRNA. CD44 and EGFR coexpression and colocalization were observed in 80% (4/5) of HNSCC cases and in CAL 27 xenografts. CONCLUSION: Based on these studies, targeting CD44 may provide an additional therapeutic option for HNSCC that does not respond favorably to other treatments. Anti- CD44 therapy in HNSCC may target the cancer stem cell population and alter EGFR signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 279. doi:1538-7445.AM2012-279