Background The purpose of this study was to identify mechanisms of innate resistance to an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, erlotinib, in a panel of head and neck squamous cell carcinoma (HNSCC) cell lines. Specifically, we analyzed the role of HRAS mutations in erlotinib resistance. Methods Erlotinib sensitivity was determined by methyl thiazolyl-tetrazolium (MTT) assays. Molecular signaling pathways and somatic mutations were examined. Changes in sensitivity after modulation of HRAS expression were evaluated. Results All 7 cell lines were wild-type for EGFR and KRAS regardless of erlotinib sensitivity; however, 1 erlotinib-resistant cell line (HN31) harbored an HRAS G12D mutation. Downregulation of HRAS expression by small interfering RNA (siRNA) or short hairpin RNA (shRNA) in HN31 led to increased erlotinib sensitivity in vitro and in vivo. Transfection of activating HRAS-mutant (G12D and G12V) constructs into erlotinib-sensitive cell lines made them more resistant to erlotinib. Conclusion Activating HRAS mutations can confer erlotinib resistance in an HRAS mutant HNSCC cell line.
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