Reverse-phase protein array profiling of oropharyngeal cancer and significance of PIK3CA mutations in HPV-associated head and neck cancer

Clin Cancer Res. 2014 May 1;20(9):2300-11. doi: 10.1158/1078-0432.CCR-13-2585. Epub 2014 Mar 5.

Abstract

Purpose: 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.

Experimental design: 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.

Results: 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.

Conclusions: 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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Cell Line, Tumor
  • Class I Phosphatidylinositol 3-Kinases
  • Cluster Analysis
  • Female
  • Gene Expression Regulation, Neoplastic
  • Head and Neck Neoplasms / diagnosis
  • Head and Neck Neoplasms / genetics*
  • Head and Neck Neoplasms / mortality
  • Head and Neck Neoplasms / therapy
  • Head and Neck Neoplasms / virology*
  • Humans
  • Male
  • Middle Aged
  • Mutation*
  • Neoplasm Staging
  • Oropharyngeal Neoplasms / diagnosis
  • Oropharyngeal Neoplasms / genetics*
  • Oropharyngeal Neoplasms / mortality
  • Oropharyngeal Neoplasms / therapy
  • Oropharyngeal Neoplasms / virology*
  • Papillomaviridae*
  • Papillomavirus Infections / complications*
  • Phosphatidylinositol 3-Kinases / genetics*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Prognosis
  • Protein Array Analysis
  • Risk Factors

Substances

  • Phosphatidylinositol 3-Kinases
  • Class I Phosphatidylinositol 3-Kinases
  • PIK3CA protein, human