Role of EGFR but not HER2 or HER3 gene copy number in predicting sensitivity of head and neck squamous cell carcinoma (SCCHN) cell lines to EGFR tyrosine kinase inhibitors

Abstract

6063 Background: EGFR gene copy number has previously been reported to predict for improved overall survival in NSCLC patients treated with gefitinib (IRESSA) or erlotinib compared with placebo [JCO 2006;24:5034–42 & N Engl J Med 2005;353:133–44]. The utility of EGFR gene copy number as a predictive biomarker in other tumour types such as squamous cell carcinoma of the head and neck (SCCHN) is currently under clinical investigation. The present study examined a panel of 20 SCCHN cell lines to identify potential biomarkers predicting in vitro sensitivity to EGFR tyrosine kinase inhibitors (TKIs). Methods: A panel of 20 SCCHN cell lines was screened for sensitivity to gefitinib, vandetanib or erlotinib using a viable cell number endpoint, with G150 values determined for each cell line (inhibitor concentration required to give 50% growth inhibition). Cell lines were blinded and assessed for EGFR, HER2 and HER3 protein expression by ELISA, mutation status by dye-terminator sequencing, and gene copy number by fluorescence in situ hybridisation (FISH). Results: A broad range in sensitivity was observed for all compounds across the panel of 20 SCCHN cell lines (G150 ranging from 0.001uM to =10uM). 12 cell lines were positive for EGFR genomic gain. Sensitivity (GI50 <1uM) to all EGFR TKIs was seen in 11 lines and resistance (GI50 >8uM) in 5 lines. Of the sensitive cell lines, 9 were positive for EGFR genomic gain compared with only 1 of the resistant lines. Furthermore, EGFR protein expression also had a direct association with EGFR TKI sensitivity. In contrast, only 4 cell lines were positive for HER2 or HER3 genomic gain and there was no correlation with sensitivity. The most sensitive cell line was positive for EGFR genomic gain and was the only line to have an EGFR TK mutation (S768I in exon 20). Conclusions: EGFR gene copy number and protein expression appeared to have predictive value in identifying SCCHN cell lines sensitive to EGFR TKIs. No significant financial relationships to disclose.