Purpose: Head and neck squamous cell carcinoma (HNSCC) represents the eighth most common malignancy worldwide. Standard-of-care treatments for patients with HNSCC include surgery, radiation, and chemotherapy. In addition, the anti-EGFR monoclonal antibody cetuximab is often used in combination with these treatment modalities. Despite clinical success with these therapeutics, HNSCC remains a difficult malignancy to treat. Thus, identification of new molecular targets is critical.

Experimental Design: In the current study, the receptor tyrosine kinase AXL was investigated as a molecular target in HNSCC using established cell lines, HNSCC patient-derived xenografts (PDX), and human tumors. HNSCC dependency on AXL was evaluated with both anti-AXL siRNAs and the small-molecule AXL inhibitor R428. Furthermore, AXL inhibition was evaluated with standard-of-care treatment regimens used in HNSCC.

Results: AXL was found to be highly overexpressed in several models of HNSCC, where AXL was significantly associated with higher pathologic grade, presence of distant metastases, and shorter relapse-free survival in patients with HNSCC. Further investigations indicated that HNSCC cells were reliant on AXL for cellular proliferation, migration, and invasion. In addition, targeting AXL increased HNSCC cell line sensitivity to chemotherapy, cetuximab, and radiation. Moreover, radiation-resistant HNSCC cell line xenografts and PDXs expressed elevated levels of both total and activated AXL, indicating a role for AXL in radiation resistance.

Conclusions: This study provides evidence for the role of AXL in HNSCC pathogenesis and supports further preclinical and clinical evaluation of anti-AXL therapeutics for the treatment of patients with HNSCC. Clin Cancer Res; 21(11); 2601–12. ©2015 AACR.