Data from RAS/PI3K Crosstalk and Cetuximab Resistance in Head and Neck Squamous Cell Carcinoma

Abstract

<div>Abstract<p><b>Purpose:</b> Cetuximab, an antibody directed against the EGF receptor, is an effective clinical therapy for patients with head and neck squamous cell cancer (HNSCC). Despite great clinical promise, intrinsic or acquired cetuximab resistance hinders successful treatment outcomes but little is known about the underlying mechanism.</p><p><b>Experimental Design:</b> To study the role of oncogenic <i>HRAS</i> in cetuximab resistance in HNSCC, the frequency of oncogenic <i>HRAS</i> mutations was determined in a cohort of 180 genomic DNAs from head and neck cancer specimens. We also used a combination of cetuximab-resistant cell lines and a transgenic mouse model of RAS-driven oral cancer to identify an oncogenic RAS-specific gene expression signature that promotes cetuximab resistance.</p><p><b>Results:</b> Here, we show that activation of RAS signaling leads to persistent extracellular signal–regulated kinase 1/2 signaling and consequently to cetuximab resistance. <i>HRAS</i> depletion in cells containing oncogenic <i>HRAS</i> or <i>PIK3CA</i> restored cetuximab sensitivity. In our study, the gene expression signature of c-MYC, BCL-2, BCL-XL, and cyclin D1 upon activation of MAPK signaling was not altered by cetuximab treatment, suggesting that this signature may have a pivotal role in cetuximab resistance of RAS-activated HNSCC. Finally, a subset of patients with head and neck cancer with oncogenic HRAS mutations was found to exhibit <i>de novo</i> resistance to cetuximab-based therapy.</p><p><b>Conclusions:</b> Collectively, these findings identify a distinct cetuximab resistance mechanism. Oncogenic <i>HRAS</i> in HNSCC promotes activation of ERK signaling, which in turn mediates cetuximab resistance through a specific gene expression signature. <i>Clin Cancer Res; 20(11); 2933–46. ©2014 AACR</i>.</p></div>