Inhibition of EGFR-dependent Oral Cancer Cells With Fendiline

Objectives: The epidermal growth factor receptor (EGFR) is often over-expressed or mutated in human tumors, including 50% of oral squamous cell carcinomas (OSCC). Cetuximab, a monoclonal antibody against EGFR, is currently in clinical use for the treatment of OSCC; however, response rates and survival durations with cetuximab remain low. Therefore, there is an unmet need for discovery of effective inhibitors of EGFR. Proper localization of EGFR on the plasma membrane (PM) is essential for its function and is regulated by cholesterol. Goals of our study were to determine effects of fendiline, a previously used anti-anginal agent that depletes PM cholesterol, on localization and signaling of EGFR and characterize inhibition of proliferation and clonogenic survival of OSCC cell lines by fendiline.
Methods: Confocal microscopic analysis of CHO and CaCO-2 cells stably expressing GFP-tagged human EGFR was carried out to determine effects of fendiline on EGFR localization. Western blot analysis, CyQUANT® cell proliferation assay and clonogenic survival assay were utilized to determine the effects of drug treatment on cell signaling, proliferation, and ability to form clones, respectively.
Results: Our results show the following important findings: (1) Fendiline causes mislocalization of EGFR from the PM to the cytoplasm in CHO and CaCO-2 with or without EGF stimulation; (2) Fendiline inhibits signaling of EGFR in CHO and EGFR-overexpressing OSCC cell line SCC-25 when activated with EGF; (3) Fendiline is more potent in inhibiting proliferation of EGFR-dependent OSCC cell lines compared to erlotinib (a clinically used EGFR inhibitor) or FTI-276 (inhibitor of H-Ras, a downstream effector of EGFR); (5) Fendiline, although not as potent as erlotinib, inhibits clonogenic survival of EGFR-dependent OSCC cells.
Conclusions: Fendiline inhibits EGFR-mediated cell signaling, proliferation and clonogenic survival of OSCC cell lines. This study identifies a novel mode of inhibition of EGFR and demonstrates that fendiline is a viable treatment option for EGFR-dependent OSCC.