Abstract 78: Inhibiting anaplastic lymphoma kinase (ALK) overcomes epidermal growth factor receptor (EGFR) inhibitor resistance in head and neck squamous cell carcinoma (HNSCC) patient-derived models

Abstract

HNSCC is the sixth most common cancer worldwide. EGFR is overexpressed in up to 90% of HNSCC and associated with poor outcome. An EGFR monoclonal antibody, cetuximab, was the only approved molecular targeted therapy for HNSCC; however, resistance eventually occurs in all patients. Functional screens including a small-molecule kinase inhibitor were used to identify agents that synergized with EGFR inhibitors in reducing viability in HNSCC patient-derived tumor cells. Effective combination therapies were validated in scale-up experiments, and their true targets were evaluated using siRNAs to rule out off-target effects of the drugs. Cell number, cell apoptosis, and colony formation ability were determined in tumor cells treated with single agents and drug combination. ALK expression and phosphorylation in tumor cells before and after anti-EGFR treatment was tested by Western immunoblotting. Two ALK inhibitors on the drug screen panel showed synergistic effects with EGFR inhibitors in 4/8 HNSCC patients9 tumor cells, despite ineffectiveness of single drug. siRNA targeting ALK synergized with gefitinib in reducing cell viability, indicating specificity to ALK. Scale-up dose-response experiments confirmed patient cell sensitivity to 4 different ALK inhibitors in combination with the EGFR inhibitor gefitinib. Combination indices were below 1 in the sensitive patients9 cells, indicating synergy. Cotargeting EGFR and ALK decreased HNSCC patients9 tumor cell number, colony formation ability, and increased apoptosis. Because of low expression of ALK mRNA in original tumors and patient tumor-derived cells, we hypothesized that EGFR inhibition induced ALK expression. Indeed, inhibition of EGFR by gefitinib increased ALK protein expression and phosphorylation, suggesting induction of ALK expression and activation as a novel mechanism of EGFR inhibitor resistance in HNSCC amenable to combination therapy. In conclusion, we identified induction of ALK by EGFR inhibitor as a potential novel mechanism relevant to resistance to cetuximab in the clinic, and EGFR/ALK inhibition as a potential combination therapeutic strategy for treating EGFR inhibitor resistant HNSCC. Citation Format: Xiaoming Ouyang, Ashley Barling, Aletha Lesch, Jeffrey Tyner, Sophia Jeng, Christina Zheng, Sara A. Courtneidge, Shannon McWeeney, Molly Kulesz-Martin. Inhibiting anaplastic lymphoma kinase (ALK) overcomes epidermal growth factor receptor (EGFR) inhibitor resistance in head and neck squamous cell carcinoma (HNSCC) patient-derived models [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 78.