title: Erlotinib resistance in EGFR-amplified glioblastoma cells is associated with upregulation of EGFRvIII and PI3Kp110δ.
abstract: BACKGROUND
  The treatment efficacy of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors like erlotinib has not met expectations for glioblastoma therapy, even for EGFR-overexpressing tumors. We determined possible mechanisms of therapy resistance using the unique BS153 glioblastoma cell line, which has retained amplification of the egfr gene and expression of EGFR variant (v)III.
  
  
  METHODS
  Functional effects of erlotinib, gefitinib, and cetuximab on BS153 proliferation, migration, and EGFR-dependent signal transduction were systematically compared in vitro. The tumor-initiating capacity of parental and treatment-resistant BS153 was studied in Naval Medical Research Institute/Foxn1(nu) mice. Potential mediators of resistance were knocked down using small interfering (si)RNA.
  
  
  RESULTS
  Erlotinib and gefitinib inhibited proliferation and migration of BS153 in a dose-dependent manner, whereas cetuximab had no effect. BS153 developed resistance to erlotinib (BS153(resE)) but not to gefitinib. Resistance was associated with strong upregulation of EGFRvIII and subsequent activation of the phosphatidylinositol-3-OH kinase (PI3K) pathway in BS153(resE) and an increased expression of the regulatory 110-kDa delta subunit of PI3K (p110δ). Knockdown of EGFRvIII in BS153(resE) largely restored sensitivity to erlotinib. Targeting PI3K pharmacologically caused a significant decrease in cell viability, and specifically targeting p110δ by siRNA partially restored erlotinib sensitivity in BS153(resE). In vivo, BS153 formed highly invasive tumors with an unusual growth pattern, displaying numerous satellites distant from the initial injection site. Erlotinib resistance led to delayed onset of tumor growth as well as prolonged overall survival of mice without changing tumor morphology.
  
  
  CONCLUSIONS
  EGFRvIII can mediate resistance to erlotinib in EGFR-amplified glioblastoma via an increase in PI3Kp110δ. Interfering with PI3Kp110δ can restore sensitivity toward the tyrosine kinase inhibitor.
authors.affiliation: Corresponding Author: Dr Alexander Schulte, PhD, Laboratory for Brain Tumor Biology, Department of Neurosurgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. aschulte@uke.uni-hamburg.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schulte
authors.forename: Katrin
authors.initials: K
authors.lastname: Liffers
authors.forename: Annegret
authors.initials: A
authors.lastname: Kathagen
authors.forename: Sabine
authors.initials: S
authors.lastname: Riethdorf
authors.forename: Svenja
authors.initials: S
authors.lastname: Zapf
authors.forename: Adrian
authors.initials: A
authors.lastname: Merlo
authors.forename: Katharina
authors.initials: K
authors.lastname: Kolbe
authors.forename: Manfred
authors.initials: M
authors.lastname: Westphal
authors.forename: Katrin
authors.initials: K
authors.lastname: Lamszus
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002470:Cell Survival; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D000069347:Erlotinib Hydrochloride; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D051858:Forkhead Transcription Factors / Q000502:physiology; D005784:Gene Amplification; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007124:Immunoenzyme Techniques; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D008819:Mice, Nude; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: D051858:Forkhead Transcription Factors; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; C090140:Whn protein; C410723:epidermal growth factor receptor VIII; D000069347:Erlotinib Hydrochloride; D019869:Phosphatidylinositol 3-Kinases; C512478:EGFR protein, human; D066246:ErbB Receptors
keywords: BS153; EGFR; PI3K; glioma; invasion; resistance