title: Antitumor mechanisms of targeting the PDK1 pathway in head and neck cancer.
abstract: G-protein-coupled receptors (GPCR) activate the epidermal growth factor receptor (EGFR) and mediate EGFR-independent signaling pathways to promote the growth of a variety of cancers, including head and neck squamous cell carcinoma (HNSCC). Identification of the common signaling mechanisms involved in GPCR-induced EGFR-dependent and EGFR-independent processes will facilitate the development of more therapeutic strategies. In this study, we hypothesized that phosphoinositide-dependent kinase 1 (PDK1) contributes to GPCR-EGFR cross-talk and signaling in the absence of EGFR and suggests that inhibition of the PDK1 pathway may be effective in the treatment of HNSCC. The contribution of PDK1 to the EGFR-dependent and EGFR-independent signaling in HNSCC was determined using RNA interference, a kinase-dead mutant, and pharmacologic inhibition. In vivo xenografts studies were also carried out to determine the efficacy of targeting PDK1 alone or in combination with the U.S. Food and Drug Administration-approved EGFR inhibitor cetuximab. PDK1 contributed to both GPCR-induced EGFR activation and cell growth. PDK1 also mediated activation of p70S6K in the absence of EGFR. Blockade of PDK1 with a small molecule inhibitor (AR-12) abrogated HNSCC growth, induced apoptosis, and enhanced the antiproliferative effects of EGFR tyrosine kinase inhibitors in vitro. HNSCC xenografts expressing kinase-dead PDK1 showed increased sensitivity to cetuximab compared with vector-transfected controls. Administration of AR-12 substantially decreased HNSCC tumor growth in vivo. These cumulative results show that PDK1 is a common signaling intermediate in GPCR-EGFR cross-talk and EGFR-independent signaling, and in which targeting the PDK1 pathway may represent a rational therapeutic strategy to enhance clinical responses to EGFR inhibitors in HNSCC.
authors.affiliation: Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Bhola
authors.forename: Maria L
authors.initials: ML
authors.lastname: Freilino
authors.forename: Sonali C
authors.initials: SC
authors.lastname: Joyce
authors.forename: Malabika
authors.initials: M
authors.lastname: Sen
authors.forename: Sufi M
authors.initials: SM
authors.lastname: Thomas
authors.forename: Anirban
authors.initials: A
authors.lastname: Sahu
authors.forename: Andre
authors.initials: A
authors.lastname: Cassell
authors.forename: Ching-Shih
authors.initials: CS
authors.lastname: Chen
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Grandis
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000201:enzymology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D000068818:Cetuximab; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D000077195:Squamous Cell Carcinoma of Head and Neck
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D043562:Receptors, G-Protein-Coupled; D066246:ErbB Receptors; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D017346:Protein Serine-Threonine Kinases; D000068818:Cetuximab