title: Targeting GPCR-mediated p70S6K activity may improve head and neck cancer response to cetuximab.
abstract: OBJECTIVE
  Epidermal growth factor receptor (EGFR) overexpression is correlated with decreased survival in head and neck cancer (HNC) where the addition of EGFR inhibition to standard chemoradiation approaches has improved treatment responses. However, the basis for the limited efficacy of EGFR inhibitors in HNC is incompletely understood. G-protein-coupled receptors (GPCR) have been shown to be overexpressed in HNC where GPCR activation induces HNC growth via both EGFR-dependent and -independent pathways. We hypothesized that targeting GPCR-induced EGFR-independent signaling would improve the efficacy of EGFR inhibition.
  
  
  METHODS
  Using a high-throughput phosphoproteome array, we identified proteins that were phosphorylated in HNC cells where EGFR expression was downmodulated by RNA interference (RNAi) in the presence or absence of a GPCR ligand. We confirmed the findings from the array by Western blotting followed by in vitro and in vivo phenotypic assays.
  
  
  RESULTS
  p70S6K phosphorylation was elevated approximately sixfold in EGFR siRNA-transfected cells treated with a GPCR ligand. In addition to RNAi-mediated EGFR downmodulation, GPCR-mediated phosphorylation of p70S6K was modestly increased by EGFR inhibitor cetuximab approved by the Food and Drug Administration. Biopsies from cetuximab-treated patients also displayed increased phospho-p70S6K staining compared with pretreatment biopsies. HNC cells were growth inhibited by both genetic and pharmacologic p70S6K targeting strategies. Furthermore, p70S6K targeting in combination with cetuximab resulted in enhanced antitumor effects in both in vitro and in vivo HNC models.
  
  
  CONCLUSIONS
  These results indicate that increased phosphorylation of p70S6K in cetuximab-treated patients may be due to increased GPCR signaling. Therefore, the addition of p70S6K targeting strategies may improve treatment responses to EGFR inhibition.
authors.affiliation: Departments of Pharmacology and Chemical Biology, Otolaryngology, Medicine, and Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Bhola
authors.forename: Sufi M
authors.initials: SM
authors.lastname: Thomas
authors.forename: Maria
authors.initials: M
authors.lastname: Freilino
authors.forename: Sonali
authors.initials: S
authors.lastname: Joyce
authors.forename: Anirban
authors.initials: A
authors.lastname: Sahu
authors.forename: Jessica
authors.initials: J
authors.lastname: Maxwell
authors.forename: Athanassios
authors.initials: A
authors.lastname: Argiris
authors.forename: Raja
authors.initials: R
authors.lastname: Seethala
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Grandis
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D000068818:Cetuximab; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D006258:Head and Neck Neoplasms / Q000188:drug therapy; D006801:Humans; D008024:Ligands; D058990:Molecular Targeted Therapy; D010766:Phosphorylation; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors* / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D008024:Ligands; D043562:Receptors, G-Protein-Coupled; D066246:ErbB Receptors; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D000068818:Cetuximab