title: Differential compensation mechanisms define resistance to PI3K inhibitors inPIK3CAamplified HNSCC.
abstract: OBJECTIVE
  Recent sequencing studies of head and neck squamous cell carcinomas (HNSCCs) have identified the phosphatidylinositol 3-kinase (PI3K) pathway as the most frequently mutated, oncogenic pathway in this cancer type. Despite the frequency of activating genomic alterations in PIK3CA (the gene encoding the catalytic subunit of PI3K, targeted inhibitors of PI3K have not shown clinical efficacy as monotherapies. We hypothesized that co-dependent pathways, including the Ras-MEK-ERK pathway, may still be functional in the presence of PI3K inhibitors and might serve as mediators of this resistance.
  
  
  METHODS
  We assessed the hypothesis using resazurin cell viability and trypan blue exclusion assays. We also used Western blot to characterize Ras-MEK-ERK pathway activity.
  
  
  METHODS
  We evaluated this hypothesis in six PIK3CA-amplified, PI3K inhibitor-resistant HNSCC cell lines following treatment with pan and alpha-isoform selective PI3K inhibitors (BKM120 and HS-173 respectively). We also tested the effect of combination treatment with PI3K inhibitor HS-173 and MEK inhibitor trametinib or EGFR inhibitor gefitinib.
  
  
  RESULTS
  Our results displayed maintenance of Ras-MEK-ERK pathway activity in 4 of 6 HNSCC cell lines after PI3K inhibitor treatment. We also found that UM-SCC-69 and UM-SCC-108 cells display synergistic responses to dual therapy.
  
  
  CONCLUSIONS
  This study suggests that inhibition of the PI3K and Ras-MEK-ERK pathways might be effective in some HNSCC patients; however, it also prompts the study of additional resistance mechanisms to identify synergistic combination therapies for tumors resistant to these di-therapies.
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Michigan Medical School, Ann Arbor, MI.; Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI.
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Michmerhuizen
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Michigan Medical School, Ann Arbor, MI.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Leonard
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Michigan Medical School, Ann Arbor, MI.
authors.forename: Aditi
authors.initials: A
authors.lastname: Kulkarni
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Michigan Medical School, Ann Arbor, MI.; Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, MI; Comprehensive Cancer Center, University of Michigan Medical School, Ann Arbor, MI.
authors.forename: J Chad
authors.initials: JC
authors.lastname: Brenner
keywords: Compensatory Resistance; Head and Neck Cancer; PIK3CA; Personalized Medicine; Targeted Therapy