The EGFR antibody cetuximab is used to treat numerous cancers, but intrinsic and acquired resistance to this agent is a common clinical problem. In this study we show that overexpression of the oncogenic receptor kinase AXL is sufficient to mediate acquired resistance to cetuximab in models of non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC), where AXL was overexpressed, activated and tightly associated with EGFR expression in cells resistant to cetuximab (CtxR cells). Using RNAi methods and novel AXL targeting agents, we found that AXL activation stimulated cell proliferation, EGFR activation and MAPK signaling in CtxR cells. Notably, EGFR directly regulated the expression of AXL mRNA through MAPK signaling and the transcription factor c-Jun in CtxR cells, creating a positive feedback loop that maintained EGFR activation by AXL. Cetuximab-sensitive parental cells were rendered resistant to cetuximab by stable overexpression of AXL or stimulation with EGFR ligands, the latter of which increased AXL activity and association with the EGFR. In tumor xenograft assays, the development of resistance following prolonged treatment with cetuximab was associated with AXL hyperactivation and EGFR association. Furthermore, in an examination of patient-derived xenografts established from surgically resected HNSCCs, AXL was overexpressed and activated in tumors that displayed intrinsic resistance to cetuximab. Collectively, our results identify AXL as a key mediator of cetuximab resistance, providing a rationale for clinical evaluation of AXL targeting drugs to treat cetuximab-resistant cancers.

The epidermal growth factor receptor (eGFR) is a receptor tyrosine kinase belonging to the HeR family of receptor tyrosine kinases. Receptor activation upon ligand binding leads to down stream activation of the Pi3K/AKT, RAs/RAF/MeK/ eRK and PLCγ/PKC pathways that influence cell proliferation, survival and the metastatic potential of tumor cells. increased activation by gene amplification, protein overexpression or mutations of the eGFR has been identified as an etiological factor in a number of human epithelial cancers (e.g., NsCLC, CRC, glioblastoma and breast cancer). Therefore, targeting the eGFR has been intensely pursued as a cancer treatment strategy over the last two decades. To date, five eGFR inhibitors, including three small molecule tyrosine kinase inhibitors (TKis) and two monoclonal antibodies have gained FdA approval for use in oncology. Both approaches to targeting the eGFR have shown clinical promise and the anti-eGFR antibody cetuximab is used to treat HNsCC and CRC. despite clinical gains arising from use of cetuximab, both intrinsic resistance and the development of acquired resistance are now well recognized. in this review we focus on the biology of the eGFR, the role of eGFR in human cancer, the development of

The epidermal growth factor receptor (EGFR) has been one of the most targeted receptors in the field of oncology. While anti-EGFR inhibitors have demonstrated clinical success in specific cancers, most patients demonstrate either intrinsic or acquired resistance within one year of treatment. Many mechanisms of resistance to EGFR inhibitors have been identified, one of these being attributed to alternatively localized EGFR from the cell membrane into the cell’s nucleus. Inside the nucleus, EGFR functions as a co-transcription factor for several genes involved in cell proliferation and angiogenesis, and as a tyrosine kinase to activate and stabilize proliferating cell nuclear antigen and DNA dependent protein kinase. Nuclear localized EGFR is highly associated with disease progression, worse overall survival in numerous cancers, and enhanced resistance to radiation, chemotherapy, and the anti-EGFR therapies gefitinib and cetuximab. In this review the current knowledge of how nuclear EGFR enhances resistance to cancer therapeutics is discussed, in addition to highlighting ways to target nuclear EGFR as an anti-cancer strategy in the future.