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

Purpose:Human papilloma virus (HPV)–associated (HPVþ) oropharyngeal squamous cell carcinomas (OPSCC) have different molecular and biologic characteristics and clinical behavior compared with HPVnegative (HPV ) OPSCC. PIK3CA mutations are more common in HPV(þ) OPSCC. To define molecular differences and tumor subsets, protein expression and phosphorylation were compared between HPV(þ) and HPV( ) OPSCC and between tumors with and without PIK3CA mutations. Experimental Design: Expression of 137 total and phosphorylated proteins was evaluated by reversephase protein array in 29 HPV(þ) 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 inHPV(þ) head and neck cancer cells overexpressing wild-type or mutant PIK3CA. Results: Analyses revealed 41 differentially expressed proteins between HPV(þ) 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(þ) samples. A total of 8 of 33 HPV(þ) and 0 of 14 HPV( ) tumors contained activating PIK3CA mutations. Despite all activating PIK3CA mutations occurring in HPV(þ) samples, HPV(þ) tumors had lower mean levels of activated AKT and downstream AKT target phosphorylation. Ectopic expression of mutant PIK3CA inHPV(þ) cells increasedmTOR, but not AKT activity.HPVE6/E7overexpression 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. Conclusions: Protein expression analyses suggest that HPV(þ) and HPV( ) OPSCC differentially activate DNA repair, cell cycle, apoptosis, PI3K/AKT/mTOR, and receptor kinase pathways. PIK3CA mutations are more common in HPV(þ) OPSCC and are associated with activation of mTOR, but not AKT. These data suggest that inhibitors for mTOR may have activity against HPV(þ) PIK3CA mutant oropharyngeal cancers. Clin Cancer Res; 20(9); 2300–11. 2014 AACR.