Data from Reverse-Phase Protein Array Profiling of Oropharyngeal Cancer and Significance of PIK3CA Mutations in HPV-Associated Head and Neck Cancer

Abstract

<div>Abstract<p><b>Purpose:</b> Human papilloma virus (HPV)–associated (HPV+) oropharyngeal squamous cell carcinomas (OPSCC) have different molecular and biologic characteristics and clinical behavior compared with HPV-negative (HPV−) OPSCC. PIK3CA mutations are more common in HPV(+) OPSCC. To define molecular differences and tumor subsets, protein expression and phosphorylation were compared between HPV(+) and HPV(−) OPSCC and between tumors with and without PIK3CA mutations.</p><p><b>Experimental Design:</b> Expression of 137 total and phosphorylated proteins was evaluated by reverse-phase protein array in 29 HPV(+) and 13 HPV(−) prospectively collected OPSCCs. Forty-seven OPSCCs were tested for hotspot-activating mutations in PIK3CA and AKT. Activation of PIK3CA downstream targets and sensitivity to pathway inhibitors were determined in HPV(+) head and neck cancer cells overexpressing wild-type or mutant PIK3CA.</p><p><b>Results:</b> Analyses revealed 41 differentially expressed proteins between HPV(+) and HPV(−) OPSCC categorized into functional groups: DNA repair, cell cycle, apoptosis, phosphoinositide 3-kinase (PI3K)/AKT/mTOR, and receptor kinase pathways. All queried DNA repair proteins were significantly upregulated in HPV(+) samples. A total of 8 of 33 HPV(+) and 0 of 14 HPV(−) tumors contained activating PIK3CA mutations. Despite all activating PIK3CA mutations occurring in HPV(+) samples, HPV(+) tumors had lower mean levels of activated AKT and downstream AKT target phosphorylation. Ectopic expression of mutant PIK3CA in HPV(+) cells increased mTOR, but not AKT activity. HPV E6/E7 overexpression inhibited AKT phosphorylation in HPV-negative cells. Mutant PIK3CA overexpressing cells were more sensitive to a dual PI3K/mTOR inhibitor compared with an AKT inhibitor.</p><p><b>Conclusions:</b> Protein expression analyses suggest that HPV(+) and HPV(−) OPSCC differentially activate DNA repair, cell cycle, apoptosis, PI3K/AKT/mTOR, and receptor kinase pathways. PIK3CA mutations are more common in HPV(+) OPSCC and are associated with activation of mTOR, but not AKT. These data suggest that inhibitors for mTOR may have activity against HPV(+) PIK3CA mutant oropharyngeal cancers. <i>Clin Cancer Res; 20(9); 2300–11. ©2014 AACR</i>.</p></div>