SILAC-based proteomic approach to delineate molecular alterations associated with erlotinib resistance in head and neck squamous cell carcinoma

Although Epidermal growth factor receptor (EGFR) is overexpressed in 90% of Head and neck squamous cell carcinoma (HNSCC) patients. Clinical trials with EGFR-targeted small molecule inhibitors such as erlotinib have shown a modest activity in recurrent or advanced HNSCC. To investigate the acquired mechanisms of erlotinib resistance we employed SILAC-based total proteomic analysis of an isogenic pair of erlotinib sensitive (SCC-S) and resistant (SCC-R) HNSCC cell line. This resulted in the identification of 5,427 proteins of which 532 proteins were overexpressed and 527 proteins were downregulated in SCC-R cells as compared to SCC-S cells (≥2 fold). Several proteins known to mediate erlotinib resistance in HNSCC and lung cancer were found to be dysregulated. Bioinformatics analysis of differentially expressed proteins showed enrichment of proteins involved in focal adhesion kinase (FAK) pathway downstream of EGFR. We identified CUB-domain containing protein 1 (CDCP1) and integrin β1 as upstream regulators of FAK signalling pathway to be overexpressed. We further demonstrated that CDCP1 and FAK can be targeted in combination as an alternative to erlotinib in HNSCC.